US 3136614 A
Description (OCR text may contain errors)
J1me 1964 J. N. KUZMICK COATED ABRASIVE PRODUCTS Filed June 4, 1958 FLEX/BLE BACK/Ne; 1: 1.
V/IlI/I/I/l/I/I/ EL/IJTUMEE/C UZET/MNE MYLAZ SHEET JNVEN TOR. JOSEPH M KUZM/ CK 14 TTOE/VEYS United States Patent 3,136,614 COATED ABRASIVE PRODUCTS Joseph N. Kuzmick, Clifton, N.J., assignor to Raybestos- Manhattan, Inc., Passaic, N.J., a corporation of New Jersey Filed June 4, 1958, Ser. No. 739,933 5 Claims. (Cl. 51297) cutting ability as contrasted to solid bonded abrasive products, and also because of the greater convenience in adapting coated abrasive products to intricate contour grinding. In the present state of the coated abrasive art, reliance is had mainly on relatively rigid binders or adhesives for bonding the abrasive grains to the backing of the product, since retention of the surface abrasive grains is of primary importance for economy of service. Accordingly, most of the conventional abrasive coated products utilize as the bonding adhesive natural or synthetic glues, phenol-aldehyde, resins or modifications thereof.
In spite of the substantial industrial acceptance of these coated abrasive products, their use has been limited or restricted for a number of reasons. Due to the hard and rigid character of the bonding adhesive used, the abrasive products are relatively rigid and stiff. In the abrading of surfaces of intricate convolutions and compound curves it is difficult to properly abrade or polish such surfaces because of the nonconformability or stiffness of these conventional coated products. Extreme bending to achieve conformability to the object being ground usually cracks the abrasive surface and at times the backing material also. For service where greater resistance to such failure is required the backing material may be sized cloth such as cotton twills, cambric, etc.; however, even with reliance on fabrics, the conventional adhesives are sufficiently rigid so that the end product retains sufficient rigidity to promote cracking, spalling and breakage when used under extreme conditions of flex and deflection. The adhesive bond is faulty in its inability to distend, deform and stretch consistent with the requisite adhesion of the abrasive grains to the backing of the abrasive product. In use, the abrasive surface becomes prematurely loaded with abraded particles, which latter stay embedded between the grains of the abrasive surface, impeding or inhibiting further abrading use of the abrasive product. The rigid adhesives are, furthermore, relatively weak as a bond, resulting in the tendency of the abrasive grains to loosen and fall away particularly if worked over surfaces other than flat.
The prime object of my present invention relates to the production of coated abrasive products characterized by such flexibility and suppleness as to enable the same, with continued grinding efficiency to be draped about and be made to conform to compound and intricate curves or convolutions of the article being abraded.
In accomplishing this prime object, I utilize a binder or adhesive for the abrasive grains in the form of an elastomeric film which on the one hand can be bent, distorted and distended or stretched to a high degree, and on the other hand possesses such bonding adhesion for the abrasive grains even in its distorted or distended state as to adheringly retain the abrasive grains for continued and prolonged service. While such elastomeric film bond may be used with conventional backing materials in achieving the object of the invention, 1 preferably employ a plastic backing also possessing flexing and stretching 3,136,614 Ce Patented June 9, 1964 stretch characteristics of the abrasive bond.
As a result of the distensibility or stretchability combined with the abrasive grain retentivity of the elastomeric abrasive bond, I am able to produce coated abrasive products (a) which can be made to stretchably conform to intricately shaped surfaces to a high degree, (b) in which the tendency of the abrasive grains to be loosened and to fall out with distortion of the product is substantially obviated and (c) which is also capable, due to its flexibility and highly distensible character, of being cleaned or unloaded of abraded or ground material lodged therein, thereby permitting the reuse of the abrasive product and thus greatly extending its useful life.
I have found that these described results and characteristics are produced with the use of urethane elastomers as the elastomeric film bond for the abrasive grains in the coated abrasive products. These urethane elastomers comprise the non-foaming group of polyol isocyanate products in solid or liquid phase, which, for example are made from diisocyanates and a linear polyester such as ethylene glycol adipate.
The results achieved, compared to conventional products, may be better seen from the following table which illlustrates the physical properties of urethane elastomer binders, viz., conventional rigid binders such for example as phenol-formaldehyde resins used in present day coated abrasive products:
A comparison of the above physicals clearly illustrates the dissimilarity between the two classes of binders and accounts for the striking product improvement of the present invention. The urethane film bond as a result, may be bent, distorted and stretched without failure and of vital importance because of its excellent strength, adhesive and abrasion resistant properties it retains to surface abrasive grains for prolonged use.
While these urethane elastomer film bonds may be used with conventional backing materials such as paper, size twills and vulcanized fiber sheeting, their use now makes it possible to utilize plastic films as backing materials with unexpected advantages. Mylar polyester film manufactured by Du Pont is an excellent example, as
this film is extremely strong and tear resistant, can be This cleaning can be accomplished by rustling, brushing,
washing or any convenient means and this is made possible by virtue of the elastic properties of the adhesive, the tenacious bonding of the abrasive grains and the indestructible properties of the plastic backing. Other plastic films may be substituted for polyester film such as vinylidene chloride, cellulose esters, etc.
As is well known, the polyurethanes comprise a group of synthetics with end products characterized as rigid and flexible foams, flexible coatings and adhesives and elastomeric rubber-like products of superior strength, abrasion and adhesive properties. Basically they are reaction products of polyols and isocyanates, the major contributing variable being the polymers or polyfunctional resins Which can be alkyd, polyesters or polyethers. These resins are of a class based 011 polyhydric alcohols and organic or polybasic acids. Adipic acid and glycols of various types are the prime source of polyols used in the manufacture of polyurethanes. The class of urethane foams briefly are reaction products of polyols and isocyanates with proper adjustment of variable free hydroxyl groups or Water to react with the free available isocyanate liberating carbon dioxide, which gas produces the foaming.
The class of urethane elastomers whether solid or liquid phase differ in that they are lower in reactivity with slight or practically zero free isocyanate terminals. They usually and preferably are made from prepolymers of polyols and isocyanates and cross-linked or set under substantially anhydrous conditions to providea non-foam material. Such end reactions are usually cross-linked by a group of reagents, for example amines or dichlorobenzidenes. Thin films may be triggered by atmospheric moisture which is sufiicient to cross-link the molecules.
The product of the invention is illustrated in the accompanying drawings in which:
FIG. 1 is a perspective .view of a coated abrasive product embodying the principles of the invention; and
FIG. 2 is an enlarged view thereof taken in cross-section in the plane of the line 2-2 of FIG. 1.
In the drawings, the flexible backing may comprise any conventional fiexible backing but preferably comprises a Mylar polyester film and the like, the bond 12 comprises the described elastomeric urethane film of high elongation and 14 represents the layer of abrasive grains bonded by and to the elastomeric film 12.
The following are typical examples of practicing the present invention:
Example I As an example of the practice of this invention I may take Mylar polyester film 1 mil thick. Mylar is a polyester film made from polyethylene terephthalate, the polymer formed by the condensation reaction between ethylene glycol and terephthalic acid. On one side of this film is spread a fluid polymer of urethane elastomer, 3 to 4 mils in thickness by means of a conventional'knife spreader. Prior to spreading, the urethane elastomer, in this instance a product sold as Adiprene manufactured by Du Pont is compounded or mixed with 12% by weight of 'a cross-linking agent dichlorobenzidene. Adiprene is a liquid urethane elastomer reaction product of diisocyanate and a polyalkylene ether glycol. Following the spreading of the binder and while in forward motion #200 silicon carbide abrasive is sprinkled on the surface of the binder. The motion of the abrasive coated film is continued over suitable supporting rolls and inverted to permit excess abrasive and above that attached to the surface by adhesion to the sticky binder to fall off. The coated film continues through a tunnel oven heated at 250 F. to vulcanize or cross-link the elastomer. Subsequent cutting into sheets, belts or discs provides an end product of exceptional durability, conformability and capable of being reused indefinitely by virtue of being able to unload the surface of adhering ground material.
Example II As another example of the practice of this invention I may take sized cotton twill for the backing material. On one side of this twill is spread by means of a typical spread coater a film of urethane elastomer previously heated with a cross-linking agent to reduce viscosity for convenience in spreading. In this instance the urethane elastomer is a product sold as Vibrathane, a product of Naugatuck Chemical Division of United States Rubber Co. combined with 10% by weight of a cross-linking agent, namely, 3,3 dichloro 4,4 diatnino diphenylethane. Vibrathane 6001 is a highly reactive polyurethane liquid polymer, with terminal isocyanate groups. The coated fabric is sprinkled with #100 garnet, a natural alumina abrasive, followed by heating at 250300 F. to set the adhesive.
Example III Still another example relies on the use of a good grade of sized kraft paper for the backing material. The urethane polymer in this example is again Vibrathane 6001 without the use of a cross-linkingagent. Methyl ethyl ketone is used to reduce the viscosity suitable for roller coating. The coated paper is sprinkled with mesh screen flint as the abrasive. The coated material is set or triggered by atmospheric moisture at room temperature.
It is to be understood that the urethane polymer can be varied by a choice of polybasic acids and polyhydric alcohols and through a Wide choice of cross-linking agents. The end products therefore can vary from very soft elastic films to tough products with reduced elongation. Furthermore, urethane elastomers and epoxy resins being compatible in all proportions and with both components capable of being simultaneously set with the same crosslinking agents, provide a further means of varying the end properties to suit special applications. The types and mesh size of abrasives can also be varied in accordance with common practice in the prior art. It is also to be understood that the adhesive layer on the supporting backing material may vary in thickness. This variation as a rule is dictated by the mesh size of the abrasive used.
1. A coated abrasive product comprising a flexible sheet backing, a flexible and stretchable binder film adheringly coated onto a face of said backing, and a layer of abrasive grains deposited onto said binder film, said binder film consisting essentially of a cured film of nonfoamed polyurethane elastorner, said binder film forming the medium for its adherence to said backing and forming the binder for the abrasive grains, the resulting coated abrasive product being characterized by such flexibility and suppleness as to enable the same to be draped about and to be made to conform to intricate convolutions of the article being abraded.
2. The coated product of claim 1 in which the flexible backing consists essentially of a polyester film of polyethylene terephthalate.
3. The coated product of claim 1 in which the flexible backing consists essentially of a sized cotton twill.
4. The coated product of claim 1 in which the flexible backing consists essentially of a sized kraft paper sheet.
5. A coated abrasive product comprising a flexible sheet backing, a cured binder film of non-foamed polyurethane elastomer on said backing, and a layer of abrasive grains embedded in said binder film.
References Cited in the file of this patent UNITED STATES PATENTS 2,673,826 Ness Mar. 30, 1954 2,819,186 Franck Ian. 7, 1958 2,824,024 Chapman Feb. 18, 1958 2,881,065 Reuter Apr. 7, 1959 FOREIGN PATENTS 716,422 Great Britain Oct. 6, 1954 118,147 Australia Mar. 2, 1944