Coating material, coating layer, and spring

Abstract

The invention provides a coating material, a coating layer, and a spring using the coating layer. The bubble rate of a cured product layer after curing of the coating material is 0-50%.

Description

Technical Field

[0001] The present disclosure relates to coating materials, coatings, and springs. Background Art

[0002] Automobiles, railway vehicles, etc. use various springs. Most of these springs are made of steel, and their surfaces are usually coated to impart corrosion resistance.

[0003] For example, Patent Document 1 discloses "a method for forming a covering portion of a helical spring, characterized in that at least an axial portion of a helical spring preheated to a specified surface temperature is rolled in a trough-shaped container containing a thermoplastic resin powder having a melting point of 250°C or lower, and the resin powder adhering to the spring wire of the helical spring is heated and melted and then cured".

[0004] In addition, Patent Document 2 discloses "a highly durable spring, characterized in that it has a single coating film with a thickness of 450 μm or less, and the coating film contains an epoxy resin, a phenolic resin, and zinc". Patent Document 2 also discloses that "the coating film is a cured product of an epoxy resin-based powder coating containing an epoxy resin, a phenolic resin, and zinc".

[0005] In addition, Patent Document 3 discloses "an anti-flaking powder topcoat on a steel substrate, the steel substrate having a corrosion-resistant powder coating primer, the topcoat comprising a cured product or a molten product of a coating powder comprising: one or more resin components of one or more toughened epoxy resins, one or more waxes in an amount of 0.1 to 5 parts per hundred parts of resin (phr), and optionally one or more extenders up to 200 phr".

[0006] In addition, Patent Document 4 discloses "a suspension spring, which is a helical spring for a vehicle suspension, characterized in that the coating film at a portion satisfying at least one of the conditions that the stress during use is higher than that of other portions and the probability of coating film damage caused by flying stones is higher than that of other portions is thicker than the coating film at a portion adjacent to the portion".

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Unexamined Patent Application Publication No. 57-136972

[0010] Patent Document 2: International Publication WO2017 / 163877

[0011] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2009-120812

[0012] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-308067

[0013] Problems to be Solved by the Invention

[0014] Regarding the coating material for springs, the cured product layer (coating) after coating on the spring is required to have durability (tear strength).

[0015] The problem of the present disclosure is to provide a coating material capable of forming a coating with excellent tear strength, a coating with excellent tear strength, and a spring using the coating. Summary of the Invention

[0016] Solutions to the Problems

[0017] The solutions to solve the above problems include the following solutions.

[0018] <1>

[0019] A coating material, wherein the bubble rate of the cured product layer after curing is 0% to 50%.

[0020] <2>

[0021] The coating material according to <1>, wherein the bubble rate of the cured product layer after curing is 5% to 50%.

[0022] <3>

[0023] The coating material according to <1> or <2>, wherein the average diameter of the bubbles in the cured product layer after curing is 30 μm to 2000 μm.

[0024] <4>

[0025] The coating material according to any one of <1> to <3>, wherein the tear strength of the cured product layer at 25°C is 45 kN / m or more.

[0026] <5>

[0027] The coating material according to any one of <1> to <3>, wherein the cured product layer after curing is a cured product layer having a urethane bond.

[0028] <6>

[0029] The coating material according to <1>, wherein the coating material is used for a spring.

[0030] <7>

[0031] A coating, wherein the bubble rate is 0% to 50%.

[0032] <8>

[0033] The coating according to <7>, wherein the bubble rate is 5% to 50%.

[0034] <9>

[0035] The coating according to <7> or <8>, wherein the average diameter of the bubbles in the coating is 30 μm to 2000 μm.

[0036] <10>

[0037] The coating according to any one of <7> to <9>, wherein the tear strength of the coating at 20 °C is 45 kN / m or more.

[0038] <11>

[0039] The coating according to any one of <7> to <10>, wherein the coating is formed of a cured product layer having a urethane bond.

[0040] <12>

[0041] The coating according to any one of <7> to <11>, wherein the coating is used for a spring.

[0042] <13>

[0043] A spring having, on at least a part of its surface, a coating according to any one of <7> to <12>.

[0044] Advantageous Effects of the Invention

[0045] According to the present disclosure, it is possible to provide a coating material capable of forming a coating having excellent tear strength, a coating having excellent tear strength, and a spring using the coating. Detailed Description of the Invention

[0046] Hereinafter, an embodiment as an example of the present disclosure will be described. These descriptions and examples illustrate the present disclosure, but do not limit the present disclosure.

[0047] In the present specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively.

[0048] In the numerical ranges described in sections in the present specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other sections. Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may also be replaced with the value shown in the examples.

[0049] In the present specification, each component may contain a plurality of corresponding substances. When the amount of each component is mentioned in the present specification and there are a plurality of substances corresponding to each component, unless otherwise specified, it means the total amount of the plurality of substances.

[0050] (Coating material / Coating)

[0051] The bubble rate of the cured product layer (i.e., the coating) of the coating material of this embodiment is 0% to 50%. In the cured product layer of the coating material of this embodiment, the bubbles that are the starting points of strength reduction are as low as 0% to 50%, so a coating with excellent tear strength can be formed.

[0052] Moreover, in the coating of this embodiment, the bubbles that are the starting points of strength reduction are as low as 0% to 50%, so the tear strength is excellent.

[0053] Hereinafter, the details of the coating material and the coating of this embodiment will be described.

[0054] It should be noted that hereinafter, the cured product layer of the coating material of this embodiment will also be referred to as "coating".

[0055] (Characteristics)

[0056] -Bubble rate-

[0057] For the coating material of this embodiment, the bubble rate of the cured product layer (coating) is 0% to 50%, more preferably 5% to 50%, and still more preferably 10% to 50%.

[0058] In particular, by setting the bubble rate of the cured product layer (coating) to 5% to 50% (preferably 10% to 50%), the generation of abnormal noise can be suppressed.

[0059] Here, conventionally, when an article having a coating on at least a part of its surface comes into contact between the article and other articles or between parts of the article (for example, between the wires of a helical spring when the article is a helical spring), even when the contact is through the coating, abnormal noise sometimes occurs.

[0060] Therefore, when the bubble rate of the coating is set to 5% to 50%, the bubbles in the coating reflect and attenuate the sound generated during contact, and the sound pressure of the generated sound can be reduced. Therefore, the generation of abnormal noise can be suppressed.

[0061] It should be noted that when the bubble rate increases, the tear strength decreases and the durability of the coating decreases. Specifically, for example, when the bubble rate exceeds 50%, the tear strength tends to become 45 N / mm or less, and the durability of the coating decreases. Therefore, the upper limit of the bubble rate is 50%.

[0062] The method of setting the bubble rate of the cured product layer (coating) to 5% or more can be adjusted, for example, by the methods shown in the following (1) to (3).

[0063] (1) Method of making the coating material contain a foaming agent that expands upon heating.

[0064] (2) Method of pre-stirring the raw materials to dissolve gas into the coating material and using it as nuclei to grow bubbles when forming a coating.

[0065] (3) In the case where the cured layer is a cured layer having a urethane bond, method of adding water to the coating, reacting with isocyanate to generate carbon dioxide and making it foam.

[0066] On the other hand, in order to make the bubble ratio of the cured layer (coating) 0% or close to 0%, for example, it is preferable not to implement the methods shown in (1) to (3) above.

[0067] The bubble ratio of the cured layer (coating) is measured by the specific gravity method in water using the "Specific Gravity Measurement Kit AD-1654" manufactured by A&D Co., Ltd.

[0068] - Average diameter of bubbles -

[0069] From the viewpoints of improving tear strength and suppressing abnormal noise, the average diameter of the bubbles in the cured layer (coating) is preferably 30 μm to 2000 μm, more preferably 30 μm to 1200 μm, and further preferably 30 μm to 700 μm.

[0070] When the average diameter of the cured layer (coating) is within the above range, it is not easy to generate parts where the film thickness of the coating is locally reduced due to the increase in the diameter of the bubbles, and the reduction of tear strength is suppressed. In addition, the situation where the vibration of sound is directly transmitted from the surface of the cured layer (coating) to the interface with the article is suppressed, and the abnormal noise suppression effect is improved. In addition, it is not easy to generate irregularities on the surface of the cured layer (coating).

[0071] The average diameter of the bubbles can be adjusted, for example, by the methods shown in (11) to (13) below.

[0072] (11) In the method (1) of making the coating material contain a foaming agent that expands upon heating, adding a foaming agent and a foam stabilizer to the coating material simultaneously.

[0073] (12) In the method (2) of pre-stirring the raw materials to dissolve gas into the coating material and using it as nuclei to grow bubbles when forming a coating, adding a foam stabilizer to the coating material.

[0074] (13) In the method (3) where, in the case where the cured layer is a cured layer having a urethane bond, adding water to the coating, reacting with isocyanate to generate carbon dioxide and making it foam, adding water and a foam stabilizer to the coating material simultaneously.

[0075] The method for measuring the average diameter of the bubbles in the cured cured product layer (coating) is as described below.

[0076] First, a specimen obtained by slicing the cured cured product layer (coating) to be measured in a direction parallel to the thickness direction is obtained.

[0077] Using the cut surface of the specimen as the observation surface, observation is carried out through an optical microscope ("One-touch 3D shape measuring machine probe VR-3100" manufactured by Keyence Corporation).

[0078] Then, in the observation image, the maximum diameters of any ten bubbles are measured, and the arithmetic average of the ten maximum diameters is set as the average diameter of the bubbles.

[0079] -Tear strength-

[0080] The tear strength of the cured cured product layer (coating) at 25°C is preferably 45 kN / m or more, more preferably 60 kN / m or more.

[0081] Here, the tear strength is measured according to the tear test specified in JIS K 7311:1995.

[0082] Among them, the tear strength of the cured product layer of the coating material of the present embodiment is the value measured under the condition of a thickness of 2 mm.

[0083] (Composition)

[0084] The coating material of the present embodiment can be any one of a composition of a thermoplastic resin and a composition for forming a thermosetting resin as long as it can form a cured product layer (coating) that satisfies the above characteristics.

[0085] Examples of the thermoplastic resin include: acrylic resin, polystyrene resin, polyethylene resin, polypropylene resin, polyamide resin, nylon resin, vinyl chloride resin, polyacetal resin, polycarbonate resin, polyphenylene ether resin, polybutylene terephthalate resin, polysulfone resin, polyarylate resin, polyetherimide resin, etc.

[0086] Examples of the thermosetting resin include: urethane resin, epoxy resin, cyanate ester resin, melamine resin, phenolic resin, etc.

[0087] In addition, examples of rubber materials include: natural rubber, butadiene rubber, chloroprene rubber, nitrile rubber, styrene-butadiene rubber, etc.

[0088] Among them, for the coating material of the present embodiment, the cured product layer preferably has a cured product layer with a urethane bond, specifically, preferably a urethane resin layer.

[0089] In particular, the coating material of the present embodiment is preferably a composition containing (A) a high molecular polyol, (B) an isocyanate, and (C) a chain extender, or a composition containing a prepolymer obtained by reacting (D) a polyol and an isocyanate.

[0090] [Composition containing (A) a high molecular polyol, (B) an isocyanate, and (C) a chain extender]

[0091] -(A) High molecular polyol-

[0092] As the (A) high molecular polyol, from the viewpoint of improving the durability at normal temperature and high temperature and the impact resistance at low temperature, it preferably contains at least one selected from the group consisting of (A1) a polycarbonate polyol, (A2) a polyether polyol having a bisphenol structure, (A3) a lactone polyol, (A4) a polyester polyol, and (A5) a copolymer of a polycarbonate polyol and a lactone polyol.

[0093] As the (A1) polycarbonate polyol, for example, polyols obtained by reacting a diol with an alkylene carbonate, polyols obtained by reacting a diol with a diaryl carbonate, polyols obtained by reacting a diol with a dialkyl carbonate, etc. can be cited.

[0094] As the alkylene carbonate, for example, ethylene carbonate, 1,2-propylene carbonate, 1,2-butylene carbonate, etc. can be cited.

[0095] As the diaryl carbonate, for example, diphenyl carbonate, 4-methyl diphenyl carbonate, 4-ethyl diphenyl carbonate, 4-propyl diphenyl carbonate, 4,4'-dimethyl diphenyl carbonate, 2-tolyl-4-tolyl carbonate, 4,4'-diethyl diphenyl carbonate, 4,4'-dipropyl diphenyl carbonate, phenyl toluoyl carbonate, bis(chlorophenyl) carbonate, phenyl chlorophenyl carbonate, phenyl naphthyl carbonate, dinaphthyl carbonate, etc. can be cited.

[0096] As the dialkyl carbonate, for example, dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, di-n-butyl carbonate, diisobutyl carbonate, di-tert-butyl carbonate, di-n-pentyl carbonate, diisopentyl carbonate, etc. can be cited.

[0097] Examples of the polyether polyol (A2) having a bisphenol structure include polyether polyols obtained by adding poly(ethylene oxide) and / or poly(propylene oxide) to a cyclic diol (such as bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P, etc.), a propylene oxide adduct of bisphenol A, an ethylene oxide adduct of bisphenol A, an ethylene oxide adduct of hydrogenated bisphenol A, a propylene oxide adduct of hydrogenated bisphenol A, and the like.

[0098] Among them, as the polyether polyol, a propylene oxide adduct of bisphenol A is preferred.

[0099] Examples of the lactone polyol (A3) include ring-opening polymers of lactones (such as ε-caprolactone, β-methyl-δ-valerolactone, etc.).

[0100] Among them, a ring-opening polymer of caprolactone (caprolactone polyol) is preferred.

[0101] Examples of the polyester polyol (A4) include condensation polyester polyols of polyacids and polyols other than lactone polyols.

[0102] Examples of the polyacid include polycarboxylic acids. Specifically, examples of the polyacid include phthalic acid, isophthalic acid, tetrahydrophthalic acid, tetrahydroisophthalic acid, hexahydrophthalic acid, hexahydroterephthalic acid, trimellitic acid, adipic acid, sebacic acid, succinic acid, azelaic acid, fumaric acid, maleic acid, itaconic acid, pyromellitic acid, and their acid anhydrides.

[0103] Examples of the polyol include diols and polyols having three or more hydroxyl groups. Specifically, examples of the diol include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, neopentyl glycol, hexanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, methylpropanediol, cyclohexanedimethanol, 3,3-diethyl-1,5-pentanediol, and the like. Examples of the polyol having three or more hydroxyl groups include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, and the like.

[0104] Examples of the copolymer of the polycarbonate polyol and the lactone polyol (A5) include copolymers of the above-mentioned (A1) polycarbonate polyol and the above-mentioned (A3) lactone polyol.

[0105] It should be noted that each of the (A) high molecular polyols can be used alone or in combination of two or more.

[0106] The number average molecular weight of the (A) high molecular polyol is preferably 300 to 12000, more preferably 800 to 4000.

[0107] Here, the number-average molecular weight is the molecular weight calculated based on the measured value of the hydroxyl value according to JIS K0070 and the number of functional groups. It should be noted that the number-average molecular weights of other components are also measured in the same way.

[0108] -(B) Isocyanate-

[0109] Examples of the (B) isocyanate include: aromatic diisocyanates such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, xylene-1,4-diisocyanate, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 3,3'-dichloro-4,4'-diphenylmethane diisocyanate; aliphatic diisocyanates such as hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, cyclohexylene diisocyanate; and other well-known polyisocyanates.

[0110] (B) Isocyanate can be used alone or in combination of two or more.

[0111] -(C) Chain extender-

[0112] Examples of the (C) chain extender include difunctional to tetrafunctional polyols with a molecular weight of 60 to 300.

[0113] Examples of the difunctional polyol also include: aliphatic diols such as ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, neopentyl glycol, methylpentylene glycol, hexylene glycol, heptylene glycol, octylene glycol, nonylene glycol, decylene glycol, dodecylene glycol; alicyclic diols such as cyclohexylene glycol, xylylene glycol; aromatic diols such as phthalyl alcohol; and polyether polyols formed by the addition polymerization of alkylene oxide (ethylene oxide, propylene oxide, etc.) with diols. It should be noted that the addition polymerization of multiple alkylene oxides can be random addition polymerization or block addition polymerization.

[0114] Examples of the trifunctional polyol, as a triol, include triols with 3 to 10 carbon atoms such as glycerol and trimethylolpropane. Examples of the trifunctional polyol also include: polyether polyols formed by the addition polymerization of alkylene oxide (ethylene oxide, propylene oxide, etc.) with triols. It should be noted that the addition polymerization of multiple alkylene oxides can be random addition polymerization or block addition polymerization.

[0115] Examples of the tetrafunctional polyol include polyether polyols formed by the addition polymerization of alkylene oxide with ethylenediamine, pentaerythritol, etc.

[0116] In addition, as the low molecular weight polyol, there may also be mentioned ester polyols obtained by condensing adipic acid with short-chain diols such as ethylene glycol and 1,4-butanediol and polyfunctional triols such as glycerol, etc.

[0117] (C) The chain extender may be used alone or in combination of two or more. It may also be pre-reacted with the polyisocyanate in the form of a prepolymer.

[0118] Among them, as the (C) chain extender, from the viewpoints of improving the durability at normal temperature and high temperature and the impact resistance at low temperature, ethylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, and glycerol are preferred, and 1,4-butanediol and 1,6-hexanediol are more preferred.

[0119] [Composition containing a prepolymer obtained by reacting (D) polyol with isocyanate]

[0120] -(D) prepolymer-

[0121] The prepolymer is a prepolymer obtained by reacting a polyol with an isocyanate.

[0122] As the polyol, there may be mentioned: the above-mentioned (A) high molecular weight polyol, the low molecular weight polyol exemplified by the above-mentioned (C) chain extender.

[0123] As the isocyanate, there may be mentioned: the above-mentioned (B) isocyanate.

[0124] In the composition containing the (D) prepolymer, in addition to the (D) prepolymer, it may further contain at least one selected from the group consisting of the (A) high molecular weight polyol, the (B) isocyanate, and the (C) chain extender.

[0125] -Other components-

[0126] The coating material of the present embodiment may contain other components.

[0127] As the other components, there may be mentioned: known additives such as catalysts, thickeners, antioxidants, colorants, ultraviolet absorbers, inorganic fillers (such as calcium carbonate), water, foam stabilizers, defoamers, etc.

[0128] In addition, in order to improve the mechanical properties in the warm state, the structure of the resin itself may be made into a structure with high heat resistance. In addition to this, a crosslinking agent and a reinforcing agent (such as CNT) may also be added to improve the heat resistance.

[0129] -Ratio of components-

[0130] The equivalent ratio ((A + C) / (B + D)) of the (A) high molecular weight polyol and the (C) chain extender, the (B) isocyanate and the prepolymer obtained by reacting the (D) polyol with the isocyanate is preferably 0.5 to 1.5 or 0.8 to 1.2.

[0131] (A) The mass ratio (A / C) of the polymer polyol to the (C) chain extender is preferably 1.0 to 35.0 or 1.5 to 10.0.

[0132] (D) The mass ratio (D / C) of the prepolymer obtained by reacting the polyol with the isocyanate to the (C) chain extender is preferably 1.0 to 15.0 or 5.0 to 10.0.

[0133] (Use of the coating material)

[0134] The coating material of the present embodiment can, for example, preferably be used as a coating material for forming a protective layer of articles such as springs, stabilizers, bumpers, and building materials (wall tiles, etc.). The article can be an article that has been painted.

[0135] Among them, the coating material of the present embodiment can be alternatively listed as a coating material for springs.

[0136] Specifically, the article of the present embodiment has a cured product layer (i.e., a coating) of the spring coating material of the present embodiment on at least a part of its surface.

[0137] The spring of the present embodiment has a cured product layer of the spring coating material of the present embodiment on at least a part of its surface. The spring can be either a coil spring or a leaf spring.

[0138] As a method of providing the cured product layer of the coating material, for example, it is as follows.

[0139] 1) For the purpose of preventing abnormal noise caused by contact between spring wires, the surface of the part where the spring wires of the coil spring contact each other.

[0140] 2) For the purpose of protecting the paint, the surface of the end coil part of the coil spring or a part or the entire surface of the coil spring.

[0141] 3) For the purpose of cushioning impact and preventing burrs, a part or the entire surface of the FRP leaf spring.

[0142] (Coating method)

[0143] The coating method of the coating material of the present embodiment is not particularly limited, and coating methods such as dip coating, spray coating, roll coating, brush coating method, and flow coating method can be applied.

[0144] Here, when the coating material of the present embodiment is coated on a coil spring, the thickness of the formed cured product layer is preferably set to 1 mm or more (especially 1 mm to 2 mm), so there is a concern about the problem of sagging of the coating film.

[0145] Therefore, it is preferable to incorporate a thickener into the coating material of the present embodiment to increase the viscosity.

[0146] In addition, in order to enable ultraviolet curing, it is also preferable to incorporate an acrylate resin and a photoinitiator into the coating material of the present embodiment, and irradiate ultraviolet rays immediately after the coating film is formed to cure the surface layer portion of the coating film.

[0147] [Examples]

[0148] Hereinafter, examples of the present disclosure will be described, but the present disclosure is not limited to these examples. It should be noted that in the following description, unless otherwise specified, "parts" and "%" related to the blending amount (content, addition amount) are based on weight.

[0149] <Examples 1 to 15, Comparative Example 1>

[0150] Weigh accurately the amounts (parts) of the components shown in Table 1 (except for isocyanate) preheated to 50 °C into a plastic cup, and mix them using a rotation-revolution mixer (ARE-310 manufactured by HINKY Corporation). The mixing conditions are 2000 rpm × 30 seconds.

[0151] It should be noted that in the case of physical foaming (the case of "yes" in the "pre-stirring" column in the table), after mixing the amounts (parts) of the components shown in Table 1 (except for isocyanate), perform pre-stirring at 2000 rpm × 1 minute using a disperser to dissolve air into the solution.

[0152] Next, add the isocyanate shown in Table 1 to the obtained solution, and mix it using a rotation-revolution mixer (ARE-310 manufactured by HINKY Corporation). The mixing conditions are 2000 rpm × 30 seconds.

[0153] Thus, the coating material is prepared.

[0154] <Evaluation>

[0155] Prepare test pieces with a cured layer (coating) having a thickness of 2 mm formed by curing under the conditions of 180 °C and 10 minutes after coating the coating materials of each example on an SPCC steel plate with a width of 12.5 mm, a length of 70 mm, and a thickness of 3.2 mm.

[0156] Then, perform the following evaluations using the test pieces.

[0157] (Bubble rate, average diameter of bubbles)

[0158] According to the above method, the bubble rate of the coating and the average diameter of the bubbles were measured.

[0159] Tear strength

[0160] According to the above method, the tear strength of the coating at 25 °C was measured.

[0161] Fatigue durability

[0162] A fatigue testing machine (linear-torsional composite dynamic fatigue testing machine 'E10000') manufactured by Instron was used to evaluate the fatigue durability. Specifically, it is as follows.

[0163] A round bar with a diameter of Φ15 mm was pressed against the test piece by clamping the coating, and the load was repeatedly applied under the conditions of a minimum load of 10 N and a maximum load of 3000 N, and thus the number of excitations (hereinafter, the number of fractures) until the coating fractured was measured. Then, the evaluation was carried out based on the following criteria.

[0164] A: The number of fractures exceeds 100,000 times.

[0165] B: The number of fractures is greater than or equal to 10,000 times and less than 100,000 times.

[0166] C: The number of fractures is greater than or equal to 1,000 times and less than 10,000 times.

[0167] D: The number of fractures is less than 1,000 times.

[0168] Abnormal noise evaluation

[0169] The manufactured test piece was suspended with a kite string, and a hammering test was performed by hitting the test piece from the coating side with an impulse hammer, and the sound pressure at a frequency of 5000 Hz was measured.

[0170] Moreover, based on the sound pressure of Example 1, the sound pressure difference (dB) between the sound pressure of Example 1 and that of each example was obtained.

[0171] It should be noted that the equipment used in the hammering test is as follows.

[0172] Impulse hammer: "GK-3100" manufactured by Ono Sokki.

[0173] Pickup microphone: "LA-5570" manufactured by Ono Sokki.

[0174] FFT (Fast Fourier Transform) analysis equipment: "DS-3000" manufactured by Ono Sokki

[0175] Then, the evaluation was carried out based on the following criteria.

[0176] A: The sound pressure difference is less than 20 dB.

[0177] B: The sound pressure difference is greater than or equal to 10 dB and less than 20 dB.

[0178] C: The sound pressure difference is greater than or equal to 5 dB and less than 10 dB.

[0179] D: The sound pressure difference is greater than or equal to 0 dB and less than 5 dB.

[0180] The details of the descriptions in Table 1 are as follows.

[0181] - Polyol

[0182] · Capa7203: Copolymer of polycarbonate polyol and lactone polyol ("Capa7203" manufactured by INGEVITY).

[0183] - Isocyanate

[0184] · MP-102: 4,4'-Diphenylmethane diisocyanate ("MP-102" manufactured by BASF INOAC Polyurethane).

[0185] - Chain extender

[0186] · 1,4-BD: 1,4-Butanediol.

[0187] - Blowing agent

[0188] · 920DE40d30: Thermally expandable microcapsules ("Expancel 920DE40d30" manufactured by Japan Fillite: average particle size 35 - 55 μm).

[0189] - Foam stabilizer

[0190] · B 8737LF2: Silicone-based foam stabilizer ("TEGOSTAB B 8737LF2" manufactured by Evonik).

[0191] The measurement results of the physical properties of each example and the results of various tests are shown in Table 1 below.

[0192] [Table 1]

[0193]

[0194] From the above results, it can be seen that the coating material of this example can form a coating with excellent tear strength.

[0195] In addition, it can be seen that the coatings of the examples with a bubble rate of 5% or more can suppress the generation of abnormal noises.

[0196] It should be noted that the entire disclosure of Japanese Patent Application No. 2022-197520 is incorporated herein by reference.

[0197] All documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and separately indicated to be incorporated by reference.

Claims

1. A coating material, wherein the bubble rate of the cured product layer after curing is 0% to 50%.

2. The coating material according to claim 1, wherein the bubble rate of the cured product layer after curing is 5% to 50%.

3. The coating material according to claim 1, wherein the average diameter of the bubbles in the cured product layer after curing is 30 μm to 2000 μm.

4. The coating material according to claim 1, wherein the tear strength of the cured product layer at 25°C is 45 kN / m or more.

5. The coating material according to claim 1, wherein the cured product layer after curing is a cured product layer having a urethane bond.

6. The coating material according to claim 1, wherein the coating material is used for springs.

7. A coating, wherein the bubble rate is 0% to 50%.

8. The coating according to claim 7, wherein the bubble rate is 5% to 50%.

9. The coating according to claim 7, wherein the average diameter of the bubbles in the coating is 30 μm to 2000 μm.

10. The coating according to claim 7, wherein the tear strength of the coating at 20°C is 45 kN / m or more.

11. The coating according to claim 7, wherein the coating is formed of a cured product layer having a urethane bond.

12. The coating according to claim 7, wherein the coating is used for springs.

13. A spring, at least a part of the surface of which has the coating according to any one of claims 7 to 12.

Images