US3442681A - Transfer elements and method of making same - Google Patents

Description

' y 6, 1969 D. A. NEWMAN ETAL 3,442,681

TRANSFER ELEMENTS AND METHOD OF MAKING SAME Filed July 20, 1967 INVENTORS Douylas f2. Newman 4/!40 T 5ofi/oiz/muer United States Patent 3,442,681 TRANSFER ELEMENTS AND METHOD OF MAKING SAME Douglas A. Newman, Glen Cove, and Allan T. Schlotzhauer, Locust Valley, N.Y., assignors to Columbia Ribbon and Carbon Manufacturing Co., Inc., Glen Cove,

N.Y., a corporation of New York Filed July 20, 1967, Ser. No. 654,882 Int. Cl. B41c 1/06 U.S. 'Cl. 117--36.4 10 Claims ABSTRACT OF THE DISCLOSURE In the manufacture of pressure-sensitive transfer elements of the squeeze-out type, the step of rendering such transfer elements cleaner to the touch and resistant to producing typewriter roller marks on the copy sheet which comprises treating the ink-releasing surface of such transfer elements with a layer of a dilute solution of a resin containing a solid particulate heat-activatable blowing agent, and thereafter applying heat to activate the blowing agent and render said layer porous.

This application is a continuation in part of copending application Ser. No. 623,322, filed Mar. 15, 1967.

The present invention relates to the field of the so-called squeeze-out carbon papers and ribbons on which the transfer layer comprises a microporous non-transferable resinous structure containing within the pores thereof a pressure-exudable ink comprising an oily vehicle and imaging matter. Such transfer elements are illustrated by United States Patents Nos. 2,820,717; 2,944,037; 3,037,879 and 3,117,018, among others.

Such known transfer elements have been exceptionally successful primarily because of their reusability. The resinous binder is not transferable and its porosity permits the flowable ink to migrate and replenish areas from which ink has been transferred. However, while the ease of flowability has this advantage, it has the disadvantage that some amount of the ink can exude to the copy sheet with which it is superposed when the sheets are inserted into a typewriter or similar business machine having rollers between which the sheets are compressed.

It is possible to avoid or at least diminish this undesirable offsetting by formulating the ink layer from harder, less pressure-compressible resins or resin mixtures or by using semi-solid ink vehicles. However, this reduces the pressure-sensitivity of the ink layer so that the typed copies are not as dense as desired, particularly when interleaved carbon papers are used to produce a number of copies at one typing.

It is the principal object of the present invention to provide improved squeeze-out type transfer elements which are clean to the touch and do not produce roller marks on the copy sheet and which retain a high degree of pressure-sensitivity so as to produce images of high intensity even when interleaved to produce several copies at one typing.

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

FIGURE 1 is a diagrammatic illustration of the process of applying the present supercoatings; and

FIG. 2 is a diagrammatic cross-section, to an enlarged scale, of a transfer element produced according to the present invention.

The objects and advantages of the present invention are attained by treating the ink-releasing surface of a squeezeout type resinous ink layer with a liquid wash coating consisting essentially of a dilute solution of a synthetic thermoplastic resin, incompatible with the ink of the ink layer, dissolved in a volatile organic solvent and having uniformly dispersed therein a heat-activatable blowing agent which preferably is insoluble in said solvent, and then applying heat to first evaporate the solvent and then cause activation of the blowing agent whereby the wash coating is rendered porous and permeable by the ink released from said ink layer under the effects of imaging pressure.

The porous supercoatings of the present invention function similarly to a resinous screen applied over the inkreleasing layer in that they are uniformly porous to permit exuded ink to flow therethrough under the effects of imaging pressure, and are sufliciently thick to prevent ink from flowing completely therethrough under the efiects of lesser pressures such as those applied by the rollers of a typewriter, printing machine, adding machine or other business machines. It is possible to use extremely thin wash coats without including a blowing agent since the wash coat will shed from the exposed ink pores of the ink layer to leave openings in the wash coat. However, the degree of protection aiforded by such thin wash coats is limited and the amount of pressure exerted by the rollers of some heavy duty business machines is sufiicient to cause the ink to exude through the thin Wash coat and produce roller marks on the copy paper. Heavier wash coats, free of blowing agents, seal the ink layer and prevent or retard flow of the ink to the copy sheet and result in the production of images of uneven tone or density.

It has also been found that the wash coating must be free of oils orother oleaginous materials which are incompatible with the resin of the wash coating since such materials separate from the resin to form unpigmented droplets through which the ink of the transfer layer must be transmitted. This results in a dilution of the ink and a reduction in its tone or imaging strength, and a lack of uniformity of imaging strength over the surface of the transfer element. The inclusion of pigment in such oil phase overcomes this problem but results in a transfer element which is dirty to the touch and produces roller marks during use.

The present Wash coating compositions consist essentially of solutions of from about 5% up to about 20% by weight of a synthetic thermoplastic resin dissolved in a volatile organic solvent which preferably is also a solvent for the resinous binder of the ink layer, the resin being incompatible with the oily ink vehicle of the ink layer to prevent commingling therewith, and from 0.001% to 1% by Weight of a blowing agent which preferably is insoluble in said organic solid and is activatable at a temperature at least slightly in excess of the evaporation temperature of said organic solvent. Vinyl resins in general are preferable and include polyvinyl acetate, vinyl chloride polymers and copolymers with vinyl acetate, polystyrene, polyvinyl butyral, acrylic acid and ester polymers and copolymers such as polymethyl methacrylate, methyl methacrylate-ethyl acrylate copolymers and the like. Other resins such as the polycarbonates, polyethylene, chlorinated rubber, butadiene styrene, polyurethanes and the like are also suitable. Preferred volatile organic solvents are methyl ethyl ketone, ethyl acetate, acetone, methylene chloride, toluol and the like, depending upon the solubility of the resin of the wash coat. Of course small amounts of compatible plasticizers, fillers, colorants or the like may be included provided that such additives do not interfere with the intended performance of the wash coating.

Blowing agents suitable for use according to the present invention are solid heat-decomposable materials which evolve a gas such as nitrogen, a nitrogen oxide, carbon dioxide or any other harmless vapor. The blowing agent preferably is insoluble in the wash coating solvent and is dispersed uniformly in the wash coating composition in finely divided particulate form. Also the blowing agent must be one which is decomposable at a temperature at least slightly in excess of the evaporation temperature of the volatile slovent with which it is used. Otherwise the blowing agent is activated while the wash coating is still very fluid and the pores formed are quickly resealed by the fluid resin binder material. The solvent must first evaporate, at least to a major extent, so that the wash coat is no longer fluid. At this point the blowing agent is activated by heat in excess of that amount required for evaporation of the solvent, whereby the blowing agent decompass to liberate a gas which forms an air space within the wash coating. Some of the gas breaks through the surface of the wash coat to create surfaces pores while the remainder stays within the wash coat in interior pores to form an internal sponge of interconnected pores through which ink can be freely transmitted.

The selection of blowing agents suitable for use in accordance with the limitations referred to supra is a matter of choice in view of the numerous materials available for this purpose. Illustrative materials are p,p-oxybis (benzenesulfonyl hydrazine) which is available from Naugatuck Chemical Co. under the trademark Celogen, N,N' dimethyl-N,N-dinitroso terephthalamide, diazoaminobenzene, dinitrosopentamethylene tetramine, and the like. These materials are activated by temperatures in excess of about 90 C. whereas most volatile organic solvents evaporate at temperatures well below this temperature. Also, since the wash coat and the ink-releasing layer are resinous, they are heat-stable and can withstand high temperatures Without any ill effects.

The wash coating is applied to the surface of the ink layer and spread to form a wet film having a thickness of from about /2 point, applied by means of a (zero) doctor blade, up to about 25 points. This is the thickness of the liquid wash coating which consists mainly of the volatile solvent. The dried wash coating has an approximate thickness range in excess of from 5% to 20% the thickness of the wet layer since the wet layer contains slightly more than from 5% to 20% solids. Broadly the dried wash coating may have a thickness ranging from 5% of /2 point (0.0025 mil) up to 20% of 25 points (0.5 mil). The preferred range is from 0.1 mil up to 0.3 mil. These are theoretically accurate mean ranges although it is recognized that the gas formation within the resin of the wash coating expands the wash coating and increases its thickness at the peak areas of the dried coating. A point is equal to 0.1 mil and 0.0001 inch.

The present wash coatings may be applied in the manner illustrated by FIG. 1 of the drawing. The web of transfer element is expended from supply roll 11, over idler roller 12 and against application roller 13 which is immersed in vat 14 containing a supply of the wash coating composition. The wash coating is applied to the underside 10a of the web over the squeeze-out ink-releasing layer thereon and is spread to the desired thickness by means of doctor blade 15. The wet web then passes under idler roller 16 and through heated air tunnel 17 in which evaporation of the volatile solvent, activation of the blowing agent and solidification of the supercoating occurs. The web then passes under idler roller 18 and onto take-up roll 19. The heating tunnel preferably has two connected heating chambers, the first of which has a temperature sulficiently high to evaporate the volatile solvents, from about 50 C. to about 80 C., and the second of which has a temperature above about 90 C. to decompase the blowing agent after all or most of the solvent has been evaporated.

The structure of the final transfer element is somewhat uncertain but appears to be as illustrated in FIG. 2 of the drawings. The transfer element has a flexible foundation 20 carrying a microporous squeeze-out type ink-releasing layer 21 and a non-transferable porous synthetic thermoplastic resin supercoating 24 over said ink-releasing layer. The ink-releasing layer comprises a non-transferable microporous resinous structure 23 containing droplets 22 of pressure-transferable oily ink within the pores thereof. The supercoating has a non-transferable porous resin structure 25 containing open surface pores 26 and interconnected interior pores 27 containing the gas liberated by the blowing agent. Thus, while imaging pressure is suflicient to exude the oily ink from the ink layer and through the supercoating to a copy sheet, the lesser pressure exerted by the rollers of a business machine is not sufficient to cause the oily ink to exude through the supercoatingj24.

Preferably the solvent used in the wash coat composition is a non-solvent for resin structure 23 of the ink layer so that the porous structure of the ink layer is not disturbed. Otherwise the application of the wash coating is diflicult and the wash coating composition becomes contaminated.

The following example illustrates the production of one type of transfer element according to the present invention and should not be considered limitative.

A film web of /2 mil. polyethylene terephthalate polyester (Mylar) is first coated with a thin layer of polyvinylidene chloride (Saran) dissolved in methyl ethyl ketone to provide a receptive undercoating having a thickness of about 0.1 mil. After evaporation of the solvent, the undercoating is coated with the following ink composition.

Parts by Ingredients: weight Styrene-methyl methacrylate copolymer (Zerlon 150) 12.0 Mineral oil 8.0 Refined rapeseed oil 6.0 Sulfonated vegetable oil 1.7 Blue toning paste 2.2 Black toner pigment 6.6 Ethyl acetate 36.5 Toluol 27.0

The applied ink composition is dried at elevated temperatures to form a microporous ink layer having a thickness of about 0.6 mil.

As shown in FIG. 1, the transfer element 10 formed as above is passed in contact with an application roller 13 so that the ink layer on side 10a is provided with a layer of the wash coating composition in vat 14 which is a 10% solution of polyvinyl acetate (Vinylite AYAF) dissolved in methyl ethyl ketone and containing 0.1 part by weight of Celogen blowing agent. Doctor blade 15 spreads the wash coating to a wet thickness of about 10 points (1 mil.). Thereafter the transfer element is heated in tunnel 17 to temperatures of about 70 C. and C. to evaporate the methyl ethyl ketone and toluol and activate the Celogen causing it to liberate nitrogen. The dried polyvinyl acetate structure has a porous structure with a thickness of between 0.1 and 0.2 mil.

The finished film web is collected on take-up roll 19 for cutting into sheets or ribbons of the desired dimensions. The present invention is principally concerned with the production of transfer sheets for typewriter use and transfer strips or wide ribbons for other business machine use.

While pigments such as the carbon black, magnetic iron oxides, particulate dyestuffs and toned pigments having dyes of the desired colors precipitated and absorbed on the surface of porous pigments are the preferred coloring materials, other coloring materials are also useful including the substantially colorless color-forming reactive chemicals which form colored reaction products on contact with other colorless coreactive chemicals present on the copy sheet surface.

It should be understood that the present invention also applies to the production of self-supporting ink-releasing microporous layers which are formed on a casting surface and thereafter stripped therefrom in known manner. Such transfer elements are preferably coated on both surfaces with the present wash coatings for complete coverage.

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

We claim:

1. The process of producing pressure-sensitive transfer elements of the squeeze-out type which are clean to the touch and resistant to exuding ink under the effects of pressure less than imaging pressure which comprises:

(a) producing a pressure-sensitive squeeze-out type ink layer comprising a pressure non-transferable microporous structure of synthetic thermoplastic resin containing within the pores thereof a pressure-exudable ink comprising an oily vehicle and coloring matter;

(b) applying over the ink-releasing surface of said ink layer a supercoating of a dilute solution of a synthetic thermoplastic resin in a volatile organic solvent containing a blowing agent which is decomposable to evolve a gas at a temperature higher than the evaporation temperature of said volatile organic solvent; and

(c) applying sufiicient heat to evaporate said volatile organic solvent, decompose said blowing agent and solidify said supercoating as a pressure non-transferable porous layer having a thickness ranging between about 0.0025 mil. and 0.5 mil., and through which the ink of the ink layer can be exuded under the effects of imaging pressure.

2. The process of claim 1 in which said dilute solution comprises from about 5% to about 20% by weight of said resin and from about 0.001 to about 1% by weight of said blowing agent.

3. The process of claim 1 in which the synthetic resin of the ink layer comprises an acrylic resin and said dilute solution comprises a vinyl acetate polymer.

4. The process of claim 1 in which the dried supercoating has a thickness of from about 0.1 mil. to 0.3 mil.

5. The process of claim 1 in which the blowing agent is selected from the group consisting of p,p'-oxy-bis (benzene-sulfonyl hydrazide), N,N'-dimethyl-N,N-dinitroso terephthalamide, diazoaminobenzene, and dinitrosopentamethylene tetramine.

=6. Pressure-sensitive transfer elements produced according to the process of claim 1.

7. Pressure-sensitive transfer elements produced according to the process of claim 2.

8. Pressure-sensitive transfer elements produced according to the process of claim 3.

9. Pressure-sensitive transfer elements produced according to the process of claim 4.

10. Pressure-sensitive transfer elements produced according to the process of claim 5.

References Cited UNITED STATES PATENTS 1,962,082 6/ 1934 Miller 117-364 2,313,645 9/ 1940 Antrim 11736.4 2,790,742 4/ 1957 Waart on 11736.4 2,803,579 8/1957 Stolle et a1 11736.4 3,080,954 3/1963 Neinman et a1 11736.4 3,104,980 9/ 1963 Maiersom 117-36.4 3,260,612 7/1966 Dulmage et al 117-36.2

MURRAY KATZ, Primary Examiner.

US. Cl. X.R.

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