GB2189802A - Process for the production of a grinding foam body composite - Google Patents

Abstract

A process for the production of a grinding foam body composite, especially of a homogeneous, elastic, microcellular grinding foam body, based on a fibre fleece containing a grinding agent and on a polyurethane foam, wherein onto the fibre fleece containing a grinding agent there is superficially applied a liquid, solvent-free NCO-terminated polyurethane pre-polymer, the coated fleece is assembled to give a formed body and the formed body obtained is polymerised by foam-forming chain elongation, an additional elastic fixing of the grinding agent on the fleece fibres thereby being brought about, the foamed structure formed in the resulting grinding foam body having at least 80% of micropores with a diameter of from 0.1 to 10 mu m. and a fine foam coating on the fibres with a layer thickness of 0.5 to 10 mu m. of at least 90% of micropores with a diameter of 0.05 to 3 mu m.

Description

SPECIFICATION Process for the production of a grinding foamed body composite The present invention is concerned with a process for the production of a grinding foamed body composite based upon grinding fleece and polyurethanefoam (PUR foam), thefield of use of which isthe surface cleaning orthegrinding of materials orworkpieceswith plane or complicated geometry, the materials to be worked possibly having different degrees of hardness and/or different degrees offlexibility.

Grinding bodies based on an elastic foam, mostly PUR foam, are known. The grinding particles are either embedded in a foam orthegrinding body is additionally strengthened by fabrics orfleece.

For this purpose, according to Federal Republic of Germany Patent Specification No.3218009 and U.S.

Patent Specification No.4,466,218, grinding particles are introduced into a liquid PUR foam system and hardened to give a solid, elastic foamed body.

According to Federal Republic of Germany Patent Specification No.1 303 365, forthis purpose, a PUR prepolymer is employed in which, by the use of centrifugal force during hardening, an integral distribution of the grinding agent is obtained. Other processes, such as according to British Patent Specification No. 1,257,708, use fabrics as plate- or roll-shaped intermediate layers for increasing the strength of the grinding body. According to the Federal Republic of Germany Design Patent No.7 601 155,the the hollow spaces of a fleece of polyamide are filled with a PUR propellantfoam of long-chained diol,toluylene diisocyanate and water containing grinding particles.

According to other processes, grinding fleece are used in which, for example, in U.S. Patent Specification No. 4,355,489, the grinding agent particles have been previously bound to the fibres with a compact binding agent, usually with a phenolic resin or PUR. The quality of such grinding fleece bodies can be substantially improved by the incorporation of a polymeric foamed material structure. Besides foams of phenolic and amino resins, those based on PUR are especially suitable because of their elastic character. The polymeric material thereby simultaneously serves as an integral adhesive in order to bind together the fleece layers.

The first technical solutions describe, as in Federal Republic of Germany Patent Specifications Nos. 2 308258 and 2 342 869, the use of conventional foam material formulations (propeilantfoams) for this purpose. However, these processes have two disadvantages: the so-called PUR systems show, in the starting phase, a strongly increased viscosity caused by the hardening mechanism which makes difficulttheir homogeneous distribution in the fleece so that special technological means, such as the use of centrifugal force, as in Federal Republic of Germany Patent Specification No. 1 427 586, must be employed. Furthermore, these foamed materials have cell sizes in the range offrom Sto 50 iim. and thus only have an average elasticity.

An improvement of the process is achieved when solvent material-containing systems are used, such as in Federal Republic of Germany Patent Specification No. 108 157. With these products there can be achieved a homogeneous through impregnation ofthe grinding fleece body. However, in the case of thins process, the disadvantage must be taken into accountthat coagulation structures result.

These structures are, in all, coarser in their dimensions than the grinding particles without thereby having a direct foam character so thatthey impairthe grinding action. This PUR foam possesses, essentially, apart from its fleece strip-adhering function, only a consolidation functionforthegrinding body in the sense of an elastic supportforthefibre structure.

In the case of all the known processes, it is necessary either to distribute the PUR foam system uniformly in the grinding fleece before hardening or, after surface application, to homogenise it by means of appropriate technical steps in the fleece body.

It is an object of the present invention to provide a process with a non-complicated technologyforthe production of a PUR foam grinding body of high strength and high elasticity, the grinding agent being fixed in such a mannerthatthere is achieved a higher inner elasticity and thus a prolongation ofthe period of use of the grinding body.

There is a need to develop a process with very simple technology which, on the one hand, by means of an elastic foamed structure, improves the strength behaviour of the grinding fleece body and, on the other hand, with a uniform distribution in the fleece, ensures an isotropic structure and finally improves the fixing and thus the effectiveness of the grinding particles present in the fleece.

Thus, according to the present invention, there is provided a process for the production of a grinding foam body composite, especially of a homogeneous, elastic, microcellular grinding foam body, based on a fibre fleece containing a grinding agent and on a polyurethane foam, wherein on to the fibre fleece containing a grinding agent there is superficially applied a liquid, solvent-free NCO-terminated PUR prepolymerfoam reactive system, the coated fleece is assembled to give a formed body and the formed body is polymerised by foam-forming chain elongation, an additional elastic fixing of the grinding agent on the fibre fleece thereby being brought about, the foamed structure formed in the resulting grinding foam body having at least 80% of micropores with a diameter of from 0.1 to 10 Fm. and preferablyoffrom 0.3 io5 Fm. and afinefoam coating on the fibres with a layer thickness of 0.5 to 10 um. and preponderantly of 2 to 5 pom., with a pore diameter of 0.05 - 3 um. and preponderantly of 0.1 - 2 Fm.

The main mass of the PUR foams fills out, in finely divided form, the hollow spaces ofthefleece material as support material orfirmly sticks together with assembled strips so that there results a uniform and elastic grinding foam body with the grinding agent elastically embedded therein which can be used for a long period oftime.

The PUR prepolymer is preferably applied to the fleece strip by rake application, by means of a spray device or by some other appropriate process, a distribution in depth thereby not being necessary.

Subsequently, on to the coating is applied the fleece Strip for the desired final form and, after fixing the outer limitations, it is hardened byfoam-forming chain elongation, for example by dipping into a waterbath with a temperature of 20 to 90 C. and preferably of 50 to 600C.,for a period of 5to 30 minutes and preferably of about 15 minutes, by the formation of polyurea with the splitting off of carbon dioxide.

The weight applied can be varied from one at least necessaryforthe wetting of the fibres to one such that, in the end product, it corresponds to 75% ofthe total weight. There is preferred a weight distribution of grinding fleece/PUR foam of equal parts. In principle, there is no limitation to the fleece thickness. For practical reasons, it will normally be from 2to 30 mm. and preferablyfrom Sto 15 mm.

On the basis ofthe high elasticity ofthe grinding body in combination with the inner elasticity ofthe grinding agent according to the flexible embedding ofthe present invention, depending upon the pressure of the grinding body on the material to be worked, there is achieved a varyingly strong and also, in the degree of fineness, differing working up ofthe material surface.

Appropriate fleece for the grinding foam body according to the present invention can be produced by pressing, needling, consolidation or other appropriate process from natural orsyntheticfibres.

As grinding agents, there can be used, for example, corundum silicon carbide, glass powder, quartz powder orthe like in various grain sizes. As primary binding agentforthe grinding particles on the fibres, there can be used a phenolic resin, epoxide resin, PUR elastomerorthe like.

Appropriate PUR foam systems include, for example, solvent-free NCO-containing prepolymers which are prepared from one or more hydroxyl compounds with a functionality of 2 to 3 and one or more isocyanates with a functionality of 2 to 3.

Polyhydroxyl compounds preferred for the prepolymerformation are mixed polyether di- and triols from one or more alkylene oxides with a mixed functionality of 2.1 to 2.5 and preferably of 2.1 5 to 2.30 and with an average molecularweight of 500 to 5000. Appropriate isocyanates include toluylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, technical products or reaction products with low molecular weight di and/or polyalcohols. Preferred PUR prepolymers include those described in German Democratic Republic Patent Application No. WP 242 609/1 (C 08 G).

A preferred solvent4ree NCO-terminated polyurethane prepolymer is one with an NCO equivalent of 500 to 1500 glmole NCO and a viscosity of 2000 to 30,000 mPa.s.

The grinding foam bodies produced according to the present invention can, on the one hand, be used for the industrial working of metal surfaces, for example for removing burrs and/or polishing copper conductor plates, and for domestic purposes for working up the surfaces of metal, wood, synthetic resin, lacquer parts and the like, including those of complicated geometry. Different kinds of coarse, fine and very fine working are conceivable.

Thefollowing Examples are given forthe purpose of illustrating the present invention: Example? A) Production of the PUR prepolymer.

From 10 kg. toluylene diisocyanate, to which has been added 0.05% benzoyl chloride, and 31 kg. of a triol, which has been produced by co-polymerisation of ethylene oxide and propylene oxide on the starting substance glycerol and has an average molecularweight of 4000, is produced, by further reaction at 50"C. for 6 hours, a semi-prepolymerwith an NCO equivalent of about 350 g./mole NCO. This is subsequently mixed at ambienttemperature with a mixture of 11 kg. polypropylene glycol with an average molecu lar weight of 2000 and 1 kg.

dipropylene glycol, in which has been dissolved half of its weight of diazabicyclooctane. After warming for 3 to 5 minutes to 40to 50 C.,the prepolymerto be used is obtained which has an NCO equivalent of about 960 g./mole NCO.

B) Production of the grinding foam body.

Ontoafleeceofpolyamideofl m. breadth and 4 m. length with about 0.75 texfilament strength on to which has been fixed silicon carbide grinding particles No.6 (TG L) with phenolic resin and which has a weight per unit surface area of about 1100 g./m2, there is coated with a rake PUR prepolymerA in an amount of 1000 g./m2. The coated fleece is wound up on a solid phenolic resin-paper roll of 6 mm. thickness with an outer diameter of 60 mm.

There is obtained a roll of, in all, 135 mm. diameter, corresponding to a volume of 3.5 l./m2 grinding fleece. Subsequently, the fleece strip end is fixed with small aluminium hooks on to the underlying strip. Thereafter, the roll is dipped for hardening in a waterbath of 50 C. After about 1 minute, the foaming and hardening process starts from outside inwardly and is ended after about 15 minutes. After removal of the hooks, for smoothing of the surface, the grinding fleecefoam roll can be over-wound, for example, with a steel. Furthermore, depending upon the intended use, it can be cut up into smaller breadth dimensions.

With the grinding foam roll, copper plate material, for example, with board holes can be simultaneously freed from burrs and polished. With the grain size used in the example, there can thereby be achieved a rough depth of 0.5 - 1 Fm. A 1 litre grinding amount ofthis roll suffices for working up 600 m2 of plate material, which means an about 50% greater period of use than in the case of comparable products.

Example 2 On to a grinding fleece strip corresponding to Example 1 of 0.25 m. breadth and 11 m. length with fibres of about 0.45 tex, which has a weight per unit surface area of 630 g./m2, there is applied with a conventional one-component spray head, an analogous PUR prepolymerwith an NCO equivalent of 750 g./mole NCO in an amount of 430 g./m2. The coated fleece is rolled up on a roll core of 10 mm.

thicknesswith an outer diameter of 120 mm. and hardened as in Example 1 within 10 minutes. There is obtained a roll of, in all, 200 mm. diameter, corresponding to a volume of 2.2 litres/m2 offleece.

Example 3 Analogouslyto Example 1 or 2,the coated grinding fleece is wound round a massive aluminium core of 22 mm. diameter and hardened correspondingly. Subsequently after removal ofthe corefor re-use, the resultant grinding foam roll is separated into 30 mm. wide pieces and, via a receiver, fixed in the middle of a short, 6 mm.thick metal rod. In this form, the grinding foam body can be clamped in a hand boring machine and used, for example, for carrying out the following treatment work: derusting iron parts, for example on motor vehicles, removal of corrosion places on various metallic objects, which can also have a complicated geometry, grinding and polishing wooden articles and figures, removal of old lacquer residues, removal of burrs from and polishing of thermoplastic synthetic resin parts, without melting the cut edges, coarse and fine grinding of UP resin formed parts, such as polyester bodies and the like.

Further most varied coarse, fine and very fine work are conceivable.

Claims (11)

1. Processfortheproduction of a grinding foam body composite, especially of a homogeneous, elastic, microcellulargrinding foam body, based on afibrefleececontaining agrinding agent and ona polyurethane foam, wherein on to the fibre fleece containing a grinding agent there is superficially applied a liquid, solvent-free NCO-terminated polyurethane pre-polymer, the coated fleece is assembled to give a formed body and the formed body obtained is polymerised byfoam-forming chain elongation, an additional elasticfixing ofthe grinding agent on the fleece fibres thereby being brought about, the foamed structure formed in the resulting grinding foam body having at least 80% of microporeswith a diameteroffrom 0.1 to 10 #m. and a fine foam coating on the fibres with a layer thickness of 0.5 to 10 Fm. of at least 90% of microporeswith a diameter of 0.05to 3 lim.

2. Process according to claim 1, wherein the foamed structure contains micropores with a diameter of from 0.3 to 5 Fm.

3. Process according to claim 1 or 2, wherein the fine film coating has athickness of 2 to 5 clam.

4. Process according to any of the preceding claims,whereinthemicroporesofthefinefilm coating have a diameter of to2#m.

5. Process according to any of the preceding claims, wherein there is used a solvent-free NCO-terminated polyurethane pre-polymerwith an NCO equivalent of 500 to 1500 9 ./mole NCO and a viscosity of 2000 to 30,000 mPa.s.

6. Process according to any of the preceding claims, wherein the polyurethane pre-polymer is applied by rake application or by means of a single component spray device.

7. Process according to any of the preceding claims, wherein the coated, grinding agent-containing fibre fleece, before the foam-forming polymerisation, is wound over a hollow or solid core to give a grinding roll.

8. Process according to any of claims 1 to 6, wherein the coated, grinding body-containing fibre fleece, before the foam-forming polymerisation, is assembled in several overlying layers to give a planargrinding body.

9. Process according to any of the preceding claims, wherein water orwatervapour is used as chain elongator.

10. Process according to claim 1 for the production of a grinding foam body composite, substantially as hereinbefore described and exemplified.

11. A grinding foam body composite, whenever produced by the process according to any of claims 1 to 10.