METHOD FOR PRODUCING PATTERNS ON A FIBER FELTING SCREEN

Abstract: The top wire of a Fourdrinier machine is converted into a negative mold for imparting a textured pattern of fiberboard. A positive mold (10) of the pattern (13) is covered with a resin precursor (16) to fill the depressed areas of the pattern. Upon partial curing, the resin forms convex menisci (15) above the depressed areas and the wire (17) is pressed onto the mold. The protruding resin is bonded to the wire when curing is completed. The negative of the pattern is thus transferred to the wire.

Description: ETHOD FOR PRODUCING PATTERNS ON A FIBER FELTING SCREEN This invention relates, to the production of wet-felted fiberboard having a textured surface. It relates more particularly to the texturing of a fiberboard surface before the mat is fully de-watered. It relates still more particularly to the creation of a pattern on a fiber felting screen. The production of fiberboard on a Fourdrinier machine or Oliver cylinder machine is well known. Such machines are described in U.S. Patent Nos. 3,39Ϊ,013 (Re. 27,109), 3,511,744 and 3,121,660. Other descriptions are abundantly- available. Generally, the fiberboard is processed further to form acoustical ceiling tiles or panels, wall panels, and the like. It is often desirable to impart a pleasing texture to such products for esthetic reasons, and, to some extent, for improved acoustical properties. Methods known for imparting a texture include the patterned sandblast¬ ing of the dried fiberboard, rough screeding of the partially de-watered slurry of fibers, and pressing of the wet mat under a solid press roll having the reverse of the desired pattern in the metal. The sandblasting procedure must be very carefully controlled and it is wasteful of the eroded material. The screeding procedure is limited as to the number of distinctive patterns that can be formed. The solid press rolls do not achieve high fidelity in the reproduction of the pattern. In some versions of the Fourdrinier machine for making fiberboard, the removal of water from the slurry of fibers is accomplished not only by free drainage through the felting wire near the headbox and by vacuum during passage over the suction boxes but also by vacuum as the slurry passes under a series of suction press rolls mounted above the bottc wire and mated with a series of rolls which contact the bottαii wire. The top suction press, rolls are perforated cylinders, each having a vacuum slice which is stationary- but mounted within the perforated cylinder in slidable contact with the inner wall. The top wire of the Fourdrinier forms- a continuous loop around the set of suction rolls. Usually, these suction rolls are used only to consolidate the slurry and smooth its surface. It is an object of this invention to provide a method for texturing a fiberboard during its production on a Fourdrinier machine at the wet end of the fiberboard manufacturing process. It is an object of this invention to provide a method for form¬ ing a texturing pattern on the top wire of a Fourdrinier machine. It is a related object of this invention to provide a Fourdrinier top wire having a texturing pattern thereon but rei^ining a sufficient porosity for efficient drainage of water frαit a fiberboard mat. In accordance therewith, this invention is a method for forming a texturing pattern on a fiber felting screen, said method cαnprising casting a * positive mold of a texture pattern having a iltiplicity of cavities, coating the mold with a release agent, spreading a resin precursor over the mold to fill the cavities, partially curing the resin precursor to form a convex meniscus above each cavity, pressing a fiber felting screen into the resin precursor protruding from the cavities, curing the resin, and separating the screen and the negative mold bonded thereto from the positive mold. The invention will be understood readily by reference to the accom¬ panying drawings and a brief description thereof. FIG. 1 is a cross section of a positive mold of a texturing pattern having a partially cured resin precursor in the mold cavities. FIG. 2 is a cross section of the positive mold of FIG. 1 on which a fiber felting screen is laid. FIG. 3 is a cross-section of positive mold iπmediately after having a resin precursor distributed over the surface of the mold and into the mold cavities. FIG. 5 is a cross section of a fiber felting screen to which a negative mold of the texturing pattern has been bonded by the method of this inventio FIG. 6 is an enlarged view of a portion of the screen in FIG. 5. In FIG. 1, the positive mold 10 has a body 11 which is surrounded by the frame 12. The body 11 and the frame 12 are coated with a mold release agent; alternatively one or both may be formed from a silicone rubber or a like material which will not adhere to a cured resin. The cavities 13 are of irregular shapes and are randomly placed according to the pattern chosen for the textured fiberboard to be produced on a Fourdrinier machine equipped with the top wire of this invention. The ridges 14 are substan¬ tially flat so that the convex meniscus 15 of partially cured resin 16 in each cavity 13 protrudes beyond them. In FIG. 2, the screen 17 is pressed against the mold 10 so that the partially cured resin precursor 16 is forced into the voids of the screen wherever a meniscus 15 rises from a cavity 13. In FIGS. 3 and 4, the mounds 18 of resin precursor are generated by spreading the uncured resin precursor over the mold with a serrated trowel or the like. During the initial curing of the precursor, the cohesive forces within the precursor exceed the adhesive forces between the mold and. the precursor and as a result the mounds disappear quickly as the precursor creeps away from the ridges 14 and gathers to form the convex menisci 15. Although a layer of the resin precursor may be spread across the mold 10 by a straightedge, distribution by a serrated trowel or the like is preferred because the thickness of the layer can be more accurately gauged and the mounds 18 seem to provide pathways to the cavities 13. An initially even layer of precursor may creep haphazardly along the ridges 14 without finding a cavity and form nodes of partially cured resin which would block out more than just the textured portions of the screen, thus reducing the porosity. In FIGS. 5 and 6, the screen 17 is bonded to the cured resin at the dots 20 from which the nodules 21 extend. The screen 19 is a negative of the pattern which is to be impressed on wet mat of fibers during the pro¬ duction of a textured fiberboard on a Fourdrinier or similar machine. The partial curing of the resin precursor has reached the proper state for placement of the fiber felting screen on the mold when the resinous liquid will hold a peak for about 60 seconds. By this time, -4- the low viscosity liquid will have crawled on the mold, creating the convex meniscus in each mold detail. The resin precursor is the reaction mixture in a two-part resin system. It is preferable that the polymerization, i.e., curing, takes place at from about 65° to about 90°F (18°-32°C) and at atmospheric pressure. It is essential that the resin precursor be such that the cohesive forces therein are greater than the adhesive forces with respect to the surface of the mold. Polyurethane and epoxy resins exemplify the two-part resin contemplated for use in the method of this invention. The mold release agent is exemplified by a silicone resin such as is sold under the trademark KRAKO 1711 by Eager Plastics; other examples of the release agent include waxes, fluoroplastics, metallic stearates, fatty amides, and polyethylene. A dilute solution, suspension or emulsion of the release agent may be brushed or sprayed onto the mold and allowed to penetrate the crevices and cavities therein. Upon evaporation of the vehicle, a thin film of the release agent remains on the mold. The liber felting screen may be a woven mesh of metal wires or plastic fibers. A double or triple weaved mesh is preferred because the extra thickness provides more space for the vertical distribution of excess resin as opposed to a horizontal spreading of the resin which would reduce the porosity of the texturing screen. A plastic screen is pre¬ ferred because its flexibility provides for better contact with the mold. To ensure such contact, the screen is pressed down onto the surface of the mold by a uniformly distributed weight exerting a pressure of at least about 0.5 psi. The weight may be supplied by a water-filled plastic bag or some other suitable means. The plastic bag or other weight must be coated with a mold release agent also to prevent adhesion of the cured resin to the weight when the weight is removed from the screen. ' While particular embodiments of the invention have been described in detail, it will be understood that the invention may be modified within the spirit and scope of the appended claims.

Claims: -5- The subject matter claimed is: 1. A method for forming a texturing pattern on a fiber felting screen, said method comprising casting a positive mold of a texture pattern having a multiplicity of cavities, spreading a resin precur— 5 sor over the mold to fill the cavities, partially curing the resin precursor to form a convex meniscus above each cavity, pressing a fiber felting screen into the resin precursor protruding from the cavities, curing the resin, and separating the screen and the resin bonded thereto from the positive mold. ]_Q 2. The method of claim 1 wherein the positive mold is coated with a mold release agent before the resin precursor is spread over the mold. 3. The method of claim 1 wherein the resin precursor is such that the cohesive forces are greater than the adhesive forces with respect to the surface of the mold. * L5 4. The method of claim 1 wherein the resin precursor is the reaction mixture in a two-part epoxy resin system. 5. The method of claim 1 wherein the fiber felting screen is pressed down onto the- surface of the mold by a uniformly-distributed weight exerting a pressure of at least about 0.5 psi. 20 6- The method of claim 1 wherein the resin precursor is spread over the mold with a serrated trowel. 7. A Fourdrinier top wire having a texturing pattern thereon. 8. A fiber felting screen having bonded thereto a negative mold of a pattern to be impressed on a wet mat of fibers during the pro- 25 duction of fiberboard. 9. The fiber felting screen of claim 8 wherein the negative mold is an array of resinous nodules. 10. The fiber felting screen of claim 9 having a multiplicity of pores. 30 11. A method for texturing a fiberboard at the wet end' of the manufacturing process on a Fourdrinier machine which comprises fitting a felting screen having a pattern of resinous nodules bonded thereto as a continuous loop around a series of suction press rolls in a Four¬ drinier machine, passing a wet mat of fibers beneath the suction press 35 rolls thus fitted and contacting the mat with the resinous nodules.

Inventors: IZARD DAVID GRAHAM, MAYERS THOMAS MICHAEL, IZARD, DAVID, GRAHAM, MAYERS, THOMAS, MICHAEL
Applicants: USG CORP, USG CORPORATION
Application year: 1986
Main classification: D21F1
IPC codes: D21F1, D21F11, D21J1