DE1569157A1 - Coated abrasives - Google Patents

Description

Coated Abrasives This invention relates to coated abrasives having a backing of saturated fibrous sheet material. It is a general object of the invention to reduce and simplify the cost of producing coated abrasives by reducing the number of primers and treatments required for the various layers of the product. The invention proposes an abrasive which has an auxiliary coating a glue made of animal hide (animal hide glue "make" coat) is connected directly and firmly to a saturated fibrous substrate that is essentially insensitive to temperature and moisture. The present invention proposes in particular a coated abrasive sheet material which consists of a layer of sole grains which are firmly bonded to a base via a hardened binding adhesive, the base being made of a fibrous sheet material with a smooth, flexible, film-forming copolymer is treated from monomers) which consists essentially of acrylonitrile and at least one aerylic acid ester, which is formed by reacting an acrylic acid with a monohydric aliphatic alcohol having up to 8 carbon atoms, the esters in this copolymer being selected so that, if they are by themselves are polymerized alone, the resulting copolymer has a glass transition temperature of below 40 ° C. In one embodiment of the coated abrasive sheet material of the invention, the mixed polymer of monomers contains up to 15% by weight of a polymerizable α, B-unsaturated acid with a methyl group at the a-carbon atom.

Large coated sanding belts for industrial dry sanding processes are usually made from drill or coarse cloth backings that are equipped with a combination of animal glue, starch and clay. The documents are satisfactory for many purposes, but their disadvantages are also known. For example, repeated flexing changes the degree of stiffness that the base possesses. As the relative humidity increases, the temperature at which the base becomes soft and plastic becomes lower. Conventional substrates therefore tend to become soft, sticky and elastic in the summer months, unless special treatments are carried out, and the glue made from animal skin and other auxiliary adhesives is not particularly sticky to the substrate; As a consequence of this, abrasive belts often lose their effectiveness because the adhesive and the abrasive mineral are prematurely separated from the backing.Usually, waterproof synthetic and / or natural polymers are used to saturate cloth bases for coated abrasive belts for wet grinding processes. Ethyleell has been used for over 20 years. Ulose saturated wipe, one of the most common underlays used in conjunction with phenolic auxiliary adhesives; however, animal glue adheres poorly to ethyl cellulose treated cloth. In fact, it has generally been believed that animal glue would actually adhere to synthetic polymeric resins Anything that can be used as a satiety agent does not stick very well, an assumption that is due to the relatively poor adhesion between an auxiliary material and a cloth or padding pad filled with natural or synthetic, elastomers or rubber e seemed to be sustained. An extremely versatile group of blend polymers has now been discovered which can be used as sizing or saturating agents for cloth, paper or other fibrous sheet material normally used as the backing for coated abrasives. Backings containing these treatments are resistant to water and oil, which can be used as lubricants or coolants during the grinding process, and they are resistant to aging and becoming brittle under the influence of heat. In spite of their water resistance, the substrates treated with preference are surprisingly receptive to four-glue, which adheres more firmly to these substrates than to conventional substrates. Indeed, these liners have an unusually high affinity for virtually any adhesive that has been tested, whether it is aqueous or in solution in an organic solvent. A fibrous backing is used to make the new coated abrasive gowns of the invention, which is made with a smoothing, flexible, film-forming copolymer of monomers is treated which consist of a polymerizable nitrile such as acrylonitrile, one or more alkyl acrylates and preferably a polymerizable α, β-unsaturated acid with a methylene group on the α-carbon atom. The or, de monomeric esters are selected so that, if they are polymerized alone up to a molecular weight of about 40,000, the resulting polymer has a glass transition temperature of not more than 400C. Tg, which is closely related to the embrittlement point, represents the temperature below which a polymer film can no longer be bent without it splintering. In an article by Harry Burrel in the February 1962 issue of "Official Digest", the glass - Transition temperatures listed for over 100 polymers, although all esters of acrylic acid have a glass transition temperature of below 40 ° C, only the n-propyl and higher alkyl esters of methacrylic acid are below this value * It is possible to use a monomeric ester such as ethyl methacrylate to use which, when polymerized, has a glass transition temperature of about 650C; in this case, however, other monomeric aerylic acid esters must be present, so that the mixed polymer, which is formed from these ester constituents alone, has a glass transition temperature of below 40.degree. The Tg for such ester copolymers can be calculated using the following equation: in which Tg is the glass transition temperature of the copolymer; E1, E2 and En is the weight fraction of the monomers E1, E2 and En and Tg1 9 T92 and Tgn are the corresponding absolute glass transition temperatures of the copolymers of these monomeric esters.

Generally speaking, Nisehpolymerisate have from relatively short chain monoxeren Entern a better oil resistance and poorer water resistance than copolymers that are prepared from relatively long chain monomeric esters. According to the invention, it has been found that copolymers are based on. of n-butyl acrylate or methacrylate have a satisfactory resistance to oil and water and that they are extremely useful for the purposes of the invention. Ethyl acrylate-based interpolymers have somewhat higher heat softening points and tear strengths, making them useful as saturants for short belt backings such as those used in abrasive plates which can generate a great deal of heat .

To prepare the polymeric saturation agent or sizing agent for the product according to the invention, about 30 to 60 parts by weight of nitrile are copolymerized with about 30 to 70 parts of monomeric aerylic acid ester. Since a honopolymer made from acrylonitrile is comparatively stiff (Tg = 800C) , copolymers with a high percentage of acrylonitrile monomers are consequently also stiff. Such copolymers are, however, solid and have a tensile strength of over 400 kg / cm 2 with an external elongation (ultimate elongation) of up to 150%. In the same way, the flexibility increases sharply when the amount of monomeric acrylonitrile in the copolymer is reduced. For example, a copolymer with 25% monomeric acrylonitrile can have a tensile strength of about 70 kg / cm 2 with an external elongation of 350%. In general, the higher the percentage of monomeric ester, the lower the resistance to solvents of the finished copolymers.

The preferred one used in practicing the present invention Saturation agent also contains up to 15 wt .-% of a polymerizable α, ß-unsaturated Acid with the methyl group on the a-carbon atom. Such acids are Acrylic, methacrylic, itaconic, α-alkyl acrylic, α-arylacryl, α-chloroacrylic acid and so on Further; Acrylic acid and methaeric acid are particularly preferred. It was found, that the acid surprisingly has the tendency to reduce the wet drawability of the .to reduce saturated documents and also the adhesion of at least some To improve auxiliary adhesives for coated abrasives. All in all, there is a preferred pad satiety agent to be used in conjunction with any usual auxiliary adhesive for coated abrasives can be used from a mixed polymer, which consists of 30 to 60 parts by weight of acrylonitrile, 40 to 65 parts by weight of acrylic acid ester and 5 to 10 parts by weight of acid is formed. the Copolymers used to carry out the present invention are on are not new and can be done according to known processes by emulsion polymerization e.g. according to the US Patents 2,753,318 and 2,866,763 and other methods described, one suggested by the prior art The primary use for the satiety agents used herein is for manufacture waterproof materials; it has surprisingly been found that adhesives based on water, e.g. phenol-formaldehyde resins and especially animal glue can be successfully glued with these saturant-containing documents.

For a better understanding of the invention, the following illustrative examples are given in which all parts are parts by weight, unless otherwise stated. Example 1 This example relates to the production of a coated abrasive belt on a cloth backing with an auxiliary adhesive made from animal glue.

A process for the preparation of the polymers in a suitable polymerization container equipped with a stirrer, reflux condenser with inlet and outlet tubes, a thermocouple, and heating and cooling device were 189 parts of water and 8.9 parts of a dispersant "Triton.X-200" input , a surfactant consisting of the sodium salt of an alkylaryl polyether sulphate (commercially available from Rohm & Haas Company, Philadelphia, Pennsylvania, under the trade designation "Triton" X-200). Nitrogen was bubbled through the solution to remove the air dissolved therein and then continuously bubbled over the reaction mixture to maintain an inert atmosphere in the reaction kettle.

In a separate container, 58.0 parts of n-butyl erylate (Tg -520G), 37.0 parts of acrylonitrile, 5.0 parts of methacrylic acid and 0.1 part of tert -dodecyl mercaptan are mixed. About 25% of the monomer mixture was then added to the polymerization kettle and the emulsion obtained is heated to 45-50 ° C., then an initiator consisting of 0.06 part of potassium persulfate and 0.03 part of sodium metabisulfite is added. The remaining monomer solution was then added continuously at a rate such that the reaction temperature was kept at 60 to 650 ° C .; at the end of the reaction, additional heat and initiator are added in order to ensure practically complete polymerization of the monomers. Unreacted monomers were removed by vacuum distillation. The pH of the reaction product from mixed polymer latex was increased to 5.2 by adding 28% ammonium hydroxide in order to improve the mechanical stability. The final product contained 33.2% solids of a terpolymer with a calculated glass transition temperature Tg of -4o0. Other known prior art methods can also be used to carry out this polymerization.

General methods for saturation Dyed and stretched coarse cloth (jeans cloth) with a basis weight of about 18.5 mg / cm 2 was immersed in the copolymer latex described in the preceding paragraph in order to completely saturate the fibers.

It was then passed through nip rollers, leaving about 8.6 mg of saturation solids per cm 2 were retained in the cloth, the saturated substrate was through Passing through a hot air oven heated to about 820C and passing over dried over a series of heated rollers.

A 0.635 mm thick cast film of the ILatea saturant of this invention was found to be pliable and to have tensile atrength (Ty, tensile atrength t- at yield) of about 90 kg / cms2 and an external elongation (Eb) of about 270% when tested at about 23 ° C and a relative humidity of 48%.

Production and testing of a coated abrasive sheet material The saturated and dried backing was then coated on the sanding side with a customary auxiliary adhesive made from glue from animal skin in an amount of about 8.6 mg of residual substances per cm 2. Aluminum oxide mineral with an average particle diameter of 95% was then electrostatically deposited on this adhesive layer in an amount of about 16.7 mg per cm 2. The glue was gelled to maintain the orientation of the mineral; then the abrasive was coated with a base-catalyzed phenolic resin in an amount of about 8.6 mg resin solids per cm 2. The material was dried in the form of a garland, wound up into rolls and placed in a hot air oven heated to 1000 ° C. for 12 hours in order to cause the phenolic resin to cure. The finished abrasive was then bent in the conventional manner by passing it around a rubber roller with the abrasive side inward while a steel roller was pressed against the back.

The adhesion between the auxiliary coating of glue and the backing was measured by adhering the abrasive surface of an approximately 5 cm wide strip of the coated abrasive just described to a wooden board, bending the strip 180o and measuring the force in a tensile strength tester. which is required to separate the glue from the substrate at a speed of about 5 cm per minute. The adhesive strength was found to be about 2 kg / cm width, whereas a control sample, which was identical to the one described above except that it contained a standard cloth backing treated with starch-glue-clay, had an adhesive strength of only about 1 , 9 kg / cm, (It should be noted that the adhesion of an auxiliary coating of glue to an ethyl cellulose-treated backing of the type commonly used to make waterproof coated abrasives is much lower and, in fact, difficult to measure If the monomeric aerylic acid is omitted from the reactants used to form the copolymer saturant, the adhesion value of the auxiliary coating to the substrate is reduced to about 1.5 kg / cm, whereas an increase in the acid content to about 15% increases this value somewhat , The importance of good adhesion between the auxiliary cover and the base was demonstrated by: a us the coated abrasive sheet material of this example, about 8 cm x 235 cm endless belt was formed, which was mounted on a conventional grinding apparatus in which it is a smooth rubber contact roller with a diameter of about 65 cm at a surface speed of about 2000 m per minute was operated, with the tape protruding about 1 cm above the edge of the roller. The front of a 6 cm x 10 cm x 1 cm cold rolled steel bar was pressed against the edge of the roller at an angle of about 45 ° under a force of about 2.7 kg. The tape removed nearly 30% more steel before becoming unusable than a control tape which was identical in construction to the above except that the backing contained the usual glue-starch clay mass. It has been found that this approach is in good agreement with the industrial grinding of zinc cast nozzles, in which an abrasive belt is often used to smooth out streaks, grooves and internal curves. It has also been observed that the backing for the coated abrasive of this invention maintained substantially consistent stretchability and flexibility properties at temperatures from about 10 to about 380 ° C. and relative humidities between 10 and 90 percent. In contrast, a common abrasive became much more pliable and tacky at temperatures around 320C, especially when the relative humidity exceeded 50. Example 2 This example describes the preparation of an improved, water-resistant, coated, paper-based abrasive sheet.

A common saturation paper with a basis weight of about 5 ¢ mg per cm 2 was saturated with a butadiene-acrylonitrile copolymer to reduce the Basic weight to about 8.1 mg / cm 2. On top this paper then became a 58: 37: 5 n-butyl acrylate aeryl nitrile: methaeryl acid copolymer latex (prepared as in Example 1) applied using a squeegee (air keife) was to regulate the application so that about 1.6 mg of solids applied per cm 2 became. The paper sized in this way was dried for 1 hour at about 900C, A 54: 43: 3 n-butyl acrylate: acrylonitrile was then applied to the back of the paper Methaeric acid copolymer latex with a content of 20% diatomaceous earth (on Solids related) applied, again using a squeegee (air keife) in order to limit the amount applied to 1.0 mg per cm 2. The paper was then dried at about 900C for one hour.

It was then done in exactly the same way as in the previous paragraph produced a paper for comparison purposes that corresponds to the state of the art, only that a modified polyvinyl chloride latex instead of the acrylate aeryl nitrile : Acid Zateces was used.

Both the test and the comparison documents were now with about 2.7 mg of an auxiliary coating made of conventional oil-based varnish (oleoresinous varnish make coat) coated per cm 2; then about 8 mg / cm 2 of silicon carbide was included an average particle diameter of about 55 @ applied electrostatically and the auxiliary coating dried at about 90 ° C for 24 hours. The abrasive grains in the Samples were subsequently modified with about 5.5 mg of a common phenol Alkyd resin coated per cm 2 and the coating cured at 90 ° C for 24 hours.

The test abrasive coated in accordance with the invention sanded a automatically moving surface (automotive surfacer) faster and longer Time off than the comparative sample. The test material according to the invention also showed greater adhesion of the auxiliary coating to the substrate and retained its original "Body" usable longer. It had about 30% more wet strength than the comparison sample.

If the acrylonitrile: acrylate: acid latex is used as the original saturant instead of the butadiene: acrylonitrile, abrasives coated on this backing have even greater water resistance. Example 3 This example explains the production of a waterproof, coated abrasive belt on a cloth backing. Unsized, kerboiled, colored and stretched drill cloth was immersed in a 50:50 n-butyl acrylate: acrylonitrile copolymer dispersion, which was produced as in Example-1, and then passed through nip rollers, with 8.4 mg of polymer solids per cm 2 3 m of cloth being retained. (A cast film from this copolymer had a tensile strength of about 340 kg / cm 2 and an elongation at break of less than 50 °.) The saturated cloth was dried and subjected to saturation with the same polymer, with about 3.7 mg of polymer solids per cm 2 were retained. The doubly saturated substrate was dried again and then primed by immersion in a 47% strength aqueous solution of a base-catalyzed phenol-formaldehyde resin and passed through nip rollers, about 3.4 mg resin solids per cm 2 being retained. The cloth was then held at about 820C in an air oven for 80 minutes.

The backing was then coated on the abrasive side with an auxiliary coating of a conventional phenol-formaldehyde resin in such an amount that about 8 mg of resin solids per cm2 were retained on the cloth. On this adhesive layer, silicon carbide with an average particle diameter of 115% was electrostatically deposited in an amount of 22.2 mg per cm 2. This coated sheet was passed through a hot air drying oven and a layer of phenolic adhesive was applied over the coated material at a rate of 15.7 milligrams of resin solids per square centimeter. After it had been pulled through a drying oven in the form of a garland, the material was dried in the form of a garland, wound up into rolls and placed in an air oven heated to 1000 ° C. for 12 hours to cause the adhesive layers to cure. The finished coated abrasive was then bent in a conventional manner. Stripback adhesion was about 3.9 kg / cm width, compared to about 297 kg / cm width for a product identical to the above, except that it was made from conventional ethylcellulose-saturated backing® This process product can be used for dry grinding, but it is particularly intended for use under wet grinding conditions. For such uses, a low level of wet stretchability and wet flatness are essential for good operating conditions. The wet veratreekbarkeit is measured by immersing an approximately 2.5 x 15 cm sample in water of approximately 210 ° C. for 60 minutes and then measuring the elongation under a tension of approximately 18 kgfem width. The wet stretchability of the product of this example was 2.0% compared to 2.0% for a material of the prior art made from a substrate saturated with ethyl cellulose. If, however, the copolymer saturant is prepared from monomers which contain at least 3% of an α, β-unsaturated acid, the value for the wet drawability is significantly reduced, ie to 1.3%.

The wet flatness or resistance to "cupping" is measured by dipping an approximately 15 cm wide strip of the coated abrasive with the sanding side up in about 280C water. One end of the strip is clamped while that the other end, which protrudes over the water trough, is hung with a weight of about 13.6 kg; the corrugation is measured as the height of a string drawn from one edge of the strip to the other, in units of about 0.8 mm (1/32 of an inch). After 15 minutes, the product of this example had a curl value of less than 1, whereas a conventional product made from ethyl cellulose-saturated substrate had a curl value of 20. If the phenol-formaldehyde primer layer is omitted from the product of this example, the result is a curl value of about 9. The following table lists examples of copolymers that can be used according to the invention to saturate coated abrasive substrates Properties and general usability of the polymers are given. The above examples are only intended to illustrate various embodiments of the invention, but various modifications are also possible which the person skilled in the art can easily carry out the acrylate-7 monomer are copolymerizable. In the same way, 2 or more acrylate monomers, as well as 2 or more nitrile monomers or 2 or more acid monomers, can be used to form suitable saturants. .

The copolymers disclosed herein can also be used for this purpose a variety of documents other than ordinary paper and cotton cloth to saturate, Such documents can, for example, made of woven or non-woven nonwovens consist of nylon, polyethylene terephthalate, glass, polyethylene and polypropylene, It can also be paper-like sheet materials made of "fiber-bonded" ("fibrid" -bonded) natural or synthetic fibers are used, den in this application polymeric saturants described can include various modifying agents can be added. Z, Bo can form polymers containing free carboxyl groups, a dibasic oxide like zinc oxide be added. Through implementation of the zinc oxide with the acid groups are crosslinks between the various Polymer chains formed, reducing the solubility and thermoplasticity of the Polymerisate is reduced, the latex can continue to contain various water-soluble, thermosetting resins, such as those based on urea-formaldehyde, Phenol-formaldehyde and melamine-formaldehyde produced as reinforcing agents can be added.

Claims (1)

P atentanaprü ch e 1, Coated abrasive sheet material, which consists of a layer of abrasive grains which are bonded to a backing by a hardened binding adhesive, characterized in that the backing consists of a fibrous sheet material made with a smoothing, flexible, film-forming copolymer Treated monomers is' which consist essentially of acrylonitrile and at least one acrylic acid ester, which is formed by reacting an aerylic acid with a monohydric aliphatic alcohol having up to 8 carbon atoms, the esters in this copolymer being selected so that, if they are for themselves be polymerized alone, which corresponds standing polymer has a glass transition temperature of less than 400G z. Sheet material according to claim 1, characterized in that one of the monomers is n-butyl anylate, 3-. Sheet material according to Claim 1 or 2, characterized in that the monomeric polymer consists essentially of aoryl nitrile 0 to 15% by weight of a polymerizable α-unsaturated acid with the methylene group on the α-carbon atom and at least one acrylic acid ester which , which can be acrylic acid or methacrylic acid, is formed with an alcohol having up to 8 carbon atoms. 4. Sheet material according to claim 1, characterized in that the base consists of a flexible fibrous sheet material which is saturated by treatment with a saturant which essentially consists of the dry Abaeheidenaprodukt an aqueous emulsion of a copolymer of monomers, the @ essentially consists of 30 to 70 parts by weight of acrylic acid ester, which, when polymerized on its own, has a glass transition temperature of less than 4000, 30 to 60 parts by weight of acrylonitrile and 0 to 15% of a polymerizable α, ß-unsaturated acid with the M ethyl group on the α-carbon atom . 5, sheet material according to claim 4, characterized in that the mixed polymer of monomers consists essentially of 40 to 65 parts by weight of acrylic acid ester, 30 to 60 parts by weight of aeryl nitrile and 1 to 10% of the polymerizable α, ß-unsaturated acid 6, sheet material according to claim 5, marked thereby characterized, that the Misehpolymerisat of monomers is mainly made up 40 to 65 weight parts of n-butyl acrylate, 30 to 60 parts by weight of acrylonitrile and 1 to 10% w ethacrylic acid consists. 7o sheet material according to claim 1, characterized in that the abrasive grains are connected to the flexible base by an auxiliary adhesive made of animal glue (animal glue react 1 ° adhesive) and that the base is saturated and smoothed with a copolymer of monomers, which is essentially from 30 to 70 parts by weight of aerylic acid ester, 30 to 60 parts by weight of aeryl nitrile and 5 'to 10 parts of a homopolymerizable α-unsaturated olefinic carboxylic acid, preferably an X-onocarboxylic acid, with the methyl group on the α-carbon atom, 8® sheet material according to one of claims 3 to 5 or claim 7, characterized in that the polymerizable α, β-unsaturated acid is acrylic acid, methacrylic acid, itaconic acid, α-alkyl acrylic acid, α-arylacrylic acid or α-chloroacrylic acid. 9. Sheet material according to any one of claims 1 to 8, characterized in that the fibrous base consists of woven cloth, paper or the like. 10, use of a film-forming copolymer of monomers consisting essentially of acrylonitrile and at least one acrylic acid ester, which is formed by reacting an acrylic acid with a monohydric, aliphatic alcohol having up to 8 carbon atoms, as a saturant for fibrous substrates of a particle-coated one Sheet material to give it high strength, heat resistance and oil and water repellent properties,