Vibration-Damping Sheet

1. Field of the Invention

The invention relates to an improved light weight vibration-damping sheet which mainly comprises an asphalt component and a hollow filler component and is manufactured by melting asphalt, mixing hollow fillers therewith and rolling the mixture into a form of sheet.

2. Prior Art

It is well known to employ a vibration-damping sheet in vehicles, particularly in automobiles, in order to reduce vibration caused by an engine. Usually, the sheets are firmly fixed by fusion or placed on the steel panel of the car floor, of the door, or of the trunk.

The applicants have already disclosed a heat fusible light weight vibration-damping sheet composition, which mainly comprises an asphalt component and a hollow silicate filler component in order to reduce the weight of said composition, in the specification of Japanese laid open 77-39723 Kokai 52-39723). In this prior art light weight vibration-damping sheet composition, the objective of the weight reduction is accomplished by the use of a hollow silicate filler whereas the workability of said composition into a sheet form is not satisfactory.

In general, for the purpose of reducing the weight of the automobile, a thinner vibration-damping sheet is often applied to the automobile but, on the other hand, the vibration-damping effect of the thinner sheet decreases and the level of the vibration is not tolerable to the drivers or the passengers.

By use of the above mentioned light weight vibration-damping sheet composition having a hollow filler component, weight reduction purpose is achieved but the sheet forming workability of said composition is not sufficient because it is difficult to disperse hollow silicate filler uniformly in asphalt.

The objective of this invention is to solve the above mentioned problem, that is, to disperse hollow silicate filler uniformly in asphalt.

The inventors of this invention reached their objectives as a result of an intensive research.

The vibration-damping effect of this invention is equal or superior to that of the prior art, while on the other hand, the weight of the vibration-damping sheet according to this invention is lighter than conventional ones and its sheet forming workability is considerably improved by adding surface treated calcium carbonate into the composition.

The vibration-damping sheet of this invention comprises a binder, mainly consisting of asphalt, a hollow filler and surface treated calcium carbonate in order to disperse the hollow filler uniformly in the binder.

The composition of the fusible vibration-damping sheet of this invention comprises at least one binder component, a hollow filler and a surface treated calcium carbonate as a filler component.

Preferred examples of the binder component include well known material such as straight asphalt, blown asphalt, and modified asphalt with rubber (rubberized asphalt).

The binder component described above may be used either solely or in combination. Petroleum resins are also used as a binder component if desired.

Preferred examples of the hollow filler include, glass balloon, silas balloon (trade name of baked volcanic ash) and carbon balloon as inorganic hollow fillers organic balloon of copolymers of methyl acrylate, ethyl acrylate, methyl methacrylate, acrylo nitrile, and copolymers of vinyl acetate, vinyl chloride, and styrene copolymerized with acrylic acid resin.

Since the follow fillers are mixed with the binder component and pressed while the mixture is formed into a sheet, these hollow fillers should have a compression strength of 35.about.1100 kg/cm.sup.2, preferably 135.about.950 kg/cm.sup.2, and a heat resistance of more than 150.degree. C.

The amount of hollow filler is preferably from 3 to 50% by weight based on the total weight of the composition. A content of less than 3% by weight will cause no weight reduction effect, whereas a content of more than 50% by weight will cause poor sheet forming workability.

The nature of the hollow filler is not critical and any kind of hollow filler material in the art may be used.

It is essential to use surface treated calcium carbonate to disperse the hollow fillers uniformly into the binder. The surface-treated calcium carbonate is manufactured by treating calcium carbonate with a higher fatty acid, or a mixture of a fatty acid and its salt, is an amount of more than 30% by weight, and having a carbon number of more than 18, such as stearic acid, palmitic acid and oleic acid. A preferable ratio of the hollow filler to the calcium carbonate, while treating, is from 20/80 to 80/20, more preferably 50/50.

Other examples of the filler component are talc, clay and barium sulfate which are powdery inorganic fillers, mica, which is a flaky inorganic filler, and crushed used paper, unwoven fibers, glass wool, or rock wool, which are inorganic or organic fibrous fillers.

Additives such as calcium oxide are added to the composition if desired.

When the composition of the invention is formed into a vibration-damping sheet, it may contain one or more conventional additives in the field such as a plasticizer, stabilizer, flame retardant, foaming aid, vulcanizer, or the like.

The surface treated calcium carbonate acts as an agent for dispersing the hollow filler into the binder so that the hollow filler is uniformly dispersed into the binder of the vibration-damping sheet composition.

Consequently, the sheet forming workability of the composition is greatly improved and a light weight vibration-damping sheet is provided.

The invention will be explained in more detail by the following examples, which by no means limit the scope of this invention, in which parts and percentages are all by weight.

The specific materials used in the following examples and comparative examples are as follows:

A mixture of 51 parts of modified straight/blown rubberized asphalt, as a binder component, 15 parts of glass balloon as a hollow filler component, 15 parts of surface treated calcium carbonate (Calseeds PL; manufactured by Konoshima Chemical), treated with aluminium stearate, 15 parts of mica, 3 parts of organic fiber, and 1 part of calcium oxide were blended in a vacuum kneader and rolled into a sheet by a calender roll.

A mixture of 51 parts of modified straight/blown asphalt, as a binder component, 18 parts of silas balloon, as a hollow filler component, 12 parts of surface treated calcium carbonate (Hakuenka CCR; manufactured by Shiraishi Calcium), treated with aluminium stearate, 15 parts of mica, 3 parts of organic fiber, and 1 part of calcium oxide were blended in a vacuum kneader and rolled into a sheet by a calender roll.

A mixture of 51 parts of modified straight/blown rubberized asphalt, as a binder component, 10 parts of an acrylic series vinyl chloride copolymer micro balloon, as a hollow filler component, 20 parts of surface treated calcium carbonate (Calseeds PL; manufactured by Konoshima Chemical), treated with aluminium stearate, 15 parts of mica, 3 parts of organic fiber, and 1 part of calcium oxide were blended in a vacuum kneader and rolled into a sheet by a calender roll.

A mixture of 45 parts of modified straight/blown rubberized asphalt, as a binder component, 46 parts of surface untreated calcium carbonate, 5 parts of mica, 3 parts of organic fiber, and 1 part of calcium oxide were blended in a vacuum kneader and rolled into a sheet by a calender roll.

A mixture of 51 parts of modified straight/blown rubberized asphalt, as a binder component, 15 parts of glass balloon, as a hollow filler component, 15 parts of surface untreated calcium carbonate, 15 parts of mica, 3 parts of organic fiber, and 1 part of calcium oxide were blended in a vacuum kneader and rolled into a sheet by a calender roll.

A mixture of 45 parts of modified straight/blown rubberized asphalt, as a binder component, 46 parts of surface treated calcium carbonate (Calseeds PL; manufactured by Konoshima Chemical), 5 parts mica, 3 parts or organic fiber, and 1 part of calcium oxide were blended in a vacuum kneader and rolled into a sheet by a calender roll.

In order to determine the degree of improvement of the invention, the following tests were conducted.

a. To evaluate the sheet forming workability of the composition, the hollow filler dispersion in the binder is observed with the eye.

b. The specific gravity of the composition was measured.

c. The mechanical loss factor value .eta. was measured according to the resonance method (described in the Handbook of Counter Measure Against Noise, edited by the Japanese Acoustic Material Association, page 438) at temperatures 20.degree. C., 40.degree. C., 60.degree. C. respectively. It is believed that the vibration-damping effect is proportional to the mechanical loss factor value .eta. and if the loss factor .eta. is greater than 0.04, the vibration-damping effect is considered to be sufficient. The results of the tests are shown in the following Table 1.

As indicated in the table, the light weight vibration-damping sheet according to this invention has an equal vibration-damping effect to that of the prior art vibration-damping sheets in terms of the loss factor and the sheet forming workability of the composition according to this invention is satisfactory. Further, the specific gravity of the composition is low, that is, the composition is light weight and the weight reduction of the vibration-damping sheet is achieved.