Damping material

Abstract: 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.

Description: The present invention relates to a damping material which has a high damping effect, especially a material which has a wide operating temperature range and which has excellent adhesion strength and adhesive followability. The damping material of the present invention is mainly used for vehicles, vessels, electric and machine appliances, and building materials. As is well known, damping materials are used in various fields in order to prevent and suppress the vibration and noise which are caused by the rotation of, for example, an engine or a motor which is incorporated into vehicles such as automobiles and electric cars, vessels, and electric and machine appliances such as washing machines, drying machines, acoustic apparatuses, precision machine tools, and factory and plant machines and tools; to prevent and suppress the vibration and noise generated in water or gas conduits or air-conditioning ducts in office buildings and houses; and to prevent the vibration caused by vehicles running on the road or railroad tracks. With the recent tendency of lightening and/or miniaturizing the vehicles, vessels, electric and machine appliances and building materials, the damping materials used therefor have also been required to be lightened, thinned and miniaturized. For this purpose, a damping material is strongly required to have a high damping effect (for example, the peak value of the loss factor η is not less than 0.30). In addition, since damping materials are often used under the circumstances of a wide temperature range, it is further desirable that a high damping effect can be maintained in as wide a temperature range as possible, in other words, that the operating temperature range is wide (for example, the width of the operating temperature range of the loss factor η of not less than 0.3 is at least 20°C). A damping material is also required both to fully display a high damping effect when mounted on a base material and to have an excellent operability such as ease of handling and mounting on the base material. For this purpose, a damping material is strongly required to have excellent adhesion with the base material, in other words, to have an excellent adhesive strength (e.g., not less than 30 kg/cm 2 ), and to closely and conformingly adhere to the base material, in other words, to have an excellent adhesive followability (e.g., not more than 2 mm) which enables the damping material to sufficiently closely-conformingly adhere to the base material while adapting it to the rough surface or the complicated shape of the base material. A damping material is generally produced by molding a filler such as mica powder and a binder into a sheet form or block form by, for example, extrusion-molding, calendering, compression-molding, injection-molding or cast-molding. A damping material is most frequently used in the sheet form together with a base material such as a steel plate to which the damping material is attached by fusion-bonding or adhesion. As a method of enhancing the damping effect of a damping material, a method of thickening the damping material and a method of adding a large amount of filler having a high density so as to increase the weight of the damping material are well known. However, it is still difficult to lighten, thin and miniaturize a damping material as described above by these methods. As a countermeasure, investigations of methods of enhancing the damping effect by adjusting the composition and the mixing ratio by varying the kinds of the filler and the binder, and the mixing ratio thereof have recently been carried out. For example, the present applicant has proposed the following vehicle damping sheet in JP-A-2-302,455 (1990) (corresponding to EP-A-383,580): "A vehicle damping sheet comprising a blend-mixture comprising: (1) a filler composed of mica, iron oxide particles and an auxiliary filler; and (2) a binder composed of an ethylene-vinyl acetate copolymer, each of the amounts of the mica, the iron oxide particles and the auxiliary filler being 5 to 200 parts by weight per 100 parts by weight of the binder; the total amount of the mica, the iron oxide particles and the auxiliary filler being not less than 30 parts by weight per 100 parts by weight of the binder; and the content of the iron oxide particles in said blend-mixture being from 2 to 40% by weight." JP-A-2-302,455 (1990) discloses examples of the auxiliary filler such as calcium carbonate, clay, talc, barium sulfate, asbestos, silica balloons, and a fibrous material such as waste paper, chemical fibers and wood fibers. These are used alone or as a mixture thereof. The fibrous material such as waste paper, chemical fibers or wood fibers can in particular reduce the flow property of the damping sheet when it is thermally fused to the floor panel of an automobile, thereby preventing disconnection or sagging. JP-A-2-302,455 discloses in Example 6 that to a binder of 40 parts by weight of ethylene-vinyl acetate copolymer and 60 parts by weight of petroleum resin, a filler of 20 parts by weight of Fe 3 O 4 particles (size: 0.3 µm) as the iron oxide particles, 90 parts by weight of mica (size: 150 µm), 25 parts by weight of calcium carbonate, 10 parts by weight of waste paper and 10 parts by weight of a process oil was added and blended, and after mixing under heating the blend in a dispersion mixer at a temperature of 120 to 140°C for 10 min., the thus obtained blend-mixture was rolled spread by a calender rolls to prepare a vehicle damping sheet of 2 mm in thickness. Although a damping material having a high damping effect, and excellent adhesion strength and adhesive followability is now in the strongest demand, the damping sheet disclosed in JP-A-2-302,455 cannot be said to have either a sufficiently high damping effect or a wide operating temperature range because the width of the temperature range thereof in which the loss factor η is not less than 0.3 is at most 18°C. In addition, the adhesive strength and the adhesive followability of the damping material disclosed in JP-A-2-302,455 are about 28 kg/cm 2 and about 2 to 3 mm, respectively, which cannot be said to be satisfactory. The present invention seeks to provide a damping material having a high damping effect and excellent adhesion strength and adhesive followability, particularly a damping material having an adhesive strength of not less than 35 kg/cm 2 and an adhesive followability of not more than 2mm as well as having a damping effect of a peak loss factor η of not less than 0.40 and a wide operating temperature range in which the width of the operating temperature range of not less than 0.3 of the loss factor η is at least 20°C. The present invention provides 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 not less than 65 wt% of an aromatic petroleum resin, 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') at least 30 parts by weight, per 100 parts by weight of said binder, of 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 ethylene-vinyl acetate copolymer contains 30 to 65 wt% vinyl acetate units. If the vinyl acetate content is less than 30 wt% or more than 65 wt%, it is difficult to obtain a damping material which has a high damping effect, especially, which has a wide operating temperature range and which has excellent adhesive strength and adhesive followability. In consideration of the damping effect, the adhesive strength and the adhesive followability, the vinyl acetate content is preferably 32 tc 65 wt%, more preferably 35 to 63 wt%. The petroleum resin contains not less than 65wt%, preferably not less than 80 wt%, of an aromatic petroleum resin. Aliphatic petroleum resin components such as isoprene and piperylene may be contained as the balance. If the aromatic petroleum resin content is less than 65 wt%, it is difficult to attain a sufficient damping effect, and the adhesive strength is apt to be lowered. The petroleum resin containing an aromatic petroleum resin is obtained by, for example, polymerizing at least one petroleum fraction which is obtained by thermal-decomposition of petroleum and which has a boiling point of 140 to 220°C, namely, at least one selected from styrene, vinyl toluene, indene, divinyl benzene and vinyl naphthalene. In consideration of the damping effect, the petroleum resin preferably has a softening point of 80 to 170°C, more preferably 90 to 130°C. An aromatic petroleum resin containing not more than 55 wt%, more preferably 65 wt%, of a C 9 component such as styrene and indene is preferred. The amount of petroleum resin containing an aromatic petroleum resin is 160 to 330 parts by weight based on 100 parts by weight of the ethylene-vinyl acetate copolymer. If the petroleum resin content is less than 160 parts by weight, it is difficult to attain a sufficient damping effect, and the adhesive strength is apt to be lowered. If the petroleum resin content exceeds 330 parts by weight, it is difficult to obtain a damping material resin which has a high damping effect, and excellent adhesive strength and adhesive followability. In consideration of the damping effect, the adhesive strength and the adhesive followability, the petroleum resin content is preferably 160 to 300 parts by weight, more preferably 160 to 240 parts by weight. A scaly powder is generally a powder composed of flakes. Examples of the scaly powder in the present invention are mica, plate-like iron oxide particles and graphite. The average plate diameter of such powders is generally 1 to 2,000 µm, preferably 1 to 1,000 µm, more preferably 1 to 350 µm, and the average plate thickness is generally 0.01 to 100 µm, preferably 0.20 to 10 µm. The amount of scaly powder is 30 to 180 parts by weight based on 100 parts by weight of the binder. If the scaly powder content is less than 30 parts by weight, it is difficult to attain a high damping effect. If it exceeds 180 parts by weight, it is difficult to attain a sufficient damping effect, and both the adhesive strength and the adhesive followability are apt to be lowered. In consideration of the damping effect, the adhesive strength and the adhesive followability, the scaly powder content is preferably 70 to 150 parts by weight. It is preferable to use a granular powder and/or a fibrous material in addition to the scaly powder as the filler of the damping material of the present invention because the width of the operating temperature range is thereby enlarged. The amount of scaly powder when a granular powder and/or a fibrous material used in addition thereto is 30 to 150 parts by weight, preferably 50 to 150 parts by weight, more preferably 50 to 140 parts by weight based on 100 parts by weight of the binder. As the granular powder in the present invention, particles having an average particle diameter of 0.05 to 100 µm, preferably 0.05 to 30 µm are usable. Examples of granular powers are iron oxides particles such as hematite particles, magnetite particles, maghemite particles, strontium ferrite particles and barium ferrite particles, quartz sand, talc, clay, lead powder, iron powder, titanium oxide, zinc white, barium sulfate and calcium carbonate. As the fibrous material in the present invention, particles having an average major axial diameter of 0.1 to 50,000 µm, preferably 0.4 to 20,000 µm, an average minor axial diameter of 0.02 to 250 µm, preferably 0.05 to 100 µm and an aspect ratio (average major axial diameter : average minor axial diameter) of not less than 3:1, preferably not less than 5:1, are usable. As the fibrous material, fibers, acicular materials and spindle-shaped materials are usable. More specifically, as the fibrous material, iron oxides such as magnetite and maghemite, calcium carbonate, synthetic fibers, asbestos, natural organic fibers, glass fibers and carbon fibers are usable. The amount of granular powder and/or fibrous material is less than 50 parts by weight, preferably not less than 1 part by weight and less than 50 parts by weight, more preferably 1 to 40 parts by weight, based on 100 parts by weight of the binder. If the amount of granular powder and/or fibrous material is not less than 50 parts by weight, the operating temperature range is apt to become narrow. From the point of view of a wide operating temperature range, which is one of the objects of the present invention, the amount of granular powder and/or fibrous material is less than 50 parts by weight. In the present invention, the total amount of scaly powder and granular powder and/or fibrous material is 30 to 180 parts by weight based on 100 parts by weight of the binder. If the total amount is less than 30 parts by weight, it is difficult to attain a sufficient damping effect. If it exceeds 180 parts by weight, it is also difficult to attain a sufficient damping effect, and in addition, the adhesive strength and the adhesive followability are also lowered. From the point of view of the damping effect, the operating temperature range, the adhesive strength and the adhesive followability, the total amount is preferably 70 to 151 parts by weight. In the present invention, it is possible to add at least one plasticizer which is generally used, such as process oil, DOP, stearic acid, Zn stearate, Mg stearate and Ca stearate, in order to enhance the properties of the damping material. The effect intended in the present invention cannot be attained in any of the cases in which:the vinyl acetate content in the ethylene-vinyl acetate copolymer is out of the specified range; the amount of ethylene-vinyl acetate copolymer containing vinyl acetate within the specified range is out of the specified range; a petroleum resin which does not contain an aromatic petroleum resin is used; the amount of petroleum resin containing an aromatic petroleum resin as the main ingredient is out of the specified range; only granular powder and/or fibrous material is used as the filler; the amount of scaly powder is out of the specified range; and the total amount of scaly powder and granular powder and/or fibrous material is out of the specified range, as shown in the later-described Comparative Examples. The present inventors, therefore, consider that it is due to the synergistic effect of the specified ethylene-vinyl acetate copolymer and the specified amount thereof, the specified petroleum resin and the specified amount thereof, and the filler having the specified shape and the specified amount thereof, that a damping material produced according to the present invention has a high damping effect and excellent adhesive strength and adhesive followability. In the damping material of the present invention, the peak value of the loss factor η is not less than 0.40, preferably not less than 0.41, the adhesive strength is not less than 35 kg/cm 2 , preferably not less than 40 kg/cm 2 , and the adhesive followability is less than 2 mm. Especially, when a granular powder and/or a fibrous material is used in addition to the scaly powder, the width of the operating temperature range in which the loss factor η is not less than 0.3, is 20 to 32°C. The damping material of the present invention has a high damping effect and excellent adhesive strength and adhesive followability, as shown in the later-described Examples. It is therefore possible to lighten, thin and miniaturize the damping material while maintaining the high damping effect. Thus, since the damping material has good workability and operability, it is suitable for use in vehicles, vessels, electric and machine appliances and building materials. The damping material of the present invention having the above-described advantages is especially suitable as a material for vehicles such as automobiles in which the variation of the surrounding temperature is large, large vibration is constantly caused, and the base material on which the damping material is mounted has a complicated shape and a rough surface. Examples The present invention is now further described in the following Examples. The loss factor η, the adhesive strength and the adhesive followability were measured as follows: Loss factor η The loss factor η was measured by a cantilever resonance method using a damping property measurement system composed of a Complex Modulus Apparatus (ME-3930, manufactured by Brüel & Kjaer Corporation), a Dual Channel Signal Analyzer (Model-2034, manufactured by Brüel & Kjaer Corporation) and a personal computer (HP-300, manufactured by Hewlett Packard Corporation). Adhesive strength Two steel plates (30 mm length, 30 mm width and 5 mm thickness) were prepared and a shaft 10 mm diameter was welded to the central portion of one side of each plate. A damping sheet (30 mm length, 30 mm width and 2 mm thickness) was sandwiched between the two steel plates with the shafts facing outward. After the thus-obtained test piece was heated at 150°C for 30 minutes in a drying machine, it was taken out into air and cooled to an ordinary temperature. The adhesive strength of the damping sheet was expressed by the tensile strength measured by an universal testing machine AUTOGRAPH AGS-500A (manufactured by Shimazu Co., Ltd). That is, the shafts of the testing piece were pulled at a rate of 50 mm/min, and the load at the time when the damping sheet was broken was measured. The adhesive strength was expressed by the value obtained by dividing the load (kg) by the area (9 cm 2 ) of the damping sheet. Adhesive followability 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 of each concavity in the front view was approximately a trapezoid having a longer upper side. In the front view, the height of the trapezoid was 20 mm, the length of the upside in the trapezoid was 80 mm, and the angle of inclination between the base and lateral in the trapezoid at the contact point of both sides was 140°. The inner curvature radius of the base surface in the concavity was 3 mm. A damping sheet (2 mm thickness, 150 mm width and 200 mm length) was placed on the thus-produced base plate, and the test piece was heated at 150°C for 30 minutes in a drying machine. Thereafter, the test piece was taken out into air and cooled to an ordinary temperature. The adhesive followability of the damping sheet was expressed by the distance between the steel plate and the damping sheet at the curved portion of the bottom portion of the steel plate. Example 1 140 parts by weight of mica (average plate diameter: 150 µm, average thickness: 1.9 µm) was added to the binder composed of 30 parts by weight of an ethylene-vinyl acetate copolymer containing 60 wt% of vinyl acetate (VA = 60 wt%) and 70 parts by weight of a petroleum resin composed of 100 wt% of an aromatic petroleum resin (softening point: 103°C, main ingredients: 10 wt% of styrene, 20 wt% of vinyl toluene and 33 wt% of indene). The mixture was kneaded under heating for 10 minutes by an intensive mixer. The kneaded mixture was then rolled by calender rolls, thereby obtaining a damping sheet of 2 mm thickness. The damping sheet obtained was cut into a sheet of 15 mm width and 220 mm length and set on a steel plate substrate(15 mm width, 300 mm length and 0.8 mm thickness). The thus-obtained test piece was heated at 150°C for 30 minutes so as to fusion-bond the sheet to the base plate. The loss factors η were measured at various temperatures by a cantilever resonance method. The peak value of the loss factor η was 0.50 at a temperature of 40°C, which shows the damping sheet had an excellent damping effect. The adhesive strength was 40 kg/cm 2 , and the adhesive followability was 1 to 2 mm, both being excellent. Examples 2 to 4, Comparative Examples 1 to 9 Damping sheets were produced and the test pieces for evaluating the damping effect were obtained in the same way as in Example 1 except that the compositions were varied as shown in Table 1. The peak value of the loss factor η, the temperature at that time, the adhesive strength and the adhesive followability of each test piece are shown in Table 1. The petroleum resin containing 90 wt% of an aromatic petroleum resin in Example 2 had a softening point of 94°C and contained 15 wt% of styrene, 31 wt% of vinyl toluene and 16 wt% of indene as the main ingredients. The petroleum resin containing 10 wt% of an aromatic petroleum resin in Comparative Example 3 had a softening point of 80°C and contained 10 wt% of an aromatic petroleum resin mainly composed of styrene, vinyl toluene and indene and 90 wt% of an aliphatic petroleum resin mainly composed of isoprene and piperylene. The petroleum resin containing 60 wt% of an aromatic petroleum resin in Comparative Example 9 had a softening point of 101°C and contained 60 wt% of an aromatic petroleum resin mainly composed of styrene, vinyl toluene and indene and 40 wt% of an aliphatic petroleum resin mainly composed of isoprene and piperylene. Example 5 130 parts by weight of mica (average plate diameter: 150 µm, average thickness: 1.9 µm) and 25 parts by weight of granular magnetite powder were added to the binder composed of 30 parts by weight of an ethylene-vinyl acetate copolymer containing 60 wt% of vinyl acetate (VA = 60 wt%) and 70 parts by weight of a petroleum resin composed of 100 wt% of an aromatic petroleum resin (softening point: 103°C, main ingredients: 10 wt% of styrene, 20 wt% of vinyl toluene and 33 wt% of indene). The mixture was kneaded under heating for 10 minutes by an intensive mixer. The kneaded mixture was then rolled by calender rolls, thereby obtaining a damping sheet of 2 mm thickness. The damping sheet obtained was cut into a sheet of 15 mm width and 220 mm length and set on a steel plate substrate(15 mm width, 300 mm length and 0.8 mm thickness). The thus-obtained test piece was heated at 150°C for 30 minutes so as to fusion-bond the sheet to the base plate. The loss factors η were measured at various temperatures by a cantilever resonance method. The loss factors η at various temperatures are shown in Table 3. A loss factor η of not less than 0.3 (which shows a high damping effect) was maintained in such a wide temperature range as 26 to 56°C (the width of the temperature range is 30°C). That is, the damping sheet had a wide operating temperature range. The adhesive strength was 41 kg/cm 2 , and the adhesive followability was 1 to 2 mm, both being excellent. Examples 6 to 11, Comparative Examples 10 to 17 Damping sheets were produced and the test pieces for evaluating the damping effect were obtained in the same way as in Example 5 except that the compositions were varied as shown in Table 2. The loss factors η at various temperatures, the temperature range when the loss factors η was at not less than 0.3, the adhesive strength and the adhesive followability of each test piece are shown in Table 3. The petroleum resin containing 90 wt% of an aromatic petroleum resin in Example 6 had a softening point of 94°C and contained 15 wt% of styrene, 31 wt% of vinyl toluene and 16 wt% of indene as the main ingredients. The petroleum resin containing 10 wt% of an aromatic petroleum resin in Comparative Example 12 had a softening point of 80°C and contained 10 wt% of an aromatic petroleum resin mainly composed of styrene, vinyl toluene and indene and 90 wt% of an aliphatic petroleum resin mainly composed of isoprene and piperylene. The petroleum resin containing 60 wt% of an aromatic petroleum resin in Comparative Example 17 had a softening point of 101°C and contained 60 wt% of an aromatic petroleum resin mainly composed of styrene, vinyl toluene and indene and 40 wt% of an aliphatic petroleum resin mainly composed of isoprene and piperylene.

Claims: 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 not less than 65 wt% of an aromatic petroleum resin, 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') at least 30 parts by weight, per 100 parts by weight of said binder, of 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. A damping material according to claim 1 wherein said petroleum resin contains not less than 80 wt% of said aromatic petroleum resin. A damping material according to claim 1 or 2 wherein the softening point of said petroleum resin is 80 to 170°C. A damping material according to any one of the preceding claims wherein said scaly powder is at least one of mica, plate-like iron oxide particles or graphite. A damping material according to any one of the preceding claims wherein said scaly powder has an average plate diameter of 1 to 2000 µm and an average plate thickness of 0.01 to 100 µm. A damping material according to any one of the preceding claims wherein the content of said vinyl acetate is 32 to 65 wt%, the weight ratio of said ethylene-vinyl acetate copolymer to said petroleum resin is from 100:160 to 100:300, and the amount of said filler is 70 to 150 parts by weight per 100 parts by weight of said binder. A damping material according to any one of the preceding claims wherein said filler comprises not less than 1 part by weight to less than 50 parts by weight of the granular powder, the fibrous material or the mixture thereof per 100 parts by weight of said binder. A damping material according to claim 7, which comprises 31 to 180 parts by weight of the filler composed of the scaly powder and the granular powder, the fibrous material orthe mixture thereof, the amount of said scaly powder being 30 to 150 parts by weight per 100 parts by weight of said binder. A damping material according to claim 8, wherein the content of said vinyl acetate is 32 to 65 wt%, the weight ratio of said ethylene-vinyl acetate copolymer to said petroleum resin is from 100:160 to 100:300, the amount of said scaly powder is 50 to 150 parts by weight per 100 parts by weight of said binder, the amount of said granular powder, said fibrous material or the mixture thereof is 1 to 40 parts by weight per 100 parts by weight of said binder, and the total amount of said filler is 70 to 151 parts by weight per 100 parts by weight of said binder. A damping material according to any one of the preceding claims wherein said granular powder has an average particle diameter of 0.05 to 100 µm, and said fibrous material is a fibrous, acicular or spindle-shaped material having an average major axial diameter of 0.1 to 50,000 µm, an average minor axial diameter of 0.02 to 250 µm and an aspect ratio of not less than 3.0. A damping material according to any one of the preceding claims wherein said granular powder is at least one of hematite particles, magnetite particles, maghemite particles, strontium ferrite particles, barium ferrite particles, quartz sand, talc, clay, lead powder, iron powder, titanium oxide, zinc white, barium sulfate or calcium carbonate. A damping material according to any one of the preceding claims wherein said fibrous material is at least one of magnetite, maghemite, a synthetic fiber, asbestos, natural organic fibers, glass fibers or carbon fibers.

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
Applicants: HIROTANI CO LTD, TODA KOGYO CORP, HIROTANI CO., LTD., TODA KOGYO CORP.
Application year: 1992
Main classification: C08L31
IPC codes: C08K7, C08K3