US3811773A

US3811773A - Thermographic copying

Info

Publication number: US3811773A
Application number: US00149039A
Authority: US
Inventors: M Vrancken
Original assignee: Agfa Gevaert NV
Current assignee: Agfa Gevaert NV
Priority date: 1965-11-26
Filing date: 1971-06-01
Publication date: 1974-05-21
Anticipated expiration: 1991-05-21
Also published as: BE683054A; CH477295A; GB1154568A; NL6608711A

Abstract

A process for the reproduction of a transparent original having infrared radiation and visible light absorptive image markings thereon by exposing the original to infrared radiation and/or light while the image markings are arranged in heat-conductive contact with a recording layer composed at least 80 percent by weight of gelatin and having distributed therethrough a finely divided substance transforming absorbed visible and infrared radiation into heat, for a period not longer than 10 1 second and developing the recording layer by washing with water to remove the gelatin in the area corresponding with the non-image area of the original.

Description

United States Patent [19'] Vrancken 1111 3,811,773 [451 May 21, 1974 1 THERMOGRAPHIC COPYING Marcel Nicolas Vrancken, Parklaan, Belgium [73] Assignee: Agfa-Gevaert N.V., Mortsel,

Belgium [22] Filed: June 1, 1971 [21] Appl. No.: 149,039

Related US. Application Data [75] Inventor:

[63] Continu'ation-in-part of Serv No. 560,314, June 24,

1966, abandoned.

[30] Foreign Application Priority Data Nov. 26, 1965 Great Britain 50441/65 [52] US. Cl 355/132, 96/35, 250/317, 355/32, 355/78, 355/88 [51] Int, Cl. G03b 27/02 [58] Field of Search 96/27 R, 35, 36.3; 260/317, 316; 355/132 [56] ReferencesCited- UNITED STATES PATENTS,

3,523,791 8/1970 Vranck-en et al. 96/35 X Gosnell 250/316 X 3,476,578 11/1969 Bl'inckmannn. 250/317 X 3,514,597 5/1970 Haes et a1. 250/317 X 3,121,162 2/1964 Roman et a1. 117/17 X 3,298,833 l/l967 Gaynor 96/27 Primary Examiner-Richard L. Moses Attorney, Agent, or Firm-William J. Daniel [5 7] ABSTRACT A process .for the reproduction of a transparent original having infrared radiation and visible light absorptive image markings thereon by exposing the original to infrared radiation and/or light while the image markings are arranged in heat-conductive contact with a recording layer composed at least 80 percent by weight of gelatin and havingdistributed therethrough a finely divided substance transforming absorbed visible and infrared radiation into heat, for a period not longer than 10 second and developing the recording layer by washing with waterto remove the gelatin in the area corresponding with the non-image area of the original.

12 Claims, 1 Drawing Figure PATENTEDIAYZI mm 381L773 INVENTOR I 5% M d/Qww ATTORNEY THERMUGRAPHHC corriur;

The present invention is a continuation-in-part application of the US. Patent application Ser. No. 560,314 now abandoned filed with the US. Patent Office on June 24, 1966.

The present invention relates to a method for recording'and reproducing information by means of electromagnetic radiation which by absorption in a thermosensitive layer produces an increase in temperature therein.

From the US. Pat. No. 3,121,162 by P. A. Roman and U. E. lfaff, issued Feb. 11, 1964 a reproduction process is known comprising irradiating a subject having heat absorptive image areas with infrared radiation in heat-conductive contact with a supported layer of high jelly strength gelatin, sufficiently to raise the temperature of the gelatin substantially in regions of. said heat absorptive image areas so .that a substantial increase in swelling tendency of the gelatin in said areas is caused, moistening the gelatin layer and pressing it into contact with an absorbent support to cause the gelatin in said areas to adhere to said support, and separating the gelatin layer from said support to leave a stratum of the gelatin of said areas on the support.

According to one contact-printing embodiment described in said patent specification a documenthaving a transparent or slightly diffusing support is copied by placing the printed characters of the document in heat conductive contact with the gelatin layer which may contain a pigment that does not absorb infra-red radiation and exposing the gelatin layer to infra-red radiation through the support of the document. A laterally reversed master sheet is thus obtained and accordingly, right-reading positive copies are obtained by transfer. In this case only one-sided documents can be copied.

According to another contact-printing embodiment described in said US. Pat. specification an original comprising a heat-diffusing support is placed with that support in contact with the gelatin layer which may contain colouring materials, carbon black, etc., and exposure is made through the document towards the gelatin layer. The copy obtained on a receivingsheet by transfer is laterally reversed and the image-sharpness is not of high quality.

According to the present invention, a process for recording information is provided wherein is used a recording material comprising a gelatin layer containing a uniformly distributed visible and infra-red lightab sorbing substance which as a result of such absorption becomes heated; and this gelatin layer is exposed, through a copying light transmitting original disposed with its image-markings in direct thermal contact with the gelatin layer of said recording material, said image markings being light-absorbing and heatable by copying lightin the wavelength range of visible and infra-red light, the exposure being of a'duration not longer than second and of such intensity that a substantial increase in the swelling tendency of the gelatin in said recording layer is produced selectively in correspondence with the non-image parts of said original but insufficient to produce a substantial increase in the swellimage area.

' It will be apparent that by this process a laterally reversed record of the original text or other matter constituted by said light-absorbing image portions, is ob tained. If the support of the recording layer is transparent, the copy will belegible through its backing. De-

pending on the composition of the recording material, this record may be rendered visible in or on the said recording material and/or may be used for forming one or more non laterally reversed copies on another material.

It is stressed that the 'lightabsorbing image portions of the original and the gelatin recording layer are in heat-conductive contact during the exposure, hereby the distance between the copying material and the recording medium is as small as possible. This is an important feature in the production of very sharp copies.

An important discovery leading to the invention is that by a sufficiently brief exposure to light (an exposure time not higher than 10 sec.) the existence of a heat-conductive relationship between the lightabsorbing image portions and the gelatinrecording layer is of no effect or substantially no effect in forming the record in the gelatin recording layer. On the contrary, the record is produced by virtue of the internal heating of the gelatin recording layer where it is irradiated with light passing through the non-image areas of the original. Consequently there is no need to insulate the light-absorbing image portions from the gelatin recording layer; they can be maintained in intimate contact during the exposure, by pressing the original and the recording material together. If the materials are merely laid next to each other and the image-bearing face of the original or the gelatin recording layer are i not coated in any way, then there may be present a very thin air interlayer which would however not prevent effective heat conduction of the lighbabsorbing image performed using for the exposure a gas discharge lamp V having an exposure time of no longer than 10 seconds.

According to a preferred embodiment the exposure is carried out by means of electromagnetic radiation the greater part of which (at least percent of the ir-. radiation energy) is composed of electromagnetic radiation of the visible spectrum. By a short duration exposure of sufficient intensity (at least 0.2 watt sec per'sq. cm and preferably 0.50 to 1.0 watt. sec per sq. cm) sufficient heat can be produced in the light-in-heatconverting particles distributed throughout the gelatin layer which are irradiated, for suddenly increasing the temperature of the gelatin surrounding such particles 1 and conferring on such surrounding gelatin a substantial increase in swelling tendency in water and solubility in 'water or an aqueous composition. On the other hand, the dosage of short duration high intensity exposing light is such'that not enough heat can be absorbed in he light-absorbing image portions of the original for being transferred to the gelatin recording layer to bring about any significant differentiation in water solubility.

According to our invention due to the intimate contact of the image portions of the original with the heat-sensitive gelatin layer at the moment of exposure legible images of extremely high resolution and sharpness can be obtained by washing-off the internally heated gelatin portions of the recording layer.

The copying light-absorbing substance in the gelatin layer may be dispersed or dissolved in the gelatin layer. One or more than one such substance may be present in one and the same layer.

It is preferred to use in the heat-sensitive gelatin layer a copying lightabsorbing substance in such a proportion that the absorption therein of light energy produced on flash exposure effects a sufficient increase in temperature of the gelatin to increase its water solubility to such an extent that it can be dissolved in the heated areas by coldwater (2025"C).

In order to achieve as high a conversion of light into heat as possible inthe substance(s) dispersed or dissolved in the gelatin, it is preferable that such substance(s) neither take'part in an endothermic chemical reaction during exposure nor undergo a change in aggregation state.

In order to obtain an economic use of the light energy penetrating into the gelatin layer, the light absorbing substance is preferably present therein in such an amount that at least 80 percent of such light is absorbed and converted into heat. in general it is recommended that the optical density of the gelatin layer be comprised between 1 and 3, the gelatin content of such layer being in that case between 1 and 4' g per square metre. Thus the gelatin recording layer may contain light-absorbing substance to an optical density of at least 1. I

In preparing a heat-sensitive material for use in the .process of the present invention the gelatin recording layer may be applied to a transparent support but this is not essential. An opaque or translucent support may be used. By way of example the said recording layer may be applied to atransparent film, a paper support or a metal support. The selected support iscoated with a composition preferably containing at least 80 percent by weight of gelatin. That gelatin composition contains one or more dissolved or finely dispersed visible light absorbing or visible light and infra-red absorbing substances which transform such light into heat. Certain preferred substances which absorb visible light and infra-red light and convert the absorbed radiation into heat are finely divided carbon black, graphite, prussian blue, oxides, sulphides or carbonates of heavy metals, particularly of those heavy metals having an atomic weight between 45 and 210, such as manganese or lead sulphide or such heavy metals themselves in finely divided state, e.g., silver, bismuth, lead, iron, cobalt and nickel. Carbon particles and silver are among the most suitable substances.

For further examples and data relating to pigments form part of the present disclosure and should be read in conjunction herewith.

It is preferred to employ dispersed light absorbing particles, preferably having a particle size or an average particle size not greater than 0.1 u.

The gelatin of the heat-sensitive layer may be of the type of gelatin normally used in silver halide photography.

A sufficient Bloom gel strength (preferably at least 150) of the gelatin is important in cases wherein the gelatin has to be swollen and transferred in swollen state to a receiving support, e.g. a screening master blank such as a Japan paper, however, in the case that the original is to be reproduced merely by exposure and washing away of the heated areas a high bloom gel strength of the gelatin is not necessary. Suitable gelatin for application in the present invention is described eg in UK. Patent Specification 1,154,902. 7

The differential swelling tendency of the gelatin layer can be observed directly when moistening the layer with water. The swelling tendency and solubility of the gelatin varies with the hardening degree. After a sudden heating above C a substantially unhardened gelatin layer will have regions which can be washed away completely by water at 25C.

According to a special embodiment the gelatin layer contains during the exposure uniformly distributed coloured substances which absorb light of a determined part of the visible spectrum and convert it into heat. A gelatin layer made spectrally sensitive in this way can be used for recording coloured originals in terms of differences in solubility and in swelling tendency in water.

it will be understood that mixtures of said coloured substances can also be used, so that light of the entire visible spectrum is absorbed. Furthermore, the substances need not absorb exclusively in the range of the visible spectrum; they may also absorb in the infrared region.

The coloured substances or mixtures of said substances preferably absorb light corresponding to at least one of the primary colours (red, green, blue) or subtractive colours (cyan, magenta, yellow).

Substances that absorb visible light of a part of the visible spectrum and wherein absorbed light energy is converted into heat are e.g. dyes belonging to the which absorb visible light and convert it into heat, reference is particularly made to Belgian Patent Specification 7,502 and the UK. Patent Specification 1,160,221 corresponding with the US. Pat. application Ser. No. 550,834, which specifications are deemed to classes of the azo dyes, the triarylmethane dyes, the xanthene dyes, the acridine dyes, the methine dyes, the azine dyes, the phthalocyanine dyes, the anthraquinone dyes and allied dyes.

Said substances can be used in dispersed or dissolved condition; when they are used in dispersed form they should preferably have a grain size lowe than 0.1 1.4..

According to the present invention, when using spectrally sensitive gelatin layers, it is possible to produce printing masters suitable for colour printing and for producing multicolour copies of colour originals. For that purpose three materials are used that contain a heat-sensitive gelatin layer comprising a substance which is heated on absorbing red, green and blue light respectively, i.e. a gelatin layer containing a cyan dye,

a magenta dye and a yellow dye respectively. Said dyes may be dyes suitable for hectographic printing.

By the heat produced in the heat-sensitive gelatin layer containing the cyan dye said layer is made more swellable and water-dissolvable in the areas corre- By the heat produced in the heat-sensitive gelatin I layer containing the magenta dye said layer is made more swellable and water-dissolvable in the areas corresponding to the green areas of the original to which it was exposed.

By the heat produced in the heat-sensitive gelatin layer containing the yellow dye said layer is made more swellable and water-dissolvable in the areas corresponding to the blue areas of the original to which it was exposed.

Multicolour prints can be produced by using the three exposed materials to prepare three separate masters which are used to print in register.

For reproducing originals that contain separate markings in the pure primary colours, blue, green and red (e.g. a transparency containing blue, green and red letters), three separate gelatin layers can be used which are sensitized'for blue, green and red respectively by a blue, green and red dye or pigment that is uniformly distributed therein. By washing away the selectively heated gelatin portions copies of the image markings in the primary colours are obtained that canbe inspected in overlay.

The effectiveness of the recording substantially depends on the intensity of the radiant energy. For example, a gelatin recording layer, that does not provide a I sufficient differentiation in swelling tendency with a particular source of electromagnetic radiation energy may be fully effective if the energy level is substantially increased. r

Lamp structures and exposure systems producing electromagnetic radiation at least 70 percent of which consists of visible light (in other words containing only small amounts of U.V. light and infra-red light) and which are capable of providing high intensity radiation in a very small lapse are preferably used.

Radiation sources emitting visible light of high intensity in a very small lapse of time are so-called flash lamps and more particularly the discharge lamps containing a noble gas.

in the present invention good results are obtained with a Xenon gas discharge lamp, which can supply an energy of 300l,000 watt. sec in a time interval of to 10" seconds and can irradiate the recording layer with an energy of at least 0.2 watt. sec per sq. cm and preferably in the range of 0.2 to 1.5 watt. sec per sq.

According to a preferred embodimentof the invention a gas discharge lamp is used, which is in the form of a thin tube fitted in a hollow glass cylinder in order to makepossible a uniform exposure of the recording material applied according to the periphery of the cylinder.

More details about copying apparatus containing such a discharge lamp can be found in Belgian Patent Specification 664,868. The intensity of the emitted light is particularly high in the regions of the visible spectrum. v y

it is possible to employ a number of flash tubes operating simultaneously, or to obtain a suitable imagedifferentiation by flashing a single tube at suitable intervals. Reflectors and other optical components may be included to provide irradiation of maximum uniformity.

Evidently lamps with a lower energy output can be used if the emitted light energy is focused onto a relatively small heat-sensitive area. So, e.g., a gas discharge lamp with an energy output of 40 watt. sec. is suited for copying 6 cm X 6 cm and 6 cm X 9 cm originals on a heat-sensitive material as described in the present invention. It is further self-explanatory that exposure may be progressive and intermittent. In other words the heat-sensitive material may be scanned through an original with a light-spot of high intensity, e.g. a laser beam, or may be progressively exposed through a slit wherein, e.g., copying light of a continuously emitting tube-like radiation source is focused.

As a particular example of the use of the invention it may be used for producing positive-positive prints of an original provided in the form of a silver image transpar- The. following examples illustrate the present invention without limiting it thereto. Example 1 i A poly(ethylene terephthalate) support of 0.1 mm thickness provided with a subbing layer for gelatin is coated with the following composition pro rata of 30 g/sq.m:

l0 aqueous solution of gelatin having a Bloom gel strength value of 240 250 g 50 aqueous dispersion of carbon black, having a particle size of 0.1 p. 50 g water 200 g 5 aqueous solution of sodium tetradecyl sulphate 25 g.

The layer is dried at,20C.

One arrangement of the materials of the invention for effective reflectographic exposure is shown in the accompany drawing. In this drawing, the copying material 1 consisting of a transparent support 5 and the thermosensitive gelatin layer 6 is laid on a photographic silver image containing transparency 2 having radiationabsorbing markings 3 and radiation transmitting parts 4, the thermosensitive gelatin layer 6 being in contact with the image layer 7 of the silver image transparency.

The sandwich of copying material and original is then braced around a glass cylinder 9 with the support 8 of the transparency in contact with said cylinder having a diameter of 8 cm.

Along the axis of this cylinder a xenon glass discharge lamp 110 is placed which at the discharge between the electrodes 11 produces a radiation energy of 600 watt.

rate and extremely sharp copy of the original is ob-.

tained. Example 2 A cellulose triacetatesupport of 0.12 mm thickness provided with a subbing layer for gelatin is coated with the following composition pro rata of 50 g per sq.m

l0 aqueous solution of gelatin with Bloom gel strength l 300 g 10 aqueous dispersion of colloidal silver (average particle size 0.] p.) 230 g 10 aqueous saponine solution 15 g The layer is dried at 20C, exposed and treated as described in Example 1. A very sharp and accurate p ,o th sri is Q z a n Example 3 A poly(ethylene terepththalate) support of 0.1 mm thickness provided with a subbing layer for gelatin is coated with the following composition pro rata of 50 g per sq.m:

l aqueous solution of gelatin having a Bloom gel strength of 240 430 g A violet pigment dispersion known as Permanent violett R.L. Colanyl Teig" (C.l. 51,300) 20 g A green pigment dispersion known as Pigment grun B Pigmosol (C.l. 10,006) 20 g 10 aqueous saponin solution 15 g 3 aqueous solution of the sodium salt of the condensation product of oleic acid and methyltaurine 15 g The layer is dried at 20C, exposed and treated as described in Example 1. A very sharp and accurate copy of the original is obtained.

Example 4 v A paper support weighing 120 g per sq.m., provided on both sides with a polyethylene coating and a subbing layer for gelatin, is coated with the following composition pro rata of 50g per sq. m.:

'10 aqueous solution of gelatin having a Bloom gel strength of 190 410 g 50 aqueous dispersion of carbon black of particle size 0.1 p. 30 g water 50 g 5 aqueous solution of sodium tetradecylsulphate 25 g a finely divided substance transforming absorbed visible and infrared radiation into heat, said substance being present in such an amount that at least about 80 percent of said radiation towhich said recording layer is exposed is absorbed and converted into heat, said exposure being of a duration not longer than 10 second and of such an intensity that a substantial increase in the swelling tendency of the gelatin in said recording layer is produced selectively in correspondence with the non-image parts of said original but insufficient to produce a substantial increase in the swelling tendency of the gelatin in the area of the recording layer corresponding to the image area of the original, and developing said layer by washing with water to remove the gelatin in the area corresponding to said non-image area.

2. A method for recording information according to claim 1, wherein said gelatin has 21 Bloom gel strength value above 200.

3. A-method for recording information according to claim 1, wherein said finely divided substance(s) is a (are) pigment(s).

4. A method for recording information according to claim 3, wherein said pigment(s) is (are) finely divided carbon particles.

5. A method for recording information according to claim 1, wherein the exposing radiation light contains at least percent of visible light.

6. A method for recording information according to claim 1, wherein the exposure is carried out with a flash lamp, and the irradiation is of an intensity of at least 0.2 watt.sec per sq.cm.

7. A method for recording information according to claim 6, wherein the radiation source is a high-intensity discharge lamp containing a noble gas.

8. A method for recording information according to claim 1, wherein the gelatin layer is applied to a support which is transparent to visible light.

9. A method for recording information according to claim 1, wherein said substance(s) absorb(s) light within a determined part of the visible spectrum and transform(s) it into heat.

10. A method for recording information according to claim 1, wherein said substance(s) is (are) present in the recording layer in such an amount that at least percent of the copying light is absorbed.

' 1 l. A method for recording information according to claim 1, wherein the transmission exposure occurs through a silver image transparency.

12. A method for recording information according to claim 1, wherein the exposure has a duration not longer than 10" seconds.

Claims

1. A reproduction process which comprises contact exposing a transparent original, having infrared and visible radiation absorptive image markings, to radiation in the visible to infrared region of the spectrum while said markings stand in direct face to face contact with a recording layer containing at least 80 percent by weight of a gelatin and having distributed therethrough a finely divided substance transforming absorbed visible and infrared radiation into heat, said substance being present in such an amount that at least about 80 percent of said radiation to which said recording layer is exposed is absorbed and converted into heat, said exposure being of a duration not longer than 101 second and of such an intensity that a substantial increase in the swelling tendency of the gelatin in said recording layer is produced selectively in correspondence with the non-image parts of said original but insufficient to produce a substantial increase in the swelling tendency of the gelatin in the area of the recording layer corresponding to the image area of the original, and developing said layer by washing with water to remove the gelatin in the area corresponding to said non-image area.

2. A method for recording information according to claim 1, wherein said gelatin has a Bloom gel strength value above 200.

3. A method for recording information according to claim 1, wherein said finely divided substance(s) is a (are) pigment(s).

5. A method for recording information according to claim 1, wherein the exposing radiation light contains at least 70 percent of visible light.

10. A method for recording information according to claim 1, wherein said substance(s) is (are) present in the recording layer in such an amount that at least 80 percent of the copying light is absorbed.

11. A method for recording information according to claim 1, wherein the transmission exposure occurs through a silver image transparency.

12. A method for recording information according to claim 1, wherein the exposure has a duration not longer than 102 seconds.