PLASTISOL COMPOSITION, UNDERCOATING AND BLOCKED POLYISOCYANURATE

Abstract: A plastisol composition comprising a vinyl chloride polymer, a plasticizer and an adhesion-imparting agent, characterized in that the adhesion-imparting agent is a diisocyanate polymer blocked with an oxybenzoic acid ester or with an alkylphenol and having an average molecular weight within a range of from 1,000 to 10,000. Also disclosed is a blocked polyisocyanurate having the formula: wherein each of X, Y and Z which may be the same or different, is a residue of a diisocyanate compound devoid of the isocyanate groups, each of R¹, R² and R³ which may be the same or different, is a group selected from the group consisting of C₁-C₂₀ alkyl, alkoxyalkyl, aryl, alkaryl and aralkyl, and n is an integer of from 1 to 10.

Description: The present invention relates to a plastisol composition most suitable for applications for bonding or coating, and an undercoating material composed of such a plastisol useful as a sealer or undercoating material for automobile industries and various other industries. The present invention also relates to a novel blocked polyisocyanurate which is curable at a low temperature, more particularly, to a novel blocked polyisocyanurate useful as a coating material, an adhesive or a cross-linking agent therefor, or as a modifier or cross-linking agent for polymers having active hydrogen atoms. A coating (top coating) is applied to automobiles and various industrial products. Prior to the application of this coating, it is common to apply a pre-treatment coating commonly called an undercoating for the purpose of sealing, protection of the substrate or facilitating the surface finish. Such an undercoating is essential particularly to an automobile body to which a cation-type electrodeposition precoating is applied. A polyvinyl chloride plastisol composition as an undercoating material for such an undercoating is not yet widely used because its adhesion is not adequate. As a method for improving the adhesion of the plastisol, it is known to incorporate an organic polyisocyanate compound to the plastisol. For instance, it is disclosed to add to the plastisol an isocyanate polymer obtained by trimerizing tolylene diisocyanate (TDI) in UK Patent No. 1,455,701 or an isocyanate polymer of isocyanate-isocyanurate obtained by partially trimerizing a two component mixture comprising TDI and diphenylmethane diisocyanate (MDI). These isocyanate polymers have free isocyanate groups (NCO) at their terminals, and they are extremely reactive and thus inferior in the storage stability of the plastisol, in the operation efficiency such as non-uniformity in the application of the plastisol to the substrate or formation of air bubbles, and in the quality stability. Namely, when a plastisol is prepared by mixing an isocyanate polymer having terminal NCO groups in an inert solvent e.g. a plasticizer, there have been problems such as (1) a substantial decrease in the adhesion strength, (2) gradual viscosity increase or solidification as time passes and (3) formation of air bubbles, by the influence of a small amount of moisture or a metal catalyst remaining in the plasticizer. Therefore, with respect to the metal component, it has been required to limit the amount to the minimum, and there has been a problem that if the amount is too small, the formed sheet undergoes substantial coloring. Therefore, the application has been limited to a very restricted blend system, and there have been various drawbacks such that the processing and operation process are restricted. In recent years, there have been proposed a method wherein an active amino group-containing mono- or poly-amide compound is added, as an agent for promoting the dissociation of a blocked polymer (hereinafter referred to simply as a "block dissociation-promoting agent") to a plastisol of a urethane polymer containing an oxime as a blocking agent (Japanese Examined Patent Publication No. 52901/1984); a method wherein a compound selected from the group consisting of nitrogen-containing polyols, amino-alcohols and fatty acid alkanol amides, is added, as a block dissociation-promoting agent, to a urethane prepolymer containing an oxime or lactam as a blocking agent (Japanese Unexamined Patent Publication No. 78279/1984); a method wherein a mono- or poly-carboxylic acid is further added to the above-mentioned composition of Japanese Examined Patent Publication No. 52901/1984 and Japanese Unexamined Patent Publication No. 120651/1984; and a method wherein an alkylene oxide-added polyol is added to a lactam-blocked polyisocyanate, an active amino group-containing polyamide and a low molecular weight amine (Japanese Unexamined Patent Publication No. 131669/1984). However, in the above references, (a) the method wherein an active amino group-containing mono- or poly-amide is used as a block dissociation-promoting agent, has drawbacks such that dehydrochlorination from the polyvinyl chloride is promoted, and the product tends to undergo a color change by heat and is inferior in the color fastness to light and in the water resistance; (b) the polyisocyanate contains urethane linkages of a polyol and an aliphatic or aromatic isocyanate, whereby there is a problem of the formation of air bubbles during the processing, and the product is not satisfactory as to the water resistance and weather resistance for a long run; and (c) the blocking agent is an oxime or a lactam, whereby the compatibility with the resin component after dissociation or with a plasticizer is inferior, thus leading to blooming or bleeding, and when contacted with an acid, the oxime undergoes hydrolysis, and the lactam forms a crystalline salt, such being problematic. Thus, they are likely to impair the stability, such as the heat resistance or the water resistance, of the shaped product. Urethane resins are usually prepared by a reaction between a component having an isocyanate group and a component having an active hydrogen group. In the fields of coatings and adhesives, a so-called two-part liquid system is employed wherein a curing agent having an isocyanate group and a resin having hydroxyl groups are mixed, coated and cured to form a coating film. In this system, the reaction starts immediately upon mixing the two liquids, and therefore the usable life is relatively short and there exists a so-called pot time. On the other hand, blocked polyurethane are known wherein isocyanate groups are reacted with and protected by a blocking agent. Unless heated, they do not undergo a reaction even when they are mixed with a hydroxyl group-­ containing resin, and they are thus stable. Phenols, oximes, alcohols or lactams are commonly known as such blocking agents. However, none of them is fully satisfactory with respect to the curability at a low temperature, the odor of the blocking agent and properties of the cured resin (such as heat resistance, solvent resistance, adhesive strength, etc.). The present inventors have conducted extensive researches to overcome the conventional difficulties and to develop a plastisol composition which can be used in combination with various additives, which is free from the deterioration of the properties even in a high temperature, high humidity atmosphere, which does not undergo a color change or the formation of air bubbles, which can be processed in a stabilized state, and yet which is capable of providing a high adhesive strength. As a result, it has been found possible to achieve the above object by adding a certain specific blocked diisocyanate polymer to the plastisol, as an adhesion-­ imparting agent. The present invention has been accomplished on the basis of this discovery. Namely, it is an object of the present invention to provide a plastisol composition which is capable of being processed under various conditions such as high temperature and high humidity conditions without a color change, formation of air bubbles or a deterioration of the adhesive strength. Another object of the present invention is to provide an undercoating material composed essentially of such a plastisol composition containing an adhesion-imparting agent having good storage stability and being capable of firmly bonding to a electro-deposited metal in a short period of time within a wide temperature range from a relatively low temperature to a high temperature. It is a further object of the present invention to provide a blocked polyisocyanurate which is stable and curable at a low temperature in a short period of time and which has good heat resistance. The present invention provides a plastisol composition comprising a vinyl chloride polymer, a plasticizer and an adhesion-imparting agent, characterized in that the adhesion-imparting agent is a diisocyanate polymer blocked with an oxybenzoic acid ester or with an alkylphenol and having an average molecular weight within a range of from 1,000 to 10,000, and has an effective isocyanote content of from 0.03 to 1% by weight. Further, the present invention provides an undercoating material composed of a plastisol composition comprising a vinyl chloride polymer and a plasticizer as main components, wherein the plastisol composition contains a diisocyanate polymer blocked with an oxybenzoic acid ester or with an alkylphenol, as an adhesion-imparting agent. The present invention also provides a blocked polyisocyanurate having the formula: wherein each of X, Y and Z which may be the same or different, is a residue of a diisocyanate compound devoid of the isocyanate groups, each of R¹, R² and R³ which may be the same or different, is a group selected from the group consisting of C₁-C 20 alkyl, alkoxyalkyl, aryl, alkaryl and aralkyl, and n is an integer of from 1 to 10. Now, the present invention will be described in detail with reference to the preferred embodiments. The vinyl chloride polymer as the main component of the plastisol composition of the present invention, is a paste resin having an average particle size of at most 5 µm, preferably from 0.05 to 3 µm, prepared by the emulsion polymerization of vinyl chloride or a mixture of vinyl chloride with a comonomer copolymerizable therewith, in the presence of an emulsifier and an aqueous polymerization initiator, or a paste resin or a resin to be blended with a paste resin prepared by microsuspension polymerization which comprises mechanically finely dispersing a part or entire amount of vinyl chloride or a mixture of vinyl chloride with a comonomer copolymerizable therewith, in the presence of a dispersant and an oil-soluble polymerization initiator, followed by polymerization. Further, a vinyl chloride resin or a vinyl chloride copolymer resin having a large particle size produced by a usual suspension polymerization may be incorporated in an amount not to adversely affect the viscosity, fluidity, processability, etc. of the plastisol or organosol. As the comonomer copolymerizable with vinyl chloride, there may be mentioned a vinyl ester such as vinyl acetate, vinyl propionate or vinyl laurate; an acrylate such as methyl acrylate, ethyl acrylate or butyl acrylate; a methacrylate such as methyl methacrylate or ethyl methacrylate; a maleate such as dibutyl maleate or diethyl maleate; a fumarate such as dibutyl fumarate or diethyl fumarate; a vinyl ether such as vinyl methyl ether, vinyl butyl ether or vinyl octyl ether; a nitrile such as acrylonitrile or methacrylonitrile; an α-olefin such as ethylene, propylene or styrene; a vinylidene halide or vinyl halide other than vinyl chloride, such as vinylidene chloride or vinyl bromide; and N-methylol acrylamide. At least one of these comonomers may be employed in an amount of not more than 30% by weight, preferably not more than 20% by weight. For the polymerization of a vinyl chloride polymer, it is common to use an emulsifier containing an alkali metal salt. However, in view of the adhesive properties of the composition of the present invention, it is desirable in the present invention to select an emulsifier so that the alkali metal content in the vinyl chloride polymer will be not higher than 900 ppm. As an emulsifier which brings about such a low alkali metal content in the vinyl chloride polymer, an ammonium salt or an alkali metal salt of an fatty acid having an alkyl group with from 8 to 18 carbon atoms may be mentioned as an example. However, the emulsifier is not restricted to such a specific example. There is no particular restriction as to the plasticizer to be used as a component of the plastisol composition of the present invention, and any plasticizer may be employed so long as it is suitable for use for a vinyl chloride polymer. For instance, there may be mentioned a phthalate plasticizer such as di-n-butyl phthalate, di-n-octyl phthalate, di-2-ethylhexyl phthalate (DOP), diisooctyl phthalate, octyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate, di-2-ethylhexyl isophthalate or a mixed alkyl phthalate; a fatty acid ester plasticizer such as di-2-ethylhexyl adipate (DOA), di-n-decyl adipate, diisodecyl adipate, di-2-ethylhexyl azelate, dibutyl sebacate or di-2-ethylhexyl sebacate; a phosphate plasticizer such as tributyl phosphate, tri-2-ethylhexyl phosphate, 2-ethylhexyldiphenyl phosphate or tricresyl phosphate; and an epoxy plasticizer such as epoxidized soybean oil or epoxidized tall oil fatty acid-2-ethylhexyl. These plasticizers may be used alone or in combination as a mixture of two or more different kinds. The amount of the plasticizer to be used is properly selected depending upon the desired solid content or the fluidity of the paste sol, and is usually within a range of from 30 to 600 parts by weight, preferably from 50 to 200 parts by weight, relative to 100 parts by weight of the vinyl chloride resin. Further, a part of the plasticizer may be substituted by a diluent such as hexanol isobutyrate or dodecylbenzene or by an organic solvent capable of permitting the vinyl chloride resin to swell such as toluene or xylene, to form an organosol. The amount of the diluent or the organic solvent is properly determined depending upon the particular use. The plastisol composition of the present invention contains a diisocyanate polymer blocked with an oxybenzoic acid ester or an alkylphenol as its one component. The blocked diisocyanate polymer preferably has an average molecular weight within a range of from 1,000 to 10,000. If the average molecular weight of the blocked polymer is less than 1,000, no adequate adhesion is obtainable, and the adhesive strength will be inadequate. On the other hand, if the average molecular weight is greater than 10,000, the viscosity of the sol composition tends to be extremely high. As the diisocyanate (monomer) constituting the isocyanate polymer, there may be mentioned an fatty acid diisocyanate such as hexamethylene diisocyanate or lysine diisocyanate; an alicyclic diisocyanate such as hydrogenated diphenylmethane diisocyanate, isophorone diisocyanate or hydrogenated tolylene diisocyanate; and an aromatic diisocyanate such as tolylene diisocyanate, diphenylmethane diisocyanate, naphthylene diisocyanate or xylene diisocyanate. Among them, the aromatic diisocyanate, particularly tolylene diisocyanate or diphenylmethane diisocyanate is especially preferred. Then, the diisocyanate polymer can be obtained by the polymerization in accordance with a conventional method in an inert solvent such as ethyl acetate, methyl acetate, butyl acetate, methyl ethyl ketone or dioxane, or in a plasticizer such as a phthalate, a phosphate, an adipate or a trimellitate by using a well known catalyst such as a tertiary amine, a Mannich base, an alkali metal salt of a fatty acid or an alcoholate. The isocyanate polymer is then subjected to a blocking reaction with an oxybenzoic acid ester or with an alkyl phenol, to obtain a blocked diisocyanate polymer. When the polymerization reaction or the blocking reaction is conducted in a highly volatile solvent, it is preferred to finally substitute the solvent by a proper high boiling point solvent such as a plasticizer. It is particularly preferred to employ a diisocyanate polymer obtained by the polymerization of a diisocyanate monomer and containing isocyanurate rings, as the diisocyanate polymer to be used in the present invention. The polymer containing isocyanurate rings may be prepared in accordance with the above-mentioned method. It is of course possible to employ as the isocyanate polymer, a polyurethane or polyurea having so-called isocyanate terminal groups, obtained by the reaction of diisocyanate with an active hydrogen compound. The oxybenzoic acid ester to be used as the blocking agent, includes an o-oxybenzoic acid ester, a m-oxy­ benzoic acid ester or a p-oxybenzoic acid ester. Among them, particularly preferred is a p-substituted ester. The other group constituting the oxybenzoic acid ester is preferably a long chain alkyl group such as a n-heptyl group, a n-octyl group, a 2-ethylhexyl group, a nonyl group or a dodecyl group; an alkoxyalkyl group having a long chain polyoxyethylene or polyoxypropylene group bonded thereto, or an alkoxy alkyl group having a long chain alkyl group with an oxyethylene or oxypropylene group bonded thereto, in the case of m- and p-substituted esters. In the case of o-substituted esters, an alkyl group such as a methyl group, an ethyl group, an isopropyl group, an isoamyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a n-heptyl group, a n-octyl group, a 2-ethylhexyl group, a nonyl group or a dodecyl group; an alkoxyalkyl group having a (poly)oxyethylene or (poly)oxypropylene group bonded thereto; or an aryl group such as a phenyl group or a benzyl group, may be mentioned. The alkylphenol used as a blocking agent is a phenol having, as a substituent, an alkyl group having at least 4 carbon atoms. For instance, butylphenol, hexylphenol, octylphenol or nonylphenol may be mentioned. Of course, the useful alkylphenol is not restricted to these specific exmaples. The blocking agent is used usually in an amount about stoichiometric to free isocyanate groups of the diisocyanate polymer. The amount of the blocked diisocyanate polymer is usually within a range of from 1 to 25 parts by weight, preferably from 2 to 17 parts by weight, per 100 parts by weight of the vinyl chloride polymer, so that the effective NCO content in the plastisol composition is within a range of from 0.03 to 1% by weight, preferably from 0.03 to 0.6% by weight, more preferably from 0.05 to 0.5% by weight. For instance, when a dibutyl phthalate solution containing 33% by weight of a diisocyanate polymer blocked with an oxybenzoic acid ester prepared by the polymerization and blocking in dibutyl phthalate, is to be used, the solution is employed in an amount of from 2 to 50 parts by weight per 100 parts by weight of the vinyl chloride polymer. If the amount of the plasticizer is inadequate, the plasticizer is supplemented to obtain a plastisol composition. Likewise, since the effective NCO content in the 33% dibutyl phthalate solution may vary, the diluent is properly adjusted to bring the NCO content in the plastisol composition to a desired level. If the NCO content is less than 0.03% by weight, the effects for adhesion tends to be poor. On the other hand, if the content exceeds 1% by weight, undesirable phenomena such as an increase of the viscosity and coloring of the sol, are likely to occur, and a bubble-forming phenomenon due to absorption of moisture and vigorous reaction is observed at the bonding interface, whereby the adhesive strength tends to deteriorate. The plastisol composition of the present invention preferably contains an agent for promoting the dissociation of the blocked structure of the oxybenzoic acid ester- or alkylphenol-blocked diisocyanate polymer. As such a block dissociation-promoting agent, an inorganic or organic compound of an alkali metal and an inorganic or organic compound of a metal such as lead, tin, or zinc, may be mentioned. It is desirable to use at least one of these compounds. As the alkali metal compound, a potassium or sodium salt or a potassium-zinc or sodium-zinc composite stabilizer of a fatty acid, particularly a fatty acid having an alkyl group with from 8 to 18 carbon atoms, an alkylsulfuric acid, an alkylarylsulfonic acid, an alkylsulfonic acid or a polyoxy ethylene adduct thereof, may be mentioned. The metal compound other than the alkali metal compound, includes an inorganic metal compound such as white lead, basic lead silicate, tribasic lead sulfate, tribasic lead phosphite, silica gel co-precipitated lead silicate or zinc white, and an organic compound such as a metal salt, e.g. a cadmium, barium, calcium, zinc, lead, tin or magnesium salt, of lauric acid, stearic acid, ricinolic acid, naphthenic acid, salicylic acid, 2-ethylhexoinic acid fatty acid or resin acid, and it also includes zinc octylate, dibutyltin laurate, dioctyltin maleate and dibutyltin mercaptide. Further, it is possible to employ organic acid liquid composite stabilizers of e.g. calcium-zinc, barium-zinc, magnesium-zinc, cadmium-barium-zinc types, which are commercially available usually as stabilizers for vinyl chloride resins. Among them, lead-type or tin-type compounds are particularly preferred. With respect to the amount of the block dissociation-­ promoting agent, the alkali metal compound may be incorporated in the plastisol composition preferably in an amount of not higher than 900 ppm as the alkali metal relative to the vinyl chloride polymer. In a case where an alkali metal is already contained in an emulsifier used for the preparation of the vinyl chloride polymer, such an amount is taken into account as the alkali metal amount for the calculation of the content of the alkali metal, so that a proper amount of the alkali metal compound as the block dissociation-promoting agent may be added. If the alkali metal content exceeds 900 ppm, the hygroscopic properties of the plastisol during or after its preparation tend to increase, whereby the stability of the plastisol viscosity and the adhesion reaction will be substantially impaired and the processability tends to deteriorate, and the adhesion strength is likely to deteriorate. When the metal compounds other than the alkali metal compounds are used as the block dissociation-promoting agents, there is no particular restriction as to the amount used, as they serve also as stabilizers. However, it is common to use them in an amount of from 0.5 to 10 parts by weight, preferably from 1 to 5 parts by weight, per 100 parts by weight of the vinyl chloride polymer, to attain the object. Further, the adhesion strength can be synergistically improved by using the alkali metal compound together with the compound of a metal such as lead, tin, cadmium or zinc. For the preparation of the plastisol composition of the present invention, the vinyl chloride polymer, the plasticizer and the adhesion-imparting agent, are uniformly mixed, if necessary, together with the block dissociation-promoting agent and other additives. In the present invention, it is preferred (1) to use a vinyl chloride polymer which has been stored in a completely sealed state immediately after its preparation, (2) to apply a vacuum defoaming step during the plastisol preparation prior to the addition of the adhesion-imparting agent, and (3) to conduct, after the addition of the adhesion-imparting agent, the stirring and mixing with the gas phase either vacuumed for defoaming or substituted by an inert gas such as nitrogen. During the preparation of the composition, the entrance of moisture into the composition should be avoided as far as possible. More specifically, it is desirable that the preparation is conducted in an atmosphere having a relative humidity of not higher than 80%. In general, if the mixing is conducted in an atmosphere having a relative humidity of higher than 80%, a very small amount of moisture at a level of at least 0.2% by weight will be absorbed in the plastisol. The plastisol composition of the present invention may be used as an adhesive, as a rust preventive or as a laminating agent, for nylon fibers or woven fabrics, polyester fibers or woven fabrics, or for sheet-form substrates such as sheets or films of a natural leather or a synthetic resin such as nylon or polyester, or for cationic electrodeposition coated plates. The application to the sheet-form substrates may be conducted by various means such as a reverse roll method, a knife coater method, a spray method, a curtain flow method, a dip coating method, a rotary screen method, a flat screen method, a flexor method or a gravure printing method. The sheet-form substrate coated with the plastisol composition, is heated to a temperature of from 120 to 210°C to dissociate the block polymer to form a vinyl chloride resin coating layer firmly on the sheet-form substrate. Otherwise, after the sheet-form substrate coated with the plastisol composition, was heated to a temperature lower than the dissociation temperature of the block polymer structure and the plastisol composition was melted, cooled and solidified, a separate woven fabric, sheet or film is laid thereon and press-bonded under heating at a temperature higher than the dissociation temperature of the blocked polymer, to obtain a laminated sheet. The plastisol composition of the present invention can be prepared without losing the adhesive properties even in a high temperature and high humidity atmosphere, and has the stability in the sol viscosity and the adhesion strength remarkably improved over the conventional adhesive sol compositions. In the case where the adhesion-imparting agent is an oxybenzoic acid ester-blocked diisocyanate polymer, it is possible to obtain a laminate having high adhesion strength even by lamination at a low temperature of about 160°C. In this case, the blocking agent undergoes dissociation at a relatively low temperature of from 120 to 160°C to provide excellent adhesion. In the case where the adhesion-imparting agent is a long chain alkyl phenol-blocked diisocyanate polymer, the dissociation of the blocking agent does not proceed at a low temperature of up to 130°C, and various or complicated treating methods may be employed, for instance, the composition once treated for gelation at a low temperature can be again used for lamination. Since the adhesion-imparting agent contained in the plastisol composition is a diisocyanate polymer blocked with an oxybenzoic acid ester or with a long chain alkyl phenol, and no amine-type block dissociation-promoting agent is contained, there will be no formation of air bubbles, no coloring or no decomposition of the vinyl chloride polymer during the processing, and the adhesion strength will be remarkably high. Further, in the composition, the dissociation of the blocking agent does not proceed, even when heated to a temperature not higher than about 100°C, and thus the composition has good stability in the sol viscosity and good storage stability. For the undercoating material of the present invention, it is preferred to employ, as a combination which satisfies the low temperature melting properties, the adhesive properties and the storage stability, a mixture comprising, as a vinyl chloride polymer, a paste resin composed of a homopolymer of vinyl chloride having an average degree of polymerization of at most 1600, and a resin to be blended with the paste resin (i.e. a blending resin) composed of a vinyl chloride-vinyl acetate copolymer having an average particle size of from 10 to 50 µm and having a vinyl acetate content of from 1 to 10% by weight. The amount of the blending resin to be incorporated, is usually preferably within a range of from 5 to 50% by weight based on the total vinyl chloride polymer. To the undercoating material of the present invention, various additives other than the above components, such as a filler, a thickener, a coloring agent and the like may be incorporated. Of course, other additives are not restricted to such specific examples. The filler includes an inorganic filler such as precipitated or ground calcium carbonate, talc, diatomaceous earth, kaolin or barium sulfate, and an organic filler such as cellulose powder, rubber powder or regenerated rubber. The thickener includes anhydrous silica, organic bentonite or a metal soap. When the plastisol composition contains moisture, a small amount of a powder such as calcium oxide, magnesium oxide or silicon oxide, may be added as a moisture absorber. The undercoating material of the present invention may be applied to various industrial purposes as a coating material for primer coating or for pretreatment of the substrate surface. Particularly, in the automobile industry, it is particularly useful as a primer coating material for a top coating synthetic resin coating material such as an alkyd resin coating material, an epoxy resin coating material or an acrylic resin coating material, as applied on an automobile body to which a cationic, electrodeposition coating has been applied, for the purpose of the prevention of rusts, or for the purpose of damping the shock when hit by an object such as a small stone, or for the purpose of sealing pin holes or the like. The above-mentioned cationic electrodeposition coating may be conducted in such a manner that a coating material such as an aqueous solution or aqueous dispersion prepared by neutralizing e.g. a polyamide resin (e.g. an epoxy resin having amino groups in the molecule) with a lower organic acid, is deposited on the surface of the object to be coated (automobile body) by conducting a direct current by using the object (automobile body) as the cathode. The undercoating material of the present invention may be applied usually in a coating amount of from 500 to 3000 g/m². The thickness of the coating layer may be adjusted within a wide range of from 0.3 to 2 mm. Of course, the coating amount and the thickness are not restricted to the above ranges, and may be adjusted to any desired levels. The undercoating material may be applied by any conventional method. For instance, spray coating, brush coating, dipping and spreading are main coating methods. As other means, the coating may be made by using various equipments such as a reverse rolls, a knife coater, a rotary screen, a flat screen, a flexor or a gravure printer. The undercoating material coated on the object, is then heated usually to a temperature of from 120 to 210°C to dissociate the block polymer to form a coating layer on the surface of the object. The heat treatment after the coating in the present invention is preferably conducted at a temperature within a range of from 120 to 150°C for from 20 to 40 minutes by using a block dissociation-promoting agent, whereby a coating layer having good properties will be obtained. The undercoating material of the present invention contains a diisocyanate polymer blocked with an oxybenzoic acid ester or with an alkylphenol, as an adhesion-imparting agent in the plastisol composition, and is capable of being firmly bonded to a metal surface or to a cation electrodeposition coated surface by heat treatment at a relatively low temperature in a short period of time. The plastisol composition constituting the undercoating material has good storage stability, whereby no substantial increase in the viscosity is observed even when left for a long period of time, and the coating operation to the object is simple. Further, even when the blocking agent is dissociated from the diissocynate polymer, there will be no substantial bleeding or blooming phenomena since the compatibility with the plasticizer and/or the vinyl chloride polymer is good. Further, the undercoating material of the present invention does not contain an amine-type block dissociation-promoting agent, there will be no coloring or no substantial decomposition of the vinyl chloride polymer during or after the coating operation. Therefore, there will be no problem of color change even when the top coating layer is relatively thin. The coating layer obtained by the undercoating material of the present invention has various advantages such as excellent water resistance. The novel blocked polyisocyanurate of the present invention may be prepared by (A) a process wherein a polyisocyanate compound having isocyanurate rings is reacted with a compound having the formula: wherein R is the same as R¹, R² and R³ of the compound of the formula I, and is a group selected from the group consisting of C₁-C₂₀ alkyl, alkoxyalkyl, aryl, alkaryl and aralkyl; (B) a process wherein a polyisocyanate and a compound of the formula II are reacted so that isocyanate groups remain, followed by isocyanuration; and (C) a process wherein the reaction of the polyisocyanate and the compound of the formula II and the isocyanuration are conducted simultaneously. Now, the method for the preparation of the novel blocked polyisocyanurate of the present invention will be described in detail with reference to the first process. In the present invention, the polyisocyanate compound having isocyanurate rings is a product obtained by subjecting an aromatic diisocyanate, an aliphatic diisocyanate, an alicyclic diisocyanate or a mixture thereof, to an isocyanuration reaction. As the polyisocyanate compound having isocyanate groups, a polyurethane obtained by reacting a diisocyanate compound with a polyfunctional polyhydroxy compound is most common. However, a blocked product of such a polyurethane is poor in the heat resistance, and there will be problems of coloring, odor, foaming, etc. when it is heated. Whereas, the polyisocyanurate according to the present invention is excellent in the heat resistance, and does not have such problems. The polyisocyanurate is prepared usually by a method wherein a catalyst is added to a diisocyanate to form an isocyanurate, and then, if necessary, an excess diisocyanate monomer is removed. The diisocyanate includes an aromatic diisocyanate, an aliphatic diisocyanate and an alicyclic diisocyanate. As the aromatic diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate or naphthalene diisocyanate may be mentioned. As the aliphatic diisocyanate, 1,6-hexane diisocyanate, 1,10-decamethylene diisocyanate, lysine diisocyanate or 2,4,4-trimethylhexamethylene diisocyanate may be mentioned. Likewise, as the alicyclic diisocyanate, 3-isocyanatomethyl-3,5,5-tri­ methylcyclohexyl isocyanate or 1,4-cyclohexane diisocyanate. As the catalyst, an alkali metal salt of an organic carboxylic acid, a tertiary amine compound, a quaternary ammonium compound, an epoxy-amine compound or a phenol-­ amine compound may be mentioned. The reaction is conducted usually at a temperature of from 0 to 150°C. The removal of the monomer is conducted preferably by extraction or by a thin layer evaporation method. The resulting polyisocyanurate has a degree of polymerization represented by n = 1 to 10 (statistical average number) in the formula I. If n is greater than 10, the molecular weight tends to be too high, whereby the compatibility with the solvent or with other resins tends to decrease and there will be practical problems. Various studies have been made to develop a blocked polyisocyanurate capable of being cured at a low temperature in a short period of time by using such a polyisocyanurate and taking advantage of its heat resistance, and it has been found that the compound of the formula II is extremely effective as the blocking agent. The present invention has been accomplished on the basis of this discovery. As the compound of the formula II, an o-oxybenzoic acid ester, a m-oxybenzoic acid ester, a p-oxybenzoic acid ester and a mixture thereof, may be mentioned. Particularly preferred among them is a p-oxybenzoic acid ester. A compound having a melting point of at most 50°C, preferably at most 40°C is suitable. A compound having a melting point of higher than 50°C, tends to have poor solubility in a solvent, and the curing reaction is slow, and such a compound is likely to remain, after the dissociation from the polyisocyanurate, in the form of a powder in the cured resin, whereby the transparency or mechanical properties of the cured resin tend to be inferior. The compound of the formula II according to the present invention is liquid at room temperature, and after the curing reaction, it is present uniformly in the cured resin and functions effectively as a plasticizer, whereby there will be no such drawbacks as the deterioration of the properties of the resin. The length of R in the compound of the formula II affects the melting point. For the compound to be liquid, the length of R tends to increase in the order of o-substitution, m-substitution and p-substitution. In the case of m- or p-substitution, R is preferably a long chain alkyl group such as n-heptyl, n-octyl, 2-ethylhexyl, nonyl or dodecyl, or a long chain alkoxyalkyl group including oxyethylene or oxypropylene groups. In the case of o-substitution, R is preferably methyl, ethyl, isopropyl, isoamyl, n-butyl, isobutyl, sec-butyl, n-heptyl, n-octyl, 2-ethylhexyl, nonyl, dodecyl, phenyl, benzyl or an alkoxyalkyl group including oxyethylene or oxypropylene groups. The number of carbon atoms or the total number of carbon and oxygen atoms, is preferably at least 4 so that the odor is minimum and the evaporation during the curing operation is little. The reaction of the polyisocyanurate with the compound of the formula II as a blocking agent, is conducted preferably in a solvent inert to isocyanate groups. There is no particular restriction as to the reaction temperature. However, the reaction temperature is preferably from 20 to 100°C. A catalyst may be added to facilitate the reaction. As the solvent, there may be mentioned an acetate such as ethyl acetate or butyl acetate; a ketone such as methyl ethyl ketone or methyl isobutyl ketone; a plasticizer for polyvinyl chloride such as dibutyl phthalate or dioctyl phthalate; an ether such as dioxane or tetrahydrofuran; an aromatic compound such as toluene or xylene; and dimethylformamide and N-methylpyrrolidone. As the catalyst to facilitate the reaction, there may be mentioned a tin compound such as dibutyltin dilaurate, dioctyltin dilaurate or stannous octoate; a metal salt of naphthenic acid such as zinc naphthenate or cobalt naphthenate; acetylacetone iron; acetylacetone manganese; and a tertiary amine compound. The catalyst is used usually in an amount of from 10 to 10,000 ppm relative to the entire composition for reaction. Now, the second process will be described. The starting material diisocyanate, the blocking agent (compound of the formula II), the solvent, the catalyst, the method for the blocking reaction and the method for the isocyanating reaction, are all the same as in the first process. The reaction of this process is conducted in such a manner that the diisocyanate and the compound of the formula II as a blocking agent are reacted so that isocyanate groups are in excess of the amount of the hydroxyl groups of the blocking agent, and then the remaining isocyanate groups are completely isocyanurated by adding and reacting an isocyanurate catalyst. The NCO/OH ratio in the first reaction of the diisocyanate with the compound of the formula II is preferably from 1.5 to 4. If the ratio is less than 1.5, the content of isocyanurate rings in the final product tends to be small, whereby there will be problem in the heat resistance, etc. On the other hand, if the ratio exceeds 4, the content of the blocked isocyanate groups decreases, whereby the function as a cross-linking agent during the curing operation tends to decrease. As another process, there is a process wherein the diisocyanate, the blocking agent (compound of the formula II) and the solvent are mixed, and then the blocking and the isocyanuration are conducted simultaneously in the presence of both the above-mentioned urethane-forming catalyst (to facilitate the reaction of the isocyanate groups and the hydroxyl groups) and the isocyanurating catalyst. However, with a view to efficient control of the reaction and the product, the preceding two processes are preferred to this process. The blocked polyisocyanurate thus obtained is capable of forming a three dimensional resin when mixed with an active hydrogen-containing resin and heated for cross-linking (curing). Now, the present invention will be described in further detail with reference to Examples. However, it should be understood that the present invention is by no means restricted to these specific Examples. The methods for the evaluation of plastisol compositions in the following Examples, are as follows: (1) Quantitative analysis of an alkali metal The amount of the alkali metal was determined by an atomic-absorption spectroscopy. Namely, 10 g of a sample such as a vinyl chloride polymer or a block dissociation-promoting agent, was stirred in 300 ml of distilled water for 8 hours, and then filtered with a filter paper (5A, manufactured by Toyo Kagaku Sangyo K.K.). The filtrate was further filtered through a millipore filter of 0.22 µm. The filterate was analyzed by an atomic spectroscopy (by using Joulel Ash AA 8200 analyzer, manufactured by YANACO). The metal content was quantitatively analyzed based on the values of an external calibration chart preliminarily obtained. (2) Measurement of the plastisol viscosity The plastisol viscosity at 5 rpm was measured at a plastisol temperature of 23°C by means of B8H Model viscometer manufactured by Tokyo Keiki K.K. For the measurement of the plastisol viscosity as time passes, the plastisol was stirred gently for one minute with a stirring rod two hours before the measurement. (3) Peel strength A plastisol composition was coated on a polyethylene terephthalate woven fabric of 335 g/m² or on a polyethylene terephthalate film having a thickness of 90 µm by a knife coater in a thickness of 0.8 mm or 0.1 mm, respectively, and then heated for five minutes at a temperature of 160°C, 175°C or 190°C in a hot air circulation-type dryer to obtain a laminate wherein a vinyl chloride resin was laminated on the polyethylene terephthalate woven fabric or the polyethylene terephthalate film. The laminate was left for three days in a constant temperature room, and then cut into test pieces having a width of 2.54 cm and a length of 8 cm. From one end of each test piece, the coating layer was peeled in the direction of the length at a pulling speed of 50 mm/min by 180° T-type peeling test to determine the adhesion strength to the polyethylene terephthalate woven fabric or to the polyethylene terephthalate film. The peel strenght was represented by an average peel strenght (unit: kg/2,54 cm (kg/inch)) of five test pieces. (4) Evaluation of the coloring and the formation of air bubbles The formation of air bubbles and the coloring state in the vinyl chloride polymer layer of the laminate prepared for the peel strength test, were examined by visual observation and evaluated in accordance with the following standards. ○ : None Δ : Some X : Substantial EXAMPLE 1 and COMPARATIVE EXAMPLES 1 to 3 The above identified components were left to stand for a few days in a constant temperature and humidity chamber at a temperature of 23°C under a relative humidity of 50%, then weighed and mixed in a constant temperature room in the following manner. The paste resin, DOP (corresponding to 45 phr), the stabilizer and block dissociation-promoting agent, were introduced into a Hobart mixer, and uniformly mixed and kneaded, and then a predetermined amount of a dibutyl phthalate (DBP) solution of the adhesion-imparting agent was added thereto. Further, DOP was added to bring the amount to 60 parts by weight, and the composition was uniformly mixed, and then vacuumed for defoaming to obtain a plastisol composition. The details of the composition, the plastisol viscosity, the peel strength (adhesive strength to the polyethylene terephthalate woven fabric), the formation of air bubbles and the coloring, were as shown in Table 1. For the purpose of comparison, tests were conducted in the same manner as the above Example with respect to a composition wherein no adhesion-imparting agent was added, a composition wherein a non-blocked TDI polymer was used and a composition wherein a commercially available polyisocyanate was used. In the case of the TDI polymer in Comparative Example 2, the plastisol viscosity stability is extremely poor, and the composition underwent gelation and solidification as soon as one day later, whereby it was impossible to measure the viscosity. In the case of the polyisocyanate/polyamide type adhesion-imparting agent in Comparative Example 3, the coloring was substantial, and the peel strength was low. In the case of the plastisol composition of the present invention, the plastisol-viscosity stability was substantially equal to the composition of Comparative Example 1, and yet a remarkable improvement in the peel strength was observed. EXAMPLES 2 and 3 and COMPARATIVE EXAMPLE 4 Tests were conducted in the same manner as in Example 1 except that the amount of the DBP solution containing 32% by weight of the TDI polymer blocked with nonyl phenol, was changed to 5 parts by weight and 15 parts by weight, respectively to examine the peel strength due to the difference in the NCO content. The results are shown in Table 2. At the same time, a test was conducted in the same manner as in Example 1 except that 10 parts by weight of a DBP solution containing 32% by weight of TDI having an average molecular weight of 614 and blocked with nonyl phenol (effective NCO content: 4.4 wt.%) was used, to examine the peel strength, etc. due to the difference in the average molecular weight of the adhesion-imparting agent (Comparative Ex. 4). The results are also shown in Table 2. From the above results, it is evident that in order to maintain adequate peel strength, the adhesion-imparting agent is required to have a relatively high molecular weight at a level of an average molecular weight of at least 1000 and the effective NCO content in the plastisol is required to be at least 0.07% by weight. In Example 3, the heating rate under the heating condition of 190°C was rapid, whereby a certain amount of air bubbles appeared. EXAMPLES 4 to 8 Tests were conducted in the same manner as in Example 1 except that various paste resins having different alkali metal contents were used. The results are shown in Table 3 together with the results in Example 1. It is evident that the adhesion strength (peel strength) improves almost in proportion to the alkali metal content. However, if the alkali metal content exceeds 1000 ppm, the adhesion strength decreases, and it is evident that a resin containing an alkali metal within a range of from 45 to 770 ppm is preferred. EXAMPLES 9 and 10 and COMPARATIVE EXAMPLES 5 and 6 Tests were conducted in the same manner as in Example 1 except that the paste resins used in Examples 1 and 4 (alkali metal content: 770 ppm and less than 30 ppm) were used as the vinyl chloride polymer, and the operation after the addition of the DBP solution of the adhesion-­ imparting agent during the preparation of the plastisols was conducted under a relative humidity of 80%. The plastisol viscosity, the peel strength and the formation of air bubbles were examined in the same manner as in Example 1, and the results are shown in Table 4. For the purpose of comparison, a test was conducted in the same manner with respect to the adhesion-imparting agent used in Comparative Example 2 (non-blocked TDI polymer), and the results are also shown in Table 4. In the tests under a relative humidity of 80%, the plastisol viscosity stability was good in Examples 9 and 10, whereas in Comparative Examples, the plastisols underwent solidification as time passed, whereby the plastisol viscosity stability was too poor to be practically useful. In Example 9 where the alkali metal content was high, the peel strength was even higher than that in Example 10 probably because the dissociation of the blocked polymer was thereby facilitated. However, the absorption of moisture tends to increase, thus leading to the formation of air bubbles. In Comparative Example 5, the effective NCO content decreased due to the absorption of moisture, whereby the peel strength became extremely poor. Thus, the peel strength varies depending upon the alkali metal content. From the results of various tests, the most appropriate amount is within a range of from 200 to 800 ppm. EXAMPLES 11 to 15 Tests were conducted in the same manner as in Example 1 except that the paste resins having alkali metal contents of 770 ppm and 220 ppm as used in Examples 1 and 6, respectively, were used, and the type of the stabilizer and block dissociation-promoting agent was changed to (A) tribasic lead sulfate, (B) dibutyltin mercaptide and (C) a Na-Zn type composite stabilizer (alkali metal content relative to the resin: 285 ppm). The results are shown in Table 5. EXAMPLE 16 The above identified components were left to stand for a few days in a constant temperature and humidity chamber at a temperature of 23°C under a relative humidity of 50%, then weighed and mixed in a constant temperature room in the following manner. The paste resin, DOP (corresponding to 45 PHR), the stabilizer and block dissociation-promoting agent, were introduced into a Hobart mixer, and uniformly mixed and kneaded, and then a predetermined amount of a dibutyl phthalate (DBP) solution of the adhesion-imparting agent was added thereto. Further, DOP was added to bring the amount to 60 parts by weight, and the composition was uniformly mixed, and then vacuumed for defoaming to obtain a plastisol composition. The details of the composition, the plastisol viscosity, the peel strength (adhesive strength to the polyethylene terephthalate woven fabric), the formation of air bubbles and the coloring, were as shown in Table 6. Whereas in the plastisol composition of the present invention, the plastisol viscosity stability is good, and a remarkable improvement was observed in the peel strength even at such a low heating temperature as 160 or 175°C, as compared with the composition of Comparative Example 2. EXAMPLES 17 and 18 and COMPARATIVE EXAMPLE 7 Tests were conducted in the same manner as in Example 16 except that the amount of the DBP solution containing 33% by weight of the TDI polymer blocked with p-oxybenzoic acid 2-ethylhexyl ester was changed to 5 parts by weight and 10 parts by weight, to examine the peel strength due to the differencein the NCO content. The results are shown in Table 7. At the same time, a test was conducted in the same manner as in Example 16 except that 10 parts by weight of a DBP solution containing 33% by weight of TDI having an average molecular weight of 674 and blocked with p-oxybenzoic acid 2-ethylhexyl ester (effective NCO content: 4.2 wt.%), was used, to examine the peel strenght due to the difference in the average molecular weight of the adhesion-imparting agent (Comparative Example 7)). The results are shown in Table 7. From the above results, it is evident that in order to maintain adequate peel strength, the adhesion-imparting agent is required to have a relatively high molecular weight at a level of an average molecular weight at least 1000, and the effective NCO content in the sol is required to be at least 0.05% by weight. EXAMPLES 19 to 21 Tests were conducted in the same manner as in Example 18 except that paste resins having different alkali metal contents were used. The results are shown in Table 8 together with the results of Example 18. As shown by Example 21, when a resin having a high alkali metal content is employed, a decrease is observed in the plastisol viscosity stability and in the peel strength. It is evident that a resin containing an alkali metal within a range of from 45 to 600 ppm is preferably employed. Further, the composition containing a high alkali metal content stays in the state of a plastisol for a period of about five days and then solidifies, and such a composition will be required to be used quickly. EXAMPLES 22 to 25 and COMPARATIVE EXAMPLE 8 The adhesion strength to the polyethylene terephthalate film was evaluated. Tests were conducted in the same manner as in Example 16 except that the type of the stabilizer and block dissociation-promoting agent was changed. The results are shown in Table 9. The test results of a plastisol wherein no adhesion-imparting agent was added, are also shown in Table 9 (Comparative Example 8). Compositions according to the present invention show excellent adhesion also to the polyester-type film. As shown by Examples 22 and 23, lead type and tin type stabilizers are preferred as the stabilizer and block dissociation-promoting agent, since they serve to improve the adhesion strength in a low temperature lamination. EXAMPLE 26 and COMPARATIVE EXAMPLE 9 By using a plastisol composition according to the present invention, the properties for application to an automobile undercoating and sealant, were evaluated. The blend for evaluation was as shown below, and the results of a plastisol in which the adhesion imparting agent used in Example 16 was added and a plastisol in which no such an agent was added, are shown in Table 10. The plastisol was prepared by mixing and kneading in the same manner as in Example 16, then adding the adhesion-imparting agent, and adding the plasticizer to bring the total content of the plasticizer to a predetermined level. The plastisol was coated on a plate having an undercoating formed by cationic electrodeposition, in a thickness of 0.5 mm. Separately, a pair of undercoated electrodeposited plates were laminated with a coating layer of the plastisol composition having a thickness of 0.5 mm interposed therebetween in the form of a sandwiched structure. The coated plate and the laminate of the sandwiched structure were respectively heated at 130°C for 30 minutes in an oven to obtain shaped products. With respect to the former, the 90° peel strength (pulling speed: 50 mm/min) was obtained, and with respect to the latter, the shearing peel strength (pulling speed: 5 mm/min) was obtained. Further, with respect to the viscosity stability, the plastisol was left to stand at 40°C for 72 hours, and the viscosity at 5 rpm was measured. It is evident that the plastisol composition according to the present invention has excellent adhesion strenght to the cationic electrodeposition coated plate. In the following Examples, the methods for the evaluation of the undercoating materials are as follows. (1) Tests for the viscosity and the storage stability of the undercoating materials (plastisol compositions) The plastisol viscosity at 5 rpm was measured at a plastisol temperature of 40±1°C by using B8H Model viscometer #7 rotor, manufactured by Tokyo Keiki K.K. The storage stability was determined in such a manner that a glass container containing the plastisol composition was immersed in a constant temperature water tank at a temperature of 40±1°C, after a predetermined number of days, the composition was stirred gently for one minute by a stirring rod two hours before the measurement of the viscosity, and the plastisol viscosity was measured as mentioned above. (2) Test for shearing peel strength The shearing adhesion strength was measured in accordance with JIS K 6830 (method for testing an automobile sealing material) by using a cationic electrodeposition coated plate with a coating layer as a test piece. The test was conducted with a plastisol layer thickness of 0.5 mm with heat treatment at a temperature of from 120 to 140°C for 30 minutes under a pulling speed of 5 mm/min. (3) Test for water resistance The same test piece as used for the test for measuring the shearing peel strength in above item (2), was immersed in warm water at 40°C for 7 days, and then dried in air for 1 day. Then, the shearing adhesion strength was measured in the same manner as in the above item (2) to determine the water resistance. (4) Evaluation of coloring The coloring and the outer appearance of the vinyl chloride polymer layer in the coating after the shearing peel strength test in the above item (2), were examined by visual observation, and evaluated in accordance with the following standards. ○: No coloring Δ: Some coloring X: Substantial coloring EXAMPLES 27 to 30 and COMAPRATIVE EXAMPLES 10 and 11 The above-identified components were left to stand in a constant temperature and humidity chamber at 23°C under a relative humidity of 50% for a few days, then weighed and mixed in a constant temperature room in the following manner. The paste resin, the blending resin, DOP, the filler and the stabilizer and block dissociation-promoting agent were introduced into a Hobart mixer, and uniformly mixed. Then, the solution of the adhesion-imparting agent was added, and the mixture was again uniformly mixed. Then, the mixture was vacuumed for defoaming to obtain a plastisol composition as an undercoating material. The detailed composition of the undercoating material, the plastisol viscosity, the shearing peel strength, the coloring state, etc. are shown in Table 11. For the purpose of comparison, tests were conducted in the same manner as in the above Example with respect to the composition wherein no adhesion-imparting agent was added and the composition wherein a commercially available adhesion-imparting agent was added. The results are also shown in Table 11. Cohesive failure was observed in all cases of the peeling states in Examples 27 to 30 wherein undercoating materials of the present invention were used, thus indicating excellent adhesion properties. The shearing peel strength value remarkably improves by the use of a lead type stabilizer. The viscosity stability is good in the case of a combination of a paste resin of the homopolymer and a blending resin of the copolymer. A further feature of the present invention is that as compared with the commercial product in Comparative Example 11, no substantial thermal coloring is observed after the heat treatment for lamination. EXAMPLES 31 and 32 Tests were conducted in the same manner as in Example 27 except that the composition of the vinyl chloride polymer i.e. the paste resin and the blending resin was changed. The results are shown in Table 12 together with the result of Example 27. Examples 27, 31 and 32 show the low temperature melting properties and the low temperature adhesive properties according to the present invention. According to the present invention, a uniform cohesive failure state is observed at the peeled surface even under a low temperature lamination condition at 120°C for 30 minutes. It is seen that among them, the above-mentioned resin blend of Example 27 is preferred as a combination of resins which provides good physical properties such as shearing peel strength as well as excellent viscosity stability. EXAMPLES 33 to 38 With the above composition wherein the type and amount of the adhesion-imparting agent were varied, the evaluation was carried out in the same manner as in Examples 27 to 30. The results are shown in Table 13. As shown by Examples 34 and 37, in each of the adhesion-imparting agents A and B, adequate adhesive properties to the cation electrodeposition coated plate can be obtained if the blocked diisocyanate polymer component is added in an amount of about 5 parts by weight and at least 1% of the entire plastisol. EXAMPLES 39 and 40 and COMPARATIVE EXAMPLE 12 With the above composition wherein A, B or C was used as the adhesion-imparting agent, the evaluation was carried out. The diluent was added later and mixed. The results are shown in Table 14. In the case of the adhesion-imparting agents A and B according to the present invention, the deterioration in the adhesive properties or adhesion after the hot water dipping treatment is small, thus indicating that the water resistance is improved remarkably as compared with C of the Comparative Example 12. EXAMPLES 41 to 44 Tests were conducted in the same manner as in Example 40 except that in the composition in Example 40, a half (40 phr) of 80 phr of the paste resin VINIKA P-540 was substituted by the following paste resins, and the amount of the diluent was reduced to 8 phr, and various proper­ ties were measured. The results are shown in Table 15. As the vinyl chloride polymer of the present invention, various homopolymers and copolymers may be used alone or in combination as a mixture. EXAMPLE 45 Into a four necked flask equipped with a thermometer, a condenser, a stirrer and a dropping funnel, 147 g of 80-TDI (tolylene diisocyanate comprising 80% of 2,4-isomer and 20% of 2,6-isomer) and 406 g of dibutyl phthalate were introduced. The internal temperature was adjusted to 30°C, and 2.0 g of a 5% methanol solution of potassium acetate was gradually dropwise added under stirring. Then, the reaction was conducted at a temperature of from 30 to 40°C for 12 hours to obtain a polyisocyanurate having isocyanate groups at the terminals. The isocyanate group content of this product was 4.92% (the isocyanate group content at the initiation of the reaction was 14.5%), and in the infrared absorption spectrum, an absorption was observed at 1410 cm⁻¹ attributable to the vibration of the isocyanurate ring. Further, from the measurement by gel permeation chromatography (GPC), the number average molecular weight was found to be 1400. Then, the internal temperature of the flask was adjusted to 60°C, and 0.5 g of dibutyltin dilaurate was added and uniformly mixed and dissolved. Then, a solution obtained by dissolving 170 g of p-oxybenzoic acid 2-ethylhexyl ester in 386 g of dibutyl phthalate, was dropwise added over a period of 1 hour, and the reaction was conducted at a temperature of from 60 to 65°C for 8 hours. From the infrared absorption specturm for detection of isocyanate groups, no absorption was observed at 2250 cm⁻¹. The blocked polyisocyanurate thus obtained had an effective isocyanate group content of 2.51%. The blocked polyisocyanurate and a polyester polyol were mixed in a ratio as identified in Table 16, and the mixture was coated on a glass sheet, whereby the curing rate was confirmed. The results are shown in Table 16. It was found that the curing could be conducted at a low temperature for a short period of time. EXAMPLE 46 Into a four necked flask equipped with a thermometer, a condenser, a stirrer and a dropping funnel, 250 g of MDI (4,4′-diphenylmethane diisocyanate) and 750 g of dioctyl phthalate were introduced. The internal temperature was adjusted to 60°C, and a solution comprising 0.5 g of dibutyltin dilaurate, 250 g of p-oxybenzoic acid 2-ethylhexyl ester and 750 g of dioctyl phthalate, was dropwise added and reacted over a period of 2 hours. Then, reaction was continued for 4 hours, and when the isocyanate group content became 2.1% (i.e. 50% of the isocyanate groups at the time of charging), 4.0 g of a 5% methanol solution of potassium acetate as an isocyanurating catalyst, was dropwise added. Then, the reaction was conducted at a temperature of 60°C for about 10 hours until isocyanate groups were no longer detected by infrared absorption spectrum (2250 cm⁻¹). In this spectrum, an absorption at 1410 cm⁻¹ attributable to the vibration of an isocyanurate ring was observed. The number average molecular weight was measured by GPC, and was found to be 2500. This product had an effective isocyanate group content of 2.1%. The curing rate was examined in the same manner as in Example 45 and found to be as shown in Table 16. It was found that curing could be conducted at a low temperature for a short period of time. EXAMPLE 47 Into a four necked flask equipped with a thermometer, a condenser, a stirrer and a dropping funnel, 400 g of hexamethylene diisocyanate was introduced. The internal temperature was adjusted to 50°C, and 1.0 g of N,N,N-­ trimethyl-N-(2-hydroxyethyl)ammonium was added and mixed. The heat generation was suppressed by cooling, and while maintaining the internal temperature at a level of 60°C, the reaction was continued for 3 hours, whereupon the isocyanate group content became 35.0%. To this reaction solution, 1.5 g of phosphoric acid was added as a terminating agent. After stirring the reaction solution for one hour, the remaining hexamethylene diisocyanate was removed by a thin layer distillation apparatus. The solution thus obtained had an isocyanate group content of 21.5%, and in the infrared absorption spectrum, an absorption at 1680 cm⁻¹ and 1470 cm⁻¹ attributable to an isocyanurate ring was observed. Further, from the measurement by GPC, the number average molecular weight was found to be 830. 100 g of the polyisocyanurate thus obtained and 100 g of dioctyl phthalate were introduced into a separate reactor, and the internal temperature was adjusted to 60°C. A solution comprising 121 g of p-hydroxybenzoic acid n-heptyl ester, 121 g of dioctyl phthalate and 0.1 g of dibutyltin dilaurate, was dropwise added over a period of 1 hour, and the reaction was conducted at 60°C for 6 hours to complete the blocking reaction. The blocked polyisocyanurate thus obtained had an effective isocyanate group content of 4.9%. The curing rate was examined in the same manner as in Example 45. The results are shown in Table 16. EXAMPLE 48 Into a four necked flask equipped with a thermometer, a condenser, a stirrer and a dropping funnel, 500 g of 3-isocyanatomethyl-3,5,5-trimethylhexyl isocyanate was introduced, and the internal temperature was adjusted to 65°C. Then, 2.0 g of N,N,N-trimethyl-N-(2-hydroxyethyl)­ ammonium was added and mixed. The reaction was exothermic, and therefore the reaction was conducted under cooling at 70°C for 3 hours, whereupon the isocyanate group content became 26.5%. To this reaction solution, 3.0 g of phosphoric acid was added as a terminating agent. After stirring the mixture for 1 hour, the remaining 3-isocyanatomethyl-­ 3,5,5-trimethylhexyl isocyanate was removed by a thin layer distillation apparatus. The isocyanate group content of the obtained product was 17.2%, and in the infrared absorption spectrum, an absorption at 1690 cm⁻¹ and 1440 cm⁻¹ attributable to an isocyanurate ring was observed. Further, from the measurement by GPC, the number average molecular weight was found to be 720. 100 g of the polyisocyanurate thus obtained and 100 g of dioctyl phthalate were introduced into a separate reactor, and the internal temperature was adjusted to 70°C. A solution comprising 95 g of o-hydroxylbenzoic acid isoamyl ester, 95 g of dioctyl phthalate and 0.2 g of dibutyltin dilaurate, was dropwise added over a period of 1 hour, and the reaction was conducted at 70°C for 8 hours to complete the blocking reaction. The effective isocyanate group content in the blocked polyisocyanurate was 4.4%. The curing rate was examined in the same manner as in Example 45. The results are shown in Table 16. Conventional blocked polyurethanes require a high temperature and long time treatment for cross-linking. Whereas, the blocked polyisocyanurate of the present invention forms adequate cross-linking even at a low temperature. Further, under a high temperature heating at a level of e.g. at least 180°C, the cross-linkage will be formed in a short period of time at a level of 1 minute. Besides, even when heated at a high temperature at a level of about 200°C, it does not bring about phenomena such as coloring and foaming as in the case of the blocked polyurethane, and thus useful for blending with a thermoplastic material such as a polyvinyl chloride. The blocked polyisocyanurate of the present invention is useful as a coating material, an adhesive, a curing agent for an ink, plastics or rubber, a modifier for paper and fibers or an impregnation treating agent (binder) for a wood and inorganic shaped product.

Claims: 1. A plastisol composition comprising a vinyl chloride polymer, a plasticizer and an adhesion-imparting agent, characterized in that the adhesion-imparting agent is a diisocyanate polymer blocked with an oxybenzoic acid ester or with an alkylphenol and having an average molecular weight within a range of from 1,000 to 10,000, and has an effective isocyanate content of from 0.03 to 1 % by weight. 2. The plastisol composition according to Claim 1, wherein the diisocyanate polymer is a polymer of an aromatic diisocyanate. 3. The plastisol composition according to Claim 2, wherein the diisocyanate polymer contains isocyanurate rings. 4. The plastisol composition according to Claim 2, wherein the aromatic diisocyanate is tolylene diisocyanate or diphenylmethane diisocyanate. 5. The plastisol composition according to Claim 1, which contains an agent for promoting the dissociation of the blocked polymer of the adhesion-imparting agent. 6. The plastisol composition according to Claim 5, wherein the dissociation promoting agent is at least one member selected from the group consisting of inorganic and organic compounds of an alkali metal, zinc, tin and lead. 7. The plastisol composition according to Claim 1, which contains an alkali metal in an amount of not higher than 900 ppm relative to the vinyl chloride polymer. 8. An undercoating material composed of a plastisol composition comprising a vinyl chloride polymer and a plasticizer as main components, wherein the plastisol composition contains a diisocyanate polymer blocked with an oxybenzoic acid ester or with an alkylphenol and having an average molecular weight within a range of from 1,000 to 10,000, with an effective isocyanate content of from 0.03 to 1 % by weight, as an adhesion-imparting agent. 9. The undercoating material according to Claim 8, wherein the diisocyanate polymer contains isocyanurate rings. 10. The undercoating material according to Claim 9, wherein the plastisol composition contains an agent for promoting the dissociation of the blocked polymer of the adhesion-imparting agent. 11. The undercoating material according to Claim 8, which contains an alkali metal in an amount of not higher than 900 ppm relative to the vinyl chloride polymer. 12. A blocked polyisocyanurate having the formula: wherein each of X, Y and Z which may be the same or different, is a residue of a diisocyanate compound devoid of the isocyanate groups, each of R¹, R² and R³ which may be the same or different, is a group selected from the group consisting of C₁-C 20 alkyl, alkoxyalkyl, aryl, alkaryl and aralkyl, and n is an integer of from 1 to 10. 13. The blocked polyisocyanurate according to Claim 12, wherein the diisocyanate compound is selected from the group consisting of tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, naphthalene diisocyanate, 1,6-hexane diisocyanate, 1,10-decamethylene diisocyanate, lysine diisocyanate, 2,4,4-trimethylhexa methylene diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate and 1,4-cyclohexane diisocyanate. 14. A process for preparing a blocked polyisocyanurate having the formula: wherein each of X, Y and Z which may be the same or different, is a residue of a diisocyanate compound devoid of the isocyanate groups, each of R¹, R² and R³ which may be the same or different, is a group selected from the group consisting of C₁-C 20 alkyl, alkoxyalkyl, aryl, alkaryl and aralkyl, and n is an integer of from 1 to 10, which comprises: (A) reacting a polyisocyanate compound having isocyanurate rings with a compound having the formula: wherein R is a group selected from the group consisting of C₁-C 20 alkyl, alkoxyalkyl, aryl, alkaryl and aralkyl, (B) reacting a polyisocyanate with a compound of the formula II so that isocyanate groups remain, followed by isocyanuration, or (C) conducting the reaction of a polyisocyanate with a compound of the formula II and the isocyanuration simultaneously.

Inventors: HOTTA, HISAHARU, KOBAYASHI, YOSHIMICHI C/O MITSUBISHI CHEM. I. LTD., SUGINO, SATORU
Applicants: MITSUBISHI KASEI CORPORATION, MITSUBISHI KASEI VINYL COMPANY
Application year: 1986
Main classification: C08G18
IPC codes: C08G18, C08L27, C08L75