A method for preparing flame-retardant materials with complex shapes based on sequential curing

Abstract

A method for preparing a complex-shaped flame-retardant material based on sequential curing belongs to the technical field of flame-retardant material preparation. The method is: vinyl phosphoric acid and imidazole compounds are mixed in a solvent at a molar ratio of 1:2, stirred at 25-50°C for 2-8h, and the solvent is removed to obtain an oily product; epoxy resin, acrylate resin, acrylate resin curing agent and the oily product of step one are mixed, vacuumed, bubbles are removed, poured into a mold, and a first-stage flexible material is prepared by ultraviolet irradiation or heating, and the flexible material is shaped, pre-cured at 70-120°C for 1-3h, and post-cured at 130-180°C for 2-5h to obtain a final complex-shaped flame-retardant material. The present invention is based on sequential curing technology, is not limited by traditional molds, can prepare complex-shaped flame-retardant materials, provides a way of thinking for preparing complex-shaped flame-retardant materials, and broadens the application field of flame-retardant materials.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant material preparation, and in particular relates to a method for preparing a flame retardant material with a complex shape based on sequential curing. Background Art

[0002] At present, the processing of flame-retardant thermosetting resins and their composite materials is still the traditional molding methods such as injection molding, molding, lamination, and casting. These methods can only produce some simple shapes, such as strips, blocks, etc. If you want to produce more complex shapes, you can only customize the corresponding molds, which undoubtedly complicates the processing and increases the production cost. Therefore, the application of flame retardant materials in some special scenarios is limited. The sequential curing technology can be simply summarized as mixing two reactive monomers and corresponding curing agents, initiating a flexible material through the first stage, and initiating a rigid material through the second stage. Since the flexible material has excellent shaping ability, the flexible material is shaped into a spring or other shape and then the second state is induced to obtain a rigid material with a complex final shape. Based on this, if a flame retardant is added to the system, a flame retardant material with a complex shape can be prepared by sequential curing technology, which further broadens the application scenarios of flame retardant materials.

[0003] Vinyl phosphate contains phosphorus in its molecular formula, which can play a flame retardant role. At the same time, the phosphate group contained in vinyl phosphate can undergo a ring-opening reaction with the epoxy ring. Due to the high curing activity of vinyl phosphate on epoxy resin, a small amount of vinyl phosphate can be mixed with epoxy resin at room temperature to quickly make the epoxy resin harden significantly. There is a problem of extremely short processing time, which limits the application of vinyl phosphate as a flame retardant in epoxy resin. Imidazole compounds are alkaline and nucleophilic, and are one of the important curing agents for epoxy resin. Since vinyl phosphate has strong acidity, the activity of vinyl phosphate curing epoxy resin can be passivated by alkaline imidazole compounds through acid-base neutralization, and the activity of imidazole substances curing epoxy resin can also be passivated. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that flame retardant materials with complex shapes cannot be prepared at present, and to provide a method for preparing flame retardant materials with complex shapes based on sequential curing.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a flame retardant material of complex shape based on sequential curing, the method comprising:

[0007] Step 1: Mix vinyl phosphoric acid and imidazole compounds in a solvent at a molar ratio of 1:2, stir at 25-50°C for 2-8 hours, remove the solvent, and obtain an oily product; the oily product prepared in this step can be used as a latent curing agent or flame retardant in the field of epoxy resin, or as a flame retardant in the field of vinyl resin.

[0008] Step 2: Mix the epoxy resin, acrylate resin, acrylate resin curing agent and the oily product of step 1, evacuate, remove bubbles, pour into a mold, irradiate with ultraviolet light or heat to prepare a first-stage flexible material, shape the flexible material, such as a complex shape such as a spring, pre-cure at 70-120°C for 1-3h, and post-cure at 130-180°C for 2-5h to obtain the final complex-shaped flame-retardant material.

[0009] Furthermore, in step 1, the imidazole compound is one of imidazole, 2-phenylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 4-phenylimidazole or 2,4,5-triphenylimidazole.

[0010] Furthermore, in step 1, the solvent is one of water, ethanol, methanol, tetrahydrofuran, ethyl acetate, and dioxane.

[0011] Furthermore, in step 1, the concentration of the reactant in the solution is 0.1-1 mol / L.

[0012] Furthermore, in step 2, the acrylic resin curing agent is a photocuring agent or a thermal curing agent, the photocuring agent is one or more of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-hydroxy-2-methyl-1-phenyl-1-propanone 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide; the thermal curing agent is one of dibenzoyl peroxide BPO, azobisisoheptanenitrile ABVN, and azobisisobutyronitrile AIBN.

[0013] Furthermore, in step 2, the epoxy resin is 10-90 parts by mass, the acrylate is 10-90 parts by mass, the photocuring agent is 0.1-2 parts by mass, and the oily product is 0.5-20 parts by mass.

[0014] Furthermore, in step 2, the specific parameters of the ultraviolet light irradiation are a wavelength of 365 nm and a light intensity of 20-200 mW / cm 2 , time 10-40min.

[0015] Furthermore, in step 2, the specific parameters of the heating are temperature 60° C. and time 2-3 h.

[0016] The beneficial effects of the present invention compared to the prior art are:

[0017] 1. Based on sequential curing technology, it is not limited by traditional molds and can prepare flame-retardant materials with complex shapes, which provides a way to prepare flame-retardant materials with complex shapes and expands the application field of flame-retardant materials.

[0018] 2. Vinyl phosphate is acidic and imidazole compounds are alkaline, so vinyl phosphate can undergo an acid-base neutralization reaction with imidazole compounds. After the product prepared by a simple acid-base neutralization reaction is added to the epoxy resin, the curing activity of the epoxy resin is greatly reduced. The product can be used as a latent curing agent and flame retardant for epoxy resin. At high temperatures, the ionic bonds in the product break to release imidazole and vinyl phosphate, and imidazole solidifies the epoxy resin through anionic polymerization; because N No. 3 in the imidazole ring is alkaline and nucleophilic, this N will react with epoxy through nucleophilicity, and the activity can be measured by the gel time. For example, when 5 parts by mass of imidazole is added to 100 parts by mass of epoxy resin at room temperature, the gel time is about 1 day; then because this N No. 3 is alkaline, then through acidic substances, the nucleophilicity of N No. 3 can be passivated by the acid-base neutralization effect, so that its activity in reacting with epoxy decreases. For example, when 7 parts by mass of the product is added to 100 parts of epoxy resin at room temperature, the system gel time is 7 days, which proves that the nucleophilic activity of imidazole substances to epoxy can be passivated by acid-base reaction. In order to fully compare the difference in activity, 5 parts by mass of 2-ethyl-4-methylimidazole was added to 100 parts by mass of epoxy resin and then a non-isothermal DSC test was performed, such as Figure 1 The specific data are shown in Table 2; subsequently, 7 parts by mass of the synthesized product was added to 100 parts by mass of epoxy resin and a non-isothermal DSC test was performed. Figure 2 As shown in Table 2, the specific data can be seen. It can be seen that the synthetic product needs a higher temperature to cure the epoxy resin. At the same time, the cone calorimetry test of the two systems is as follows Figure 3-7 As shown, it can be seen that the resin cured with 2-ethyl-4-methylimidazole is almost completely burned out, while the resin cured with the synthetic product can form a dense carbon layer. At the same time, the heat release rate during the combustion process is relatively small, indicating that the synthetic product can play a flame retardant role. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The DSC curves of epoxy resin E51 cured at different heating rates with 5wt.% 2-ethyl-4-methylimidazole;

[0020] Figure 2 DSC curves of epoxy resin E51 cured at different heating rates for 7wt.% synthetic product;

[0021] Figure 3 Front view of epoxy cone calorimetry after 5wt.% 2-ethyl-4-methylimidazole curing;

[0022] Figure 4 A top view of an epoxy cone calorimeter cured with 5 wt.% 2-ethyl-4-methylimidazole;

[0023] Figure 5 Front view of epoxy cone calorimetry test after curing with 15wt.% synthetic product;

[0024] Figure 6 A top view of the epoxy cone calorimetry test after curing with 15wt.% of the synthetic product;

[0025] Figure 7 It is the heat release rate-time diagram in cone calorimetry test;

[0026] Figure 8 The temperature-time diagram of the system during the first stage curing of each formula;

[0027] Fig. 9 It is the tensile strength diagram of flexible materials of each formula;

[0028] Fig.10 It is the tensile strength diagram of rigid materials of each formula;

[0029] Fig.11 It is a schematic diagram of a twisted strip-shaped complex flame-retardant material;

[0030] Fig.12 It is a schematic diagram of a spring-shaped complex flame-retardant material;

[0031] Fig.13 Schematic diagram of the Möbius ring-shaped complex flame-retardant material. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0033] Flame retardant refers to a substance that can be added to the resin to prevent it from burning. Latent curing agent: It has poor reaction activity with epoxy at room temperature, but reacts violently with epoxy at high temperature. Sequential curing: There are two monomers and initiators in the system. The first initiation produces an intermediate flexible material, and the second initiation produces a rigid material. The two reactions are orthogonal and can occur independently.

[0034] Embodiment 1:

[0035] Step 1: Flame retardant and latent curing agent: Weigh 3.24g of vinyl phosphoric acid, dissolve it in 100ml of methanol, pour the solution into a single-necked flask, then weigh 6.6g of 2-ethyl-4-methylimidazole (EMI), dissolve it in 50ml of methanol, transfer the corresponding solution to a constant pressure dropping funnel, then drip the 2-ethyl-4-methylimidazole solution into the vinyl phosphoric acid solution drop by drop, the dripping time is 1h, the reaction temperature is 40℃, after stirring for 4h, remove the methanol by rotary evaporation to obtain an oily product. The oily product is placed in a vacuum drying oven at 40℃ and dried for 12h.

[0036] Step 2: Sequential curing formula design: Use difunctional acrylate resin, the mass ratio of photoinitiator to acrylate resin is 1-2:100, and ultrasonicate for 10 minutes to dissolve the photoinitiator in the acrylate resin; the mass ratio of the oily product in step 1 to epoxy resin E51 is 7-10:100. Weigh 2g of the prepared acrylate and 8g of the prepared epoxy resin, stir and mix the two, vacuum to remove bubbles, and record it as A2-E8 system. Pour the resin into a silicone mold and heat it at 365nm, 50mW / cm 2 The flexible material was irradiated under ultraviolet light for 10 minutes. The temperature change over time during light curing is shown in the figure below. Figure 8 As shown in the figure, the maximum temperature of the system during the entire light curing process is about 42°C. Fig. 9 The tensile strength of the material is 0.16Mpa. After curing at 80℃ for 2h and 150℃ for 3h, a complex rigid flame retardant material is obtained. Fig.10 The tensile strength of the material is 50.37Mpa. The material is transformed from flexible to rigid. The flexible material after light curing can be shaped into a twisted strip, and then further transformed into a rigid material through the above-mentioned thermal curing step, such as Fig.11 shown.

[0037] Embodiment 2:

[0038] Step 1: Flame retardant and curing agent: Weigh 2.16g of vinyl phosphoric acid, dissolve it in 120ml of ethanol, pour the solution into a single-necked flask, then weigh 4.4g of 2-ethyl-4-methylimidazole (EMI), dissolve it in 25ml of ethanol, transfer the corresponding solution to a constant pressure dropping funnel, then add the 2-ethyl-4-methylimidazole solution drop by drop into the vinyl phosphoric acid solution, the dropping time is 40min, the reaction temperature is 40°C, after stirring for 5h, remove the ethanol by rotary evaporation to obtain an oily product.

[0039] Step 2: Sequential curing formula design: Use difunctional acrylate resin, the mass ratio of photoinitiator to acrylate resin is 1-2:100, and ultrasonicate for 10 minutes to dissolve the photoinitiator in the acrylate resin; the mass ratio of the oily product in step 1 to epoxy resin E51 is 11-15:100. Weigh 3g of the prepared acrylate and 7g of the prepared epoxy resin, stir and mix the two, vacuum to remove bubbles, and record it as A3-E7 system. Pour the resin into a silicone mold and heat it at 365nm, 50mW / cm 2 The flexible material was irradiated under ultraviolet light for 10 minutes. The temperature change over time during light curing is shown in the figure below. Figure 8 As shown in the figure, the maximum temperature of the system during the entire light curing process is about 43°C. Fig. 9 The tensile strength of the material is 0.42Mpa. After curing at 80℃ for 2h and 150℃ for 3h, a complex rigid flame retardant material is obtained. Fig.10 The tensile strength of the material is 48.14Mpa. The material is transformed from flexible to rigid. The flexible material after light curing can be shaped into a spring shape and then further transformed into a rigid material through the above-mentioned thermal curing step, such as Fig.12 shown.

[0040] Embodiment 3:

[0041] Step 1: Flame retardant and curing agent: Weigh 4.32g of vinyl phosphoric acid, dissolve it in 150ml of distilled water, pour the solution into a single-necked flask, then weigh 8.8g of 2-ethyl-4-methylimidazole (EMI), dissolve it in 40ml of distilled water, transfer the corresponding solution to a constant pressure dropping funnel, then add 2-ethyl-4-methylimidazole solution drop by drop into the vinyl phosphoric acid solution, the dropping time is 50min, the reaction temperature is 40°C, after stirring for 4h, remove the distilled water by rotary evaporation to obtain an oily product.

[0042] Step 2: Sequential curing formula design: Use difunctional acrylate resin, the mass ratio of photoinitiator to acrylate resin is 1-2:100, and ultrasonicate for 10 minutes to dissolve the photoinitiator in the acrylate resin; the mass ratio of the oily product in step 1 to epoxy resin E51 is 16-20:100. Weigh 4g of the prepared acrylate and 6g of the prepared epoxy resin, stir and mix the two, vacuum to remove bubbles, and record it as A4-E6 system. Pour the resin into a silicone mold and heat at 365nm, 50mW / cm 2 The flexible material was obtained by irradiating it with ultraviolet light for 10 minutes. The temperature during light curing is shown in the figure below. Figure 8 As shown in the figure, the maximum temperature of the system during the entire light curing process is about 45°C. Fig. 9The tensile strength of the material was 0.89Mpa, the elongation at break was 23%, and the complex rigid flame retardant material was obtained by curing at 80℃ for 2h and 150℃ for 3h. Fig.10 The tensile strength of the material is 30.54Mpa. The material is transformed from flexible to rigid. The flexible material after light curing can be shaped into a Möbius ring and then further transformed into a rigid material through the above-mentioned thermal curing step, such as Fig.13 shown.

[0043] Embodiment 4:

[0044] Step 1: Flame retardant and curing agent: Weigh 4.32g of vinyl phosphoric acid, dissolve it in 150ml of distilled water, pour the solution into a single-necked flask, then weigh 8.8g of 2-ethyl-4-methylimidazole (EMI), dissolve it in 40ml of distilled water, transfer the corresponding solution to a constant pressure dropping funnel, then add 2-ethyl-4-methylimidazole solution drop by drop into the vinyl phosphoric acid solution, the dropping time is 50min, the reaction temperature is 40°C, after stirring for 4h, remove the distilled water by rotary evaporation to obtain an oily product.

[0045] Step 2: Sequential curing formula design: Use difunctional acrylate resin, the mass ratio of photoinitiator to acrylate resin is 1-2:100, and ultrasonicate for 10 minutes to dissolve the photoinitiator in the acrylate resin; the mass ratio of the oily product in step 1 to epoxy resin E51 is 10:100. Weigh 5g of the prepared acrylate and 5g of the prepared epoxy resin, stir and mix them, vacuum to remove bubbles, and record it as A5-E5 system. Pour the resin into a silicone mold and heat it at 365nm, 50mW / cm 2 The flexible material was obtained by irradiating it with ultraviolet light for 10 minutes. The temperature during light curing is shown in the figure below. Figure 8 As shown in the figure, the maximum temperature of the system during the entire light curing process is about 55°C. Fig. 9 The tensile strength of the material was 1.85 MPa. The rigid material was cured at 80°C for 2 hours and at 150°C for 3 hours. Fig.10 The tensile strength of the material is 30.05Mpa.

[0046] Vinyl phosphoric acid will react with 2-ethyl-4-methylimidazole to undergo an acid-base neutralization reaction, passivating the curing activity of imidazoles and phosphoric acid on epoxy. By substituting the corresponding data in the following two tables into the Kissinger equation, it is calculated that the activation energy Eak of 5wt% 2-ethyl-4-methylimidazole curing epoxy resin is 60.91KJ / mol, and the activation energy Eak of 7wt% synthetic product curing epoxy resin is 68.08KJ / mol. The increase in activation energy fully demonstrates that there is a chemical reaction between vinyl phosphoric acid and imidazoles. It is this chemical reaction that simultaneously passivates the activity of 2-ethyl-4-methylimidazole and vinyl phosphoric acid in curing epoxy. In addition, the gel time of vinyl phosphoric acid and epoxy resin is 30min, the gel time of 2-ethyl-4-methylimidazole and epoxy resin is 1d, and the gel time of 7wt% VPPA-EMI epoxy resin can reach 7d. The reason for such a large difference is that the existence of this chemical reaction can simultaneously passivate the curing activity of both on epoxy resin. It shows that VPPA-EMI is a latent curing agent for epoxy resin compared with EMI. The above data show that the synthesized product has good flame retardant properties.

[0047] Table 15 T of E51 cured at different heating rates with 2-ethyl-4-methylimidazole wt% i 、T p 、T f value

[0048] Heating rate (℃ / min) <![CDATA[T i (℃)]]> <![CDATA[T p (℃)]]> <![CDATA[T f (℃)]]> 5 97.95 109.17 113.15 10 110.15 121.32 124.64 15 116.37 127.93 131.98 20 121.60 136.50 139.02 Extrapolate 92.23 101.58 106.46

[0049] Table 27wt% T of E51 cured at different heating rates for synthetic products i 、T p 、T f value

[0050] Heating rate (℃ / min) <![CDATA[T i (℃)]]> <![CDATA[T p (℃)]]> <![CDATA[T f (℃)]]> 5 130.02 138.10 144.39 10 143.40 151.27 158.72 15 149.02 158.92 166.23 20 152.73 166.12 172.83 Extrapolate 126.34 130.68 137.34

Claims

1. A method for preparing a complex-shaped flame-retardant material based on sequential curing, characterized in that: The method is: Step 1: Mix vinyl phosphonic acid and imidazole compound in a solvent at a molar ratio of 1:2, stir at 25-50°C for 2-8h, remove the solvent, and obtain an oily product; Step 2: Mix epoxy resin, acrylate resin, acrylate resin curing agent and the oily product of step 1, evacuate, remove bubbles, pour into a mold, and irradiate with ultraviolet light to prepare a first-stage flexible material, shape the flexible material into any complex shape, pre-cure at 70-120° C. for 1-3 hours, and post-cure at 130-180° C. for 2-5 hours to obtain a rigid flame retardant material with a final complex shape; In step 2, the epoxy resin is 10-90 parts by weight, the acrylate resin is 10-90 parts by weight, the acrylate resin photocuring agent is 0.1-2 parts by weight, and the oily product is 0.5-20 parts by weight.

2. A method for preparing a complex-shaped flame-retardant material based on sequential curing according to claim 1, characterized in that: In step 1, the imidazole compound is one of imidazole, 2-phenylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 4-phenylimidazole or 2,4,5-triphenylimidazole.

3. The method for preparing a complex-shaped flame-retardant material based on sequential curing according to claim 1, characterized in that: In step 1, the solvent is one of water, ethanol, methanol, tetrahydrofuran, ethyl acetate, and dioxane.

4. The method for preparing a complex-shaped flame-retardant material based on sequential curing according to claim 1, characterized in that: In step 1, the concentration of the reactants in the solution is 0.1-1 mol / L.

5. The method for preparing a complex-shaped flame-retardant material based on sequential curing according to claim 1, characterized in that: In step 2, the acrylic resin photocuring agent is one or more of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-hydroxy-2-methyl-1-phenyl-1-propanone 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

6. The method for preparing a complex-shaped flame-retardant material based on sequential curing according to claim 1, characterized in that: In step 2, the specific parameters of the ultraviolet light irradiation are wavelength 365nm, light intensity 20-200mW / cm 2 , time 10-40min.

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