阅读说明：本技术 无卤阻燃热固性树脂组合物、印刷电路用预浸料及覆金属层压板 (Halogen-free flame-retardant thermosetting resin composition, prepreg for printed circuit, and metal-clad laminate ) 是由 潘子洲 方克洪 于 2019-03-01 设计创作，主要内容包括：本公开提供无卤阻燃热固性树脂组合物、印刷电路用预浸料及覆金属层压板。所述无卤阻燃热固性树脂组合物包含：改性双马来酰亚胺预聚物；苯并噁嗪树脂；含磷环氧树脂；酸酐类化合物；和固化促进剂。通过使用无卤阻燃热固性树脂组合物,制得的覆金属层压板可以至少具有粘结性好,高耐热性、高玻璃化转变温度(Tg)、阻燃性、低介电常数与损耗等特性中的一个。(The present disclosure provides a halogen-free flame-retardant thermosetting resin composition, a prepreg for a printed circuit, and a metal-clad laminate. The halogen-free flame-retardant thermosetting resin composition comprises: a modified bismaleimide prepolymer; a benzoxazine resin; a phosphorus-containing epoxy resin; acid anhydride compounds; and a curing accelerator. By using the halogen-free flame-retardant thermosetting resin composition, the metal-clad laminate can have at least one of the characteristics of good adhesion, high heat resistance, high glass transition temperature (Tg), flame retardancy, low dielectric constant, loss and the like.)

1. A halogen-free flame retardant thermosetting resin composition comprising:

modified bismaleimide prepolymer: 10 to 50 parts by weight;

benzoxazine resin: 5 to 50 parts by weight;

phosphorus-containing epoxy resin: 30 to 90 parts by weight;

acid anhydride compound: 10 to 50 parts by weight; and

curing accelerator: 0.01 to 1 part by weight of a stabilizer,

the modified bismaleimide prepolymer is prepared by prepolymerization of maleimide, aromatic diamine and hydroxyl-containing aromatic amine, wherein the molecular structure of the maleimide is provided with at least two N-substituted maleimide groups.

2. The halogen-free flame-retardant thermosetting resin composition according to claim 1, wherein the maleimide having at least two N-substituted maleimide groups in the molecular structure is represented by the following formula (I) or (II):

wherein R is

3. The halogen-free, flame-retardant thermosetting resin composition according to claim 1, wherein the hydroxyl-containing aromatic amine is selected from one or a combination of any two or more of the following:

wherein R is₁And R₂Each independently is H or C₁To C₄Alkyl groups of (a);

preferably, the aromatic diamine is an aromatic diamine having 2 or more and 4 or less aromatic rings;

preferably, the aromatic diamine is selected from one or a combination of any two or more of the following: 4, 4 ' -diaminodiphenylmethane, 4 ' -diaminodiphenylpropane, 4 ' -diaminodiphenyl ether, 4 ' -diaminodiphenylsulfone, 3 ' -diaminodiphenylsulfone, 1, 5-diaminonaphthalene, 2, 6-diaminonaphthalene, 4 ' -diamino-3, 3 ' -diethyl-5, 5 ' -dimethyldiphenylmethane, 4 ' -diamino-3, 3 ' -dimethyl-5, 5 ' -diethyldiphenylmethane, 4 ' -diamino-3, 3 ' -diethyldiphenylmethane and 4, 4 ' -diamino-3, 3 ', 5, 5 ' -tetraethyldiphenylmethane, 4-diaminobiphenyl, 4-diaminoanisole, 2-diaminodiphenylether, 4-diaminodiphenylsulfone, 4 ' -diaminonaphthalene, 2-diaminonaphthalene, 5-diaminodiphenylether, 4-diaminodiphenyl, 3, 3 '-dimethoxybenzidine or 3, 3' -dimethylbenzidine.

4. The halogen-free flame-retardant thermosetting resin composition according to claim 1, wherein in the modified bismaleimide prepolymer, the weight ratio of the structural unit derived from the maleimide having at least two N-substituted maleimide groups in the molecular structure, the structural unit derived from the aromatic diamine and the hydroxyl group-containing aromatic amine derived is (6 to 12): (0.5 to 3).

5. The halogen-free flame-retardant thermosetting resin composition according to claim 1, wherein the benzoxazine resin comprises any one of or a mixture of at least two of bisphenol a type benzoxazine resin, bisphenol F type benzoxazine resin, diamine type benzoxazine resin, phenolphthalein type benzoxazine resin, dicyclopentadiene type benzoxazine resin, or bisphenol fluorene type benzoxazine resin;

preferably, the phosphorous-containing ring resin is selected from the group consisting of: any one or a mixture of at least two of multifunctional epoxy resins containing 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10- (2, 5-dihydroxyphenyl) -9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide or 10- (2, 5-dihydroxynaphthyl) -10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide structure;

preferably, the acid anhydride-based compound comprises a compound having not less than two acid anhydride groups in the molecular structure;

preferably, the acid anhydride-based compound is selected from any one of or a mixture of at least two of styrene-maleic anhydride copolymer, 3, 3 ', 4, 4' -diphenyl ether tetracarboxylic dianhydride, 2, 3, 3 ', 4' -diphenyl ether tetracarboxylic dianhydride, 3, 3 ', 4, 4' -biphenyl tetracarboxylic dianhydride, 2, 3, 3 ', 4' -biphenyl tetracarboxylic dianhydride, 3, 3 ', 4, 4' -benzophenone tetracarboxylic dianhydride, or 1, 2, 4, 5-pyromellitic dianhydride;

preferably, the curing accelerator is any one or a mixture of at least two of tertiary amine, imidazole, 4-dimethylamino pyridine, triphenylphosphine or boron trifluoride monoethylamine;

preferably, the halogen-free flame-retardant thermosetting resin composition further comprises an inorganic filler;

preferably, the inorganic filler accounts for 30 to 70 percent of the total weight of the halogen-free flame retardant thermosetting resin composition;

preferably, the inorganic filler is selected from: any one or a mixture of at least two of silicon dioxide, soft glass powder, talcum powder, kaolin, mica powder, boehmite, hydrotalcite, zinc borate, aluminum hydroxide, magnesium hydroxide, aluminum oxide, boron nitride, aluminum nitride, barium sulfate or wollastonite;

preferably, the silica is any one of spherical silica, fused silica or crystalline silica or a mixture of at least two of them.

6. A resin cement, comprising:

the halogen-free flame-retardant thermosetting resin composition according to any one of claims 1 to 5; and

a solvent.

7. A prepreg for a printed circuit comprising a reinforcing material and the halogen-free flame-retardant thermosetting resin composition according to any one of claims 1 to 5 attached thereto by impregnation drying.

8. An insulating board comprising at least one sheet of prepreg according to claim 7 for printed circuits.

9. A metal clad laminate comprising at least one prepreg according to claim 7 for a printed circuit and a metal foil clad on one or both sides of the outside of the prepreg.

10. A printed circuit board, the printed circuit board comprising: at least one prepreg according to claim 7 for printed circuits, or at least one insulating sheet according to claim 8, or at least one metal-clad laminate according to claim 9.

Technical Field

The present disclosure relates to the field of printed circuit board technology. In particular, the present disclosure relates to a halogen-free flame retardant thermosetting resin composition, a prepreg for a printed circuit, and a metal clad laminate.

Background

The metal-Clad Laminate is a plate-like material obtained by immersing electronic glass fiber cloth or other reinforcing materials in a resin solution, coating one or both surfaces with a metal foil, and hot-pressing, and is called a metal-Clad Laminate, which is simply referred to as a metal-Clad Laminate or a metal-Clad plate, such as a Copper-Clad Laminate or a Copper-Clad Laminate (CCL). Metal clad laminates such as copper clad laminates are base laminates for manufacturing Printed Circuit boards (PCBs for short), which are one of the important parts in the electronics industry. Almost every kind of electronic equipment, as small as electronic watches, calculators, as large as computers, communication electronics, military weaponry systems, requires printed boards for electrical interconnection as long as there are electronic components such as integrated circuits. The metal clad laminate is provided on the entire printed circuit board and mainly performs three functions of conduction, insulation and support.

With the rapid progress of electronic technology, wireless communication and networks are going deep into every corner of society, and signal transmission of network infrastructures such as communication devices, base stations, servers and routers, large computers, and the like is continuously progressing to high speed and large capacity in order to meet the demand of people for fast response and large capacity of information acquisition. Accordingly, printed wiring boards mounted on these electronic devices are required to have characteristics of high-frequency transmission and low transmission loss, and low dielectric constant and low dielectric loss tangent are required for the substrate materials. In addition, due to the high performance and miniaturization of electronic information equipment, the circuit of the PCB tends to have high density and high multilayering, so that the plate is required to have higher reflow soldering heat resistance and through hole reliability, reflected to material performance indexes, and required to have a glass transition temperature of more than 190 ℃ or even higher; the thermal expansion rate is lower, and the Z-axis CTE below Tg is below 45 ppm/DEG C, even below 40 ppm/DEG C; in consideration of environmental protection, the final trend of the product development is towards non-halogenation.

Conventionally, as a resin composition used for printed wiring boards which are required to have low transmission loss, patent CN103131131A discloses a method of using a styrene maleic anhydride copolymer in combination with an epoxy resin or a benzoxazine resin, but the resulting sheet material has a glass transition temperature of only 170 ℃, a large Coefficient of Thermal Expansion (CTE), a large water absorption of the sheet material, and poor heat resistance of a multilayer sheet. In CN201510106304, a combination of amine-modified bismaleimide, benzoxazine resin and epoxy resin can obtain the effects of high glass transition temperature and low CTE by using the advantages of bismaleimide, but the dielectric constant of the plate is high, which is not favorable for signal transmission in PCB at high frequency.

Disclosure of Invention

An object of the present disclosure is to provide a halogen-free flame-retardant thermosetting resin composition, a prepreg for a printed circuit obtained by impregnating the halogen-free flame-retardant thermosetting resin composition with a reinforcing material such as glass fiber cloth (abbreviated as glass fiber cloth), and a metal-clad laminate including the prepreg for a printed circuit, such that the metal-clad laminate has at least one of characteristics of good adhesion, high heat resistance, high glass transition temperature (Tg), flame retardancy, low dielectric constant and loss.

Another object of the present disclosure is to provide an insulating board including the prepreg for a printed circuit and a printed circuit board including the prepreg for a printed circuit, the insulating board or the metal clad laminate, wherein the insulating board or the metal clad laminate has one of characteristics of good adhesion, high heat resistance, high glass transition temperature (Tg), flame retardancy, low dielectric constant and loss.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present disclosure provides a halogen-free flame retardant thermosetting resin composition comprising the following components: modified bismaleimide prepolymer, benzoxazine resin, phosphorus-containing epoxy resin, anhydride compounds and curing accelerator.

Specifically, the present disclosure provides a halogen-free flame retardant thermosetting resin composition comprising:

modified bismaleimide prepolymer: 10 to 50 parts by weight;

benzoxazine resin: 5 to 50 parts by weight;

phosphorus-containing epoxy resin: 30 to 90 parts by weight;

acid anhydride compound: 10 to 50 parts by weight; and

curing accelerator: 0.01 to 1 part by weight of a stabilizer,

the modified bismaleimide prepolymer is prepared by prepolymerization of maleimide, aromatic diamine and hydroxyl-containing aromatic amine, wherein the molecular structure of the maleimide is provided with at least two N-substituted maleimide groups.

In a second aspect, the present invention provides a resin glue solution, including: a thermosetting resin composition as described in the first aspect and a solvent.

In a third aspect, the present invention provides a prepreg for a printed circuit, which comprises a reinforcing material and the halogen-free flame retardant thermosetting resin composition according to the first aspect attached thereto by impregnation and drying.

In a fourth aspect, the present invention provides an insulating board containing a prepreg for printed circuits as described in the third aspect.

In a fifth aspect, the present invention provides a metal clad laminate comprising a prepreg for a printed circuit according to the third aspect and a metal foil clad on one or both sides of the outside of the prepreg.

In a sixth aspect, the present invention provides a printed circuit board comprising: at least one prepreg for printed circuits according to the third aspect, or an insulating sheet according to the fourth aspect, or a metal clad laminate according to the fifth aspect.

According to the disclosure, the halogen-free flame-retardant thermosetting resin composition contains the modified bismaleimide prepolymer, and by utilizing the characteristic that the solidified bismaleimide has a high rigid molecular chain, higher Tg and heat resistance can be brought, and meanwhile, active phenolic hydroxyl can react with epoxy resin, so that higher toughness and cohesiveness are brought; secondly, the halogen-free flame-retardant thermosetting resin composition contains phosphorus-containing epoxy resin, so that the halogen-free flame-retardant thermosetting resin composition not only provides better cohesiveness, but also brings a flame-retardant effect; the halogen-free flame-retardant thermosetting resin composition contains the anhydride compound, and can provide good dielectric property for lacing. In addition, the halogen-free flame-retardant thermosetting resin composition preferably contains inorganic filler, so that the expansion coefficient of the halogen-free flame-retardant thermosetting resin composition can be greatly reduced, and meanwhile, the cost can be reduced and the flame retardancy can be improved. Therefore, the copper clad laminate prepared by the composition is suitable for halogen-free high-multilayer copper clad laminates, and has the characteristics of good adhesion, high heat resistance, high glass transition temperature (Tg), flame retardance, low dielectric constant, loss and the like.

Therefore, according to the present disclosure, there can be provided a halogen-free flame-retardant thermosetting resin composition, a prepreg for a printed circuit obtained by impregnating the halogen-free flame-retardant thermosetting resin composition with a reinforcing material, a metal-clad laminate or an insulating board comprising the prepreg for a printed circuit, and a printed circuit board comprising the prepreg for a printed circuit, the insulating board or the metal-clad laminate, so that the metal-clad laminate can have at least one of the characteristics of good adhesion, high heat resistance, high glass transition temperature (Tg), flame retardancy, low dielectric constant and loss, preferably at least two of the above characteristics, and more preferably all of the above characteristics.

Detailed Description

The technical solutions in the examples of the present disclosure will be clearly and completely described below in connection with the specific embodiments of the present disclosure, and it is obvious that the described embodiments and/or examples are only a part of the embodiments and/or examples of the present disclosure, and not all embodiments and/or examples. All other embodiments and/or all other examples that can be obtained by one of ordinary skill in the art without making any inventive step based on the embodiments and/or examples in the present disclosure are within the scope of the present disclosure.

In the present disclosure, all numerical features are meant to be within the error of measurement, for example within ± 10%, or within ± 5%, or within ± 1% of the defined numerical value.

The term "comprising", "including" or "containing" as used in this disclosure means that it may have, in addition to the recited components, other components which impart different properties to the prepreg. In addition, the terms "comprising," including, "or" containing "as used in this disclosure may also include" consisting essentially of, and may instead be "or" consisting of.

In the present disclosure, amounts, ratios, etc., are by weight if not specifically indicated.

For purposes of this disclosure, the term "halogen-free flame retardant" means that the composition of the present disclosure does not contain intentionally added halogen-containing flame retardants.

As described above, the present disclosure may provide a halogen-free flame retardant thermosetting resin composition comprising:

modified bismaleimide prepolymer: 10 to 50 parts by weight;

benzoxazine resin: 5 to 50 parts by weight;

phosphorus-containing epoxy resin: 30 to 90 parts by weight;

acid anhydride compound: 10 to 50 parts by weight; and

curing accelerator: 0.01 to 1 part by weight of a stabilizer,

the modified bismaleimide prepolymer is prepared by prepolymerization of maleimide, aromatic diamine and hydroxyl-containing aromatic amine, wherein the molecular structure of the maleimide is provided with at least two N-substituted maleimide groups.

Modified bismaleimide prepolymer

As described above, the modified bismaleimide prepolymer may be prepared by pre-polymerizing maleimide having at least two N-substituted maleimide groups in its molecular structure, an aromatic diamine, and a hydroxyl-containing aromatic amine.

Examples of the maleimide having at least two N-substituted maleimide groups in the molecular structure may be represented by the following formula (I) or (II):

wherein R is

R₁And R₂Each independently is H or C1 to C4 alkyl; in the formula II, n is an integer of 1 to 8.

The hydroxyl-containing aromatic amine may be selected from one or a combination of any two or more of the following:

wherein R is₁And R₂Each independently is H or C₁To C₄Alkyl group of (1).

C₁To C₄Examples of the alkyl group of (a) may include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl.

In this disclosure, for substituent R₁And R₂The substitution position of (3) is not limited. For example, having a substituent R in a phenyl ring₁Or R₂In the case of (3), the substituent R₁Or R₂Can be located in any possible location. Having two substituents R on a benzene ring₁And R₂In the case of (3), the substituent R₁And R₂Can be in any possible position and can be in the ortho, meta or para position relative to one another. In the case of naphthalene rings, this also applies.

The aromatic diamine may be an aromatic diamine having 2 or more and 4 or less aromatic rings. Examples of the aromatic diamine may be selected from one or a combination of any two or more of the following: 4, 4 ' -diaminodiphenylmethane, 4 ' -diaminodiphenylpropane, 4 ' -diaminodiphenyl ether, 4 ' -diaminodiphenylsulfone, 3 ' -diaminodiphenylsulfone, 1, 5-diaminonaphthalene, 2, 6-diaminonaphthalene, 4 ' -diamino-3, 3 ' -diethyl-5, 5 ' -dimethyldiphenylmethane, 4 ' -diamino-3, 3 ' -dimethyl-5, 5 ' -diethyldiphenylmethane, 4 ' -diamino-3, 3 ' -diethyldiphenylmethane and 4, 4 ' -diamino-3, 3 ', 5, 5 ' -tetraethyldiphenylmethane, 4-diaminobiphenyl, 4-diaminoanisole, 2-diaminodiphenylether, 4-diaminodiphenylsulfone, 4 ' -diaminonaphthalene, 2-diaminonaphthalene, 5-diaminodiphenylether, 4-diaminodiphenyl, 3, 3 '-dimethoxybenzidine or 3, 3' -dimethylbenzidine.

The modified bismaleimide prepolymer can be prepared by the following prepolymerization method: mixing maleimide with at least two N-substituted maleimide groups in a molecular structure, aromatic amine containing hydroxyl groups, aromatic diamine and an organic solvent in proportion, heating and stirring gradually to form a solution, introducing nitrogen atmosphere and continuing stirring, keeping the reaction temperature at about 100-150 ℃ for reflux reaction for about 0.5-8 h, and stopping heating and cooling after the reaction is finished to obtain the modified bismaleimide prepolymer solution containing amino groups and phenolic hydroxyl groups.

In the modified bismaleimide prepolymer, the weight ratio of the structural unit derived from the maleimide having at least two N-substituted maleimide groups in the molecular structure, the structural unit derived from the aromatic diamine, and the hydroxyl-containing aromatic amine is about (6 to 12): (0.5 to 3).

The modified bismaleimide prepolymer has a molecular weight of about 500 to 2500, with a preferred lower limit of the molecular weight being 600, 750, 900, 1000, or 1200. And controlling the end capping of the prepolymerization reaction by controlling the feeding weight ratio to obtain the modified bismaleimide prepolymer. When the molecular weight is less than about 500, the flowability of the halogen-free flame-retardant thermosetting resin composition becomes large, which results in deterioration of thickness uniformity of the metal-clad laminate. When the molecular weight exceeds about 2500, the wettability of the prepreg deteriorates, and the insulation reliability of the insulating layer, the metal-clad laminate or the printed wiring board is lowered. The molecular weight can be measured according to the test method specified in GB/T21863-2008 Gel Permeation Chromatography (GPC) using tetrahydrofuran as the eluent.

Benzoxazine resins

Examples of the benzoxazine resin may include any one of or a mixture of at least two of bisphenol a type benzoxazine resin, bisphenol F type benzoxazine resin, diamine type benzoxazine resin, phenolphthalein type benzoxazine resin, dicyclopentadiene type benzoxazine resin, or bisphenol fluorene type benzoxazine resin, and preferably include any one of or a mixture of at least two of bisphenol F type benzoxazine resin, diamine type benzoxazine resin, phenolphthalein type benzoxazine resin, or bisphenol fluorene type benzoxazine resin.

In the invention, the benzoxazine plays a role of a curing agent, can be subjected to ring opening at high temperature to generate hydroxyl, and the hydroxyl can react with the modified bismaleimide and the epoxy resin to form a cross-linked network, so that the benzoxazine can endow the corresponding cured product with good comprehensive performance.

Phosphorus ring-containing resin

Examples of the phosphorus ring-containing resin may be selected from: any one or a mixture of at least two of multifunctional epoxy resins containing 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10- (2, 5-dihydroxyphenyl) -9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide or 10- (2, 5-dihydroxynaphthyl) -10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide structure.

The molecular weight of the phosphorus-containing ring resin is about 800 to 2500. The molecular weight can be measured according to the test method specified in GB/T21863-2008 Gel Permeation Chromatography (GPC) using tetrahydrofuran as the eluent.

According to the present disclosure, in the halogen-free flame retardant thermosetting resin composition, in addition to the phosphorus-containing epoxy resin, other polyfunctional epoxy resins may be contained to further increase the crosslinking density of the resin composition and to increase Tg, and examples of other polyfunctional epoxy resins that may be listed include a phenol novolac type epoxy resin, a cresol novolac type epoxy resin, a bisphenol a novolac type epoxy resin, a phenol aralkyl type epoxy resin, a naphthol novolac type epoxy resin, a naphthol aralkyl type epoxy resin, and the like, a naphthalene skeleton-containing type epoxy resin, a biphenyl aralkyl type epoxy resin, a dicyclopentadiene type epoxy resin, a dihydroanthracene type epoxy resin, and the like. These may be used alone in 1 kind, or may be used in combination of 2 or more kinds. From the viewpoint of high frequency characteristics, heat resistance, thermal expansion characteristics and flame retardancy, naphthalene skeleton-containing, biphenyl and aralkyl group-containing epoxy resins are preferably used.

Acid anhydride compound

The acid anhydride compound comprises a compound with a molecular structure containing not less than two acid anhydride groups.

Examples of the acid anhydride-based compound may be selected from any one of styrene-maleic anhydride copolymer, 3, 3 ', 4, 4' -diphenyl ether tetracarboxylic dianhydride, 2, 3, 3 ', 4' -diphenyl ether tetracarboxylic dianhydride, 3, 3 ', 4, 4' -biphenyl tetracarboxylic dianhydride, 2, 3, 3 ', 4' -biphenyl tetracarboxylic dianhydride, 3, 3 ', 4, 4' -benzophenone tetracarboxylic dianhydride or 1, 2, 4, 5-pyromellitic dianhydride or a mixture of at least two thereof.

In the styrene-maleic anhydride and phenylpropene-maleic anhydride copolymer, the copolymerization ratio of styrene or phenylpropene and maleic anhydride may be about 1: 10 to 10: 1, preferably about 1: 5 to 5: 1, more preferably about 1: 2 to 2: 1, on a molar basis.

Curing accelerator

Examples of the curing accelerator are any one or a mixture of at least two of tertiary amines, imidazoles, 4-dimethylaminopyridine, triphenylphosphine or boron trifluoride monoethylamine.

Examples of the tertiary amine may include triethylamine, benzyldimethylamine, 2, 4, 6-tris (dimethylaminomethyl) phenol, and salts thereof.

Examples of the imidazoles may include 2-methylimidazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole and 1-cyanoethyl-2-phenylimidazole.

The halogen-free flame-retardant thermosetting resin composition may further include an inorganic filler.

The inorganic filler accounts for 30 to 70 percent of the total weight of the halogen-free flame-retardant thermosetting resin composition.

The inorganic filler is selected from: any one or a mixture of at least two of silicon dioxide, soft glass powder, talcum powder, kaolin, mica powder, boehmite, hydrotalcite, zinc borate, aluminum hydroxide, magnesium hydroxide, aluminum oxide, boron nitride, aluminum nitride, barium sulfate or wollastonite. The silica is any one or a mixture of at least two of spherical silica, fused silica or crystalline silica.

There is a certain limit to the particle diameter of the inorganic filler, and the inorganic filler having a particle diameter of preferably about 0.01 to 30 μm, more preferably about 0.1 to 15 μm is used.

If the particle size of the inorganic filler is less than about 0.01 μm, the flowability of the halogen-free flame-retardant thermosetting resin composition is lowered, and therefore, moldability in the production of a prepreg or a metal-clad laminate is deteriorated, voids are likely to be generated, or the surface area thereof is increased, and therefore, the bonding area between metal and resin is reduced, and the peel strength of a printed wiring board is lowered, which is not preferable. On the other hand, a particle size of more than about 30 μm is not preferable because it causes a decrease in insulation reliability between wirings of a printed wiring board or an insulating layer.

In the present disclosure, in order to further improve the flame retardant effect, other flame retardants containing a phosphorus structure, such as any one of or a combination of at least two of phosphorus-containing phenol formaldehyde, phosphazene compound, ammonium polyphosphate, tris (2-carboxyethyl) phosphine, tris (isopropyl chloride) phosphate, trimethylphosphate, dimethyl-methyl phosphate, resorcinol dixylylphosphate, melamine polyphosphate, melamine cyanurate, or tris-hydroxyethyl isocyanurate, may also be incorporated.

In the case of the flame retardant containing other phosphorus-containing structure, the content of the other phosphorus-containing structure flame retardant in the halogen-free flame retardant thermosetting resin composition may be about 1 to 60% by weight, preferably about 2 to 40% by weight.

The halogen-free flame-retardant thermosetting resin composition may further include a solvent. Examples of the solvent may be one or more selected from acetone, butanone, cyclohexanone, N, N-dimethylformamide, N, N-dimethylacetamide, ethylene glycol methyl ether, propylene glycol methyl ether acetate, and dimethyl sulfone. In the case of containing a solvent, the content of the solvent in the halogen-free flame-retardant thermosetting resin composition may be 10 to 99.5% by weight, preferably about 20 to 99% by weight.

The halogen-free flame retardant thermosetting resin composition containing a solvent may be referred to as a resin cement in the present disclosure. The resin cement may be obtained by dissolving or dispersing the above-mentioned halogen-free flame-retardant thermosetting resin composition in a solvent.

In addition, the halogen-free flame-retardant thermosetting resin composition may further contain various auxiliaries. Specific examples of the auxiliary include a filler dispersant, an antifoaming agent, an antioxidant, a heat stabilizer, an antistatic agent, an ultraviolet absorber, a pigment, a colorant, and a lubricant. These auxiliaries may be used alone or in admixture of any two or more.

The halogen-free flame-retardant thermosetting resin composition of the present disclosure may be prepared by known methods such as compounding, stirring, mixing modified bismaleimide prepolymer, benzoxazine resin, phosphorus-containing epoxy resin, acid anhydride compound and curing accelerator; and optionally any one or a mixture of at least two of a solvent, a filler, a flame retardant, a dispersant, an antifoaming agent, an antioxidant, a heat stabilizer, an antistatic agent, an ultraviolet absorber, a pigment, a colorant and a lubricant.

The halogen-free flame-retardant thermosetting resin composition is prepared into resin glue solution by mechanical stirring, emulsification or ball milling dispersion, then the reinforcing material is soaked by the resin glue solution, and the prepreg is obtained by drying. The prepreg and a metal foil such as a copper foil or an aluminum foil are hot-pressed in a vacuum press to prepare a metal-clad laminate.

Examples of the reinforcing material may include: glass fiber cloth, glass fiber non-woven fabric, organic non-woven fabric and the like.

In order to reduce the viscosity of the resin dope, the impregnation may be performed under heating. Heating to make the resin glue solution temperature less than the boiling point of the solvent, preferably the resin glue solution temperature is about 20-90 deg.C, more preferably about 25-55 deg.C.

In another aspect, the present disclosure may also provide a prepreg for a printed circuit including a reinforcing material and the halogen-free flame retardant thermosetting resin composition according to any one of the above attached thereto by impregnation and drying.

In a further aspect, the present disclosure may also provide an insulating board or metal clad laminate containing at least one sheet of prepreg for printed circuits as described above. For example, the metal-clad laminate may include at least one sheet of the prepreg for a printed circuit described above and a metal foil clad on one or both sides of the outer side of the prepreg.

In yet another aspect, the present disclosure may also provide a printed circuit board including: at least one prepreg for printed circuits as described above, or at least one insulating sheet as described above, or at least one metal-clad laminate as described above.

According to the present disclosure, there can be provided a halogen-free flame-retardant thermosetting resin composition, a prepreg for a printed circuit obtained by impregnating the halogen-free flame-retardant thermosetting resin composition with a reinforcing material, a metal-clad laminate or an insulating board comprising the prepreg for a printed circuit, and a printed circuit board comprising the prepreg for a printed circuit, the insulating board or the metal-clad laminate, so that the metal-clad laminate can have at least one of characteristics of good adhesion, high heat resistance, high glass transition temperature (Tg), flame retardancy, low dielectric constant and loss.