GB2314791A - Polymeric coatings containing embedded particles - Google Patents

Abstract

A polymeric coating material comprising embedded particles which may be used to produce abrasive or other articles is characterised in that the coating material is a hot-melt adhesive comprising the polyamide or polyester condensation product of one or more fatty acid dimers with one or more di- or poly-amines and/or di-or poly-ols. The fatty acid dimer is derived from fatty acids having chains of at least 8 and up to 24 carbon atoms or mixtures of these. The coating may be flexibilised by the presence of side chains on the di- or poly-amine or di- or poly-ol, and/or by the addition of flexibilising agents, and/or by the addition of tackifiers such as rosin derivatives, and may contain chain termination agents, adhesion promoters, melting point elevation agents or other substances. The coating material is suitable for coating foam or flexible sheet materials.

Description

Polymeric coatings This invention relates to polymeric coatings and to articles incorporating such coatings.

Abrasive articles may be prepared by applying a polymeric coating in a softened form to the surface of a carrier, partially embedding abrasive particles in the polymer and hardening the polymer. The carrier may be shaped to conform to the intended use of the abrasive article and may, for example, be in the form of a block or sheet for manual use, or of a wheel or disk or other suitable form for mechanical use.

It is always desirable that the abrasive particles are resistant to rub-off in use and that the coating in which they are embedded is firmly attached to the carrier. Where the carrier is itself flexible these desirable properties may be difficult to attain fully. Flexible abrasive articles in the form of pads, blocks or wheels, or the like, commonly formed of polyurethane, polyester, or other foam, or of sheet material which may be of paper or textile, are commonly used. Hitherto the polymeric coating used to attach abrasive particles to a flexible carrier may have comprised a solvent-based polymer, or a polymer containing free isocyanate but the use of these has itself been disadvantageous from the environmental viewpoint.

The invention will be described hereafter with particular reference to adhesive articles based on flexible carriers but it is intended that the broadest scope of the invention should not exclude those based on non-flexible carriers. It is also envisaged that the invention may be applied to articles bearing particles other than abrasive particles, for example organic, inorganic or mineral particles or spheres of a decorative nature, having a reflective purpose or being intended to provide non-slip properties and it is also intended that the broadest scope of the invention should not exclude coatings containing these particles.

A nitrile rubber adhesive has been in common use to bond abrasive particles to a foam carrier. This may be in the form of 30 to 358 solids in an organic solvent such as acetone or methyl ethyl ketone. On the usual scale of production used in the industry this involves very large scale solvent emission or recovery. Increasing the solids content of the adhesive may be possible to an extent but not sufficiently to cure this problem. Water-based adhesives have been tried but these tend to give relatively poor adhesion to the foam or poor resistance to use under wet conditions, as is sometimes required.

It would be advantageous to eliminate the use of solvent-based polymers to adhere abrasive particles to foam. Reactive hot-melt polyurethane adhesives have been proposed for this purpose in GB-2 282 144-A of the Minnesota Mining and Manufacturing Company. These adhesives, containing free isocyanate, are applied to the foam at a temperature such that the viscosity is suitable for coating and for the incorporation of the abrasive particles and the adhesive is then cured by contact with water or with atmospheric moisture. A priming or pre-size coat to improve the "wetting" of the foam by the viscous polyurethane is advised on substrates which have rough surfaces or on surfaces with voids such as open-cell foam surfaces. Reactive hotmelt adhesives of this type tend to be relatively expensive and the process is complicated by the need to handle isocyanate-containing materials and by the use of a pre-size coating.

The present invention relates to a polymeric coating material for a flexible or other carrier article, the coating comprising embedded abrasive or other particles and avoiding or alleviating some or all of the disadvantages outlined above. The invention also relates to abrasive or other articles comprising the polymeric coating and embedded particles and to a process for the production of such articles.

The present invention provides a polymeric coating material comprising embedded particles characterised in that the coating material is a hot-melt adhesive comprising the polyamide and/or polyester condensation product of one or more fatty acid dimers with one or more di- or poly-amines and/or one or more di- or poly-ols.

The invention also provides an article, for example an abrasive article, comprising a carrier, for example a flexible or foam carrier, coated with the particle-embedded hot-melt adhesive wherein the particles are, for example, abrasive particles. Such hot-melt adhesives are non-reactive, i.e. do not involve the operation of a chemical cure to bind the particles, and if formulated correctly do not require the presence of a pre-size coating to achieve satisfactory adherence to a polyurethane, polyester or other foam carrier.

According to the invention it is usually desirable for the majority, or a substantial proportion, of the particles to protrude from the surface of the polymeric coating material although some of the particles, depending on their size, the thickness of the polymeric coating and on other factors, may be completely embedded in the coating. The word "embedded" is used to include partially embedded particles.

The fatty acid dimer used to form the condensation product is preferably derived from fatty acids having chains of at least 8 and up to 24 carbon atoms or mixtures of these. The fatty acids having chains of about 16 to 18 carbon atoms are particularly suitable. The fatty acids may be saturated or unsaturated and in the latter case may suitably contain one or two double bonds. Particularly suitably the fatty acids include or consist of one or more of stearic, palmitic, oleic or linoleic acids. Fatty acid dimers may be obtained as articles of commerce or may be produced under the action of heat in the presence of a suitable catalyst, such as a clay catalyst or a peroxidic catalyst as appropriate and as known in the art. The method for the production of the fatty acid dimers is not a part of the present invention and will not be further described herein. The fatty acid dimer product used in the practice of the invention may contain residual monomer and a proportion of trimer and may contain 50-z to 100%, for example 70E to 985, by weight of dimer. The presence of trimer modifies the reaction and it is therefore preferably present in less than 20e by weight of the dimer acid product.

The di- or poly-amine component of the condensation product, while not excluding polyamines, suitably comprises one or more diamines, for example aliphatic or cycloaliphatic diamines.

Preferably one or more aliphatic diamines are present such as the dior poly-methylene diamines, for example ethylene diamine, hexamethylene diamine or homologous diamines intermediate these, or substituted derivatives of any of these.

The di- or polyol component of the condensation product may suitably comprise one or more diols, for example aliphatic or cycloaliphatic diols. Suitably, the one or more diols comprise one or more compounds having one or more of the general formula (i) HO (CH2)xOH, (ii) HO-(CH2)y-NH-(CH2)Z-OH or (iii) H(-0C2H4)X,-NH- (C2H4O-)ysH in which x represents a number from 2 to 40, y and z represent numbers from 1 to 20 and x' and y' represent numbers from 1 to 10 or substituted derivatives thereof.

While the polyamide and/or polyester condensation product as described above may be a suitable coating material for use according to the invention in relation to non-flexible carriers it may be found to have somewhat low flexibility for optimum use in relation to flexible carriers such as polymeric foams or sheet materials. It is an important subsidiary feature of the invention that, to increase flexibility, (a) there is preferably included with the condensation reaction mixture a suitable quantity of one or more polyether diamines, suitably polyoxyalkylene diamines such as those having the general formula H2N-R1-(RO > x-R2-NH2 where x represents a number from 1 to 80, R1 and R2 represent aliphatic or cycloaliphatic hydrocarbon groups containing 1 to 8 carbon atoms and R represents an aliphatic hydrocarbon group containing 1 to 8 carbon atoms or (b) the di- or poly-amine and/or the di- or poly-ol is/are preferably substituted to include one, two or more side chains containing, for example, 3 to 30 carbon atoms each and being aliphatic, cycloaliphatic or aromatic in nature but preferably being selected from saturated or unsaturated fatty acid residues. Preferred substituted diols are diols (ii) or (iii) bearing the side chain on the nitrogen atom or (c) other means of flexibilising polyamides, such as the inclusion of thermoplastic polymers, for example polyethylene vinyl acetate, amorphous polyolefins,polyethylene acrylates or block copolymers are employed.

A particularly suitable range of polymeric coating materials according to the invention contain, in addition to, or in replacement of, one or more of the flexibilising additives defined in (a) to (c) above, one or more of the following tackifiers, namely, rosin or rosin derivatives, hydrocarbon resins and hydrocarbon liquids e.g.

oils. The rosin derivatives are preferably selected from, or include, one or more of hydrogenated rosin, fractionated rosin rosin esters, hydrogenated rosin esters, polymarised rosin, polymerised rosin esters, modified rosin, modified rosin esters, disproportionated rosin, fractionated rosin derivatives or polymerised and hydrogenated rosin esters. The hydrocarbon resins are preferably selected from or include aliphatic resins, aromatic resins, cycloaliphatic resins, aliphatic aromatic resins, pure monomer resins and polyterpenes. The hydrocarbon oils are preferably selected from or include aliphatic, aromatic and naphthenic oils.

The flexibiliser and/or tackifier is preferably present in up to 40E by weight of the condensation reaction mixture, that is, of the polyamide and/or polyester/dimer condensation product including other materials added to it but excluding the particles to be embedded in it. Preferably, the flexibiliser and/or tackifier is present in more than 1, particularly suitably in more than 4 and in less than 35%, particularly suitably less than 309 by weight on the basis indicated above.

Glass transition temperature measurements may be used as a test for flexibility and is an important feature of the condensation product of the invention. Preferably the glass transition 0 temperature of the condensation product is below 0 C but more suitably below minus 100C, for example minus 200C, and down to minus 0 40 0. This gives excellent flexibility at normal ambient temperatures and compares with a glass transition temperature of about OOC to 50C in the absence of the flexibilising agent.

The melting point of the condensation product is important in relation to the satisfactory coating of the carrier article and in relation to the stability of the coated article to varying use temperatures. Preferably the melting point of the condensation product may be low, that is above 900C and up to below 1300C, or 0 higher, for example, suitably, at least 130 C for example above 0 150 C. Suitably the melting point may be higher than this, for 0 example up to 180 C or more, subject to the temperature not being so high that a foam or other carrier may be damaged through contact with the molten polyamide. The melt point of the polyamide may be increased by the inclusion in the condensation reaction mixture one or more dicarboxylic acids. Suitably the dicarboxylic acids are selected from the straight chain saturated aliphatic dicarboxylic acids. Preferably, but not essentially, the straight chain contains 1 to 12 carbon atoms although it may be up to 20 carbon atoms or more. Alternatively, branched chain dicarboxylic acids may be used.

Particularly suitable dicarboxylic acids for use in the practice of the invention are adipic, sebacic or azelaic acids.

One or more monocarboxylic acids may be included in the condensation reaction mixture to control the molecular weight of the polyamide by acting as a chain-termination agent. The monocarboxylic acid, if present, may be a monomeric fatty acid, suitably one having 16 to 18 carbon atoms. A portion of the monocarboxylic acid may be supplied by residual monomer acid present in the dimeric acid product used.

If required to improve the adhesion between the coating and the carrier one or more heterocyclic diamines may be added to the condensation reaction mixture. Suitably the heterocycli diamine is piperazine or a dipiperidyl amine.

Suitable and preferred quantities of the reactants are set out below as ranges of mole proportions of the total reaction mixture.

It is understood that the reactants are to be combined by selection from these ranges to achieve a total of 100%. If other ingredients, such as diluents, solvents or fillers are also included the proportion of the reactants are scaled down correspondingly.

Preferably, however, liquid diluents or solvents amount to less than 20%, particularly preferably less than 105, by weight of the total composition. Fillers or plasticisers may be present in up to 505, for example in from 5 to 455, but preferably in less than 25, by weight of the composition.

The molar proportions of the condensation reactants are preferably such that the acid functional reactants and the amineand/or hydroxyl-functional reactants are present in from 30 to 70 mole ; to 70 to 30 mole%, more preferably from 40 to 60 mole to 60 to 40 mole respectively.

Of the acid functional reactants the dimer acid may suitably be present in at least 20 mole% preferably in at least 25 mole and up to 55 mole% preferably not more than 45 mole%. The melting point elevation agent may suitably be present in 0 mole% to below 10 mole if a low melting point condensation product is required. Otherwise, it is preferably present in at least 10 mole%, preferably at least 12 mole; and up to 30 mole preferably not more than 25 mole%. The chain termination agent, if present, may be in up to 10 moles, for example in at least 0.1 mole% of the composition.

Of the amine- and/or hydroxyl-functional reactants the aliphatic or cycloaliphatic di- or poly-amine and/or di- or poly-ol may suitably be present in at least 5 mole preferably in at least 10 mole and, especially in internally flexibilised products, that is in products flexibilised by method (b) above, in up to 60 mole preferably not more than 50 mole. If a separate flexibilising agent is present it may preferably be in up to 25 moles preferably in not more than 15 mole and in at least 0.5 mole. If an adhesion promoter is present it may suitably be in up to 50 mole preferably in not more than 40 mole% and in at least 5 mole%.

Without limitation thereto a suitable condensation reaction mixture for use in relation to a flexible polyurethane, polyester or other foam carrier is 20 to 40 mole% dimer acid, 10 to 30 dicarboxylic acid, 0 to 5 mole% monocarboxylic acid, 20 to 40 mole% heterocyclic diamine, 12 to 25 mole5 aliphatic di- or poly-amine and/or di- or poly-ol and 0 to 5 moles polyether diamine in admixture with from l to 40 % of a flexibilising agent and/or tackifier.

The condensation product according to the invention may be produced by mixing the reactants, for example in a reaction kettle, an extruder or a low speed kneader, at a temperature such that a viscous mixable mass is produced. The temperature may be taken to about 1000C by the condensation exotherm and, thereafter, the 0 reactants are heated, for example to at least 150 C, and up to a maximum of 220 0C or 250 0C to allow the condensation product to form.

The condensation product may be coated onto a suitable carrier in the molten state by spraying, by slot-coating or by any other coating method suitable for use with a molten coating material. The coating rate depends in part on the size of the particles to be embedded in it and may be, for example, from 1 to 500, but preferably 2 from 10 to 250 g/m . A presize coating, for example of a hot melt polyvinyl material, is not normally necessary even when the carrier is a sliced section of a flexible polyurethane or other foam which has open cells at least at the surface but may be used if desired.

The carrier may be flexible or rigid sheet material, for example of paper or of textile or may be flexible or rigid blocks or other articles such as grinding disks or wheels or may be of masonry or of any other material which requires a particulate coating.

The particles to be embedded in the coating may suitably be particles of, for example, one or more of alumina, zirconia, hafnia, alumina spinel, diamond, boron nitride, silicon nitride, ceramic aluminium oxide, silicon carbide, tungsten carbide, garnet, ceria, iron oxide, silica, garnet, abrasive grit or other mineral, glass or metallic particles. The size range of the particles is preferably from 16 to 400 mesh BSS, for example, very suitably not greater in size than 30 mesh BSS. A size of at least 350 mesh BSS may be desirable. The coating rate of the particles may be, for example, up to 1000 g/m2 but preferably falls in the range of about 50 to 500 2 g/m . The particles are applied to the polyamide coating material while the latter is in molten form or in a form sufficiently soft or viscous to allow them to become at least partially embedded. To reduce cooling of the coating the particles may suitably be preheated, for example to or above the temperature of the coating.

The particle-containing coating may be applied to more than one surface of a carrier article, such as two sides of a foam block, and the size or nature of the particles may be the same or different on different surfaces.

The particle-embedded coating material may be treated with a post-size coating of, for example a water-based acrylic, epoxy or polyurethane coating material, a solvent-based coating material or a hot-melt coating material.

The production of an abrasive-embedded coating according to the invention and its application to a foam block to produce an abrasive article will now be described in the following Examples 1 to 15 but without any intention to limit the scope of the invention thereto.

Examples 1 to 15 are all according to the invention although Examples 7 and 8 represent less preferred embodiments of the invention.

A series of abrasive elements were made by coating sheets of an 3 open cell polyurethane foam having a density of 60 kg/m3, selected 3 from a preferred range of 20 to 150 kg/m , and a thickness of 15 mm.

A polyamide hot-melt adhesive was applied to the foam from an 0 extrusion dye at a temperature of 180 C. The coated foam was immediately passed through a curtain of abrasive particles. Excess particles were then shaken from the coated sheet. A size layer was applied in all except one of the examples at a coating weight of 20 2 to 50 g/m . The abrasive article was then force dried in an oven at 60 0C for 90 seconds and then stored at ambient temperature for 24 hours.

The hot-melt adhesive, abrasive particles and size material used in the Examples are identified as follows: Hot-melt adhesive A. A polyamide condensation product of 29.9 moles dimer acid, 19.9 moles dicarboxylic acid, 30.3 moles piperazine, 17.4 moles ethylene diamine and 2.5 moles polyoxyethylene diamine. This product had a glass transition temperature of minus 350C.

B. A similar polyamide condensation product containing a lesser amount of polyoxyethylene diamine and having a glass transition temperature of OOC to minus 50C.

C. A similar polyamide condensation product containing no flexibilising agent and having a glass transition temperature of 50C to 100C.

D. A mixed polyamide/polyester condensation product of 41.6 moles dimer acid, 0.84 moles sebacic acid, 0.35 moles ethylene diamine, 0.1 moles hexamethylene diamine and 0.05 moles bis(2hydroxyethyl)cocoamine having a glass transition temperature of minus 10 to minus 150C. Generally, the molar ratio of di- or poly-amine to di- or poly-ol in mixed polyamide/polyester products of the invention preferably vary from 20:1 to 2:1.

Abrasive particles P120 Aluminium oxide - tradename "lox" 120 mesh BSS P60 II lv II 60 mesh BSS Size Acrylic Tradename "Evode Gritlock" Water-based Nitrile 45 solution of nitrile rubber/PVC in acetone.

The combination of adhesive, abrasive and size, and the weights of each, used in each Example are identified as follows: Ex.No 1 2 3 4 5 6 7 8 9 10 11 12 Adhesive Adhesive g/m2 A 80 160 80 160 80 80 B 80 160 C 60 160 D 80 160 Abrasive P120 120 120 120 120 120 120 120 120 120 120 P60 350 350 Size Acrylic # # # # # # # 4 Nitrile # - The symbol "#" indicates the presence of the size coat.

The products of the Examples were tested for adhesion of the polyamide to the foam, for adhesion of the abrasive to the polyamide and the effectiveness of the product as as abrasive. Adhesion of the polyamide to the foam was assessed manually by trying to effect cleavage of the bond. The adhesion of the abrasive to the polyamide was tested by scraping the abrasive with a wooden tongue depressor and by rubbing two samples of the product together. Overall effectiveness was tested by use to abrade a painted mild steel surface.

The products of each of Examples 1 to 6, 9 and 10 satisfactorily passed all three tests. The lower flexibility products of Examples 7 and 8 performed adequately as abrasives.

However loss of abrasive material occurred at a greater rate than in the case of the products of the previous Examples. The loss in Example 7 was particularly significant and was deemed to be unduly detrimental to performance. The loss in Example 8 was tolerable but the use of the higher coating weight of the lower flexibility polyamide made the entire product unduly rigid. In Examples 11 and 12 the abrasives performed satisfactorily and were acceptable although they were inferior to the abrasives of Examples 1 to 6, 9 and 10 due to slightly higher abrasive loss in use.

In Examples 13 to 15 the adhesive, abrasive particles and size coat identified in Example 1 were used with 80 parts by weight of the adhesive being in admixture respectively with 20 parts by weight of the triethylene glycol ester of hydrogenated rosin, 20 parts by weight of disproportionated rosin and 10 parts by weight of the glycerol ester of highly hydrogenated rosin. Examples 13 and 14 produced abrasive pads having a very high degree of flexibility although with a greater than average abrasive loss. Example 15 produced an abrasive pad of satisfactory performance.

Claims (26)

Claims.

1. A polymeric coating material comprising embedded particles characterised in that the coating material is a hot-melt adhesive comprising the polyamide and/or polyester condensation product of one or more fatty acid dimers with one or more di- or poly-amines and/or di- or poly-ols.

2. A coating material as claimed in claim 1 wherein the fatty acid dimer is derived from fatty acids having chains of at least 8 and up to 24 carbon atoms or mixtures of these.

3. A coating material as claimed in claim 2 wherein the fatty acids have chains of from 16 to 18 carbon atoms.

4. A coating material as claimed in any preceding claim wherein the di- or polyamine is a di- or poly-methylene diamine.

5. A coating material as claimed in any preceding claim wherein the di- or poly-ol comprises a secondary or tertiary nitrogen atom bearing two or more aliphatic groups.

6. A coating material as claimed in any preceding claim also including one or more flexibilising agents.

7. A coating material as claimed in claim 6 wherein the flexibilising agent is selected from or includes one or more polyether diamines, one or more aliphatic, cycloaliphatic or aromatic side chains on the di- or poly-amine or the di- or poly-ol, the side chains containing each from 3 to 30 carbon atoms, or one or more thermoplastic polymers.

8. A coating material as claimed in claim 6 or 7 wherein the flexibilising agent is present in from 1% to 40 E by weight of the condensation product mixture.

9. A coating material as claimed in claim 6 containing one or more tackifiers.

10. A coating material as claimed in claim.9 wherein the tackifier is selected from or includes one or more rosins, rosin derivatives, hydrocarbon resins or hydrocarbon oils.

11. A coating material as claimed in claim 9 or 10 wherein the tackifier is present in from 1% to 40* by weight of the condensation product mixture.

12. A coating material as claimed in any preceding claim wherein the condensation product has a glass transition temperature below OOC.

13. A coating material as claimed in any preceding claim also including a melting point elevation agent.

14. A coating material as claimed in claim 10 wherein the melting point elevation agent is selected from or includes one or more straight chain saturated dicarboxylic acids having 4 to 20 carbon atoms in the chain.

15. A coating material as claimed in any preceding claim also including a chain-termination agent.

16. A coating material as claimed in claim 12 wherein the chain termination agent is selected from or includes one or more monocarboxylic acids.

17. A coating material as claimed in any preceding claim also including an adhesion promoter.

18. A coating material as claimed in claim 14 wherein the adhesion promoter is selected from or includes one or more heterocyclic diamines.

19 A coating material as claimed in any preceding claim comprising a combination of 20 to 55 mole% dimer acid, 5 to 60 mole% aliphatic or cycloaliphatic di- or poly-amine, 5 to 30 mole% melting point elevation agent, 0 to 10 mole! chain termination agent and 0 to 50 A mole adhesion promoter, the combination being mixed with from 1 to 40e of one or more flexibilising agents and' one or more tackifiers.

20. A coating material as claimed in claim 19 comprising the combination of 20 to 40 mole; dimer acid, 10 to 30 mole dicarboxylic acid, 0 to 10 mole% monocarboxylic acid, 12 to 25 mole% aliphatic di- amine, 0 to 5 mole% polyether diamine and 20 to 40 mole heterocyclic diamine.

21. A coating material as claimed in claim 19 or 20 wherein the combination defined therein is in admixture with 4E to 30- by weight of one or more hydrogenated rosin derivatives.

22. A coating material as claimed in any preceding claim having embedded therein particles of one or more of alumina, zirconia, hafnia, alumina spinel, diamond, boron nitride, silicon nitride, ceramic aluminium oxide, silicon carbide, tungsten carbide, garnet, ceria, iron oxide, silica, garnet, abrasive grit, glass or other mineral or metallic particles.

23. A coating material as claimed in any preceding claim also containing additives selected from one or more organic or inorganic solid fillers, one or more liquid diluents and one or more thermoplastic polymers or resins as part of the combination.

24. An article comprising a carrier bearing a coating material comprising embedded particles as claimed in any preceding claim.

25. An article as claimed in claim 24 comprising abrasive particles and a carrier of foam, paper or textile.

26. A coating material, or article coated with the same, as claimed in claim 1 or claim 24 and substantially as described herein with reference to any one of Examples 1 to 15.