SELF-FUSIBLE DAMPING MATERIAL

Abstract: A self-fusible damping material comprising powdery hard ferrite particles as a filler molded by using a binder, wherein an ethylene-vinyl acetate copolymer and a petroleum resin are used as the binder and 100 parts by weight in total of the binder is compounded with 150 to 600 parts by weight of the filler; or a self-fusible damping material comprising powdery hard ferrite particles as a filler and containing, if necessary, an auxiliary filler, the filler mixture being molded by using a binder, wherein an ethylene-vinyl acetate copolymer and a petroleum resin art used as the binder and 100 parts by weight in total of the binder is compounded with 50 to 400 parts by weight of the ferrite particles and 1 to 200 parts by weight of the auxiliary filler in such a manner that the total amount of the filler mixture ranges from 100 to 600 parts by weight per 100 parts by weight of the binder.

Description: The present invention relates to a self-fusion type damping material having excellent self-fusibility and a high damping effect. The main application fields for this material are, for example, vehicles, marine vessels, electric apparatus, machinery, architecture and building materials. As is generally known, a damping material is widely used in various fields to prevent and suppress vibration and noise generated due to rotation of, for example, an engine or a motor used in electric and mechanical apparatus, such as a vehicle, for instance an automobile or electric train, marine vessel, laundry machine, dryer, acoustic instrument, precision machine tool, or plant equipment; vibration and noise generated with pipes and conduits of, for example, water or gas or with ducts, for example for air conditioning, in buildings such as houses; and vibration generated when a vehicle travels on a road or railroad. Generally speaking, a damping material is manufactured by forming a filler, such as mica powder, with a binding material into a sheet or block by a molding method such as extrusion molding, calendering, compression molding, injection molding or cast molding. Specifically, a sheet form damping material is often used by applying through heat fusion or adhering on a substrate, such as a steel plate. Recently, vehicles, marine vessels, electric and mechanical apparatus, architecture and building materials, for instance, have tended to be lighter in weight and smaller in size. A damping material to be used therein correspondingly needs to be lighter, thinner and smaller. Accordingly, the damping material is strongly required to have a high damping effect. Further, when a damping material is mounted on a substrate, it is necessary that the material has excellent applicability and workability, such as easy handling and easy mounting. To that end it is strongly required that the material has excellent adhesion to a substrate: in other words, the material should be excellent in adhering firmly to the substrate, namely adhesion strength, and in being sufficiently fitted to an uneven surface or a complex shape of the substrate, that is adaptability. When a damping material is mounted on a ceiling or vertical part, a method using an adhesive or an adhesive double coated tape, or a method comprising applying a hot melt on the surface on which the material is to be mounted and then subjecting the hot melt to heat fusion has generally been utilized. However, when the former method is used, a release paper added to the adherent surface must be peeled off upon application thereof and accordingly it is inconvenient to handle. In the latter method, the damping material should be adhered through heat fusion while continually taking care to prevent the material from sagging or dropping out and this has caused a reduction of the applicability and workability. A method has been proposed and brought into practice in which a hard ferrite powder is used as a filler. A damping material is formed from the filler with a binder and magnetized so that a magnetic adsorption force is imparted to the material, hereinafter referred to as a "self-fusion type damping material". The material is placed in a predetermined position with the aid of the magnetic adsorption force in a manner such as to prevent the material from being dislocated or sagging, followed by heat fusion. The self-fusion type damping material must have a sufficient magnetic adsorption to suppress and prevent its dislocation and sagging. Further, the material is required to have not only the above-described adhesion properties such as adhesion strength and adaptability but also excellent heat fusibility when it is adhered through heat fusion. Conventionally known self-fusion type damping materials include damping materials manufactured by forming a magnetic material having high residual magnetism, such as barium ferrite powder or strontium ferrite powder, with a fusible bituminous material [JP-B-42-9880 (1967)] and by forming a magnetic material having residual magnetism and a powder obtained by baking solid materials in a waste liquid from paper making with a bituminous material and/or a synthetic rubber and/or a synthetic resin [JP-A-51-90323 (1976)]. Although a self-fusion type damping material having excellent self-fusibility and a high damping effect is most strongly demanded at present, the damping materials described in JP-B-42-9880 (1967) and JP-A-51-90323 (1976) cannot necessarily be deemed to sufficiently fulfil these characteristics, as will be shown in the Comparative Examples described later. Thus, as shown in the Comparative Examples, their damping effect is not high enough; that is, their loss factor,η, is 0.12 at the highest. The present invention seeks to provide a damping material having excellent self-fusibility and a high damping effect. JP-A-59/80,454 discloses a damping composite comprising as a vibration-absorbing layer a resin composition which comprises a crystalline polyolefin (A) modified with at least one monomer (B) selected from unsaturated carboxylic acids and their anhydrides, an amorphous polymer (C) and optionally an ethylenic polymer (D) and/or an inorganic filler (E). EP-A-545,625 (Art. 54(3) EPC) discloses a damping material comprising: (a) a binder composed of (i) an ethylene-vinyl acetate copolymer containing 30 to 65 wt% vinyl acetate units and (ii) a petroleum resin containing an aromatic petroleum resin as the main component thereof, the weight ratio of the ethylene-vinyl acetate copolymer to the petroleum resin being from 100:160 to 100:330; and (b) 30 to 180 parts by weight, per 100 parts by weight of said binder, of a filler composed of (i') a scaly powder and (ii') from 0 to less than 50 parts by weight, per 100 parts by weight of said binder, of a granular powder, a fibrous material, or a mixture thereof. The present invention provides a self-fusion type damping material comprising 150 to 600 parts by weight of a hard ferrite powder as a filler mixed with a binder comprising 100 parts by weight in total of an ethylene-vinyl acetate copolymer and a petroleum resin. The present invention also provides a self-fusion type damping material comprising 50 to 400 parts by weight of a hard ferrite powder and 1 to 200 parts by weight of an auxiliary filler as a combined filler, the combined filler being present in an amount of 100 to 600 parts by weight being mixed with a binder comprising 100 parts by weight in total of an ethylene-vinyl acetate copolymer and a petroleum resin. The self-fusion type damping material of the present invention has a shear strength of not less than 1.0 kg/cm 2 so that it hardly drops out, has excellent self fusibility, i.e., an adaptability of not higher than 2.0 mm, and further has an excellent damping effect, i.e., a peak value of loss factor, η, of not less than 0.3. The self-fusion type damping material of the present invention containing, as a filler, a hard ferrite powder and an auxiliary filler can be further reduced in weight, thickness and size, while keeping the above-mentioned characteristics. Especially, in case where the auxiliary filler used with the hard ferrite powder is a scaly powder, the material can be lighter, thinner and smaller as compared with the material using only a hard ferrite powder while the peak value of the loss factor can also be improved. The hard ferrite powder used in the present invention is, for example, barium ferrite powder or strontium ferrite powder. Any shape of the particles can be used. For example the particles may be granular or platelike. With respect to the particle size of the hard ferrite powder, taking its kneadability with resins into consideration, a BET specific surface area of 0.1 to 10 m 2 /g is preferable. Regarding the magnetic properties, a coercive force of not less than 1000 Oe and a residual magnetization of not less than 15 emu/g are preferable taking the adsorption by magnetic force into consideration. A coercive force of not less than 1500 Oe and a residual magnetization of not less than 20 emu/g are more preferable. The binder used in the present invention comprises an ethylene-vinyl acetate copolymer and a petroleum resin. Commercially available products can be used. The ethylene-vinyl acetate copolymer used is preferably a copolymer of ethylene and vinyl acetate containing 30 to 65 % by weight of vinyl acetate, taking its self-fusibility and damping effect into consideration. The petroleum resin used is preferably an aromatic petroleum resin having a softening point of 70 to 130°C obtained by polymerizing a fraction (C9 fraction) containing aromatic unsaturated hydrocarbons having 9 carbon atoms as a main constituent, which is produced as a by-product in, for example, petroleum purification and petroleum cracking, or an aliphatic-aromatic petroleum resin having a softening point of 60 to 120°C obtained by copolymerizing not less than 65% by weight of the C9 fraction and a fraction (C4, C5 fractions) containing aliphatic unsaturated hydrocarbons having 4 to 5 carbon atoms as a constituent, taking its self-fusibility and damping effect into consideration. The aromatic petroleum resin can be obtained, for example, by polymerizing a cracked fraction having a boiling point of 140 to 220°C obtained by petroleum cracking, that is, a fraction containing one or more of, for example, styrene, vinyltoluene, indene, divinylbenzene and vinylnaphthalene. The ratio of the ethylene-vinyl acetate copolymer to the petroleum resin is preferably 160 to 330 parts by weight of the petroleum resin per 100 parts by weight of the ethylene-vinyl acetate copolymer, taking the self-fusibility and damping effect into consideration. The ratio of the binder to the hard ferrite powder in the invention is 150 to 600 parts by weight of hard ferrite powder based on 100 parts by weight in total of the ethylene-vinyl acetate copolymer and petroleum resin. When it is less than 150 parts by weight, the loss factor of the damping material is not higher than 0.3 and sufficient damping effect cannot be obtained. When it is over 600 parts by weight, the shear strength of the material is not enough and its adaptability is low as well. The auxiliary filler used with hard ferrite powder in the present invention can be, for example, a scaly powder, such as mica powder, platelike iron oxide powder or graphite powder; balloons of glass, silica or resin; calcium carbonate; clay; barium sulfate; or zinc oxide. The scaly particle have a diameter of 1 to 1000 µm. 1 to 500 µm is preferable. The hard ferrite powder is used in an amount of 50 to 400 parts by weight based on 100 parts by weight in total of the ethylene-vinyl acetate copolymer and petroleum resin. If it is less than 50 parts by weight, a sufficient adsorption by magnetic force cannot be obtained and the resulting damping material cannot be mounted on a ceiling or vertical surface. If it is over 400 parts by weight, although a damping effect may be obtained by the present invention, it is meaningless to use the filler in an amount more than necessary. The auxiliary filler is used in an amount of 1 to 200 parts by weight based on 100 parts by weight in total of the ethylene-vinyl acetate copolymer and petroleum resin. If it is less than 1 part by weight, it is difficult to make the damping material lighter, thinner and smaller effectively. If it is over 200 parts by weight, a sufficient shear strength cannot be obtained and the adaptability is low. To make the material lighter, thinner and smaller effectively while maintaining its damping effect, the lower limit of the auxiliary filler is preferably 10 parts by weight. The total amount of the hard ferrite powder and auxiliary filler combined is 100 to 600 parts by weight based on 100 parts by weight in total of the ethylene-vinylacetate copolymer and petroleum resin. If it is less than 100 parts by weight, a sufficient damping effect of the material cannot be obtained. If it is over 600 parts by weight, the adhesion strength and adaptability become low. When the scaly powder is used as the auxiliary filler, the damping effect can be improved more effectively than when the hard ferrite powder is only used, and the peak value of the loss factor, η, can be higher than 0.32. In the present invention, the damping material may contain a plasticizer, such as a process oil, DOP, stearic acid, Zn stearate, Mg stearate or Ca stearate; or a polymer, such as a thermoplastic resin or rubber, which is usually used to improve various properties of a damping material. The most important point of the present invention is the fact that a self-fusion type damping material obtained by forming a hard ferrite powder as a filler with a binder, in which said binder comprises an ethylene-vinyl acetate copolymer and a petroleum resin and 100 parts by weight of the combined binder and 150 to 600 parts by weight of said filler are mixed, has excellent self-fusibility and a high damping effect. An important point of the present invention is the fact that a self-fusion type damping material obtained by compounding a hard ferrite powder filler and an auxiliary filler with a binder, in which said binder comprises an ethylene-vinyl acetate copolymer and petroleum resin, and 100 parts by weight of the combined binder are mixed with 100 to 600 parts by weight of said combined filler, with amounts of said hard ferrite powder and auxiliary filler being in the range of 50 to 400 parts by weight and 1 to 200 parts by weight, respectively, based on 100 parts by weight of the combined binder, can be further lighter, thinner and smaller while keeping the properties, that is, excellent self-fusibility and a high damping effect. The present inventors believe that the reason why the self-fusion type damping material of the present invention has excellent self-fusibility and a high damping effect may be a synergistic effect of the hard ferrite powder and the specifically combined binder comprising the ethylene-vinyl acetate copolymer and petroleum resin, since when either a bituminous material or an ethylene-vinyl acetate copolymer only is used as a binder, the effect which is an object of the present invention cannot be obtained, as shown in the Comparative Examples described later. Further, when a petroleum resin is only used as a binder, the toughness is too poor to form the material. The present invention will be explained in the Examples and Comparative Examples. In the present invention, the loss factor, η, was measured by a cantilever resonance method using a damping sheet of 2 mm thickness. Self-fusibility is shown with values measured by two methods based on an overhang baking test as described below. That is, in the first overhang baking test method, after a test piece 200 mm long, 200 mm wide and 2.0 mm thick is applied by its magnetic force on a steel plate 300 mm long, 300 mm wide and 0.8 mm thick at room temperature, the steel plate with the test piece applied thereon is held horizontally while keeping the piece underneath the plate and the plate is heated at 180°C for 60 minutes to determine whether the test piece drops or not. The second method is as described below: A set of two steel test plates is prepared in which a steel test plate 50 mm long, 70 mm wide and 0.8 mm thick having a protrusion 25 mm long and 25 mm wide at the center of one side 70 mm wide of the plate in the same plane and another steel test plate 150 mm long, 70 mm wide and 0.8 mm thick having a concave to be engaged with said protrusion are superimposed on a base steel plate 200 mm long, 70 mm wide and 2 mm thick and four corners of the superimposed plates are fixed firmly. Then, a test piece 25 mm wide, 100 mm long and 2 mm thick is put on the steel test plates with the longitudinal side of the test piece being parallel to the longitudinal side of the steel plates, so that the protrusion of the steel test plate is covered with the test piece, and thus the test piece is applied to the steel test plates by magnetic force. Thereafter, the set of steel plates, to which the test piece is applied, is held horizontally while keeping the test piece underneath, baked at 180°C for 60 minutes, and allowed to cool at room temperature. The base steel plate is then removed. The steel test plates to which the test piece is adhered are pulled by a tension tester at a speed of 200 mm/minute to measure the maximum breaking load of the adhered surface and obtain a shear strength by dividing the measured value by the adhered surface area (6.25 cm 2 ). If the shear strength is not less than 1.0 kg/cm 2 , there is no problem in practical use. Adaptability is measured as follows. Unevenness was formed on the surface of a steel plate of 0.8 mm thickness and 300 mm width as a base plate. The shape in the front view of the formed concave is an upwardly flared trapezoid (20 mm height, 80 mm upper base length, 140° slope angle of bottom steel plate at curved ends, 3 mm radius of curvature at bottom). A damping sheet 2 mm thick, 150 mm wide and 200 mm long is mounted. After the sheet on the substrate is heated in a dryer at 150°C for 30 minutes, it is taken out in the air and cooled to an ordinary temperature to obtain a test piece. At the curved bottom steel plate of the test piece, the gap between the steel plate and the damping sheet is measured. The density is a value measured by an electronic density meter EW120SG (manufactured by Mirage Trading Co. Ltd.). Example 1: To a binder comprising 33 parts by weight of an ethylene-vinyl acetate copolymer containing 40% by weight of vinyl acetate and 67 parts by weight of an aromatic petroleum resin (softening point 102°C, Gardner colour scale 6, bromine value 21.4) obtained by polymerizing a C9 fraction, 160 parts by weight of barium ferrite powder (BET specific surface area 1.9 m 2 /g, coercive force 2400 Oe, residual magnetization 33.4 emu/g) and 70 parts by weight of mica powder [average particle diameter:340 µm, aspect ratio (average particle diameter:thickness):80:1] added and blended. The blend was mixed with heating for 10 minutes in a pressurized kneader, then calender rolled, and magnetized with a magnetizer to prepare a damping sheet having a thickness of 2 mm. Thus obtained damping sheet was cut into pieces 15 mm wide and 220 mm long, mounted on a substrate made of a steel plate having a thickness of 0.8 mm (15 x 300 mm), and adhered to the substrate by heating at 150°C for 30 minutes to obtain a test piece. Loss factors, η, of the test piece at given temperatures were measured by a cantilever resonance method. The peak value of the loss factor was 0.42 at 40°C, showing that the damping effect of the sheet was excellent. The shear strength of the test piece by the overhang baking test was 1.9 kg/cm 2 and the adaptability was not more than 1 mm, showing the excellency of the sheet. The density of the sheet was 2.0. Examples 2 to 10 and Comparative Examples 1 to 3: Damping sheets were manufactured in the same manner as in Example 1 except that the kinds and amounts of ethylene-vinyl acetate copolymer, petroleum resin, hard ferrite powder and auxiliary filler were varied. The main manufacturing conditions and various properties of each of the damping sheets are shown in Tables 1 and 2. In Table 1, the average particle diameter of calcium carbonate was measured by the dry method according to JIS Z 8801. Comparative Example 4: To a binder comprising 87 parts by weight of blown asphalt (penetration 20/30, melting point 90°C) and 13 parts by weight of butyl rubber (Trade name: JSR·Butyl 268, manufactured by Japan Synthetic Rubber Co.), 125 parts by weight of barium ferrite powder (BET specific surface area 1.9 m 2 /g, coercive force 2400 Oe, residual magnetization 33.4 emu/g) and 25 parts by weight of mica powder [average particle diameter 340 µm, average plate ratio (average particle diameter:thickness) 80:1] were added and blended. The blend was mixed with heating for 10 minutes in a pressurized kneader, calender rolled, and magnetized with a magnetizer to obtain a damping sheet having a thickness of 2 mm. Thus obtained damping sheet was cut into pieces 15 mm wide and 220 mm long, mounted on a substrate made of a steel plate having a thickness of 0.8 mm (15 x 300 mm), and adhered to the substrate by heating at 150°C for 30 minutes to obtain a test piece. Loss factors, η, of the test piece at given temperatures were measured by a cantilever resonance method. The peak value of the factor was 0.12 at 10°C, showing that damping effect of the sheet was bad. Examples and Comp. Examples Property of Damping Sheet Loos Factor η Overhang Baking Test Adaptability (mm) Density Peak Value (-) Temperature at Peak (°C) Drop Out or Not Shear Strength (kg/cm 2 ) Example 1 0.42 40 Adhere 1.9 1 or Less 2.0 Example 2 0.35 40 Adhere 1.7 1 or Less 1.9 Example 3 0.33 20 Adhere 1.5 1 or Less 2.1 Example 4 0.31 30 Adhere 1.7 1 or Less 2.2 Example 5 0.32 10 Adhere 1.6 1 ∼ 2 2.8 Example 6 0.34 40 Adhere 1.3 1 ∼ 2 1.9 Example 7 0.31 30 Adhere 1.8 1 ∼ 2 2.2 Example 8 0.34 50 Adhere 1.8 1 ∼ 2 2.1 Example 9 0.35 40 Adhere 1.7 1 ∼ 2 2.4 Example 10 0.31 20 Adhere 1.4 1 or Less 1.8 Comp. Ex. 1 0.41 40 Drop Out Can not Measure 1 or Less 1.8 Comp. Ex. 2 0.29 30 Drop Out Can not Measure 2 ∼ 3 2.2 Comp. Ex. 3 0.04 20 Adhere 0.4 1∼ 2 2.4 Comp. Ex. 4 0.12 10 Adhere 1.0 1 ∼ 2 1.8 (Effect of The Invention) Since the self-fusion type damping material of the present invention has excellent self-fusibility and a high damping effect as shown in Examples described before, it can be made lighter, thinner and smaller. Its applicability and workability are excellent because it is possible to suppress and prevent dislocation and sagging thereof at the time of mounting.

Claims: A self-fusion type damping material comprising 150 to 600 parts by weight of a hard ferrite powder as a filler mixed with a binder comprising 100 parts by weight in total of an ethylene-vinyl acetate copolymer and a petroleum resin. A self-fusion type damping material comprising 50 to 400 parts by weight of a hard ferrite powder and 1 to 200 parts by weight of an auxiliary filler as a combined filler, the combined filler being present in an amount of 100 to 600 parts by weight and being mixed with a binder comprising 100 parts by weight in total of an ethylene-vinyl acetate copolymer and a petroleum resin. A material according to claim 2 wherein the auxiliary filler is a scaly powder. A material according to claim 3 wherein the scaly powder is a mica powder, platelike iron oxide powder or graphite powder. A material according to claim 3 or 4 wherein the peak value of the loss factor is higher than 0.32. A material according to any one of the preceding claims wherein the hard ferrite powder is barium ferrite powder or strontium ferrite powder. A material according to any one of the preceding claims wherein the hard ferrite powder has a BET specific surface area of 0.1 to 10 m 2 /g, a coercive force of not less than 1000 Oe and a residual magnetization of not less than 15 emu/g. A material according to any one of the preceding claims wherein the ethylene-vinyl acetate copolymer contains 30 to 65% by weight of vinyl acetate. A material according to any one of the preceding claims wherein the petroleum resin is an aromatic petroleum resin having a softening point of 70 to 130°C obtained by polymerizing a fraction containing aromatic unsaturated hydrocarbons having 9 carbon atoms as a main constituent or an aliphatic-aromatic petroleum resin having a softening point of 60 to 120°C obtained by copolymerizing not less than 65% by weight of a fraction containing aromatic unsaturated hydrocarbons having 9 carbon atoms and a fraction containing aliphatic unsaturated hydrocarbons having 4 to 5 carbon atoms as a constituent. A material according to any one of the preceding claims wherein the binder contains 160 to 300 parts by weight of the petroleum resin per 100 parts by weight of the ethylene-vinyl acetate copolymer.

Inventors: FUJII TAKASHI, FUJII YASUHIKO, KISHIMOTO ATSUNORI, OHSHITA KAZUTAKA, TODA TETSURO, YAMAMOTO KAZUMI, FUJII, TAKASHI, FUJII, YASUHIKO, KISHIMOTO, ATSUNORI, OHSHITA, KAZUTAKA, TODA, TETSURO, YAMAMOTO, KAZUMI, YAMAMOTO, KAZUMI, 1901, IIDA
Applicants: HIROTANI CO LTD, TODA KOGYO CORP, HIROTANI CO., LTD., TODA KOGYO CORP.
Application year: 1992
Main classification: C08L57
IPC codes: C08K3, C08L23, F16F15, C08L31, C08L57, F16F9