US3418149A - Thermographic copy process - Google Patents

Description

D 24, 1968 D. A. NEWMAN 1 3,418,149

THERMOGRAPHIC COPY PROCESS Filed May 18, 1965 TAAwLucEA/r Fou/Vo r/ox/ Mask/H6, LA 75e figg INVENTOR.

HTTOQ/EYS United States Patent O 3,418,149 THERMOGRAPHIC COPY PROCESS Douglas A. Newman, Glen Cove, N.Y., assigner to Columbia Ribbon and Carbon Manufacturing Co., Inc., Glen Cove, N.Y., a corporation of New York Filed May 18, 1965, Ser. No. 456,754 6 Claims. (Cl. 117-37) ABSTRACT OF THE DISCLOSURE Reflex thermographic method of producing single copies of original images through the use of infrared radiation. The copy sheet has a semi-opaque coating which reflects infrared radiation to some substantial degree except in the areas to which imaging composition is transferred. This permits selective heating in the image areas and prevents heat build-up in the non-image areas.

The present invention relates to an improved transfer method for the thermographic reproduction of imaged original sheets and to the novel copy sheets which are used in such process.

According to known transfer methods for thermographic reproduction, an imaged original sheet is superposed with a copy sheet and a transfer sheet carrying a layer of heat-meltable colored composition, the heat-meltable layer being free of infrared radiation-absorbing materials and being positioned in contact with the copy sheet. When infrared radiation is applied to the sheets it is absorbed by the images on the original sheet to generate a heat pattern which is conducted to the heat-meltable layer to cause it to transfer to the copy sheet in the heated areas to form a duplicate copy of the original sheet.

Since most original sheets are either opaque or carry images on both sides thereof, they must be positioned furthest from the radiation source for exposure in What is known as the reflex process. In this position they are not required to transmit the radiation since the radiation passes through the transfer sheet and the copy sheet and is absorbed by the images on the top surface of the original sheet. In the reflex process the transfer sheet must he positioned closest to the radiation source with its transfer layer positioned aaginst the copy sheet which is sandwiched between the transfer and original sheets in order that the images transferred to the copy sheet are directreading duplicates of the original images.

Such an arrangement of sheets has been found disadvantageous for a number of reasons. The most important disadvantage of such an arrangement is that it results in poor duplicate copies on which the duplicate images are broader and much less sharp than the original images and have lled-in areas and ragged borders. This is the result of the diffusion of the heat pattern which is generated by the original images and which becomes diffused to a greater or lesser extent during its conduction by the copy sheet to the heat-meltable layer. The extent of diffusion depends upon the thickness and homogeneity of the copy stock.

Another important disadvantage of such an arrangement is that it results in the transfer of either too little or too much heat-meltable imaging composition unless the period of exposure of infrared radiation is Very closely controlled. This lack of latitude in the exposure step is a critical disadvantage since the radiation-absorbing properties of any given original image are unpredictable and will vary depending upon whether the image is printed, typed with a ribbon or a carbon paper, written in ink or pencil, etc. lnsuflcient exposure results in illegible copy and excess exposure results in background staining.

The reason for the criticality in the exposure duration is uncertain but appears to be the fact that the transfer sheet has the poorest reflecting ability of al1 of the exposed sheets since it generally has a relatively dark color due to the absorption or penetration of the transfer layer into its foundation. All of the applied infrared radiation is transmitted by the transfer sheet and is directed in concentrated form to the original sheet to cause overheating unless the time of exposure is very brief. This disadvantage is not present in cases Where the sheet closest to the radiation source is the original sheet since the original sheets are generally white and reflect a large amount of the radiation from the nonimaged areas.

It is an object of the present invention to provide a new and improved reflex exposure process for thermographically reproducing an imaged original sheet by the transfer of sharp, clear, duplicate images to a copy sheet.

It is another object of this invention to eliminate the criticality of the period of exposure in the reflex process of producing a duplicate copy of an original sheet. v

It is another object of this invention to provide a method for imaging thermographic copy sheets which are semi-opaque prior to thermographic imaging but which permit images which are thermographically transferred to the rear surface thereof to be clearly ilegible through the front surface thereof.

Other objects and advantages of the present invention will be made clear to those skilled in the art by the present disclosure including the drawings in which:

FIGURE 1 is a diagrammatic cross-section, to an enlarged scale, of a copy sheet which can be imaged according to this invention, and

FIG. 2 is a diagrammatic cross-section, to an enlarged scale, of an original sheet, transfer sheet and copy sheet superposed under the effects of infrared radiation but separated from one another for purposes of illustration.

The Objects and advantages of the present invention are made possible by the discovery of the present novel process and copy sheets Vwhich permit the formation of direct-reading duplicate images on a copy sheet by means of the reflex exposure .process while permitting the transfer sheet to be retained in surface contact with the original images being copied.

There are several advantages of having the transfer sheet in surface contact with the images being copied. The most important advantage is that the heat pattern generated by the images is conducted directly to the transfer sheet to cause the transfer layer to melt and transfer to the copy sheet in the form of sharp, clear images which correspond nearly exactly to the sharpness and clarity of the original images. This avoids the diffusion of the heat pattern inherent in the conduction of the heat pattern by the copy sheet prior to reaching the transfer sheet according to prior known single copy processes.

The positioning of the sheets according to the present reex process is unobvious in cases where direct-reading copies are desired and is made possible by the nature of the novel copy sheets used herein. Such copy sheets are semi-opaque but permit infrared radiation to pass therethrough in large amounts while reflecting some of the infrared radiation. Unlike conventional opaque sheets, however, the present copy sheets permit images which have been heat-transferred to the rear surface thereof to be clearly legible through the front surface thereof due to the critical nature of the semi-opaque masking coating on the rear surface.

The copy sheets 10 of the present invention, as illustrated by FIG. l of the drawing, have a transpicuous foundation 11, which may be a transparent or translucent paper or plastic lm, and carry on one surface thereof a masking layer 12 which is based mainly upon a porous, absorbent filler which has a light color, preferably white, which contrasts sharply with the dark color of the transfer composition with which it is to be imaged.

The reflex imaging process is as illustrated `by FIG. 2 of the drawing. The copy sheet 10, transfer sheet and original sheet are superposed in the order shown and are subjected to exposure to a radiation source rich in infrared, such as lamps 30. The radiation is transmitted in large part by the copy sheet but a portion of the radiatm is reected because of the light color of the copy s eet.

The radiation is transmitted substantially completely by the transfer sheet and is absorbed by the infrared radiation-absorbing images 21 on the upper surface of the original sheet foundation 22. The absorbed radiation generates a heat pattern corresponding to the shape of the original images and the heat pattern is conducted back to the transfer sheet foundation 17 causing melting of portions of the transfer layer 16 thereon. The melted portions of the transfer layer are absorbed into the areas of the masking layer 12 in contact therewith to form d imaged areas 13 in the masking layer which are closely legible as direct-reading images through the copy sheet foundation because the impregnation destroys the masking property of the masking layer and contracts with the color thereof.

The term transpicuous is used to define the required translucency of the copy sheet foundations used according to the present invention. This term includes both transparent and non-transparent transclucent sheets, the only requirement being that an object placed in surface contact with one surface thereof must be clearly visible from the other surface through the sheet.

The final copy sheet is preferably non-transpicuous due to the semi-opacity of the masking coating. However, it is only required that the iinal copy sheet be less transpicuous than the foundation per se in order that the images which are heat-penetrated into the masking coating -will 'be more clearly visible through the foundation than would be images which are merely placed on the surface of the masking coating such as by typing or the like. The greater the degree of masking power, the less critical is the duration of exposure to infrared radiation and the strength and proximity of the infrared radiation source.

The concept of transferring reverse-reading images to :1 transclucent foundation and then reading them as direct images through the foundation is well-known and broadly forms no part of the present invention. The essential features of the present invention are the discoveries that a melted heat-transfer composition will transfer more sharply .and cleanly to a porous masking coating than to an uncoated foundation and will form more legible images thereon due to the sharp contrast between the light color of the masking coating and the dark color of the transfer composition. Equally important is the discovery that the criticality of the time-temperature relationship of prior known reiiex exposure processes is substantially reduced, thereby permitting exposure to infrared radiation for longer periods of time than heretofore possible without causing excessive transfer and background staining of the copy sheet in unintended areas.

The following example is given by way of illustration to demonstrate the production of one specific copy sheet useful according to the present invention and should not be considered limitative.

A translucent copy paper having a weight of 8 pounds per ream Iand commercially available under the name Badger regular white paper is coated with the following composition applied in a weight of about 3 pounds per ream and dried by evaporation of the volatile ingredients:

Example I Ingredients: Parts by wt. Ethyl cellulose binder 7.9 Albacar (calcium carbonate) 13.3 Xylene 52.8

4 Ingredients: lParts by wt.

Ethyl alcohol 14.2 Water 11.8

In place of the calcium carbonate filler of the above composition, other porous, absorbent fillers such as barium carbonate, barium sulfate, magnesium carbonate, zinc oxide, clay, attapulgite, bentonite, silica, kaolin or the like may be used. Such fillers have a porosity which permits them to absorb or at least absorb melted wax cornposition. The hiding power or masking power of the pigments is due to their ability to refract light, the preferred pigments having an index of refraction of about 1.6 or below. However, when these pigments are impregnated with colored molten wax composition, their refractive properties are destroyed or masked by the color of the Wax composition.

The iller materials, alone or in combination, are the major ingredients by weight of the dried masking coatings of the copy sheets. The amount of binder material required to bond the filler as a unitary porous coating depends upon the surface area or size of the ller. More iinely divided fillers have larger surface areas and require larger amounts of binder material to form a stable masking coating. In general the ller to `binder ratio ranges from above about 1:1 up to about 4:1.

The nature of binder material is not particularly critical aside from the requirement that it be a film-forming material which is not meltable at the temperature generated by the thermographc process in which it is used. In other words, the binder material must have a higher melting point than the wax transfer layer with which it is imaged so that at the thermographic temperature the Wax transfer composition liqueies and ows into the unmelted porous masking coating.

The transfer sheets used according to the present invention are of the known thermographic type which absorb little, if any, infrared radiation. The foundation may Ibe of thin translucent paper or of translucent plastic ilm. The transfer layer thereon is based primarily upon relatively low melting point wax binder material and contains an amount of pigment or preferably dissolved dyestuff having a color which contrasts sharply with the color of the iiller in the masking layer. The transfer layer also preferably includes an amount of oil which renders the melted composition more flowable.

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. In the reliex thermographic process of producing duplicate images on a copy sheet corresponding to infrared radiation-absorbing images on `an original sheet by means of a transfer sheet carrying a layer of heat-transferable dark-colored imaging composition which does not absorb infrared radiation to any substantial degree, the improvement which comprises using as the copy sheet a transpicous foundation sheet having on one surface thereof a porous masking coating comprising a porous filler material which has a light color which contrasts sharply with the color of the said imaging composition and which has a higher melting point than said imaging composition and is semi-opaque and reflective of infrared radiation to a substantial extent, Said filler material being penetrable -by said imaging composition in its melted state to render it non-reflective of infrared radiation in areas so penetrated, superposing the original, transfer and copy sheets so that the original images are in contact with the transfer sheet and the heat-transferable layer is in contact with the masking coating of the copy sheet, and applying infrared radiation against the copy sheet whereby portions thereof are transmitted by the copy sheet and by the transfer sheet to the original images to cause heating thereof and to cause the heat-transferable layer to melt in areas corresponding to the location of the original images and penetrate the masking coating and filler material of the copy sheet to destroy the infrared radiation-reflecting and masking properties of the ler material in the penetrated areas whereby the heattransferred composition is clearly visible through the transpicuous copy sheet foundation as correct-reading duplicate images of the original images.

2. The process according to claim 1 in which the transpicuous foundation of the copy sheet is selected from the group consisting of paper and plastic film.

3. The process according to claim 1 in which the masking coating on the copy sheet comprises a film-forming binder material containing a major amount by weight of a porous ller material which does not absorb substantial amounts of infrared radiation.

4. The process according to claim 3 in which the ratio of filler to binder material is from above about 1:1 up to about 4: 1.

5. The process according to claim 3 in which the filler comprises nely-divided calcium carbonate.

6. The method according to claim 3 in which the lmforming binder material comprises a cellulose plastic.

References Cited UNITED STATES PATENTS 972,742 10/1910 West 117-36.1 2,854,350 9/ 1958 Phillpotts 117-36.7 3,034,428 5/1962 Ellam 117-36.1 3,054,692 9/1962 Newman et al. 117-36 3,109,748 11/1963 Newman 117-36 MURRAY KATZ, Primary Examiner.

U.S. Cl. X.R.

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