AN ACOUSTICAL-DAMPING FIBROUS OR CELLULAR MATERIAL, A PROCESS FOR ITS PREPARATION AND A LATEX COMPOSITION USEFUL FOR ITS PREPARATION

Abstract: An acoustic damping material is disclosed comprising a fibrous mat or polymeric cellular material coated with a dried composition selected from elastomeric and plasticised plas­ tomeric latices or emulsions of styrenebutadiene rubbers, ne­ oprene, polyvinyl chloride, or ethylene-vinylacetate copoly­ mers or mixtures of two or more thereof, the composition con­ taining a filler having a specific gravity of at least 2.5 and a parti­ cle size of from 1 to 200 microns, the amount of filler being ef­ fective to provide from 60 to 85% total solids by weight of wet composition prior to drying, together with an amount of an an­ ionic or non-ionic surfactant effective to stabilise the rubber, neoprene, polyvinyl chloride, or ethylene-vinylacetate copo­ lymer. The method of preparing it and a composition suitable for application to the desired fibrous mat or polymeric cellular material substrate are also enclosed. The use of neoprene la­ tices and of fillers having a specific gravity of 3 or more, for ex­ ample barytes, is desirable and the preferred substrate is com­ pressed or uncompressed glass fibre. The composition is re­ tained as a coating on the substrate by mechanical adhesion, thereby obviating disadvantages inherent in other forms of adhesion and the material is of particular application in the au­ tomobile industry.

Description: "Improvements in or relating to acoustic damping" This invention relates to improvements in or relating to acoustic damping. More particularly it relates to an acoustic damping structure prepared from a filled polymer latex or emulsion and a filled polymer latex or emulsion composition itself. It has been proposed to incorporate fillers into viscoelastic materials, including neoprene, polyvinylidene chloride and polyvinyl chloride, so as to provide compositions which when adhered to metal or other substrates provide acoustic damping structures. Our British Patent Specification No. 1,305,768 describes some such proposals and the results obtained. We have now found that a more convenient and efficient acoustic damping material suitable for use in, for example, automotive applications and building applications may be obtained if a substrate comprising a fibrous mat e.g. of cotton or felt or glass fibre or a polymeric cellular material e.g. a foam, is coated with a heavily filled polymer latex or emulsion and then dried, thereby avoiding the need to adhere a sheet composition as described in British Patent Specification No. 1,305,768 which operation is complicated for adhesion to a complex moulded body. The substrate i.e. coated mat or cellular material may be provided in a variety of shapes and sizes to suit the requirements of the user, for example on building or automobile body panels. Such coated substratesmay also, in certain circumstances, be themselves mouldable which is a further advantage. Accordingly, we provide an acoustic damping material comprising a fibrous mat or polymeric cellular material coated with composition selected from elastomeric and plasticised plastomeric latices or emulsions of styrenebutadiene rubbers, neoprene, polyvinyl chloride, or ethylene -vinylace tate copolymers or a mixture of two or more thereof, and dried, the composition containing a filler having a specific gravity of at least 2.5 and a particle size of from 1 to 200 microns, the amount of filler being effective to provide from 60 to 85% total solids by weight of wet composition prior to drying, together with an amount of an anionic or non-ionic surfactant effective to stabilise the rubber, neoprene, polyvinyl chloride or ethylene-vinylacetate copolymer. The term "neoprene" is generally understood in the art to cover both chloroprene homopolymers and copolymers obtained by the copolymerisation of chloroprene with minor amounts of dichloro-1,3-butadiene and/or methacrylic acid. If methacrylic acid is employed it will desirably provide from 1 to 3% by weight of carboxyl groups in the copolyme; Ethylene-vinylacetate copolymers include copolymers containing amounts of a third monomer, for example vinyl chloride. Styrene-butadiene rubbers may optionally contain a minor proportion of a carboxylic acid group-containing monomer, such as methacrylic acid, thus providing the so-called carboxylated SBR. We also provide a method for the preparation of an acoustic damping material which comprises coating the fibrous mat or polymeric cellular material with a filled latex or emulsion composition selected from elastomeric andplastcised plastomeric latices of styrene-butadiene rubber, neoprene, polyvinyl chloride or ethylenevinylacetate copolymers or a mixture of two or more thereof, the composition being filled with a filler having a specific gravity of at least 2.5 and a particle size of from 1 to 200 microns, the amount of filler being effective to provide from 60 to 85% total solids by weight of wet composition prior to drying, together with an amount of an anionic or non-ionic surfactant effective to stabilise the rubber, neoprene, polyvinyl chloride, or ethylene-vinylacetate copolymer and then drying the coated fibrous mat or polymeric cellular material. We further provide a composition comprising a latex or emulsion selected from elastomeric and plasticised plastomeric latices or emulsions of. styrene- butadiene rubber, neoprene, polyvinyl chloride, or ethylene-vinylacetate copolymer or a mixture of two or more thereof, containing a filler having a specific gravity of at least 2.5 and a particle size of from 1 to 200 microns, the amount of filler being effective to provide from 60 to 85% total solids by weight of wet composition prior to drying, together with an amount of an anionic or non-ionic surfactant effective to stabilise the rubber, neoprene, polyvinyl chloride or ethylene vinylacetate copolymer. It is preferred to employ a neoprene latex composition in this invention. Neoprene itself is generally to be preferred for the resistance it provides to heat, oil and flame, all of which are found in an automotive environment. The neoprene latex itself will desirably be one of the latices currently available and which generally contain between 45 and 60% by weight of solids, though this is not critical. The latex will desirably comprise a sol polymer or low or medium gel polymer. Such polymers are well-knownsee for example "Neoprene Latex", Internat. Edn. by J.C. Carl of E.I. Du Pont de Nemours and Company (1962). Such polymers generally provide a higher wet gel strength which tends to reduce the tendency for the filled polymer coating to crack when it is ultimately dried. Minor fissures in the surface of the dried polymer coating are not considered to be significant from the point of view of acoustic properties though it is preferred to avoid them if possible. The filler will desirably be an inert inorganic material, advantageously having a specific gravity of 3 or more, and preferably of more than 4. Some particularly preferred fillers have a specific gravity of about 4.5. Suitable heavy fillers of this type include ilmenite or other titanium dioxide-based ores, iron oxide and iron pyrites but the most preferred filler is barytes. However, it may also be desirable in the interests of economy to use a lighter filler, e.g. one having a specific gravity of between 2.5 and 3.0 such as slate dust. Although this would necessitate increasing the thickness of the acoustic coating, it might still prove economical in view of having, for example, 60% of the specific gravity of barytes at 30% of the cost. It is preferred to use a filler of average particle size between 1 and 150 microns, most desirably from 75 to 100 microns. For reasons of economy, it is clearly preferred to employ the maximum amount of filler compatible with the minimum amount of polymer latex or emulsion. The amount of filler used and the solids content of the final composition are principally determined by the particle size of the filler employed,and the nature of the polymer. In general, it is preferred that the amount of filler be sufficient to provide from 500 to 1500 parts thereof per 100 parts of dry rubber or other polymer in the polymer product The filler will -J,:-all-y be added to the composition in dry form though it may be desirable under certain circurastances to add it in the form of an aqueous dispersion or slurry. Care should always be exercised that where fillers are employed from a crude mineral source, they do not give rise to any reaction in the presence of water which would affect the stability of the latex or emulsion. Typical of such reaction would be the presence of soluble polyvalent metal ions or.an acidic pH reaction. Such problems will be readily apparent to those skilled in the art. The surfactant is employed to stabilise the latex or emulsion and assist in avoiding adverse reaction of it with the filler. It also assists in providing the composition with adequate mechanical stability during the coating process. The surfactant employed must generally be anionic or non-ionic. Cationic surfactants are unsuitable for use with anionic latices of the type employed in this invention. The surfactant will most desirably be a non-ionic surfactant and will preferably be a polyethylene oxide alkyl phenol condensate containing, for example, from 10 to 50 ethylene oxide units. Particularly suitable non-ionic surfactants include polyethylene oxide nonyl phenol condensates such as Arkopal N 230, obtainable from Farbwerke Hoechst A.G. Other suitable non-ionic surfactants include Synperonic NP 20 available from ICI Ltd. or Ethylan HA available from Lankro. vHowevere anionic surfactants may be employed in order to achieve specific effects, such as enhanced mechanical stability such as obtained when using sodium alkyl sulphates e.g. sodium lauryl sulphate, or in facilitating the dispersion of dry filler in the latex or emulsion, as is achieved using a sodium alkyl sulphosuccinate. Such surfactants will generally be used in conjunction with a non-ionic surfactant. The amount of surfactant employed will be in proportion to the quantity of filler employed. There is no real restriction on the amount of surfactant that may be employed provided stabilisation of the polymer occurs. Although amounts of total surfactant of up to 10 parts per hundred parts of dry rubber or other polymer in the final product may be employed, the amount of total surfactant will in general vary between 1.5 and 5 parts per hundred parts of dry rubber or other polymer in the final product. The latex or emulsion composition will generally also contain other components which are conventional in the compounding of latices or emulsions of the particular polymer concerned. Such other components are well-known in the art, and are generally added in the form of aqueous dispersions or emulsions. Thus, for example, a neoprene latex will generally also contain an acid acceptor such as zinc oxide in an amount of 5 to 15 parts parts per hundred of dry rubber or other polymers and an antioxidant such as a substituted or hindered phenol e.g. alkylated phenols or bisphenols or aromatic amine condensation products e.g. Antioxidant 2246 as obtainable from Cyanamid of Great Britain Limited and present in from 1 to 4 parts per hundredparts of dry rubber or other polymer. Auxiliary stabilisers such as potassium or ammonium caseinate may be employed in neoprene latices particularly for mechanical stability and as an agent to minimise caking of the composition and may be present in from 0.5 to 2 parts per hundred parts of dry rubber or other polymer. A thickener may be present in ordér to achieve a viscosity which will minimise the sedimenting of high density fillers and also render the latex or emulsion suitable for the method of application to the substrate selected, the thickener being either cellulosic e.g. methylcellulose, or a natural gum e.g. guar gum, or a polyacrylate. Ingredients may be added to assist in the dispersion of dry fillers, e.g. Calgon T (sodium hexametaphosphate) available from Albright and Wilson). Flame-retardants are, for example, sometimes used when compounding styrene-butadiene rubbers. These and many other additives appropriate in the compounding of the particular polymer being employed may be included without any adverse effects. Water may be added to the composition as desired to alter the final solids content to a suitable level within the 60 to 85% by weight solids required, preferably to a level of from 75 to 85% by weight. The amount of water added will clearly depend on the solids content of the latex used and on the amount of any water, if any, that has been added with any of the other ingredients of the composition. It may, for example, have been desirable to add the zinc oxide or filler in the form of an aqueous slurry. The substrate when in the form of a fibrous mat will most desirably be a non-woven mat of glass fibre. This may be coated when in the form of a resin-bonded glass fibre panel or mat or may be rather more loose in the form of glass fibre batting. The glass fibre will generally having a density of from 0.02g/cm3 for lightly compacted material up to 0.1 g/cm3 for compressed material though these ranges are not critical. We have found the coating of compressed material to be of greater value in use as acoustic material since the composite provides a sprung mass. The fibrous mat may also be non-woven in the form of a cotton or other felt, or woven in the form of a natural or synthetic fabric such as could be used in laminated constructiön. The. substrate when in the form of a polymeric cellular material may be one of many types of foam and may be for example, à polyurethane foam or reconstituted polyurethane foam. The fibrous mat or polymeric cellular material will desirably be coated so as to provide a coating of from 0.15 to 0.90 g/cm2,more preferably about 0.30 to 0.60g/cm2 of material. Ingredients designed to promote accelerated gelling of the polymer may be added shortly before or during the coating process. These include delayed action gelling agents, e.g. silicofluorides, or heat sensitisers such as ammonium salts or polyvinylmethylethers. A full description of ingredients suitable for compounding with latices or emulsions in order to enhance their properties is to be found in the above-mentioned reference "Neoprene Latex". In addition bitumen emulsions may also be used for compounding in certain latices or emulsions in the interests of economy e.g. in synthetic rubber latices. The composition may be compounded for application to the substrate by a variety of means, the viscosity of the composition varying according to. the means chosen. Thus, if the substrate is to be flow-coated with the composition a viscosity of from 5000 to 20000 mPa.s should be attained For application by spraying, the composition should have a viscosity of from 1000 to 5000 mPa.s. If the composition is to be spread over the substrate, a viscosity of at leas 20000 mPa.s or even higher may be suitable. Whichever form of application is selected, it is clearly envisaged that the porosity of the substrate will enable sufficient impregnation of it by the composition so that the composition will be retained both on the substrate and within a portion thereof by a mechanical adhesion. This obviates the need f6r any chemical adhesion and is a further advantage of the process. It is intended that the composition is applied as a coating on the substrate and impregnatibn only occurs to the extent of allowing mechanical adhesion or keying at the surface of the substrate. The acoustic material may be attached to whichever article it is intended for by generally conventional means Thus, for automotive use, the material may be clipped to O2 adhered to the metallic backing member e.g. bulkhead or panel where it is desired to create the damping effect. As has been mentioned, some materials of the invention may themselves be moulded after they have been dried and this allows coverage of awkwardly shaped surfaces. The invention will now be more particularly described in the following Examples which should not be construed as limiting: Example 1. The following ingredients were mixed together in a vessel provided with mechanical agitation. The thickener is premixed with a small portion of the mixture and then added to the bulk under conditions of high shear in order to achieve a uniform consistency. Parts by Equivalent to parts weight by weight when dry (wet) ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ Neoprene latex NPG 178 100 4328 (medium gel polymer approx. 56% by weight solids) Zinc Oxide 20 10 Ammonium caseinate 10 1 Antioxidant 2246 9 3 Arkopal N-230 surfactant 16 1.6 (an ethoxylated nonyl phenol with an average of 23 ethoxy nits) Water 37 g (to provide 80% solids when wet) Barytes 200 Mesh 500 (about 83% pure, S.G. about 4.05) Texigel 23-005 3 (a sodium polyacrylate gel available from Scott Bader) After mixing, the viscosity of the composition was about 1300G mPa.s as measured on a Brookfield LVF instrument Spindle No.4 at 12 r.p.m. The composition was applied to a compressed resin-bonded glass fibre mat to provide a coating weight of 0.36 g/cm2. The coated product was then passed into an oven for drying at 150 0C for about 30 minutes depending on the oven efficiency to provide an acoustic damping material. Example 2. The procedure of Example 1 was followed using the following ingredients Parts by Equivalent to parts weight by weight when dry (wet) ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ Neoprene latex NPG 4328 178 100 Zinc Oxide . 20 10 Ammonium caseinate 10 1 Antioxidant 2246 9 3 Arkopal N-230 surfactant 30 3 Water 153 g (to provide 80% solids when z when wet) Barytes 200 Mesh 1000 (about 83% pure, S.G. about 4.05) Texigel 23-005 3 Examples 3 and 4. The following compositions were prepared using the conditions described in Example 1. Example 3 4 (equivalent to parts by weight when dry) Neoprene latex 654 100 (medium/low gel polymer, approx. 59% by weight solids) Neoprene latex 635 - 100 (low gel polymer, approx. 60% by weight solids) Zinc oxide 7.5 7.5 Antioxidant 2246 2 2 Carbon black 3 3 Ammonium caseinate 2 2 Sodium dioctyl sulpho- 1.5 1.5 succinate Arkopal N-230 surfactant 1.5 1.5 Water to give finished solids content of 81% Crude ilmenite 100 mesh 750 750 (S.G.4 .1) Texigel 23-005 4 4 After compounding, the compositions were spread onto a fibreglass mat to give a coating weight of 0.5 g/cm2 and dried at 120 0C without cracking. It was possible to place sheets of these composites into a mould, such as of a car bulkhead and by compressing them for a period of five minutes at 150 C to form them into the appropriate shape. Example 5. The following constituents were mixed under the conditions of Example 1. Equivalent z Equivalent to parts by weight when dry Neoprene latex 102 100 (low gel non-ionic latex, approx. 46% by weight solids) Zinc oxide 5 Cymel 301 30 (a grade of hexamethoxymelamine from Cyanamid (UK) Ltd.) Wingstay L 2 (butylated reaction product of p-cresol and dicylopentadiene from Goodyear) Butyl carbitol 5 Propylene glycol 2 Barytes 200 mesh 700 (about 83% purity, S.G. about 4.05) Carbon black 3 Water to give finished solids content of 80% The zinc oxide used in this Example was prepared as an aqueous dispersion by ball-milling in sodium hydroxide solution - the dispersion comprises Zinc oxide 81 parts by weight, sodium hydroxide 40 parts by weight, water 360 parts by weight and polyvinyl alcohol 4 parts by weight. Example 6. The following constituents were mixed under the conditions of Example 1. Equivalent to parts by weight when dry Mowilith 122 100 (a vinyl acetate/ethylene/ vinyl chloride terpolymer emulsion from Hoechst A.G.) Triton X-100 2 Water to give finished solids - - content of 80% Barytes 200 mesh 700 (approx. 83% pure, S.G. about 4.05) Carbon black 3 Texigel 23-005 3 The composition may be applied to a substrate in the manner previously disclosed. Two evaluations of the acoustic performance of a latex/ substrate system 6f this invention have been made. 1. Transmission loss by Apamat Tester. An Apamat machine (as manufactured by Interkeller, Zurich, Switzerland and referred to, inter alia, in French Patent Publication No. 2,108,435) was used to test the increase in transmission loss over a range of frequencies provided by neoprene latex composition coatings of 0.326 and 0.544 g/cm2 on glass fibre boards. The neoprenecoated glass fibre boards may be obtained by a process as described in Example 1 except that for the tests carried out, the composition contained 750 parts by weight when dry of barytes per 100 parts of neoprene. The increase in loss is that increase over an uncoated glass fibre board. The thickness of the coating is approx. 2mm. The results are shown in Table 1. Table 1. terial Total Total Thickness Transmission Loss (dB) wt including g/cm2 coating Frequency (Hz) 100 200 300 400 500 600 700 800 900 1K 2K 3K 4K 5K 6K 7K 8K 9K 10K Light Neoprene 0.366 #1.27cm 7 6 6 3 4 4 6 8 9 10 12 16 17 18 19 19 19 19 18 Coating (0.326g/cm2) on Fibreglass Crown S200 (0.0396g/cm2) Light Neoprene 0.385 #1.27cm 8 6 6 2 3 3 4 7 7 9 11 15 17 18 21 22 22 22 22 Coating 2 (0.326g/cm ) on Fibreglass Crown S300 (0.0593g/cm2) Heavy Neoprene 0.583 #1.27cm 8 7 7 5 6 6 9 12 13 14 17 20 22 22 22 22 22 21 20 Coating (0.543g/cm2) on Fibreglass Crown S200 (0.0396g/cm2) Heavy Neoprene 0.603 #1.27cm 8 5 6 5 6 8 10 12 12 12 15 17 21 21 22 22 22 22 22 Coating (0.543g/cm2) on Fibreglass Crown S300 (0.0593g/cm2) 2. Transmission loss measured according to BS2750 Losses were measured under laboratory conditions at Sound Research Limited generally in accordance with BS2750 - "Recommendations for field and laboratory measurement of airborne and impact sound transmission in buildings". The loss in decibels at different frequencies is as follows, for coatings on approx. 1.27cm thick glass fibre, as compared to uncoated glass fibre. Loss (dB) Frequency (Hz) 63 125 250 500 1K 2K 4K 8K 1. Coating wt2 13 11 12 15 19.5 24.5 29.5 32.5 0.326 g/cm 2. Coating wt2 11 13.5 17.5 19.5 24 28 32.5 35 - 0538, g/cm2

Claims: Claims 1. An acoustic damping material comprising a fibrous mat or polymeric cellular material coated with a composition selected from elastomeric and plasticised plastomeric latices or emulsions of styrenebutadiene rubbers, neoprene, polyvinyl chloride, or ethylene-vinylacetate copolymers, or a mixture of one or more thereof,and dried,the composition containing a filler having a specific gravity of at least 2.5 and a particle size of from 1 to 200 microns, the amount of filler being effective to provide from 60 to 85% total solids by weight of wet composition prior to drying, together with an amount of an anoinic or non-ionic surfactant effective to stabilise the rubber, neoprene, polyvinyl chloride or ethylene-vinylacetate copolymer. 2. A material as claimed in claim 1 wherein the latex or emulsion is a neoprenè latex. 3. A material as claimed in claim 1 or claim 2 wherein the filler has a specific gravity of 3 or more. 4. A material as claimed in any of claims 1 to 3 wherein the filler has an avwrage particle size of from 75 to 100 microns 5. A material as claimed in any of claims 1 to 4 wherein the filler is barytes. 6. A material as claimed in any of claims 1 to 5 wherein the amount of filler provides from 500 to 1500 parts thereof per hundred parts dry rubber or other polymer in dried polymer product. 7. A material as claimed in any of claims 1 to 6 wherein the surfactant is a non-ionic surfactant being a polyethylene oxide alkyl phenol condensate containing 10 to 50 ethylene oxide units and is present in from 1.5 to 5 parts per hundred parts of dry rubber or other rolvmer in the final product. 8. A material as claimed in any of claims 1 to 7 wherein the fibrous mat is glass fibre or is cotton felt. 9. A material as claimed in any of claims 1 to 8 wherein the fibrous mat or polymeric cellular material is coated to provide a coating of from 0.30 to 0.60 g/cm2 of material. 10. A material as claimed in claim 1 substantially as hereinbefore described. 11. A material as claimed in claim 1 substantially as hereinbefore described with reference to the Examples. 12. A method for the preparation of an acoustic damping material which comprises coating the fibrous or polymeric cellular material with a filled latex or emulsion composition selected from elastomeric and plasticised plastomeric latices of styrene-butadiene rubbers, neoprene, polyvinyl chloride or ethylene-vinylacetate copolymers or a mixture of two or more thereof, the composition being filled with a filler having a specific gravity of at least 2.5 and a particle size of from 1 to 200 microns, the amount of filler being effective to provide from 60 to 85% total solids by weight of wet composition prior to drying, together with an amount of an anionic or nonionic surfactant effective to stabilise the rubber, neoprene, polyvinyl chloride, or ethylene-vinylacetate copolymer and then drying the coated fibrous mat or polymeric cellular material. 13. A method as claimed in claim 12 wherein the viscosity of the composition prior to coating is effective to enable sufficient impregnation of the fibrous mat or cellular polymeric material by the composition whereby the composition is retained both on the fibrous mat or cellular polymeric material and within a portion thereof by mechanical adhesion. 14. A method as claimed in claim 12 substantially as hereinbefore described. 15. A method as claimed in claim 12 substantially as hereinbefore described with reference to the Examples. 16. A latex composition comprising a latex or emulsion selected from elastomeric and plasticised plastomeric latices or emulsions of styrene-butadiene rubbers, neoprene, polyvinyl chloride, or ethylene-vinylacetate copolymers or a mixture of two or more thereof containing a filler having a specific gravity of at least 2.5 and a particle size of from 1.to 200 microns, the amount of filler being effective to provide from 60 to 85% total solids by weight of the wet composition ;together with an amount of an anionic or non-ionic surfactant effective to stabilise the rubber, neoprene, polyvinyl chloride, or ethylene-vinylacetate copolymer. 17. A composition as claimed in claim 16 substantially as hereinbefore described. 18. A composition as claimed in claim 16 substantially as hereinbefore described with reference to the Examples.

Inventors: COE, DAVID GORDON, PRICE, DAVID WHARTON RUSSELL
Applicants: E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1980
Main classification: E04B1
IPC codes: C08K3, E04B1, C04B38, C08L21, C08J9, G10K11, D06N7