GB1566890A

GB1566890A - Binder compositions

Info

Publication number: GB1566890A
Application number: GB53637/76A
Authority: GB
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1975-12-22
Filing date: 1976-12-22
Publication date: 1980-05-08
Also published as: FR2336445A1; FR2336445B1; SE7614331L; IT1070441B; ES454274A1; FI763648A; NL7614051A; JPS5281694A; AT353920B; ATA942276A; BE849755A; DE2557789B2; DE2557789C3; DE2557789A1; CH602852A5

Description

(54) BINDER COMPOSITIONS (71) We, HOECHST AKTIENGESELLSCHAFT, a body corporate organised according to the laws of the Federal Republic of Germany, of 6230 Frankfurt/Main 80, Postfach 80 03 20, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to binder compositions.

Binders which may be suitably used for affixing grains of an abrasive material to a support made of a tissue, papcr, vulcanized fibres or a bonded fabric are thermosetting, water-dilutable synthetic resin pre-condensates, especially a phenol-formaldehyde precondensate, or, alternatively hide glue.

Phenolic resins yield abrasive products which have excellent thermal and mechanical properties, but which are, however, too hard for use in delicate grinding operations. They require, moreover, a preliminary treatment of the abrasive support and a long period of time for perfect curing.

Melamine resins and urea resins can be cured at moderate temperatures and are softer than phenolic resins, but they have a tendency to become brittle and they lose their strength when kept in a humid atmosphere.

Hide glue can be processed without special treatment of the abrasive support and at moderate temperatures, and abrasives bound therewith are especially suitable for delicate grinding operations. They have, however, poor thermal stability under load and poor resistance to humidity.

It has been proposed in German Offenlegungsschrift No. 1 694 123 to add a polyvinyl alcohol to a phenol-formaldehyde pre-condensate to accelerate curing of the first coating with no shifting of the abrasive grains or brittleness of the resin, as is the case in the rapid hardening of pure phenolic resins. The polyvinyl alcohol used in this reference is a saponification product of a polyvinyl acetate having a K value of 30. The setting time of the first coating can be reduced by adding the polyvinyl alcohol, but a rather long setting time for the second coating must still be taken into account.

The present invention provides binder compositions which comprise (A) a water-soluble or water-dilutable thermosetting pre-condensate of formaldehyde and phenol or melamine or urea, and (B) polyvinyl alcohol having an ester number in the range of from 5 to 270, preferably from 160 to 210, mg of KOH/g and the 4% by weight aqueous solution of which has a viscosity at 20"C of at most 4 cP, preferably in the range of from 2.3 to 3.5 cP, the weight ratio of the components A and B being in the range of from 1:9 to 9:1, preferably from 1.5:1 to 1:1.

The present invention also provides aqueous binder compositions which comprise the above components A and B in the above weight ratio and water, a process for preparing an abrasive material which comprises fixing a granular abrasive to an abrasive support material using such an aqueous binder composition, and abrasive materials comprising a granular abrasive fixed to an abrasive support material by a binder composition according to the invention and which has been hardened.

The binder compositions according to the invention can be applied to an abrasive support without special pre-treatment of the support, and they can be hardened very rapidly at relatively high temperatures without becoming brittle, without sliding of the abrasive grains during hardening, and without distortion of the support, which can be observed especially during the rapid setting of phenolic resins. When using melamine resins and urea resins the resistance to humidity is, moreover, considerably improved.

This is rather surpising since the polyvinyl alcohols used according to the invention give abrasives which have a totally insufficient service life and a high sensitivity to humidity when one of the polyvinyl alcohols is used as the sole binding agent.

The synthetic resin binders used according to the invention are water-soluble or water-dilutable pre-condensates of formaldehyde and phenol or melamine or urea, which may be hardened under the action of heat. Typical materials of this kind are, for example, formaldehyde-phenol pre-condensates having a formaldehyde to phenol molar ratio of 1.85:1, formaldehyde-melamine pre-condensates which are partially methyl-etherified trimethylolmelamine compounds, and formaldehyde-urea pre-condensates which have a formaldehyde to urea molar ratio of 2.4:1 and which may be partially methyl-etherified.

The following Examples illustrate the invention: The polyvinyl alcohol used in all of the Examples had a viscosity when measured as a 4% by weight aqueous solution at 20"C of 3 cP, and an ester number of 200 mg of KOH/g. The granular abrasive used in all Examples was a standard corundum having a particle size FEBA-no. 36 according to DIN(=German industrial standard) No. 69,100, sheet 1, and was used in an amount of 700 g/m2.

The support used was a special kraft paper for abrasive belts, which had an area weight of 180 glm".

For determining the cutting index, which is a measure of the thermal and mechanical resistance of the abrasive, the abrasive papers were kept for three days at 200C at a relative humidity of 60% and glued to give continuous bands. These bands were pressed against a sheet of chrome nickel steel having a thickness of 3 mm, under a pressure of 20 N/m2 and with a speed of 28 m/s. The cutting index is the ratio of the weight of the steel grindings to the weight loss of the abrasive band.

Example 1: Pre-condensate of urea and formaldehyde having a molar ratio of 1:2.4.

Binder: 50 parts by weight of a 40% by weight aqueous solution of the polyvinyl alcohol, 36 parts by weight of a 55% by weight aqueous solution of the pre-condensate; pH 7, viscosity 400 cP at 20"C, 14 parts by weight of water.

pot life: about 60 hours.

110 glm2 of the binder were applied to the support at 220C and the granular abrasive was added by spreading. The layer obtained was dried for 15 minutes at 900C in a circulating air stove. Another 450 g/m2 of binder were applied to the dried layer, and the abrasive paper was cured for 30 minutes at 90"C and for 20 minutes at 1300C.

Cutting index: 46 Example 2: Pre-condensate of formaldehyde and phenol having a weight ratio of 1.85:1.

Binder: 50 parts by weight of a 40% by weight aqueous solution of the polyvinyl alcohol, 30 parts by weight of a 70% by weight aqueous solution of the pre-condensate, pH 8, viscosity 500 cP at 200C, contact agent: barium hydroxide, 20 parts by weight of water.

pot life: about 4 weeks.

Preparation of the abrasive papers as in Example 1.

Cutting index: 58.

Example 3: Pre-condensate: partially methyl-etherified trimethylol-melamine.

Binder: 50 parts by weight of a 40% by weight aqueous solution of the polyvinyl alcohol, 27 parts by weight of a 75% by weight aqueous solution of the pre-condensate, pH 8.5, viscosity 500 cP at 200C, 23 parts by weight of water.

pot life: about 4 days.

Preparation of the abrasive papers as in Example 1.

Cutting index: 29.

COMPARATIVE EXAMPLES: Example la: 37 parts by weight of the pre-condensate of Example 1 were mixed with 13 parts by weight of water and 1.5 parts by weight of a solution of 20 parts by weight of ammonium chloride and 10 parts by weight of concentrated ammonia solution in 70 parts by weight water. The mixture had a pot life of about 30 minutes. The preparation of the abrasive paper and the examination were carried out as for the preceding Examples.

The abrasive papers were so brittle that a considerable part of the abrasive band prepared therefrom broke when passing over a deflection roller having a radius of 45 mm.

The cutting index was 8.

Example 2a: 29 parts of weight of the pre-condensate of Example 2 were mixed with 21 parts by weight of water, and abrasive papers were prepared with the quantities indicated in the preceding Examples. The abrasive obtained under the setting conditions of the preceding Examples was unsuitable, since the pre-condensate gave expanded coatings of foamy structure under these conditions. For this reason the ground bond was hardened for 60 minutes at 900C and the top bond for 90 minutes at 90"C and for 30 minutes at 1300C, in difference to Example 2.

The cutting index was 85, but the abrasive papers had a noticeable tendency to rupture due to brittleness.

Example 3 could not be repeated using solely the melamine pre-condensate. When using the polyvinyl alcohol contained in the binders as sole binder under the coating and hardening conditons of the preceding Examples, the abrasive paper obtained had a cutting index of 14 (Example 4 a of the following table).

The abrasive papers according to Examples 1, 2, 3 and Comparative Examples 1 a and 4 a were kept, in a further test, for 3 days at a relative humidity of 90%. The cutting index was determined. The following Table shows the superiority of the abrasive bands prepared according to the invention.

TABLE Cutting index Abrasive band 3 days after according to Example originally storage in humid air 1 46 38 2 58 52 3 29 25 la 8 2 4 a 14 1.6 WHAT WE CLAIM IS: 1. A binder composition which comprises (A) a water-soluble or water-dilutable thermosetting formaldehyde/phenol, formal dehyde/melamine or formaldehyde/urea pre-condensate, and (B) a polyvinyl alcohol having an ester number in the range of from 5 to 270 mg of KOH/g and a viscosity, measured on a 4% by weight aqueous solution at 200C, of at most 4 cP, the weight ratio of the components A and B being in the range of from 1:9 to 9:1.

2. A binder composition as claimed in claim 1, wherein the plyvinyl alcohol has an ester number in the range of from 160 to 210 mg of KOH/g.

3. A binder composition as claimed in claim 1 or claim 2, wherein a 4% by weight aqueous solution of the polyvinyl alcohol has a viscosity at 20"C in the range of from 2.3 to 3.5 cP.

4. A binder composition as claimed in any one of claims 1 to 3, wherein the weight ratio of the components A and B is in the range of from 1.5:1 to 1:1.

5. A binder composition as claimed in any one of claims 1 to 4, wherein a formaldehyde/phenol pre-condensate is used having a formaldehyde to phenol molar ratio

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. 27 parts by weight of a 75% by weight aqueous solution of the pre-condensate, pH 8.5, viscosity 500 cP at 200C, 23 parts by weight of water. pot life: about 4 days. Preparation of the abrasive papers as in Example 1. Cutting index: 29. COMPARATIVE EXAMPLES: Example la: 37 parts by weight of the pre-condensate of Example 1 were mixed with 13 parts by weight of water and 1.5 parts by weight of a solution of 20 parts by weight of ammonium chloride and 10 parts by weight of concentrated ammonia solution in 70 parts by weight water. The mixture had a pot life of about 30 minutes. The preparation of the abrasive paper and the examination were carried out as for the preceding Examples. The abrasive papers were so brittle that a considerable part of the abrasive band prepared therefrom broke when passing over a deflection roller having a radius of 45 mm. The cutting index was 8. Example 2a: 29 parts of weight of the pre-condensate of Example 2 were mixed with 21 parts by weight of water, and abrasive papers were prepared with the quantities indicated in the preceding Examples. The abrasive obtained under the setting conditions of the preceding Examples was unsuitable, since the pre-condensate gave expanded coatings of foamy structure under these conditions. For this reason the ground bond was hardened for 60 minutes at 900C and the top bond for 90 minutes at 90"C and for 30 minutes at 1300C, in difference to Example 2. The cutting index was 85, but the abrasive papers had a noticeable tendency to rupture due to brittleness. Example 3 could not be repeated using solely the melamine pre-condensate. When using the polyvinyl alcohol contained in the binders as sole binder under the coating and hardening conditons of the preceding Examples, the abrasive paper obtained had a cutting index of 14 (Example 4 a of the following table). The abrasive papers according to Examples 1, 2, 3 and Comparative Examples 1 a and 4 a were kept, in a further test, for 3 days at a relative humidity of 90%. The cutting index was determined. The following Table shows the superiority of the abrasive bands prepared according to the invention. TABLE Cutting index Abrasive band 3 days after according to Example originally storage in humid air

1 46 38

2 58 52

3 29 25 la 8 2

4 a 14 1.6 WHAT WE CLAIM IS: 1. A binder composition which comprises (A) a water-soluble or water-dilutable thermosetting formaldehyde/phenol, formal dehyde/melamine or formaldehyde/urea pre-condensate, and (B) a polyvinyl alcohol having an ester number in the range of from 5 to 270 mg of KOH/g and a viscosity, measured on a 4% by weight aqueous solution at 200C, of at most 4 cP, the weight ratio of the components A and B being in the range of from 1:9 to 9:1.

of 1.85:1.

6. A binder composition as claimed in any one of claims 1 to 4, wherein a formaldehyde/melamine pre-condensate is used which is a partially methyl-etherified trimethylolmelamine compound.

7. A binder composition as claimed in any one of claims 1 to 4, wherein a formaldehyde/urea pre-condensate is used which has a formaldehyde to urea molar ratio of 2.4:1 and which may be partially methyl-etherified.

8. A binder composition as claimed in claim 1 and described in any one of Examples 1 to 3.

9. An aqueous binder composition which comprises a binder composition as claimed in any one of claims 1 to 7 and water.

10. An aqueous binder composition as claimed in claim 9 and described in any one of Examples 1 to 3.

11. A process for preparing an abrasive material which comprises fixing a granular abrasive to an abrasive support material using an aqueous binder composition as claimed in claim 9 or claim 10.

12. An abrasive material comprising a granular abrasive fixed to an abrasive support material by a binder composition as claimed in any one of claims 1 to 8 and which has been hardened.

13. An abrasive material as claimed in claim 12 and described in any one of Examples 1 to 3.