JP2008050557A - Fiber composite and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fiber composite having low dielectric constant and dielectric dissipation factor (dielectric loss) and excellent tensile strength, tensile modulus and elongation in good balance and to provide a method for producing the fiber composite. <P>SOLUTION: The fiber composite composed of a ring opening polymer of a bi- or multifunctional dihydrobenzoxazine compound as a matrix and a liquid crystalline polyester fiber nonwoven fabric as a reinforcing material is provided. Furthermore, the method for producing the fiber composite comprising impregnating the liquid crystalline polyester fiber nonwoven fabric with the bi- or multifunctional dihydrobenzoxazine compound and finally heating and integrating the whole under pressure is provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fiber composite comprising a ring-opening polymer of a bi- or polyfunctional dihydrobenzoxazine compound as one of the constituent components and a method for producing the same.

  Glass fiber woven fabric has been used as a base material for printed wiring boards for a long time, but glass fiber has a disadvantage that it has a high dielectric constant and a high dielectric loss tangent in a high frequency region.

  In addition, phenolic resin, melamine resin, epoxy resin, unsaturated polyester resin, cyanate resin, bismaleimide resin, etc. have been used as the matrix resin to be impregnated, but the dielectric constant and dielectric loss tangent are still high and will be required in the future. There was a problem with high frequency response.

  Recently, in order to eliminate these drawbacks, a technique for using an organic fiber woven fabric using a heat-resistant polymer as a substrate has been developed. For example, Japanese Patent Application Laid-Open No. 62-36892 describes a printed wiring board having a woven fabric made of liquid crystalline polyester fiber as a base material.

  However, as a matrix to be impregnated, no resin that satisfies the performance has been found yet. In recent years, dihydrobenzoxazine compounds in which a dihydrobenzoxazine ring undergoes a ring-opening polymerization reaction and thermosets without generation of volatile components have been actively studied as new resins.

  For example, JP-A-2000-154225 proposes a thermosetting resin comprising a compound having a structure represented by the following general formula (3) and / or a ring-opening polymer thereof.

（式中、Ｒ₁ は置換もしくは無置換の炭素数５個以上１２個以下の脂環式炭化水素基、あるいは炭素数４個以上１２個以下の直鎖もしくは分岐アルキリデン基または芳香族炭化水素置換アルキリデン基であり、Ｒ₂ 及びＲ₃ は炭素数１０個以下の脂肪族基、フェニル基、またはｔ−ブチル基がオルト位もしくはパラ位に置換されたフェニル基で、互いに同じでも異なっていてもかまわない。）

(In the formula, R ₁ represents a substituted or unsubstituted alicyclic hydrocarbon group having 5 to 12 carbon atoms, or a linear or branched alkylidene group having 4 to 12 carbon atoms or substituted with an aromatic hydrocarbon. An alkylidene group, wherein R ₂ and R ₃ are an aliphatic group having 10 or less carbon atoms, a phenyl group, or a phenyl group in which a t-butyl group is substituted in the ortho or para position, and may be the same or different from each other; It doesn't matter.)

  However, a molded product obtained by thermosetting the above-mentioned dihydrobenzoxazine compound has high bending strength, flexural modulus, etc., but has low elongation, flexibility, etc., and is hard and brittle. The thin molded body is difficult to manufacture and cannot be used, and has been used by mixing with a phenol resin, an epoxy resin or the like.

  The dihydrobenzoxazine compound is a compound in which benzene rings are bonded with an alkylene group, and a compound in which nitrogen atoms in a dihydrobenzoxazine ring are bonded with an alkylene group is disclosed in US Pat. No. 5,543,516 with the following structure. Only the dihydrobenzoxazine compound of the formula (4) is described, and the ring-opening polymerization and the ring-opening polymer have not been studied at all.

JP-A-62-36892 JP 2000-154225 A US Pat. No. 5,543,516

One of the problems to be solved by the present invention is the above problem.
Accordingly, an object of the present invention is to provide a fiber composite having a low dielectric constant and dielectric loss tangent (dielectric loss) and excellent balance of tensile strength, tensile elastic modulus, and elongation, and a method for producing the same.

  The present invention provides a fiber composite constituted by using a ring-opening polymer of a bifunctional or polyfunctional dihydrobenzoxazine compound as a matrix and a liquid crystalline polyester fiber nonwoven fabric as a reinforcing material, and a method for producing the same, and provides the above object. Is achieved.

That is, the present invention provides the following inventions 1) to 9).
1) A fiber composite composed of a ring-opening polymer of a bifunctional or polyfunctional dihydrobenzoxazine compound as a matrix and a liquid crystalline polyester fiber nonwoven fabric as a reinforcing material.

  2) The fiber composite according to 1), wherein the bifunctional dihydrobenzoxazine compound is represented by the following molecular structure (1).

（式中、Ｒは炭素数２以上の直鎖状アルキレン基又はその水素がアルキル置換された分岐状アルキレン基、或いは脂環式構造を有する炭化水素基を示し、べンゼン環の水素はアルキル基又はアルコキシ基で置換されていてもよい。また、Ｒは、ジフェニルエーテル基であってもよい。）

(In the formula, R represents a linear alkylene group having 2 or more carbon atoms, a branched alkylene group in which hydrogen is alkyl-substituted, or a hydrocarbon group having an alicyclic structure, and hydrogen in the benzene ring is an alkyl group. Or may be substituted with an alkoxy group, and R may be a diphenyl ether group.)

  3) The fiber composite according to 1), wherein the polyfunctional dihydrobenzoxazine compound is represented by the following molecular structure (I):

〔式（Ｉ）において、
Ar¹は、４価の芳香族基を示し、
Ｒ¹は、脂肪族または脂環式構造を有する炭化水素基であり、
ｎは、２〜５００の整数を示す。〕
なお、本発明においては、脂環式構造には、ＩＵＰＡＣでのシクロアルキル、ビシクロアルキルを含むものとする。

[In Formula (I),
Ar ¹ represents a tetravalent aromatic group,
R ¹ is a hydrocarbon group having an aliphatic or alicyclic structure;
n represents an integer of 2 to 500. ]
In the present invention, the alicyclic structure includes cycloalkyl and bicycloalkyl in IUPAC.

  4) The fiber composite according to 2) above, wherein R in the molecular structure (1), which is the bifunctional dihydrobenzoxazine compound, is a group represented by the following (i).

〔式中、*印は前記式（１）におけるＮへの結合部位を示す。また、シス−トランス異性
体を含む。〕

[In the formula, * indicates a binding site to N in the formula (1). Also includes cis-trans isomers. ]

5) R ¹ in the molecular structure (I) which is the polyfunctional dihydrobenzoxazine compound is
The fiber composite according to 3) above, which is a group represented by (i) below.

〔式中、*印は前記式（Ｉ）におけるＮへの結合部位を示す。また、シス−トランス異性
体を含む。〕

[In the formula, * indicates a binding site to N in the formula (I). Also includes cis-trans isomers. ]

6) The dielectric constant at 23 ° C., 100 MHz, and 1 GHz is 2.0 to 3.2, and the dielectric loss tangent is 10 ^{−4 to} 6.0 × 10 ^−3. Fiber composite.

  7) The fiber composite according to any one of 1) to 6) above, which contains a resin having a dielectric constant of 2.5 or less in addition to the ring-opening polymer of the bifunctional or polyfunctional dihydrobenzoxazine compound as a matrix. .

  8) The fiber composite as described in any one of 1) to 7) above, wherein the non-woven fabric is treated with a surface treatment agent comprising a copolymer polymer of butadiene-acrylonitrile.

  9) A method for producing a fiber composite, wherein a liquid crystalline polyester fiber nonwoven fabric is impregnated with a bifunctional or polyfunctional dihydrobenzoxazine compound, and finally the whole is heated and integrated under pressure.

  10) A liquid crystalline polyester fiber nonwoven fabric is impregnated with a resin having a dielectric constant of 2.5 or less in the form of an emulsion, dried, then impregnated with a bifunctional or polyfunctional dihydrobenzoxazine compound, and finally added entirely. A method for producing a fiber composite, wherein the fiber composite is heated and integrated under pressure.

  11) After treating the liquid crystalline polyester nonwoven fabric with a surface treatment agent comprising a copolymer polymer of butadiene-acrylonitrile in advance, impregnating a resin having a dielectric constant of 2.5 or less in the form of an emulsion, drying, and then 2 Or the manufacturing method of a fiber composite which impregnates a polyfunctional dihydrobenzoxazine compound and finally heat-integrates the whole under pressure.

  12) A prepreg comprising the fiber composite as described in 1 above, which can be cured by heating.

  13) The film comprising the fiber composite as described in 1 above, which is cured by heating.

  14) The electronic circuit board comprising the film as described in 13 above, which is integrated with a copper foil.

ADVANTAGE OF THE INVENTION According to this invention, the dielectric constant and dielectric loss tangent are low, and the fiber composite which is excellent in the balance of tensile strength, the tensile elasticity modulus, and elongation, and the manufacturing method of such an excellent fiber composite are provided.
Moreover, according to this invention, the outstanding prepreg and film which consist of such a fiber composite, and the outstanding electronic circuit board which consists of this film are provided.

[Fiber composite]
Hereinafter, the fiber composite of the present invention will be described in detail based on preferred embodiments thereof.
The fiber composite of the present invention uses a ring-opening polymer of a bifunctional or polyfunctional dihydrobenzoxazine compound as a matrix and a liquid crystalline polyester fiber nonwoven fabric, which is one of organic fiber nonwoven fabrics using a heat-resistant polymer, as a reinforcing material. It is a composed fiber composite. That is, in the fiber composite of the present invention, a resin (matrix resin) obtained by ring-opening polymerization reaction of a bifunctional or polyfunctional dihydrobenzoxazine compound is a liquid crystalline polyester fiber nonwoven fabric (organic fiber nonwoven fabric using a heat-resistant polymer). It is a reinforced fiber composite. Since the fiber composite of the present invention has such a configuration, the dielectric constant and dielectric loss tangent are low, and the tensile strength, tensile elastic modulus, and elongation are excellent in a well-balanced manner. Further, since the benzoxazine resin is combined with the liquid crystalline polyester fiber nonwoven fabric, the flame retardancy is superior to that of a single liquid crystalline polyester fiber nonwoven fabric.

  Although it does not restrict | limit especially as a ring-opening polymer of the bifunctional or polyfunctional dihydrobenzoxazine compound which is a matrix resin used for this invention, From the point of dielectric constant, the molecule | numerator shown by following formula (1) A ring-opening polymer of a bifunctional dihydrobenzoxazine compound having a structure is preferable.

（式中、Ｒは炭素数２以上の直鎖状アルキレン基又はその水素がアルキル置換された分岐状アルキレン基、或いは脂環式構造を有する炭化水素基であり、べンゼン環の水素はアルキル基又はアルコキシ基で置換されていてもよい。また、Ｒは、ジフェニルエーテル基であってもよい。）

(In the formula, R is a linear alkylene group having 2 or more carbon atoms, a branched alkylene group in which hydrogen is alkyl-substituted, or a hydrocarbon group having an alicyclic structure, and hydrogen in the benzene ring is an alkyl group. Or may be substituted with an alkoxy group, and R may be a diphenyl ether group.)

  Regarding the linear alkylene group represented by R in the above formula (1), when the number of carbon atoms decreases, the Young's modulus (E ′) and glass transition temperature of the obtained molded article increase, but the dielectric constant increases. When the number of carbons is increased, the elongation and flexibility of the obtained molded body are increased, the dielectric constant is decreased, and the dielectric loss tangent (especially at 1 GHz) is slightly decreased. However, Young's modulus (E ′) and glass transition temperature are lowered. From this viewpoint, the carbon number of the linear alkylene group represented by R in the above formula (1) is preferably 2 to 16, more preferably 6 to 12.

  R may be a branched alkylene group in which hydrogen of a linear alkylene group having 2 or more carbon atoms is alkyl-substituted. When the branched alkylene group is used, the Young's modulus (E ′) is increased, the glass transition temperature, which is an index of heat resistance, is increased, and the elongation and flexibility are decreased. Moreover, when the carbon number of the linear alkylene group as the main chain is increased aiming at a decrease in dielectric constant and elongation of the molded product, the glass transition point, which is an index of heat resistance, is lowered. When the carbon number of the linear alkylene group is large in order to secure the low dielectric constant and elongation of the molded body and at the same time balance with a high glass transition point, the carbon number is preferably 4 or more, more preferably carbon. In the case where the number is 5 to 12, it is preferable that hydrogen of the linear alkylene group is substituted with an alkyl group to form a branched alkylene group. Examples of the substituted alkyl group include a methyl group, an ethyl group, A propyl group, a butyl group, etc. are mentioned.

Further, regarding the hydrocarbon group having an alicyclic structure represented by R in the above formula (1), in particular, in the case of a diethylidenetricyclodecane group in which R is a group represented by the following (i), It is preferable because of its excellent properties, low dielectric constant, and low dielectric loss.

  The hydrogen of the benzene ring in the bifunctional dihydrobenzoxazine compound represented by the above formula (1) may be substituted with an alkyl group or an alkoxy group. Examples of the alkyl group include a methyl group, an ethyl group, and the like. Group, propyl group, butyl group, octyl group, nonyl group and the like. Examples of the alkoxy group include methoxy group, ethoxy group, propoxy group and butoxy group.

  Further, as a ring-opening polymer of a bi- or polyfunctional dihydrobenzoxazine compound, a polyfunctional dihydrobenzo having a molecular structure represented by the following formula (I) is used because heat resistance, low dielectric constant, and low dielectric loss are improved. A ring-opening polymer of a xazine compound is also preferable.

〔式（Ｉ）において、
Ar¹は、４価の芳香族基を示し、
Ｒ¹は、脂肪族または脂環式構造を有する炭化水素基であり、
ｎは、２〜５００の整数を示す。〕

[In Formula (I),
Ar ¹ represents a tetravalent aromatic group,
R ¹ is a hydrocarbon group having an aliphatic or alicyclic structure;
n represents an integer of 2 to 500. ]

As the tetravalent aromatic group represented by Ar ¹ in formula (I), in particular, from the viewpoint of availability and reactivity, any one of the following structures (iii), (iv), and (v) What is shown is preferred.

〔式（iii）〜（v）中、*印はＯＨへの結合部位、もう一方はオキサジン環４位のメチレ
ン基への結合部位を示す。
また、各芳香環の水素は、炭素数１〜１０の脂肪族炭化水素基、脂環式炭化水素基、又は置換もしくは無置換フェニル基で置換されていてもよい。
式（iii）におけるＸは、直接結合手（原子もしくは原子団が存在しない）、またはヘ
テロ元素もしくは官能基を含んでいても良い脂肪族、脂環式もしくは芳香族の炭化水素基を示す。〕

[In formulas (iii) to (v), * indicates a binding site to OH, and the other indicates a binding site to a methylene group at the 4-position of the oxazine ring.
Moreover, hydrogen of each aromatic ring may be substituted with a C1-C10 aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or a substituted or unsubstituted phenyl group.
X in the formula (iii) represents a direct bond (no atom or atomic group) or an aliphatic, alicyclic or aromatic hydrocarbon group which may contain a hetero element or a functional group. ]

In the case where Ar ¹ is the structure (iii), it is more preferable that X in the structure (iii) is at least one selected from the following group A.
Such a structure is very preferable because it is easily available and the polymer has excellent mechanical and electrical characteristics.

〔各式中、*印は前記構造（iii）における芳香環への結合部位を示す。〕

[In each formula, * indicates a binding site to the aromatic ring in the structure (iii). ]

  Among the groups A, those having a structure shown in the following group B are particularly preferable because they are excellent in electric characteristics and heat resistance.

〔各式中、*印は前記構造（iii）における芳香環への結合部位を示す。〕

[In each formula, * indicates a binding site to the aromatic ring in the structure (iii). ]

In the above, Ar ¹ is particularly preferably one represented by at least one structure selected from the following group C from the viewpoints of availability, electrical characteristics of the cured product, and heat resistance.

〔各式中、両端部における*印はＯＨへの結合部位、もう一方はオキサジン環４位のメチ
レン基への結合部位を示す。
また、各芳香環の水素は、炭素数１〜１０の脂肪族炭化水素基、脂環式炭化水素基、又は置換もしくは無置換フェニル基で置換されていてもよい。］

[In each formula, the * mark at both ends indicates the bonding site to OH, and the other indicates the bonding site to the methylene group at the 4-position of the oxazine ring.
Moreover, hydrogen of each aromatic ring may be substituted with a C1-C10 aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or a substituted or unsubstituted phenyl group. ]

In the case where Ar ¹ is at least one selected from the above group C, Ar ¹ is also the above (iii)
, (Iv), and (v), for the same reason, R ¹ representing a hydrocarbon group having an alicyclic structure is an alicyclic carbonization having a condensed ring structure. A hydrogen group is preferred, and among them, the group represented by (i) is more preferred.

Specific examples of such compounds include the structure of (iii): 4,4′-biphenol, 2,
2'-biphenol, 4,4'-dihydroxydiphenyl ether, 2,2'-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenylmethane, 2,2'-dihydroxydiphenylmethane, bisphenol A, bisphenol S, 4,4'-dihydroxydiphenyl Sulfide, 4,4′-dihydroxybenzophenone, 1,1-bis (4-hydroxyphenyl) ethane, 1,1-bis (4-hydroxyphenyl) propane, 1,1-bis (4-hydroxyphenyl) butane, 2 , 2-bis (4-hydroxyphenyl) butane, 1,1-bis (4-hydroxyphenyl) -2-methylpropane, 1,1-bis (4-hydroxyphenyl) cyclohexane, 1,1-bis (4- Hydroxyphenyl) cyclopentane, 1,1-bis (4-hydroxy) Droxyphenyl) -1-phenylethane, bis (4-hydroxyphenyl) diphenylmethane, 4,4 ′-[1,4-phenylenebis (1-methyl-ethylidene)] bisphenol (Mitsui Chemicals' bisphenol P, Tokyo Kasei) “Sold under the compound name of“ α, α′-bis (4-hydroxyphenyl) -1,4-diisopropylbenzene ”), 4,4 ′-[1,3-phenylenebis (1-methyl-ethylidene)] bisphenol ( Bisphenol M), 9,9-bis (4-hydroxyphenyl) fluorene, 2,2-bis (4-hydroxyphenyl) hexafluoropropane, 1,3-bis (4-hydroxyphenoxy) benzene, 1, 4-bis (3-hydroxyphenoxy) benzene, 2,6-bis ((2-hydroxyphenyl) methyl) As such phenol, except the connecting portions X, has two benzene rings in the molecule, compounds OH groups to one benzene ring are single bonds,
Structure of (iv): 1,3-dihydroxynaphthalene, 1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, 2, A compound having one naphthalene ring in the molecule and two OH groups bonded to the naphthalene ring, such as 7-dihydroxynaphthalene,
(V) Structure: 1,2-dihydroxybenzene (catechol), 1,3-dihydroxybenzene (resorcinol), 1,4-dihydroxybenzene (hydroquinone) and having one benzene ring in the molecule, And compounds having two OH groups bonded to the ring.

As an example of the above, in the aromatic ring to which the OH group is bonded, the OH group and the connecting portion X ((iii
In the case of the structure of (), an unsubstituted one was mentioned, but any of the ortho positions of the OH group may be H which can be substituted, and the other part of the aromatic ring may be various substituents, For example, it may be substituted with a linear or branched aliphatic hydrocarbon group or alicyclic hydrocarbon group having 1 to 10 carbon atoms, or a substituted or unsubstituted aromatic group. In addition, even when the linking part X contains an aromatic ring, the aromatic ring may have various substituents such as a linear or branched aliphatic hydrocarbon group or alicyclic hydrocarbon group having 1 to 10 carbon atoms. May be substituted.

As a simple example of a substituted aromatic ring,
Structure of (iii): 2,2-bis (4-hydroxy-3-methylphenyl) propane, 2,
2-bis (4-hydroxy-3-methylphenyl) methane,
The structure of (v): 2-methylresorcinol, 2,5-dimethylresorcinol and the like can be mentioned, but of course not limited thereto.

As R ¹ in the formula (I), when it is a hydrocarbon group having an alicyclic structure, it is preferably used because the resulting resin has very good electrical characteristics and heat resistance. In particular, an alicyclic hydrocarbon group having a condensed ring structure is preferable, and specific examples of the compound in which a primary amino group is bonded to the alicyclic hydrocarbon group having such a condensed ring structure include, for example, 3 (4), 8 (9), - bis (aminomethyl) tricyclo [5,2,1,0 ^2,6] decane, 2,5 (6) - bis (
Aminomethyl) bicyclo [2,2,1] heptane, 1,3-diaminoadamantane, and the like. 3 (4), 8 (9), - bis (aminomethyl) tricyclo [5,2,1,0 ^2,6] decane are used those sold under the product name "TCD Diamine" from Celanese Corp. As the 2,5 (6) -bis (aminomethyl) bicyclo [2,2,1] heptane, those sold by Mitsui Chemicals under the product name “NBDA” can be used. These may be used alone or in combination.

  The bifunctional dihydrobenzoxazine compound is preferably synthesized from a monovalent phenol compound, an aliphatic or alicyclic diamine represented by the following general formula (2), and formaldehyde. On the other hand, the polyfunctional dihydrobenzoxazine compound is preferably synthesized from a divalent phenol compound, an aliphatic or alicyclic diamine represented by the following general formula (2), and formaldehyde.

（式中、Ｒは炭素数２以上の直鎖状アルキレン基又はその水素がアルキル置換された分岐状アルキレン基、或いは脂環式構造を有する炭化水素基を示す。）

(In the formula, R represents a linear alkylene group having 2 or more carbon atoms, a branched alkylene group in which hydrogen is alkyl-substituted, or a hydrocarbon group having an alicyclic structure.)

  The monohydric phenol compound is a compound having one phenolic hydroxyl group and at least one of the ortho positions being hydrogen, such as phenol, cresol, 2-bromo-4-methylphenol, xylenol, nonylphenol, p -T-butylphenol, octylphenol, etc. are mentioned.

Specific examples of the divalent phenol compound include 4,4′-biphenol, 2,2′-biphenol, 4,4′-dihydroxydiphenyl ether, 2,2′-dihydroxydiphenyl ether, and 4,4′-dihydroxy. Diphenylmethane, 2,2′-dihydroxydiphenylmethane, bisphenol A, bisphenol S, 4,4′-dihydroxydiphenyl sulfide, 4,4′-dihydroxybenzophenone, 1,1-bis (4-hydroxyphenyl) ethane, 1,1- Bis (4-hydroxyphenyl) propane, 1,1-bis (4-hydroxyphenyl) butane, 2,2-bis (4-hydroxyphenyl) butane, 1,1-bis (4-hydroxyphenyl) -2-methyl Propane, 1,1-bis (4-hydroxyphenyl) cyclohexa 1,1-bis (4-hydroxyphenyl) cyclopentane, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, bis (4-hydroxyphenyl) diphenylmethane, 4,4 ′-[1,4 -Phenylenebis (1-methyl-ethylidene)] bisphenol (Bisphenol P manufactured by Mitsui Chemicals, sold under the compound name "α, α'-bis (4-hydroxyphenyl) -1,4-diisopropylbenzene" by Tokyo Chemical Industry) 4,4 ′-[1,3-phenylenebis (1-methyl-ethylidene)] bisphenol (Bisphenol M manufactured by Mitsui Chemicals), 9,9-bis (4-hydroxyphenyl) fluorene, 2,2-bis (4- Hydroxyphenyl) hexafluoropropane, 1,3-bis (4-hydroxyphenoxy) benzene, 1,4-bis (3-hydride) Roxyphenoxy) benzene, 2,6-bis ((2-hydroxyphenyl) methyl) phenol, etc., except for the linking part X, has two benzene rings in the molecule, and one benzene ring A compound in which one OH group is bonded,
1,3-dihydroxynaphthalene, 1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, A compound having one naphthalene ring in the molecule and two OH groups bonded to the naphthalene ring,
It has one benzene ring in the molecule such as 1,2-dihydroxybenzene (catechol), 1,3-dihydroxybenzene (resorcinol), 1,4-dihydroxybenzene (hydroquinone), and OH group with respect to the benzene ring And the like, and the like.

R in the aliphatic or alicyclic diamine represented by the general formula (2) is the same as R in the bifunctional dihydrobenzoxazine compound represented by the formula (1), or the formula (I R ¹ in the polyfunctional dihydrobenzoxazine compound represented by
-Diaminoethylene, 1,3-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, 1,8-diaminooctane, 1,12-diaminododecane and the like can be mentioned.

In addition to the above, 3 (4), 8 (9), - bis (aminomethyl) tricyclo [5,2,1,0 ^2,6] decane, 2,5 (6) - bis (aminomethyl) bicyclo [ 2,2,1] heptane, 1,3-diaminoadamantane, and the like. 3 (4), 8 (9), - bis from (aminomethyl) tricyclo [5,2,1,0 ^2,6] decane Celanese Corp. "
The product sold under the product name “TCD Diamine” can be used, and 2,5 (6) -bis (aminomethyl) bicyclo [2,2,1] heptane is the product name “NBDA” from Mitsui Chemicals. You can use what is sold in. These may be used alone or in combination.

  Examples of the formaldehydes include formalin, which is an aqueous formaldehyde solution, and paraformaldehyde, which is a polymer of formaldehyde.

  The bifunctional dihydrobenzoxazine compound is synthesized by reacting 2 mole equivalents of monovalent phenol, 1 mole equivalent of aliphatic diamine represented by the formula (2) and 4 mole equivalents of formaldehyde. Any known synthesis method may be employed as the synthesis method.

  For example, the bifunctional dihydrobenzoxazine compound is prepared by mixing 2 moles of a monovalent phenol compound, 1 mole of a diamine represented by the general formula (2) and 4 moles of formaldehyde and heating to 100 to 130 ° C. It can be easily synthesized by stirring for 1 minute to 1 hour.

  The polyfunctional dihydrobenzoxazine compound is prepared by mixing 1 mol of a divalent phenol compound, 1 mol of a diamine represented by the general formula (2) and 4 mol of formaldehyde, and heating to 100 to 130 ° C. It can be easily synthesized by stirring for 1 minute to 1 hour.

  In the synthesis of the above bi- or polyfunctional dihydrobenzoxazine compounds, halogenated solvents such as chloroform, methylene chloride, dichloroethane and trichloroethane, aromatic solvents such as benzene, toluene and xylene, methanol, ethanol, propanol and butanol It may be carried out by dissolving in a solvent such as lower alcohol such as 1,4 dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether. In this case, the reaction may be carried out for 1 to 20 hours while heating to 50 to 130 ° C., and after the reaction is completed, the solvent is removed, and if necessary, washing with an alcohol such as an alkaline aqueous solution or methanol is carried out to make the reaction unreacted. The phenolic compounds, diamines and formaldehydes may be removed.

  As the ring-opening polymerization method of the bi- or polyfunctional dihydrobenzoxazine compound, any conventionally known polymerization method may be adopted, and generally it may be heated at 120 to 260 ° C. for several hours, but the heating temperature is low, If the heating time is insufficient, the glass transition temperature is not improved, and heat resistance and mechanical strength may be insufficient. On the other hand, if the heating temperature is too high or the heating time is too long, the glass transition temperature may decrease, and the heat resistance and mechanical strength may also decrease. Therefore, the ring-opening polymerization is preferably performed at 165 to 195 ° C. for 0.3 to 4 hours.

  A curing accelerator may be added when ring-opening polymerization of the bifunctional or polyfunctional dihydrobenzoxazine compound. As the curing accelerator, any curing accelerator generally used in ring-opening polymerization of dihydrobenzoxazine compounds can be used. For example, polyfunctional phenols such as catechol and bisphenol A, p-toluene Sulfonic acids such as sulfonic acid and p-phenolsulfonic acid, carboxylic acids such as benzoic acid, salicylic acid, oxalic acid and adipic acid, cobalt (II) acetylacetonate, aluminum (III) acetylacetonate, zirconium (IV) acetylacetate Metal complexes such as nates, metal oxides such as calcium oxide, cobalt oxide, magnesium oxide and iron oxide, calcium hydroxide, imidazole and its derivatives, tertiary amines such as diazabicycloundecene, diazabicyclononene and these Salt, triphenylphosphine, triphenylphosphine -Phosphorus compounds such as benzoquinone derivatives, triphenylphosphine / triphenylboron salts, tetraphenylphosphonium / tetraphenylborate, and derivatives thereof. These are used alone or as a mixture of two or more.

  Although the addition amount of the curing accelerator is not particularly limited, it is generally 5 parts by weight or less with respect to 100 parts by weight of the above-mentioned bifunctional or polyfunctional dihydrobenzoxazine compound. Is 3 parts by weight or less.

Moreover, the ring-opening polymer of the bifunctional or polyfunctional dihydrobenzoxazine compound as the matrix in the fiber composite of the present invention has a dielectric constant of 2.0 to 3.2 at 23 ° C., 100 MHz, and 1 GHz. The dielectric loss tangent is preferably 10 ^{−4 to} 6.0 × 10 ⁻³ .

  In general, electronic materials such as laminated boards are required to have low dielectric constant characteristics due to high density of electronic equipment, high-speed signal transmission, high-frequency compatibility, etc., especially as the performance of multilayer substrates such as IC packages. Is preferably used as the dielectric constant at 23 ° C., 100 MHz and 1 GHz is low. Therefore, the fiber composite of the present invention using a ring-opening polymer of a bifunctional or polyfunctional dihydrobenzoxazine compound having a dielectric constant at 23 ° C., 100 MHz and 1 GHz, and a dielectric loss tangent within the above range is suitable for such applications. It can be used suitably.

  Further, as a means for lowering the dielectric constant, it is also preferable to add a resin having a dielectric constant of 2.5 or less as the second component in addition to the ring-opening polymer of the bifunctional or polyfunctional dihydrobenzoxazine compound as a matrix. As such a resin, a tetrafluoroethylene resin or an ultrahigh molecular weight polyethylene resin can be suitably used.

  The resin having a dielectric constant of 2.5 or less is preferably supplied in the form of an emulsion in order to facilitate the composite to the fiber composite. The concentration of the emulsion is preferably 10% by weight or more and 60% by weight or less. If it is less than 10%, the impregnation rate decreases, and the effect of lowering the dielectric constant may be impaired. On the other hand, if it exceeds 60%, the emulsion may become unstable.

  In the present invention, in order to reinforce the ring-opening polymer of the above-mentioned bifunctional or polyfunctional dihydrobenzoxazine compound, as described at the beginning, a liquid crystalline polyester fiber nonwoven fabric is used as a reinforcing material. The liquid crystalline polyester fiber nonwoven fabric used in the present invention is one of organic fiber nonwoven fabrics using a heat-resistant polymer so as not to impair the dielectric constant and dielectric loss tangent. Examples of the liquid crystalline polyester include a melted liquid crystalline polyester obtained by cooling a polyester that melts and exhibits a liquid crystal state, and a liquid crystalline polyester obtained by drying a solution of a polyester that exhibits a liquid crystal state in a solution. A melted liquid crystalline polyester fiber nonwoven fabric or a liquid crystalline polyester fiber nonwoven fabric that is made into a nonwoven fabric after making them into a fibrous form can be used. In addition, liquid crystal aramid fiber is mentioned as a heat resistant fiber that exhibits liquid crystallinity, but aramid fiber is not suitable because of its high hygroscopicity. The form of the reinforcing material may be a woven fabric, a non-woven fabric, or the like.

  Examples of the liquid crystalline polyester constituting the liquid crystalline polyester fiber nonwoven fabric as the reinforcing material include those using aromatic diol, aromatic dicarboxylic acid, aromatic hydroxycarboxylic acid and the like as raw materials. There are no particular restrictions on these components such as aromatic diol, aromatic dicarboxylic acid, and aromatic hydroxycarboxylic acid, but the melting point of the liquid crystalline polyester after polymerization should be 300 ° C. or higher from the viewpoint of solder heat resistance. It is preferable to select. If the melting point is less than 300 ° C., defects such as deformation may occur during solder immersion.

  Examples of suitable combinations of the raw materials for the liquid crystalline polyester include a combination of 2-hydroxy 6-naphthoic acid and parahydroxybenzoic acid. The melting point of the liquid crystalline polyester after polymerization in this combination is 350 ° C. Incidentally, the dielectric constant of the liquid crystalline polyester is 2.86 (23 ° C., 100 MHz and 1 GHz), and the dielectric loss tangent is 0.0025 (23 ° C., 100 MHz and 1 GHz).

  The liquid crystalline polyester constituting the liquid crystalline polyester fiber nonwoven fabric preferably has a fiber diameter in the range of 1 μm to 30 μm. If the thickness is less than 1 μm, the reinforcing performance is inferior, and if it exceeds 30 μm, the fiber composite surface may be uneven.

  Moreover, as a fiber length of this liquid crystalline polyester, the range of 1-20 mm is a preferable range. If it is less than 1 mm, the reinforcing performance is inferior, and if it exceeds 20 mm, the fiber composite surface may be uneven.

  The method for producing the liquid crystalline polyester fiber nonwoven fabric is not particularly limited, and examples thereof include a wet papermaking method and a melt blow method.

  In order to improve the wettability with the matrix resin to be impregnated, it is desirable that the liquid crystalline polyester fiber nonwoven fabric has its fiber surface treated by a method such as corona discharge treatment, glow discharge treatment, plasma treatment, or heating in an oxygen atmosphere. . Moreover, what processed with surface treatment agents, such as what apply | coated the surface treatment agent, may be used. As the surface treatment agent, a material containing a rubber component is desirable from the viewpoint of stress relaxation between the nonwoven fabric and the matrix. Specific examples of the rubber component include butadiene rubber, modified butadiene rubber, styrene butadiene rubber, silicone rubber, and modified silicone rubber, but are not limited to those described above.

  In the case of using a liquid crystalline polyester fiber nonwoven fabric treated with a surface treatment agent, a typical example of the surface treatment agent is a reactive liquid polymer. Examples of the reactive liquid polymer include a copolymer of butadiene and acrylonitrile. In particular, the molecular weight is 1000 to 5000, preferably 2000 to 4000, and the proportion of acrylonitrile is 5% in terms of molar ratio, preferably 10%. %, The upper limit is 50%, desirably 30%, and the terminal is preferably amine-modified.

[Production method of fiber composite]
The manufacturing method of the fiber composite based on this invention is demonstrated.
One of the production methods of the present invention is a method in which a liquid crystalline polyester fiber nonwoven fabric is impregnated with a bifunctional or polyfunctional dihydrobenzoxazine compound, and finally the whole is heated and integrated under pressure. Since the production method of the present invention has such a configuration, a fiber composite having a low dielectric constant and dielectric loss tangent and excellent balance of tensile strength, tensile elastic modulus, and elongation can be easily obtained.

  Another production method of the present invention is that a liquid crystalline polyester fiber nonwoven fabric is impregnated with a resin having a dielectric constant of 2.5 or less in the form of an emulsion, dried, and then bi- or polyfunctional dihydrobenzoic acid. In this method, a sazine compound is impregnated and finally the whole is heated and integrated under pressure. Since the production method of the present invention has such a configuration, a fiber composite having a low dielectric constant and dielectric loss tangent and excellent balance of tensile strength, tensile elastic modulus, and elongation can be easily obtained.

  Further, in another production method of the present invention, a liquid crystalline polyester nonwoven fabric is treated with a surface treatment agent comprising a copolymer polymer of butadiene-acrylonitrile in advance, and then a resin having a dielectric constant of 2.5 or less is added to the emulsion. This is a method for producing a fiber composite, which is impregnated in a form and dried, then impregnated with a bi- or polyfunctional dihydrobenzoxazine compound, and finally heat-integrated under pressure. Since the manufacturing method of this invention consists of this structure, the said effect can be improved further.

Preferred embodiments of the production method of the present invention are shown below.
In the first step, the liquid crystalline polyester nonwoven fabric subjected to the surface treatment described above is impregnated with a resin having a dielectric constant of 2.5 or less in the form of an emulsion and dried at 50 to 140 ° C. If the drying temperature is less than 50 ° C., the drying efficiency is poor, and if it exceeds 140 ° C., a film is likely to be formed on the surface, and impregnation in the next step may be difficult.

  Next, the liquid crystal polyester fiber nonwoven fabric is impregnated after the viscosity is preferably 30 centipoise or less by melting or dissolving the bi- or polyfunctional dihydrobenzoxazine compound in a solvent. The basis weight is preferably 20 to 60 g, particularly 20 to 30 g per square meter of the nonwoven fabric.

Then, it is compressed with a roll to remove excess resin.
Next, when using a solvent in an oven at 50 ° C. to 150 ° C., the solvent is removed and the resin is temporarily cured. If the temporary curing temperature is less than 50 ° C., the efficiency of temporary curing is poor, and if it exceeds 150 ° C., the surface may be cured and the surface property may be deteriorated. Temporary curing is commonly used as semi-curing.

  When heating is completed until the provisional curing described in the preceding stage, a prepreg having curability by heating can be configured.

  Finally, the curing of the resin is completed while maintaining the smoothness of the surface while passing the roll surface heated to a surface temperature of 165 ° C. or higher.

  It can be used as a film with the resin cured. Further, when the fiber composite is passed through the heating roll surface at the same time, a copper-clad laminate integrated with the copper foil can be formed. Moreover, you may adhere | attach copper foil on the film after completion of hardening. Such a film can be used as, for example, an electronic circuit board made of a film integrated with a copper foil.

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[Fiber composite evaluation method]
The measurement method of the dielectric constant and dielectric loss tangent of the fiber composite of the present example is as follows.
A sheet-like molded body having a thickness of 1 mm was cut into 15 mm × 15 mm, supplied to a dielectric constant measuring apparatus, measured by a capacitance method at 23 ° C., and the dielectric constant and dielectric loss tangent at 100 MHz and 1 GHz were read.

The measurement method of Young's modulus (E ′), yield point strength, and elongation rate of the fiber composite of this example is as follows.
A sheet-like molded body having a thickness of about 50 μm is cut into 80 mm × 10 mm, and supplied to a tensile testing machine (product name: “Tensilon”, manufactured by Orientec Co., Ltd.). A tensile test was performed at 0 ° C. to measure the tensile properties of the material.
The measurement direction was performed with respect to the winding direction of the nonwoven fabric.

The method for evaluating the solder heat resistance of the fiber composite of this example is as follows.
25 × fiber composite bonded with copper foil (Mitsui Metals Co., Ltd., model number 3EC-III)
Cut to 25 mm and floated in a solder bath with a solder temperature of 260 ° C. for 20 seconds to determine the presence or absence of blisters. The case where there was no blister was marked with ◯ and the case where there was no blister was marked with ×.

Since the fiber composite of this example is composed of a matrix resin and fibers having a low dielectric constant, the composite has a low dielectric constant, and the dielectric constant at 23 ° C., 100 MHz, and 1 GHz is 2.0 to 3.2. The dielectric loss tangent is 10 ^{−4 to} 6.0 × 10 ⁻³ .
Therefore, a low dielectric constant characteristic such as that of a printed wiring board is required, and it can be suitably used for applications.

1 mol of 1,2-diaminoethane, 2 mol of phenol, 4 mol of paraformaldehyde and 1500 g of chloroform were mixed. This mixture was heated to 60 ° C. with stirring, and reacted for 2 hours after chloroform began to circulate. After completion of the reaction, the reaction mixture was transferred to a separatory funnel, washed with a 1N aqueous sodium hydroxide solution, and then washed with ion-exchanged water. After the chloroform layer was dried with anhydrous sodium sulfate, chloroform was distilled off by a rotary evaporator to obtain a bifunctional dihydrobenzoxazine compound in which R in the formula (1) is an ethylene group.
The obtained bifunctional dihydrobenzoxazine compound was dissolved in THF to prepare an impregnation solution as a 40 w / w /% solution.

On the other hand, the following materials were used as reinforcing materials.
Molten liquid crystalline polyester fiber nonwoven fabric (Kuraray Co., Ltd., trade name “Vecruz MBBK-25CKJ” original thickness 80 μm, equivalent to 25 μm at calendar), reactive liquid polymer (Ube Industries, trade name “ATBN 1300 × 16”) 3600, amine terminal, acrylic group 18 mol%) in 10% THF solution, and then dried in an oven at 100 ° C. for 2 minutes. Thereby, the liquid crystalline polyester fiber nonwoven fabric as a reinforcing material was obtained.

After applying the above-mentioned solution to the reinforcing material by roll coating, it was dried at 100 ° C. for 10 minutes and temporarily cured. Subsequently, it was sandwiched between two Teflon (registered trademark) plates (thickness 1 mm), pressed with an iron plate heated to 180 ° C., and cured (ring-opening polymerization) as it was for 1 hour. (The applied pressure was 5 kg / cm ^2. ) The obtained fiber composite became a sheet having a thickness of about 30 μm.

After cutting out a sample for evaluation of the fiber composite, the dielectric constant, dielectric loss tangent (100 MHz and 1 GHz, respectively), and tensile properties (tensile elastic modulus, yield point strength, yield point elongation) were evaluated. For evaluation of soldering heat resistance, the above temporarily cured sample was laminated on a copper foil (manufactured by Mitsui Kinzoku Co., Ltd., 3EC-III 35 μm) and then two Teflon (registered trademark) plates (thickness 1 mm). ) And pressed with an iron plate heated to 180 ° C. and cured as it was for 1 hour. (The applied pressure was 5 kg / cm ^2. )

1 mol of 1,4-diaminobutane, 2 mol of phenol, 4 mol of paraformaldehyde and 1500 g of chloroform were mixed. This mixture was heated to 60 ° C. with stirring, and reacted for 4 hours after chloroform began to circulate. After completion of the reaction, the reaction mixture was transferred to a separatory funnel, washed with a 1N aqueous sodium hydroxide solution, and then washed with ion exchange water. After the chloroform layer was dried over anhydrous sodium sulfate, chloroform was distilled off by a rotary evaporator to obtain a bifunctional dihydrobenzoxazine compound in which R in the formula (1) is a butylene group.
Subsequent operations were performed in the same manner as in Example 1 to prepare samples.

1 mol of 1,6-diaminohexane, 2 mol of phenol, 4 mol of paraformaldehyde and 1500 g of chloroform were mixed. This mixture was heated to 60 ° C. with stirring, and reacted for 8 hours after chloroform began to circulate. After completion of the reaction, the reaction mixture was transferred to a separatory funnel, washed with a 1N aqueous sodium hydroxide solution, and then washed with ion exchange water. After the chloroform layer was dried over anhydrous sodium sulfate, chloroform was distilled off by a rotary evaporator to obtain a bifunctional dihydrobenzoxazine compound in which R in Formula (1) is a hexamethylene group.
Subsequent operations were performed in the same manner as in Example 1 to prepare samples.

1,8-diaminooctane 1 mol, phenol 2 mol, paraformaldehyde 4 mol and chloroform 1500 g were mixed. This mixture was heated to 60 ° C. with stirring, and reacted for 10 hours after chloroform began to circulate. After completion of the reaction, the reaction mixture was transferred to a separatory funnel, washed with a 1N aqueous sodium hydroxide solution, and then washed with ion-exchanged water. After the chloroform layer was dried over anhydrous sodium sulfate, chloroform was distilled off by a rotary evaporator to obtain a bifunctional dihydrobenzoxazine compound in which R in the formula (1) is an octamethylene group.
Subsequent operations were performed in the same manner as in Example 1 to prepare samples.

As the reinforcing material, a liquid crystalline polyester fiber non-woven fabric subjected to surface treatment with a reactive liquid polymer in the same manner as in Example 1 was used.
Further, a fluororesin emulsion (trade name “Neofluon FEP-ND1” manufactured by Daikin Industries, Ltd.) as a matrix resin was roll-coated on this nonwoven fabric and dried at 100 ° C. As the amount of impregnation, the basis weight of the nonwoven fabric is 25 g / m ² while the basis weight is 40 g / m ² .
It was adjusted to m ^2. The basis weight represents the number of grams of resin per 1 m ² of nonwoven fabric.
Samples were prepared in the same manner as Example 1 except for the above.

The evaluation results of Examples 1 to 5 are shown in Table 1 and Table 2.

3 (4), 8 (9), - bis (aminomethyl) tricyclo [5,2,1,0 ^2,6] decane 1 mole, (3 (4), 8 (9), - bis (aminomethyl) tricyclo [5,2,1,0 ^2,6] decane was mixed with "TCD Diamine" using those sold under the product name), phenol 2 mol, paraformaldehyde 4 mol and chloroform 1500g from Celanese Corp. . This mixture was heated to 60 ° C. with stirring, and reacted for 10 hours after chloroform began to circulate. After completion of the reaction, the reaction mixture was transferred to a separatory funnel, washed with a 1N aqueous sodium hydroxide solution, and then washed with ion-exchanged water. After the chloroform layer was dried over anhydrous sodium sulfate, chloroform was distilled off by a rotary evaporator to obtain a bifunctional dihydrobenzoxazine compound in which R in the formula (1) is a dimethylidenetricyclodecane group.
Subsequent operations were performed in the same manner as in Example 1 to prepare samples.

2,5 (6) -bis (aminomethyl) bicyclo [2,2,1] heptane 1 mol (2,5 (6) -bis (aminomethyl) bicyclo [2,2,1] heptane The product sold under the product name "NBDA" was used), 2 mol of phenol, 4 mol of paraformaldehyde and 1500 g of chloroform were mixed. This mixture was heated to 60 ° C. with stirring, and reacted for 10 hours after chloroform began to circulate. After completion of the reaction, the reaction mixture was transferred to a separatory funnel, washed with a 1N aqueous sodium hydroxide solution, and then washed with ion-exchanged water. After the chloroform layer was dried over anhydrous sodium sulfate, chloroform was distilled off by a rotary evaporator to obtain a bifunctional dihydrobenzoxazine compound in which R in the formula (1) was a dimethylidene norbornene group.
Subsequent operations were performed in the same manner as in Example 1 to prepare samples.

3 (4), 8 (9), - bis (aminomethyl) tricyclo [5,2,1,0 ^2,6] decane 1 mole, (3 (4), 8 (9), - bis (aminomethyl) tricyclo [5,2,1,0 ^2,6] decane was mixed with "TCD Diamine" using those sold under the product name), bisphenol A1 mole, paraformaldehyde 4 mol and chloroform 1500g from Celanese Corp. . This mixture was heated to 60 ° C. with stirring, and reacted for 10 hours after chloroform began to circulate. After completion of the reaction, the reaction mixture was transferred to a separatory funnel, washed with a 1N aqueous sodium hydroxide solution, and then washed with ion-exchanged water. After the chloroform layer was dried with anhydrous sodium sulfate, chloroform was distilled off by a rotary evaporator to obtain a polyfunctional dihydrobenzoxazine compound in which R ¹ in the formula (I) was a dimethylidenetricyclodecane group. In measurement of molecular weight by GPC, the weight average molecular weight was 4,600 in terms of standard polystyrene.
Subsequent operations were performed in the same manner as in Example 1 to prepare samples.

2,5 (6) -bis (aminomethyl) bicyclo [2,2,1] heptane 1 mol (2,5 (6) -bis (aminomethyl) bicyclo [2,2,1] heptane The product sold under the product name "NBDA" was used), 1 mol of bisphenol A, 4 mol of paraformaldehyde and 1500 g of chloroform were mixed. This mixture was heated to 60 ° C. with stirring, and reacted for 10 hours after chloroform began to circulate. After completion of the reaction, the reaction mixture was transferred to a separatory funnel, washed with a 1N aqueous sodium hydroxide solution, and then washed with ion-exchanged water. After the chloroform layer was dried over anhydrous sodium sulfate, chloroform was distilled off by a rotary evaporator to obtain a polyfunctional dihydrobenzoxazine compound in which R ¹ in the formula (I) was a dimethylidene norbornene group. In measurement of molecular weight by GPC, the weight average molecular weight was 4,900 in terms of standard polystyrene.
Subsequent operations were performed in the same manner as in Example 1 to prepare samples.

The evaluation results of Examples 6 to 7 are shown in Table 3.

  The present invention relates to a fiber composite having a low dielectric constant and dielectric loss tangent and excellent balance in tensile strength, tensile elastic modulus, and elongation, a method for producing the same, and a prepreg and a film comprising such a fiber composite. As an electronic circuit board made of the film, it has industrial applicability.

Claims (14)

  A fiber composite comprising a ring-opening polymer of a bi- or polyfunctional dihydrobenzoxazine compound as a matrix and a liquid crystalline polyester fiber nonwoven fabric as a reinforcing material. The fiber composite according to claim 1, wherein the bifunctional dihydrobenzoxazine compound is represented by the following molecular structure (1).

(In the formula, R represents a linear alkylene group having 2 or more carbon atoms, a branched alkylene group in which hydrogen is alkyl-substituted, or a hydrocarbon group having an alicyclic structure, and hydrogen in the benzene ring is an alkyl group. Or may be substituted with an alkoxy group, and R may be a diphenyl ether group.) The fiber composite according to claim 1, wherein the polyfunctional dihydrobenzoxazine compound is represented by the following molecular structure (I).

[In Formula (I),
Ar ¹ represents a tetravalent aromatic group,
R ¹ is a hydrocarbon group having an aliphatic or alicyclic structure;
n represents an integer of 2 to 500. ] The fiber composite according to claim 2, wherein R in the molecular structure (1) which is the bifunctional dihydrobenzoxazine compound is a group represented by the following (i).

[In the formula, * indicates a binding site to N in the formula (1). Also includes cis-trans isomers. ] The fiber composite according to claim 3, wherein R ¹ in the molecular structure (I), which is the polyfunctional dihydrobenzoxazine compound, is a group represented by the following (i).

[In the formula, * indicates a binding site to N in the formula (I). Also includes cis-trans isomers. ] The fiber composite according to any one of claims 1 to 5, wherein a dielectric constant at 23 ° C, 100 MHz, and 1 GHz is 2.0 to 3.2, and a dielectric loss tangent is 10 ^{-4 to} 6.0 × 10 ^-3. body.   The fiber composite according to any one of claims 1 to 6, further comprising a resin having a dielectric constant of 2.5 or less in addition to the ring-opening polymer of the bifunctional or polyfunctional dihydrobenzoxazine compound as a matrix.   The fiber composite according to any one of claims 1 to 7, wherein the nonwoven fabric is treated with a surface treatment agent comprising a copolymer polymer of butadiene-acrylonitrile.   A method for producing a fiber composite, wherein a liquid crystalline polyester fiber nonwoven fabric is impregnated with a bifunctional or polyfunctional dihydrobenzoxazine compound, and finally the whole is heated and integrated under pressure.   A liquid crystalline polyester fiber nonwoven fabric is impregnated with a resin having a dielectric constant of 2.5 or less in the form of an emulsion, dried, then impregnated with a bi- or polyfunctional dihydrobenzoxazine compound, and finally the whole is subjected to pressure. A method for producing a fiber composite which is integrated by heating.   The liquid crystalline polyester nonwoven fabric is treated with a surface treatment agent comprising a copolymer polymer of butadiene-acrylonitrile in advance, impregnated with a resin having a dielectric constant of 2.5 or less in the form of an emulsion, and then dried. A method for producing a fiber composite, wherein a functional dihydrobenzoxazine compound is impregnated and finally the whole is heated and integrated under pressure.   The prepreg comprising the fiber composite according to claim 1, which can be cured by heating.   2. The film comprising the fiber composite according to claim 1, which is cured by heating.   The electronic circuit board comprising the film according to claim 13, wherein the electronic circuit board is integrated with a copper foil.