COMPOSITE MATERIALS AND METHOD OF PREPARATION

Abstract: A method for making a non-woven, dimensionally stable composite sheet comprising a polymeric binder, cellulosic fibers, and glass fibers comprising the following steps (A) - (D) in sequence: (A) forming an aqueous dispersion of: (i) cellulosic fibers in the form of a wood pulp consisting essentially of soft wood fibers of a particular type; and (ii) a water-soluble surfactant comprising a dispersion aid for said glass fibers in an amount sufficient to disperse said glass fibers in said dispersion; (B) adding to said dispersion containing said cellulosic fibers and said surfactant chopped glass fibers in an amount such that the partial consistency of said glass fibers in said dispersion is from about 0.5 to about 3.0 %, said added glass fibers having only residual water content, an average length of from about 0.1 to 0.7 inch and a diameter of about 6 mu to about 13 mu ; (C) adding to said dispersion containing said surfactant and said fibers an organic, water-insoluble, film-forming, polymeric binder; and (D) forming from said aqueous dispersion a dried, non-woven dimensionally stable composite sheet comprising from about 5 to about 50 wt.% of said cellulosic fibers and from about 5 to about 25 wt.% of said glass fibers.

Description: COMPOSITE MATERIALS AND METHOD OF PREPARATION Technical Field This invention pertains to non-woven, fibrous composite materials in sheet form which are particularly useful as backings and interliners for surface covering laminates. A method of producing these sheets and laminates is also disclosed. Background of the Invention Laminated surface coverings for walls, ceilings, floors and furniture, such as counter, table and desk tops have been known for many years. These coverings are typically formed of polyvinylchloride as a homopolymer or copolymer, or some other resinous material such as polyurethane. To supplement the mechanical strength of the resins during processing and in the final product, such surface coverings generally incorporate a fibrous backing or interliner. The fibrous material employed for many years has been asbestos, which has set a standard for SUBSTITUTE SHEET dimensional stability, strength and other physical and chemical properties, including the ability to retain dimensional stability over a wide range of temperature and moisture conditions. However, asbestos has been linked to serious health hazards and its use has been banned or severely limited in many countries. A long list of fibrous materials has been suggested to be used alone or in combination in an effort to replace asbestos in backing and interliner sheets employed for this purpose. The various fibers have included polyolefins, polyesters, polyamides, or the like alone or in combination with mineral fibers, such as glass, and wood pulp as well as other cellulosic fibers. The use of cellulosic fibers,such as wood pulp, as the sole f ibrous component in the laminates and backing sheets has been suggested. However, sheets incorporating only cellulose fibers are typically subject to marked hygroexpansivity. The resulting product is often dimensionally unstable and swelling will often occur in the sheet and in any laminated surface covering in which the sheet is incorporated. A marked curl about the borders of the laminate and buckling between the lateral margins will also occur, sometimes resulting in the delamination of the backing sheet from the surface covering. To illustrate the significance of dimensional stability, surface coverings must be capable of use in a wide variety of climatic conditions, particularly humidity and temperature. These surface coverings are applied to walls, floors, and other substrates, using adhesives. The alignment and abutment of contiguous segments of surface covering must remain in registry after application. Excessive expansion or contraction of the backing sheet may result in delamination from the surface coating which is typically a stable vinyl layer. In extreme cases, this SUBSTITUTE SHEET may result in the separation of the laminate from the surface of the floor or wall to which the laminate has been applied. A method in which a standard paper-making apparatus could be employed in the manufacture of a material for use as a backing sheet or interliner that would be substantially dimensionally stable and substantially resistant to delamination would be particularly useful. If, in addition, the material also exhibited a high internal bond and did not become brittle and, further, exhibited the physical properties of a material incorporating asbestos fibers, it would also represent a significant step forward in the art. As noted above, many references have suggested the use of glass fibers in composite sheets of this type. Processing such glass fibers has proven to be difficult however. Glass fibers in their common commercial form contain some residual moisture, tend to agglomerate and, even after dispersal,, tend to reagglomerate even under agitation. One solution to this problem has been to add such glass fibers only after they have been pre-slurried in water in a separate step. U.S. Patent No. 4,609,431 discloses the off-line slurrying of glass fibers which are then combined and mixed together with the other ingredients. Several references disclose the direct addition of glass fibers, or at least lack sufficient description so that direct addition is inferred. For example, U.S. Patent No. 4,024,014 to Akerson, the subject matter of which is a process for preparing a hardboard sheet, discloses the use of glass fibers as a minor constituent among mineral fibers and materials. Added directly into a slurry of about five percent consistency, the glass fibers represent a partial consistency of no more than one- SUBSTITUTE SHEET quarter of a percent (0.25%). Published Defensive Disclosure T103903 to Campbell, particularly in Example 17, shows an order of addition similar to that of the present invention. Yet glass fibers are added to an overall mixture representing about a 2 to 2.5% consistency at a partial consistency of glass fibers of about 0.18%. U.S. Patent 4,225,383 to McReynolds, particularly in Examples 63 and 64 which deal with glass fiber, also shows what appears to be the direct addition of glass fibers. The fibers are added to a mixture having an overall consistency of about 6 percent. However, the partial consistency of the glass fibers is only about 0.06%. No filler is present at the time glass fibers are added and no dispersant is employed. * J.S. Patent 4,274,916 to Grose, having a common assignee with the present application, also discloses the direct addition of glass fiber. However, no filler is present at the time the glass f ber .s added and-"a different class of dispersants are employed. Objects of the Present Invention It is a primary object of the present invention to provide non-woven, fibrous materials in sheet form which are useful as dimensionally stable backings and interliners for surface covering laminates. It is a further object of the present invention to provide a method for the manufacture of non-woven, fibrous composite materials useful as dimensionally stable backings and interliners for surface covering laminates which method employs standard paper-making apparatus. It is also an object of the present invention to provide the aforementioned type composite material and one which contains a relatively high proportion of glass SUBSTITUTE SHEET fibers . Summary of the Invention According to one embodiment of the present invention, there is provided a method for making a non-woven, dimensionally stable composite ≤heet comprising a polymeric binder, cellulosic fibers, and glass fibers comprising the following steps (A) - (D) in sequence: (A) forming an aqueous dispersion of: (i) cellulosic fibers in the form of a wood pulp consisting essentially of soft wood fibers having an external fibrillation characterized as a drainage of from 260 to 600 cc (Canadian Standard Freeness) and an internal fibrillation characterized as a breaking length of from 4 to 12 km measured at room temperature and a density of from about 0.50 to about 0.75 gm/cσ, determined from a Tappi Standard Handsheet and, measured according to TAPPI- T494 om 81 and T220 om 83 respectively, the amount of said pulp in said dispersion being such that the consistency thereof is from about 0.75 to about 5%, as measured at a temperature of about 70 to 80°F; and (ii) a water-soluble surfactant comprising a dispersion aid for said glass fibers in an amount sufficient to disperse said glass fibers in said dispersion; (B) adding to said dispersion containing said cellulosic fibers and said surfactant chopped glass fibers in an amount such that the partial consistency of said glass fibers in said dispersion is from about 0.5 to about 3.0%, said added glass fibers having only residual water content, an average length of from about 0.1 to SUBSTITUTE SHEET 0.7 inch and a diameter of about 6μ to about 13μ; (C) adding to said dispersion containing said surfactant and said fibers an organic, water-insoluble, film-forming, polymeric binder; and (D) forming from said aqueous dispersion a dried, non-woven, dimensionally stable composite sheet comprising from about 5 to about 50 wt.% of said cellulosic fibers and from about 5 to about 25 wt.% of said glass fibers. In preferred form, a filler is included in the dispersion formed in Step (A) above, that is, the filler is added prior to the addition of the glass fibers of Step (B) above. In accordance with the method of the present invention, there can be produced an improved composite sheet which is dimensionally stable and which 'contains a ' relatively high proportion of glass fibers. Accordingly, the present invention provides also a non-woven, dimensionally-stable composite sheet characterized by a relatively high content of glass fibers and useful as a backing or interliner for surface covering laminates, said sheet comprising: (a) from about 5 to about 50 wt.% of soft wood fibers having an external fibrillation characterized as a drainage of from 260 to 600 cc (Canadian Standard Freeness), an internal fibrillation characterized as a breaking length of from 4 to 12 km at room temperature and a density of about 0.50 to about 0.75 gm/cc, determined from a TAPPI Standard Handsheet and measured according to TAPPI T494 om 81 and T220 om 83 respectively; an average fiber length of SUBSTITUTE SHEET 8/01319 ' ' 7 about 0.05 to about 0.2 inch; and a ratio of length to diameter of about 60:1 to 120:1; (b) from about 5 to about 25 wt.% of chopped glass fibers having an average length of about 0.1 to 0.7 inch and an average diameter of about 6μ to about 13μ; (σ) at least about 15 wt.% of filler; and (d) an organic, water-insoluble, film- forming, polymeric binder. In preferred form, the sheet of the present invention contains about 9 to about 20 wt.% of glass fibers, most preferably about 12.5 to about 15 wt.% of glass fibers. Excellent properties of sheets prepared in accordance with the present invention are exemplified in the Example section of the present application which includes also a detailed description of the invention. Brief Description of the Drawing The figure is a diagrammatical view of an apparatus illustrating the method of the present invention. Detailed Description of the Present Invention The present invention provides non-woven, fibrous composite materials in sheet form which are particularly useful as backings and interliners for surface covering laminates. Also, as noted above, the composites are prepared from: i) cellulosic fibers; and refined softwood pulp is preferred; ii) non-σellulosic fibers including at least glass fibers; iii) preferably inorganic fillers; and talc is SUBSTITUTE SHEET preferred; iv) latex binder resins; and acrylic resins and styrene-butadiene rubbers are preferred; and v) at least one dispersant; and polyoxyethylated alkylamines are preferred. As set out in aforementioned Patent No. 4,609,431, attention to the refining of the softwood pulp, as measured by breaking length and density, may assist in securing the internal strength necessary to a satisfactory backing sheet or interliner. In addition, it was disclosed there that the separate dispersal of the glass fiber may be facilitated by the use of a surfactant anti¬ static agent. Such an anti-static agent is believed to assist in preventing the re-agglomeration of glass fibers in the aqueous slurry. It has now been determined that the use of such an anti-static agent, together with control over the order of addition of the various materials, will allow the addition of glass fibers in thei.r common commercial form, i.-e., containing only residual moisture, directly into the aqueous slurry of other materials at a consistency level higher than previously shown. Further, the formulations herein disclosed are believed to produce composite materials which have independent novelty over the art and offer great strength characteristics per unit thickness at lower cost. In the preferred embodiment, the composite materials of the present invention are precipitated into a final slurry from which they may then be formed into a sheet. The sheet is carried into a standard paper-making machine on a forming wire or other support, where the liquid, which is primarily water, is drained away and the sheet is dried. An optional size may then be deposited on one or both sides- of the resulting sheet in a manner well known SUBSTITUTE SHEET to the art . After the non-woven fibrous composite material has been formed into a sheet in this manner, it may be used for some purpose in that form or it may be further processed, as by processing into a surface covering material. This is typically done by depositing one or more layers of polymeric material, such as vinyl chloride polymers or copolymers on one or both sides of the sheet. Any of these layers may be applied in liquid form, such as a plastisol, organosol or aqueous latex which is then gelled or dried, or by fusing a calendered sheet, or some other method, and, if desired, printing the polymer surface. The product would then typically be coated on the printed surface with a transparent resinous wear-layer and heated to fuse the resins. The figure is intended to be a diagrammatic view of an apparatus illustrating the method of the present invention. This apparatus, shown generally as (10) includes a plurality of mixing and holding tanks, collectively referred tc* herein as the "stock preparation area" (12) coupled with relatively standard paper-making and drying machinery, collectively referred to herein as the "wet end" (14) and the "dry end" (16). In the stock preparation area (12), water and refined wood pulp are introduced via feed line (18) from a suitable refiner (not shown) into a mixing vessel (20), such as a standard hydrapulper, and agitated. The wood pulp should be composed of softwood pulp fibers that are refined to a high degree of internal and external fibrillation as an aqueous dispersion in one or more refiners (not shown), which is specially equipped with agitation means adapted to brush and fibrillate the pulp fibers. When suitably treated, the aqueous dispersion- in the refiner is transferred by some means such as a pump through feed line (18) into the mixing vessel (20). To SUBSTITUTE SHEET assure effective dispersion and fibrillation, the concentration of pulp fibers in the refiner should not be too high. Although operable with at least about 0.5 percent, a concentration of about 3 percent pulp is recommended for commercial purposes. The term "consistency" as used throughout this specification, and in the claims which follow, shall be used to refer to the dry weight proportion of dispersed or dissolved materials in aqueous dispersions or solutions, respectively. It is believed to be beneficial to pre-soak the wood fibers before treatment, allowing the fibers to absorb water and swell. The refining step is also believed to be important to the present invention and the primary objective of the refining step is the roughening of the wood fiber surface, severing of the fibers along their lengths, and swelling of the treated fibers. This treatment is referred to as external and internal fibrillation as opposed to predominantly external fibrillation which includes a cross-sectional chopping action which abbreviates the length of the fibers. When properly fibrillated r the wood pulp fibers should have a tensile strength, expressed as breaking length in a TAPPI Standard Handsheet prepared according to TAPPI Method T-205 om-81, of at least 4 to 12 kilometers (km) at room temperature, and preferably within the range of 6 to 12 kilometers (km). The fibers should also have a density in such a Handsheet of from about 0.50 to about 0.75 grams per cubic centimeter (gm/cc), and preferably from about 0.67 to about 0.72 gm/cc. The wood pulp fibers employed in the process as thus described and incorporating the particular tensile strength and bonding properties expressed as breaking length and density, while retaining generally maximum SUBSTITUTE SHEET fiber length, have been obtained using a Double Disc refiner, manufactured by the Beloit Corporation-Jones Division, for large volume mill production. Small laboratory control samples and handsheets, can be advantageously prepared with a laboratory Valley beater. The cross-sectional chopping of the fibers can be minimized in the foregoing refiners. Another desirable beater for use in the practice of the present invention is the Jones Bertrams beater. Other suppliers of suitable production equipment in the United States include: Bolton-Emerson; C-E Bauer, a subsidiary of Combustion Engineering; and the Sprout- Waldron Division of the Koppers Co., Inc. Operative only with respect to some pulp types, and therefore less preferred refiners include the breaker beater of the Hollander type, the Hydrapulper manufactured by Black Clawson, Inc., Middletown, Ohio, the Dynopulper and Vortex beater. Typically, pulp is initially received as a-dry sheet that is slushed, that is, dispersed and then refined, in an aqueous medium. As noted previously, pre-soaking the pulp is believed to be beneficial. A refiner, such as one of those named above, is employed for refining the pulp, as described above, and the pulp is treated for a sufficient period of time to obtain the desired properties. This time will vary with the particular type of pulp employed. Typically, the pulp may be first brought to a consistency of from about 0.75 percent to about 5 percent, preferably from about 2 percent to about 4 percent, at a temperature of about 70° to 80°F. To secure all of the advantages of such highly refined wood pulp, it is believed to be advantageous to employ as the cellulosic fiber component, wood pulp derived from softwoods (gymnosperms) . Included within this term are the evergreens such as spruce, pine, and the SUBSTITUTE SHEET like, having longer fibers than those of the hardwoods. The softwoods preferred for- use herein are characterized by an average length to thickness (diameter) ratio, determined microscopically, of about 60:1 to 120:1 and preferably about 100:1 respectively. The softwood fibers vary in length from about 0.05 inch to about 0.2 inch. Commercially available pulps of this kind will typically contain a percentage of hardwood, which, when present, may comprise up to twenty percent or more of pulp. Providing the necessary external and internal fibrillation can be obtained, such pulps are entirely operable for the purposes of the present invention. The operative softwood pulps include those characterized as mechanical pulp or groundwood and chemical pulp including sulfite, and preferably sulfate kraft, pulp as described in Kirk-Othmer, Encyclopedia of Chemical Technology, pages 495 and 496, vol. 14 (1967) or, indeed, that derived from the soda process. In the practice of the sulfite process, the wood is digested in a .solution of calcium bisulfite and sulfurous acid. In the sulfate or kraft process, a mixture of sodium hydroxide and sodium sulfide is used; the sulfide being derived from the reduction of sodium sulfate introduced into the process in the course of treatment. The unbleached variety of mechanical, semi-chemical or chemical pulp is generally preferred over the bleached or semi-bleached pulp because of the greater absorbency of the unbleached pulp in general. Unbleached chemical pulp is preferred, too, because of its generally greater strength and durability. However, any of the foregoing pulps may be used if they are capable of attaining a density and breaking length as a result of internal and external fibrillation which will provide the necessary strengths in the composite material. Preferred pulps will attain these characteristics more easily. SUBSTITUTE SHEET A preferred source of pulp fibers for use herein, although bleached, is Alberta Hi-Brite bleached softwood pulp available commercially from the Champion Corporation. This pulp has been refined to a breaking length after refining of as high as 10 to 11 kilometers. Also preferred is MacKenzie unbleached softwood manufactured by British Columbia Forest Products, Inc., Vancouver, British Columbia, Canada. Also useful, although less preferred, is St. Croix bleached pulp manufactured by Georgia-Pacific Corporation at Woodland Maine. Particularly preferred in the practice of the present invention are kraft sulfate softwood pulp fibers having an average fiber length of 0.05 inch to 0.2 inch and a length to width ratio of about 80:1 to 120:1 and more particularly about 100:1. Fibrillation, as the term is used, throughout this specification, has previously referred to only the external fibrillation of wood pulp fibers, a property measurable by use of standard visual microscopic techniques and determination of drainage properties or freeness. The usual measure of this latter property is the Canadian Standard Freeness Test (CSF) wherein the freeness value is determined according to TAPPI Standard T 227 m58 on a sample of 3 grams of pulp fibers diluted with water to 1000 cubic centimeters (cc). In terms of the external fibrillation, the pulp fibers should have a CSF of from at least about 260cc to 600cc, but this only measures the degree of external fibrillation. Internal fibrillation may be demonstrated by an increase in fiber swelling and flexibility. These characteristics are not measured adequately by drainage or freeness determinations. High internal fibrillation together with a significant degree of external fibrillation are preferred for the development of high internal bond strength in the practice of the present invention. SUBSTITUTE SHEET The increase in fiber swelling and flexibility resulting from internal fibrillation causes the density of the pulp handsheet to increase. By requiring minimum strength properties of the wood fibers together with a minimum density, the degree of internal bond strength of the pulp fibers can be defined. The internal bond properties obtained by the combination of external and internal fibrillation is believed to result in the promotion of sites for latex and filler deposition and adhesion. In addition, these properties aid in the development of a suitable wet tensile strength, necessary when a wet web formed of the proper materials is transferred from a standard Fourdrinier papermaking machine to the drying rollers typically employed in papermaking. Finally, these properties are believed to aid in obtaining a dry composite sheet final product with a density appropriate for use as a backing sheet or interliner in a surface covering laminate. It has been found, generally, that the higher the degree of internal fibrillation, the more of ari inexpensive inorganic filler which can be employed to reduce the concentration of expensive polymeric latices while still obtaining a composite sheet with a satisfactory internal bond. The degree of external and internal fibrillation may be accurately determined by the combination of density and the tensile strength, as measured by breaking length, of the pulp fibers. Breaking length and density are each determined from a TAPPI Standard handsheet prepared from the pulp fibers by TAPPI T205 om 81, and measured by TAPPI T494 om 81 and TAPPI T220 om 83, respectively. To determine breaking length using hand sheets so prepared, TAPPI T494 om 81 is employed to yield a value in kilometers by means of the equation: SUBSTITUTE S HEET 3.658 x Tensile Strength in lb/in. Breaking Length = basis weight in lb./lOOO sq. ft. Density is determined using TAPPI T220 om 83 to yield 5 a value in grams per cubic centimeter using the equation: R (mass per unit area in g/m 2 Density = 25.4 x thickness in mils, or 0 0.1922 x basis weight in lb/1000 sq.ft. thickness in mils. Using these standards, a softwood pulp having a breaking length of from 4km to 12km and a density of about 5 0.50 gm/cc to about 0.75 gm/cc is considered important in the attainment of a composite sheet material having the advantages of the present invention. It should be noted in this context, that density and breaking length may be determined conveniently for a G particular refined pulp by preparation of handsheet samples using the Valley Beater. These results should be fairly well-matched by the pulp handsheet compared to high volume mill production of refined pulp sheet of an equivalent density and breaking length and, therefore, a 5 similar degree of internal fibrillation, using a Beloit Double-Disc refiner, for example. It should also be noted that multipass refining of the pulp may be employed in both the laboratory and mill to secure the desired density and breaking length, if necessary. The concentration of wood pulp fibers in the final product composite sheet by dry weight is within the range by weight of from about 5 percent by weight to about 50 percent. A concentration of 18 percent to 40 percent, and more particularly about 20 percent to 25 percent, by dry weight of the 'composite sheet, is preferred. SUBSTITUTE SHEET 16 With continued reference to the Figure, also charged into the mixing vessel (20) is a quantity of one or more water insoluble particulate fillers. Although various water-insoluble organic and inorganic fillers may operably be employed in the present invention, the fillers employed in the preferred embodiments of the present invention include talc and calcium carbonate. The other fillers which may be used advantageously in the practice of this invention are finely-divided, essentially water-insoluble, inorganic materials. Such materials include, for example, titanium dioxide, amorphous silica, zinc oxide, barium sulfate, calcium carbonate, calcium sulfate, aluminum silicate, clay, magnesium silicate, diatomaceous earth, aluminum trihydrate, magnesium carbonate, partially calcinated dolomitic limestone, magnesium hydroxide and mixtures of two or more of such materials. Chemically treated calcium carbonate is commercially available in a grade in which the particles are comminuted to a particle size such that 100 percent of the particles will pass through a 60 mesh screen (using U.S. Standard Mesh sizes) ** and 96 percent of the particles will pass through a 100 mesh screen. Another commercial grade which is useful in the practice of the present invention has a distribution of particle sizes such that 100 percent of the particles will pass through a 12 mesh screen and 96 percent of the particles will pass through a 325 mesh screen (44 microns). Particularly preferred in the practice of the present invention is a commercially available grade of crushed limestone containing from about 96% to about 98% calcium carbonate. This material would have an oxide analysis of about 1 percent magnesium oxide, about 0.1 percent ferric oxide, about 0.25 percent to 0.75 silica, and 0.2 percent to 0.3 percent alumina as well as traces of sulfur and phosphorous pentoxide on the order of about 0.003 percent SUBSTITUTE SHEET and 0.004 percent, respectively. Talc is commercially available in a grade in which 100 percent of the platy-shaped particles will pass through a 200 Mesh screen and 99.5 percent of the particles will pass through a 325 Mesh screen. Available commercially from Vermont Talc under the Tradename Vertal 7, this material has an oxide analysis of about 38.3% silicon dioxide (Si0 2 ), about 34.0 percent magnesium oxide (M O), about 2.6 percent iron oxide (Fe 2 0 3 ) and less than 2.0 percent aluminum oxide (A1 2 0 3 ). The amount of filler employed in practice of the present invention will vary from about 0 percent to about 55 percent on a dry weight basis and will preferably be from about 15 percent to about 45 percent, on the same basis. With further reference to the mixing vessel (20), it has been found useful to also introduce a water-soluble surfactant, serving in this instance as an antistatic agent. As noted hereinabove, it has previously been found that the dispersal of glass fibers in separate aqueous dispersion may be facilitated by the use of a surfactant antistatic agent. It has now been determined that a separate aqueous dispersion of glass fiber need not be prepared. Rather, employing the teachings of the present invention, commercially available glass fiber, having only residual water content, may be added directly with the other materials in process at a partial consistency of over one-half of one percent. It should be understood that the above-recited order of addition is not critical up to this point, it being only necessary that the dispersion aid, and preferably the filler, be dispersed in the aqueous dispersion prior to addition of the glass fiber. The surfactant employed in the preferred embodiment of the present invention is a polyoxyethylated alkylamine SUBSTITUTE SHEET 18 in which the alkyl moiety is within the range of from nine to eighteen carbon atoms and preferably within a range of nine to ten carbon atoms. Nonylamine and decylamine are particularly preferred. Each molecule of polyoxyethylated a l kylamine contains from 5 to 10 ethylene oxide moieties, and the amine has an average molecular weight of from about 400 to 700. This surfactant is generally incorporated in the aqueous dispersion in a concentration by weight of about one one-hundredth of one percent (0.01%) to about five one-hundredth of a percent (0.05%). One such surfactant is commercially available from the GAF Corporation under the trademark KATAPOL and has been employed advantageously herein. Anioniσ and cationic surfactants are well known in the art and suitable materials of those classes can be selected, for example, from among those listed in the annual issues of "MσCutcheon's ' Detergents and Emulsifiers", published by McCutcheon's Division, Allured Publishing Corporation, Ridgewood, NJ. Examples of non- ionic surfactants are also provided in the above-noted reference. To this mixture containing at least the surfactant and preferably the inorganic filler is added a non- cellulosic fiber consisting of at least glass fibers, while rock wool and other suitable mineral or organic fibers may also be present. The preferred glass fiber material is chopped glass fibers such as one of the available commercial grades of glass fiber of Owens- Corning Fiberglas'Or Johns-Manville Corporations. Glass fibers do not absorb any moisture, have high tensile strengths, very high densities and excellent dimensional stability. The glass fibers have average- lengths of from about 0.1 inch to 0.7 inch and have an average diameter in the range of twenty-four one hundredth-thousands of an SUBSTITUTE SHEET inch (24 hts. ) or about six microns (6μ) to about fifty one hundred-thousandths of an inch (50 hts) or about thirteen microns (13μ). The partial consistency of glass fibers for effective dispersion is within the range of up to about 3.0 percent, and preferably at least 0.5 percent and most desirably at least about 1 percent, by weight of the dispersion. It is believed that the presence of the surfactant and the inorganic filler prevents the re- agglomeration of the glass fibers. The proportion of glass fibers in the final composite product sheet is within the range of about 5 percent to about 25 percent by dry weight. Further, satisfactory results are generally secured at from about 9 percent to about 20 percent and most desirably from about 12.5 percent to about 15 percent by dry weight. However, it should be noted that cost, rather than process or finished product requirements, represents the most serious limitation on the use of such fibers and such fibers may be employed in excess of the ranges given above. While not required, it may be advantageous to also include a portion of some type of synthetic fibrous material as part of the make-up of the composite material. In this regard, it should be noted that polyethylene fibers have been used advantageously at levels of about ten percent of the dry substance, although again, cost rather than process or finished product requirements limit the use of such fibers. It is assumed, therefore, that higher levels of such fibers could be employed advanta¬ geously, as well as other synthetic fibers and mixtures thereof. It should also be apparent to one skilled in the art that preparation of a composite material of this nature and kind is assisted by the addition of various water treatment additives, conditioning agents and the like, such as wet and dry strength resins, defoaming agents, pH adjustments and the like. Many such agents are known to those skilled in the art, and neither the process nor the products of the present invention are intended to be limited thereby. The water-soluble wet-strength resins which have been used advantageously herein include polycaprolactone- epichlorohydrin resins or epiσhlorohydrin-polycaprolactone polyols. Illustrative of the former are those available commercially from the E.F. Houghton & Co., Valley Forge, Pennsylvania, under the trade name and grade designation REZOSOL 388-15. Illustrative polyols are those available commercially from the Union Carbide Corp. under the trade name NIAX. Particularly useful in the practice of the present invention are epichlorohydrinpolyamide resins such as those commercially available from Hercules Incorporated under the trade name and grade designation KYMEME 557 and POLYCUP 361. Illustrative of a dry-strength resin useful in the practice of the present invention is a partially hydrolyzed pβlyacrylamide resin commercially available " from the Dow Chemical Company under the Tradename Separan 87D. Illustrative of defoaming agents which has been used effectively herein are compositions commercially available under the tradenames NOPCO NXZ from the Diamond Shamrock Company, and DeAirex 1027 from E.F. Houghton & Co. Alum, a common water treatment chemical, has also been employed advantageously herein as well as Ammonium Hydroxide, which has been employed to adjust pH. A trace amount of an antioxidant may also be added to improve the qualities of the final product. All of these materials, additives and agents may be added to the mixing vessel (20) or some may be added later, such as after the aqueous dispersion is transferred to a drop chest (24) via feed line (26). Although a latex binder resin may be added at this point, it has proven more expeditious to first screen the dispersion, as illustrated by screen (28), and then transfer the aqueous dispersion to a precipitation tank (30) via feed line (32). In addition to the latex binder resin, any treatment chemicals and additives not previously added may be introduced at this point. The film-forming, water-insoluble, organic polymers useful in the practice of this invention may be natural or synthetic and may be a homopolymer, a copolymer of two or more ethylenically unsaturated monomers or a mixture of such polymers. Representative organic polymers are natural rubber, the synthetic rubbers such as styrene- butadiene rubbers, isoprene rubbers, butyl rubbers and nitrile rubbers and other rubbery or resinous polymers of ethylenically unsaturated monomers which are film-forming, preferably at room temperature or below, although in a particular instance a polymer may be used which is film- forming at the temperature used in preparing ihat sheet. Non film-forming polymers may be used in blends provided that the resulting blend is film-forming. Polymers which are made film-forming by the use of plasticizers also may be used. In the preferred embodiments of the present invention, acrylic resins and styrene-butadiene rubbers are advantageously employed. With respect to acrylic resins, soft resin components, comprising of anionic, water insoluble acrylic resins, which have glass transition temperatures of from -30°C to -10°C are materials such as Amsco Res 6922, from Union Oil Co., TR 934 from Rohm and Haas, and Hycar 2671 from B.F. Goodrich. Hard resin components, comprising of anionic, water soluble acrylic resins, which have glass transition temperatures of from 20°C to 40°C are materials such as Amsco Res 3112, from Union Oil Co., TR 407 from Rohm and SUBSTITUTE SHEET Haas, and Hycar 26138 from B.F. Goodrich. Other suitable acrylic resins, having glass transition temperatures of from -10°C to 20°C are materials such as Dur-0-Cryl 720 from National Starch and Chemical Corp., and Hycar 2600X349 from B.F. Goodrich. While acrylic resins are preferred as the binder for Example II, other film forming, water insoluble, organic polymers useful in the practice of this invention are natural rubber, synthetic rubbers such as styrene- butadiene, isoprene, butyl and nitrile polymers and copolymers, and vinyl and vinylidene chloride polymers and copolymers, depending on the particular properties desired. The styrene-butadiene rubber latices most useful in the practice of the present invention, particularly as set out in Example I, comprise anionic, water-insoluble copolymers or blends of copolymers of styrene and butadiene, together with modifiers for carboxylation and stabilization. The glass transition .temperatures typical Of these latices will range from about -20°C to about +45°C. Suitable latices which have been employed advantageously include those styrene-butadiene resins commercially available from the Dow Chemical Company under the tradenames XD30636.02, XD30571.40, and XD30192 and from the General Tire and Rubber Co. under trade name Genflr 2526. The aqueous dispersion prepared in this manner is next transferred to a machine chest (34) through feed line (36), where the dispersion undergoes continued agitation, as illustrated by agitation means (38). From the machine chest (34) the dispersion is conveyed by some means such as an in-line pump (40), again screened, illustrated as (42), and then transferred through feed line (44) to the headbox (50) of a substantially standard Fourdrinier papermaking machine, shown generally as (60). Between the SUBSTITUTE SHEET pump (42) and . the headbox (50), a supplemental feed line (46) connects into feed line (44). A flocculent may be introduced as necessary from reservoir (48) through feed line (46). This flocculent is employed as necessary to maximize processing ease and the physical properties of the final sheet, typically in amounts from 0 percent to about 0.25 percent. Although many flocculents are known to the art which are useful for this purpose, particularly preferred and employed advantageously herein is an acrylamide polymer and copolymer such as that commercially available under the trademark RETEN 521 from Hercules Incorporated. Also used advantageously, especially where color is of less concern, is a product available from the E.F. Houghton Corp. under the tradename STABILEX 573, and a cationic polyacryl amide available from the Dow Chemical Company under the tradename XD 8494. Employing relatively standard papermaking techniques, the rapidly coagulating mass is taken up on a forming wire " (52) and drained, with the draining water conveyed 'through drainage box (54). The resulting composite sheet (56) is advantageously consolidated by passing through press roll (58) and then conveyed through a series of heated rolls (62) to effect evaporative drying of the composite sheet to a final moisture level of approximately 6 percent. A size dispersed in an aqueous medium may be applied to one or both surfaces of the formed composite sheet (56) following some or all of the evaporative drying. In the preferred embodiment of the invention, such a sizing is employed to assure a smooth uninterrupted surface from errant fibers, or the like. This size serves as well to assure adherence of any minor residues of impurities, filler or fibers that may remain loose or above the surface of the formed sheet. In the figure, the application of the size is SU B S TITUTE SHEET represented by a size press (64). However, such a sizing agent may be applied by any conventional system known to the art, such as a reservoir with a knife coater, knife- over-roll, reverse roll, roll coaters or the like. The sizing applied should be permitted to cure, and additional heated rollers may be provided for this purpose. Finally, the cured composite sheet with or without the application of a size, may be used immediately for some purpose such as a backing or interliner for surface covering laminates. Alternatively, the composite sheet (56) may be taken up and rolled upon itself for storage, transportation or the like, and storage roll (66) illustrates such a supply. To further illustrate the composite sheets prepared in accordance with -the present invention, the following illustrative examples were carried out. Example I Alberta Hi-Brite wood pulp having a dry weight of five hundred and fifty pounds (550 lbs. ) was slurried in a • Tornado mixer with thirty-two hundred gallons (3200 gal.) of river water, and allowed to soak for several days. At the time of use, the pulp was determined to have a Canadian Standard Freeness of 400 and the consistency was three percent (3.0%). All resins were also prepared in advance. Stock was prepared by adding each of the following materials to a Hydrapulper in approximately thirty second intervals: SUBSTITUTE SHEET Formula % Dry Weight (in pounds) 1. Clarified water 2. Alum 0.15 4.1 3. Wood pulp 20.00 550.0 4. Polyethylene fibers 10.00 275.0 (Pulpex E A321 from Hercules, Inc. ) 5. Defoamer (De-Airex 1027 0.20 5.5 from E.F. Houghton) 6. Talc (Vertal 7 from 29.09 800.0 Vermont Talc) 7. Wet-strength resin 2.40 66.0 (Kymene 557H from Hercules, Inc. ) 8. Dry-strength resin 0.60 16.5 (Separan 87D from Dow Chemical) 9. Anti-static 0.02 0.7 (Katapol VP532 from the GAF Corp. ) 10. Glass fiber 14.55 400.0 (Owens-Corning 691-20, 3/16 inch, llμ. fiber) 11. Anti-oxidant , 0.73 20.1 77.74 2137.9 In preparing the stock as noted above, one and one- tenth pounds (1.1 lbs.) of liquid ammonium hydroxide were added to adjust the pH to 7.0. The total mixing time was approximately fifteen minutes (15 min. ) and the final consistency was about 5.4%. The aqueous dispersion prepared in this manner was first transferred to a drop chest, where it was further diluted with water for a consistency of about 2.5% and then screened through a slotted screen having openings of 0.045 inch into a slurry tank. From this tank, a portion of the above aqueous dispersion representing three hundred and forty-four pounds (344.0 lbs.) by dry weight was transferred to a precipitation tank and combined with a quantity of styrene-butadiene latex (XD30571.40 from Dow Chemical) having a dry weight of ninety-eight and three-tenths SUBSTITUTE SHEET pounds (98.3 lbs.) and representing 22.21 percent of the formula by weight. The precipitation cycle was approximately one hundred seconds (100 sec. ). At this point, the aqueous dispersion had a consistency of about 3.1% and was transferred to a machine chest. This aqueous dispersion further diluted to a final consistency of about one percent, representing ninety-nine and ninety-five one-hundredths of the formula by weight, was again screened through 0.014 inch horizontal slots and delivered to the headbox at a flow rate of fifteen hundred ninety-six gallons per minute (1596 gal./min.). To this flow, prior to delivery to the headbox, a one gallon per minute (1.0 gal./min.) flow of a "touch-up" flocculent, diluted in additional water to 0.2% was added, (XD8494 from Dow Chemical). This flocculent represented the final five one-hundredths of the formula by weight. The rapidly coagulating mass was introduced into the headbox of a relatively standard papermaking machine and taken up on a forming wire to form a sheet. The sheet was partially dried and coated on both sides. The sheet was then fully dried and taken up on a storage roll. Physical properties for the composite sheet prepared in this manner are listed in the following table. Example II One thousand dry weight pounds of Alberta HiBrite wood pulp was slurried in a Tornado mixer and allowed to soak as in Example I. At the time of use, this pulp had a Canadian Standard Freeness of 540 and the consistency was three percent (3.0%). Stock was prepared by adding each of the following materials to a Hydrapulper in approximately 60 second intervals: SUBSTITUTE SHEET Formula % Dry Weight (in pounds) 1. Clarified water 2. Talc (Vertal 7 from 31.07 1,250 Vermont Talc) 3. Calcium Carbonate No. 9.92 400 (from H.M. Royal) 4. Wood pulp 24.86 1,000 5. Anti-static (Katapol 0.05 2 VP-532 from GAF) 6. Glass fibers (Owens 12.43 500 Corning 691-20, 1/8 in. , 7-hv- fiber) 7. Defoamer (NXZ from 0.15 Diamond Shamrock) 78.48 3,156 The total mixing time was approximately 12 minutes, and the consistency was about 6%. The aqueous dispersion prepared in this manner was transferred to a drop chest where it was further diluted with clarified water to a consistency of about 2.5%. Also added to this chest was forty pounds (by dry weight) of a wet strength resin (Kymene 557H from Hercules, Inc. ) and representing 1.0% of the total formula by weight. This new aqueous dispersion was then transferred through a screen having openings of 0.045 inch wide, into a slurry tank. From this tank, a portion of the above aqueous dispersion representing three hundred and thirty pounds (330.0 lbs.) by dry weight was transferred to a precipitation tank where it was combined with a quantity of acrylic latex emulsion (Hycar 26138 from B.F. Goodrich) having a dry weight of eighty-two and five-tenths pounds (82.5 lbs.), representing 19.95% of the formula by weight. Also added to this aqueous dispersion after latex addition was one and one-half pounds (1.5 lbs.) of Aluminum Sulfate, representing 0.37% of the formula by weight. After agitation for about ten seconds, the latex emulsion was broken and latex particles deposited uniformly on the SUBSTITUTE SHEET solid particles of slurry. At this point the slurry gave the appearance of very fine particles which would drain slowly on a papermaking machine. While this aqueous dispersion was still under agitation, a high molecular weight, anionic acrylamide-based copolymer flocculating agent RETEN 521 from Hercules, Inc.), having a dry weight of eighty-five one hundredths of a pound (0.85 lbs.) was added. This material transformed the fine slurry appearance into a coarser slurry of the sort which would be expected to drain more quickly on a paper machine. Total agitation time required for the addition of Aluminum Sulfate and RETEN 521 in this manner was about 45 seconds. At this point the aqueous dispersion had a consistency of about 3.0%, and was transferred to a machine chest. From the machine chest, the aqueous dispersion was transferred to the headbox of the paper machine. During transportation, the aqueous dispersion was further diluted with water to 1% consistency, and was screened through a screen having 0.014 inch wide horizontal slots. Delivery of the dispersion to the headbox was at a flow of seventeen hundred and fifty gallons per minute (1,750 gal./min.). To this flow, prior to delivery to the headbox, a four gallons per minute (4.0 gal./min.) flow of "touch-up" flocculent, diluted in water to 0.25% was added (RETEN 521 from Hercules). The quantity of this flocculent added represented 0.2% of the formula weight. The rapidly coagulating mass was introduced at the headbox of a relatively standard papermaking machine and taken up on a forming wire to form a sheet. The sheet was partially dried and coated on both sides. The sheet was then fully dried and taken up on a storage roll. Physical properties for the composite sheet prepared in this manner are listed in the following table. SUBSTITUTE SHEET TABLE Example Property Unit __ 2 Control 1 Ream Weight Lbs. per 480 sq.ft 26.0 24.1 57.8 Weight per Lbs. per sq. yard .49 0.45 1.08 square yard Gauge Inches x 1000 14.0 14.6 20.5 Gauge per Caliper per ream 0.54 0.61 0.35 weight ratio weight Ambient Pounds per inch 89 71 35 Tensile - Elongation Percent 2.8 2.3 2.3 Mullen Pounds per sq.in. 103 96 56 Stiffness T/2 Units/2 33 50 43 Hot tensile - Pounds per inch 21 19 8 350°F Water Percent 51 108 38 Absorption Water Growth Percent .14 .20 .43 * Non-Asbestos Dimensionally Stable Felted Sheet Commercially Available from Congoleum Corporation under the tradename 020 White Shield II (WSIIB). Terms appearing in Table 3 are defined as follows: Ambient Tensile: The tensile strength of the composite material conditioned for 24 hours at 73° Fahrenheit and 50% relative humidity. Portions of the sheets are cut into 1 inch by 7 inch strips and the minimum thickness over the test area is determined. The tested strip is placed in an Instron testing machine having a 5 inch span and the elongation and pounds at break are measured as the machine is operated at a cross head speed of 1 inch per minute. SUBSTITUTE SHEET Elongation: The percent elongation of the composite material is determined at 73° Fahrenheit over a 5 inch span at the time the ambient tensile is made. Mullen: The lateral burst of the composite material as determined by TAPPI test method T 403-os-76. Stiffness (T/2): Regular stiffness of the composite material is determined according to TAPPI test method T 489-OS-76. The Taber value is obtained in gram centimeters and divided by 2. Hot Tensile: The tensile strength of the composite material at 350°F. This physical property is tested in the same manner as ambient tensile except that the test specimen is heated to 350°F for two minutes while clamped in the jaws of the Instron testing machine. Water Absorption: The water absorption of a preconditioned portion of material held for 24 hours at 73°F and 50% relative humidity is determined by soaking the sample (12 inches by 12 inches) in water for 24 hours and recording the weight increase and.calculating the percentage increase. Water Growth: After following the same procedure as that set out for Water Absorption, the percent increase in the width of the sample in both the machine and cross- machine direction is compared with the original conditioned sample. It will be evident that the terms and expressions that have been employed herein are used as terms of description and not of limitation. There is no intention in the use of such terms and expressions of excluding equivalences of the features shown and described or portions thereof, and it is recognized that various modifications are possible within the scope of the invention claimed. SUBSTITUTE SHEET

Claims: Claims 1. A method for making a non-woven, dimensionally stable composite sheet comprising a polymeric binder, cellulosic fibers, and glass fibers comprising the following steps (A) - (D) in sequence: (A) forming an aqueous dispersion of: (i) cellulosic fibers in the form of a wood pulp consisting essentially of soft wood fibers having an external fibrillation characterized as a drainage of from 260 to 600 cc (Canadian Standard Freeness) and an internal fibrillation characterized as a breaking length of from 4 to 12 km measured at room temperature and a density of from about 0.50 to about 0.75 gm/cc, determined from a Tappi Standard Handsheet and measured according to TAPPI T494 om 81 and T220 om 83 respectively, the amount of said pulp in said dispersion being such that the consistency thereof is from about 0.75 to about 5%, as measured at a temperature of about .70 to 80°F; and (ii) a water-soluble surfactant comprising a dispersion aid for said glass fibers " in an amount sufficient to disperse said glass fibers in said dispersion; (B) adding to said dispersion containing said cellulosic fibers and said surfactant chopped glass fibers in an amount such that the partial consistency of said glass fibers in said dispersion is from about 0.5 to about 3.0%, said added glass fibers having only residual water content, an average length of from about 0.1 to 0.7 inch and a diameter of about 6μ to about 13μ; (C) adding to said dispersion containing said surfactant and said fibers an organic, water-insoluble, film-forming, polymeric binder; and (D) forming from said aqueous dispersion a dried, non-woven dimensionally stable composite sheet comprising from about 5 to about 50 wt.% of said cellulosic fibers and from about 5 to about 25 wt.% of said glass fibers. 2. A method according to Claim 1 wherein the concentration of said surfactant in the dispersion formed in Step (A) is from about 0.01 to about 0.05 wt.%. 5 3. A method according to Claim 1 wherein said dispersion formed in Step (A) includes a polyoxyethylated alkylamine surfactant. 4. A method according to Claim 3 wherein said 10 surfactant is a polyoxyethylated nonylamine or decylamine. 5. A method according to Claim 1 wherein the binder added in Step (C) comprises and acrylic polymer or a styrene-butadiene polymer. 6. A method according to Claim 1 in which a filler 15. is included in the dispersion formejd in Step (A). 7. A method according to Claim 6 wherein the filler is talc or calcium carbonate or a mixture of talc and calcium carbonate. 8. A non-woven, dimensionally-stable composite sheet 20 characterized by a relatively high content of glass fibers and useful as a backing or interliner for surface covering laminates, said sheet comprising: (a) from about 5 to about 50 wt.% of soft wood fibers having an external fibrillation characterized as a 5 drainage of from 260 to 600 cc (Canadian Standard Freeness), an internal fibrillation characterized as a breaking length of from 4 to 12 km at room temperature and a density of about 0.50 to about 0.75 gm/cc, determined from a TAPPI Standard Handsheet and measured according to SUBSTITUTE ' SHEET TAPPI T494 om 81 and T220 om 83 respectively; an average fiber length of about 0.05 to about 0.2 inch; and a ratio of length to diameter of about 60:1 to 120:1; (b) from about 5 to about 25 wt.% of chopped glass fibers having an average length of about 0.1 to 0.7 inch and an average diameter of about 6μ to about 13μ; (c) at least about 15 wt.% of filler; and (d) an organic, water-insoluble, film-forming, polymeric binder. 9. A sheet according to Claim 8 comprising from about 15 to about 45 wt.% of said filler. 10. A sheet according to Claim 9 comprising from about 18 to about 40 wt.% of said wood fibers and from about 9 to about 20 wt.% of said glass fibers. 11. A sheet according to Claim 10 comprising from about 20 to about 25 wt.% of said wood fibers and from about 12.5 to about 15 wt.% of said glass fibers. 12. A sheet according to Claim 8 comprising from about 9 to about 20 wt.% of glass fibers. 13. A sheet according to Claim 12 comprising from about 12.5 to about 15 wt.% of said glass fibers. SUBSTITUTE SHEET

Inventors: BAILEY WILLIAM J, BUHNER ROBERT WALTER, FOWLER JOSEPH ALLEN, GROSE REGINALD EUGENE, JACKEY PHILIP ALBERT, MORTON JOHN FRASER, PEARSON JOHN DOUGLAS, PIACENTE ANTHONY NIEL, BAILEY, WILLIAM, J., BUHNER, ROBERT, WALTER, FOWLER, JOSEPH, ALLEN, GROSE, REGINALD, EUGENE, JACKEY, PHILIP, ALBERT, MORTON, JOHN, FRASER, PEARSON, JOHN, DOUGLAS, PIACENTE, ANTHONY, NIEL
Applicants: CONGOLEUM CORP, CONGOLEUM CORPORATION
Application year: 1987
Main classification: D21H5
IPC codes: D21H13, D21H17