EP2195383A2

EP2195383A2 - Liquid resin composition for abrasive articles

Info

Publication number: EP2195383A2
Application number: EP08842341A
Authority: EP
Inventors: Alix Arnaud; Philippe Espiard; Sandrine Pozzolo
Original assignee: Saint Gobain Abrasifs Technologie et Services SAS; Saint Gobain Abrasives Inc
Current assignee: Saint Gobain Abrasifs Technologie et Services SAS; Saint Gobain Abrasives Inc
Priority date: 2007-10-01
Filing date: 2008-10-01
Publication date: 2010-06-16
Also published as: CN101883824A; FR2921666A1; WO2009053580A2; CN101883824B; CL2008002931A1; US20100298505A1; US8523967B2; FR2921666B1; TWI523909B; WO2009053580A3; AR068643A1; TW200932823A

Abstract

The invention relates to a liquid resin composition intended for the production of abrasives, containing at least one novolac resin having a glass transition temperature of less than or equal to 60°C, at least one diluting reagent and optionally at least one crosslinking agent. The resin composition can be used to produce abrasive articles, such as bonded abrasives and coated abrasives. The invention also relates to abrasive articles including abrasive grains bonded by one such liquid resin composition.

Description

LIQUID RESIN COMPOSITION FOR ABRASIVE ARTICLES

The present invention relates to a liquid resin composition suitable for use in the manufacture of abrasive articles, and to the resulting abrasive articles.

Abrasive articles in general contain a multitude of abrasive grains securely bonded to a carrier or to each other via a binder. These articles are widely used for the machining of various materials, especially in cutting, grinding, deburring and polishing operations.

Conventionally, abrasive coated abrasives and abrasive bonded abrasives are distinguished.

The abrasives applied comprise a support material, generally flexible, on the surface of which are distributed abrasive grains embedded in a binder. The flexible support may be a sheet of paper, a film or a network of fibers, for example a mat, a felt, a fabric or a knit of natural or synthetic fibers, in particular made of glass or a polymer. These abrasives can take various forms: sheets, strips, discs, etc. The manufacture of the coated abrasives includes the application of a base coat ("make coat") on the support material, the distribution of the grains of abrasives on said layer, the heat treatment of the base adhesive layer to partially cure it and the application of a top adhesive layer ("size coat") which ensures a firm anchoring of the grains on the support. An additional adhesive layer ("supersize coat") may be deposited on the upper adhesive layer and the abrasive grains.

The base, top and extra adhesive layers are applied in liquid form. They are generally made of a thermosetting resin, in particular a phenolic resin of resol type. The agglomerated abrasives consist of abrasive grains bonded together by a binder which provides a three-dimensional structure adapted to ensure the abrasion operations, including the cutting of hard materials such as steel. Generally, these abrasives have the appearance of a grinding wheel, a grinding wheel segment and a whetstone. Agglomerated abrasives in the form of "conventional" grinding wheels consist of a single region composed of abrasive grains embedded in the binder which extends from the bore to the periphery of the grinding wheel. In the "superabrasive" wheels, the abrasion region is located in the periphery, in the form of a strip supported by a central core generally made of metal, and the abrasive grains consist of a very hard material, for example diamond or cubic boron nitride.

Agglomerated abrasives are obtained by the process using compression molding techniques, cold or hot. In cold compression molding ("CoId Molding

Compression "), the most widespread, the mixture of constituents of the abrasive, in granular form, is introduced into a mold, then a sufficient compressive force is applied, of the order of 15 to 25 N / mm ² , for placing said mixture in the shape of the mold and ensuring that after extraction of the mold, the piece obtained (green part or "green item") has sufficient strength to be manipulated without losing its original shape. The part is then heated in an oven at a temperature to crosslink the binder, this temperature depending on the nature of the binder used.

Hot compression molding (Hot Molding Compression) achieves a higher compaction level than cold molding, which results in a smaller pore volume in the final article. In this process, the granular mixture introduced into the mold is compacted under pressure and heated simultaneously in order to allow the binder to be better distributed between the abrasive grains and to occupy the empty spaces. After being removed from the mold, the part generally undergoes a post-crosslinking heat treatment to improve its operating life and abrasion performance.

Whatever the type of compression molding used, cold or hot, it is essential that the mixture of constituents of the abrasive is in granular form.

The granular mixture is prepared by pre-treating the abrasive grains with a liquid impregnating resin, usually a resol type phenolic resin, and then mixing the wet grains with a novolak type phenolic resin powder containing a crosslinking agent - powder which will subsequently constitute the binder itself - and optionally additives, also in powder form. The resulting mixture thus consists of abrasive grains on the surface of which are adhered solid particles of resin and additives. This mixture has a good ability to be uniformly distributed in the mold (called "flowability") and to be shaped under the effect of pressure.

The resole type thermosetting resins used for the manufacture of coated and agglomerated abrasives have numerous advantages in the intended use conditions, in particular: they ensure a solid connection of the grains with the support material and grains between them,

they are resistant to the strong mechanical stresses that occur under conditions of grinding at high peripheral speed, which makes it possible to avoid bursting of the tool; their high thermal resistance makes it possible to limit the risk of excessive accumulation of heat within the tool.

A disadvantage of the aforementioned resols is that they contain formaldehyde detrimental to human health and the environment.

It is known that the resols contain free formaldehyde which can be emitted into the atmosphere during the manufacture of the abrasives, and that they can further generate formaldehyde under the conditions of use of the abrasive, when the temperature reaches a level leading to the degradation of the resol with release of formaldehyde.

For a number of years, formaldehyde emission regulations have become stricter and tend to limit the amount of formaldehyde contained in abrasives or that can be emitted from these products.

Many low formaldehyde resin compositions have been proposed.

In US 6,133,403, reactive diluents for phenolic compositions and crosslinkable novolacs for the production of composite materials having high impact resistance are provided.

WO 2005/108454 A1 discloses a novolac resin and non-formaldehyde hardener composition for reinforcing composite materials. In US 5,523,152 there is disclosed a polymerizable abrasive composition which comprises an aminoplast resin and a reactive diluent which each contain pendant unsaturated groups.

US 5,178,646 discloses a binder precursor composition for abrasives, especially coated, which comprises a heat-curable resin having a plurality of pendant methylol groups and a reactive diluent having at least one functional group that reacts with the groups of the resin.

The present invention aims to reduce the amount of formaldehyde in an abrasive product.

To this end, the invention proposes a liquid resin composition which replaces the resole used as an adhesive in the coated abrasives and as an impregnating resin in the agglomerated abrasives, this liquid resin composition being characterized in that it comprises at least one novolak resin having a glass transition temperature of less than or equal to 60 ^° C., at least one reactive diluent and optionally at least one crosslinking agent.

The novolac resin according to the invention is chosen from novolaks having a glass transition temperature of less than or equal to 60 ^° C., preferably less than or equal to 50 ° C. and advantageously of between 35 ° and 45 ° C.

The novolak may be selected from novolacs known to those skilled in the art which are obtained by reaction of a phenolic compound and an aldehyde in an aldehyde / phenolic compound molar ratio of less than 1, in the presence of an acid catalyst.

The phenol compound is chosen from phenol and substituted phenols such as cresols, guaiacol, methoxyphenols, catechol, resorcinol, tert-butyl phenol and nonyl phenol, bisphenols such as bisphenol A, naphthols and mixtures of these compounds. Preferably, the phenol is selected.

The aldehyde is selected from alicyclic aldehydes such as formaldehyde, cyclic aldehydes such as furfural, aromatic aldehydes such as benzaldehyde, para-anisaldehyde, orthoaldehyde and the like. anisaldehyde and veratraldehyde, and mixtures of these aldehydes. Preferably, the formaldehyde is chosen.

Preferably, the formaldehyde / phenol molar ratio ranges from 0.2 to less than 1, advantageously from 0.35 to 0.9, and more preferably from 0.5 to 0.9. The novolak resin may be prepared using a known acidic catalyst, for example a strong mineral acid such as sulfuric acid, phosphoric acid and hydrochloric acid, or an organic acid such as oxalic acid, acid salicylic acid or anhydrides such as maleic anhydride. The amount of acid should be sufficient to allow the condensation of the phenolic compound and the aldehyde. The amount of acid used generally represents 0.02 and 1% of the weight of the starting phenolic compound, preferably 0.1 to 0.6% in the case of a strong mineral acid, and 0.3 to 3% of the weight of the starting phenolic compound in the case of an organic acid.

Preferably, the novolac resin obtained at the end of the condensation reaction is treated so as to reduce the content of free phenolic compound, for example by distillation under reduced pressure.

The novolaks that can be used in the context of the invention contain less than 0.1% by weight of free formaldehyde, and preferably less than 0.05%. The resin composition may comprise at least one resin capable of reacting with the crosslinking agent different from the novolac, for example an epoxy resin, in particular a novolac resin bearing one or more pendant epoxy groups. Such epoxidized novolac resin may be obtained in conventional manner by treating a novolak resin with an excess of epichlorohydrin in the presence of a basic catalyst, e.g. sodium hydroxide, at a temperature of about 100 ⁰ C. The proportion of novolac resin according to the invention must however remain greater than or equal to 50% by weight of all the resins, novolac (s) and other (s), preferably greater than or equal to 75% and advantageously the proportion is equal to 100%. The novolak resin according to the invention represents at least 30% by weight of the resin composition, preferably at least 40%, advantageously at least 50%, and does not exceed 85%. The reactive diluent according to the invention is a liquid compound at ambient temperature, of the order of 20 to 25 ° C, which makes it possible to solubilize the novolak resin and to adjust the viscosity of the resin composition.

Preferably the reactive diluent has a viscosity of less than or equal to 1000 mPa.s, preferably less than or equal to 700 mPa.s, preferably less than 500 mPa.s and more preferably less than 350 mPa.s.

The reactive diluent also contains at least one function capable of reacting with the resin and optionally with the crosslinking agent, which function is chosen from the hydroxy, aldehyde, epoxy, oxazolidine and lactone functional groups.

As examples of reactive diluents comprising hydroxyl functional groups, mention may be made of alicyclic alcohols, saturated or unsaturated, such as ethylene glycol, 1,3-butylene glycol, glycerol, trimethylolpropane and the monoallyl ethers of these cyclic, saturated or unsaturated alcohols, such as furfuryl alcohol, mono- or polynuclear aromatic alcohols such as benzyl alcohol and its derivatives, m-cresol, 3,5-xylenol, nonylphenol, cardanols and their derivatives such as cardols, methylcardols and anacardial acids contained in particular in the cashew nut shell liquid (CNSL) and naphthol, and the precursors of these alcohols, in particular the acetals and trioxanes.

As examples of reactive diluents comprising aldehyde functions, mention may be made of glyoxal.

As examples of reactive diluents comprising epoxy functional groups, mention may be made of glycidyl ethers of saturated or unsaturated alcohols such as the diglycidyl ether of hexane-1,6-diol, the epoxidized fatty acids in particular contained in epoxidized oils. , in particular soybean oil (Ecocet ^®; Arkema) and linseed oil (Vikoflex ^®, Arkema), and aromatic epoxy such as epoxidized cardanols, including 3-n-pentadécadiénylphénol.

By way of examples of reactive diluents comprising oxazolidine functional groups, mention may be made of 3-ethyl-2-methyl- (3-methylbutyl) -1,3-oxazolidine, 1-aza-3,7-dioxa-5-ethylbicyclo ( 3.3.0) octane and bis-oxazolidines, notably marketed under the reference Incozol ^® LV by Incorez.

The preferred lactone functional reactive diluent is gamma-butyrolactone. Advantageously, the gamma butyrolactone mixed with triphenylphosphite, which makes it possible to improve the thermal resistance of the liquid resin composition,

Preferred diluents are glycerol, furfuryl alcohol, benzyl alcohol, cardols and their derivatives (CNSL), diglycidyl ether of hexane-1,6-diol, epoxidized cardanols, 3-ethyl-2- methyl- (3méthylbutyl) -

1,3-oxazolidine, 1-aza-3,7-dioxa-5-ethylbicyclo [3.3.0] octane, bis-oxazolidines and gamma-butyrolactone.

The reactive diluent represents at least 10% by weight of the resin composition, preferably at least 20%, and preferably does not exceed 69%, preferably 30%. Below 10%, the viscosity of the resin composition is too great for it to be used in the targeted applications. Above 69%, the mechanical properties of the final abrasive product are not satisfactory.

The crosslinking agent must have a high reactivity with respect to the novolac resin and the reactive diluent.

The crosslinking agent is chosen from compounds containing at least one hydroxyl or aldehyde function, the heterocyclic compounds containing a structure containing a nitrogen atom and an oxygen atom separated by a carbon atom, nitroacetals and nitrones. As examples of compounds containing at least one hydroxyl function, mention may be made of nitroalcohols such as ths (hydroxymethyl) nitromethane.

As examples of compounds containing at least one aldehyde function, mention may be made of glyoxal and 2,2-dimethoxyethanal. As examples of heterocyclic compounds containing a nitrogen atom and an oxygen atom separated by a carbon atom, there may be mentioned oxazolines such as 1,3-phenylenebisoxazoline, and oxazolidines such as 3 ethyl-2-methyl-2- (3-methylbutyl) -1,3-oxazolidine and 1-aza-3,7-dioxa-5-ethylbicyclo (3.3.0) octane. The preferred crosslinking agent is tris (hydroxymethyl) nitromethane, glyoxal, 3-ethyl-2-methyl-2- (3-methylbutyl) -1,3-oxazolidine and 1-aza-3,7-dioxa. -5-éthylbicyclo- (3.3.0) octane. 1 -aza-3,7-dioxa-5-ethylbicyclo [3.3.0] octane is particularly advantageous because it can act as both a reactive diluent and a crosslinking agent. The crosslinking agent preferably represents at least 1% by weight of the liquid resin composition, advantageously at least 20%, and more preferably at least 30%, and generally does not exceed 40%.

The liquid resin composition may further comprise at least one crosslinking catalyst. The catalyst is chosen from compounds comprising at least one secondary or tertiary amine function such as hydroxylamine, triethylamine, diazabicycloundecene, benzyldimethylamine and 2,4,6-tri (dimethylaminomethyl) phenol, imidazoles and imidazole derivatives, for example 2-methyl-imidazole, 2-ethyl-4-methyl-imidazole and 1-benzyl-2-methyl-imidazole, trialkyl- and triaryl-nucleophiles of Group V elements ( A) for example triethanolamine, trimethylphosphine and triphenylphosphine, borates, for example tetraphenylphosphonium tetraphenylborate and tetraphenylphosphonium tetrafluoroborate, and ammonium salts such as tetramethylammonium hydroxide and benzyltrimethylammonium hydroxide. The preferred catalysts are triethylamine, 2,4,6-tri (dimethylaminomethyl) phenol, 2-methylimidazole, 2-ethyl-4-methylimidazole and trimethylphosphine.

Catalysts in liquid form are preferred, essentially for reasons of ease of implementation. The amount of catalyst in the liquid resin composition is less than or equal to 10 parts by weight per 100 parts by weight of novolak resin, of reactive diluent and optionally of crosslinking agent, and preferably is less than or equal to 5 parts .

The preparation of the liquid resin composition can be done by simply mixing the constituents in a suitable container, advantageously provided with stirring means; preferably, the novolac resin is introduced into the reactive diluent, then the crosslinking agent and the catalyst are optionally added.

The mixture of the constituents may be at room temperature, of the order of 20 to 25 ° C, or at a higher temperature, preferably at least 10 ^° C. higher than the glass transition temperature of the novolac resin. and advantageously less than or equal to 50 ^° C. so as to prevent the crosslinking and / or the thermal degradation of the constituents of the resin composition. The viscosity of the liquid resin composition depends on the intended application but remains less than or equal to 7000 mPa.s.

According to a first embodiment, the liquid resin composition according to the invention is used to manufacture agglomerated abrasives. The liquid resin composition is first mixed with abrasive grains in a conventional mechanical mixer until the grains are suitably "wetted", i.e., coated with the resinous composition, and then the binder powder and the additives, also in powder form, until a homogeneous granular mixture is obtained. Preferably, the liquid resin composition has a viscosity at most equal to 3000 mPa.s, and advantageously greater than or equal to 600 mPa.s.

The starting temperature of crosslinking of the resin in the granular mixture is at most equal to 245 ° C., and advantageously at most equal to 195 ° C.

The time required to obtain complete crosslinking of the resin composition in the granular mixture is less than or equal to 36 hours, preferably less than or equal to 20 hours.

The abrasive grains may be any type of known abrasive grains, for example composed of alumina, including fused aluminas and sintered aluminas obtained by sol-gel, seeded or not with a material of the same crystalline nature, chemically modified or not, iron oxide, molybdenum oxide, vanadium oxide, alumina-zirconia, boron-alumina, silicon carbide, aluminum-oxynitride, diamond or cubic boron nitride, and mixtures of such grains. Preferably, the abrasive grains are alumina.

Preferably, the abrasive grains are pretreated with an organic compound which improves the adhesion between the grain and the liquid resin composition, chosen from compounds containing silicon, for example a silane functionalized with organic groups such as vinylsilane, especially vinyltriethoxysilane, an aminosilane, especially gamma-aminopropyltrimethoxysilane, gamma-aminopropyltriethoxysilane and diaminopropylethoxysilane, or an epoxysilane. Preferably, gamma-aminopropyltriethoxysilane is used. The treatment of the abrasive grains with the organic compound containing silicon can be carried out for example by spraying a solution of said compound in a suitable solvent, most often water, or by dispersing the grains in the aforementioned solution. The treated abrasive grains are dried before being mixed with the liquid resin composition.

If appropriate, a liquid organic carrier can be added to the abrasive grain mixture and the resinous composition, which aids in grain wetting and the formation of a uniform grain network, and which is subsequently removed in the course of time. crosslinking step. The organic carrier may be water, an aliphatic alcohol, a glycol, high molecular weight oil fractions of oily or waxy consistency, mineral oil or any other known vehicle.

The binder may be a phenol-aldehyde, melamine-aldehyde, urea-aldehyde, polyester, polyimide, epoxy, polyurethane or polybenzimidazole resin. Preferably, the binder is a low formaldehyde resin, advantageously a novolak type phenol-aldehyde resin, and more preferably a phenol-formaldehyde novolac resin.

The additives are, for example, fillers, crosslinking agents and other compounds which are useful for the manufacture of agglomerated abrasives, in particular bound by an organic resin.

The fillers are generally in the form of a finely divided powder comprising particles that may have the appearance of granules, spheres or fibers. By way of examples, mention may be made of sand, silicon carbide, alumina hollow spheres, bauxite, chromites, magnesite, dolomites, hollow mullite spheres, borides, silica fume, titanium dioxide, carbon products (carbon black, coke, graphite, ...), wood flour, clay, talc, hexagonal boron nitride, molybdenum disulfide, feldspar, nepheline syenite and glass, especially in the form of solid, hollow or hollow beads, and fibers. In general, the fillers represent 0.1 to 30% by weight of the granular mixture.

Crosslinking agents are used when the powder binder is a novolac resin. They may be chosen from compounds known to perform the aforementioned function such as hexamethylenetetramine or precursors of it. The crosslinking agent is added in an amount of 5 to 20 parts by weight per 100 parts by weight of novolac resin powder.

The additives may further comprise agents which assist in the implementation of the process, for example anti-static agents and lubricants. The amount of these additives can be easily determined by those skilled in the art.

Preferably, the granular mixture is subjected to a ripening treatment at room temperature for a period of about 12 hours. The granular mixture is then introduced into a mold equipped with compression means for forming a green part which has sufficient cohesion to be handled and processed in the following steps without substantially changing its shape. The binder at this stage is in the uncrosslinked state. The green part is then heated to a temperature sufficient for the binder to crosslink and give a rigid polymeric network which gives the piece its final shape. The crosslinking is carried out according to a conventional baking cycle which consists of bringing the green part to a temperature of the order of 100 ^° C. and keeping it at this temperature for 30 minutes to several hours so that the volatile products formed can be removed. . Then, the room is heated to the final temperature over a period that generally ranges from 10 to 36 hours.

The final crosslinking temperature depends in particular on the nature of the resin used, the size and shape of the piece to be treated and the cooking time. In general, the final crosslinking temperature is between 100 and 200 ^° C.

The thermal crosslinking is carried out in a controlled atmosphere, preferably with a maximum relative humidity level.

The agglomerated abrasives obtained may be in the form of grinding wheels, segments of grinding wheels, discs and whetstones.

According to a second embodiment, the liquid resin composition according to the invention is used to produce coated abrasives.

As already indicated, the manufacture of the coated abrasives comprises the steps of depositing a base coat ("make coat") on a support material, to distribute the grains of abrasives on said layer, subjecting said material to a heat treatment for partially cross-linking the resin composition, depositing a top adhesive layer ("size coat") and subjecting the heat treated coated material to in order to obtain complete crosslinking of the resin composition. If necessary, an additional adhesive layer may be deposited on the upper adhesive layer and crosslinked by a suitable heat treatment.

The support material generally has a moderate to strong flexibility, and has the appearance of a sheet, in particular paper, a film, in particular polymer, or a more or less dense network of natural or synthetic fibers, for example. examples of glass fibers and vulcanized fibers.

The abrasive grains may be chosen from the grains already mentioned which form part of the agglomerated abrasives.

The application of the grains on the base adhesive layer can be done by the usual techniques operating by gravity or electrostatically. The density of the abrasive grains on the support is to be chosen according to the intended application.

The liquid resin composition according to the invention may be used to form the base adhesive layer ("make coat"), the upper adhesive layer ("size coat") or the additional adhesive layer "supersize coat"). Preferably, the liquid resin composition serves to form the base adhesive layer and the upper adhesive layer, and optionally the additional adhesive layer.

Preferably, the liquid resin composition has a viscosity of less than or equal to 6000 mPa.s and a start of crosslinking temperature at most equal to 150 ⁰ C, preferably at most equal to 120 ⁰ C.

More preferably, the liquid resin composition contains at least one aforementioned crosslinking agent.

The time necessary to obtain complete crosslinking of the resin composition is less than 36 hours, preferably less than 20 hours.

The basic, superior and additional adhesive layers which are not formed from the liquid resin composition according to the invention may be chosen from phenolic resins, urea formaldehyde, epoxy, urethane, acrylic, aminoplast, melamine and mixtures of these resins. Preferably, the resin or resin mixture has the lowest possible free formaldehyde level.

The liquid resin composition may further comprise additives, for example wetting agents, fillers, coupling agents, dyes, pigments and antistatic agents.

When the liquid resin composition is used to form the upper adhesive layer and / or the additional adhesive layer, it advantageously comprises at least one agent which enhances the abrasive performance of the final abrasive. Such an agent can be chosen from waxes, halogenated organic compounds, halogen salts, metals and metal alloys.

The heat treatment of the support material coated with the liquid resin composition forming the base adhesive layer is carried out at a temperature of less than or equal to 150 ^° C., preferably less than or equal to 120 ^° C. for 1 to 120 minutes, preferably 1 to 60 ^° C. minutes.

The conditions of the heat treatment for the crosslinking of the resin composition forming the upper adhesive layer or the additional adhesive layer may be at a temperature of less than or equal to 150 ° C., preferably less than or equal to 120 ^° C. for at most 36 hours. preferably at most 20 hours.

The examples given below make it possible to illustrate the invention without however limiting it.

In the examples, the properties of liquid resin compositions and test specimens are measured under the following conditions: Resin compositions

The crosslinking start temperature is measured by Dynamic Mechanical Analysis (DMA): the liquid resin composition is introduced between two glass plates and the assembly is placed horizontally on a device comprising two fixed lower jaws remote from each other; 40 mm and an upper jaw applied against the upper sheet located 20 mm from each of the preceding jaws. On the upper jaw, a force of 8OmPa is applied with an oscillation frequency of 1 Hz and heating the whole 25 to 300 ° C at a rate of 4 ° C / minute. The elastic modulus of the resin composition is measured as a function of the temperature and from the established curve the starting temperature of the crosslinking is determined.

The loss of mass at 500 ^° C. is determined by thermogravimetric analysis (DTA): the liquid resin composition is deposited in an aluminum cup and heated according to a given temperature cycle. 10 to 20 mg of the crosslinked resin composition are placed in an alumina crucible which is placed in an apparatus continuously measuring the loss of mass during a temperature cycle ranging from 25 ° to 700 ^° C. at a rate of 10 ° C. C / minute. On the recorded curve, the loss of mass is determined at 500 ^° C.

Test specimens

• Flexural strength and Young's modulus are measured under the conditions of ASTM D790-91 using a three-point bend test with a gauge of 50.8 mm and a crosshead speed of 2.54 mm. /minute. For each test specimen, the average bending strength and mean Young's modulus are given on 6 test points and the standard deviation (ds).

EXAMPLES 1 TO 12 Liquid resin compositions for the manufacture of agglomerated abrasives. a) Preparation of resin compositions

Liquid resin compositions having the composition given in Table 1 (in parts by weight) are prepared. The resins are obtained by solubilizing the novolak resin in the reactive diluent at ambient temperature (20-25 ° C.) and with moderate stirring, and then adding the crosslinking agent and the catalyst while maintaining the stirring conditions.

These liquid resin compositions, as well as the reference composition containing a resol (Reference 1), are treated according to the following temperature cycle:

- Bearing at 70 ° C for 35 minutes

- 70 to 80 ⁰ C in 5 minutes

- Bearing at 80 ° C for 50 minutes - 80 to 90 ° C in 5 minutes

- Bearing at 90 ⁰ C for 50 minutes

- 90 to 100 ° C in 5 minutes

- Bearing at 100 ⁰ C for 42 minutes

- 100 to 115 ° C in 5 minutes

- Bearing at 115 ° C for 42 minutes.

The compositions are then subjected to an annealing treatment at 200 ^° C. for 2 hours, and then they are cooled to ambient temperature.

The starting temperature of crosslinking and the loss of mass at 500 ° C. for these resinous compositions are given in Table 1. b) Preparation of test specimens

Granular mixtures having the composition given in the following Table 2 are prepared:

Table 2

The test pieces are obtained by molding 75.64 g of the granular mixture obtained under b) in a mold measuring 10.224 cm × 2.591 cm × 1.27 cm. The green test pieces are removed from the mold, sealed in aluminum foil and cured in an oven according to the following temperature cycle:

- 25 to 60 ° C in 10 minutes

- 60 to 100 ⁰ C in 40 minutes

- Bearing at 100 ⁰ C for 80 minutes - 100 to 160 ° C in 180 minutes

- Bearing at 160 ° C for 10 hours The test pieces are separated into two series: the first series undergoes no treatment, the second is immersed in boiling water for 2 hours to simulate the conditions of accelerated aging.

The measurements of the flexural strength and the Young's modulus are given in Table 3 below:

Table 3

EXAMPLES 13 TO 26

Liquid resin compositions for the manufacture of coated abrasives. Resin compositions having the composition given in Table 4 (in parts by weight) are prepared under the conditions of Examples 1 to 12.

The resin compositions of Examples 13 to 26, as well as the reference resole (Reference 2) are treated according to the temperature cycle described in paragraph a) of Examples 1 to 12 above, and then cooled. The starting temperature of crosslinking and the loss of mass at 500 ^° C. for these resinous compositions are given in Table 4. EXAMPLES 27 TO 38

Liquid resin compositions for the manufacture of coated abrasives. Resin compositions having the composition given in Table 5 (in parts by weight) are prepared under the conditions of Examples 1 to 12.

The resin compositions of Examples 27 to 38 are processed according to the temperature and annealing cycle described in paragraph a) of Examples 1 to 12 above. The starting temperature of crosslinking and the loss of mass at 500 ^° C. for these resinous compositions are given in Table 5. EXAMPLES 39 TO 41

Liquid resin compositions for the manufacture of agglomerated abrasives. a) Liquid resin compositions having the composition given in the following Table 6 (in parts by weight) are prepared:

Table 6

The resins are obtained by solubilizing the novolac resin in the reactive diluent at a temperature of the order of 35 to 40 ^° C.

These liquid resin compositions are processed according to the temperature and annealing cycle described in paragraph a) of Examples 1 to 12 above.

The mass loss at 500 ⁰ C for those resin compositions is as follows:

Example Loss of mass at 500 ° C (%)

39 48

40 43

41 48 b) preparation of test specimens

Granular mixtures having the following composition are prepared:

The abrasive grains are grains of 60 grain alumina (406 μm) ⁽⁹⁾ which were previously immersed in an aqueous solution of gamma-aminopropyltriethoxysilane at 2% by weight, and then dried in an oven at 120 ^° C. for 2 hours. .

The test specimens are obtained by molding the granular mixture under the conditions of Examples 1 to 12.

The test pieces are separated into two series: the first series undergoes no treatment, the second is immersed in boiling water for 2 hours to simulate the conditions of accelerated aging.

The measurements of flexural strength and Young's modulus are given in Table 7 below:

Table 7

(1) marketed under the reference "Bakélite PF8505F" by the company

HEXION SPECIALTY CHEMICALS; glass transition temperature:

42 ° C (2) marketed under the reference "Bakelite ^® 043SW07" by the company

HEXION SPECIALTY CHEMICALS (3) marketed under the reference "NC513" by the company CARDOLITE

EUROPE

(4) marketed under the reference "Cashew Nut Shell Liquid CNSL" by PALMER Ltd; cardanols content (> 60% by weight)

(5) marketed under the reference "Heloxy ^® Modify HD" by the company HEXION (6) marketed under the reference "Incozol ^® LV" by the company INCOREZ

(7) marketed under the reference "Highlink-CDO" by the company CLARIANT; 60% solution in water

(8) sold under the reference "Bakelite ^® 8686" by Hexion Specialty Chemicals; contains 7% by weight of hexamethylenetetramine (HEXA)

(9) marketed under the reference "Alumina 57A" by Saint-Gobain Ceramics and Plastics

(10) sold under the reference "Bakelite ^® PF0361SW01" by the company HEXION SPECIALTY CHEMICALS

(11) marketed under the reference "Epikote ^® 600" by the company HEXION SPECIALTY CHEMICALS

TABLE 1

TNE: tris (hydroxymethyl) nitromethane; TEA: triethanolamine

TABLE 4

TABLE 4 (CONTINUED)

TNE: tris (hydroxymethyl) nitromethane; TEA: triethanolamine; TPP: triphenylphosphine

TABLE 5 (CONTINUED)

nd: not determined

Claims

1. Liquid resin composition intended for the manufacture of abrasives, characterized in that it comprises at least one novolak resin having a glass transition temperature of less than or equal to 60 ^° C., at least one reactive diluent and optionally at least one agent crosslinking.

2. Composition according to Claim 1, characterized in that the novolak resin has a glass transition temperature of less than or equal to 50 ^° C., preferably of between 35 ° and 45 ° C.

3. Composition according to claim 1 or 2, characterized in that the novolac resin is obtained by reaction of formaldehyde and phenol.

4. Composition according to claim 3, characterized in that the molar ratio formaldehyde / phenol ranges from 0.2 to less than 1, preferably from 0.35 to 0.9, and more preferably from 0.5 to 0.9.

5. Composition according to one of claims 1 to 4, characterized in that the composition further comprises a resin capable of reacting with the crosslinking agent different from the novolac, in particular an epoxy resin, in particular an epoxidized novolak.

6. Composition according to Claim 5, characterized in that the proportion of novolac resin is greater than or equal to 50% by weight of all the resins, preferably greater than or equal to 75% and advantageously the proportion is equal to 100%. .

7. Composition according to one of claims 1 to 6, characterized in that the novolac resin represents at least 30% by weight of the resin composition, preferably at least 40% and preferably at least 50%, and does not exceed 85%.

8. Composition according to one of claims 1 to 7, characterized in that the reactive diluent has a viscosity of less than or equal to 1000 mPa.s, preferably less than or equal to 700 mPa.s, advantageously less than 500 mPa.s. and better still less than 350 mPa.s.

9. Composition according to one of claims 1 to 8, characterized in that the reactive diluent contains at least one function selected from hydroxy, aldehyde, epoxy, oxazolidine and lactone functions.

10. Composition according to Claim 9, characterized in that the reactive diluent is chosen from alicyclic alcohols, saturated or unsaturated, such as ethylene glycol, 1,3-butylene glycol, glycerol, trimethylolpropane and monoallyl ethers. of these compounds, cyclic alcohols, saturated or unsaturated, such as furfuryl alcohol, mono- or polynuclear aromatic alcohols such as benzyl alcohol and its derivatives, m-cresol, 3,5-xylenol, nonylphenol cardanols and their derivatives such as cardols, methyl-cardols and anacardial acids, and naphthol, the precursors of these alcohols, in particular acetals and trioxanes, glyoxal, glycidyl ethers of saturated or unsaturated alcohols such as diglycidyl ether of 1,6-hexanediol, epoxidized fatty acids especially contained in epoxidized oils, in particular soybean oil and linseed oil aromatic epoxies such as cardanols and oxazolidines, such as 3-ethyl-2-methyl- (3-methylbutyl) -1,3-oxazolidine, 1 -aza-3,7-dioxa-5-ethylbicyclo- (3.3.0) -octane and bis oxazolidines and lactones such as gamma-butyrolactone.

11. Composition according to claim 10, characterized in that the reactive diluent is glycerol, furfuryl alcohol, benzyl alcohol, cardanols and their derivatives, diglycidyl ether of hexanediol-1, 6, cardanols. epoxidized, 3-ethyl-2-methyl- (3-methylbutyl) -1,3-oxazolidine, 1-aza-3,7-dioxa-5-ethylbicyclo (3.3.0) -octane, a bis-oxazolidine or gamma - butyrolactone.

12. Composition according to one of claims 1 to 11, characterized in that the reactive diluent represents at least 10% by weight of the resin composition, preferably at least 20%, advantageously does not exceed 69%, and better still does not exceed 30%.

13. Composition according to one of claims 1 to 12, characterized in that the crosslinking agent is chosen from compounds containing at least one hydroxy or aldehyde function, the heterocyclic compounds containing a structure containing a nitrogen atom and a oxygen atom separated by a carbon atom, nitroacetals and nitrones.

14. Composition according to Claim 13, characterized in that the crosslinking agent is tris (hydroxymethyl) nitromethane, glyoxal, 2,2-dimethoxyethanal, an oxazoline such as 1,3-phenylenebisoxazoline, or an oxazolidine such as 3-ethyl-2-methyl-2- (3-methylbutyl) -1,3-oxazolidine and 1-aza-3,7-dioxa-5-ethylbicyclo (3.3.0) octane.

15. Composition according to one of claims 1 to 14, characterized in that the crosslinking agent represents at least 1% by weight of the liquid resin composition, preferably at least 20%, preferably at least 30%, and better still does not exceed 40%.

16. Composition according to one of claims 1 to 15, characterized in that it further comprises at least one crosslinking catalyst selected from compounds comprising at least one secondary or tertiary amine function such as hydroxylamine, triethylamine, diazabicycloundecene, benzyldimethylamine and 2,4,6-tri (dimethylaminomethyl) phenol, imidazoles and imidazole derivatives, for example 2-methylimidazole, 2-ethyl-4-methylimidazole and benzyl-2 methyl-imidazole, the trialkyl- and triaryl-nucleophiles of Group V (A) elements, for example triethanolamine, trimethylphosphine and triphenylphosphine, borates, for example tetraphenylphosphoniumtetraphenylborate and tetraphenylphosphonium tetrafluoroborate, and the salts of ammonium such as tetramethylammonium hydroxide and benzyltrimethylammonium hydroxide.

17. A composition according to claim 16, characterized in that the amount of catalyst is less than or equal to 10 parts by weight per 100 parts by weight of novolac resin, reactive diluent and optionally crosslinking agent, and preferably is less or equal to 5 parts.

18. Abrasive article comprising abrasive grains bonded by a binder based on a thermosetting resin, characterized in that the binder is the crosslinking product of the liquid resin composition according to one of claims 1 to 17.

19. Article according to claim 18, characterized in that the abrasive grains are grains consisting of alumina, including fused aluminas and sintered aluminas obtained by sol-gel, seeded or not with a material of the same crystalline nature, chemically modified or unmodified iron oxide, molybdenum oxide, vanadium oxide, alumina-zirconia, boron-alumina, silicon carbide, aluminum-oxynitride, diamond or nitride cubic boron, and mixtures of such grains.

20. Article according to claim 19, characterized in that the abrasive grains are treated with an organic compound containing silicon, for example a silane functionalized with organic groups.

21. Article according to claim 20, characterized in that the silane is a vinylsilane, in particular vinyltriethoxysilane, an aminosilane, especially gamma-aminopropyltrimethoxysilane, gamma-aminopropyltriethoxysilane and diaminopropylethoxysilane, or an epoxysilane.

22. Article according to one of claims 17 to 20, characterized in that it is an agglomerated abrasive.

23. Article according to one of claims 17 to 20, characterized in that it is an applied abrasive.