US3914510A - Thermal sensitive transparency - Google Patents

Abstract

A thermal-sensitive transparency is disclosed. A transparent film substrate is coated with a mixture of a binder and sulfonic acid. A second coating of a binder and a chromogenic compound is applied over the first coating. The binder of the first coating is not soluble in the solvent used to apply the second coating. The thus coated transparency can be imaged in conventional thermal copy machines and used in conventional projection equipment.

Description

United States Patent Glanz et al.

THERMAL SENSITIVE TRANSPARENCY Inventors:

Assignee:

Filed:

Appl. No.:

Kenneth D. Glanz; David B.

McQuain, both of Appleton, Wis.

NCR Corporation, Dayton, Ohio Mar. 20, 1974 Related US. Application Data Continuation-impart of Ser. No. 263,569, June 16,

1972, abandoned.

References Cited UNITED STATES PATENTS Berman 260/326.l1

1 1 Oct. 21, 1975 3,483,013 12/1969 Berg et al. 117/362 3,594,208 7/1971 Wiese et al.. 117/368 3.664.858 5/1972 Huffman 117/368 3,666,525 5/1972 Kimura et al. 117/368 3.746.675 7/1973 Blose et a1. 117/362 X Primary ExaminerThomas J. Herbert. Jr. Attorney, Agent, or FirmRobert J. Shafer; E. Frank McKinney [57] ABSTRACT A thermal-sensitive transparency is disclosed. A transparent film substrate is coated with a mixture of a binder and sulfonic acid. A second coating of a binder and a chromogenic compound is applied over the first coating. The binder of the first coating is not soluble in the solvent used to apply the second coating. The thus coated transparency can be imaged in conventional thermal copy machines and used in conventional projection equipment.

18 Claims, No Drawings THERMAL SENSITIVE TRANSPARENCY This application is a continuation-in-part of patent application Ser. No. 263,569, filed June 16, 1972. now abandoned.

This invention relates to a thermal-sensitive transpar' ent film. In another aspect, this invention relates to a method of making such a heat-responsive transparency.

Heat-sensitive record materials are known in the art. Typically, colorless mark-forming components such as crystal violet lactone and a phenolic material are arranged in juxtaposition in a single support sheet. Application of heat to the sheet causes a migration of the liquefied or vaporized material to a juxtapositioned markforming component to produce a mark, as the markforming components generally react upon contact to produce a color. Often, these known heat-sensitive copy sheets prematurely color before the application of heat. Another problem is the development of color in areas of the sheet where heat is not applied.

One solution to these problems is disclosed in US. Pat. No. 3,666,525 issued May 30, 1972. That patent discloses a support coated with a layer of a spirochromene compound and a solid sulfonic acid in a substance capable of dissolving the spiro compound and the sulfonic acid when fused. The patent discloses that when crystal violet lactone or indolinobenzospiropyran compounds are substituted for the spirochromene compound, the sheet develops a color fog at the time of copy printing.

A thermal-sensitive transparent film now has been developed which employs any colorless, but colorable chromogenic compound. The thermal-sensitive transparency of this invention consists of a transparent film coated with a base coating and a surface coating. The base coating is a film formed from a solution containing a film-forming polymer binder and a sulfonic acid. The base coating is thoroughly dried prior to the coating of the surface coating. The surface coating is coated from a solution containing a film-forming polymer binder, a colorless but colorable chromogenic compound, and a solvent in which the binder of the base coating is insoluble.

Accordingly, an object of this invention is to provide a thermal-sensitive transparent film.

Another object of this invention is to provide a process for making a thermal-sensitive transparent film.

Another object of this invention is to provide a thermal-sensitive film of decreased background color and increased stability with regard to developed hue. It is also an object of this invention to provide a process for making such a thermal-sensitive film of decreased background color and increased stability.

Other objects, aspects and advantages of this invention will be apparent to one skilled in the art from the following disclosure and appended claims.

The transparent substrate employed in this invention can vary widely. Generally, a transparent polymeric film is used. Specific examples include films of cellulose acetate, cellulose acetate butyrate, cellophane, polyester, polyethylene, polystyrene, polyethylene terephthalate and the like. Preferably, polyethylene terephthalate, polyester or polystyrene is employed. The thickness of the transparent substrate varies widely. Generally, the substrate has a thickness ranging from 0.2 to 5 mils.

The base coating is prepared by dissolving a binder and a sulfonic acid in a solvent liquid. The solution then is coated onto the transparent substrate by conventional means. Generally, the thickness of the web base coating ranges from 1 to. 10 mils, preferably 1 to 3 mils. The base coating then is thoroughly dried prior to the application of the surface coating.

Specific solvents used in applying the base coating include water, methanol, ethanol, propano], and the like and mixtures thereof.

The binder employed in the base coating is a film forming polymer which is insoluble in the volatile organic solvents which are used to apply the surface coating. Specific examples of this binder include polyvinyl alcohol, gelatin, polyamide, cellulose nitrate, or polyvinyl butyral and the like. Polyvinyl alcohol is preferred.

The sulfonic acid employed in this invention is represented by the formula R-SO H wherein R is wherein R is the radical OH, Cl, Cl-l NO or SO H.

Specific examples of the sulfonic acids employed in this invention include:

IO-camphorsulfonic acid;

catechol-3,5-disulfonic acid;

2-chloroaniline-5-sulfonic acid;

2-chloro-6-methylaniline-4-sulfonic acid;

4-chloroaniline-3-sulfonic acid;

m-benzenedisulfonic acid;

p-chlorobenzene sulfonic acid;

2-naphthalenesulfonic acid xylenesulfonic acid;

toluenesulfonic acid;

4-nitrotoluene2-sulfonic acid;

2,4,6-trinitrobenzenesulfonic acid, or

2,4-dinitro-1-naphthol-7-sulfonic acid and the like.

After the base coating has been thoroughly dried, by allowing it to stand for a few minutes or by the application of mild heating or both, the surface coating is pre pared by dissolving a binder and a colorless chromogenic compound in a volatile organic solvent in which the binder of the base coating is not soluble. If desired, a low melting material can be included. Generally, the thickness of the wet surface coating ranges from 1 to mils, preferably 1 to 3 mils. The surface coating is dried prior to use.

The binder employed in the surface coating is a filmforming polymer which is soluble in a volatile organic solvent. Specific examples of this binder include:

polystyrene;

cellulose acetate butyrate;

polyvinyl acetate;

ethyl hydroxyethyl cellulose;

ethyl cellulose;

polysulfone;

cellulose triacetate;

polyvinyl butyral;

polyvinyl formal;

methyl methacrylate;

styrene copolymer;

dicyclopentadiene resin; or

polyindene resin and the like.

The volatile organic solvents employed in applying the surface coating include toluene, benzene, ethyl acetate, benzene-ethanol mixtures, cyclohexanone, chlorobenzene, methyl ethyl ketone and the like.

Any colorless, but colorable chromogenic compounds can be employed in the surface coating of this invention. The following examples merely represent a few such compounds:

1. 3,3-spirobi [3fl-naphtho [2,1-b] pyran];

2. 2-decyl-3,3-spirobi [Mi-naphtho [2,l-b] pyran];

3. 2-chloro-3,3'-spirobi [31;l-naphtho [2,l-b] pyran];

4. 2,2-trimethylene-3,3-spirobi [3 l-l-naphtho [2,l-b]

5. 2-n-amyl-3,3'-spirobi [Mi-naphtho [2,l-b] pyran];

6. 2,2-trimethylene-3,3-spirobi [3ll-naphtho [2,l-b]

7. 2,2-trimethylene-2"-methyl-3,3'-spirobi naphtho [2,l-b] pyran];

8. 2-n-heptyl-3,3'-spirobi [3 1-l -naphtho [2,l-b] pyran];

9. 2-isobutyl-3,3-spirobi [3fl-naphtho [2,l-b] pyran];

10. 2-methyl-3,3-spirobi [31;l-naphtho [2,1-b] pyran];

l1. 2-ethyl-3,3'-spirobi [3lj-naphtho [2,l-b] pyran];

12. spiro [21;1-l-benzopyran-2,3-[3l;l]-naphtho [2,1-

13. 2-isopropyl-spiro [21;1-l-benzopyran-2,3-[3l l naphtho [2,l-b] pyran];

l4. 2'-methyl-spiro [2l l-l-benzopyran-2,3'-[3l l]- naphtho [2,1-b] pyran];

15. 2,2-spirobi [2lj-1-benzopyran];

l6. 3 ,3 '-trim ethylene-2,2 -spirobi [21;1-1 -benzopyran];

l7. 2,3-diphenyl-7-methoxy spiro [4ll-l-benzopyran- 4,3'-[3l;l] naphtho [2,l-b] pyran];

18. 2-phenyl-3-methylspiro [4fl- 1 -benzopyran-4,3

[3fl] naphtho [2,l-b] pyran]; l9. 2,2-spirobi [21;1-naphtho [1,2-b] pyran];

20. 2-(2,5-dichloroanilino)-2-(p-methoxyphenyl-2(H) benzopyran);

21. 1',3',3'-trimethyl-8-methoxy spiro [21;1-1-benzopyran-2,2'-indoline]:

22. 1,3,3-trimethylspiro [indoline-2,3'-[31;l]-naphtho 23. 1,3,3-trimethylspiro [indoline-2,3-[3fl]-naphtho 24. 3,3-bis (p-dimethylamino dimethylamino phthalide; 25. 3,3-bis (l-ethyl-2-methylindol-3-yl) phthalide;

phenyl )-6- 26. 2'-anilino-6-diethylamino-3'-methylfluoran; or 27. 2-methoxy-6-diethylaminofluoran; or 28. 1,3, 4'-trimethyl-6'-diethylaminofluoran and the like.

Small amounts of a plasticizer, such as a phthalate like butylbenzyl phthalate, can be employed, if desired.

The amounts of materials employed vary widely. The wet base coating generally consists of, by weight, 2.0 to 10.0 percent of the sulfonic acid, 3.0 to 10.0 percent of the binder and 80.0 to 95.0 percent liquid. Preferably, these percentages range from 2.0 to 5.0, 4.0 to 6.0 and 90.0 to 95.0 respectively. The wet surface coating generally consists of, by weight, 2.0 to 10.0 percent of the chromogenic compound, 3.0 to 15.0 of the binder and 75.0 to 95.0 of the volatile organic solvent. Preferably, these percentages range from 2.0 to 5.0, 5.0 to 10.0 and 85.0 to 93.0, respectively.

In the dry base coating, the ratio by weight of sulfonic acid to the binder ranges from 1:5 to 3:1, preferably 1:1 to 1:3. 1n the dry surface coating, the ratio by weight of the chromogenic compound to the binder ranges from 1:8 to 3:1, preferably 1:5 to 1:1.

The coating is allowed to dry and the resulting transparent sheet is ready for imaging as follows.

The coated support is now capable of being imaged with heat. The image can be produced by contact with a heated surface or by superimposing on an original drawing and heating on any suitable infrared, thermal transparency maker or copy machine to produce a colored image on a transparent background. The imaged transparency is then ready for projection in or on conventional projection equipment.

If desired, the base coating and the surface coating can be reversed depending upon the solvent sensitivity of the transparent film. A three layer system is also possible with layer containing the chromogenic compound sandwiched between two layers each containing sulfonic acid. Such a construction will yield a transparency with increased print density. Naturally, the binder employed in one coating cannot be soluble in the solvent used to apply the next coating. A wide variety of colored prints are possible depending on the chromogenic compound employed.

The advantages of this invention are further illushated by the following examples. The materials and the proportions and other specific conditions are presented as being typical and should not be construed to limit the invention unduly.

EXAMPLE 1 A transparent polystyrene film substrate was coated as follows:

A first solution was prepared by dissolving 3.0 grams of polyvinyl alcohol, 0.67 grams of IO-camphorsulfonic acid, and 0.67 grams of Z-naphthalenesulfonic acid in 37 grams of water. The mixture was coated onto the polystyrene film at a wet thickness of 1 mil. The base coating was thoroughyl dried.

A second solution was prepared by dissolving 0.7 grams of polystyrene, 0.02 grams of 3,3-spirobi [31inaphtho [2,l-b] pyran], 0.1 grams of 2-methyl-3,3'- spirobi [31;l-naphtho [2,1-b] pyran], 0.1 grams of 2- ethyl-3,3-spirobi [3fl-naphtho [2,l-b] pyran], and

0.07 grams of a plasticizer (butylbenzyl phthalate), in 6.3 grams of toluene. This mixture was coated on top of the base coating at a wet thickness of 1 mil. The coating was thoroughly dried and the resulting transparent film was imaged on a conventional copying machine. The imaged film was employed on a conventional overhead projection and projected a dark blue image on a clear background. No premature coloring or color fogging in unimaged areas was observed.

EXAMPLE II Other thermal-sensitive transparencies were prepared according to the procedure described in Example I employing the 28 colorless, but colorable chromogenic compounds listed in the specification. All of these compounds were employed alone and in various mixtures. However, in the interest of brevity, only a few of the prepared transparencies will be described herein.

Four separate runs were carried out according to the procedure of Example I except that only one colorless, but colorable compound was employed instead of the mixture of Example I. The compound and amount employed were:

a. 0.2 grams of 2-methyl-3,3-spirobi [3I;I-naphtho l Py b. 0.2 grams of 2-ethyl-3,3'-spirobi [31;I-naphtho c. 0.3 grams of 2'-anilino-6'-diethylamino-3'- methylfluoran; and

0.2 grams diethylaminotluoran.

Runs (a), (b) and (d) were coated on top of the base coating at a wet-thickness of 2 mils, while run (c) was coated at 1 mil as in Example I. The amount of polystyrene and toluene in each run was approximately the same as in Example I. The base coating was the same as Example I.

After coating and drying, the films each were imaged as in Example I. The imaged films projected a blue, blue, green and orange color, respectively. No premature coloring or color fogging in unimaged areas was observed.

EXAMPLE III A 2-mil thick transparent film substrate of polyethylene terephthalate was used as the substrate. A first layer (base coating) composition was prepared by dissolving 3.0 grams of polyvinyl alcohol, 1.20 grams of Z-naphthalenesulfonic acid, 0.40 grams of methylated urea-formaldehyde, and 0.80 grams of bisphenol A, in 17.8 grams of ethanol and 25.0 grams of water.

The polyvinyl alcohol serves as binder for the layer. Any polyvinyl alcohol is eligible;--the only requirement being water solubility and formation of a film on drying.

The methylated urea-formaldehyde is a cross-linking agent for the polyvinyl alcohol and serves to minimize the formation of an undesirable background coloration which occurs under certain conditions in the absence of the cross-linking agent. An eligible methylated ureaformaldehyde is sold by American Cyanamid Co.,

Wayne, New Jersey, under the trademark designation Beetle When the ambient conditions at the second coating application are extreme, such as more than about 50 percent relative humidity and more than about Fahrenheit, an undesirable background coloration occurs in the absence of the cross-linking agent. The reason for the effectiveness of a crosslinking agent is not well understood but it is believed that when the film which binds the sulfonic acid is crosslinked, there is a reduced tendency for reabsorption of atmospheric moisture into the film. Further, it is believed that reabsorbed atmospheric moisture results in premature generation of color. Generally, any material which can crosslink the binder is eligible for use herein. In the case of polyvinyl alcohol binder, additional eligible crosslinking materials are, for example: urea-formaldehyde one being that material sold by American Cyanamid Co. under the trademark designation Urac melamine-formaldehyde-one being that material sold by Monsanto Corporation, St. Louis, Missouri, under the trademark Resloom M-80"; polyfunctional aziridine-one being that material sold by Ionac Chemical Co., Birmingham, New Jersey, under the trademark designation PFAZ-300. The abovenamed, exemplary, crosslinking agents are also effective with binders such as gelatin, polyvinylbutyral, and the like. Crosslinking material is generally present at about 0.25 to 3.0 and, preferably, about 1.0 weight percent of the total coating composition. The dry coating weight ratio of crosslinking agent to binder material is generally about 1:4 to 1:12 and, preferably, about 1:8.

The bisphenol A (4,4-isopropylidenediphenol) is used to assure color stability of the thermally developed image. For example, an imaged thermal coating using 2-methyl-3,3'-spirobi [3fl-naphtho [2,l-b] pyran], colorable blue, tends to shift to the red. It has.

been discovered that the addition of a substantial amount of bisphenol A to the system prevents this shift to the red. Bisphenol H (4,4'-isopropylidene-bis-(2- tertbutylphenol)) can also be used to prevent the red shift by being dissolved in the coating composition which contains the colorless, but colorable chromogenic compound. Bisphenol A or H is generally used at about 1 to 5 and, preferably, 2 to 2.5 weight percent of the total coating composition. It should be understood that the lower limit, while being largely a matter of convenience and efficiency, bears some critical significance in that bisphenol material levels much below the above minimum do not effectively prevent the color shift.

The ethanol was added to provide ease of solution but its use is optional when solution is otherwise accomplished.

The first layer composition was coated onto the substrate film at a wet thickness of about 1 mil and the coating was thoroughly dried.

A second layer (surface coating) composition was prepared by combining 0.80 grams of polystyrene-type material, 0.30 grams of 2-methyl-3,3-spirobi [3B- naphtho [2,1-b] pyran], 0.045 grams crystal violet lactone, 0.20 grams chlorobenzene, 0.17 grams of butylbenzyl phthalate, and 7.1 grams of toluene. The polystyrene-type material serves as binder for the layer and can be, for example, a styrene-acrylonitrile copolymer. Polymeric film forming materials, generally, are available; the only requirement being solubility in the solvent of the composition. An eligible copolymer of styrene and acrylonitrile is sold by The Dow Chemical Company, Midland, Michigan, under the trademark designation Tyril 867.

The chlorobenzene was added to promote solution of the components, the butylbenzyl phthalate was added as a plasticizer and the use of either or both of those components is optional when solution is otherwise accomplished and plasticization is not required or desired.

The crystal violet lactone is a weak base added to the system to aid in prevention of background color development. Although its function is not completely understood, it is believed that the weak base reacts with residual sulfonic acid which might find its way to the layer surface prior to the imaging'step thereby preventing premature reaction between the sulfonic acid and the chromogenic material. Weak bases are generally eligible. Secondary amines such as piperazine, piperidine, and the like have been found to be too strongly basic and are, therefore, ineligible. Tertiary amines which are soluble in the coating composition and which do not otherwise create coloration or undesirable side reactions with other layer components, are eligible. Examples of such tertiary amines include dialkylamines such as leucomalachite green, benzoylleucomethylene blue, methane base (bis(pdimethylaminophenyl)methane), methyl-mdiethylaminobenzoate, tribenzylamine, and the like. Weak base material is generally present at about 0.2 to l and, preferably, 0.4 to 0.6, weight percent of the total coating composition. The dry coating weight ratio of chromogenic material to weak base is, preferably, about 6:1.

The second layer composition was coated on top of the dried first layer at a wet thickness of about 1 mi] and the coating was thoroughly dried. The resulting sheet is imaged on a conventional thermal imaging copy machine-and displayed on a conventional transparency projecting device such as a conventional overhead projector. The thermally-developed image is blue with substantially no background color.

When the cross-linking agent was omitted from the first layer coating composition, and when the second layer coating composition was applied under conditions of greater than 50 percent relative humidity and greater than 80 Fahrenheit without the weak base, a blue background color developed over the entire sheet surface. Under those conditions, the addition of either one of the cross-linking agent or the weak base decreased the development of the, still noticeable, blue background color; and addition of both the crosslinking agent and the weak base effectively prevented the development of the background color.

When transparency sheets of this Example are made omitting the bisphenol material from the coatings, blue heat-developed images undergo considerable shift in hue toward red in only short times. For example, at 90 percent relative humidity and 90 Fahrenheit, images developed from coatings made without the bisphenol material suffered a considerable and substantial hue shift in less than 8 hours while images developed from coatings made including the bisphenol material exhibited no significant shift in more than days. At about 50 percent relative humidity and about 70 Fahrenheit, images on coatings without the bisphenol material exhibited noticeable shift in color after only 30 days while 8 images on coatings with the bisphenol material were unchanged after more than 1% years.

EXAMPLE IV In this Example, any of the previous Examples are repeated with the exception that an additional colorless chromogenic material was used. The additional colorless chromogenic material was one selected to be responsive to, and colorable by, ultraviolet light. The amount of the ultraviolet light responsive material to be used is from about 10 to weight percent of the amount of the heat responsive chromogenic materials. Such amount of ultraviolet light responsive material is generally equivalent to about 0.2 to about 15.0 weight percent of the wet coating composition. The ultraviolet light responsive materials are compounds generally derived from l',3',3'-trimethyl-spiro [2I;I-l-benzopyran- 2,2'-indoline] in especial accordance with the disclosure of US. Pat. No. 3,100,778, issued Aug. 13, 1963 and are generally known as photochromic materials. Eligible photochromic compounds can also have substitution on the indoline moiety, however, such as chloro, methyl, methoxy and the like. The photochromic material is dissolved in the coating composition along with the heat-responsive material and the composition is applied as a layer, as previously taught, above.

Specific examples of coating compositions to make heat and light responsive layers in this Example IV include: (a) addition of about 0.3 grams of l-phenyl- 3 ',3 -dimethyl-5-bromo-6-nitro-8-methoxy-spiro [21il-benzopyran-2,2-indoline] to each of the heat responsive chromogenic materials disclosed in Example II, above; (b) addition of about 0.2 grams of 5'-methyll ,3 ',3 '-trimethyl-6-nitro-spiro [211- l -benzopyran- 2,2-indoline] to the combination of heat responsive chromogenic materials disclosed in Example I, above; and (c) addition of about 0.25 grams of 5'-chlorol ,3 ',3 '-trimethyl-6-nitro-8-methoxy-spiro [Zfl- 1 benzopyran-2,2'-indoline] to the heat responsive chromogenic material disclosed in Example III, above. The coating compositions are applied in the same amounts as previously disclosed, above; and the resulting transparencies are heat responsive as previously disclosed, above. The transparencies of this example, however, are also imageable by incident ultraviolet light due to presence of the photochromic material. The photochromic images are reversible and erasable, depending on the photochromic material used, either by permitting fade over a period of time or by exposing the images to light of wavelength longer than blue to redevelop the colorless photochromic state. A transparency of this example which has been imaged by heat can be subsequently, repeatedly, imaged by ultraviolet light and erased.

Although this invention has been described in considerable detail, it must be understood that such detail is for the purposes of illustration only and that many variations and modifications can be made by one skilled in the art without departing from the scope and spirit thereof.

What is claimed is:

l. A thermal-sensitive transparent film comprising a transparent film substrate coated with (a) a base coating comprising a binder, a crosslinking agent for the .binder, and at least one sulfonic acid represented by the formula wherein R is:

wherein R is the radical OH, Cl, CH;,, NO or SO H, wherein the binder is crosslinked, and wherein the sulfonic acid and the binder of the base coating have a ratio of the sulfonic acid to the binder ranging from 1:5 to 3:1, and (b) a surface coating comprising a binder which is soluble in volatile organic solvents and at least one colorless, but colorable chromogenic compound selected from the group consisting of: 3,3- spirobi [3ll-naphtho [2,1-b] pyran]; 2-decyl-3,3- spirobi [31;1-naphtho [2,1-b] pyran]; 2-chloro-3,3- spirobi [3l;1-naphtho [2,l-b] pyran; 2,2'-trimethylene- 3,3'-spirobi [31;i-naphtho [2,1-b] pyran; 2-n-amyl-3,3- spirobi [3 ll-naphtho [2,l-b] pyran]; 2,2'-trimethylene- 3,3'-spirobi [3l i-naphtho [2,1-b] pyran]; 2,2- trimethylene-2 '-methyl-3 3 '-spirobi [3l-i-naphtho [2,l-b] pyran]; 2-n-heptyl-3,3'-spirobi [3l;I-naphtho [2,1-b] pyran]; 2-isobutyl-3,3'-spirobi [31;l-naphtho [2,l-b] pyran]; 2-methyl-3,3-spirobi [3fl-naphtho [2,1-b] pyran]; 2-ethyl-3,3'-spirobi [3li-naphtho [2,lb] pyran]; spiro [2 l- I-1-benzopyran-2,3-[3fl]-naphtho [2,l-b] pyran]; 2'-isopropyl-spiro [Zfld-benzopyran- 2,3'-[3fl]-naphtho [2,l-b] pyran]; 2'-methyl-spiro [2- fl-1-benzopyran-2,3 -[3fi]-naphtho [2,1-b] pyran 2,2-spirobi [Zfll -benzopyran]; 3,3 -trimethylene-2,2 -spirobi [Zfi-l-benzopyran]; 2,3-diphenyl-7-methoxy spiro [4fl-1-benzopyran-4,3-[3Il] naphtho [2,1-b] pyran]; 2-phenyl-3-methylspiro [41-I -1-benzopyran-4,3 [3 l;l naphtho [2,1-b] pyran]; 2,2-spirobi [2gnaphtho [1,2-b] pyran]; 2-(2,5-dichloroanilino)-2-(pmethoxyphenyl-2(l-I) benzopyran); 1 ',3 ',3 '-trimethyl- 8-methoxy spiro [21-1- 1 -b enzopyran-2,2 '-indoline 1,3,3-trimethylspiro [indoline-2,3 31-1] -naphtho [2, lb] pyran]; 1,3,3-trimethylspiro [indoline-2,3-[3fl]- naphtho [2,1-b]-l ,4-oxazine]; 3 ,3-bis (pdimethylamino phenyl)-6-dimethylaminor phthalide; 3,3-bis (l-ethyl-2-methylindol-3-yl) phthalide; 2- anilino-6 -diethylamino-3 -methylfluoran; 2 '-methoxy- 6-dimethylaminofluoran; and l ',3 ',4 -trimethyl-6 diethylaminofluoran wherein the chromogenic compound and the binder of the surface coating have a ratio of the chromogenic compound to the binder ranging from 1:8 to 3:1, wherein the chromogenic compound is reacted with the sulfonic acid on heating to form color wherein the base, coating is sandwiched between the transparent film and the surface coating, and wherein the binder of the base coating is insoluble in the volatile organic solvents.

2. A transparent film according to claim 1 wherein the ratio of the sulfonic acid to the binder of the base coating ranges from 1:1 to 1:3, the ratio of crosslinking agent to the binder of the base coating is 1:4 to 1:12, and the ratio of the chromogenic compound to the binder of the surface coating is 1:5 to 1:1.

3. A transparent film according to claim 1 wherein the transparent film substrate is polyester, polyethylene terephthalate or polystyrene.

4. A transparent film according to claim 1 wherein the binder of the base coating is polyvinyl alcohol and the binder of the surface coating is a styreneacrylonitrile copolymer or polystyrene.

5. A transparent film according to claim 1 wherein bisphenol A is included in the base coating in an amount exceeding one weight percent of the total base coating.

6. A transparent film according to claim 1 wherein bisphenol H is included in the surface coating in an amount exceeding one weight percent of the total surface coating.

7. A transparent film according to claim 1 wherein the surface coating includes a tertiary amine weak base.

8. A transparent film according to claim 1 wherein the surface coating includes photochromic materialv 9. The transparent film of claim 8 wherein the photochromic material is present in an amount 10 to weight percent of the heat responsive chromogenic material.

11. A process for producing a thermal-sensitive transparent film consisting essentially of sequentially:

a. providing a transparent film;

b. coating the transparent film with a wet base coating having a thickness ranging from 1 to 10 mils wherein the wet base coating comprises, by weight, 2.0 to 10.0 percent of at least one sulfonic represented by the formula wherein R is the radical Ol-l, Cl, Cl-l --NO or SO H, 3.0 to 10.0 percent of a binder, 0.25 to 3.0

percent of a cross-linking agent for the binder, and 80.0 to 85.0 percent water or alcohol;

c. thoroughly drying the wet base coating and crosslinking the binder;

d. coating the dried base coating with a wet surface coating having a thickness ranging from l to 10 mils wherein the wet surface layer comprises, by weight, 2.0 to 10.0 percent of at least one colorless, but colorable chromogenic compound selected from the group consisting of: 3,3-spirobi [3l -l naphtho [2,l-b] pyran]; 2-decyl-3,3'-spirobi [3gnaphtho [2,l-b] pyran]; 2-chloro-3,3'-spirobi [3gnaphtho [2,l-b] pyran]; 2,2-trimethylene-3,3'- spirobi [3fl-naphtho [2,l-b] pyran]; 2-n-amyl- 3,3'-spirobi [3fl-naphtho [2,1-b] pyran]; 2,2- trimethylene-3,3-spirobi [3fl-naphtho [2,l-b] pyran]; 2,2 -trimethylene-2 -methyl-3 ,3 -spirobi [3 li-naphtho [2,l-b] pyran]; 2-n-heptyl-3,3'- spirobi [3fl-naphtho [2,l-b] pyran]; 2-isobutyl- 3,3'-spirobi [3fl-naphtho [2,l-b] pyran]; 2- methyl-3,3'-spirobi [3fl-naphtho [2,l-b] pyran]; 2-ethyl-3,3-spirobi [Fig-naphtho [2,l-b] pyran]; spiro [2l -l l -benzopyran-2,3 '-[3fl[-naphtho [2, l b] pyran]; 2'-isopropyl-spiro [Zfl-l-benzopyran- 2,3'-[3fl]-naphtho [2,l-b] pyran]; 2'-methyl-spiro [Zfll -benzopyran-2,3 3fl[-naphtho [2, l -b] pyran]; 2,2-spirobi [Zfl-l-benzopyran]; 3,3-

trimethylene-2,2 -spirobi [Zfi- 1 -benzopyran 2,3- diphenyl-7-methoxy spiro [4 l;l l -benzopyran-4,3 [3fi] naphtho [2,l-b] pyran] 2-phenyl-3-methylspiro [4fl-l-benzopyran-4,3'-[3fl] naphtho [2,lb] pyran]; 2,2-spirobi [Zfl-naphtho [1,2-b] pyran]; 2-( 2,5-dichloroanilino )-2-(p-methoxyphenyl- 2(fl) benzopyran); 1',3',3'-trimethyl-8-methoxy spiro [2H 1 -benzopyran-2,2 '-indoline l ,3,3- trimethylspiro [indoline-2,3 3 ll ]-naphtho [2, lb] pyran]; 1,3,3-trimethylspiro [indoline-2,3- [3fl1-naphtho [2,l-b]-l,4-oxazine]; 3,3-bis (pdimethylamino phenyl)-6-dimethylamino phthalide; 3,3-bis (l-ethyl-2-methylindol-3-yl) phthalide; 2'-anilino-6'-diethylamino-3'-methyl-fluoran; 2-methoxy-6-diethylaminofluoran; and l',3',4'- trimethyl-6 diethylaminofluoran, 3.0 to 15.0 percent of a binder which is soluble in volatile organic solvents and 75.0 to 95.0 percent of a volatile organic solvent; and

thoroughly drying the wet surface'coating, wherein the binder of the base coating is insoluble in the volatile organic solvents and wherein the chromogenic compound is reacted with the sulfonic acid on heating to form color.

12. A process according to claim 11 wherein the 7 thickness of the wet base coating and the wet surface coating each range from 1 to 3 mils and the wet base coating comprises 2.0 to 5.0 percent of the sulfonic acid, 4.0 to 6.0 percent of the binder of the base coating, 0.25 to 3.0 percent of the crosslinking agent, and 90.0 to .0 percent of the water or alcohol and the wet surface coating comprises 2.0 to 5.0 percent of the chromogenic compound, 5.0 to 10.0 percent of the binder of the surface coating and 85.0 to 93.0 of the organic solvent.

13. A process according to claim 11 wherein the binder of the base coating is polyvinyl alcohol and the binder of the surface coating is styrene-acrylonitrile copolymer or polystyrene.

14. A processaccording to claim 11 wherein the wet base coating includes, by weight, 1 to 5 percent of bisphenol A.

15. A process according to claim 11 wherein the wet surface coating includes, by weight, 1 to 5 percent of bisphenol H.

16. A process according to claim 11 wherein the wet surface coating includes, by weight, 0.2 to 1 percent of a tertiary amine weak base.

17. A process according to claim 11 wherein the wet surface coating includes photochromic material.

18. The process of claim 17 wherein the photochromic material is present as about 0.2 to about 15.0

weight percent of the wet surface coating.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Q PATENT NO. 3 914, 510

DATED I October 21, 1975 INVENTOMS) 1 Kenneth D. Glanz and David B. McQuain it is certified that error appears in the ab0veidentified patent and that said Letters Patent are hereby corrected as shown below:

In Claim 1 at Column 9 line 55, "6"-dimethylaminofluoran;" should be 6 -diethylaminof1uoran;-.

In Claim 1 at Column 9, line 61, "base, coating" should be base coating".

g Signed and Sealed this twenty-fourth Day Of February 1976 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ojlarents and Trademarks

Claims (18)

1. A THERMAL-SENSITIVE TRANSPARENT FILM COMPRISING A TRANSPARENT FILM SUBSTRATE COATED WITH (A) A BASE COATING COMPRISING A BINDER, A CROSSLINKING FOR THE BINDER, AND AT LEAST ONE SULFONIC ACID REPRESENTED BY THE FORMULA

2. A transparent film according to claim 1 wherein the ratio of the sulfonic acid to the binder of the base coating ranges from 1:1 to 1:3, the ratio of crosslinking agent to the binder of the base coating is 1:4 to 1:12, and the ratio of the chromogenic compound to the binder of the surface coating is 1:5 to 1:1.

3. A transparent film according to claim 1 wherein the transparent film substrate is polyester, polyethylene terephthalate or polystyrene.

4. A transparent film according to claim 1 wherein the binder of the base coating is polyvinyl alcohol and the binder of the surface coating is a styrene-acrylonitrile copolymer or polystyrene.

5. A transparent film according to claim 1 wherein bisphenol A is included in the base coating in an amount exceeding one weight percent of the total base coating.

6. A transparent film according to claim 1 wherein bisphenol H is included in the surface coating in an amount exceeding one weight percent of the total surface coating.

7. A transparent film according to claim 1 wherein the surface coating includes a tertiary amine weak base.

8. A transparent film according to claim 1 wherein the surface coating includes photochromic material.

9. The transparent film of claim 8 wherein the photochromic material is present in an amount 10 to 150 weight percent of the heat responsive chromogenic material.

10. The thermal-sensitive transparent film of claim 1 wherein the binder of the base coating is polyvinyl alcohol, the cross-linking agent is methylated urea-formaldehyde, the sulfonic acid is 2-naphthalenesulfonic acid, and the base-coating also includes bisphenol A; and the binder of the surface coating is styrene-acrylonitrile copolymer, the colorable chromogenic compound is 2-methyl-3,3''-spirobi (3H-naphtho (2,1-b) pyran), and the surface coating also includes crystal violet lactone.

11. A PROCESS FOR PRODUCING A THERMAL-SENSATIVE TRANSPARENT FILM CONSISTING ESSENTIALLY OF SEQUENTIALLY A. PROVIDING A TRANSPARENT FILM B. COATING THE TRANSPARENT FILM WITH A WET BASE COATING HAVING A THICKNESS RANGING FROM 10 MILS WHEREIN THE WET BASE COATING COMPRISES, BY WEIGHT, 2.0 TO 10.0 PER CENT OF AT LEAST ONE SULFONIC REPRESENTED BY THE FORMULA R-SO3H WHEREIN R IS R1-PHENYL; R1-NAPHTHYL OR

12. A process according to claim 11 wherein the thickness of the wet base coating and the wet surface coating each range from 1 to 3 mils and the wet base coating comprises 2.0 to 5.0 percent of the sulfonic acid, 4.0 to 6.0 percent of the binder of the base coating, 0.25 to 3.0 percent of the crosslinking agent, and 90.0 to 95.0 percent of the water or alcohol and the wet surface coating comprises 2.0 to 5.0 percent of the chromogenic compound, 5.0 to 10.0 percent of the binder of the surface coating and 85.0 to 93.0 of the organic solvent.

13. A process according to claim 11 wherein the binder of the base coating is polyvinyl alcohol and the binder of the surface coating is styrene-acrylonitrile copolymer or polystyrene.

14. A process according to claim 11 wherein the wet base coating includes, by weight, 1 to 5 percent of bisphenol A.

15. A process according to claim 11 wherein the wet surface coating includes, by weight, 1 to 5 percent of bisphenol H.

16. A process according to claim 11 wherein the wet surface coating includes, by weight, 0.2 to 1 percent of a tertiary amine weak base.

17. A process according to claim 11 wherein the wet surface coating includes photochromic material.

18. The process of claim 17 wherein the photochromic material is present as about 0.2 to about 15.0 weight percent of the wet surface coating.