Sound dampening composition

Feb. 6, 1962

R. H. CUBBERLEY ETAL

3,020,184

SOUND DAMPENING COMPOSITION

Filed Sept. 30, 1955

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3,020,184

Patented Feb. 6, 1962

United States Patent Office

3,020,184

SOUND DAMPENING COMPOSITION

Richard H. Cubberley, Morristown, and Vincent C. Harold, Jr., Lodi, NJ., and Harold J. Zinaman, Brooklyn, N.Y., assignors to The Patent and Licensing Corporation, New York, N.Y., a corporation of Massachusetts Filed Sept. 30, 1955, Ser. No. 537,702

Claims. (CI. 154—44)

The present invention relates to an improved sound dampening material or composition and more particularly to an improved composition of felt or the like, for sound dampening of steel surfaces such as automotive bodies.

Since the introduction of all steel automotive bodies, it has been necessary to treat the steel surfaces .with sound dampening materials to effectively reduce the noise level within the car. The parts of the car which may require sound dampening treatment include the roof, door panels, quarter panels, trunk lids, etc. For many years the automotive industry has generally utilized a product of dry felt saturated with asphalt after forming on a paper machine for the purpose of sound dampening. Certain areas in the car, as for example, the floor and dash require greater sound dampening and these requirements have been made by multiple felt compositions of two, three and four layers which are laminated together by asphalt or mineral stabilized asphalt. These felt compositions are widely used in the industry and exceed the use of any other type material.

The sound dampening or vibration dampening material is formulated so as to possess requisite physical properties to dampen or absorb the vibratory sounds of the metal part with which it is to be used. To that end the sound dampening material generally takes the form of sheets or pads of a bibulous fibrous felt, the felt being partially but substantially uniformly impregnated with bituminous material for the purpose of imparting added mass and strength and other desirable properties thereto.

More specifically illustrative thereof is a fibrous felt which in its raw, unimpregnated state weighs, say, from 11 to 14 pounds per hundred square feet, possesses a kerosene number of approximately 250, a tensile strength of approximately 16 across the grain (one inch strip), a porosity (as measured by a Gurley Densometer) less than 11 and a caliper of approximately 0.080 inch.

Typical of bituminous material with which such a felt may be readily impregnated for the purpose aforesaid, is an asphalt having a softening point of. approximately 70° F.; a viscosity (Saybolt Furol at 210° F.) of approximately 80 seconds; penetration values (needle, 100 grams, 5 seconds) of approximately 160 at 32° F., and approximately 15 to 0° F.; and a flash point (C.O.C.) of above 500° F. .

. Ordinarily, in most instances, the fibrous felt of the type above-illustrated, is partially but uniformly impregnated with a bituminous material such as typified by the one above-described, to a degree such that the bituminous component will constitute approximately 20% to 60% by weight of the impregnated felt. In any case, the thus treated felt, in order to serve efficiently as a dampening material for vibratory metal members, such as the roof or door panels of an automobile body, should exhibit a stiffness (as measured by the Olsen Tester at 75° F. at 0.15 pound added weight) of less than 65 with the grain of the felt, and less than 35 across the grain; a tensile strength (two inch strip) greater than 20 with the grain and at least 10 across the grain; a porosity (measured by the Gurley Densometer) less than 12; a caliper (measured by the Randall Stickney gauge with one pound added and one inch diameter circular foot) of approximately 0.909 inch; and a cold flexibility sufficient to withstand bending around a 1½ inch mandrel at 0° F, without delamination or cracking.

It is an object of the present invention to provide a sound dampening material of felt, or the like, with improved sound dampening.

It is a further object of the present invention to provide an improved sound dampening material of the multilayer type which also utilizes air pockets for sound absorption.

It is a further object of the present invention to provide an improved sound dampening material which also has improved thermal insulation value.

It is a further object of the present invention to provide an improved sound dampening material which is easily manufactured, economical and which provides improved sound dampening and sound absorption as well as thermal insulation.

These and other objects are attained by the present invention which relates to an improved sound dampening material comprising three layers of felt adhered together by spaced parallel rows of adhesive. Preferably, the middle of the three layers in the area between the rows of adhesive contains holes for the passage of air.

The invention may be best understood by reference to a specific embodiment thereof disclosed in the drawings but it will be understood that variations and substitutions may be made within the scope of the claims.

In the drawings:

FIG. 1 is a plan view of the centei· layer of the felt assembly;

FIG. 2 is a perspective view of the three layers of felt in position for assembly;

FIG. 3 is a cross-sectional view of the assembled felt adhered to a steel sheet, and

FIG. 4 is an enlarged cross-sectional view of the assembled felt adhered to a steel sheet.

It will be seen from the drawings that the material comprises essentially three sheets of felt, 10, 11 and 12, adhered together by strips of adhesive, 13. The middle layer of felt contains a plurality of holes, 15—15. The holes are preferably uniformly placed in rows, as indicated in the drawings, so that the strips of adhesive may fall rather uniformly between the rows of holes.

As illustrated at FIGS. 3 and 4, the sound dampening material is adhered to a steel auto body 16, by means of adhesive 17. The use of adhesive strips 13, permits a tufting or festooning, as indicated at FIG. 4, such that air pockets 19 and 20 may be formed connected by a hole 15. It has been found that this tufting or festooning adds very substantially to the value of the material for sound dampening purposes. The incorporation of the thus formed air cavities has resulted in a three- to sevenfold increase in sound dampening value.

As an example of one specific embodiment of the invention, there may be utilized a center sandwich sheet of dry felt weighing 1.48 pounds per square yard and saturated with 45% of its weight with an asphalt flux. The sheet contains rows of holes punched in it as shown at FIG. 1. A backing and facing sheet of dry felt weighing 1.12 pounds per square yard was saturated with 45% of its weight with an asphalt flux. These three pieces of felt were adhered together as a composite by means of longitudinal beads of an asphalt-rubber emulsion adhesive. Upon the application of pressure the beads become the bands of adhesive illustrated in the drawings. As a further specific example the holes 15 may be V/2 in diameter placed about 4 on center with adhesive placed in strips about 4 on center between the rows of holes.

In the use of such dampening felts in the construction of automobiles, the felt is best secured to a surface of the metallic member by adhesive material, desirably

3,020,184 throughout the area of the confronting faces of the felt and the metallic member.

The adhesives most commonly used for this purpose are of the nature of aqueous dispersions of bituminous material, rubber, resin, and the like, and aqueous dispersions of suitable combinations of these, and suitable mixtures of such dispersions.

In the use of these materials for adhering fibrous felt of the character referred to herein, to a surface of a metallic member, it is necessary that the bonding material be of such a character that it may readily be applied to the fibrous felt; that it readily adhere the latter to the surface of the metal part when the two are brought into contact; that it retain an adequate bond therebetween during the subsequent handling of the laminated assembly while the layer of the bonding adhesive is still incompletely set; and that, moreover, when the assembly is subjected to heat, such as prevails in the baking ovens through which the assembly is later passed, for the purpose of baking a paint or enamel applied to the outer surfaces of the metal part, the film of the adhesive will not thereby be deleteriously or unfavorably affected.

Suitable aqueous dispersions of adhesive material which have been widely used for laminating such dampening felts to metal parts of automobile bodies are exemplified in the patent to Groskopf, 2,180,305.

While we have described a material in which the center layer contains holes and this is the preferable example of the invention, the invention is not limited thereto and it is possible to obtain a desirable effect by utilizing strips of felt in the middle layer in the area of and parallel to the adhesive strips 13. A substantial proportion of the area between the adhesive strips 13, which in the preferred embodiment of the invention is occupied by the felt containing holes, may be utilized as space between the strips so that there is no middle layer at all in a part of the area between the adhesive strips 13.

The following table is a comparison between the sound dampening results of the preferred embodiment of the present invention and standard products on the market of equal weight.

Table

Product

Pounds, wt. in 480 sq. ft.

Sound Dampening Geiger Plate Method, Decibel Decay/ Sec.

I. A sound dampening material consisting of two layers of felt________

II. An assembly as in I with the addition of a center ply of felt_________

III. The composition shown in the drawings....................

360-400

360-400

350

11-14

12-15

60-70

From. the above table it will be obvious that the sound dampening effect of the present invention is substantial. The decibel decay figures of 60-70 may even be increased by a larger number of holes. It is also desirable in some cases to have very small holes in the facing sheet 12.

The air cavity effect contributes towards an improvement of the thermal resistance of the composition. The composition III in the above table has a thermal conductivity constant K—-0.425 B.t.u./ft.^s/hr./° F./inch.

This value is in the range of values obtained for commercial heat insulation materials such as blankets of felted rock wool and insulating boards.

In addition, more favorable sound absorption properties are obtained by the use of the air cavities. Compo10 sition III of the above table whose thickness was only 0.3 inch was tested in a reverberation chamber. The noise reduction coefficient (average of the coefficients at frequencies from 256 to 2048 cycles inclusive) is 0.34 and with 1 x 2 furring the value is 0.45. These re15 suits are in the same range as some commercial acoustical materials of greater thickness.

It will be understood that the sound dampening and absorption and the thermal properties are dependent upon the overall composite thickness and by increasing the 20 thickness enhanced values can be obtained.