US 3628979 A
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Inventors Douglas A. Newman Glen Cove; Allan T. Schlotzhauer, Locust Valley, both of N.Y.
App]. No. 738,497
Filed June 20, 1968 Patented Dec. 21, 1971 Assignee Columbia Ribbon and Carbon Manufacturing Co. Inc. Glen Cove, N.Y.
TRANSFER ELEMENTS AND METHOD OF MAKING SAME 8 Claims, 2 Drawing Figs.
US. Cl 117/364, 117/76, 117/155 Int. Cl 841m 5/10 Field of Search 117/364 References Cited UNITED STATES PATENTS 3,065,099 11/1962 Newman 117/361 3,080,954 3/1963 Newman et al.. 117/364 3,104,980 9/1963 Maierson 1 17/364 3,442,681 5/1969 Newman et a1. 117/364 3,079,351 2/1963 Stameslow et a1. 117/362 Primary Examiner-Murray Katz Attorney-Johnson & Kline ABSTRACT: The manufacture of novel pressure-sensitive transfer elements of the squeezeout type which are cleaner to the touch and resistant to producing typewriter roller marks on the copy sheet. The ink-releasing surface of a squeezeouttype ink layer is printed with a very thin layer of a composition comprising a dilute volatile solvent solution of a synthetic thermoplastic resin and a minor amount of a liquid oily material which is incompatible with said resin but which is compatible with the ink vehicle in the squeezeout layer. The volatile solvent is also at least a partial solvent for the resin binder of the squeezeout layer.
PATENIED on an Daugas A e wmar; Adan T .5cbloiz e/7 BY TRANSFER ELEMENTS AND METHOD OF MAKING SAME The present invention relates to the field of the so-called squeezeout carbon papers and ribbons on which the transfer layer comprises a microporous nontransferable resinous structure containing within the pores thereof a pressure-exudable ink comprising an oily vehicle and imaging matter. Such transfer elements are illustrated by US. Pat. Nos. 2,820,717; 2,944,037; 3,037,879; 3,117,018 and 3,314,814, 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 semisolid 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 also possible to avoid or diminish such undesirable offsetting by applying a thin continuous resin supercoating over the ink-releasing layer, which supercoating permits the ink to be forced therethrough from the ink-releasing layer under the effects of imaging pressure. Unless such a supercoating has openings therein, it greatly impedes the passage of ink so that the first copy produced from any particular area of such a transfer element is noticeably weak in tone. Subsequent copies have uneven tone due to the prior rupture of the supercoating in some areas and not in others.
In an effort to overcome these problems, the resin supercoating has been either printed in the form of a screen or coated on as a solution of a resin which is incompatible with the ink vehicle of the ink-releasing layer so that the resin is shed from the exposed ink pore areas on the surface of the ink-releasing layer but forms a continuous supercoating over the other areas. While these procedures are effective in reducing undesirable offsetting to some extent, they necessarily represent a compromise due to the fact that they present no continuous or overall barrier or resistance to the exudation of ink from the ink layer under the effect of pressure. Such supercoatings merely space the ink-releasing layer from the hands or from the copy sheet and the extent of such spacing is limited by the necessary thinness of the supercoating which must be maintained no' greater than about 0.0001 inch in.
order not to interfere with the uniform imaging strength of the transfer element. Such supercoatings will permit roller marks to be produced on a copy sheet under the pressure exerted by the typewriter roller during insertion of the sheets into a typewriter, particularly during repeated use, or if applied in greater thicknesses to avoid this disadvantage, will provide images of uneven or nonuniform tone clue to the sealing of the ink-releasing pores in some areas of the ink-releasing layer. Also, screen supercoatings have the important disadvantage that they meter the ink through the openings in the screen and thereby result in images which contain a clearly visible crosshatch pattern. Such images are lighter in tone than,
desired and in fact are similar to halftone printed images.
It is the principal objects of the present invention to provide improved squeezeout type transfer elements which are clean to the touch and do not produce roller marks on the copy sheet and which substantially completely retain pressure sensitivity so as to produce images of uniform tone and high intensity even during initial use.
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:
FIG. 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 printing over the ink-releasing surface of a squeezeout-type resinous layer containing pressure-exudable liquid ink with a thin supercoating composition comprising a dilute volatile solvent of 1 part by weight of a synthetic thermoplastic resin and up to about 0.8 part by weight of one or more liquid oily materials which are incompatible with said resin but which are compatible with the liquid ink of the resinous layer below. The solvent is one which is at least a partial solvent for the resinous binder of the ink-releasing layer, and when it is evaporated there remains a uniformly thin porous resinous supercoating which contains within the pores thereof said oily material and which is completely clean to the touch and nontransferable from the ink-releasing layer under the effects of imaging pressure.
The oily material is soluble or dispersible in the solvent used to apply the supercoating and therefore is evenly distributed throughout the supercoating during application. When the solvent evaporates, the oily material separates from the resin in the form of tiny droplets uniformly distributed throughout the dried supercoating. While the supercoating is extremely thin, less than about 0.0001 inch, the dispersed droplets are barriers against exudation of the ink to the hands or to a copy sheet unless imaging pressures are applied. Such pressures permit the ink to pass freely through the pores of the supercoating and the small amount of oily material present in the supercoating blends with the ink during such passage and has been found to have no noticeable effect on the uniformity of the tone of the images produced.
The chemical properties of the liquid oils used in the present supercoating compositions are very important. The only suitable oils are those which are incompatible with the resin of the supercoating and which are compatible with at least one of the oleaginous ingredients of the ink vehicle of the ink-releasing layer. This latter compatibility permits the supercoating composition to have an affinity for the surface of the ink-releasing layer so that it remains where printed rather than being shed or repelled. This is critical to the present invention in view of the extreme thinness of the applied layer. The oily liquid may be or function as a wetting agent in that it gives the supercoating composition an affinity for the surface of the inkreleasing layer and thereby permits the supercoating to remain as a thin layer where printed over the ink-releasing layer.
According to a preferred embodiment, a conventional wetting agent is added to the supercoating composition. The wetting agent further assists in the reliable application of supercoatings of the required uniform thinness. Preferably the wetting agent is an oily liquid which is incompatible with the resin of the supercoating and compatible with the ink vehicle of the ink-releasing layer so that a single material can be used in the supercoating to perform both functions. The wetting agent reduces the surface tension of the supercoating composition and results in a composition which can be spread more evenly over the ink-releasing layer to form a very thin supercoating of high uniformity of caliper. The wetting agent may be any liquid or solid material which is soluble or dispersible in the volatile solvent used to apply the supercoating.
The solvent used to apply the present supercoatings is also very critical. Such solvent must be only a partial solvent for the resinous binder of the ink-releasing layer and must not be a good solvent for the ink vehicle of said layer at an operating temperature which is generally room temperature.
Most aromatic solvents such as toluene, xylene and the like dissolve said ink vehicle excessively and cause the ink to contaminate the supercoating composition and thus interfere with the objects of the invention. Therefore only those volatile solvents are useful which are capable of dissolving the resin binder of the ink-releasing layer to some substantial degree under ideal dissolving conditions such as with the assistance of heat and agitation. It should be understood that no extensive dissolving of the resin of the ink layer occurs during application of the supercoating since the supercoating is applied at about room temperature and the solvent is evaporated almost immediately, However, this inherent dissolving ability has been found to be critical to the application of uniformly thin supercoatings which resist transfer under the effects of imaging pressure. The preferred solvents are those conventional aliphatic liquids which are volatile at room temperatures, including ketones such as acetone and methyl ethyl ketone, alcohols such as ethanol, and esters such as ethyl acetate. Water is also a suitable solvent in systems employing water-soluble or swellable resins and water-dispersible oils.
It appears that the solvent does wet and soften the resin binder present at the surface of the ink-releasing layer so that the supercoating becomes solvent bonded with the surface of the ink layer. The solvent has a strong affinity for the resin of the ink layer and thus functions somewhat as a wetting agent even though it does not dwell long enough to cause any extensive dissolving of the resin. This wetting action further permits the thin supercoating layer to lay where printed, rather than being shed by the ink layer, so that a uniformly thin layer is produced when the solvent is evaporated. While some solvents are capable of dissolving oily liquids under ideal dissolving conditions, it has been found that they are not capable of dissolving contaminating amounts of such materials at room temperatures during the brief dwell time permitted by the present process.
The preferred supercoating compositions of the present invention comprise solutions containing from 80 to 95 percent by weight of volatile solvent, :from 5 to l percent by weight of synthetic thermoplastic resin binder material, from 1 to 5 percent by weight of the oily liquid material and from 0.] to lpercent by weight of wetting agent. In terms of dry weight the preferred supercoatings comprise from about 55 to 80 percent by weight of resin, from about 20 to about 45 percent by weight of oily liquid material and from about 0.01 to 5 percent by weight of wetting agent. These proportions may be varied depending upon the desired imaging strength.
The supercoating is printed onto the surface of the ink layer and levelled to form a wet film having a thickness of from about 0.00005 inch using a smooth rod, up to about 0.0005 inch using a wire wound rod. This is the thickness of the liquid supercoating which consists mainly of the volatile solvent. The dried supercoating has an approximate thickness range of from 5 to 20 percent the thickness of the wet layer since the wet layer contains only from 5 to 20 percent solids. The preferred dried thickness range is from 0.05 point to 0.5 point. A point equals 0.0001 inch. In terms of weight, the supercoating composition is applied at the rate of from about 0.] pound up to about 0.5 pound per ream and preferably at the rate of about 017 pound per ream. A ream, as used herein, equals 500 sheets 22X34 inches in dimensions or about 2,600 square feet. After evaporation of the solvent, the dried supercoating has a weight ranging between about 0.01 pounds up to about 0.05 pounds/ream.
The present supercoatings 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 printing roller 13 which receives a continuous supply of composition from application roller 14 which is immersed in vat 15 containing the supercoating composition. The supercoating is applied to the underside of the web over the squeezeout ink-releasing layer and is levelled by means of bar 16. The wet web then passes under idler roller 17 and over heat lamps 18 which cause evaporation of the volatile solvent and solidification of the thin resin structure. This preferably takes place in a drying tunnel. The web then passes under second idler roller 17 and onto takeup roll 19.
The structure of the final transfer element is somewhat uncertain as stated supra but appears to be as illustrated in FIG. 2 of the drawings. The transfer element has a flexible foundation 20 carrying a microporous squeezeout-type, ink-releasing layer 21 and a thin nontransferable synthetic thermoplastic resin supercoating 24 over said ink-releasing layer. The inkreleasing layer comprises a nontransferable microporous resinous structure 23 containing droplets 22 of pressure-transferable oily ink within the pores thereof. The supercoating contains the incompatible liquid oily material in the form of uniform droplets 25 which comprise areas of the supercoating which transmit ink under the efiects of imaging pressure but do not transmit ink under lesser pressures. Thus while imaging pressure is sufiicient to exude the oily ink through droplets 25 to copy sheet, the lesser pressure exerted by a typewriter roller or the like is not sufficient to cause the oily ink to penetrate the oleaginous droplets.
The ingredients suitable for use in preparing the present supercoating compositions may be varied widely depending upon the composition of the ink-releasing layer. Thus the synthetic thermoplastic resinous binder may be a vinyl resin such as a copolylmer of vinyl chloride and vinyl acetate or a polymer of methyl rnethacrylate of copolymer thereof with ethyl acrylate, or a nonvinyl resin such as an alcohol-soluble nylon, cellulose acetate-butyrate, or a polycarbonate. ln general, any of the resins suitable for use as the binder for the ink-releasing layer are also suitable for use in the supercoating, and U.S. Pat. Nos. 2,820,717; 2,944,037; 3,117,018 and 3 ,3 14,814 are cited as illustrative of such suitable resins.
Similarly the oily liquid material of the supercoating may be the same as the incompatible ink vehicle of the ink-releasing layer and the aforementioned U.S. patents are illustrative of suitable materials. Liquid oily materials are preferred such as mineral oil, butyl stearate, silicone oil and the like. However, in sharp contrast to the proportions used in the ink-releasing layer where the amount of oily ink vehicle is at least equal to the amount of resin, the liquid oily material of the supercoating is present in an amount equal to at most 0.8 part per part by weight of the resinous binder material. Preferably the oily liquid material equals from 0.3 parts to 0.5 parts by weight per part by weight of the resinous binder. Oil-to-resin ratios in excess of about 08 result in supercoatings which are oily to the touch, which interfere with the density ofthe duplicate images on the copy sheet producing nonuniformity in tone, and which permit transmission of the ink from the ink layer to the copy sheet under the effects of pressure less than imaging pressure, such as roller pressure.
The wetting agent may be an anionic, cationic or nonionic material which is soluble in the volatile solvent used to apply the supercoating. Preferred materials are lecithin, sorbitan esters such as sorbitan sesquioleate and related esters commercially available under the trademark Tween, dioctyl sodium sulfosuccinate and related dialkyl salts commercially available under the trademark Aerosol, polyoxyethylene compound, and the like.
If desired, the present supercoatings may contain a small amount of a nonstaining, low oil absorption pigment or filler which is present for decorative purposes and preferably is oleophobic so as to be bound in the resin phase. Pigments such as bronzed powders are preferred. The amount of such material should not exceed about 5 percent of the dry weight of the supercoating. However, in all cases the liquid oily droplet phase of the supercoating is substantially free of coloring matter and has no color transfer value of its own.
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 /z-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:
Ingredients Parts by Weight Styrene-Methyl methucrylate copolymer (Zerlon I50) l2.0 Butyl stearrite 7.0 Refined rapeseed oil 7.0 Sulfonated vegetable all 1.7 Blue tuning paste 2.2 Black toner pigment 6.6 Ethyl acetate l0.2 Methyl ethyl ketone 26.3 Toluol 27.0 Total 100.0
Ingredients Parts by Weight Formula 1 Formula 2 Polymethyl methacrylate 7 7 Butyl stearate 2 S Silicone oil (Dow Fluid 556) l Lecithin 0.5 Methyl ethyl ketone 89.5 88
The supercoating composition is applied at a preferred weight of 0.17 pounds/ream over the ink-releasing layer. Thereafter the transfer element is heated to evaporate the methyl ethyl ketone and leave the dried polymethyl methacrylate structure as a uniformly thin layer over the ink-releasing layer. The supercoating is at least partially solvent bonded to the resin structure of the ink layer due to the solubility of the latter in methyl ethyl ketone.
The finished film web is collected on takeup 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 blacks, 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 in the ink layer, 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.
According to the present invention and claims, two or more materials are compatible if they are capable of forming a single-phase solution when they are mixed in liquid form in the proportions used. An oil is compatible with another oil if it mixes with the other oil to form a single-phase solution and does not separate on standing; an oil is compatible with a semisolid material such as lanolin if it mixes with the semisolid when the latter is liquefied by heating to form a single-phase solution and does not separate therefrom to any substantial degree or cooling; an oil is compatible with a resin when it is codissolved with the resin in a mutual solvent and does not separate therefrom when the solvent is evaporated. In many cases materials are compatible with each other when used in certain relative proportions which, if exceeded, result in the formation of a second incompatible phase. The present invention contemplates the use of such materials but only in such relative proportions which produce compatible single-phase solutions.
1. The process of producing pressure-sensitive typewriter carbons of the squeezeout type which are clean to the touch and resistant to exuding ink under the effects of roller pressures less than imaging pressure and which produce images of uniform tone and 1g intensity under the effects of imaging pressure which comprises:
a. producing on a flexible plastic film foundation a pressuresensitive squeezeout-type ink layer comprising a pressure-nontransferable microporous structure of synthetic thermoplastic resin containing within the pores thereof a pressure-exudable ink comprising an oleaginous vehicle and coloring matter;
b. printing over the ink releasing surface of said ink layer, a
uniformly thin layer of supercoating composition consisting essentially of l part by weight of synthetic thermoplastic resin, from 0.3 to 0.8 part by weight of a liquid oily material which is incompatible with said resin and is compatible with said pressure-exudable ink and a major amount of a volatile solvent for said resin which is only a partial solvent for the resin of said ink layer under the conditions of application of the supercoating composition; and
c. applying heat to evaporate said volatile organic solvent and solidify said resin as a pressure-nontransferable supercoating having a thickness of from 0.05 to 0.5 point, said liquid oily material being uniformly dispersed throughout said supercoating in the form of droplets which transmit ink from said ink layer under the effects of imaging pressure but have no initial color transfer value of their own.
2. The process of claim 1 in which said supercoating composition comprises from about 0.3 to about 0.5 parts by weight of said liquid oily material per 1 part by weight of said resin.
3. The process of claim 1 in which the synthetic resins of the ink layer and the supercoating composition comprise acrylic resins.
4. The process of claim 1 in which the supercoating composition also comprises a wetting agent which reduces the surface tension of the composition and permits the application of a thin supercoating layer of increased uniformity.
5. A pressure-sensitive typewriter carbon of the squeezeout type, which is clean to the touch and resistant to exuding ink under the effects of roller pressures less than imaging pressure, which comprises a flexible plastic film foundation having thereon an ink layer of pressure nontransferable microporous synthetic thermoplastic resin containing with the pores thereof a pressure-exudable ink comprising an oleaginous vehicle and coloring matter, and having bonded to said layer a thin pressure nontransferable supercoating having a thickness of from 0.05 point to 0.5 point consisting essentially of 1 part by weight of a synthetic thermoplastic resin and from 0.3 part to 0.8 part by weight of a liquid oily material which is incompatible with said resin and is compatible with said pressure-exudable ink and which is uniformly dispersed in said supercoating in the form of droplets which transmit ink from said ink layer under the effects of imaging pressure but have no color transfer value of their own.
6. A transfer element according to claim 5 in which the synthetic resins of the ink layer and of the supercoating comprise acrylic resins.
7. A transfer element according to claim 5 in which the supercoating has a weight of from about 0.01 to about 0.05 pounds per ream.
8. A transfer element according to claim 7 in which the supercoating also comprises a wetting agent.