Latent amine compositions for flame retardant epoxy systems

Abstract

The present disclosure provides latent amine compositions, amine-epoxy resin compositions, and cured products derived from amine-epoxy compositions for use as curing agents for flame retardant epoxy systems.

Description

Technical Field

[0001] The present invention relates to latent amine compositions, amine-epoxy resin compositions and cured products obtained from amine-epoxy compositions used as curing agents for flame retardant epoxy systems. One-component epoxy systems are superior to conventional two-component epoxy systems because they do not have the possibility of misformulation and can be used continuously. One-component epoxy systems require latent curing agents that do not react with epoxy compounds at room temperature but react with epoxy resins to achieve curing by heating. Background Art

[0002] Fiber reinforced composites are used in a variety of applications due to their low density and high strength. An example of one such application is in the automotive industry where it is desirable to save fuel by reducing vehicle weight. Fiber reinforced composites provide a material with a lower density while maintaining mechanical properties comparable to steel and aluminum.

[0003] The demands of the automotive industry require that the production of molded parts be accomplished at speeds and automation typically seen in automotive factories. As such, epoxy formulations used to produce molded parts must have relatively fast cure rates and must be capable of being processed in automated systems.

[0004] Fiber reinforced composite materials include a resin matrix reinforced with fibers, and the resin matrix is ​​usually an epoxy resin. Fiber reinforced composite materials are prepared in a method in which chopped fibers are impregnated in a resin to form a so-called sheet molding compound (SMC). SMC is generally described as a reinforced composite material comprising chopped fibers impregnated in a resin in an uncured or partially cured state. The SMC can then be molded into a finished or semi-finished molded part by applying conditions to the SMC that cure the resin. Heat is used to cure the SMC in the mold at a temperature and time sufficient to cure the resin.

[0005] Examples of articles manufactured from epoxy resin systems are evaluated including sheet molding compound (SMC) composites. There are many requirements for efficient manufacturing, especially when complex manufacturing processes are used. These processes include composite applications such as SMC, prepregs, high pressure resin transfer molding, filament winding, etc.

[0006] US Patent No. 9,862,798 discloses an epoxy liquid curing agent composition comprising dicyandiamide and at least one polyamine.

[0007] Chinese patent publication number CN 112063118A discloses a low-density flame-retardant epoxy resin composition with no VOC emission for preparing sheet molding compounds.

[0008] There is a need in the art for epoxy systems with good flame retardancy and high curing efficiency. Epoxy systems used for composite materials in the transportation and automotive industries must meet flame retardancy requirements. In these industries, flame retardants, such as ammonium polyphosphate, are used to meet fire resistance requirements due to their high flame retardancy and cost efficiency.

[0009] Another demand in this area is that epoxy systems cure rapidly at high temperatures. According to the processing properties of SMC composites, epoxy systems must gel within 100 seconds at 150-160°C and cure within 10 minutes. Rapid curing of epoxy systems is highly desirable because it reduces the production cycle of composite parts, enabling improved production efficiency. Flame retardants, such as ammonium polyphosphate, will reduce the reactivity of amine-based epoxy systems, especially in dicyandiamide curing systems. Therefore, a higher ratio of accelerator is used to meet the fast curing speed requirements. A higher ratio of accelerator will also reduce the Tg and latency of the composite material.

[0010] Another demand in this field is the good latency of epoxy systems at ambient temperature. Epoxy systems used for SMC composites must have a shelf life greater than 30 days at ambient temperature. According to the processing properties of SMC, the material should reach the B stage after the aging process and should maintain relatively stable properties such as Tg and gel time within 30 days to meet production requirements.

[0011]

[0006] Therefore, there is a need in the art for improved curing agents for producing epoxy resin systems having good flame retardancy, fast cure at elevated temperatures and good latency at ambient temperature while maintaining desired mechanical properties and good processing properties. Summary of the invention SUMMARY OF THE INVENTION

[0013] The present disclosure includes a curing agent composition comprising dicyandiamide, at least one alicyclic amine, at least one additive, at least one urea accelerator and at least one inorganic base used as a reaction promoter. The curing agent composition of the present invention has several advantages. These advantages include (i) being able to be formulated with liquid bisphenol A diglycidyl ether (DGBPA) epoxy resin and a flame retardant, (ii) rapidly curing at high temperatures, (iii) having stable latency at room temperature, (iv) having good mechanical properties and heat resistance, and (v) having excellent flame retardant properties and good processing properties. Another advantage includes that the latent epoxy system can be used for fiber-reinforced composite materials.

[0014] Another aspect of the present disclosure includes an epoxy system prepared from at least one epoxy resin and a curing agent composition comprising dicyandiamide, at least one cycloaliphatic amine, at least one additive, at least one urea accelerator, and at least one inorganic base. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention relates to a curing agent composition of the present invention, which comprises dicyandiamide (A), at least one alicyclic amine (B), at least one additive (C), at least one urea accelerator (D), at least one inorganic base (E) and an additive (F).

[0017] The particle size of the dicyandiamide in the curing agent composition needs to be significantly smaller and have a narrow size distribution. Preferred examples of the particle size of dicyandiamide that can be used in the composition include, but are not limited to, D90 < 10 μm, 10 < D90 < 35 μm, 35 < D90 < 100 μm, and D90 > 100 μm. In a preferred embodiment, the particle size of dicyandiamide is D90 < 10 μm.

[0018] Preferably, the at least one alicyclic amine is selected from m-xylylenediamine (MXDA), 1,3-cyclohexanedimethanamine, N-aminoethylpiperazine (NAEP), isophorone diamine (IPD), methylcyclohexanediamine, cyclohexylpropylenediamine, bis(aminocyclohexyl)methane, 1,2-cyclohexanediamine, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, other alicyclic amines, and combinations thereof. In a preferred embodiment, the alicyclic amine is isophorone diamine. In this system, polyether diamines, aliphatic amines, aromatic amines, and amidoamines can preferably also be used in combination with the alicyclic amine. Preferred polyetheramines include those commercially available from Huntsman under the trade names D230, D400, D2000. Although not specifically mentioned, other polyetheramines commercially available from Huntsman under the trade names D series and T series, or polyetheramines of the same grade from other manufacturers can also be used. Preferred aliphatic amines include triethylenetetramine (TETA), diethylenetriamine (DETA), tetraethylenepentamine (TEPA), other aliphatic amines, and combinations thereof. Preferred aromatic amines include 4,4'-methylenedianiline (MDA), diethyltoluenediamine (DETDA), other aromatic amines, and combinations thereof. Preferred amidoamines include those commercially available from Evonik under the trade names 502, 503, 504, 505, 506, other aromatic amines, and combinations thereof.

[0019] Preferably, the at least one additive is selected from release agents, defoamers, leveling agents, coupling agents, other additives, and combinations thereof.

[0020] Preferably, the at least one urea accelerator is selected from 1-phenyl-3,3-dimethylurea, 1,1'-(4-methyl-m-phenylene)bis(3,3-dimethylurea), 3-(3-chloro-4-methylphenyl)-1,1-dimethylurea, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-(4-chlorophenyl)-1,1-dimethylurea, 4,4'-methylenebis(phenyldimethylurea) or a urea accelerator and combinations thereof. In a preferred embodiment, the urea accelerator is 4,4'-methylenebis(phenyldimethylurea). In this system, imidazoles and blocked amines may preferably be used in combination with the urea accelerator. Preferred imidazoles include those available from Ajimoto under the trade name PN-23, PN-40, PN-40J, other modified imidazoles, and combinations thereof. Preferred blocked amines include those available from Evonik under the trade names 2014FG, 2337S, 2014AS, 2441, other blocked amines and combinations thereof.

[0021] Preferably, the at least one inorganic base is selected from calcium carbonate, calcium oxide, calcium hydroxide, magnesium hydroxide, barium hydroxide, potassium hydrate, magnesium oxide, barium oxide, potassium oxide, sodium hydroxide, other inorganic bases and combinations thereof. In a preferred embodiment, the inorganic base is calcium hydroxide.

[0022] In a preferred embodiment, the weight percentages of the curing agent composition of the present invention are 1-50% dicyandiamide, 1-50% alicyclic amine, 1-50% additives, 1-30% urea accelerator and 1-30% inorganic base. In another preferred embodiment, the weight percentages of the curing agent composition of the present invention are 10-30% dicyandiamide, 25-40% alicyclic amine, 15-30% additives, 5-15% urea accelerator and 5-15% inorganic base.

[0023] Another aspect of the present disclosure includes an epoxy system prepared from at least one epoxy resin, at least one flame retardant, and a curing agent composition comprising dicyandiamide, at least one cycloaliphatic amine, at least one additive, at least one urea accelerator, and at least one inorganic base.

[0024] Preferably, the at least one epoxy resin is selected from the group consisting of liquid diglycidyl ether of bisphenol A, liquid diglycidyl ether of bisphenol F, phenol novolac epoxy resin and multifunctional epoxy resin. In a preferred embodiment, the epoxy resin is liquid diglycidyl ether of bisphenol A. Preferred multifunctional epoxy resins include trifunctional epoxy resins based on p-aminophenol, m-aminophenol, methylenedianiline, tetrafunctional epoxy resins based on methylenedianiline, other multifunctional epoxy resins and combinations thereof. In a preferred embodiment, a multifunctional epoxy resin is used in combination with liquid diglycidyl ether of bisphenol A to improve heat resistance.

[0025] Preferably, the at least one flame retardant is selected from ammonium polyphosphate, aluminum hydroxide, tributyl phosphate, tri(2-ethylhexyl) phosphate, tri(2-chloroethyl) phosphate, tricresyl phosphate, triphenyl phosphate and 2-ethylhexyl diphenyl phosphate.

[0026] In another embodiment, the epoxy system further comprises at least one epoxy reactive diluent. Preferably, the at least one epoxy reactive diluent is selected from alkyl (C 12- C 14 ) glycidyl ether, p-tert-butylphenol glycidyl ether, cresyl glycidyl ether, 1,4-butanediol diglycidyl ether, cyclohexane dimethylol diglycidyl ether, resorcinol diglycidyl ether, trimethylolpropane triglycidyl ether, glycerol triglycidyl ether and neopentyl glycol diglycidyl ether. In a preferred embodiment, the epoxy reactive diluent is 1,4-butanediol diglycidyl ether.

[0027] Preferably, the mixing ratio of the at least one epoxy resin to the at least one epoxy-reactive diluent is 50-99 wt %: 1-50 wt %. In a preferred embodiment, the mixing ratio is 75 wt %-95 wt %: 5 wt %-25 wt %.

[0028] Preferably, the mixing ratio of the curing agent composition to the at least one epoxy resin is 1-40 wt %: 60-95 wt %. In a preferred embodiment, the mixing ratio is 10-25 wt %: 75-90 wt %. The ratio of the curing agent composition to the at least one epoxy resin is preferably the stoichiometric point.

[0029] Curing agent composition can be produced with other fillers and additives. Epoxy system can also be produced with other fillers and additives. Curing agent composition and at least one epoxy resin are mixed for testing and composite material manufacturing. Additives include release agents, defoamers, leveling agents, coupling agents, other additives and combinations thereof. In one embodiment, additives can be premixed into epoxy resin or curing agent or matrix to improve process performance.

[0030] In another embodiment, the epoxy system further comprises reinforcing fibers. Preferred examples of reinforcing fibers that can be used in the epoxy system include, but are not limited to, glass fibers, carbon fibers, ceramic fibers, polymer fibers, polyester fibers, polyamide fibers, aramid fibers, and the like.

[0031] The fiber-reinforced composite material of the present invention comprises an epoxy system reinforced with fibers. The fiber-reinforced composite material is prepared in a method in which chopped fibers are impregnated in an epoxy system to form a sheet molding compound (SMC). Preferably, the reinforcing fibers are present in the SMC in an amount of about 10-60% by weight. In a preferred embodiment, the reinforcing fibers are present in the SMC in an amount of about 20-40%. DETAILED DESCRIPTION

[0032] Example

[0033] These examples are provided to demonstrate certain aspects of the invention and should not limit the scope of the claims appended hereto.

[0034] The epoxy system described below is formed by blending the epoxy resin and the curing agent in a mixing device. The epoxy resin and the curing agent can be prepared as a single component pack.

[0035] Various terms and names used in the following examples are explained and described in Table 1 as follows:

[0036] Table 1

[0037]

[0038]

[0039] Definition and test methods:

[0040] -EEW is the epoxy equivalent weight.

[0041] -AHEW is the amine hydrogen equivalent weight.

[0042] -PHR is the amount of curing agent per hundred parts of resin.

[0043] - The stoichiometric point is the ratio of the AHEW of the curing agent to the EEW of the epoxy resin.

[0044] -Viscosity measured by Brookfield viscometer according to ASTM D445-83

[0045] -Glass transition temperature (Tg)

[0046] Glass transition temperature (also referred to as Tg) was measured by differential scanning calorimetry (DSC) according to ASTM D 3418-82, with a heating rate of 10°C / min from 0 to 250°C for the example tests. The midpoint of the steep portion of the cure curve was taken as Tg. The DSC instrument used was a TA Instruments DSC Model Q2000.

[0047] For the wet mixture, Tgwet is determined on the second scan curve.

[0048] - Gel time test

[0049] A hot plate with a metal surface can control the surface temperature within ±1°C of the set point. Set the hot plate at 150°C for 30 minutes to stabilize. Take out 1 ml of the prepared sample and place it on the plate, start the timer immediately, and start stroking with a wooden scraper immediately. Stroking is performed by gently pushing the resin to an area of ​​approximately 7cm*7cm. The resin gradually thickens. The resin eventually becomes stringy and immediately turns into a rubbery gel that sticks to the scraper. At this point, stop the timer and record the gel time.

[0050] Example 1 Curing of SMC formulation containing ammonium polyphosphate and reaction accelerator

[0051] Resin NPEL 127, hardener Dicyanex 1400F and IPD, imidazole accelerator Curezol2MZ-Azine, reaction promoter and ammonium polyphosphate were mixed with a high-speed mixer to obtain a uniform resin varnish formulation. The gel time required for the SMC formulation before aging is less than 140 seconds, and should be in the range of 60-90 seconds after aging. When used in the automotive or transportation industry, in order to maintain good flame retardancy of the SMC material, at least 6% of flame retardant should be used relative to the liquid epoxy resin. The formulation is shown in Table 2 below. As can be seen from Table 2, ammonium polyphosphate reduces the reactivity of the epoxy SMC sample (SAH-2), and the addition of calcium hydroxide shows the best acceleration effect and good latency compared to other accelerator materials.

[0052]

[0053] Example 2

[0054] In epoxy SMC formulations, diamines are used as thickeners to react with liquid epoxy resins during the curing process to increase the viscosity of the matrix. The epoxy SMC formulation will reach a stable B stage with a viscosity range that meets storage and transportation requirements. As shown in Table 3A, when combined with liquid epoxy resins, DICY, Curezol 2MZ-Azine and calcium hydroxide, Vestamin IPD shows a good balance between curing efficiency and latency. As shown in Table 3B, different ratios of IPD have an impact on the reactivity of epoxy SMC formulations and the latency when stored at room temperature for 30 days. For good handling properties, epoxy SMC formulations should have a flexible state.

[0055] Table 3A

[0056]

[0057] Table 3B

[0058]

[0059] Example 3

[0060] In epoxy SMC formulations, the use of accelerators reduces the curing temperature and leads to faster curing speeds for DICY-based epoxy systems. At the same time, it also has an impact on latency and heat resistance. As shown in Table 4A, Amicure UR-M has the best balance of reactivity and latency at room temperature storage compared to other accelerators, and Amicure UR-M at a 2% ratio relative to epoxy resin remains flexible after 30 days of storage at room temperature.

[0061] Table 4A

[0062]

[0063] Table 4B

[0064]

[0065] Example 4

[0066] Optimized hardener composition for fast cure, good latency, high heat resistance and mechanical properties

[0067] In the SMC production process, high curing efficiency is very important, especially in the automotive industry. The gel time required in the molding process is in the range of 60-90 seconds at 150°C and depends on the design of the produced parts. At the same time, SMC is a two-step process for composite materials, and the SMC material should have a latent period of 30 days at room temperature to meet daily production requirements, and the gel time after 30 days should be in the range of 60-90 seconds. For the special requirements of the automotive and transportation industries, the glass transition temperature (Tg) should be higher than 120°C, and the mixed viscosity at 30°C should be less than 2500cps to obtain good handling properties. As shown in Table 5, SAH-28 exhibits good handling properties (mixed viscosity and Tg after curing) and meets the curing speed and latency requirements.

[0068] Table 5

[0069]

[0070] Table 6

[0071]

[0072] As shown in Table 6, the examples of the epoxy resin composition of the present invention have improved demolding effects by adding additives. In addition, when the multifunctional epoxy resin is combined with the diglycidyl ether resin of bisphenol A, heat resistance and mechanical properties are improved.

Claims

1. A curing agent composition comprising dicyandiamide, at least one alicyclic amine, at least one additive, at least one urea accelerator and at least one inorganic base.

2. The curing agent composition according to claim 1, wherein the at least one alicyclic amine is selected from the group consisting of meta-xylylenediamine, 1,3-cyclohexanedimethylamine, N-aminoethylpiperazine, isophoronediamine, methylcyclohexanediamine, cyclohexylpropylenediamine, bis(aminocyclohexyl)methane, 1,2-cyclohexanediamine and 3,3'-dimethyl-4,4-diaminodicyclohexylmethane, and combinations thereof.

3. The curing agent composition according to any one of the preceding claims, wherein the at least one additive is selected from the group consisting of a release agent, a defoamer, a leveling agent, a coupling agent, other additives and combinations thereof.

4. The curing agent composition according to any one of the preceding claims, wherein the at least one urea accelerator is selected from 1-phenyl-3,3-dimethylurea, 1,1'-(4-methyl-m-phenylene)bis(3,3-dimethylurea), 3-(3-chloro-4-methylphenyl)-1,1-dimethylurea, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-(4-chlorophenyl)-1,1-dimethylurea, 4,4'-methylenebis(phenyldimethylurea), and combinations thereof.

5. The curing agent composition according to any one of the preceding claims, wherein the at least one inorganic base is selected from the group consisting of calcium carbonate, calcium oxide, calcium hydroxide, magnesium hydroxide, barium hydroxide, potassium hydroxide, magnesium oxide, barium oxide, potassium oxide, sodium hydroxide and combinations thereof.

6. An epoxy system prepared from at least one epoxy resin, at least one flame retardant and a curing agent composition according to any one of the preceding claims.

7. The epoxy system of claim 6, wherein the at least one epoxy resin is selected from the group consisting of liquid diglycidyl ether of bisphenol A, liquid diglycidyl ether of bisphenol F, phenol-based novolac epoxy resins, multifunctional epoxy resins, and combinations thereof.

8. The epoxy system according to claim 7, wherein the multifunctional epoxy resin is selected from trifunctional epoxy resins based on p-aminophenol, m-aminophenol or methylenedianiline, tetrafunctional epoxy resins based on methylenedianiline, and combinations thereof.

9. The epoxy system according to any one of claims 6 to 8, wherein the at least one flame retardant is selected from ammonium polyphosphate, aluminum hydroxide, tributyl phosphate, tri(2-ethylhexyl) phosphate, tri(2-chloroethyl) phosphate, tricresyl phosphate, triphenyl phosphate and 2-ethylhexyl diphenyl phosphate.

10. The epoxy system according to any one of claims 6 to 8, wherein the epoxy system further comprises at least one epoxy-reactive diluent selected from alkyl (C 12- C 14 ) glycidyl ether, p-tert-butylphenol glycidyl ether, cresyl glycidyl ether, 1,4-butanediol diglycidyl ether, cyclohexane dimethylol diglycidyl ether, resorcinol diglycidyl ether, trimethylolpropane triglycidyl ether, glycerol triglycidyl ether and neopentyl glycol diglycidyl ether.

11. The epoxy system according to claim 10, wherein the mixing ratio of the at least one epoxy resin to the at least one epoxy-reactive diluent is 50-99 wt%: 1-50 wt%.

12. The epoxy system according to any one of claims 6 to 11, wherein the mixing ratio of the curing agent composition to the at least one epoxy resin is 1-40 wt%: 60-95 wt%.

13. The epoxy system according to any one of claims 6 to 12, wherein the epoxy system further comprises reinforcing fibers.

14. The epoxy system according to claim 13, wherein the reinforcing fiber is selected from glass fiber, carbon fiber, ceramic fiber, polymer fiber, polyester fiber, polyamide fiber, aramid fiber, etc.

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