US2220549A - Art of transferring preformed films to various bases - Google Patents

Description

Patented Nov. 5, 1940 UNITED STATES ART OF TRANSFERRING .PREFORM'ED FIIMS TO VARIOUS BASES Milton 0. Schur and Benjamin G. Hoos, Berlin,

N. H., assignors to Brown Company, Berlin, N. H., a corporation of Maine No Drawing. Application June 10, 1937, Serial No. 147,490

2 Claims.

This invention relates to the art of transferring preformed films to various bases and deals more specifically with preformed films of materials capable of being gelled by or dissolved in volatile organic solvents. While the method hereof might be applied in transferring preformed films to various bases, including leather and many kinds of fabric, it is particularly useful in providing an artificial. leather consisting essentially of a rubber-impregnated felt base with a smooth and attractive wear layer or surface simulating in appearance and approximating in moisture-proofness, scuff-resistance, handle or feel, and other physical properties, the grain or enamel side of such natural leather as calfskin. In this connection, it should be noted that the transferred film must be of extreme thinness or light weight and yet be free from even minute blemishes or imperfections especially when transferred to a rubber-impregnated felt base to serve in lieu of natural calfskin or the like for such exacting purpose as making ladies handbags.

Inasmuch as the film-forming materials used for the purposes hereof are soluble in volatile organic solvents but include materials falling into such different chemical categories as cellulose esters (e. g. nitrocellulose), cellulose ethers (e. g. ethyl cellulose), and artificial resins, (e. g. vinyl resins), we shall for convenience of designation hereinafter use the term lacquer as applied to all of such materials. Indeed, organic solvent solutions of such materials, from which the films hereof are prepared, are common called lacquers by reason of their usefulness in depositing so-calIed lacquer films on various surfaces to be protected against weathering or wearing influences and/or to present a finished or. ornamental appearance.

The transfer of a lacquer film to a rubber-impregnated felt base is by no means a simple problem when the film-weight is low, say, less than 20 grams per square foot, and when the transferred film must additionally be free from imperfections and yet be made to adhere tenaciously to such base. When one stops to consider also that tenacious adherence of the transferred film to such base can be had only by pressing the film while in solvent-activated condition against such base, that is, while the film is especially susceptible to marring or crushing, he realizes at once some of the troublesome aspects of the problem.

After considerable work on the foregoing problem, we have found it advantageous to preform the lacquer film on a smooth metal plate or its equivalent; to activate the film, preferably while still on the plate, with alacquer solvent admixed with a large amount of non-solvent, preferably a preponderant amount of the non-solvent; to press the solvent-activated film, preferably plate and all, against the rubber impregnated felt base; to dry, preferably air-dry, the film thus pressed against the base; and finally to strip the base from the plate, preferably after exposure of the pressed-together layers to an atmosphere of warm air saturated with water vapor. By properly performing such a method, we have found that not only is a transfer of the lacquer film to the base accomplished but that the transferred film is to all intents and purposes free from surface imperfections and is very tenaciously adherent to the base.

In carrying out the method hereof, the lacquer film may be preformed by thinly applying a lacquer solution in any suitable way on a smooth metal plate, for instance, a stainless steel plate, and then drying the applied lacquer under suitable temperature conditions. Specifically, the usual nitrocellulose lacquers of commerce may be employed; and they may be of such controlled solids content and viscosity or fluency that a momentary dipping of the metal plate thereinto will leave, after drainage of the excess lacquer from thedipped plate maintained in substantially vertical position, a lacquer film or deposit oi the desired thickness or weight and-smoothness. If desired, the lacquers may be sprayed, painted, or otherwise applied as a substantially uniform film of the appropriate thinness on the metal plate. The lacquer film is then dried on the metal plate, preferably under temperature conditions below the boiling point of such volatile solvents as may be present in the lacquer solution, thereby avoiding pin holes or other imperfections in the film.

The activation of the lacquer film after having thus been dried against the metal plate is preferably effected by dipping the plate into an activating bath under conditions designed to develop the requisite adhesiveness on the exposed film face to be pressed against the rubber-impregnated felt base. While various factors, including thetemperature of the activating bath, the length of time the film is kept therein, and the pressure exerted when the activated film is laid on the base, should be carefully controlled for the securement' of the results desired herein, the most important single factor is perhaps the composition of the activating liquid; and such com-- position depends, among other considerations, upon the thickness of the lacquer film, upon the porosity of the base to which its transfer is to be effected, upon the pressure exerted in transferring the film to the base, etc. A typical activating bath, which has been found to give consistently excellent results with nitrocellulose films weighing about 6 to 8 grams per square foot, is composed by weight of 5 parts of ethyl acetate, 5 parts of cellosolve acetate, and 90 parts of 95% ethyl alcoliol. It might be noted that the ethyl alcohol is the inactive or non-solvent ingredient in such bath. With heavier film it becomes necessary to increase the proportions of ethyl acetate and/or cellosolve acetate in the activating bath, other factors being maintained constant. The trade-mark cellosolve designates an organic liquid solvent whose chemical name is ethylene glycol mono-ethyl ether. Cellosolve" acetate is simply the acetate of such ether.

As to the pressure exerted during the transfer of the activated film to the rubber-impregnated felt base, it is to be observed that, although heavy pressure tends to improve the tenacity with which the film adheres to the base,

yet the activated film may be marred or crushed under unduly heavy pressure, especially when the film weight is low and when the base is of comparatively rough texture and/or high porosity. Since the rubber-impregnated felt bases designed to carry the transferred film hereof desirably consist of highly absorptive webs of interfelted cellulose fibers, for instance, refined wood pulp fibers of high alpha cellulose content, and are impregnated with rubber very considerably short of complete saturation or filling of their pores or voids, the pressure exerted in laying the activated film on such bases should be carefully controlled to be well below that inlurious to the film. For nitrocellulose films that weigh about 6 to 8 grams per square foot and that are to be transferred to a rubber-impregnated felt of the character just described, the activating solution or bath may advantageously be composed by weight of 15 parts of cellosolve" acetate, 7.5 parts of ethyl acetate, and 77.5- parts of toluol. The inactive or non-solvent ingredient in such bath is the toluol. It has been found that such activating bath possessed the important advantage over that previously described in that it makes for greater tolerance in the range of pressures applicable to the activated film as it is being laid onto the rubber-impregnated felt base while avoiding injury to the film.

Once the activated film and the smooth metal plate backing therefor have been pressed and dried against the rubber-impregnated artificial leather base, such film evidently has vastly greater grip or hold on the base than on the metal plate.

"It is hence not surprising that the base can be stripped or removed with the film cleanly transferred thereto from the metal plate, especially when stripping is facilitated by exposing the superposed layers or plies for a short period, say, about a half hour, in an atmosphere of warm air saturated with water vapor, which atmosphere probably diffuses in between the film and plate surfaces and thus weakens the already comparatively weak bond or hold of the film on the smooth plate surface.

It is well to note the particular kind of adhesive activation effected on the preformed lacquer films hereof, that is, the condition of the activated films after they have been steeped or soaked in the activating volatile organic liquid media employed for the purposes hereof. In this connection, it should be observed that such activating media cause actual gelling of the lacquer films and that the films are applied to the receiving bases in such gelled condition. To show that the lacquer films hereof are actually gelled before they are applied to the receiving bases, we submerged strips of preformed nitrocellulose film after they had been removed from the forming background in the activating baths hereinbefore described, namely a bath in which alcohol served as the inactive ingredient and in a bath in which toluol served as the inactive ingredient. For purposes of comparison we also put strips of the preformed film into ordinary so-called thinner for nitrocellulose lacquer. In the case of the activating liquid media hereof, the strips of nitrocellulose film were intact even after they had been in contact with such media for one-half hour and longer and despite the fact that the containing vessels were mildly shaken during this period. In the case of the lacquer thinner, on the other hand, the strips of nitrocellulose film began to dissolve in a few seconds and they were badly disintegrated within a minute. When the strips of nitro-cellulose film after exposure to the activating liquid media hereof were rubbed with a stirring rod, they were found to be very slimy and to have the appearance and other earmarks of being swollen and gelled. It is thus seen that the activating or conditioning liquid media hereof are truly swelling and/or gelling agents for the preformed lacquer films rather than powerful solvents of such films. While the activating or conditioning liqiuid media hereof may act as solvents for the preformed lacquer films under some conditions of use, for instance, if heated and/or if kept in contact with such films for a sufficiently long time and/or if vigorously agitated, yet they are used pursuant to the invention hereof under conditions such that they swell and/or gelatinize such films while such films are maintained intact and substantially undissolvedf Accordingly, the activating liquid media hereof may well comprehend single volatile organic liquids in contradistinction to the mixtures of such liquids hereinbefore described.

Although the invention hereof has been described more particularly in connection with the transfer of preformed lacquer films to an artificial leather base consisting essentially of rubber-impregnated waterlaid felt, it may be applied also in transferring such films to porous fibrous bases generally and to fibrous bases impregnated with binders other than rubber. When a binder-impregnated waterlaid felt base is coated with lacquer, as opposed. to being provided with a transferred lacquer film by the invention hereof, the uneven texture or internal structure of such base will show through the coating when the weight of the coating or film is less than about 20 grams per square foot, especially when such base is unembossed. The undesirable revelation or "show-through of the uneven texture or surface irregularities in an impregnated waterlaid felt base is especially noticeable when the base contains more than about 25% binder, based on the Weight of fiber, and is possessed of substantial residual porosity. Despite the fact that the transferred lacquer films hereof are of a weight not exceeding about 20 grams per square foot and despite the fact that the artificial leather bases to which they are transferred by the invention hereof may consist of rubber-impregnated waterlaid felts containing distinctly more than 25% rubber, based on the weight of fiber, and possessed of substantial residual porosity, such transferred lacquer films besides being tenaciously adherent to such artificial leather bases and being free from blemishes serve the highly desirable purpose of completely masking the uneven .tex ture or internal structure of such base.

Artificial leathers to which films have been transferred by the method hereof may be used in various fields in lieu of such natural leather as calfskin. For instance, they have proven acceptable to manufacturers of better grades of ladies handbags; and handbags made from the finished artificial leathers hereof are now available on the market with the designation that they are made from Solkalf, which quoted term is the trade-mark for such artificial leathers. The lacquer films transferred by the methods hereof may, of course, present such color as may be desired by adding pigment and/or dye of the appropriate color and in appropriate amount to the lacquer from which such films are formed. It is to be understood that the foregoing examples of the method hereof are subject to considerable variation as regards the temperature and composition of the activating bath, the length of time the preformed film is kept in the bath, the pressure applied when the activated film is laid on the base, the particular kind of lacquer film being transferred, the particular base to which transfer of the film is effected, the extent to which the activated film is dried against the base before the base is stripped with the film transferred thereto from the smooth metal plate or its equivalent, etc. while still falling within the purview of the present invention as defined by the appended claims. Again, it is to be understood that adhesive substances such as shellac, resins, or the like may be added to the activating medium or bath hereof without departing from the spirit or scope of the instant invention. In such case, too, it is necessary that the activating medium or bath swell and gell the film properly, for it has been found that the use of cementing substances in such medium does not makefor the desired tenacity of bond between the lacquer film and the base to which it is transferred unless the film itself has been adhesively activated to the proper extent, that is, has been transformed to a swollen and gelled condition. While a smooth metal plate has been described as the smooth background for preforming the lacquer films hereof, since such a plate may be conveniently and economically handled in actual practice, it should be understood that other smooth backgrounds might be used for preforming such films and that;

the expression smooth background as used in the appended claims is meant to include various smooth backgrounds serviceable for preforming the films, for instance, metal, glass, porcelain, glazed papers, or the like to which lacquer films adhere comparatively poorly; and it might also be noted that the background might be etched or embossed to impart the desired grain to the film. It is not necessary that the background be rigid or inflexible, since a flexible steel belt, transfer papers, etc., might be used for preforming the lacquer films hereof.

-We claim:

1. A method of finishing a rubber-impregnated felt base witha lacquer film soluble in a volatile organic solvent, which comprises preforming such film on a smooth background'at a weight not exceeding about grams per square foot, said background having much lower adhesive affinity for said film than said base, dipping the background carrying such lacquer film into a liquid bath containing a volatile organic solvent of said lacquer and a volatile organic non-solvent of said lacquer to activate adhesively the surface of such film, pressing said activated film, background and all, against the surface of said rubber-impregnated felt base, drying the film against said base surface, and stripping the base with the film cleanly transferred thereto from said background.

2. A method of finishing a rubber-impregnated felt base of high residual porosity with a lacquer film soluble in a volatile organic solvent, which comprises preforming such film on a smooth background at a weight not exceeding about 20 grams per square foot, said background having much lower adhesive affinity for said film than said base, dipping the background carrying such base surface, exposing the superposed layers to warm moist air, and stripping the base with the film cleanly transferred thereto from said background.

MILTON O. SCHUR. BENJAMIN G.- HOOS.