Process for the preparation of polyamino resins modified

Abstract

This invention discloses a process for preparing modified polyamine resin. The process includes: first, reacting polytetramethylene ether glycol with isophorone diisocyanate to prepare an NCO-terminated polyurethane prepolymer; then, premixing methylated melamine resin with bisphenol A type epoxy resin in a certain proportion; subsequently, adding the polyurethane prepolymer, a blocked sulfonic acid catalyst, an epoxy silane coupling agent, and a cosolvent while cooling, dispersing evenly, and curing at 100-120°C for 30-40 minutes to form an epoxy-polyurethane-amino resin interpenetrating network structure. The mass fractions of each component are: 60-80 parts of methylated melamine resin, 20-40 parts of epoxy resin, 15-25 parts of polyurethane prepolymer, 0.5-1.2 parts of catalyst, and 0.5-2 parts of coupling agent. This invention reduces the curing temperature of traditional amino resins from 150-180°C to 100-120°C, significantly reducing energy consumption and making it suitable for heat-sensitive substrates; at the same time, it greatly improves the resin's flexibility, impact resistance and adhesion, and is a single-component latent curing system with excellent storage stability.

Description

Technical Field

[0001] This invention relates to the field of polyamine resin preparation technology, and in particular to a modified polyamine resin preparation process. Background Technology

[0002] Polyamino resins, especially methyl etherified melamine-formaldehyde resins, are widely used in coatings, adhesives, composite materials and inks due to their excellent hardness, chemical resistance, heat resistance and gloss. They are often used as crosslinking agents in combination with alkyd resins, polyester resins or acrylic resins.

[0003] However, traditional polyurethane resins suffer from several common problems in practical applications, hindering their widespread adoption in high-performance applications. First, the curing temperature of existing polyurethane resins is generally high. For example, the effective crosslinking temperature of methyl etherified melamine resin under acid catalysis is typically 150–180°C. This high temperature not only leads to a significant increase in energy consumption but also limits the direct coating or bonding of the resin to heat-sensitive substrates (such as wood-plastic composites, polycarbonate, and ABS plastics), forcing manufacturers to use multiple processes or low-temperature primer transition layers, increasing process complexity and cost. Second, the crosslinked network formed after curing of traditional polyurethane resins is dense and overly rigid, resulting in low elongation at break (typically below 2%) and poor impact resistance. Coatings or adhesive layers are prone to cracking or peeling when subjected to mechanical impact or bending. This brittleness severely affects its application life in dynamically stressed workpieces (such as automotive interior parts and sheet metal rolls) and packaging materials requiring a certain degree of flexibility. Furthermore, conventional polyamine resins exhibit insufficient adhesion to substrates such as metals, glass, and engineering plastics, with cross-cut adhesion ratings typically ranging from 2 to 3 (out of 0). They are particularly prone to interfacial debonding in humid and hot environments. While existing technologies have attempted to add silane coupling agents or primers, poor compatibility or incompatible reactivity between the coupling agent and the resin system often results in limited adhesion improvement and poor batch-to-batch stability. In addition, methods such as external plasticizers, the introduction of flexible segments, or elastomer blends have been reported to lower curing temperatures or improve flexibility. However, external plasticizers are prone to migration and precipitation, leading to coating performance degradation over time; simple elastomer blends often exhibit macroscopic phase separation, affecting transparency and mechanical uniformity. Some studies have also used epoxy resins to modify amino resins, which has improved adhesion to some extent, but the curing temperature remains high, and the improvement in brittleness is not significant.

[0004] In summary, developing a polyamine resin modification process that can achieve low-temperature curing, significant toughening, enhanced adhesion, and maintain the latent curing characteristics of single components is of great significance for expanding its application range, improving product performance, and reducing manufacturing costs. Summary of the Invention

[0005] Therefore, it is necessary to provide a modified polyamine resin preparation process to address the technical problem of insufficient comprehensive performance of existing polyamine resins.

[0006] A process for preparing modified polyamine resin, comprising the following steps: S1 Preparation of NCO-terminated polyurethane prepolymer: Polytetramethylene ether glycol and isophorone diisocyanate are reacted at 70-90℃ for 1.5-3h under nitrogen protection to obtain a polyurethane prepolymer with an NCO content of 3.0-4.0%. S2 Preparation of epoxy-amino resin premix: Mix methyl etherified melamine resin and bisphenol A type epoxy resin at a mass ratio of (60-80):(20-40) and stir at 70-90℃ for 20-40 min to obtain a clear premix; Construction of S3 ternary blend and latent curing system: Cool to 50-60℃, add the polyurethane prepolymer obtained in step S1, blocked sulfonic acid catalyst, epoxy silane coupling agent and cosolvent to the premix, disperse at high speed until uniform and transparent, and control the pH value to 6.5-7.0. S4 Crosslinking and Curing: After coating or molding the mixture obtained in step S3, heat and cure at 100-120℃ for 30-40 minutes to form an epoxy-polyurethane-amino resin interpenetrating network structure. The components, by weight based on solid content, are as follows: 60-80 parts of methylated melamine resin, 20-40 parts of bisphenol A epoxy resin, 15-25 parts of polyurethane prepolymer, 0.5-1.2 parts of blocked sulfonic acid catalyst, 0.5-2 parts of epoxy silane coupling agent, and an appropriate amount of cosolvent to adjust the solid content to 50-60%.

[0007] In one embodiment, the degree of methyl etherification of the melamine resin is ≥90%, and its number average molecular weight is 400-600.

[0008] In one embodiment, the epoxy equivalent of the bisphenol A type epoxy resin is 184-194 g / eq.

[0009] In one embodiment, the polyurethane prepolymer has a mass ratio of polytetramethylene ether glycol to isophorone diisocyanate of (2.5-3.5):1, and the number average molecular weight of polytetramethylene ether glycol is 1800-2200.

[0010] In one embodiment, the unblocking temperature of the blocked sulfonic acid catalyst is 100-130°C, its pH value at room temperature is 6.0-7.0, and its latency in the mixture of step S3 is ≥6 months.

[0011] In one embodiment, the epoxy silane coupling agent is pre-hydrolyzed with a water / alcohol mixture before use to convert its methoxy group into silanol groups.

[0012] In one embodiment, the co-solvent is a mixture of propylene glycol methyl ether acetate and n-butanol in a volume ratio of 1:1. The mixed solvent is miscible with methyl etherified melamine resin, bisphenol A type epoxy resin and polyurethane prepolymer, and has a boiling point range of 110-150°C.

[0013] In one embodiment, hindered amine light stabilizer and / or phenolic antioxidant are added in step S3, in amounts of 0.2-0.5 parts and 0.1-0.3 parts, respectively.

[0014] In one embodiment, the curing temperature of step S4 is 50-80°C lower than the conventional curing temperature of the unmodified methylated melamine resin; and the elongation at break of the cured product coating obtained by this process is 8-12%, the impact strength is ≥40 kg·cm, and the cross-cut adhesion is grade 0-1.

[0015] In one embodiment, the modified preparation process further includes adding 1-3 parts of fumed silica nanoparticles in step S3, wherein the primary particle size of the fumed silica nanoparticles is 7-40 nm and the specific surface area is [missing information]. .

[0016] The aforementioned modified polyamine resin preparation process introduces an NCO-terminated polyurethane prepolymer and bisphenol A type epoxy resin, along with methylated melamine resin to construct a ternary blend system, thereby improving the overall performance of the polyamine resin. Firstly, under the action of a blocked sulfonic acid catalyst, it forms an interpenetrating network structure at 100-120℃, significantly reducing the 150-180℃ high-temperature curing requirements of traditional amino resins, thus saving energy and broadening the applicability to heat-sensitive substrates. Secondly, the synergistic effect of the flexible segments of polyurethane and the rigid crosslinking points of epoxy resin effectively overcomes the inherent brittleness of traditional amino resins, resulting in a cured product with both high hardness and excellent toughness, with significantly improved elongation at break and impact strength. Thirdly, the introduction of an epoxy-based silane coupling agent enhances the chemical bonding ability of the resin with various substrates, improving adhesion from the conventional 2-3 grade to 0-1 grade, significantly improving the long-term service reliability of coatings or adhesive layers. Fourth, the blocked sulfonic acid catalyst is neutral at room temperature, giving the system excellent storage stability. Its high solids content design also reduces the amount of volatile organic solvents used, aligning with green manufacturing trends. Finally, the entire process is a single-component latent curing system, eliminating the need for on-site mixing during application, simplifying the operation process, and ensuring compatibility with existing coating equipment. Detailed Implementation

[0017] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying questions. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0018] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0019] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0020] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0021] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0022] This invention discloses a process for preparing modified polyamine resin, which includes the following steps: S1 Preparation of NCO-terminated polyurethane prepolymer: Polytetramethylene ether glycol and isophorone diisocyanate are reacted at 70-90℃ for 1.5-3h under nitrogen protection to obtain a polyurethane prepolymer with an NCO content of 3.0-4.0%. S2 Preparation of epoxy-amino resin premix: Mix methyl etherified melamine resin and bisphenol A type epoxy resin at a mass ratio of (60-80):(20-40) and stir at 70-90℃ for 20-40 min to obtain a clear premix; Construction of S3 ternary blend and latent curing system: Cool to 50-60℃, add the polyurethane prepolymer obtained in step S1, blocked sulfonic acid catalyst, epoxy silane coupling agent and cosolvent to the premix, disperse at high speed until uniform and transparent, and control the pH value to 6.5-7.0. S4 Crosslinking and Curing: After coating or molding the mixture obtained in step S3, heat and cure at 100-120℃ for 30-40 minutes to form an epoxy-polyurethane-amino resin interpenetrating network structure. The components, by weight based on solid content, are as follows: 60-80 parts of methylated melamine resin, 20-40 parts of bisphenol A epoxy resin, 15-25 parts of polyurethane prepolymer, 0.5-1.2 parts of blocked sulfonic acid catalyst, 0.5-2 parts of epoxy silane coupling agent, and an appropriate amount of cosolvent to adjust the solid content to 50-60%.

[0023] This embodiment fully defines the four-step process from prepolymer synthesis, premixing, blending to low-temperature curing, thereby achieving: (1) Low temperature curing (100-120℃): The low temperature reaction of polyurethane NCO and epoxy hydroxyl compensates for the high temperature self-condensation requirement of amino resin, saving more than 30% energy compared with traditional process, and can be coated on heat-sensitive substrates such as wood-plastic and PC / ABS.

[0024] (2) Interpenetrating network toughening: Epoxy-polyurethane-amino resin forms an IPN structure, which increases the elongation at break to 8-12% and the impact strength to ≥40kg·cm, overcoming the defect of high brittleness of traditional amino resin.

[0025] (3) Enhanced adhesion: The epoxy silane coupling agent and the epoxy ether bond work synergistically to improve the adhesion from level 2-3 to level 0-1.

[0026] (4) Single-component latent curing: The closed catalyst is inactive at room temperature, has a storage stability of ≥6 months, and is easy to construct.

[0027] Furthermore, the degree of methyl etherification of the methylated melamine resin is ≥90%, and its number-average molecular weight is 400-600. A high degree of methyl etherification reduces hydroxymethyl self-condensation, improves compatibility with epoxy and polyurethane, and prevents phase separation; an appropriate molecular weight ensures a balance between reactivity and film-forming properties, thereby obtaining a coating with high transparency and high hardness.

[0028] Furthermore, the epoxy equivalent of the bisphenol A type epoxy resin is 184-194 g / eq. Too low an epoxy equivalent will reduce flexibility, while too high an equivalent will result in insufficient reactivity. This parameter allows for the optimal reaction rate with polyurethane NCO, while simultaneously enabling ether exchange with amino resins, further reducing the curing activation energy.

[0029] Furthermore, in the polyurethane prepolymer, the mass ratio of polytetramethylene ether glycol to isophorone diisocyanate is (2.5-3.5):1, and the number average molecular weight of polytetramethylene ether glycol is 1800-2200. This ratio ensures that the NCO content of the prepolymer is stable at 3.0-4.0%, with a suitable molecular weight: the PTMEG soft segments provide flexibility for toughening, and sufficient NCO groups to react with the epoxy hydroxyl groups. Exceeding this range will lead to insufficient toughening or excessively high system viscosity and difficulty in dispersion.

[0030] Furthermore, the deblocking temperature of the blocked sulfonic acid catalyst is 100-130°C, its pH value at room temperature is 6.0-7.0, and its latency in the mixture of step S3 is ≥6 months. The deblocking temperature of 100-130°C matches the curing window, ensuring effective acid release at 100-120°C; the neutral pH at room temperature avoids pre-gelling; and the latency of ≥6 months ensures industrial storage and transportation. These limitations allow the catalyst to reduce the curing temperature without sacrificing its pot life.

[0031] Furthermore, the epoxy-based silane coupling agent is pre-hydrolyzed in a water / alcohol mixture before use to convert its methoxy groups into silanol groups. Pre-hydrolysis converts the methoxy groups into silanol groups (Si-OH). During curing, the silanol groups condense with the hydroxyl groups on the substrate (metal, glass, etc.) surface to form covalent bonds. Simultaneously, the epoxy groups of the silane participate in the cross-linking network, achieving a "chemical bridging" effect. This elevates the adhesion from physical adsorption to chemical bonding, maintaining excellent adhesion even in humid environments. Furthermore, the co-solvent is a mixture of propylene glycol methyl ether acetate and n-butanol in a 1:1 volume ratio. This mixed solvent is miscible with methyl etherified melamine resin, bisphenol A epoxy resin, and polyurethane prepolymer, and has a boiling point range of 110-150°C. PMA's strong dissolving ability ensures complete miscibility of the three resins, while n-butanol regulates the evaporation rate and participates in the ether exchange reaction to control the crosslinking density. The boiling point of 110-150°C prevents the coating from drying too quickly and causing defects, while also supporting high-solids application and reducing VOC emissions.

[0032] Furthermore, in step S3, hindered amine light stabilizers and / or phenolic antioxidants are added at amounts of 0.2-0.5 parts and 0.1-0.3 parts, respectively. The hindered amines scavenge free radicals to inhibit photo-oxidation, while the phenolic antioxidants decompose hydroperoxides. Together, they reduce the yellowing index ΔE in the QUV aging test by more than 50%. Since the system already uses aliphatic isocyanate (IPDI), the weather resistance is further improved after addition, making it suitable for long-term exposure scenarios such as automotive paints and outdoor industrial coatings.

[0033] Furthermore, the curing temperature in step S4 is 50-80°C lower than the conventional curing temperature of the same type of methyl etherified melamine resin; and the cured product coating obtained by this process has an elongation at break of 8-12%, an impact strength ≥40 kg·cm, and a cross-cut adhesion grade of 0-1.

[0034] Furthermore, the modified preparation process also includes adding 1-3 parts of fumed silica nanoparticles in step S3, wherein the primary particle size of the fumed silica nanoparticles is 7-40 nm and the specific surface area is [missing information]. These nanoparticles, uniformly dispersed in an interpenetrating network, can increase the scratch resistance (pencil scratch test) of the coating from ≤200g to ≥500g without significantly increasing brittleness, while maintaining high transparency (haze <2%). They are particularly suitable for highly decorative wood coatings, automotive clear coats, or anti-fingerprint coatings, combining aesthetics and abrasion resistance.

[0035] In summary, the polyamine resin modification process disclosed in this invention introduces an NCO-terminated polyurethane prepolymer and bisphenol A type epoxy resin to construct a ternary blend system with methylated melamine resin. Under the action of a blocked sulfonic acid catalyst, an interpenetrating network structure is formed at 100-120℃, significantly reducing the high-temperature curing conditions of 150-180℃ required for traditional amino resins, thereby saving energy and broadening the applicability of heat-sensitive substrates. Secondly, the synergistic effect of the flexible segments of polyurethane and the rigid crosslinking points of epoxy resin effectively overcomes the inherent defect of high brittleness in traditional amino resins. The resulting cured product possesses both high hardness and excellent toughness, with significantly improved elongation at break and impact strength. Thirdly, the introduction of an epoxy-based silane coupling agent enhances the chemical bonding ability of the resin with various substrates, improving adhesion from the conventional 2-3 grade to 0-1 grade, significantly improving the long-term service reliability of coatings or adhesive layers. Fourth, the blocked sulfonic acid catalyst is neutral at room temperature, giving the system excellent storage stability. Its high solids content design also reduces the amount of volatile organic solvents used, aligning with green manufacturing trends. Finally, the entire process is a single-component latent curing system, eliminating the need for on-site mixing during application, simplifying the operation process, and ensuring compatibility with existing coating equipment.

[0036] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0037] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A process for preparing modified polyamine resin, characterized in that, Includes the following steps: S1 Preparation of NCO-terminated polyurethane prepolymer: Polytetramethylene ether glycol and isophorone diisocyanate are reacted at 70-90℃ for 1.5-3h under nitrogen protection to obtain a polyurethane prepolymer with an NCO content of 3.0-4.0%. S2 Preparation of epoxy-amino resin premix: Mix methyl etherified melamine resin and bisphenol A type epoxy resin at a mass ratio of (60-80):(20-40) and stir at 70-90℃ for 20-40 min to obtain a clear premix; Construction of S3 ternary blend and latent curing system: Cool to 50-60℃, add the polyurethane prepolymer obtained in step S1, blocked sulfonic acid catalyst, epoxy silane coupling agent and cosolvent to the premix, disperse at high speed until uniform and transparent, and control the pH value to 6.5-7.

0. S4 Crosslinking and Curing: After coating or molding the mixture obtained in step S3, heat and cure at 100-120℃ for 30-40 minutes to form an epoxy-polyurethane-amino resin interpenetrating network structure. The components, by weight based on solid content, are as follows: 60-80 parts of methylated melamine resin, 20-40 parts of bisphenol A epoxy resin, 15-25 parts of polyurethane prepolymer, 0.5-1.2 parts of blocked sulfonic acid catalyst, 0.5-2 parts of epoxy silane coupling agent, and an appropriate amount of cosolvent to adjust the solid content to 50-60%.

2. The polyamine resin modification preparation process according to claim 1, characterized in that, The methyl etherified melamine resin has a degree of methyl etherification ≥ 90% and a number average molecular weight of 400-600.

3. The polyamine resin modification preparation process according to claim 1, characterized in that, The epoxy equivalent of the bisphenol A type epoxy resin is 184-194 g / eq.

4. The polyamine resin modification preparation process according to claim 1, characterized in that, In the polyurethane prepolymer, the mass ratio of polytetramethylene ether glycol to isophorone diisocyanate is (2.5-3.5):1, and the number average molecular weight of polytetramethylene ether glycol is 1800-2200.

5. The polyamine resin modification preparation process according to claim 1, characterized in that, The unblocking temperature of the blocked sulfonic acid catalyst is 100-130℃, its pH value at room temperature is 6.0-7.0, and its latency in the mixture of step S3 is ≥6 months.

6. The polyamine resin modification preparation process according to claim 1, characterized in that, The epoxy silane coupling agent is pre-hydrolyzed with a water / alcohol mixture before use to convert its methoxy group into silanol groups.

7. The polyamine resin modification preparation process according to claim 1, characterized in that, The co-solvent is a mixture of propylene glycol methyl ether acetate and n-butanol in a volume ratio of 1:

1. The mixed solvent is miscible with methyl etherified melamine resin, bisphenol A type epoxy resin and polyurethane prepolymer, and has a boiling point range of 110-150℃.

8. The polyamine resin modification preparation process according to claim 1, characterized in that, In step S3, hindered amine light stabilizers and / or phenolic antioxidants are also added, in amounts of 0.2-0.5 parts and 0.1-0.3 parts, respectively.

9. The polyamine resin modification preparation process according to claim 1, characterized in that, The curing temperature of step S4 is 50-80℃ lower than the conventional curing temperature of the same type of methyl etherified melamine resin without modification; and the elongation at break of the cured product coating obtained by this process is 8-12%, the impact strength is ≥40kg·cm, and the cross-cut adhesion is grade 0-1.

10. The polyamine resin modification preparation process according to claim 1, characterized in that, The modified preparation process further includes adding 1-3 parts of fumed silica nanoparticles in step S3, wherein the primary particle size of the fumed silica nanoparticles is 7-40 nm and the specific surface area is [missing information]. .