CA1084677A - Fine grit abrasive - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Calendering of woven polyester fabric at 20 to 60 tons pressure and 200 to 380°F, provides a smooth surface, upon which fine grit abrasive may be applied, to produce flexible coated abrasive articles for polishing applications.

Description

FIELD OF THE INVENTION
_ The invention relates to fine grit coated abrasive products on woven polyester fabric backings.
BACKGROUND OF THE INVENTION -Recently, dimensionally stable woven-polyester backings have been commercially employed as backings for coarse grit (coarser than 100 grit) flexible coated abrasive -products. Because of the inherent roughness of the surface - of woven fabric relative to the dimensions of very fine grit, some difficulty has been experienced in employing standard types of such backings for fine grit (100 or 120 to 600 grit), because conventional calendering (as used for cotton), or the use of fill coatings, to smooth the surface to which the abrasive is applied, have not been satisfactory.
SUMMARY OF THE INVENTION
The present invention resides in the discovery that -~ the use of very high calendering pressure together with the use of a limited range of elevated temperature, enables the production of a smooth surface on commercially available polyester woven cloth, for coa-ted abrasive use, suitable for the production of fine grit (100 to 600 grit size) products.
Specifically, the use of from 600 to 2000 pounds per lineal inch of cloth, and a temperature of 210 to 380F, have been found sa-tisfactory, when -the web is passed between " a set of conventional calender rolls at a speed of from 20 to 75 feet per minute. More preferable the pressure is from 800 to 1600 pounds per lineal inch, and the temperature from 230 to 300F.
After calendering the cloth is finished in a conventional manner, by application of adhesive and abrasive grain on one side, to produce a coated abrasive produc-t.

- ..

6~'7 Suitable cloth for this application is a dimensionally stable polyester woven fabric having a weight of up to 9 ounces per square yard (most cloth lighter than 3.5 ounces per square yard can be manufactured smooth enough). The weave can be square, twill, or sateen weave, but square weave is preferred.
The yarn weight can vary from yarn numbers of 1-1/2 to 3 for staple fibers (cotton count), to 100 to 1100 denier, for continuous multifilament yarns.
Conventional manufacturing methods are used to produse a finished coated abrasive product from the backing. The cloth, -as calendered according to this invention will show a flattening of the fill yarns of the cloth, but will show no indication of any fusion to the yarns. Excessive heat or heat and pressure will destroy the desired dimensional stability of the cloth, significantly reduce the adhesion of the maker coat to the backing, and will weaken it in tensile and tear strength.
Calendering within the limits of pressure and temperature of , this invention, will produce a smooth surface, dimensional stability within the required limits, proper base adhesion, and, surprisingly, no decrease in tear strength.
The elongation profile in the warp direction of the cloth, after calendering should have the ollowing character: -Elon~ation Load-Pounds Per Inch of Width ~ .. _ ___ . .. . .: .
No greater than 6~ 50 9~ 100 ,..... ..
~ 15~ 200 Since the calendering does not improve the ~tability of the cloth, the fabric, prior to calendering must also have equivalent dimensional stability.

- ,, . :,; .. . . . . .. .... . . . . .. . . . .. .

6~7 By fine grit, we mean abrasive grains (e.g. silicon carbide, aluminum oxide, co-fused alumina zirconia, garnet and flint), having a grit size of from 100 to 600 grit (approximately 170 microns or 6700 microinches to 8 microns or 315 microinches).
Suitable cloth for this application should thus have a roughness in terms of valleys and peaks in its surface no greater than about 2500 microinches, for the course grits, and 200 microinches for the finest grits.

EXAMPLE OF SPECIFIC EMBODIMENT OF THE INVENTION

_ A woven (greige) fabric of staple polyester fibers, 66 in. wide, weighing 6.3 oz./sq.yd. in a 2 x 1 left handed twill constructlon having a nominal yarn count of 66 x 44, and with warp yarns of 12/1 and fill yarns of 15/1 having a warp breaking tensile of 206 lb./in. (ASTM Strip s) with an elongation at breaking tensile of 63.7% and a fill tensile strength of 105 lbs./in. with an elongation at breaking tensile of 51.9% is heat stretched in a manner such as disclosed in U.S. Patent application Serial No. 590,989, filed June 27, 1975. Such heat stretched fabrics are commercially available.
In a two roll padder which is positioned immediately in front of the heatstretching machine, the fabric is prefinished with a composition comprising 11 parts resorcinal, 16.2 parts formalin solution (37% formaldehyde), 0.3 parts ;~ sodium hydroxide and 238.4 parts water. The fabric is not scoured or boiled off prior to the prefinishing and heat -stretching operations.
The width of the fabric after heatstretching is 53.5 in. The yarn count of the heatstretched fabric is 75 x 37 and the warp yarn are noticeably smaller in diameter in _4_ .: . . . - , ' : .

.; . . . ' . :.

0l~6~
the heatstretched fabrlc than they are in the original greige fabric. The fill yarns appear to be somewhat heaver in the heatstretched than in the greige fabric. The fabric weight is approximately 5.9 oz./sq.yd. The web thickness after heatstretching is 17.1 mils. --The elongation profile of the heatstretched fabric is determined according to the usual techniques on an Instron Tensile Tester. A one inch strip of heatstretched and prefinished polyester fabric is used, gage length 3 inch., chart speed 12 inch/min. and jaw speed of 12 in./min.
The tensile strength of the heatstretched fabric is ~; 279 lbs./in. width with an elongation of 16.9%, the fill - tensile strength is 86 lbs./in. width with an elongation of 53%. The elongation profile of the warp is 3.2% at 100 lbs., 8.8% at 200 lbs. and 16.9% at breaking tensile.
Tne fabric is then subjected to a high temperature, high pressure calender to smooth and densify the fabric while maintaining dimensionally stability of the calendered fabric.
The calender empolyed is a three roll (roll length, 62 inches~ gas fired Schreiner calender stack. The top and bottom rolls are mirror finished stainless steel, the center roll is a corn husk roll made of 100% cotton fabric having a hardness of 82 durometer. The top steel roll is heated by gas.
The bottom steel roll is heated with stream, the center husk -roll is heated by contact transfer from the top and bottom rolls. -The prefinished and dimensionally stabilized ; polyester fabria is calendered at 230F., 40 tons pressure (1290 pounds/lineal inch of roll) and at a speed of 30 ft./min.
The warp tensile strength of the prefinished, heatstretched -i77 and calendered fabric is 276 lbs./in. with an elonyation atbreaking -tensile of 19.4%. The elongation profile of the warp is 4.8% at 100 lbs., 10.4% at 200 lbs. and 19.4% at breaking tensile. The thickness of the calendered fabric is 11.9 mils. The surface roughness of the heatstretched fabric is about 4000 microinches and after calendering it is reduced to about 1500 microinches in terms of the absolute average difference between the peaks and valleys.
The elongation profile and the reduction in surface roughness of the heatstretched fabric is very important where the fabric is to be used on a backing member for the fine grits of coated abrasive material. If the surface roughness of the original heatstretched fabric is not reduced significantly, it will be imparted to the coated abrasive surface which will result in an undesirable scratch pattern on the workpiece being ground.
The dimensionally stabilized and calendered fabric is next coated in its back size (twill) with a composition as ` follows:
Component Parts by Weight A
B
CaC03 2 parts per each part solids A and B.
Component A is an aqueous resinous composition (72% solids concentration) comprising bisphenol A and formaldehyde (alkaline catalyzed) having a formaldehyde to phenol (F/P) ratio of 3.8 to 1. Component B is a copolymer ; dispersion, Dur-0-Cryl, obtainable from the C. S. Tanner Co., having a composition in terms of the monomer constituents as follows:

67~
Component% by Weight - acrylonitrile 13 methyl methacrylate 13 butyl acetate 17 acrylamide monionic surfactant 3 water 53 Sufficient composition is applied to result in ~ after drying 5.2 lb./sand paper maker's ream. Drying is ; 10 accomplished by heating for 0.33 min. at 200F., 0.33 min. -at 225F. and 0.33 min. at 200F.
A front size is then applied to the fabric front surface of the following composition:
ComponentParts by Weight (1) a phenol-formaldehyde resin, .~ ~ . '. , ' :
F/P 0.94, NaOH catalyzed until pH = 8.1 ~.................................................................... . .
78% solids in H20 .~................................................................... - ' . .: .
78% solids in H20 .

(2) bisphenol A resin (component A above) 9

(3) CaC03 particulate filler equal to solids in ~ (1) and (2) - Drying is accomplished by heating for 0.33 min. at 225F., 0.33 min. at 275F; and 0.33 min. at 250F.
Sufficient front size composition is applied to result in a dry weight of 4.8 lbs./SPMR.
' A maker adhesive having the following composition is then applied to the frontsized backing member in accordance , with the usual techniques:
', ' ~
~ _7_ :, , :, ' . , . ~ ':, , .

-6~

Component Parts b~ Weight (1) Phenol-formaldehyde alkaline 7 catalyzed resol resin F/P
factor 2.08, pH 8.7 solids 78% in water.
(2) Phenol-formaldehyde alkaline 3 catalyzed resol resin F/P
0.94, pH 8.1, solids in H20 78~
(3) CaC03 particulate filler 1.54 x total solids (1) + (2) The maker is applied in an amount equal to 2 lbs./SPMR.
To the adhesively coated fabric is then applied by conventional elastostatic means 8.3 lbs./5 SPMR grit 320 high purity aluminum oxide abrasive grain. The abrasive-adhesive coated backing member is then heated for 25 mins. at 170F., 25 min. at 190F., and 47 min. at 225F. to provide a dry adhesion layer (1.8 lbs./SPMR) to anchor the abrasive grains to the desired orientation.
Afterwards a size coat (3.3 lbs./SPMR, dry) of the same composition as the maker coat, except for a lower viscosity, is then applied according to the usual techniques. The wet adhesive layer is then dried - 25 mins. at 125F., 25 min. at 135F., 18 min. at 180F., 25 mins. at 190F., and 15 minutes at 225F. after which a final cure at 230F for 8 hours is given. The coated abrasive material is then ready to be manufactured according to the usual techniques, into belts, discs and other desired abrasive products.
In a grit 150, the same backing was used as described above except the prefinish was not applied to the ;.
-8- ~

.. . . . . . .
. ,' ' ' ,' ~' .. ', ' ' , ~ ~ ' , , .
, 67~

fabric. The maker weight for grit 150 Al203, is 4 oz. lbs./SPMR
with a grain deposition of 10.6 lbs./SPMR. The size adhesive of lower viscosity than the makeris appiied 3.3 lbs./SPMR
dry.

':' "' ~

'; .' . ~:
.: .
, ~ . .
" . . ' ~, :
~, - . .
': , i`
:. , '. ~ ' ' ~'' :' -: - ~ . , , , : , ~ ,, .. : , : . : ..
- ~,, ' ~ ' ', ' ' i , , , ""
~' ''', ''' ' ' ' '

Claims (4)

The embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A fine grit flexible coated abrasive sheet characterized in that the backing is a heat calendered cloth woven from polyester yarns, said backing, exclusive of coatings, having a weight of from 3-1/2 to 9 ounces per square yard, a stretch profile, in the warp direction of not more than 6% at 50 pounds less than 9% at 100 pounds, and less than 15% at 200, and having, on the side to which the maker coat is applied, a surface roughness less than 2500 microinches.

2. A woven polyester cloth for the making of fine grit flexible coated abrasive having a weight of from 3.5 to 9 ounces per square yard, an elongation load profile in the warp direction of not more than: 6% at 50 pounds, 9% at 100 pounds, and 15% at 200 pounds, and having been heat calendered to a surface roughness value on at least one side of not more than 2500 microinches.

3. A method of heat calendering polyester woven fabric for use as a backing for manufacturing fine grit abrasive products comprising subjecting the cloth, in a calender, to a pressure of from 600 to 2000 pounds per inch of width and a temperature of from 210 to 380°F, at a speed of from 20 to 75 feet per minute.

4. A method as in Claim 3 in which the temperature is between 230 and 300°F, and the pressure between 800 and 1600 pounds per lineal inch.