POLYMER PRODUCTS

Abstract: Polymer and polymerisable composition suitable for use as anti-fogging materials comprise blends of hydrophilic polyurethane together with polymers preferably derived from monomers or oligomers containing ethylenic unsaturation or with curable polymer precursors which have acrylic unsaturation.

Description: Polymer Products This invention relates to polymer compositions and more particularly to compositions for use in the manufacture of transparent or reflective articles. The use of polymer films for improving the light transmission through or from transparent or reflective articles is known. For example, in U.S. Patent No. 4844983 there is described a glass or plastics substrate which in use is susceptible to misting which has on at least one surface an antimist coating of a hydrophilic polyurethane which when hydrated contains from 35 to 60% by weight water and which has a thickness of 3 μm to 50 μ. . Whilst such coatings have good antimist properties, they are not very scratch or abrasion resistant. Moreover, the hyάropnilic polyurethanes have to be employed as coatings since they are not amenable to fabrication as free-standing structures such as films or sheets. In US-A-4800122 there are described scratch resistant coatings for peroxide curaole polyurethane elastomers which comprise a polyfunctionai monomer having three or more acrvloioxv groups per molecule and at least one N-vinyl imido group containing monomer. The coatinσs are ror eά bv first coatinσ the inside of the mold for the polyurethane with the acryioloxy-N-vinyl/i ido group containing monomers, curing the in-mold coating, casting the urethane composition into tne mold and curing the urethane. The surface characteristics of products formed by this process are stated to include scratch resistance. However, such coatings do not confer antimist properties to the surface. The invention seeks to provide a polymer composition which not only has the good antimist properties of the known hydrophilic polyurethane materials but also has good scratch and abrasion resistance and is capable of being formed into free standing structures sucn as films or sheets as well as being useful for coating substrates such as those of glass or plastic material. The present invention therefore provides a composition of matter naving antifog properties comprising a hydrophilic polyurethane in admixture with a compatible polymer. By the term 'compatible' is meant that the polymers will co-exist with the polyurethane component without anv ohase seDaration when the oolvurethane and polymer components are admixed. Suitably such polyurethane polymer mixtures will exhibit good light transmitting properties. The compatible polymers may be homopoly ers or copolymers or mixtures of such polymers. Aptly such polymers are derived from monomers or oligomers having ethylenic unsaturation. The composition of the invention may be formed by, for example, drying mixtures of the polyurethane - and other polymer components from a solution thereof or by polymerising the precursors for compatible polymer in the presence of the hydrophilic polyurethane component, optionally in the presence of suitable catalysts and/or polymerisation initiators. Suitable precursors include monomers or oligomers which contain ethylenic saturation. Thus in accordance with an embodiment of the present invention there is provided a curable composition comprising a hydrophilic polyurethane and a polymerisable compound containing acrylic unsaturation. The polymerisable compound containing acrylic unsaturation (hereinafter called 'acrylic component') mav be oliαomeric in nature. The component mav contain aerylate or methacrylate groups. Aptly the acrylic component is a poiyfunctionai compound. iore aptly the acrylic component contains at least three acrylicaily unsaturated groups. Favoured acrylic components are poiyfunctionai ether acrylates, preferably containing at least three acrvloioxv groups. More favoured ether acrylates are penta or hexacrylates. Preferred acrylic components for use in the present invention are dipentaerithrytol penta- and hexacrylates pentaerithrytol triacrylate and 1,6 hexane diol - diacrylate. Suitable hardness and antimist properties may be achieved by the use of less than 50% by weight of the acrylic component. The compositions of the invention contain acrylic unsaturation and are cured by cross-linking through the ethylenic bonds. Accordingly, the compositions of the invention may desiraoiy contain initiators to promote cross-linking. The compositions may be cured by radiation including thermal radiation, actinic, infra-red and ultra-violet radiation and electron beam. Favoured compositions may contain a photo-initiator reactive to U.V. light. Such initiators may be present in the compositions of the invention or solutions thereof in conventional amounts. In addition to cross-linking of the acrylic component of the composition, the polyurethane component may also contain ethylenic unsaturation which may be cross-linkable. For example, the polyurethane may be a urethane-acrylate block copolymer. Oligomeric materials which contain unsaturation and which are suitable for use in the present invention include hexafunctional aliphatic or aromatic urethane acrylates, difunctional aliphatic or aromatic urethane acrylates, epoxy Novalac acrylates, polyester tetra-acrylates and siloxane di-or hexa acrylates. A less preferred but still useful component is methyl methacrylate. In accordance with another emoodiment of the invention the composition will comprise a mixture of a hydrophilic polyurethane and at least one other compatible polymer containing residues of a monomer having vinyl unsaturation. Precursors for compositions of this type may comprise a mixture of the polyurethane and the compatible polymer in a single or mixture of co-solvents. Suitably the compositions of the invention are formed upon drying precursor mixture and evaporatinσ the solvent therefrom. Apt polymer materials derived from vinyl or ethylenically unsaturated precursors herein after referred to as the 'vinyl component' include vinyl chloride-vinyl acetate copolymers, hydroxy modified vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate copolymers modified with alpha-beta unsaturated carboxylic acids or epoxy compounds, polyacrvlates and methacrylates, for example polymethyl methacrylates and styrene polymers and polymer blends such as styrene-acrylonitrile and styrene-maleic acid anhydrid polymers. Suitable vinyl components are available under the trade name UCAR from Union Carbide. Aptly, compositions of the present invention based on hydrophilic polyurethanes and vinyl components will contain at least 5% by weight of the total composition of vinyl component. Favourably, the composition will contain at least 50% by weight of hydrophilic polyurethane. Preferably, the compositions of the present invention will contain at least 10% by weight of the vinyl component and typically will contain about 15% be weight of vinyl component. The hydrophilic polyurethane contributes properties of water-absorption to the compositions of the invention. Suitably, the compositions of the invention, when cured, will contain at least 30% by weight water when hydrated. Aptly the hydropnilic polyurethanes for use in the composition of the invention will contain at least 35% by weight water when hydrated. Favourably, the hydrophilic polyurethane will contain at least 40% by weight when hydrated and more favourably may contain up to 60% or up to 90% water when hydrated. Suitable hydrophilic polyurethanes for use in the compositions of the invention include those described in US-A-4844983. Hydrophilic polyurethanes which may be used in the present invention will be any of those which have the water content as hereinbefore described. The saturation water content of the hydrophilic polyurethane will not however be such as to cause it to delaminate from a substrate. Favoured hydrophilic polyurethanes for use in the invention are those which are linear, that is are substantially free of cross links and which therefore are soluble in organic solvents. The hydrophilic polyurethanes suitable for use in the present invention may be polyether or polyester polyurethanes. Suitable polyesters which give rise to polyurethanes include polyesters of adipic acid such as butylene adipate. However it is preferred to use hydropnilic polyurethanes which are polyether polyurethanes. It is particularly preferred therefore to use hydrophilic polyurethanes which are linear polyether polyurethanes. Apt linear polyether polyurethanes may be random polymers containing ether units derived from diolic compounds which have been reacted with diiεocyanates. Suitable linear polyether polyurethanes include those described in European Patent Specification No.050035 at page 12 line 1 to page 14 line 10 and at page 32 line 7 to 33 line 12, which are incorporated herein by cross-reference and which have the required water content when hydrated. Particularly apt is a linear polyether polyurethane which employs poly (ethylene glycol) derived blocks along together with a chain extender and a diisocyanate. Suitably the poly (ethylene glycol) may have a molecular weight of between 600 and 6000 and more suitably of between 800 and 2000. A particularly preferred poly (ethylene glycol) has a molecular weight of 1540. Suitably the chain extender will be an aliphatic diol or diamine or amineol containing up to 10 carbon atoms and most suitably up to 4 carbon atoms. Suitably the diisocyanate such as toluene diisocyanate, 1, 6-hexamethylene diisocyanate or 4, 4 '-dicyclohexyl-methane diisocyanate. A preferred diisocyanate is 4 , 4 '-dicyclohexylmethane diisocyanate. The ratio of hydrophilic polyurethane to acrylic vinyl component as well as the hydrophilic nature of the polyurethane will affect the physical properties of the cured composition of the invention. The greater the amount of polymer component the greater will be the resistance to abrasion, especially where acrylic components are employed whereas the greater the amount of hydrophilic polyurethane and/or the greater the hydrophilicity of the polyurethane component the better will be the antimist properties. The concentration of hydrophilic polyurethane in the composition may range from 10% to 99.0% by weight of the total weight of the composition. Aptly the composition of the present invention may contain from 10 to 90% by weight of the hydrophilic polyurethane. The composition of the invention may be cast, for example, from solution, to form self supporting sheets or film coatings. Thus the compositions may also contain other processing aids such as flow promoters. Suitable flow aids may include fully reacted materials such as silicone fluids or reactive materials such as di-and hexa-functional silicone acrylates. Both the nature and concentration of the acrylic or vinyl component will also affect the shaping or forming properties of the composition. The composition of the invention may be in the form of a solution suitable for casting or moulding in which the solvents for each of the resin components are compatible with each other. Aptly both the polyurethane and acrylic or vinyl components will be dissolved in a common solvent therefor. Favourably the solvent or solvents will be chosen to provide a solution having a viscosity suitable for- it to be cast into a sheet or formed into a film. Apt solvents for use in the present invention are ketones, esters and alcohols as well as mixtures thereof. Examples of suitable organic solvents include propyl acetate, halogenated hydrocarbons such as ethylene dichloride, alkanols such as methanol or ethanol (optionally containing small amounts of water) , ketones such as acetone or methyl ethyl ketone, methyl isobutylketone, 2-methoxyethanol 2-ethoxyethanol, diacetone alcohol or mixtures of these solvents. Preferred solvents are 2-ethyoxyethanol, industrial methylated spirits (IMS) or IMS together with 2 methoxyethanol in a ratio of 3:1. Normally and preferably the hydrophilic polyurethane component will be applied in its non-hydrated state. Those compositions or precursors of the invention which contain acrylic unsaturation are cured by cross-linking through the ethylenic bonds. Accordingly, the compositions of the invention may desirably contain initiators to promote cross-linking. The compositions may be cured by radiation including thermal radiation, actinic, infra-red and ultra-violet radiation and electron beam. Favoured compositions may contain a photo-iniator reactive to U.V. light. Such inhibitors may be present in the compositions of the invention or solutions thereof in conventional amounts. In addition to cross-linking of the acrylic component of the composition, the polyurethane component may also contain ethylenic unsaturation which may be cross-linkable. For example, the polyurethane may be a urethane-acrylate block copolymer. Preferably the compositions of the invention are dried to remove solvent prior to cross linking. The solids contents of solutions of compositions of the invention are chosen to provide a balance of good rheological, drying and film-forming properties. Aptly, the solids content (polyurethane and acrylic or vinyl components) will be less than 50%, more aptly less than about 25%. Coatings in accordance with the invention may be prepared by conventional methods of coating surfaces such as dip coating, spraying, painting, knife-coating, on line coating or by printing. In such processes the composition of the invention is dissolved in a suitable organic solvent, for example having a solids content of up to 30% (by weight) or more favourably as a 5 to 15% solution for dip coating and 5 to 25% for spray coating. When the coating is to be used in a high quality optical product, such as on a lens, it is preferred that the coating is applied as the result of dip coating. In this process the solution of the polymer composition is placed in a suitable container which is raised mechanically in a controlled manner to immerse the substrate. Th.2 container is then lowered at an appropriate rate to give the desired coating thickness. The thickness of the coating depends upon both the solution strength, the viscosity of the solution and the rate of withdrawal of the substrate from the container. Favourably the process is carried out at between 15 and 30°C. The solvent is removed from the coating after withdrawal from the solution using a current of air and preferably a current of warm air at a temperature of 50 to 70°. Drying at this temperature imparts a gloss to the coating thereby presenting a better optical appearance to the coated substrate. It is possible, to apply a coating by preforming the thin film of the hydrophilic polyurethane - polymer compositions of the invention and adhering it to the surface of the glass or plastics substrate which is required to be rendered anti isting. Aptly, the thin film may be adhered by means of a transparent adhesive which is inert to the film and the substrate. The composition of the invention may be cast, for example, from solution, to form self supporting sheets or film coatings. Thus the compositions may also contain other processing aids such as flow promoters. When cast into sheets the compositions may be used for glazing purposes such as for window panes. Alternatively, the compositions may be cast as films onto preformed substrates such as those formed from glass or plastics materials, e.g. polyacrylic or polycarbonate resins to maintain or improve light transmission or, if used as mirror, to improve or maintain reflective properties. When cast into films the compositions of the invention may be applied from solutions typically containing greater than 30% by weight solids e.g. 30-40% by weight solids. Although the compositions of the present invention are light transmitting some sacrifice of the light transmitting properties compared with the base polyurethane in favour of scratch or abrasion resistance may occur when the compositions comprise an acrylic component. We have found however that the light transmitting properties of the hydrophilic polurethane can be retained when vinyl component formations are utilised. Such compositions although not so scratch resistant as the urethane-acrylic components may be formulated into free-standing films for use in multilayer applications such as 'peel-off visors for helmets sucn as those for motor-cycling and sports activities without loss of optical clarity. The antifogging properties of composition of the present invention will greatly exceed the performance specification described in DIN 4646 part 8 (1986) for 'Lenses for eye protectors - Antifogging test'. Preferred compositions of the invention comprising 10% of the vinyl based resins when tested to DIN 4646/8 will transmit 80% of the original trans ittence for longer than 10 seconds. The present invention will be illustrated by the following example. Example l Ninety parts by weight of a hydrophilic polyurethane, prepared in accordance with the method described at lines 4 to 23, column 7 of US-A-4844983 were mixed with nine parts by weight dipentaerithrylol penta aerylate, 0.5 part of a photo initiator, 0.5 parts of a silicone fluid flow aid and blend of solvents comprising methylisobutylketone, propyl acetate 2-ethoxyethanol to produce a solution being a 15% by weight solids content, v. The solution was sprayed onto a sheet of polymethyl methacrylate and cured under a UV lamp. A further sheet was left uncoated. Both sheets were then placed over a water bath containing water at 45°C. After two seconds the uncoated sheet began to mist over and was completely 'opaque' after about ten seconds. The coated sheet did not start misting over until two minutes had elapsed and then did not completely mist over. Further samples of both sheets were affixed to a mirror mounted within a shower cubicle. The shower unit was operated at maximum temperature. Inspection of the sheets showed that the uncoated sheet misted over whereas the reflective properties of the coated sheet remained intact. Example 2 A solution of a hydrophilic polyurethane, prepared in accordance with the procedure described in Example 1, was found by slowly adding 80 parts by weight to 2 ethyoxyethanol maintained at room temperature. 19 parts by weight of dipentaaerithroy ol hexa-acrylate were added slowly with agitation to the polyurethane solution until dissolved and thereafter a photo initiator (DAROCURE 1173, available from CIBA-GEIGY) and liquid flow aid (silicone acrylate) added. The solids content of the result mixture was adjusted to 17% by weight. The solution was then coated onto a sheet of perspex and passed through a drying tunnel maintained at 50°C for a period of 5 minutes and then under a UV lamp to cure the resin. After drying and curing, the coated sheet was subjected to testing according to DIN 4646 part 8. Under the test conditions fogging did not commence until 15 seconds had elapsed. Example 3 A 20% by weight solution was first formed by dissolving 85 parts by weight in ethoxyethanol. A hydroxyl modified vinyl chloride-vinyl acetate copolymer (14.9 parts by weight) was added slowly with agitation until the mixture was clear and free from striations. Liquid silicone acrylate (0.1 part by weight) was then added as a flow aid and the solids concentration adjusted to 15% by weight. The solution was then applied as an antimist coating to a motor cycle helmet visor. The coated visor was passed through a drying tunnel, maintained at 50°C for a period of 5 minutes.

Claims: CLAIMS 1. A composition of matter having antifog properties comprising a hydrophilic polyurethane in admixture with a compatible polymer. 2. A composition according to claim 1 wherein the compatible polymer is derived from at least one ethylenicaly unsaturated monomer or oligomer. 3. A composition according to claim 1 wherein the polymer comprises a mixture of homo - or co-polymers. 4. A composition according any one of the preceeding claims wherein the polymer is derived from at least one monomer or oligomer containing acrylic unsaturation. 5. A composition according to any one of claims 1 to 3 wherein the polymer is derived from at least one monomer or oligomer containing vinyl unsaturation. 6. Precursor for a composition as defined in any one of the preceding claims comprising a hydrophilic polyurethane and a polymerisable compound containing acrylic unsaturation. 7. A precursor according to claim 6 wherein the polymerisable compound contains at least three acrylically unsaturated groups. 8. A precursor according to claim 6 or 7 wherein the polymerisable compound is a poiyfunctionai ether aerylate. 9. A precursor according to claim 8 wherein the aerylate is dipentaerithrytol pent- or hexa - aerylate. 10. A precusor according to any one of claims 6 to 9 comprising a photo initiator. 11. A composition according to any one of claims 2 to 10 wherein the ethylenically unsaturated monomer is a vinyl monomer. 12. A composition or precursor according to any one of the preceding claims wherein the hydrophilic polyurethane contains at least 35% by weight water when hydrated. 13. A composition or precursor according to claim 12 wherein the hydrophilic polyurethane contains up to 60% by weight water when hydrated. 14. A composition or precursor according to any one of the preceding claims comprising up to 30% by weight water when hydrated. 15. A light transmitting article formed from a composition or precursor as defined in any one of the preceding claims. 16. An article according to claim 12 comprising a light transmitting substrate having coated thereon a layer of composition or precursor as defined in any one of claims 1 to 14. 17. An article according to claim 15 moulded, formed or shaped from a composition or precusor as defined in any one of claims 1 to 14. 18. An article according to any one of claims 15 to 17 in form of an eye-protector.

Inventors: HEYS BRIAN, HEYS, BRIAN
Applicants: HEYS BRIAN, SMITH & NEPHEW RES, SMITH & NEPHEW RESEARCH LTD
Application year: 1993
Main classification: C08G18
IPC codes: C08L33, C08L75, C09D133, C09D175