JPH0125515B2 - - Google Patents

Description

[Detailed description of the invention]

"Field of Industrial Application" The present invention relates to an undercoat comprising a vinyl chloride plastisol composition used as a base hardening paint (sealer) or undercoat paint in various industries including the automobile industry. ``Conventional technology'' Many automobiles and various industrial products are painted (top coated), and before this painting is applied, sealants,
It is common to apply a pretreatment coating called an undercoat to protect the base material and make the final finish easier. This undercoat is especially essential for automobile bodies that are coated with cationic electrodeposition coatings. Vinyl chloride plastisol compositions as the undercoat used in this undercoat have not been widely used because their adhesive properties are insufficient. In recent years, methods have been proposed to improve the adhesion of plastisols, such as adding to plastisol a urethane prepolymer containing an oxime as a blocking agent and an active amino group-containing mono- or polyamide compound as a block body dissociation promoter ( Japanese Patent Publication No. 59-52901), urethane prepolymer with oxime or lactam as a blocking agent, nitrogen-containing polyol as a block body dissociation promoter,
A method of adding a compound selected from amino alcohol, fatty acid alkanolamide, etc.
78279), a method of adding a mono- or polycarboxylic acid to the invention of JP-B-59-52901 (JP-A-59-120651)), lactam-blocked polyisocyanate, active amino group-containing polyamide, and low molecular weight amine Method of adding polyol to which alkylene oxide has been added (JP-A-59-131669)
Examples include. However, in the above-mentioned known literature, the use of active amino group-containing mono- or polyamide as a block body dissociation accelerator has a significant effect of accelerating the dehydrochlorination of polyvinyl chloride, causes thermal discoloration, and has poor light resistance and discoloration. It has a drawback in terms of water resistance. b. Since the polyisocyanate is a urethane bond of a polyol and an aliphatic or aromatic isocyanate, there is a problem of bubble generation during processing, and the long-term water resistance and weather resistance are also unsatisfactory. c. Since the blocking agent is an oxime or lactam, it has poor compatibility with the resin component and plasticizer after dissociation, resulting in bloom and bleed phenomena.
There was also the problem that the former would be hydrolyzed by acids, while the latter would produce crystalline salts. This is a cause of inhibiting the heat resistance, water resistance, and stability of the molded product. "Problems to be Solved by the Invention" The present inventors have developed a vinyl chloride plastisol that has improved the conventional drawbacks and has strong adhesion to painted metal surfaces at relatively low temperatures and in a short period of time, and has excellent storage stability. As a result of intensive studies to develop an undercoat agent containing oxybenzoic acid ester or alkyl phenol as a blocking agent, we added a diisocyanate polymer containing oxybenzoic acid ester or alkyl phenol as a blocking agent to a plastisol composition as an adhesion promoter. The present inventors have discovered that the object of the present invention can be achieved, and have completed the present invention. That is, the object of the present invention is to provide a vinyl chloride plastisol composition containing a vinyl chloride plastisol composition as a main component containing an adhesion imparting agent with good storage stability that firmly adheres to metal in a short time in a temperature range from relatively low to high temperatures. To provide a primer. "Means for Solving the Problems" Therefore, the gist of the present invention is to provide an undercoat comprising a sol composition containing a vinyl chloride polymer and a plasticizer as main components. The present invention relates to an undercoat characterized by containing an oxybenzoic acid ester of a diisocyanate polymer or an alkyl phenol block as an adhesion imparting agent. To explain the present invention in detail, the vinyl chloride polymer, which is the main component of the plastisol composition that serves as the primer of the present invention, is prepared by combining vinyl chloride or a mixture of vinyl chloride and a comonomer copolymerizable therewith with an emulsifier and a water-soluble polymer. Paste resin with a particle size of 5 μ or less, preferably about 0.05 to 3 μ, produced by emulsion polymerization in the presence of a polymerization initiator, or vinyl chloride or vinyl chloride and it in the presence of a dispersant and an oil-soluble polymerization initiator. This is a paste resin or resin for base range mixing produced by a fine suspension polymerization method in which all or part of a mixture with a copolymerizable comonomer is mechanically finely dispersed and then polymerized. In addition, it is acceptable to use vinyl chloride resin or vinyl chloride copolymer resin with large particle size produced by ordinary suspension polymerization in combination as long as it does not adversely affect the viscosity, fluidity, processability, etc. of the paste sol. do not have. Examples of comonomers copolymerizable with vinyl chloride include vinyl esters such as vinyl acetate, vinyl propionate, and vinyl laurate, methyl acrylate, ethyl acrylate, butyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3 -acrylic acid esters such as hydroxybutyl acrylate,
Methyl methacrylate, ethyl methacrylate,
2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-chloro-2
- Methacrylic acid esters such as hydroxypropyl methacrylate, maleic acid esters such as dibutyl maleate, diethyl maleate, ethyl 2-hydroxyethyl maleate, fumaric acid esters such as dibutyl fumarate and diethyl fumarate, vinyl methyl ether , vinyl ethers such as vinyl butyl ether, vinyl hydroxybutyl ether, and vinyl octyl ether, vinyl cyanides such as acrylonitrile and methacrylonitrile, α-olefins such as ethylene, propylene, and styrene, and vinyl chlorides such as vinylidene chloride and vinyl bromide. Other examples include vinylidene halides, vinyl halides, and N-methylol-acrylamide, and one or more of these is used in an amount of 30% by weight or less, preferably 20% by weight or less. When vinyl chloride polymers are polymerized, emulsifiers containing alkali metal salts are often used, but from the viewpoint of the balance between sol viscosity stability and adhesive properties of the sol composition for the undercoat of the present invention, chloride-based polymers are often used. The alkali metal content in the vinyl polymer is 0 to 900 ppm,
It is desirable to select and use emulsifiers so that the concentration is preferably in the range of 40 to 600 ppm. Emulsifiers that produce such low alkali metal-containing vinyl chloride polymers include alkyl groups having 8 to 18 carbon atoms.
Examples include ammonium salts or alkali metal salts of fatty acids. Among these, ammonium salts are preferred. Of course, the emulsifier is
It is not limited to what is described above. In the undercoat of the present invention, a paste resin made of a vinyl chloride homopolymer with an average degree of polymerization of 1600 or less as a vinyl chloride polymer and an average particle size of 10 to Nyl acetate content in the range of 50μ from 1 to
It is preferred to use a mixture with a resin for mixing into a paste resin consisting of 10% by weight vinyl chloride vinyl acetate copolymer. The amount of resin used for mixing is
Usually, it is preferably in the range of 5 to 50% by weight of the total vinyl chloride polymer. The plasticizer that is a component of the undercoat of the present invention is not particularly limited as long as it is used for vinyl chloride polymers, but for example, phthalate di-n
- Phthalates such as butyl, di-n-octyl phthalate, di-2-ethylhexyl phthalate (DOP), diisooctyl phthalate, octyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate, di-2-ethylhexyl isophthalate, etc. Acid plasticizer, di-2-ethylhexyl adipate (DOA), di-n-decyl adipate, diisodecyl adipate, di-2-ethylhexyl azelaate, dibutyl sebacate, di-2 sebacate
- Fatty acid ester plasticizers such as ethylhexyl,
Tributyl phosphate, tri-2-ethylhexyl phosphate, 2-ethylhexyldiphenyl phosphate,
Examples include phosphate ester plasticizers such as tricresyl phosphate, epoxy plasticizers such as epoxidized soybean oil, and epoxidized tall oil fatty acid-2-ethylhexyl, and these can be used alone or in combination of two or more. do. The amount of plasticizer used is appropriately selected depending on the desired solid content concentration and fluidity of the paste sol, the amount of blowing agent used, the purpose of the foam, etc., and is 30 to 400 parts by weight per 100 parts by weight of vinyl chloride resin. weight part,
Preferably it is in the range of 50 to 200 parts by weight. In addition, a part of the plasticizer can be replaced with a diluent such as texanol isobutyrate or dodecylbenzene, or an organic solvent that swells the vinyl chloride resin such as toluene or xylene, or an organosol may be used. . The amount of the diluent and organic solvent to be added is appropriately determined depending on the application. Plastisol compositions used as primers of the present invention can be used to impart adhesive properties to the plastisol composition or for use as an adhesive.
It contains an oxybenzoic acid ester of diisocyanate polymer or a block form of alkyl phenol as one of its components. The average molecular weight of the diisocyanate polymer block is preferably in the range of 1,000 to 10,000. The average molecular weight of the block body is 1000
If it is smaller than 10,000, the adhesion cannot be sufficiently exhibited and the adhesive strength is insufficient. On the other hand, if it is larger than 10,000, the viscosity of the sol composition is likely to increase significantly. Therefore, the diisocyanate (monomer) constituting the diisocyanate polymer is, for example, fatty acid diisocyanate such as hexamethylene diisocyanate or lysine diisocyanate, or alicyclic diisocyanate such as hydrogenated diphenylmethane diisocyanate, isophorone diisocyanate, or hydrogenated tolylene diisocyanate. , tolylene diisocyanate, diphenylmethane diisocyanate, naphthylene diisocyanate, xylene diisocyanate, and other aromatic diisocyanates.
Among these, aromatic diisocyanates, particularly tolylene diisocyanate and diphenylmethane diisocyanate are preferred. The diisocyanate polymer can be prepared, for example, in an inert solvent such as ethyl acetate, methyl acetate, butyl acetate, methyl ethyl ketone, dioxane, or in a phthalate ester.
It is obtained by polymerization in a plasticizer such as phosphoric acid ester, adipic acid ester or trimellitic acid ester by a known method using a known catalyst such as a tertiary amine, a Mannitz base, an alkali metal of a fatty acid, an alcoholate, etc. Thereafter, a blocking reaction is carried out with oxybenzoic acid ester or alkyl phenol to produce a diisocyanate polymer block. When a polymerization reaction or a blocking reaction is carried out in a highly volatile solvent, it is desirable to finally perform a solvent substitution treatment with a suitable high-boiling point solvent, such as a plasticizer. As the diisocyanate polymer used in the present invention, it is particularly preferable to use one containing an isocyanurate ring obtained by polymerizing diisocyanate monomers. Those containing isocyanurate rings are produced according to the method described above. Of course, the diisocyanate polymer may also be a so-called isocyanate group-terminated polyurethane, polyurea, etc., which are obtained by the reaction of a diisocyanate and an active hydrogen compound. Examples of oxybenzoic acid esters used as blocking agents include o-oxybenzoic acid ester, m-oxybenzoic acid ester, and p-oxybenzoic acid ester. Preferably, it is a substituted product. One group constituting the oxybenzoic acid ester is, for example, a long chain alkyl group such as n-heptyl group, n-octyl group, 2-ethylhexyl group, nonyl group, dodecyl group in the case of m- and p-substituted products. , an alkoxyalkyl group having a long-chain polyoxyethylene group or a polyoxypropylene group bonded thereto, or an alkoxyalkyl group having an oxyethylene group or an oxypropylene group bonded to a long-chain alkyl group. In the case of o-substituted groups, methyl group, ethyl group, isopropyl group, isoamyl group, n-butyl group, isobutyl group, sec-butyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, nonyl group, Examples thereof include alkyl groups such as dodecyl groups, alkoxyalkyl groups bonded to (poly)oxyethylene or (poly)oxypropylene groups, and aryl groups such as phenyl groups and benzyl groups. The alkylphenol used as the blocking agent is a phenol having an alkyl group having 4 or more carbon atoms as a substituent, and examples thereof include butylphenol, hexylphenol, octylphenol, nonylphenol, and the like. The amount of the blocked diisocyanate polymer added is 1 to 25 parts by weight per 100 parts by weight of the vinyl chloride polymer.
Parts by weight preferably range from 2 to 17 parts by weight, and the effective NCO in the plastisol composition is
Preferably it is present in the range 0.03 to 1% by weight, preferably 0.03 to 0.6% by weight, especially 0.05 to 0.5% by weight. For example, when using a dibutyl phthalate diluted solution of 3% by weight of an oxybenzoic ester blocked diisocyanate polymer after polymerization and blocking in dibutyl phthalate, 2 to 3% by weight dibutyl phthalate solution is used per 100 parts by weight of vinyl chloride polymer. 50
A plastisol composition is prepared by using parts by weight, and if the amount of plasticizer is insufficient, the deficiency is made up. Furthermore, since the content of effective NCO in the diluted solution of 33% by weight dibutyl phthalate also differs, the diluted solution is appropriately adjusted and added so as to obtain the desired NCO content of the plastisol composition. If the effective NCO is less than 0.03% by weight, the adhesion effect will be small, and if it is more than 1% by weight, undesirable phenomena such as increased sol viscosity and coloring will likely occur, and the adhesion will be impaired due to moisture absorption and rapid adhesive reaction. A bubble generation phenomenon is observed at the interface, which tends to cause a decrease in adhesive strength. The plastisol composition that is the primer of the present invention preferably contains an adhesion promoter, that is, an accelerator for dissociating the blocks of oxybenzoic acid ester or alkylphenol blocked diisocyanate polymer. . Examples of the dissociation promoter include inorganic or organic compounds of alkali metals, and inorganic or organic compounds of metals such as lead, tin, cadmium, and zinc, and it is desirable to use at least one of these. Examples of the alkali metal compound include fatty acids, especially fatty acids whose alkyl group has 8 to 18 carbon atoms, alkyl sulfuric acids, alkyl sulfonic acids, or potassium salts of polyoxyethylene adducts thereof;
Examples include sodium salts, and further potassium-zinc type and sodium-zinc type composite stabilizers. Metal compounds other than alkali metals include inorganic metal compounds such as lead white, basic lead silicate, tribasic lead sulfate, tribasic lead phosphite, silica gel co-precipitated lead silicate, zinc white, and lauric acid. , stearic acid, ricinoleic acid, naphthenic acid, salicylic acid,
Cadmium, barium, calcium, zinc, lead, such as 2-ethylhexoic acid fatty acid or resin acid,
Examples include organic compounds such as metal salts such as tin or magnesium, and further examples include zinc octylate, dibutyltin laurate, dioctyltin malate, dibutyltin mercaptide, and the like. Organic acid liquid composite stabilizers such as calcium-zinc, barium-zinc, magnesium-zinc, and cadmium-barium-zinc stabilizers, which are usually commercially available as stabilizers for vinyl chloride resins, can also be used. Among these, lead-based and tin-based compounds are particularly preferred. In the case of an alkali metal compound, the dissociation promoter is preferably contained in the plastisol composition in an amount of 900 ppm or less based on the vinyl chloride polymer. If the emulsifier used in the production of vinyl chloride polymer already contains alkali metal, the content of alkali metal is determined by adding up the amount as the amount of alkali metal and dissociating an appropriate amount of the alkali metal compound. Preferably, a promoter is added. Alkali metal content
If it exceeds 900 ppm, it will increase the hygroscopicity during sol preparation or the obtained sol, and will instead impede the sol viscosity stability and adhesive reaction, significantly worsening processability, and will likely lead to a decrease in adhesive strength. When a metal compound other than an alkali metal is used as a dissociation promoter, it may act as a stabilizer, and the amount added is not particularly limited.
Usually, 0.5 parts per 100 parts by weight of vinyl chloride polymer.
~10 parts by weight, preferably 1 to 5 parts by weight can achieve that purpose. Furthermore, when an alkali metal compound and a metal compound such as lead, tin, cadmium, or zinc are used together, the adhesive strength is synergistically improved. In addition to the above components, the primer of the present invention includes:
Various other additives can be added, such as fillers, thickeners, colorants, etc. Of course, other additives are not limited to these. Fillers include light or heavy calcium carbonate, talc,
Examples include inorganic fillers such as diatomaceous earth, kaolin, and barium sulfate, and organic fillers such as cellulose powder, powdered rubber, and recycled rubber.Thickeners include anhydrous silica, organic bentonite, and metallic soaps. Can be mentioned. Furthermore, when the sol composition contains water, it is also possible to add and mix a relatively small amount of powder such as calcium oxide, magnesium oxide, silicon oxide, etc. as a water adsorbent. To produce the plastisol composition that serves as the undercoat of the present invention, a vinyl chloride polymer, a plasticizer, an adhesion imparting agent, and if necessary a dissociation promoter and other additives are uniformly mixed. In the present invention, a vinyl chloride polymer that is completely sealed and stored immediately after production is used, and a vacuum defoaming process is performed during plastisol production before adding an adhesion agent. After the addition, it is preferable to perform stirring and mixing after the gas phase is degassed under vacuum or replaced with an inert gas such as nitrogen. The undercoat agent of the present invention is applied to various industrial uses as a base hardening or undercoating paint. Particularly in the automobile industry, cationic electrodeposition coatings are applied to automobile bodies for the purpose of rust prevention, cushioning in case of contact with flying pebbles, etc., and furthermore, for the purpose of sealing pinholes, etc. For example, it has high utility value as a base paint for top coat synthetic resin paints such as alkyd resin paints, epoxy resin paints, and acrylic resin paints. In the above-mentioned cationic electrodeposition coating, an aqueous solution or aqueous dispersion of a polyamine resin (for example, an epoxy resin having an amino group in the molecule) neutralized with a lower organic acid is applied to the object to be coated (car body). ) is used as a cathode and a direct current is applied to deposit it on the surface of the object to be coated. The coating amount of the primer of the present invention is usually 500 to 3000.
g/m ² , and the coating film thickness is usually in the range of 0.3 to 2 mm, and can be adjusted from fairly thin to thick.
Of course, the coating amount and coating thickness are not limited to the above ranges, and may be set to a desired coating amount and coating thickness depending on the purpose. Therefore, the usual methods for applying the primer are applied, such as spraying, brushing, dipping, and pouring, as well as reverse roll, knife coater, rotary screen, flat screen, flexo, gravure printer, etc. It is applied using various equipment. The primer applied to the object is then heated to typically 120-210°C.
The block body is dissociated by heating to a temperature of 100 to form a coating film on the surface of the object to be coated. In the present invention, the heat treatment after coating is carried out at a temperature of 20 to 150°C using a block body dissociation promoter.
It is preferable to carry out the treatment for 40 minutes in terms of operation and properties of the coating film. "Effects of the Invention" Since the primer of the present invention contains an oxybenzoic acid ester or alkylphenol block of diisocyanate polymer as an adhesion promoter in the plastisol composition,
Strongly adheres to metal surfaces or cationic electrodeposition coated surfaces by short-term heat treatment at low temperatures. The sol composition used as the undercoat has good storage stability, does not exhibit an extreme increase in viscosity even when left for a long period of time, and is easy to apply to the object to be coated. Furthermore, even if the blocking agent dissociates from the diisocyanate polymer, phenomena such as bleeding and blooming are extremely rare because of its good compatibility with the plasticizer and vinyl chloride polymer. moreover,
Since the undercoat of the present invention does not contain an amine-based block body dissociation promoter, there is no coloration during or after application, and the decomposition of the vinyl chloride polymer is small, so that the topcoat film is There is no need to worry about discoloration even if it is thin. Furthermore, the coating film obtained from the undercoating agent of the present invention has various advantages such as excellent water resistance. "Examples" Next, the present invention will be explained using Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. In addition, the evaluation method of the undercoat agent in the examples is as follows:
It is as follows. (1) Viscosity and storage stability test of undercoat (sol composition) Sol viscosity was measured at 5 rpm at a sol temperature of 40±1° C. using a B8H type viscometer #7 rotor manufactured by Tokyo Keiki. Storage stability was determined by immersing the sol composition in a glass container in a constant temperature water bath at 40 ± 1°C, and after a predetermined number of days, stirring gently for 1 minute using a stirring rod 2 hours before measuring the viscosity. Sol viscosity was measured as described above. (2) Shear peel strength test Using a cationic electrodeposition coated plate as a test piece, the shear adhesive strength was measured in accordance with JIS K-6830 (Test method for automotive sealants). However, sol thickness 0.5 mm, heat treatment 120-140℃ x 30 minutes,
It was carried out at a pulling speed of 5 mm/min. (3) Water resistance test A test piece similar to that used in the above (2) shear peel strength measurement test was immersed in warm water at 40°C for 7 days, air-dried for 1 day, and then subjected to shear adhesion similar to (2) above. The strength was measured and a water resistance test was performed. (4) Evaluation of coloration Visually evaluate the coloration and appearance of the vinyl chloride polymer layer of the coating film after the shear peel strength test in (2) above.
I gave the following evaluation. 〇 - No coloring △ - Slightly colored × - Significantly colored Examples 1 to 4, Comparative Examples 1 to 2 Vinyl chloride polymer (paste resin) 80 parts by weight Blending resin 20 〃 Plasticizer (DOP) 120 〃 Filler ( CaCO ₃ , = 5μ) 200 〃 Stabilizer and dissociation promoter 3 〃 Adhesive agent solution 15 〃 After leaving each of the above combinations in a constant temperature and humidity room at 23℃ and 50% relative humidity (RH) atmosphere for several days It was weighed and mixed in a constant temperature room according to the following procedure. paste resin, blending resin,
DOP, filler, and stabilizer/dissociation promoter were put into a Hobart mixer and mixed uniformly, and then the adhesion promoter solution was added and mixed uniformly again. Next, a plastisol composition was prepared by vacuum defoaming and used as an undercoat. The detailed composition, sol viscosity, shear peel strength, coloring state, etc. of the undercoat are listed in Table 1. For comparison, those with adhesion promoter powder added,
Table 1 also shows the results of tests conducted in the same manner as in the examples for each of the commercially available adhesives containing adhesion promoters.

[Table] In the peeling state of Examples 1 to 4 using the undercoat of the present invention, cohesive failure was observed in all cases, and the adhesion was good. Shear peel strength values are significantly improved by the use of lead-based stabilizers. Viscosity stability is Homo−
A good combination is a polymer paste resin and a co-polymer blending resin. Furthermore, one of the features of the present invention is that, compared to the commercially available product of Comparative Example 2, no thermal coloring is observed after hot molding. Examples 5-6 Tests were conducted in the same manner as in Example 1, except that the compositions of the vinyl chloride polymers, ie, paste resin and blending resin were changed, and the results are shown in Table 2 together with Example 1.

【table】

[Table] Examples 1, 5, and 6 demonstrate low-temperature melting properties and low-temperature adhesion properties obtained by the method of the present invention. According to the method of the present invention, even under low temperature molding conditions of 120°C x 30 minutes, a uniform cohesive failure state is observed on the peeled surface, but the resin has better physical properties such as shear peel strength and good viscosity stability. It can be seen that the resin formulation of Example 1 described above is more preferable as a combination. Examples 7 to 12 Paste resin (used in Example 1) 80 parts by weight Blending resin (used in Example 1) 20 Butylbenzyl phthalate (BBP) 130 CaCO ₃ (average particle size = 5μ) 200 〃 Tribasic lead sulfate 5 〃 Adhesive agent solution Predetermined amount Evaluations were carried out in the same manner as in Examples 1 to 4 above by changing the type and amount of the tackifier in the above formulation. The results are shown in Table 3.

[Table] As shown in Examples 8 and 11, adhesion promoters A and B are sufficient for cationic electrodeposited plates when added at about 5 parts by weight as the blocked diisocyanate polymer component, or at least 1% of the total amount of the sol. It can be seen that adhesive properties can be obtained. Example 13, 14 VINIKA P-540 (paste resin, manufactured by Mitsubishi Kasei Vinyl Co., Ltd.) 80 parts by weight blending resin (3% Co-Polymer)
(Those used in Example 1) 20 〃 Polyester plasticizer (=1200) 100 〃 BBP 20 〃 Tribasic lead sulfate 3 〃 CaCO ₃ (=5μ) 200 〃 Adhesiveness imparting agent 5 〃 (Amount of active ingredient) Diluent (Mineral Spirit) 10 〃 Adhesion imparting agents A, B and C were used for evaluation with the above formulation. Note that the diluent was added and mixed later. Table 4 shows various evaluation results.

【table】

[Table] Adhesion imparting agents A and B obtained by the method of the present invention showed little decrease in adhesiveness or adhesion after immersion in hot water, Comparative Example 3
It can be seen that the water resistance is significantly improved compared to C. Examples 15-18 In the formulation of Example 14, paste resin
VINIKA P-540 Half of 80phr (40phr) was substituted with the following paste resin and the amount of diluent was reduced to 8phr, but the same procedure as in Example 14 was carried out to measure various performances, and the results are shown in Table 5. .

[Table] Various vinyl chloride polymers used in the method of the present invention include:
Homo-Polymer and Co-Polymer can be used alone or in combination.

Claims (1)

[Scope of Claims] 1. An undercoat comprising a sol composition containing a vinyl chloride polymer and a plasticizer as main components, wherein the sol composition contains oxybenzoic acid of a diisocyanate polymer as an adhesion imparting agent. An undercoat characterized by containing an ester or alkylphenol block. 2. The undercoat according to claim 1, wherein the diisocyanate polymer constitutes an isocyanurate ring. 3. The undercoat according to claim 1, wherein the sol composition contains a block body dissociation promoter as an adhesion imparting agent.