US3312564A - Transfer sheet, process of making and using - Google Patents

Description

A ril 4, 196 7 M; s. LBARBQUR. 3,312,564

TRANSFER SHEET, PROCESS OF MAKING AND USING Filed ens, 1965 TRANSFER COATING CONTAINING A HARD WAX, FATTY ACID NON-FILM FORMING RESIN PARTICLES AND A. BASE REACTIVE WITH THE FATTY ACID BASE- (PAPER ORPLASTIC FILM) INVENTOR MARSHALL S. HARBOUR ATTORNEYS ilnited States Patent Maine Filed Feb. 2, H65, Ser. No. 429,912 10 Claims. (Cl. 11736.1)

This application is a continuation-in-part of application Ser. No. 192,327, filed May 4, 1962, now Patent No. 3,170,809, which application is, in turn, a continuationin-part of application Ser. No. 134,156, filed Aug. 28, 1961, now abandoned.

This invention relates to transfer sheets and the method of making same, and more particularly to transfer sheets prepared by coating a suitable base sheet with a coating composition comprising an aqueous emulsion of a hard wax, a non-film-forming resin, a fatty acid, and a base, and thereafter hardening the coating on to the base sheet, said transfer sheets being capable of being heated so as to affix the coating to the base sheet after transfer of a portion of the coating.

It is known from United States Patent No. 2,931,752 that transfer sheets can be prepared by coating a suitable base sheet with a wax emulsion containing dispersing agents such as alkali metal soaps. These soaps are generally prepared by reacting a fatty acid with an alkali such as sodium or potassium hydroxide. Local pressure applied to these transfer sheets effects a transfer of the coating to a receptor sheet.

It has been found that when a volatile base is employed, instead of such non-volatile bases as sodium or potassium hydroxide, in conjunction with a hard wax, the resulting transfer sheets are considerably superior to previously known transfer sheets, particularly with respect to the sharpness of outline of the relatively dry, non-greasy transferred coating and also with respect to the ease of transfer of the coating. Moreover, the use of a volatile base in these wax coatings enables better control of the hardness or brittleness and smudge resistance of the wax film.

Apparently, when a volatile base is employed in these coatings in place of potassium hydroxide, for example, the volatile base is driven off as the coating is dried, leaving the wax particles in such a physical state that, although the smudge resistance of the sheet is high, the wax particles are readily transferred in response to local pressure. The wax globules are in intimate contact with each other, but are non-coalesced, and tend to remain on the surface of the sheet rather than penetrate the sheet. It is likely that the physical state of the coating is such that'there is formed a fragile trans-fer layer of wax weakly adhered to the surface of the base but efficiently removable in the form of an image. The non-coalesced nature of the wax layer weakens the coherence within this layer so that the transferred image is strong and sharply defined.

The transfer sheets of this invention are therefore prepared from coating compositions containing an aqueous emulsion of a hard wax and a non-film-forming resin, together with either a non-volatile or volatile base as referred to above. These transfer sheets possess the ability of being deactivated by application of heat, usually by temperatures above about 190 F. for about -10 seconds. Coatings which are deactivated in such a manner are permanently set and capable of only a very faint transfer. Moreover, they are highly resistant to smudging.

FIG. 1 shows a base 10, which may be either paper or plastic film having a transfer coating 11 prepared according to the present invention adhered thereto. The presence of the non-film-forming thermoplastic particles permits the transfer coating to be rendered nontransferable by the. application of heat.

Broadly, the transfer sheets of this invention are prepared by forming an aqueous dispersion, or emulsion, of a hard wax in admixture with a non-film-forming resin, a fatty acid, and a base, coating the emulsion onto a suitable base sheet, and drying the coating. Suitable coloring matter, such as a dye or pigment, can advantageously be incorporated into the dispersion. Additives, such as additional dispersing agents, solvents, or non-filmforming thermoplastic resins can also be incorporated in the dispersion.

The bases which can be used according to this. invention are capable of being reacted with a fatty acid under emulsion-forming conditions to form a fatty acid soap suitable as a dispersing or emulsifying agent. Amine soaps made from volatile bases are examples of emulsifying agents which can be advantageously employed. Ammonia, morpholine, N-methyl morpholine, 2,6-dimethyl morpholine, N-ethyl morpholine, N,N-dimethyl ethanolamine, N,N-diethyl ethan-olamine, 2-amino-2-methyl-1- propanol, N,N-dimethyl isopropanolamine, and the like, are some examples of volatile bases which can be used. Alkali metal soaps may also be used, i.e., prepared from alkali bases.

The fatty acids which can be used are those which are generally used in the art to prepare emulsifying agents for waxes and these can be readily determined by one skilled in the art. Examples of such fatty acids are oleic, palmitic, stearic, linoleic acids, and the like. Preferably, all or part of the fatty acid is blended with the melted wax and .the blend is then added to a hot solution containing water, a base, and any remaining portion of fatty acid. Any other suitable emulsifying or dispersing agent which functions as the fatty acid-base compounds described above can be used as recognized by those skilled in the art.

In forming the wax emulsion of this invention, a hard wax is employed. The term hard wax, as used herein, defines a class of waxes which is characterized by a particular degree of hardness as determined by the so-called Penetration Test. The Penetration Test measures the depth to which a weighted needle penetrates a sample of wax. The wax sample is melted by heating it to about 30 F. above its melting point and then cooled to 77 F. The hardness of the wax is measured with a penetrometer whereby a standard needle, under a load of grams, is applied to the wax sample for 5 seconds. The depth to which the needle penetrates the wax during the 5 seconds time interval is measured in tenths of a millimeter. If the needle penetrates the wax to a depth of 0.2 millimeter, the hardness rating of the wax is 2. If the needle penetrates the wax to a depth of 0.8 millimeter, the rating is 8, and so forth. The hard waxes which can be used according to this invention are those which have a rating from 0 to about 6, and include such waxes as Montan, Duroxon (a trademark for a light colored oxidized type of synthetic Fischer-Tropsch hydrocarbon wax, manufactured by Krupp Kohlenchemie G.m.b.H., Germany), Carnauba, and the like. The wax may be a petroleum, vegetable, synthetic or a mineral wax or a combination of waxes so long as the wax is stable, emulsifiable, and has the required degree of hardness and so long as its physical properties are not adversely altered when the emulsion is dried.

Various coloring agents such as organic or inorganic pigments are advantageously incorporated in the wax emulsions, such as, for example, phthalocyanine pigments (organic pigments which have a structural unit of 4 isoindole groups, (C HQC N, linked by 4 nitrogen atoms to form a conjugated chain), carbon black, such as Aquablak (a carbon black and a bone black aqueous dispersion marketed by Columbia Carbon Company),

. is not particularly critical.

Calcotones (highly dispersed pigment pastes manufactured 'by American Cyanamid Company), etc. The amount of pigment employed will depend upon the type of pigment being used, the color desired, etc. Three parts of a 35% dispersion of carbon black, for example, can advantageously. be used along with 29.6 parts of a 20% wax emulsion. Considerably higher or lower amounts of pigment can also be used.

The ability of the transfer coating to become deactivated by application of heat to the coating is accomplished by incorporating into the wax emulsion a small amount of a non-film-forming thermosplastic resin. The term non-filrn-forming resins as used herein refers to resins which will not form films at the temperatures used to apply and dry the coating. The amount of non-filmforming resin which can be used depends upon the particular resin used and upon the various other ingredients of the wax emulsion.

Various non-film-forming resins have been employed in amounts up to about 10% by weight and above, and preferably 20 to 30% by weight,

based on the amount of the wax plus fatty acid. Methyl methacrylate polymers, vinyl chloride-vinylidine chloride copolymers, polystyrene polymers (manufactured by The Borden Chemical Company under the trade name Polyco 2306), and styrene-butadiene copolymers (manufactured by Koppers Company, Inc. under the trade name Dylex K 55) are examples of non-film-forming resins which can be incorporated in the wax emulsions. Transfer coatings which are made from such resin containing emulsions and which have been heated to, for example, 360 F. for 5 seconds were found to be substantially deactivated and smudge proof. In forming the coating composition of this invention, the proportion of the various ingredients The most suitable amount of each ingredient which can be used can readily be determined by one skilled in the art. For example, the amount of volatile base used is advantageously only as much as is needed to react with the fatty acid, such as an amount chemically equivalent to that of the fatty acid. Higher amounts could be used however. Advantageously, about 5% by weight of the fatty acid, based on the wax, is used. The amount of fatty acid could probably be within the range of from about 3 to 10% or even beyond this range.

The combined weight of the wax and the fatty acid in the aqueous wax emulsion is advantageously around 20% by weight based on the total weight of the emulsion. Of course, a higher or lower proportion of the wax-fatty acid component may be employed depending upon the various ingredients used in the emulsion, etc. Potassium hydroxide can be used in amounts as described in United States Patent 2,931,752, mentioned above.

The wax emulsions of this invention are prepared by standard emulsifying techniques. Advantageously, part or all of the fatty acid is blended with the melted wax and the blend is then added to a hot solution containing water and avolatile base and/or a non-volatile base and the ingredients vigorously agitated. Coloring matter, nonfilm-forming resins, or other additives can then be added and thoroughly admixed. The emulsion is then applied V ties of the transfer coatings of this invention can be im- 7 proved by applying a suitable release coating to the base sheet prior to the application of the transfer coating. Examples of release coatings which can be used include colloidal silica such as that marketed by Monsanto under the trade name Syton, magnesium aluminum silicate, hydroxyethyl cellulose, sodium stearate, attapulgite clay,

4: acetylated starch, hydrated alumina, sodium silicate, and so forth.

The release coatings are particularly helpful where the receiving base or paper does not have particularly high receptive properties for the transfer coating.

The invention includes, if desired, a receptor paper for receiving the transferable image from the transfer coating. The receptor paper is described in my copending application Ser. No. 79,980, filed Jan. 3, 1961, now U.S. Patent No. 3,118,782, and assigned to the same assignee as this application. Such a receptor paper comprises a base sheet on which is coated a dispersion of calcium carbonate having a relative sedimentation volume of between about 2 and 6 in admixture with an adhesive and in which the pigment-adhesive ratio is between about 7 :1 and 2:1. Significantly improved transfer properties are obtained by using such a receptor sheet in conjunction with the transfer coating of this application whether a release coating is used under the transfer coating or not.

A particular embodiment of the invention involves coating one surface of the base sheet with the calcium carbonate coating composition described in application Ser. No. 79,980, now U.S. Patent No. 3,118,782, and then coating the other surface with the wax emulsion transfer coating described above. The calcium carbonate coating acts as a receptor coating for the transfer coating. Thus two sheets can be placed together so that the transfer coating of one sheet is in contact with the receptor coating of the other sheet so that when local pressure is applied to the transfer coating, an intensely clear image is transferred to the receptor coating at the point at which the pressure was applied.

The following examples show the manner in which the transfer sheets and the coating compositions employed in this invention can be made. These examples are given by way of illustration and are not intended in any way to limit the scope of the invention. Parts are by weight.

Example 1 Transfer sheets prepared from coating compositions containing a non-film-forming resin were prepared as follows: 1 part Aquablak B, 2 parts water, 0.05 part Pluronic L62, and 1.4 parts vinyl chloride-vinylidine chloride copolymer were admixed with 27.5 parts of a wax emulsion. The emulsion thus formed was applied to a paper base and dried. When the resulting transfer sheet was heated at 360 F. for 20 seconds, the sheet became deactivated and substantially non-transferable.

Example 11 Transfer sheets prepared from a coating composition containing a non-film-forming resin were prepared as follows: 0.77 part of carbon black and 0.4 part of polystyrene polymer were admixed with 20 parts of a wax emulsion. The emulsion thus formed was applied to a paper base. When the resulting transfer sheet was heated at 360 F. for 5-l0 seconds, the sheet became deactivated and substantially non-transferable. Additional transfer sheets were made according to the above procedure using a polyacrylate in place of the polystyrene polymer. The resulting transfer sheets became considerably deactivated after application of heat at 360 F. for 5 seconds. All of the transfer sheets prepared in accordance with Examples I and II were tested by placing the transfer coating in contact with a sheet of paper and pressure applied by means of a stylus to the backside of the paper having the transfer coating adhered thereto. The coating transferred readily in areas coextensive with the pressure. All of the transfer sheets prepared as set forth in Examples I and II were also tested using a receptor paper as defined in copending application Ser. No. 79,980, now U.S. Patent No. 3,118,782, referred to above, and in each instance, the transfer of the image was considerably improved.

Ordinarily the non-film-forming resin employed in accordance with this invention is used in an amount which is at least sufliciently high to deactivate the transfer coating when the transfer sheet is ultimately heated to a temperature at Which the non-film-forming resin is softened. Excess amounts of the non-film-forming resin can, of course, be employed, as well known to those skilled in the art, i.e., advantageously up to about 50% by weight of Y the coating.

I claim:

1. The method of preparing a transfer sheet which comprises coating a suitable base sheet with a coating composition comprising an aqueous emulsion of a hard wax, a non-film-forming resin, a fatty acid, and a base which is reactive with the fatty acid, and thereafter drying the coating onto the base sheet, said resin being non-filmforming under the conditions used to coat said composition to said base and to dry said coating and being capable of deactivating the transfer coating when the transfer sheet is ultimately heated to a temperature at which the non-film-forming resin is softened.

2. The method of claim 1 in which coloring matter is incorporated into the wax emulsion.

3. The method of claim 2 in which the coloring is carbon black.

4. The method of transferring images from a transfer sheet to a receptor sheet which comprises coating a base sheet with a composition comprising an aqueous emulsion of a hard wax, a non-film-forming resin, a fatty acid, and a base which is reactive with the fatty acid, drying the coating onto the base sheet, said resin being non-filmforming under the conditions used to coat said composition on said base and to dry said coating placing the transfer coating of the transfer sheet in contact with a receptor sheet, applying local pressure to the assembly to effect the transfer of an image from the coating to the receptor sheet in areas coextensive with the applied pressure, and subsequently heating the transfer sheet to a temperature above the softening point of the non-filmforming resin for a suflicient length of time to destroy the transfer properties of the transfer sheet.

5. The process of claim 4 in which the transfer sheet is heated to a temperature above about 190 F.

6. The method of transferring images from a transfer sheet to a receptor sheet which comprises coating a base sheet with a composition comprising an aqueous V emulsion of a hard wax, a non-film-forming resin, a fatty acid, and a base which is reactive with the fatty acid, drying the coating onto the base sheet, said resin being non-film-forming under the conditions used to coat said composition on said base and to dry said coating placing the transfer coating of the transfer sheet in contact with a receptor sheet, applying local pressure to the assembly to effect the transfer of an image from the coating to the receptor sheet in areas co-extensive with the applied pressure, and subsequently heating the receptor sheet to a temperature above the softening point of the non-film-forming resin of the transferred image for a sufficient length of time to render the transferred image afiixed to the receptor sheet.

7. The process of claim 6 in which the receptor sheet is heated to a temperature above about F.

8. Transfer sheets prepared according to the method of claim 1.

9. Transfer sheets prepared according to the method of claim 2.

10. Transfer sheets prepared according to the method of claim 3.

References Cited by the Examiner UNITED STATES PATENTS 655,067 7/1900 Dun Lany 117-361 1,328,188 l/1920 Ohashi 1l736.1 2,931,752 4/ 1960 Newman 11736.1 3,170,809 2/1965 Barbour 117-361 MURRAY KATZ, Primary Examiner.

Claims (1)

1. THE METHOD OF PREPARING A TRANSFER SHEET WHICH COMPRISES COATING A SUITABLE BASE SHEET WITH A COATING COMPOSITION COMPRISING AN AQUEOUS EMULSION OF A HARD WAX, A NON-FILM-FORMING RESIN, A FATTY ACID, AND A BASE WHICH IS REACTIVE WITH THE FATTY ACID, AND THEREAFTER DRYING THE COATING ONTO THE BASE SHEET, SAID RESIN BEING NON-FILMFORMING UNDER THE CONDITIONS USED TO COAT SAID COMPOSITION TO SAID BASE AND TO DRY SAID COATING AND BEING CAPABLE OF DEACTIVATING THE TRANSFER COATING WHEN THE TRANSFER SHEET IS ULTIMATELY HEATED TO A TEMPERATURE AT WHICH THE NON-FILM-FORMING RESIN IS SOFTENED.

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