Heat-sensitive copying material

March 22, 1966 w. schOtzner

HEAT-SENSITIVE COPYING MATERIAL

Filed April 27, 1962

3,241,997

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INVENTOR.

WALTER SCHUTZNER BY

Okavcu-cUisATTORREYS

United States Patent Office

3,241,997

Patented Mar. 22, 1966

3,241,997 HEAT-SENSITIVE COPYING MATERIAL

Walter Schiitzner, Getreidemarkt 17,

Vienna VI, Austria

Filed Apr. 27, 1962, Ser. No. 190,724

Claims. (Cl. 117—36.9)

This invention relates to heat-sensitive copying paper for producing copies of graphic subjects and a method of making such paper. In use the original sheet which is to be reproduced is illuminated by a lamp. The dark areas of the sheet absorb the heat rays of the lamp, while the lighter unprinted areas partly reflect them and partly allow them to pass through. Thus a heat pattern is produced in the original at the dark areas and is transmitted to the copying paper which is in heat-conductive contact therewith.

One of the prior art copying papers of this type includes a dark supporting sheet carrying an opaque waxlike layer. The layer is made opaque by applying the wax-like substance jointly with a binder, whereby the wax-like substance should be distributed as finely as possible in the binder. The heat transmitted by the original melts the wax particles in areas corresponding to those of the original, so that in these areas the layer becomes transparent and the color of the supporting sheet becomes visible.

It.has been also suggested to apply upon a flexible supporting material a layer having a binder which does not melt below 150° C. and is not volatile. Two chemical reagents which are stable at room temperatures are distributed in this binder. They react with each other under the influence of heat to develop a color, whereby at least one of them must be liquid at temperatures above 60° C. Copying paper of this type is brought into heat-transmitting contact with the original which is to be reproduced and is illuminated by a lamp, whereupon the rays are absorbed at the dark areas of the original. The heat pattern produced in the original will affect the copying paper, so that at locations corresponding to those of the original the two heat-sensitive components will react with each other developing a color and producing a copy corresponding to the original.

The first-mentioned type of heat-sensitive copying paper has the drawback that the heat-sensitive layer is easily damaged by pressure, wiping and by scratches. The second-mentioned type of heat-sensitive copying paper has the drawback, that the manufacture of this paper is quite difficult, since it is necessary to take special care that the two substances should not react with each other during the process of manufacturing the copying paper. For that reason the application of the layer and the removal of the solvent must take place at room temperatures, particularly since at least one of the two substances has a very low melting point. Preferably ferric stearate and gallic acid are used as color producing components. Furthermore, oxalic acid or a similar complex former are added to the mass of the coating as masking means for any possible colorations of the ferric salt which may appear. This addition of masking means not only increases the price of the copying paper, but also complicates its manufacture, since it is comparatively difficult to determine the precise amount of the complex formers which is necessary to be added. If too little is added a coloring reaction always takes place during the manufacturing process and then the paper is unusable. If too much of the complex former is added, the finished paper is again unusable, since no effective and well visible indicia appear during the copying when the sheet runs through the apparatus for a comparatively short time.

It has also been suggested to apply one of the two color-forming reagents jointly with a binder from the solution or dispersion upon a supporting material, to dry the applied layer and thereupon to apply upon it a second layer consisting of an agent reacting with the first-mentioned agent to form a color, and of the same binder which was used for the first layer. The same solvents or dispersing agents which are used for the first layer are used to dissolve or disperse the two substances. By using the same solvents and binders, the two layers flow one into the other at the surfaces limiting the two layers, so that finally a single layer is carried by the supporting sheet. Since particles of the two color-producing reagents are located one next to the other in the area wherein the two layers are in contact with each other, it is also necessary to add complex formers to prevent a premature reaction. Other embodiments of the described copying papers carry a protective layer over the heatsensitive layer.

It has also been suggested to apply a layer consisting of a binder with one of the two color-producing reagents upon a suitable supporting material and thereover to apply the second color-producing reagent also jointly with a binder, whereby two different binders are used for the two layers, and whereby the application is such that two entirely separate, clearly discernible layers appear upon the supporting sheet. This is also simultaneously attained by the use of solvents or dispersing means for the second layer which do not dissolve either the binder or the color-forming reagent of the first layer. As binders only such substances are used which do not melt at the melting and reacting temperatures of the color-forming substances. This has the drawback that the two color components which are separated from each other by two non-melting binder layers, react with each other only with difficulty, since the binder structure remaining after one color-reacting component has been “melted out,” prevents the two color-reacting components from getting together.

An object of the present invention is the provision of a heat-sensitive copying paper which will avoid the drawbacks of prior art copying papers.

Other objects of the present invention will become apparent in the course of the following specification.

A most important characteristic feature of the process of the present invention is that two layers containing color-producing reagents are applied separately upon a supporting sheet, they have different melting points, they are dissolved or soluble in different solvents and under no circumstances does the solvent of the subsequently applied layer dissolve the first layer.

. In carrying out the present invention it was found desirable to manufacture heat-sensitive copying paper by applying upon a supporting material a chemical reagent capable of reacting with another to produce color, along with a binder the melting point of which is located close to or below the melting point of one of the two colorforming reagents. Thereupon a second layer is applied consisting of a binder which does not melt at the melting temperature of said one color-forming reagent. At least one of the reagents must melt within the range of 60° C. to 150° C. It is particularly advantageous to color the outer one of the two binders with titanium white or the like in such manner that it forms a strong optical contrast to the color of the indicia produced during the copying.

In accordance with another embodiment of the present invention a binder layer composed of one of the two color-forming reagents and of a binder melting at or below. 150° C. is applied upon a transparent supporting material. Then a binder layer with the second colorforming reagent is applied over the first layer, whereby cellulose derivatives are used as binders and whereby a mixture of solvent and precipitant for the cellulose deriva3,241,997 normal circumstances, and that it is not sensitive against lengthy illumination by sun rays.

In the accompanying drawing:

FIGURES 1 and 2 are diagrammatic enlarged rep5 lesentations of cross-sections of two embodiments of the copying paper of the present invention.

FIGURE 1 shows a finished copying material 10 consisting of a supporting base 11 and two layers 12 and 13 which are separate and clearly distinguishable one from •|₀ the other. Each of the layers 12 and 13 contains at least one color-producing reagent.

FIGURE 2 shows that a protective layer 14 may be applied over the layers 12 and 13. The protective layer 14 may be transparent, translucent or opaque.

The following specific examples will illustrate this invention, but are not to be construed as limiting the scope of the invention, since many other modifications will become apparent on consideration of the disclosures here made.

All parts hereinfter indicated are by weight.

EXAMPLE 1

The following layers are applied upon a transparent paper of about 40 g./m.²;

First layer parts of hard paraffin (having a melting point of about 100° C.) are molten, and parts of pyrogallol are stirred in and finely divided ₃₀ by milling.

A layer of about 3-5 g./m.² is applied upon the aforesaid paper out of the melt.

Second layer parts of polystyrol are dissolved in ^3,&gt; 60 parts of tri-chloro-ethylene, parts of ferric III stearate are stirred in and are finely divided by milling in a pebble mill.

The dry layer amounts to 4-6 g./m².

EXAMPLE 2

The copying material made in accordance with Example 1 is provided with a protective layer consisting of the dried residue of a solution of parts of cellit-K800, in

70 parts of acetone, and parts of water.

A white coating of the layers is produced by blowingin directly after the application.

The dry layer amounts to 3-5 g./m.².

EXAMPLE 3

The following layers are applied upon the paper base described in Example 1:

First layer

2-3 g./m.² of ferric III stearate, which is applied out of the melt.

Second layer parts of ethyl cellulose, ⁰⁰ 10 parts of gallic acid, parts of acetone, parts of kaolin, and parts of water are dissolved or milled in a pebble mill.

⁶⁵ By blowing upon the layer immediately after its application a white coating thereof is produced.

The dry layer amounts to about 7 g./m.².

EXAMPLE 4

The following layers are applied upon the paper base described in Example 1:

First layer parts of gallic acid are dissolved in the melt in

90 parts of L-wax (Hoechst) tive is so applied in a manner known per se that the coating is caused to become white.

In accordance with yet another embodiment of the present invention, a transparent protective layer is applied over the two binder layers. In that case it is advantageous to use an opaque supporting material, such as a sheet of paper or an opaquely colored synthetic foil, which has a strong optical contrast to the indicia produced during the copying.

However, it is found particularly advantageous to use a transparent supporting material. In that case it is desirable to provide a transparent or opaquely colored protective layer over the two heat-sensitive layers, or to use cellulose derivatives or the like for forming the layers and to apply the cellulose derivative in a mixture of solvent and precipitant in a manner known per se that the coating is caused to become white.

When the heat-sensitive copying paper made in accordance with the present invention is provided with a protective layer, it is obviously not necessary to use solely for the inner layer the binder which melts at or below the melting temperature of one or both color-forming substances; on the contrary a binder which melts in the described manner can be also used for the outer one of the two binder layers, so that, consequently, the two layers will contain a meltable binder. However, it is also possible to use a non-melting binder for the inner layer and a meltable binder for the outer layer.

It is also possible to carry out the present invention by applying a color-producing reagent in the form of a layer without a binder. For that purpose it is advantageous to use a reagent which melts between 60° C. and 150° C., for example, ferric (III) stearate which is well suitable for forming a layer due to its wax-like consistency. The second reagent is applied by means of a binder as described above.

It is also possible in carrying out the present invention to use combinations of color-producing reactive components none of which melts within the range of 60° C. to 150° C. However, then at least one of the two reacting agents must be soluble in the “meltable” binder; this reacting agent is preferably introduced into the layer containing the meltable binder.

The present invention includes not only systems which require two components for producing a color, for example, an iron salt and gallic acid; on the contrary the present invention also includes systems wherein more than two components are required for color formation, for example, two color-producers and one coupling reagent. In this embodiment the different reactants are also divided and applied in two separate layers, for example, one component in the inner layer and two in the outer layer.

Practical experience has shown that when the copying apparatus is not particularly expertly operated, namely, when too much heat is applied, there is the drawback that parts of the uppermost layer are dabbed upon the surface which is in contact therewith. This can be avoided by including in the outermost layer a certain amount of a suction-capable pigment, such as kaolin. This pigment can form a covering, although it does not have to do so. In this manner by a proper selection of suitable pigments it is possible to strengthen the contrasting effect and also prevent the detrimental dabbing.

It is apparent that all of the above described embodiments of the present invention have the common characteristic feature that the two layers containing colorproducing reagents are applied separately upon a supporting sheet and that, as already stated, they have different melting points, and are dissolved or soluble in different solvents, whereby the solvent of the second layer never dissolves the first layer.

By placing the reaction components in two separate layers, the copying material of the present invention has the great practical advantage that it is not sensitive against the effects of heat and light, which occur in rooms under

3,241,997

The coating applied out of the melt amounts to about 6 g./m.².

Second layer parts of polystyrene, parts of ferric III sulfate, parts of tri-chloroethylene are dissolved or rubbed in a pebble mill.

The dry layer amounts to 4-6 g./m.².

Thereupon a protecting layer is applied which consists of the dried residue of the following application mass:

parts of cellit-K 800, parts of titanium white, and parts of acetone.

The dry coating amounts to 3-5 g./m.².

It is apparent that the examples described above have been given solely by way of illustration and not by way of limitation and that they are subject to many variations and modifications within the scope of the present invention. All such variations and modifications are to be included within the scope of the present invention.