Constraint type vibration damping material

Abstract: A constraint type vibration damping material, which exhibits a high vibration damping performance, ease of processing and low cost, is provided, in which a polymer viscoelastic layer (2a) is formed on at least one surface of a rigid body such as a metal plate (1a), and a hard cover layer (3a) is formed on the polymer viscoelastic layer and has a rigidity modulus greater than that of the viscoelastic layer (2a) and smaller than that of the rigid body (1a).

Description: The present invention relates to a constraint type vibration damping material consisting of a rigid body such as a metal plate and a polymer viscoelastic body having a good vibration absorbing property, and in particular to an improvement of the constraint type vibration damping material suitable for use as shim for preventing brake squeal in an automobile or as a facing plate for a building. Heretofore, as composite vibration damping materials formed by combining metal plates and polymer viscoelastic layers there are known vibration damping materials having a structure, in which one or two polymer viscoelastic layer(s) 2 made of rubber or synthetic resin is/are superposed on one or two surface(s) of a thin metal plate 1, as indicated in Fig. 14. A structure in which a polymer viscoelastic layer 2 is provided between two metal plates 1 in the form of a sandwich, as indicated in Fig. 15, is also known. The vibration damping material indicated in Fig. 14 is called "a non-constraint type", in which vibration is absorbed by "expansion and contraction deformation" of the polymer viscoelastic layer due to bending vibration, while the vibration damping material indicated in Fig. 15 is called "a constraint type", in which vibration is absorbed by "shearing deformation" of the polymer viscoelastic layer due to bending vibration. As explained above, there are basically two kinds of structures of non-constraint type and constraint type in composite vibration damping materials, either of which has advantages and disadvantages. For example, the following vibration damping structures are used as conventional shims for preventing brake squeal in an automobile, each of which has advantages and disadvantages. a) Rubber coat metal type: in which the two surfaces of a metal plate are coated with rubber and which in use, is fixed by spring-like nails on a brake pad. Vibration is absorbed by viscoelasticity of the rubber, which alleviates brake squeal. Advantages: low cost, both in raw material and in mounting work. Disadvantages: low vibration absorbing capacity because it is of the non-constraint type (in which vibration is absorbed by expansion and contraction deformation of rubber). b) Vibration damping steel plate type: in which a viscoelastic layer is provided between two metal plates and which, in use, is fixed by spring-like nails as described in (a) above. Vibration is absorbed by the viscoelastic layer, which prevents squeal. Advantages: it exhibits a higher vibration absorbing capacity with respect to the non-constrained type owing to its constraint type damping structure (shearing deformation of the viscoelastic layer); and since the surfaces thereof are metallic, it is resistant to damage by piston pressure. Disadvantages: raw materials are expensive; it is difficult to perform processing (nail bending, etc.); and it can be pealed off. c) Type stuck by using adhesive, e.g. in which damping steel plates are stuck by using thermosetting resin. Although all of them have the constraint type vibration damping structure and a high squeal preventing effect, they are more expensive both in raw materials and in adhering work. The following vibration damping structures are used for conventional sound isolation facing plates, each of which has advantages and disadvantages. a) Damping steel plate type: in which a viscoelastic layer is provided between two metal plates and vibration is absorbed by the viscoelastic layer, generation of noise being thus suppressed . Advantages: it exhibits a high vibration absorbing effect owing to its constraint type vibration damping structure (shearing deformation of the viscoelastic body); since the viscoelastic layer is in the interior, it is hardly influenced by environmental effects and has an excellent durability. Disadvantages: raw materials therefor are expensive; in general, it is difficult to perform bending work, etc; and if interlayer adhering strength is low, pealing can occur. b) Damping paint type: in which paint, etc., having a vibration damping property is applied mainly on the building site to one surface (on the inner side). Advantages: bending work, etc. can be easily performed owing to its non-constraint type structure; and raw material costs are low. Disadvantages: the vibration absorbing property is low because of its non-constraint type damping structure (vibration is absorbed by expansion and contraction deformation); application costs are high; and it has a poor stability in quality and it is affected by the environment. From the foregoing it is clear that the performance and the cost of the prior art shims for preventing brake squeal and sound isolation facing plates using vibration damping materials conflict in many respects with each other. Generally vibration damping performance as the vibration damping material can be improved remarkably by adopting the constraint type vibration damping structure. As described above, the constraint type vibration damping structure is one, in which a polymer viscoelastic body is provided (constrained) between two metal plates, etc. having a high rigidity and vibration energy is transformed into thermal energy at vibration by the shearing deformation of the polymer viscoelastic body, which attenuates the vibration as the result. Therefore this type of vibration damping structure exhibits a performance almost equal to that of the non-constraint type (in which a viscoelastic body is stuck only to one surface of a vibrating body) with a thickness of the polymer viscoelastic body 1/5 time as small as that of the latter. Consequently it can be said, in order to improve vibration damping performance, that it is preferable to adopt the constraint type vibration damping structure rather than the non-constraint type, and a number of these types of product, represented by the vibration damping steel plate, are currently on the market. However, for the constraint type (specifically the vibration damping steel plate), since two constraining plates (metal plates, etc) are adhered through a polymer viscoelastic body, there are disadvantages such as poor ease of processing, e.g. bending, dishing, etc. Furthermore, even if the processing can be executed, the damping performance decreases because of internal peeling, and raw materials and work costs are considerably higher. EP-A-0335642 relates to a composite vibration damping material. US-A-4204022 relates to a laminate material that comprises a viscoelastic layer. The principal object of the present invention is to provide a constraint type vibration damping material capable of exhibiting a high vibration damping performance for use in a variety of technical fields including prevention of brake squeal and sound isolation facing plates. Ease of processing and low costs are also associated with the damping material of the present invention. Accordingly the present invention provides a constraint type vibration damping material comprising: (i) a rigid member, (ii) a polymer viscoelastic layer formed directly on at least one surface of the rigid member, and (iii) a hard cover layer formed directly on the polymer viscoelastic layer and disposed on an outer surface of the constraint type vibration damping material, wherein the rigid member comprises a metal plate, an inorganic plate or a thermosetting resin plate, the polymer viscoelastic layer comprises a synthetic rubber or a thermosetting resin, and the hard cover layer comprises molybdenum bisulphide or a thermosetting type resin or a resin of the type hardened by ultraviolet rays, and wherein the hard cover layer has a rigidity modulus less than that of the rigid member and greater than that of the polymer viscoelastic layer. For the rigid body a high rigidity plate can be used, which is a metal plate made of iron, aluminium, stainless steel, copper, etc.; an inorganic board such as a calcium silicate plate, a gyps board; and a thermosetting resin plate made of phenol resin, polyimide resin, etc. For the polymer viscoelastic layer formed on the surface of the rigid body raw materials having high vibration loss coefficients can be used, which are synthetic rubbers such as natural rubber, NBR, SBR, butyl rubber, acryl rubber, silicone rubber, fluorine rubber, etc.; and thermosetting resins such as polyethylene resin, polyamide resin, etc. The hard cover layer comprises molybdenum bisulphide or a polymer resin of thermosetting type such as phenol resin, urea resin, or a polymer resin hardened by ultraviolet ray. They can be arbitrarily selected according to object of utilization or required characteristics just as the polymer viscoelastic layer. It is preferable to select the rigid body, the polymer elastic layer and the hard cover layer as indicated in TABLE 1. Among them there should be a relation of RIGID BODY > HARD COVER LAYER > POLYMER VISCOELASTIC LAYER. In case where the rigidity of these constituent materials varies, dependent on the temperature, similar effects can be obtained, if the relation is valid in a temperature domain, where they are used. RIGIDITY / RAW MATERIAL RIGIDITY MODULUS (N/m 2 ) PREFERABLE RIGIDITY MODULUS (N/m 2 ) RIGID BODY (IRON PLATE, ETC.) 1x10 8 ∼2x10 11 1x10 8 ∼2x10 11 POLYMER VISCOELASTIC LAYER (RUBBER, ETC.) 1x10 3 ∼1x10 9 1x10 5 ∼1x10 8 HARD COVER LAYER (THERMOSETTING RESIN, ETC.) 1x10 7 ∼1x10 10 1x10 8 ∼1x10 9 The vibration damping material can be easily fabricated by a following concrete method. For example, one (or two) surface(s) of a metal plate is (are) coated with rubber dissolved in a solvent. After vulcanization, the surface of this rubber layer is coated with a thermosetting resin layer having a rigidity modulus, which is greater than that of the rubber layer and smaller than that of the metal layer. Thereafter the resin layer is hardened by heating it. In this case, it can be fabricated in continuous fabrication steps. In particular, since a conventional coating step can be used for both the coating steps for the polymer viscoelastic layer and the hard cover layers, this method is advantageous also from the point of view of the cost. In a practical application, e.g. for a brake shim, a thermosetting polymer resin having a high rigidity may be selected, which has a resistance against compression and rigidity so high that the resin layer can resist attack by a brake piston as well as a high heat resistance. In case where the sliding property has influences on the brake squeal, it is possible to realize an alleviation of vibration generating force and a high vibration damping effect by the constraint type vibration damping structure at the same time by selecting a thermosetting polymer resin having a high sliding property or by coating the surface thereof with a cover layer made of molybdenum bisulfide having a higher sliding property. On the other hand, for facing plates for a building, it can be realized by using a surface decorating metal plate for the metal layer and by selecting a thermosetting polymer resin, which can follow bending or dishing processing, for the resin layer having a high rigidity. These are strictly only examples and since a constraint type vibration damping structure can be easily realized by selecting constituent raw materials according to the object, it can be applied to all the fields, where it was heretofore not able to be used because of bottle-necks such as high cost, difficulty of processing, etc. It can be said that this is another advantage of the present invention. By the vibration damping material thus constructed, since the cover layer, which is formed on the surface of the polymer viscoelastic layer on the rigid body and has a high rigidity, acts as a constraining material forming a pair with the rigid body, without adhering another rigid body such as a metal plate, etc. as a constraining plate, it is possible to obtain a constraint type vibration damping structure as the result having a high vibration damping performance. In case where rubber, etc. having a specifically small rigidity modulus are selected for the polymer viscoelastic layer, since rubber itself is isotropic, it is easily deformed in any direction. Nevertheless, since flow of the rubber from the end portion can be suppressed against compressive force owing to the presence of the hard cover layer, apparent elastic modulus is increased and as the result compression resisting force can be reinforced. Further, since no constraining force acts in the shearing direction, it is possible to realize an anisotropy so that the elastic modulus of rubber can be exhibited as it is. This is efficient for alleviating the vibration generating force caused by a stick slip phenomenon accompanied by the rotating force of a rotor in the shearing direction, when a high strength is needed against the compressive force, which is effective a shim for preventing the squeal. From the point of view of the cost, the rubber coat metal type can be fabricated in same fabrication steps. Therefore, although the raw material cost used for the hard cover layer is raised up, since the thickness of the polymer viscoelastic layer can be decreased by adopting the constraint structure, it can be fabricated at an almost same cost. For the vibration damping steel plate, since the adhering step on the metal plate is unnecessary, cost can be decreased considerably. Further, in either case, since not only the vibration damping property but also easiness of processing and durability can be improved, also from the collective point of view it is possible to obtain a remarkable cost lowering effect. The present invention will now be further described with reference to the following drawings, in which: Fig. 1 is a schematical diagram showing the construction of the vibration damping material according to an embodiment of the present invention; Fig. 2 is a schematical diagram showing the construction of the vibration damping material according to another embodiment of the present invention; Fig. 3 is a schematical diagram showing the construction of the vibration damping material according to still another embodiment of the present invention; Fig. 4 is a schematical diagram showing the construction of the vibration damping material according to still another embodiment of the present invention; Fig. 5 is a schematical diagram showing the construction of the vibration damping material according to still another embodiment of the present invention; Fig. 6 is a schematical diagram showing the construction of the vibration damping material according to still another embodiment of the present invention; Fig. 7 is a schematical diagram showing the construction of the vibration damping material according to still another embodiment of the present invention; Fig. 8 is a schematical diagram showing the construction of a vibration damping material representing a compared example; Fig. 9 is a schematical diagram showing the construction of another vibration damping material representing another compared example; Fig. 10 is a schematical diagram showing the construction of still another vibration damping material representing still another compared example; Fig. 11 is a graph indicating vibration damping characteristics of several vibration damping materials; Fig. 12 is a graph indicating vibration damping characteristics of other vibration damping materials; Fig. 13 is a graph indicating vibration damping characteristics of still other vibration damping materials; Fig. 14 is a schematical diagram showing the construction of a prior art non-constraint type vibration damping material; and Fig. 15 is a schematical diagram showing the construction of a prior art constraint type vibration damping material. Hereinbelow various embodiments of the present invention will be explained in detail, together with several compared examples, referring to the drawings. EMBODIMENT (1) As indicated in Fig. 1, in the present embodiment, a surface of a rubber coat metal (RCM) mode by coating one surface of a metal plate 1a, which is a cold pressed steel plate (SPCC), with a rubber layer 2a of NBR is coated with a phenol resin layer 3a having a rigidity greater than that of the rubber layer, the phenol resin layer 3a being hardened by thermal processing to obtain a hard cover layer. The RCM is a plate having an overall thickness of 0.52mm widely used usually as brake shim material, in which one surface of a cold pressed steel plate (SPCC) 0.4mm thick is coated with NBR dissolved in a solvent in a thickness of 0.12mm which is thereafter dried and vulcanized. Subsequently the surface of the rubber layer is coated with solution-like phenol resin, which is dried and hardened in an oven for heat treatment to form a resin layer 0.15mm thick, in order to obtain a vibration damping material. Further, the vulcanization of rubber and the hardening processing can be effected simultaneously by coating the surface of the rubber layer with phenol resin in the course of the fabrication of the RCM (in a state where the rubber is not yet vulcanized). In this way it is possible to intend increase in adhering force between the rubber layer and the phenol resin layer as well as decrease in the number of fabrication steps and cost reduction. EMBODIMENT (2) As indicated in Fig. 2, in the present embodiment, a color steel plate 1b having a decorative layer is used as the metal plate. One surface thereof is coated with a rubber layer 2a, which is dried and subjected to vulcanization processing. The surface of the rubber layer is coated with a phenol resin layer 3a, which is hardened by thermal processing to obtain a hard cover layer. A color plate is used usually as a facing plate and here a plate 0.27mm thick is used, which is coated with rubber so that a layer 0.12mm thick is obtained after vulcanization. Thereafter the surface of the rubber layer is coated with solution-like phenol thermosetting resin, which is dried and hardened in an oven for heat treatment to form a resin layer 0.5mm thick, in order to a vibration damping material. EMBODIMENT (3) As indicated in Fig. 3, in the present embodiment, the two surfaces of a metal plate 1a are coated with rubber layers 2a of NBR in a thickness of 0.12mm and the surface of one of the rubber layers 2a is coated with a phenol resin layer 3a in a thickness of 0.15mm. EMBODIMENT (4) As indicated in Fig. 4, in the present embodiment, the two surfaces of a metal plate 1a are coated rubber layers 2a of NBR in a thickness of 0.12mm and the two outer surfaces of the rubber layers is coated with phenol resin layers 3a in a thickness of 0.15mm. EMBODIMENT (5) As indicated in Fig. 5, in the present embodiment, the two surfaces of a metal plate 1a are coated with rubber layers 2a of NBR in a thickness of 0.12mm and after vulcanization of the rubber the surface of one of the rubber layers is coated with a molybdenum bisulfide layer 3b in a thickness of 0.05mm. EMBODIMENT (6) As indicated in Fig. 6, in the present embodiment, the two surfaces of a metal plate 1a are coated with rubber layers 2a of NBR in a thickness of 0.12mm and the surface of one of the rubber layers 2a is coated with a phenol resin layer 3a in a thickness of 0.15mm, while the surface of the other rubber layer 2a is coated with a molybdenum bisulfide layer 3b in a thickness of 0.05mm. EMBODIMENT (7) As indicated in Fig. 7, in the present embodiment, one surface of a metal plate 1a is coated with a rubber layer 2a of NBR in a thickness of 0.12mm, while the other surface of the metal plate is coated with an acryl rubber layer 2b in a thickness of 0.12mm. The surface of the rubber layer 2a is coated with a phenol resin layer 3a to obtain a hard cover layer. Further the surface of the rubber layer 2b is coated with a polyimide resin layer 3c to obtain another hard cover layer. COMPARED EXAMPLE (1) As indicated in Fig. 8, in the present compared example, the two surfaces of a metal plate 1a are coated with rubber layers 2a. This is widely used usually as a brake shim material and its overall thickness is 0.64mm. COMPARED EXAMPLE (2) As indicated in Fig. 9, in the present compared example, color steel plates 1b, each of which has a decorative layer, are used as metal plates and a vibration damping steel plate is formed by putting a thermoplastic resin film 4 generally used between the two steel plates by adhesion. Here a polyethylene resin film 65µm thick is used for the thermoplastic resin film and the color steel plates used are 0.27mm thick. It is fabricated by fixing the polyethylene resin film on the first color steel plate in a state where a tensile force is applied thereto so that no wrinkles are produced and after having superposed the second plate thereon by adhering them to each other by applying heat and pressure thereto by hot press. COMPARED EXAMPLE (3) A color steel plate 1b 0.27mm thick having a decorative layer corresponding to JIS G3312 as indicated in Fig. 10 is used. The graph indicated in Fig. 11 shows vibration damping characteristics of EMBODIMENT (3) in comparison with COMPARED EXAMPLE (1). The loss coefficient η is used as an index showing speed of vibration attenuation and vibration damping characteristics are evaluated by investigating its dependence on measurement temperature and its height in the level. The loss coefficient is measured by the mechanical impedance method. As indicated in the graph, it can be admitted that the damping characteristics are significantly improved with respect to the prior art vibration damping material by using the vibration damping material according to EMBODIMENT (3), in which the surface of the rubber layer is coated with the thermosetting resin layer. This is because the thermosetting resin layer acts as a constraining layer. For this reason it is possible to obtain a high vibration damping performance at a same cost as a prior art RCM. The graph indicated in Fig. 12 shows vibration damping characteristics of EMBODIMENT (2) in comparison with COMPARED EXAMPLES (2) and (3). As it can be seen from this graph, it can be admitted that the vibration damping characteristics are significantly improved with respect to a usual color steel plate and that although the peak level is somewhat lower than that of the vibration damping steel plate, it has a small temperature dependency and it can be used in a wide temperature domain. The graph indicated in Fig. 13 shows vibration damping characteristics of EMBODIMENT (5) in comparison with COMPARED EXAMPLE (1). TABLE 2 shows superficial properties of matter of EMBODIMENT (5) in comparison with COMPARED EXAMPLE (1). PENCIL HARDNESS STATIC FRICTION COEFFICIENT EMBODIMENT (5) STAND 3H∼4H 0.1∼0.2 COMPARED EXAMPLE (1) STAND HB∼H 0.3∼0.5 As indicated in TABLE 2, according to EMBODIMENT (5), since it is possible to realize not only improvement of the vibration damping characteristics but also increase in superficial hardness and decrease in friction coefficient at the same time, the vibration damping material is resistant specifically to compressive force of the brake piston for the disk brake of an automobile. Apart therefrom it is confirmed that it has a number of satisfactory characteristics that it gives rise hardly to stick slip, which causes presumably vibration generation, because it slides easily, etc. As explained in detail in the above, the vibration damping material according to the present invention has following effects. (1) Since it is resistant to compressive force and there are no bulging out of the polymer viscoelastic layer, etc., it stands a severe environment of use. (2) Since it is so constructed that a usual polymer viscoelastic layer is provided between a rigid body such as a metal plate, etc. and a hard cover layer having a rigidity, a high vibration damping effect due to shearing deformation can be obtained. (3) Processing can be effected for the vibration damping material using a hard cover layer having a high rigidity, while for a usual constraint type vibration damping material (in which a polymer viscoelastic layer is between two metal plates), since the two metal plates acting as rigid bodies push each other, processing such as bending, dishing, etc. can be hardly effected. (4) Since particularly a vibration damping material having a hard cover layer made of molybdenum bisulfide can realize improvement of the vibration damping characteristics, increase in superficial hardness of the vibration damping material, and decrease in friction coefficient at the same time, it resistant to compressive force of the brake piston and further it has a number of satisfactory characteristics at the same time that it gives rise hardly to stick slip, which causes presumably vibration generation, because it slides easily, etc. (5) The polymer viscoelastic layer and the hard cover layer can be formed on the surface of the rigid body by continuous fabrication steps, it can be advantageous also from the point of view of the cost.

Claims: A constraint type vibration damping material comprising: (i) a rigid member, (ii) a polymer viscoelastic layer formed directly on at least one surface of the rigid member, and (iii) a hard cover layer formed directly on the polymer viscoelastic layer and disposed on an outer surface of the constraint type vibration damping material, characterised in that the rigid member comprises a metal plate, an inorganic plate or a thermosetting resin plate, the polymer viscoelastic layer comprises a synthetic rubber or a thermosetting resin, and the hard cover layer comprises molybdenum bisulphide or a thermosetting type resin or a resin of the type hardened by ultraviolet rays, and wherein the hard cover layer has a rigidity modulus less than that of the rigid member and greater than that of the polymer viscoelastic layer. A constraint type vibration damping material as claimed in claim 1, wherein first and second polymer viscoelastic layers are formed on a front and a rear surface of the rigid member, respectively, and first and second hard cover layers are formed on the first and second polymer viscoelastic layers, respectively. A constraint type vibration damping material as claimed in claim 1 or claim 2, wherein the rigidity modulus of the rigid member is in the range of from 1x10 8 to 2x10 11 N/m 2 , the rigidity modulus of the polymer viscoelastic layer is in the range of from 1x10 3 to 1x10 4 N/m 2 and the rigidity modulus of the hard cover layer is in the range of from 1x10 7 to 2x10 8 N/m 2 . A constraint type vibration damping material as claimed in any one of the preceding claims, wherein the rigid member comprises a metal plate made of iron, aluminium, stainless steel or copper, or an inorganic material plate made of calcium silicate, or a gyps board, or a thermosetting resin plate made of phenol resin or polyimide resin; and wherein the polymer viscoelastic layer comprises a synthetic rubber, natural rubber, NBR, SBR, butyl rubber, acryl rubber, silicone rubber, fluorine rubber, a thermosetting polyimide resin or a polyamide resin; and wherein the hard cover layer comprises molybdenum bisulphide, a thermosetting type resin or a resin of the type hardened by ultraviolet rays, preferably urea resin, phenol resin or polyimide resin. A constraint type vibration damping material as claimed in any one of the preceding claims for use as a brake shim, wherein the hard cover layer comprises a thermosetting polymer resin layer having a high heat resistance and a resistance against compression and rigidity such that the resin layer can resist attack by a brake piston. A constraint type vibration damping material as claimed in claim 5, wherein the thermosetting polymer resin has a high sliding property. A constraint type vibration damping material as claimed in claim 5 or claim 6, wherein the hard cover layer is coated with a cover made of molybdenum bisulfide having a high sliding property. A constraint type vibration damping material as claimed in any one of claims 1 to 4 for use as a sound isolation facing building material, wherein the rigid member comprises a surface decorating metal plate and the hard cover layer comprises a thermosetting polymer resin layer which can follow bending and dishing processing. A constraint type vibration damping material as claimed in any one of claims 1 to 3, wherein the rigid member comprises a cold press steel plate; the polymer viscoelastic layer comprises a rubber layer; and the hard cover layer comprises a phenol resin layer. A constraint type vibration damping material as claimed in any one of claims 2 to 4, wherein the first and second polymer viscoelastic layers are rubber layers; the first hard cover layer is a phenol resin layer; and the second hard cover layer is a phenol resin layer, a molybdenum bisulfide layer or a polyimide resin layer. A constraint type vibration damping material as claimed in claim 10, wherein the first polymer viscoelastic layer is an NBR rubber layer and the second polymer viscoelastic layer is an acryl rubber layer.

Inventors: NIWA TAKAHIRO, SAITO HIROSHI, YANO KUNIHIKO, NIWA, TAKAHIRO, SAITO, HIROSHI, YANO, KUNIHIKO
Applicants: NICHIAS CORP, NICHIAS CORPORATION
Application year: 1996
Main classification: B32B27
IPC codes: F16D65, B32B27, B32B15