EP0536596A1 - Abrasive material - Google Patents

Abstract

An abrasive material (abradant) based on finely divided abrasive particles bonded to one another and/or to a support by means of a binder, where the binder is the solid component of an aqueous polymer dispersion obtainable by polymerising unsaturated monomers which can be polymerised by means of free radicals, in the aqueous phase in the presence of a monosaccharide, oligosaccharide or polysaccharide, oxidatively, hydrolytically and/or enzymatically degraded polysaccharides, chemically modified mono-, oligo- and polysaccharides, or mixtures of said compounds, by the process of free-radical aqueous emulsion polymerisation.

Description

The present invention relates to abrasives based on finely divided abrasive particles bonded to one another and / or on a carrier by means of a binder, the binder being the solids content of an aqueous polymer dispersion which can be obtained by free-radically polymerizable unsaturated monomers in the presence of an aqueous phase Monosaccharides, oligosaccharides, polysaccharides, oxidatively, hydrolytically and / or enzymatically degraded polysaccharides, chemically modified mono-, oligo- or polysaccharides or mixtures of the compounds mentioned are polymerized by the process of free-radical aqueous emulsion polymerization.

From EP-A 261 098, abrasives are known whose abrasive particles are bonded with a radiation-curable polymeric binder to achieve satisfactory properties. The disadvantage of radiation curing is disadvantageous.

The object of the present invention was therefore to provide fully satisfactory abrasives based on polymeric binders which do not require radiation curing. Accordingly, the abrasives defined at the outset were found.

The following are particularly suitable as finely divided abrasive particles: fused or sintered corundum, zirconium corundum, silicon carbide and emery. Flexible substrates, such as e.g. Paper, vulcanized fiber, woven fabrics, knitted fabrics, nonwovens based on natural and / or synthetic fibers, plastic films or metal foils.

Radically polymerizable monomers include, in particular, monoethylenically unsaturated monomers such as olefins, for example ethylene, vinylaromatic monomers such as styrene, α-methylstyrene, o-chlorostyrene or vinyltoluenes, vinyl and vinylidene halides such as vinyl and vinylidene chloride, esters of vinyl alcohol and 1 to 18 C Monocarboxylic acids containing atoms, such as vinyl acetate, vinyl propionate, vinyl n-butyrate, Vinyl laurate and vinyl stearate, esters of preferably 3 to 6 carbon atoms have α, β-monoethylenically unsaturated mono- and dicarboxylic acids, such as in particular acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid, with generally 1 to 12, preferably 1 to 8 and in particular Alkanols containing 1 to 4 carbon atoms, such as, in particular, acrylic acid and methacrylic acid, methyl, ethyl, n-butyl, isobutyl and -2-ethylhexyl ester, dimethyl maleate or n-butyl maleate, nitriles α, β-monoethylenically unsaturated carboxylic acids such as acrylonitrile and C₄₋₈ conjugated dienes such as 1,3-butadiene and isoprene. The monomers mentioned are essentially insoluble in an aqueous medium and generally form the main monomers which, based on the total amount of the monomers to be polymerized, normally account for more than 50% by weight. Monomers which, when polymerized on their own, usually give homopolymers which have an increased solubility in water, are normally only used as modifying monomers in amounts, based on the total amount of the monomers to be polymerized, of less than 50% by weight, generally 0.5 up to 20, preferably 1 to 10 wt .-%, co-polymerized.

Examples of such monomers are α, β-monoethylenically unsaturated mono- and dicarboxylic acids and their amides such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, acrylamide and methacrylamide, furthermore vinylsulfonic acid and its water-soluble salts and N- Vinyl pyrrolidone. Monomers, which usually increase the internal strength of the films of the aqueous polymer dispersion, are generally also copolymerized only in minor amounts, usually 0.5 to 10% by weight, based on the total amount of the monomers to be polymerized. Such monomers normally have an epoxy, hydroxy, N-methylol, carbonyl or at least two non-conjugated ethylenically unsaturated double bonds. Examples of these are N, alkylolamides of α, β-monoethylenically unsaturated carboxylic acids having 3 to 10 carbon atoms and their esters with alcohols having 1 to 4 carbon atoms, among which the N-methylolacrylamide and the N-methylolmethacrylamide are very particularly preferred, two monomers containing vinyl residues, two monomers having vinylidene residues and two alkenyl residues Monomers. The di-esters of dihydric alcohol with α, β-monoethylenically unsaturated monocarboxylic acids are particularly suitable, among which in turn acrylic and methacrylic acid are preferably used. Examples of such monomers having two non-conjugated ethylenically unsaturated double bonds are alkylene glycol diacrylates and dimethacrylates such as ethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butylene glycol diacrylate as well as propylene glycol diacrylate, dicinylbenzene, allala methacrylate, methacrylate, methacrylate, methacrylate, methacrylate, methacrylate, methacrylate, methacrylate, methacrylate, methacrylate, methacrylate, methacrylate, methacrylate, methacrylate. In addition to monomers containing unsaturated double bonds, minor amounts, usually 0.01 to 4% by weight, based on the monomers to be polymerized, can also be used to copolymerize substances which regulate the molecular weight, such as tert-dodecyl mercaptan. Such substances are preferably added to the polymerization zone in a mixture with the monomers to be polymerized.

• zu 50 bis 100 Gew.-% aus Estern der Acryl- und/oder Methacrylsäure mit 1 bis 12 C-Atome aufweisenden Alkanolen und/oder Styrol (Klasse I)

oder

• zu 70 bis 100 Gew.-% aus Styrol und/oder Butadien (Klasse II)

oder

• zu 70 bis 100 Gew.-% aus Vinylchlorid und/oder Vinylidenchlorid (Klasse III)

zusammengesetzt sind, wobei die Klasse I besonders bevorzugt ist und vorzugsweise nachfolgende Monomerenzusammensetzungen umfaßt:
90 bis 99 Gew.-%   aus Estern der Acryl- und/oder Methacrylsäure mit 1 bis 8 C-Atome aufweisenden Alkanolen und/oder Styrol und
1 bis 10 Gew.-%   Acrylsäure, Methacrylsäure oder deren Gemisch.Preferred classes of aqueous polymer dispersions to be used according to the invention are those whose polymers can be obtained by free-radical polymerization of monomer mixtures which

• 50 to 100% by weight of esters of acrylic and / or methacrylic acid with alkanols and / or styrene (class I) containing 1 to 12 carbon atoms

or

• 70 to 100% by weight of styrene and / or butadiene (class II)

or

• 70 to 100% by weight of vinyl chloride and / or vinylidene chloride (class III)

are composed, class I being particularly preferred and preferably comprising the following monomer compositions:
90 to 99% by weight of esters of acrylic and / or methacrylic acid with 1 to 8 carbon atoms and alkanols and / or styrene and
1 to 10 wt .-% acrylic acid, methacrylic acid or a mixture thereof.

The following monomer compositions are of particular interest:
90 to 99% by weight of n-butyl acrylate and / or styrene
1 to 10 wt .-% acrylic acid and / or methacrylic acid.

According to the invention, the monomers mentioned are polymerized by the process of free-radical aqueous emulsion polymerization in the presence of polysaccharides, oligosaccharides, monosaccharides and / or their derivatives. They can be of vegetable or animal origin, soluble in water or only dispersible therein. Among other things, the so-called swelling starches are suitable, which are obtainable, for example, by hydrothermal treatment of native starch. Thin-boiling starches are also suitable. These are starches that are slightly broken down with acids or enzymes or oxidized with mild oxidizing agents, which, even in higher concentrations, do not produce viscous paste but rather thin liquids when boiled with water. Also suitable are acid-modified starches which are obtained by heating an aqueous starch suspension below the gelatinization temperature in the presence of small amounts of acid. Oxidatively modified starches are also suitable. Chromic acid, permanganate, hydrogen peroxide, nitrogen dioxide, hypochlorite or periodic acid can be used as the oxidizing agent. Basically, all native starches such as cereal starches (e.g. corn, wheat, rice or millet), tuber and root starches (e.g. potatoes, tapioca roots or arrowroot) or sago starches are suitable as starting starches. The use of roasted dextrins as described, for example, in EP-A 408 099 and in EP-A 334 515 is particularly advantageous. They can be obtained by heating moist, dry starch, usually in the presence of small amounts of acid. Typical roasted dextrins are, for example, commercially available white and yellow dextrins; it also includes dextrins that are sold under the trademark Noredux® and Tackidex® are sold. The term dextrin is used here generally for starch breakdown products. However, radical emulsion polymerization in the presence of saccharified starches is recommended with particular advantage. This is a starch degradation product obtainable by hydrolysis in the aqueous phase, which preferably has a weight-average molecular weight M _w of 2500 to 25,000. More detailed information on the production of the starches and starch derivatives mentioned can be found in G. Tegge, Starch and Starch Derivatives, Behr's Verlag, Hamburg 1984. Of course, the starches and starch derivatives mentioned can be used according to the invention in, for example, etherification or esterification in a chemically modified form.

This chemical modification can be carried out on the starch before it is broken down or afterwards. Esterifications are possible with both inorganic and organic acids, their ahydrides or chlorides. Phosphated and acetylated derivatives are of particular interest. The most common etherification method is treatment with organic halogen compounds, epoxides or sulfates in aqueous alkaline solution. Particularly suitable ethers are alkyl ethers, hydroxyalkyl ethers, carboxyalkyl ethers and allyl ethers. Cyanoalkylated derivatives and reaction products with 2,3-epoxypropyltrimethylammonium chloride are also suitable. Products that are not chemically modified are preferred. Of course, mono- and oligosaccharides and cellulose degradation products, for example cellobiose and its oligomers, are also suitable.

The saccharified starches of a weight average molecular weight of 2500 to 25,000 to be used with particular preference according to the invention are commercially available as such (for example the C * PUR products 01906, 01908, 01910, 01912, 01915, 01921, 01924, 01932 or 01934 from Cerestar Deutschland GmbH , D-1150 Krefeld 12). Such saccharified starches are chemically different from roasted dextrins in that hydrolytic degradation in an aqueous medium (usually suspensions or solutions), which is generally carried out at solids contents of 10 to 30% by weight and preferably acid or enzyme-catalyzed, is carried out Possibility of recombination and branching essentially is not given, which is not least expressed in other molecular weight distributions. For example, saccharified starches which have a bimodal molecular weight distribution have proven to be particularly advantageous according to the invention. The production of saccharified starches is generally known and, inter alia, in G. Tegge, Starch and Starch Derivatives, Behr's Verlag, Hamburg 1984, pp. 173 u. Pp. 220 ff and described in EP-A 441 197. The saccharified starches to be used according to the invention are preferably those whose weight-average molecular weight M _{w is} in the range from 4000 to 16,000, particularly preferably in the range from 6500 to 13,000.

The saccharified starches to be used according to the invention are normally completely soluble in water at room temperature, the solubility limit generally being above 50% by weight, which proves to be particularly advantageous for the preparation of the aqueous polymer dispersions according to the invention.

It has also proven to be advantageous if the saccharified starches to be used according to the invention have an unevenness U (defined as the ratio of weight-average molecular weight M _w to number-average molecular weight M _n ; U characterizes the molecular weight distribution) in the range from 6 to 12. U is particularly advantageously 7 to 11 and a U of 8 to 10 is very particularly favorable.

It is also advantageous if the proportion by weight of the saccharified starches to be used according to the invention, which has a molecular weight below 1000, is at least 10% by weight, but not more than 70% by weight. This weight fraction is particularly preferably in the range from 20 to 40% by weight.

In addition, it is advisable to use such saccharified starches to be used according to the invention, whose dextrose equivalent DE is 5 to 40, preferably 10 to 30 and particularly preferably 10 to 20. The DE value characterizes the reducing power in relation to the reducing power of anhydrous dextrose and is determined according to DIN 10308 edition 5.71, the standards committee for food and agricultural products (cf. also Günther Tegge, Starch and starch derivatives, Behr's Verlag, Hamburg 1984, p. 305).

In addition, it has been shown that particularly favorable aqueous polymer dispersions are obtained in their property profile when using saccharified starches to be used according to the invention, the 40 wt .-% aqueous solutions at 25 ° C and a shear rate of 75 s⁻¹ one after DIN 53 019 determined dynamic viscosity η⁴⁰ [Pa · s] from 0.01 to 0.06, preferably from 0.015 to 0.04 and particularly preferably from 0.02 to 0.035.

Säulen:

3 Stück 7.5 x 600 mm Stahl gefüllt mit TSK-Gel G 2000 PW; G 3000 PW u. G 4000 PW. Porenw. 5 µm

Eluent:

Wasser dest.

Temp.:

RT (Raumtemperatur)

Detektion:

Differentialrefraktometer (z.B. ERC 7511)

Fluss:

0.8 ml/min. Pumpe: (z.B. ERC 64.00)

Injectv.:

20 µl Ventil: (z.B. VICI 6-Wege-Ventil)

Auswertung:

Bruker Chromstar GPC-Software

Eichung:

Die Eichung erfolgte im niedermolekularen Bereich mit Glucose, Raffinose, Maltose und Maltopentose. Für den höhermolekularen Bereich wurden Pullulan-Standards mit einer Polydispersität < 1.2 verwendet.

At this point it should be noted that, unless stated otherwise, statements in this document about the molecular weight of saccharides to be used according to the invention and their derivatives are based on determinations by means of gel permeation chromatography, chromatography being carried out under the following conditions:

Columns:

3 pieces of 7.5 x 600 mm steel filled with TSK-Gel G 2000 PW; G 3000 PW u. G 4000 PW. Porenw. 5 µm

Eluent:

Distilled water

Temp .:

RT (room temperature)

Detection:

Differential refractometer (e.g. ERC 7511)

Flow:

0.8 ml / min. Pump: (e.g. ERC 64.00)

Injectv .:

20 µl valve: (e.g. VICI 6-way valve)

Evaluation:

Bruker Chromstar GPC software

Calibration:

The calibration was carried out in the low molecular weight range with glucose, raffinose, maltose and maltopentose. Pullulan standards with a polydispersity <1.2 were used for the higher molecular weight range.

The mono-, oligo-, polysaccharides and / or their derivatives which are present according to the invention during the free radical aqueous emulsion polymerization can nevertheless be present as the only dispersants and also in a mixture with other surface-active substances. If they are used as the sole dispersant, they are normally present in the aqueous polymer dispersions according to the invention in amounts of 1 to 120% by weight, based on the amount of monomers to be polymerized.

In principle, the protective colloids and emulsifiers normally used as dispersants come into consideration as accompanying surface-active substances. A detailed description of suitable protective colloids can be found in Houben-Weyl, Methods of Organic Chemistry, Volume XIV / 1, Macromolecular Substances, Georg-Thieme-Verlag, Stuttgart, 1961, pp. 411 to 420. Both anionic, cationic and nonionic emulsifiers are also considered. Preferably, only accompanying emulsifiers are used as accompanying surface-active substances, the relative molecular weights of which, in contrast to the protective colloids, are usually below 2000. Of course, if mixtures of surface-active substances are used, the individual components must be compatible with one another, which can be checked in the case of doubt using a few preliminary tests. Anionic and nonionic emulsifiers are preferably used as accompanying surfactants. Common accompanying emulsifiers are, for example, ethoxylated fatty alcohols (EO degree: 3 to 50, alkyl radical: C₈ to C₃₆), ethoxylated mono-, di- and tri-alkylphenols (EO degree: 3 to 50, alkyl radical: C₄ to C₉), alkali metal salts of dialkyl esters of sulfosuccinic acid and alkali and ammonium salts of alkyl sulfates (alkyl radical: C₈ to C₁₂), of ethoxylated alkanols (EO degree: 4 to 30, alkyl radical: C₁₂ to C₁₈), of ethoxylated alkylphenols (EO degree: 3 to 50, Alkyl radical: C₄ to C₉), of alkyl sulfonic acids (alkyl radical: C₁₂ to C₁₈) and of alkylarylsulfonic acids (alkyl radical: C₉ to C₁₈). Further suitable emulsifiers can be found in Houben-Weyl, Methods of Organic Chemistry, Volume XIV / 1, Macromolecular Substances, Georg Thieme Verlag, Stuttgart, 1961, pages 192 to 208. Accompanying surface-active substances are usually in amounts of up to 5% by weight, based on the amount of the monomers to be polymerized, also used.

The emulsion polymerization temperature is usually 30 to 95, preferably 75 to 90 ° C. The polymerization medium can consist only of water, as well as mixtures of water and thus miscible liquids such as methanol. Preferably only water is used. The emulsion polymerization can be carried out either as a batch process or in the form of a feed process, including a step or gradient procedure. Preference is given to the feed process, in which part of the polymerization batch is introduced, heated to the polymerization temperature, polymerized and then the rest of the polymerization batch, usually via a plurality of spatially separate feeds, one or more of which contain the monomers in pure or in emulsified form , gradually or with superimposition of a concentration gradient while maintaining the polymerization of the polymerization zone. Advantageously in terms of application technology, the initial charge and / or the monomer feed contains small amounts of emulsifiers, based on the total amount of the monomers to be polymerized, as a rule less than 0.5% by weight, in order to reduce the surface tension of the dispersing medium and thus to stir it in facilitate. The monomers are therefore frequently fed to the polymerization zone in a manner pre-emulsified with these auxiliary emulsifiers. The total amount of the mono-, oligo-, polysaccharide and / or their derivatives to be used is advantageously contained in an aqueous receiver.

Free radical polymerization initiators are all those which are capable of initiating a free radical aqueous emulsion polymerization. Both peroxides, e.g. Alkali metal peroxidisulfates or H₂O₂, as well as azo compounds.

Combined systems which are composed of at least one organic reducing agent and at least one peroxide and / or hydroperoxide, for example tert-butyl hydroperoxide and the sodium metal salt of hydroxymethanesulfinic acid or hydrogen peroxide and ascorbic acid, are also suitable. Combined systems are also suitable also contain a small amount of a metal compound soluble in the polymerization medium, the metallic component of which can occur in several valence stages, for example ascorbic acid / iron (II) sulfate / hydrogen peroxide, the sodium metal salt of hydroxymethanesulfinic acid, sodium sulfite, sodium hydrogen sulfite or sodium metal bisulfite and often instead of ascorbic acid of hydrogen peroxide, tert-butyl hydroperoxide or alkali metal peroxydisulfates and / or ammonium peroxydisulfates can be used. In the combined systems, it is also expedient to use the saccharified starches as a reducing component. As a rule, the amount of free-radical initiator systems used is 0.1 to 2% by weight, based on the total amount of the monomers to be polymerized. Ammonium and / or alkali metal peroxydisulfates are particularly preferably used by themselves or as a component of combined systems as initiators. Sodium peroxydisulfate is particularly preferably used.

The manner in which the free radical initiator system is added to the polymerization vessel in the course of the free radical aqueous emulsion polymerization according to the invention is of minor importance. It can either be completely introduced into the polymerization vessel or, depending on its consumption, can be used continuously or in stages in the course of the free-radical aqueous emulsion polymerization. Specifically, this depends on the chemical nature of the initiator system and on the polymerization temperature in a manner known per se to the person skilled in the art. A portion is preferably introduced and the remainder is fed to the polymerization zone in accordance with the consumption.

The free radical aqueous emulsion polymerization according to the invention can of course also be carried out under elevated or reduced pressure.

The aqueous polymer dispersions according to the invention are generally prepared with a total solids content of 15 to 65% by weight, with those from 10 to 75, very particularly preferably 20 to 60% by weight, based on those to be polymerized, being particularly preferred in terms of application technology Monomers containing mono-, oligo-, polysaccharides and / or their derivatives to be used according to the invention.

The binders for abrasive particles for the production of abrasives are very particularly advantageously aqueous polymer dispersions according to the invention, the polymers of which can be obtained by free-radical polymerization of monomer mixtures, the following monomer composition consisting of
39 to 69% by weight of at least one ester of α, β-monoethylenically unsaturated mono- and dicarboxylic acids containing 3 to 6 carbon atoms and alkanols (monomers a) having 1 to 6 carbon atoms,
30 to 60% by weight of styrene (monomer b),
1 to 10 wt .-% of at least one monomer from the group comprising 3 to 6 carbon atoms containing α, β-monoethylenically unsaturated carboxylic acids, their amides and nitriles (monomers c) and
0 to 10% by weight of one or more monomers from the group comprising N-alkylolamides of α, β-monoethylenically unsaturated carboxylic acids having 3 to 6 C atoms and having 1 to 4 C atoms in the alkyl group and containing up to 25 C atoms two non-conjugated ethylenically unsaturated double bonds (monomers d),
and which, based on the monomers to be polymerized, contain 1 to 120, preferably 10 to 65 and particularly preferably 35 to 55% by weight of mono-, oligo-, polysaccharides and / or their derivatives. Of course, the monomers d can be replaced in whole or in part by other crosslinking monomers mentioned in this document.

The transfer of the abrasive particles into abrasives can e.g. in such a way that the finely divided abrasive particles are mixed with the aqueous polymer dispersions to be used according to the invention while adjusting the desired binder content, generally (calculated dry) 0.1 to 10% by weight, based on the amount of finely divided starting material, the mixture optionally forms after the addition of known aids, optionally compressed by applying pressure, and then hardens.

To produce abrasives according to the invention, a so-called base binder layer is preferably first applied to a carrier, into which the abrasive particles are introduced when wet. After a first fixation of the abrasive grain by drying (hardening), a second, so-called cover binder layer is usually applied for better embedding and fastening of the grain. In principle, the base and cover binder layers can consist of different binders. According to the invention, at least one of the two, preferably the top layer and particularly preferably both, consists of the aqueous polymer dispersions according to the invention.

It is noteworthy that when using the aqueous polymer dispersions according to the invention, which are usually used for this purpose with a total solids content of 40 to 60% by weight, the curing process does not necessarily require the use of elevated temperatures (normally 50 to 250 ° C.), but also left to harden at room temperature with satisfactory speed. In a particularly skillful manner in terms of application technology, through-hardening can also be achieved by exposing the mass to be hardened to the action of microwaves. In this regard, aqueous polymer dispersions according to the invention which are obtainable by free radical aqueous emulsion polymerization of mixtures of monomers a, b, c and d, the monomer composition of which is selected so that a polymer composed only of monomers a, b and c have a glass transition temperature, are particularly recommended would have in the range of 0 to 40 ° C.

wobei X¹, X², ..., X^s die Massenbrüche der Monomeren 1, 2, ..., s und Tg¹, Tg², ..., Tg^s die Glasübergangstemperaturen der jeweils nur aus einem der Monomeren 1, 2, ..., s aufgebauten Polymeren in Grad Kelvin bedeuten. Die Glasübergangstemperaturen der Monomeren a, b und c sind im wesentlichen bekannt und z.B. in J. Brandrup, E.H. Immergut, Polymer Handbook 1^st Ed. J. Wiley, New York 1966 und 2^nd Ed. J. Wiley, New York 1975, aufgeführt.According to Fox (TG Fox, Bull. Am. Phys. Soc. (Ser. II) 1, 123 [1956]), the glass transition temperature of copolymers is a good approximation:

where X¹, X², ..., X ^{s are} the mass fractions of the monomers 1, 2, ..., s and Tg¹, Tg², ..., Tg ^{s are} the glass transition temperatures of only one of the monomers 1, 2, .. ., s mean polymers in degrees Kelvin. The glass transition temperatures of the monomers a, b and c are essentially known and are described, for example, in J. Brandrup, EH Immergut, Polymer Handbook 1 ^st Ed. J. Wiley, New York 1966, 2 ^nd Ed. J. Wiley, New York 1975.

• gute Haftung, sowohl auf der Unterlage als auch am Schleifpartikel
• rasch und schonend härtbar
• möglichst geringe Beanspruchung des Trägermaterials
• hohe Wärmestandfestigkeit
• erhöhte Fließfähigkeit beim Auftrag
• gute mechanische Eigenschaften beim Schleifvorgang (harte, zähe Verfilmungen).

Typical requirements that are placed on binders suitable for the production of abrasives are, for example

• good adhesion, both on the base and on the abrasive particle
• can be hardened quickly and gently
• as little stress on the carrier material as possible
• high heat resistance
• increased flowability when applied
• good mechanical properties during the grinding process (hard, tough filming).

The aqueous polymer dispersions according to the invention meet these requirements in a completely satisfactory manner. Hardening does not necessarily require elevated temperatures when used, but can be carried out at room temperature and particularly advantageously under the influence of microwaves. This is particularly gentle on the carrier material and avoids extreme water removal, making complicated regeneration of the carrier material in climate zones unnecessary.

Their favorable flow behavior proves to be particularly advantageous when the aqueous polymer dispersions according to the invention are used as a top layer, since it enables the binder to penetrate into the interstices of the abrasive grain.

In addition, the binders according to the invention are particularly characterized by increased heat resistance, so that the abrasive grains remain fixed in their position even under the elevated temperatures (150 ° C. and more) that occur during the grinding process. This prevents suppression of the abrasive grains (which reduces the grinding effect) or even chipping. Usually the base layer is applied in dry layer thicknesses of 10 to 100 µm and the top layer in dry layer thicknesses of 20 to 10³ µm.

zusetzt, wobei solche Dialdehyde der allgemeinen Formel I mit n = 0 bis 2 bevorzugt sind. Ferner kommen als die Wärmestandfestigkeit erhöhende Zusätze Kondensationsprodukte auf der Basis Formaldehyd, Melamin, Phenol und/oder Harnstoff, z.B. Urecoll® 118, in Betracht. Die zu verwendenden Mengen können sich dabei, bezogen auf den abzüglich der verzuckerten Stärke bestimmten Feststoffgehalt der erfindungsgemäßen wäßrigen Polymerisatdispersionen, auf bis zu 250 Gew.-% belaufen.If the polymers contain built-in monomers d, particularly high heat resistance results. In addition, the heat resistance can be further increased by using saturated dialdehydes, preferably those of the general formula I, in amounts of up to 20% by weight, based on polymerized monomers, before use of the aqueous polymer dispersions to be used according to the invention

adds, such dialdehydes of the general formula I with n = 0 to 2 being preferred. Also suitable as additives which increase the heat resistance are condensation products based on formaldehyde, melamine, phenol and / or urea, for example Urecoll® 118. The amounts to be used can be up to 250% by weight, based on the solids content, determined less the saccharified starch, of the aqueous polymer dispersions according to the invention.

However, the last-mentioned additives only have an advantageous effect in the manner described if curing takes place at elevated temperature, generally 100 to 250 ° C., or in the presence of acid. The latter can be achieved in a simple manner by adjusting the pH of the dispersion medium of the aqueous polymer dispersions to be used according to the invention to 1 to 5, preferably 2 to 3. If heat resistance in the usual range is required, it is preferable to work without additives.

Examples

• 1. Preparation of aqueous polymer dispersions to be used according to the invention
  A mixture of
  400 g water
  200g sugared starch C * PUR 01910
  71 g feed 1 and
  10 g feed 2
  was heated to 85 ° C and held at this temperature for 15 min. Subsequently, while maintaining the 85 ° C., the remaining amounts of feeds 1 and 2 were fed into the polymerization zone continuously (feed 1 within 2.5 h, feed 2 within 3 h). The mixture was then polymerized for one hour (85 ° C) and cooled to room temperature. The total solids content of the resulting aqueous polymer dispersion was approximately 50% by weight.

  Inlet 1:

  250 g n-butyl acrylate
  225 g styrene
  25 g acrylic acid

  pre-emulsified in 204 g of water using 0.5 g of the sodium salt of dodecylbenzenesulfonic acid.

  Inlet 2:

  2.5 g of sodium peroxydisulfate dissolved in 100 g of water.

• 2. Abrasive articles based on finely divided abrasive particles bound on a carrier with an aqueous polymer dispersion according to the invention
  100 g of various aqueous polymer dispersions according to the invention, which were prepared as in Example 1 and to which 0.062 part by weight of glyoxal were added per part by weight of saccharified starch contained, were mixed with 1 g of Lumiten® (wetting agent) and applied with a coating weight of 20 g / m² (dry) a backing paper is applied. Semi-precious corundum 60 was sprinkled into the wet application layer and the paper coated in this way was dried at 90 ° C. for 3 minutes. The same binder was then applied as an overcoat with an application weight of 60 g / m² (dry) and also dried (30 min). The sandpaper thus obtained was tested using an APG 100/20 abrasion device (from Maag & Schank, Gomaringen). Bodies with dimensions of 40 mm x 20 mm x 5 mm made of hard PVC were used as test specimens. The area of 20 mm x 5 mm was sanded down with 500 strokes (load 1 kg), the sanding paper being moved back and forth under the test specimen over a length of 10.5 cm. The measure of the quality of the binder is the abrasion, which is defined as follows:
  

X:

50 Gew.-% n-Butylacrylat,
45 Gew.-% Styrol,
5 Gew.-% Methacrylsäure;

Y:

50 Gew.-% n-Butylacrylat,
40 Gew.-% Styrol,
10 Gew.-% Acrylsäure;

Bei Austausch von C*PUR 01910 gegen C*PUR 01906, 01908, 01912, 01915, 01921, 01924, 01932 oder 01934 wurden Ergebnisse derselben Größenordnung erhalten. C*PUR 01910 und 01915 erwiesen sich als besonders voreilhaft. Die genannten verzuckerten Stärken lassen sich wie folgt charakterisieren: Typ M_w U Gew.-% < 1000 DE η⁴⁰ [Pa·s] 01906 20080 10,9 12,2 2-5 - 01908 19290 10,0 15,9 8-10 0,056 01910 10540-12640 8,5-9,9 24,7-26,4 11-14 0,030 01915 6680-8350 6,8-8,4 32,9-34,7 17-19 0,021 01921 6700 7,4 39,1 20-23 0,017 01924 4730 6,8 53,6 26-30 0,014 01932 4500 7,9 63,2 33-35 0,011 01934 3000 6,0 68,4 36-39 0,009
Bestimmungen von M_n mittels Dampfdruckosmose ergaben für die bevorzugten Typen 01910 und 01915 folgende Werte:
1560 g/mol (1910)
980 g/mol (1915)The results are shown in the table. table binder Glyoxal Drying temperature (° C) top layer Abrasion [%] Ex. 1 - 90 8.7 Ex. 1 + 90 10.7 X + 150 7 Y + 150 7.5
X and Y are produced as in Example 1, but with different monomer compositions;

X:

50% by weight of n-butyl acrylate,
45% by weight styrene,
5% by weight methacrylic acid;

Y:

50% by weight of n-butyl acrylate,
40% by weight styrene,
10% by weight acrylic acid;

When replacing C * PUR 01910 with C * PUR 01906, 01908, 01912, 01915, 01921, 01924, 01932 or 01934, results of the same order of magnitude were obtained. C * PUR 01910 and 01915 proved to be particularly hasty. The saccharified starches mentioned can be characterized as follows: Type M _w U % By weight <1000 DE η⁴⁰ [Pa · s] 01906 20080 10.9 12.2 2-5 - 01908 19290 10.0 15.9 8-10 0.056 01910 10540-12640 8.5-9.9 24.7-26.4 11-14 0.030 01915 6680-8350 6.8-8.4 32.9-34.7 17-19 0.021 01921 6700 7.4 39.1 20-23 0.017 01924 4730 6.8 53.6 26-30 0.014 01932 4500 7.9 63.2 33-35 0.011 01934 3000 6.0 68.4 36-39 0.009
Determinations of M _n by means of vapor pressure osmosis gave the following values for the preferred types 01910 and 01915:
1560 g / mol (1910)
980 g / mol (1915)

Claims (2)

Abrasives based on finely divided abrasive particles bound to one another and / or on a carrier by means of a binder, the binder being the solids content of an aqueous polymer dispersion which can be obtained by free-radically polymerizable unsaturated monomers in the aqueous phase in the presence of a monosaccharide, oligosaccharide, Polysaccharides, oxidatively, hydrolytically and / or enzymatically degraded polysaccharides, chemically modified mono-, oligo- or polysaccharides or mixtures of the compounds mentioned are polymerized by the process of free-radical aqueous emulsion polymerization. Abrasives according to claim 1, the binders of which can be obtained by free-radical polymerization of monomer mixtures, the subsequent monomer composition consisting of
39 to 69% by weight of at least one ester of α, β-monoethylenically unsaturated mono- and dicarboxylic acids containing 3 to 6 carbon atoms and alkanols containing 1 to 6 carbon atoms,
30 to 60% by weight of styrene,
1 to 10 wt .-% of at least one monomer from the group comprising 3 to 6 carbon atoms containing α, β-monoethylenically unsaturated carboxylic acids, their amides and nitriles and
0 to 10% by weight of crosslinking monomers.