CA1332796C - Photopolymerizable compositions and elements for refractive index imaging - Google Patents

Abstract

Solid photopolymerizable compositions and photosensitive elements are provided that are useful in preparing optical elements, and especially holograms. The composition contains a polymeric binder, a liquid ethylenically unsaturated monomer, and a photoinitiator system. Typical compositions have a refractive index modulation of at least 0.005 when measured per the specified test.

Description

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PHOTOPOLYMERIZABLE COMPOSITIONS AND
ELEMENTS FOR REFRACTIVE INDEX IMAGING

5 Field of the Invention This invention relates to solid imaging compositions and elements which, after exposure, contain image areas having an index of refraction which is different from that of non-image areas.
More particularly this invention relates to such systems wherein the refractive index image is a hologram.

Discussion of the Backqround and Prior Art The term "image recording'l is conventionally taken to mean a process which produces a spatial pattern of optical absorption in the recording medium. Photographic pcocesses are well known examples of this type of process.
In a broader sense, however, the word "image" means a spatial variation of the optical properties of a sample in such a way as to cause a desired modification of a beam of light passing through the sample. Refractive index images in general, and holograms in particular, which modulate the phase, rather than the amplitude of the beam passing through them, are usually referred to as phase holograms. Phase holographic image recording systems produce a 6patial pattern of varying refractive index rather than optical absorption in the recording medium and, thus, can modulate a beam of light without absorbing it.
This type of refractive index image also includes a number of optical elements or devices which superficially bear little resemblance to ~'~

133~7~6 absorption images. Examples are holographic lenses, gratings, mirrors, and optical waveguides.
Holography is a form of optical information storage. The general principles are described in a number of references, e.g., "Photography by Laser" by E. N. Leith and J. Upatnieks in SCIENTIFIC AMERICAN, 212, No. 6,Z4-35 (June, 1965). In brief, the object to be photographed or imaged is illuminated with coherent light, e.g., from a laser, and a light sensitive recording medium, e.g., a photographic plate, is positioned so as to receive light reflected from the object. Each point on the object reflects light to the entire recording medium, and each point on the medium receives light from the entire object.
This beam of reflected light is known as the object beam. At the same time, a portion of the coherent light is beamed by a mirror directly to the medium, bypassing the object. This beam is known as the reference beam. What is recorded on the recording medium is the interference pattern that results from the interaction of the reference beam and the object beam impinging on the medium. When the processed recording medium is subsequently illuminated and observed appropriately, the light from the illuminating source i~ diffracted by the hologram to reproduce the wave-front that originally reached the medium from the object, so that the hologram resembles a window through which the virtual image of the object is observed in full three-dimensional form, complete with parallax.
Holograms that are formed by allowing the reference and object beams to enter the recording medium from the same side are known as transmi66ion holograms. Interaction of the object and reference beams in the recording medium forms fringes of 13327~

material with varying refractive indices which are normal or near normal to the plane of the recording medium.
When the hologram is played back by viewing with transmitted light, these fringes refract the light to produce the viewed virtual image. Such transmission holograms may be produced by methods which are well known in the art such as disclosed in U.S. Patent 3,506,327;
U.S. Patent 3,838,903 and U.S. Patent 3,894,787.
Holograms formed by allowing the reference and object beams to enter the recording medium from opposite sides, so that they are traveling in approximately opposite directions are known as reflection holograms.
Interaction of the object and reference beams in the recording medium forms fringes of material with varying refractive indices which are, approximately, planes parallel to the plane of the recording medium. When the hologram is played back these fringes act as mirrors reflecting incident light back to the viewer. Hence, the hologram is viewed in reflection rather than in transmission. Since the wavelingth sensitivity of this type of hologram is very high, white light may be used for reconstruction. Reflection holograms produced by an off-axis process are disclosed in U.S. Patent 3,532,406.
A diffraction grating is the simplest possible transmission hologram. It is the hologram of two coherent plane waves. It can be created by splitting a single laser beam and recombining the beams at the recording medium.
The interference pattern produced by two plane waves which are coherent and are not polarized perpendicular to each other is a set of uniformly 1~3,~7~6 _ 4 spaced fringes with a sinusoidal intensity distribution.
When incident on a recording medium they produce a set of uniformly spaced fringes which have a sinusolidal variation in refractive index, generally referred to as a grating, oriented parallel to the bisector of the angle between the two beams. If the two waves are incident at equal angles with respect to the surface of the recording medium and are both incident on the same side of the recording medium, the fringes are perpendicular to the surface of the medium and the grating is said to be unslanted. The hologram grating produced is said to be a tranmission grating since light passing through it is diffracted. The grating is said to be thick if it is much thicker than the distance between the fringes, generally referred to as the grating spacing.
A diffraction grating can be characterized by its diffraction efficiency, that is the percent of incident radiation which is diffracted, and by its thickness. A
simple but useful theory for thick hologram gratings, generally known as the "coupled wave theory", has been developed by Kogelnik (H. Kogelnik, Coupled wave theory for thick hologram gratings, Bell Syt. Tech. J. 48, 2909-2947, 1969). This theory treats the relationship between diffraction efficiency, granting thickness, wavelength of incident radiation, and the angle of incident radiation. A useful discussion of this theory in regard to refractive index recording systems has been presented in Section II of an article by Tomlinson and Chandross (W.J. Tomlinson and E.A. Chandross, Organic photochemical refractive-index image recording systems, Adv. in Photochem., Vol. 12, J.N. Pitts, Jr., G.S.
Hammond, and K. Gollnick, eds., Wiley-Interscience, New York, 1980, pp 201-281).

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Reractive index modulation i6 a quantitative measure of the change in refractive index between image and non-image portions of a hologram or other recording medium containing a refractive index image. For the diffraction grating, refractive index modulation is the measure of the amplitude of the 6inusoidal modulation of the refractive index within the recording medium produced when the holographic image is recorded. The refractive index modulation, or index modulation, for a recording medium is best determined by holographically forming a grating in the medium and calculating the index modulation using Kogelnik's coupled wave theory and the measured parameter~ of the grating formed, i.e., the diffraction e~ficiently, medium thickness, etc.
A variety of materials have been used to record volume holograms. Among the more important are: silver halide emulsions, hardened dichromated 20 gelatin, ferroelectric crystals, photopolymers, photochromics and photodichroics. Characteristics of these materials are given in Volume HoloqraPhy and Volume Gratinqs, Academic Press, New York, 1981 Chapter 10, pp. 254-304 by L. Solymar and D. J. Cook.
Dichromated gelatin is the material most widely used for recording volume holograms. This material has become the popular choice because of its high diffraction efficiency and low noise characteristics. However, the material has poor 30 shelf life and requires wet proces6ing. Plates must be freshly prepared, or prehardened gelatin must be used. Wet processing means that an additional step is required in hologram preparation and may also cause the hologram to change due to swelling and then 35 shrinkage of the gelatin during processing. The I~32~S

requirement that plates by freshly prepared each time a hologram is made, plus the problems as60ciated with wet processing, make reproducibly extremely difficult to achieve with dichromated gelatin.
While early holograms were prepared from 6ilver halide, liquid photopolymers, or dichromated colloids which required several proces6ing 6teps, solid photopolymerizable element6 have been propo6ed that require only a single proces6 step. U.S. Patent 3,658,526, to Haugh, discloses preparation of 6table high-resolution holograms from solid photopolymerizable layers by a single 6tep-proces6 wherein a permanent refractive index image is obtained by a single imagewise exposure of the 15 photopolymerizable layer to actinic radiation bearing holographic information. The holographic image formed i6 not destroyed by sub6equent uniform actinic exposure, but rather is fixed or enhanced.
Although the solid photopolymerizable layers 20 proposed by Haugh offer many advantage6 over the prior art, their efficiency is low. The~e layer~
typically have a refractive index of modulation in the range of 0.001 to 0.003. As a re6ult, reconstructed holographic images formed in thin 25 layers of the photopolymer only have limited brightness. While brightness can be increased by employing thicker layers of the photopolymer, this 601ution result6 in a substantial reduction to the viewing angle and causes the manufacturer to use much 30 more of the expensive photopolymer. It al60 should be noted that the coated layers propo6ed by Haugh generally cannot be stored at room temperature for extended times without 1066 of speed and diffraction efficiency. Thus, there continues to be a need for 35 improved photopolymer compo6itions and element6 for 1~3~7~fi refractive index imaging applications, including holography.

Summary of the Invention This invention provides storage stable, solid, photopolymerizable compositions and photosensitive elements that have improved response to actinic radiation and produce holograms of improved brightness. More particularly, in one embodiment this invention provides a substantially solid, photopolymerizable composition that orms a refractive-index imaqe upon exposure to actinic radiation as the sole processing step, said composition consisting essentially of:
(a) 25 to 75% of a solvent soluble, thermoplastic polymeric binder;
(b) 5 to 60% of a liquid ethylenically unsaturated monomer, said monomer having a boiling point above 100C and being capable zO of addition polymerization:
(c) 0.1 to 10% of a photoinitiator system that activates polymerization of said unsaturated monomer upon exposure to actinic radiation;
wherein said percentages are weight percentages of the total binder, unsaturated monomer and photoinitiator system of components (a), (b), and (c), the composition having a refractive index modulation of at least 0.005 as determined with 632.8 nm radiation from a transmission grating having a 30 spatial frequency of 1000 lines per millimeter, which transmission grating is prepared holographically from a layer of said composition.

The refractive index modulation for 35 compositions of this invention i6 calculated, using ~33~79~

Kogelnik's coupled wave theory, from diffraction efficiency measured with 632.8 nm radiation and layer thickness of a holographically formed grating in the layer of each composition, wherein the grating has a spatial frequency of about 1000 lines per mm, i.e., between 900 and 1100 lines per mm. Using this method and the constant conditions as defined hereinunder, index modulations for materials of this invention are diferentiated from those of the prior art.
In a preferred embodiment of this invention, components (a) and (b) are selected so that either the polymeric material (a) or the liquid monomer (b) contains a substituent from the group consisting of phenyl, phenoxy, naphthyl, naphthyloxy, heteroaromatic containing up to three aromatic rings, chlorine, bromine atom, and mixtures thereof, and wherein the remaining component is substantially free of said groups or atoms.
In a further embodiment of this invention 20 the solid, photopolymerizable composition contains as a fourth component (d~ a liquid plasticizer taken from the group consisting of tris(2-ethylhexyl)-phosphate, glyceryl tributyrate, and a compound having the general formula:

ll ll RlC(OCH2CH2)xOCR2;
O O
.. ..
RlOC(CH2)yCOR2; or R3(ocH2cHR4)zOH
wherein Rl and R2 each is an alkyl group of 1 to 10 carbon atoms; x is 1-4; y is 2-10, R3 i6 H or an alkyl group of H to 16 carbon atoms, R4 i6 H or CH3, and z is 1-20.

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Brief DescriPtion of the Drawinq The Figure illu6trates the experimental arrangement used to holographically determine the refractive index modulation.

Detailed Description of the Invention The improved photopolymerizable compositions of this invention are substantially solid and are typically used as a layer applied to a permanent substrate. The composition may be directly coated onto the substrate by any conventional method or may be laminated thereto as a storage stable preformed element comprising the photopolymerizable layer releasably adhered to a temporary 6upport film 6uch as polyethylene terephthalate.
The photopolymerizable layer is a thermopla6tic compo6ition which, upon exposure to actinic radiation, forms crosslinks or polymers of higher molecular weight to change the refractive 20 index and rheological character of the composition.
Preferred photopolymerizable composition6 are compositions wherein free radical addition polymerization and cro6slinking of a compound containing one or more ethylenically unsaturated 25 groups, usually in a terminal position, harden and insolubilize the compo6ition. The 6ensitivity of the photopolymerizable compo6ition is enhanced by the photoinitiating system which may contain a component which sen6itizes the composition to practical 30 radiation sources, e.g., vi6ible light.
Conventionally a binder i6 the most significant component of a substantially dry photopolymerizable film or layer in terms of what physical propertie6 the film or laminate will have 35 while being used in the invention. The binder 6erves - 13327~
as a containing medium for the monomer and photoinitiator prior to exposure, provide6 the base line refractive index, and, after exposure, contributes to the physical and refractive index characteristics needed for the refractive index image formed. Cohe6ion, adhesion, flexibility, miscibility, tensil strength, in addition to index of refraction, are some of the many propertie6 which determine if the binder is suitable for use in a refractive index medium. In practicing this invention, dry film photopolymerizable elements of various types may be used, provided they contain a liquid monomer and the refractive index modulation criterion i6 met.
Elements of these types are prepared by conventionally coating the photopolymerizable composition on a wide variety of transparent substrates. By ~'substrate" is meant any natural or synthetic 6upport, preferably one which is capable of 20 existing in a flexible or rigid film or 6heet form.
For example, the substrate could be a sheet or film of synthetic organic resin, or a composite of two or more materials. Specific substrates include polyethylene terephthalate film, e.g., re6in-subbed 25 polyethylene terephthalate film, flame or electrostatic discharge treated polyethylene terephthalate film, glass, cellulo6e acetate film, and the like. The particular substrate will generally be determined by the application involved.
While the photopolymerizable layer is a solid sheet of uniform thicknes6, it is composed of three major component~: (A) a solid, 601vent soluble, preormed polymeric material; (B) at least one liquid ethylenically unsaturated monomer capable 35 of addition polymerization to produce a polymeric material with a refractive index 6ub6tantially different from that of the preformed polymeric material: and (C) a photoinitiator sy6tem activatable by actinic radiation. Although the layer i6 601id composition, components interdiffuse before, during and after imaging expo6ure until they are f ixed or destroyed by a f inal uniform treatment, which u6ually is a further uniform exposure to actinic radiation.
Interdiffusion may be further promoted by incorporation into the composition of an otherwise inactive plasticizer of this invention. In addition to the liquid monomer, the composition may contain solid monomer components capable of interdiffusing in the solid composition and reacting with the liquid 15 monomer to form a copolymer with a refractive index shifted from that of the preformed polymeric material.
The refractive index 6hift resulting from imaging polymerization of the monomer of the composition is best measured as the refractive index 20 modulation as calculated from the parameters of a grating formed holographically in a layer of the composition. This measurement i6 achieved using the 30 holographic grating 6ystem illustrated in the Figure. In the 6ystem an argon ion laser (10) 25 operating at 488 nm and TEMoo produces a laser beam (12) which is directed by mirrors (14) and a beam elevator (16) through an attenuator (18) and into a beam splitter (Z0) wherein the beam i6 divided into two approximately equal beam 6egment6 (22). Each 30 beam segment (22) is reflected by a mirror (24), through a 6patial filter (26) and collimator (40) to converge in the plane of glas6 mounted 6ample (28) to subtend an angle of about 30 whose bisector is approximately normal to the plane of the 6ample (28) 35 so as to form a grating hologram (30). Grating (30) 1~327~

formation is measured in real time by passing a 632.8 nm beam (32) from a He:Ne laser (34) through the center of the exposure area at the Bragg angle and the intensity of the laser beam (32) defracted by the sample (28) is monitored with a detector (36).
In the practice of this invention a film element is prepared comprising a flexible, transparent, polyethylene terephthalate support sheet having coated thereon a solid photopolymerizable layer about 10 to 60 um thick which optionally is protected with a polypropylene, polyethylene, or polyethylene terephthalate cover sheet.
A section of the film element is cut, the cover sheet removed, if present, and then mounted onto a lOX13 cm glass plate by hand laminating the uncovered layer surface to the glass surface. Even though the layer is solid, its surface typically is tacky and adheres readily to the glass surface. In those instances where tack is absent, heat and pressure may be used to laminate the photopolymerizable layer to the glass substrate surface.
Typically the polyethylene terephthalate film support is left in place on the laminate and serves to protect the layer during handling and exposure operations.
The glass mounted photopolymerizable layer (28) is evaluated in the 30 holographic grating system described above wherein the emerging collimated beam (38) intensity ratio is maintained at approximately 1:1, with absolute intensities ranging from 3-10 mW/cm2 per beam (38). The diameter of each emèrging beam (38) is about 1 cm. The photopolymerizable layer (28) is exposed for 4-32 seconds to the modulated laser radiation at the convergence of beams (38) corresponding to 50-600 mJ/cm2 total exposure.
About one minute after this 13 1~7~
image-wise exposure the grating i6 reexposed for approximately 1-2 minutes using one of the two emerging beams (38) to fix or complete polymerization throughout the photopolymerizable layer (28). As described earlier, grating (30) formation is monitored using the non-actinic 632.8 nm beam (32) of a He:Ne laser (34) and a detector (36) which is a Coherent model 212 power meter attached to a strip chart recorder. Diffraction efficiency (~) is calculated as the ratio of the diffracted beam intensity (Idiff) to the pre-exposure undiffracted beam intensity (I ) after passing through the coating:
Tl = Idiff/ o (1) Coating thickness is measured for the photocured sample using a conventional thicknes6 measuring sy6tem.
The refractive index modulation in the 20 recorded grating is calculated from the measured diffraction efficiency and coating thicknes6 using Kogelnik's coupled wave theory, which for unslanted transmission diffraction gratings gives:

M = ~coseO sin (~) (2) ~d Where: M = refractive index modulation = probe radiation wavelength in free space (632.8 nm) eO = angle within the recording medium between the probe radiation and a line perpendicular to the plane of the medium (eO = 12.93 for = 632.8 nm) ~ = diffraction efficiency of the grating 35 d = grating thicknes6 ~377~

The internal angle eO= 12.93 of the probe beam within the recording medium is calculated from the external angle e = 15 between the line normal to the film plane and the 488 nm recording beams using Snell's law:
sine = nOsin~O
and Bragg's law:
2As iI~3o = 1` / nO
where A is the fringe spacing and nO is the average refractive index of the medium. A value of 1.50 for nO is used in all calculations.
Holographic gratings prepared and measured using the specified procedure typically have a spatial frequency of about 1000 lines per mm, i.e., between 900 and 1100 lines per mm. For the purpose of this invention refractive index modulation is defined as the refractive index modulation as measured with 632.8 nm probe radiation from a transmission grating having a spatial frequency of about 1000 lines per mm as prepared by the specified procedure. This refractive index modulation is contrasted to refractive index modulations wherein the spatial frequency is substantially different, is measured with a different probe radiation, or wherein totally different measurement procedure is used, e.g., interference microscopy procedures.
The improved solid photopolymerizable compositions of this invention, which produced acceptably bright and sharp transmission holograms, have a refractive index modulation, M, which is at least about 0.005 as calculated using this procedure and system.
In the compositions of this invention, the preformed polymeric material and the liquid monomer are selected so that either the preformed polymeric material or the monomer contains one or more moietie6 taken from the group consi6ting of 6ub6tituted or unsubstituted phenyl, phenoxy, naphthyl, naphthyloxy, and heteroaromatic group6 containing up to three aromatic rings, chlorine, bromine, and wherein the remaining component is 6ubstantially free of the specified moieties. In the in6tance when the monomer contains these moieties, the photopolymerizable system hereinafter i6 identified as a "Monomer 10 Oriented System", and when the polymeric material contains the6e moieties, the photopolymerizable system hereinafter is identified as a "Binder Oriented System".
The 6table, 601id, photopolymerizable 15 compositions of thi6 invention will be more fully described by reference to the "Monomer Oriented System" and "Binder Oriented Sy6tem".

MONOMER ORIENTED SYSTEM
The monomer of the Monomer Oriented System is a liquid, ethylenically unsaturated compound capable of addition polymerization and having a boiling point above 100C. The monomer contains a sub6tituent from the group consi6ting of phenyl, 25 phenoxy, naphthyl, naphthyloxy, heteroaromatic containing up to three aromatic rings, chlorine, and bromine. The monomer contains at least one such moiety and may contain two or more of the 6ame or different moieties of the group, provided the monomer 30 remains liquid. Contemplated a6 equivalent to the groups are 6ubstituted group6 where the 6ubstitution may be lower alkyl, alkoxy, hydroxy, carboxy, carbonyl, amino, amido, imido or combinations thereof, provided the monomer remains liquid and 35 diffusable in the photopolymerizable layer. Suitable 1~32796 Monomers which can be used as the sole monomer or in combination with liquid monomers of this type include, but are not limited to, styrene, 2-chlorostyrene, 2-bromostyrene, methoxystyrene, 5 phenyl acrylate, p-chlorophenyl acrylate, 2-phenylethyl acrylate, 2-phenoxyethyl acrylate 2-phenoxyethyl methacrylate, phenol ethoxylate acrylate, 2-(p-chlorophenoxy)-ethyl acrylate, benzyl acrylate, 10 2-(1-naphthyloxy)ethyl acrylate, 2,2-ditp-hydroxy-phenyl)-propane diacrylate or dimethacrylate, 2,2-di-(p-hydroxyphenyl)-propane dimethacrylate, polyoxyethyl-2,2-di-(p-hydroxyphenyl)-propane dimethacrylate, di-(3-methacryloxy-2-hydroxypropyl) lS ether of bisphenol-A, di-(2-methacryloxyethyl) ether of bisphenol-A, ethoxylated bisphenol-A diacrylate, di(3-acryloxy-2-hydroxypropyl) ether of bisphenol-A, di(2-acryloxyethyl) ether of bisphenol-A, di(3-methacryloxy-2-hydroxpropyl) ether o~
20 tetrachloro-bisphenol-A, di-(2-methacryloxyethyl) ether of tetrachloro-bisphenol-A, di-(3-methacryloxy-2-hydroxypropyl) ether of tetrabromo-bisphenol-A, di-(2-methacryloxyethyl) ether of tetrabromo-bisphenol-A, 25 di-(3-methacryloxy-2-hydroxypropyl) ether of diphenolic acid, l,4-benzenediol dimethacrylate, 1,4-diisopropenyl benzene, 1,3,5-triisopropenyl benzene, hydroquinone monomethacrylate, and 2-[~-(N-carbazyl)propionyloxy]ethyl acrylate.
Particularly preferred liquid monomers for use in the Monomer Oriented System of this invention are 2-phenoxyethyl acrylate, 2-phenoxyethyl methacrylate, phenol ethoxylate acrylate, 2-(p-chlorophenoxy)ethyl acrylate, p-chlorophenyl acrylate, phenyl acrylate, 2-phenylethyl acrylate, di(2-acryloxyethyl)ether of bi6phenol-A, ethoxylated bisphenol-A diacrylate, and 2-(1-naphthyloxy)ethyl acrylate.
While monomer6 useful in thi6 invention are liquids, they may be used in admixture with a 6econd 601id monomer 6uch a6 N-vinylcarbazole: ethylenically unsaturated carbazole monomers such as disclo6ed in Journal of Polymer Science: Polymer Chemi6try Edition, Vol. 18, page6 9-18 (1979) by H. Kamogawa et al.: 2-naphthyl acrylate: pentachlorophenyl acrylate:
2,4,6-tribromophenyl acrylate, bisphenol A
diacrylate: 2-(2-naphthyloxy)ethyl acrylate: and N-phenyl maleimide.
The 601vent 601uble polymeric material or binder of the Monomer Oriented Sy6tem i8 substantially free of a 6ubstituent from the group consisting of phenyl, phenoxy, naphthyl, naphthyloxy, heteroaromatic containing up to three aromatic rings, chlorine, and bromine.
Suitable binder6 of thi6 clas6, which are 601vent 601uble, thermopla6tic polymer6, can be used alone, or in combination with one another and include the following: acrylate and alpha-alkyl acrylate ester and acid polymer6 and interpolymer6 e.g., 25 polymethyl methacrylate and polyethyl methacrylate:
polyvinyl esters, e.g., polyvinyl acetate, polyvinyl acetate/acrylate, polyvinyl acetate/methacrylate and hydrolyzed polyvinyl acetate: ethylene/vinyl acetate copolymer6: saturated and un6aturated polyurethane6;
30 butadiene and i60prene polymer6 and copolymer6 and high molecular weight polyethylene oxides of polyglycol6 having average molecular weights from about 4,000 to 1,000,000; epoxide6, e.g., epoxide6 containing acrylate or methacrylate group6;
polyamides, e.g., N-methoxymethyl polyhexamethylene ~-327~

adipamide; cellulose esters, e.g., cellulose acetate, cellulose acetate succinate and cellulose acetate butyrate; cellulose ethers, e.g, methyl cellulose, and ethyl cellulose; polycarbonates; and polyvinyl acetals, e.g., polyvinyl butyral and polyvinyl formal. Acid containing polymers and copolymers functioning as suitable binder include those disclosed in U.S. Patent 3,458,311 and in U.S. Patent 4,273,857. As well as the amphoteric polymeric binders disclosed in U.S. Patent 4,293,635.
Particularly preferred binders for use in the Monomer Oriented System of this invention are cellulose acetate butyrate polymers; acrylic polymers and interpolymers including polymethyl methacrylate, methyl methacrylate/methacrylic acid and methyl methacrylate/acrylic acid copolymers, terpolymers of methylmethacrylate/C2-C4 alkyl acrylate or methacrylate/acrylic or methacrylic acid;
polyvinylacetate; polyvinyl acetal; polyvinyl butyral;
polyvinyl formal; and as well as mixtures thereof.

BINDER ORIENTED SYSTEM
The monomer of the Binder Oriented System is a liquid, ethylenically unsaturated compound capable of addition polymerization and having a boiling point above 100C. The monomer is substantially free of moieties taken from the group consisting of phenyl, phenoxy, naphthyl, naphthyloxy, heteroaromatic containing up to three aromatic rings, chlorine and bromine. Suitable monomers of this type which can be used as the sole monomer or in combination with other monomers include, but are not limited to, the following: t-butyl acrylate, cyclohexyl acrylate, 1~32~9~

iso-bornyl acrylate, l,5-pentanediol diacrylate, N,N-diethylaminoethyl acrylate, ethylene glycol diacrylate, 1,4-butanediol diacrylate, diethylene glycol diacrylate, hexamethylene glycol diacrylate, 1,3-propanediol diacrylate, decamethylene glycol diacrylate, decamethylene glycol dimethacrylate, 1,4-cyclohexanediol diacrylate, 2,2-dimethylolpropane diacrylate, glycerol diacrylate, tripropylene glycol diacrylate, glycerol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, polyoxyethylated trimethylolpropane triacrylate and trimethacrylate and similar compounds as disclosed in U.S. Patent 3,380,831, pentaerythritol tetraacrylate, triethylene glycol diacrylate, triethylene glycol 15 dimethacrylate, polyoxypropyltrimethylol propane triacrylate (462), ethylene glycol dimethacrylate, butylene glycol dimethacrylate, l,3-propanediol dimethacrylate, l,2,4-butanetriol trimethacrylate, 2,2,4-trimethyl-1,3-pentanediol dimethacrylate, 20 pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, trimethylolpropane trimethacrylate, l,5-pentanediol dimethacrylate, diallyl fumarate, lH,lH-perfluorooctyl acrylate, lH,lH,2H,2H-perfluorooctyl methacrylate, and 25 1-vinyl-2-pyrrolidinone.
In addition to the ethylenically unsaturated monomers mentioned above, the photohardenable layer can also contain one or more free radical-initiated, chain-propagating, addition-polymerizable, 30 ethylenically unsaturated compounds generally having a molecular weight of at least about 300. Preferred monomers of this type are an alkylene or a polyalkylene glycol diacrylate prepared from an alkylene glycol of 2 to 15 carbons or a polyalkylene 35 ether glycol of 1 to 10 ether linkages, and those 1~3~79~

disclo6ed in U.S. Patent 2,927,022, e.g., those having a plurality of addition polymerizable ethylenic linkages particularly when pre6ent as terminal linkages.
Particularly preferred liquid monomer6 for use in Binder Oriented Systems of this invention include decanediol diacrylate, iso-bornyl acrylate, triethylene glycol diacrylate, diethyleneglycol diacrylate, triethylene glycol dimethacrylate, 10 ethoxyethoxyethyl acrylate, triacrylate ester of ethoxylated trimethylolpropane, and l-vinyl-2-pyrrolidinone.
While monomers useful in Binder Oriented Systems are liquids, they may be used in admixture 15 with a second 601id monomer of the 6ame type, e.g., N-vinylcaprolactam.
The 601vent 601uble, polymeric material or binder of the Binder Oriented System contains in its polymeric structure moieties taken from the group 20 consisting of phenyl, phenoxy, naphthyl, naphthyloxy, heteroaromatic containing up to three aromatic rings, chlorine, bromine and mixtures thereof. Contemplated as equivalent to the groups are 6ubstituted groups where the 6ubstitution may be lower alkyl, alkoxy, 25 hydroxy, carboxy, carbonyl, amido, imido or combinations thereof, provided the binder remains 601vent 601uble and thermoplastic. The moieties may form part of the monomeric unit6 which constitute the polymeric binder or may be grafted onto a preprepared 30 polymer or interpolymer. The binder of this type may be a homopolymer or it may be an interpolymer of two or more 6eparate monomeric units wherein at least one of the monomeric units contains one of the moieties identified above.

21 13327~
Suitable binders of this class which are solvent soluble, thermoplastic polymers or interpolymers can be used alone, or in combination with one another, include the following: polystyrene polymers and copolymers, e.g., with acrylonitrile, maleic anhydride, acrylic acid, methacrylic acid and esters thereof; vinylidene chloride copolymers, e.g., vinylidene chloride/acrylonitrile; vinylidene chloride/methacrylate and vinylidene chloride/vinyl 10 acetate copolymers; polyvinyl chloride and copolymers, e.g., polyvinyl chloride/acetate;
polyvinyl benzal synthetic rubbers, e.g., butadiene/acrylonitrile, acrylonitrile/butadiene/styrene, 15 methacrylate/acrylonitrile/butadiene/styrene copolymers, 2-chlorobutadiene-1,3 polymers, chlorinated rubber, and styrene/butadiene/6tyrene, styrene/isoprene/styrene block copolymers;
copolyesters, e.g., those prepared from the reaction 20 product of a polymethylene glycol of the formula HO(CHZ)nOH, where n is a whole number 2 to 10 inclusive, and (1) hexahydroterephthalic, sebacic and terephthalic acids, (2) terephthalic, isophthalic and sebacic acids, (3) terephthalic and sebacic acids, 25 (4) terephthalic and isophthalic acids, and (5) mixtures of copolyesters prepared from said glycols and (i) terephthalic, isophthalic and sebacic acids and (ii) terephthalic, isophthalic, sebacic and adipic acids; cellulose ethers, e.g., ethyl benzyl 30 cellulose; poly N-vinyl carbazole and copolymers thereof; and carbazole containing polymers such as disclo6ed in Journal of Polymer Science: PolYmer Chemistry Edition, Vol. 18, pages 9-lB (1979) by H.
Kamogawa, et al.

133279~

Particularly preferred binders for use in the Binder Oriented System include polystycene, poly (styrene/acrylonitrile), poly(styrene/methyl methacrylate), and polyvinyl benzal as well as admixtures thereof.
The same photoinitiator system activatable by actinic radiation may be used in either the Monomer Oriented System or the Binder Oriented System. Typically the photoinitiator system will contain a photoinitator and a sensitizer which extends the spectral response into regions having special utility, e.g., the near U.V. region and the visible spectral regions where lasers emit.
Suitable free radical-generating addition 15 polymerization initiators activatable by actinic light and thermally inactive at and below 185C
include the substituted or unsubstituted polynuclear quinones which are compounds having two intracyclic carbon atoms in a conjugated carbocyclic ring system, 20 e.g., 9,10-anthraquinone, l-chloroanthraquinone, 2-chloroanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, octamethylanthraquinone, l,4-naphthoquinone, 9,10-phenanthrenequinone, 1,2-benzanthraquinone, 25 2,3-benzanthraquinone, 2-methyl-1,4-naphthoquinone, 2,3-dichloronaphthoquinone, 1,4-dimethylanthraquinone, 2,3-dimethylanthraquinone, 2-phenylanthraquinone, 2-3-diphenylanthraquinone, sodium salt of anthraquinone alpha-sulfonic acid, 30 3-chloro-2-methylanthraquinone, retenequinone, 7,8,9,10-tetrahydronaphthacenequinone, and 1,2,3,4-tetrahydrobenz(a)anthracene-7,12-dione.
Other photoinitiators which are also useful, even though some may be thermally active at temperatures 35 as low as 85C, are described in U.S. Patent 1~279~
_ 23 2,760,863 and include vicinal ketaldonyl alcohols, such as benzoin, pivaloin, acyloin ethers, e.g., benzoin methyl and ethyl ethers; ~-hydrocarbon-substituted aromatic acyloins, including ~-methylbenzoin, ~-allylbenzoin and ~-phenylbenzoin. Photoreducible dyes and reducing agents, such as those disclosed in U.S.
Patents: 2,850,445: 2,875,047; 3,097,096; 3,074,974;
3,097,097; 3,145,104 and 3,579,339; as well as dyes of the phenazine, oxazine, and quinone classes; Michler's ketone, benzophenone; 2,4,5-triphenylimidazolyl dimers with hydrogen donors, and mixtures thereof as described in U.S. Patents: 3,427,161; 3,479,185; 3,549,367;
4,311,783; 4,622,286; and 3,784,557 can be used as initiators. A useful discussion of dye sensitized photopolymerization can be found in "Dye Sensitized Photopolymerization" by D.F. Eaton in Adv. in Photochemistry, Vol. 13, D.H. Volman, G.S. Hammon, and K.
Gollnick, eds., Wiley-Interscience, New York, 1986, pp.
427-487. Similarly the cyclohexadienone compounds of U.S. Patent No. 4,341,860 are useful as initiators.
Preferred photoinitiators include CDM-HABI, i.e., 2-(o-chlorophenyl)-4,5-bis(_-methoxyphenyl)imidazole dimer; o-Cl-HABI, i.e., l,l'-biimidazole, 2,2'-bis (o-chlorophenyl)-4,4',5,5'-tetraphenyl-; and TCTM-HABI, i.e., lH-imidazole, 2,5-bis (o-chlorophenyl)-4-3,4-dimethoxyphenyl-,dimer, each of which is typically used with a hydrogen donor, e.g., 2-mercaptobenzoxazole.
Sensitizers useful with photoinitiators include methylene blue and those disclosed in U.S. Patents 3,554,753; 3,563,750; 3,563,751; 3,647,467; 3,652,275;
4,162,162; 4,268,667; 4,351,893;

~.~ . .

13327.g~ `

4,454,218; 4,535,052; and 4,565,769. Particularly preferred sensitizers include the following:

S DBC, i.e., cyclopentanone, 2,5-bis {[4-(diethylamine)-2-methylphenyl]-methylene};
DEAW, i.e., Cyclopentanone, - 2,5-bis{t4-(dlethylamino)-phenyl] methylene}; and dimethoxy-JDI, i.e., lH-inden-1-one, 2,3-dihydro-5,6-dimethoxy-2-[(2,3,6,7-tetra-hydro-lH,5H-benzo [i,j] quinolizin-9-yl)methylene]-.

which have the following structures respectively:

(CH3CH2)2N ~ ~ CH ~ ~ CH ~ ~ N(CH2CH3)2 DBC

(CH3CH2)2N ~ CH ~ CH ~ - N(CH2CH3)2 DEAW

CH30 ~ ~ ~ CH ~ ~ N

DIMETHOXY - JDI

~ ~3~79~

The solid, photopolymerizable compositions of this invention may contain a plasticizer to enhance the refractive index modulation of the imaged composition. Plasticizers typically may be used in amounts varying from about 2% to about 25% by weight of the composition, preferably 5 to about 15 wt.%.
Suitable plasticizers include, triethylene glycol, triethylene glycol diacetate, triethylene glycol diproprionate, triethylene glycol dicaprylate, triethylene glycol dimethyl ether, triethylene glycol bis(2-ethyl-hexanoate), tetraethylene glycol diheptanoate, poly(ethylene glycol), poly(ethylene glycol) methyl ether, isopropylnaphthalene, diisopropylnaphthalene, poly(propylene glycol), glyceryl tributyrate, diethyl adipate, diethyl sebacate, dibutyl suberate, tributyl phosphate, tris (2-ethylhexyl) phosphate, Brij~ 30 tC12H2s(CH2CH2)4H]~ and Brij~ 35 t 12 25(0CH2CH2)2oOH]~ Many of the plasticizers can be expressed by the following general formulae:
O O
,. ..
RlC(0CH2cH2)xOc R2;
O O
q r .. ..
RlOC(CH2)yC~OR2; or R3(OCH2CHR4)zOH
wherein each of Rl and R2 is alkyl group of 1 to 10 carbon atoms; R3 is H or an alkyl group having 8 to 16 carbon atoms, R4 is H or CH3; x is 1 to 4;
y is 2 to 10 and z is 1 to 20. Particularly preferred plasticizers for use in simple cellulose acetate butyrate systems are triethylene glycol dicaprylate, tetraethylene glycol diheptanoate, diethyl adipate, Brij~30 and ~332~

tris-(2-ethylhexyl)phosphate. Similarly, triethylene glycol dicaprylate, diethyl adipate, Brij~30, and tris-(2-ethylhexyl)phosphate are preferred in "Monomer Oriented Systems" where cellulose acetate butyrate is the binder.
Other plasticizers that yield equivalent results will be apparent to those skilled in the art, and may be employed in accordance with the invention. It also will be appreciated that plasticizers may be substituted for some or all of the liquid monomer in the event that a solid monomer is present, provided that the mixture of plasticizer and monomer(s) remain liquid. Other conventional components that are used in photopolymer systems may be utilized with the compositions and elements of this invention if so desired.
Such components include: optical brighteners, ultraviolet radiation absorbing material, thermal stabilizers, hydrogen donors, oxygen scavengers and release agents.
Optical brighteners useful in the process of the invention include those disclosed in Held U.S. Patent 3,854,950. A preferred optical brightener is 7-(4'chloro-6'-di-ethylamino-1',3',5'-triazine-4'-yl) amino 3-phenyl coumarin. Ultraviolet radiation absorbing materials useful in the invention are also disclosed in Held U.S. Patent 3,854,950.
Useful thermal stabilizers include: hydroquinone, phenidone, p-methoxyphenol, alkyl and aryl-substituted hydroquinones and quinones, tert-butyl catechol, pyrogallol, copper resinate, naphthylamines, beta-naphthol, cuprous chloride, 2,6-di-tert-butyl p-cresol, phenothiazine, pyridine, nitrobenzene, dinitrobenzene, p-toluquinone and chloranil.
The dinitroso dimers described in Pazos X

~L~32~9~
_ 27 U.S. Patent 4,168,982 are also useful. Normally a thermal polymerization inhibitor will be present to increase stability in the storage of the photopolymerizable composition.
Hydrogen donor compounds useful as chain transfer agents in the photopolymer compositions include: 2-mercaptobenzoxazole, 2-mercaptobenzothiazole, etc.; as well as various types of compounds e.g., (a) ethers, (b) esters, (c) alcohols, (d) compounds containing allylic or benzylic hydrogen cumene, (e) acetals, (f) aldehydes, and (g) amides as disclosed in column 12, lines 18 to 58 of MacLachlan U.S. Patent 3,390,996.
Compounds which have been found useful as release agents are described in Bauer U.S. Patent 4,326,010. A
useful release agent is polycaprolactone.
Amounts of ingredients in the photopolymerizable compositions will generally be within the following percentage ranges based on total weight of the photopolymerizable layer: monomer, 5-60%, preferably 15-50%; initiator 0.1-10%, preferably 1-5%: binder, 25-75%, preferably 45-65%; plasticizer, 0-25%, preferably 5-15%;
and other ingredients 0-5%.
The invention now will be further described by reference to the following examples.

GENERAL PROCEDURES
Sample Preparation Coating solutions without visible sensitizer, DEAW
unless othewise indicated, were prepared under yellow or red light. After addition 13~g~

of visible sensitizer, all operations on solutions and the resulting coatings were performed under red light only. To further protect them from light, solutions were prepared and stored in amber bottles. Solutions were prepared by adding components to the solvent and then mixing with a mechanical stirrer until they completely dissolved. The solvent used was either dichloromethane;
a mixture of dichloromethane (80-85 wt%), chloroform (10%), and methanol (5-10%): or dichloromethane (90-92%) and 2-butanone (8-10%). The components of all solutions were used as received from the manufacturer without purification, except for the monomer TDA which was chromatographed on aluminum oxide (activity-1) just prior to use.
Solutions were coated onto a clear film support of polyethylene terephthalate (Cronar~C72 or 400 D Mylar~) at a web speed of 4 cm/sec using a Talboy coater equipped with a doctor knife, 3.7 m drier set at 50-70C, and a laminator station. A cover sheet of 25 micron polypropylene was laminated to the coatings after drying.
Coating samples were stored in black polyethylene bags at room temperature until used. Identification of the chemical components used in sample preparation is contained in the "glossary of chemical names" which follows.

Sample Evaluation Sections of coated film were cut, the cover sheet removed, and then mounted onto lOX13 cm glass plates by hand laminating the tacky coating directly to the glass surface. The polyethylene terephthalate film support was left in place and served to protect the coating during handling and exposure operations.

_ 'b 1~32796 _ 29 Glass mounted coatings were evaluated by recording a series of holographic diffraction gratings and determining their efficiency. Gratings were obtained by actinic exposure at the intersection of two interfering collimated beams of an argon ion laser operating at 488 nm and TEM~. See the Figure. The beam intensity ratio was maintained at about 1:1, with absolute intensities ranging from 3-10 mW/c* per beam. The diameter of each beam was about 1 cm. Exposure times ranged from about 1 sec to several minutes, depending on the system, corresponding to 12.5-2,000 mJ/cm2 total exposure. About one minute after the image-wise exposure just described, each grating was given a 1-2 minute fixing exposure using one of the two 488 nm laser beams. Grating formation was measured in real time by passing a 632.8 nm He:Ne laser beam through the center of the exposure area at the Bragg angle. The intensity of the He:Ne laser beam was monitored with a Coherent model 212 power meter attached to a strip chart recorder. Gratings so produced have a spatial line frequency of about 1000 lines per mm; i.e., between 900 and 1100 lines per mm. Diffraction efficiency (~) was calculated as the ratio of the diffracted beam intensity (Id~) to the pre-exposure undiffracted beam intensity (Io) after passing through the coating:
~ = Id~/Io A series of exposure times was used so maximum ~ could be determined. Coating thicknesses were measured for photocured samples using either a Sloan DEKTAK* 3030 surface profile monitoring system or a Brown and Sharpe model 975 Electronic Comparator.
For each sample, the refractive index modulation in the recorded gratings was calculated * denotes trademark t~

13327!~

from measured diffraction efficiencies and coating thicknesses using Kogelnik's coupled wave theory, previously described.
s Glossary of Chemical Names BHT 2,6-Di-tert-butyl-4-methylphenol CAB Cellulose acetate butyrate Carboset*XL-27 Poly(methyl methacrylate/ethyl-acrylate/acrylic acid) wt. av. MW
40,000, Acid No. 80, Tg53C

5 Carboset*525 Poly(methyl methacrylate/ethyl-acrylate/acrylic acid) wt. av. MW
200,000, Acid No. 80, Tg37C
o-C1-HABI 1,1'-Biimidazole, 2,2'-bis[o-chloro-phenyl]-4,4',5,5'-tetraphenyl-;

CPA p-Chlorophenyl acrylate CP19-Y 90:10 poly(methyl methacrylate-methacrylic acid) DDA 1,10-Decanediol diacrylate DEAW Cyclopentanone, 2,5-bis{{4-(diethyl-amino)-phenyl]methylene};

Dimethoxy-JDI lH-Inden-1-one, 2,3-dihydro-5,6-dimethoxy-2-[(2,3,6,7-tetra-hydro-lH,5H-benzo ti,j]
quinolizin-9-yl)methylene]-;

Elvacite~2008 98:2 poly(methyl methacrylate-methacrylic acid); MW=25,000 Elvacite~2051 poly(methyl methacrylate); MW=350,000 lH,lH-PFOA lH,lH- Perfluorooctyl acrylate lH,lH,2H,2H- lH,lH-2H,2H-Perfluorooctyl PFOMA methacrylate *denotes trademark ~ g~3 MHQ 4-methoxyphenol MBO 2-Mercaptobenzoxazole; 2-Benzoxazole-thiol; CAS 2382-96-9 NVC N-Vinyl carbazole; 9-Vinyl carbazole;

PA Phenyl acrylate; 2-Propenoic acid, phenyl ester; CAS 937-41-7 POEA 2-Phenoxyethyl acrylate;

10 TCTM-HABI lH-Imidazole, 2,5-bisto-chlorophenyl]-4-t3,4-dimethoxyphenyl]-, dimer;

TDC Triethylene glycol dicaprylate;

15 TDA Triethylene glycol diacrylate;

TMPEOTA Triacrylate ester of ethoxylated trimethylolpropane; CAS 28961-43-5 TMPTMA Trimethylolpropane trimethacrylate;
2-ethyl-2-(hydroxymethyl)-1,3-propanediol trimethacrylate;
CAS 3290-92-4.
CONTROL EXAMPLES A - I
The following examples illustrate representative prior art compositions using cellulose acetate butyrate binder (Eastman CAB#531-1), a hexaarylbiimidazole/dye-sensitizer initiator system and various monomers.
Photopolymerizable compositions were prepared according to the general procedure as follows: 78 g dichloromethane, 12.5 g (50.4% of solids) CAB 531-1, 11.5 g (46.4%) of monomer, 0.45 g (1.89%) of MBO, 0.3 g (1.29%) o-Cl-HABI, 0.07 - 0.28%
DEAW (depending on thickness) and 0.0025 q BHT
dissolved in 1 mL of dichloromethane.

13327~

The compositions were evaluated according to the general procedure. Refractive index modulation and diffraction efficiency values measured for the resulting holographic diffraction gratings are shown 5 in the table below.

Refractive Index Control Modulation Thickness Example Monomer (X100) (Microns) DE(%) A Triethylene glycol diacrylate 0.24 14 3.0 B Triethylene glycol diacrylate 0.28 38.1 27 C Triethylene glycol diacrylate 0.30 66.3 78 D Triethylene glycol dimethacrylate 0.27 49.5 39 E Diethylene glycol diacrylate 0.30 49.5 48 F Decanediol diacrylate 0.18 50.8 21 G Ethoxyethoxyethyl acrylate 0.13 48.8 10 H Trimethylolpropane triacrylate 0.24 53.3 37 I iso-Bornyl acrylate 0.20 53.8 27 CONTROL EXAMPLES J - O
The following examples illustrate compositions where both the polymeric binder and the unsaturated monomer used therein contain one or more phenyl or phenoxy qroups. Coating compo~itions were prepared and evaluated as for Control Example~ A - I.

13~2~6 The compositions were evaluated according to the general procedure. Refractive index modulation and diffraction efficiency values measured for the resulting holographic diffraction gratings are shown in the table below.

Control Modulation Example Monomer (X100) Thickness DE(%) Poly(styrene) Binder J 2-Phenoxyethyl 0.52 30.5 52 acrylate 70:30 Poly(styrene-methylmethacrylate) K 2-Phenoxyethyl 0.16 60.9 23 acrylate L 2-Phenylethyl 0.28 20.3 8 acrylate 75:25 Poly(stYrene acrylonitrile) M 2-Phenoxyethyl 0.31 64.8 71.5 acrylate N 2-Phenylethyl 0.46 20.3 21 methacrylate 0 2-Phenylethyl 0.15 22.9 3 methacrylate This example illustrates a useful composi-tion using CAB binder, a hexaarylbiimidazole/dye sensitizer initiator system, and POEA monomer.
A photopolymerizable composition was prepared according to the general procedure given above as follows: 78 g dichloromethane, 12.5 g (50.4%
of solids) CAB-531-1, 11.5 g (46.3%) POEA, 0.45 g (1.8%) MBO, 0.3 g (1.2%) TCTM-HABI, 0.070 g (0.3%) 133~7~

DEAW, and 0.0025 g (0.01%) of MHQ dissolved in 1 mL
of dicholoromethane.
The composition was evaluated according to the general procedure described above. An 11.2 micron coating of this composition had a measured refractive index modulation 0.010. A 17.3 micron coating of the same composition had a measured refractive index modulation of 0.011.

A 23.1 micron coating of a composition similar to that of Example 1, except that it contained 0.040 g of DEAW instead of 0.070 g DEAW, had a measured refractive modulation of O.O10.

These examples illustrates other useful compositions using CAB binders, a hexaarylbiimidazole/dye sensitizer initiator system, and other photopolymerizable monomers.
The procedure of Example 1 was followed with a number of other photopolymerizable monomers in place of POEA and with other grades of CAB to illustrate their utility in the practice of this invention. The compositions in Examples 3 and 4 contained 0.070 g of DEAW; the compositions in Examples 5-11 contained 0.040 g of DEAW: and the compositions in Examples 12 and 13 contained 0.017 g of DEAW. The monomers and binders used, as well as the measured refractive index modulations, are set forth below.
It can be seen that greatly improved refractive index modulation was achieved in these examples compared to control examples A - I.

1~3~7g~

Refractive Index Modulation Thickness Ex. Monomer ~X100) (Microns) DE(%) CAB TYpe 531-1 1 POEA 1.0 11.2 30 POEA 1.1 17.3 70 2 POEA 1.0 23.1 84 3 2-Phenoxyethyl methacrylate 0.7713.5 24 2-Phenoxyethyl methacrylate 0.5522.6 35 4 2-(D-Chlorophenoxy)ethyl acrylate 1.0 12.7 36 2-(p-Chlorophenoxy)ethyl acrylate 1.1 23.1 90 5 p-Chlorophenyl acrylate 1.1 18.8 72 6 2-Phenylethyl acrylate 0.5518.8 25 7 Phenyl acrylate (PA) 0.9611.7 29.5 8 80% POEA - 20%
2,4,6-tribromo PA 1.3 19.3 90 9 80% POEA - 20%
2-naphthyl acrylate 1.3 8.9 31 80% POEA - 20%
2-naphthyl acrylate 1.4 11.7 57 80% POEA - 20S
2-naphthyl acrylate 1.4 21.3 100 10 80% POEA - 20%
pentachloro PA 1.2 19.1 85 11 63% POEA - 37%
NVC 1.5 9.7 47 63% POEA - 37%
NVC 1.5 10.9 53 35~

~3~27~

(continued) Refractive Index Modulation Thickne66 Ex. Monomer (~100) (Microns) DE(%) CAB Type 531-1 12 85% POEA - 15% NVC 1.5 8.1 33 85% POEA - 15% NVC 1.5 10.2 49 CAB Type 551-0.2 13 POEA 1.0 21.3 80 CAB Type 553-0.4 14 POEA 0.58 24.4 43 1~3279~`

These examples illustrate other useful compositions using poly(methyl methacrylate) and its copolymers as binders, a hexaarylbiimidazole/dye sensitizer initiator system, and POEA monomer.
The procedure of Example 1 was followed with the exception that the binder6 set forth in the following table were used. All the compositions in these examples contained 0.017 g of DEAW. The measured refractive index modulations are significantly higher than in control examples A-I.

Refractive Index Modulation Thickness E BINDER (X100) (Microns) DE(%) Elvacite~ 2008 0.81 27.9 83 16 CP-19Y 1.0 20.1 74 17 Elvacite~ 2051 1.0 24.1 8g 18 Carboset~ XL-27 0.57 28.0 53 19 Carboset~ 525 0.89 29.2 94 These examples illustrate useful compositions wherein decanediol diacrylate (DDA) monomer and various binders containing phenyl groups are used. The refractive index modulation values are set forth in the following table and are significantly higher than in the corre~ponding control examples E and J-O.

The procedure of Example 1 was followed with the exception that poly(styrene), Mn=116,000, MW306,000, was used as the binder and DDA

was used as photopolymerizable monomer. The composition contained 0.017 g of DEAW.

The procedure of Example 1 was followed with the exception that poly(styrene-methyl methacrylate) (70:30), Mn=108,000, MW=233,000, was used as the binder. The photopolymerizable monomer was DDA. The composition contained 0.017 g of DEAW.

The procedure of Example 1 was followed with the exception that poly(styrene-acrylonitrile) (75:25) was used as the binder with DDA monomer. The composition contained 0.040 g of DEAW.
Refractive Index Modulation Thickness Ex. BINDER (X100) (Microns) DE(~) Poly(styrene) 1.1 23.4 92 21 70:30 Poly(styrene-methylmethacrylate) 0.90 27.9 92 22 75:25 Poly(styrene-acrylonitrile) 1.1 25.4 97 These examples illustrate other useful compositions wherein different monomers are used with a poly(styrene) binder.
The procedure of Example 1 was followed with the exception that poly(styrene), Mn=116,000, MW=306,000, was used as the binder and various other photopolymerizable monomers were u~ed. All the compositions in these examples contained 0.017 g of D~AW. The monomer6 used and the measured refractive index modulations are set forth in the following 133279~

table. It can be seen that the results are superior to control examples, e.g., Example 25 vs. control Example I.

Refractive Index Modulation Thickness Ex. Monomer (X100) (Microns) DE(%~
23 80% DDA - 20%
lH,lH-PFOA 0.94 20.8 70 24 80% DDA - 20%
lH,lH,2H,2H- 0.98 26.2 93 PFOMA
iso-Bornyl acrylate 0.68 22.9 51 These examples illustrate other useful compositions wherein different monomers are used with 70:30 poly(styrene-methyl methacrylate) binder.
The procedure of Example 1 was followed with the exception that poly(styrene-methyl methacrylate) (70:30), Mn=108,000, MW=233,000, was used as the binder and various other photopolymerizable monomers were used. The compositions in Examples 26-28 contained 0.040 g of DEAW: the compositions in Examples 29-30 contained 0.017 g of DEAW. The monomers used and the measured refractive index modulations are set forth in the following table.
The results are superior to control Examples, particularly control Examples A, D, E, I, K and L.

13~27~
Refractive Index Modulation Thickness Ex. Monomer (X100) (Microns) DE(%) 26 Triethylene glycol diacrylate 0.90 23.9 78.5 27 Diethylene glycol diacrylate 0.86 22.1 67.5 28 Triethylene glycol dimethacrylate 0.67 18.3 34 29 iso-Bornyl acrylate 0.65 27.9 6g 30 TMPEOTA 0.52 21.1 28 These examples illustrate other useful compositions wherein different monomers are used with 75:25 poly(styrene-acrylonitrile) binder.
The procedure of Example 1 was followed with the exception that poly(styrene-acrylonitrile) (75:25) was used as the binder and various other photopolymerizable monomers were used. The compositions in Examples 31-32 contained 0.040 g of DEAW: the compositions in Examples 33-36 contained 0.017 g of DEAW. The monomers used and the measured refractive index modulations are set forth in the following table. The results are superior to control Examples, particularly control Examples A, D, E, I, M, N and O.

41 13327~36 Refractive Index Modulation Thickness Ex. Monomer (X100) (Microns) DE(%) 31 Triethylene glycol diacrylate 1.1 19.3 75.5 32 Diethylene glycol diacrylate 0.93 24.6 84 33 80% DDA - ZO%
lH,lH-PFOA 1.2 20.8 90 34 Triethylene glycol dimethacrylate 0.62 24.4 48.5 35 Ethoxyethoxyethyl acrylate 1.3 20.3 93 36 iso-Bornyl acrylate 0.68 28.2 69 This example illustrates a useful composition using 70:30 poly(styrene-methyl methacrylate) binder, a hexaarylbiimidazole/dye sensitizer initiator system, and TDA monomer, wherein a different dye sensitizer is used.
The following were dissolved in 88 g of dichloromethane: 13.0 g (50.4%) 70:30 poly(styrene-methyl methacrylate), 11.5 g (44.5%) TDA, 0.45 g (1.7%) MBO, 0.8 g (3.1%) TCTM-HABI, 0.066 g (0.3%) dimethoxy-JDI, and 0.0025 (0.01%) MHQ
dissolved in 1 mL of 95% dichloromethane - 5%
methanol. The composition was evaluated by the procedure described in Example 1. A refractive index modulation of 0.0054 was measured.

1 3 ~

This example illustrates a useful composition wherein a sensitizing dye and an amine are used to initiate photopolymerization.
The following were dissolved in 88 g of 95%
dichloromethane - 5% methanol:13.9 g (53.8%) 70:30 poly(styrene-methyl methacrylate), 11.5 g (44.5%) TDA, 0.35 g (1.36%) N-phenyl glycine, 0.066 of (0.3%) acridine orange, and 0.0025 (0.01%) MHQ dissolved in 1 mL of 95%
dichloromethane - 5% methanol.
The composition was evaluated by the procedure described in Example 1. A refractive index modulation of 0.0054 was measured.

These examples are useful compositions containing TDC plasticizer, PEOA monomer, and CAB 531-1 binder.
Two formulations were prepared, each containing different amounts of TDC and POEA, as tabulated below, and each containing 2.67 g CAB 531-1 (44.8%), 0.24 g TCTM-HABI (4.0%), 0.12 g MBO (2.0%), 0.0030 g DEAW
(0.05%), 0.006 g MHQ (001%), 1.9 g 2-butanone, and 17.09 g dichloromethane. The formulations were coated and evaluated as in Example 1, except the doctor knife had a 100 micron gap and the drier was set at 40-50C. Results are presented in table below. The refractive index modulation is greater than for the corresponding Examples 1 and 2 which did not contain TDC plasticizer.

These examples are useful compositions containing TDC plasticizer, CPA monomer, and CAB 531-1 binder.

43 133279~
Two formulations were prepared, each containing dif~erent amount~ of TDC and CPA, as tabulated below, and each containing 5.34 g CAB 531-1 (44.8%), 0.48 g TCTM-HABI (4.0%), 0.24 g MBO (2.0%), 0.0060 g DEAW (0.05%), 0.0012 g MHQ (0.01%), 3.8 g 2-butanone, and 34.18 g dichloromethane. The formulations were coated and evaluated as de6cribed in example6 39 - 40; result6 are presented in the table below. The refractive index modulation is greater than for the corresponding Example 5 which did not contain TDC pla~ticizer.

Monomer Grams Plasticizer Thickness Refractive Index Ex. (wt%) Grams (wt%) (~icrons) DE(%) ~odulation (~100) 39 POEA, TDC, 0.30 (5%) 9.32 28% 1.2 2.6 (44%) 40 POEA, TDC, 0.90 (15%) 8.95 37% 1.4 2.0 (34%) 41 CPA, TDC, 0.60 (5~) 6.27 16% 1.3 5. 3 (44%) 42 CPA, TDC, 1.80 (15%) 5.89 18% 1.5 4.1 (34%) Thi6 example i6 a useful composition containing TDC pla~ticizer, POEA monomer, NVC
monomer, and CAB 531-1 binder.
A formulation was prepared containing 8.06 g ~30 CAB 531-1 (44.8%), 5.58 g POEA (31%), 1.08 g NVC
(6.0%), 2.70 g TDC (15%), 0.18 g TCTM-HABI (1.0%), 0.36 g MBO (2.0%), 0.040 g DEAW (0.22%), 0.0018 g BHT
(0.01%), 4.56 g 2-butanone, and 52.4 g dichloromethane. The formulation was coated and _ 44 1~3279~

evaluated as described in examples 39 - 40; re~ults are as follows:
Coating Thickness: 8.96 microns Diffraction Efficiency: 72%
Index Modulation X100: 2.2 (Greater than Examples 11-12) These examples show the concentration effect 10 of TDC plasticizer in compositions containing TDA
monomer and CAB 531-1 binder.
Five formulations were prepared, each containing different amounts of TDC and TDA, as described below, and each containing 12.6 g CAB 531-1 (54.8%), 0.23 g TCTM-HABI (1.0%), 0.46 g MB0 (2.0%), O.0104 g DEAW (0.045%), 0.0023 g MHQ (0.01%), 3.85 g methanol, 7.7 g chloroform, and 65.45 g dichloromethane. The formulations were coated and evaluated as described in Example l; results are presented in the following table.
Refractive TDC TDA Index Grams Grams Thickness Modulation Ex. (wt%) (wt%) (Microns) DE(%) (X100) 44 0.00 (0.0%) 9.66 (42%) 47.8 25 0.22 45 2.30 (10%) 7.36 (32%) 54.0 51 0.29 46 3.45 (15%) 6.21 (27%) 52.1 97 0.52 47 4.60 (20%) 5.06 (22%) 53.8 66 0.35 48 5.75 (25%) 3.91 (17%) 53.2 54 0.30 These examples illustrate useful compositions containing TDC plasticizer, TDA monomer, and different CAB binders.

A formulation was prepared containing 131.52 g CAB 531-1 (54.9%), 64.8 g TDA (27%), 36 g TDC
(15%), 2.4 g TCTM-HABI (1.0%), 4.8 g MB0 (2.0%), 5 0.108 g DEAW (0.0451%), 0.024 g MHQ (0.01%, 76 g methanol, 76 g chloroform, and 608 g dichloromethane. The solution was coated and evaluated according to the procedure of Example l;
results are presented below.

A formulation was prepared containing 65.76 g CAB S00-S (54.9%), 32.4 g TDA (27%), 18 g TDC
(15%), 1.2 g TCTM-HABI (1.0%), 2.4 g MBO (2.0%), 0.054 g DEAW (0.045%), 0.012 g MHQ (0.01%), 38 g methanol, 38 g chloroform, and 304 g dichloromethane. The formulation was coated and evaluated as described in Example 1: results are presented below.

A formulation was prepared containing 65.76 g CAB 381-20 (56.6%), 31.4 g TDA (27%), 17.5 g TDC
(15%), 1.2 g TCTM-HABI (1.0%), 2.3 g MB0 (2.0%), 0.052 g DEAW (0.045%), 0.012 g MHQ (0.01%), 37.7 g methanol, 37.7 g chloroform, and 301 g dichloromethane. The formulation was coated and evaluated as described in Example l; results are presented below:

13327~6 Refractive Index Thickness Modulation Ex. Binder Plasticizer (Microns) DE(%) (X100) 49 CAB 531-1 TDC (15%) 51.0 94% 0.51 CAB 500-5 TDC (15%) 50.9 92% 0.50 51 CAB 381-20 TDC (15%) 50.0 90% 0.49 The materials described herein, particularly in Examples 3-14, and the apparatus in the figure is also used to form holographic optical elements, commonly called HOE~s.
For example, a holographic lens is formed exposing the glass-mounted sample (28) to two interfering laser beams (38), one which is collimated as in the figure and the other which i8 diverging.
The diverging beam is formed by removing one of the collimating lens (40). The focal length of the holographic lens thus formed is equal to the distance from the spatial filter's (26) pin hole and the glass-mounted sample.
Once the holographic lens is formed in this manner, its focusing ability is demonstrated by rotating the holographic lens, i.e., the glass-mounted sample (28), 180 degrees about a vertical axis through its center and passing only the collimated laser beam (38) through it. The collimated laser beam is diffracted by the holographic lens 60 as to focus the beam to a point at a distance from the holographic lens which is equal to the lens's focal length, as determined above.
Other holographic optical elements may similarly be prepared by replacing one of the collimating lens (40) with a suitable optical 47 1 33~ 79 6 component, e.g., a converging lens or some other complex optical component. Such holographic optical elements may be inexpensively reproduced and replace polished and molded elements currently in use, e.g., 5 Fresnell lenses, head light lenses, etc.
Having described the invention, we claim:

Claims (27)

1. A substantially solid, photopolymerizable composition that forms a refractive-index image upon exposure to actinic radiation as the sole processing step, said composition consisting essentially of:
(a) 20 to 75% of a solvent soluble, thermoplastic polymeric binder;
(b) 5 to 60% of a mixture of (i) a liquid ethylenically unsaturated monomer and (ii) a solid ethylenically unsaturated monomer, said monomers having boiling points above 100°C and being capable of addition polymerization; and (c) 0.1 to 10% of a photoinitiator system that activates polymerization of said unsaturated monomer on exposure to actinic radiation;
wherein said percentages are weight percentages based on the total weight of components (a), (b), and (c), the composition having a refractive index modulation of at least 0.005 as determined with 632.8 nm radiation from a transmission grating having a spatial frequency of about 1000 lines per millimeter, which transmission grating is prepared holographically form a layer of said composition, wherein said solid monomer contains a substituent selected from the group consisting of (1) aromatic moieties selected from the group consisting of (i) substituted or unsubstituted naphthyl and (ii) substituted or unsubstituted heteroaromatic moieties having up to three rings; (2) chlorine; and (3) bromine, and said binder is substantially free of substituents selected from the group consisting of (1) aromatic moieties selected from the group consisting of (i) substituted or unsubstituted phenyl; (ii) substituted or unsubstituted naphthyl and (iii) substituted or unsubstituted heteroaromatic moieties having up to three rings; (2) chlorine; and (3) bromine.

2. The composition of claim 1 wherein said liquid monomer contains a substituent selected from the group consisting of (1) aromatic moieties selected from the group consisting of (i) substituted or unsubstituted phenyl; (ii) substituted or unsubstituted naphthyl and (iii) substituted or unsubstituted heteroaromatic moieties having up to three rings; (2) chlorine; and (3) bromine.

3. The composition of claim 1 or 2 wherein said solid monomer contains a carbazole group.

4. The composition of claim 3 wherein said solid monomer is selected from the group consisting of N-vinyl carbazole and 3,6-dibromo-9-vinyl carbazole.

5. The composition of claim 1 or 2 wherein said solid monomer is selected form the group consisting of 2,4,6-tribromophenyl acrylate and methacrylate, pentachlorophenyl acrylate and methacrylate, 2-naphthyl acrylate and methacrylate, 2-(2-naphthyloxy)ethyl acrylate and methacrylate, the di-(2-acryloxyethyl)ether of tetrabromo-bis-phenol A, and mixtures thereof.

6. A substantially solid, photopolymerizable composition that forms a refractive-index image upon exposure to actinic radiation as the sole processing step, said composition consisting essentially of:
(a) 20 to 75% of a solvent soluble, thermoplastic polymeric binder;
(b) 5 to 60% of a mixture of (i) a liquid ethylenically unsaturated monomer, (ii) a solid ethylenically unsaturated monomer, said monomers having boiling points above 100°C and being capable of addition polymerization, and (iii) a plasticizer; and (C) 0.1 to 10% of a photoinitiator system that activates polymerization of said unsaturated monomer on exposure to actinic radiation;
wherein said percentages are weight percentages based on the total weight of components (a), (b), and (c), the composition having a refractive index modulation of at least 0.005 as determined with 632.8 nm radiation from a transmission grating having a spatial frequency of about 1000 lines per millimeter, which transmission grating is prepared holographically from a layer of said composition, wherein said solid monomer contains a substituent selected from the group consisting of (1) aromatic moieties selected from the group consisting of (i) substituted or unsubstituted phenyl, (ii) substituted or unsubstituted naphthyl, and (iii) substituted or unsubstituted heteroaromatic moieties having up to three rings; (2) chlorine; and (3) bromine, and said binder is substantially free of said substituent; and wherein said plasticizer is selected from the group consisting of tris(2-ethylhexyl)phosphate, glyceryl tributyrate, and compounds having the general formula:

R1C(O) (OCH2CH2)xOC(O)R2;

R1O2C(CH2)yCO2R2; or R3(OCH2CHR4)ZOH, wherein R1 and R2 are each alkyl groups of 1 to 10 carbon atoms, R3 is H or an alkyl group of 8 to 16 carbon atoms, R4 is H or CH3, x is 1-4, y is 2-20, and z is 1-20.

7. The composition of claim 6 wherein said liquid monomer contains a substituent selected from the group consisting of (1) aromatic moieties selected from the group consisting of (i) substituted or unsubstituted phenyl; (ii) substituted or unsubstituted naphthyl and (iii) substituted or unsubstituted heteroaromatic moieties having up to three rings; (2) chlorine; and (3) bromine.

8. The composition of claim 6 or 7 wherein said solid monomer contains a carbazole group.

9. The composition of claim 7 wherein said solid monomer is selected from the group consisting of N-vinyl carbazole and 3,6-dibromo-9-vinyl carbazole.

10. The composition of claim 6 or 7 wherein said solid monomer is selected from the group consisting of 2,4,6-tribromophenyl acrylate and methacrylate, pentachlorophenyl acrylate and methacrylate, 2-naphthyl acrylate and methacrylate, 2-(2-naphthyloxy)ethyl acrylate and methacrylate, the di-(2-acryloxyethyl)ether of tetrabromo-bix-phenol A, and mixtures thereof.

11. An element containing a hologram formed by exposing to modulated actinic radiation bearing holographic information an element comprising a substrate that supports a substantially solid, photopolymerizable composition comprising:
(a) 20 to 75% of a solvent soluble, thermoplastic polymeric binder;
(b) 5 to 60% of at least one liquid ethylenically unsaturated monomer, said monomer having a boiling point above 100°C and being capable of addition polymerization; and (c) 0.1 to 10% of a photoinitiator system that activates polymerization of said unsaturated monomer on exposure to actinic radiation;

wherein said percentages are weight percentages based on the total weight of components (a), (b), and (c), the composition having a refractive index modulation of at least 0.005 as determined with 632.8 nm radiation from a transmission grating having a spatial frequency of about 1000 lines per millimeter, which transmision grating is prepared holographically from a layer of said composition wherein said monomer is an acrylate or methacrylate that contains a substituent selected from the group consisting of (1) aromatic moieties selected from the group consisting of (i) substituted or unsubstituted phenyl, (ii) substituted or unsubstituted naphthyl, and (iii) substituted or unsubstituted heteroaromatic moieties having up to three rings; (2) chlorine; and (3) bromine, and said binder is substantially free of said substituent.

12. The element of claim 11 wherein a solid photopolymerizable monomer is replaces a portion of said liquid photopolymerizable monomer.

13. The element of claim 11 or 12 wherein a plasticizer replaces a portion of said liquid monomer.

14. The element of claim 12 wherein siad solid photopolymerizable monomer contains a carbazole group.

15. The element of claim 11 or 12 wherein said hologram is a holographic optical element.

16. The element of claim 15 wherein said holographic optical element is a lens or diffraction grating.

17. A process for forming a light-stable hologram in a photopolymerizable layer on a substrate surface, said process comprising, in order:
(A) exposing to modulated actinic radiation bearing holographic information an element comprising a support and a photopolymerizable layer, said photopolymerizable layer comprising:
(a) 20 to 75% of a solvent soluble, thermoplastic polymeric binder;
(b) 5 to 60% of at least one ethylenically unsaturated monomer, said monomer having a boiling point above 100°C and being capable of addition polymerization; and (c) 0.1 to 10% of a photoinitiator system that activates polymerization of said unsaturated monomer on exposure to actinic radiation;
(B) exposing said photopolymerizable layer overall with actinic radiation;
wherein said percentages are weight percentages based on the total weight of components (a), (b), and (c);
wherein either said monomer or said binder contains a substituent selected from the group consisting of (1) aromatic moieties selected from the group consisting of (i) substituted or unsubstituted phenyl, (ii) substituted or unsubstituted naphthyl, and (iii) substituted or unsubstituted heteroaromatic moieties having up to three rings; (2) chlorine; and (3) bromine, and the other of said monomer and said binder is substantially free of said substituent; and wherein said actinic radiation bearing holographic information is formed by interaction of a reference beam of coherent actinic radiation with an image beam of coherent actinic radiation in the plane of the photopolymerizable layer.

18. The process of claim 17 wherein said monomer contains said substituent and said binder is substantially free of said substituent.

19. The process of claim 17 wherein said binder contains said substituent and said monomer is substantially free of said substituent.

20. The process of claim 19 wherein said binder is a styrene polymer or interpolymer, and wherein said unsaturated monomer is an acrylate or methacrylate of a polyol or of an ethoxylated polyol.

21. The process of claim 17 wherein said reference beam and said object beam enter the same side of the photopolymerizable layer.

22. The process of claim 17 wherein said reference beam enters one side and said object beam enters the other side of the photopolymerizable layer.

23. The process of claim 22 wherein said substrate surface is reflective.

24. A process for forming a reflection hologram in a photopolymerizable element, said element comprising (A) a support that is transparent to actinic radiation and (B) a photopolymerizable layer, said layer comprising:
(a) a solvent soluble, thermoplastic polymeric binder;
(b) at least one ethylenically unsaturated monomer, said monomer having a boiling point above 100°C
and being capable of addition polymerization;
and (c) a photoinitiator system that activates polymerization of said unsaturated monomer on exposure to actinic radiation;
wherein either said monomer or said binder contains a substituent selected from the group consisting of (1) aromatic moieties selected from the group consisting of (i) substituted or unsubstituted phenyl, (ii) substituted or unsubstituted naphthyl, and (iii) substituted or unsubstituted heteroaromatic moieties having up to three rings; (2) chlorine; and (3) bromine, and the other of said monomer and said binder is substantially free of said substituent;
said process comprising exposing said element to modulated actinic radiation bearing holographic information wherein said modulated actinic radiation is formed by interaction of a reference beam of coherent actinic radiation with an image beam of coherent actinic radiation in the plane of the photopolymerizable layer;
and wherein said reference beam enters from one side of the photopolymerizable layer and the image beam enters form the other side of the photopolymerizable layer.

25. The process of claim 24 wherein said binder is a styrene polymer or interpolymer, and wherein said unsaturated monomer is an acrylate or methacrylate of a polyol or of an ethoxylated polyol.

26. The process of claim 24 wherein said reference beam passes through said photopolymerizable layer and is reflected from an object to generate the object beam.

27. The process of claim 26 wherein said said object is a reflection hologram.