JP2003252957A - Preliminarily hardened and hardened products of epoxy resin composition and their production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a preliminarily hardened product and a hardened product of an epoxy resin composition having a stable and low dielectric loss tangent, high adhesion strength and high heat resistance and a method of producing the products. <P>SOLUTION: The products are made from an epoxy resin composition consisting of an epoxy resin, an active ester compound and a hardening accelerator and have a content of a residual organic solvent of 0.10 wt.% or lower. The method comprises hardening preliminarily an epoxy resin composition consisting of an epoxy resin, an active ester compound, a hardening accelerator and an organic solvent while evaporating the solvent to a content of residual organic solvent of 0.10 wt.% or lower, heating the resultant preliminarily hardened product further to obtain a hardened product of a content of residual organic solvent of 0.10 wt.% or lower with a difference between the content of residual organic solvent of the preliminarily hardened product and that of the hardened product of 0.02% or smaller. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a pre-cured product of an epoxy resin composition having excellent low dielectric loss tangent and adhesiveness, which uses an active ester compound as a curing agent, a cured product, and a method for producing the same. The pre-cured product and cured product of the epoxy resin composition of the present invention are preferably used for various molding materials, particularly low dielectric materials such as communication devices.

[0002]

2. Description of the Related Art Epoxy resins have been used in large amounts in electrical insulating materials such as printed wiring boards because of their excellent adhesiveness, insulation, heat resistance and chemical resistance. However, this epoxy resin is also required to have a further lower dielectric loss tangent in order to effectively suppress the transmission loss in recent high frequency communication, for example, high frequency communication at 1 GHz or higher.

Japanese Patent Publication No. 4-8444 and Japanese Unexamined Patent Publication No. 10-
JP 101775 discloses a curable epoxy resin composition using an active ester compound as a curing agent for an epoxy resin. A cured product of an epoxy resin composition using these active ester compounds as a curing agent has a lower hydroxyl group than that of an epoxy resin composition cured with another curing agent because it does not generate a hydroxyl group. It has excellent characteristics that it is dielectric and has low water absorption.

However, even a cured product of a curable epoxy resin composition using these active ester compounds has a dielectric loss tangent of 3 × 10 in a high frequency range, for example, 1 GHz.
^-3 or less, and further improvement is desired.

[0005]

The present inventors have conducted various studies to develop an epoxy resin composition using an active ester compound as a curing agent as a low dielectric material. Even when a resin composition is used in combination with a curing accelerator, the glass transition temperature and the adhesive strength of the resulting cured product are not stable, and in some cases it takes a long time to cure, and the curing is unstable. was there.

[0006] Therefore, the problem to be solved by the present invention is to provide a pre-cured product of an epoxy resin composition, a cured product, and a method for producing the cured product, which stably provide excellent low dielectric loss tangent, adhesive strength and heat resistance. To provide.

[0007]

An epoxy resin composition is usually a pre-cured product containing about 1% by mass of residual solvent, and the pre-cured product obtained is optionally cured to give a molded article. Generally, a cured product is obtained, and it is not necessary to control the residual solvent concentration to a low level of 0.5% by mass or less except for environmental considerations and suppression of bubble generation.

However, as a result of intensive studies conducted by the present inventors in order to solve the problem, in a curing system of an epoxy resin composition using an active ester compound as a curing agent, the amount of residual solvent in the epoxy resin composition is It was found that the properties of the cured product of the epoxy resin composition are seriously affected. Furthermore, the present inventors have determined the content of the residual organic solvent of the pre-cured product of the epoxy resin composition using the active ester compound as a curing agent and the content of the residual organic solvent of the cured product obtained by curing the pre-cured product. The present invention has been completed by confirming that the above problems can be solved by controlling the content of the residual organic solvent to be below a certain value and controlling the difference between the two residual organic solvent contents to below a certain value.

That is, the present invention is a pre-cured product of an epoxy resin composition comprising an epoxy resin (A), an active ester compound (B) and a curing accelerator (C), the residual organic matter of the pre-cured product. A pre-cured product of an epoxy resin composition, characterized in that the content (x) of the solvent is 0.10% by mass or less.

Further, the present invention is a cured product of an epoxy resin composition comprising an epoxy resin (A), an active ester compound (B) and a curing accelerator (C), wherein the residual organic solvent of the cured product is A cured product of an epoxy resin composition, characterized in that the content (y) is 0.10% by mass or less.

Furthermore, the present invention provides an epoxy resin (A),
The epoxy resin composition comprising the active ester compound (B), the curing accelerator (C) and the organic solvent (D) is added until the content of the residual organic solvent (x) in the preliminary cured product becomes 0.10% by mass or less. Preliminary curing is performed while volatilizing the organic solvent, and the obtained preliminary cured product is further heated and cured. The residual organic solvent content (y) of the obtained cured product is 0.10% by mass or less, and preliminary The difference between the content (x) of the residual organic solvent of the cured product and the content (y) of the residual organic solvent of the cured product is 0.0.
Provided is a method for producing a cured product of an epoxy resin composition, which is 2% or less.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The epoxy resin (A) used in the present invention refers to a compound having two or more epoxy groups in the molecule, and is not particularly limited as long as it is generally called an epoxy resin. can do. Specific examples include cresol novolac type epoxy resin, phenol novolac type epoxy resin, naphthol novolac type epoxy resin, biphenyl novolac type epoxy resin,
Bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, tetrabromobisphenol A type epoxy resin, biphenyl type epoxy resin, tetramethylbiphenyl type epoxy resin, triphenyl type epoxy resin,

Tetraphenyl type epoxy resin, naphthol aralkyl type epoxy resin, naphthalenediol aralkyl type epoxy resin, fluorene type epoxy resin, dicyclopentadiene type epoxy resin containing dicyclopentadiene skeleton, alicyclic type epoxy resin, polypropylene glycol And a glycidyl ether type epoxy resin of alcohol such as hydrogenated bisphenol A, a glycidyl amine type epoxy resin made of polyamine such as diaminodiphenylmethane as a raw material, and a mixture thereof.

Active ester compound (B) used in the present invention
Can be used without particular limitation as long as it has two or more ester groups in the molecule, does not contain a hydrophilic group such as a hydroxyl group, and can cure the epoxy resin. These are obtained by esterifying at least one of a polyvalent carboxylic acid and a polyhydric phenol with another compound having a phenolic hydroxyl group or a carboxylic acid. The polyvalent carboxylic acid referred to here is a carboxylic acid having two or more carboxyl groups, and 2 to 4 hydrogen atoms of an aliphatic carboxylic acid such as adipic acid or an aromatic compound are substituted with a carboxyl group. Aromatic carboxylic acids are mentioned. The polyhydric phenol is a compound having two or more phenolic hydroxyl groups, and examples thereof include those obtained by substituting 2 to 4 hydrogen atoms of an aromatic compound with hydroxyl groups.

Particularly, the active ester preferably used in the present invention includes 2 to 4 hydrogen atoms of an aromatic ring such as benzene, naphthalene, biphenyl, diphenylpropane, diphenylmethane, diphenylether and diphenylsulfone.
An aromatic carboxylic acid component selected from those in which one of them is substituted with a carboxyl group, a monovalent phenol in which one of the hydrogen atoms of the aromatic ring listed above is substituted with a hydroxyl group, and 2 to 4 of the hydrogen atoms of the aromatic ring An aromatic ester obtained by a condensation reaction of an aromatic carboxylic acid and a phenolic hydroxyl group from a phenol component having a molar ratio of a polyhydric phenol substituted with a hydroxyl group in a range of 100: 0 to 10:90 is exemplified. To be

When obtaining an aromatic ester, an aromatic carboxylic acid may be used in the condensation reaction in the form of a carboxylic acid halide in order to accelerate the reaction.

The active ester compound (B) is preferably blended in such a manner that the epoxy group of the epoxy resin (A) and the ester group of the active ester compound (B) are in a molar ratio of 0.8 to 1.1. If it is less than 0.8, the curing of the epoxy resin tends to be incomplete, which is not preferable, and if it exceeds 1.1, the dielectric properties tend to deteriorate, which is not preferable.

The epoxy resin composition of the present invention comprises a curing accelerator (C) together with an active ester compound (B) which is a curing agent.
To use. The curing accelerator (C) allows the reaction between the epoxy resin (A) and the active ester compound (B) to proceed efficiently.

As the curing accelerator (C), a general curing accelerator used for curing an epoxy resin can be used. Examples of the curing accelerator (C) include imidazole compounds such as 2-methylimidazole and 2-ethyl-4-methylimidazole, organic phosphine compounds such as triphenylphosphine and tributylphosphine, trimethylphosphite and triethylphosphite. An organic phosphite compound,

Phosphonium salts such as ethyltriphenylphosphonium bromide and tetraphenylphosphonium tetraphenylborate, amines such as triethylamine and 4-dimethylaminopyridine, 1,8 diazabicyclo (5,4,0) -undecene-7 (hereinafter referred to as DBU and Abbreviated) such as amines and DBU and terephthalic acid or 2,
Salts with 6-naphthalenedicarboxylic acid, quaternary ammonium salts such as tetrabutylammonium chloride, 3-
Examples thereof include urea compounds such as phenyl-1,1-dimethylurea, bases such as potassium hydroxide, and salts of crown ethers such as potassium phenoxide and potassium acetate. These may be used alone or as a mixture of two or more kinds. it can.

The compounding amount of the curing accelerator (C) is usually 0.01 to 12 parts by mass, preferably 0.1 to 4 parts by mass, more preferably 100 parts by mass of the epoxy resin (A). It is 0.2 to 1 part by mass. If the compounding amount of the curing accelerator (C) is less than 0.01 parts by mass, the curing reaction will be slow, and if it exceeds 12 parts by mass, the storage stability will be deteriorated and the epoxy resin will tend to self-polymerize.

Since the active ester compound (B) is usually a solid and it is difficult to dissolve it in the epoxy resin (A) even if the temperature is raised, it is preferable to obtain a composition with the epoxy resin (A) in a suitable manner. It is necessary to use an organic solvent (D) that dissolves the active ester compound (B).

The organic solvent (D) in which the active ester compound (B) is dissolved preferably has a boiling point of 220 ° C. or lower, and is a hydrocarbon-based organic solvent such as toluene, xylene or hexane, dioxolane or tetrahydrofuran (THF). ), An ether type organic solvent such as anisole,
Ketone-based organic solvents such as ethyl acetate, methyl isobutyl ketone, acetone, cyclohexanone, amide-based organic solvents such as N-methylpyrrolidone (NMP), N, N'-dimethylformamide, N, N'-dimethylacetamide, ethylene glycol Examples thereof include glycol-based organic solvents such as coal monomethyl ether and ethylene glycol monobutyl ether, and halogen-containing organic solvents such as methylene chloride and chlorobenzene.

To prepare the epoxy resin composition, the epoxy resin (A), the active ester compound (B) and the curing accelerator (C) are mixed in the organic solvent (D) and stirred. The temperature condition may be 0 to 50 ° C.
The stirring equipment may be either a batch type or a continuous type, and the mixing can be easily performed with a known and commonly used stirring equipment. The order of adding the epoxy resin (A), the active ester compound (B) and the curing accelerator (C) is not particularly limited.

The amount of the organic solvent (D) is the same as the organic solvent (D):
The mass ratio of [epoxy resin (A), active ester compound (B) and curing accelerator (C)] is 10:90 to 8 by mass.
It is preferably used in the range of 0:20. In this way, a uniform epoxy resin composition suitable for impregnation, coating and drying can be obtained. Inorganic fillers such as silica may be blended in the composition, and other leveling agents,
An antifoaming agent, a pigment, etc. may be added appropriately. Further, an excipient mainly composed of an inorganic substance such as glass fiber or aramid fiber may be added for pre-curing.

Further, after the epoxy resin composition is applied to a sheet, a plurality of sheets obtained by laminating a pre-cured product obtained by pre-curing while volatilizing an organic solvent at a predetermined temperature are laminated and further heat-formed. By this, the epoxy resin composition can be completely cured, and a laminate in which the cured epoxy resin composition is laminated can be obtained. These sheets or laminates have high dielectric strength and heat resistance in addition to low dielectric loss tangent and water absorption, and are useful as low dielectric materials.

In the present invention, the residual organic solvent content in the pre-cured product and the cured product of the epoxy resin composition is set to 0.10.
When the content is at most mass%, a cured product of an epoxy resin composition having a high glass transition temperature, an adhesive strength and a low dielectric loss tangent can be stably obtained. The content of the residual organic solvent of the present invention is calculated by the following formula.

[0028]

## EQU1 ## Content of residual organic solvent (mass%) = [(mass of organic solvent) / (epoxy resin, active ester compound,
Total mass of curing accelerator and organic solvent)] × 100

In the production of a cured product of the epoxy resin composition,
Most of the organic solvent contained in the epoxy resin composition is removed by so-called pre-curing, in which preliminary curing is performed while volatilizing the organic solvent. In the subsequent heat molding / curing process, the solvent is hard to evaporate because it is heated in a form close to a closed state. Therefore, in the curing system of the epoxy resin composition using the active ester compound of the present invention as a curing agent, the residual organic solvent content of the preliminary cured product is 0.10% by mass.
It is important that the content of the residual organic solvent in the pre-cured product and the cured product obtained by curing the pre-cured product is controlled to 0.10% by mass or less by controlling as follows.

The difference (x-y) between the residual organic solvent content (x) of the pre-cured product and the residual organic solvent content (y) of the cured product obtained by curing the pre-cured product is 0.02. It is preferable to control the content to be not more than mass%. When the residual organic solvent content of the pre-cured product and the cured product exceeds 0.10% by mass, the physical properties of the resulting cured product are likely to deteriorate. Further, when the difference (x-y) between the residual organic solvent content (x) of the preliminary cured product and the residual organic solvent content (y) of the cured product obtained by curing the preliminary cured product exceeds 0.02% by mass. Similarly, the physical properties of the cured product obtained in the same manner are likely to deteriorate.

The heating conditions for making the residual solvent content of the pre-cured product 0.10% by mass or less include factors that affect the conditions, such as the vapor pressure of the solvent used in the epoxy resin composition and the epoxy resin composition. It cannot be specified uniformly because there are many factors such as the diffusion rate of the solvent, the coating thickness, and the amount of air in the drying equipment, but normally, drying conditions of 40 to 160 ° C. for 1 to 80 minutes can be exemplified, and it is generally a rigid or horizontal type. It is preferable to carry out stepwise with a continuous dryer.

In order to remove the organic solvent (D) in a short time, it is preferable that the coating thickness of the epoxy resin composition is 1000 μm or less and the air is blown simultaneously with heating in the drying equipment. Particularly when a continuous drying equipment is used, it is effective to blow the air in the direction opposite to the traveling direction of the sheet coated with the epoxy resin composition to accelerate the removal of the solvent. Further, the heating temperature does not have to be constant, and for example, it is 30 to
It is preferable to carry out at 100 ° C. (primary drying step in the pre-curing step) and subsequently heat at a temperature of 100 to 200 ° C. (secondary drying step in the pre-curing step).

By such a stepwise heating operation, it is possible to prevent a problem that the outer surface of the coated epoxy resin composition is temporarily hardened and the diffusion and volatilization of the internal organic solvent (D) are prevented. . Such a pre-curing method by stepwise heating can be performed using a drying equipment of two or more stages, for example, 2 to 5 stages, but if the number of stages is unnecessarily increased, equipment cost and space will increase, which is not preferable. The above heating method is practical. It is also possible to set a temperature raising program at each stage. Further, it is preferable to connect the drying equipment of each stage.

The temperature distribution in the drying equipment is preferably as small as possible, and the width of the temperature distribution is preferably less than 10 ° C, more preferably less than 5 ° C. If the temperature distribution is large, it tends to increase the drying time and cause non-uniformity of the cured product.

It depends on the epoxy resin to be used, the active ester compound and the curing accelerator, the components of the epoxy resin composition such as solvent species, the mode of drying equipment, the coating thickness and the degree of preliminary curing of the desired epoxy resin. , For example, THF
When used as a solvent, it is pre-cured by primary drying at 30 to 100 ° C. for 3 to 20 minutes and then secondary drying at 100 to 160 ° C. at 6 to 15 minutes. When toluene is used as a solvent, primary drying is performed at 50 to 110 ° C. for 5 to 30 minutes, then 100 to 160 ° C., 12 to 4
Pre-cure by secondary drying for 0 minutes.

The subsequent complete curing of the pre-cured product is 130
It is carried out at a temperature of up to 250 ° C. for 0.5 to 15 hours, and a general batch press machine or a continuous double belt press machine can be used. For example, it may be carried out under a pressure of 0 to 50 MPa. A vacuum type press machine can also be used.

The cured product of the epoxy resin composition of the present invention thus obtained has a dielectric loss tangent of 3 × 10 ⁻³ or less at 1 GHz and 25 ° C., which shows an extremely low dielectric loss tangent. Further, the cured product of the epoxy resin composition of the present invention usually has an adhesive strength of 1.0 kN / m or more, and has excellent adhesiveness.

[0038]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these ranges. The measuring method and evaluation method used are as follows.

(Measurement Method of Residual Solvent Amount) 1 part by mass of a cured product (laminate) of an epoxy resin composition or a pre-cured product of an epoxy resin composition (a sheet obtained by laminating a pre-cured product of an epoxy resin on a PET film). Was collected and immersed in 99 parts by mass of anisole at 30 ° C. for 24 hours to obtain an anisole solution in which the residual solvent was extracted. The obtained anisole solution was analyzed by gas chromatography to determine the amount of each residual solvent.

The conditions of gas chromatography are shown below. Gas chromatography device: Shimadzu Corporation,
GC-14B column: Shimadzu Corporation 5% PEG20M carrier gas: nitrogen gas, flow rate 50 mL / min Column temperature condition: 3 when quantifying THF and toluene
After the temperature was raised to 200 ° C. at 100 ° C. for 10 minutes and 10 ° C./minute, the temperature was kept at 200 ° C. for analysis. When quantifying NMP, it was always kept at 160 ° C. for analysis.

[Method for measuring glass transition temperature (Tg)] D
The peak temperature of the tan δ curve measured using MS (manufactured by Seiko Instruments Inc., DMS200: dynamic viscoelasticity measuring instrument, bending mode, 1 kHz) at 5 ° C./minute was measured as Tg.

(Measurement method of dielectric loss tangent) Impedance / material analyzer manufactured by Agilent Technology Co., Ltd., test fixture 16453A manufactured by Agilent Technology Co., Ltd. is connected to HP4291B, and dielectric loss tangent at 25 ° C. and 1 GHz is measured. did.

(Measuring method of adhesive strength) Autograph AG
Width 1 cm x using S-H (manufactured by Shimadzu Corporation)
The PET film of the laminate, which was cut into a length of 10 cm, was peeled from the cured resin in the vertical direction at a rate of 5 mm / min for 5 cm, and the minimum strength thereof was determined as the adhesive strength.

<Production Example 1> (Production of active ester B-1) 0.2 mol (33.23 g) of isophthalic acid was placed in a 4-neck separable flask equipped with a stir bar, a cooling tube and a nitrogen introducing tube. (Manufactured by AJ International Chemical Co., Ltd.), 0.4 mol (57.67 g) of α-naphthol (manufactured by Sugai Chemical Co., Ltd.) and 0.48 mol (4
9.00 g) of acetic anhydride (manufactured by Wako Pure Chemical Industries, Ltd.) was put therein, and nitrogen was passed through for 30 minutes to replace the inside of the system with nitrogen.

Then, the temperature was raised with stirring while flowing nitrogen, and the temperature was maintained at 145 ° C. for 3 hours to acetylate the hydroxyl group of α-naphthol. It was confirmed by proton NMR that the hydroxyl groups were almost acetylated. When the temperature rises to 230 ° C, hold for 1 hour and gradually increase to 2
The temperature was raised to 50 ° C. over 3 hours, a deacetic acid reaction was performed, and esterification was performed. The obtained product was washed with boiling methanol three times and then vacuum dried at 60 ° C. for 17 hours to obtain 63 g of the active ester compound (B-1).

<Production Example 2> (Production of active ester B-2) 1 L of methylene chloride solution in which 0.3 mol (79.64 g) of trimesic acid chloride (manufactured by Tokyo Kasei Co., Ltd.) was dissolved in a 5 L beaker. And 0.9 mol (191.15 g) of 4-α-cumylphenol and 2 L of an aqueous solution having 38.00 g of sodium hydroxide dissolved therein, and stirred at 4000 rpm with a homogenizer T50 manufactured by Squid Co., Ltd. did. The obtained precipitate was washed with boiling methanol three times and then vacuum dried at 60 ° C. for 17 hours to obtain 190 g of an active ester compound (B-2).

Examples 1 to 5 and Comparative Examples 1 to 10 Epoxy resins, active ester compounds and curing accelerators were mixed in the amounts shown in Table 1 at 30 ° C. with stirring to prepare epoxy resin compositions. The obtained epoxy resin composition is made to have a thickness of 38.
A PET film (polyethylene terephthalate film, made by Unitika) having a thickness of 600 μm was cast-coated at a thickness of about 600 μm and pre-cured under the conditions shown in Tables 2 and 3 to prepare a sheet in which an epoxy resin was laminated on the PET film. . The prepared sheets were laminated so that the resin sides overlap each other, and pressure-molded in a batch type hot press at 190 ° C. for 4 hours under heating at 4 MPa to prepare a laminate. The drying conditions and the measurement results of the residual solvent in Examples and Comparative Examples are shown in Tables 2 and 3, and
Table 4 shows Tg, adhesive strength and dielectric loss tangent of the obtained cured product (laminate).

The epoxy resins used are as follows. HP-7200H: Dicyclopentadiene type epoxy resin (manufactured by Dainippon Ink and Chemicals, Inc., epoxy equivalent 2
78 g / eq), N-660: Cresol novolac type epoxy resin (manufactured by Dainippon Ink and Chemicals, Inc., epoxy equivalent 205 g)
/ Eq)

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

[Table 3]

[0052]

[Table 4]

The residual solvent concentration of each of the precured product and the cured product of the examples was 0.10% by mass or less, and the difference (xy) value in the residual solvent concentration of the precured product and the cured product was 0.02. %
The cured product of the present invention stably exhibited high Tg, adhesive strength, and low dielectric loss tangent of 3 × 10 ⁻³ or less.

On the other hand, the residual solvent concentration of the pre-cured product and the cured product exceeded 0.10% by mass, and the difference (xy) value in the residual solvent concentration of the pre-cured product and the cured product was 0.02. The cured product of the comparative example, which was not controlled to be less than%, compared with the example,
Both Tg and adhesive strength were low, and the dielectric loss tangent was also high. From these, it is clear that the cured product of the epoxy resin composition produced by the production method of the present invention is stable and has excellent low dielectric loss tangent, high adhesive strength and heat resistance.

[0055]

INDUSTRIAL APPLICABILITY The present invention can provide a pre-cured product, a cured product, and a method for producing the cured product of an epoxy resin composition which provides stable low dielectric loss tangent, excellent adhesive strength and heat resistance. The pre-cured product and cured product of the epoxy resin composition of the present invention are useful as various molding materials, particularly low dielectric materials such as communication equipment.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsuhito Kuroki             4-21-3 Inaridai, Sakura City, Chiba Prefecture (72) Inventor Yoshinari Shandong             1-27-1-1 203 Osakidai, Sakura City, Chiba Prefecture F-term (reference) 4J036 AA01 DA02 DB23 HA13 JA15

Claims (5)

[Claims] 1. A pre-cured product of an epoxy resin composition comprising an epoxy resin (A), an active ester compound (B) and a curing accelerator (C), the content of residual organic solvent of the pre-cured product. (X) is 0.10 mass% or less, the pre-cured material of the epoxy resin composition characterized by the above-mentioned. 2. A cured product of an epoxy resin composition comprising an epoxy resin (A), an active ester compound (B) and a curing accelerator (C), wherein the residual organic solvent content (y ) Is 0.10 mass% or less, a cured product of an epoxy resin composition. 3. The dielectric loss tangent at 25 ° C. and 1 GHz is 3 × 1.
The cured product of the epoxy resin composition according to claim 2, which is 0 to ³ or less. 4. An epoxy resin composition comprising an epoxy resin (A), an active ester compound (B), a curing accelerator (C) and an organic solvent (D) containing a residual organic solvent (x) of a pre-cured product. Precuring is carried out while volatilizing the organic solvent until the amount becomes 0.10% by mass or less, and the resulting precured product is further heated and cured, and the content (y) of the residual organic solvent in the obtained cured product. Is 0.10% by mass or less, and the difference between the residual organic solvent content (x) of the pre-cured product and the residual organic solvent content (y) of the cured product is 0.02% or less. A method for producing a cured product of a characteristic epoxy resin composition. 5. A cured product of an epoxy resin composition at 1 GHz
5. The method for producing a cured product of an epoxy resin composition according to claim 4, wherein the dielectric loss tangent is 3 × 10 ⁻³ or less.