US3458335A - Heat sensitive transfer sheet having screen layer and method of making - Google Patents

Description

July 29, 1969 D. A. NEWMAN HEAT SENSITIVE TRANSFER SHEET HAVING SCREEN LAYER AND METHOD OF MAKING Flled Feb 14 1967 INVENTOR. qyl 14A/M7700 6 fa@ \\v United States Patent 3,458,335 HEAT SENSITIVE TRANSFER SHEET HAVING SCREEN LAYER AND METHOD OF MAKING Douglas A. Newman, Glen Cove, N.Y., assignor to Columbia Ribbon and Carbon Manufacturing Co., Inc., Glen Cove, N.Y., a corporation of New York Filed Feb. 14, 1967, Ser. No. 616,025 Int. Cl. B41m I/24; B44d 1/22 U.S. Cl. 117-15 8 Claims ABSTRACT F THE DISCLOSURE There are several known systems for thermographicallyproducing copies of infrared radiation-absorbing images using a transfer layer which liberates image-forming vapors in the heated areas, corresponding to the location of the original images, to form duplicate copies of the original. The vapor images may be transferred rst to the original sheet, such as over the original images, and then transferred to one or a succession of copy sheets in a second heating step, or may be transferred directly to the copy sheet in a single operation to make a single copy or a master copy sheet such as a planographic printing plate. U.S. Patents Nos. 3,121,650 and 3,262,386 are illustrative of such processes and the colored and colorforming vaporizable or sublimable materials useful therein.

In a related copying process, illustrated by British Patent No. 943,401, the image-forming vapors consists of oil which is deposited on the copy sheet in the heated image areas to form latent images which may be developed by contact with a thermoplastic powdered ink which adheres to the copy sheet only over the oily latent images and which can be set thereon by heating to render the ink tacky and to cause it to bond to the copy sheet surface. In cases where the copy sheet is a planographic plate, the oily images are oleophilic and the plate is suitable for use since the images become developed with color in the planographic printing process.

While these processes produce fair results, they have the disadvantage that the vapor donor layer is either wet, as is the case with oils, or is relatively unstable so that the vaporizable or sublirnable material transfers or leaches to the sheet in contact therewith on storage so as to provide overall staining of the second sheet after a relatively short time and prior to use. It is not possible to avoid this diiculty by means of a conventional supercoating over the donor layer since this seals the layer and prevents escape of the vapors in the heated areas.

Some prior processes and materials of this type have the added disadvantage that the vaporizable imaging material is trapped to a large extent in a binder material in the donor coating and is unable to volatilize and escape and form the duplicate images. Only that portion at or near the surface of the donor layer is available for imaging purposes and the remainder is wasted within the donor layer, so that the formed images are weaker in intensity than is desired. To avoid this difficulty, the image-forming material is often used as a pure impregnation or surface coating on the donor sheet, free of binder material, and

lice' this is generally undesirable since much is lost within the foundation and escapes through the uncoated surface during the heating operation.

It is the principal object of the present invention to provide a vapor donor sheet which may be stored in contact with an original sheet or a copy sheet for prolonged periods of time without straining the original or copy sheet.

It is an object of one embodiment of this invention to provide a vapor ydonor -sheet which contains a large source of vaporizable imaging material which is substantially completely available for imaging purposes free 0f masking binder materials.

These and other objects and advantages of this invention will be obvious to one skilled in the art in the light of the present disclosure including the drawings in which:

FIGURE 1 is a perspective view of a vapor donor sheet according to the present invention.

FIGS. 2 and 3 are perspective views 0f a continuous foundation web carrying a donor coating and being printed thereover with different types of open screen layers.

FIG. 4 is a diagrammatic cross-section, to an enlarged scale, of an imaged original sheet, a vapor donor sheet and a copy sheet superposed under the influence of infrared radiation but spaced for purposes of illustration.

The present invention involves the discovery that the provision of an open line screen layer over a coating or impregnation of heat vaporizable or sublimable material prevents the transfer of the material to sheets in contact therewith, even over prolonged contact during storage, without interfering with the ability of the material to transfer freely under the effects of applied heat. This discovery is quite surprising in view of the migratory nature of vaporizable and sublimable materials to materials in contact therewith and appears to be due, at least in part, to the fact that the applied open screen consists of a synthetic thermoplastic resinous or plastic composition which is incompatible with and a non-solvent for the vaporizable or sublimable image-forming material.

Aside from the presence of the open screen layer, the donor sheets and copy sheets and image-forming materials of the present invention may be identical to those known in the art as exemplified by the aforementioned patents. However, according to the preferred embodiment the donor layer containing the image-forming material has a formulation and structure which is novel in this field and which provides for the inclusion of large amounts of image-forming material in a form which is more readily and more completely releasable under the effects of applied heat.

Donor sheets 10 according to one embodiment of this invention are shown in the drawings and comprise a flexible foundation 11 such as paper or plastic iilm, a donor layer l2 containing an image-forming material which is releasable as a gas under the effects of applied heat, and an open screen layer 13 over the donor layer and consisting of intersecting strips which form a multiplicity of openings 14 through which the gaseous image-forming material can escape during the heating operation.

Suitable donor layers are those which consist of the image-forming material coated onto the foundation or impregnated therein in the case of absorbent foundations such as paper, or layers containing a suitable heat-resistant binder material such as a synthetic thermoplastic resin or plastic material. According to the preferred embodiment, the image-forming material is present as a solution or dispersion in an oil contained within a porous structure of a synthetic thermoplastic resin with which the oil is incompatible or insoluble. Structures of this type are well known in the carbon paper iield, as illustrated by U.S.

Patents Nos. 2,820,717; 2,944,037; 3,037,879 and 3,117,- 018, and the formulations taught by said patents are useful according to this invention provided that the present image-forming materials are substituted for the pigments and dyestuls of the patents. The amount of image-forming material may be increased as much as desired and the donor sheet is re-usable since the image-forming material circulates through the porous resin structure so that heated portions of the donor layer are continuously supplied with fresh imaging material particularly in cases where the latter is dissolved in its oily vehicle.

The open screen layers suitable for use according to the present invention may have several different forms and structures. The preferred structure is that shown in FIG. 1 of the drawings in which the screen consists of intersecting strips to form discrete openings. Such a screen is preferably applied as shown in FIG. 2 by means of an offset printing technique. A thin layer of a solution of the synthetic thermoplastic film-forming composition is supplied from a solution fountain (not shown) to applicator roll using a doctor blade (not shown) to control the thickness. The applicator roll transfers a thin layer of the solution to the peaks of a printing cylinder 16 containing raised line areas or peaks 17 and discrete valleys 18 which receive no ink. The donor sheet 10 is expended from supply roll 40 and is passed in the nip between the printing cylinder 16 and an impression roll 41 whereby the donor layer 12 is overprinted with screen layer 13. The printed web is then heated to evaporate the solvent and dry the screen layer prior to the rolling of the final web on take-up roll 42.

According to another embodiment illustrated by FIG. 3, the open screen layer may have a gravure structure which is a negative of the structure shown in FIG. 2 in that the screen has open intersecting line areas 22 which surround spaced islands or spots 23 of the synthetic thermoplastic film-forming composition. Such a structure is formed in the manner shown in FIG. 1 whereby the printing cylinder 16 is coated with a solution of the film-forming composition by immersion in a solution fountain (not shown) and a doctor blade (not shown) is used to scrape the solution from the peaks 17 of the cylinder so that only the discrete valleys 18 of the cylinder contain a supply of the solution. The solution is printed over the donor layer and dried to form a screen of the type shown.

It should also be pointed out that it is not necessary that the open screen layers of the present invention have a square configuration consisting of intersecting printed or unprinted areas as shown in FIGS. 2 and 3. The printing cylinder may have its raised area or peaks in the form of closely spaced parallel lines running in only one direction and forming between them hollow depressions or valleys which are also parallel and uninterrupted. Such screens may also be applied according to the techniques of either FIG. 2 or FIG. 3.

The synthetic thermoplastic film-forming composition for the screen is preferably a solution of a resin or plastic in a volatile organic solvent which is a non-solvent for the binder of the donor layer if one is present. Also the resin or plastic of the screen layer is incompatible with and a nonsolvent for the imaging material of the donor layer.

Preferred resins for the screen layer are vinyl resins such as vinyl chloride-vinyl acetate copolymer, acrylic resins such as polymethyl methacrylate, polystyrene, cellulose plastics such as cellulose acetate, cellulose nitrate, ethyl cellulose, and the like.

The open screen layer need not have a straight or square configuration as shown in the drawings. The printed areas may be curved or zig-zag or may intersect each other at any desired angle. The only requirement is that the screen consists of printed areas which are at least 0.00001 inch and not more than 0.01 inch in height or thickness and that parallel strips or spots be spaced from each other by at least 0.00001 inch and not more than about 0.01 inch. Preferably the strips are from 0.0001 inch to about 0.001

. 4 inch in height and thickness and are spaced by at least 0.0001 inch and no more than about 0.05 inch.

The following examples are given by way of illustration and should not be considered as limitative.

Example 1 A donor sheet was prepared by coating a paper web with the following composition to form a donor layer having a thickness of 0.001 inch after evaporation of the solvents.

Ingredients: Parts by weight, gm.

Vinyl chloride-vinyl acetate copolymer (Vinylite VYHH 10.0

Mineral oil 5.0

Butyl stearate 5.0

Du Pont Oil Orange 0.1

Ethyl acetate 50.0

Toluol 10.0

Ingredients: Parts by weight, gm. Ethyl cellulose 10 Ethyl alcohol 40 Bronze powder '2 After evaporation of the solvent, the open screen layer nearly completely masks the underlying donor layer from view, -due primarily to the presence of the bronze powder, but actually contains a number of openings through which the Oil Orange vapors can pass under the effects of heat. The ethyl cellulose screen consists of intersecting strips which are about 0.0001 inch in height and width and which are spaced by 0.001 inch.

In carrying out the copying process, the donor sheet 10 is superimposed with an imaged original sheet 20 and a copy sheet 30 in the order shown by FIG. 4 and infrared radiation is applied to the original sheet such as by lamps 50. The radiation is selectively absorbed by radiation-absorbing images 21 and converted to heat of at least C. which is conducted to the donor sheet as an image pattern. The heated areas of the donor layer give ot vapors of the Oil Orange which stain contacting portions of the copy sheet to form an exact duplicate of the original. The images formed on the copy sheet appear continuous and no sign of the etect of the intervening screen layer is visible to the naked eye.

Example 2 A donor sheet was prepared by coating a web of 0.5 mil polyethylene terephthalate polyester lm (Mylar) with a 5% solution of rubeanic acid dissolved in methyl ethyl ketone and, if desired, 2% by weight of a soluble binder such as polyvinyl butyral. After evapation of the solvent a thin donor layer of about 0.001 inch thickness remains. y

Next a white-colored open screen layer is printed over the donor layer in the manner shown in FIGURE 1 using the following composition for the screen layer.

Ingredients: Parts by weight, gm. Polyvinyl acetate l0 Titanium dioxide 2. Butyl acetate 40 The copy sheets adapted for direct imaging by means of the donor sheets of this example are prepared by coating sheets of paper on one surface with an aqueous solution containing 15% by weight nickelous acetate and 50% by weight urea and dissolving the water to leave hydrated nickelous acetate and urea deposited on or near the paper surface in an amount equal to about 4% by weight of the paper.

The copying process was effected by superimposing the sheets in the order shown in FIG. 4 of the drawing, the coated surface of the copy sheet being in contact with the open screen layer of the donor sheet and applying infrared radiation to heat the original images to at least 150 C. and cause the rubeanic acid to sublime in the heated image and transfer to the copy sheet as an image pattern and react with the nickel ions to form a deep blue nickel-dithioxamide complete reaction product in the form of images corresponding to the images 0n the original sheet. The urea functions as a catalyst or flux for the reaction.

In cases where it is desired to employ a vaporizable oily material as the imaging material for the formation of latent images to be developed by contact with dry pigment, the procedure of Example 1 may be followed with the exception that the Oil Orange is omitted from the donor composition and the mineral oil and butyl stearate are replaced with parts by weight of a lightbodied mineral oil having a boiling point of about 330 C. A longer exposure is generally required to insure adequate heat build-up in the image.

After the transfer of the mineral oil vapors to the copy sheet, the oily images are contacted with a powdered mixture of equal parts by weight of carbon black and a resin binder such as colophony resin. The powder adheres only to the oily latent images and is shaken from the remainder of the sheet. Then the sheet is heated by the infrared radiation source again to fuse the resin powder in place and form the duplicate copy of the original.

The printing cylinders useful according to the present invention are commercially-available engraved rolls having fine linear peaks at the rate of from about 50 to about 200 per inch, the depressions between the peaks being from about 0.00001 inch to about 0.01 inch in depth.

Finally it should be understood that the phrase copy sheet is used herein and in the amended claims to include sheets developed as final copies and also sheets imaged for use as masters or planographic printing plates.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

I claim:

1. A thermographic transfer sheet which absorbs substantially no infrared radiation and which comprises a flexible foundation sheet carrying a uniform distribution of imaging material which is vaporizable from one surface thereof under the effects of heat, and having printed over said surface a multiplicity of uniform, parallel, nontransferable strips of synthetic thermoplastic resin which is incompatible with said imaging material, said strips being between 0.00001 inch and 0.01 inch in height and thickness and being uniformly spaced from each other by between 0.00001 inch and 0.01 inch in distance, the spaces between said strips permitting the unimpeded free transfer of said imaging material, in vapor form, to a copy sheet to form images thereon which appear substantially unbroken to the naked eye, said strips spacing said imaging material from a copy sheet in contact with said strips to prevent contact-migration of said imaging material to said copy sheet in unheated areas.

2. A transfer sheet according to claim 1 in which said imaging material comprises a layer positioned on the surface of the foundation sheet.

3. A transfer sheet according to claim 2 in which said layer comprises a porous structure of nlm-forming binder material having said imaging material dispersed in the pores thereof.

4. A transfer sheet according to claim 1 in which said strips are between about 0.001 inch and 0.0001 inch in height and thickness and are spaced from parallel strips by from about 0.05 to 0.0001 inch.

5. The process of producing a thermographic transfer sheet which absorbs substantially no infrared radiation which comprises the steps of (a) applying a uniform distribution of a heat-Vaporizable imaging material to a exible foundation sheet.

(b) printing over said imaging material a multiplicity of uniform, parallel strips comprising a volatile solvent solution of a synthetic thermoplastic resin which is incompatible with said imaging material, and

(c) evaporating said volatile solvent to produce dried strips which are non-transferable and which are from 0.00001 inch to 0.01 inch in height and thickness and which are uniformly spaced from each other by from 0.00001 inch to 0.01 inch in distance, the spaces between said strips permitting the unimpeded free transfer of said imaging material, in vapor form, to a copy sheet to form images thereon which appear unbroken to the naked eye, said strips spacing said imaging material from a copy sheet in contact with said strips to prevent contact migration of said imaging material to said copy sheet in unheated areas.

6. The process according to claim 5 in which the imaging material is present within the pores of a porous layer of film-forming binding material.

7. The process according to claim 5 in which said strips are between about 0.001 inch and 0.0001 inch in height and thickness and are spaced from parallel strips by from about 0.05 to 0.0001 inch.

8. In the process for producing copies of original infrared radiation-absorbing images in which said images are superposed with a transfer sheet carrying an imaging layer comprising heat-Vaporizable imaging material and infrared radiation is applied to heat the original images and cause the imaging material in corresponding portions of said layer to vaporize and deposit on a copy sheet in the form of images corresponding to said original images, the improvement which comprises using as the transfer sheet one having an open ne screen layer over the transfer layer in order to space the transfer layer from the copy sheet and prevent contact-migration of the imaging material to unintended areas of the copy sheet, said screen layer comprising a multiplicity of uniform, parallel, non-transferable strips of synthetic thermoplastic resin which is incompatible with said imaging material, said strips being between 0.00001 inch and 0.01 inch in height and thickness and being uniformly spaced from each other by between 0.00001 inch and 0.01 inch in distance, the spaces between said strips permitting the unimpeded free transfer of said imaging material, in vapor form, to the copy sheet so that the images formed on the copy sheet appear substantially unbroken to the naked eye.

References Cited UNITED STATES PATENTS 1,962,082 6/1934 Miller 117-364 2,313,645 9/1940 Antrim 117-364 2,790,742 4/ 1957 Wharton 117-364 2,803,579 8/1957 Stolle et al 117-36.4 3,080,954 3/1963 Newman et al 117-364 3,104,980 9/ 1963 Maierson 117-4364 3,121,650 2/1964 Meissner 117-362 3,260,612 7/1966 Dulmage et al 117-36.2 3,262,386 7/ 1966 Gordon 117-362 MURRAY KATZ, Primary Examiner U.S. Cl. X.R.

PO-Ofo UNTED STATES RATENT OFFICE @emmene cow-Recueil Patent No. 31,458,335 Dated July Z9, 1969 Inventor(s) Douglas A. Newman lt is certified that: error appears in the above-dentifie'd'patent and that said Letters Patent; are hereby corrected as shown below:

- Column I?, line 7, "straining" should read staining;

Column )4, line M3, "superimposedn should read superposed line 65, "FIGURE l" should read Example l Column 5, line E, "superimposlngg" should reed superposing line ll*a after "image' insert areas line 13, "complete" should read complex line 26, "image" should reed images line gl, "amended" should read appended Column 6, line 9, the period should read under' References Cited, No."2,313,645" should read 2,213,6u5

SIGNED ND SEALED MAR 24.1970

(SEAL) Attest:

Edward M. Fletcher, Ir,

Attesting Officer WILLIAM E. SGHUYIER, JR.

Commissioner of Patents

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