US3446646A - Pressure sensitive receiving and transfer sheet - Google Patents

Description

United States Patent ice 3,446,646 PRESSURE SENSITIVE RECEIVING AND TRANSFER SHEET Jack H. Terry, Pittsford, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York No Drawing. Filed Apr. 29, 1965, Ser. No. 451,986

Int. Cl. B41m 5/02; C08f 45/22 US. Cl. 117-35.6 5 Claims ABSTRACT OF THE DISCLOSURE A novel pressure transfer sheet comprising a wax and an adhesive resin, coated on a substrate, in a thickness ranging from about 0.5 to about 3.5 lbs/ream, is disclosed.

This invention relates to a pressure transfer duplicating technique and, more particularly, to an improved transfer sheet particularly adapted for use therein.

Various techniques have been developed for making multiple copies of original documents by the transfer of a relatively dry imaging material or ink. Perhaps the most well known of these techniques involves the use of an ordinary sheet of carbon paper between the original and a copy sheet in a typewriter. As is well known, this technique of making duplicates of an original typed document suffers from many drawbacks. For example, the carbon paper itself is easily smudged and tends to dirty the hands and clothing of the operator. In addition, because the ink on the carbon paper must transfer readily from the paper sheet under the application of pressure, it also tends to smudge and spread on the duplicates producing fuzzy, illegible and non-permanent images on the copy sheet. Generally, only a few copies are possible because it is extremely ditficult to transmit the pressure of the typed character throughout the whole thickness of the sandwich formed by the carbon sheets and the copy papers; so that the readability in the carbon copies most remote from the typed characters drops off drastically. It is also very laborious to make corrections on carbon copies, since each copy must be individually corrected.

In order to overcome the many difiiculties inherent in the production of duplicates with carbon paper, outlined above, a number of duplicating techniques have been developed such as spirit duplicating, mimeograph, offset and the like. Although some of these techniques produce copies which are vastly superior to carbon copies, they are somewhat more expensive than the use of carbon paper for short runs, sometimes involve messy liquids, and require the preparation of a separate master apart from the original. In addition, present day duplicating techniques require a fairly large capital investment in equipment while no such investment is required in making carbon copies. Accordingly, these techniques become prohibitive in cost if they are used to produce less than about twenty copies. In summary then, it may be said that there is not available at the present time any process for making a relatively small number of duplicates of an original document with simple, inexpensive apparatus which is competitive in price and yet still superior in quality to carbon copies.

Now in accordance with the present invention there is provided an extremely simple duplicating process for making copies from an original directly by pressure transfer. This technique involves typing the original with a rib- 3,446,646 Patented May 27, 1969 bon bearing an ink which is specially adapted to the process, placing the original in face-to-face contact with a transfer sheet and pressing the two together as with a pair of rollers so as to transfer a portion of the original ink to the transfer sheet. After separation of the transfer sheet and the original, which leaves a portion of the original ink on each of these two members, the inked transfer sheet is pressed in face-to-face contact with the copy sheets so as to transfer a portion of the ink on the transfer sheet to each of these copy sheets and form a rightreading duplicate of the original on them.

Although similar duplicating techniques have been proposed as, for example, in German Patent 646,530 and US. Patent 3,122,094, pressure transfer duplicating techniques of this type have not become commercial because in the present state of the art they are not capable of producing a sufficiently high number of high resolution, high density copies so as to make them sufiiciently attractive to the user to replace the use of carbon paper and other duplicating or copying techniques. Since a large portion of the ink once transferred to the original must then be transferred to the transfer sheet under the much lower shearing stresses applied when the original is pressed in face-to-face contact with the transfer sheet and passed between a pair of pressure rollers, the transfer sheet must be capable of picking up and holding a large proportion of the thickness of the ink from the typed original. On the other hand, the transfer sheet must at the same time give up just sufficient ink to each copy sheet when successive copy sheets are placed in face-to-face contact with theink transfer sheet and passed between the pressure rolls so that good high quality duplicates are produced in sufficient number. Since the system should produce from about 10 to 15 copies in order to be a feasible duplicating process, it can be seen that a small but controlled amount of ink must be transferred from the transfer sheet to each copy which is made. If too much ink is transferred from the transfer sheet to the copy sheet, the master ink will be so rapidly depleted that an inadequate number of copies will be produced while, on the other hand, if too little ink is transferred the quality of all of the copies will be poor. In addition to the fact that the transfer sheet must pick up and release controlled amounts of the imaging material or ink it must also be inexpensive enough so that its cost may be amortized over the 10 to 20 duplicates which it used to reproduce without adding excessively to their cost. In addition to the aforementioned requirements, the transfer sheet must also be of a material that can be easily separated from the original and the copies so as to avoid tearing or spottiness of images in either the originals or the duplicates.

It is therefore an object of this invention to provide a novel duplicating process.

Another object of this invention is to provide a simple, inexpensive pressure transfer duplicating process.

A still further object of this invention is to provide a transfer sheet for use in pressure transfer duplicating which is capable of producing a relatively large number of high quality copies.

Still another object of this invention is to provide a transfer sheet which is specially adapted for use with particular inks in pressure transfer duplicating processes and devices.

These and still other objects are accomplished in accordance with the present invention, generally speaking,

by employing an ink with a wax and adhesive resin base and a transfer sheet which is compatible with the ink. The transfer sheet is made compatible by coating it with a material having the same wax binder and adhesive resin as are used in the ink formulation. In other words, the transfer sheet contains all the ingredients of the imaging ink with the exception of the dyes, the pigments and a modifying agent such as a silicone which is added to the ink formulation to make it more readily transferable.

In order to fabricate the transfer sheet this nonpigmented transfer sheet formulation is coated on an inexpensive substrate such as paper, aluminum foil, a plastic web such as polyethylene or the like. Preferably the thickness of the coating on the transfer sheet will be from about 0.5 lb./ream to about 3.5 lb./ream. It has generally been found that when the coatings on the transfer sheet are thicker than those in this range some of the coating from the transfer sheet tends to back transfer to the copies producing an undesirable wax film on the copy surface. When the transfer sheet coating is too thin it cannot pull off an adequate ink supply from the original to produce the desired number of copies. The selection of the particular substrate employed will, of course, depend to some extent on the particular ink and transfer sheet coating formulations to be employed since the transfer sheet coating must be capable of adhering very strongly to its substrate to prevent transfer of this coating during the imaging process. Although the ink itself must be miscible with and wet the surface of the transfer sheet coating, this coating and the ink have very distinctly different cohesive properties because the ink must be readily transferable from one surface to another while the transfer sheet coating must be as adherent as possible to its substrate so as to permit ink transfer while preventing the transfer of the transfer sheet coating.

The most desirable transfer inks for use in the pressure transfer process which produce the best results are composed of from about 33 to about 72 parts by weight of pigment, from about 2 to about parts by weight of wax soluble dyes, from about 1 to about 7 parts by weight of microcrystalline wax, from 1 to about 4 parts by weight an adhesive resin and from about to about 50 parts by weight of a modifying agent such as petrolatum or a polysiloxane such as a silicone gum. Typical pressure transfer inks of this type are disposed in greater detail in copending application No. 451,960, filed April 29, 1965.

The dyes and pigments of the ink formulations are, of course, unnecessary in the transfer sheet coating since the master is not employed for marking. The ink vehicle modifying agents are also omitted from the transfer sheet coating in the formulation since these materials are only included in the ink formulation in order to change the rheological properties of the ink vehicle so as to make the ink readily transferable in the duplicating process, and this type of modification is, of course, highly undesirable for the transfer sheet coating. (Modifying agents in the ink generally act to physically soften the ink, as in the' case of a petrolatum modifying agent or to form an incompatible mixture with the other ink vehicle components to impart a texture to the ink vehicle which fractures sharply and transfers readily as is the case with the silicone gum modifying agents.) The ratio of adhesive resin to wax in the ink formulation should be as close as possible to their ratio in the transfer sheet coating formulation although slight differences on the order of 10% either way may be tolerated without significant deterioration in quality. There may also be minor departures in the materials employed for the transfer sheet versus those used in the ink formulation. Thus, for example, one grade of microcrystalline wax may be employed in the transfer sheet with a softer grade being employed in the ink. It should be remembered that it is desirable to have the transfer sheet be slightly harder than the ink to facilitate penetration. In short then, it may be stated that the inks and transfer sheet coatings which are to be used together each contain the same amounts of wax and adhesive resin.

The coating may be applied to the transfer sheet substrate by any suitable technique such as hot melt, solvent coating or the like so long as it is capable of producing a fairly smooth coating. In general, the ink and transfer sheet coating formulations may include any suitable waxes; however, it has been found preferable if both a fairly hard wax such as microcrystalline wax and a softer wax, such as a beeswax or paraffin wax, are employed. Other typical waxes are palm Wax, carnauba wax, polyethylene wax, ouricury wax, candelilla wax, etc., and mixtures thereof. With respect to the adhesive resin, any

suitable adhesive resin whether natural, modified natural or synthetic in nature may be employed. Typical adhesive resins include: low molecular weight polystyrenes, polyterpenes, styrene-butadienes, chlorinated rubbers, polymers made from hydrocarbon fractions, polyvinyl acetates, polya-crylics, cellulose acetate and the like.

The general nature of the invention having been described above, the following examples are given in more specific illustration of preferred embodiments thereof:

Examples I and II A coating formulation employing 10 parts by weight of microcrystalline wax, 4 parts by weight of beeswax and 8 parts by weight of Piccolyte S70 (a polyterpene resin available from Pennsylvania Industrial Chemical Co. and having a ring and ball melting point of 70 C.) is prepared in a hot melt. This batch is then divided in half, and one half is coated at 2 lbs/ream on a paper substrate from the melt. To the other half there is then added 5 parts by weight of a wax soluble dye (available under the tradename Waxoline Black from the Imperial Chemical Industry), 13 parts by weight of black iron oxide, 10 parts by weight of carbon black, and 2 /2 parts by weight of coal fines and 3 parts by weight of petrolatum. After uniform blending in the hot melt at about 250 F. for 30 minutes, the pigmented formulation is coated onto paper sheets to a weight of about 6 lbs./ ream.

Two identical originals are then typed from the ribbon prepared with the pigmented formulation, and the first of these is placed in face-to-face contact with the compatible transfer sheet formed with the unpigmented coating formulation and the second original is placed in face-to-face contact with a sheet of commercial wax paper available under the tradename Freshrap. Each of the sandwiches thus prepared is then passed between a pair of driven rollers set to apply 200 lbs./lineal inch to the sandwich. In each instance the original is then separated from the transfer sheet which is then placed in face-to-face contact with a second sheet of office bond paper followed by a second passage through the pressure rollers. When the transfer sheet is separated from the bond paper, a pressure transfer copy is left behind on the paper. This process is repeated with the transfer sheet and fresh sheets of copy paper using each transfer sheet until it no longer produces legible copy on the paper. Upon comparison it is seen that the compatible master produces 10 high quality copies and that all the copies up to the 20th are quite legible with the 20th copy having a reflection density of 0.4, whereas the wax paper produces only 6 fairly good quality copies and only 11 copies which are legible.

Examples 111 and IV The procedure of Examples I and II is repeated except that 25 parts by weight of a polysiloxane gum, marketed by the General Electric Co. under the name silicone gum SE-76, is employed in the ink formulation in place of the petrolatum. With this ink formulation, the compatible transfer sheet produces 15 high quality copies and, here again, even the 20th cOpy was fairly legible and only about 8 high quality copies are produced from the wax paper transfer sheet and 13 legible copies.

What is claimed is:

1. A pressure transfer sheet comprising: (1) a wax material, said material consisting of microcrystalline wax and beeswax, said microcrystalline wax being present in an amount ranging from about 1 to about 7 parts by weight and said beeswax being present in an amount ranging from about 1 to about 4 parts by weight, and (2) about 2 to about 10 parts by weight of an adhesive resin, said resin being selected from the group consisting of low molecular weight polystyrene, polyterpene, styrenebutadiene, chlorinated rubber, polymers made from hydrocarbon fractions, polyvinyl acetate, polyacrylics, cellulose acetate, and mixtures thereof, coated on a substrate in a thickness ranging from about 0.5 to about 3.5 pounds per ream.

2. The transfer sheet of claim 1 wherein a mixture of said wax material and said resin is coated on a substrate in a thickness of about 2.0 pounds per ream.

3. The transfer sheet of claim 1 wherein said resin is a polyterpene resin.

4. The transfer sheet of claim 1 wherein about 4 parts by weight of said beeswax is present.

5. The transfer sheet of claim 1 wherein about 8 parts by weight of said resin is present.

References Cited UNITED STATES PATENTS 2,882,182 4/1959 Tench 117-158 2,892,735 6/1959 Curler et a1 117-158 3,122,094 2/ 1964 Leclerc et a1 101-468 3,205,186 9/1965 Zaayenga l17158 FOREIGN PATENTS 257,294 5/ 1963 Australia.

MURRAY KATZ, Primary Examiner.

US. Cl. X.R.