WO1988000221A1

WO1988000221A1 - Sound deadening material

Info

Publication number: WO1988000221A1
Application number: PCT/AU1987/000184
Authority: WO
Inventors: David Morris Caithness; Graeme Matthew Ball
Original assignee: Sound Deadeners Pty. Ltd.
Priority date: 1986-06-27
Filing date: 1987-06-26
Publication date: 1988-01-14

Abstract

A sound deadening material for use in the automotive and other manufacturing industries comprising bitumen (in proportion from 5 to 25 % by weight), a filler (in proportion from (10 to 80 % by weight), aluminium trihydrate (in proportion from 0 to 25 % by weight), stearic acid (in proportion from 0.5 to 3 % by weight), nitrile rubber or polychloroprene (in proportion from 1 to 10 % by weight), terpene resin or other tackifier (in proportion from 1 to 10 % by weight), and a coupling agent (in proportion from 0.01 to 2 % by weight).

Description

SOUND DEADENING MATERIAL

This invention relates to sound deadening material including sound deadening material of the bitumen rubber type in sheet or pad form. Sound deadening material of this type is most often adhered to metal panels by simply heating the two together, with the pad lying on top of the panel and the self-adhesive properties of the sound deadener at elevated temperatures creating a good bond between the two surfaces. Alternatively, an adhesive may be applied to either surface to enable a bond to be made at room temperature. In either case the bond needs to have good tenacity both to obtain good sound attenuat¬ ion and to obviate the probability of the sound dead- ener falling off with time and vibration. A necessary requirement for sound deadening material is that it have suitable adhesion properties.

Materials used for sound deadening in large commercial quantities in Australia by the automotive industry and by dishwasher manufacturers, for example, have a sound decay rate, measured by the Geiger Thick Plate method, under Australian standard K 154.10, of about 17 db per second at 21°C, for 2.5 mm thickness. In Australian Patent Application No. 14241/86 a decay rate of 9 db per second for 3.2 mm thick material is mentioned.

It is an object of the invention to provide sound deadening material with higher sound decay rates than those presently in use. Sound deadening material can also be assessed on the basis of rate of sound decay in decibels per second per 100 g of sound deadener applied under the abovementioned test method. In many respects this may be considered a more legitimate method of rating, as the weight of sound deadener applied and its efficiency are thus both taken into account. Under this method, Australian industry currently employs sound deadening materials having a rating of 1.6 to 1.7 db/sec/100 g at 21°C. It is an object of the present invention to provide sound deadening materials having ratings higher than those previously mentioned when tested under the same conditions.

Because of the use of relatively thin steel by industries such as those referred to above, there would be an unacceptable level of sound transmission in the absence of the use of sound deadening material. In the automotive industry, weight is a very important consideration. Hence a sound deadening material which has greater efficiency is clearly beneficial. In the manufacture of dishwashers, greater sound attenuation is always being sought because dishwashers are house¬ hold products and noisy machines will not be tolerated. However, frequently there are space limitations for the sound deadening material and, further, greater thicknesses of sound deadening material generally cost more money. Material formulated according to the invention enables a lesser thickness of sound deaden¬ ing material to be used to achieve the same level of performance. This leads to a saving of money. Alter- natively, the same thickness of sound deadening mater¬ ial can be used. This results in a similar cost but with a considerably improved level of sound attenuat¬ ion.

A means of obtaining greater efficiency in sound deadening is through improvements to the formul¬ ation of the sound deadener. Specifically, these improvements relate to the use of agents which assist to give bonding, coupling and wetting (compatibilising) between the non-binder ingredients (mineral fillers or reinforcements, flame retardants etc.) and the binder ingredients (for example bitumen, rubber, hydrocarbon resins, polymers, etc.) . As well as giving improved properties per se such as greater impact strength for the volume percentage of filler employed the compat- ibilising effect of these agents yields a material with a lower viscosity during sheet manufacture. This enables the use of a higher volume percentage of fillers, without causing manufacturing problems or a too easily breakable product. The use of a higher volume percentage of fillers gives greater sound dead¬ ening properties, but without the compatibilising agents at such a high volume percentage of fillers, the sheets tend to be very stiff and brittle (and therefore hard to handle), difficult to manufacture by the known methods, and tend to exhibit inferior prop¬ erties in bonding to steel when suitably heated.

A test which is applied to a sound deadening material is- known as the* "hot slump" test. This con¬ sists of a strip of sound deadening material bridging a groove of 25 mm radius in a steel -substrate and the whole being heated for 30 minutes at 160°C. After cooling, no less than 95% of the area of the sound deadening material must be firmly adhered to the steel. This method tests both the adhesion to steel and whether the material will satisfactorily "slump" to conform to the radius, without a rupture, under its own weight. Sound deadening material made according to the present invention passes such a test. Different automotive manufacturers have varying requirements for this test, particularly regarding the fusing cycle, but each demands a high degree of adhesion and the ability to slump and to conform to the shape of the steel sub¬ strate. Furthermore, it is important that all of the ingredients in the formulation must be in balance with each other to yield the optimum in properties. According to the present invention, a signif¬ icant development over the prior art is the use of agents to make the fillers used in the sound deaden¬ ing formulations more compatible with the binders. This permits the use of higher volume fractions of filler while still providing a formulation which may be processed into sheet and which will conform and adhere to a metal surface when suitably heated. The increase in the volume fraction of filler leads to enhanced sound deadening properties, which are believed to be of an order henceforth unknown for such sound deadening materials. Without the presence of compatibilising agents sound deadening materials containing high volume fractions of filler would be extremely difficult to process by the known methods and would be very fragile and difficult to use. Furthermore, the bond strength to steel would be very poor. The use of compatibilising agents, and their effects, has not been disclosed in any of the prior art known to the applicant. Such prior art includes Australian Patent Applications 22604/77, 14241/76, 57264/86, 43088/79 and 26186/77.

Australian Patent Application No. 22604/77 teaches the use of asbestos and a particulate filler having a specific gravity of at least 3 in noise reducing materials. It Is not a feature of the present invention that asbestos be used in sound deadening materials nor has it been found advantag¬ eous to use particulate fillers having specific gravity of greater than 3.

Australian Patent Application No. 14241/76 teaches the use of ethylene-vinyl acetate copolymer and the use of hydrocarbon rubber combined with bitumen In specified proportions in the manufacture of sound deadening compositions. Sound deadening materials produced in accordance with the present invention do not contain ethylene-vinyl acetate copolymer or butadiene styrene rubber and contain different proportions of rubber to bitumen. Further- more sound deadening materials produced in accordance with the said invention have been found to exhibit sound decay rates considerably in excess of that referred to in Australian Patent Application No. 14241/76. Australian Patent Application No. 57264/86 teaches the use of a powder form binder concentrate containing silane, with the apparent object of preparing a concentrate containing high levels of silane. The concentrate may then be used to rejuven- ate used bitumen. Further, this application teaches the use of carriers having a large surface area, such as a synthetic silica or a zeolite.

Australian Patent Application No. 43088/79 teaches an elastomeric material employing fillers having specific gravity between 4 and 10. Sound deadening material produced according to the present invention is not normally termed elastomeric nor does it contain fillers of such high specific gravity. Australian Patent Application No. 26186/77 teaches the use of vulcanized vegetable oil combined with bitumen and filler to make sound deadening mater¬ ial. Vegetable oil is not used in sound deadening material made according to the present invention.

It has been found that a combination of silanes and stearic acid have proved to be improved- compatib¬ ilising agents. Whilst silanes are known and used in the plastics industry, their use in bituminous rubber sheets has not been known to date. Sound deadening material made according to the present invention passes the aforementioned hot slump test, but the same formula without coupling agent or stearic acid has been found to fail on both grounds of the test. It has been found that stearic acid in a small prop¬ ortion in combination with the other ingredients, contributes, (apparently, synerglsticall ) to the ability of sound deadening material made according to the present invention to pass both the hot slump test and the adhesion test. Stearic acid also plays an important role in the processing of the sound dead- ening material into sheet as it contributes to the compatibilising In lowering the viscosity of the material and generally making it a more readily processable product. Without the presence of stearic acid in combination with a coupling agent in the sound deadening material, such a formulation would be extremely difficult to process by the known methods.

It has been found possible, by using the invention, to produce sound deadening materials with a sound decay rate of more than 27 db per second for sheets of 2.5 mm thickness, or a rate of sound decay of 2.1 to 2.4 db/sec/100 g at 21°C.

The invention in one^' form consists of a sound deadening material composition containing, inter alia, bitumen, rubber, filler, tackifier, anti-oxidants (optionally), flame retardants (optionally) , silane and stearic acid. In a more specific form the inven¬ tion consists of a chemical composition comprising a mixture of bitumen (in proportion from 5 to 25% by weight) , a filler (in proportion from 10 to 80% by weight), aluminium trihydrate (also known as aluminium trioxide) (in proportion from 0 to 25% by weight) , stearic acid (in proportion from 0.5 to 3% by weight) , acrylonitrile-butadiene synthetic rubber, or polychloro¬ prene (in proportion from 1 to 10% by weight) , a terpene resin or other tackifier (in proportion from 1 to 10% by weight) and a coupling agent (in proportion from 0.01 to 2% by weight) .

The bitumen employed may be straight-run or blown. It is preferred that the bitumen be a mixture of Esso grades 190/18 and 280/17, in proportion from 1:2 to 4:1 or that it be Esso grade 190/18 by itself, depending upon the particular application to which the material is to be put. However, other suppliers' grades of bitumen are equally applicable. It is preferred that the proportion of bitumen be between 10 and 20% by weight.

Filler, preferably in the form of calcium carbonate, may be from any sour-ce. It is preferred that it is in the range of 1 to 100 micron average particle size. Other fillers which may be used in the invention include talc, barytes, diatomaceous earth or clays, depending upon the particular applic¬ ation to which the material is to be put and upon the economics involved. Currently, calcium carbonate is the preferred filler to be used in accordance- with the invention. In sound deadening material composit¬ ions prepared according to the present invention it is preferred that the proportion of filler be between 40 and 80% by weight. The preferred rubber employed is acrylonitrile- butadiene synthetic rubber (also known as nitrile rubber or NBR) preferably containing between 33 and 50% acrylonitrile . Alternatively, polychloroprene may be used. It is preferred that the proportion of nitrile rubber be between 2 and 5% by weight.

Aluminium trihydrate may be used to provide flame retardancy to the product where required, for example, in dishwashing machines. When it is incor¬ porated into the formulation it is preferred that the proportion of aluminium trihydrate be between 10 and 25% by weight.

The tackifier is normally a hydrocarbon resin which gives hot tack, but is not tacky when cold. Preferred grades include those as sold in Australia under the following designations:

Kolon 90, Wingtack 10 or 95, Escorez 217 or Escorez 2101. The preferred proportion of tackifier is between 1 and 5% by weight of the overall composition. An anti-oxidant may be used to lessen the hardening caused by oxidation during processing and ageing, which could lead to embrittlement. It is not essential for all applications but it has been found that properties of the resultant formulation are improved by its presence. A preferred anti-oxidant is Ciba-Geigy Irganox 565 combined with Irgastab PS802 in a ratio of 4:1. It is preferred that the proportion of anti-oxidant, if used, is between 0.1 and 1% by weight of the overall composition. The coupling agent is preferably a silane or a titanate. Coupling refers to the obtaining of some bonding between the filler and the binder. Currently employed in one form of the invention is either the silane sold under the designation Dow Corning Z6044 or a titanate sold under the designation Ken React KR TTS. Other silanes are equally applicable, as too are the wetting agents of the ricinoleate family. The combination of such coupling agents with stearic acid gives an enhancement of the compatibilising effect, particularly shown in the improvement In the bond strength to steel, when hot bonded and In improved hot draping properties. It has been found that the coupling agent Is best applied by diluting it with methanol In the case of a silane, or mineral oil in the case of a titanate, and spraying the resultant solution or mixture onto the filler, whilst rapidly agitating that filler, for example, in a high shear mixture. In this manner a very small quantity of coupling agent can be coated evenly over the filler. The preferred proportion of coupling agent is between 0.01 and 1% by weight.

In addition, approximately 1% by weight of liquid polyisobutylene may be included in the sound deadening material compositions produced in accordance with the present invention to soften or plasticize the material and impart to it a greater degree of toughness. How¬ ever, this result would be at the expense of the acoustic properties.

In a specifically preferred form the invention consists of a sound deadening material composition comprising a mixture of bitumen (in proportion from 10 to 20% by weight) , a filler (optionally calcium carbonate) (in proportion from 40 to 80% by weight) , aluminium trihydrate ( in proportion from 0 to 25% by weight) , acrylonitrile-butadiene rubber (in proportion from 1 to 10% by weight) , stearic acid (in proportion from 0.5 to 3% by weight) , terpene resin (in proportion from 1 to 5% by weight) , and a coupling agent (in prop¬ ortion from 0.01 to 1% by weight) . A non-limiting example of the invention consists of a sound deadening material composition comprising a mixture of bitumen, filler being a calcium carbonate, nitrile rubber, stearic acid, terpene resin, aluminium trihydrate and a coupling agent in the following res- pective proportions by weight:

15.7%: 62.8%: 2.51%: 1.05%: 2.20%: 15.7%: 0.05%.

In this instance, the coupling agent may be either a silane, a titanate, a ricinoleate or any other known agent. Other formulation examples are as follows: No. 1

(a) (b) bitumen 14-20 18.0 14.3 calcium carbonate 57-65 60.0 63.5 aluminium trihydrate 12-17 15.0 15-9 acrylonitrile- butadiene rubber 2.5-4 3.5 2.8 stearic acid 0.5-1.5 1.0 1.0 tackifier 1-3 2.0 2.0 silane or titanate 0.01-0.5 0.1 0.1 anti-oxidant 0-0.5 0.4 0.4

(All percentages are "by weight") . Formulation 1 contains no flame-retardant

(aluminium trihydrate) and is intended for use in the automotive industry.

Formulation 2(a) has been found to be softer than formulation 2(b) and has lower sound deadening proper- ties. Whilst formulation 2(b) is harder and has significantly better sound deadening properties, it is more brittle than formulation 2(a) . More care in handling Is required, therefore. However, formulation 2(b) can give better results If that care is taken. This invention also makes use of the known method of applying sound deadening materials to sub¬ strates. In a specifically preferred form, the invention relates to a method of applying sound dead¬ ening material to a substrate, which method comprises intimately mixing the components of a sound deadening material as aforesaid, forming the resultant mixture into a sheet or sheets, cutting the sheets into shapes to fit the substrate as required, and applying the shaped sound deadening material to the substrate either by means of its self-adhesive properties when hot, by means of an adhesived applied to either surface or by means of heating the substrate and sound deadening material together in an oven.

It is to be understood that various additions, alterations and modifications may be introduced into the foregoing without departing from the ambit of the invention.

Claims

The claims defining the invention are -as follows:

1. A sound deadening material composition comprising bitumen (in proportion from 5 to 25% by weight) , a filler (in proportion from 10 to 80% by weight), aluminium trihydrate (in proportion from 0 to 25% by weight), stearic acid (in proportion from 0.5 to 3% by weight), nitrile rubber or polychloroprene (in proportion from 1 to 10% by weight), terpene resin or other tackifier (in proportion from 1 to 10% by weight) , and a coupling agent (in proportion from 0.01 to 2% by weight) .

2. A composition as claimed in claim 1 wherein the coupling agent is either a silane or a titanate.

3. A composition as claimed in either claim 1 or claim 2 wherein the proportion of coupling agent is between 0.01 and 1% by weight.

4. A composition as claimed in any one of claims 1 to 3 wherein the filler is calcium carbonate.

5. A composition as claimed in any one of claims 1 to 4 wherein the proportion of bitumen is between 10 and 20% by weight.

6. A composition as claimed in any one of claims

1 to 5 wherein the proportion of filler is between -~- 40 and 80% by weight.

7. A composition as claimed in any one of claims

1 to 6 wherein the proportion of aluminium trihydrate is between 10 and 25% by weight.

8. A composition as claimed in any one of claims 1 to 7 wherein the proportion of nitrile rubber is between 2 and 5% by weight.

9. A composition as claimed in any one of claims 1 to 8 wherein the proportion of terpene resin or other tackifier is between 1 and 5% by weight.

10. A composition as claimed in any one of claims

1 to 9 wherein the composition also contains an anti- oxidant (in proportion from 0.1 to 1% by weight).

11. A composition as claimed in any one of claims

1 to 10 wherein the composition also contains liquid polyisobutylene in proportion from 0 to 1% by weight.

12. A sound deadening material composition comprising bitumen, calcium carbonate filler, nitrile rubber, stearic acid, terpene resin, aluminium trihydrate and a coupling agent in the following respective proportions by weight:

15.7%: 62.8%: 2.51%: 1.05%: 2.20%: 15.7%: 0.05%.

13. A sound deadening material composition comprising bitumen (in proportion from 15 to 20% by weight) , calcium carbonate (in proportion from 73 to 82% by weight) , acrylonitrile-butadiene rubber (in proportion from 2.5 to 4% by weight) , stearic acid (in proportion from 0.5 to 1.5% by weight) , tackifier (in proportion from 1 to 3% by weight) , coupling agent (in proportion from 0.01 to 0.5% by weight) and anti-oxidant (in proportion from 0 to 0.5% by weight) .

14. A sound deadening material composition comprising bitumen, calcium carbonate, acrylonitrile-butadiene rubber, stearic acid, tackifier, coupling agent, being either silane or titanate, and an anti-oxidant in the following respective proportions by weight:

17.2%: 76.4%: 2.8%: 1.1%: 2.2%: 0.1%: 0.2%.

15. A sound deadening material composition comprising bitumen (in proportion from 14 to 20% by weight) , calcium carbonate (in proportion from 57 to 65% by weight) , aluminium trihydrate (in proportion from 12 to 17% by weight) , acrylonitrile-butadiene rubber (in proportion from 2.5 to 4% by weight), stearic acid (in proportion from 0.5 to 1.5% by weight) , tackifier ( in proportion from 1 to 3% by weight) , coupling agent (in proportion from 0.01 to 0.5% by weight) , and anti- oxidant (in proportion from 0 to 0.5% by weight) .

16. A sound deadening material composition comprising bitumen, calcium carbonate, aluminium trihydrate, acrylonitrile-butadiene rubber, stearic acid, tackifier, silane or titanate, and anti-oxidant in either of the two following sets of respective proportions by weight:

18.0%: 60.0%: 15.0%: 3.5%: 1.0%: 2.0%: 0.1%:

0.4%;

14.3%: 63.5%: 15.9%: 2.8%: 1.0%: 2.0%: 0.1%:

0.4%.

17. A composition as claimed in any one of claims

1 to 16 substantially as hereinbefore described with reference to any one of the formulation examples.

18. A method of applying sound deadening materials to substrates in which a composition as claimed in any one of claims 1 to 17 is formed into a sheet or sheets, which sheets are then cut into shapes to fit the substrate as required, and which sheets are then applied to the substrates either by means of the self- adhesive properties of the composition when hot, b ^ _ means of an adhesive applied to either the substrate surface or the surface of the sound deadening material composition, or by means of heating the substrate and sound deadening material together in an oven.