JPH06106676A - Flame-retardant epoxy resin copper-clad laminate - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a flame-retardant epoxy resin laminate suitable for a multilayer printed wiring board for high-speed arithmetic processing. [Structure] General Formula 1 (N is a number of 1 to 10, R and R'at least one is an alkyl group having 2 to 10 carbon atoms, P and Q are each independently, at least one of them is an alkyl group having 4 to 10 carbon atoms,
i and j are integers from 1 to 4), a halogen-containing bisphenol compound and an epoxy resin obtained by reacting a diglycidyl ether of the halogen-containing bisphenol compound are used. Copper-clad laminate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame retardant epoxy resin copper clad laminate, and more particularly to a flame retardant epoxy resin copper clad laminate excellent in low dielectric property.

[0002]

2. Description of the Related Art Conventionally, among epoxy resin compositions used for electric and electronic applications, a combination of a bisphenol type epoxy resin and dicyandiamide has been mainly used as a material for a printed wiring board. In recent years, as the density of printed wiring boards has increased and the number of layers has increased, low dielectric properties of resins have been required mainly for the purpose of improving signal speed. In the conventional epoxy resin composition as a means for meeting this demand, the addition of a low-dielectric thermoplastic resin is known, but this method has the drawback of impairing the heat resistance and adhesiveness of the epoxy resin. It has been pointed out that the demand for a low dielectric resin that can withstand practical use cannot be sufficiently satisfied. Therefore, a resin having a low dielectric constant of the epoxy resin itself has been developed by introducing an appropriate skeleton into the epoxy compound (Japanese Patent Laid-Open No. 64-52768). On the other hand, printed wiring boards are required to be flame retardant. As a general flame retardancy imparting method, a halogenated bisphenol compound such as tetrabromobisphenol A,
Preliminary reaction of an epoxy compound has been attempted (JP-A-1-304110).

[0003]

However, in order to introduce an amount of halogen atoms that achieves the UL standard 94V-0, which is an index of flame retardancy, it is possible to avoid increasing the viscosity of the resin by the above method. Therefore, it is not necessarily suitable for practical use in terms of operability such as impairing impregnation into a substrate such as glass cloth. Therefore, a laminated plate using a flame-retardant epoxy resin composition, which has a low viscosity, good impregnability into a substrate such as glass cloth, excellent operability, without impairing the low dielectric property of an epoxy compound, has been earnestly desired. It was

[0004]

Means for Solving the Problems The inventors of the present invention continued to earnestly study the skeleton structure of an epoxy compound, the operability in producing a copper clad laminate, and various properties of the obtained laminate, and as a result, The inventors have found that the composition has excellent low dielectric properties, flame retardancy and operability, and have completed the present invention.

That is, the present invention provides the following general formula 4

[Chemical 4] (In the formula, n represents an average number of repeating units and takes a value of 0 to 10. R and R ′ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or a cycloalkyl having 5 to 7 carbon atoms. Group is shown, but at least one is an alkyl group having 2 to 10 carbon atoms or a cycloalkyl group having 5 to 7 carbon atoms, and P and Q are each independently at least one alkyl group having 4 to 10 carbon atoms. Alternatively, it is a cycloalkyl group having 5 to 7 carbon atoms, and the other is an alkyl group having 1 to 10 carbon atoms or a cycloalkyl group having 5 to 7 carbon atoms, which may be the same or different from each other. , J each independently have an integer value of 1 to 4), and an epoxy compound (A) represented by

The following general formula 5

[Chemical 5] (In the formula, A represents a divalent organic group having 1 to 20 carbon atoms.
X and X ′ may be each independently at least one halogen atom and the other may be an alkyl group having 1 to 10 carbon atoms or a cycloalkyl group, and X and X ′ may be the same as each other. It may be different. k and l each independently take an integer value of 1 to 4. ) A halogen-containing bisphenol compound (B) represented by

The following general formula 6

[Chemical 6] (In the formula, B represents a divalent organic group having 1 to 20 carbon atoms.
Y and Y'may each independently be at least one halogen atom and the other may be an alkyl group having 1 to 10 carbon atoms or a cycloalkyl group, and Y and Y'may be the same as each other. It may be different. m and n each independently take an integer value of 1 to 4. ) A flame-retardant epoxy resin composition containing an epoxy resin obtained by reacting a diglycidyl ether (C) of a halogen-containing bisphenol compound (C) and an epoxy resin curing agent as essential components is dissolved in an organic solvent to form a base material. The present invention relates to a flame-retardant epoxy resin copper-clad laminate obtained by heat-molding a prepreg obtained by impregnation and a copper foil.

The present invention will be described in more detail below. As a general method for synthesizing the epoxy compound (A) used in the copper-clad laminate of the present invention, the following general formula 7

[Chemical 7] (In the formula, R, R ′, P, Q, i, and j are defined by the above general formula 1
As defined in. ) And a bisphenol type compound represented by the formula (1) and an epihalohydrin exemplified by epichlorohydrin or epibromohydrin can be synthesized by a known method such as a dehydrohalogenation reaction with a base, and dimethyl sulfoxide (DMS).
A method of highly purifying using an aprotic polar solvent such as O) is more preferably used.

The above-mentioned bisphenol type compounds can be used in addition to the methods described in US Pat. No. 4,560,808, German Patent 2418975, etc., as well as those obtained by any known method.

As a general method for producing the above bisphenol type compound, the following general formula 8

[Chemical 8] (In the formula, P and i are defined in the same manner as in General Formula 1 above.)

The following general formula 9

[Chemical 9] (In the formula, Q and j are defined in the same manner as in General Formula 1 above.), And

The following general formula 10

[Chemical 10] (In the formula, R and R ′ are defined in the same manner as in the above-mentioned general formula 4.) A carbonyl compound represented by the formula or an acetalized compound thereof can be obtained by reacting in the presence of an acid catalyst. Although illustrated, it is not limited to this.

In the above general formula 4, the average number of repeating units n can take any value from 0 to 10. However, in order not to impair the operability and curing reaction rate of the epoxy resin, n is
It is preferably 0-5.

Further, R and R'in the above general formula are each a hydrogen atom, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group or the like, and an alkyl group having 1 to 10 carbon atoms, Examples thereof include cycloalkyl groups having 5 to 7 carbon atoms represented by a cyclopentyl group, a cyclohexyl group, a cycloheptyl group and the like, but at least one of them is used in view of achieving a low dielectric constant and economy as a raw material in the present invention. Is an alkyl group having 2 to 10 carbon atoms or a cycloalkyl group having 5 to 7 carbon atoms, of which n-propyl group, is
o-propyl group, n-butyl group, iso-butyl group, s
It is preferably an ec-butyl group or a cyclohexyl group.

P and Q in the above general formula are each independently a C 1-10 alkyl group represented by a methyl group, an ethyl group, a propyl group, a butyl group, etc., a cyclopentyl group, a cyclohexyl group, and a methylcyclohexyl group. Group, cyclohexylmethyl group, cycloheptyl group and the like are exemplified by cycloalkyl groups having 5 to 7 carbon atoms. In order to achieve the object of the present invention to achieve a low dielectric constant, P, Q
For each, at least one is an n-butyl group, i
so-butyl group, sec-butyl group, tert-butyl group, n-amyl group, iso-amyl group, sec-amyl group, tert-amyl group, n-hexyl group, iso-hexyl group, heptyl group, octyl group Such as an alkyl group having 4 to 10 carbon atoms, or a cyclopentyl group,
A cycloalkyl group having 5 to 7 carbon atoms, which is represented by a cyclohexyl group and a cycloheptyl group, is preferable.

Among the bisphenols represented by the above general formula 4 as a raw material of the epoxy compound (A), preferred ones are specifically exemplified by 1,1-bis (4-hydroxy-5-t-). Butyl-2-methylphenyl) butane, 1,1-bis (4-hydroxy-3-t-butylphenyl) butane, 1,1-bis (4-hydroxy-5)
sec-butyl-2-methylphenyl) butane, 1,1
-Bis (4-hydroxy-3-sec-butylphenyl) butane, 1,1-bis (4-hydroxy-5-t-
Amyl-2-methylphenyl) butane, 1,1-bis (4-hydroxy-3-t-amylphenyl) butane,
1,1-bis (4-hydroxy-5-sec-amyl-
2-methylphenyl) butane, 1,1-bis (4-hydroxy-3-sec-amylphenyl) butane, 1,1
-Bis (4-hydroxy-5-cyclohexyl-2-methylphenyl) butane, 1,1-bis (4-hydroxy-3-cyclohexylphenyl) butane, 2,2-bis (4-hydroxy-5-t-butyl) -2-Methylphenyl) heptane, 2,2-bis (4-hydroxy-3-t)
-Butylphenyl) heptane, 2,2-bis (4-hydroxy-5-cyclohexyl-2-methylphenyl) heptane, 2,2-bis (4-hydroxy-3-cyclohexylphenyl) heptane, 1,1-bis ( 4-hydroxy-5-t-butyl-2-methylphenyl) hexane, 1,1-bis (4-hydroxy-3-t-butylphenyl) hexane, 1,1-bis (4-hydroxy-5)
-Cyclohexyl-2-methylphenyl) hexane,
1,1-bis (4-hydroxy-3-cyclohexylphenyl) hexane, 3,3-bis (4-hydroxy-5)
-T-butyl-2-methylphenyl) hexane, 3,3
-Bis (4-hydroxy-3-t-butylphenyl) hexane, 3,3-bis (4-hydroxy-5-cyclohexyl-2-methylphenyl) hexane, 3,3-bis (4-hydroxy-3-cyclohexyl) Phenyl) hexane and the like.

In the halogen-containing bisphenol compound (B) used in the present invention, A in the above general formula represents a divalent organic group, for example, methylene, ethylidene, propylidene, isopropylidene, butylidene, isobutylidene, pentylidene. , Alkylidene groups such as isopentylidene, hexylidene, isohexylidene, cycloalkylidene groups such as cyclopentylidene, cyclohexylene, cycloheptylene, arylalkylidene groups such as phenylmethine, naphthylmethine, phenylethylidene, naphthylethylidene, cyclohexylmethine, cycloheptylmethine, etc. The cycloalkylalkylidene group and the like can be mentioned, but methylene, isopropylidene and cyclohexylidene are preferable.

In the above general formula, X and X'independently represent at least one halogen atom, preferably a bromine atom among fluorine atom, chlorine atom, bromine atom and iodine atom. In the case of a substituent other than a halogen atom, it may be an alkyl group having 1 to 10 carbon atoms or a cycloalkyl group, preferably a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, sec-
A butyl group, a t-butyl group, a t-amyl group, an isoamyl group, a cyclopentyl group, a cyclohexyl group, and a cycloheptyl group. Further, they may be the same as or different from each other.

Specific examples of the halogen-containing bisphenol compound (B) in the present invention include tetrabromobisphenol A, tetrachlorobisphenol A,
Tetraiodobisphenol A, tetrabromobisphenol F, tetrachlorobisphenol F, tetrabromobisphenol C, tetrachlorobisphenol C,
Examples thereof include tribromobisphenol A and 2,2′-dibromobisphenol A, and tetrabromobisphenol A is preferably used from the viewpoints of economical efficiency and imparting efficient flame retardancy.

Regarding the diglycidyl ether (C) of the halogen-containing bisphenol compound in the present invention, B in the above general formula may have the same definition as in the above A,
Y and Y ′ may have the same definition as X and X ′ above.

Specific examples of the diglycidyl ether (C) of the halogen-containing bisphenol compound are tetrabromobisphenol A diglycidyl ether, tetrachlorobisphenol A diglycidyl ether, and tetraiodobisphenol A diglycidyl ether, Tetrabromobisphenol F diglycidyl ether, tetrachlorobisphenol F diglycidyl ether, tetrabromobisphenol C diglycidyl ether, tetrachlorobisphenol C diglycidyl ether, tribromobisphenol A diglycidyl ether, 2,2′- Examples of the diglycidyl ether of dibromobisphenol A include diglycidyl tetrabromobisphenol A from the viewpoint of economical efficiency and efficient flame retardancy. Zyl ether is preferably used.

The reaction between the epoxy compound (A), the halogen-containing bisphenol compound (B) and the diglycidyl ether (C) of the halogen-containing bisphenol compound may be carried out by a known method. For example, the above components can be reacted in the presence of a basic catalyst such as triphenylphosphine or imidazole. By reacting, the glass transition temperature can be controlled and the flame retardancy can be imparted by changing the distance between the cross-linking points without volatilization of the low molecular weight substance at the time of curing.

In the present invention, a known curing agent can be used as the epoxy resin curing agent. For example, phenol novolac, cresol novolac, 1,1,1
-Tris (hydroxyphenyl) ethane, polycondensation product of phenols and aromatic aldehydes, oligomer of adduct of phenols and unsaturated alicyclic compound, xylylene bond oligomer of phenols, polyhydroxystyrene, polyhydroxybromo Amine curing agents such as polyhydric phenols such as styrene, aromatic amines and aliphatic amines,
Examples thereof include acid anhydrides, dicyandiamide, hydrazide compounds and Lewis acid complexes. Preferred are dicyandiamide and polyhydric phenols. Further, the blending amount thereof is preferably 0.2 to 1.2 equivalents with respect to the epoxy group.

Further, to the extent that the effects of the present invention are not impaired,
Conventionally known bifunctional epoxy resin, polyfunctional epoxy resin,
It is also possible to use another thermosetting resin or a thermoplastic resin having a functional group in combination. Specifically, glycidyl ether of bisphenol A, glycidyl ether of phenol novolac, glycidyl ether of cresol novolac, glycidyl ether of brominated phenol novolac, unsaturated polyester resin, cyanate resin, maleimide resin, glycidyl modified polybutadiene,
Examples thereof include maleic anhydride-modified polyethylene. These resins may be mixed in the resin of the present invention, or may be used after being reacted with the resin of the present invention in advance.

In the present invention, known additives such as a curing accelerator, a flame retardant and a surface treatment agent may be added to the composition depending on the purpose. Examples of the curing accelerator include imidazoles, tertiary amines and phosphorus compounds, examples of the flame retardant include antimony trioxide, aluminum hydroxide and red phosphorus, and examples of the surface treatment agent include silane coupling agents.

The copper-clad laminate of the present invention can be prepared by a known method. That is, it is a method of impregnating a base material with a resin varnish prepared by dissolving the above resin composition in an organic solvent, heat-treating the prepreg, and then heat-molding the prepreg and the copper foil to form a copper-clad laminate.

The organic solvent used is one or more of acetone, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, toluene, xylene, N, N-dimethylformamide, dioxane and tetrahydrofuran. Is selected as a mixed solvent of.

The base material impregnated with the resin varnish is an inorganic fiber such as glass fiber, polyester fiber or polyamide fiber,
Woven cloth made of organic fibers, or non-woven cloth or mat,
Paper or the like may be used alone or in combination.

The heat treatment conditions for the prepreg are the solvent used,
The temperature is usually 80 ° C. to 220 ° C. and the time is 3 minutes to 30 minutes, although it is appropriately selected depending on the type and amount of the added catalyst and various additives. The heat molding conditions are 150 ° C to 30
0 temperature 10kg / cm ² ~100kg / cm 20 to 300 minutes of heat-pressed at ² of the molding pressure ℃ are exemplified.

[0030]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto. In the examples, the epoxy equivalent is defined as the molecular weight of the epoxy resin per epoxy group. The OH equivalent is defined by the molecular weight of the OH compound per hydroxyl group. Bromine content is defined as the weight percent of bromine based on resin solids.

Synthesis Example 1 This synthesis example relates to a method for producing an epoxy compound (A) which is a constituent of the epoxy resin composition used in the present invention. 1,1-bis (5-t-butyl-4-hydroxy-2-methylphenyl) butane 114.6 g (0.
6 OH moleq, OH equivalent 191 g / eq. ),
388.5 g (4.2 mol) of epichlorohydrin and 195.3 g of dimethyl sulfoxide were placed in a 1-liter 4-neck flat-bottomed flask equipped with a thermometer, a stirrer, and a condenser with a separating tube, and the conditions were 48 ° C. and 41 torr. 49.38 g (0.6 m of 48.6% caustic soda aqueous solution)
ol) Add dropwise over 4 hours. During this time, while keeping the temperature at 48 ° C., the azeotropically-formed epichlorohydrin and water were cooled and liquefied, and the reaction was performed while returning the organic layer into the reaction system.

After completion of the reaction, the unreacted epichlorohydrin is removed by concentration under reduced pressure, the by-product salt and the epoxidized product containing dimethylsulfoxide are dissolved in methyl isobutyl ketone, and the by-product salt and dimethylsulfoxide are washed with warm water. Removed. By removing the solvent under reduced pressure, 143.1 g of an epoxy compound was obtained.

The epoxy equivalent of the epoxy compound thus obtained was 260 g / eq. As a result of infrared absorption spectrum measurement, absorption of phenolic OH 3200-
3600 cm ^-1 disappeared, epoxide absorption 1240,
It was confirmed to have an absorption of 910 cm ^-1 .

Synthesis Example 2 In this synthesis example, the epoxy compound obtained in Synthesis Example 1 was added to the diglycidyl ether of tetrabromobisphenol A and tetrabromobisphenol A to give a flame-retardant material having a bromine content of 20% by weight. The present invention relates to a method for obtaining a terminal epoxy resin.

Epoxy compound 70. obtained in Synthesis Example 1
0 g (0.108 moleq), diglycidyl ether of tetrabromobisphenol A (Sumitomo Chemical Co., Ltd.)
Made, trade name: Sumiepoxy ESB-400, epoxy equivalent 403g / eq) 28.55g (0.0354mol)
eq) is equipped with a thermometer, condenser and stirrer 50
A 0 ml four-neck round bottom flask was charged, and after heating and melting at 110 ° C., tetrabromobisphenol A 14.34
g (0.0264 mol) is added and dissolved. 2-Ethyl-4-methylimidazole 15.8 mg (0.14
(3 mmol) dissolved in 2.0 g of methyl ethyl ketone, and then heated to 130 ° C. while removing the solvent,
After holding for 3 hours, the reaction product is cooled and taken out to obtain 112.0 g of the desired adduct. The epoxy equivalent of the obtained adduct was 390.0 g / eq. Met.

Comparative Synthesis Example This synthesis example relates to a method for obtaining a flame-retardant terminal epoxy resin having a bromine content of 20% by weight by an addition reaction of the epoxy compound obtained in Synthesis Example 1 and tetrabromobisphenol A. Is.

Epoxy compound 13 obtained in Synthesis Example 1
1.98 g and tetrabromobisphenol A 68.02
g, 500 m equipped with a thermometer, cooling tube and stirrer
14 A four-neck round bottom flask is charged and heated and melted at 120 ° C. After adding a solution of 40.0 mg of triphenylphosphine dissolved in 1.0 g of methyl ethyl ketone, the temperature was raised to 130 ° C. and held for 5 hours, and the reaction product was cooled and taken out to obtain 200.0 g of the desired adduct. At the end of the reaction, the viscosity of the resin was remarkably increased and stirring became difficult. The epoxy equivalent of the obtained adduct was 835 g / eq. Met.

EXAMPLE The flame-retardant terminal epoxy resin obtained in Synthesis Example 2, dicyandiamide and 2-ethyl-4-methylimidazole were mixed in the proportions shown in Table 1 and mixed in a mixed solvent of methyl ethyl ketone and ethylene glycol monomethyl ether. Dissolved into a uniform resin varnish. The varnish is glass cloth (trade name: KS-1600S962LP, Kanebo Co., Ltd.)
Manufactured) and treated with a hot air dryer at 150 ° C. for 5 to 10 minutes to obtain a prepreg. 5 sheets of prepreg and copper foil (TTA
I-treated 35 μm thick, Furukawa Circuit Foil Co., Ltd. was overlaid and hot press molded at 170 ° C. and 50 kg / cm ^{2 for} 120 minutes to obtain a 1 mm thick copper clad laminate. The copper foil peeling strength and solder heat resistance of the laminate are JIS-C-64.
81 was measured. The glass transition temperature (Tg) was determined from the inflection point of the thermal expansion curve using a thermal analyzer DT-30 manufactured by Shimadzu Corporation. Room temperature dielectric constant and dielectric loss tangent are 4275, manufactured by Yokogawa Hewlett-Packard Co., Ltd.
A Multi-Frequency LCR met
er was used to calculate the value of the dielectric constant from the capacitance of the sample. The measurement results are shown in Table 1.

Comparative Example 1 The flame-retardant terminal epoxy resin obtained in Comparative Synthesis Example was mixed with dicyandiamide and 2-ethyl-4-methylimidazole in the proportions shown in Table 1, and a resin varnish was prepared in the same manner as in Example. Created. When the glass cloth was impregnated with this varnish and treated with a hot air dryer, foaming and resin superposition were observed in the obtained prepreg. Using this prepreg, a copper-clad laminate having a thickness of 1 mm was obtained in the same manner as in the example. The physical properties of the laminated plate were measured in the same manner as in Examples, and the results are shown in Table 1.

Comparative Example 2 Epoxy resin with brominated epoxy resin (Sumitomo Chemical Co., Ltd., trade name: Sumiepoxy ESB-500, epoxy equivalent 472 g / eq) and cresol novolac type epoxy resin (Sumitomo Chemical Co., Ltd.) , Brand name: Sumiepoxy ESCN-220, Epoxy equivalent 215g / e
q) with dicyandiamide and 2-ethyl-4-
Methyl imidazole was mixed in the ratio shown in Table 1 and dissolved in a mixed solvent of methyl ethyl ketone and ethylene glycol monomethyl ether to obtain a uniform resin varnish. Glass varnish (trade name: KS-1600S962L)
P, manufactured by Kanebo Co., Ltd., and treated with a hot air dryer at 150 ° C. for 5 to 10 minutes to obtain a prepreg. 5 sheets of prepreg and copper foil (TTAI treated 35μ thick, Furukawa Circuit Foil Co., Ltd.) are piled up, 160 ° C, 50kg / cm ²
Was hot pressed for 90 minutes to obtain a 1 mm thick copper clad laminate. The physical properties of the laminate were measured in the same manner as in Example 1,
The results are shown in Table 1.

[0041]

[Table 1]

[0042]

EFFECTS OF THE INVENTION The flame-retardant epoxy resin composition used in the present invention has a low viscosity, so that it can be easily impregnated into a substrate such as glass cloth and has excellent operability, and the copper-clad resin of the present invention can be efficiently used. Laminates can be produced. The flame-retardant epoxy resin copper-clad laminate of the present invention has a good appearance, adhesiveness, and flame retardancy of a prepreg, and also has excellent heat resistance and a low dielectric constant, so that it is a multilayer print for high-speed arithmetic processing. Suitable for wiring boards.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuhiro Shibata 6 Kitahara, Tsukuba, Ibaraki Prefecture Sumitomo Chemical Co., Ltd. (72) Inventor Shuichi Kanagawa 6, Kitahara, Tsukuba, Ibaraki Sumitomo Chemical Co., Ltd.

Claims (1)

[Claims] 1. (A) The following general formula 1 (In the formula, n represents an average number of repeating units and takes a value of 0 to 10. R and R ′ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or a cycloalkyl having 5 to 7 carbon atoms. Group is shown, but at least one is an alkyl group having 2 to 10 carbon atoms or a cycloalkyl group having 5 to 7 carbon atoms, and P and Q are each independently at least one alkyl group having 4 to 10 carbon atoms. Alternatively, it is a cycloalkyl group having 5 to 7 carbon atoms, and the other is an alkyl group having 1 to 10 carbon atoms or a cycloalkyl group having 5 to 7 carbon atoms, which may be the same or different from each other. , J each independently have an integer value of 1 to 4), and (B) the following general formula 2 (In the formula, A represents a divalent organic group having 1 to 20 carbon atoms.
X and X ′ may be each independently at least one halogen atom and the other may be an alkyl group having 1 to 10 carbon atoms or a cycloalkyl group, and X and X ′ may be the same as each other. It may be different. k and l each independently take an integer value of 1 to 4. ) And a halogen-containing bisphenol compound represented by the formula (C) below. (In the formula, B represents a divalent organic group having 1 to 20 carbon atoms.
Y and Y'may each independently be at least one halogen atom and the other may be an alkyl group having 1 to 10 carbon atoms or a cycloalkyl group, and Y and Y'may be the same as each other. It may be different. m and n each independently take an integer value of 1 to 4. The epoxy resin obtained by reacting a diglycidyl ether of a halogen-containing bisphenol compound represented by) and a flame-retardant epoxy resin composition containing an epoxy resin curing agent as essential components are dissolved in an organic solvent and impregnated into a substrate. A flame-retardant epoxy resin copper-clad laminate obtained by heat-molding the obtained prepreg and copper foil.