JP2568089B2 - Resin composition for composite type damping steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Object of the Invention "Industrial field of application" The present invention relates to a resin composition used for a composite vibration-damping steel sheet formed by forming a resin layer between two steel sheets. Things
Particularly, the present invention relates to a resin composition that enables production of a composite vibration-damping steel sheet having excellent vibration damping action and high adhesion performance at or near room temperature, and the obtained composite vibration-damping steel sheet is a noise suppressing material. As a building material such as stairs, doors, floor materials, etc., it is also used for oil pans of automobiles, dash panels around the body, floor panels, loop panels, etc. that were difficult to use conventionally, or for motors, compressor covers, etc. It can be used and can be widely used in the automobile industry, the civil engineering and construction industry, and the electrical machinery industry.

"Prior Art" A vibration-damping steel plate is a noise-preventing material that interposes a viscoelastic resin (hereinafter referred to as intermediate resin) layer between two steel plates and converts the vibration applied to the steel plate by the intermediate resin layer into heat energy. is there. This vibration-damping steel plate has been used or is being considered for automobile oil pans, stairs, doors, flooring and other building materials, motors, compressor covers, etc. in response to the recent needs for noise regulation.

As an intermediate resin for this damping steel sheet, polyurethane (Japanese Patent Laid-Open No. 47-19277) and vinyl urethane resin (Japanese Laid-Open Patent Publication No.
0-39737), polyester resin (JP-A-50-143880),
Polyamide resin (JP-A-51-79146), polyisobutylene (JP-A-54-43251), ethylene / α-olefin (JP-A-55-84655), EVA (JP-A-57-34949), cross-linked polyolefin (JP-A-57-34949) 59-152847), polyvinyl acetal (JP-A-60-38149), and the like have been studied, and asphalt, synthetic rubber, acrylic adhesives, epoxy resins, etc. are known to have vibration damping performance. Of these, acrylic pressure-sensitive adhesives, isobutylene rubber, and resins such as EVA that are flexible at room temperature have relatively high vibration damping at temperatures near room temperature, but the adhesive strength is low because the cohesive force of the resin at room temperature is weak. Since the vibration-damping steel plate using the resin is weak and cannot withstand the forming process and has no heat resistance, these vibration-damping steel plates were only used for building materials used in a state close to a flat plate.

In addition, polyolefin resins modified by copolymerization, blending, etc., such as ethylene / α-olefin resins, are relatively superior in vibration damping at the high temperature side of 50 ° C to 100 ° C compared to the former, and the resin aggregates at room temperature. It is said that the vibration-damping steel plate using the resin is suitable as a vibration-damping steel plate for use in high temperatures such as oil pans of automobiles because of its high strength and compatibility with molding. However, even if both are limited in their uses, it cannot be said that they have reached a level sufficient to satisfy vibration damping performance and adhesive performance,
Furthermore, there are still resins suitable for damping steel plates that have high damping performance at temperatures near room temperature, including parts around automobile bodies, and that require strong bonding performance to follow molding processing and bonding heat resistance at high temperatures. Not found.

Further, as an example of studying a polyester resin as a resin for a vibration damping steel plate, a so-called foamed polyurethane resin prepared by making a urethane prepolymer from a polyester resin having a molecular weight of 1800 or less and an isocyanate compound and using an amine compound or the like as a curing agent 47-19277) Polyester resin composed of glycol and phthalic acid and having a glass transition temperature of 0 ° C to 60 ° C (Japanese Patent Laid-Open No. 50-143880), which includes a resin obtained by mixing an organic peroxide and a filler with a polyester resin. Polyurethane resin has poor vibration damping property and insufficient adhesion performance, and the resin does not have sufficient adhesion performance at room temperature, and lacks heat resistance and durability around 100 ° C, for example. Does not have sufficient performance as. Or, the purpose is to prevent strength deterioration due to high temperature processing or heating after processing by organic peroxide cross-linking, but if cross-linked before lamination with steel sheet, adhesive strength will be insufficient, and At times, there are problems such as foaming due to generation of oxygen from the peroxide if crosslinking occurs, and resin flowing out when the crosslinking reaction does not proceed sufficiently, and the adhesive performance itself is poor, which is not a satisfactory level.

"Problems to be Solved by the Invention" The present invention solves the above problems, has high vibration damping performance at around room temperature, specifically in the range of 0 to 50 ° C, and is excellent in following molding processing. Adhesive performance and high temperature, specifically 10
An object of the present invention is to provide a resin composition for a composite type vibration-damping steel sheet that has heat resistance at 0 ° C. or higher and is excellent in laminating processability.

(B) Structure of the Invention “Means for Solving Problems” In order to achieve the above-mentioned object, the present inventors diligently studied,
The inventors have found that a composite vibration-damping steel sheet having extremely excellent properties can be obtained by using a resin composition composed of a specific saturated copolyester and a polyvalent isocyanate compound, and arrived at the present invention.

That is, the present invention is characterized in that it has a weight average molecular weight of more than 6000 and a softening point of 50 ° C. or more and 150 ° C. or less and a saturated copolymerized polyester and a polyvalent isocyanate compound as a cross-linking agent and does not contain a chain extender. The present invention relates to a resin composition for a composite type vibration damping steel plate.

 The present invention will be described in more detail below.

○ Saturated Copolyester Resin The saturated copolymer polyester resin used in the present invention is R
The softening point measured by & B softening point (JIS-K-2531) is 5
If the softening point is 0 ° C or more and 150 ° C or less and the softening point is less than 50 ° C, the resin may flow out during lamination adhesion, and stains during processing due to the adhesiveness of the resin may cause problems due to stickiness, and softening may occur. If the point is higher than 150 ° C, not only a high temperature is required for lamination heating and adhesion, but also the adhesion performance itself is deteriorated. The preferred softening point for the present invention is
It is above 80 ℃ and below 120 ℃.

The molecular weight of the resin is 60 as the weight average molecular weight measured by liquid gas chromatography in terms of polyethylene.
If it is more than 00 and the weight average molecular weight is 6000 or less, not only the vibration damping performance is deteriorated but also the adhesion performance is poor, and the resin flows out during lamination and the strength immediately after adhesion is extremely low. Cause Preferred for the present invention are those having a weight average molecular weight of 20,000 or more and 50,000 or less.

Saturated copolyester is dimethyl terephthalic acid,
Aromatic dibasic acids such as terephthalic acid, isophthalic acid, phthalic acid, succinic acid, glutaric acid, adipic acid, β-methyladipic acid, pimelic acid, 1,6-hexanedicarboxylic acid, azelaic acid, sebacic acid, nonanedicarboxylic acid acid,
Aliphatic dibasic acids such as decanedicarboxylic acid and hexadecanedicarboxylic acid and ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,2 -Pentadiol, 1,
5-pentadiol, 3-methylpentadiol, 1,3-
Hexanediol, 1,6-hexanediol, 1,4-cyclohexanediol, hydrogenated bisphenol A, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, polytetramethylene glycol, and other glycols or their residue formation Polyesters composed of derivatives or caprolactones are preferred, but the preferred saturated copolyesters of the present invention are those having a terephthalic acid residue of 30 mol% or more and 90 mol% or less among the acid components. The polyester having a content of less than 30 mol% has insufficient cohesive force, weakening the adhesive strength, and it is difficult to obtain the strength immediately after laminating and bonding, which may cause a trouble during processing. Further, if it exceeds 90 mol%, the adhesive performance may be similarly deteriorated, which is not preferable. When the terephthalic acid residue is used in the above range, examples of the dibasic acid used in combination include the above-mentioned aromatic dibasic acid or aliphatic dibasic acid, but preferred are one or more. Aliphatic dibasic acids, especially adipic acid,
Any of sebacic acid may be mentioned. The glycol component is preferably an ethylene glycol residue of 30 mol% or more and 80 mol% or less, and an ethylene glycol residue of 30 mol% or more.
If it is less than mol%, the adhesive performance will be reduced, and if it exceeds 80 mol%, not only the adhesive performance will be similarly deteriorated, but also good vibration damping performance may not be obtained. % And 70 mol% or less. When the ethylene glycol residue is used in the above range, examples of the glycol component used in combination include the above-mentioned glycols, and more preferable ones are hexanediol-based glycols having 6 carbon atoms, polyethylene glycol, and polytetramethylene. Mention may be made of polyoxyalkylene glycols such as glycols. Examples of the saturated copolyester of the present invention include unsaturated fatty acids such as maleic acid, fumaric acid, and dimer acid, fatty acids having more than two functions such as trimellitic acid, trimethylolpropane,
It is also possible to use those obtained by copolymerizing a compound having a hydroxyl group exceeding bifunctionality, such as pentaerythritol, but these monomers reduce the adhesion performance, impair the adhesion durability, or the vibration damping performance itself. Therefore, use within a range that does not impair the features of the present invention is preferable.

As the saturated copolyester of the present invention, those having a glass transition temperature of 20 ° C. or less measured by a viscoelastic spectrometer are preferable, and those having a glass transition temperature of more than 20 ° C. are not only low in vibration damping performance at around room temperature. There is also a risk that the adhesive performance will be reduced. More preferred is one having a glass transition temperature of 0 ° C. or lower.

Further, considering the lamination processability of the vibration-damping steel sheet, the saturated copolyester of the present invention is preferably toluene, MEK, those soluble in a general-purpose solvent such as ethyl acetate, by dissolving in the solvent, to the steel sheet Advantages such as easy coating, no gas entrapment in the laminated portion, and easy mixing of conductive powder, filler, and additive necessary for imparting spot weldability during processing are obtained.

○ Synthetic method of saturated copolyester The saturated copolyester used in the present invention can be synthesized by a conventional method. Generally, the esterification reaction of the above-mentioned dibasic acid and glycol and subsequent excess at high temperature and reduced pressure are excessive. Synthesized by transesterification while distilling off the glycol of, or pre-synthesized polyethylene terephthalate, polybutylene terephthalate, etc. in the presence of the desired dibasic acid and excess glycol,
It can be depolymerized and similarly synthesized by a transesterification reaction. For example, while heating at 150 ℃ ~ 220 ℃, dibasic acid and glycol as a main raw material under normal pressure, in the presence of a catalyst mainly composed of a metal salt, oligoesterification by an esterification reaction, followed by normal 200 ℃ under pressure and reduced pressure
By heating to ~ 270 ° C and distilling off excess glycol, a saturated copolymerized polyester having a high molecular weight is synthesized. At this time, it is preferable to add 1.5 times to 2 times the amount of glycol in the desired polyester composition to synthesize, and the composition of the polyester produced at this time is to measure the molar ratio of monomer residues by ¹ H-NMR. Adjusted by. The polymerization catalyst is tetra-n-butoxytitanium,
It is appropriately selected from ordinary catalysts composed of metal salts such as zinc acetate, antimony trioxide, potassium oxalate titanate and the like.

○ Polyvalent isocyanate As the polyvalent isocyanate used in the present invention, a compound having at least two or more isocyanate groups in the molecule, specifically, 2,4-tolylene diisocyanate, 2,6-
MDI derivatives such as tolylene diisocyanate (commonly known as TDI), methylene-bis-4phenyl isocyanate (commonly known as MDI), polymethylene polyphenyl polyisocyanate or polyol modified MDI, hexamethylene diisocyanate (commonly known as HDI) and its derivatives , Isophorone diisocyanate (commonly known as IPDI) and its derivatives, TDI-based adduct polyisocyanate obtained by adding TDI to trimethylolpropane, etc., for example, as commercially available products, Coronate L, Coronate HL (Nippon Polyurethane), Dismophen L,
Dismodur N (Sumitomo Bayer Urethane), pre-reacted polymerized polyisocyanate, for example, as commercially available products, Sprasec 3240, 3250, Coronate 2030,
2031, Dismodule IL, HL (Sumitomo Bayer Urethane), blocked isocyanate with isocyanate masked with caprolactam, etc., terminal isocyanate prepolymer obtained by previously reacting low molecular weight polyether with the above-mentioned polyvalent isocyanate, etc. Can
Although any of them can be used, adduct polyisocyanate and polymerized polyisocyanate are preferable for the present invention because they significantly improve the adhesiveness. The amount of isocyanate added to the saturated copolyester is 0.5 equivalent or more per 1 equivalent of the hydroxyl group in the saturated copolyester calculated from the weight average molecular weight 2
It is preferably 0 equivalent or less, and if it is less than 0.5 equivalent, the adhesion performance may be insufficient, the heat resistance after lamination may be insufficient, and the vibration damping performance may be deteriorated. On the other hand, if it exceeds 20 equivalents, the durability after lamination may be reduced, or the vibration damping performance itself may be unsatisfactory. More preferably 2 equivalents or more
It is preferable to add an excess amount of isocyanate of 10 equivalents or less, particularly 3 equivalents or more and 8 equivalents or less. At this time, the effect obtained by the present invention can be obtained even when a part of the isocyanate is reacted with the above polyester in advance.

Other additives Various additives may be used in combination in the resin composition of the present invention, and examples of the additives that can be used in combination include polyesters other than the saturated copolyester constituting the resin of the present invention,
Acrylic resins having terminal hydroxyl groups, bisphenol epoxy resins, epoxy resins such as cresol novolac epoxy resins, styrene resins such as styrene and α-methylstyrene, terpene resins, terpene phenol resins, rosin resins, hydrocarbon resins, fragrances Group resins, tackifying resins such as phenolic resins, polyalkylene glycol polyester plasticizers, melamine resins, organofunctional silanes (commonly known as silane coupling agents),
Examples thereof include cross-linking agents such as peroxides, metal salts such as n-butyltin dilaurate, isocyanate curing catalysts such as amines and glycols, chain extenders, and the like, and fillers such as calcium carbonate, talc, and hard seal. Inorganic fillers, metal powders such as iron, copper, zinc, and aluminum added for the purpose of imparting spot weldability and thermal conductivity to damping steel plates, conductive metal oxides, conductive materials such as carbon powders or carbon fibers However, it is desirable that these additives be added within a range that does not impair the characteristics of the present invention.

○ Application method to damping steel sheet Steel sheets to which the resin composition of the present invention is applied for manufacturing damping steel sheet include cold rolled steel sheet (commonly known as SPCC), chromate treated steel sheet, zinc treated steel sheet, phosphoric acid treated steel sheet, etc. The surface-treated steel plate, copper plate, aluminum plate, stainless plate, etc. may be used, and either a coil-shaped original plate or a cut plate may be used. Further, the plate thickness is preferably 0.3 mm or more and 2 mm or less in consideration of moldability and shape retention.

The resin composition consisting of the saturated copolymerized polyester and the polyvalent isocyanate, the saturated copolymerized polyester and the polyvalent isocyanate are separately stored, both are used in the production of the vibration damping steel sheet, so-called It is generally used like a two-component adhesive consisting of a main agent and a curing agent, but when a blocked isocyanate is used as the polyvalent isocyanate, the saturated copolymerized polyester of the present invention is used. Since it exists fairly stably with isocyanate, it can be supplied as a mixed liquid.

More specifically, for example, an extruded film obtained by heating and melt mixing, or after being mixed in a solvent and coated on a release sheet, the solvent is distilled off, which is used as a so-called casting film and laminated between two steel plates. Although it is also possible to laminate adhesion by heating roll, hot press adhesion or subsequent cooling roll or cooling press, preferably after mixing a predetermined saturated copolyester, isocyanate and additives in a solvent, directly of the steel plate At least one, preferably applied to the laminated surface of both, at room temperature preferably
After heating at a temperature of 100 ° C. or higher and 150 ° C. or lower to distill off the solvent, continuous or standing is followed by heat lamination. At this time, the film thickness of the resin is preferably 1/50 or more and 1/5 or less of that of the steel sheet, and substantially 20 μ or more and 150 μ or less. If it is less than 20μ, the vibration damping property and the adhesive performance are deteriorated, and if it exceeds 150μ, it may cause a deviation or cracking of the steel sheet during the forming process.

The lamination adhesion temperature is usually such that the resin layer is heated to 150 ° C. or higher and 250 ° C. or lower. The contact time is about 30 seconds to 2 minutes for a hot press and about 1 to 10 seconds for a heating roll. However, the steel plates may be heated to the same temperature in advance and laminated and bonded by a cooling press or a cooling roll. As described above, the resin of the present invention has the characteristics that, under the same processing conditions as the thermoplastic resin, heat resistance equal to or higher than the adhesion temperature can be obtained, and the predetermined adhesion performance can be obtained immediately after the lamination and adhesion. It also has the feature that the pot life of the coated product is practically no problem. In addition, if the resin can be applied as a solution during lamination processing, the adhesion between the steel sheet and the resin can be improved, the entrainment of the gas layer can be prevented, and the spot welding of the formed steel sheet is also possible. In order to facilitate the addition of conductive metal powder, carbon, etc. added for the purpose of imparting the property, it is the most preferred method for the present invention, and according to the saturated copolymerized polyester of the present invention, it is an easily achievable method. is there.

"Action" Conventionally, saturated copolyester has a narrow melting temperature range due to its sharp melting behavior, and the cohesive force is insufficient in the viscoelastic temperature range. The adhesive strength is weak even at a temperature exhibiting the property, and of course, at a temperature higher than that, sufficient strength cannot be obtained and it cannot be used as a resin for vibration damping steel sheet. As a combination of polymerized polyester and polyvalent isocyanate compound was found, as a vibration-damping steel sheet, the vibration-damping performance near the above-mentioned normal temperature, that is, the value of loss coefficient is large, and the temperature range is wide, and it is necessary for molding. It is also possible to provide a product that has excellent adhesion performance, and further has extremely high performance in adhesion stability, chemical resistance, and durability after molding at high temperatures.
Further, the resin of the present invention, even when laminated with two steel plates, is a reactive liquid such as a two-component polyurethane or a curable epoxy resin composed of a low-molecular weight liquid polyester or polyether and an isocyanate compound. The resin does not require a long heating time, does not have the problem of resin flowing out during lamination bonding, and is used for bonding using the thermoplasticity of the resin itself such as polyurethane resin or modified polyolefin resin. In addition, since it requires a melting point above the temperature that it is exposed to during use, it does not require the high lamination temperature and lamination pressure that are indispensable, and even at a lamination temperature below the practical temperature, high adhesive strength can still be obtained and it is extremely excellent. It has excellent workability such as having workability.

[Examples] * The method of measuring the properties of the polyester used in the examples, the method of laminating and bonding, the method of measuring the properties of the damping steel sheet, etc. are as follows.

Softening point of polyester Measured by R & B softening point according to JIS K-2531, and the temperature was expressed in ° C.

Weight average molecular weight of polyester Dissolve polyester resin in tetrahydrofuran,
It was measured by liquid chromatography and the weight average molecular weight was calculated in terms of polystyrene.

Glass transition temperature of polyester Using a 1 mm thick sheet of polyester, the dynamic elastic modulus (E ') was measured by a viscoelastic spectrometer (10 Hz), and the temperature at which the elastic modulus started to decrease was displayed.

Addition amount and equivalent amount of polyvalent isocyanate The equivalent number of isocyanate group was calculated based on the terminal hydroxyl group measured from the addition amount of isocyanate and the weight average molecular weight of polyester based on 100 parts by weight of polyester.

Steel sheet used Cold rolled steel sheet (SPCC-SD) with a thickness of 0.6 mm was degreased and used.

Laminate adhesion method Polyester was dissolved in toluene / MEK mixed solvent in advance to form a solution with a solid content of 30%, polyvalent isocyanate was mixed, and a resin film was formed on one side of the steel sheet using a roll coater.
Coat to 25μ, and after coating, oven (100 ℃ × 1
And the solvent was distilled off. Then, the resin-coated surfaces were overlaid and heat-bonded with a hot press (200 ° C. × 1 minute × pressure 5 kg / cm ² ) for evaluation.

Adhesion performance The steel sheets laminated and adhered as described above were cut into a width of 25 mm, and the T-peel strength was measured. The tensile speed was measured at 200 mm / min. Similarly, the bonded portion was cut into an area of 25 mm × 25 mm, and the tensile shear strength was measured at room temperature of 23 ° C.

Molding performance Similarly, the above laminated and adhered product was cut into a size of 25 mm width × 100 mm length and bent to 4 mmφ, and those with a bent portion were marked with ×, and those without change were marked with ◯. Similarly, the bent product was left in an oven at 150 ° C. for 24 hours, and the product immersed in boiling water for 24 hours was taken out.

Damping performance As a vibration damping performance evaluation, loss factor (η) of laminated adhesive products
Was measured by the mechanical impedance method, and the temperature dependence of the loss coefficient at 1000 Hz was displayed.

Example 1 80 moles of terephthalic acid residue, 20 moles of adipic acid residue, 45 moles of ethylene glycol residue, 55 moles of 1,6-hexanediol residue were used, and the weight average molecular weight was 2300.
A polyester having a softening point of 120 ° C. and a glass transition point of −10 ° C. was synthesized by a conventional method. This polyester was dissolved in toluene and a solvent with a MEK weight ratio of 1/1 to obtain a solid content of 30%, and Coronate L (NV: 75) was added as a polyvalent isocyanate.
%, NCO%: 13.2, manufactured by Nippon Polyurethane Industry Co., Ltd., was added and mixed in an amount of 10 parts by weight with respect to 100 parts by weight of polyester, and the mixture was applied to a steel plate and dried, and then two steel plates were stacked and laminated and bonded by hot pressing. At this time, the isocyanate equivalent was 3.6 equivalent parts with respect to 1 equivalent of the terminal hydroxyl group of the polyester. The results of measuring the adhesion performance, formability and loss coefficient of the laminated steel sheets are shown in FIGS. 1 and 1. As the damping steel plate, excellent performance was obtained. Similarly, Table 1 shows the results of Examples 2 to 5 composed of a predetermined polyester and a polyvalent isocyanate, and the loss coefficient values of Examples 3, 4, and 5 are shown in FIG.
At this time, polyethylene glycol having a number average molecular weight of 200 was used. Similarly, the polyester used in Example 1 and MDI (Millionate MT, NCO) as a polyvalent isocyanate were used.
%: 30, an example using Nippon Polyurethane Co., Ltd. is shown in Table 1 as Example 6. An example in which 1,4-butanediol is used as the glycol component is shown in Table 1 as Example 7. As compared with the comparative example, good adhesive performance and moldability in the normal state were obtained, but the heat resistance to molding is insufficient and the application is limited. Similarly, Comparative Example 1 shows a conventional two-component urethane, but polyester is liquid at room temperature, and resin flows out at the time of laminating and bonding,
The adhesive performance after standing was not satisfactory either. Comparative Example 2 was a case where the polyester used in Example 1 was used alone, but satisfactory performances were not obtained in terms of adhesiveness and moldability. Thus, it can be seen that good performance as a vibration damping steel plate can be obtained only by the combination of the present invention.

(C) Effects of the Invention As described above, the present invention uses a specific saturated copolyester and a polyvalent isocyanate together as an intermediate resin layer for exerting a vibration damping effect, so that at around room temperature, specifically, 0 Since it has excellent vibration damping property at ℃ ~ 50 ℃, and has adhesive performance that can withstand moldability, and has heat resistance durability of 100 ℃ or more, it can be used as a building material that is close to a flat plate that does not require moldability. Of course, it becomes possible to use damping steel plates with extremely excellent performance, such as being able to be used for applications that were difficult to use in the past such as dash panels, floor panels, roof panels around automobile bodies. It is suitable as a method for producing a vibration-damping steel sheet that can be widely used in the industry, and the effect on those industries is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing the measurement results of the loss coefficient of a vibration damping steel sheet produced by using the resin of the present invention, where 1, 3, 4 and 5 are obtained in Examples 1, 3, 4 and 5, respectively. It shows the measurement results of the loss coefficient of the damping steel sheet.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masatoshi Shinozaki 1st Kawasaki-cho, Chiba-shi, Chiba Inside Kawasaki Steel Co., Ltd. Technical Research Institute (72) Inventor Toshio Okuyama 1-chome, Funami-cho, Minato-ku, Nagoya, Aichi Synthetic Chemical Industry Co., Ltd. (72) Inventor Toshiyoshi Hirose 1-1, Funami-cho, Minato-ku, Nagoya, Aichi Pref. Toago Synthetic Chemical Industry Co., Ltd. Researcher, Hideji Sasaki (56) Reference JP-A-63-48321 (JP, A) JP 63-202613 (JP, A) JP 63-207809 (JP, A) JP 61-258743 (JP, A)

Claims (1)

(57) [Claims] 1. A weight average molecular weight of more than 6000 and a softening point of 50 ° C.
A resin composition for a composite vibration-damping steel sheet, comprising a saturated copolyester having a temperature of 150 ° C. or lower and a polyvalent isocyanate compound as a cross-linking agent and containing no chain extender.