Latent epoxy resin curing agent and preparation method thereof

Abstract

The invention provides a latent epoxy resin curing agent and a preparation method thereof.The preparation method comprises the steps that firstly, micron particles and dopamine hydrochloride are added into a mixed solvent composed of water and an organic solvent, ultrasonic dispersion is conducted to be uniform, the pH of a reaction system is adjusted to 5-9, a stirring reaction is conducted, suspension liquid is obtained after the reaction is completed, centrifugation, washing and drying are conducted, and an amine curing agent is obtained; further mixing with epoxy resin to prepare a microcapsule type latent epoxy resin curing agent; the amine curing agent in the method is adjustable in composition, controllable in particle size and narrow in distribution; the micron particles of different materials endow the amine curing agent with flexible and adjustable physical and chemical properties, and the microcapsule type latent epoxy resin curing agent can be customized as required; the preparation method provided by the invention has the advantages of simple process, low cost, safety, sanitation and the like, and shows a good industrial prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of epoxy resin curing agents, and particularly relates to a latent epoxy resin curing agent and a preparation method thereof. Background Art

[0002] Epoxy resin is a type of thermosetting resin that can cross-link with epoxy resin curing agent to form a network structure. It has the characteristics of rich types, huge output, and wide range of uses. For a long time, two-component epoxy resin curing agents have been widely used. Amine substances are mixed with epoxy resin instantly, and they are quickly cured and cross-linked within a few hours, with very high bonding strength. Despite this, the two components must be stored separately and mixed as needed, which not only makes the process cumbersome, but also inevitably causes waste. In contrast, one-component epoxy resin curing agents (also known as latent epoxy resin curing agents) are gradually gaining market favor due to their simple process and user-friendliness, but they still face the major challenge of how to balance storage stability and curing characteristics.

[0003] To date, numerous types of latent epoxy resin curing agents have been developed. Among them, microencapsulated latent epoxy resin curing agents have attracted widespread attention due to their potential universal applicability. Changing environmental conditions during use, such as increasing temperature or exposure to light, allows the microencapsulated latent epoxy resin curing agent to fully and rapidly cure and crosslink with the epoxy resin, fundamentally avoiding the complex steps of preparing the curing agent on-the-fly. This is fully reflected in numerous patents, such as Chinese patents CN200480029599.6, CN200680005736.1, CN200680036309.X, and CN200780004384.2.

[0004] The amine curing agents disclosed in the above patents are often processed into particles with an average particle size of several microns by a crusher, ball mill, or jet mill during use. If the particle size of the amine curing agent is too large, it is difficult for the amine curing agent to fully diffuse out of the microcapsule, resulting in a significant reduction in the amine substance that actually undergoes a cross-linking reaction with the epoxy resin, and an unsatisfactory cross-linking effect. In addition, amine curing agent particles with too large a particle size are prone to sedimentation or agglomeration, making it difficult to uniformly disperse them in the epoxy resin matrix through mechanical stirring. Moreover, the particle size is affected by various factors such as material properties, sample volume, and grinding time. Especially when preparing small quantities in the laboratory, the particle size of the amine curing agent is difficult to maintain a stable size. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a latent epoxy resin curing agent and a preparation method thereof. First, a series of amine curing agents with adjustable composition, controllable particle size and narrow distribution are prepared. The micron particles used in the amine curing agent give the amine curing agent flexible and adjustable physical and chemical properties due to their different materials, and microcapsule-type latent epoxy resin curing agents can be customized on demand.

[0006] The present invention also provides a one-component epoxy resin composition, which is composed of an epoxy resin and the latent epoxy resin curing agent of the present invention. When the micron particles are selected from silicon dioxide, the obtained one-component epoxy resin composition has good storage stability and excellent curing performance.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a method for preparing a latent epoxy resin curing agent, the preparation method comprising the following steps:

[0009] (1) adding micron particles and dopamine hydrochloride to a mixed solvent consisting of water and an organic solvent, uniformly dispersing them by ultrasonication, adjusting the pH of the reaction system to 5-9, stirring the reaction, and obtaining a suspension after the reaction is completed. The suspension is centrifuged, washed, and dried to obtain an amine curing agent having a particle size of 2-5 μm;

[0010] (2) The amine curing agent obtained in step (1) is mixed with the epoxy resin, water and diisocyanate are added thereto, and the mixture is stirred at 35-45° C. for 20-24 hours to obtain a latent epoxy resin curing agent.

[0011] In step (1), the average particle size of the micron particles is 1-10 μm, preferably 1-5 μm.

[0012] In step (1), the micron particles are at least one of metal, inorganic non-metallic oxide, metal oxide, plastic, rubber, fiber or a composite material thereof.

[0013] In step (1), the concentration of dopamine hydrochloride in the mixed solvent is 0.1-1.0 mg / mL, preferably 0.5 mg / mL.

[0014] Furthermore, the metal is at least one of gold, silver, and copper;

[0015] The inorganic non-metallic oxide is silicon dioxide;

[0016] The metal oxide is at least one of titanium dioxide, zinc oxide, and iron oxide;

[0017] The plastic is at least one of polyethylene terephthalate, high-density polyethylene, polyvinyl chloride, low-density polyethylene, polypropylene, and polystyrene;

[0018] The rubber is at least one of natural rubber, styrene-butadiene rubber, butadiene rubber, chloroprene rubber, butyl rubber, nitrile rubber, ethylene-propylene rubber, silicone rubber, and fluororubber;

[0019] The fiber is at least one of cotton, linen, wool, silk, polyester, nylon, carbon fiber, and regenerated cellulose.

[0020] In step (1), the mass ratio of the micron particles to dopamine hydrochloride is 1:0.1-2, preferably 1:0.8-1.0.

[0021] In step (1), the organic solvent is at least one of methanol, ethanol, acetic acid, acetonitrile, acetone, glycerol, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone, preferably ethanol.

[0022] In step (2), the mass ratio of the amine curing agent to the epoxy resin is 1:1-10, preferably 1:2-5.

[0023] In step (2), the mass ratio of water to diisocyanate is 1:1-10, preferably 1:3-5; the sum of the mass of water and diisocyanate is 1-5%, preferably 3-4%, of the sum of the mass of the amine curing agent and the epoxy resin.

[0024] In step (2), the diisocyanate is at least one of toluene diisocyanate, 1,8-diisocyanato-4-(isocyanatomethyl)octane, methyl diisocyanate, diphenyl diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate;

[0025] In step (2), the epoxy resin is at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, novolac epoxy resin, alicyclic epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin, and biphenyl epoxy resin.

[0026] The present invention also provides a latent epoxy resin curing agent prepared according to the preparation method of the present invention.

[0027] The present invention also provides a one-component epoxy resin composition, which consists of an epoxy resin and the latent epoxy resin curing agent of the present invention.

[0028] The present invention provides a method for preparing a latent epoxy resin curing agent. A polydopamine coating rich in amino and hydroxyl groups is constructed on the surface of micronized particles. The polydopamine coating does not alter the particle size and distribution of the micronized particles, resulting in an amine curing agent with adjustable composition and controllable particle size. This amine curing agent is then reacted with an epoxy resin in the presence of an isocyanate to produce a microcapsule-type latent epoxy resin curing agent.

[0029] The latent epoxy resin curing agent provided by the present invention can be further used to prepare a one-component epoxy resin composition, and some examples thereof exhibit excellent storage stability and curing properties.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] This application directly uses commercial micronized particles as templates, utilizing the self-polymerization reaction of dopamine to form a coating layer on them. Meanwhile, amino groups are introduced onto the surface of the micronized particle templates, thereby producing an amine-based curing agent with uniform particle size and adjustable composition. During the preparation of the microencapsulated latent epoxy resin curing agent, the reaction between diisocyanate and water facilitates the complete encapsulation of small micronized particles, resulting in improved low-temperature storage stability.

[0032] The method for preparing an amine curing agent in the preparation method of a latent epoxy resin curing agent provided by the present invention is applicable to micronized particles of any material, demonstrating excellent versatility. Micronized particles of different materials can be selected to prepare the amine curing agent as needed. These micronized particles impart flexible and adjustable physical and chemical properties to the amine curing agent, laying a solid foundation for customized microencapsulated latent epoxy resin curing agents and overcoming the drawbacks of amine curing agents, such as uncontrollable particle size and wide particle size distribution.

[0033] The preparation method provided by the present invention has the advantages of simple process, low cost, safety and hygiene, and shows good industrialization prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The scanning electron microscope image (A) and particle size distribution diagram (B) of the amine curing agent A4 prepared in Example 4;

[0035] Figure 2 The scanning electron microscope image (A) and particle size distribution diagram (B) of the polypropylene powder used in Example 4. DETAILED DESCRIPTION

[0036] The present invention is described in detail below with reference to the embodiments.

[0037] Example 1

[0038] A method for preparing a latent epoxy resin curing agent comprises the following steps:

[0039] (1) 250 mg of copper powder with an average particle size of 3 μm and 225 mg of dopamine hydrochloride were mixed, 225 mL of ultrapure water and 25 mL of ethanol were added, and ultrasonic treatment was performed for 1 hour to obtain a homogeneous dispersion. Tris buffer solution with a pH of 8.5 was added to adjust the pH of the reaction system to 8.0. The mixture was stirred at room temperature for 24 hours to obtain a suspension. The suspension was centrifuged, washed alternately with water and ethanol three times, and dried naturally to obtain an amine curing agent A1.

[0040] (2) To 200 parts of bisphenol F epoxy resin, 100 parts by mass of amine curing agent A1, 2 parts by mass of water, 1 part by mass of toluene diisocyanate (TDI), and 7 parts by mass of 1,8-diisocyanato-4-(isocyanatomethyl)octane were added, and the mixture was mechanically stirred at 40°C for 24 hours to obtain a masterbatch curing agent F1. This masterbatch was placed in a plastic cup and left open at 40°C and 95% relative humidity for 12 hours. No significant change in appearance was observed, indicating good moisture resistance.

[0041] Example 2

[0042] The other steps are the same as those in Example 1, except that the copper powder with an average particle size of 3 μm is replaced by silicon dioxide powder with an average particle size of 2 μm. Amine curing agent A2 and masterbatch curing agent F2 are prepared through steps (1) and (2) respectively.

[0043] Example 3

[0044] The other steps are the same as those in Example 1, except that the copper powder with an average particle size of 3 μm is replaced by silicon dioxide powder with an average particle size of 5 μm. Amine curing agent A3 and masterbatch curing agent F3 are prepared through steps (1) and (2) respectively.

[0045] Example 4

[0046] The other steps are the same as those in Example 1, except that the copper powder with an average particle size of 3 μm is replaced by polypropylene powder with an average particle size of 3 μm. Amine curing agent A4 and masterbatch curing agent F4 are prepared through steps (1) and (2) respectively.

[0047] The SEM image and particle size distribution of the amine curing agent A4 prepared in this example are as follows: Figure 1 As shown, the SEM image and particle size distribution of the polypropylene powder used in the raw materials are as follows Figure 2 As shown in the figure, it can be seen that the particle size and distribution of the amine curing agent A4 relative to the polypropylene powder are almost unchanged. It can be seen that the particle size and distribution of the micron particles will not be changed after polydopamine coating. The particle size of the obtained amine curing agent is 2 to 5 μm, and the composition can be adjusted and the particle size can be controlled.

[0048] Example 5

[0049] The other steps are the same as those in Example 1, except that the copper powder with an average particle size of 3 μm is replaced by silicone rubber powder with an average particle size of 3 μm. Amine curing agent A5 and masterbatch curing agent F5 are prepared through steps (1) and (2) respectively.

[0050] Example 6

[0051] The other steps are the same as those in Example 1, except that the copper powder with an average particle size of 3 μm is replaced by carbon fiber powder with an average particle size of 3 μm. Amine curing agent A6 and masterbatch curing agent F6 are prepared through steps (1) and (2) respectively.

[0052] Comparative Example 1

[0053] A method for preparing a latent epoxy resin curing agent comprises the following steps:

[0054] (1) Mix 1 equivalent of bisphenol A epoxy resin with 1.5 equivalents of 2-methylimidazole, add a mixed solvent consisting of methanol and xylene in a volume ratio of 1:1, at which the mass fraction of the solute is 50%, and mechanically stir at 80°C for 6 hours to obtain a light yellow viscous substance. Transfer the substance to an open container and heat-treat it at 180°C in a vacuum drying oven for 8 hours. After removing the solvent, a dark reddish-brown solid is obtained. After crushing the solid, an amine curing agent A7 with an average particle size of 3 μm is obtained.

[0055] (2) To 200 parts of bisphenol F epoxy resin, 100 parts by mass of amine curing agent A7, 2 parts by mass of water, 1 part by mass of toluene diisocyanate (TDI) and 7 parts by mass of 1,8-diisocyanato-4-(isocyanatomethyl)octane were added and mechanically stirred at 40°C for 24 hours to obtain a masterbatch curing agent F7.

[0056] Application and test cases

[0057] 30 parts by weight of the masterbatch curing agent prepared in each of the above examples and comparative examples were added to 100 parts by weight of bisphenol A epoxy resin, and stirred evenly to obtain a one-component epoxy resin composition.

[0058] The storage stability of the masterbatch curing agent prepared in each embodiment and comparative example and the storage stability and curing characteristics of the one-component epoxy resin composition were evaluated. The evaluation process is as follows:

[0059] (1) Storage stability of masterbatch curing agent

[0060] The masterbatch curing agent was stored at 40°C for one week. The viscosity values ​​before and after storage were measured using a BM viscometer (test temperature: 25°C). The storage stability was evaluated by the viscosity increase ratio. If the viscosity of the masterbatch curing agent increased by more than 10 times after storage or gel formed, it was marked as ×; if the viscosity increased by 5-10 times, it was marked as △; if the viscosity increase ratio was less than 2, it was marked as ◎.

[0061] (2) Storage stability of one-component epoxy resin composition

[0062] The one-component epoxy resin composition was stored in a thermostatic bath at 40°C. The viscosity of the mixture was measured at the initial stage and after 30 days using an E-type viscometer (test temperature was 25°C). The storage stability of the masterbatch curing agent was determined by the viscosity increase ratio from the initial stage to 30 days. The viscosity of samples with viscosity values ​​between 3-40 Pa·s, 40-200 Pa·s and 200-1000 Pa·s was tested using a cone-plate viscometer at rotation speeds of 10 rpm, 2.5 rpm and 0.5 rpm, respectively. If the viscosity increase rate after 30 days is less than 25%, it is judged as AA; if it is between 25%-50%, it is judged as A; if it is between 50%-100%, it is judged as B; if it is higher than 100%, it is judged as C.

[0063] (3) Curing characteristics of one-component epoxy resin compositions

[0064] The phase transition behavior of single-component epoxy resin compositions was investigated using a TA Q2000 differential scanning calorimeter (temperature range: 30°C-300°C; heating rate: 10°C / min; nitrogen sweep rate: 50 mL / min). If the curing and crosslinking exothermic peak temperature was below 115°C, the composition was classified as AA; if it was between 115°C-120°C, it was classified as A; if it was between 120°C-130°C, it was classified as B; and if it was above 130°C, it was classified as C. The lower the curing and crosslinking exothermic peak temperature, the better the low-temperature curing performance of the masterbatch curing agent.

[0065] The evaluation results are shown in Table 1.

[0066] Table 1

[0067]

[0068]

[0069] As can be seen from Table 1, if polypropylene and silicone rubber are used as the main raw materials of the amine curing agent, the storage stability of the corresponding masterbatch curing agent and the storage stability of the one-component epoxy resin composition are slightly poor. This is because the amine curing agent made of softer materials has stronger fluidity and is therefore more likely to react with the epoxy resin during storage.

[0070] The amine curing agent with copper and carbon fiber as the main raw materials has a too rigid structure, which is not conducive to chain movement, making it difficult to initiate the cross-linking reaction of the peripheral epoxy groups, resulting in the corresponding single-component epoxy resin composition having inferior curing properties.

[0071] The amine curing agents prepared with silica powders having particle sizes of 2 μm and 5 μm, respectively, ultimately only affect the curing properties of the single-component epoxy resin composition because the migration ability of the large-particle powder is slightly weaker.

[0072] The masterbatch curing agent prepared using 2 μm silica powder (Example 2) and the 3 μm amine curing agent A7 (Comparative Example 1) as raw materials exhibited excellent storage stability, storage stability, and curing properties of the one-component epoxy resin composition. This suggests that 2 μm silica powder has promising practical applications in the preparation of latent epoxy resin curing agents.

[0073] As can be seen from the above, by selecting micronized particle raw materials with appropriate materials and particle sizes to prepare amine curing agents, it is expected to achieve precise control of the properties of masterbatch curing agents and one-component epoxy resin compositions.

[0074] The detailed description of a latent epoxy resin curing agent and its preparation method with reference to the above-mentioned embodiments is illustrative rather than restrictive. Several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a latent epoxy resin curing agent, characterized in that: The preparation method comprises the following steps: (1) adding micron particles and dopamine hydrochloride to a mixed solvent consisting of water and an organic solvent, uniformly dispersing them by ultrasonication, adjusting the pH of the reaction system to 5-9, stirring the reaction, and obtaining a suspension after the reaction is completed, centrifuging, washing, and drying to obtain an amine curing agent; (2) The amine curing agent obtained in step (1) is mixed with the epoxy resin, water and diisocyanate are added thereto, and the mixture is stirred at 35-45° C. for 20-24 hours to obtain a latent epoxy resin curing agent.

2. The preparation method according to claim 1, characterized in that In step (1), the average particle size of the micron particles is 1-10 μm; the micron particles are at least one of metal, inorganic non-metallic oxide, metal oxide, plastic, rubber, fiber or a composite material thereof.

3. The preparation method according to claim 2, characterized in that The metal is at least one of gold, silver, and copper; the inorganic non-metallic oxide is silicon dioxide; the metal oxide is at least one of titanium dioxide, zinc oxide, and iron oxide; the plastic is at least one of polyethylene terephthalate, high-density polyethylene, polyvinyl chloride, low-density polyethylene, polypropylene, and polystyrene; the rubber is at least one of natural rubber, styrene-butadiene rubber, butadiene rubber, chloroprene rubber, butyl rubber, nitrile rubber, ethylene-propylene rubber, silicone rubber, and fluororubber; and the fiber is at least one of cotton, linen, wool, silk, polyester, nylon, carbon fiber, and regenerated cellulose.

4. The preparation method according to any one of claims 1 to 3, characterized in that In step (1), the mass ratio of the micron particles to dopamine hydrochloride is 1:0.1-2.

5. The preparation method according to claims 1-3, characterized in that In step (1), the organic solvent is at least one of methanol, ethanol, acetic acid, acetonitrile, acetone, glycerol, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

6. The preparation method according to claims 1-3, characterized in that In step (2), the mass ratio of the amine curing agent to the epoxy resin is 1:1 to 10.

7. The preparation method according to claims 1-3, characterized in that In step (2), the mass ratio of water to diisocyanate is 1:1-10; the sum of the mass of water and diisocyanate is 1-5% of the sum of the mass of the amine curing agent and the epoxy resin.

8. The preparation method according to claims 1-3, characterized in that In step (2), the diisocyanate is at least one of toluene diisocyanate, 1,8-diisocyanato-4-(isocyanatomethyl)octane, methyl diisocyanate, diphenyl diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate; and the epoxy resin is at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, novolac epoxy resin, alicyclic epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin, and biphenyl epoxy resin.

9. A latent epoxy resin curing agent prepared by the preparation method according to any one of claims 1 to 8.

10. A one-component epoxy resin composition, characterized in that: The one-component epoxy resin composition consists of an epoxy resin and the latent epoxy resin curing agent according to claim 9.

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