JP5833900B2 - Resin crosslinking agent and aqueous resin composition - Google Patents

Description

  The present invention includes a water-soluble or water-dispersible polycarbodiimide amine-modified product derived from an aromatic diisocyanate compound, and the above-mentioned polycarbodiimide amine-modified product that can suppress the reactivity with an aqueous resin and improve storage stability. The present invention relates to a resin crosslinking agent.

Water-soluble or water-dispersible water-based resins are used in many fields such as paints, inks, fiber treatment agents, adhesives, and coating agents.
This water-soluble or water-dispersible water-based paint uses an aqueous medium, so there is no concern about environmental pollution or fire, and cleaning of painting equipment such as brushes, rollers, spray guns, etc. Etc. can be easily made with water, and in particular, its demand has been increasing in recent years.
In general, a carboxyl group is introduced into the aqueous resin in order to impart water solubility or water dispersibility to the resin itself. For this reason, the carboxyl group remaining in the coating film may induce hydrolysis, thereby impairing the strength, durability, and aesthetics of the coating film.

As means for improving various physical properties such as the strength, water resistance and durability of the coating film of such an aqueous resin, an aqueous melamine resin, an aziridine compound, and a water dispersion capable of forming a crosslinked structure by reacting with the carboxyl group described above A method in which an external crosslinking agent such as a type isocyanate compound is used in combination is generally employed.
However, these cross-linking agents may be difficult to use due to problems such as toxicity and reactivity. That is, since the crosslinking reaction by the crosslinking agent proceeds while crushing the carboxyl group, the reduction of the carboxyl group can improve the strength, water resistance, durability, etc. of the coating film, but it has not been reacted. If the cross-linking agent remains, the coating film may be toxic. On the other hand, if unreacted carboxyl groups remain in the coating film, the water resistance and durability of the coating film are reduced. Thus, various problems will arise if the crosslinking agent and the carboxyl group in the aqueous resin do not react 100%.

In order to solve the toxicity problem, carbodiimide compounds have recently attracted attention.
For example, it is known that polycarbodiimide is used as a resin crosslinking agent because a carbodiimide group and a carboxyl group of polycarbodiimide react with each other. As a technique for using polycarbodiimide as a resin cross-linking agent for aqueous resin, for example, Patent Document 1 discloses that the end of polycarbodiimide derived from tetramethylxylylene diisocyanate is sealed with a hydrophilic segment to form an aqueous polycarbodiimide and a resin cross-linking agent. It is disclosed that handling is facilitated by making the storage stability of itself good.

For example, Patent Document 2 discloses aqueous dicyclohexylmethane carbodiimide that has good reactivity and storage stability and is easy to handle as a crosslinking agent for aqueous resins.
This aqueous dicyclohexylmethane carbodiimide has characteristics that it is not toxic and has a good pot life at room temperature.
Patent Document 3 discloses glycolic acid that can improve water resistance, solvent resistance, and adhesion, and has a structure close to that of a water-based urethane resin or water-based acrylic resin when making a carbodiimide compound aqueous. A water-soluble or water-dispersible carbodiimide compound in which methyl / methyl lactate is introduced at the terminal is disclosed.

  On the other hand, polycarbodiimide has low solubility in various solvents, and in the solution state, there is a problem that the reaction of carbodiimide groups and the aggregation of the polymer progress to gelation, which is not suitable for long-term storage. In contrast, for example, Patent Document 4 discloses a technique for improving heat resistance and adhesiveness suitable for use in electronic parts by modifying a carbodiimide group with an amino group and improving the storage stability of the carbodiimide itself in a solution. Has been.

JP 7-330849 A JP 2000-7462 A JP 2009-235278 A JP 2007-235278 A

However, due to the high reactivity between the carbodiimide group and the carboxyl group, there is a problem that the storage stability is inferior when the resin crosslinking agent having a carbodiimide group and the aqueous resin having a carboxyl group are mixed.
For example, Patent Document 1 uses tetramethylxylylene diisocyanate to improve the storage stability of the resin cross-linking agent per se rather than using a chain aliphatic diisocyanate containing isophorone diisocyanate. Although the effect of stability after addition to is evaluated, only the stability of about 3 days to 1 week is shown, and it is not sufficiently satisfactory as the storage stability with respect to the aqueous resin. Patent Documents 2 and 3 disclose resin cross-linking agents that improve the water resistance, solvent resistance, and adhesion of aqueous resins. Patent Document 4 discloses storage stability of carbodiimide itself in a solvent such as toluene or cyclohexane. In any document, there is no disclosure of sufficient storage stability after adding a resin cross-linking agent to an aqueous resin, particularly storage stability at high temperatures.

  Accordingly, an object of the present invention is to provide a polycarbodiimide and a resin crosslinking agent that can be used as a resin crosslinking agent that exhibits water solubility or water dispersibility and has improved storage stability with respect to an aqueous resin.

As a result of intensive studies to achieve the above object, the present inventor solved the above problems by sealing the end of polycarbodiimide with a hydrophilic compound and modifying the carbodiimide group with a secondary amine. The present invention was completed.
That is, this invention is the following polycarbodiimide and resin crosslinking agent.

1. A water-soluble or water-dispersible modified polycarbodiimide amine obtained by modifying a polycarbodiimide derived from an aromatic diisocyanate compound whose end is sealed with a hydrophilic compound with a secondary amine.
2. 2. The modified polycarbodiimide amine according to 1 above, wherein the polymerization degree of the polycarbodiimide is 2 to 12.
3. The polycarbodiimide amine modification according to 1 or 2 above, wherein the aromatic diisocyanate compound is at least one selected from 4,4′-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, and 2,6-tolylene diisocyanate. object.
4). 4. The modified polycarbodiimide amine according to any one of 1 to 3 above, wherein the secondary amine is di-n-propylamine or diisopropylamine.
5. The resin crosslinking agent for water-based resins containing the polycarbodiimide amine modified material in any one of said 1-4.
6). 6. The resin cross-linking agent according to 5 above, wherein the aqueous resin is at least one selected from a water-soluble or water-dispersible urethane resin having a carboxyl group in the molecule, an acrylic resin, and a polyester resin.

  The modified polycarbodiimide amine of the present invention can exhibit water solubility or water dispersibility, and has high storage stability in an aqueous medium. Furthermore, the resin cross-linking agent containing the modified polycarbodiimide amine can suppress the reaction with the carboxyl group even after being added to the aqueous resin, and can improve the storage stability compared to the conventional resin cross-linking agent, even in a cold and dark place. Even if the storage state is about 40 ° C., excellent storage stability can be exhibited.

[Modified polycarbodiimidoamine]
The modified polycarbodiimide amine of the present invention is obtained by modifying a polycarbodiimide derived from an aromatic diisocyanate compound whose end is sealed with a hydrophilic compound with a secondary amine, and exhibits water solubility or water dispersibility.
The polycarbodiimide whose end is sealed with a hydrophilic compound may be synthesized by reacting an aromatic diisocyanate compound with a hydrophilic compound to seal a part of the end and then polycarbodiimide, or aromatic diisocyanate. After the compound is polycarbodiimidized, it may be synthesized by reacting with a hydrophilic compound and sealing the end.

(Aromatic diisocyanate compound)
In the present invention, the polycarbodiimide is a polycarbodiimide derived from an aromatic diisocyanate compound, and the aromatic diisocyanate compound is polycarbodiimidized by, for example, decarboxylation condensation reaction as described later.
Here, the aromatic diisocyanate compound refers to an isocyanate compound in which two isocyanate groups present in the molecule are directly bonded to an aromatic ring.
Aromatic polycarbodiimides derived from aromatic diisocyanate compounds have superior heat resistance compared to aliphatic polycarbodiimides. For example, when polycarbodiimide is used as a resin crosslinking agent in a coating composition, dissociation of amines Considering the step of forming the coating film because the temperature is close to the temperature at which the coating film is formed, aromatic polycarbodiimide is preferred from the viewpoint of excellent heat resistance.

Specific examples of the aromatic diisocyanate compound include, for example, 4,4′-diphenylmethane diisocyanate, 4,4′-diphenyl ether diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 3,3′-dimethoxy-4,4′-biphenyl. Diisocyanate, o-tolidine diisocyanate, naphthylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 3,3′-dimethyl-4,4′-diphenyl ether diisocyanate, 3,3′-dimethyl-4 , 4'-diphenyl ether diisocyanate and the like. These may be used alone or in combinations of two or more.
Among these, 4,4′-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, and 2,6-tolylene diisocyanate are highly versatile industrial materials, and the resulting polycarbodiimide has high reactivity. This is preferable.

(Hydrophilic compound)
The hydrophilic compound for sealing the end of polycarbodiimide is not particularly limited as long as it is hydrophilic and is a hydrophilic organic compound having reactivity with an isocyanate group at the end of an aromatic diisocyanate compound or polycarbodiimide, for example, The compound represented by the following general formula (a)-(e) can be mentioned.

Examples of the hydrophilic organic compound include polyalkylene oxides end-capped with an alkoxy group or a phenoxy group represented by the following general formula (a).
R ¹ —O— (CH ₂ —CHR ² —O) _m —H (a)
In formula (a), R ¹ represents an alkyl group having 1 to 4 carbon atoms or a phenyl group, R ² represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and m is an integer of 1 to 30.
Examples of the alkyl group having 1 to 4 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, s-butyl group, isobutyl group, and t-butyl group.

Examples of the hydrophilic organic compound include dialkylamino alcohols represented by the following general formula (b).
(R ³ ) ₂ —N—CH ₂ —CHR ⁴ —OH (b)
In formula (b), R ³ represents an alkyl group having 1 to 4 carbon atoms, and R ⁴ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. The alkyl group having 1 to 4 carbon atoms has the same meaning as described above.

Examples of the hydrophilic organic compound include hydroxycarboxylic acid alkyl esters represented by the following general formula (c).
R ⁵ —O—CO—CHR ⁶ —OH (c)
In formula (c), R ⁵ represents an alkyl group having 1 to 3 carbon atoms, and R ⁶ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.
Examples of the alkyl group having 1 to 3 carbon atoms include a methyl group, an ethyl group, a propyl group, and an isopropyl group.

Examples of the hydrophilic organic compound include dialkylaminoalkylamines represented by the following general formula (d).
(R ⁷ ) ₂ —N—R ⁸ —NH ₂ (d)
In formula (d), R ⁷ represents an alkyl group having 1 to 4 carbon atoms, and R ⁸ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. The alkyl group having 1 to 4 carbon atoms has the same meaning as described above.

Examples of the hydrophilic organic compound include alkyl sulfonates represented by the following general formula (e).
_{^{HO-R 9 -SO 3 M ···}} (e)
In the formula (e), R ⁹ represents an alkylene group having 1 to 10 carbon atoms, and M represents an alkali metal such as Na or K.
Examples of the alkylene group having 1 to 10 carbon atoms include methylene group, ethylene group, propylene group, tetramethylene group, pentamethylene group, hexamethylene group, heptamethylene group, octamethylene group, nonamethylene group, decamethylene group and the like. Can be mentioned.
As the hydrophilic compound represented by the general formulas (a) to (e), one kind may be used alone, or two or more kinds may be used in combination.

When the degree of polymerization of polycarbodiimide is large, or when the ratio of water in the aqueous medium to be dissolved or dispersed used when polycarbodiimide is used as a resin crosslinking agent is high as described later, polycarbodiimide is dissolved or dispersed in an aqueous medium. When it is necessary to impart a higher hydrophilicity, a more preferred hydrophilic compound is an alkoxy group or phenoxy represented by the general formula (a) having a high hydrophilicity among the general formulas (a) to (e). It is a polyalkylene oxide end-capped with a group.
Specific examples of the polyalkylene oxide represented by the general formula (a) include polyethylene glycol monomethyl ether, polyethylene glycol monoethyl ether, polypropylene glycol monomethyl ether, polypropylene glycol monoethyl ether, polypropylene glycol monophenyl ether, and the like. In particular, polyethylene glycol monomethyl ether is suitable.

(End-capping agents other than hydrophilic compounds)
In addition to the above hydrophilic compound, a compound that can react with a terminal isocyanate group and that alone does not impart sufficient hydrophilicity to polycarbodiimide can be used in combination as a terminal blocking agent. The end-capping agent other than the hydrophilic compound is mixed with the hydrophilic compound and used in a range that exhibits hydrophilicity in which polycarbodiimide can be dissolved in an aqueous medium.

The end-capping agent other than the hydrophilic compound is not particularly limited as long as it is a compound having reactivity with an isocyanate group at the end of an aromatic diisocyanate compound or polycarbodiimide.
Examples of end-capping agents other than hydrophilic compounds include the above-mentioned reactive aliphatic compounds, aromatic compounds, alicyclic compounds, and the like, specifically, methanol, ethanol, phenol having —OH group. , cyclohexanol, N- methyl ethanolamine; = diethylamine with an NH group, dicyclohexylamine and the like; butylamine with -NH ₂ group, cyclohexylamine and the like; propionic acid having a -COOH group, benzoic acid, cyclohexanecarboxylic acid, and the like; Examples include compounds having an —SH group, such as ethyl mercaptan, allyl mercaptan, thiophenol, or an epoxy group.
Terminal blockers other than the hydrophilic compound may be used alone or in combination of two or more.

Moreover, in order to seal the terminal of polycarbodiimide and control the degree of polymerization, monoisocyanate may be used as the terminal blocking agent. As monoisocyanate, for example, phenyl isocyanate, p-nitrophenyl isocyanate, p- and m-tolyl isocyanate, p-formylphenyl isocyanate, p-isopropylphenyl isocyanate and the like can be used. In particular, p-isopropylphenyl isocyanate is preferably used.
The said monoisocyanate may be used individually by 1 type, and may be used in combination of 2 or more type.

(Reaction of terminal isocyanate group with end capping agent other than hydrophilic compound and hydrophilic compound)
The reaction between the terminal isocyanate group and the end capping agent other than the hydrophilic compound and the hydrophilic compound is about 25 ° C. with the aromatic diisocyanate compound or polycarbodiimide and the end capping agent other than the hydrophilic compound and the hydrophilic compound. It proceeds easily by mixing at room temperature, and may be heated as necessary. Moreover, it is preferable to react in inert gas atmosphere, and what is necessary is just to use terminal blocking agents other than a hydrophilic compound and hydrophilic compound equivalent to the terminal isocyanate group to seal.

  In addition, as a method for obtaining a water-dispersible polycarbodiimide, a method of emulsifying using a dispersant, for example, a polymer-type dispersant, a surfactant-type dispersant, an inorganic-type dispersant (ultrasonic wave, stirring), or an aqueous polyurethane In addition, a method of mixing with a hydrophilic polymer such as water-based polycarbodiimide and simultaneously dispersing in water can also be used.

(Polycarbodiimidization)
In the present invention, polycarbodiimide is a polycarbodiimide derived from an aromatic diisocyanate compound, and can be produced by various methods using an aromatic diisocyanate compound as a raw material. For example, a process for producing an isocyanate-terminated polycarbodiimide by a decarboxylation condensation reaction involving decarbonation of an aromatic diisocyanate compound (US Pat. No. 2,941,956, Japanese Patent Publication No. 47-33279, J. Org. Chem, 28 2069-2075 (1963), Chemical Review 1981, Vol. 81, No. 4, p619-621, and the like.

The decarboxylation condensation reaction of the aromatic diisocyanate compound proceeds in the presence of a carbodiimidization catalyst. Examples of the carbodiimidization catalyst include 1-phenyl-2-phospholene-1-oxide, 3-methyl-1-phenyl-2-phospholene-1-oxide, 1-ethyl-2-phospholene-1-oxide, 3 -Methyl-2-phospholene-1-oxide and phospholene oxides such as these 3-phospholene isomers can be mentioned, and among these, from the viewpoint of reactivity, 3-methyl-1-phenyl-2- Phosphorene-1-oxide is preferred.
The amount of the carbodiimidization catalyst is usually 0.1 to 1.0% by mass with respect to the aromatic diisocyanate compound used for carbodiimidization.

  The decarboxylation condensation reaction of the aromatic diisocyanate compound can be performed without a solvent or in a solvent. Solvents that can be used include alicyclic ethers such as tetrahydroxyfuran, 1,3-dioxane and dioxolane: aromatic hydrocarbons such as benzene, toluene, xylene and ethylbenzene: chlorobenzene, dichlorobenzene, trichlorobenzene, perchlene, trichloroethane, Halogenated hydrocarbons such as dichloroethane, cyclohexanone and the like. These may be used alone or in combinations of two or more. Among these, tetrahydroxyfuran is preferable.

Although it does not specifically limit as temperature in the said decarboxylation condensation reaction, Preferably it is 40-200 degreeC, More preferably, it is 50-130 degreeC.
When the reaction is carried out in a solvent, it is preferably from 40 ° C. to the boiling point of the solvent. Moreover, when reacting in a solvent, as a density | concentration of an aromatic diisocyanate compound, Preferably it is 5-55 mass%, More preferably, it is 5-20 mass%. If the concentration of the aromatic diisocyanate compound is 5% by mass or more, it will not take too much time to synthesize polycarbodiimide, and if it is 55% by mass or less, gelation during the reaction can be suppressed.
Moreover, as solid content concentration at the time of performing reaction, Preferably it is 5-50 mass% of the total amount of a reaction system, More preferably, it is 20-30 mass%.

  In particular, when an aromatic diisocyanate compound is reacted with a hydrophilic compound and an end-capping agent other than a hydrophilic compound, the end is first capped, and then a catalyst is added to perform carbodiimidization, the temperature of the carbodiimidization reaction Is preferably 40 to 180 ° C, more preferably 50 to 100 ° C, and the concentration of the aromatic diisocyanate compound in the solvent is preferably 5 to 55% by mass, more preferably 35 to 50% by mass. is there.

  The polymerization degree of the polycarbodiimide used in the present invention is preferably 2 to 12 and more preferably 3 to 9 from the viewpoint that the polycarbodiimide does not gel in an aqueous medium and becomes water-soluble or water-dispersible. It is.

(Amine modification)
A secondary amine is used as the compound that modifies the polycarbodiimide whose end is sealed with a hydrophilic compound or is sealed with a hydrophilic compound and a terminal sealing agent other than the hydrophilic compound.
In the primary amine, since two active hydrogens can react with two separate carbodiimide groups, they become crosslinking points, and the carbodiimide resin solution is gelled. In addition, the tertiary amine does not cause an addition reaction with a carbodiimide group, but exhibits a catalytic action for activating the crosslinking reaction of the carbodiimide group, and in this case, the solution is gelled. For the above reasons, secondary amines having only one active hydrogen group are preferred.

Furthermore, in the present invention, among the secondary amines, those in which the hydrocarbon group of the secondary amine has 3 carbon atoms are preferred.
When the number of carbon atoms of the hydrocarbon group of the secondary amine is 2 or less, the amine is hardly detached during the heat treatment, and when the amine is not detached, the performance of the coating film may be deteriorated. When the number of carbon atoms is 4 or more, the boiling point of the amine is high, so that the amine desorbed by the heat treatment does not volatilize and tends to remain, causing deterioration in the performance of the coating film. Moreover, since the remaining amine reacts with the carbodiimide group again after the heat treatment, the ratio of the carbodiimide group to be regenerated decreases, and the reactivity decreases.

For the above reasons, amines which are secondary amines and have a hydrocarbon group with 3 carbon atoms are preferred, and among them, di-n-propylamine and diisopropylamine are more preferred industrially.
Compared to di-n-propylamine in which the hydrocarbon group bonded to the N atom is a straight chain, diisopropylamine is bulky and has a large steric hindrance, so that the amine is easily detached during heating. In addition, since the boiling point of each amine is 84 ° C. for diisopropylamine and 107 ° C. for di-n-propylamine, it eliminates residual amine that causes recombination reaction with carbodiimide groups and degradation of coating film performance. Therefore, diisopropylamine is more preferable.

The amine modification of the polycarbodiimide can be performed without a solvent, but the polycarbodiimide is mixed with an aqueous solvent, and a secondary amine is added to the carbodiimide group so as to have a predetermined equivalent amount, followed by stirring. Can be synthesized easily.
The amount of secondary amine added in the case of using an aqueous solvent is preferably 1 to 2 equivalents relative to 1 equivalent of a carbodiimide group, because the amount of excess amine is small, and the amine is easily dissipated during heat treatment. More preferably, it is 1-1.5 equivalent.
The reaction temperature for amine modification is preferably room temperature (about 25 ° C.) or 40 to 120 ° C. from the viewpoint of suppressing the reaction rate and side reactions during modification.
The modification is preferably carried out with stirring, and the reaction time varies depending on the temperature, but is preferably about 0.1 to 2 hours.

The aqueous solvent used in the amine modification reaction may be water alone or a mixed solvent with a hydratable liquid compound.
Examples of hydratable liquid compounds include polyalkylene glycols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, and dipropylene glycol monomethyl ether. Monoalkyl ethers; polyalkylene glycol dialkyl ethers such as diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, dipropylene glycol dimethyl ether; ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate , Polyalkylene glycol monoalkyl ether acetates such as diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate; polyalkylene glycol diesters such as ethylene glycol diacetate and propylene glycol diacetate Acetates; Polyalkylene glycol monophenyl ethers such as ethylene glycol monophenyl ether and propylene glycol monophenyl ether; Monoalcohols such as propanol, butanol, hexanol and octanol, N-methyl-2-pyrrolidone (NMP), N- N-substituted such as ethyl-2-pyrrolidone (NEP) Bromide like; 2,2,4-trimethyl-1,3-pentanediol mono-isobutyrate, and the like. These may be used alone or in combination of two or more.

[Resin cross-linking agent]
The present invention also provides a resin cross-linking agent for an aqueous resin containing the polycarbodiimide amine-modified product described above.
The resin crosslinking agent is obtained by dissolving or dispersing a polycarbodiimide amine-modified product in an aqueous medium.
The solid content concentration of the modified polycarbodiimide amine in the aqueous medium is preferably 10 to 50% by mass from the viewpoint of ease of use as a resin crosslinking agent in consideration of the physical properties of the coating film.

It does not specifically limit as said aqueous medium, For example, the mixed solvent of water and water, and another solvent can be mentioned. The other solvent is not particularly limited as long as it is compatible with water. For example, hydrocarbons (for example, xylene or toluene), alcohols (for example, methyl alcohol, n-butyl alcohol, isopropyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, propylene glycol, 2- (2-n-butoxyethoxy) ethanol, ethers (eg, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monoethyl ether) 3-methyl-3-methoxybutanol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether), ketones (for example, methyl isobutyl ketone, cyclohexane Sanone, isophorone, acetylacetone), esters (for example, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate), and mixtures thereof, etc. These may be used alone or in combination of two or more. May be used in combination.
The aqueous medium is preferably a complete aqueous system composed only of water from the viewpoint of the environment.

(Amine dissociation reaction)
The modified polycarbodiimide amine of the present invention can exhibit excellent stability even in an aqueous solution state because a highly reactive carbodiimide group is modified to a guanidine group by amine modification. When added to the aqueous resin as a resin crosslinking agent, the crosslinking reaction is suppressed and the storage stability is excellent.
In addition, the polycarbodiimide amine-modified product in the resin cross-linking agent is converted into the original polycarbodiimide by dissociating the amine by heat treatment and returning to the carbodiimide group.
On the other hand, the secondary amine generated by dissociation volatilizes and therefore hardly remains in the polycarbodiimide.
In the modified polycarbodiimide amine, the amine is dissociated by the heat treatment as described above, but the dissociation start temperature is about 120 ° C. Diisopropylamine has a boiling point of 84.1 ° C and di-n-propylamine has a temperature of 107 ° C. From the viewpoint of volatilizing and removing the secondary amine generated by dissociation and the dissociation, a preferable heating temperature is 120 to 180 ° C.

(Crosslinking reaction of carbodiimide)
As described above, in the modified polycarbodiimide amine, the amine dissociates and returns to the carbodiimide group to become the original polycarbodiimide, so that the carboxyl group of the aqueous resin and the carbodiimide group of the polycarbodiimide may undergo a crosslinking reaction. it can.
The carbodiimide group from which the amine has been dissociated and the carboxyl group that the aqueous resin has can be cross-linked by the heat of heat treatment during amine dissociation. Moreover, when there exists an uncrosslinked reactive group after the heat processing at the time of dissociation, a crosslinking reaction can be accelerated | stimulated by adding heat processing. The preferable heating temperature when adding the heat treatment is 60 to 150 ° C, more preferably 80 to 120 ° C.

The aqueous resin suitable for the resin cross-linking agent of the present invention is not particularly limited as long as it is water-soluble or water-dispersible and has a cross-linking reaction with a carbodiimide group.
Specific examples include water-soluble or water-dispersible urethane resins having a carboxyl group in the molecule, acrylic resins, polyester resins, etc. Among them, urethane resins and acrylic resins are preferable. These aqueous resins may be used alone or in combination of two or more.

  Examples of water-soluble or water-dispersible urethane resins having a carboxyl group in the molecule include, for example, polyisocyanate compounds, carboxyl group-containing polyols and / or amino acids, and carboxyl group-containing urethane prepolymers obtained from polyols. And a resin obtained by reacting with a basic organic compound and a chain extender in the presence of an organic solvent or water and then removing the solvent under reduced pressure.

Examples of water-soluble or water-dispersible acrylic resins having a carboxyl group in the molecule include polymerizable unsaturated carboxylic acids or anhydrides thereof, (meth) acrylic acid esters, and acrylic monomers other than (meth) acrylic acid. And acrylic resin obtained by copolymerizing α-methylstyrene, vinyl acetate or the like, if necessary, by a polymerization method such as emulsion polymerization, solution polymerization, bulk polymerization or the like.
Specific examples of polymerizable unsaturated carboxylic acids and anhydrides thereof include (meth) acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and anhydrides thereof.
Examples of (meth) acrylic esters include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and 2-hydroxy (meth) acrylate. And ethyl.
Examples of acrylic monomers other than (meth) acrylic acid include (meth) acrylamide and (meth) acrylonitrile.

  Examples of water-soluble or water-dispersible polyester resins having a carboxyl group in the molecule include, for example, chain extension by selective monoesterification reaction between glycol or polyester glycol having a hydroxyl group at the terminal and tetracarboxylic dianhydride. Polyester-type resin obtained by doing this.

The resin crosslinking agent of the present invention can be, for example, an aqueous resin composition mixed with an aqueous resin.
When it is set as the said aqueous resin composition, although the mixture ratio of each component is arbitrary, from points, such as balance of the physical property of the coating film obtained, and economical efficiency, a resin crosslinking agent is set to 0.1 mass with respect to 100 mass parts of aqueous resin. It is preferable to use it in the ratio of 5-15 mass parts, and it is more preferable to use it in the ratio of 1-10 mass parts.
In the aqueous resin composition, if necessary, various additive components such as pigments, fillers, leveling agents, surfactants, dispersants, plasticizers, ultraviolet absorbers, antioxidants, etc. It can mix | blend suitably.

By apply | coating an aqueous resin composition on a predetermined base material, a coating layer can be formed and a coating film can be obtained.
In this case, conventionally known methods can be appropriately used as the coating method, for example, brush coating, tampo coating, spray coating, hot spray coating, airless spray coating, roller coating, curtain flow coating, flow coating, dipping coating, A knife fudge coat or the like can be used. After forming the coating layer, heat treatment may be performed to promote the crosslinking reaction. There is no restriction | limiting in particular in the heat processing method, For example, the method using an electric heating furnace, an infrared heating furnace, a high frequency combustible path, etc. is employable.

Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely, the present invention is not limited to these. In the text below, “%” is based on mass unless otherwise specified.
Moreover, in the synthesis example, infrared absorption (IR) spectrum analysis was performed using FT-IR8200PC (made by Shimadzu Corporation).

[Example 1] TDI + PEGME + DIPA
(1) Tolylene diisocyanate partially terminal polyethylene glycol monomethyl ether sealing Tolylene diisocyanate (composition 80% 2,4-tolylene diisocyanate, 20% 2,6-tolylene diisocyanate) (TDI) 33.96 g and polyethylene glycol 33 g of monomethyl ether (PEGME) (molecular weight 550, trade name UNIOX M-550, manufactured by NOF Corporation) was put into a 300 mL separable flask and stirred at 25 ° C. for 1 hour under a reflux tube and a nitrogen stream. Thereafter, it was confirmed by infrared absorption (IR) spectrum measurement that the decrease of the isocyanate group having a wavelength of 2200 to 2300 cm ⁻¹ was stopped, and TDI partially sealed with PEGME was obtained.
(2) Carbodiimidization of TDI partially blocked at the end Following (1) above, 0.68 g of carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) was added to the flask, The mixture was stirred at 85 ° C. for 6 hours under a reflux tube and a nitrogen stream to obtain PEGME-terminated tolylenecarbodiimide (degree of polymerization = 5).
An absorption peak due to a carbodiimide group having a wavelength of around 2150 cm ⁻¹ was confirmed by infrared absorption (IR) spectrum measurement.
(3) Amine modification of carbodiimide 16.7 g of diisopropylamine (DIPA) was added to 66.96 g of the PEGME-terminated tolylene carbodiimide obtained in (2) above, and the mixture was stirred at 40 ° C. for 2 hours. It was confirmed by infrared absorption (IR) spectrum measurement that the peak due to the carbodiimide group having a wavelength of 2150 cm ⁻¹ had almost disappeared, and a polycarbodiimide amine-modified product whose ends were sealed with PEGME was obtained.

[Example 2] TDI + PEGME + DPA
In Example 1 (3), except that di-n-propylamine (DPA) was used instead of DIPA, the same procedure as in Example 1 was performed to obtain a modified polycarbodiimide amine whose ends were blocked with PEGME. .

[Example 3] MDI + PEGME + DIPA
(1) 4,4′-Diphenylmethane diisocyanate partially end-capped with polyethylene glycol monomethyl ether 37.54 g of 4,4′-diphenylmethane diisocyanate (MDI) and polyethylene glycol monomethyl ether (PEGME) (molecular weight 550, trade name UNIOX M -550, manufactured by NOF Corporation) was charged in a 300 mL separable flask and stirred at 25 ° C. for 1 hour under a reflux tube and a nitrogen stream. Then, it was confirmed by infrared absorption (IR) spectrum measurement that the decrease of the isocyanate group having a wavelength of 2200 to 2300 cm ⁻¹ stopped, and an MDI partially sealed with PEGME was obtained.
(2) Carbodiimidation of MDI partially blocked at the end Following (1) above, 0.38 g of carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) was added to the flask, The mixture was stirred at 85 ° C. for 6 hours under a reflux tube and a nitrogen stream to obtain PEGME-terminated 4,4′-diphenylmethanecarbodiimide (degree of polymerization = 5).
An absorption peak due to a carbodiimide group having a wavelength of around 2150 cm ⁻¹ was confirmed by infrared absorption (IR) spectrum measurement.
(3) Amine modification of carbodiimide 12.75 g of DIPA was added to 70.92 g of PEGME-terminated 4,4′-diphenylmethanediimide obtained in (2) above, and the mixture was stirred at 40 ° C. for 2 hours. It was confirmed by infrared absorption (IR) spectrum measurement that the peak due to the carbodiimide group having a wavelength of 2150 cm ⁻¹ had almost disappeared, and a polycarbodiimide amine-modified product whose ends were sealed with PEGME was obtained.

[Example 4] MDI + PEGME + DPA
The same procedure as in Example 3 was performed except that DPA was used in place of DIPA in (3) of Example 3 to obtain a modified polycarbodiimide amine whose ends were blocked with PEGME.

[Examples 5 to 8] Adjustment of resin cross-linking agent To each of the modified polycarbodiimide amines obtained in Examples 1 to 4, ion-exchanged water was added so that the solid content concentration would be 40% by mass, and 12 hours. A carbodiimide solution (resin cross-linking agent) that was made water by stirring as described above was obtained, and Examples 5 to 8 were used respectively.
[Comparative Examples 1 and 2] Adjustment of resin cross-linking agent The end-capped carbodiimide obtained in each of Example 1 (2) and Example 3 (2) was used, and ion-exchanged water was used as a solid concentration in each. Was added so as to be 40% by mass and stirred for 12 hours or more to obtain an aqueous carbodiimide solution (resin crosslinking agent), which were referred to as Comparative Examples 1 and 2, respectively.

<Measurement of shelf life>
For each of the resin crosslinking agents of Examples 5 to 8 and Comparative Examples 1 and 2, the number of days until solids were formed in the solution at room temperature (25 ° C.) and 40 ° C. was measured.
As a result of the measurement, in Examples 5 to 8, no solid matter was generated in the solution even when 40 days passed at both room temperature and 40 ° C.
On the other hand, in Comparative Examples 1 and 2, no solid matter was generated in the solution even after 40 days at room temperature, but a solid matter was generated in the solution in two weeks at 40 ° C.

<Pot life measurement>
Examples 5-8 and Comparative Examples 1-2, 0.5 g of resin crosslinking agent, urethane resin (trade name Sancure 776, manufactured by Noveon) 10 g, and acrylic resin (trade name Sancure HG-54C, manufactured by Rohm & Haas) 10 g, respectively. The aqueous resin composition was prepared by mixing.
With respect to the obtained aqueous resin composition, the number of days until solids were generated in the solution at room temperature (25 ° C.) and 40 ° C. was measured.
As a result of the measurement, in Examples 5 to 8, no solid matter was generated in the solution even when 40 days passed at both room temperature and 40 ° C.
On the other hand, in Comparative Examples 1 and 2, no solid matter was generated in the solution even after 40 days at room temperature, but a solid matter was generated in the solution in one month at 40 ° C.

(Preparation of test piece)
Examples 5-8 and Comparative Examples 1-2, 0.5 g of resin crosslinking agent, urethane resin (trade name Sancure 776, manufactured by Noveon) 10 g, and acrylic resin (trade name Sancure HG-54C, manufactured by Rohm & Haas) 10 g, respectively. The aqueous resin composition was prepared by mixing and stored at 40 ° C. for 1 month.
After storage, the aqueous coating composition was cast on an aluminum plate (200 mm × 100 mm × 1 mm) to a thickness of 20 μm to form a coating film, and thermally crosslinked at 150 ° C. for 30 minutes to prepare a test piece. .

<Rubbing test>
About the produced test piece, ethanol is used as a solvent and double rubbing is performed with a friction tester ER-1B (manufactured by Suga Test Instruments Co., Ltd.) at a load of 900 g / cm ² . The coating state was scored according to the following criteria and evaluated as a total score. The results are shown in Table 1.
(Whitening)
The whitening of the coating film after 100 rubbing was visually observed and evaluated. There are three levels of whitening: lightening, whitening, and darkening, and 10 points when no whitening occurs.
・ Lightening -2 points -Whitening -2 points, if it is whitened at the time of 10 rubbing times -2 points -Darkening -2 points, if it is whitened at the time of 10 rubbing times- 4 points (number of holes)
The rubbing frequency when the coating film had a hole was visually observed and evaluated.
・ 0-19 times 1 point ・ 20-39 times 2 points ・ 40-59 times 3 points ・ 60-79 times 4 points ・ 80-100 times 5 points (coating film residual ratio)
The area (%) of the remaining coating film after 100 times of rubbing is measured visually, and is 100% when there is no hole, and 0% when there is no coating film.
・ 0-19% 1 point ・ 20-39% 2 points ・ 40-59% 3 points ・ 60-79% 4 points ・ 80-100% 5 points (coating condition)
The state of the coating film was visually observed after 100 times of rubbing, and in a five-step evaluation, it was hard 10 points, soft (no whitening) 8 points, soft (whitening) 6 points, slightly melted 4 points, melted 2 points .

<Spot test>
About the prepared test piece, cotton (15 mm × 15 mm) moistened with the following target solvent or the like is left on the coating film for 1 hour (the cotton always keeps wet), and after 1 hour, the cotton is removed. The state of the coating film was removed and scored according to the score table shown in Table 2. Furthermore, in the state where the coating film was completely dried after removing the cotton, the appearance was observed again, and scored in the same manner, and the total score was obtained by adding the scores in the wet state. The results are shown in Tables 3-10.
(Target solvents, etc.)
・ Solvent 1: Sodium hydroxide aqueous solution (1% by mass)
・ Solvent 2: Methyl ethyl ketone ・ Solvent 3: 50% by mass ethanol aqueous solution ・ Solvent 4: 70% by mass isopropyl alcohol aqueous solution ・ Solvent 5: 1.4 mass% ammonia water ・ Detergent 1: Windex (glass cleaner manufactured by Johnson SC)
・ Detergent 2: FORMULA 409 (kitchen cleaner manufactured by The Clorox Company)
·water

From the above shell life test, it can be seen that the resin cross-linking agent containing the modified polycarbodiimide amine exhibits high storage stability itself, and from the pot life test, the resin cross-linking agent is also stable after addition to the aqueous resin. It turns out that it is excellent.
Also, from the rubbing test and spot test, the aqueous resin composition using the resin cross-linking agent of the present invention shows the same solvent resistance as the initial state even after storage, and is stable in storage even at about 40 ° C. It turns out that it is excellent.

  The modified polycarbodiimide amine of the present invention is water-soluble or water-dispersible, and can improve storage stability with respect to an aqueous resin, so that it is useful as a resin crosslinking agent for an aqueous resin.

Claims (7)

A resin crosslinking agent for an aqueous resin, comprising a water-soluble or water-dispersible polycarbodiimide amine-modified product obtained by modifying a polycarbodiimide derived from an aromatic diisocyanate compound whose end is sealed with a hydrophilic compound with a secondary amine. The resin crosslinking agent of Claim 1 whose polymerization degree of the said polycarbodiimide is 2-12. The aromatic diisocyanate compound, 4,4'-diphenylmethane diisocyanate is at least one selected from 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, resin crosslinking according to claim 1 or 2 Agent . The resin crosslinking agent according to any one of claims 1 to 3, wherein the secondary amine is di-n-propylamine or diisopropylamine. The resin crosslinking agent according to any one of claims 1 to 4, wherein the modified polycarbodiimide amine is dissolved or dispersed in an aqueous medium . The resin cross-linking agent according to any one of claims 1 to 5, wherein the aqueous resin is at least one selected from a water-soluble or water-dispersible urethane resin having a carboxyl group in the molecule, an acrylic resin, and a polyester resin. . An aqueous resin composition comprising the resin crosslinking agent according to any one of claims 1 to 6 and an aqueous resin.