Abstract:
A breathable, printable, washable wallcovering prepared by applying an aqueous coating composition to a glass fiber fabric. The composition contains a modified starch such as a phosphate ester of potato starch, a polymeric latex binder, a thickener such as polyacrylic acid, and optionally, a pigment and a cross-linking agent. The wallcovering is permeable to water vapor such that moist air can pass through and not accumulate between walls and the wallcovering.

Description:
BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to breathable glass fiber wallcoverings which are washable, printable and allow moisture vapor to pass therethrough.  
         [0003]     2. Discussion of Related Art  
         [0004]     Vinyl wallcoverings are well-known articles of commerce. Conventional vinyl wallcoverings are often relatively impermeable to water vapor and act as moisture barriers. This is a desirable characteristic for commercial and residential buildings where it is desirable to keep the wall cavity dry thus helping to prevent the growth of mold and mildew. However, the application of moisture impermeable vinyl wallcoverings in humid environments, particularly in commercial buildings such as hotels and hospitals, can cause severe problems. In a humid environment, moist air can accumulate between walls and wallcoverings. Since the vinyl wallcoverings are not breathable, moist air cannot pass through and remains trapped between the walls and the vinyl wallcoverings. This trapped moisture provides a favorable environment for the growth of mold and mildew. Such growth may lead to the production of offensive odors and discoloration of the wallcovering as well as potential medical problems for those individuals susceptible to mold and mildew.  
         [0005]     Other characteristics desirable in wallcoverings include washability and printability. To achieve commercial acceptance, wallcoverings should allow commercial wallcovering designs similar to those applied to vinyl wallcoverings to be printed thereon. Further, the printed products should be able to withstand repeated washings. Desirably, printed wallcoverings should allow for a minimum of at least 300 scrubs per cycle, a figure which meets or exceeds the testing requirements for existing commercial vinyl wallcoverings.  
         [0006]     U.S. Pat. No. 4,495,012 to Berenger is an example of the preparation of a glass fabric wallcovering coated with a vinyl plastisol. U.S. Pat. No. 5,545,441 also discloses vinyl resin-coated glass fabric wallcoverings. U.S. Pat. No. 4,006,273 to Wolinski et al. discloses washable wallcoverings.  
         [0007]     Breathable wallcoverings are described in U.S. Pat. Nos. 5,876,551 and 6,238,789 to Jackson. These products are vinyl-coated substrates.  
         [0008]     An environmentally friendly wallcovering which could be substituted for commercial vinyl wallcoverings would be highly desirable. Also highly desirable in the marketplace would be a wallcovering which combines the positive attributes of glass fiber fabrics, i.e., fire resistance, flexibility, abrasion resistance, etc., with the capability to accept printed designs which retain their appearance through repeated scrubbings.  
       SUMMARY OF THE INVENTION  
       [0009]     It is an object of the invention to provide an environmentally friendly glass fabric wallcovering which is breathable, washable and printable.  
         [0010]     Another object of the invention is to provide a process for preparing a glass fabric wallcovering which is breathable, washable and printable.  
         [0011]     Still another object of the invention is to provide an aqueous composition, which, when applied to glass fiber fabrics, provides a layer which is breathable, washable and printable.  
         [0012]     These and other aspects of the invention may be attained by preparing an aqueous composition comprising a modified starch, a polymeric latex binder, a thickener, and optionally a pigment and a cross-linking agent, applying a coating of the aqueous composition to a glass fiber fabric and drying the coating to obtain a glass fabric wallcovering which is breathable, i.e., permeable to water vapor, washable and printable. According to a preferred embodiment, the modified starch is a phosphate ester of a starch, the polymeric binder is an acrylic latex, the thickener is a polymer of acrylic acid, and the cross-linking agent is a zirconium compound.  
     
    
     BRIEF DESCRIPTION OF THE FIGURE OF THE DRAWING  
       [0013]      FIG. 1  shows an arrangement of a process for producing the breathable wallcovering of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     Suitable glass fiber fabrics for use in the wallcoverings of the invention include woven and non-woven materials. Preferably, the fabric is a woven product derived from glass fiber yarn. Many glass fiber yarns could be selected for use in preparing the fabric substrates. Preferred glass fabrics include woven materials prepared from C-glass or E-glass. The invention is also applicable to non-woven glass fabrics, such as those prepared by conventional wet-laid or dry-laid processes.  
         [0015]      FIG. 1  shows a process for preparing a wallcovering in accordance with the present invention. A glass fabric  12  is provided in roll form. A rotary screen  11  provides a layer of an aqueous coating composition  14  to the fabric. The coated fabric is subsequently conveyed to a drying apparatus  16 , preferably air-dried, and then collected in roll form  18 . Instead of a rotating screen, other well-known means such as knife coating and pad coating may be employed to apply a layer of the aqueous coating formulation to the glass fabric.  
         [0016]     The breathable coating formulation of the invention is preferably applied in the form of an aqueous dispersion having a total solids content in the range of about 5 to 25 wt. %, preferably about 10 to 20 wt. %, most preferably about 10 to 13 wt. %. The formulation includes a modified starch, a polymeric binder, a thickener, and optionally, a pigment and a cross-linking agent. The relative amounts of each ingredient can be widely varied as long as the wallcovering product has the desired moisture vapor permeability, printability and washability. Suitable dry weight ranges for the ingredients are as follows:  
                                                       Ingredient   Proportions   Preferred Proportions                           Modified Starch   5-25   15-20           Polymeric Binder   20-70    40-60           Thickener   0.1-10     0.5-5             Pigment   5-25   10-20           Cross-Linker   0-15    3-12                      
 
         [0017]     Suitable modified starches which can be employed include various commercially available anionic starches. A preferred material is a cold water-soluble phosphate ester derived from potato starch, e.g., Solvitose GF-104®. Modified starches derived from corn are also applicable.  
         [0018]     The polymeric binders used in the formulations of the invention preferably are polymeric latices. Preferred binders include acrylic latices such as styrene/acrylic copolymers. Other suitable polymeric binders include polymers of vinyl acetate, polyacrylates and the like.  
         [0019]     Thickeners and similar reagents used to control rheology are also present in the formulations. Polymeric thickeners are preferred and polyacrylic acids are most preferred. Polyacrylic acid thickeners are commercially available in the form of aqueous dispersions.  
         [0020]     The aqueous formulations of the invention preferably contain a pigment. White pigments such as TiO 2  are preferred and can be added usually in the form of an aqueous dispersion. Colored pigments can also be included to create colored glass fabrics.  
         [0021]     A cross-linking agent is preferably added to the formulation. Suitable agents include zirconium compounds, urea-formaldehyde condensates and glyoxal derivatives. Zirconium compound are preferred and ammonium zirconium carbonate is particularly preferred.  
       EXAMPLE 1  
       [0022]     The following formulation was prepared:  
                                                       Modified starch, a phosphate ester derived from potato   13 kg           (Retabond AP, powder 5% moisture, AVEBE)           Cross-linker, Ammonium zirconium carbonate   12 kg           (MelCross A, 20% solids, MEL Chemicals)           Co-polymer binder, styrene acrylic   62 kg           (Appretan TA2250S, 50% solids, Clariant)           White pigment, TiO 2  dispersion   17 kg           (CWP 103, 59% solids, Exofix)           Thickener, poly-acrylic acid    6 kg           (Acrysol TT-615, 30% solids, Rohm and Haas)           Water   325 kg                       
 
 The mixing starts by dissolving the starch in the water. Hereafter, all other components are mixed in. The thickener goes in last. The formulation is water based with a total solids content of approximately 13-14%. The pH is 8-9 and the character is slightly anionic. The viscosity is approximately 2000-2500 cP. 
 
         [0023]     The formulation is applied to a woven glass fiber fabric. The resultant product is used as a wallcovering. The product is permeable to water vapor. The coated surface is ink-receptive and can be printed with various patterns and designs. The printed surface can be repeatedly washed without fading in appearance. Thus, when subjected to the same scrubbing test as that applied to commercial vinyl wallcoverings, the wallcovering of the invention achieved a minimum of 300 scrubs per cycle.  
       EXAMPLE 2  
       [0024]     The following formulation was prepared:  
                                                       Modified starch, a phosphate ester derived from potato   13 kg           (Solvitose GF-104, powder 5% moisture, AVEBE)           Cross-linker, Ammonium zirconium carbonate   12 kg           (Zirlink, 20% solids, Brenntag)           Co-polymer binder, styrene acrylic   62 kg           (Mowilith TA2250S, 50% solids, Celanese)           White pigment, TiO 2  dispersion   18 kg           (CWP 103, 59% solids, Exofix)           Thickener, poly-acrylic acid    7 kg           (Acrysol TT-615, 30% solids, Rohm and Haas)           Water   435 kg                       
 
 The modified starch is dissolved in the water and all other components are then mixed in with the thickener added last. The formulation has a total solids content of approximately 10-12%. The pH is 8-9 and the character is slightly anionic. The viscosity is approximately 2000-2500 cP. 
 
       EXAMPLE 3  
       [0025]     The following formulation was prepared:  
                                                                 Components   Recipe (kg)                                        Retabond AP   13.0           Zirlink   11.8           Mowilith TA 2250 S   62.0           CWP 103   17.6           Acrysol TT-615   7.3           Release Agent   2.6           Total Water   435                      
 
         [0026]     The components were admixed as above described. The formulation exhibited the following properties:  
                                                       Temperature   Max 22° C.           pH   8.5-9.0           Viscosity   3000 cP           Solid content   10.8%           Dry weight   59.2 kg           Batch weight    549 kg                      
 
         [0027]     Other conventional additives can be incorporated into the coating compositions. These would include fillers, organic solvents, plasticizers, release agents, heat and light stabilizers, fungicides and the like.  
         [0028]     All of the above-mentioned patents are herein incorporated by reference in their entirety to the same extent as if each individual reference was specifically and individually indicated to be incorporated herein by reference in its entirety.  
         [0029]     Although the invention has been described with a preferred embodiment, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and scope of the clams appended hereto.