JP2024092074A - Vinyl chloride plastisol composition - Google Patents

Abstract

The present invention relates to a composition that can exhibit curing and adhesive properties even when baked and dried at a low temperature.
[Solution] The vinyl chloride-based plastisol composition is a vinyl chloride-based plastisol composition containing a vinyl chloride-based 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.
[Selection diagram] None

Description

The present invention relates to a vinyl chloride-based plastisol composition suitable for use in coatings for interlayer chipping resistance, underbody coatings, and body sealers for vehicles such as automobiles, and in particular to a vinyl chloride-based plastisol composition that can exhibit curing and adhesive properties even when baked and dried at low temperatures.

In the lower structural parts of an automobile body, such as the underside of the floor, the wheel house (tire house), the rocker panel (side sill), the front apron, the front and rear fenders, the lower part of the door, the bottom of the gasoline tank, etc., chipping occurs, in which the paint film is scratched or peeled off due to collision with pebbles and gravel kicked up by the tires while the automobile is running. Therefore, coating paints such as chipping-resistant paints and undercoats are applied to such parts for the purpose of chipping resistance, rust prevention, soundproofing, etc., which prevent peeling and scratching of the paint film caused by stones and sand splashes and protect the automobile body.
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 for the purposes of watertightness, airtightness, waterproofing, rust prevention, and dust prevention.

Traditionally, this type of chipping-resistant, undercoat, and sealing paint has been made by turning polyvinyl chloride resin into a sol with a plasticizer, called a polyvinyl chloride plastisol. After being applied to the vehicle body, this polyvinyl chloride plastisol is baked and dried to form a hardened coating.

In recent years, with the rise in environmental conservation awareness, measures to reduce carbon dioxide emissions and energy conservation are being implemented in automobile factories, where automobiles are produced, in order to reduce the environmental impact. As part of this, there is a demand to reduce carbon dioxide emissions generated by the energy consumption of baking ovens in the painting process of paints used on automobiles. In order to achieve energy savings and reduce carbon dioxide emissions, there is a demand to lower the temperature of baking ovens and shorten the drying time, that is, to reduce the load of heating and drying in the baking and drying process after painting. However, with conventional polyvinyl chloride plastisols, the compounding materials were selected on the premise of high-temperature baking, and therefore coating properties such as curing ability and coating strength and adhesion could not be expressed under low-temperature baking and drying conditions.

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% by mass.

JP 2021-011525 A

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 upper coatings are applied. On the other hand, if an adhesive other than an aromatic isocyanate, such as polyamide, is used, there is a problem that the polyamide reacts with the powdered acrylic resin and the adhesive properties are not expressed.

Therefore, the objective of the present invention is to provide a chlorinated plastisol composition that can exhibit curing properties and adhesiveness even when baked and dried at low temperatures.

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, and the acrylic resin is a liquid acrylic resin containing one or more functional hydroxyl groups in the molecule.

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.

The liquid acrylic resin has one or more functional hydroxyl groups in the molecule, preferably at the molecular end, and is preferably a low molecular weight resin with 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.

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.

The vinyl chloride resin of the vinyl chloride plastisol composition of the invention of claim 2 is a vinyl chloride-vinyl acetate copolymer.

The vinyl acetate group content of the vinyl chloride resin of 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.

The liquid acrylic resin of 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.

The liquid acrylic resin in the vinyl chloride plastisol composition of the invention of claim 5 is preferably blended in a range 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.

The polyamide in the vinyl chloride plastisol composition of the invention of claim 6 is preferably blended in a range 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.

According to the vinyl chloride plastisol composition of the invention of claim 1, it contains a vinyl chloride resin, an acrylic resin, a polyamide, and a plasticizer, and 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 physical properties such as coating film strength can be ensured. In addition, if the liquid acrylic resin contains one or more functional hydroxyl groups in the molecule, the adhesiveness of the polyamide is exhibited even under low-temperature baking and drying conditions without reacting with the polyamide as an adhesion imparting agent, and adhesiveness can be ensured.

According to the vinyl chloride-based plastisol composition of the invention of claim 2, the vinyl chloride-based 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.

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

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.

According to the vinyl chloride plastisol composition of the invention of claim 5, the liquid acrylic resin is blended in a range of 5 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the vinyl chloride resin, so in addition to the effect of claim 1, the coating strength can be increased by baking and drying at a low temperature without impairing the coatability.

According to the vinyl chloride plastisol composition of the invention of claim 6, the polyamide is blended in a range of 1 part by mass or more and 20 parts by mass or less per 100 parts by mass of the vinyl chloride resin, so in addition to the effect described in claim 1, the adhesion of the coating film can be improved without impairing the coatability.

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 imparting agent (adhesion imparting agent).

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 a substrate (substrate) such as metal, low-temperature curing property, strength for enhancing chipping resistance, and elongation, it is preferable to contain a copolymer. 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 acid esters such as diethyl maleate, fumaric acid esters such as dibutyl fumarate, acrylic acid or methacrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate, acrylic acid or methacrylic acid hydroxyalkyl esters such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate, acrylic acid or methacrylic acid hydroxyalkyl amides such as N-methylol acrylamide, N-methylol methacrylamide, N-hydroxyethyl acrylamide, and N-dihydroxyethyl methacrylamide, acrylonitrile, and vinylidene chloride. Vinyl chloride can also be made into a crosslinkable copolymer having --CH ₂ ROH groups.

Among these, vinyl acetate is suitable as a monomer to be copolymerized with vinyl chloride from the viewpoints of low-temperature curing, strength to enhance chipping resistance, elongation, swelling and gelling properties against plasticizers, adhesion and adhesion to objects to be coated such as metals, etc. Furthermore, if 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 liquid acrylic resin even under low-temperature baking and drying conditions. Furthermore, if 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 good plasticizer absorption (low-temperature melting property, swelling and gelling property) and compatibility with liquid acrylic resin having hydroxyl groups even at low temperatures. In terms of the average degree of polymerization, 1300 to 3000 is preferable, and more preferably 1500 to 2500. If it is within this range, a strong coating film can be formed even with low temperature curing.

The vinyl chloride resin may be used alone or in combination of two or more kinds. For example, a resin obtained by emulsion polymerization or suspension polymerization may be used. When added to or blended in the composition, a fine powder or granular resin may be used. In the composition, the vinyl chloride resin may be dispersed in a granular form or may be dissolved in an organic solvent if one is included.

The amount of vinyl chloride resin is set according to the desired coating film properties, etc., but if the content of vinyl chloride resin in the paint composition is too low, the toughness, mechanical strength, pitting resistance, adhesion, etc. of the coating film will decrease, or the amount of liquid acrylic resin will increase relatively, resulting in high costs. On the other hand, if the content is too high, the composition will not have suitable structural viscosity and thixotropy, and the composition will have poor storage stability, coating workability, and applicability. The vinyl chloride resin is preferably contained in the composition in a range of 5 to 50 mass% in terms of solid content, more preferably in a range of 10 to 45 mass%, even more preferably in a range of 15 to 40 mass%, and particularly preferably in a range of 18 to 35 mass%. Within these ranges, the composition will have good storage stability, coating workability, and applicability, and the coating film performance such as adhesion, strength, and pitting resistance will be good.

From the viewpoint 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. Since such a particle size is non-porous, it has an excellent thixotropic effect, good coatability, and good storage stability with little change in viscosity over time. More preferably, it is in the range of 0.1 to 5 μm, and even more preferably, 0.1 to 2 μm.

The liquid acrylic resin contains one or more functional hydroxyl groups in the molecule, preferably one or more functional hydroxyl groups at the molecular end, and may be a copolymer of a monomer having a hydroxyl group. Particularly preferred is one having one hydroxyl group at only one end.
The liquid acrylic resin has 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. Within this range, the resin has good compatibility with vinyl chloride resins, has high plasticity, and can toughen the coating film without impairing the coatability.

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

By combining such liquid acrylic resins, which have one or more functional hydroxyl groups in the molecule, with vinyl chloride resins, it is possible to obtain coating properties with high strength and high elongation even under low-temperature baking and drying conditions, and even if polyamide is added, it is difficult to react with it, so adhesion can be guaranteed. This is presumably 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.

As the plasticizer, basically, any of those generally used to form this type of vinyl chloride plastisol composition can be used, for example, compounds (esters) synthesized from acids such as phthalic acid, trimellitic acid, adipic acid, etc. and alcohols such as octanol, nonanol, and higher mixed alcohols are 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-C10 mixed higher alcohol phthalates, butyl ... 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); tricresyl phosphate (TCP), trioctyl phosphate (TOF), trixylenyl phosphate (TXP), monooctyl diphenyl phosphate, and monobutyl-dixylenyl phosphate (B-Z-X); phosphate esters such as trioctyl trimellitate (TOTM), tri-n-octyl trimellitate, triisodecyl trimellitate, triisooctyl trimellitate, and other benzoate esters; butyl phthalate butyl glycolate (BPBG), tributyl citrate, trioctyl acetyl citrate, trimellitate, citric acid ester, sebacic acid ester, azelaic acid ester, maleic acid ester, tri- or tetraethylene glycol ester of C6 to C10 fatty acid, alkyl sulfonic acid ester, methacrylic acid ester, etc. Examples of usable oils include esters such as ethyl acetyl ricinoleate, epoxidized vegetable oils such as those in which the double bonds of unsaturated fatty acid glycerides such as soybean oil are epoxidized with hydrogen peroxide or peracetic acid (ESBO), epoxy compounds such as butyl or octyl alkyl oleate, viscous low-polymerization polyesters (e.g., adipic acid polyesters, phthalic acid polyesters) with an average molecular weight of about 500 to 8000 in which propylene glycol ester units of dibasic acids such as adipic acid are linearly linked, and alkylsulfonic acids such as Mezamol (registered trademark). These oils may be used alone or in combination of two or more.

Among these, substances that are liquid at room temperature are desirable, and phthalic acid esters are the most common plasticizers, are easily available, and are inexpensive. They also enable uniform dispersion of vinyl chloride resins, and can form stable vinyl chloride plastisol compositions. Among phthalic acid 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 not being an environmental burden, ease of handling, solubility, applicability, storage stability, etc.

Such plasticizers are appropriately selected according to the desired viscosity characteristics, curing properties, coating strength, etc. of the plastisol composition, and the blending amount is set, but if the blending amount is too small, the storage stability and application workability of the plastisol composition are reduced, and the flexibility and elongation rate of the coating film are reduced. In particular, when baking is performed at a lower temperature and for a shorter time than the current baking conditions, good coating film performance such as strength, impact resistance, chipping resistance, etc. cannot be exhibited. On the other hand, if the blending amount is too large, sagging, etc., is likely to occur, and good coating film performance such as strength, impact resistance, chipping resistance, etc. cannot 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 can be made soft to obtain appropriate flexibility (elasticity), and coating film performance such as strength, impact resistance, and chipping resistance can be ensured.

Furthermore, in the vinyl chloride plastisol composition of the present embodiment, an adhesion imparting agent is blended in order to improve the adhesion (adhesiveness, adhesion) to the object to be coated.
As the adhesion imparting agent in this embodiment, polyamidoamine, polyimideamine, polyamine, etc. are used, but in the case of paint applications such as chipping resistance and undercoat for automobiles, since the vinyl chloride-based plastisol composition is generally applied after undercoating by electrodeposition coating, etc., it is preferably used in combination with a blocked isocyanate (e.g., xylylene 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 acrylics, imines, other amines, polyols, etc. in combination.

Polyamides are polyamide compounds containing active amino groups or amide groups that are generally used as curing agents for epoxy resins, etc., and are generally obtained by reacting polyamines such as aliphatic diamines, such as hexamethylenediamine, or aromatic diamines, with polybasic acids, such as dimer acids. As such polyamides, typically used are polyamidoamines, which are reaction products of polyamines and polymerized fatty acids, such as dimer acids or trimer acids, which are obtained by thermally polymerizing unsaturated fatty acids, such as linoleic acid.
Such polyamides contain active amino groups or amide groups which 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.

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

Blocked isocyanates are compounds that are relatively low molecular weight polyisocyanate components, preferably compounds that generally have two or more isocyanate groups (-N=C=O) in the molecule, blocked with a blocking agent that is a compound that has active hydrogen, such as methyl ethyl ketone oxime (MEKO). Examples of polyisocyanate components include aliphatic diisocyanates such as hexamethylene diamine (HDI), aromatic diisocyanates such as tolylene diisocyanate (TDI), xylylene diisocyanate, and diphenylmethane diisocyanate (MDI), aliphatic diisocyanates such as hexamethylene diisocyanate, alicyclic diisocyanates such as isophorone diisocyanate, hydrogenated TDI, and hydrogenated MDI, or biuret bodies, isocyanurate bodies, adducts with polyhydric alcohols such as ethylene glycol and trimethylolpropane, and urethane prepolymers. As blocking agents for these isocyanate compounds, ketoximes such as methyl ethyl ketoxime (MEKO), active methylene compounds such as acetylacetone and acetoacetate, lactams such as ε-caprolactam, oxybenzoic acid esters, alkylphenols, etc. can be used, but methyl ethyl ketoxime is particularly preferred in terms of compatibility with vinyl chloride resins and plasticizers.

Among them, blocked urethane prepolymers, which are urethane prepolymers consisting of a prepolymer of a diisocyanate compound (diisocyanate such as TDI, polyisocyanate, etc.) and a polyol (polyether polyol, polyester polyol, polymer polyol, etc.) and having an isocyanate group at the end, blocked with a blocking agent, are generally most suitable for use. 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 middle and upper coating, and do not impair appearance and coating performance.
Such blocked isocyanates allow the blocking agent of the blocked isocyanate to dissociate at the temperature during heating and baking, and the isocyanate group of the regenerated isocyanate component to bond with 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.

When a blocked isocyanate is blended to ensure excellent adhesion with the cationic electrodeposition coating film, 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%. For 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 bonding properties of the coating film can be improved without impairing the coatability.

In particular, when polyamide and blocked isocyanate are used in combination, the polyamide promotes the dissociation of the blocked isocyanate, so that it is possible to develop better adhesion and adhesiveness. According to the combined use of polyamide component and 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 it show excellent adhesion and adhesiveness to the cationic electrodeposition coating surface, but it can also develop high adhesion and adhesiveness even under baking conditions at low temperatures. Furthermore, polyamide and blocked isocyanate have good storage stability. Preferably, the combined use of polyamide amine 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 their types, equivalent weights, etc.

The adhesion promoter is preferably blended in the vinyl chloride plastisol composition in an 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% in total. 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 vinyl chloride resin (solid content). Within this range, the adhesion and bonding properties of the coating film can be improved without impairing the coatability.

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

As rheology control agents, thixotropic agents, and anti-sagging agents for imparting anti-sagging performance when applied to a substrate, for example, colloidal calcium carbonate (ultrafine calcium carbonate particles), fine silica particles, etc. are used. As colloidal calcium carbonate, ultrafine synthetic calcium carbonate or ultrafine precipitated calcium carbonate having an average particle size of 0.1 μm or less is generally used, and basically, those used in conventional vinyl chloride plastisol compositions of this type, for example, precipitated calcium carbonate having a cubic shape, and surface-treated with fatty acid, etc. are suitable. From the viewpoint of thixotropy, for example, colloidal calcium carbonate having a BET specific surface area in the range of 10 to 40 m ² /g, more preferably 13 to 30 m ² /g is used. When colloidal calcium carbonate is blended, it is blended in the vinyl chloride plastisol composition preferably in the range of 1 to 30 mass%, more preferably 5 to 25 mass%, and even more preferably 10 to 20 mass%. The amount of the compounded resin is preferably 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.

When a rheology control agent/thixotropic agent such as colloidal calcium carbonate is added, the vinyl chloride plastisol composition is given thixotropy, increasing the viscosity of the composition at low shear rates (at rest) while decreasing the viscosity at high shear rates. That is, at low shear rates (at rest), the colloidal calcium carbonate fine particles loosely bond (aggregate) to each other in the plastisol composition to form a three-dimensional structure (finely dispersed colloidal structure), increasing the viscosity of the plastisol composition. However, because the bonding strength between these fine particles is weak, at high shear rates, the structure is partially or entirely destroyed by the high shear force, increasing the fluidity and decreasing the apparent viscosity. As a result, the viscosity and flow characteristics suitable for coating operations are obtained. That is, when a plastisol composition is subjected to high-speed shear during preparation or application, the apparent viscosity of the composition decreases, allowing it to be applied at a viscosity suitable for application work, while after it adheres to the substrate, its thixotropy (time dependency) causes the structure to recover and the viscosity of the plastisol composition to return to its original high state, preventing sagging after application.

As a moisture absorbent for improving the moisture absorption and foaming resistance, which traps the 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 suitably used.
When the 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.

When a moisture absorbent such as calcium oxide is added, it is possible to capture the remaining moisture contained in fillers such as calcium carbonate and polyvinyl chloride resins, and prevent foaming of the coating film during baking. In addition, when the plastisol composition is left to stand after application, foaming of the coating film during baking due to moisture absorption can be prevented. Furthermore, the moisture contained in relatively large amounts in paint residue can also be absorbed by this moisture absorbent.

As a solvent (thinner) used to improve the mixing workability of the compounding materials, the application workability and storage stability, the leveling (smoothness) of the coating film after coating, and the appearance of the coating film, from the viewpoint of application workability and application property, for example, petroleum solvents such as naphtha, turpentine oil, paraffin, mineral spirits, aliphatic hydrocarbon solvents such as butane, pentane, hexane, heptane, octane, isooctane, nonane, alcohol, aromatic solvents such as benzene, toluene, xylene, etc., and organic solvents with a relatively high boiling point (preferably a boiling point of 150°C or more and 220°C or less) are used. From the viewpoint of thickening and thixotropic effect, non-polar hydrocarbons, for example, paraffin-based hydrocarbons, are preferably used.

If too much of such a solvent is added, sagging properties will be impaired, so when a solvent such as a paraffin-based hydrocarbon is added, it is preferably added in the vinyl chloride-based plastisol composition in a range of 1 to 10% by mass, more preferably 2 to 9% by mass, and even more preferably 3 to 8% by mass.

In addition, pigments, leveling agents, fillers, stabilizers, etc. may also be appropriately added.
Examples of the pigment include color pigments, extender pigments, anti-rust pigments, functional pigments, etc. Examples of the color pigment 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, phthalocyanine blue, etc. Examples of the anti-rust pigments that can be used include 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 the viewpoint of environmental protection, it is desirable to use an anti-rust pigment that does not contain harmful heavy metals such as chromium. Examples of the extender pigments that can be used include talc, calcium carbonate, barium sulfate, calcium sulfate, mica, clay, silica, diatomaceous earth, alumina, baryta, and silicon dioxide. In particular, talc forms many layers stacked in the coating film, and the denseness of the layers formed by the arrangement can prevent the intrusion of corrosive factors.

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

Examples of fillers for increasing the amount, thickening, improving the workability and applicability of coating, improving the strength of the coating film, etc. include calcium carbonate such as heavy calcium carbonate, carbonates and sulfates of alkaline earth metals such as magnesium carbonate and barium sulfate, mica, silica, talc, diatomaceous earth, kaolin, clay, organic bentonite, alumina, gypsum, cement, powdered converter slag, powdered shirasu, powdered glass, graphite, vermiculite, zeolite, calcium metasilicate, zonolite, potassium titanate, rock wool, glass fiber, carbon fiber, aluminum silicate, aramid fiber, cellulose powder, powdered rubber, vinylidene chloride, acrylonitrile, polyvinylidene chloride, or synthetic resins (plastics) such as copolymers of these, thermoplastic resin balloons such as expanded resin microcapsules (thermally expandable microspheres), resin balloons (lightweight materials) such as phenol balloons, and foaming agents. These may be used alone or in combination of two or more types. Among these, hollow particles as fillers, unexpanded thermally expandable microcapsules, foaming agents, etc. are effective in lowering the specific gravity of the coating film, thickening the coating film, improving soundproofing, and forming an escape route (water escape passage) for moisture absorbed in the composition. In other words, when hollow particles, unexpanded thermally expandable microcapsules, or foaming agents are added, it is possible to lower the specific gravity without increasing the coating weight by thickening the coating film, and a coating film that combines soundproofing and light weight can be formed.

Specifically, hollow particles (hollow fillers) may be hollow balloons that do not melt, expand, or burst even when baked and heated after application, and that maintain a specified degree of hollowness. For example, 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 glassy volcanic debris such as shirasu, and organic hollow particles with an organic shell, such as thermoplastic resin balloons such as expanded resin microcapsules (thermally expandable microspheres) made of synthetic resins (plastics) such as vinylidene chloride, acrylonitrile, polyvinylidene chloride, or copolymers of these, resin balloons such as phenol balloons, or carbon hollow spheres, are used. These hollow particles have a low true specific gravity, which makes them highly effective in reducing the weight (specific gravity) of the coating film. From the viewpoints of ease of handling, workability, and lightweight effect, the true specific gravity is preferably within the range of 0.02 to 0.8, and more preferably 0.1 to 0.5.

Thermally expandable microcapsules may be formed from a material in which the shell softens when heated during baking after painting, and the vaporized substance in the shell turns into gas, causing the shell to expand due to the resulting pressure (vapor pressure), and the expansion can be controlled by heat. In other words, thermally expandable microcapsules may be formed from a material in which the shell softens at a predetermined temperature, and the liquid inside vaporizes, and may be formed from a shell (shell wall, outer shell) 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 methacrylic acid, methyl copolymer, etc.). The microcapsules are unexpanded thermoplastic resin microcapsules having 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 constituting the shell is enclosed in the core of the microcapsules.

These thermally expandable thermoplastic resin microcapsules are capsule-shaped with a shell structure made of thermoplastic resin with a vaporized substance in the core. After application to the surface to be coated, the shell is heated above the softening temperature of the shell, and when the temperature reaches a predetermined range, the shell softens and the vaporized substance contained inside the shell turns into gas. The shell expands due to an increase in the pressure (expansion force/vapor pressure) of the gas inside the shell, increasing its volume and becoming a hollow thermoplastic resin microballoon. For example, in the case of a particle diameter (median diameter) of 5 to 50 μm, the volume change is about 50 to 100 times. The shell (outer shell) made of thermoplastic resin may be coated with inorganic powder such as calcium carbonate. In other words, a hybrid shell made of thermoplastic resin with inorganic powder attached to the surface, specifically, a shell of thermoplastic resin coated with inorganic metal salt or metal oxide, such as calcium carbonate, talc, titanium oxide, etc., may be used.

Examples of the foaming agent include organic foaming agents such as ADCA (azodicarbonamide), azobisisobutyronitrile (AIBN), dinitrosopentamethylenetetramine (DPT), p-toluenesulfonylhydrazide (TSH), p-toluenesulfonyl azide, p-methylurethanebenzenesulfonylhydrazide, benzenesulfonylhydrazide (BSH), and oxybenzenesulfonylhydrazide (OBSH), as well as inorganic foaming agents such as sodium bicarbonate (sodium bicarbonate) and ammonium carbonate. A heat-type foaming agent is preferably used. A heat-type foaming agent is one in which the foaming agent decomposes when heated to generate gas and foam. When such a heat-type foaming agent is contained, it is desirable to use one in which the foaming agent decomposes and foams depending on the heat treatment temperature when the coating film is cured after the composition is applied to a specified location. If necessary, it is possible to use a foaming assistant (e.g., salicylic acid, phthalic acid, stearic acid, uric acid, benzoic acid, urea, zinc and its compounds, etc.) to assist the foaming action of the foaming agent. The foaming assistant may be blended so that the foaming occurs according to the heating conditions during baking and drying to harden the coating film, but depending on the heating conditions, a foaming assistant is not necessarily required.

In addition, two or more of the hollow particles, unexpanded thermally expandable microcapsules, and foaming agents intended to lower the specific gravity of the coating film may be used in combination.
In particular, when a thermally expandable microcapsule is blended with the composition, the vaporized material inside the thermally expandable microcapsule is vaporized by heating during baking, and the shell expands under the pressure to become a hollow microballoon, and the coating film made of the composition applied to a specified location expands and becomes a thick film due to the expanded hollow microballoon. Therefore, a coating film with high soundproofing properties can be formed without increasing the amount of coating. Furthermore, the coating film thickened by utilizing the volume expansion of the thermally expandable microcapsule has a low specific gravity, and the increase in the coating weight due to the thickening is suppressed. Furthermore, when hollow particles or a foaming agent are used in combination, a coating film with an extremely low specific gravity and a lightweight coating film can be formed.

In addition, for example, in applications such as sealing by coating and filling the joints, seams, hemmings, etc. of steel plates, when applied to oily steel plates with anti-rust oil still attached, it is possible to compound 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-based compounds, in order to obtain sufficient adhesion to the oily steel plates. In addition to the epoxy resin and its hardener, aliphatic blocked isocyanates, titanate coupling agents, and organotin stabilizers (e.g., alkyl tins such as dibutyltin dilaurate, dioctyltin laurate, dibutyltin maleate, and dibutyltin phthalate, organotin mercaptides, etc.) may be added to obtain high adhesion even when applied to zinc-plated surfaces of steel sheets, soft steel surfaces, organic coating surfaces, etc.

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

The vinyl chloride plastisol composition of this embodiment can be used as, for example, a chipping-resistant coating composition for automobile bodies, an undercoat coating composition, or a sealing coating composition, and is applied to a predetermined portion and cured by baking and drying to form a coating film. The vinyl chloride plastisol composition of this embodiment, which contains a vinyl chloride resin, a liquid acrylic resin, a plasticizer, and a polyamide such as polyamide amine as an adhesion imparting agent, can be used as one liquid rather than two liquids, making it easy to handle. In addition, since the shape can be adjusted before heating, any coating shape can be selected. Naturally, a coating robot or a brush can be used, and since there is no need to mold the composition in a closed mold, a film can be formed as an open mold, and it can be used for chipping resistance, undercoat, and sealing.

The form and means of applying the paint made of the vinyl chloride-based plastisol composition of the present embodiment to a predetermined portion can be a conventionally known application method, for example, coating application such as brush application, roller application, and dipping, spray application such as airless spray and air spray, electrostatic coating, and the like.
For example, in the case of chipping resistance or undercoat, the coating is applied to the underside of the floor, wheel house, front part, rear fender part, front apron, etc. of an automobile, side sill part (rocker panel part), lower side of the door, etc. In addition, in the case of sealing, the coating is applied to the joints, seams, edges, etc. of the steel plates that constitute the car body.

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 applying a vinyl chloride plastisol composition for chipping resistance, undercoat, or sealing of an automobile to the steel plate surface of an automobile, for example, the wheel house part or the underside of the floor of an automobile, the composition is applied to the electrodeposition-coated surface of the steel plate that has been subjected to a degreasing process, a chemical conversion treatment process, and a primer coating process by electrodeposition coating in the coating line of the automobile production line. Then, the intermediate coating or finish coating of the outer plate part 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 coating or finish coating, 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 the intermediate coating or top coating is layered on top of the composition, and then baked and cured 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 at this time 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 coating surface, before the baking curing of the undercoat paint, topcoat paint, etc.

In particular, in the painting line of an automobile manufacturing line, a cured coating film made of a vinyl chloride-based plastisol composition was conventionally formed by baking and drying at 140 to 160°C for 20 to 40 minutes. However, according to the vinyl chloride-based plastisol composition of the present embodiment, by using a vinyl chloride-based thermoplastic resin and a hydroxyl-containing liquid acrylic resin in combination, a tough coating film with high elongation and tensile strength can be formed and chipping resistance can be ensured even under baking and drying conditions lower than the above temperature, for example, baking and drying at 100 to 130°C. Furthermore, adhesion can be ensured by blending polyamide as an adhesion imparting agent, and if polyamide is used, a coating film with good appearance and no yellowing can be formed. In addition, these blending materials are inexpensive, and a combination of vinyl chloride-based resin and liquid acrylic resin can be used at low cost.

In the vinyl chloride-based plastisol composition of the present embodiment, a strong coating film can be formed even under low-temperature baking and drying conditions by using a vinyl chloride-based resin and a hydroxyl-containing liquid acrylic resin in combination, i.e., the coating film can be hardened even at low temperatures to ensure chipping resistance, etc. However, even in such a combination system of vinyl chloride-based resin and acrylic resin, by using a hydroxyl-containing liquid acrylic resin as the acrylic resin, the polyamide of the adhesion imparting agent does not react with the acrylic resin, and the adhesion of the polyamide is not inhibited by the acrylic resin, and high adhesion is exhibited by the polyamide. In other words, since the acrylic resin is a liquid acrylic resin having a hydroxyl group, even if polyamide is blended as an adhesion imparting agent, the liquid acrylic resin having the hydroxyl group penetrates between the molecules of the vinyl chloride-based resin and is oriented like a plasticizer, and the presence of the hydroxyl group of the liquid acrylic resin inhibits the reaction of the acrylic resin with the polyamide, and high adhesion is exhibited by the polyamide. And, if polyamide is used, a coating film with good appearance that does not yellow can be formed.

Thus, according to the vinyl chloride plastisol composition of the present embodiment, a strong coating film can be formed by combining a vinyl chloride resin and a hydroxyl-containing liquid acrylic resin even under low-temperature baking and drying conditions, and further, if the hydroxyl-containing liquid acrylic resin is used, the adhesiveness is not inhibited by reacting with the polyamide, and the high adhesiveness of the polyamide is expressed, thereby obtaining adhesiveness of the coating film. In other words, coating film physical properties (mechanical properties) such as coating film strength and adhesiveness are expressed by baking and drying at a lower temperature than before.
In particular, the combined use of vinyl chloride resin and acrylic resin is inapplicable because the adhesive mechanism of the vinyl chloride resin is inhibited by the acrylic resin, and the adhesive mechanism of the acrylic resin is inapplicable to the adhesion of vinyl chloride resin, making their combined use difficult. However, with a hydroxyl group-containing liquid acrylic resin, the hydroxyl groups prevent the resin from reacting with polyamide, allowing the adhesive properties of the polyamide to be expressed, thereby providing high adhesion and ensuring an appearance that does not yellow.

In addition, 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 the upper layer of paint from peeling off. Vinyl chloride plastisol compositions used as sealing paints for automobile bodies provide a sealing function (watertightness and airtightness) for joints, etc.

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 embodiment is a mixture of vinyl chloride resin, liquid acrylic resin, plasticizer, adhesion imparting agent, thixotropic agent, moisture absorbent, viscosity reducer, and filler.

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) having a vinyl acetate residue content of 9% by mass was blended as the vinyl chloride resin, and in Examples 5 to 8, a vinyl chloride-vinyl acetate copolymer resin (average polymerization degree: 1800) having a vinyl acetate residue content of 7% by mass was blended as the vinyl chloride resin.

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

In Examples 1 to 8, dioctyl phthalate (DINP) was blended as a plasticizer. Polyamidoamine and block urethane were used in combination as an adhesion imparting agent. In addition, synthetic calcium carbonate was blended as a thixotropic agent, calcium oxide as a moisture absorbent, a paraffin-based hydrocarbon solvent that is a high-boiling point solvent with a boiling point of 150 to 200°C as a viscosity reducer, and heavy calcium carbonate was blended as a filler.

On the other hand, in Comparative Example 1, no acrylic resin was blended, 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 not blending liquid acrylic resin, the same materials as in Examples 1 to 4 were blended in the amounts shown in Table 1.

In Comparative Example 2, no acrylic resin was added, and a vinyl chloride-vinyl acetate copolymer resin with a vinyl acetate residue content of 7% by mass was added as the vinyl chloride resin. Except for not adding liquid acrylic resin, the same materials as in Examples 5 to 8 were added in the amounts shown in Table 1.

In Comparative Example 3, the liquid acrylic resin was a solvent-free liquid acrylic resin with butyl acrylate as the main 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 ends 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 whose functional group is a carboxyl group was used instead of the liquid acrylic resin whose functional group is a hydroxyl group used in the examples.

In Comparative Example 4, instead of the liquid acrylic resin 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 the use of a solid acrylic resin instead of the liquid acrylic resin in the Examples, the same materials as in Examples 1 to 4 were blended in the amounts shown in Table 1.

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

When measuring the 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 being careful 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 into a dumbbell No. 2 shape as specified in JIS K6251 to prepare test specimens for measuring the elongation and tensile strength.

In measuring the elongation and tensile strength, two benchmark lines were marked on the test piece at a position 10 mm on either side from the center in the longitudinal direction (the distance between the benchmark lines was 20 mm), and the test piece with the benchmark lines was attached to a universal tensile tester with a grip distance of 50 mm. The test piece was then pulled at a pulling speed of 50 mm/min at room temperature (normal temperature), and the maximum load and the gauge distance when the coating film of the test piece broke were measured, and 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/ ^mm2 ) = maximum load (N) ÷ cross-sectional area of test piece ( ^mm2 ) (2)
In this case, the higher the elongation percentage, the greater the elongation until breakage, and the higher the tensile strength, the greater the force required to break. The higher the values for both, the greater the strength and toughness of the coating film.

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 120°C for 14 minutes were rated as "good" if they had an elongation of 100% or more, a tensile strength of 0.2 MPa or more, and a hardness of 50 or more, as having good curability and therefore good coating strength, whereas 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 rated as "poor" as they had poor curability and insufficient coating strength.

Regarding adhesion, tensile shear adhesive strength test was carried out.Specifically, first, two test panels (25mm x 100mm x 1.0mm) made of electrocoated steel plate were prepared, one of them was coated with the prepared vinyl chloride plastisol composition, and the other one was superimposed in parallel and joined in a straight line, and the test panels were heated and dried by a dryer under baking conditions of 120°C x 14 minutes, so that the coating film (coating film) of the vinyl chloride plastisol composition applied to the test panel was heat cured, and a test sample for measuring adhesion force was prepared.Note that, here, the vinyl chloride plastisol composition was coated so that the thickness of the heat cured coating film was 3mm.
Then, using a tensile tester (manufactured by Shimadzu Corporation), the test sample was pulled in the longitudinal direction (pulling speed 50 mm/min) until it broke, and the fracture surface at the time of break was visually observed to judge the state of failure, i.e., cohesive failure (CF) or interfacial failure (AF). If the fracture mode determined by the test sample was cohesive failure (CF), the adhesiveness was evaluated as good, and if the fracture mode was interfacial failure (AF), the adhesiveness was evaluated as poor, and x.

As shown in the lower part of Table 1, in all of the plastisol compositions according to Examples 1 to 8, the coating film formed by baking and drying at a low temperature for a short time of 120°C for 14 minutes has an elongation rate of 100% or more, a tensile strength of 0.6 MPa or more, and a hardness of 50 or more. From these high elongation rates and high tensile strengths, as well as the hardness, it is clear that the coating film is strong and tough. Therefore, even with low-temperature baking and drying, the curing properties are good, and the strength and chipping resistance of the coating film can be ensured. In addition, in an adhesion strength test of the coating film baked at a low temperature for a short time of 120°C for 14 minutes, the failure state at the time of breakage is cohesive failure (CF), so the adhesion of the coating film is ensured even with low-temperature baking and drying.

Thus, according to the vinyl chloride plastisol compositions of Examples 1 to 8, even when baked and dried at a low temperature of 120°C for a short period of time of 14 minutes, the compositions have good adhesion and good curing properties, so that the desired coating film properties of elongation and tensile strength can be obtained and the coating film has high strength.
This is presumably because by blending acrylic resin in addition to vinyl chloride resin, the acrylic resin is a liquid acrylic resin having hydroxyl groups, and the liquid acrylic resin having hydroxyl groups penetrates between the molecules of the vinyl chloride resin like a plasticizer, orienting it and allowing high elongation and tensile strength to be obtained, and even if 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 the polyamidoamine, allowing the adhesiveness due to the polyamidoamine to be expressed.

In particular, while there is a general tendency for the tensile strength to increase as the molecular weight of the resin increases, the blended amount of liquid acrylic resin was the same at 15 parts by mass in both cases, but in Example 1, which blended a liquid acrylic resin with a smaller molecular weight and one hydroxyl group than the liquid acrylic resin blended in Example 3, the tensile strength was higher than in Example 3. Also, the blended amount of liquid acrylic resin was the same at 30 parts by mass in both cases, but in Example 2, which blended a liquid acrylic resin with a smaller molecular weight and one hydroxyl group than the liquid acrylic resin blended in Example 4, the elongation and tensile strength were higher than in Example 4. 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 amount of liquid acrylic resin blended was the same at 15 parts by mass, but Example 5, which blended a liquid acrylic resin with a smaller molecular weight and one hydroxyl group than the liquid acrylic resin blended in Example 7, had a higher tensile strength than Example 7. Also, although the amount of liquid acrylic resin blended was the same at 30 parts by mass, Example 6, which blended a liquid acrylic resin with a smaller molecular weight and one hydroxyl group than the liquid acrylic resin blended in Example 8, had a higher elongation and tensile strength than Example 8.

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 the end is used, the elongation and tensile strength increase as the amount of the resin is increased.

This is presumably because in Examples 3 and 4, where a liquid acrylic resin with two hydroxyl groups is used, the liquid acrylic resin tends to be randomly arranged in 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 is used, the liquid acrylic resin is highly oriented in the molecules of the vinyl chloride resin, thereby increasing the elongation and tensile strength. For this reason, it is preferable to use a liquid acrylic resin that contains a hydroxyl group, or one with one hydroxyl group, which can further increase the strength and toughness of the coating film.

In addition, from a comparison between Examples 1 to 4 and Examples 5 to 8, Examples 1 to 4, in which the vinyl acetate residue content of the vinyl chloride-vinyl acetate copolymer resin is higher than 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 liquid acrylic resins having hydroxyl groups, particularly with their hydroxyl groups and plasticizers. That is, those with a high vinyl acetate residue content have high compatibility with liquid acrylic resins having hydroxyl groups and plasticizers, and can incorporate liquid acrylic resins having hydroxyl groups and plasticizers into the vinyl chloride resins even at low temperatures, thereby promoting the plasticization of the vinyl chloride resins. This is thought to enable the elongation and tensile strength to be sufficiently high and tough even under low-temperature baking and drying conditions.
For this reason, preferably, the vinyl chloride resin is 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.

The coating films formed from the vinyl chloride plastisol compositions of Examples 1 to 8 also have good appearance and no yellowing due to the combined use of polyamide and aliphatic block urethane as adhesion-imparting agents.

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

That is, in Comparative Example 1 and Comparative Example 2, in which the blending of the liquid acrylic resin having a hydroxyl group was omitted, the elongation rate of the coating film obtained under the low-temperature drying and baking conditions of 120°C x 14 minutes in the above evaluation test was insufficient at less than 100%. When the elongation rate is insufficient, the coating film has poor strength and flexibility, and is difficult to disperse and relieve stress, so that the coating film is less compliant with vibrations of the substrate, and coating film breakage, cracks, defects, etc. are likely to occur, or the desired high chipping resistance cannot be ensured. Therefore, the coating film formed from the vinyl chloride plastisol composition according to Comparative Example 1 and Comparative Example 2 is inferior to the Examples in coating film strength, chipping resistance, and other coating film performance.

Comparing Comparative Example 1 and Comparative Example 2 with the Examples, it can be seen that by using a liquid acrylic resin containing hydroxyl groups in addition to a vinyl chloride resin as a thermoplastic resin, it is possible to obtain a desired high elongation rate that can ensure pitting resistance and other properties, as well as good curing properties even under low-temperature, short-time, low-stress drying conditions, and also good tensile strength and hardness, ensuring coating film strength.

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 Example, the adhesion of 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 was insufficient. This is thought to be because the liquid acrylic resin having carboxyl groups reacted with the polyamide, inhibiting its adhesiveness, and thus preventing the adhesiveness of the polyamide from being expressed. Furthermore, Comparative Example 3, in which a liquid acrylic resin having carboxyl groups was used, also produced a coating film with inferior tensile strength and hardness.

In addition, 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 adhesion of 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 was insufficient. This is thought to be because the powdered acrylic resin reacted with the polyamide, inhibiting its adhesion, preventing the adhesive properties of the polyamide from being expressed.

From a comparison of Comparative Examples 3 and 4 with the Examples, it can be seen that if a liquid acrylic resin having a hydroxyl group is used, the adhesiveness is ensured by the polyamide without reacting with the polyamide.
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 a low molecular weight substance in the range of 5,000 or more, 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, because it has high orientation in the vinyl chloride resin and therefore a stronger coating film can be obtained.

In addition, vinyl chloride-vinyl acetate copolymers with a vinyl acetate group content in the range of 5% by mass or more and 15% by mass or less have excellent curing properties at low temperatures. Particularly preferably, vinyl chloride-vinyl acetate copolymers with a vinyl acetate group content in the range of 7% by mass or more and 10% by mass or less have improved compatibility with plasticizers, excellent absorption of plasticizers and liquid acrylic resins at low temperatures, and increased melt viscosity even at low temperatures. Even at low temperatures, the vinyl chloride resin particles melt and completely melt, resulting in a uniform phase. In addition, the plasticizing effect of the liquid acrylic resin is obtained, resulting in high strength, elongation, and adhesion.

Thus, according to the vinyl chloride plastisol compositions of Examples 1 to 8, coating films having good adhesion and strong coating film properties can be formed even under bake drying conditions at low temperatures and for a short time.
That is, according to the vinyl chloride plastisol compositions of Examples 1 to 8, by using a vinyl chloride resin as a thermoplastic resin and a hydroxyl-containing liquid acrylic resin in combination, a tough coating film with high elongation and tensile strength can be formed at low cost even under low-temperature short-time baking and drying conditions, and the coating film strength and chipping resistance can be ensured. In addition, the hydroxyl-containing liquid acrylic resin penetrates between the molecules of the vinyl chloride resin like a plasticizer and is oriented, so that the coating film has excellent vibration durability due to its high elongation. Furthermore, since the acrylic resin is a hydroxyl-containing liquid acrylic resin, the polyamide does not react with the acrylic resin, and the adhesiveness is ensured by the adhesiveness of the polyamide. In particular, by using a polyamide and an aliphatic block urethane in combination, high adhesiveness is exhibited even under low-temperature short-time baking and drying conditions, and a coating film with good appearance without yellowing is obtained. That is, according to the combination of polyamide component and block urethane, the block is dissociated at the temperature of 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 adhesiveness. Therefore, not only does it show excellent adhesiveness to the cationic electrodeposition coating surface, but it can also develop adhesiveness under baking conditions at a relatively low temperature, and furthermore, the storage stability of the plastisol composition is excellent. In addition, the combination of block polyurethane prepolymer and polyamide amine also provides good water resistance of the coating film.

The vinyl chloride plastisol compositions of Examples 1 to 8 have good applicability and are less likely to drip due to the inclusion of a thixotropic agent, and the inclusion of a moisture absorbent (dehydrating agent) prevents the coating from swelling due to moisture. The vinyl chloride plastisol compositions of Examples 1 to 8 are also compatible with current one-component coating equipment, since they are a blend of thermoplastic vinyl chloride resin and liquid acrylic resin, plasticizer, adhesion imparting agent, thixotropic agent, moisture absorbent, viscosity reducer, and filler.

As described above, the vinyl chloride-based plastisol composition of the above embodiment is a vinyl chloride-based plastisol composition containing a vinyl chloride-based 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.

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 physical 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, adhesion can be ensured by exhibiting the adhesive properties of the polyamide even under low-temperature baking and drying conditions without reacting with the polyamide as an adhesion imparting agent. In addition, since the vinyl chloride resin is inexpensive, low costs are required, and storage stability is also good.

And even under low-temperature baking and drying conditions (100°C to 130°C), it is possible to achieve coating film properties such as high strength and elongation, and because it also has good adhesion, it is possible to shorten the heating time, reduce carbon dioxide emissions and energy costs, and furthermore, it is possible to increase the speed and productivity of line production for automobiles, etc.

A liquid acrylic resin containing one or more functional hydroxyl groups in the molecule is preferably blended in an amount within the range of 5 parts by mass or more and 60 parts by mass or less per 100 parts by mass of vinyl chloride resin, so that the coating film strength can be increased even by low-temperature baking and drying without impairing the coatability, including sagging properties.
Furthermore, when the polyamide is blended in an amount within the range of 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 properties.

Furthermore, if the vinyl chloride resin is a vinyl chloride-vinyl acetate copolymer, it has excellent curing properties at low 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, when the weight average molecular weight of the liquid acrylic resin containing one or more functional hydroxyl groups in the molecule is within the range of 500 to 5,000, the coating film can be strengthened without impairing the coatability.

When implementing the present invention, the configuration, ingredients, blending, materials, manufacturing method, etc. of other parts of the vinyl chloride plastisol composition are not limited to those in this example. 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 even if the above numerical values are slightly changed, it does not negate the implementation.

Claims (6)

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. The vinyl chloride-based plastisol composition according to claim 1, characterized in that the vinyl chloride-based resin is a vinyl chloride-vinyl acetate copolymer. The vinyl chloride-based plastisol composition according to claim 2, characterized in that the vinyl chloride-based resin has a vinyl acetate group content in the range of 5% by mass or more and 15% by mass or less. The vinyl chloride plastisol composition according to claim 1, characterized in that the liquid acrylic resin has a weight average molecular weight in the range of 500 to 5,000. The vinyl chloride plastisol composition according to claim 1, characterized in that the liquid acrylic resin is blended in a range of 5 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the vinyl chloride resin. The vinyl chloride plastisol composition according to claim 1, characterized in that the polyamide is blended in an amount ranging from 1 part by mass to 20 parts by mass per 100 parts by mass of the vinyl chloride resin.