Abstract:
A crease resistant scrim reinforced coated fabric and associated high density polyethylene (HDPE) tapes that can be used in areas where esthetics are important such as rental tents where the material is constantly folded and installed. The scrim has woven HDPE tapes made from a resin to soften the tape, and a coating comprising a UV masterbatch to resist UV radiation, a Flame resistant (FR) masterbatch to resist fire. The resin with a relatively low flexural modulus and a relatively high Vicat softening point would reduces the scrim&#39;s crystallinity and avoids tape shrinkage during coating without overly weakening the tape.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/295,356 filed Jan. 15, 2010, which is hereby incorporated by reference in its entirety for all purposes and specifically for the concept, structure and functions of a crease resistant tape comprising high density polyethylene (HDPE) and an olefinic based elastomer with the combination of a relatively high Vicat softening point and a relatively low flexural modulus, which is incorporated herein. The concept, structure and functions of crease resistant HDPE scrim comprising such interwoven oriented crease resistant tapes comprising HDPE and an olefinic based elastomer with the combination of a relatively high Vicat softening point and a relatively low flexural modulus, as well as products comprising such a scrim, is also incorporated herein. 
     
    
     BACKGROUND AND SUMMARY 
       [0002]    Tents, awnings and outdoor structures are typically flexible in nature and are supported by a framework. In some cases these structures are temporary in nature and are erected and dismantled on a frequent basis. Additionally, while such structures are all waiting purchase or use, they may be stored in a folded fashion pending their deployment. The fabric or scrim from which these temporary structures are made can vary in composition and thickness. Depending on the environment in which they are stored, the length of time that they are stored, and the number of times they are deployed, are folded, and stored such scrims can become seriously creased. It is generally more attractive for those using such coated scrims for temporary structures to have as few creases as possible since to do so, will result in a more attractive structure. 
         [0003]    Various embodiments relate generally to polymer scrims, and more particularly to a type of high density polyethylene (“HDPE”) scrim that is resistant to creasing. 
         [0004]    An embodiment relates to a crease resistant scrim reinforced coated fabric that can be used in areas where esthetics are important such as rental tents where the material is constantly folded and installed. Such an embodiment will also be useful in permanent membrane structures since the building cover is typically shipped in a folded configuration. Depending on the length of time that the material is folded and the environmental conditions in which it is stored, fold lines can show after installation. 
     
    
     DETAILED DESCRIPTION 
       [0005]    Scrims woven from oriented polymer tapes serve many purposes, such as providing a layer of reinforcement to coated fabrics or protection from exposure to the environment. While scrims can provide support and strength to softer coating materials, the scrims can also be found to be the main source of the retention of creases. These creases can become worse over time and negatively affect the appearance and structure of the material in which they are used. 
         [0006]    Through much experimentation, the inventors have found that the main reason for crease retention in coated oriented tape scrim products is the crease memory of the scrim. Adjustments in the composition of the coating could increase crease resistance by a small degree, but many creases would still be held by the scrim. Therefore, various embodiments seek to decrease crease retention by reducing the crystallinity of, or softening, the polymer previously used to create the scrim&#39;s oriented tapes without eliminating the scrim&#39;s useful properties related to strength and support. However, the new tape may also have to stand up to the heat of extrusion when a coating is applied and withstand the forces that lead to shrinkage of the tape or the puckered appearance the shrinkage can cause in the material when a molten coating is applied. 
         [0007]    In an embodiment a scrim comprises HDPE tape and a resin to soften the tape, and a coating comprising a UV masterbatch to resist UV radiation, a Flame resistant (FR) masterbatch to resist fire. In an embodiment it was determined that a resin with a relatively low flexural modulus and a relatively high Vicat softening point would reduce the scrim&#39;s crystallinity and avoid tape shrinkage during coating without overly weakening the tape. As used herein, a relatively low flexural modulus refers to a flexural modulus below about 50 MPa, and a relatively high Vicat softening point refers to a Vicat softening point between about 40° C. and about 100° C. 
         [0008]    The flexural modulus is the ratio of stress and strain in flexural deformation and provides an indication of how soft or flexible a material is. A lower modulus indicates a softer material. 
         [0009]    The Vicat softening point is the determination of the softening point for materials that have no definite melting point, such as HDPE. It is taken as the temperature at which the material is penetrated to a depth of 1 mm by a flat-ended needle. A higher Vicat softening point means that the tape would be less prone to shrinkage during the extrusion coating process and subsequent puckering. 
         [0010]    After multiple trials, a preferred embodiment for a tape was determined to comprise an olefinic based elastomer, such as that marketed by ExxonMobil Chemical and sold under the name Vistamaxx 6102 as the resin to be mixed with the HDPE to create a tape that could be woven and coated to produce a crease resistant scrim. In a preferred embodiment it was found that Vistamaxx 6102 possessed the desired balance of properties, including a low flexural modulus and a high Vicat softening point, while retaining tear and tensile strength after extrusion coating. Vistamaxx 6102, when tested in accordance with ASTM D 1525 was found to have a typical Vicat softening point of 59° C. (138° F.) for a 200 g sample cut from compression molded plaques per ASTM D 4703, Procedure A, Type I and conditioned at 23° C. for a minimum of 40 hours per ASTM D 618 prior to testing. When a sample of Vistamaxx 6102 cut with a Type C die and tested with a grip separation of 25 mm and a crosshead speed of 20 in/min was tested in accordance with ASTM D 790, it was found to have a typical 1% secant flexural modulus value of 11.4 MPa (1650 psi. Vistamaxx is part of a family of elastomers designed for high elasticity, softness, toughness, flexibility and adhesion to various polyolefins. However, this is not meant as a limitation. Other olefinic based elastomers such as propylene copolymer elastomers, propylene/olefin elastomers, made with a single site or metallocene catalyst, propylene-ethylene copolymers and polyolefin thermoplastic elastomers may also find suitability for the preferred embodiments noted herein. 
         [0011]    In an embodiment a preferred the HDPE tape comprises a mixture of about 64.75% HDPE by weight, about 1.25% by weight UV masterbatch, about 9% by weight FR masterbatch, and about 25% by weight Vistamaxx 6102. This tape may then be produced in a suitable denier and woven into a crease resistant scrim, and this scrim can be coated to create a crease resistant fabric. 
         [0012]    In another preferred embodiment the HDPE tape is manufactured with a tape fineness of about 825 denier, which is unit of measurement of linear mass-density of textile fiber. 
         [0013]    A scrim produce in accordance with the embodiments noted above has a low shrinkage when coated with a heated molten coating. When coated with a flame retardant coating, embodiments of the scrim were found to pass the very strict requirements of the California Fire Marshal Test which is one of the most stringent fire resistant tests in North America. 
         [0014]    An embodiment of a crease resistant scrim comprises interwoven oriented HDPE tapes, wherein each tape comprises high density polyethylene (HDPE) and an olefinic based elastomer with a combination of a Vicat softening point between about 40° C. and about 100° C. and a flexural modulus below about 50 MPa. Variations of this embodiment can comprise a flame resistant (FR) masterbatch, with about 9 percent by weight being a preferred amount, and/or an ultraviolet (UV) resistant master batch, with about 1.25 by weight being a preferred amount. Other variation of this embodiment include those wherein the each tape comprises about 64.75 percent by weight high density polyethylene and those wherein the olefinic based elastomer comprises about 25 percent by weight. In yet another variation of this embodiment, the olefinic based elastomer has a Vicat softening point of approximately 59° C. and 1% secant flexural modulus of approximately 11.4 MPa. 
         [0015]    An embodiment of a crease resistant tape comprises high density polyethylene (HDPE) and an olefinic based elastomer with a combination of a Vicat softening point between about 40° C. and about 100° C. and a flexural modulus below about 50 MPa. Variations of this embodiment comprise those wherein the olefinic based elastomer comprises propylene copolymer elastomers, those wherein the olefinic based elastomer comprises propylene/olefin elastomers, made with a single site or metallocene catalyst, those wherein the olefinic based elastomer comprises propylene-ethylene copolymers, and those wherein the olefinic based elastomer comprises polyolefin thermoplastic elastomers. In another variation of this embodiment, the tape further comprises about 64.75 percent by weight high density polyethylene, about 25 percent by weight olefinic based elastomer, about 9 percent by weight FR masterbatch, and about 1.25 by weight percent UV masterbatch. In yet another variation of this embodiment, the olefinic based elastomer has a Vicat softening point of approximately 59° C. and 1% secant flexural modulus of approximately 11.4 MPa. Preferably, the tape fineness is about 825 denier. 
         [0016]    In yet another embodiment, a crease resistant product comprises a flexible substrate and a crease resistant scrim attached to the flexible substrate. The crease resistant scrim in this embodiment comprises interwoven oriented HDPE tapes, wherein each tape comprises high density polyethylene (HDPE) and an olefinic based elastomer with a combination of a Vicat softening point between about 40° C. and about 100° C. and a flexural modulus below about 50 MPa. The flexible substrate can comprise a coated fabric. In a variation of this embodiment, the tape further comprises about 64.75 percent by weight high density polyethylene, about 25 percent by weight olefinic based elastomer, about 9 percent by weight FR masterbatch, and about 1.25 by weight percent UV masterbatch. In yet another variation of this embodiment, the olefinic based elastomer has a Vicat softening point of approximately 59° C. and 1% secant flexural modulus of approximately 11.4 MPa. Preferably, the tape fineness is about 825 denier. 
         [0017]    The preceding description of the disclosed embodiments is not meant to be a limitation. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the following claims and the principles and novel features disclosed herein. Preferably, the tape fineness is about 825 denier.