Abstract:
A building material for roofing and the like has a UV curable top coating with a resin component and a photoinitiator component. The top coating may include pigments, such as those which increase reflectivity of the coating. The speed with which the coating can be cured permits use in a roofing material assembly line without slowing the feed rate and eliminates energy intensive drying procedures.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to building materials and compositions for making same, and more particularly, to a top coating composition for roofing material that promotes energy conservation, is durable, fire-retardant, and resists the growth of unwanted plant life, such as algae, moss, mold and fungi. 
       BACKGROUND OF THE INVENTION 
       [0002]    Building materials, such as roofing materials, preferably exhibit weather, fire and rot resistance, structural strength and durability, as well as being economical to make and easy to use on the job site during the construction of buildings. Roofing materials are exposed to the effects of rain, wind and sun and are expected to have a long and trouble-free service life. Over the years, various types of roofing materials and roofing systems have been developed and used to meet these demands for commercial and residential buildings with varying roof pitches ranging from flat to steeply pitched, including stone, ceramic, wood, metal, rubber and asphalt/bitumen. Each type of material has benefits and limitations in performing it&#39;s intended function. 
         [0003]    Asphalt roofing materials have wide popularity and can be made in many forms and compositions to provide different desirable properties, depending upon the application. For example, asphalt roofing material may be reinforced using different fabric mat materials, such as fiberglass, polyester or other natural and synthetic materials. The asphalt may be modified by incorporating other compositions, such as styrene-butadiene-styrene (SBS) or atactic polypropylene (APP). Asphalt roofing material may be made in a variety of forms including shingles of various shapes and sizes, as well as continuous sheets of roofing (roll roofing). Asphalt roofing materials intended to be used as the top layer of a roofing system typically have an outer/upper surface incorporating crushed stone, ceramic or other hard, finely divided materials which are imbedded in the outer surface while the asphalt material is still hot and flowable. Selecting the color of the finely divided material determines the color of the roof material. Similarly, metal roofs have typically been painted to prevent corrosion and to control the color of the roof. 
         [0004]    One significant implication of selecting a particular color for a roof is the degree to which the roof absorbs/reflects solar energy, with lighter roofs reflecting more energy and darker roofs absorbing more of the sun&#39;s energy. This attribute of roof color has become more significant as energy costs have increased, since dark roofs increase the cost of air conditioning buildings in warm, sunny climates and seasons. Greater energy absorption also results in quicker degradation of the roofing materials. 
         [0005]    Besides the natural incentive for building owners to decrease air conditioning costs and increase the useful life of their roofing systems, governmental entities have passed laws and regulations pertaining to the use of roofing materials having a prescribed reflectivity. The Cool Roof Rating Council has developed a system of standards whereby roofing materials may be tested and rated for reflectivity (the ENERGY STAR® rating). Paints and coatings have been proposed for applying a reflective top coat on asphalt-type roofing. These coatings are typically water-based acrylic coatings having a white pigment and may contain additives, such as reinforcing fibers, glycol, intumescents/fire retardants, and biocides. As with most painted-on coatings, these known coatings have limitations pertaining to convenience of application (painting a roof) coverage (the granular upper surface of asphalt roofing is rough and irregular with a three dimensional component), and retention to the surface (cracking, chipping and peeling with age and exposure to weather and temperature changes). Some of these issues are addressed by applying a prime coat, which represents an additional step, with associated costs and inconvenience. 
         [0006]    Patent applications owned by the Assignee herein include publication Nos. 2005/0139126 A1, 2005/0145139 A1, 2005/0257875 A1, 2005/0261407 A1, all of which relate to coatings that are applied to roofing material. As noted in, e.g., Patent Publication No. 2005/0261407 A1, there are disadvantages associated with applying coatings to roofs on-site, such as the difficulty in attaining complete coverage and maximal adhesion due to non-optimal temperatures and weather conditions, as well as the generally difficult process of applying a liquid coating over a large, elevated and potentially sloped surface. Factory application of coatings alleviates some of these problems. Application of top coatings at the factory has other associated requirements, e.g., the coating must be cured prior to further processing of the roofing material, such as rolling the material into rolls, or cutting and packing it into bundles. Known curing methods utilizing heat require a large expenditure of energy in order to conduct curing at a rate which does not significantly slow production. Accordingly, alternative coating compositions and methods for applying and curing them remain of interest in the field. 
       SUMMARY OF THE INVENTION 
       [0007]    The limitations of prior art building and roofing materials are overcome by the present invention which involves the provision of a building material having a substrate with a bottom surface and a top surface, the bottom surface being applied proximate to a building when the substrate is used. A top coating applied to the top surface has a resin component and a photoinitiator component. The photoinitiator component functions to induce polymerization of the resin component when a mixture of the resin component and the photoinitiator component are exposed to UV radiation, curing the top coating. 
     
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0008]    The novel features of the present invention will be more readily apparent upon reading the following description in conjunction with the accompanying drawings, in which: 
           [0009]      FIG. 1  is a diagrammatic cross-sectional view of a portion of roofing material made in accordance with an embodiment of the present invention; and 
           [0010]      FIG. 2  is diagrammatic view of a manufacturing apparatus and method for making roofing material in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]      FIG. 1  shows roofing material  10  having a reinforcing mat  12 , which is made from fiberglass or polyester, and asphalt layers  14 ,  16 , each of which is formed from modified asphalt such as SBS or APP. A layer of granules  18 , such as crushed stone, ceramic or minerals, is embedded in the asphalt layer  16 . The granules  18  are covered with a coating  20 , such as those described in any of the following applications, which are owned by the present Assignee and were published as: 2005/0139126 A1, 2005/0145139 A1, 2005/0257875 A1 and/or 2005/0261409 A1, each of which is incorporated by reference herein. As further alternatives, the coating  20  may be eliminated or it may be modified to include a UV-curable coating as disclosed in the present application. After the granules  18  are embedded in the asphalt layer  16 , a UV-curable coating layer  22  is applied over them. 
         [0012]    The roofing material  10  in accordance with the present invention therefore utilizes at least one UV-curable coating, i.e., on the individual granules  18  and/or applied as the coating layer  22 . While the present invention has been explained with reference to granule-faced roofing material, the UV-curable coating may be applied to roofing material that does not have granules. 
         [0013]    A bottom coating  24  is embedded or otherwise adhered to the asphalt layer  14 . The bottom coating  24  may be conventional, such as a coating of sand or talc. Before describing the composition and preparation of the UV-curable material used in forming the UV-curable coating layer  22 , the method and apparatus for making the roofing material  10  will be described below with reference to  FIG. 2 . 
         [0014]      FIG. 2  shows fiberglass or polyester mat material  30  being provided to mat unwinder stand and splicer apparatus  32 , which produces a continuous woven mat or felt  34  forming a fibrous reinforcement for the roofing material to be produced. Simultaneously, asphalt  36 , modifying polymers  38  and optional mineral stabilizers  40  are added to a mixing tank  42  from which liquefied modified asphalt  44  issues and which is directed to impregnation vat  46 . The impregnation vat  46  receives the continuous mat  34 , which is then dipped into liquid modified asphalt contained in the vat  46 , producing an asphalt impregnated mat  48 . Optionally, granules  50  and a granule coating  52  are introduced to a granule coater  54 , producing coated granules  56 . The coated granules  56  may be coated with a coating that is heat or air curable or it may be a UV-curable coating in accordance with the present invention. In the latter case, the coated granules  56  would be exposed to UV radiation  58  before being fed to the granule application station  60 . Alternatively, uncoated granules  50  may be fed to the granule application station  60  and applied to the mat  48 . The granule application station  60  distributes the granules  50  or  56  onto the asphalt impregnated mat  48  producing a granule-faced roofing material  62 . The granules  50 / 56  will embed into the surface of the asphalt impregnated mat  48  due to the temperature of the asphalt and its softened state at high temperatures. 
         [0015]    The granule-faced roofing material  62  is then fed through water cooling trays  64  to lower the temperature of the asphalt for further processing and to lock the applied granules  50 / 56  onto the surface of the mat  48 . After leaving the water cooling tray  64 , the cool roofing material  66  has a backing material  68  applied at a backing applicator station  70 . The backing is typically sand or talc. The backed roof material  72  is then cooled and dried by air knives and/or cooling fans  74 , and passed to the top coater  78 . The top coater  78  receives the top coating composition  76  and applies it to the roofing material  72  producing top coated roofing material  80 . In the event that the top coating  76  is UV-curable in accordance with the present invention, it is cured by UV light  82  after leaving the top coater  78 . The top coater  78  may apply a top coating using any of the well known methods for applying coatings, such as by roller, brush, spray, dip and knife coating methods. The cured, top coated roofing material  80  is accumulated on a finish looper (accumulator)  84  and then fed to a roll winder/cutter  86  to produce the finished roofing material  88 , either in the form of roll roofing or cut shingles which are then placed in storage  90 . 
       The Preparation and Composition of the U-V Curable Coating 
       [0016]    An exemplary UV-curable coating in accordance with the present invention includes resin, pigment and photoinitiator component packages as follows, in the weight percentages indicated. The operable weight percentage range is stated first, followed by a preferred weight percentage applicable to the specific example given. 
       Resin Package 
       [0017]    Between 10.00%-40.00%, preferably 30.00% BE-111 low viscosity, non-yellowing, polyester acrylate (primary oligomer); 
         [0018]    Between 6.00%-25.00%, preferably 17.5% PONPGDA propoxylated neopentylglycol diacrylate (primary monomer due to its good pigment/filler compatibility, its good diluent properties and low cost); 
         [0019]    Between 2.00%-15.00%, preferably 7.7% DPGDA dipropyleneglycol diacrylate (a secondary monomer, being an economical high cross-linker with good physical properties); 
         [0020]    Between 0.50%-7.00%, preferably 3.0% PETA pentaerythritol triacrylate (another high cross-linking secondary monomer). The foregoing resins are obtainable from San Esters (www.sanesters.com). 
       Pigment Package 
       [0021]    Between 0.30%-5.50%, preferably 2.5% Disperbyk 168 (disperse aid for limestone); 
         [0022]    Between 0.02%-1.50%, preferably 0.3% Disperbyk 111 (disperse aid or TiO 2 ); 
         [0023]    Between 0.10%-1.50%, preferably 0.5% BYK 1790 (non-silicone de-foamer, for UV applications); Each of the foregoing may be obtained from BYK Chemie (www.byk-chemie.com). 
         [0024]    Between 5.00%-45.00%, preferably 23.5% Omycarb #10 (limestone)available from Omya AG (omya.com); 
         [0025]    Between 5.00%-40.00%, preferably 6.0% Titanium Kronos 2160; 
         [0026]    Between 5.00%-40.00%, preferably 5.0% Titanium Ukraine 2160; The foregoing pigments may be obtained from Kronos, Inc. (kronostio2.com). 
       Photoinitiator Package 
       [0027]    Between 0.50%-5.50%, preferably 3.0% Omnirad 481; 
         [0028]    Between 0.10%-5.50%, preferably 1.0% Omnirad TPO; The foregoing can be obtained from IGM Resins (igmresins.com). 
         [0029]    Adding the weight percents of all of the foregoing compounds in the resin, pigment and photoinitiator packages gives a total weight percent of 100%. To combine these components into the UV-curable coating, the BE-111 and the PONGDA may be utilized as the grind media for the pigment/extender package to form an intermediate resin/pigment dispersion. The DPGDA and the PETA may be utilized together as a solvent for the photoinitiator package to form a resin/photoinitiator solution. The resin/pigment dispersion and the resin/photoinitiator solution are then mixed together using low to medium shear mixing. It is preferable to degas the resin/pigment dispersion before combining it with the resin/photoinitiator solution. While mixing the resin/pigment dispersion with the resin/photoinitiator solution to form the UV-curable coating of the present invention, it is preferable to minimize the introduction of air. 
         [0030]    An iron-doped or, more preferably, a gallium-doped UV bulb producing at or above 300 watts per inch of power would be suitable to cure the UV-curable coating of the present invention. The lower the viscosity of the coating, the quicker the cure time. Since non-aqueous acrylated systems rarely support the growth of microbes, fungus, moss or other unwanted flora or fauna, a biocide is not required for most applications. For tropical or other bio-promoting enviroments/applications, a biocide, such as Nuosept from International Specialty Products Corporation (ispcorp.com)may be added. 
         [0031]    The foregoing UV-curable coating composition can be applied using conventional apparatus and methods for applying coatings, such as roller coating, spray coating, etc. The coating starts to cure immediately upon exposure to UV light and when using a 300 W/in bulb can cure in two to four seconds, thus allowing movement of the roofing material through the production line at a normal speed, i.e., the curing of the top coating composition is accomplished at a quicker rate than other processes used during manufacture of the roofing material, e.g., application of the granules, cooling of the hot roofing material, etc., which are conducted at a slower rate than curing. 
         [0032]    While the present invention has been described in reference to a specific embodiment thereof, those with normal skill in the art may see the potential to change certain aspects of the disclosed embodiment without departing from the scope of the present invention. It is therefore intended that such variations fall within the scope of the appended claims. For example, various pigments may be used as alternatives to those listed above to obtain different colors for the UV-cured top-coating composition. In the event that the color of the granular layer is the desired finish color, the U-V curable composition can be made without adding a pigment resulting in a clear coating. A clear coating may be desired to lock in, unify and protect the granular layer, while still permitting the color of the granular layer to show through the coating. Similarly, the granules may be coated with a clear coating prior to being embedded in the asphalt. If granules are not utilized on the roofing material, the UV-curable coating may be applied to the upper surface of the roofing material.