Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D11/00—Constructional features of flexible abrasive materials; Special features in the manufacture of such materials
  • B24D11/02—Backings, e.g. foils, webs, mesh fabrics

Definitions

• the present invention relates to immediately useful abrasive products comprising a flexible backing on at least one side of which are adhered abrasive grits, such products being referred to in the art as coated abrasives; more particularly it relates to endless abrasive belts formed from such coated abrasive products.
• Coated abrasives in general, have been made on backings ranging from paper, cloth, leather, to plastic films and metal sheets. Except for specialty items the greater majority of all coated abrasive products are made on paper or woven cloth backings.
• Coated abrasives often subject to high stresses in operation, are made from strong paper backings, vulcanized fiber backings, or, for strength and flexibility, woven cloth backings. Laminates of various of these materials have also been used and taught in the patent literature.
• Knuckles are the small bumps on the surface of woven cloth caused by yarns curving to cross over other yarns. The presence of such knuckles is believed to be responsible for the catastrophic failure of coated abrasive articles, particularly belts, in certain severe grinding operations.
• an array of yarns is substantially coplanar if all the yarns of the array can be accomodated in the space between two parallel planes which are separated by a distance of four times the average diameter of the yarns in the array.
• An array is substantially coparallel if the largest angular difference in direction between any two yarns in the array is no more than thirty degrees.
• a major advantage of the non-interlaced fabrics when employed as substrates for coated abrasive is the fact that such fabrics can be produced at much higher rates of speed than can conventional woven textiles, thus increasing the productivity and lowering the cost of manufacture.
• these materials are produced by laying fill yarns over warp yarns and, with a third yarn, stitching the warp and fill yarns together. Because of the space requirement for the multiple stitching needles, there is an upper limit on the number of warp ends per inch in such fabrics. Because of this, the stitch bonded fabrics tend to be or may be of more open construction than conventional woven cloth for coated abrasive use. The greater openness, combined with the use of strong multifilament yarns permits design of fabric having lower weight than conventional woven fabrics of the same or lower strength and tear resistance, thus economizing on the use of raw materials. Thus special procedures may be required in filling the spaces between the yarn in such fabrics. The overall production of coated abrasive from stitch bonded fabrics is, however, closely analogous to production from conventional woven cloth.
• the steps of sizing the yarn, back filling or sizing, saturating, front sizing, applying a maker coat, applying abrasive, and finally applying a "sand" size coat may all be used in coated abrasive production from the Malimo type, or stitch bonded fabrics.
• Adhesive bonded fabrics may be produced in a similar manner as the stitch bonded, but with an application of suitable adhesive, at the point in the manufacture where otherwise the third yarn would be used to stitch bond the warp and crossin q threads together.
• thermallv bonded fabrics mav be produced by applying heat at the points of junction of the warp and cross threads to fuse or soften the yarns or a coating previously applied to the yarns.
• tissue sheetin q between the warp and fill yarns, to aid in preventing the back-fill treatment from penetrating too far into the cloth. This can be done in the Malimo machine during the manufacture of the backing.
• a random web of fill yarns can be employed, as in the Maliwatt type of Malimo fabric (as opposed to the Malimo type). Such web should be selected to contain fibers which present sufficient surface for good adhesion. Machines are available (such as the Model 14001) which will produce both the Malimo type and the Maliwatt type fabrics.
• the present invention is particularly suitable for producing coated abrasive stock suitable for forming coated abrasive belts.
• the ability to control the longitudinal strength and stretch properties of the material are important in this reqard. While the total strength of a woven fabric in the warp direction cannot always be predicted by summing the stren q ths of the individual warp yarns and the stretch properties can almost never be predicted from the stretch of the individual yarns, both these properties can be more readily controlled and predicted in the fabric designs employed in the present invention.
• any tendency of coated abrasive belts to split when subject to stresses in use due to the effect of the interlaced filling (weft) yarns is eliminated by the use of the non-interlaced backing construction disclosed herein.
• non-interlaced backing I mean a backing reinforced with non-interlaced arrays of substantially coplanar and coparallel yarns as described above.
• finishing materials employed are not critical and many variations are possible provided proper cover and adhesion are achieved.
• finishing is obtaining good adhesion to the backing, properly filling the cloth and preparing its surface for the maker coat to hold the abrasive, and adequately bonding the yarns so that the end product resists delamination, splitting, and tearing. Adequate flexibility for the end use intended is also important.
• the particular chemical structure of the finishing compositions is not critical, except to the extent that it affects the physical properties described above.
• the presently preferred material for the warp yarns is continuous filament polyester having relatively high strength and low elongation properties. Obviously other yarns of similar or higher strength properties and similar or lower elongation under load, may be used. In less critical applications yarns with less strength and higher elongation could be used, and other advantages of the present invention be still retained.
• glass or metal yarns may be employed as part or all of the yarn arrays.
• the preferred yarns in the fill direction are texturized continuous filament synthetic yarns, as in the example below. Natural and synthetic staple fiber textile yarns may be employed. Continuous filament yarns are particularly useful if they are texturized, given a false twist, or are otherwise produced to have a high bulk or surface area so that good adhesion to the cloth finishing materials is achieved.
• This example employs a stitch bonded backing of the type disclosed in Figure 9 ' of U.S. Patent 2,890,579.
• the fabric of the example was made on a Malimo machine (available from Unitechna Aussenhandelqesellschaft mbH, DDR-108 Berlin, Mohrenstrasse 53/54 GDR).
• the approximately 4 inch wide carrier for the fill yarns holds 61 ends, and makes one complete cycle from one edge of the web and back for every 4 inch longitudinal forward motion of the web. For a 60 inch wide machine this produces a fill which crosses the warp yarns at an angle of about 88° in one direction and 92° in the other.
• the stitching yarns, which bind the warp to the fill are 70 denier continuous filament polyester.
• the stitch length is 1.2 mm.
• the warp yarns are 1000 denier duPont type 68 continuous filament high tenacity polyester (9.2 grams per denier breaking strength), and the warp count is 14 ends per inch.
• the fill yarns are continuous filament 170 denier (containing 33 filaments) available from Celanese Corporation as type 731 polyester. These yarns have a low twist (0.25 per inch) and are texturized to provide a bulky yarn for optimum adhesion to coatings later applied.
• the tenacity is 3.5 to 3.9 grams/denier and the elongation is 18 to 24% at break.
• the yarn is preferably not treated with a coning oil.
• the above described backing was then saturated with a resin and acrylic latex composition to prepare it for front-filling, back-filling, and coating with maker grain and size coat.
• a heat settinq step is combined with the drying of the saturant.
• Standard sizing rolls are employed to apply the following composition in the amount of 3 to 4 pounds per sandpaper makers ream (330 sauare feet). The fill yarn side of the fabric was facing up.
• the fabric Upon completion of the application of the saturant the fabric is dried on a tenter frame for at least 3 minutes in a hot air oven in which the temperature in the entry zone is 205°F, and the temperature at the exit zone is 350°F. A tension of at least 2 pounds per inch of width is maintained on the fabric during its travel through the oven. This process not only dries the saturant but also heat-sets the fabric.
• composition of the front fill coating applied to the fill yarn side in this example, but which can instead be applied to the warp yarn side if desired, is as follows:
• the front fill coatinq composition is applied with a box knife in the amount of 10 to 11 pounds per ream, and water may be added as necessary to maintain the required viscosity for proper coating.
• the coated cloth is again dried on a tenter frame with a tension of at least 2 pounds per inch of width by passinq through a hot air oven in which the entry temperature is 205°F and the exit zone temperature is 300°F.
• composition is applied by knife coating in the amount of 10 pounds per ream, and dried in an oven having an entry zone temperature of 150°F and an exit zone of 200°F.
• a suitable formulation to be applied to the front sized side of the backing is as follows:
• abrasive-adhesive coated backing member is then heated for 25 minutes at 170°F., 25 minutes at l90°F., and 47 minutes at 225°F. to provide a dry adhesive layer (17.4 lbs./S.P.M.R.) and to anchor the abrasive grains in the desired orientation.
• the wet adhesive layer is then dried: 25 minutes at 125°F., 25 minutes at 135°F., 18 minutes at 180°F., 25 minutes at 190°F., and 15 minutes at 225°F., after which a final cure at 230°F. for 8 hours is given.
• the coated abrasive material is then ready to be converted according to usual techniques, into belts, discs, and other desired abrasive products.
• a central feature of the invention is the use of yarn arrays which are not interlaced as in conventional woven fabrics, and the use of the terms "warp” and “fill” in the description of fabrics bonded by other means than weaving does not imply such interlacing.
• the abrasive sheet material of the above example can be formed into belts by conventional joining techniques well known in the art. Particularly suitable are the butt joints described in U.S. Patents 3,665,600 and 3,787,273. Lapped joints as described in U.S. Patent 4,194,618 may also be used. In such cases it may be desirable to apply the front fill coating and the abrasive and maker on the warp side of the backing, instead of on the fill side. In the case of butt joints, the backing may be coated on either one side or the other.
• An adhesively bound coated abrasive backing of this invention was prepared by crossing two sets of substantially parallel spun polyester-yarn (3-5 gm/denier tenacity, 19 singles, cotton count) between the top and bottom platens of a photographic dry mounting press (manufactured by Seal, Inc.), the upper platen of which is electrically heated to a temperature of 340° to 350°F.
• a sheet of polyamide hot melt adhesive web (Bostik No. 5350 available from USM Corp.) was inserted between the yarn layers and the press closed to fuse and set the adhesive. A laminating time of approximately 45 seconds was used.
• the press was opened, the cross-direction yarn beam cut free, and the machine direction yarn beam advanced to bring the next adjacent portion of yarn over the bottom platen of the press.
• the cross-direction yarn beam was then brought through the press to cross the other beam and the bonding process repeated.
• Approximately 8 yards of fabric was prepared in this manner.
• the fabric so prepared contained a density of 93 yarns/inch in the machine direction and 47 yarns/inch in the cross-direction, yielding a calculated areal weight of 6.81 oz/yd 2 .
• the count and density of fabrics thus prepared are readily varied by varying the counts and weights of yarn(s) used in the respective beams.
• the fabric was then heat-stretched by passing it over a catenary-shaped surface at a speed of 20 ft/min while under a linear tension of 15 lbs/inch of width. During this operation, the fabric was heated to 400°F by infrared radiators on the opposite side of the web from the catenary surface. In this way the machine direction breaking strength of the fabric was increased from 158 lbs/inch of width to 179 lbs/inch of width, and the elongation to break of the fabric was reduced from 32% to 20%.
• This material was then oven dried for 5 minutes at 250°F.
• the thus prepared fabric may be henceforward denoted as a backing.
• a typical formulation applied to the front sized side (i.e., the side on which machine direction yarns were originally exposed) of the backing was as follows:
• the wet adhesive layer was then dried: 25 minutes at 125°F, 25 minutes at 135°F, 18 minutes at 180°F, 25 minutes at 190°F and 15 minutes at 225°F, after which a final cure at 230°F for 8 hours is given.
• the coated abrasive material was then ready to be manufactured according to usual techniques, into belts, discs, and other desired abrasive products.
• Other coated abrasive belts were also prepared, using the same means and formulations as the material of this invention, with the exception that the backing substrate fabric used was a conventionally woven polyester spun yarn backing (2 x 1 drills construction; 66 ends per inch and 44 picks per inch; yarn 3-5 gm/denier, warp, 12's and filling, 15's cotton count). The warp (twill) side of this cloth was used as the frontside.
• the product of this invention, using the previously disclosed adhesively bound backing (Product A) was compared to the product prepared by using the conventionally interwoven backing (Product B) in a series of grinding operations.
• both belts tested showed evidence of severe damage to the filling yarn, with the second belt of the two splitting and breakinq apart to terminate the test. No such damage was found to have occurred to the backing of the product A herein disclosed.
• Example 2 above has illustrated one of the coated abrasives of this invention having a backing without bonding yarns of any kind. It will be appreciated by those skilled in the art that many variations from this specific example could be made within the scope of this invention. For example, if greater economy in the product were necessary, the cross-direction set of reinforcing yarns could have been eliminated. Belts made from the product would then have had less resistance to splitting but could have been satisfactory for certain uses. The choice of adhesive could be varied within wide limits to give the combination of flexibility and damage resistance most suitable to the intended use of the coated abrasive product.
• a suitable backing can be made with only one array of reinforcing yarns.
• cotton 18's singles yarn was wound onto the surface of a cylinder coated with polytetrafluoroethylene at a spacing to give 72 yarns per inch when measured parallel to the axis of the cylinder.
• the cylinder with its wet coating of adhesive was turned slowly in slightly warmer than ambient air until the adhesive had dried completely to a continuous film encapsulating the cotton yarns.
• the yarn-adhesive composite is then used as the backing for the preparation of a coated abrasive, usinq the same maker and size adhesives and abrasive grain and the same techniques as described for example 1 and 2.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Polishing Bodies And Polishing Tools (AREA)
• Knitting Of Fabric (AREA)
• Nonwoven Fabrics (AREA)
• Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)

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Applications Claiming Priority (2)

Publications (3)

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ID=22634705

Family Applications (1)

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Cited By (14)

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Citations (6)

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• 1981
  • 1981-07-14 DE DE8181105516T patent/DE3170492D1/de not_active Expired
  • 1981-07-14 EP EP81105516A patent/EP0045408B2/de not_active Expired - Lifetime
  • 1981-07-14 AT AT81105516T patent/ATE13267T1/de not_active IP Right Cessation
  • 1981-07-14 DE DE198181105516T patent/DE45408T1/de active Pending
  • 1981-07-21 ZA ZA814982A patent/ZA814982B/xx unknown
  • 1981-07-31 JP JP56120605A patent/JPS57114366A/ja active Granted
  • 1981-07-31 DD DD81232268A patent/DD201652A5/de unknown
• 1982
  • 1982-07-16 ES ES514058A patent/ES514058A0/es active Granted

Patent Citations (6)

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