Hydrophilic tetramethylxylylenecarbodiimides

Abstract: The present invention provides a hydrophilic tetramethylxylylenecarbodiimide represented by the following general formula (1): (wherein n is an average polymerization degree and is an integer of 1 to 30; R₁ is a residue of an organic compound having a hydrophilic segment and at least one functional group reactive with an isocyanate group; and X is a group formed by the reaction of said functional group with said isocyanate group). Said carbodiimide is free from the problems of the prior art, has good storage stability and accordingly is usable as an easy-to-handle crosslinking agent for hydrophilic resin.

Description: The present invention relates to a novel hydrophilic carbodiimide. More particularly, the present invention relates to a hydrophilic carbodiimide having good storage stability owing to the reduced reactivity and accordingly usable as an easy-to-handle crosslinking agent for hydrophilic resin. 2. Description of the Prior Art Carbodiimides, particularly polycarbodiimides are known as a thermosetting resin having high heat resistance and find applications in molded materials, etc. obtained, for example, by hot-pressing a powdery polycarbodiimide. Of the polycarbodiimides, aromatic polycarbodiimides have hitherto been used mainly. Recently, however, production and application of aliphatic polycarbodiimides were reported. For example, Japanese Patent Application Kokai (Laid-Open) No. 187029/1984 and Japanese Patent Publication No. 27450/1993 disclose a polycarbodiimide derived from isophorone diisocyanate and a method for crosslinking a resin for aqueous coating with said polycarbodiimide. The above crosslinking of resin for aqueous coating utilizes a reaction between the carbodiimide group of polycarbodiimide and the active hydrogen of active-hydrogen compound. The reaction includes, for example, one between carbodiimide group and a carboxylic acid residue present in hydrophilic acrylic resin. Conventional aliphatic polycarbodiimides (e.g. a polycarbodiimide derived from isophorone diisocyanate), however, are highly reactive. Therefore, they give rise to a reaction even after their addition to a resin for aqueous coating, providing a coating of poor storage stability and short shelf life. Further, conventional aliphatic polycarbodiimides, when added to a resin for aqueous coating, etc., must be emulsified beforehand together with a surfactant, mechanically by the use of an expensive high-shear mixer, making complicated the emulsification operation. Moreover, conventional aliphatic polycarbodiimides, when emulsified, inevitably generate urea owing to the reaction with water, making short the storage stability of the emulsion. European patent application EP 0 548 815 A2 discloses a polytetramethylxylylenecarbodiimide which is synthesized for example from m- or p-tetramethylxylylenediisocyanate and a monoisocyanate in the presence of a carbodiimidization catalyst in a suitable solvent. The formed carbodiimide shows good storage stability and good handleability due to a reduced rate of reaction with an active hydrogen compound of a coating resin, for example with a carboxylic acid residue contained in an aqueous acrylic resin. Object and Summary of the Invention The present invention aims at providing a hydrophilic carbodiimide which is free from the problems of the prior art, which has good storage stability and accordingly is usable as an easy-to-handle crosslinking agent for hydrophilic resin and which shows good adhesivity. According to the present invention there is provided a hydrophilic tetramethylxylylenecarbodiimide represented by the following general formula (1): (wherein n is an average polymerization degree and is an integer of 1-30; m is an integer of 4-30; R 1 is a lower alkyl group of 1-4 carbon atoms; and R 2 is a hydrogen atom or a methyl group). Detailed Description of the Invention The present invention is hereinafter described in detail. The hydrophilic carbodiimide of the present invention is represented by the above general formula (1) and is synthesized from (a) an isocyanate-terminated tetramethylxylylenecarbodiimide obtained from, for example, m-tetramethylxylylene diisocyanate or p-tetramethylxylylene diisocyanate and (b) an organic compound having a hydrophilic segment and at least one functional group reactive with an isocyanate group (said organic compound is hereinafter abbreviated as hydrophilic segment group), the hydrophilic segment compound being a poly(alkylene oxide) represented by the general formula: R 1 -O-(CH 2 -CHR 2 O-) m H. In the above general formula (1), n is an integer of 1-30 and is an average polymerization degree of the hydrophilic carbodiimide of the present invention. As easily appreciated from the formula, the present carbodiimide has stereoisomers. The present hydrophilic carbodiimide can be produced specifically by subjecting tetramethylxylylene diisocyanate to a condensation reaction (carbon dioxide removal takes place in the reaction) to synthesize an isocyanateterminated tetramethylxylylenecarbodiimide and then reacting it with a hydrophilic segment compound. The above production of isocyanate-terminated tetramethylxylylenecarbodiimide can be conducted basically by conventional processes for production of polycarbodiimide [U.S. Patent No. 2,941,956; Japanese Patent Publication No. 33279/1972; J. Org. Chem., 28, 2069-2076 (1963); Chemical Review 1981, Vol. 81, No. 4, pp. 619-621]. The above condensation reaction of tetramethylxylylene diisocyanate wherein carbon dioxide removal takes place, proceeds in the presence of a carbodiimidization catalyst. The catalyst includes, for example, 1-phenyl-2-phospholene-1-oxide, 3-methyl-2-phospholene-1-oxide, 1-ethyl-2-phospholene-1-oxide, 1-ethyl-3-methyl-2-phospholene-1-oxide, 3-methyl-1-phenyl-2-phospholene-1-oxide and 3-phospholene isomers thereof. Of these, 3-methyl-1-phenyl-2-phospholene-1-oxide is preferred in view of the reactivity. The temperature of the above condensation reaction is preferably 80-180°C. When the temperature is lower than 80°C, the reaction time is very long. When the temperature is higher than 180°C, side reactions take place, making it difficult to obtain a carbodiimide of good quality. The condensation degree obtained is preferably 30 or less. A condensation degree higher than 30 results in lower water dispersibility. In order to complete the condensation reaction quickly, the reaction of tetramethylxylylene diisocyanate is conducted in a stream of an inert gas such as nitrogen or the like. The hydrophilic segment compound includes a poly(alkylene oxide) having at least one reactive hydroxyl group, blocked with an alkoxyl group at one end, said poly(alkylene oxide) being represented by the following general formula: R 1 -O-(CH 2 -CHR 2 -O-) m H (wherein m is an integer of 4-30; R 1 is a lower alkyl group of 1-4 carbon atoms; and R 2 is a hydrogen atom or a methyl group). Specific examples of the poly(alkylene oxide) are poly(ethylene oxide) monomethyl ether, poly(ethylene oxide) monoethyl ether, poly(ethylene oxide-propylene oxide) monomethyl ether and poly(ethylene oxide-propylene oxide) monoethyl ether. Poly(ethylene oxide) monomethyl ether is preferred particularly. When the poly(alkylene oxide) having at least one reactive hydroxyl group, blocked with an alkoxyl group at one end is used as the hydrophilic segment compound, the resulting hydrophilic tetramethylxylylenecarbodiimide of the present invention has the following molecular structure and is a nonionic type. The above addition reaction between isocyanateterminated tetramethylxylylenecarbodiimide and poly(alkylene oxide) may use a catalyst but proceeds easily only by heating. The reaction temperature can be 60-140°C, preferably 80-120°C. When the reaction temperature is lower than 60°C, the reaction time is very long. When the reaction temperature is higher than 140°C, side reactions take place, making it impossible to obtain a hydrophilic carbodiimide of good quality. The hydrophilic tetramethylxylylenecarbodiimide produced as above can be used in various forms. When it is added to an aqueous coating, etc., it may be added as it is, but it is preferably added in the form of an aqueous solution or dispersion in view of easier mixing. In the present invention, the term "hydrophilic" used for tetramethylxylylenecarbodiimide refers to that the tetramethylxylylenecarbodiimide is water-soluble or self-emulsifiable in water and is uniformly compatible with water. The present invention is hereinafter described in more detail with reference to Examples. (Synthesis of hydrophilic tetramethylxylylenecarbodiimides) Example 1 700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl- 1-phenyl-2-phospholene-1-oxide) at 180°C for 22 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree = 5). 124.4 g of the carbodiimide was reacted with 63.6 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 6 at 100°C for 48 hours. Thereto was slowly added, at 50°C, 282.0 g of distilled water so as to give a resin concentration of 40% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25°C for 12 months, showed neither separation nor precipitation and was very stable. Example 2 700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180°C for 22 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree = 5). 124.4 g of the carbodiimide was reacted with 115.0 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 12 at 100°C for 48 hours. Thereto was slowly added, at 50°C, 359.1 g of distilled water so as to give a resin concentration of 40% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constanttemperature chamber of 25°C for 12 months, showed neither separation nor precipitation and was very stable. Example 3 700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180°C for 32 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree = 10). 224.4 g of the carbodiimide was reacted with 63.6 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 6 at 100°C for 48 hours. Thereto was slowly added, at 50°C, 432 g of distilled water so as to give a resin concentration of 40% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25°C for 12 months, showed neither separation nor precipitation and was very stable. Example 4 700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180°C for 32 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree = 10). 224.4 g of the carbodiimide was reacted with 82.6 g of poly(oxyethylene) monomethylether having a polymerization degree (m) of about 8 at 100°C for 48 hours. Thereto was slowly added, at 50°C, 716.3 g of distilled water so as to give a resin concentration of 30% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25°C for 12 months, showed neither separation nor precipitation and was very stable. Example 5 700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180°C for 32 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree = 10). 224.4 g of the carbodiimide was reacted with 115.0 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 12 at 100°C for 48 hours. Thereto was slowly added, at 50°C, 509.1 g of distilled water so as to give a resin concentration of 40% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25°C for 12 months, showed neither separation nor precipitation and was very stable. Example 6 700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180°C for 58 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree = 15). 324.4 g of the carbodiimide was reacted with 115.0 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 12 at 100°C for 48 hours. Thereto was slowly added, at 50°C, 659.1 g of distilled water so as to give a resin concentration of 40% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25°C for 12 months, showed neither separation nor precipitation and was very stable. Example 7 700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180°C for 58 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree = 15). 324.4 g of the carbodiimide was reacted with 160.2 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 18 at 100°C for 48 hours. Thereto was slowly added, at 50°C, 726.9 g of distilled water so as to give a resin concentration of 40% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25°C for 12 months, showed neither separation nor precipitation and was very stable. Comparative Example 1 700 g of isophorone diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180°C for 6 hours to obtain an isocyanate-terminated isophoronecarbodiimide (polymerization degree = 4). 93.4 g of the carbodiimide was reacted with 17.8 g of 2-dimethylaminoethanol at 80°C for 24 hours. Thereto was added 37.2 g of methyl p-toluenesulfonate, followed by stirring for 1 hour to conduct quaternization. Thereto was slowly added 148.4 g of distilled water so as to give a resin concentration of 50% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25°C, became cloudy and showed separation in 3 months. Comparative Example 2 700 g of isophorone diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180°C for 6 hours to obtain an isocyanate-terminated isophoronecarbodiimide (polymerization degree = 4). 93.4 g of the carbodiimide was reacted with 20.4 g of 3-dimethylamine-n-propylamine at 80°C for 1 hour. Thereto was added 37.2 g of methyl p-toluenesulfonate, followed by stirring for 1 hour to conduct quaternization. Thereto was slowly added 151 g of distilled water so as to give a resin concentration of 50% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25°C, became cloudy and showed separation in 3 months. Comparative Example 3 700 g of isophorone diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180°C for 14 hours to obtain an isocyanate-terminated isophoronecarbodiimide (polymerization degree = 10). 200.2 g of the carbodiimide was reacted with 20.4 g of 3-dimethylamine-n-propylamine at 80°C for 1 hour. Thereto was added 37.2 g of methyl p-toluenesulfonate, followed by stirring for 1 hour to conduct quaternization. Thereto was slowly added 257.8 g of distilled water so as to give a resin concentration of 50% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25°C, showed separation in 2 months. Comparative Example 4 700 g of isophorone diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180°C for 14 hours to obtain an isocyanate-terminated isophoronecarbodiimide (polymerization degree = 10). 200.2 g of the carbodiimide was reacted with 41.2 g of sodium hydroxypropanesulfonate at 100°C for 24 hours. Thereto was slowly added, at 80°C, 563.3 g of distilled water so as to give a resin concentration of 30% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25°C, showed separation in 2 months. Comparative Example 5 700 g of isophorone diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180°C for 8 hours to obtain an isocyanate-terminated isophoronecarbodiimide (polymerization degree = 5). 111.2 g of the carbodiimide was reacted with 63.6 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 6 at 100°C for 24 hours. Thereto was slowly added, at 50°C, 262.2 g of distilled water so as to give a resin concentration of 40% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25°C, became cloudy and showed separation in 4 months. Comparative Example 6 700 g of isophorone diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180°C for 14 hours to obtain an isocyanate-terminated isophoronecarbodiimide (polymerization degree = 10). 200.2 g of the carbodiimide was reacted with 82.6 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 8 at 100°C for 48 hours. Thereto was slowly added, at 50°C, 660 g of distilled water so as to give a resin concentration of 30% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25°C, showed separation in 2 months. Comparative Example 7 700 g of isophorone diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180°C for 14 hours to obtain an isocyanate-terminated isophoronecarbodiimide (polymerization degree = 10). 200.2 g of the carbodiimide was reacted with 115.0 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 12 at 100°C for 24 hours. Thereto was slowly added, at 50°C, 472.8 g of distilled water so as to give a resin concentration of 40% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25°C, became cloudy and showed separation in 4 months. The results of syntheses in Examples 1-7 and Comparative Examples 1-7 are shown in Tables 1-1 and 1-2. As is clear from Tables 1-1 and 1-2, the hydrophilic tetramethylxylylenecarbodiimides of Examples 1-7 according to the present invention are superior in storage stability to the hydrophilic isophoronecarbpdiimides of Comparative Examples 1-7. Reference Example (Reactions between hydrophilic tetramethylxylylenecarbodiimides and aqueous resins) Each of the aqueous carbodiimide solutions obtained in Examples 1, 4 and 5 and Comparative Examples 5, 6 and 7 was added to a solution of a styrene-acrylic resin of acid value = 300 (solvent in solution: water/alcohol = 95/5, resin concentration in solution = 30% by weight) so that the carbodiimide group and the carboxyl group became 1:1 in equivalent. Each of the resulting mixtures was meausred for viscosity change at 25°C. Further, each mixture was coated on a polyethylene terephthalate film by the use of an applicator so that the resulting film had a thickness of 100 µm; the film was dried at 80°C for 5 minutes; and the dried film was cut into a piece of 5 cm x 5 cm and immersed in 300 ml of distilled water for 24 hours to observe the change of the film condition. The results of the above test are shown in Table 2. As is clear from Table 2, the hydrophilic tetramethylxylylenecarbodimides of Examples 1, 4 and 5 according to the present invention are superior to the aqueous isophoronecarbodiimides of Comparative Examples 5, 6 and 7 in stability after addition to hydrophilic resin as well as in potency as crosslinking agent.

Claims: A hydrophilic tetramethylxylylenecarbodiimide represented by the following general formula (1): (wherein n is an average polymerization degree and is an integer of 1-30; m is an integer of 4-30; R 1 is a lower alkyl group of 1-4 carbon atoms; and R 2 is a hydrogen atom or a methyl group).

Inventors: HORIE NAOFUMI, IMASHIRO YASUO, SASAKI EIJI, TAKAHASHI IKUO, HORIE, NAOFUMI, IMASHIRO, YASUO, SASAKI, EIJI, TAKAHASHI, IKUO, HORIE, NAOFUMI, C/O NISSHINBO IND. INC., TOKYO, IMASHIRO, YASUO, C/O NISSHINBO IND. INC., TOKYO, SASAKI, EIJI, C/O NISSHINBO IND. INC., TOKYO, TAKAHASHI, IKUO, C/O NISSHINBO IND. INC., TOKYO
Applicants: NISSHIN SPINNING, NISSHINBO INDUSTRIES, INC.
Application year: 1995
Main classification: C07C267
IPC codes: C07C267, C08G18