Abstract:
A sheet material may be prepared and stored by applying an adhesive to one side of a first sheet and applying a second sheet to the adhesive to form a trilaminate. The trilaminate is placed into a container that is substantially free of moisture and the container is sealed so that the trilaminate can be stored in an atmosphere substantially free of moisture. The adhesive is a cross-linking polymer that reacts with moisture to form cross-linked bonds.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. application Ser. No. 08/963,308, filed on Nov. 3, 1997, which itself claims priority from U.S. application Ser. No. 08/743,392, filed Nov. 4, 1996, and U.S. application Ser. No. 08/229,685, filed Apr. 19, 1994. All of these applications are incorporated by reference. 
    
    
     BACKGROUND 
     This invention relates to sheet materials with adhesives used in making, for example, covered foam products. 
     Automobile seat cushions and other foam products are typically produced by a foam-in-place process in which the seat cushion is chemically foamed against a finish fabric covering the seat. The process often begins by first laminating a lubricant-free urethane barrier layer to the finish fabric by, for example, flame lamination. A thin layer of foam placed between the fabric and the barrier layer acts as an adhesive to bond the fabric to the barrier. The resulting tri-layer fabric/foam/barrier composite is then cut and sewn into a sock cushion. 
     When the finished seat is sewn together from several different pieces of finish fabric, the seams of the sock cushion are sealed prior to foaming to prevent liquid components in the foaming process from bleeding through the finish fabrics and to assure a good vacuum barrier during the process of molding the foam cushion. 
     For ease of handling in cutting and sewing the composite, a slip sheet may be bonded to a surface of the barrier. For example, a polyethylene sheet may be heat bonded to the barrier to provide a slippery surface that prevents the composite from catching under the presser foot of a sewing machine. 
     SUMMARY 
     In one general aspect, a sheet material may be prepared and stored by applying an adhesive to one side of a first sheet, applying a second sheet to the adhesive to form a trilaminate, placing the trilaminate into a container that is substantially free of moisture, and sealing the container so that the trilaminate can be stored in an atmosphere substantially free of moisture. The adhesive is a cross-linking polymer that reacts with moisture to form cross-linked bonds. 
     Embodiments may include one or more of the following features. For example, the adhesive may include an isocyanate terminated oligomer and may soften in a temperature range between 60 and 72° Celsius. The cross-linked adhesive also may form a strong chemical bond that is heat resistant and will withstand temperatures greater than 100° Celsius and relative humidities of approximately 95%. 
     The adhesive may be heated to approximately 125° Celsius in a hot melt premelter prior to applying the adhesive to a roller. The adhesive may be applied to the first sheet from the roller by pressing the roller against the first sheet. The adhesive may form a continuous layer or may define discrete patterns, such as patterns resembling rows of pyramids. 
     The first sheet may include a polymer, such as polypropylene, that does not distort at temperatures of approximately 125° Celsius. Another property of the first sheet is that it may be peeled away from the solidified adhesive. 
     The second sheet may be nipped to the applied adhesive and may include a high molecular weight polyether-based thermoplastic urethane that is substantially free of moisture. The second sheet also may include an ethylene/vinylacetate copolymer, an ethylene acrylate copolymer, a metalocene-catalyzed olefin whose surface is treated for adhesion, an ionomer, or a film made using a resin having a relatively low softening or forming temperature and being free of lubricants or slip adhesives. 
     After the second sheet is nipped to the applied adhesive to form the trilaminate, the trilaminate may be passed over a cooling roll to cool the trilaminate and solidify the adhesive. After the trilaminate is placed in the container, dry air with a dew point below −10° Celsius may be used to purge the container. 
     In another general aspect, a sheet material includes a first polymer layer, a layer of adhesive bonded to the first polymer layer, and a second polymer layer covering the adhesive. The adhesive may include an isocyanate terminated oligomer. 
     In another general aspect, an article, such as a seat cushion, may be made by placing a barrier layer and a cover material in a shaped mold, creating foam by an exothermic reaction in a cavity defined by the barrier layer in the mold, and bonding the barrier layer to the cover material. The bonding is accomplished by using the reaction heat created in the exothermic reaction and the moisture in the ambient air and cover material. 
     Embodiments may include one or more of the preceding or following features. For example, prior to creating foam in the cavity, a vacuum may be applied to the mold to cause the barrier layer and cover material to conform in shape to the interior of the mold. The foam may be created by pouring chemicals into the mold, with the chemicals reacting to form the foam. The chemicals may include an isocyanate and a polyol mixture. After the foam sets, the cover material, barrier layer, and foam may be removed from the mold. 
     The cover material may be cut into pieces and sewn together to form a shell of the article, with the shell having an opening. The barrier layer may be formed by applying a cross-linking isocyanate terminated oligomer adhesive to one side of a sheet of polypropylene. A second sheet may be applied to the cross-linking adhesive to form a trilaminate. The second sheet may include a freshly-produced, high molecular weight polyether-based thermoplastic urethane. The trilaminate may be placed and stored in a container that is substantially free of moisture. 
     Other features and advantages of the invention will be apparent from the following description, including the drawings, and from the claims. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is cross-sectional view of a multi-layered cushion. 
     FIG. 1B is a cross-sectional view of a multi-layered cushion having a preformed foam layer. 
     FIG. 2 is a cross-sectional view of a lamination process. 
     FIG. 3 is a plan view of patterns for making an automobile seat. 
     FIG. 4 is a perspective view of a shell of a seat cushion formed of the patterns of FIG.  3  and partially turned inside-out. 
     FIG. 5 is a cross-sectional view of a trilaminate in which one layer is partially peeled away. 
     FIG. 6 is a cross-sectional view of a seat cushion shell and a mold. 
     FIG. 7 is a cross-sectional view of the shell and mold of FIG. 6, with another mold, and foam between the molds. 
     FIG. 8 is a cross-sectional view of a covered automobile seat cushion. 
     FIG. 9 is a magnified schematic side view of the sheet material. 
    
    
     DESCRIPTION 
     Referring to FIG. 1A, a cushion  5  (not drawn to scale) may be used, for example, as a covered automobile seat cushion through a foam-in-place process. The cushion  5  has a cover material  10 , such as a finish fabric or leather. A urethane film  15  bonded to a discontinuous, non-tacky adhesive layer  20  forms a sheet material  25  that acts as a barrier layer for the cover material. Urethane film  15  is substantially pin-hole free and thus provides an air-tight vacuum barrier and also a liquid foam chemical barrier during the foaming-in-place of a foam pad  30  for the finished cushion. The urethane film is also lubricant-free to adhere chemically to liquid foaming agents used in the foaming process. 
     Referring to FIG. 1B, cushion  5  also may have a preformed foam layer  35  bonded to the cover material  10 . 
     Referring to FIGS. 1A and 1B, the discontinuous adhesive layer  20  has gaps or holes  40 , i.e., regions without adhesive material. The gaps may be distributed either randomly or in a pattern across adhesive layer  20 . The proportion of gap area to total surface area for the adhesive layer may be in the range of 10% to 30%, typically 10% to 20%, more typically about 15%. 
     The sheet material  25  is separately assembled in an adhesive printing and film nipping process as shown in FIG.  2 . The adhesive is heated to approximately 125° Celsius in a hot melt premelter  50 . The hot melt premelter pumps the adhesive into a pan  52  in a viscous form. A print (or engraved gravure) roll  55  turns in the pan  52 . A doctor blade  57  scrapes excess adhesive from the roll, leaving a layer of adhesive  59  on the roll  55 . Hot melt premelters are available from Nordson in Norcross, Ga. 
     The adhesive layer  20  of the sheet material  25  softens at 65.5 20   Celsius±5.5° Celsius, and becomes tacky at lower temperatures approaching that range. The adhesive, an isocyanate oligomer, has terminal isocyanate groups that react with moisture and cross-link. The cross-linked adhesive forms a strong chemical bond that is heat resistant. For instance, the adhesive-based bond between the urethane  15  and cover material  10  will withstand temperatures greater than 100° Celsius and 95% relative humidity to provide the durability needed for automobile seat cushions. 
     A continuous sheet of polypropylene  60  is pulled between the print roll  55  and an opposite roll  65 . The print roll impresses the polypropylene sheet with the adhesive according to the roll&#39;s surface pattern as the polypropylene passes between the print roll  55  and opposite roll  65 . This results in a more controlled adhesive pattern than would occur if the adhesive were sprayed directly onto the sheet  60 . This step is performed while the adhesive is sufficiently hot and tacky so that the adhesive will wet and bond to the surface of the urethane film  15  during the nipping step. 
     Polypropylene is used because it does not distort when the heated adhesive is applied to its surface. Moreover, the adhesive will freely release from the surface of the polypropylene after it cools and solidifies. The adhesive is placed on the polypropylene in discrete patterns. For example, referring to FIGS. 2B and 2C, the adhesive may be placed on the polypropylene so that it resembles rows of pyramids  67 . This pattern has been shown to effect good adhesive contact. The adhesive also may be applied as a continuous layer. 
     Adjacent to rolls  55  and  65 , a pair of nip rolls  70  and  75  nip a film  15  of freshly produced high molecular weight polyether-based thermoplastic urethane against the layer of adhesive to form a trilaminate  80 . An example of such a film is Vacuflex®, which is available from Omniflex Limited Partnership of West Bridgewater, Mass. Film  15  also may be an ethylene/vinylacetate copolymer, an ethylene acrylate copolymer, a metalocene-catalyzed olefin whose surface is treated for adhesion, an ionomer, or a film made using a resin having a relatively low softening or forming temperature and being free of lubricants or slip adhesives. 
     The trilaminate then is passed over a series of cooling rolls  85  to bring the trilaminate to room temperature and solidify the adhesive layer. The trilaminate  80  is then spooled as a roll (not shown), removed, and placed in a bag (not shown) constructed of a polyester film/aluminum foil/polyethylene film. The bag is purged with dry air with a dew point below −10° Celsius to eliminate all moisture in the bag. The bag is then heat sealed to ensure an airtight package. 
     During use, trilaminate  80  is removed from the bag and cut to lengths or left as a continuous piece, as desired. Removing the trilaminate  80  from the bag exposes the materials to air. Moisture in the air has the potential to cause the adhesive to begin cross-linking prematurely. To avoid premature cross-linking, the trilaminate  80  should be used soon after exposure to air (e.g., less than two hours after opening). In some tests, after 24 hours of exposure to ambient air, the first 15 to 20 yards of the rolled trilaminate  80  did not function suitably because of premature cross-linking of the adhesive. 
     Pattern pieces  100  are then cut from a bolt of the cover material  10  as shown in FIG.  3 . Pattern pieces  100  may include a front piece  105 , a pair of side pieces  110  and  115 , a top piece  120 , and a rear piece (not shown). These pieces are sewn together with a row of stitches  123  to form a seat cushion shell  125 . As shown in FIG. 4, shell  125  is then turned inside out, so that an inner surface  130  is exposed on the outside of the shell. 
     As shown in FIG. 5, prior to the foam-in-place process, the polypropylene layer  60  of the trilaminate  80  is peeled away from the sheet material  25  (i.e., the adhesive bonded to the urethane layer). The polypropylene layer  60  is discarded. Next, as shown in FIG. 6, the cover material  10  of a shell  135  (not shown to scale) is positioned over mold  140 . The depth D of the mold  140  is slightly smaller than the width W of the front pattern  105  and the width of each side piece  110 ,  115  (FIG.  3 ). The sheet material  25  is then placed over the cover material  10  and held in place by a perimeter clamp frame  145 . A space  150  between the mold  140  and the sheet material  25  is then evacuated to pull the sheet material and the cover material  10  snugly against the mold  140 . This forces the sheet material and the cover material to conform to a contour  155  of the mold. Thus, the sheet material  25  serves to conform to the mold cavity. 
     Referring to FIG. 7, after the space between the mold and the sheet material is evacuated, as shown, liquid reactive chemical foam constituents, such as isocyanate and polyol, are poured into a mold cavity  160 . A second mold  165  is placed over the main mold  140  and the perimeter clamp frame  145  to close the mold cavity  160  to contain the chemical constituents in the mold cavity, and to regulate the final shape and density of the foam in the mold cavity. The chemical constituents react to create a foam which increases in volume to fill the mold cavity. The foam flows over and bonds inseparably to the sheet material  25 . The foam then “sets” to form urethane foam pad  30  having a surface detail corresponding to mold contour  155 . 
     The chemical constituents react exothermically to create the foam. The heat of this reaction generates an exotherm of approximately 65.5° Celsius. The adhesive layer  20  of the sheet material  25  softens at 65.5° Celsius±5.5° Celsius. Thus, during the foam reaction the adhesive is softened so that it covers the seams and causes the adhesive to penetrate into the surface of the cover material  10 . As explained above, the adhesive has terminal isocyanate groups that react with moisture in the air and cover material  10  and cross-link. The cross-linked adhesive thereby forms a strong chemical bond with the cover material that is heat resistant. 
     After the foam has set, the second mold  165  is removed and the perimeter clamp frame  145  loosened to allow the shell  135  and the attached foam pad  30  to be removed from the mold. Other components, e.g., plastic or metal parts (not shown), may now be added to the foam pad. 
     Referring to FIG. 8, the foam pad  30  and shell  135  removed from the mold provide a seat cushion  175  having an upholstery covering the foam pad  30 . Detail work for the finished seat, such as a vinyl reinforcement  180  at a non-stitched end  185 , may then be added. Alternatively, the final detail work and vinyl reinforcement may be done before the foaming process. 
     Urethane film  15  in sheet material  25  is formed of urethane resin (e.g., a Vacuflex film available from Omniflex Limited Partnership in West Bridgewater, Mass., BASF SP806, or other products within the same family of resins) with a constant thickness T in the range of about 0.5 to 10 mils, typically 1 to 3 mils, and more typically about 2 mils. Because urethane film  15  faces the liquid agents which become the urethane foam pad, film  15  is pinhole-free, even when stretched slightly. Film  15  also is essentially lubricant-free to enhance bonding to the foam. Preferably, the film is completely lubricant-free, but it may have small amounts (e.g., less than an aggregate of 2%) of impurities such as heat stabilizers or UV stabilizers or other processing additives. Other materials that could be used for the film include an ethylene/vinylacetate copolymer, an ethylene acrylate copolymer, a metalocene-catalyzed olefin whose surface is treated for adhesion, an ionomer, or a film made using a resin having a relatively low softening or forming temperature and being free of lubricants or slip adhesives. Generically, the materials that would work best would have the properties of being elastic, thermoplastic, pin-hole free, able to adhere to the chemicals or substrates involved in the process, and durable and able to withstand whatever flexing takes place in the ultimate product. 
     Referring to FIG. 9, the adhesive layer may be applied to the polypropylene layer using the print or engraved gravure roll at a typical basis weight of 0.8 oz/yd 2  to 0.4 oz/yd 2 . Other concentrations of adhesive also may be applied. After nipping the urethane film  15  to the adhesive layer  20 , the thickness T w  of the adhesive layer may be between 0.002 inches to 0.020 inches, but is typically 0.007 inches. The resulting discontinuous adhesive layer on the urethane has a large exposed surface area to volume ratio and a small heat mass. The discontinuous adhesive layer provides a severalfold increase in the thickness of the layer over a continuous adhesive layer of identical weight. Thus, a smaller amount of adhesive can be used to obtain the same power of adhesion provided by the continuous layer. These features allow the adhesive to be rapidly and evenly melted when heated and also to bond in a stable manner to the cover material. 
     Other embodiments are within the scope of the following claims.