Abstract:
Crushed foam coated leather and leather-like materials characterized by excellent foam adherence, are prepared by flowing foamed compounded polymeric latices into contact with a leather or leather-like substrate and partially drying same, followed by compressive crushing of the dried foam, plating or embossing to achieve optimum adhesion, and further heating and curing to develop maximum physical properties.

Description:
BACKGROUND OF THE INVENTION 
     This is a continuation-in-part of U.S. Pat. application Ser. No. 410,837 filed Oct. 29, 1973, now abandoned which in turn is a continuation-in-part of Ser. No. 123,871 filed Mar. 12, 1971, now abandoned. 
    
    
     The present invention relates to crushed foam coated leather and leather substitutes useful in any area natural leather is employed; for example, shoes, purses garments, belts, upholstery, wallets and the like. In another aspect, it relates to a crushed foam coating on such materials and methods of accomplishing same. 
     Present techniques for the coating of leather and leather substitutes leave much to be desired, often involving as many as 5 to 6 coatings in order to achieve a tough, abrasion resistant topcoat on leathers of poorer quality. Even after coating, there still may be surface reflecting imperfections in the substrate. 
     Thus, in the art of finishing leather and leather substitutes, means for upgrading low grade materials is still being sought after. Also, much sought after is an attractive low cost alternative to the microporous urethane laminate presently used to surface the nonwoven base web of poromeric materials, such as Corfam. 
     Textile fabrics have been successfully coated with foamed polymeric compositions or foamable polymeric compositions which foam on the textile (U.S. Pat. No. 3,527,654). This procedure has not been successfully adapted to the nonwoven substrates, such as the leather finishing arts, because the balance of properties required for leather and leather-substitutes is different and more difficult to achieve than with conventional textile fabrics. 
     We have found that the properties of the crushed foam coated grain side leather and leather splits, when prepared according to the teachings of this invention, are better than those obtained with conventional systems. For example, the present techniques involve but a single coating and the thus-coated substrates are not stiffened by the coating. Also, such techniques may be used in a continuous production line. This invention eliminates many of the operations presently being employed in standard leather finishing methods. 
     One advantage of the present invention is that it provides crushed foam coated leather and leather-like materials rivaling natural leather. Also, this invention provides a more economical process for upgrading leather substrates. 
     Another advantage of this method is to mask many of the natural defects in the leather substrate. Still another advantage is to provide a controlled build up of the coating which results in lack of &#34;photographing&#34; of the underlying web. 
     SUMMARY 
     Broadly, the crushed foam coated leather and leather substitutes are prepared as follows: 
     A. foaming a compounded polymeric latex with a foam generator; 
     B. coating the foam on the leather or leather substitute at a thickness in the range of from 5 mils to about 60 mils; 
     C. partially drying the foam coating on the leather or leather substitutes at a temperature in the range of from about 120° F. to about 400° F. and, preferably, at a temperature in the range of from 125° F. to 300° F.; and simultaneously or separately: 
     D. crushing the partially dried foam coating at a pressure in the range of from 1 to about 50 psi; and 
     E. embossing and curing the crushed foam coated leather or leather substitutes to achieve optimum adhesion of the crushed foam coating to the substrate at a pressure in the range of from about 50 to 2000 psi at a temperature in the range of from 100° to about 200° F. 
     Thus, in accordance with the present invention, a leather or leather substitute, such as a substrate suitable for making a poromeric or other leather substitutes, has a crushed foam material securely adhered thereto. The term &#34;leather substitute&#34;, is as defined in U.S. Pat. Nos. 3,537,883; 3,100,721 and 3,000,757. 
     DETAILED DESCRIPTION 
     The latex compositions that produce the foams used in the present invention contain a copolymer prepared from the following groups of monomers: 
     i. 20-90% of butyl acrylate, 2-ethylhexyl acrylate, ethylene or any mixtures thereof; 
     ii. 40-95% of ethyl acrylate, vinyl chloride or any mixtures thereof; 
     iii. 20-50% of methyl methacrylate, acrylonitrile, styrene, vinylidene chloride or any mixtures thereof; 
     iv. 10-30% of methyl acrylate, butyl methacrylate, vinyl acetate or any mixtures thereof; 
     v. 0.1-5% of acrylic acid, itaconic acid, methacrylic acid or any mixtures thereof; and 
     vi. 3-7% of hydroxyethyl methacrylate, methylol acrylamide, acrylamide, methylol methacrylamide or acrolein, or any mixtures thereof. 
     The copolymer may be prepared from any combination of the foregoing monomers provided that the sum thereof is 100%. It is not required that a monomer from each of the groups be present but the copolymers preferably contain at least one monomer from group vi to facilitate cross-linking. If more than one monomer is selected from any one group, such mixture must nevertheless not be outside the % range for that group of monomers. 
     Especially preferred are copolymers having the following compositions: 80 butyl acrylate/15 acrylonitrile/2 itaconic acid/3 methylol acrylamide; 66 butyl acrylate/30 methyl methacrylate/2 acrylic acid/2 acrolein; 95 ethyl acrylate/1.5 acrylic acid/3.5 methylol methacrylamide; 40 butyl acrylate/33 ethyl acrylate/20 methyl acrylate/2 itaconic acid/5 hydroxyethyl methacrylate; 86 ethyl acrylate/10 acrylonitrile/2.7 methylol acrylamide/1.3 acrylamide; 96 ethyl acrylate/3.5 acrylamide/0.5 acrylic acid. 
     The polymeric latices preferably are compounded with an aminoplast cross-linking agent prior to foaming. Such reagents include water soluble formaldehyde condensates with urea, melamine or N,N&#39;-ethyleneurea. The aminoplast is used in an amount of about 1-10% by weight based on the copolymer solids of the latex. A preferred resin is a melamine-formaldehyde resin-forming precondensate, preferably used in an amount of about 3-5% by weight on copolymer solids. Certain of the copolymers will be self-crosslinking without the aminoplast, such as copolymers containing acrolein. The cross-linking helps to reduce tack and thereby eliminates or minimizes &#34;blocking&#34;-the sticking together of folds of foam-coated substrates. Therefore, cross-linking particularly by addition of the aminoplast, is preferred in the foamed polymeric emulsions of the invention. 
     A crushed foam coating means a coating which, after obtaining a cellular structure, is compressed by crushing or embossing. It is essential in the preparation of the crushed foam coated leather and leather substitutes that the embossed products possess a sharp and well-defined underlying pattern which is essential in yielding the leather-like surface and aesthetics required by the industry. This requires that after the system is crushed there will be minimal bounce back of the foam so that there will be substantially no loss of pattern definition. In a similar vein, if a smooth plate is used, a smooth appearance should be obtained. The crushed foam has a thickness in the range from about 3 mils to 25 mils with the preferred range being from about 5 mils to about 20 mils. 
     In the sequence of steps, it is necessary to conduct Steps (A) and (B) separately; however, it is possible to provide for various combinations of the subsequent crushing, embossing and final curing steps. 
     It is possible to crush and emboss in substantially one operation, i.e., to combine Steps (D) and (E) under suitable heat and pressure. 
     When a leather substitute is employed, postcuring after embossing and drying may be necessary to yield a product with improved physical performance in comparison to a product which is not postcured. This postcuring step completes many crosslinking reactions both in the foam and substrate itself. This postcuring is conducted at a temperature in the range of from 150° to about 500° F. 
     Regarding the maximum pressures that the substrate itself will tolerate: 
     On leather splits, for example, trials have been conducted up to 40 to 50 tons ram pressure, which is the equivalent of about one-thousand lbs./sq.in. On poromeric materials, however, or other types of leather substitutes, such high pressures are not required to achieve the embossing. Preferably, one would increase temperature rather than pressure to achieve satisfactory crushing and curing. 
     With material such as leather, splits or grain leathers, normally the preference here is for higher pressures such as 500 to 2000 psi, and preferably 500 to 1200 psi. 
     The pressure and temperatures that would be used on a commerical basis will depend on what the skilled artisan determines as providing a proper visual and textural effect for the system, in addition to ensuring satisfactory adhesion. 
     The pressures and temperatures will vary, depending upon the nature of the substrate, the smoothness of its surface, and further depending upon the inherent degree of adhesion of the crushed foam coating to different types of substrates. For example, with different types of leather, the optimum conditions will depend upon the manner of tanning. Different temperature and pressure combinations will be required to obtain adequate adhesion for a particular substrate. 
     Thus, we have set forth the optimum conditions for preparing a crushed foam coated leather and leather substitute. It can be seen how the various combinations of these steps can be put together by varying temperature and pressure to accomplish an acceptable product for a given type of substrate. 
     For example, where engaged in coating a web for a poromeric base, one could crush, emboss and cure in one operation, by applying a pressure in the range from 5 to 500 psi at a temperature in the range of from 175° to 350° F. With low crushing pressures it is desirable to operate at a temperature in the range of from about 300° to 350° F. to ensure adequate deformation of the web, if the web is bound by a polymer-like material, which itself is cured to some extent. These ranges apply to synthetic substrates, for the most part. Thus, in the range of 300° to 350° F., with a pressure in the range of 50 to 1000 psi, it is possible to crush the foam, emboss in the pattern and cure in one operation. 
     One can accomplish the same objective with a leather material by utilizing a pressure in the range of from 500 to 1200 psi, at a temperature in the range of from 175° to 300° F., whereby this would in substantially one operation, cause crushing, embossing and curing. 
     One can crush at room temperature, with minimal pressure, so as to place the substrate in a form that it can be handled. Then it goes through a combined embossing and curing step in one operation, but utilizing conditions similar to that just described for the crushing, embossing and curing sequence. 
     For embossing, the plate is either smooth, or grained, or can be textured to any of the various prints available for leather finishing. 
     It is possible to crush, separately from the embossing and curing steps, with almost any of the substrates of interest. One can crush and emboss in one operation with all the substrates, but with the poromerics, it is usual that curing occurs in the same operation. In the case of leathers, one can crush and emboss at low enough temperatures so as to require a subsequent curing step. 
     In Table I there is set forth a typical formulation for the foams that are useful in the coating of a nonwoven web used as a base for a poromeric material, side leather, and split leather. 
     
                                           TABLE I__________________________________________________________________________               Nonwoven Web                         Split               and Side Leather                         LeatherFormulation         (parts by wt.)                         (parts by wt.)__________________________________________________________________________Latices A or B      100.0     100.0China Clay          15.0      15.0Ammonium Stearate 33%               7.0       7.0 (Foam Stabilizer)Aerotex MW melamine/HCHO Condensate               2.3       2.3 (Amer. Cyanamid Co.)Ammonium Hydroxide 28%               2.0       2.0Colorants: PRIMAL® Black 110        15.0 85 Pts. PRIMAL® White          Beige in               15.0 10 Pts. PRIMAL® Ochre          Mixture  5 Pts. PRIMAL® D. BrownTOTALS              141.3     141.3__________________________________________________________________________ PRIMAL® is a registered trademark of the Rohm and Haas Company for a series of various pigments in a vehicle of a water soluble polymer binder a sulfonated tallow, an auxiliary dispersant and water. 
    
     The formulations were foam-coated on various substrates, including a (1) nonwoven web (Corfam) from Fleming-Joffe Company, (2) PRIMAL ®571 -- Impregnated Griess-Pfleger Combotan leather, (3) chrome tanned work shoe splits from Lannom Mfg. Co., (4) vegetable tanned splits, and (5) Hartland&#39;s chrome tanned splits. 
     The following copolymers were in the latices of the formulations (the monomer amounts are in parts by weight): 
     Latex A: 86 ethyl acrylate/10 acrylonitrile/2.7 methylol acrylamide/1.3 acrylamide 
     Latex B: 96 ethyl acrylate/3.5 acrylamide/0.5 acrylic acid 
     The formulations were partially cured and niprolled (crushed) smooth and then nip-rolled (crushed) over Warren&#39;s morocco-grained release paper to achieve a texture. After final curing, one set was topcoated with a vinyl urethane lacquer while another set was left without a topcoat. 
     By substituting the following latices for Latex A or B similar formulations and coated substrates may be obtained: 80 butyl acrylate/15 acrylonitrile/2 itaconic acid/3 methylol acrylamide; 66 butyl acrylate/30 methyl methacrylate/2 acrylic acid/2 acrolein; 95 ethyl acrylate/1.5 acrylic acid/3.5 methylol methacrylamide; 40 butyl acrylate/33 ethyl acrylate/20 methyl acrylate/2 itaconic acid/5 hydroxyethyl methacrylate. 
    
    
     The following physical tests were run on the foregoing crushed foam-coated substrates: Taber abrasion, Mul-Tech wet soak resistance, Satra Dome, Bally Flex, and Cold Crack (-20° C.) flexibility. Certain of the results are described immediately below and the data is summarized in Table II. 
     1. CORFAM WEB -- The Latex B-containing crushed foam-coated nonwoven web, nip-rolled smooth, and topcoated with a vinyl urethane lacquer had a good balance of properties and met commercial requirements. 
     
         ______________________________________Typical            Crushed FoamCommercial Requirements              Coating Results______________________________________Good Wet Bally Flex adhesion              &gt;40,000 Wet Bally FlexesGood Wet Bally Flex flexibility              &gt;40,000 Wet Bally FlexesCold Crack Resistance at -20° C.              No cracking at -28.9° C.Embossibility      GoodReceptivity to Topcoats              Good______________________________________ 
    
     In addition, this system was passed over 1000 cycles on the Tabor Abraser without wear. It passed 750 cycles on the Mul-Tech, and passed the Satra Dome Test. 
     2. CORRECTED GRAIN SIDE LEATHER -- The Latex B-containing foam coating, nip-rolled smooth (crushed) on Griess-Pfleger&#39;s corrected grain side leather with PRIMAL 571 impregnated and topped with a vinyl urethane lacquer resulted in a good balance of properties. Results (following) are better than usually obtained with a conventional coating system: 
     
         ______________________________________           Crushed Foam Coating Results______________________________________Mul-Tech Wet Soak Resistance               430 CyclesTaber Abrasion Resistance             &gt;1000 CyclesCold Crack Flexibility             Slight CrackingAppearance        Smooth and Well-filledCoverage          Excellent______________________________________ 
    
     4. SPLIT LEATHER -- The Latex A-containing foam coating nip-rolled smooth (crushed) on a reverse side of a vegetable split also had a good balance of properties. Results (following) are better than usually obtained with a conventional coating system: 
     
         ______________________________________           Crushed Foam Coating Results______________________________________Appearance        Smooth and well filledCoverage          ExcellentTaber Abrasion Resistance             600 CyclesMul-Tech Wet Soak Resistance             270 CyclesBally Flex Flexibility (Wet)             Slight cracking______________________________________ 
    
     Table II presents the physical measurements made on a number of typical substrates which had been crushed foam-coated, according to the present invention, and demonstrates the significant results obtained. 
     Based on the data in Table II, certain meaningful comments are possible. 
     In general: The Latex A-containing foam coating resulted in good wet soak resistance and abrasion resistance, but poor Bally Flex and Cold Crack flexibility. The opposite is true with the Latex B-containing foam coatings. On the nonwoven web and side leather substrates, the best balance of properties is obtained with the Latex B-containing coating, nip-rolled smooth, and topcoated with lacquer. This system results in good Taber abrasion resistance, the best Bally Flex and Cold Crack flexibility. The Mul-Tech wet soak resistance is not as good as its Latex A counterpart, but is the best of the Latex B foam coatings. 
     Topcoat: The Latex B formulation combined with the vinyl urethane lacquer topcoat considerably upgraded the wet soak resistance, Taber abrasion, and in some cases, flexibility. 
     Surface Texture: Some of the physical parameters appear to have been affected by the surface texture (smooth or embossed). With a Latex A-containing coating, the smooth-coated, untopped Corfam web shows less cold cracking than its embossed counterpart. The Mul-Tech wet soak resistance of the embossed and untopped Latex A-containing coating was better than its smooth-coated counterpart; however, the reverse was true when it was topcoated. 
     Wet-soak Resistance: With the Latex B-containing coating, both the smooth and embossed untopped nonwoven web had equally poor Mul-Tech wet soak resistance, while the smooth topcoated nonwoven web had much better wet soak resistance than its embossed counterpart. The other substrates were all nip-rolled smooth. 
     Substrates: The nonwoven web is the easiest to foam coat as it is available in a continuous roll of uniform thickness. The impregnated side leathers give some mechanical handling problems because of low spots in the leather. Certain splits are more difficult to foam-coat, because the coating does not adhere to the loose &#34;fuzz&#34; on a heavily sueded surface. However, a vegetable tanned split which was foam coated with the Latex A-containing coating on a smoother surface and then topcoated, resulted in good abrasion resistance, respectable wet soak resistance, and wet Bally Flex flexibility, but to be foam coated, splits will have to be free of dust or &#34;fuzz&#34; to obtain adequate adhesion. 
     EXAMPLE II 
     Split leather was foam-coated with a composition containing Latex A, the coating was partially dried, and crushed at less than 5 psi and at room temperature. One piece was embossed at a pressure of 550 psi and a temperature of 200° F., and was subsequently cured at a temperature of 325° F. Another piece was embossed at a pressure of 1000 psi and a temperature of 200° F., and subsequently cured at a temperature of 325° F. Both sections were then topcoated with conventional side leather finishing materials. 
     The adhesion of the foam coating to the substrate for the low pressure embossed was inadequate, while the adhesion of the foam coating embossed at the higher pressure was adequate. 
     A third section was first cured at 325° F., and then embossed at a pressure of 1000 psi and a temperature of 200° F. The adhesion of the foam coating to the substrate for this process was also inadequate. The trial demonstrates that the sequence of operation described and the conditions of pressure and temperature set forth are necessary to achieve the desired end results. 
     EXAMPLE III 
     A piece of a nonwoven web coated with a foam coating composition, containing Latex B, was partially dried at 225° F., crushed with minimal pressure, subsequently topcoated with a urethane lacquer, and cured at 300° F. Another section was smooth embossed at a pressure of 10 psi and a temperature of 350° F. prior to topcoating. 
     The foam coating of the former section showed inadequate adhesion to the web, while the foam coating embossed according to the second sequence, showed adequate adhesion. 
     This trial further demonstrates the need for adequate pressure, combined with a temperature during embosssing, to adhieve the desired end result, including the critical good adhesion of the crushed foam coat. 
     
                                           TABLE II__________________________________________________________________________Physicals of Representative Acrylic Crushed Foam-Coated Substrates   Latex          Taber Abrasion.sup.1                            Mul-Tech Wet Soak Resistance.sup.2                                             Wet Bally   Used           Initial   Initial                                 Cycles      Flex  Cracking   in       Surface                  Failure                      % Wear at                            Failure                                 at 10%                                      % Damage                                             Amount                                                   AmountSubstrate   Foam       Topcoat            Texture                  Cycles                      1000 cycles                            Cycles                                 Failure                                      at/Cycles                                             Failure                                                   Cracking__________________________________________________________________________Non-Woven Web   L-A None Smooth                  215 70    30   40   100/100                                             Moderate                                                   ModerateNon-Woven Web   L-A Lacquer            Smooth    None  &gt;10,000.sup.6                                 &gt;10,000.sup.6                                      None/10,000.sup.6                                             Moderate                                                   Consid.Non-Woven Web   L-A None Embossed                  185 20    110  200   10/200                                             Moderate                                                   Consid.Non-Woven Web   L-A Lacquer            Embossed  None  300  &gt;1,000                                      &gt;10/1000                                             Moderate                                                   Consid.Non-Woven Web   L-B None Smooth                  165 100 at 550                            20   23   100/50 Slight                                                   Very Slight                      cyclesNon-Woven Web   L-B Lacquer            Smooth    None  750  800   100/1000                                             Very Slight                                                   NoneNon-Woven Web   L-B None Embossed                  120 100 at 350                            15   20   100/50 Slight                                                   Very Slight                      cyclesNon-Woven Web   L-B Lacquer            Embossed  None  65   80    15/100                                             Very Slight                                                   NoneImpregnated   L-A None Smooth    None  170  200   10/200                                             None  Consid.Side LeatherImpregnated   L-A Lacquer            Smooth    None  &gt;1,000                                 &gt;1,000                                      None/1000                                             None  Consid.Side LeatherImpregnated   L-B None Smooth    None  35   40    90/100                                             None  NoneSide LeatherImpregnated   L-B Lacquer            Smooth    None  430  450   90/500                                             Blister.sup.4                                                   SlightSide LeatherReverse SideVegetable Split   L-A None Smooth                  300 40    40   60    50/100                                             Consid.                                                   Consid.Vegetable Split   L-A Lacquer            Smooth                  600 15    270  285   40/300                                             Slight                                                   Consid.__________________________________________________________________________ .sup.1 Taber Abrasion: Wheel No. CS-17; Suction 60; 1000 g. Load. .sup.2 Mul-Tech: 1/2 hour soak; 4 lb. Load. .sup.3 Bally Flex: 1/2 hour soak; rated at 40,000 cycles. .sup.4 Blister: There was one large blister on this sample. .sup.5 Cold Crack: -20° F.; samples conditioned 3/4 hour. .sup.6 This was the only sample tested for this many cycles. Note: All the above foam-coated substrates passed the Satra Dome Test.