United States Patent 3617328

Pressure-sensitive transfer elements of the squeezeout type which are rendered cleaner to the touch and resistant to producing typewriter roller marks on the copy sheet by covering the ink-releasing surface of such transfer elements with a very thin porous layer of thermoplastic resin particles which are fused to each other and to the ink layer to provide an ink-permeable protective layer over the ink layer.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
428/327, 428/337, 428/339, 428/483, 428/520, 428/914
International Classes:
B41M5/10; (IPC1-7): B41M5/10
Field of Search:
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US Patent References:
3227637Method of bonding coatings1966-01-04De Hart
3104980Pressure sensitive record and transfer sheet material1963-09-24Maierson
3080954Supercoated transfer elements1963-03-12Newman et al.
2489466Method of making stiffened permeable sheet material1949-11-29Schramm
2163601Transfer article1939-06-27Humes
1971306Transfer device1934-08-21Antrim
1962082Typewriter ribbon1934-06-05Miller

Primary Examiner:
Katz, Murray
I claim

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

2. The process of claim 1 in which the resin particles are provided over the ink-releasing surface by applying them as a dispersion in a volatile vehicle which is a nonsolvent for the resin of the ink layer, and heat is applied to evaporate said vehicle and form said discrete, dry particles.

3. The process of claim 2 in which the dispersion of resin particles is applied in a thickness to provide a dried resin layer having a thickness of from about 0.0005 inch to 0.005 inch.

4. The process of claim 1 in which the synthetic resin of the ink layer and the resin particles comprise vinyl resins.

5. The process of claim 1 in which the resin particles are provided over the ink-releasing surface by applying them as discrete, dry particles.

6. A reusable pressure-sensitive transfer element of the squeezeout type, which is clean to the touch and resistant to exuding ink under the effects of pressure less than imaging pressure, which comprises an impervious flexible plastic film of polyethylene terephthalate polyester having on one surface thereof a thin receptive undercoating of vinyl resin and having on said undercoating a pressure-sensitive 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 oily vehicle and coloring matter, and having heat-fused to the surface of said ink layer a thin porous fused particulate layer having a thickness of from about 0.0005 inch to about 0.01 inch consisting essentially of small, relatively uniform particles of thermoplastic resin which have been heated sufficiently to cause them to heat-fuse to particles in contact therewith without destroying the porosity of the layer and sufficiently to heat-fuse them to the surface of the ink layer whereby they are not transferable from the ink layer under the effects of imaging pressure during repeated reuse of the transfer element.

7. A transfer element according to claim 6 in which the synthetic resin of the ink layer and the thermoplastic resin of the particulate layer comprise vinyl resins.

8. A transfer element according to claim 6 in which the particulate layer of thermoplastic resin comprises polyvinyl chloride.

9. A transfer element according to claim 6 in which the particulate layer of thermoplastic resin has a thickness of from about 0.0005 inch to 0.01 inch.

10. A transfer element according to claim 9 in which the particulate layer has a thickness of from about 0.002 inch to 0.005 inch.

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 U.S. Pats. 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 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 the principal object 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 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:

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 covering the ink-releasing surface of a squeezeout-type resinous ink layer with a thin coating consisting essentially of thermoplastic resin particles, preferably dispersed in a volatile vehicle which is thereafter evaporated, and then applying sufficient heat to soften the surface of the resin particles, without melting the particles themselves, to cause the particles to adhere to particles in contact therewith and to adhere to the surface of the ink layer, if in contact therewith, and thereafter cooling the particulate coating as a porous, ink-permeable layer over the ink layer.

It should be made clear that the present particulate coating does not form a continuous film or layer over the ink layer. This effect is to be avoided since such a continuous film seals the ink layer and prevents the ink layer from exuding ink under the effect of imaging pressure. Care must be taken in heating the particulate coating so that the resin particles are fused together at only their contact points whereby the interstices between contacting particles are retained unsealed.

It has also been found that the wash coating must be free of oils or other oleaginous materials which are incompatible with the resin particles of the wash coating since such materials separate from the resin particles 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. However, it should be pointed out that the resin particles of the present invention may contain true oily plasticizers which are compatible with the particles and form solid solutions therewith to produce the desired melting or softening temperature for the particles.

It is difficult to say with certainty how the present wash coats prevent the formation of roller marks without reducing the imaging pressure sensitivity of squeezeout-type layers. The present porous particulate coatings form a microporous screen on the ink-releasing surface due to the fact that the particulate coating contains interstices or voids between fused particles which permit ink to be forced therethrough under the effect of imaging pressure. The interstices are so small, actually microporous, and the particulate supercoating has such a thickness above the surface of the ink layer that the pressure exerted by typewriter rollers or during handling is insufficient to cause the ink to penetrate through the supercoating whereas imaging pressures such as typing pressures are sufficient to transfer the ink through to a copy sheet.

The preferred particulate coating compositions of the present invention consist essentially of dispersions of from about 5 percent up to about 50 percent by weight of a thermoplastic resin in water or a volatile organic vehicle which is not a solvent for the resin particles or for the resinous binder of the ink layer. Particulate vinyl resins in general are suitable and include polyvinyl chloride, polyvinyl acetate, vinyl chloride 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 thermoplastic resins of natural and synthetic origin are also suitable such as rubber latices, copal, colophony, polyethylene, polypropylene, polycarbonates, cellulose acetate, ethyl cellulose and other thermoplastics.

Aqueous emulsions or latices of these resins are preferred. Suitable volatile organic vehicles are toluene, xylene, naphtha, butanol, propanol, ethylene glycol and similar nonsolvents depending upon the solubility properties of the resin particles of the supercoating and the resin binder of the ink layer. Of course small amounts of compatible plasticizers, fillers, colorants or the like may be included in the resin particles provided that such additives do not interfere with the porosity and intended performance of the supercoating.

The particle size of the resin used may be varied over a relatively wide range depending upon the degree of pressure sensitivity of the ink-releasing layer and the degree of pressure sensitivity desired in the final transfer element. Some elements are subjected to heavy imaging pressures, such as typewriter carbons and ribbons and printing machine ribbons, while others are used under lighter pressures, such as pencil carbons and roller-pressure carbons. In general, the large particle sizes, from about 150 mesh up to about 100 mesh per inch, provide larger pores and freer ink escape and are preferred for the latter uses. Smaller particle sizes provide smaller but more numerous pores and therefore produce more uniform copy and are preferred for the former uses where the degree of imaging pressure is sufficient to insure adequate ink exudation. In this regard, particle sizes in the range of from 1000 mesh up to about 200 mesh per inch are suitable, with sizes ranging from 300 to 600 mesh being preferred.

Similarly the thickness of the supercoating may be varied depending on the degree of pressure sensitivity desired and the degree of cleanliness required. Generally the thickness will vary from a single layer of particles, each adhered to the surface of the ink layer, to a multi layer of particles adhered to one another. Thicknesses ranging as low as 0.0005 inch and up to 0.01 inch are possible, the preferred range being from about 0.002 to 0.005 inch.

According to the preferred embodiment, the particles are applied to the surface of the ink layer in a volatile vehicle and spread by means of a doctor blade to form a wet film which, after evaporation of the vehicle, has the desired thickness.

The present supercoatings may be applied in the manner illustrated by FIG. 1 of the drawing when using a volatile vehicle. The web of transfer element 10 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 supercoating dispersion. The dispersion is applied to the underside of the web over the squeezeout ink-releasing layer and is spread to the desired thickness by means of doctor blade 15. The wet web then passes under idler roller 16 and over heat lamps 17 which cause evaporation of the volatile solvent and drying of the thin resin structure. The web then passes through oven 18 to cause surface fusion of the resin particles and then under idler roller 19 and onto takeup roll 20.

The structure of the final transfer element is as illustrated in FIG. 2 of the drawings. The transfer element has a flexible foundation 21 carrying a microporous squeezeout-type ink-releasing layer 22 and a thin nontransferable particulate fused resin supercoating 23 over said ink-releasing layer. The ink-releasing layer comprises a nontransferable microporous resinous structure 24 containing droplets 25 of pressure-transferable oily ink within the pores thereof. The supercoating consists of discrete resin particles 26 bonded to each other and forming between each other interstices or voids 27 through which the liquid ink droplets 25 can be exuded under imaging pressure. Thus while imaging pressure is sufficient to exude the oily ink droplets 25 to a copy sheet, the lesser pressure exerted by a typewriter roller or the like is not sufficient to cause the oily ink to exude beyond the surface of the particulate supercoating 23.

It should be understood that the present particulate supercoatings may also be applied as a dry resin powder without any liquid vehicle. The powder may be brushed on or attracted by a static charge placed on the ink layer or merely deposited thereon by gravity as a layer of uniform thin caliper. Thereafter the powder particles are heated to cause bonding without complete melting as discussed supra, to produce the desired results.

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 1/2-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: ---------------------------------------------------------------------------

Ingredients Parts by Weight __________________________________________________________________________ Vinyl chloride-vinyl acetate copolymer (Vinylite VYHH) 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 __________________________________________________________________________ 100.0 __________________________________________________________________________

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 is provided with a thin layer of the resin particle coating composition in vat 14 which is a 40 percent dispersion of polyvinyl chloride (600 mesh per inch) in xylene as the nonsolvent vehicle. Doctor blade 15 spreads the wash coating to a wet thickness of about 30 points (0.003 inch). Thereafter the transfer element is heated to evaporate the xylene and leave the dried polyvinyl chloride particle structure having a thickness of about 1.2 mil (0.0012 inch). The polyvinyl chloride coating is next heated in oven 18 to a temperature of about 350° F. to soften the particles and cause them to adhere to one another and to the surface of the ink layer.

The finished film web is cooled and collected on takeup roll 20 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, 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 particulate supercoatings for complete coverage.

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