DE1569511B2 - SANDING COMPOUND - Google Patents

Description

contains per 100 parts of the thermosetting binder, in which D is the residue of a dihydric phenol, E is a hydroxyl group-containing residue of an epoxy and η is the degree of polymerization and has a value of at least 30.

2. Composition according to claim 1, characterized in that the thermosetting resin binder is a Mixture of a liquid resole resin and a novolak resin mixed with a hardening one Amount of a curing agent donating methylene groups is.

3. Composition according to claim 1 and 2, characterized in that it also contains 0 to 200 weight parts of filler, per 100 parts by weight of the thermosetting phenolic resin binder.

4. Composition according to claim 3, characterized in that the filler is cryolite.

The present invention relates to an abrasive molding compound consisting of a main amount Abrasive grains and a binding amount of a thermosetting resin binder.

Abrasives, such as grinding disks, grinding wheels, etc., expediently have good flexural strength and toughness at room temperatures, for example to break apart due to centrifugal forces to avoid. One known to improve the toughness and flexural strength of abrasives Method consists in the incorporation of thermoplastic materials ^ such. B. polyvinyl acetate and others Vinyl resin modifiers (polyvinyl chloride and vinyl chloride copolymers). When using however, the abrasives get very hot. The addition of these materials reduces the strength of the Abrasives to an unacceptably low level at their normal use temperatures. Low Limits in the use temperatures make low grinding speeds necessary and are otherwise undesirable.

From the USA. Patent 25 21911 are already Known masses of a phenol, formaldehyde resin, a thermoplastic polyhydroxy ether and a hardener which supplies methylene groups. These masses are in combination with inert fillers and abrasives suitable for the production of grinding heads. These known masses contain So an epoxy resin, in which the binder properties only after the crosslinking of the epoxy groups occurrence. The epoxy resin is irreversibly transformed into a three-dimensional structure convicted. However, abrasive compositions based on such a binder are

not yet satisfactory in practice, in particular with regard to their mechanical flexural properties. The object of the present invention is therefore to create abrasive molding compositions with improved Flexural strength and toughness at room and elevated temperatures.

The invention therefore relates to abrasive molding compounds, consisting of abrasive grains and a Thermosetting phenolic resin binder, which is characterized in that the composition contains up to 60 parts by weight of a thermoplastic polyhydroxyether formula

-fD - Ο - Ε - Ο ifrr

contains per 100 parts of the thermosetting binder, in which D is the residue of a dihydric phenol, E is a hydroxyl group-containing residue of an epoxy and η is the degree of polymerization and has a value of at least 30.

Surprisingly, it was found that the incorporation of the thermoplastic polyhydroxyether in abrasive molding compounds, an improvement in flexural strength and toughness of around 50% at room temperatures instead of the usual 10 to

20% improvement achieved with thermoplastic additives. ^:

It was totally unpredictable, however, that this thermoplastic additives actually increases the flexural strength and toughness by about 50% at 26O ⁰ C or more and not, as other thermoplastic additives do so deteriorated use properties at high temperatures.

This marked improvement in flexural strength is illustrated quantitatively in the following table, in which identical abrasives are compared, where "A" using a commonly used heat-resistant, unmodified phenolic resin binder and "B" using a resin binder according to the invention, prepared according to Example 1, was produced.

Table 1 Flexural strength (kg / cm ² ) Actual Test temperature percentage improvement from B A. B. . compared to A CC) 248.5 388.5 + 56 - 25th 112.0 163.8 + 46 260 87.5 136.5 + 56 290

The term "thermoplastic polyhydroxyether" used here refers to practical linear polymers of the general formula

-ED-O

in which D stands for the remainder of a dihydric phenol; E is a radical of an epoxide containing hydroxyl groups, and η stands for the degree of polymerization and has a value of at least 30 and preferably 80 or more. The term "thermoplastic polyhydroxy ethers" is also intended to include mixtures of at least two thermoplastic polyhydroxy ethers.

The dihydric phenol supplying the phenol radical D can either be a dihydric, mononuclear phenol, such as hydroquinone and resorcinol, or a divalent polynuclear phenol such as e.g. B. Materials of the following general formula, be: S.

(Y ') .- HO-f-Ar — R— Ar

OH

IO

in which Ar is an aromatic divalent hydrocarbon such as naphthylene and preferably phenylene; Y and Y ', which can be identical or different, are alkyl radicals, preferably having 1 to 4 carbon atoms, halogen atoms, ie fluorine, chlorine, bromine and iodine, or alkoxy radicals, preferably having 1 to 4 carbon atoms; r and ζ are integers with a value from 0 to a maximum of the value that corresponds to the number of hydrogen atoms on the aromatic radical (Ar) which can be replaced by substituents; and R 'is a bond between adjacent carbon atoms, as in dihydrodiphenyl, or a divalent radical, such as e.g. B.

—C— —O— —S—

O
-SO-

-SO,

and —S — S-

and divalent hydrocarbon radicals such as alkylene, alkylidene, cycloaliphatic radicals, e.g. B. cycloalkylene and cycloalkylidene, halogenated, alkoxy- or aryloxy-substituted alkylene, alkylidene and cycloaliphatic radicals and alkarylene and aromatic radicals including halogenated, alkyl, alkoxy or aryloxy-substituted aromatic radicals and a ring attached to an Ar group; R 'can also stand for polyalkoxy or polysiloxy or for two or more alkylidene radicals which are separated by an aromatic ring, a tertiary amino group, an ether bond, a carbonyl group or a sulfur-containing group such as a sulfoxide group, etc. _; , · ..; .. _;

Examples of particular dihydric polynuclear phenols include:

i bis (hydroxyphenyl) alkanes, such as 2,2-bis (4-hydrophenyl) propane, 2,4'-dihydrodiphenylmethane, bis- (2-hydrophenyl) -methane, bis- (4-hydrophenyl) -methane,

Bis (4-hydroxy-2,6-dimethyl-3-methoxyphenyl) methane, ·

l, l-bis- (4-hydrophenyl) -ethane, 1,2-bis- (4-hydrophenyl) -ethane,

l, l-bis (4-hydroxy-2-chlorophenyl) ethane,. . l, l-bis- (3-methyl-4-hydrophenyl) -ethane, 1,3-bis- (3-methyl- _; 4-hydroxyphenyl) -propane,

2,2-bis- (3-phenyi _r 4-hydroxyphenyl) -propane,

2,2-bis- (3-isopropyl-4-hydroxyphenyl) propane,:, _; 2j2-bis (27isbpropylr4-hydroxyphenyl) propari ,; _{i ;:} 2,2-bis (4-hydroxynaphthyl) propane, -: 2,2-bis (4-hydroxyphenyl) pentane,

3,3-bis (4-hydroxyphenyl) pentane, •; 2,2-bis (4-hydroxyphenyl) heptane, Bis (4-hydroxyphenyl) phenylmethane,

Bis - ^ - hydroxyphenylj-cyclohexylmethane,

1,2-bis (4-hydroxypheny 1-1,2-bis (pheny I) -

propane,

2,2-bis (4-hydroxyphenyl) -1 -phenylpropane, etc .;
Di (hydroxyphenyl) sulfones, such as
Bis (4-hydroxyphenyl) sulfone,
2,4'-dihydrodiphenyl sulfone,
5'-chloro-2,4'-dihydrodiphenyl sulfone,
5'-chloro-4,4'-dihydroxydiphenyl sulfone, etc .;
Di (hydroxyphenyl) ethers, such as
Bis (4-hydroxyphenyl) ether,
the 4,3'-, 4,2'-, 2,2'-, 2,3'-dihydroxydiphenyl

ether,.

4,4'-dihydroxy-2,6-dimethyldiphenyl ether,
Bis (4-hydroxy-3-isobutylphenyl) ether,
Bis (4-hydroxy-3-isopropylphenyl) ether,
Bis (4-hydroxy-3-chlorophenyl) ether,. ■ ■,
Bis (4-hydroxy-3-fluorophenyl) ether,
Bis (4-hydroxy-3rbromophenyl) ether,. -, '

Bis (4-hydroxynaphthyl) ether,
Bis (4-hydroxy-3-chloronaphthyl) ether,
Bis (2-hydroxy-diphenyl) ether,
4,4'-dihydroxy-2,6-dimethoxydiphenyl ether,
4,4'-dihydroxy-2,5-diethoxydiphenyl ether, etc.

The bisphenol reaction products of 4-vinylcyclohexene and phenols are also suitable, such as z. B.!, S-Bis-ip-hydroxypheny ^ -l-ethylcyclohexanjUnd the bisphenol reaction products of diperites or its isomers and phenols such as 1,2-bis- (p - Hydroxyphenyl) - 1 - methyl - 4 - isopropylcyclohexane, and bisphenols such as 1,3,3 - trimethyl-1. (4. hydroxyphenyl) - 6 - hydroxyindane and 2,4 - bis-4-hydroxyphenyl) -4-methylpentane etc.

Particularly suitable dihydric polynuclear phenols have the formula

HO

(Y ') ₂

OH

in which Y and Y 'have the meaning given above; r and ζ have a value from 0 to 4, and R 'is a divalent saturated aliphatic hydrocarbon radical, in particular an alkylene or alkylidene radical having 1 to 3 carbon atoms, and a cycloalkylene radical having up to; 10 carbon atoms.
Mixtures of dihydric phenols can also be used, and where the term "dihydric phenol" or "dihydric: polynuclear phenol" is used in the present application, mixtures of these compounds are also to be included. ^; = · ■■; - · ■ "· ; yiu> l '-' i ■? - (: <:;: U, ' ^: - \ - ■": ■'. ■■■

.The epoxide,: the ^J yields a radical R containing deh-hydroxyl groups, can be a monoepoxide or diepoxide. ' Oxirane-containing compound veriständeni ^d: Under "epoxy" a Eirie is. H. an oxygen atom that is bonded to a two vizirial aliphatic carbon atoms, such as e.g. B.

-C -

A monoepoxide contains such an oxirane group and provides a radical E with a single hydroxyl

group; a diepoxide contains two such oxirane groups and yields a radical E with two hydroxyl groups. Saturated epoxies, d. H. Diepoxde derived from ethylenically unsaturated bonds, d. H.

C = C

and acetylenically unsaturated bonds, i.e. - C = C -, are free, are preferred. Particularly Halogen-substituted saturated monoepoxides are preferred, i. H. the epihalohydrins, and saturated Diepoxde containing only carbon, hydrogen and oxygen, especially those in which the vicinal or adjacent carbon atoms are part of an aliphatic hydrocarbon chain form. The oxygen in these diepoxides can, in addition to the oxirane oxygen, ether oxygen - O -, Oxacarbonyl oxygen

Diglycidyl carbonate,
Bis (2,3-epoxybutylphenyl) -2-ethylhexylphosphate

phat,

Diepoxydioxan, - ...

Butadiene dioxide and 2,3-dimethylbutadiene ^:

dioxide.

Those diepoxides in which the oxirane groups are attached to an electron donating are preferred Substituents are bound that are not bound directly to the carbon atoms of this oxirane group is.

Such diepoxies have the grouping

Carbonyl oxygen

-C — O—

etc. be.

Special monoepoxides are z. B. epichlorohydrins, such as

Epichlorohydrin,

Epibromohydrin,

1,2-epoxy-1-methyl-3-chloropropane, 1,2-epoxy-1-butyl-3-chloropropane, 1 ^ -Epoxy ^ -methyl-S-fluoropropane etc.

Suitable diepoxides are e.g. B.

Diethylene glycol-bis-P ^ -epoxycyclohexanecarboxylate),

Bis (3,4-epoxycyclohexylmethyl) adipate, bis (3,4-epoxycyclohexylmethyl) phthalate, o-methyl-S ^ -epoxycyclohexylmethyl-o-methyl-

3,4-epoxycyclohexane carboxylate,. I-chloro-S ^ -epoxycyclohexylmethyl-l-chloro-

3,4-epoxycyclohexanecarboxylate, diglycidyl ether,

Bis- (3,4-epoxycyclopentyl) -ether,!, S-pentanediol-bis-io-methyl-S ^ -epoxycyclohexylmethyl) -ether,
Bis (2,3-epoxy-2-ethylhexyl) adipate, diglycidyl maleate,
Diglycidyl phthalate,
lW

2,8-epoxypropyl ether,
Bis (2,3-epoxycyclopentyl) sulfone, bis (3,4-epoxyhexoxypropyl) sulfone, 2,2'-sulfonyl diethyl bis (2,3-epoxycyclopentanecarboxylate),

2,3-epoxybutyrate,
4-pentenal-di- (6-methyl-3,4-epoxycyclohexyl-

methyl) acetal,
Ethylene glycol bis (9,1O-epoxystearate),

35

40

45

50

55

60

65 -A-C-C-

-C—

in which A stands for the electron donating substituent, how

-O-

—N—

-S— —SO—

-SO ₂ -

C — O or —N—

SO,

where Q is a saturated hydrocarbon radical, such as an alkyl, cycloalkyl, aryl or aralkyl radical, stands.

A single monoepoxide or diepoxide can be used in the manufacture of thermoplastic polyhydroxy ethers or a mixture of at least two monoepoxides or diepoxides can be used; and the terms "monoepoxide" and "diepoxide" should also include mixtures of at least two monoepoxides or diepoxides include.

The thermoplastic polyhydroxy ether used was prepared by reacting equimolar amounts of 2,2-bis (4-hydroxyphenyl) propane and epichlorohydrin together with sodium hydroxide. the The device used was provided with a sealed stirrer, thermometer and reflux condenser. In these were given:

2,2-bis (4-hydroxy-

phenyl) propane ...... 114.5 parts (0.5 mol)

Epichlorohydrin

(Purity 99.1%) ...: '46.8 parts (0.5 mol)

Ethanol, 96.0 parts

Butanol ...; ...... Λ, 10.0 parts

Sodium hydroxide ^,

(Purity 97.5%) .... 22.6 parts
Water ..i.: .. y. ·; 70.0 parts,

The above mixture was left for 16 hours at room temperature stirred to achieve the initial coupling reaction; then 'was 1 hour on 80 ° C heated, 60 ecm of a 7: 3 mixture of toluene and butanol are added and the mixture is heated to 80 ° C. for a further 2 hours. Then there were more 50 parts of a 7: 3 mixture of toluene and butanol

and 4.5 parts of phenol was added and heated for about an additional 2.5 hours at 8O ⁰ C (reflux) of the vessel contents. After cooling, the reaction mixture was admixed with 200 parts of a 7: 3 mixture of toluene and butanol, 100 parts of water were added and the contents were stirred to dissolve the salts present in the reaction mixture. The contents of the vessel were allowed to settle for 10 minutes, a lower salt phase forming which was decanted off. The upper phase containing the polymer solution was washed twice in succession, each time with 160 parts of water containing 4.5% butanol. The washed polymer solution was acidified by stirring with a mixture of 1 part of 85% phosphoric acid with 100 parts of water (pH = 2) for 1 hour. The upper polymer solution phase was again separated off by decanting and washed four times with 200 parts each of water containing 4.9% butanol. The washed polymer was then coagulated in 1000 parts of isopropanol, filtered and dried. A thermoplastic polyhydroxy ether made from 2,2-bis (4-hydroxyphenyl) propane and epichlorohydrin with a melt flow rate of 7.0 dg / min was obtained.

Thermoplastic polyhydroxy ethers with a melt flow between 0.5 and 20 or more, in particular 2 through 7, make excellent abrasive preparations and structures when in phenolic resin binders in accordance with the present invention be incorporated.

The thermoplastic polyhydroxyether can contain one or more fillers, opacifying agents, Extenders, colorants or other additives customary for thermoplastic resins contain. These preparations can be used according to the thermoplastic Materials conventional mixing processes are produced.

Thermosetting resins which can be improved in strength at room temperature and elevated temperature by incorporating a thermoplastic polyhydroxyether are those resins which are commonly used in abrasives. Typical thermosetting resins are phenol-aldehyde, amine-aldehyde and modified, e.g. B. amine-modified phenol-aldehyde resins. According to the invention, both novolaks and resoles are suitable, the former in combination with hardening agents. A complete description of suitable resins can be found in the book by Robert W. Martin, "The Chemistry of Phenolic Resins" (published by John Wiley & Sons, 1956), and in the book by TS Carswe 11, "Phenoplasts" (published by Interscience publishers , 1947). These and other thermosetting resins are described in U.S. Patents 2,559,664, 2,779,668, and 2,521,911. ■ ·.: .., ; d , ■ -: ·.

The term used here »phenol-aldehyde-! Resin "refers to acid or base catalyzed thermosetting resins resole or novolac type, consisting of a phenol as ^ \ phenol, cresol, Xylonol, p-tert-Butylphenpi, p-phenylphenol, bisphenols and resorcinol, and an aldehyde such as formaldehyde and furfural (see U.S. Patents 25 85196; 24 75 587; 25 57 922; 2617 785; 26 75 335 and 25 51 025),. =,:,;,

The abrasive molding compositions according to the invention are prepared in a preferred manner by a liquid resole resin or resin solvent, a solid, powdered noyolak resin that, with a hardening amount, produces fine methylene groups Curing agent is mixed, as well as the thermoplastic polyhydroxyether and abrasive grains together mixes. Abrasive grains that can be used include metal oxides, in particular aluminum

5 oxides, e.g. with a particle size below 1.19mm, 1.41 mm or 1.68 mm, natural corundum and diamond, although also any other abrasive grains, such as B. silicon carbide coated with a wetting agent can be used. That

ίο Wetting agent for the grains can be a liquid, thermosetting Resin or a resin solvent such as furfural or a mixture of furfural and Be cresol, or a solution of a thermoplastic polyhydroxyether. This mixture is in pressed a mold and the binder by curing due to the action of the hardening agent or cured by the self-reaction of the resin. In this connection it is noted that the designation "Heat" in "thermosetting" should also include room temperatures (e.g. 25 ° C).

The abrasive molding compositions of the invention can contain up to about 200 parts per 100 parts by weight of the thermosetting resin binder in common fillers such as cryolite, fluorspar, magnesium oxide, Silica and other known modifying agents. The greater flexural strength of the invention Abrasive molding compounds may be a sign of greater oil tolerance for such modifiers. ·

The abrasives according to the invention are usually prepared in a manner customary for known materials, with the exception of the use of the thermoplastic polyhydroxyether. Previously known abrasives, such as grinding wheels, are generally made from "grit", ζ. Β. 780 parts of molten Al ₂ O ₃ (J ^e 260 parts of a particle size below 1.19 mm, 1.41 mm or 1.68 mm), the filler, for example cryolite, and resin binder (120 parts). The binder consists of solid material and liquid wetting agent, usually in a ratio of about 80 parts powdered resin binder to about 40 parts liquid resin binder. In another known formulation, the binder consists of 120 parts of solid resin and about 10 to 20 parts of furfural as a wetting agent. The abrasive mixture is mixed into a free-flowing mass by first coating the abrasive grit with the liquid binder (wetting agent) at room temperature. The cryolite filler and the one with sufficient hardening agent, such as. B: Hexamethylenetetramine, mixed powdery binders are mixed, and this dry mixture is circulated with the wetted semolina.

The agglomerates are made by passing them through

crushed through a sieve. The abrasive molding compounds should be up by the time they are put into the mold become, stay free flowing.

The thermoplastic polyhydroxyether can be used in an amount of up to 60 percent by weight, based on the amount of the thermosetting resin binder (without taking the abrasive grains into account) to produce the abrasive molding compositions according to the invention. For easier handling and to achieve optimal properties, 0.5 to 50% polyhydroxy ethers are preferably used. Maximum strengths at high temperatures (260 ⁰ C) and room temperature (25 ° C) by using: ^5; up to 25% thermoplastic polyhydroxyether achieved, and the ^; Preparations within

509 583/421

in this area are particularly suitable for use as grinding wheels.

In one embodiment of the present invention, abrasive molding compositions are made by one abrasive grit with a potential thermosetting or thermosetting resin, the polyhydroxyether contains, mixes. Thus, the powdered thermosetting resin can be combined with a tableted, finely divided or powdery thermoplastic polyhydroxy ether circulated, mixed, in a screw mixer be ground or otherwise intimately mixed. It can be dry blends of the thermoplastic Polyhydroxy ethers and a potentially thermosetting resin together with a curing agent produced before or after the pulverization of the mass for the production of abrasive molding compositions will.

Loops ("snagging"), as described on p. 909 in the "Tool Engineers Handbook" (published by McGraw-Hill Book Co., Inc., New York City) is primarily a metal removal process manual pressure application by the processor and is used extensively in foundries, welding shops and Forging applied to cast bars, gutters, steam lines, pipe connectors, burrs and protruding parts Grinding away welding bumps. It is also used in rolling mills for rough grinding from slabs, ingots, pre-rolled iron rods and blocks, where hard or strong grinding wheels can be used with organic binders.

The abrasive molding compounds according to the invention are not just for the production of grinding and metal grinding wheels * suitable, but also in other grinding elements, such as high-performance sand and polishing belts, - cones, discs, etc.

The following examples illustrate the present invention without restricting it. If Unless otherwise stated, all parts and percentages are parts and percentages by weight.

40

example 1

Manufacture of test abrasives a) Manufacture of dense metal abrasives

Parts by weight

Grit, molten aluminum oxide (Al ₂ O ₃ ) (mixture of each: 260 parts of one particle size /

under 1.19 mm, 1.41 mm or _

Cryolite (filler) y. ............... 100., Liquid phenolic resin.: .. J .......... 40

Powdered Harr ^ ...; ..:. · '. ...... 80 '

1: = 1-stage ν phenol-formaldehyde resole resin;

ν :: 100 to 3000 cP at 25 ° C. - .; ■ · ■. '. -γ.-. ;

. 2 = 2-stage phenol-formaldehyde novolak resin

·; ■ ... and thermoplastic polyhydroxy ether in

ν .. · -. · an 88:12 mixture (10% hexamethylene

.:. ; . tetramine, based on the entire modifi-

■?; ■■ ;;;: ■. ' adorned novolak) -; ::;, ν} - ';';■.; -

The resin portion of the formulation was liquid. and powdered solid phenolic resins. in the 40 parts of liquid phenolic resin and 80 parts of powdered phenolic resin were used in the comparative system Used to produce a free-flowing abrasive molding compound. The amount of liquid and powdered Resin was adjusted to give a dry, free flowing mixture.

b) Procedure

The liquid surfactant was added at 25 ⁰ C for abrasive grit in a metal pan and mixed with a spatula, was wetted until each grain semolina. A mixture of cryolite filler and the powdered resin mixed with enough hexamethylenetetramine to harden the novolak resin was passed through a sieve three times and placed on a piece of Kraft paper. The moistened semolina was then poured onto this dry powder mixture and coated by hand by rotating it with a swing arm on the Kraft paper and mixing. The agglomerates of the original mixture were broken up by passing them through a large mesh sieve. Agitation on the Kraft paper continued until it was completely coated and little or no residual powdered resin remained. The ratio of powdered to liquid resin was considered correct if the abrasive molding compound remained free flowing until the point in time it was placed in the mold.

Six equal parts of the mixture obtained were then each put into a 15 χ 2.5 χ l, 25 cm hollow mold given, smoothed and cold to a density using a ramming pressure of 30 tons deformed by 2.93 g / ccm. Then the test abrasive molding compound was staged by means of a conventional 24 hour Cured cycle: 10 hours from 66 to 186 ° C; 12 hours at 186 ° C and 2 hours to cool.

Three abrasives were each tested according to ASTM D-709-61 on their flexural strength at 25 and 26O ⁰ C. The average values are given in the following table:

Tabel

Powdered test. ■■ · .. Flexural strength (kg / cm ² ) Perzen resin temperature tuale

('C) unmodified. polyhydroxy- better-

Phenolic resin ether modified. tion

■ .-; ·: .- ■ · ■ -. · ■■ ' ^: ·.'■■■; ■ ■ "-.V.; Phenolic resin ³ )

Fine ¹ ) / 25, 248.5

Coarse ² ) 25 248.5

Fine ¹ ) '260 112

Coarse ² ) "260 V 112

; 373.8 ... 50

■ 388.5, 56; ■ 118.3 6 ' ¹ ■ ·

¹ 163.8 ^-; . \ 46

'■') Micro-crushed, powder density 0.26 to 0.29 g / ccm, sieve analysis:. 97 to 99% below a particle size of 0.074 mm.
² Y micro-comminuted, powder density 0.43 to 0.47 g / ccm, sieve dialysis: \ .76 to 78% below a particle size of 0.074 mm. '■ - ·' ■
- ,. ³ ) polyhydroxyether content about 12% - :; l ·:. _...: ■ :: ..

The phenolic resin having a _{polyhydroxyäthermodifizierte:} Bulk density (density powder) 0.43 to 0.47 g / cc gives an optimum balance of the improvement in the strength at room temperature and at. high temperatures' compared to heat

permanent, unmodified phenolic resin binders. at with a decrease in the powder density or the particle size of the resin, the strength remains at room temperature essentially constant, but the strength at high temperatures decreases progressively. With higher powder densities or coarser particle sizes, the strength of the polyhydroxyether remains modified phenolic material essentially constant, but the strength at room temperature increases.

To demonstrate the technical progress achieved according to the invention compared to the US-PS 25 21 911 known abrasives are the following described comparative tests carried out in which a total of three abrasive molding compounds were prepared, two using a thermoplastic polyhydroxyether used in accordance with the invention (Preparations A and B) and one using an epoxy resin binder according to of said USA patent (preparation C).

All three preparations contained the same amounts of alumina, cryolite filler and liquid phenolic resin. In addition, 8 parts of a powdered resin composed of a novolak resin were added and a thermoplastic polyhydroxyether or an epoxy resin having a molecular weight of 1400 and an epoxy equivalent weight of 870 to 1025 are used. In detail, the three had Preparations the following compositions:

Composition of the abrasive preparations in parts by weight

A B C

Alumina 780 780 780

Cryolite 100 100 '100'

Liquid phenolic resin 40 40 40

Powdered resin ¹ ) V 8Ö ² ) .. 80 ³ ); 80 *);

Tabel

Ratio of powdery flexural strength (kg / cm ² )
to liquid phenolic resins

(Parts) at 25 "C

at 260 "C

80:40 ¹ )

ro 84:36 ² )

94:26 ² ) 237.3
372.0
415.8

148.4-217.0
211.4

') Unmodified phenolic resin.

² ) Phenolic resin modified with polyhydroxyether.

'5 The abrasive molding compositions according to the invention can also contain flow accelerators to reduce the Melt viscosity can be incorporated for particular end uses. Bisphenol-Α is suitable for this as well as other phenols, such as. B. phenol itself and hexatriphenol.

B e i s ρ i e 1 3

Phenolic resin binder systems for abrasives made from a 2-stage novolak resin and / or a 1-stage resol resin. If mainly only a 2-stage novolak is used, so is formaldehyde in any of its forms, like paraformaldehy'd and trioxane, or a compound, which contains available formaldehyde, such as a hexamethylenetetramine and methylol containing Resin (resole) required to provide the cross-links necessary to thermoset the system.

In practice, however, the grinding wheel industry prefers 2-stage hardened with hexamethylenetetramine phenolic novolak binders; The effect of novolaks modified with polyhydroxyether is shown in table 4, the data for the flexural strengths using the grinding wheel material and vlen Curing conditions of Example 1 with different amounts of hexamethylenetetramine and Polyhydroxyether contains: ::. .

') 1-stage phenolic formaldehyde resole resin with a viscosity table at 25 C from 100 to 300 ocP. :

² ) 71.3 parts of a 2-stage phenol-formaldehyde novolak resin and 8.7 parts of a thermoplastic polyhydroxyether. . ·: · ... '■■ - •• ^ V': '

³ ) 65.0 parts of a 2-stage phenol-formaldehyde novolak resin and 15.0 parts of a thermoplastic polyhydroxyether. .

⁴ ) 68.0 parts of a 2-stage phenol-formaldehyde novolak resin and 12.0 parts of an epoxy resin as mentioned above.

hydroxyether im
Phenolic novolak resin

% Hexamethylene
tetramine *)

Flexural strengths (kg / cm ² )

at 25''C

at 60'C

Relationship**)

The abrasive preparations were like. hardened above. Then they were _{evaluated by measurement 55} - their flexural strength at 25 ° G according to ASTM D-790-61; It was found that the inventive abrasives A and B had flexural strengths of 438 and 497 kg / cm ² , respectively, while the known abrasive C had a flexural strength of only 316 kg / cm 2. had .. ';'. · '- ¹ ''■ ■■ ■:'"':: ■ 1 ■' ■■■■

12 12 20 20 7
10

7th
10

7th
10

253.4
237.3
443.6
443.1
353.5
469.0

36.4
148.4

64.6
235.2
117.6
213.5

7.0
1.6
7.0
1.8

⁴ '²;

2.2-

Example 2 ' ]

The effect of changing the ratio of pulverized to liquid phenolic resin is given in Table 3 : '- ■■' ·· -, '■■■■' - ■ '

*) Percent, based on the weight of the modified novolak, - **) Ratio of flexural strength at room temperature (25''C) for flexural strength at 260 "C.

. A hexamethylenetetramine content of 10% results in an optimal balance between the flexural strength at room temperature and elevated temperatures for grinding wheel-type abrasives; Included

Good strengths at high temperatures are required.

When using abrasives in foundries, however, higher strengths are required at room temperature and lower strengths at elevated temperatures are necessary. Using a lower hexamethylene tetramine content provides agents with a higher strength ratio Room temperature versus elevated temperatures.

The use of a hexamethylenetetramine content above 10% results in lower strengths Room temperature and the same or lower strengths at elevated temperatures.

Table 5

For general purposes, however, 2-stage modified with polyhydroxy ether are suitable Phenolic resins with a hexamethylenetetramine content between 3 and 20% as grinding wheel materials.

Example 4

The effect of the concentration of the thermoplastic polyhydroxyether on the flexural strength of Grinding wheel materials are given in Table 5, with the grinding wheel base molding compounds and curing conditions of Example 1 were used with the exception of a changed polyhydroxyether content.

% Poly flexural strengths (kg / cm ² )

hydroxy ether

in novolak- at 25 "C% at 200 ° C%

preparation increase increase

Ver
same
(no
Polyoxy
ether) 227.5 130.9 5 *) 247.1 9 202.3 55 9 *) 286.3 26th 186.9 43 15 *) 326.9 44 189.7 45 50 *) 411.6 81 149.1 14th 10 **) 401.8 77 198.8 52 12 **) 414.1 83 224.0 71

*) The polyhydroxy ether and the novolak resin were at 82

mixed up to 121 ° C in a hot two-wheel mill. **) After the novolak was manufactured, the polyhydroxy ether was in the reaction vessel before the novolak was isolated by adding a hot melt through the distillation flask.

As can be seen from Table 5, the addition of the hot melt solution of the polyhydroxyether to the phenolic Novolak is more effective and is therefore preferred for modification.

Improvements can be achieved with a polyhydroxyether content between 0.25 and 50%, based on on the weight of the phenolic novolak. The preferred range of polyhydroxy ethers is between about 5 and 20 percent by weight.

Example 5

The effect of the various polyhydroxy ethers on the heat resistance of grinding wheels is shown in Table 6 shown, the samples being prepared according to the procedure of Example 1.

Table 6. '". · ' ■■, ': ■

% Polyhydroxy ether im Flexural strength (kg / cm ² ) % Increase at 260 ° C % Increase. % be Novolak preparation opposite to opposite to lasted at 25 ° C comparison comparison strength
get UCI
room : ',.'. '■ ■ .. ■;. · ■■' ■ ■. · ■■ - temperature 130.9; ^ 57; ν 26th 186.9 - Τ '.. ^; \ '"'" 43 65 Comparison; 0% 227.5 31 217.7 66 73 9 ¹ ) 286.3 14th 184.1 41 71 298,2 '': '■ :: "■ ::: ■; 24 220.5 69 78 9 ^s ) 259.0 - - 9 ⁴ y 282.8

¹ J A polyhydroxyether derived from bisphenol-A (melt flow 1 to 6).

² ) A polyhydroxy ether derived from bisphenol A base (melt flow 30). ^:

³ ) A polyhydroxy ether derived from 1,2-bis (p-hydroxyphenyl) -1-methyM-isopropylcyclohexane. . '.

⁴ ) Polyhydroxy ether derived from bisphenol-A (melt flow 1 to 6) plus 4% phenol-blocked toluene diisocyanate as a crosslinking agent.

The heat resistance of a test abrasive is indicated by its flexural strength at elevated temperature (260 ° C) and percent strength retained at room temperature when tested hot. Therefore, it is believed that a resin that has higher strength at elevated temperatures and / or gives a higher percentage of retained strength at room temperature, also greater Heat resistance in the abrasive results.

Greater heat resistance, both through strength at elevated temperatures and through

Table 7

percent strength retention measured at room temperature is obtained with a Polyhydroxy ethers of a lower molecular weight (higher melt flow) and a crosslinked polyhydroxy ether with low melt flow.

Example 6

The effects of the curing times of the resin and the temperature changes are shown in Table 7 which compares the preparation of Example 1 with an unmodified novolak.

Final curing stage ¹ ) resin Flexural strengths (kg / cm ² ) at 260-C % % preserved at 25-C % increase strength increase at room temperature 148.4 62 12 hours at 185''C unmodified. 237.3 Novolak 217.0 47 59 12 hours at 185'C preparation 372.4 57 from example 1 211.4 43. 62 6 hours at 185 "C preparation 345.8 46 from example 1 245.7 66 70 6 hours at 185 ° G and preparation ! 35O; O 48 ' 4 hours at 232 ¹ "'C from. example 1

') Initial hardening from 65.5 to 185 ° C in 10 hours.

It was found that the usual cure cycle required a 12 hour hold 18 5 ° C requires an optimal balance of strength at room temperature and elevated temperatures for the unmodified novolak reference material results.

However, the resin modified with the polyhydroxyether gave the same relative improvement in strength with a shorter curing cycle and significantly higher (66%) strengths at elevated temperatures with a higher peak temperature for post-curing. Furthermore, the cycle resulted in. the higher the final cure, a higher percentage of strength retained, at room temperature.

Table 8

For example 7

The heat resistance of the preparation described in Example 1 modified with polyhydroxy ether was compared to an unmodified novolak resin. The data shown in Table 8 illustrate that the heat resistance of the polyhydroxyether modified novolak resin (measured by the strength at elevated temperatures) is much higher and that the modified novolak resin is more stable than the unmodified one. Regardless of the special Cure cycle of time and temperature was the strength at elevated temperatures with the modified resin by 40 to 100% larger than with the unmodified material.

Final curing stage ¹ ) Flexural strength at 260''C (kg / cm ² ) unmodified with polyhydroxy Novolak ■ ether modified Novolak 154.7 149 ° C - 199.5 ;: 95.9 185 ° C - 216.3 113.4 ; ή '; i: .b ■ . ·.;: V; 228, O; . ^ u, -. λ- -93, ^h:; ■ ^{; ί} ^ ^; 228 ^ 4ί ^: · -ΐ · - · ΐ '·' ^Γ 156.8 · /: ■ - ■ · -: 204 ° C ^ '' ^; --230.3 ^; "^;;; :: '. ^;;:;: 128.8 ^{: i:} 233, a " ^{: i} - ^:; "^;" 170.8 238 ° C - . 205.1 184.1 256.2 195.3 253.4 172.2 272 ⁰ C - 216.3 165.9 233.1 173.6 240.8 - 4h '., - 2 hours.' ■: ■ 4h :-; · ■: 8 hours ^; - ^ 4h; ^bt 8 hours - 2 hours. 4 hours 8 hours - 2 hours 4 hours 8 hours

') Initial curing from 77 to 174'C in 2 hours.

509 583/421

Example 8

Preparations containing sintered aluminum oxide grains were used in high-performance grinding wheels in a mixture with the polyhydroxyether-modified novolak described in Example 1 9

compared with unmodified novolak resin. Furthermore, 20 parts of furfural with 3 parts of calcium oxide were used instead of the liquid resole resin of the Preparation of Example 1 used. The data are given in Table 9:

Aluminum oxide grit

resin

Flexural Strength (kg / cm ²

25 C

% 260 C
increase

%
increase

Melted ¹ )
Melted ¹ )
Sintered ² )
Sintered ² )

unmodified novolak ³ )
Polyhydroxyether - modified novolak ³ ) Polyhydroxyether - modified novolak ³ ) Polyhydroxyäther - modified novolak ⁴ ) 237.3
372.4
492.8
534.1

57
110
125

148.4
217.0
226.8
271.6

47
53
85

') "Aloxite" grain of the Carborundum Co.

² ) "Alundum75A" grain from Norton Co.

³ ) Resole liquid wetting agent.

⁴ ) Furfural wetting agent (20 parts) with 120 parts of powdered novolak.

It has been found that in certain high-performance grinding jobs Abrasives with a lower percentage of voids (porosity) show the best behavior. The application of heat and pressure (hot pressing) in opposition pressure alone (cold pressing) accelerates better resin flow and wetting of the grit, thereby reducing the porosity of the agent.

Example 9

For some high-performance grinding work, agents with a lower percentage of cavities, than they are obtained by cold pressing, purposeful

35 moderate. A series of experiments were carried out in which the test samples were produced by hot pressing, since this results in improved resin flow and wetting of the grit, which reduces the porosity of the agent obtained. The preparation described in Example 1 was used, which, due to the 10-minute hot deformation (157 to 160 ^° C.) instead of cold pressing, had a density of 3.03 g / ccm. However, the usual 24 hour cure cycle of Example 1 was the same. Instead of the liquid resole in the preparation of Example 1, furfural (20 parts) and calcium oxide (3 parts) were also evaluated. The results are given in Table 10:

Table 10 Al ₂ O ₃ -GHeB Test temperature
Γ C) Flexural strength
Polyoxyether
unmodified.
Novolak (kg / cm ² ) ^:
Polyoxyether
modif.
Novolak % Increase
the
strength Wetting agent component melted
melted
sintered 25th
260
• 25
260
25,
260 '"- ■" ^: 122.5
86.1
162.4
109.2
145.6
101.5 "" 189.0
93.1
273.7
123.9
301.0
'' 139.3 55
8th
68
14th
100
37 Liquid resol
Furfural
Liquid resol

Regardless of the type of wetting agent or grits used, the polyhydroxyether modified one provided Novolak resin shows a 55 to 100% improvement in room temperature strength over unmodified Novolak using liquid resole or. Furfural as a wetting agent component. the Improvement in strength ranged from 8 to 37%.

Claims (1)

Patent claims: 1. Abrasive molding compound, consisting of abrasive grains and a thermosetting phenolic resin binder, characterized in that the mass is up to 60 parts by weight of a thermoplastic Polyhydroxy ethers of the formula