Vinyl chloride plastisol composition

Abstract

To enable the expression of curability and adhesiveness even during low-temperature baking and drying.SOLUTION: A polyvinyl chloride-based plastisol composition contains a polyvinyl chloride resin, an acrylic resin, a polyamide, and a plasticizer. The acrylic resin is a liquid acrylic resin containing a hydroxy group with one or more functionalities in each molecule.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a vinyl chloride plastisol composition suitable for use as a coating material for interlayer chipping resistance, underbody coating, or body sealer for vehicles such as automobiles, and in particular to a vinyl chloride plastisol composition that can exhibit curability and adhesiveness even when baked and dried at a low temperature. [Background technology]

[0002] The underside of an automobile's body, such as the underside of the floor, wheel wells (tire wells), rocker panels (side sills), front aprons, front and rear fenders, the bottom of the doors, and the bottom of the gas tank, are subject to chipping, which causes the paint to be scratched or peeled off when pebbles and gravel kicked up by the tires while the automobile is moving collide with these parts. Therefore, coatings such as chipping-resistant paints and undercoats are applied to these parts to protect the automobile body from chipping, rust, soundproofing, and other chip-resistant paints and to prevent the paint from peeling or being scratched by stones and sand. Furthermore, the body of an automobile is constructed by joining and assembling steel plates, and sealing paint (body sealant, sealant) is applied (filled or painted) to the joints, seams, edges, etc. of the steel plates that make up the body to make them watertight, airtight, waterproof, rust-proof, and dust-proof.

[0003] Conventionally, polyvinyl chloride plastisols, which are polyvinyl chloride resins converted into a sol with a plasticizer, have been used for chipping resistance, undercoating, and sealing coatings of this type. After application to the vehicle body, these vinyl chloride plastisols are baked and dried to form a hardened coating film.

[0004] In recent years, with the increasing awareness of environmental conservation, automobile factories, which are the production sites of automobiles, are also implementing measures to reduce carbon dioxide emissions and save energy in order to reduce environmental impact. As part of these efforts, there is a demand for a reduction in carbon dioxide emissions generated by the energy consumption of baking ovens in the coating process for automobile paints. To achieve energy savings and reduced carbon dioxide emissions, there is a demand for lowering the temperature of baking ovens and shortening the drying time, i.e., reducing the load of heat drying during baking drying after coating. However, with conventional vinyl chloride plastisols, the compounding materials were selected based on the assumption of high-temperature baking, and therefore coating film properties such as curability and coating film strength, as well as adhesion, could not be achieved under low-temperature baking drying conditions.

[0005] Therefore, Patent Document 1 proposes a low-temperature curing plastisol composition that contains a thermoplastic resin, a plasticizer, and an adhesive, in which the thermoplastic resin contains a vinyl chloride-vinyl acetate copolymer in which vinyl acetate is copolymerized at a ratio of 7 to 12 mass %. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-011525 Summary of the Invention [Problem to be solved by the invention]

[0007] In the examples of Patent Document 1, a blend of a paste-like vinyl chloride resin and a powdered acrylic resin (polymer particles) is disclosed as the thermoplastic resin, and an aromatic isocyanate is used as the adhesive. This causes a problem of yellowing after the middle and top coatings are applied. On the other hand, if an adhesive other than an aromatic isocyanate, such as a polyamide, is used, the polyamide will react with the powdered acrylic resin, resulting in a problem of loss of adhesion.

[0008] Therefore, an object of the present invention is to provide a chlorinated plastisol composition that can exhibit curability and adhesiveness even when baked and dried at a low temperature. [Means for solving the problem]

[0009] The vinyl chloride plastisol composition of the invention of claim 1 is a vinyl chloride plastisol composition containing a vinyl chloride resin, an acrylic resin, a polyamide, and a plasticizer, wherein the acrylic resin is a liquid acrylic resin containing one or more functional hydroxyl groups in the molecule.

[0010] The vinyl chloride resin may be a homopolymer of vinyl chloride or a copolymer of vinyl chloride, i.e., a copolymer of vinyl chloride and another vinyl monomer, and preferably a copolymer resin of vinyl chloride and vinyl acetate.

[0011] The liquid acrylic resin has one or more functional hydroxyl groups in the molecule, preferably at the molecular terminals, and is a low molecular weight resin having a weight average molecular weight of preferably 500 or more and 5,000 or less, more preferably 800 or more and 4,000 or less, and even more preferably 1,000 or more and 3,500 or less.

[0012] As the polyamide, a polyamidoamine having reactive primary and secondary amines in the molecule is preferably used. As the plasticizer, phthalate esters such as diisononyl phthalate (DINP), dioctyl phthalate (DOP), and 2-ethylhexyl phthalate are preferably used.

[0013] The vinyl chloride resin of the vinyl chloride plastisol composition of the invention according to claim 2 is a vinyl chloride-vinyl acetate copolymer.

[0014] The vinyl acetate group content of the vinyl chloride resin in the vinyl chloride plastisol composition of the invention of claim 3 is preferably in the range of 5% by mass or more and 15% by mass or less, more preferably 6% by mass or more and 12% by mass or less, and even more preferably 7% by mass or more and 10% by mass or less.

[0015] The liquid acrylic resin in the vinyl chloride plastisol composition of the invention of claim 4 preferably has a weight average molecular weight in the range of 500 or more and 5,000 or less, more preferably 800 or more and 4,000 or less, and even more preferably 1,000 or more and 3,500 or less.

[0016] The liquid acrylic resin in the vinyl chloride plastisol composition of the invention of claim 5 is preferably blended in an amount of 5 parts by mass or more and 60 parts by mass or less, more preferably 10 parts by mass or more and 55 parts by mass or less, and even more preferably 12 parts by mass or more and 50 parts by mass or less, per 100 parts by mass of the vinyl chloride resin.

[0017] The polyamide in the vinyl chloride plastisol composition of the invention of claim 6 is preferably blended in an amount of 1 part by mass or more and 20 parts by mass or less, more preferably 2 parts by mass or more and 15 parts by mass or less, and even more preferably 3 parts by mass or more and 8 parts by mass or less, per 100 parts by mass of the vinyl chloride resin. [Effects of the Invention]

[0018] The vinyl chloride plastisol composition according to the invention of claim 1 contains a vinyl chloride resin, an acrylic resin, a polyamide, and a plasticizer, and the combination of the vinyl chloride resin as a thermoplastic resin with a liquid acrylic resin containing one or more functional hydroxyl groups in the molecule allows curing even under low-temperature baking and drying conditions, ensuring coating film properties such as coating strength. Furthermore, the liquid acrylic resin containing one or more functional hydroxyl groups in the molecule does not react with the polyamide used as an adhesion promoter, and the polyamide's adhesiveness is exerted even under low-temperature baking and drying conditions, ensuring adhesion.

[0019] According to the vinyl chloride plastisol composition of the invention of claim 2, the vinyl chloride resin is a vinyl chloride-vinyl acetate copolymer, and therefore in addition to the effect of claim 1, it has excellent curing properties at lower temperatures.

[0020] According to the vinyl chloride plastisol composition of the invention of claim 3, the vinyl chloride resin has a vinyl acetate group content in the range of 5% by mass or more and 15% by mass or less, and therefore has excellent low-temperature melting properties and can improve the toughness of the coating film in addition to the effect described in claim 2.

[0021] According to the vinyl chloride plastisol composition of the invention of claim 4, the liquid acrylic resin has a weight-average molecular weight in the range of 500 to 5,000, and therefore, in addition to the effect of claim 1, the coating film can be strengthened without impairing the coatability.

[0022] According to the vinyl chloride plastisol composition of the invention of claim 5, the liquid acrylic resin is blended in an amount within the range of 5 parts by mass to 60 parts by mass per 100 parts by mass of the vinyl chloride resin. Therefore, in addition to the effect of claim 1, the coating film strength can be increased by low-temperature baking and drying without impairing the coatability.

[0023] According to the vinyl chloride plastisol composition of the invention of claim 6, the polyamide is blended in an amount within the range of 1 part by mass to 20 parts by mass per 100 parts by mass of the vinyl chloride resin, and therefore, in addition to the effect of claim 1, the adhesion of the coating film can be improved without impairing the coatability. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, an embodiment of the present invention will be described. The vinyl chloride plastisol composition according to the embodiment of the present invention contains at least a vinyl chloride resin, a liquid acrylic resin, a plasticizer, and a polyamide as an adhesion promoter (adhesion promoter).

[0025] As the vinyl chloride resin, a homopolymer of vinyl chloride or a copolymer of vinyl chloride and other vinyl monomers is used. From the viewpoints of adhesion and cohesion to substrates (substrates) such as metals, low-temperature curing properties, strength to enhance chipping resistance, and elongation, the inclusion of a copolymer is preferred, and examples of vinyl monomers to be copolymerized with vinyl chloride include vinyl esters such as vinyl acetate, vinyl propionate, and vinyl stearate, vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether, maleic esters such as diethyl maleate, fumaric esters such as dibutyl fumarate, acrylic acid or methacrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate, hydroxyalkyl esters of acrylic acid or methacrylic acid such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate, hydroxyalkyl amides of acrylic acid or methacrylic acid such as N-methylolacrylamide, N-methylolmethacrylamide, N-hydroxyethylacrylamide, and N-dihydroxyethylmethacrylamide, acrylonitrile, and vinylidene chloride. Vinyl chloride can also be made into a crosslinkable copolymer with -CH2ROH groups.

[0026] Among these, vinyl acetate is preferred as a monomer to be copolymerized with vinyl chloride from the viewpoints of low-temperature curing, strength for enhancing chipping resistance, elongation, swelling and gelling properties in response to plasticizers, and adhesion and adhesion to substrates such as metals. Furthermore, when the proportion of vinyl acetate to be copolymerized is preferably 5% by mass or more, more preferably 6% by mass or more, and even more preferably 7% by mass or more, a coating film with high elongation, toughness, and mechanical strength can be obtained in combination with a liquid acrylic resin even under low-temperature baking and drying conditions. Furthermore, when the proportion of vinyl acetate to be copolymerized is preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less, a coating film with high elongation, toughness, and mechanical strength can be obtained due to its good plasticizer absorption (low-temperature melting property, swelling and gelling property) and compatibility with liquid acrylic resins containing hydroxyl groups, even at low temperatures. The average degree of polymerization is preferably 1300 to 3000, more preferably 1500 to 2500. Within this range, a strong coating film can be formed even when cured at low temperature.

[0027] The vinyl chloride resin may be used alone or in combination of two or more types. For example, a resin obtained by emulsion polymerization or suspension polymerization may be used. The vinyl chloride resin may be added to or blended in the composition in the form of a fine powder or granules. The vinyl chloride resin may be dispersed in the composition in the form of granules or the like, or may be dissolved in an organic solvent if one is present.

[0028] The amount of vinyl chloride resin used is determined based on the desired coating film properties. However, if the vinyl chloride resin content in the coating composition is too low, the coating film's toughness, mechanical strength, pitting resistance, adhesion, etc. will be reduced, and the relative increase in the amount of liquid acrylic resin will result in higher costs. On the other hand, if the vinyl chloride resin content is too high, the composition will not achieve the desired structural viscosity and thixotropy, resulting in poor storage stability, application workability, and coatability. The vinyl chloride resin content in the composition is preferably within the range of 5 to 50 mass%, more preferably 10 to 45 mass%, even more preferably 15 to 40 mass%, and particularly preferably 18 to 35 mass%, calculated as solids. Within these ranges, the composition's storage stability, application workability, and coatability will be good, and coating film performance such as adhesion, strength, and pitting resistance will be excellent.

[0029] From the viewpoints of dispersibility, viscosity characteristics, etc., it is preferable that the vinyl chloride resin has a median primary particle size (average particle size) in the range of 0.1 to 10 μm. Such particle sizes result in a non-porous resin, which has an excellent thixotropic effect, good coatability, and good storage stability with little change in viscosity over time. The particle size is more preferably in the range of 0.1 to 5 μm, and even more preferably in the range of 0.1 to 2 μm.

[0030] The liquid acrylic resin contains one or more functional hydroxyl groups in the molecule, preferably one or more functional hydroxyl groups at the molecular terminal, and may be a copolymer of a monomer having a hydroxyl group. Particularly preferred is one having one hydroxyl group at only one terminal. The liquid acrylic resin preferably has a weight-average molecular weight of 500 or more and 5,000 or less, more preferably 800 or more and 4,000 or less, and even more preferably 1,000 or more and 3,500 or less. If the weight-average molecular weight is within this range, the resin will have good compatibility with vinyl chloride resins, high plasticity, and the coating film will be toughened without impairing coatability.

[0031] The liquid acrylic resin is preferably blended in an amount of 5 to 60 parts by mass, more preferably 10 to 55 parts by mass, and even more preferably 12 to 50 parts by mass, per 100 parts by mass of the vinyl chloride resin. Within this range, coating strength can be increased even with low-temperature baking and drying without impairing coatability.

[0032] By combining a liquid acrylic resin with one or more functional hydroxyl groups in its molecule with a vinyl chloride resin, high strength and elongation coating properties can be achieved even under low-temperature baking and drying conditions, and even when polyamide is added, it is difficult to react with it, ensuring adhesion. This is thought to be because the liquid acrylic resin orients itself between the vinyl chloride resins like a plasticizer, and the presence of the hydroxyl groups in the liquid acrylic resin inhibits reaction with the polyamide.

[0033] As the plasticizer, basically, any plasticizer generally used for forming this type of vinyl chloride plastisol composition can be used, and for example, a compound (ester) synthesized from an acid such as phthalic acid, trimellitic acid, or adipic acid and an alcohol such as octanol, nonanol, or a higher mixed alcohol can be used.Specifically, dibutyl phthalate (DBP), dihexyl phthalate (DHP), di-2-ethylhexyl phthalate (DOP), di-n-octyl phthalate (DnOP), diisooctyl phthalate (DIOP), didecyl phthalate (DDP), dinonyl phthalate (DNP), diisononyl phthalate (DINP), dimethyl phthalate (DMP), diethyl phthalate (DEP), bis-2-ethylhexyl phthalate (DEHP), diisodecyl phthalate (DIDP), C6 to C10 mixed higher alcohol phthalates, butyl phthalate, Phthalate esters such as benzyl phthalate (BBP), octyl benzyl phthalate, nonyl benzyl phthalate, and dimethyl cyclohexyl phthalate (DMCHP); linear dibasic acid esters such as di-2-ethylhexyl adipate (DOA), dioctyl azelate (DOZ), and dioctyl sebacate (DOS); and tricresyl phosphate (TCP), trioctyl phosphate (TOF), trixylenyl phosphate (TXP), monooctyl diphenyl phosphate, and monobutyl-dixylenyl phosphate (BZX). Phosphate esters, benzoate esters such as trioctyl trimellitate (TOTM), tri-n-octyl trimellitate, triisodecyl trimellitate, triisooctyl trimellitate, butyl phthalate butyl glycolate (BPBG), tributyl citrate, trioctyl acetyl citrate, trimellitate, citrate, sebacate, azelaate, maleate, tri- or tetraethylene glycol esters of C6-C10 fatty acids, alkyl sulfonate, methyl Examples of suitable materials include esters such as ethyl acetylricinoleate, epoxidized vegetable oils such as those in which the double bonds of unsaturated fatty acid glycerides such as soybean oil have been epoxidized with hydrogen peroxide or peracetic acid (ESBO), epoxy compounds such as butyl or octyl alkyl oleate, viscous low-polymerization polyesters with an average molecular weight of about 500 to 8,000 in which propylene glycol ester units of dibasic acids such as adipic acid are linearly linked (e.g., adipic acid polyesters, phthalic acid polyesters), and alkylsulfonic acid-based materials such as Mezamol (registered trademark).These may be used alone or in combination of two or more.

[0034] Among these, substances that are liquid at room temperature are desirable, and phthalate esters are the most common plasticizers, are easily available, and are inexpensive. They also enable uniform dispersion of vinyl chloride resins and allow the formation of stable vinyl chloride plastisol compositions. Among phthalate esters, diisononyl phthalate (DINP), which has excellent plasticizing efficiency, processability, and low-temperature solubility (gelling and melting), or dioctyl phthalate (DOP), which has excellent heat resistance and viscosity stability, are more suitable from the standpoints of environmental friendliness, ease of handling, solubility, coatability, storage stability, etc.

[0035] Such plasticizers are appropriately selected according to the desired viscosity characteristics, curability, coating strength, etc. of the plastisol composition, and their blending amounts are set. However, if the blending amount is too small, the storage stability and coating workability of the plastisol composition will be reduced, and the flexibility and elongation of the coating will be reduced. In particular, when baked at a lower temperature and for a shorter time than current baking conditions, good coating properties such as strength, impact resistance, and chipping resistance will not be exhibited. On the other hand, if the blending amount is too large, sagging will be more likely to occur, and good coating properties such as strength, impact resistance, and chipping resistance will not be exhibited. For this reason, the amount of plasticizer blended is preferably within the range of 40 to 400 parts by mass, more preferably 80 to 250 parts by mass, and even more preferably 90 to 180 parts by mass per 100 parts by mass of vinyl chloride resin (solid content). Within these ranges, good coating workability can be ensured, and even when baked at a lower temperature and for a shorter time than current baking conditions, the cured coating film is softened to obtain appropriate flexibility (elasticity), and coating film performance such as strength, impact resistance, and chipping resistance can be ensured.

[0036] Furthermore, in the vinyl chloride plastisol composition of the present embodiment, an adhesion promoter is blended to improve the adhesion (adhesion, adhesion) to the object to be coated. In this embodiment, polyamidoamine, polyimideamine, polyamine, etc. are used as the adhesion promoter, but in paint applications such as chipping resistance and undercoat for automobiles, a vinyl chloride plastisol composition is generally applied after an undercoat coating by electrodeposition coating or the like, and therefore, it is preferably used in combination with a blocked isocyanate (e.g., xylene diisocyanate, tetramethylene diisocyanate, tolylene diisocyanate, phenyl diisocyanate, methylxylene diisocyanate, etc.) that exhibits excellent adhesion to cationic electrodeposition coated surfaces. Depending on the purpose of the coating film, it is possible to use not only blocked isocyanates but also acrylic, imine, other amine, polyol, etc. in combination.

[0037] Polyamides are polyamide compounds containing active amino groups or amide groups that are commonly used as curing agents for epoxy resins, etc., and are generally obtained by reacting polyamines, such as aliphatic diamines (e.g., hexamethylenediamine) or aromatic diamines, with polybasic acids (e.g., dimer acids or trimer acids) produced by thermally polymerizing unsaturated fatty acids (e.g., linoleic acid), with polyamines. Polyamides are typically polyamidoamines, which are reaction products of polymerized fatty acids (e.g., dimer acids or trimer acids) produced by thermally polymerizing unsaturated fatty acids (e.g., linoleic acid) with polyamines. Such polyamides contain active amino groups or amide groups that can form hydrogen bonds with polar groups (amino groups, carboxyl groups, hydroxyl groups, etc.) in the cationic electrodeposition coating film, thereby improving the adhesion and bonding properties of the coating film formed from the plastisol composition.

[0038] The polyamide is blended into the vinyl chloride plastisol composition in an amount of preferably 0.3 to 2.5 mass%, more preferably 0.4 to 2.0 mass%, and even more preferably 0.5 to 1.8 mass%. The amount blended is preferably 1 to 20 mass parts, more preferably 2 to 15 mass parts, and even more preferably 3 to 8 mass parts per 100 mass parts of the vinyl chloride resin (solid content). Within this range, the adhesion and bondability of the coating film can be improved without impairing coatability.

[0039] Blocked isocyanates are compounds obtained by blocking a relatively low-molecular-weight polyisocyanate component, preferably a compound generally having two or more isocyanate groups (—N═C═O) in the molecule, with a blocking agent, which is a compound having active hydrogen, such as methyl ethyl ketone oxime (MEKO). Examples of polyisocyanate components include aliphatic diisocyanates such as hexamethylenediamine (HDI), aromatic diisocyanates such as tolylenediisocyanate (TDI), xylylenediisocyanate, and diphenylmethane diisocyanate (MDI), aliphatic diisocyanates such as hexamethylenediisocyanate, alicyclic diisocyanates such as isophorone diisocyanate, hydrogenated TDI, and hydrogenated MDI, as well as biuret compounds, isocyanurate compounds, adducts with polyhydric alcohols such as ethylene glycol and trimethylolpropane, and urethane prepolymers of these diisocyanates. Examples of blocking agents that can be used for these isocyanate compounds include ketoximes such as methyl ethyl ketoxime (MEKO), active methylene compounds such as acetylacetone and acetoacetic ester, lactams such as ε-caprolactam, oxybenzoic acid esters, and alkylphenols. However, methyl ethyl ketoxime is particularly preferred in terms of compatibility with vinyl chloride resins and plasticizers.

[0040] Among these, blocked urethane prepolymers, which are formed by blocking a urethane prepolymer having terminal isocyanate groups and consisting of a prepolymer of a diisocyanate compound (such as a diisocyanate such as TDI, a polyisocyanate, etc.) and a polyol (such as a polyether polyol, a polyester polyol, or a polymer polyol), with a blocking agent, are generally most suitable. Blocked urethane prepolymers have good stability and excellent adhesion and bonding properties to cationic electrodeposition coated surfaces. Furthermore, aliphatic blocked isocyanates such as blocked urethane prepolymers do not yellow after application of intermediate or upper coatings, and do not impair appearance or coating performance. When such a blocked isocyanate is used, the blocking agent of the blocked isocyanate is dissociated at the temperature during heating and baking, and the isocyanate group of the regenerated isocyanate component bonds with the active hydrogen remaining in the cationic electrodeposition coating film, thereby improving the adhesion and bonding of the coating film formed from the plastisol composition to the electrodeposition coating surface.

[0041] When a blocked isocyanate is blended to ensure excellent adhesion with cationic electrodeposition coating films, it is blended in the vinyl chloride plastisol composition in an amount of preferably 0.3 to 2.5 mass%, more preferably 0.4 to 2.0 mass%, and even more preferably 0.5 to 1.8 mass%. Per 100 mass parts of vinyl chloride resin (solid content), it is blended in an amount of preferably 1 to 20 mass parts, more preferably 2 to 15 mass parts, and even more preferably 3 to 8 mass parts. Within this range, the adhesion and adhesiveness of the coating film can be improved without impairing coatability.

[0042] In particular, when polyamide and blocked isocyanate are used in combination, the polyamide promotes the dissociation of the blocked isocyanate, thereby enabling the development of superior adhesion and adhesiveness. In a combination system of a polyamide component and a blocked isocyanate component, the block is dissociated at the temperature during heating and baking, and the isocyanate group of the regenerated isocyanate compound reacts with the active hydrogen (amino group) of the polyamide, polymerizing and curing to develop adhesion and adhesiveness. Therefore, not only does the system exhibit excellent adhesion and adhesiveness to cationic electrodeposition-coated surfaces, but it can also develop high adhesion and adhesiveness even under low-temperature baking conditions. Furthermore, polyamide and blocked isocyanate have good storage stability. Preferably, the combined use of polyamidoamine and blocked polyurethane prepolymer can also improve the water resistance of the coating film. When an amino compound component containing active hydrogen and a blocked isocyanate component are used in combination, they can be added in any ratio depending on the type and equivalent weight of each component.

[0043] The adhesion promoter is preferably blended in the vinyl chloride plastisol composition in a total amount of 0.5 to 3 mass%, more preferably 0.8 to 2.5 mass%, and even more preferably 1.0 to 2.0 mass%. The adhesion promoter is preferably blended in an amount of 1 to 30 mass parts, more preferably 3 to 20 mass parts, and even more preferably 5 to 10 mass parts, per 100 mass parts of the vinyl chloride resin (solid content). Within this range, the adhesion and bondability of the coating film can be improved without impairing coatability.

[0044] When carrying out the present invention, vinyl chloride plastisol compositions of this type used for chipping resistance, sealing and undercoating of vehicles may be blended with rheology control agents, thixotropic agents, anti-sagging agents, moisture absorbents, solvents and the like as needed, i.e., depending on the application purpose, use and desired coating film properties of the vinyl chloride plastisol composition.

[0045] Rheology control agents, thixotropic agents, and anti-sagging agents for imparting anti-sagging properties when applied to a substrate include, for example, colloidal calcium carbonate (ultrafine calcium carbonate particles), fine silica particles, etc. Colloidal calcium carbonate is generally ultrafine synthetic calcium carbonate or ultrafine precipitated calcium carbonate with an average particle size of 0.1 μm or less, and essentially, those used in conventional vinyl chloride plastisol compositions of this type, such as cubic precipitated calcium carbonate, are used, and those surface-treated with fatty acid or the like are preferred. From the viewpoint of thixotropy, colloidal calcium carbonate is, for example, a calcium carbonate having a BET specific surface area of ​​10 to 40 m 2 / g, more preferably 13 to 30 m 2 / g. When colloidal calcium carbonate is blended into the vinyl chloride plastisol composition, it is blended preferably in an amount of 1 to 30% by mass, more preferably 5 to 25% by mass, and even more preferably 10 to 20% by mass. It is blended preferably in an amount of 10 to 150 parts by mass, more preferably 20 to 120 parts by mass, and even more preferably 30 to 100 parts by mass per 100 parts by mass of the vinyl chloride resin.

[0046] The addition of a rheology control agent / thixotropic agent such as colloidal calcium carbonate to a vinyl chloride plastisol composition imparts thixotropy, increasing the composition's viscosity at low shear rates (at rest) and decreasing its viscosity at high shear rates. Specifically, at low shear rates (at rest), the colloidal calcium carbonate particles loosely bond (aggregate) to form a three-dimensional structure (a finely dispersed colloidal structure) within the plastisol composition, increasing the viscosity of the plastisol composition. However, because the bonding strength between these particles is weak, at high shear rates, the structure is partially or completely destroyed by the high shear force, increasing fluidity and decreasing the apparent viscosity. This results in viscosity and flow characteristics suitable for application. That is, when a plastisol composition is subjected to high-speed shear during preparation or application, the apparent viscosity decreases and the composition can be applied at a viscosity suitable for application work. However, after the composition adheres to the substrate, its structure is restored due to its thixotropy (time dependency), and the viscosity of the plastisol composition returns to its original high state, thereby preventing sagging after application.

[0047] As a moisture absorbent for improving resistance to moisture absorption and foaming, which traps moisture absorbed in the plastisol composition and prevents swelling of the coating film due to moisture, for example, calcium oxide (CaO) or magnesium oxide, which has the property of bonding with water through a hydration reaction, is preferably used. When a moisture absorbent is blended, it is blended in the vinyl chloride plastisol composition in an amount of preferably 1 to 5 mass %, more preferably 1.5 to 4.5 mass %, and even more preferably 2 to 5 mass %. The amount is preferably 5 to 30 mass parts, preferably 8 to 20 mass parts, and more preferably 10 to 15 mass parts per 100 mass parts of the vinyl chloride resin.

[0048] When a moisture absorbent such as calcium oxide is added, it can capture the residual moisture contained in fillers such as calcium carbonate and vinyl chloride resins, thereby preventing foaming of the coating film during baking. Furthermore, when the plastisol composition is left to stand after application, foaming of the coating film due to moisture absorption during baking can be prevented. Furthermore, the moisture contained in relatively large amounts in paint dregs can also be absorbed by this moisture absorbent.

[0049] As solvents (thickeners) used to improve the mixing workability of compounded materials, the application workability and storage stability, the leveling (smoothness) of the coating film after application, and the appearance of the coating film, organic solvents with a relatively high boiling point (preferably a boiling point of 150°C or higher and 220°C or lower) are used from the viewpoints of application workability, application property, etc., such as petroleum solvents such as naphtha, turpentine oil, paraffin, and mineral spirits, aliphatic hydrocarbon solvents such as butane, pentane, hexane, heptane, octane, isooctane, and nonane, and aromatic solvents such as alcohols, benzene, toluene, and xylene. From the viewpoints of thickening properties and thixotropy effect, non-polar hydrocarbons, for example, paraffin hydrocarbons, are preferably used.

[0050] If too much of such a solvent is added, sagging properties will be impaired. Therefore, when a solvent such as a paraffinic hydrocarbon is added, it is preferably added in an amount of 1 to 10 mass %, more preferably 2 to 9 mass %, and even more preferably 3 to 8 mass % to the vinyl chloride plastisol composition.

[0051] In addition, pigments, leveling agents, fillers, stabilizers, etc. may also be added as appropriate. Examples of pigments include color pigments, extender pigments, anti-rust pigments, functional pigments, etc. Further, examples of color pigments that can be used include carbon black, titanium oxide, iron oxide, zinc oxide, organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, yellow lead, yellow iron oxide, red iron oxide, titanium dioxide, cadmium yellow, and phthalocyanine blue. Anti-rust pigments that can be used include, for example, zinc phosphate, zinc phosphite, aluminum polyphosphate, aluminum tripolyphosphate, zinc calcium molybdate, zinc orthophosphate, zinc polyphosphate, zinc molybdate, zinc phosphomolybdate, aluminum phosphomolybdate, zinc oxide, zinc phosphosilicate, aluminum zinc phosphate, calcium zinc phosphate, zinc calcium cyanamide, barium metaborate, and magnesium aminophosphate. From an environmental perspective, anti-rust pigments that do not contain harmful heavy metals such as chromium are desirable. Extender pigments that can be used include, for example, talc, calcium carbonate, barium sulfate, calcium sulfate, mica, clay, silica, diatomaceous earth, alumina, baryta, and silicon dioxide. Talc, in particular, forms multiple layers within the coating, and the dense layers formed by this arrangement can prevent the penetration of corrosive agents.

[0052] Leveling agents for further improving the leveling (smoothness) of the coating film and the finished appearance of the coating film include silicone resins and dimer-modified epoxy resins. Stabilizers include epoxy stabilizers, metal salts (metallic soaps) of zinc, lead, barium, tin, calcium, etc., inorganic acid salts of metals such as lead, and organometallic compounds. The most common are organotin compounds such as dibutyltin dilaurate, and tribasic lead sulfate. When a blocked isocyanate is used as an adhesion promoter, these stabilizers also function as catalysts to promote the dissociation of the blocking agent during bake curing.

[0053] Examples of fillers used for increasing weight, thickening, improving application workability and coatability, and increasing coating film strength include calcium carbonate (e.g., heavy calcium carbonate), alkaline earth metal carbonates and sulfates (e.g., magnesium carbonate and barium sulfate), mica, silica, talc, diatomaceous earth, kaolin, clay, organic bentonite, alumina, gypsum, cement, converter slag powder, shirasu powder, glass powder, graphite, vermiculite, zeolite, calcium metasilicate, zonolite, potassium titanate, rock wool, glass fiber, carbon fiber, aluminum silicate, aramid fiber, cellulose powder, powdered rubber, pre-expanded resin microcapsules (heat-expandable microspheres) made from synthetic resins (plastics) such as vinylidene chloride, acrylonitrile, polyvinylidene chloride, and copolymers thereof, thermoplastic resin balloons (lightweight materials) such as phenol balloons, and blowing agents. These may be used alone or in combination of two or more. Among these, hollow particles as fillers, unexpanded thermally expandable microcapsules, blowing agents, etc. are effective in lowering the specific gravity of the coating film, thickening the coating film, improving soundproofing, forming escape routes (water escape paths) for moisture absorbed in the composition, etc. That is, when hollow particles, unexpanded thermally expandable microcapsules, or blowing agents are added, it is possible to lower the specific gravity without increasing the coating weight by thickening the coating film, and it is possible to form a coating film that is both soundproof and lightweight.

[0054] Specifically, hollow particles (hollow fillers) may be hollow balloons that do not melt, expand, or burst even when baked after application and maintain a predetermined hollowness. Examples include inorganic hollow particles (inorganic hollow particles, inorganic hollow bodies, inorganic microhollow bodies) with an inorganic shell, such as sodium borosilicate silica balloons, glass balloons, and shirasu balloons made by baking and foaming vitreous pyroclastic debris such as shirasu; thermoplastic resin balloons such as expanded resin microcapsules (heat-expandable microspheres) made from synthetic resins (plastics) such as vinylidene chloride, acrylonitrile, polyvinylidene chloride, or copolymers thereof; resin balloons such as phenol balloons; and organic hollow particles with an organic shell, such as carbon hollow spheres. These hollow particles have a low true specific gravity, which significantly reduces the weight (specific gravity) of the coating. From the viewpoints of ease of handling, workability, lightweight effect, etc., the true specific gravity is preferably in the range of 0.02 to 0.8, more preferably 0.1 to 0.5.

[0055] The thermally expandable microcapsules may be formed from a material whose shell softens when heated during baking after painting, and whose vaporized substance in the shell changes to gas and whose pressure (vapor pressure) causes the shell to expand, and whose expansion can be controlled by heat. That is, the thermally expandable microcapsules may be formed from a material whose shell softens at a predetermined temperature and whose internal liquid vaporizes, and may be formed from a shell (shell wall, outer wall, etc.) made of a thermoplastic resin (e.g., acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, acrylonitrile-vinylidene chloride copolymer, acrylonitrile-methyl methacrylate copolymer, acrylamide, acrylic acid, acrylic acid ester, methacrylamide, methacrylic acid, methacrylic acid ester, vinyl acetate, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-methyl methacrylate copolymer, etc.). Unexpanded thermoplastic resin microcapsules are used, which have a structure in which a vaporized substance (e.g., aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, isohexane, n-octane, n-decane, n-dodecane, etc.; alicyclic hydrocarbons such as cyclopentane, cyclohexane, methylcyclohexane, etc.; chlorinated hydrocarbons such as methyl chloride, ethyl chloride, etc.; fluorinated hydrocarbons such as 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, etc.) having a boiling point lower than the softening temperature of the thermoplastic resin that constitutes the shell is enclosed in the interior (core) of the shell.

[0056] These thermally expandable thermoplastic resin microcapsules are capsule-shaped with a shell structure made of a thermoplastic resin containing a vaporized substance in the core. After application to a surface, they are heated above the shell's softening temperature. When the temperature reaches a predetermined range, the shell softens, converting the vaporized substance contained within the shell into a gas. The gas pressure (expansion force / vapor pressure) inside the shell increases, causing the shell to expand and increase in volume, forming hollow thermoplastic resin microballoons. For example, particles with a median diameter of 5 to 50 μm can experience a volume change of approximately 50 to 100 times. The thermoplastic resin shell (outer shell) may also be coated with an inorganic powder such as calcium carbonate. Hybrids with inorganic powder attached to the surface of a thermoplastic resin shell, specifically, thermoplastic resin shells coated with inorganic metal salts or metal oxides such as calcium carbonate, talc, or titanium oxide, may also be used.

[0057] Examples of foaming agents that can be used include organic foaming agents such as ADCA (azodicarbonamide), azobisisobutyronitrile (AIBN), dinitrosopentamethylenetetramine (DPT), p-toluenesulfonylhydrazide (TSH), p-toluenesulfonylazide, p-methylurethanebenzenesulfonylhydrazide, benzenesulfonylhydrazide (BSH), and oxybenzenesulfonylhydrazide (OBSH), as well as inorganic foaming agents such as sodium bicarbonate (sodium bicarbonate) and ammonium carbonate. Heat-type foaming agents are preferably used. Heat-type foaming agents are foaming agents that decompose upon heating to generate gas. When such a heat-type foaming agent is contained, it is desirable that the foaming agent decomposes and foams at the heat treatment temperature when the composition is applied to a predetermined location and then the coating film is cured. If necessary, a foaming aid (e.g., salicylic acid, phthalic acid, stearic acid, lauric acid, benzoic acid, urea, zinc and compounds thereof) can be used to assist the foaming action of the foaming agent. The foaming aid may be blended so that foaming occurs in accordance with the heating conditions during baking and drying to harden the coating film, but a foaming aid is not necessarily required depending on the heating conditions, etc.

[0058] Two or more of the hollow particles, unexpanded thermally expandable microcapsules, and foaming agents that are used to lower the specific gravity of the coating film may also be used in combination. In particular, when thermally expandable microcapsules are blended into the composition, the heat generated during baking vaporizes the vaporized material inside the thermally expandable microcapsules, causing the shell to expand under pressure, forming hollow microballoons. These expanded hollow microballoons cause the coating film made of the composition applied to a specified location to expand and become thick. This allows for the formation of a coating film with high soundproofing properties without increasing the amount of coating. Furthermore, the coating film thickened by utilizing the volumetric expansion of the thermally expandable microcapsules has a low specific gravity, suppressing the increase in coating weight due to the thickening. Furthermore, when hollow particles or a foaming agent are used in combination, a lightweight coating film with an extremely low specific gravity can be formed.

[0059] In addition, for example, when used for sealing purposes such as applying and filling joints, seams, hemmings, etc. of steel plates, when the composition is applied to oily steel plates with rust-preventive oil still attached, it is possible to blend in epoxy resins such as bisphenol A type or bisphenol F type (including modified types) and their hardeners, such as latent hardeners such as dicyandiamide, guanidine derivatives, triazine derivatives, pyrimidine derivatives, 4,4'-diaminodiphenyl sulfone, acid hydrazide compounds, and imidazole compounds, in order to obtain sufficient adhesion to the oily steel plates. In addition to the epoxy resin and its curing agent, aliphatic blocked isocyanates, titanate coupling agents, and organotin stabilizers (e.g., alkyl tins such as dibutyltin dilaurate, dioctyltin laurate, dibutyltin maleate, and dibutyltin phthalate, and organotin mercaptides) may also be added to ensure high adhesion when applied to zinc-plated surfaces of steel sheets, mild steel surfaces, organic coating surfaces, and the like.

[0060] The vinyl chloride plastisol composition of the present embodiment, which contains a vinyl chloride resin, a liquid acrylic resin, a plasticizer, a polyamide such as polyamidoamine as an adhesion promoter, and the like, is prepared by uniformly mixing and dispersing the materials using a conventionally known mixer / disperser or kneader, such as a kneader, a disper, a planetary mixer, an attritor, a ball mill, a grain mill, a blender, a biaxial mixer, a vertical high-speed mixer, a roll mill, or a dissolver.

[0061] The vinyl chloride plastisol composition of the present embodiment can be used, for example, as a chipping-resistant coating composition for automobile bodies, an undercoat coating composition, or a sealant coating composition. It is applied to a predetermined location and baked to form a hardened coating film. The vinyl chloride plastisol composition of the present embodiment, which contains a vinyl chloride resin, a liquid acrylic resin, a plasticizer, and a polyamide such as polyamidoamine as an adhesion promoter, can be used as a one-component rather than a two-component, making it easy to handle. Furthermore, since the shape can be adjusted before heating, any coating shape can be selected. Naturally, it can be applied using a painting robot or with a brush, and since it does not require molding in a closed mold, a film can be formed in an open mold, and it can be used for chipping resistance, undercoating, and sealant.

[0062] The coating form and means for applying the coating material made of the vinyl chloride plastisol composition of this embodiment to a predetermined portion can be any conventionally known coating method, for example, coating methods such as brush coating, roller coating, and dipping, spray coating such as airless spray and air spray, and electrostatic coating. For example, in the case of chipping resistance or undercoating, it is applied to underfloor areas such as the underside of the floor, wheel house, front and rear fenders, and front apron, as well as to side sills (rocker panels), the lower sides of doors, etc. In addition, in the case of sealing, it is applied to joints, seams, edges, etc. of the steel plates that make up the car body.

[0063] The vinyl chloride plastisol composition applied to a substrate such as a steel plate is cured by baking and drying to form a cured coating film. In particular, when a vinyl chloride plastisol composition for chipping resistance, undercoat, or sealing of an automobile is applied to the surface of an automobile steel plate, for example, to the underbody of an automobile, such as the wheelhouse or underfloor of an automobile, the composition is applied to the electrodeposition-coated surface of the steel plate that has undergone a degreasing process, a chemical conversion treatment process, and an electrodeposition primer coating process in the coating line of the automobile production line. Subsequently, an intermediate coat or a finish coat, etc., of the outer panel of the automobile body is applied thereon, and the coating film of the vinyl chloride plastisol composition is heated together with the baking and drying of the intermediate coat or the finish coat, to form a cured coating film. That is, the vinyl chloride plastisol composition is applied to the electrodeposition-coated surface of a steel plate or the like, and then an intermediate coat or a top coat is applied thereon, followed by baking and curing, to form a coating film of the vinyl chloride plastisol composition. The thickness (dry coating thickness) of the cured coating film formed from the vinyl chloride plastisol composition in this case is, for example, 300 μm or more and 3000 μm or less. If necessary, the coating film of the vinyl chloride plastisol composition may be pre-cured (pre-heated) immediately after application to the electrodeposition coated surface, before the baking curing of the intermediate coating, top coating, etc.

[0064] In particular, in the painting lines of automobile production lines, cured coating films made from vinyl chloride plastisol compositions have traditionally been formed by baking and drying at 140 to 160°C for 20 to 40 minutes. However, the vinyl chloride plastisol composition of the present embodiment, which uses a thermoplastic vinyl chloride resin and a hydroxyl-containing liquid acrylic resin in combination, can form tough coating films with high elongation and tensile strength, ensuring chipping resistance, even under baking and drying conditions lower than the above temperature, for example, baking and drying at 100 to 130°C. Furthermore, the inclusion of a polyamide adhesion promoter ensures adhesion, and polyamide can form coating films with good appearance that do not yellow. Furthermore, these compounding materials are inexpensive, and the combination of vinyl chloride resin and liquid acrylic resin can be achieved at low cost.

[0065] In the vinyl chloride plastisol composition of this embodiment, the combined use of vinyl chloride resin and hydroxyl-containing liquid acrylic resin allows for the formation of a strong coating film even under low-temperature baking and drying conditions. That is, the coating film hardens even at low temperatures, providing sufficient chipping resistance. However, even in such a combined system of vinyl chloride resin and acrylic resin, the use of a hydroxyl-containing liquid acrylic resin as the acrylic resin prevents the polyamide used as an adhesion promoter from reacting with the acrylic resin, thereby preventing the polyamide from exhibiting adhesive properties. It is believed that the high adhesive properties of the polyamide are exhibited. That is, because the acrylic resin is a liquid acrylic resin containing hydroxyl groups, even when polyamide is blended as an adhesion promoter, the liquid acrylic resin containing hydroxyl groups penetrates and orients between the molecules of the vinyl chloride resin like a plasticizer, and the presence of the hydroxyl groups in the liquid acrylic resin inhibits the reaction between the acrylic resin and the polyamide, thereby allowing the polyamide to exhibit high adhesive properties. Furthermore, polyamide allows for the formation of a coating film with good appearance that does not yellow.

[0066] Thus, with the vinyl chloride plastisol composition of this embodiment, a strong coating film can be formed by the combined use of a vinyl chloride resin and a hydroxyl-containing liquid acrylic resin even under low-temperature baking and drying conditions. Furthermore, the hydroxyl-containing liquid acrylic resin does not react with the polyamide to inhibit adhesion, and the high adhesion of the polyamide is thereby exerted, resulting in the adhesiveness of the coating film. In other words, coating film physical properties (mechanical properties) such as coating film strength and adhesiveness are exerted by baking and drying at a lower temperature than conventionally. In particular, when vinyl chloride resins and acrylic resins are used together, the adhesive mechanism of the vinyl chloride resin is inhibited by the acrylic resin, making them inapplicable, and the adhesive mechanism of the acrylic resin is inapplicable to the adhesion of vinyl chloride resins, making their combined use difficult. However, with hydroxyl group-containing liquid acrylic resins, the presence of the hydroxyl groups prevents the resin from reacting with polyamide, allowing the adhesive properties of the polyamide to be expressed, resulting in high adhesiveness and ensuring an appearance that does not yellow.

[0067] Furthermore, vinyl chloride plastisol compositions used as chipping-resistant or undercoat paints for automobile bodies absorb and mitigate the impact of collisions with pebbles, gravel, etc., and prevent peeling of the upper layer of paint. Vinyl chloride plastisol compositions used as sealing paints for automobile bodies exhibit sealing functions (watertightness and airtightness) for joints, etc.

[0068] The vinyl chloride plastisol composition according to the embodiment of the present invention will be specifically described below with reference to examples. The vinyl chloride plastisol composition according to this example is a blend of vinyl chloride resin, liquid acrylic resin, plasticizer, adhesion promoter, thixotropic agent, moisture absorbent, viscosity reducer, and filler.

[0069] [Table 1]

[0070] Vinyl chloride plastisol compositions according to Examples 1 to 8 were prepared in the amounts shown in the upper part of Table 1. For comparison, vinyl chloride plastisol compositions according to Comparative Examples 1 to 4 were also prepared in the amounts shown in the upper part of Table 1. Specifically, a powdered vinyl chloride-vinyl acetate copolymer resin (primary particle size: 0.1 to 2 μm) was used as the vinyl chloride resin in Examples 1 to 8. In Examples 1 to 4, a vinyl chloride-vinyl acetate copolymer resin (average polymerization degree: 1900) with a vinyl acetate residue content of 9% by mass was used as the vinyl chloride resin, and in Examples 5 to 8, a vinyl chloride-vinyl acetate copolymer resin (average polymerization degree: 1800) with a vinyl acetate residue content of 7% by mass was used as the vinyl chloride resin.

[0071] In Examples 1 to 8, a solvent-free liquid acrylic resin (oligomer) was used as the liquid acrylic resin. In Examples 1 and 2, as well as Examples 5 and 6, a liquid acrylic resin (functional group equivalent: 600 g / eq, weight-average molecular weight: 1,000) was used, which had a methyl acrylate backbone and contained one hydroxyl group as a functional group at one end of the liquid acrylic molecule. In Examples 3 and 4, as well as Examples 7 and 8, a liquid acrylic resin (functional group equivalent: 970 g / eq, weight-average molecular weight: 3,500) was used, which had a 2-ethylhexyl acrylate backbone and contained two hydroxyl groups (1,2-diol) as functional groups at one end of the liquid acrylic molecule.

[0072] In Examples 1 to 8, dioctyl phthalate (DINP) was blended as a plasticizer. Polyamidoamine and block urethane were used in combination as an adhesion promoter. Furthermore, synthetic calcium carbonate was blended as a thixotropic agent, calcium oxide as a moisture absorbent, a paraffinic hydrocarbon solvent with a high boiling point of 150 to 200°C as a viscosity reducer, and heavy calcium carbonate as a filler.

[0073] On the other hand, in Comparative Example 1, no acrylic resin was blended, and a vinyl chloride-vinyl acetate copolymer resin having a vinyl acetate residue content of 9% by mass was blended as the vinyl chloride resin. Except for not blending liquid acrylic resin, the same materials as in Examples 1 to 4 were blended in the amounts shown in Table 1.

[0074] In Comparative Example 2, the same materials as in Examples 5 to 8 were blended in the amounts shown in Table 1, except that no acrylic resin was blended, and a vinyl chloride-vinyl acetate copolymer resin having a vinyl acetate residue content of 7% by mass was blended as the vinyl chloride resin, and no liquid acrylic resin was blended.

[0075] In Comparative Example 3, the liquid acrylic resin was a solventless liquid acrylic resin with a butyl acrylate backbone and a polyfunctional liquid acrylic resin (functional group equivalent: 570 g / eq, weight average molecular weight: 3,000) containing carboxyl groups (COOH groups) as functional groups at the terminals and within the liquid acrylic molecule, and the vinyl chloride resin was a vinyl chloride-vinyl acetate copolymer resin with a vinyl acetate residue content of 9% by mass. The same materials as in Examples 2 and 4 were blended in the amounts shown in Table 1, except that a liquid acrylic resin with a carboxyl functional group was used instead of the liquid acrylic resin with a hydroxyl functional group used in the Examples.

[0076] In Comparative Example 4, instead of the liquid acrylic resin used in the Examples, a powdered (powder particle size: 20-100 μm) acrylic resin (a spray-dried acrylic resin emulsion, weight-average molecular weight: 700,000) was used, and a vinyl chloride-vinyl acetate copolymer resin with a vinyl acetate residue content of 9% by mass was blended as the vinyl chloride resin. Except for using a solid acrylic resin instead of the liquid acrylic resin used in the Examples, the same materials as in Examples 1 to 4 were blended in the amounts shown in Table 1.

[0077] The properties (performance) of the coating films formed from the vinyl chloride plastisol compositions of Examples 1 to 8 and Comparative Examples 1 to 4 were then investigated. Specifically, measurements were carried out on the elongation, tensile strength, hardness, and adhesion of the coating films, as shown in the lower part of Table 1. In conducting these measurements, the various vinyl chloride plastisol compositions made from the ingredients shown in Table 1 were prepared by uniformly mixing and dispersing the ingredients using a planetary mixer, a mixer / disperser.

[0078] To measure elongation and tensile strength, first, release paper was attached to a 0.8-1.0 mm thick steel plate with a smooth surface, and the prepared vinyl chloride plastisol composition was applied to a thickness of 2-3 mm on top of it while taking care not to trap air bubbles, and then baked in a dryer at 120°C for 14 minutes. After leaving it at room temperature (normal temperature) for 20-24 hours, it was punched out using a dumbbell No. 2 shape specified in JIS K6251 to prepare test specimens for measuring elongation and tensile strength.

[0079] For the measurement of elongation and tensile strength, two benchmark lines were marked on the test piece 10 mm on either side from the center in the longitudinal direction (the distance between the benchmark lines was 20 mm), and the marked test piece was attached to a universal tensile testing machine with a grip distance of 50 mm. The test piece was then pulled at a pulling rate of 50 mm / min at room temperature (normal temperature), and the maximum load and the gauge distance when the coating on the test piece broke were measured. The elongation (the ratio (%) of the chuck distance before pulling to the chuck distance) was calculated using the following formula (1), and the tensile strength (tensile strength) was calculated using the following formula (2). Elongation (%) = (length between gauge lines at break (mm) - 20) ÷ 20 × 100 (1) Tensile strength (MPa=N / mm 2 ) = Maximum load (N) ÷ Cross-sectional area of ​​test piece (mm 2 )··(2) The larger the elongation percentage, the greater the elongation until breakage, and the larger the tensile strength, the greater the force required to breakage. The larger the values ​​for both, the greater the strength and toughness of the coating film.

[0080] The hardness was measured in accordance with JIS K6253 at room temperature (normal temperature) using a durometer type A (JIS A hardness meter, manufactured by Kobunshi Keiki Co., Ltd.) within 1 second. Coatings formed by baking and drying at a low temperature for a short time of 14 minutes at 120°C were evaluated as having good curability and therefore good coating strength if their elongation was 100% or more, tensile strength was 0.2 MPa or more, and hardness was 50 or more, while those with an elongation of less than 100%, a tensile strength of less than 0.2 MPa, or a hardness of less than 50 were evaluated as having poor curability and insufficient coating strength, and therefore were evaluated as poor.

[0081] Regarding adhesiveness, a tensile shear bond strength test was performed. Specifically, two test panels (25 mm × 100 mm × 1.0 mm) made of electrodeposition-coated steel plates were prepared. One of the panels was coated with the prepared vinyl chloride plastisol composition, and the other panel was placed parallel to the other and linearly joined. The test panels were then baked at 120°C for 14 minutes in a dryer to heat-cure the coating film (coating film) of the vinyl chloride plastisol composition applied to the test panel, thereby preparing a test sample for adhesive strength measurement. Note that the vinyl chloride plastisol composition was applied so that the thickness of the heat-cured coating film was 3 mm. Then, using a tensile tester (Shimadzu Corporation), the test sample was pulled in the longitudinal direction (tensile speed 50 mm / min) until it broke, and the fracture surface was visually observed at the time of breakage to determine the state of failure, i.e., cohesive failure (CF) or interfacial failure (AF). If the failure mode determined by the test sample was cohesive failure (CF), the adhesiveness was evaluated as good, and if the failure mode was interfacial failure (AF), the adhesiveness was evaluated as poor, and x.

[0082] As shown in the lower part of Table 1, for all of the plastisol compositions of Examples 1 to 8, the coating films formed by baking at 120°C for 14 minutes had elongations of 100% or more, tensile strengths of 0.6 MPa or more, and hardnesses of 50 or more. These high elongations, tensile strengths, and hardnesses indicate high coating strength and toughness. Therefore, even with low-temperature baking, the coating films exhibit good curing properties, ensuring coating strength and chipping resistance. Furthermore, in an adhesion strength test of the coatings baked at 120°C for 14 minutes, the failure mode at break was cohesive failure (CF), demonstrating that the coating films exhibit good adhesion even with low-temperature baking.

[0083] Thus, the vinyl chloride plastisol compositions of Examples 1 to 8 have good adhesion and curing properties even when baked for a short time at a low temperature of 120°C for 14 minutes, resulting in coating film properties such as desired elongation and tensile strength, and high coating film strength. This is thought to be because, by blending acrylic resin in addition to vinyl chloride resin, the acrylic resin is a liquid acrylic resin having hydroxyl groups, which penetrate between the molecules of the vinyl chloride resin like a plasticizer and orientate it, thereby obtaining high elongation and tensile strength, and even when polyamidoamine is blended as an adhesion imparting agent, the presence of the hydroxyl groups in the liquid acrylic resin inhibits the reaction between the acrylic resin and polyamidoamine, resulting in the adhesiveness due to the polyamidoamine being expressed.

[0084] In particular, while tensile strength generally tends to increase as the molecular weight of a resin increases, Example 1, which contained a liquid acrylic resin with a smaller molecular weight and one hydroxyl group than the liquid acrylic resin contained in Example 3, had a higher tensile strength than Example 3, even though the blending amount of liquid acrylic resin was the same in both cases at 15 parts by mass. Also, Example 2, which contained a liquid acrylic resin with a smaller molecular weight and one hydroxyl group than the liquid acrylic resin contained in Example 4, had a higher elongation and tensile strength than Example 4, even though the blending amount of liquid acrylic resin was the same in both cases at 30 parts by mass. Similarly, in a comparison of Examples 5 to 8, in which the vinyl acetate residue content of the vinyl chloride / vinyl acetate copolymer resin was different from that of Examples 1 to 4, the blending amount of liquid acrylic resin was the same at 15 parts by mass in both cases, but Example 5, in which a liquid acrylic resin with a smaller molecular weight and one hydroxyl group than the liquid acrylic resin blended in Example 7 was blended, had a higher tensile strength than Example 7. Furthermore, although the blending amount of liquid acrylic resin was the same at 30 parts by mass in both cases, Example 6, in which a liquid acrylic resin with a smaller molecular weight and one hydroxyl group than the liquid acrylic resin blended in Example 8 was blended, had a higher elongation and tensile strength than Example 8.

[0085] Furthermore, a comparison between Example 1 and Example 2, and a comparison between Example 5 and Example 6, shows that when a liquid acrylic resin having one hydroxyl group at its terminal is used, the elongation and tensile strength increase as the amount of the resin is increased.

[0086] This is presumably because in Examples 3 and 4, where a liquid acrylic resin with two hydroxyl groups was used, the liquid acrylic resin tended to be randomly arranged within the molecules of the vinyl chloride resin, resulting in low orientation of the liquid acrylic resin, whereas in Examples 1 and 2, where a liquid acrylic resin with one hydroxyl group was used, the liquid acrylic resin was highly oriented within the molecules of the vinyl chloride resin, thereby enabling increased elongation and tensile strength. For this reason, a liquid acrylic resin containing a hydroxyl group, or one with one hydroxyl group, is preferably used, which makes it possible to further increase the strength and toughness of the coating film.

[0087] Furthermore, a comparison of Examples 1 to 4 with Examples 5 to 8 reveals that Examples 1 to 4, in which the vinyl acetate residue content of the vinyl chloride-vinyl acetate copolymer resin is higher than that of Examples 5 to 8, have higher elongation and tensile strength than Examples 5 to 8. This is presumably because a vinyl chloride-vinyl acetate copolymer resin with a higher vinyl acetate residue content has higher compatibility with hydroxyl-containing liquid acrylic resins, particularly the hydroxyl groups, and plasticizers. That is, resins with a high vinyl acetate residue content have high compatibility with hydroxyl-containing liquid acrylic resins and plasticizers, and can incorporate hydroxyl-containing liquid acrylic resins and plasticizers into the vinyl chloride resin even at low temperatures, thereby promoting plasticization of the vinyl chloride resin. This is thought to result in sufficiently high elongation and tensile strength and toughness even under low-temperature baking and drying conditions. For this reason, the vinyl chloride resin is preferably a vinyl chloride-vinyl acetate copolymer resin having a vinyl acetate residue content of 5% by mass or more and 12% by mass or less, more preferably 6% by mass or more and 12% by mass or less, and even more preferably 7% by mass or more and 10% by mass or less, so that the elongation percentage and tensile strength can be increased and the coating film strength can be improved.

[0088] Furthermore, the coating films formed from the vinyl chloride plastisol compositions of Examples 1 to 8 have good appearance and no yellowing due to the combined use of polyamide and aliphatic block urethane as adhesion promoters.

[0089] On the other hand, the vinyl chloride plastisol compositions of Comparative Examples 1 to 4, when baked at a low temperature for a short time of 14 minutes at 120°C, did not provide the physical properties of the coating film required for applications such as automotive undercoats, chipping resistance, and sealing, and were therefore not suitable for practical use.

[0090] That is, in Comparative Examples 1 and 2, which omitted the incorporation of a liquid acrylic resin having hydroxyl groups, the coating film obtained under the low-temperature drying and baking conditions of 120°C for 14 minutes in the above evaluation test had an elongation of less than 100%, which was insufficient. When the elongation is insufficient, the coating film has poor toughness and flexibility and is difficult to disperse and relieve stress, which results in poor compliance with vibrations of the substrate, making the coating film prone to breakage, cracks, defects, etc., and making it impossible to ensure the desired high chipping resistance. Therefore, the coating films formed from the vinyl chloride plastisol compositions of Comparative Examples 1 and 2 are inferior to the Examples in coating film strength, chipping resistance, and other coating film performance.

[0091] Comparing Comparative Examples 1 and 2 with the Examples, it can be seen that by using a liquid acrylic resin having hydroxyl groups in addition to a vinyl chloride resin as a thermoplastic resin, good curing properties are obtained even under low-temperature, short-time, low-load drying conditions, the desired high elongation rate is obtained which ensures pitting resistance, etc., and the tensile strength and hardness are also good, ensuring coating film strength.

[0092] In Comparative Example 3, in which a liquid acrylic resin having carboxyl groups was used instead of the liquid acrylic resin having hydroxyl groups used in the Examples, the coating film obtained under the low-temperature, short-time baking and drying conditions of 120°C for 14 minutes in the above evaluation test showed insufficient adhesion. This is thought to be because the liquid acrylic resin having carboxyl groups reacted with the polyamide, inhibiting its adhesiveness, preventing the polyamide from expressing its adhesiveness. Furthermore, the coating film of Comparative Example 3, in which a liquid acrylic resin having carboxyl groups was used, also showed poor tensile strength and hardness.

[0093] Furthermore, in Comparative Example 4, in which a powdered acrylic resin was used instead of the liquid acrylic resin having hydroxyl groups used in the Examples, the coating film obtained under the low-temperature, short-time baking and drying conditions of 120°C for 14 minutes in the above evaluation test showed insufficient adhesion. This is thought to be because the powdered acrylic resin reacted with the polyamide, inhibiting its adhesiveness, preventing the adhesiveness of the polyamide from being expressed.

[0094] Comparison of Comparative Examples 3 and 4 with the Examples reveals that a liquid acrylic resin having hydroxyl groups does not react with the polyamide, and the adhesive properties of the polyamide are expressed, ensuring adhesiveness. According to the experimental research of the present inventors, when the liquid acrylic resin containing one or more functional hydroxyl groups in the molecule has a weight-average molecular weight of 500 or more and 5,000 or less, it has good compatibility with vinyl chloride resins, has high plasticity, and can toughen the coating film without impairing the coatability. In particular, a liquid acrylic resin containing one or more functional hydroxyl groups at the molecular end is preferred, and a liquid acrylic resin containing one functional hydroxyl group at the molecular end is more preferred, as this has high orientation in the vinyl chloride resin and allows for a tougher coating film to be obtained.

[0095] Furthermore, a vinyl chloride-vinyl acetate copolymer having a vinyl acetate group content of 5% by mass or more and 15% by mass or less exhibits excellent curing properties at low temperatures. Particularly preferably, a vinyl chloride-vinyl acetate copolymer having a vinyl acetate group content of 7% by mass or more and 10% by mass or less exhibits improved compatibility with plasticizers, excellent absorption of plasticizers and liquid acrylic resins at low temperatures, an increased melt viscosity even at low temperatures, and the melting of vinyl chloride resin particles proceeds even at low temperatures, resulting in complete melting and a uniform phase. Furthermore, the plasticizing effect of the liquid acrylic resin is also obtained, resulting in high strength, elongation, and adhesiveness.

[0096] Thus, the vinyl chloride plastisol compositions of Examples 1 to 8 can form coating films with good adhesiveness and strong coating film properties even under low-temperature, short-time baking and drying conditions. That is, the vinyl chloride plastisol compositions of Examples 1 to 8, which use a combination of a vinyl chloride thermoplastic resin and a hydroxyl-containing liquid acrylic resin, can form a tough coating film with high elongation and tensile strength even under low-temperature, short-time baking and drying conditions at low cost, ensuring coating film strength and chipping resistance. Furthermore, the hydroxyl-containing liquid acrylic resin, acting as a plasticizer, penetrates between the molecules of the vinyl chloride resin and orients it, resulting in excellent vibration durability. Furthermore, since the acrylic resin is a hydroxyl-containing liquid acrylic resin, the polyamide does not react with the acrylic resin, ensuring adhesion through the development of adhesive properties by the polyamide. In particular, the combination of a polyamide and an aliphatic block urethane provides high adhesion even under low-temperature, short-time baking and drying conditions, resulting in a coating film with good appearance and no yellowing. That is, when such a system of polyamide components and block urethane is used in combination, the block is dissociated at the temperature of the heat baking, and the isocyanate group of the regenerated isocyanate compound reacts with the active hydrogen (amino group) of the polyamide, polymerizing and curing to develop adhesive properties. Therefore, not only does it exhibit excellent adhesion to cationic electrodeposition coated surfaces, but it can also develop adhesion under relatively low baking temperatures, and the storage stability of the plastisol composition is also excellent. In addition, the combined use of block polyurethane prepolymer and polyamidoamine also provides good water resistance to the coating film.

[0097] The vinyl chloride plastisol compositions of Examples 1 to 8 contain a thixotropic agent, which makes the coating less likely to drip and provides good applicability, and a moisture absorbent (dehydrating agent) which prevents swelling of the coating due to moisture. Furthermore, the vinyl chloride plastisol compositions of Examples 1 to 8 contain a blend of a vinyl chloride resin (a thermoplastic resin) and a liquid acrylic resin, a plasticizer, an adhesion promoter, a thixotropic agent, a moisture absorbent, a viscosity reducer, and a filler, so they are compatible with current one-component coating equipment.

[0098] As explained above, the vinyl chloride plastisol composition of the above embodiment is a vinyl chloride plastisol composition containing a vinyl chloride resin, an acrylic resin, a polyamide, and a plasticizer, and the acrylic resin is a liquid acrylic resin containing one or more functional hydroxyl groups in the molecule.

[0099] Therefore, according to the vinyl chloride plastisol composition of the above embodiment, by combining a vinyl chloride resin as a thermoplastic resin with a liquid acrylic resin containing one or more functional hydroxyl groups in the molecule, curing properties are exhibited even under low-temperature baking and drying conditions, and coating film properties such as coating film strength can be ensured. Furthermore, if the liquid acrylic resin contains one or more functional hydroxyl groups in the molecule, it does not react with the polyamide used as an adhesion promoter, and the polyamide's adhesive properties are exhibited even under low-temperature baking and drying conditions, ensuring adhesion. In addition, since vinyl chloride resins are inexpensive, the composition is low cost and has good storage stability.

[0100] Furthermore, even under low-temperature baking and drying conditions (100°C to 130°C), the coating film can exhibit high strength, elongation, and other physical properties, and since the adhesion is also good, it is possible to shorten the heating time, thereby reducing carbon dioxide emissions and energy costs.Furthermore, it is possible to increase the speed and productivity of line production for automobiles, etc.

[0101] The liquid acrylic resin containing one or more functional hydroxyl groups in the molecule is preferably blended in an amount within the range of 5 to 60 parts by mass per 100 parts by mass of vinyl chloride resin, so that coating strength can be increased even when baked and dried at a low temperature without impairing application properties, including sagging properties. Furthermore, when the polyamide is blended in an amount of preferably 1 part by mass or more and 20 parts by mass or less per 100 parts by mass of the vinyl chloride resin, the adhesion of the coating film can be improved without impairing the coatability, including sagging.

[0102] Furthermore, if the vinyl chloride resin is a vinyl chloride-vinyl acetate copolymer, it has excellent curing properties at lower temperatures. Furthermore, if the vinyl acetate group content is within the range of 5% by mass or more and 15% by mass or less, the toughness of the coating film can be improved. In addition, if the weight average molecular weight of the liquid acrylic resin containing one or more functional hydroxyl groups in the molecule is in the range of 500 or more and 5000 or less, the coating film can be strengthened without impairing the coatability.

[0103] In carrying out the present invention, the constitution, ingredients, blending, materials, manufacturing method, etc. of other parts of the vinyl chloride plastisol composition are not limited to those in the present examples. Furthermore, the numerical values ​​given in the embodiments and examples of the present invention do not all indicate critical values, and some numerical values ​​indicate suitable values ​​for implementation, so slight changes to the above numerical values ​​do not negate the implementation.

Claims

1. A vinyl chloride plastisol composition containing a vinyl chloride resin, an acrylic resin, a polyamide, and a plasticizer, The vinyl chloride plastisol composition is characterized in that the acrylic resin is a liquid acrylic resin containing one or more functional hydroxyl groups in the molecule.

2. 2. The vinyl chloride plastisol composition according to claim 1, wherein said vinyl chloride resin is a vinyl chloride-vinyl acetate copolymer.

3. 3. The vinyl chloride plastisol composition according to claim 2, wherein the vinyl chloride resin has a vinyl acetate group content in the range of 5% by mass or more and 15% by mass or less.

4. 2. The vinyl chloride plastisol composition according to claim 1, wherein the liquid acrylic resin has a weight average molecular weight in the range of 500 to 5,000.

5. 2. The vinyl chloride plastisol composition according to claim 1, wherein the liquid acrylic resin is blended in an amount of 5 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the vinyl chloride resin.

6. 2. The vinyl chloride plastisol composition according to claim 1, wherein the polyamide is blended in an amount of 1 part by mass or more and 20 parts by mass or less per 100 parts by mass of the vinyl chloride resin.

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