A carboxyl-terminated modified polyamide toughening agent, its preparation method and application

Abstract

This invention provides a carboxyl-terminated modified polyamide toughening agent, its preparation method, and its application. The carboxyl-terminated modified polyamide toughening agent comprises the following components in parts by weight: 55-70 parts of dimer acid, 5-12 parts of aliphatic diamine, 5-15 parts of aromatic dicarboxylic acid, 2-8 parts of modified monomer, 0.1-0.5 parts of catalyst, and 0.2-1 parts of antioxidant. The carboxyl-terminated modified polyamide toughening agent obtained by this invention, when applied to powder coatings, exhibits good flexibility and impact strength, achieving a balance between flexibility and rigidity; it has good boiling water resistance, without defects such as blistering, peeling, discoloration, or loss of gloss; and it has good solvent resistance, resulting in a high gloss retention rate for the coating.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and particularly relates to a carboxyl-terminated modified polyamide toughening agent, its preparation method and application. Background Technology

[0002] Powder coatings are widely used in home appliances, building materials, and automotive parts due to their environmental friendliness, high efficiency, and excellent performance. However, with the expansion of application areas, higher requirements are placed on the flexibility, impact resistance, and media resistance of powder coatings, especially in high-filler systems, low-gloss systems, or thick-film coatings, where problems such as brittleness and poor toughness are prone to occur.

[0003] To improve the toughness of powder coatings, existing technologies often employ the addition of toughening agents, such as carboxyl-terminated nitrile butadiene rubber, core-shell polymers, or thermoplastic elastomers. However, the added toughening agents are usually physically blended directly with the powder coating to achieve the toughening effect. But physical blending can lead to poor compatibility between the toughening agent and the matrix resin, resulting in weakened weather resistance of the coating. During long-term use, migration or precipitation can easily occur, leading to problems such as blistering, peeling, and discoloration.

[0004] Polyamide toughening agents have attracted attention due to their good flexibility and compatibility with resins; for example, dimer acid polyamides have been widely used in the hot melt adhesive field. However, conventional dimer acid polyamides suffer from problems such as easy crystallization and insufficient reactivity with epoxy / polyester systems. Direct application in powder coatings can lead to poor coating leveling, storage adhesion, or limited toughening efficiency. Although some studies have attempted to modify them by introducing flexible segments, this often comes at the cost of increased hygroscopicity and reduced water resistance, and they lack active functional groups that can participate in the curing reaction.

[0005] Therefore, developing a high-efficiency toughening agent that is compatible with powder coating matrix, can participate in the curing reaction to form chemical bonds, and has excellent water resistance and solvent resistance has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a carboxyl-terminated modified polyamide toughening agent, its preparation method, and its application, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides a carboxyl-terminated modified polyamide toughening agent, characterized in that it comprises the following components in parts by weight: 55-70 parts of dimer acid, 5-12 parts of aliphatic diamine, 5-15 parts of aromatic dicarboxylic acid, 2-8 parts of modified monomer, 0.1-0.5 parts of catalyst, and 0.2-1 parts of antioxidant.

[0008] As a further improvement, the modified monomer is a glycidyl ether containing unsaturated double bonds; the glycidyl ether containing unsaturated double bonds is at least one of allyl glycidyl ether or glycidyl methacrylate.

[0009] The structural formula of the dimer acid is as follows: As a further improvement, the viscosity of the dimer acid is 5000-7000 mPa·s; and the acid value is ≥190 mg KOH / g.

[0010] As a further improvement, the aliphatic diamine is at least one of ethylenediamine and hexamethylenediamine.

[0011] As a further improvement, the aromatic dicarboxylic acid is at least one of terephthalic acid and isophthalic acid.

[0012] As a further improvement, the mass ratio of the added dimer acid to the aromatic dicarboxylic acid is 4-7:1.

[0013] This invention introduces aromatic dicarboxylic acids to regulate the rigidity and symmetry of the molecular chain, forming a rigid-flexible block structure with the flexible long chain of the dimer acid. This effectively suppresses the crystallization tendency of polyamides and improves compatibility and storage stability.

[0014] As a further improvement, the catalyst is hypophosphoric acid or phosphoric acid; the antioxidant is at least one of antioxidant 1010 and antioxidant 168.

[0015] This invention also provides a method for preparing a carboxyl-terminated modified polyamide toughening agent, characterized by comprising the following steps: (1) Add dimer acid, aliphatic diamine, aromatic dicarboxylic acid and antioxidant to the reaction vessel, stir and mix under nitrogen atmosphere, then heat to 120-145℃, keep the temperature for 1-3h, and the reaction ends to obtain amide prepolymer; (2) Add the modified monomer and catalyst to step (1), stir evenly, and gradually raise the temperature to 180-210℃, keep the temperature for 3-5h, then reduce the pressure of the reaction system to -0.08~-0.10MPa, continue to keep the temperature for 1-2h, and when the reaction is finished, cool the reaction product to 80-100℃, granulate it through an extruder, and crush it to a particle size of 100-200 mesh to obtain the carboxyl-terminated modified polyamide toughening agent.

[0016] This invention also provides an application of a carboxyl-terminated modified polyamide toughening agent in powder coatings.

[0017] As a further improvement, the powder coating is a polyester powder coating or an epoxy-polyester hybrid powder coating.

[0018] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a carboxyl-terminated modified polyamide toughening agent, which, when applied to powder coatings, exhibits good flexibility and impact strength, achieving a balance between flexibility and rigidity; it has good boiling water resistance, with no defects such as blistering, peeling, discoloration, or loss of gloss; and it has good solvent resistance, resulting in a high gloss retention rate of the coating. This indicates that the carboxyl-terminated modified polyamide toughening agent prepared by this invention can form a stable chemically bonded crosslinking network with the coating matrix, thereby improving the density of the coating. This invention successfully prepared a carboxyl-terminated polyamide toughening agent with both reactive terminal carboxyl groups and auxiliary crosslinking side groups by introducing a glycidyl ether-modified monomer containing unsaturated double bonds. The carboxyl groups at the end of the toughening agent participate in the curing reaction of the powder coating to form a main crosslinking network and achieve chemical bonding. During the high-temperature curing process of the coating, the unsaturated double bonds of the toughening agent side chain can initiate free radical-assisted crosslinking or react with other components in the system to form a micro-crosslinking reinforced interface around the toughening agent. While significantly improving the flexibility and impact resistance of the coating, it can also maintain the appearance and gloss of the coating, which has significant industrial practical value. Detailed Implementation

[0019] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0020] In the following examples, all the monomers and related reagents used were commercially available. Dimer acid was purchased from Greenlink (Jining) Chemical Technology Co., Ltd.; polyethylene glycol diglycidyl ether was purchased from Hubei Huiheyuan Chemical Co., Ltd., model DGEG; polyester resin was a commercially available product of our company, model P3902; leveling agent was purchased from DKSH International Chemical Trading (Shanghai) Co., Ltd., model FS444; and curing agent was purchased from Jiangsu Minglin Chemical Technology Co., Ltd., model TGIC.

[0021] Example 1 The preparation of carboxyl-terminated modified polyamide toughening agents includes the following steps: (1) Add 60 parts of dimer acid, 10 parts of hexamethylenediamine, 8 parts of isophthalic acid and 0.6 parts of antioxidant 1010 to the reactor, stir and mix under nitrogen atmosphere, then heat to 135℃ and keep the temperature for 2.5h to obtain amide prepolymer; (2) Add 5 parts of allyl glycidyl ether and 0.2 parts of hypophosphoric acid to step (1), stir evenly, heat to 200°C, keep the temperature for 4 hours, continuously drain the water generated during the reaction, then reduce the pressure of the reaction system to -0.1 MPa, continue to keep the temperature for 1.5 hours, the reaction ends, cool the reaction product to 90°C, granulate it through an extruder, and then crush it to 150 mesh to obtain the carboxyl-terminated modified polyamide toughening agent.

[0022] Example 2 (1) 65 parts of dimer acid, 12 parts of hexamethylenediamine, 10 parts of isophthalic acid, 0.25 parts of antioxidant 1010 and 0.25 parts of antioxidant 168 were added to the reactor and stirred and mixed under nitrogen atmosphere. Then the temperature was raised to 130°C and the reaction was kept at the temperature for 2.5 h to obtain amide prepolymer. (2) Add 6 parts glycidyl methacrylate and 0.3 parts hypophosphoric acid to step (1), stir evenly, heat to 190°C, keep the temperature for 4 hours, continuously drain the water generated during the reaction, then reduce the pressure of the reaction system to -0.1 MPa, continue to keep the temperature for 1 hour, the reaction ends, cool the reaction product to 90°C, granulate it through an extruder, and then crush it to 100 mesh to obtain carboxyl-terminated modified polyamide toughening agent.

[0023] Example 3 Preparation of carboxyl-terminated modified polyamide toughening agent: basically the same as in Example 1, except that 60 parts of dimer acid and 8 parts of isophthalic acid are replaced with 63 parts of dimer acid and 5 parts of isophthalic acid.

[0024] Comparative Example 1 Preparation of carboxyl-terminated modified polyamide toughening agent: basically the same as in Example 1, except that 5 parts of allyl glycidyl ether are not used.

[0025] Comparative Example 2 Preparation of carboxyl-terminated modified polyamide toughening agent: basically the same as in Example 1, except that 5 parts of allyl glycidyl ether are replaced with 5 parts of polyethylene glycol diglycidyl ether.

[0026] Comparative Example 3 Preparation of carboxyl-terminated modified polyamide toughening agent: basically the same as in Example 1, except that 60 parts of dimer acid are replaced with 60 parts of adipic acid.

[0027] Five parts of the carboxyl-terminated modified polyamide toughening agent prepared in Examples 1-3 and Comparative Examples 1-3 were mixed with 40 parts of polyester resin, 1 part of leveling agent, and 2 parts of curing agent to obtain modified polyester powder coating. The coating was then tested for flexibility, impact strength, boiling water resistance, and solvent resistance. The test methods are as follows: Flexibility (180° bending test): conducted according to GB / T 6742-2007, with a bending shaft diameter of 2 mm; Impact strength: Tested according to GB / T 1732-2020; Boiling water resistance: According to GB / T 1733-1993 Method B, immerse in 100℃ Grade III water for 2 hours, and observe whether there are defects such as blistering, peeling, discoloration, and loss of gloss on the coating surface. The coating is considered qualified if there are no obvious abnormalities on the surface. Solvent resistance: According to GB / T 23989-2023, the cured coating test panel was placed on a reciprocating wiping tester and wiped 100 times with a degreased cotton cloth soaked in methyl ethyl ketone at a speed of 1 swipe / second. The gloss (60°) of the coating was measured before and after wiping, and the gloss retention rate was calculated. Gloss retention rate (%) = (gloss after wiping / gloss before wiping) × 100%; The test results are shown in Table 1, and are as follows: Table 1 As shown in Table 1, the present invention provides a carboxyl-terminated modified polyamide toughening agent, which, when applied to powder coatings, exhibits good flexibility and impact strength, achieving a balance between flexibility and rigidity. The good boiling water resistance and high gloss retention of the coating indicate that the carboxyl-terminated modified polyamide toughening agent prepared in this invention forms a chemically bonded cross-linked network with the coating matrix, improving the density of the coating and effectively avoiding blistering and peeling problems caused by interfacial voids. This significantly improves the boiling water resistance and solvent resistance of the coating.

[0028] The test results of Example 1 and Comparative Examples 1-2 show that if allyl glycidyl ether is not added or conventional polyethylene glycol diglycidyl ether (without double bonds) is used, the resulting carboxyl-terminated modified polyamide toughening agent, when applied to coatings, produces coatings with good toughness, no cracking in the 180° bending test, and low impact strength. This indicates that the introduction of glycidyl ether containing unsaturated double bonds can initiate free radical-assisted crosslinking during the high-temperature curing process of the coating, forming a reinforced interface and thus improving the toughness of the coating. Furthermore, it can improve boiling water resistance and solvent resistance to a certain extent, while maintaining a good appearance. As can be seen from the test results of Example 1 and Comparative Example 3, if short-chain adipic acid is used instead of the dimer acid of the present invention, the toughness and impact strength of the modified polyamide toughening agent prepared and applied to the coating are reduced, and the boiling water resistance is severely deteriorated (a large number of bubbles and partial peeling). The gloss retention rate is also reduced to a certain extent. This indicates that the long-chain alkyl structure provided by the dimer acid in the present invention can enable the carboxyl-terminated modified polyamide toughening agent to have good flexibility and hydrophobicity, thereby improving the compatibility with the coating matrix and enhancing the interfacial bonding force.

[0029] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A carboxyl-terminated modified polyamide toughening agent, characterized in that, It contains the following components in parts by weight: 55-70 parts of dimer acid, 5-12 parts of aliphatic diamine, 5-15 parts of aromatic dicarboxylic acid, 2-8 parts of modified monomer, 0.1-0.5 parts of catalyst, and 0.2-1 parts of antioxidant.

2. The carboxyl-terminated modified polyamide toughening agent according to claim 1, characterized in that, The modified monomer is a glycidyl ether containing unsaturated double bonds; the glycidyl ether containing unsaturated double bonds is at least one of allyl glycidyl ether or glycidyl methacrylate.

3. The carboxyl-terminated modified polyamide toughening agent according to claim 1, characterized in that, The viscosity of the dimer acid is 5000-7000 mPa·s; the acid value is ≥190 mg KOH / g.

4. The carboxyl-terminated modified polyamide toughening agent according to claim 1, characterized in that, The aliphatic diamine is at least one of ethylenediamine and hexamethylenediamine.

5. The carboxyl-terminated modified polyamide toughening agent according to claim 1, characterized in that, The aromatic dicarboxylic acid is at least one of terephthalic acid and isophthalic acid.

6. The carboxyl-terminated modified polyamide toughening agent according to claim 1, characterized in that, The mass ratio of the added dimer acid to the aromatic dicarboxylic acid is 4-7:

1.

7. The carboxyl-terminated modified polyamide toughening agent according to claim 1, characterized in that, The catalyst is hypophosphoric acid or phosphoric acid; the antioxidant is at least one of antioxidant 1010 and antioxidant 168.

8. A method for preparing a carboxyl-terminated modified polyamide toughening agent according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Add dimer acid, aliphatic diamine, aromatic dicarboxylic acid and antioxidant to the reaction vessel, stir and mix under nitrogen atmosphere, then heat to 120-145℃, keep the temperature for 1-3h, and the reaction ends to obtain amide prepolymer; (2) Add the modified monomer and catalyst to step (1), stir evenly, and gradually raise the temperature to 180-210℃, keep the temperature for 3-5h, then reduce the pressure of the reaction system to -0.08~-0.10MPa, continue to keep the temperature for 1-2h, and when the reaction is finished, cool the reaction product to 80-100℃, granulate it through an extruder, and crush it to a particle size of 100-200 mesh to obtain the carboxyl-terminated modified polyamide toughening agent.

9. The application of a carboxyl-terminated modified polyamide toughening agent according to any one of claims 1-7 in powder coatings.

10. The application of a carboxyl-terminated modified polyamide toughening agent according to claim 9 in powder coatings, characterized in that, The powder coating is a polyester powder coating or an epoxy-polyester hybrid powder coating.

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