Abstract:
A method of manufacturing paneling and the like in which the thickness or weight of coatings applied to substrate materials is measured by infrared absorption providing a digital representation, accurate to 0.01 mil, of the coating&#39;s thickness or weight to 0.01 gram/sq. ft. The rate of application of the coating is adjusted in accordance with the measurement to maintain the coating weight or thickness within optimum limits.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a method of manufacturing paneling, siding and the like and more particularly to such method of manufacturing involving an improved method of controlling the thickness or weight of coatings applied in the manufacturing processes. 
     Hardwood and softwood plywood paneling and printed and painted particleboard have many uses in the construction trade. Some typical uses include household wall paneling, kitchen cabinets and desk and table tops. In addition to wood cabinets, there has been a growing trend in recent years to the manufacturing of vinyl-clad kitchen cabinets. 
     In the manufacture of traditional hardwood and softwood paneling and vinyl-laminated particleboards, various coatings are applied to the surface of the wood to condition the wood and prepare it for subsequent processing steps. For example, a water-based filler coating is first spread evenly over the surface of a substrate in the manufacture of printed paneling. The filler is forced into the pores in the surface of the wood mechanically and conditions the wood for the application of the base coating. In addition, a wet basecoat is later uniformly spread over the substrate. The basecoat serves as a base color for the wood substrate over which multi-head printing and/or embossing processes are used to achieve the desired color and aesthetic effect. 
     In the case of vinyl-laminated particleboard, an adhesive coating is applied to the wood substrate before lamination of the vinyl film onto the panel. It is important to control the exact amount of adhesive spread over the wood substrate to provide an adequate bond between the substrate and the vinyl. If an insufficient amount of adhesive is applied to the substrate, the vinyl will be easily stripped from its supporting surface and, in the more serious cases, may peel from the wood substrate. 
     One of the problems associated with the application of the coating materials has been the absence of an effective way to control the thickness or weight of the coating applied to the substrate. Control over the coating&#39;s thickness or weight is important to ensure a high quality product while at the same time keeping the coat of the coating material as low as possible. At the present time, the thickness or weight of the coating is roughly controlled by counting the panels that are coated for each gallon of coating material used to provide an indication of the average coating thickness or weight and making adjustments in the rate the coating material is applied in accordance with this measurement. This technique, however, fails to provide an accurate up-to-the-minute indication of each applied coating as the coating is being applied and, as a result, only a very rough control of the coating thickness is achieved. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an infrared analyzer compares the absorption by the coating of infrared radiation at different wavelengths to provide an accurate indication of the coating thickness or weight. The rate of application of the coating is adjusted in accordance with this measurement to thus provide an accurate control over the coating thickness or weight. 
     In accordance with the invention in the manufacture of wood base paneling, the thickness of a coating of filler material is measured by the infrared analyzer immediately after the filler material is applied to the substrate. If the coating thickness is outside optimum limits, the rate of application of the filler material is adjusted to bring the thickness of the coating back to within limits. Similarly, the thickness of the basecoat material is measured by an infrared analyzer immediately after the basecoat is applied to the panel substrate. If the thickness of the basecoat is outside optimum limits, the rate of application of the basecoat is adjusted to bring the thickness back within optimum limits. 
     In accordance with the present invention, in the manufacture of vinyl laminated particleboard, the weight of an adhesive applied to the particleboard substrate is measured by the infrared analyzer after the adhesive is dried. If the weight is outside optimum limits, the rate of application of the adhesive is adjusted to bring the weight back within limits. 
     The use of the infrared analyzer provides an accurate control over the thickness or weight of the applied coating materials. This accurate control of the coating provides a product with improved quality at a reduced cost. The quality is improved because the thickness of the applied coating is accurately controlled to be within optimum limits and the cost is reduced by maintaining the coating thickness or weight within optimum limits which substantially reduces the amount of coating material used. For example, in the case of the basecoat applied to wood paneling materials, the amount of basecoat material used can quite often be reduced by 20 to 25 percent while maintaining high quality in the end product. 
     Accordingly, among the objects of the present invention are the provision of an improved method for controlling the thickness or weight of a coating applied to a substrate material in the manufacture, finishing and laminating of paneling and siding and to thereby provide a high quality product at lower cost. 
     Further objects and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flow chart of a process for manufacturing printed paneling; and 
     FIG. 2 is a flow chart of a process for the manufacture of vinyl-laminated particleboard. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates an example of a manufacturing process in accordance with the present invention for manufacturing a plurality of units of printed paneling. The substrate, for example, may be lauan, hardboard or particleboard. A conventional water-based filler is applied as one or more coatings to the panels by a machine such as a reverse rollcoater. The thickness of the coating of the filler material spread by the reverse rollcoaters in this step would normally be in a range from 0.1 mil to 1.2 mils. The optimum filler coating thickness after this step is 0.4 or 0.5 mils. After the wet filler coating has been applied to a panel, an infrared analyzer, which is positioned from 3 to 15 inches above the coated surface of the panel, measures the thickness of the filler coating. 
     The infrared analyzer utilizes the phenomenon that the coating substance strongly absorbs infrared energy at a specific wavelength and does not strongly absorb infrared energy at another wavelength. To measure the amount of a coating, the coating is irradiated with a reference wavelength, and a measurement wavelength of infrared light. The measurement wavelength is selected to be one that is not strongly absorbed by the substrate but is strongly absorbed by the coating. The infrared analyzer determines the ratio of the intensity of the reflected light at the reference wavelength to the intensity of the reflected light at the measurement wavelength. This ratio will represent the ratio of the absorption of the infrared light at the measurement wavelength to the absorption at the reference wavelength. This ratio will be an indication of the amount of absorption of the coating at the measurement wavelength and, accordingly, will correlate with the thickness or weight (amount per unit area) of the coating material. The analyzer is calibrated to provide a direct digital representation of the coating thickness. 
     An infrared analyzer which will perform the above described measurement is disclosed in U.S. Pat. No. 4,097,743. A commercially available infrared analyzer which will perform the above-described measurement is the Quadra-Beam™ Model 475 Analyzer manufactured and sold by Moisture Systems Corporation. 
     If the analyzer senses and displays its measurement of the coating thickness outside of the optimum limits of 0.4 to 0.5 mils, the rate at which the filler is being applied is adjusted to bring the coating thickness of subsequent coating steps back within the optimum thickness of the coating. 
     The panels are then dried and sanded before application of a second filler coating. As in the case of the first thickness measurement of the filler material, the second coating is also measured with an infrared analyzer. The film thickness range of the second filler coating would normally range from 0.1 mils to 0.8 mils. The optimum coating thickness is 0.2 to 0.4 mils. The thickness measurement of the filler is an integrated value for the surface area irradiated by the beam of infrared light as the incremental thickness varies considerably due to the porosity of the wood surface. If the thickness measurement determines that the coating thickness is outside the optimum limits, the rate of application of the second coating of filler is adjusted to bring the coating thickness back within the optimum limits. 
     After the second application of the filler material, as depicted in FIG. 1, the panels are dried and then the panels may be grooved and the resulting grooves color sprayed in the conventional manner. 
     The panels are then dried and sanded before applying a conventional basecoat. As in the case of the thickness measurement of the filler material, the thickness of the basecoat is measured with an infrared analyzer in the same manner as described above. The film thickness range of the basecoat would normally range from 0.1 mil to 1.2 mils, whereas the optimum thickness is 0.2 to 0.6 mils. 
     If the thickness measurement determines that the basecoat thickness is outside the optimum limits, the rate of application of the basecoat is adjusted to bring the basecoat thickness back within the optimum limits. 
     After applying the basecoat and drying, the panels may pass to an embossing and/or printing operation and from there to an application of a topcoat and subsequent drying to provide the finished printed paneling. The topcoat can be applied with a direct rollcoater to the panels and, as indicated in FIG. 1, the thickness of the topcoat may also be measured by an infrared analysis in the same manner as described above and the rate of application of the topcoat adjusted in accordance with the measurement to maintain a topcoat thickness within optimum limits. 
     FIG. 2 illustrates a flow chart of a manufacturing process for the production of vinyl-laminated particleboard. Sheets or panels of particleboard varying in thickness beginning at about 3/8&#34; are sanded and brushed before a first application of conventional adhesive coating is applied with a direct rollcoater. After the adhesive is applied, the adhesive is dried and the combined film weight of one or more applications of adhesive coatings are measured with an infrared analyzer in the same manner as described above. The film weight would normally range from 1 gm per square foot to 12 gm per square foot, whereas the optimum weight should be 2-6 gm per square foot to ensure a strong bond to the vinyl film. If the measurement of the adhesive weight shows the weight to be outside of these optimum limit, the rate of application of the adhesive to the particleboard in the applications is adjusted to bring the adhesive weight back within the optimum limits. By monitoring the weight of adhesive spread on the particleboard, control over the vinyl lamination step is achieved, thereby reducing the number of vinyl-laminated particleboards that would have been subject to serious peeling problems or have an unnecessary costly excess of glue applied. 
     After measuring the weight of the adhesive coating, the boards are laminated with vinyl film using roll laminators. The laminated boards are then edge and end trimmed. The board may then be top coated with the desired topcoat material. 
     From the foregoing, it will be appreciated that the present invention represents an improved method for measuring the thickness or weight of a coating applied to various substrate materials. While the invention has been described in the context of a specific manufacturing process, namely, that of printed paneling and vinyl-laminated particleboard, it will be appreciated by those skilled in the art that the invention is applicable to the manufacture of other building materials in which coatings are used in the manufacturing process, such as the adhesive in plywood paneling, painted particleboard, paper laminated to particleboard, vinyl or paper laminated to hardboard or lauan, and hardboard siding. Accordingly, it is expressly intended that the foregoing description is illustrative of a preferred method only and is not limiting and that the true spirit and scope of the present invention should be determined by reference to the appended claims.