JP7608235B2 - Thermosetting resin composition and method for producing cured molded article using same - Google Patents

Description

The present invention relates to a thermosetting resin composition and a method for producing a cured molded article using the same.

Generally, thermosetting resins require a mold to prevent deformation during hardening, and they take time to harden. For this reason, there is a limit to how many molded parts can be mass-produced in a short period of time.

Conventionally, methods of accelerating hardening by irradiating with microwaves or high frequency waves have been known. For example, Patent Document 1 discloses a clay-like molding material that contains magnetite or ferrite and is subjected to a thermal cross-linking treatment by irradiating with microwaves.

JP 2011-184532 A

The inventors of the present invention thought that if a thermosetting resin that can melt in an uncured state could be melt-molded using a mold and then cured after removal from the mold, it would be possible to dramatically improve the productivity (production efficiency) of molded thermosetting resin bodies. To achieve this, it is necessary to complete the curing reaction faster than the time required for melt deformation after removal from the mold. However, the above-mentioned conventional techniques have not yet succeeded in suppressing melt deformation. In other words, the conventional techniques have room for improvement in terms of providing a thermosetting resin composition that can be melt-molded in a mold and then cured without using a mold.

One aspect of the present invention aims to realize a thermosetting resin composition that can be melt-molded in a mold and then cured without using a mold.

As a result of intensive research to solve the above problems, the present inventors have found that by using a microwave sensitizer and a crosslinking agent in combination, it is possible to realize a thermosetting resin composition that can be cured while retaining its shape after being removed from a mold. The present invention includes the following aspects.
<1> A thermosetting resin composition comprising: (A) a thermosetting resin; (B) 1 to 15% by weight of a microwave sensitizer; and (C) 0.1 to 30% by weight of a crosslinking agent, wherein (A) the thermosetting resin is solid at room temperature; (B) the microwave sensitizer has an average particle size of 1 nm to 100 μm; and (C) the crosslinking agent is a polyfunctional organic compound.
<2> The thermosetting resin composition according to <1>, further comprising: (D) 0.001 to 15% by weight of a curing catalyst.
<3> The thermosetting resin composition according to <1> or <2>, wherein the thermosetting resin (A) is in an uncured state.
<4> The thermosetting resin composition according to any one of <1> to <3>, wherein the thermosetting resin (A) is at least one selected from the group consisting of a phenolic resin, an epoxy resin, an imide resin, a benzoxazine resin, and a bismaleimide resin.
<5> The thermosetting resin composition according to any one of <1> to <4>, wherein the microwave sensitizer (B) is a carbon material.
<6> A method for producing a molded product of a thermosetting resin composition, comprising: a step of putting the thermosetting resin composition according to any one of <1> to <5> into a mold, and melt-molding the composition at a temperature at which the thermosetting resin composition does not completely cure, to obtain a preformed product; and a step of irradiating the preformed product with microwaves in a state where the preformed product is removed from the mold, to cure the preformed product, to obtain a cured molded product.

According to one aspect of the present invention, a thermosetting resin composition can be provided that can be melt-molded in a mold and then cured without using a mold.

The embodiments of the present invention are described in detail below. Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more (including A and larger than A) and B or less (including B and smaller than B)."

[1. Thermosetting resin composition]
The thermosetting resin composition according to one embodiment of the present invention comprises: (A) a thermosetting resin; (B) 1 to 15% by weight of a microwave sensitizer; and (C) 0.1 to 30% by weight of a (A) the thermosetting resin is solid at room temperature, (B) the microwave sensitizer has an average particle size of 1 nm to 100 μm, and (C) the crosslinking agent is a polyfunctional It is a reactive organic compound.

In the technology described in Patent Document 1, when a spherical molded body with a diameter of 30 mm was subjected to a heat crosslinking treatment, it deformed to a diameter of 26 mm even under the best conditions, and the shape retention characteristics were insufficient. In the thermosetting resin composition according to one embodiment of the present invention, the microwave sensitizer absorbs microwaves and rapidly generates heat, and the crosslinking agent acts to promote the curing reaction before the resin flows. This makes it possible to speed up the crosslinking reaction. Therefore, according to one embodiment of the present invention, after the thermosetting resin composition is once placed in a mold and melt-molded, it is possible to quickly cure the thermosetting resin composition without giving it time to lose its shape, even without using a mold.

In the manufacturing process of a molded article using a thermosetting resin composition, for example, if a high-throughput device such as an injection molding machine is used for the initial melt molding process, the subsequent curing process becomes rate-limiting. Even in such a case, by using a thermosetting resin composition according to one embodiment of the present invention, it is possible to quickly cure the article while retaining its shape without using a mold. This reduces the time and cost required to manufacture the molded article, and improves productivity.

In this specification, the term "thermosetting resin composition" refers to a resin composition before curing. In other words, the thermosetting resin (A) may be in an uncured state. The thermosetting resin composition is obtained by mixing the components described below.

<1-1. Thermosetting resin＞
The thermosetting resin according to one embodiment of the present invention is solid at room temperature (10° C. to 35° C.). Examples of the thermosetting resin include phenolic resin, epoxy resin, urea resin, imide resin, benzoxazine resin, These may be used alone or in combination of two or more. From the viewpoint of shortening the curing time by microwave irradiation, benzoxazine resin, phenol resin, etc. , imide resins and bismaleimide resins are preferred.

The benzoxazine resin may be prepared by polymerizing a diamine compound, a triamine compound, a polyamine compound, or the like. Examples of diamine compounds include 4,4'-diaminodiphenyl ether, hexamethylene diamine, paraphenylene diamine, ethylene diamine, metaphenylene diamine, diaminodiphenylmethane, xylylene diamine, and the like. Examples of triamine compounds include diethylene triamine, bis(hexamethylene) triamine, and trisaminomethylphenol, and the like. Examples of polyamine compounds include triethylene tetramine, tetraethylene pentamine, and pentaethylene hexamine, and the like. The solvent used in the polymerization reaction is not particularly limited, and examples thereof include 2-methoxyethanol, dioxane, and toluene.

<1-2. Microwave sensitizer>
In this specification, the microwave sensitizer means a substance that absorbs microwaves and generates heat. The microwave sensitizer efficiently absorbs microwaves and generates heat, thereby accelerating the thermosetting reaction.

The content of microwave sensitizer in the thermosetting resin composition is 1 to 15% by weight, preferably 2 to 12% by weight, and more preferably 3 to 10% by weight. If the content of microwave sensitizer is 1% by weight or more, the heat generation by microwaves and the accompanying curing will proceed sufficiently. If the content of microwave sensitizer is 15% by weight or less, the microwaves will reach the inside of the resin composition, and the curing of the inside of the resin composition will also proceed sufficiently. If there is too much microwave sensitizer, a lot of the microwaves will be absorbed on the surface of the resin composition, and there is a risk that the microwaves will not reach the inside of the resin composition.

The average particle size of the microwave sensitizer is 1 nm to 100 μm, preferably 10 nm to 50 μm, and more preferably 30 μm to 20 μm. A microwave sensitizer with an average particle size of 100 μm or less can increase dispersibility in the resin, so a small amount is sufficient, and the surface area is large, so the thermal conductivity is high. This allows the thermosetting resin to be cured efficiently. Furthermore, if the average particle size of the microwave sensitizer is 1 nm or more, the heat generated by absorbing microwaves can be propagated to the surroundings. In this specification, the average particle size means a value measured by dynamic light scattering, laser diffraction, centrifugal sedimentation, etc.

Examples of microwave sensitizers include carbon materials and metal oxides. Among these, carbon materials are preferred from the viewpoints of compatibility with resins and mechanical strength of the cured product. Examples of carbon materials include graphite, graphene, carbon black, carbon nanotubes, and carbon fibers. Examples of carbon black include acetylene black, furnace black, channel black, and thermal black. Examples of metal oxides include iron oxide, zinc oxide, titanium oxide, copper oxide, cobalt oxide, barium titanate, and strontium titanate. These may be used alone or in combination of two or more.

<1-3. Crosslinking agent>
The content of the crosslinking agent in the thermosetting resin composition is 0.1 to 30% by weight, preferably 0.5 to 20% by weight, and more preferably 1 to 15% by weight. If the content of the crosslinking agent is 0.1% by weight or more, the thermosetting resin can be cured efficiently. If the content of the crosslinking agent is 30% by weight or less, it is preferable from the viewpoint of the mechanical strength, particularly the toughness, of the cured product.

The crosslinking agent according to one embodiment of the present invention is a polyfunctional organic compound. In this specification, a polyfunctional organic compound means an organic compound having two or more reactive functional groups. Examples of such reactive functional groups include an epoxy group, an amino group, a hydroxyl group, a carboxyl group, a carbonyl group, a thiol group, and a vinyl group.

Examples of polyfunctional organic compounds include polyfunctional epoxy compounds, polyfunctional amine compounds, polyfunctional phenol compounds, polyfunctional carboxylic acid compounds, polyfunctional carboxylic anhydrides, polyfunctional thiol compounds, polyfunctional vinyl compounds, polyfunctional alcohol compounds, polyfunctional isocyanate compounds, polyfunctional oxazoline compounds, and the like. These may be used alone or in combination of two or more. Compounds having multiple different reactive functional groups, such as amino acids or hydroxycarboxylic acids, may also be used.

Examples of crosslinking agents that are preferably used in combination with phenolic resins include polyfunctional epoxy compounds, polyfunctional carboxylic acid compounds, and polyfunctional isocyanate compounds. In addition to polyfunctional organic compounds, hexamethylenetetramine or trioxane can also be used as a crosslinking agent for phenolic resins. Examples of crosslinking agents that are preferably used in combination with epoxy resins include polyfunctional amine compounds, polyfunctional carboxylic acid anhydrides, polyfunctional phenolic compounds, polyfunctional carboxylic acid compounds, and polyfunctional alcohol compounds. Examples of crosslinking agents that are preferably used in combination with urea resins include polyfunctional carboxylic acid compounds and polyfunctional amine compounds. Examples of crosslinking agents that are preferably used in combination with imide resins include polyfunctional carboxylic acid compounds, polyfunctional carboxylic acid anhydrides, and polyfunctional amine compounds. Examples of crosslinking agents that are preferably used in combination with benzoxazine resins include polyfunctional carboxylic acid compounds, polyfunctional epoxy compounds, polyfunctional carboxylic acid anhydrides, polyfunctional amine compounds, and polyfunctional oxazoline compounds. Examples of crosslinking agents that are preferably used in combination with bismaleimide resins include polyfunctional thiol compounds, polyfunctional vinyl compounds, and polyfunctional amine compounds.

Examples of polyfunctional epoxy compounds include bisphenol-type epoxy compounds, novolac-type epoxy compounds, glycidyl ester-based epoxy compounds such as glycidyl phthalate ester, trisphenolmethane-type epoxy compounds, and tetrakisphenolethane-type epoxy compounds. Among these, examples of polyfunctional epoxy compounds that are preferably used in combination with phenolic resins or benzoxazine resins include bisphenol-type epoxy compounds, novolac-type epoxy compounds, and glycidyl ester-based epoxy compounds.

Examples of polyfunctional amine compounds include 4,4'-diaminodiphenyl ether, hexamethylene diamine, paraphenylene diamine, melamine, etc. Among them, examples of polyfunctional amine compounds that are preferably used in combination with epoxy resins or imide resins include hexamethylene diamine, paraphenylene diamine, melamine, etc.

Examples of polyfunctional oxazoline compounds include 2,2'-bis(2-oxazoline), 1,3-bis(2-oxazolin-2-yl)benzene, and 1,4-bis(4,5-dihydro-2-oxazolyl)benzene.

Examples of polyfunctional phenolic compounds include bisphenol A, hydroquinone, resorcinol, biphenol, naphthalenediol, and phenolic resins.

Examples of polyfunctional carboxylic acid compounds include terephthalic acid, oxalic acid, malonic acid, succinic acid, adipic acid, maleic acid, fumaric acid, phthalic acid, biphenyltetracarboxylic acid, pyromellitic acid, trimesic acid, naphthalenetetracarboxylic acid, perylenetetracarboxylic acid, and esters thereof. Among these, examples of polyfunctional carboxylic acid compounds that are preferably used in combination with epoxy resins or benzoxazine resins include terephthalic acid, phthalic acid, biphenyltetracarboxylic acid, pyromellitic acid, trimesic acid, and esters thereof.

Examples of polyfunctional carboxylic acid anhydrides include phthalic anhydride, biphenyl tetracarboxylic dianhydride, pyromellitic dianhydride, maleic anhydride, naphthalene tetracarboxylic dianhydride, and perylene tetracarboxylic dianhydride. Among them, examples of polyfunctional carboxylic acid anhydrides that are preferably used in combination with epoxy resins include phthalic anhydride, biphenyl tetracarboxylic dianhydride, pyromellitic dianhydride, and maleic anhydride. Examples of polyfunctional carboxylic acid anhydrides that are preferably used in combination with imide resins include biphenyl tetracarboxylic dianhydride. Examples of polyfunctional carboxylic acid anhydrides that are preferably used in combination with benzoxazine resins include phthalic anhydride, biphenyl tetracarboxylic dianhydride, and pyromellitic dianhydride.

Examples of polyfunctional thiol compounds include decanedithiol, trimethylolpropane tris(β-thiopropionate), and Karenz MT (registered trademark) manufactured by Showa Denko.

Examples of polyfunctional vinyl compounds include divinylbenzene, divinyl adipate, diallyl adipate, allyl ether, diisopropenylbenzene, diallyl maleate, diallyl urea, bisphenol A diallyl ether, diethylene glycol divinyl ether, allyl methacrylate, diallyl phthalate, trivinylbenzene, and triallyl isocyanurate.

Examples of polyfunctional alcohol compounds include ethylene glycol, glycerin, catechol, bisphenol A, hydroquinone, resorcinol, biphenol, naphthalenediol, and phenolic resins.

Examples of polyfunctional isocyanate compounds include ethylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, and isophorone diisocyanate.

<1-4. Curing catalyst>
The thermosetting resin composition may contain a curing catalyst. The content of the curing catalyst in the thermosetting resin composition is preferably 0.001 to 15% by weight, more preferably 0.01 The content of the curing catalyst is preferably 0.001% by weight or more, and more preferably 0.1% by weight or less .... If the content of the curing catalyst is 0.001% by weight or more, the thermosetting resin can be cured efficiently. A curing catalyst content of 15% by weight or less is preferred from the standpoint of mechanical properties, heat resistance and weather resistance of the cured product.

Examples of curing catalysts that are preferably used in combination with phenolic resins include acidic catalysts (oxalic acid, acetic acid, sulfonic acid, phosphoric acid, organic phosphonic acid), basic catalysts (sodium hydroxide, potassium hydroxide, calcium hydroxide, amines), etc. Examples of organic phosphonic acids include 1,4-butylenephosphonic acid, hexylphosphonic acid, 4-phosphonobenzoic acid, propylphosphonic acid, paraxylenediphosphonic acid, 4-hydroxybenzylphosphonic acid, ethylphosphonic acid, etc. Examples of amines include triethylamine, etc.

Examples of the curing catalyst that is preferably used in combination with the epoxy resin include triphenylphosphine, tertiary amines, dicyandiamide, diazabicycloundecene, morpholine, imidazole compounds, _BF3 complexes, phenol compounds, etc. Examples of the tertiary amines include triethylamine, triphenylamine, tetramethylphenylenediamine, etc. Examples of the imidazole compounds include phenylimidazole, 2-undecylimidazole, 1-benzyl-2-methylimidazole, 2-heptadecylimidazole, 2-isopropylimidazole, 2,4-dimethylimidazole, 2-phenyl-4-methylimidazole, etc. Examples of _{the BF3} complexes include _BF3 methanol complex, _BF3 butyl ether complex, _BF3 ethyl ether complex, etc. Examples of the phenol compounds include bisphenol A, hydroquinone, resorcinol, biphenol, etc.

Examples of curing catalysts that are preferably used in combination with urea resins include sodium hydroxide, ammonium carbonate, hexamethylenetetramine, sulfuric acid, formic acid, acetic acid, oxalic acid, phthalic acid, amine hydrochlorides, etc. Examples of amine hydrochlorides include hexamethylenediamine dihydrochloride, paraphenylenediamine dihydrochloride, melamine noradamantanamine hydrochloride, ethylenediamine dihydrochloride, benzylhydroxylamine hydrochloride, tetramethylphenylenediamine dihydrochloride, and diisobutylamine hydrochloride.

Examples of curing catalysts that are preferably used in combination with imide resins include amine compounds and carboxylic acid anhydrides. Examples of amine compounds include pyridine, triethylamine, diazabicyclooctane, diazabicycloundecene, hexamethylenediamine, paraphenylenediamine, and melamine. Examples of carboxylic acid anhydrides include acetic anhydride and trifluoroacetic anhydride.

Examples of curing catalysts that are preferably used in combination with benzoxazine resins include carboxylic acid compounds, phenolic compounds, sulfonic acids, Lewis acids, triphenyl phosphite, etc. Examples of carboxylic acid compounds include terephthalic acid, pyromellitic acid, trimesic acid, acetic acid, trifluoroacetic acid, benzoic acid, etc. Examples of phenolic compounds include phenol, hydroquinone, catechol, etc. Examples of Lewis acids include titanium tetrachloride, aluminum chloride, phosphorus pentachloride, etc.

Examples of curing catalysts that are preferably used in combination with bismaleimide resins include imidazoles and peroxides. Examples of peroxides include sodium peroxide, barium peroxide, magnesium peroxide, lithium peroxide, zinc peroxide, benzoyl peroxide, ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, peroxyesters, and perbenzoic acid.

These may be used alone or in combination of two or more. Among the crosslinking agents and curing catalysts, there are compounds that function as both crosslinking agents and curing catalysts, such as terephthalic acid, phthalic acid, pyromellitic acid, trimesic acid, bisphenol A, hydroquinone, resorcinol, biphenol, hexamethylenediamine, paraphenylenediamine, and melamine.

<1-6. Other ingredients>
The thermosetting resin composition may contain various additives such as flame retardants, nucleating agents, antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, lubricants, flame retardant assistants, antistatic agents, antifogging agents, fillers, softeners, plasticizers, and colorants. These may be used alone or in combination of two or more. The content of the additives in the thermosetting resin composition is not limited and may be, for example, 0 to 20% by weight, 0 to 10% by weight, 0 to 5% by weight, or 0 to 1% by weight.

The thermosetting resin composition preferably does not substantially contain any substances with a boiling point of 120°C or less, or any compounds that decompose at a temperature of 120°C or less to generate a gas or liquid. For example, the content of such substances and compounds in the thermosetting resin composition may be 0 to 5% by weight, or may be 0 to 3% by weight.

2. Method for producing molded article from thermosetting resin composition
The method for producing a cured molded body according to one embodiment of the present invention includes the steps of putting the above-mentioned thermosetting resin composition into a mold, melt-molding the composition at a temperature at which the thermosetting resin composition does not completely cure, to obtain a preformed body, and irradiating the preformed body with microwaves in a state where the preformed body is removed from the mold to cure the preformed body. In this specification, the term "preformed body" refers to a molded body obtained by melt-molding the thermosetting resin composition put into a mold. In addition, the term "cured molded body" refers to a molded body obtained by irradiating microwaves in a state where the preformed body is removed from the mold to cure the preformed body.

Materials for the mold include metal, clay, stone, glass, resin, etc. The temperature at which the thermosetting resin composition does not completely cure is, for example, the temperature at which the degree of cure of the preform obtained by melt molding does not reach 50% when the degree of cure of the preform is measured by a method similar to that of the cured molded body described in the Examples below. The temperature can be set appropriately depending on the type and amount of the thermosetting resin, crosslinking agent, curing catalyst, etc.

The microwave wavelength is preferably 0.3 to 30 GHz, and more preferably 1 to 20 GHz. If the microwave wavelength is within the above range, the thermosetting resin composition can be heated efficiently. The heating temperature by microwaves is preferably such that the temperature of the uncured resin composition is 150 to 250°C, and more preferably 170 to 200°C.

The microwave irradiation time is preferably 1 to 10 minutes, more preferably 1 to 5 minutes, and even more preferably 1 to 3 minutes. The above-mentioned thermosetting resin composition efficiently absorbs microwaves, so it can be cured in such a short time.

The thickness of the resulting cured resin may be 0.1 to 300 mm, or 10 to 100 mm. The thickness of the thermosetting resin composition to which microwaves are irradiated may be set to the thickness described above. Since the above-mentioned thermosetting resin composition efficiently absorbs microwaves, a cured product having a certain degree of thickness can be efficiently obtained by the above-mentioned manufacturing method. Note that the "thickness" referred to here refers to the maximum thickness of the resulting cured resin, or the thermosetting resin composition that is the material.

The thermosetting resin composition may be impregnated into a sheet made of carbon fiber or the like and then cured.

3. Uses of the thermosetting resin composition
Applications of the thermosetting resin composition include, for example, films, sheets, containers, housings, building materials, dolls, and structural materials.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in different embodiments.

The following examples and comparative examples are provided to explain one embodiment of the present invention, but are not intended to limit the scope of the present invention.

[Method of measuring degree of cure]
The cured molded bodies obtained in the Examples, Comparative Examples, and Reference Examples described below were crushed uniformly. 3 to 10 mg of the crushed cured molded bodies were sampled, and the area of the exothermic peak of the curing reaction was determined by DSC analysis. In addition, the area of the exothermic peak of the curing reaction was similarly determined by DSC analysis using the resin compositions before curing in each of the Examples, Comparative Examples, and Reference Examples. The degree of curing was estimated from the ratio of the area of the exothermic peak of the curing reaction of the cured molded body to the area of the exothermic peak of the curing reaction of the resin composition before curing.

Example 1
Pd-type benzoxazine (10 g) manufactured by Shikoku Kasei Kogyo Co., Ltd. and 4,4'-diaminodiphenyl ether (3.5 g) were reacted by stirring in 2-methoxyethanol (100 mL) at 50°C for 5 days. The resulting precipitate was filtered to obtain an uncured thermosetting resin. The uncured thermosetting resin obtained by this reaction is hereinafter referred to as PDDA. This PDDA was found to be an oligomer with a number average molecular weight of 1600 and a weight average molecular weight of 9200 by GPC analysis using N-methylpyrrolidone as an eluent. This thermosetting resin PDDA (426.5 mg), acetylene black (AB) (26.1 mg, 5.2 wt%) as a microwave sensitizer, and terephthalic acid (TPA) (51.3 mg, 10.2 wt%) as a curing catalyst and crosslinking agent were placed in an agate mortar and ground and mixed for 12 minutes. The average particle size of the ground AB was 35 nm.

The obtained thermosetting resin composition (73.1 mg) was placed in a cylindrical mold and heated in an electric furnace at 120°C for 5 minutes to melt mold. The obtained preform was removed from the mold and measured to have a size of Φ5.70 mm x H5.10 mm. The preform removed from the mold was irradiated with microwaves at 150°C for 1 minute (2.45 GHz) using an Anton Paar Monowave 300. Since no exothermic peak was observed during curing in the DSC analysis, the molded product was determined to be completely cured (100% cured). The size of this cured molded product was Φ5.85 mm x H4.95 mm, which was the same as the preformed product before curing.

Comparative Example 1
P-d-type benzoxazine (950.0 mg) was used as an uncured thermosetting resin instead of PDDA, and TPA (50.4 mg, 5.0 wt%) was used as a curing catalyst and crosslinking agent, and the mixture was ground and mixed in an agate mortar for 10 minutes. The obtained thermosetting resin composition (134.2 mg) was placed in a cylindrical mold and melt-molded by heating in an electric furnace at 100°C for 5 minutes. The size of the obtained preform was Φ6.10 mm x H5.20 mm when it was removed from the mold. The preform removed from the mold was irradiated with microwaves in a microwave oven under the conditions of 200 W, 15 minutes → 500 W, 15 minutes. As a result, the obtained cured molded product was melted and deformed. The size of the cured molded product was Φ8.20 mm x H2.75 mm. The degree of curing of the obtained cured molded product was 41%.

Comparative Example 2
PDDA (990.4 mg) described in Example 1 as a thermosetting resin and single-walled carbon nanotubes (CNT) (10.2 mg, 10.2 wt%) as a microwave sensitizer were ground and mixed in an agate mortar for 30 minutes. The obtained thermosetting resin composition (88.3 mg) was placed in a cylindrical mold and heated in an electric furnace at 120 ° C for 5 minutes to be melt-molded. The size of the obtained preformed body measured after being removed from the mold was Φ4.80 mm × H4.90 mm. The preformed body removed from the mold was irradiated with microwaves in a microwave oven under the conditions of 500 W, 15 minutes → 700 W, 45 minutes. The degree of curing of the obtained cured molded body was 26%, and curing did not progress.

[Reference Example 1]
The same thermosetting resin composition (22.6 mg) as in Example 1 was placed in a cylindrical mold in the same manner as in Example 1, and melt-molded by heating in an electric furnace at 120°C for 5 minutes. The obtained preform was removed from the mold and measured for size to be Φ4.60 mm x H1.80 mm. This preform was heated in an electric furnace at 200°C for 2 hours to be cured. As a result, the obtained cured molded product was melt-deformed. The size of the cured molded product was Φ5.10 mm x H1.35 mm. The degree of curing of the cured molded product was 100%.

Example 2
Pd-type benzoxazine (P-d) (594 mg) manufactured by Shikoku Chemical Industry Co., Ltd., acetylene black (AB) (99.9 mg, 10.0 wt%) as a microwave sensitizer, 1,3-bis(2-oxazolin-2-yl)benzene (BPO) (295.3 mg, 29.5 wt%) as a crosslinker, and triphenyl phosphite (TPP) (10.3 mg, 1.0 wt%) as a curing catalyst were placed in an agate mortar and ground and mixed for 12 minutes. The average particle size of the ground AB was 35 nm.

The obtained thermosetting resin composition (74.3 mg) was placed in a cylindrical mold and melt-molded by heating in an electric furnace at 120°C for 5 minutes. The obtained preform was removed from the mold and measured for size to be Φ5.10 mm x H4.35 mm. The preform removed from the mold was irradiated with microwaves at 700 W for 3 minutes (2.45 GHz) using a microwave oven. The degree of cure determined from the heat generation peak during curing in DSC analysis was 91%. The size of this cured molded product was Φ5.05 mm x H4.20 mm, which was the same as the preform before curing.

Example 3
Ba-type benzoxazine (Ba) (797.5 mg) manufactured by JFE Chemical Corporation, acetylene black (AB) (101.3 mg, 10.2 wt%) as a microwave sensitizer, and terephthalic acid (TPA) (97.4 mg, 9.8 wt%) as a crosslinking agent and curing catalyst were placed in an agate mortar and ground and mixed for 12 minutes. The average particle size of the ground AB was 35 nm.

The obtained thermosetting resin composition (74.3 mg) was placed in a cylindrical mold and melt-molded by heating in an electric furnace at 120°C for 5 minutes. The obtained preform was removed from the mold and measured for size Φ5.65 mm x H4.60 mm. The preform removed from the mold was irradiated with microwaves using a microwave oven under the conditions of 500 W for 1 minute + 700 W for 1 minute (2.45 GHz). The degree of cure determined from the heat generation peak during curing in DSC analysis was 98%. The size of this cured molded product was Φ5.70 mm x H4.45 mm, which was the same as the preform before curing.

Example 4
A similar experiment was carried out using carbon nanotubes (CNT) instead of AB in Example 2. The size of the preform was Φ5.25 mm×H4.50 mm, while the size of the cured molded body was Φ5.40 mm×H4.40 mm, and the degree of curing was 90%.

〔summary〕
In Examples 1 to 4, in which a specific microwave sensitizer and crosslinking agent were used in combination, it was possible to obtain a cured molded product that retained its shape after removal from the mold. On the other hand, in Comparative Example 1, in which no microwave sensitizer was used, melt deformation occurred. In Comparative Example 2, in which no crosslinking agent was used, curing was insufficient.

It is also possible to harden the material by heating in an electric furnace without irradiating it with microwaves as in Reference Example 1, but this took longer to harden than in Example 1. In addition, deformation due to melting also occurred.

The present invention can be used in fields that use thermosetting resins.

Claims (5)

(A) a thermosetting resin, (B) 1 to 15% by weight of a microwave sensitizer, and (C) 0.1 to 30% by weight of a crosslinking agent;
(A) the thermosetting resin is a solid at room temperature;
(A) the thermosetting resin is a benzoxazine resin;
(B) the microwave sensitizer has an average particle size of 1 nm to 100 μm;
(C) the crosslinking agent is a polyfunctional organic compound;
(C) A thermosetting resin composition, wherein the crosslinking agent is a polyfunctional carboxylic acid compound or a polyfunctional oxazoline compound . The thermosetting resin composition according to claim 1 further comprises (D) 0.001 to 15% by weight of a curing catalyst. The thermosetting resin composition according to claim 1 or 2, wherein (A) the thermosetting resin is in an uncured state. The thermosetting resin composition according to any one of claims 1 to 3 , wherein the microwave sensitizer (B) is a carbon material. A step of putting the thermosetting resin composition according to any one of claims 1 to 4 into a mold and melt-molding the thermosetting resin composition at a temperature at which the thermosetting resin composition is not completely cured to obtain a preform;
and curing the preform by irradiating the preform with microwaves while the preform is removed from the mold to obtain a cured molded body.