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EP-4737498-A1 - MODIFIED BLOCKED POLYISOCYANATE, COATING COMPOSITION, COATING FILM, AND METHOD FOR FORMING A COATING FILM

EP4737498A1EP 4737498 A1EP4737498 A1EP 4737498A1EP-4737498-A1

Abstract

A modified blocked polyisocyanate, which is a blocked polyisocyanate modified with a hydroxyl group-containing quaternary ammonium salt (I) represented by the following formula (I).

Inventors

  • NOGUCHI, Shuto
  • YASUDA, AKIHIRO

Assignees

  • Tosoh Corporation

Dates

Publication Date
20260506
Application Date
20251029

Claims (10)

  1. A modified blocked polyisocyanate which is a blocked polyisocyanate modified with a hydroxyl group-containing quaternary ammonium salt (I) represented by the following formula (I): wherein, in the formula (I), R 1 and R 2 each independently represent a monovalent hydrocarbon group having 1 to 8 carbon atoms; R 3 represents a monovalent hydrocarbon group having 1 to 16 carbon atoms, optionally having an ether group, a thioether group, or a tertiary amino group; any two or three of R 1 to R 3 may be bonded together to form a ring; R 4 represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 8 carbon atoms; R 5 represents a divalent hydrocarbon group having 1 to 16 carbon atoms; and X - represents a monovalent anionic group.
  2. The modified blocked polyisocyanate according to claim 1, wherein the R 1 , the R 2 , and the R 3 each independently are a monovalent hydrocarbon group having 1 to 3 carbon atoms.
  3. The modified blocked polyisocyanate according to claim 1 or 2, wherein the anionic group is a fatty acid group having 1 to 12 carbon atoms, a monoalkyl carbonate group having an alkyl group having 1 to 8 carbon atoms, or a hydroxyl group.
  4. The modified blocked polyisocyanate according to any one of claims 1 to 3, comprising a structure derived from an aliphatic polyisocyanate having an aliphatic hydrocarbon group having 4 to 6 carbon atoms, or a derivative of the aliphatic polyisocyanate.
  5. The modified blocked polyisocyanate according to any one of claims 1 to 4, having at least one group selected from the group consisting of an isocyanate group blocked with an oxime-based blocking agent, an isocyanate group blocked with a pyrazole-based blocking agent, and an isocyanate group blocked with an imidazole-based blocking agent.
  6. The modified blocked polyisocyanate according to any one of claims 1 to 5, which is a reaction product of a blocked polyisocyanate having a free isocyanate group and the hydroxyl group-containing quaternary ammonium salt (I), or a derivative of the reaction product.
  7. A method for producing the modified blocked polyisocyanate according to any one of claims 1 to 6, the method comprising: reacting a blocked polyisocyanate having a free isocyanate group with the hydroxyl group-containing quaternary ammonium salt (I).
  8. A coating composition comprising a base agent and a curing agent, wherein the curing agent comprises the modified blocked polyisocyanate according to any one of claims 1 to 6.
  9. A coating film formed from the coating composition according to claim 8.
  10. A method for forming a coating film, the method comprising: applying the coating composition according to claim 8 to a substrate and curing by heating at 100 to 140 °C.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority from Japanese Patent Application No. 2024-193117, filed on November 1, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD The present disclosure relates to a modified blocked polyisocyanate, a coating composition, a coating film, and a method for forming a coating film. BACKGROUND Conventionally, polyisocyanates have been known as curing agents used in coating materials and the like. For example, polyurethane resin coating materials that combine a polyol and a polyisocyanate are known to have very excellent abrasion resistance, chemical resistance, and stain resistance. Coating materials that use a polyisocyanate as a curing agent are generally two-component compositions and include a base agent (e.g., a polyol) and a polyisocyanate. In two-component compositions, the base agent and the polyisocyanate are stored separately and are mixed for use at the time of coating. However, once mixed, the coating material cures in a short time, resulting in a short pot life, which has been a problem in terms of workability during coating. Furthermore, since polyisocyanates react easily with water, it has been impossible to use polyisocyanates in water-based coating materials such as electrodeposition coating materials. As a way to address these problems, a method of inactivating a polyisocyanate by reacting it with a blocking agent is known. The blocked polyisocyanate obtained by this method does not react with a base agent such as a polyol at room temperature, but when heated, the blocking agent dissociates to regenerate isocyanate groups, which then react with the base agent to form cross-linking. Therefore, according to the above method, the pot life is not limited, it becomes possible to prepare a coating material by mixing the base agent and the curing agent in advance, and the application of polyisocyanates to water-based coating materials also becomes possible. In coating materials that use a blocked polyisocyanate as a curing agent, a catalyst such as a quaternary ammonium salt (a deblocking catalyst) may be used to reduce the thermal energy required for the dissociation of the blocking agent (see Japanese Unexamined Patent Application Publication No. 2014-084426). SUMMARY Conventionally, the baking of coating materials has been performed at high temperatures of 150 °C or higher. However, in recent years, for the purpose of cost reduction, reduction of carbon dioxide emissions, suppression of deterioration of substrates due to heat, and the like during baking and coating, it has also been required to cure coating films at lower temperatures than before (for example, at a temperature of 140 °C or lower). Therefore, it is also important that the coating composition has good curability, that is, that it can form a coating film with good hardness and good gel fraction when a baking treatment is performed at a lower temperature than before. In this regard, the above-mentioned quaternary ammonium salt can improve the curability of a coating composition including a blocked polyisocyanate, making it possible to cure the coating film even at a temperature of 140 °C or lower. On the other hand, methods for obtaining a coating composition having excellent curability without adding a deblocking catalyst such as a quaternary ammonium salt are not well known. Some aspects of the present disclosure aim to provide a novel coating composition having excellent curability and a modified blocked polyisocyanate used in the coating composition. As a result of studies by the inventors of the present disclosure, it has been found that by using a blocked polyisocyanate modified with a hydroxyl group-containing quaternary ammonium salt (a modified blocked polyisocyanate), a coating composition having excellent curability can be obtained without adding a deblocking catalyst. The present disclosure is based on the findings of the inventors. The present disclosure provides at least the following [1] to [10]. [1] A modified blocked polyisocyanate which is a blocked polyisocyanate modified with a hydroxyl group-containing quaternary ammonium salt (I) represented by the following formula (I): wherein, in the formula (I), R1 and R2 each independently represent a monovalent hydrocarbon group having 1 to 8 carbon atoms; R3 represents a monovalent hydrocarbon group having 1 to 16 carbon atoms, optionally having an ether group, a thioether group, or a tertiary amino group; any two or three of R1 to R3 may be bonded together to form a ring; R4 represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 8 carbon atoms; R5 represents a divalent hydrocarbon group having 1 to 16 carbon atoms; and X- represents a monovalent anionic group.[2] The modified blocked polyisocyanate according to [1], wherein the R1, the R2, and the R3 each independently are a monovalent hydrocarbon group having 1 to 3 carbon atoms.[3] The