STITCH BONDED FABRIC, USE OF SAME FOR MAKING COATED ABRASIVES, AND COATED ABRASIVES

Abstract: Stitch bonded fabrics suitable to be used as backings for flexible coated abrasives with facile straight tear in either the length or cross directions have (1) an areal density be­ tween 51 and 153 gm/m², (2) a tensile strength in the length direction between 5.4 and 12.6 kN/m of width, (3) a tensile strength in the cross direction which is between 5.4 and 11.7 kN/m of length and is between 0.9 and 1.35 times as great as the length direction tensile strength, (4) an elongation to break in the length direction of not more than 40%, and (5) an elongation to break in the cross direction of not more than 35%. To make the coated abrasives, the fabric is pre­ pared for coating by saturation with at least its own weight of a finishing adhesive composed primarily of latices of acrylic homopolymers, acrylic copolymers, butadiene-sty­ rene polymers, or mixtures of these types. Conventional making, grit coating, and sizing are then performed to yield a coated abrasive with a ratio of length direction tensile modulus to cross direction tensile modulus within the range of 0.8 to 1.8.

Description: The invention relates to the field of stitch bonded fabrics, suitable for use in a backing for flexible coated abrasives, i.e., which are a major component of the backings of such coated abrasives. This invention also relates to coated abrasives and particularly to the type of such abrasives which have exceptionally flexible backings and which can readily be torn by hand to yield a reasonably straight torn edge. Before 1974, almost all coated abrasive cloth products were coated on woven cotton cloth, and it was common knowledge among manufacturers and users of coated abrasives that such products could usually be torn carefully by hand in such a way as to produce a substantially straight and unpuckered edge. This property of straight tear is particularly advantageous to users who can not always forecast in advance just what width of coated abrasive they will need at any given time and therefore prefer to buy relatively wide rolls of coated abrasive cloth and tear it to width as needed. While straight tearing capability along lines parallel to the machine direction of the cloth is most common, some products also will tear straight in the cross direction. These are particularly convenient to those who use coated abrasives without the aid of mechanical driving devices and often want to sand workpieces with small concave radii of curvature or small dimensions generally. The introduction of polyester cloth for coated abrasive backings contributed to improved ruggedness and life for coated abrasives in demanding applications, but militated against straight tear. Many coated abrasives on polyester cloth, which have gained great commercial importance, are too strong for most users to tear by hand at all, and when tearing is possible, it usually does not produce straight and unpuckered edges. Coated abrasives having arrays of straight and parallel yarns, most often of synthetic multifilament polyester, as their principal backing strength members have more recently gained commercial use. Coated abrasives of this type are described in European Patent 0 045 408. Some stitch bonded fabrics suited to reinforce coated abrasive backings are described in European Patent Application No. 82 105 651.2 (0 073 313), filed June 25, 1982, assigned to the assignee of the instant application. These references describe primarily coated abrasives which are very rugged and suited to applications in which mechanical damage to the abrasives and their backings is likely. Such coated abrasives have only limited flexibility and are difficult to use in sanding sharply contoured surfaces. Furthermore, the specific coated abrasives described in examples in these applications were almost all too strong for most potential users to tear easily by hand. If tearing was possible, a straight edge was a rare result. Resistance to tearing is obviously one component of damage resistance, but there are many applications for coated abrasives in which mechanical damage is fairly unlikely and the convenience of tearing the coated abrasives by hand to yield straight edges is prized by users of the products. Because polyester and other synthetic yarns have other advantages over cotton in addition to superior damage resistance, and because stitch bonded fabrics have considerable cost and other advantages over woven fabrics, it is an object of the present invention to provide coated abrasives, and fabrics therefor, having the advantages of stitch bonding, synthetic yarns, facile conformability to workpieces of almost any shape, and the ability to be torn straight by hand. The present invention solves this problem by providing a stitch bonded fabric as described in the main claim. Further advantageous features of this fabric are evident from the dependent claims 2 to 8. The invention also teaches use of this fabric for making flexible coated abrasives with facile straight tear in either the length or cross direction according to claim 9. A flexible abrasive which provides for the above-mentioned needs, is evident from the independent claim 10. Further advantageous features of this coated abrasive are evident from the dependent claim 11. A combination of particular types of stitch bonded fabrics with particular types of finishing adhesives has been found to yield coated abrasives with good conformability and straight tear combined with adequate damage resistance for many practical uses. Specifically, the fabrics used should have (1) an areal density between 51 and 153 grams per square meter (hereinafter gm/m²), (2) a tensile strength in the machine direction between 5.4 and 12.6 kilonewtons per meter (hereinafter kN/m) of width, (3) a tensile strength in the cross direction between 5.4 and 11.7 kN/m of length and is between 0.9 and 1.35 times as great as the machine direction tensile strength, (4) an elongation to break in the machine direction of not more than 40%, and (5) an elongation to break in the cross direction of not more than 35%. It should be noted that the fabrics are often heat set before finishing and that the heat setting usually increases the tensile strength in the machine direction; the figures above are for the greige fabric. A physical property of the final coated abrasive which has been found critical to assure straight tear is the ratio between the product of the tensile strength and the percentage elongation at break in the machine and cross directions. This product for each direction is defined and denoted herein as the "tensile modulus" for that direction. The final coated abrasive should have a ratio of machine direction tensile modulus to cross direction tensile modulus within the range of 0.8 to 1.8. Figure 1 is a schematic representation of one type of suitable fabric, made on a single guidebar stitch bonding machine, for use in this invention. Figures 2-A, 2-B, and 2-C collectively represent a more complex type of suitable fabric, which incorporates both chain and tricot stitching yarns and is made on a stitch bonding machine with two guidebars. Figure 3 represents another type of suitable fabric for this invention, made on a two guidebar stitch bonding machine and utilizing laid-in serpentine yarns in the machine direction. Figure 4 is a schematic representation of a further type of suitable fabric for this invention. Fabrics The fabrics best suited to the purposes of the present invention include four general types. If only single guidebar stitch bonding machines are used, and the best performance is needed, the preferred fabric 1 design is one with warp yarns 3, fill or weft yarns 2 and tricot stitches 4 linking the two. Fabrics of this general type are described in European Patent Application No.82 105 651.2 (0 073 313) already noted above. Although there are significant differences in the yarns used for the purposes taught in European Patent Application No. 82 105 651.2 and those taught herein, these differences do not affect a generalized pictorial description of the fabric type. For making flexible coated abrasives according to the instant invention, preferred fabrics of this type have warp yarns from 150-300 denier in size at a count of 22-14 yarns per 25mm of fabric width, fill or weft, yarns from 55-85 denier in size at a count of from 96-48 per 25 mm of fabric length, and stitch yarns from 55-85 denier in size at the same count as the warp yarns. The other general type of preferred fabric for this invention which can be made on a single guidebar stitch bonding machine is one which has no warp yarns and instead relies only on the stitching yarns for tensile strength in the machine direction. Although tricot stitching may be used, chain stitching is generally preferred for this type. Stitches made with properly chosen yarn have sufficient tensile strength and stretch resistance for the relatively non-hazardous applications of the coated abrasive products of this invention. These fabrics are more economical than those which contain warp yarns and are preferred for applications of this invention where economy is more important than maximum durability. A fabric of this economical type is illustrated in Figure 1. The fabric 10 is comprised of fill or weft yarns 11 and stitch yarns 12 . The fill yarns, as shown in the Figure, comprise two subgroups. Yarns within each subgroup are coparallel, but are oriented at a slight angle to the yarns of the other subgroup. In a sufficiently wide sample of the fabric, the yarns of the two subgroups will intersect occasionally across the fabric, but in the narrow sample illustrated in Figure 1, there are no such intersections, although there are near approaches near the right edge of the Figure. The knotting of chain stitch yarns at the points of maximum curvature 13 shown in Figure 1 creates a focus for concentrations of mechanical stresses such as those which produce tearing. Chain stitching, when performed with most commercial stitch bonding machines such as the preferred Malimo machines, produces fabrics in which the hypothetical paths that connect knot points in the yarns with their nearest neighbor knot points in a different yarn are reasonably straight and perpendicular to the general direction of the stitch yarns themselves. The dashed line 14 - 14' in Figure 1 is an example of this. Thus, when fabrics of this type are incorporated into coated abrasives as taught below, straight tear across the machine direction of the fabric or abrasive is easier than in fabrics with unknotted warp yarns. With fill yarns that are not too strong, tear along the machine direction, as for example along dashed line 15 - 15' in Figure 1, is also easy. For clarity of illustration, the relative size of the spaces between yarns, compared with the size of the yarns themselves, is shown in Figure 1 to be much larger than it usually is in practice. For fabrics of the type illustrated in Figure 1, it is preferred that the fill yarns are from 55-85 denier and present at a count of 96-48 per 25 mm of fabric length and that the stitch yarns are from 70-150 denier and present at a count of 22-14 per 25 mm of fabric width. In some applications of this invention, more complex fabric constructions available from stitch bonding machines with two guidebars are preferable to either type noted above. Such a complex fabric is illustrated in the three parts of Figure 2. This fabric comprises four distinct groups of yarns. The first group are chain stitches 22 , shown in formalized projection in Figure 2-A. The second group are tricot stitches 24 shown in projection in Figure 2-B. The third and fourth groups are straight yarns shown in Figure 2-C, which represents the full fabric in projection. Warp yarns 23 run straight in the machine direction and fill yarns 21 run straight in the cross direction, or more exactly in two subgroups at slight angles to each other and to the cross direction as shown in Figure 1. In Figure 2, this separation of the fill yarns into two subgroups is ignored. The three parts of Figure 2 are shown at the same relative scale, and it may be seen in the Figure that the loops of the tricot stitches 24 approximately overlap alternating loops of the chain stitches 22 . The warp yarns 23 all lie on one side of the fill yarns 21 , but both types of stitch yarns 22 and 24 move back and forth through and outside the two planes defined by the two types of straight yarns. The tricot stitch yarns thus "trap" the warp yarns and hold them against the fill yarns, thereby binding the otherwise unattached warp yarns into the fabric as a whole. It should be emphasized that all the parts of Figure 2 show projections in a single plane only, with no attempt to indicate depth. Also, the loops in the stitch yarns in these figures are much exaggerated in size compared to the part of the yarn between the loops. The actual shape of the chain stitch is much closer to that shown in Figure 1 than in Figure 2-A. For the type of fabric illustrated in Figure 2, the warp yarns are preferably from 150-300 denier and present at a count of from 22-14 per 25 mm of fabric width, the chain stitch yarns are preferably from 55-85 denier and present at the same count as the warp yarns, the fill yarns are preferably from 55-85 denier and are present at a count of from 96-48 per 25 mm of fabric length, and the tricot stitch yarns are from 55-85 denier and present at the same count as the warp yarns. Still another general type of construction, preferred when smoothness is especially important, is illustrated in Figure 3. Instead of the tricot stitch yarns of the fabric shown in Figure 2, this has serpentine fill yarns 34 . The serpentine fill yarns are put into place in the fabric by alternate stitching needles, but the motion of the needles is altered by changes in parts, as recommended for the purpose by the supplier, so that the yarns undulate in two dimensions between the locations of two nearest neighbor chain stitch yarns but do not form closed loops or penetrate the planes of the warp and fill, or weft, yarns. Nevertheless, as shown in Figure 3, because the serpentine yarns 34 are engaged within the loops of the chain stitches 32 , and because the warp yarns 33 lie in a plane between the two planes of the fill, or weft, yarns 31 and the serpentine yarns 34 , all four types of yarns are held together in a fabric sufficiently coherent to withstand the stresses of saturation without excessive distortion. The preferred yarn sizes and counts for the type of fabric illustrated in Figure 3 are the same as for that illustrated in Figure 2, with the serpentine fill yarns of the former replacing the tricot stitch yarns of the latter. Any tricot stitch yarns or laid-in serpentine yarns used in fabrics for this invention are sufficiently weak to present no significant obstacle to straight tearing in the finished coated abrasive. For example, 70 denier texturized polyester yarns are often preferred for these stitch or serpentine yarns. The presence of warp yarns between the chain stitches is believed to promote straightness of tear by a mechanical process analogous to the use of a ruler along one edge of the tear line when tearing finished woven cloth: The warp yarn is sufficiently strong to inhibit any tendency for tearing paths generally parallel to the warp yarn direction to deviate across the line of a warp yarn. On the other hand, the warp yarns are not strong enough to avoid being broken themselves when tearing perpendicular to the warp yarn direction is desired. As with Figure 1, the spaces between yarns in Figures 2 and 3 are shown larger relative to the yarn sizes than is usually true for actual fabrics. The distance, along the machine direction, between two successive points of maximum curvature of a looped stitch yarn, such as the two points marked 13 in Figure 1, is denoted herein as the stitch length. As will be apparent from the discussion above in connection with Figure 1, the shorter the stitch length, the smoother the torn edge is likely to be when tearing across the machine direction. This desirable effect must be balanced with cost, which increases with decreasing stitch length because less fabric is produced in each cycle of the stitch bonding machine. Stitch lengths between 0.5 and 1.2 mm have generally been found suitable for fabrics for this invention, with a stitch length of 0.8 mm most preferred. Analogously, a fabric with more numerous warp and stitch yarns per unit of fabric width will normally produce a coated abrasive product with a smoother tear line for tearing along the machine direction. Again there is a balancing consideration: To obtain the same fabric tensile strength with a larger number of finer yarns is generally more expensive. The term "gauge" is well known in the art of stitch bonding to refer to the number of yarns per 25 mm of fabric width. For this invention, fabrics with a gauge from 14-22 are preferred, with 18 gauge generally most preferred. For all four general types of preferred fabric constructions described above, texturized multifilament polyester yarn is generally preferred because of its optimization of the combination of strength, covering power, and economy. Polyamide (or nylon), polyacrylate, and many other types of yarns are equally suitable for use but generally cost more. Some specific examples of constructions of suitable fabrics from both one and two guidebar stitch bonding machines are shown in Table 1. The cloth finishing and subsequent processes and materials used to convert the fabrics into the coated abrasive products with the tensile modulus properties shown in Table 1 are specified below. Cloth Finishing Adhesives and Processes The fabric to be used is preferably finished with not less than its own weight of a saturant to give a backing ready for coating and having a ratio of machine direction to cross direction tensile strengths of not less than 1.4 and an elongation to break of not more than 35% in the cross direction nor 40% in the machine direction. The primary ingredients of preferred saturants are one or more latices of acrylic homopolymers, acrylic copolymers, butadiene-styrene polymers, or mixtures of these types. These latices should preferably yield cured films with tensile strengths in the range of 6-35 megapasclas per square meter (hereinafter MPa/m²) and elongations to break in the range of 50-500%. Some admixture of these primary ingredients with thermosetting resins which yield considerably stiffer films on cure than do the latices is sometimes preferable. The saturants may be filled with conventional finely ground solids, preferably in the range of filler weights which are 25-50% of the weight of the remainder of the solids content of the saturant. Preferred fillers are calcium carbonate, sodium silicates, or clays. The large scale method of saturant application preferably varies with the ratio of saturant weight to fabric weight. This ratio preferably lies between 1 and 3. If the ratio is near the upper limit of the preferred range, a metering roll type of coating is preferred. If the ratio is near the middle of the preferred range, a pressure roll or kiss coating technique is preferred, while if the ratio is near the lower end of the preferred range, almost any type of coating is satisfactory, with vertical calender rolls preferred. For small scale sample preparation, a laboratory method of saturation can be conveniently used. In this method, the fabric is drawn rapidly through a gap between two polished cylindrical steel bars. The gap is set by use of gauges at a specified thickness slightly greater than the fabric thickness, and the gap is filled with an adhesive having sufficient viscosity to resist flowing through the gap under the influence of gravity alone. As an example, the products shown in Table 1 were saturated in this way, using a gap 0.127 mm thicker than the thickness of the fabric as measured at a pressure of 6.6 kN/m². The saturant formula used was: Gen Flo 8513 765 parts Gen Flo 6506 254 parts Calcium carbonate 250 parts 25% aqueous solution of sodium ammonium pyrophosphate 10 parts Acrysol ASE-60 9 parts Imperon Brown CKRN Pigment Dispersion 11 parts Among the ingredients in this formulation, the two Gen Flo materials were obtained from the Polymers Division of DiversiTech General, Akron, Ohio. Both are latices of carboxylic-modified butadiene styrene polymer, with solids contents of about 50% and specific gravities of 1.01 ± 0.01. Physical properties of the cured films formed from these latices after drying and exposure to a temperature of 113°C for six hours are shown in Table 2 below. Physical Properties of Gen Flo Latex Solids Latex 100% Modulus, MPa/m² Maximum % Elongation Tensile Strength at Break, MPa/m² 22°C 121°C 22°C 121°C 22°C 121°C 8513 12.2 0.52 283 293 17.1 3.1 6506 1.3 0.38 490 216 5.4 0.56 Acrysol ASE-60 is an acrylic thickening agent latex, with about 28 % by weight solids, available from Rohm and Haas. The pigment dispersion contained 14% by weight solids and was obtained from American Hoechst Co. Other Processes and Materials The making, grain coating, sizing, and adhesive cure processes used were those conventional in the coated abrasive art. Preferred making and sizing adhesives were urea-formaldehyde resins, phenol-formaldehyde resins, melamine-formaldehyde resins, or water-dispersible epoxy resins. The resins may be used with or without appropriate fillers as is conventionally known. Abrasive grits should be adapted in size and type to the work to be done with the coated abrasives, and the amounts of making and sizing adhesives should be adapted to the grit size and the type of work to be done, in the manner conventional for prior art coated abrasives on woven cloth. For example, the products listed in Table 1 had maker and sizer adhesives of conventional urea-formaldehyde resin filled with calcium carbonate. Examples The scope of the invention may be further appreciated from the following additional specific examples. Example 1 The fabric for this example had the construction and properties shown for Fabric 3 in Table 1. The saturant used had the following formula as applied: Gen Flo 8513 765 parts Gen Flo 6506 254 parts Calcium carbonate 250 parts Imperon Brown CKRN Pigment Dispersion 11 parts The calcium carbonate had an average particle size of 13.2 microns. The other ingredients in the formula have been identified above. These ingredients were mixed in the order listed with constant stirring. The saturant was applied by metering roll and knife so as to produce a smooth deposit, with a dry weight of 145-185 grams per square meter (hereinafter gm/m²) of the fabric, throughout the interstices of the fabric. The wet saturated fabric was held on a tenter frame while passing through an oven with an entrance zone temperature of 93°C and an exit zone temperature of 218°C. Total exposure time of the wet saturated fabric to the oven was one minute. During the passage through the oven, the tenter clips were maintained at a width which was 10% less than the original greige width of the fabric, and the fabric shrank to that width during the course of drying the saturant. This treatment resulted in a backing ready to accept a maker adhesive-without problems of strike through or excessive penetration of the maker into the backing. The backing prepared as described above was subjected to conventional coating with grit 120 aluminum oxide abrasive. A conventional urea-formaldehyde resin with appropriate latent acid catalyst and calcium sulfate filler at about 40% by volume level was used for both maker and size adhesives. Example 2 The fabric for this example was the one designated as Fabric 4 in Table 1. Before saturation, the fabric was heat set at 218°C while held on a tenter spaced at the original fabric width. The heat set fabric was saturated with an adhesive composition similar to that of the saturant of Example 1 by drawing the fabric through an adhesive filled gap between two cylindrical steel bars; the gap was 1 mm wider than the thickness of the fabric as measured at a compression force of 6.6 kN/m². During saturation, the fabric width decreased by 5-10%. The saturated fabric was held on a tenter at the width to which it had naturally shrunk during saturation and dried at 79°C for fifteen minutes. An add-on dry mass of 162 gm/m² of saturant was applied. The dried saturated cloth was then subjected to making and sizing as in Example 1. Example 3 The fabric was the one designated as Fabric 2 in Table 1. The saturant adhesive formulation was: Gen Flo 8513 383 parts Gen Flo 6506 127 parts Dur-O-Cryl 820 510 parts Calcium carbonate 250 parts 25% aqueous solution of sodium ammonium pyrophosphate 10 parts Acrysol ASE-60 10 parts Imperon Brown CKRN. 11 parts Among these ingredient, Dur-O-Cryl 820 is a self cross-linking acrylic polymer latex supplied by National Starch and Chemical at a solids content of 44-48%. Films from this latex have a tensile strength of approximately 24 MPa/m² and an elongation to break of approximately 50 %. The other tradenamed ingredients have already been identified. These ingredients were mixed in the order listed with stirring continuing throughout each addition. Saturant was applied by the same method as in Example 2 to give a dry add-on mass of 182 gm/m². The saturated backing was dried on a tenter for 20 minutes at 79°C. Making and sizing on the dried saturated backing then proceeded as in Example 1. Example 4 For this example the fabric was the one designated as Fabric 2 in Table 1. The saturant formulation was: Gen Flo 8513 600 parts Gen Flo 6506 300 parts Cymel 481 100 parts Calcium carbonate 250 parts Imperon Brown CKRN 11 parts 25% aqueous solution of sodium ammonium pyrophosphate 10 parts Acrysol ASE-60 18 parts Water 50 parts Among these ingredients, Cymel 481 is a methylolated melamine-formaldehyde resin supplied by American Cyanamid. The ingredients were mixed in the order listed to yield a saturant mixture with a pH of 6.1 and a viscosity of about 6,500 centipoises (cp). The saturant was applied and dried by the same techniques as in Example 3 to give a dry add on weight of 185 gm/m². Making, grain coating, and sizing were completed as in Example 3. The presence of a thermosetting amino resin in the saturant formulation of this example produced a stiffer and more aggressively cutting product than those from the earlier examples. Example 5 The fabric for this example was that designated as No. 3 in Table 1. The saturant formulation was: Varcum 5868 100 parts Ethyl alcohol (commercial grade) 35 parts Gen Flo 8513 600 parts Gen Flo 6506 300 parts 25% aqueous solution of ammonium hydroxide 5 parts Acrysol ASE-60 70 parts Water 50 parts Varcum 5868 is a sodium hydroxide catalyzed resole phenolic resin with 73% ultimate solids content and a molar ratio of formaldehyde to bisphenol-A of about 1.5. The ingredients were mixed in the order listed to yield a formulation with a pH of about 6 and a viscosity of about 8,750 cp. Saturant application and drying by the same methods as in Example 4 to produce a saturant add-on weight of 185 gm/m² were performed on the fabric, and the saturated backing was then made into a coated abrasive by the same steps as in Example 4. The resulting product had about the same stiffness and aggressiveness of cut as the one from Example 4. Example 6 This example is like Example 1, except that conventional resole phenolic resins (sodium catalyzed with formaldehyde to phenol molar ratios of about 1.5) were used for the maker and size adhesives instead of the urea-formaldehyde resins used in Example 1. Example 7 For this example, the fabric was that designated as No. 2 in Table 1 and the saturant composition and amount the same as for Example 1. The maker adhesive had the following composition: CMD 35201 480 parts Cymel 481 480 parts AMP-95 5 parts 25% aqueous solution of NH₄Cl 12 parts Water 15 parts AMP-95 is a 95% by weight solution of 2-amino-2-methylpropanol in water. CMD 35201, available from Celanese Corp., is a water-dispersed bisphenol-A based epoxy resin with a molecular weight per epoxide group of about 635 and a particle size of about 5 µm. Other ingredients have been previously identified. The dry maker add on weight was about 78 gm/m². Grit 120 aluminum oxide at a weight of about 311 gm/m² was applied into the wet maker by conventional electrostatic upward propulsion. The maker was cured by successive exposure to 77°C for 24 minutes, 88°C for 24 min., 99°C for 15 min., and 24 min. at 113°C. After maker cure, the product was sized with a conventional calcium carbonate- filled, sodium-catalyzed resole phenolic resin with a formaldehyde to phenol molar ratio of about 1.5. The dry add-on weight of sizer adhesive was about 187 gm/m². The sized product was preliminarily cured by exposure of the web in festoons to 54°C for 24 min., 60°C for 24 min., 88°C for 17 min., 93°C for 24 min., and 113°C for 14 min. The entire product was then rolled while still hot and cured in roll form for 4 hours at 113°C. Example 8 The fabric was that designated as no. 3 in Table 1. The saturant formulation was the same as for Example 1, and the saturant dry add-on weight was 262 gm/m². The maker formulation was the same as for Example 7, except for the addition of 15 parts of water to the other ingredients listed for Example 7, and the dry weight of maker was 106 gm/m². The sizer adhesive formulation and curing conditions were the same as for Example 7. The sizing adhesive add-on weight was 101 gm/m² dry. Example 9 For this example, the fabric was that designated as No. 3 in Table 1. The saturant formula was: CMD 35201 480 parts Cymel 481 480 parts Calcium sulfate filler 300 parts AMP-95 5 parts 25% aqueous solution of NH₄Cl 12 parts Imperon Brown Pigment Dispersion CKRN 11 parts The saturant add-on weight was 262 gm/m² dry. The abrasive grits, maker and sizing adhesives compositions and amounts, and the product cures were all the same as for Example 1. Example 10 The fabric used for this example was composed of only fill and chain stitch yarns. There were 96 fill yarns, each of 70 denier multifilament polyester, per 25 mm of fabric length and 14 chain stitch yarns, each 70 denier texturized multifilament polyester, per 25 mm of fabric width. Before saturation, the fabric was heat set at 218°C for 4.5 minutes and calendered under a pressure of 180 KPa/m of width at a temperature of 104°C. The saturant formula was: Gen Flo 8513 1969 parts Gen Flo 6506 608 parts Calcium carbonate 312 parts Acrysol ASE-60 30 parts Imperon Brown CKRN 16 parts The saturant was applied using a metering knife and roll with two smoothing knives to give a dry deposit of about 127 gm/m². The maker resin used was a mixture of 711 parts of Resinox 7451 with 267 parts of water. (Resinox 7451, which has about 75% included ultimate solids, is a phenolic laminating resin in methanol available from Monsanto Chemical Co., St. Louis, Missouri.) A maker weight equivalent to 63 gm/m² dry was used, and grit 120 aluminum oxide abrasive grits at a mass of about 132 gm/m² was coated into the wet maker, which was then cured for about 5 min at 149°C. The grits were then overlaid with a sizer adhesive made by mixing 455 parts of Resinox 7451 with 114 parts of water and 17 parts of Imperon Brown CKRN. The sizer adhesive mass was about 7.7 lbs/ream dry, after cure for four hours at 149°C Comparative Testing The products as described above were compared in a laboratory grinding test to prior art products for similar uses. One type of prior art product, designated herein as "Control # 1", had a backing comprising 2 x 1 twill weave staple cotton yarns with 23's warp yarns at a count of 84 per 25 mm and 25's fill yarns at a count of 56 per 25 mm. The fabric weighed approximately 163 gm/m². It was backfilled with a mixture of starch, glue, and clay and then frontsized with glue as conventional in the coated abrasive art. A filled glue maker adhesive, followed by brown aluminum oxide abrasive grits and a urea-formaldehyde resin based sizer adhesive similar to those for Example 1 above were coated on this backing. For the second type of prior art backing, designated herein as "Control # 2", the fabric had the same type of yarns as for Control # 1 but a count of 96 per 25 mm warps and 64 per 25 mm fills, with a fabric weight of about 187 gm/m². The backfill, frontsize, maker adhesive, abrasive grits, and sizer adhesive were all essentially identical to those used for Control #1, except that the frontsize contained starch as well as glue in a ratio of about 3:10. The two control products and many of those produced by the examples detailed above were cut into rectangular sheets and the sheets tested in a standardized laboratory test procedure in grinding and finishing aluminum and copper workpieces. Test conditions were the same for all sheets and were within the large range of expected actual applications for flexible products of the type described herein. The amount of metal removed and the finish produced on the workpiece during the test interval were measured. The resulting data are shown in Table 3 below. Under the conditions of Table 3, Example 1 would normally be favored because of the combination of rapid cut and fine surface finish, but any of the other examples might be preferred under different conditions of use. Comparison of Cut and Finish Between Products of This Invention and Prior Art Coated Abrasives Product Identification Percentage of Cut, Relative to Control # 1 Workpiece Finish, µm AA Copper Aluminum Copper Aluminum Control 1 100 100 1.57 1.52 Control 2 92 83 2.34 2.11 Example 1 127 102 1.55 1.55 Example 2 119 90 2.31 2.03 Example 3 92 95 1.91 2.49 Example 4 104 105 1.83 2.72 Example 5 92 97 2.08 2.46 Example 6 91 89 1.96 2.16 Example 7 92 111 1.88 2.21 Example 9 108 104 2.49 2.31 Example 10 88 132 -- --

Claims: A stitch bonded fabric suitable for use as a backing for flexible coated abrasives comprising a plurality of stitch yarns (12;22,24;32) oriented generally in the machine direction and a plurality of weft yarns (11;21;31) oriented generally straightly and in the cross machine direction and held within loops formed by the stitch yarns (12;22,24;32), characterized in that (1) the fabric has a mass between 51 and 153 gm/m², (2) the fabric has a tensile strength in the machine direction between 5.4 and 12.6 kN/m of width, (3) the fabric has a tensile strength in the cross machine direction which is both between 5.4 and 11.7 kN/m of length and between 0.9 and 1.35 times as great as the tensile strength in the machine direction, (4) the fabric has an elongation to break in the machine direction of not more than 40%, and (5) the fabric has an elongation to break in the cross machine direction of not more than 35%. A fabric according to claim 1, wherein the stitch yarns (12;22:32) have a chain stitch pattern. A fabric according to claim 2, further characterized in that (1) said stitch yarns (12) and said weft yarns (11) are texturized multifilament polyester yarns, (2) said weft yarns (11) are from 55-85 denier in size and are present in the fabric at a count of between 48 and 96 yarns per 25 mm of fabric length, (3) said stitch yarns (12) are between 70 and 150 denier in size and are present in the fabric at a count of between 14 and 22 yarns per 25 mm of fabric width, and (4) the stitch length is between 0.5 and 1.2 mm. A fabric according to claim 1 additionally comprising straight laid warp yarns (23) in the machine direction in the same count per 25 mm of fabric width as said stitch yarns (24), said straight laid warp yarns (23) all lying on one side of said straightly oriented weft yarns (21), further characterized in that said stitch yarns (24) have a tricot stitch pattern. A fabric according to claim 4, further characterized in that (1) said stitch yarns (24), said weft yarns (21), and said warp yarns (23) are all texturized multifilament polyester yarns, (2) said weft yarns (21) are from 55-85 denier in size and are present in the fabric at a count of between 48 and 96 yarns per 25 mm of fabric length, (3) said stitch yarns (24) are between 70 and 150 denier in size and are present in the fabric at a count of between 14 and 22 yarns per 25 mm of fabric width, (4) said warp yarns (23) are from 150-300 denier in size, and (5) the stitch length is between 0.5 and 1.2 mm. A fabric according to claim 2, additionally comprising (1) straight laid-in warp yarns (23) in the machine direction between each pair of chain stitch yarns (22), and (2) tricot stitch yarns (24) interlacing with said weft yarns (21) and said warp yarns (23). A fabric according to claim 6, further characterized in that (1) said chain stitch (22) and tricot stitch yarns (24), said weft yarns (21), and said warp yarns (23) are all texturized multifilament polyester yarns, (2) said weft yarns (21) are from 55-85 denier in size and are present in the fabric at a count of between 48 and 96 yarns per 25 mm of fabric length, (3) said tricot stitch yarns (23) are between 70 and 150 denier in size and are present in the fabric at a count of between 14 and 22 yarns per 25 mm of fabric width, (4) said warp yarns (23) are from 150-300 denier in size, (5) said chain stitch yarns (22) are from 55-85 denier in size, and (6) the stitch length for both tricot and chain stitches is between 0.5 and 1.2 mm. A fabric according to claim 2, further comprising straight laid-in warp yarns (33) and further characterized in that it additionally contains laid-in, substantially coplanar serpentine yarns (34) on the opposite side of said warp yarns (33) from said straightly oriented weft yarns (31), each of said serpentine yarns (34) being held within alternate loops of two adjacent chain stitch yarns (32). Use of the stitch bonded fabric of one of the preceding claims for making flexible coated abrasives with facile straight tear in either the length or cross direction. A coated abrasive comprising a plurality of size graded abrasive grains distributed over and affixed by an adhesive to at least one major surface of a flexible backing material, characterized in that (1) said flexible backing material includes (a) a fabric according to any one of claims 1-8 and (b) a saturant which fills the interstices of said fabric and is present in an amount with mass not less than the mass of said fabric; (2) said coated abrasive has the property of tearing straight in both machine and cross machine directions; (3) said coated abrasive has a ratio of its tensile modulus in the machine direction to its tensile modulus in the cross machine direction in the range between 0.8 and 1.8. A coated abrasive according to claim 10, further characterized in that said saturant comprises the product of drying a synthetic latex of materials selected from the group consisting of polyacrylates, acrylic copolymers, butadiene-styrene polymers, and mixtures thereof.

Inventors: DARJEE, DHIRAJ H., PEMRICK, RAYMOND E.
Applicants: NORTON COMPANY
Application year: 1987
Main classification: B24D11
IPC codes: B24D11, D04B21, C08J5