US 3809473 A
This invention relates to a method of producing a copy image of a transparent relief image on at least one thermoplastic layer which comprises passing light from a substantially point source through a layer containing the relief image, and obtaining the copy image in a plane located at a distance other than zero behind the relief image.
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Description (OCR text may contain errors)
a United States Patent ['19] Moraw etal.
[ METHOD OF REPRODUCING A RELIEF IMAGE  Inventors: Roland Moraw, Naurod; Gunther Schadlich, Wiesbaden, both of Germany  Assignee: Kalle Aktiengesellschaft,
Wiesbaden'Biebrich, Germany  Filed: Dec. 21, 1972  Appl. No.: 317,194
 Foreign Application Priority Data Dec. 24, 1971 -Germany 2164622 52 us. Cl. 355/9  Int. Cl. Gllb 3/00  Field of Search 355/9, 91, 132, 133
 References Cited UNITED STATES PATENTS 1,838,312 12/1931 Kanolt 355/133 [4 1 May 7, 1974 3,653,888 4/1972 Lessman 355/9 3,207,051 9/1965 Cooper 95/4.5 3,368,471 2/1968 Beato r 355/91 3,321,308 5/1967 Walkup.....-. 355/9 Primary ExaminerJohn M. l-loran Attorney, Agent, orFirm-James E. Bryan, Esq.
[ ABSTRACT This invention relates to a method of producing a copy image of a transparent relief image on at least one thermoplastic layer which comprises passing light from a substantially point source through a layer containing the relief image, and obtaining the copy image in a plane located at a distance other than zero behind the relief image.
8 Claims, 2 Drawing Figures I METHOD OF REPRODUCING A RELIEF IMAGE The invention relates to a method of reproducing, i.e., copying by projection and/or duplicating, a transparent relief image on at least one thermoplastic coating.
Relief images are obtained by various methods, usually photographic reproduction methods. Layers of photoresists can be so treated after developing that, depending upon the nature of the'coating, either, the exposed or the unexposed portions of the coating are removed. With the aid of dies, it is possible to impress imagesin deformable materials, particularly in thermoplastic films at high temperatures. Relief duplicates also can be made from relief images by the impression method whereby the relief image is coated with a hardenable film-forming composition which is later removed. v
7 Relief images produced by electrophotographic methods may consist of a carrier, made of a dielectric, and optionally transparent material such as 'a plastic substance or glass which may have a conductive coating of tin oxide, aluminum or the like, or a conductive material such as aluminum foil having a coating usually made of thermoplastic resin together with photoconductive substances which may be present in the form of separate layers. The surface may 'be provided with a non-conducting coating which alters the light reflection. This electrophotographic recording material is electrostatically charged under a corona discharge unit, exposed to produce the image and softened.
Under the effect of the latent charge pattern the surface of the plasticized resin deforms to provide a relief image. Depending upon the test conditions and specifically upon the level of charge, different typesv of relief images are obtained. When the charge is relatively high, the surface assumes an irregular structure in the charged areas so that the image produced by lightscattering is obtained which can. be viewed or projected. This method of recording is known as the Frost process." If the recording material is not so heavily charged as for the Frost process, a continuous relief line is formed on the otherwise smooth background which line marks the boundary where there is a discontinuity in the magnitude of the charge as a result of exposure. This recording'process in which relief images consisting of continuous deformation lines are obtained is known as P-hotoplastic Recording. In this specification, the term relief image will be understood to mean this type of electrophotographic deformation image.
In recent years electrophotographic releif images have been the subject of intensive development operations, and difficulties have been encountered in projecting these images and particularly in-optically duplicating them. These relief images have been classified as phase images on account of the change in the thickness of coating. it has been necessary to view them through phase microscopes. No suitable duplicating process has existed for relief images produced by electrophotographic means. When impressions have been made, the relief image has been previously intensified by galvanic means. Casts using hardenable coatings are timeconsuming to prepare. Copying by projection has been carried out by means of Schlieren optical systems.
The object of the invention is, therefore, to provide 1 a method of reproducing relief images, and particularly relief images produced electrophotographically, which avoids the aforementioned high costs and complications and which enables copies of relief images to be obtained by projection and/or for the purpose of making duplicates.
The present invention provides a method for reproducing a transparent relief image on at least one thermoplastic coating in which parallel light or divergent or convergent light from a point of substantially point tion and good contrast when certain conditions regarding the distance between the relief image to be reproduced and the plane of the image are observed. Accordingto the invention, a distance is maintained that is large compared with the known duplicating processes used in connection with photographic reproduction wherein the original and the recording material are in contact. It has been found that the distance is roughly directly proportionalto the width of the relief line and can be determinedwith the aid of the annexed graph (FIG. 1). The width (y) of the relief line and the distance (x) can be determined by the equation wherein x and y are in millimeters, m is between approximately 0.02 and 0.15, and b is between approximately zero and -0.02.
Particularly good results can be obtained if m is between approximately 0.03 and 0.07 and b is less than minus 0.01. These equations apply approximately in the case of thicknesses of relief lineof 0.002 mm.
-'Thus, in the case of broad relief lines, the distance is greater than when the relief lines are narrow. The preferred distance between the relief image and the plane of the image that enables copies having maximum contrast and sharpness to be obtained is within the range extending from approximately 0.1 to 5 mm.
Reproductions of relief images can be obtained by projection onto screens. However, it is preferred to make copies on copying material such as diazo films or vesicular films in the plane of the copy image. Very considerable advantage results from the use of copying material that has a hard action and has a narrow exposure range in which the image builds up. In the photographic industry, this latter property is generally specified quantitatively by the gradation.
Thus, legible duplicates are obtained by using diazo films having gradation values of about 2. It has been found that contrast is considerably improved by the use of vesicular films which are therefore particularly suitable for the purpose of the present invention. These films have a softenable film-forming coating containing photosensitive substances which decompose when exposed to light-rays and form gaseous products, for example, aromatic diazo compounds, so that after developing, usually by thermal means, a high-contrast image formed by light scattering is obtained. Gradation values of between 2.6 and 4.8 are indicated for vesicular films having diazonium salts as the photosensitive compoitems, in the production of light-scattering images, these values being dependent to some extent upon the optics'of the reproduction equipment.
According to the invention, by using the optimum distances found from the above-mentioned formulae, the relief images can be duplicated with parallel light while maintaining the same scale, as shown diagrammatically in the accompanying FIG. 2 wherein therelief-image 1, having. a striation width y, is shown as being reproduced in the plane 2 at a distance of .t'. It is, however, also possible to obtain an enlarged image in the image planeby using divergent light as obtained from 'a point orsubstantiallypoint source. It is also possible to produce a reduced image by usingconvergent light as obtained from a point source with a convergent lens. As in duplicating, all these images can be used for exposing a light-sensitive recording material, or they can be captured for direct viewing on a screen. For the purposes of projection, the image in the image plane is projected onto the screen by way of an opticalsystem to the rear of the image plane. Various types of receiver's, for example light-sensitive recording elements, for example television camerasor photoelectric cells, are suitable as screens.
For the purpose of achieving uniform lighting of the objects to be reporoduced, use is generally made of areal lamps as employed in duplicating or optical reproduction methods and containing several coils. of wire; use may also be made of one or more linearly extending lamps, usually in the form of tubes, or of a sheet of ground glass interposed between the object to be reproduced and the lamp. However, the use of such means results in a considerable reduction in contrast when reproducing'relief images. According to the invention, point light sources are used for producing light having a controlled direction of propagation, such sources being, for example, gas-discharge lamps with short arcs or incandescent lamps comprising a small coil, and the light from these lamps may be reflected by way of a condensing unit. The diameter of the light zonemust in each case be very much smaller than the distance between the relief image and the lamp. The use of parallel light represents a special case for reproducing the lighted zone with the aid ofa condenser unit when the latter is located at adistance from the lighted zone that is precisely equal to the focal length. Lasers are also suitable for the reproduction method of the invention, the laser beam advantageously being broadened. When the light source is a laser, only its characteristic of an extremely small angle of divergence is employed. Moreover, the phase coincidence occurring at the same time in the laser beam leads to undesirable diffraction phenomena at the edges of the image which, although not affecting resolution, do spoil the impression given by the image.
Hitherto it has only been possible to use duplicating, in which the original is in contact with the copying material, as a basis for the duplication of holograms laser light and the phase coincidence peculiar thereto being necessary for the duplication in order to enable that portion of the beam passing through the hologram and that portion diffracted thereon to interfere at the rear of the hologram. Apart from the fact that holograms are not-directly legible interference images whereas the relief images with which the'invention is concerned contain information in the form of directly'legible symbols, in-phase light is required for the known method of duplicating holograms, whereas on the other hand phase coincidence is undesirable in the reproduction method of the invention. It follows from this thatthe method of the invention is not comparable with the'duplication of holograms.
As already stated, the plane in which a sharp copy'of the relief image is obtained is located at a certain finite distance from the relief image and it is not necessary to interpose an additional optical reproduction unit. Previously, it has been customary, when duplicating on a non-contact basis, to provide an optical system behind the object that is to be optically reproduced.
In perfecting the method of reproducing relief images in accordance with the invention, it has been found that the precise distance necessary between the relief image and the copying. material depends largely upon the method used for producing the relief image. For example, for the purpose of making sharp reproductions of relief images produced by stamping with a die having raised portions of rectangular cross-section, smaller distances are required that when producing sharp reproductions of relief images produced by electrophotographic processes and probably having a cup-shaped relief cross-section. A feature common to all relief images is that, for the purpose of reproduction, it is necessary to maintain a certain distance which can vary up-.
wards or-downwards within certain limits, and although the information becomes increasingly more difficult to read, it still can beread until comprehensibility ceases completely when the distance is too great or too small. As previously stated, this is quantitatively represented in FIG. 1 in the case of relief images produced by electrophotographic means.
Conditions are more favorable for the reproduction of a relif original consisting only of letter type, for example, of a typewritten page recorded as a relief original to a different scale, or of computer output microfilm signals recorded in the form of electrophotographic relief images.
The method of the invention will now be described in greater detail by reference to the following Examples. 1
EXAMPLE -I One gram of copper phthalocyanine, for example Microlith Blau 4 GT, marketed by CIBA, Basle, Switzerland, 5 g of low-molecular weight poly-2- methylstyrene, for example 276 V 9, marketed by Dow Chemical Company, U.S.A., and 10 g of polystyrene having an average molecular weight of appoximately 30,000, for example PS 3, marketed by Dow, were dis solved in 50 ml of CHCl The chloroform contained one spot of silicone oil per liter. Using this solution, a
50 p. thick polyester film was coated with a 2 u thick covering layer of polyvinyl chloride in a centrifuge, and was dried for 10 minutes at 21C and then for 20 minutes at 50 C in a recirculated air drying cabinet. Charging was carried out in the dark on a grounded metal plate under a -8 KV needle corona. With the aid of a projection lamp (200 watt) an image reduced to one-fifteenth was produced over a period of 10 seconds from groups of striations of different sizes on the charged film through an optical system (f 3.5 cm). The film was then developed by means of a thermal radiator, the relief image thus being created. The radiatorwas a steel sheet located at a distance of 0.5 cm and having the dimensions 20X 80 X 0.1 mm, to which 2.8 volts were applied for 1.5 seconds in the longitudinal direction; the heating effect was approximately 0.5 KW. 3
The groups of lines on the relief image were measured off with the aid of a microscope. The relief image was then irradiated with parallel light from a point source high pressure mecury lamp (200 W) having a quartz lens (f= cm). A diazo film produced in the following manner was positioned at predetermined distances behind the film carrying the relief image:
A cellulose acetate film was coated with the following solution and then dired: 2.6 g of citric acid, 6.0 g of thiourea, 1.4 g of 2-hydroxy-3-naphthoic ac'id -(/3-hydroxyethyl)-arnide, 1.75 g of -3-hydroxy-'4- methylphenyl urea,- 1.2 ml of formic acid, 70 g of 4- diethylamino-benzenediazonium-tetrafluoroborate, 38 ml of water, and 48 ml of isopropanol.
The diazo film was exposed for 60 seconds and developed with ammonia. The groups of lines recorded on the diazo film and observed in the form of a positive image in which the unexposed zones of the film were darkened were detected with the aid of a microscope. The relationships between the necessary distance (x) and the thickness (y) of the relif striation that were found are plotted in the annexed FIG. 1. The distance range which should be adhered to for producing legible duplicateswas-located between the curves marked A and B. The values determined in accordance with thestated formula are:
r m b A 0.143 0.002 B 0.022 0.01 l
The preferred range of distances that enable duplicates of maximum contrast and sharpness to be obtained was found to be approximately midway between the curves A and B and is indicated by hatching in FIG.
- 1. In accordance with the stated formula, the values for m and b were as follows:
in b 0.06 0.001 0.039 0.003
Various lettering can be reproduced simultaneously in a legible manner for differing widths of striation, for which purpose reference should be made to the graph for selecting a suitable distance.
The sharp reproduction of the relief image provided in the image plane for each width of striation can be projected by an optical system onto a screen, a legible image being obtained.
EXAMPLE 2 The diazo film used in Example 1 was replaced by a vesicular film marketed by Kalvar, New Orleans, La., USA. The exposure time was 60 seconds. Developing was effected by laying the vesicular film for 3 seconds on a plate heated to about 100 C. This resulted in a negative light-scattering image, i.e., the exposed portions of the film were cloudy. When the light-scattering image was projected, a high-contrast and very legible image was obtained. I
EXAMPLE 3 A zinc plate was coated with the following solution in a centrifuge and dried for 6 minutes at C:
100 ml of glycol monomethyl ether, 2.8 g of 1,2- naphthoquinone-2-diazide-5-sulfo-acid monoester of 2,3,4-trihydroxybenzo-phenone (esterified in position 4) and 4.5 g of novolak having a melting range of between 108 and 1 18 C. This was then exposed beneath an arc lamp through an original having groups of lines. After developing in an alkaline aqueous medium, ethching was carried out for 20 seconds at 22 C using an iron chloride solution (40 Baume). The flat etched image exhibited sharp edges under the microscope.
The zinc plate carrying the etched image was clamped, together with a colorless polyvinyl chloride film (100 1.1.), for 5 minutes in a vice having smooth jaws. The vice had been previously warmed with hot air. The impressed film was used in place of the electrophotographically produced relief image of Example 1. Sharp images were obtained at distances amounting to only about one-third of those used in Example 1. The exposure time for the diazo film when duplicating the relief image in the polyvinyl chloride film was considerably shorter'than in Example 1 and amounted to only approximately 5 seconds.
It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications;
What is claimed is:
1. A method of producing a copy image of a transparent electrophotographic deformation image having relieflines on at least one thermoplastic layer, comprising passing light from a substantially point source through a layer containing said deformation image and onto said thermoplastic layer while simultaneously maintaining a predetermined distance x between said layer containing said deformation image and the plane of said thermoplastic layer, said distance x determined by the formula:
y m x b where:
y is the width of said relief lines in mm,
m is between about 0.02 and 0.15, x is said distance x in mm, and
b is between about 0 and minus 0.02, to obtain a copy image.
2. A method as claimed in claim 1 wherein a copying material is placed in the image plane.
3. A method as claimed in claim 2 wherein the copying material is one having a hard effect.
4. A method as claimed in clairri 3 wherein the copying material is a vesicular film.
5. A method as claimed in claim 1 wherein the light is parallel light.
6. A method as claimed in claim 1 wherein the light is divergent light.
7. A methodas claimed in claim 1 wherein the light is convergent light.