US3564597A

US3564597A - Thermographic recording process for reproducing continuous tone transparencies

Info

Publication number: US3564597A
Application number: US608572A
Authority: US
Inventors: Marcel Nicolas Vrancken
Original assignee: Agfa Gevaert NV
Current assignee: Agfa Gevaert NV
Priority date: 1966-01-11
Filing date: 1967-01-11
Publication date: 1971-02-16
Anticipated expiration: 1988-02-16
Also published as: BE692423A; CH469571A; FR1507875A; DE1671515A1; NL6700358A; GB1177482A

Abstract

A PROCESS FOR RESPONDING INFORMATION WHEREIN A HEATSENSITIVE RECORDING LAYER ADAPTED TO CHANGE THE WATERPERMEABILITY THEREOF WHEN HEATED AND CONTAINING UNIFORMLY DISTRIBUTED THERETHROUGH FINELY-DIVIDED MATERIAL ABSORBING VISIBLE RADIATION AND CONVERTING THE SAME TO HEAT IS EXPOSED TO RADIATION THROUGH A CONTINUOUS TONE TRANSPARENCY TO BE REPRODUCED AND A SCREEN, THE TIME OF THE EXPOSURE BEING NOT MORE THAN ONE-TENTH OF A SECOND, AND THE INTENSITY OF THE RADIATION BEING SUFFICIENT TO PRODUCE IN THE EXPOSED PORTIONS OF THE RECORDING LAYER SUFFICIENT HEAT TO BRING ABOUT THE CHANGE IN ITS WATER-PERMEABILITY,

AND THE EXPOSED RECORDING LAYER IS TREATED WITH AN AQUEOUS LIQUID TO DEVELOP THE INFORMATION THEREIN.

Description

Feb. 16,1971 N, VRANCKE 3,564,597

THERMOGRAPHIC RECORDING PROCESS FOR REPRODUCING CONTINUOUS TONE TRANSPARENCIES Filed Jan. 11, 1967 2 Sheets-Sheet 1 ZNVENTOR' 31 WWMW ATTORNEY Feb. 16, 19 71 7 N VRANCKEN. i 3,564,597

: 'THERMOGRAPHIC RECORDING PROCESS FOR REPRODUCING CONTINUOUS TONE 'I'RANSPARENCIES" Filed Jan. 11, 1967- 2 sheets-sheet'z 7? INVENT R WaML dea-4 ATTORNEY United States Patent 3,564,597 THERMOGRAPHIC RECORDING PROCESS FOR REPRODUCING CONTINUOUS TONE TRANSPARENCIES Marcel Nicolas Vrancken, Hove, Belgium, assignor to Gevaert-Agfa N.V., Mortsel, Belgium, a Belgian comp y Filed Jan. 11, 1967, Ser. No. 608,572 Claims priority, application Great Britain, Jan. 11, 1966, 1,351/ 66 The portion of the term of the patent subsequent to Nov. 4, 1986, has been disclaimed Int. Cl. G03b 41/00 U.S. Cl. 250-65 12 Claims ABSTRACT OF THE DISCLOSURE A process of reproducing information wherein a heatsensitive recording layer adapted to change the waterpermeability thereof when heated and containing uniformly distributed therethrough finely-divided material absorbing visible radiation and converting the same to heat is exposed to radiation through a continuous tone transparency to be reproduced and a screen, the time of the exposure being not more than one-tenth of a second, and the intensity of the radiation being sufiicient to produce in the exposed portions of the recording layer suificient heat to bring about the change in its water-permeability, and the exposed recording layer is treated with an aqueous liquid to develop the information therein.

The present invention relates to a method of making screened reproductions from a continuous-tone transparency on heat-sensitive materials. Up to now thermographic copying materials were only considered to be useful for the reproduction of documents and line work.

Line work applies to those originals, which comprise but pure white and deep black, such as typed and printed texts, pen drawings, etc.

Continuous-tone work, however, applies to originals, which besides black and white may also comprise the whole range of intermediate gray tones, as e.g. in silver image negatives of soft gradation.

Continuous-tone work can be reproduced on very contrasty silver halide emulsion layers known in the graphic art by use of a screening technique, which consists in printing the continuous-tone original together with a screen. In screening technique two types of screens are commonly used viz. glass-screens and contact screens. In practice the use of a contact screen is simpler and more economical than the use of a glass screen.

On exposure the contact screen is placed in contact with the light-sensitive material. Due to the modulation of the continuous-tone transparency and the characteristics of the contact screen dots, the original is reproduced on a very contrasty copying material as a large number of very small dots the size of which is determined depending on the luminosity of the corresponding parts of the continuous-tone transparency.

According to the present invention, a latent or visible screen image of a continuous tone transparency is produced by exposing to electromagnetic radiation, through such transparency and a screen, a heat-sensitive recording layer containing substance(s) which become(s) heated by the irradiation and consequently bring(s) about a physical and/or chemical change in the said layer, the exposure being for such brief time that heating sufficient to effect such change does not occur in any areas of such layers as a result of heat conduction from the material of the screen.

3,564,597 Patented Feb. 16, 1971 The radiation used may be infrared and/ or visible light radiation provided that the composition of the heat-sensitive layer is appropriately chosen. For a disclosure of heatsensitive layers which respond to such different types of irradiation we refer to the specifications filed in the published Dutch patent application 64/ 14226 filed Dec. 7, 1964 by Gevaert Photo-Producten N.V., the published Dutch patent application 66/06719 filed May 17, 1966 and in the published Dutch patent application 66/ 08711 filed June 23, 1966 both by Gevaert-Agfa N.V. which should be read in conjunction herewith.

The invention is particularly but not exclusively concerned with using heat-sensitive layers the composition of which undergoes a decrease in solubility in water when irradiated so that after image-wise irradiation the non irradiated areas can be washed away so that a relief image results.

Provided that a high intensity radiation is emitted by the radiation source, it is easily possible to avoid heating of the heat-sensitive layer by heat conduction from the screen since the exposure time can be of such short duration that there is insuflicient time for such heat conduction to take place.

It is more particularly intended to perform the invention using radiation composed wholly or mainly of light such as, e.g., is emitted by'fiash lamps, and to employ as heat-sensitive layer a layer containing light-absorbing substance (s) that convert the light into heat and the invention will hereafter be more particularly described in that form. The following more detailed description of the invention moreover has reference to embodiments in which the screen dots of a contact screen are held in direct contact with the heat-sensitive layer during the exposure since this is recommended for obtaining very sharp screened reproductions but it is not absolutely essential for the invention for such direct contact to exist since a thin interlayer may, e.g., be present.

It has been found that when a thermo-sensitive layer containing sufficiently light-absorbing substance(s) that convert that light into heat is subjected to a very short contact-exposure to light of very high intensity through a continuous-tone transparency in contact with a contact screen, a very sharp screened print of the continuous-tone transparency can be obtained due to the very locally internally produced heat in the said substance(s).

A too high absorption of light and corresponding too high production of heat in the screen dots of the contact screen and image areas of the original (which excessive heat due to the contact of the screen dots with the thermosensitive layer would be transferred by conduction thereto if a relatively long exposure time was applied), can be avoided by a high intensity very short exposure, particularly when forming a screen image of a continuous-tone transparency of rather low density and using a corresponding contact screen. In this way very sharp high density screened prints possessing the complete tone scale of the continuous-tone transparency can be obtained. It is advisable when copying silver image transparencies for the image density to be below normal. A normal density silver transparency can be reduced in density prior to being used by a conventional reducer solution. It is also recommendable to use a contact screen of which the silver dots are of less density than normal.

The use of a rather low density continuous-tone transparency makes it possible to avoid damage of the transparency image by absorbed heat in the silver metal parts (burning ofthe gelatin binder) and offers a more economical use of the light emitted from the light source, since it is the image-wise transmitted light which produces the desired change in the recording layer.

It is self-explanatory that according to the exposure technique of the present invention the copying light absorbed in the said light-absorbing substance (s) present internally in the thermo-sensitive layer produce therein the desired image differentiation based on a heat-induced and/ or promoted chemical and/ or physical change.

In order to achieve a very true reproduction of the tone scale of the continuous-tone transparency, the maximum density in the dots of the contact-screen should not be substantially different from the maximum density of the transparency and is preferably equal thereto. Preferably the maximum optical density of the continuous-tone transparency is comprised between 0.2 and 1.0.

The composition of the heat-sensitive layer and the kind of physical and/ or chemical change obtained therein on heating determines whether a direct visible image or latent image developable by an after-treatment will be obtained.

For suitable heat-sensitive layers we particularly refer to heat-sensitive gelatin layers such as the heat-sensitive gelatin layers described in the published Dutch patent application 66/08711 filed June 23, 1966 by Gevaert-Agfa N.V., the exposed gelatin parts of which possess an increased water-permeability, water-solubility and swellability in water.

For a good differentiation in water-permeability and water-solubility heat-sensitive recording layers of the gelatin type preferably contain at least 80% by weight of gelatin.

Other suitable heat-sensitive layers are mainly cOmposed of polyvinyl alcohol and the heat-exposed parts of such layers show a decrease in water-solubility and waterpermeability in respect of the unexposed areas. As disclosed in published Dutch patent application 66/016-17 filed Feb. 9, 1966 by Gevaert-Agfa N.V. vinyl polymers containing at least 95% of vinyl alcohol units are suited.

Good results can also be obtained using hydrophilic colloid layers containing in a weight ratio of at least 1:1 in respect of the colloid dispersed particles of a hydrophobic thermoplastic polymer and showing in heated areas a decrease in water-permeability, hydrophility and watersolubility, as is disclosed in published Dutch patent application 64/14226 filed Dec. 7, 1964 by Gevaert Photo- Producten N.V. and published Dutch patent application 66/06719 filed May 17, 1966 by Gevaert-Agfa N.V.

The recording layer is preferably for at least 50% by Weight composed of the dispersion consisting of the said hydrophobic thermoplastic polymer particles in said colloid or hydrophilic binder.

The heat-sensitive recording layers for use in the recording process according to the present invention preferably adsorb at least 80% of the light passing through the sandwich of continuous-tone transparency and contact screen.

According to a preferred copying technique of the present invention heat-sensitive materials of the type described in the latter published Dutch patent application 66/06719 filed May 17, 1966 by Gevaert-Agfa N.V. are used, such material preferably having a heat-sensitive layer wherein copying light-absorbing substances are dispersed in such an amount that an optical density of at least 1 is obtained.

Heat-sensitive materials on the basis of gelatin as de scribed in the published Dutch patent application 66/ 08711 filed June 23, 1966 by Gevaert-Agfa N.V. are suited for positive-positive printing, in other words for produc ing by a selective washing away of water-soluble portions a positive screen transparency of a positive continuoustone transparency, whereas heat-sensitive materials on the basis of a dispersion of latex particles, which are solid at room temperature in a hydrophilic colloid binder as described in the published Dutch patent application 66/ 06719 filed May 17, 1966 by Gevaert-Agfa N.V. are suited for negative-positive printing.

Substances absorbing infra-red light and visible light and which are suited for being incorporated into the thermo-sensitive layer as substances converting that light into heat are described, e.g., in published Dutch patent application 66/06719 filed May 17, 1966 and published Dutch patent application 66/08711 filed June 23, 1966 both by Gevaert-Agfa N.V. As visible light and infra-red absorbing substances we would particularly mention finely divided carbon black, graphite, prussian blue, oxides, sulphides or carbonates of heavy metals having an atomic weight between 45 and 210, such as manganese or lead sulphide or these heavy metals themselves in finely divided state e.g. silver, bismuth, lead, iron, cobalt and nickel. The particle size of these substances preferably should not exceed 0.1,u.

When using visible copying light the reproduction process of the present invention is not limited to the reproduction of black-and-white transparencies. Monochromatic transparencies can be reproduced by using in the heatsensitive material substance(s) absorbing light corresponding to the colour of the original or light of a colour complementary to the colour of the original.

Thus, according to a particular embodiment the heatsensitive material can be made sensitive to light of a limited range of wavelengths. This can be done by incorporating into the heat-sensitive layer coloured substances, which absorb light of a particular part of the visible spectrum and convert that light into heat. Examples of such layers and ingredients therefor are given in the published Dutch patent application 66/06719 filed May 17, 1966 by Gevaert-Agfa N.V. wherein spectrally sensitized heat-sensitive layers are described for recording coloured originals in terms of differences in water-solubility and swelling tendency.

It is to be understood that mixtures of said coloured substances can be used too, so that light of the whole visible spectrum is absorbed. The said substances have not necessarily to absorb in the range of the visible spectrum alone, they may also absorb infrared light to a more or less extent.

The coloured substance or mixtures of said substances converting light into heat and optically sensitizing the heat-sensitive materials are preferably light-absorbing 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 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 dyes can be used in dispersed as well as in dissolved form.

Preferably they are present in such an amount that an optical density of at least 1 is attained.

It is recommendable to use a heat-sensitized recording material that can be processed by plain water (selective image-wise washing away of water-soluble portions of the recording layer).

A preferred recording material in that respect comprises a heat-sensitive recording layer that incorporates thermoplastic hydrophobic polymer particles which are solid at room temperature and are dispersed in a weight ratio of at least 1:1 in a water-soluble binder. The recording layer is coated on an interlayer or self-supporting sheet which is composed of or comprises hydrophobic substance(s) having a melting or softening point lower than, equal to, or not substantially higher than that of the hydrophobic thermoplastic particles present in the recording layer.

We particularly prefer to use a heat-sensitive recording material as just described and comprising an interlayer which contains such hydrophobic substances dispersed in a hydrophilic binder which is less soluble in water than the hydrophilic binder of the recording layer. As specific examples poly-N-vinylpyrrolidone may be used as binder for the recording layer and gelatin as binder for the interlayer or self-supporting. sheet.

Continuous-tone transparencies, which are specially suited for being reproduced according to the present invention by means of recording materials described in published Dutch patent application 66/06719 filed May 17, 1966 and published Dutch patent application 66/ 08711 filed June 23, 1966 both by Gevaert-Agfa N.V. have a maximum optical density not exceeding 0.5. The exposure time preferably does not exceed 10- sec.

Suitable radiation sources producing copying light of high intensity in a very small lapse of time and which are very suited for use in processes according to the present invention are the so-called flash lamps. Good results are obtained with xenon gas discharge lamps, Which can supply a light energy of 100 to 1000 watts sec. in a time interval of l to seconds. These flash lamps emit a greater part of energy as visible light together with infra-red light. Details about a copying apparatus containing such a discharge lamp can be found in Belgian patent specification 664,868 filed June 3, 1965 by Agfa-Gevaert AG.

Evidently gas discharge lamps with a much lower energy output can be used if the emitted 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 onto heat-sensitive materials as described in published Dutch patent application 66/06719 filed May 17, 1966 by Gevaert-Agfa N.V. In practice, for such materials having an optical density of at least 1, a light energy of 0.3 watt sec. per sq. cm. will suffice for the desired image-differentiation. It is further self-explanatory that exposure may be performed progressively and/or intermittently. In other words the recording material may be scanning-wise exposed, e.g. by a high-intensity light spot rapidly line-wise scanning the recording material, or may be progressively exposed through a slot wherein, e.g., light of a tube-like radiation source is focused.

It is evident that the heat-sensitive material, before or during the creation of the image-wise heat difierentiation, can if desired be subjected to overall heating to a certain temperature below the temperature of image differentiation in the heat-sensitive material.

The following examples illustrate the present invention.

EXAMPLE 1 A poly(ethylene terephthalate) support of 0.1 mm. thickness provided with a subbing layer is coated with the following composition pro rata of 30 g./sq. m.:

After drying, the material possesses an optical density of 3.5 measured by transmittance. The material is exposed as schematically represented in FIG. 1, to a xenon gas discharge lamp having a capacity of 1000 watt sec.

and producing light in a time of V2000 sec., through a continuous-tone negative transparency and a contact screen, each having a maximum optical density of 0.5.

In FIG. 1 element No. 1 represents the transparent support of a continuous-tone transparency of which the element 2 is the image-bearing layer. Element No. 3 represents the transparent support of a contact screen and element No. 4 represents the layer containing the contact screen dots. Element No. 5 represents the heat-sensitive layer containing the substances absorbing copying light and thermoplastic polymer particles and element No. 6 represents a transparent support for that layer.

After exposure, whereby the exposed areas are rendered relatively water-insoluble, the material is dipped into water and gently rubbed with a cotton pad. The heatsensitive layer is removed in the non-exposed areas.

A positive very true image of the continuous-tone transparency is obtained consisting of tiny dots with an equal optical density varying in diameter.

The same results are obtained when the polyethylene dispersion mentioned hereinbefore is replaced by a 40% aqueous dispersion of poly(vinyl chloride) particles sizing on the average 0.16;. and having a molecular weight of 200,000 or a 40% aqueous dispersion of polystyrene particles sizing on the average 0.13 and having a molecular weight of 50,000.

EXAMPLE 2 A paper support weighing g./ sq. m. provided with a baryta coating is covered pro rata of 50 g./sq. m. with the following composition:

10% aqueous dispersion of gelatin 200 10% aqueous dispersion of colloidal silver 600 40% dispersion of polyethylene as described in Example 1 240 3% aqueous solution of the sodium salt of the condensation product of oleic acid and methyltaurine 40 10% aqueous solution of saponin 40 When dried, the material is exposed as described in Example 1.

Subsequently the material is dipped in a conventional silver-bleaching bath.

A positive high density screen image of the negative continuous-tone transparency is obtained.

EXAMPLE 3 A cellulose triacetate support of 0.14 mm. thickness provided with a gelatin subbing layer is coated with the following composition:

When dried, the material is exposed as schematically represented in FIG. 2. The same continuous-tone transparency is used as described in Example 1, but the material is non-differentially preheated to 70 C.

In FIG. 2 the element No. 1 represents the transparent support of a continuous-tone silver image transparency and element No. 2 the layer containing the silver image. Element No. 3 represents the transparent support of a magenta contact screen and element No. 4 the layer containing the screen dots. Element No. 5 represents the heatsensitive layer and element No. 6 the transparent support therefor. Element No. 7 is a heating jacket and element No. 8 the flash exposure lamp, which is a xenon gas discharge lamp producing light with an intensity of 1000 Watt. sec. in V3000 sec. The elements No. 9 are the electrodes of that lamp. On exposure, the elements 1 to 7 are concentrically arranged around the flash exposure lamp, the axis of which is situated at a distance of 4 cm. from the continuous-tone transparency.

After exposure, the recording material is dipped in water of 20 C. and gently rubbed with a wadding of cotton. The portions of the heat-sensitive layer corresponding with the non-exposed areas are removed.

A positive magenta screen image of the negative continuous-tone transparency is obtained.

EXAMPLE 4 A cellulose triacetate support of 0.12 mm. thickness provided with a subbing layer for gelatin is coated with the following composition pro rata of 50 g./sq. m.:

% aqueous solution of sodium-tetradecylsulphate The layer is dried at 20 C. The copying material thus obtained is exposed as described in Example 1 but through a positive transparency having a maximum density of 0.3 and a silver-contact screen having a maximum density of 0.3. After exposure, the material is dipped into water of 20 C. and gently rubbed. The heat-sensitive layer is removed in the exposed areas.

A very true positive copy of the positive transparency is obtained.

What we claim is:

1. A process of reproducing information which comprises the steps of contact exposing to visible light through a continuous tone transparency to be reproduced having a maximum optical density between about 0.2 and 1.0 and a contact screen having a maximum optical density not greater than that of said transparency, a normally waterremovble heat-sensitive recording layer adapted to undergo a loss in water-removability upon heating, said layer comprising particles of at least on hydrophobic thermoplastic polymer dispersed in a film of a hydrophilic binder in a ratio of at least 1:1 by weight and containing uniformly distributed therethrough finely-divided material absorbing such radiation and converting the same into heat in sufficient amount that the layer absorbs at least 80% of the copying light impinged thereon, said exposure being of a time not exceeding one-tenth of a second and of such intensity as to produce in a screen dot pattern of exposed regions of said recording layer sufficient heat through the absorption thereby by said finely-divided material to render said dot pattern water-insoluble but not such as to significantly reduce the water-removability of the unexposed regions of said layer, and treating said layer with an aqueous liquid to remove the unexposed regions therefrom.

2. The process of claim 1 wherein the amount of visible light absorbing material is sufficient to impart to said recording layer an optical density of at least about 1.

3. The process of claim 2 wherein said light has an intensity of at least about 0.3 watt sec. per sq. cm.

4. The process of claim 1 wherein said transparency has an optical density not greater than 0.5.

5. A process for reproducing information according to claim 1, wherein the recording layer is exposed by means of a flash lamp emitting visible light.

6. A process for reproducing information according to claim 5, wherein the exposure is carried out with a xenon gas discharge lamp supplying a light energy of 100 to 1000 Watt sec. in a time interval of 10- to 10- seconds.

7. A process for reproducing information according to claim 1, wherein the said copying light-absorbing substances that convert light into heat are dispersed carbon particles.

8. A process for reproducing information according to claim 1, wherein the said copying light-absorbing substances that convert light into heat are dispersed silver metal particles.

9. A process for reproducing information according to claim 1, wherein the hydrophilic binder is a water-soluble polymer.

10. A process for reproducing information according to claim 9, wherein the water-soluble polymer is poly(N-vinylpyrrolidone) or gelatin.

11. A process for reproducing information according to claim 1, wherein the recording layer contains at least by weight of gelatin.

12. A process for reproducing information according to claim 1, wherein the recording layer mainly contains a polyvinyl polymer containing at least by weight of vinyl alcohol units.

References Cited UNITED STATES PATENTS 3,010,391 11/1961 Buskes et al. 96'45X 3,223,838 12/1965 Hoshino et al 25065(1) 3,298,833 1/1967 Gaynor 96-27 3,392,020 7/1968 YutZy et al 96-67 OTHER REFERENCES Van der Grinten Bulletin, Aug. 1, 1963, pp. 5 and 6.

A. L. BIRCH, Assistant Examiner US. Cl. X.R. 96-45