JP5184480B2 - Resin composition, method for producing resin composition, resin varnish, prepreg, metal-clad laminate, and printed wiring board - Google Patents

Description

  The present invention provides a resin composition suitably used for an insulating material of a printed wiring board, a method for producing the resin composition, a resin varnish containing the resin composition, a prepreg obtained using the resin varnish, The present invention relates to a metal-clad laminate obtained using a prepreg, and a printed wiring board produced using the prepreg.

  2. Description of the Related Art In recent years, with various types of electronic equipment, mounting techniques such as higher integration of semiconductor devices to be mounted, higher density of wiring, and multilayering have rapidly progressed as the amount of information processing has increased. Insulating materials such as printed wiring boards used in various electronic devices are required to have a low dielectric constant and dielectric loss tangent in order to increase signal transmission speed and reduce loss during signal transmission.

  Polyphenylene ether (PPE) has excellent dielectric properties such as dielectric constant and dielectric loss tangent even in the high frequency band (high frequency region) from the MHz band to the GHz band, so printed wiring boards for electronic devices that use the high frequency band, etc. The insulating material is preferably used. However, since high molecular weight PPE generally has a high melting point, it tends to have high viscosity and low fluidity. Then, using such PPE, a prepreg used for manufacturing a multilayer printed wiring board or the like is formed, and when a printed wiring board is manufactured using the formed prepreg, at the time of manufacturing, for example, at the time of multilayer molding Forming defects such as generation of voids occurred, and there was a problem of formability that it was difficult to obtain a highly reliable printed wiring board. In order to solve such problems, for example, a technique for causing molecular cleavage by causing a redistribution reaction of high molecular weight PPE in a solvent in the presence of a phenol species and a radical initiator to lower the molecular weight of PPE. It has been known. However, when the molecular weight of PPE is lowered, there is a tendency that the curing becomes insufficient and the heat resistance of the cured product is lowered.

  Therefore, in order to improve the heat resistance and the like of the cured product, it is conceivable to use a combination of a thermosetting resin such as an epoxy resin with PPE as described in Patent Document 1 below. Specifically, Patent Document 1 discloses a phenol-modified PPE obtained by a redistribution reaction of an epoxy compound having at least two epoxy groups in one molecule and PPE in the presence of a phenol and a radical initiator. And an epoxy resin composition containing a cyanate compound as an essential component.

JP-A-10-279781

  According to Patent Document 1, it is disclosed that heat resistance and electrical characteristics can be improved. However, in practice, the heat resistance of a cured product may not be sufficiently high. This is thought to be because phenol-modified PPE obtained by redistributing PPE in the presence of phenols and a radical initiator has a low molecular weight distribution and a low hydroxyl group concentration at the end, so that the reactivity is low. It is done. Therefore, it is considered that PPE and the epoxy compound cannot sufficiently react at the time of curing, and three-dimensional crosslinking cannot be sufficiently formed. In order to increase the reactivity between PPE and the epoxy compound, as an epoxy compound that is pre-reacted with PPE, simply using an epoxy compound having a high reactivity, for example, having a large number of epoxy groups in one molecule increases the viscosity. However, in some cases, it gelled, and there was a problem that it could not be used for a prepreg for producing a printed wiring board.

  The present invention has been made in view of such circumstances, and a resin composition having a low viscosity when made into a varnish and excellent in heat resistance of a cured product while maintaining the excellent dielectric properties of PPE. The purpose is to provide. Another object of the present invention is to provide a method for producing the resin composition, a prepreg using the resin composition, a metal-clad laminate using the prepreg, and a printed wiring board using the metal-clad laminate.

  The present inventors considered that in order to sufficiently improve the heat resistance of the cured product, it is necessary to sufficiently form a three-dimensional crosslink as described above. Accordingly, the present inventors have arrived at the present invention as described below from the above knowledge.

  The resin composition according to one embodiment of the present invention includes a low molecular weight polyphenylene ether having a number average molecular weight of 500 to 3000 and a ratio of the weight average molecular weight to the number average molecular weight of 1 to 3, and an epoxy resin. Reaction product (A) obtained by reacting part or all of hydroxyl groups of molecular weight polyphenylene ether with the epoxy group of the epoxy resin in advance, and cyanate resin having an average of two or more cyanate groups in one molecule A first epoxy containing (B) and a curing accelerator (C), wherein the epoxy resin has a number average molecular weight of 600 or less and an average of 1.5 to 2.4 epoxy groups in one molecule. A resin and a second epoxy resin having an average number of molecular weights of 1000 or less and having an average of 2.5 to 4.4 epoxy groups in one molecule.

  According to the said structure, the viscosity when made into a varnish form is low and the resin composition excellent in the heat resistance of hardened | cured material can be obtained, maintaining the outstanding dielectric characteristic which PPE has.

  This is considered to be due to the following.

  First, to improve the heat resistance of the cured product by using a reaction product obtained by reacting at least a part of the hydroxyl groups of low molecular weight polyphenylene ether, which tends to have low heat resistance, with the epoxy group of the epoxy resin in advance. It is thought that you can. At that time, as the low molecular weight polyphenylene ether, the ratio of the weight average molecular weight Mw to the number average molecular weight Mn (Mw / Mn) is 1 to 3, and the heat resistance of the cured product is improved by using a relatively narrow molecular weight distribution. It is thought that it can be done. As the epoxy resin, a first epoxy resin having an average of 1.5 to 2.4 epoxy groups in one molecule and a second epoxy resin having an average of 2.5 to 4.4 epoxy groups in one molecule. By using an epoxy resin, in order to increase the reactivity between the low molecular weight polyphenylene ether and the epoxy resin, not only an epoxy resin with a large number of epoxy groups in one molecule was used, but also the excellent heat resistance of the cured product was ensured. It is considered that the increase in viscosity can be suppressed. That is, it is considered that not only can the heat resistance of the cured product be improved, but also an increase in viscosity can be suppressed.

  And by containing the reaction product, the cyanate resin, and the curing accelerator, by reacting the reaction product with the cyanate resin at the time of curing, the heat resistance of the cured product can be sufficiently increased. it is conceivable that. Therefore, it is considered that a resin composition having a low viscosity when formed into a varnish and excellent in heat resistance of a cured product can be obtained while maintaining the excellent dielectric properties of PPE.

  Moreover, since the obtained resin composition has a sufficiently high heat resistance of the cured product, it contains a flame retardant that tends to reduce the heat resistance of the cured product, for example, a phosphorus-containing compound, and has sufficient flame resistance. Even if it is increased, sufficient heat resistance can be maintained. Therefore, both the heat resistance and flame retardancy of the cured product can be achieved without containing halogen and lead.

  The epoxy resin is preferably one of a bisphenol A type epoxy resin and a bisphenol F type epoxy resin. According to such a configuration, a resin composition having excellent dielectric properties and heat resistance of a cured product and a lower viscosity when formed into a varnish can be obtained. This is considered to be due to the high compatibility of each of the epoxy resins with the low molecular weight polyphenylene ether.

  Moreover, it is preferable that 1/2 or more of the total hydroxyl groups of the low molecular weight polyphenylene ether before the reaction product (A) is reacted with the epoxy resin react with the epoxy group of the epoxy resin. According to such a configuration, the dielectric properties and the heat resistance of the cured product are excellent, the viscosity when made into a varnish is low, the storage stability of the resin composition, the adhesion with the metal foil, the solvent resistance, etc. An excellent resin composition can be obtained.

  Moreover, it is preferable to contain a phosphorus containing compound. According to such a configuration, the resin composition is excellent in dielectric properties and heat resistance of the cured product, has a low viscosity when formed into a varnish, and has excellent flame retardancy without containing halogen and lead. Is obtained.

  In general, when a phosphorus-containing compound is added as a flame retardant to a resin composition containing PPE and an epoxy resin, the flame retardancy increases, but the heat resistance of the cured product tends to decrease. It is difficult to achieve both heat resistance. By adopting the configuration according to the present invention, the obtained resin composition has a sufficiently high heat resistance of the cured product, and does not contain halogen and lead, but contains a phosphorus-containing compound as a flame retardant, making it difficult. Even if the flammability is sufficiently increased, it is considered that sufficient heat resistance can be maintained.

  Moreover, it is preferable that the said low molecular weight polyphenylene ether is a compound represented by following General formula (1).

(In Formula (1), m shows 0-20, n shows 0-20, and the sum total of m and n shows 1-30.)
According to such a configuration, a resin composition superior in dielectric properties and heat resistance of the cured product can be obtained. This is considered to be because the three-dimensional crosslinking can be suitably formed while maintaining the excellent dielectric properties of the PPE made of 2,6-dimethylphenol.

  Moreover, it is preferable that the epoxy group of the said epoxy resin is 1-4 per hydroxyl group of the said low molecular weight polyphenylene ether. According to such a configuration, a resin composition having excellent dielectric properties and heat resistance of a cured product and a lower viscosity when formed into a varnish can be obtained. This is because the low molecular weight polyphenylene ether is an oligomer having a relatively low hydroxyl group concentration, and thus the epoxy resin is excessively contained relative to the low molecular weight polyphenylene ether, so that the three-dimensional crosslinking is suitably formed. It is thought that it can be done. Furthermore, it is considered that the epoxy resin that did not react with the low molecular weight polyphenylene ether can be cured between the epoxy resins and contribute to the heat resistance of the cured product.

  Moreover, it is preferable that the epoxy group of the said reaction product (A) is 0.5-1 piece per cyanate group of the said cyanate resin.

  According to such a configuration, a resin composition having excellent dielectric properties and heat resistance of a cured product and a lower viscosity when formed into a varnish can be obtained. This is considered to be because the triazine structure is formed by containing the cyanate resin excessively with respect to the epoxy resin. Furthermore, it is considered that the cyanate resin that did not react with the epoxy resin is cured by the cyanate resins and can contribute to the heat resistance of the cured product.

  In addition, the method for producing a resin composition according to another embodiment of the present invention includes a low molecular weight polyphenylene ether having a number average molecular weight of 500 to 3000 and a ratio of the weight average molecular weight to the number average molecular weight of 1 to 3, and an epoxy. By heating the mixture with the resin, a part or all of the hydroxyl groups of the low molecular weight polyphenylene ether are reacted with the epoxy groups of the epoxy resin, and the reaction product obtained by the reaction contains one molecule. And a step of blending a cyanate resin having an average of 2 or more cyanate groups and a curing accelerator, and the epoxy resin has a number average molecular weight of 600 or less and an average of 1.5 to 2.4 per molecule. A first epoxy resin having an epoxy group and an average of 2.5 to 4.4 epoxy groups in one molecule having a number average molecular weight of 1000 or less Which comprises using a 2 epoxy resin.

  According to the above configuration, it is possible to produce a resin composition having a low viscosity when formed into a varnish and having excellent heat resistance of a cured product while maintaining the excellent dielectric properties of PPE.

  Moreover, the resin varnish which concerns on another one aspect | mode of this invention contains the said resin composition and a solvent. According to such a configuration, a resin varnish having excellent dielectric characteristics and heat resistance of a cured product, low viscosity, and high fluidity can be obtained. And the prepreg obtained using this resin varnish can manufacture electronic components, such as a printed wiring board, suppressing generation | occurrence | production of a molding defect.

  The solvent is preferably at least one selected from the group consisting of toluene, cyclohexanone and propylene glycol monomethyl ether acetate. According to such a structure, the resin varnish which can manufacture electronic components, such as a printed wiring board, suppresses generation | occurrence | production of a shaping | molding defect more is obtained. This is because toluene, cyclohexanone and propylene glycol monomethyl ether acetate have relatively high boiling points and can dissolve the reaction product (A) and the cyanate resin (B), so that the obtained prepreg is appropriately dried. It is thought to be due to having speed.

  The prepreg according to another aspect of the present invention is obtained by impregnating a fibrous base material with the resin varnish. According to such a configuration, it is suitably used for producing a metal-clad laminate having excellent dielectric properties and heat resistance of a cured product, and further, the viscosity of the resin composition is low and the fluidity is low. Since it is high, the thing excellent in the reliability which can suppress generation | occurrence | production of the shaping | molding defect at the time of manufacturing a metal-clad laminated board and a printed wiring board is obtained.

  The metal-clad laminate according to another aspect of the present invention is obtained by laminating a metal foil on the prepreg and heating and pressing. According to this configuration, it is possible to obtain a highly reliable metal-clad laminate that can produce a printed wiring board excellent in dielectric properties and heat resistance of a cured product while suppressing the occurrence of molding defects.

  A printed wiring board according to another aspect of the present invention is manufactured using the prepreg. According to this structure, what is excellent in the dielectric characteristics and the heat resistance of the cured product, and further, the generation of molding defects is suppressed can be obtained.

  According to the present invention, it is possible to provide a resin composition having a low viscosity when formed into a varnish and having excellent heat resistance of a cured product while maintaining the excellent dielectric properties of PPE. Moreover, using the manufacturing method of the said resin composition, the resin varnish containing the said resin composition, the prepreg obtained using the said resin varnish, the metal-clad laminate obtained using the said prepreg, and the said prepreg A manufactured printed wiring board is provided.

  The resin composition according to the embodiment of the present invention is a low molecular weight polyphenylene having a number average molecular weight of 500 to 3000 and a ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) (Mw / Mn) of 1 to 3. A reaction product (A) obtained by previously reacting at least part of the hydroxyl groups of the low-molecular-weight polyphenylene ether with the epoxy groups of the epoxy resin, including ether and an epoxy resin; It contains a cyanate resin (B) having two or more cyanate groups and a curing accelerator (C), and the epoxy resin has an average number of 1.5-2. 1st epoxy resin which has 4 epoxy groups, and 2nd epoxy resin which has an average of 2.5-4.4 epoxy groups in 1 molecule whose number average molecular weight is 1000 or less Characterized in that there. That is, the resin composition is prepared by prereacting at least a part of the hydroxyl group of the low molecular weight polyphenylene ether with the epoxy group of the epoxy resin in advance, and then the cyanate resin (B) and the curing accelerator (C). Is obtained by blending.

  As described above, the resin composition contains the reaction product (A) obtained by previously reacting at least a part of the hydroxyl groups of the low molecular weight polyphenylene ether with the epoxy groups of the epoxy resin. The reaction product (A) includes the low molecular weight polyphenylene ether and the epoxy resin, and at least a part of hydroxyl groups of the low molecular weight polyphenylene ether is reacted (prereacted) in advance with an epoxy group of the epoxy resin. If it is a product obtained by this, it will not specifically limit. Specifically, for example, one in which 1/2 or more of the total hydroxyl groups of the low molecular weight polyphenylene ether before reacting with the epoxy resin reacts with the epoxy group of the epoxy resin. More specifically, for example, it can be obtained by reacting as follows. First, the low molecular weight polyphenylene ether and the epoxy resin are stirred and mixed in an organic solvent for 10 to 60 minutes so that the low molecular weight polyphenylene ether and the epoxy resin have a predetermined ratio. In that case, as a ratio of the low molecular weight polyphenylene ether and the epoxy resin, for example, an equivalent ratio of a hydroxyl group of the low molecular weight polyphenylene ether and an epoxy group of the epoxy resin can obtain the above reaction product. Such an equivalent ratio is preferable. And after mixing the said low molecular weight polyphenylene ether and the said epoxy resin, the said low molecular weight polyphenylene ether and the said epoxy resin are made to react by heating at 80-110 degreeC for 2 to 12 hours. By doing so, the reaction product is obtained. The organic solvent is not particularly limited as long as it dissolves the low molecular weight polyphenylene ether and the epoxy resin and does not inhibit these reactions. Specifically, toluene etc. are mentioned, for example.

  The reaction product (A) may contain the low molecular weight polyphenylene ether and the epoxy resin depending on the degree of progress of the reaction, and the low molecular weight polyphenylene ether and the epoxy resin may include All may be reacted.

  As an equivalent ratio of the hydroxyl group of the low molecular weight polyphenylene ether and the epoxy group of the epoxy resin, specifically, for example, 1 to 4 epoxy groups of the epoxy resin per hydroxyl group of the low molecular weight polyphenylene ether It is preferable that the equivalent ratio is as follows. If the amount of the epoxy resin is too small, the reaction between the low molecular weight polyphenylene ether and the epoxy resin becomes insufficient, and the heat resistance of the cured product tends to decrease. On the other hand, when the amount of the epoxy resin is too large, the amount of the low molecular weight polyphenylene ether becomes too small, and therefore the excellent dielectric properties of the polyphenylene ether tend not to be maintained.

  When the low molecular weight polyphenylene ether and the epoxy resin are reacted, a catalyst may be mixed with the mixture of the low molecular weight polyphenylene ether and the epoxy resin. The catalyst can be used without any particular limitation as long as it can promote the reaction between the hydroxyl group of the low molecular weight polyphenylene ether and the epoxy group of the first epoxy resin. Specifically, organic metal salts such as Zn, Cu, and Fe of organic acids such as octanoic acid, stearic acid, acetylacetonate, naphthenic acid, and salicylic acid; 1,8-diazabicyclo [5.4.0] undecene Tertiary amines such as -7 (DBU), triethylamine and triethanolamine; imidazoles such as 2-ethyl-4-imidazole (2E4MZ) and 4-methylimidazole; triphenylphosphine (TPP), tributylphosphine, tetra And organic phosphines such as phenylphosphonium and tetraphenylborate. These may be used alone or in combination of two or more. Among these, imidazoles, particularly 2-ethyl-4-imidazole, is particularly preferable in that the reaction time can be shortened, and further, the polymerization between the epoxy resins (self-polymerization of the epoxy resin) can be suppressed. Used. Moreover, it is preferable that content of the said catalyst is 0.05-1 mass part with respect to a total of 100 mass parts of the said low molecular weight polyphenylene ether and the said epoxy resin. If the content of the catalyst is too small, the reaction between the hydroxyl group of the low molecular weight polyphenylene ether and the epoxy group of the epoxy resin tends to take a very long time. Moreover, when there is too much content of the said catalyst, control of the said reaction will become difficult and it will tend to gelatinize easily.

  The low molecular weight polyphenylene ether is particularly limited as long as the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 500 to 3000 and the number average molecular weight (Mn) is 1 to 3. Not. Specifically, for example, those obtained directly by a polymerization reaction and having a number average molecular weight and a weight average molecular weight within the above ranges can be mentioned.

  Moreover, when the molecular weight of the low molecular weight polyphenylene ether is too low, there is a tendency that sufficient heat resistance of the cured product cannot be obtained even if the low molecular weight polyphenylene ether is reacted with the epoxy resin. In addition, if the molecular weight of the low molecular weight polyphenylene ether is too high, when the reaction product reacted with the epoxy resin is contained, the viscosity of the resin composition becomes high and sufficient fluidity cannot be obtained, resulting in poor molding. There is a tendency that cannot be suppressed.

  The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the low molecular weight polyphenylene ether is called a dispersion ratio and serves as an index of molecular weight distribution. That is, the smaller the ratio (Mw / Mn), the narrower the molecular weight distribution. When this ratio (Mw / Mn) is too high, there is a tendency that sufficient heat resistance of the cured product cannot be obtained. This is presumably because the molecular weight distribution of the low molecular weight polyphenylene ether becomes too wide and the reaction with the epoxy resin tends to be uneven.

  Therefore, by using the low molecular weight polyphenylene ether, the dielectric properties are not only good in a wide frequency range, but also have sufficient fluidity to suppress molding defects.

  In addition, the number average molecular weight (Mn) and weight average molecular weight (Mw) of the said low molecular weight polyphenylene ether here can be specifically measured using a gel permeation chromatography etc., for example.

  The low molecular weight polyphenylene ether preferably has an average number of hydroxyl groups per molecule (average number of hydroxyl groups) of 1.5 to 3, more preferably 1.8 to 2.4. . If the average number of hydroxyl groups is too small, the reactivity with the epoxy group of the epoxy resin is lowered, and it is difficult to obtain a sufficient heat resistance of the cured product. Furthermore, the hydroxyl group of the low molecular weight polyphenylene ether and the epoxy The reaction with the epoxy groups of the resin tends to be very time consuming. If the average number of hydroxyl groups is too large, the reactivity of the epoxy resin with the epoxy group becomes too high, and it becomes difficult to control the reaction between the hydroxyl group of the low molecular weight polyphenylene ether and the epoxy group of the epoxy resin. There is a tendency to become easy.

  Here, the average number of hydroxyl groups of the low molecular weight polyphenylene ether can be understood from the standard value of the product of the low molecular weight polyphenylene ether to be used. Specific examples of the average number of hydroxyl groups of the low molecular weight polyphenylene ether include the average value of hydroxyl groups per molecule of all the low molecular weight polyphenylene ethers present in 1 mol of the low molecular weight polyphenylene ether.

  Specific examples of the low molecular weight polyphenylene ether include polyphenylene ether and poly (2,6-dimethyl-1, 2,6-dimethylphenol and at least one of bifunctional phenol and trifunctional phenol. 4-phenylene oxide) and the like mainly containing polyphenylene ether. Among these, polyphenylene ether composed of 2,6-dimethylphenol and at least one of bifunctional phenol and trifunctional phenol is preferable. Moreover, as said bifunctional phenol, tetramethylbisphenol A etc. are mentioned, for example. More specifically, examples of the low molecular weight polyphenylene ether include compounds represented by the following general formula (1).

  In the above formula (1), m and n are such that both the number average molecular weight (Mn) and the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) are within the above range. Any degree of polymerization may be used. Specifically, the total value of m and n is preferably 1-30. Further, m is preferably 0 to 20, and n is preferably 0 to 20.

  Examples of the epoxy resin include a first epoxy resin having a number average molecular weight of 600 or less and an average of 1.5 to 2.4 epoxy groups in one molecule, and a number average molecular weight of 1,000 or less in one molecule. If it contains the 2nd epoxy resin which has an average 2.5-4.4 epoxy group, it will not specifically limit. The first epoxy resin and the second epoxy resin are used in combination. Specifically, for example, by using a mixture obtained by mixing the first epoxy resin and the second epoxy resin, excellent heat resistance of the cured product. It is considered that the increase in viscosity can be suppressed while securing the properties. That is, since the second epoxy resin has a large number of epoxy groups in one molecule, it has a high reactivity with the low molecular weight polyphenylene ether, but tends to increase the viscosity of the resin composition more than necessary. On the other hand, it is considered that the first epoxy resin is not so high in reactivity with the low molecular weight polyphenylene ether that the heat resistance of the cured product is sufficiently enhanced. It is considered that the above effect can be exhibited by using together epoxy resins having different average number of epoxy groups per molecule (average number of epoxy groups).

  The first epoxy resin is not particularly limited as long as the number average molecular weight is 600 or less and the epoxy group has an average of 1.5 to 2.4 epoxy resins in one molecule. The second epoxy resin is not particularly limited as long as the number average molecular weight is 1000 or less and the epoxy group has an average of 2.5 to 4.4 epoxy resins per molecule. As the first epoxy resin and the second epoxy resin, specifically, for example, dicyclopentadiene type epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, naphthalene type An epoxy resin, a biphenyl type epoxy resin, etc. are mentioned. These may be used alone or in combination of two or more. Among these, bisphenol A type epoxy resin and bisphenol F type epoxy resin are preferably used from the viewpoint of good compatibility with the low molecular weight polyphenylene ether. In addition, although it is preferable that the said resin composition does not contain a halogenated epoxy resin, as long as the effect of this invention is not impaired, you may mix | blend as needed.

  In addition, the average number of epoxy groups of the said epoxy resin here can be known from the specification value of the product of the said epoxy resin to be used. Specific examples of the number of epoxy groups of the epoxy resin include an average value of epoxy groups per molecule of all the epoxy resins present in 1 mol of the epoxy resin. The number average molecular weight (Mn) of the epoxy resin can be specifically measured using, for example, gel permeation chromatography.

  The epoxy resin preferably has a solubility in toluene of 10% by mass or more at 25 ° C. With such an epoxy resin, the heat resistance of the cured product can be sufficiently enhanced without impairing the excellent dielectric properties of PPE. This is because the compatibility with the low molecular weight polyphenylene ether is relatively high, and therefore, it easily reacts uniformly with the low molecular weight polyphenylene ether, and three-dimensional crosslinking is easily formed with the low molecular weight polyphenylene ether. it is conceivable that.

  The cyanate resin (B) is not particularly limited as long as the average number of cyanate groups per molecule (average cyanate group number) is 2 or more. Thus, when there are many cyanate groups, it is preferable from the point which the heat resistance of the hardened | cured material of the obtained resin composition increases. In addition, the average cyanate group number of the said cyanate resin (B) here can be known from the standard value of the product of the said cyanate resin to be used. Specific examples of the number of cyanate groups in the cyanate resin (B) include an average value of cyanate groups per molecule of all the cyanate resins present in 1 mole of the cyanate resin.

  Specific examples of the cyanate resin (B) include 2,2-bis (4-cyanatophenyl) propane (bisphenol A type cyanate resin) and bis (3,5-dimethyl-4-cyanatophenyl). ) Aromatic cyanate ester compounds such as methane, 2,2-bis (4-cyanatophenyl) ethane, and derivatives thereof. These may be used alone or in combination of two or more.

  The content ratio of the reaction product (A) to the cyanate resin (B) is such that the epoxy group of the reaction product (A) is 0.5 to 1 per cyanate group of the cyanate resin (B). The content ratio is preferably as follows. That is, the number of the epoxy groups of the reaction product (A) to one cyanate group of the cyanate resin (B) (equivalent ratio: epoxy group of the reaction product (A) / cyanate of the cyanate resin (B) It is preferable that the content ratio is 0.5 to 1. When there is too little said cyanate resin, there exists a tendency for the heat resistance of hardened | cured material to become inadequate. Moreover, when there is too much said cyanate resin, there exists a tendency for the influence of cyanate resin to become large and to be able to maintain the outstanding dielectric characteristic which polyphenylene ether has. That is, when the content of the cyanate resin is within the above range, the heat resistance of the cured product is sufficiently high, and the excellent dielectric properties of polyphenylene ether can be exhibited.

The curing accelerator (C) is not particularly limited as long as it can accelerate the curing reaction (crosslinking reaction) between the reaction product (A) and the cyanate resin (B). Can do. Specifically, for example, imidazole compounds such as 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, Organic phosphine compounds such as phenylphosphine, tributylphosphine, trimethylphosphine, etc., tertiary amine compounds such as 1,8-diaza-bicyclo (5,4,0) undecene-7 (DBU), triethanolamine, benzyldimethylamine, etc. , PF ₆ ^- cationic polymerization catalyst such as aromatic sulfonium salt having a fatty acid metal salt, and the like. The fatty acid metal salt is generally called a metal soap. Specifically, for example, fatty acids such as stearic acid, lauric acid, ricinoleic acid, and octylic acid, lithium, magnesium, calcium, Examples include fatty acid metal salts composed of metals such as barium and zinc. More specifically, zinc octylate etc. are mentioned. The said hardening accelerator (C) may be used independently, or may be used in combination of 2 or more type.

  Among the above, the curing accelerator (C) preferably contains an imidazole compound and a cationic polymerization catalyst from the viewpoint of obtaining a resin composition that is superior in dielectric properties and heat resistance of the cured product. Moreover, when using an imidazole compound, or when using an imidazole compound as a catalyst at the time of pre-react, it is more preferable to contain a fatty acid metal salt in addition to the imidazole compound. This is because the cationic polymerization catalyst, the imidazole compound and the fatty acid metal salt are not only a curing reaction between the reaction product (A) and the cyanate resin (B) but also a curing reaction between the cyanate resins (B). Since the curing reaction between the epoxy resins contained in the reaction product (A) can also be accelerated, even when the cyanate resin (B) or the epoxy resin is contained excessively, It is thought that it can contribute to the improvement of the heat resistance of hardened | cured material by the hardening reaction of cyanate resin (B), or the hardening reaction of the said epoxy resins.

  Moreover, in order to improve a flame retardance, you may make the said resin composition contain a flame retardant. The flame retardant is preferably a phosphorus-containing compound such as a phosphinate flame retardant and a polyphosphate flame retardant having a triazine skeleton in order to eliminate halogen. Since the resin composition has a sufficiently high heat resistance of the cured product, sufficient heat resistance can be ensured even when a phosphorus-containing compound that exhibits sufficient flame retardancy is contained.

  The phosphinate flame retardant is not particularly limited. Specific examples include phosphinic acid metal salts such as aluminum dialkylphosphinic acid salts. As said phosphinate flame retardant, the said phosphinate flame retardant may be used independently and may be used in combination of 2 or more type.

  The polyphosphate flame retardant is not particularly limited. Specific examples include polyphosphate having a triazine skeleton. Since this polyphosphate flame retardant is a polymer, it is considered that not only the flame retardancy can be improved, but also hydrolysis resistance, heat resistance and the like can be improved. Moreover, it is thought that the said polyphosphate flame retardant can exhibit the carbonization promotion effect notably with respect to the said polyphenylene ether resin rather than the said epoxy resin. And it is thought that the carbonization layer formed by exhibiting the carbonization promotion effect can suppress the spread of combustible gas and heat, and can fully raise a flame retardance. Therefore, it is considered that the flame retardancy of the cured product of the obtained resin composition can be sufficiently enhanced by using the polyphosphate together with a predetermined amount or more of the polyphenylene ether resin.

  Specific examples of the polyphosphate flame retardant include melamine polyphosphate, melam polyphosphate, melem polyphosphate, and complex salts thereof. Among these, melamine polyphosphate is preferably used. Examples of the complex salt include those described in JP-A-10-306081.

  The pH of the polyphosphate flame retardant is preferably 4-7. If the pH of the polyphosphate flame retardant is too low, the curing reaction between the reaction product (A) and the cyanate resin (B) tends to be inhibited, and the heat resistance of the cured product tends to decrease. Moreover, when the pH of the polyphosphate flame retardant is too high, the material tends to be unstable or a by-product tends to be mixed in a large amount. The pH of the polyphosphate can be measured with a general pH meter.

  The polyphosphate flame retardant is specifically preferably, for example, having an average particle size of 10 μm or less, more preferably 5 μm or less.

  As described above, the polyphosphate flame retardant can be used without particular limitation as long as it is a polyphosphate having a triazine skeleton, and specifically, for example, JP-A-10-306081 What was prepared by the method of description, etc. can be used. Examples of the method for adjusting the pH of the polyphosphate flame retardant include a method for adjusting the mixing ratio of polyphosphoric acid and melamine, melam, melem, etc. in the method for producing polyphosphate. .

  Moreover, it is preferable that content of the said phosphorus containing compound is a quantity that content of a phosphorus atom will be 3.5 mass% or more with respect to the said resin composition. When there is too little content of the said phosphorus containing compound, there exists a tendency which cannot fully raise the flame retardance of hardened | cured material. The phosphorus-containing compound content is preferably such that the phosphorus atom content is 5% by mass or less with respect to the resin composition, and is 4.5% by mass or less. Such an amount is more preferable. If the content of the phosphorus-containing compound is too large, the heat resistance and dielectric properties of the cured product tend to decrease, and the flame retardancy of the cured product cannot be sufficiently obtained due to the decrease in heat resistance. Tend. In addition, content of the said phosphorus atom is a ratio (mass%) with respect to the said resin composition, and can be computed from content of the phosphorus atom of the said phosphinate flame retardant and the said polyphosphate flame retardant to be used.

  As content of the said hardening accelerator (C), it is 0.05-1 mass part with respect to 100 mass parts of total amounts of the said reaction product (A) and the said cyanate resin (B), for example. Is preferred. When there is too little content of the said hardening accelerator (C), it exists in the tendency which cannot improve a hardening acceleration effect. Moreover, when there is too much content of the said hardening accelerator (C), there exists a tendency which produces a malfunction in a moldability, and there exists a tendency which is too disadvantageous economically because there is too much content of a hardening accelerator. Moreover, there exists a tendency for the life property of a resin composition to fall.

  Moreover, you may mix | blend an inorganic filler with the said resin composition further as needed for the purpose of improving the dimensional stability at the time of a heating, or improving a flame retardance. Specific examples of the inorganic filler include silica, alumina, talc, aluminum hydroxide, magnesium hydroxide, titanium oxide, mica, aluminum borate, barium sulfate, and calcium carbonate. In addition, the inorganic filler may be used as it is, but it is particularly preferable that the surface is treated with an epoxy silane type or amino silane type silane coupling agent. A metal-clad laminate obtained by using a polyphenylene ether resin composition containing an inorganic filler surface-treated with a silane coupling agent as described above has high heat resistance during moisture absorption and also has an interlayer peel strength. Tend to be higher.

  The resin composition may be blended with additives such as a heat stabilizer, an antistatic agent, an ultraviolet absorber, a dye, a pigment, a lubricant and the like, as necessary, as long as the effects of the present invention are not impaired. .

  When the prepreg is produced, the resin composition is often prepared and used in the form of a varnish for the purpose of impregnating a base material (fibrous base material) for forming the prepreg. That is, the resin composition is usually often prepared in a varnish form. Such a varnish is prepared as follows, for example.

  First, the reaction product (A), the cyanate resin (B), and other curing agents, if necessary, are added to an organic solvent and dissolved. At this time, heating may be performed as necessary. Further, the curing accelerator (C) and, if necessary, a flame retardant and an inorganic filler are added and dispersed using a ball mill, a bead mill, a planetary mixer, a roll mill or the like until a predetermined dispersion state is obtained. By doing so, a varnish-like resin composition is prepared. The organic solvent is not particularly limited as long as it dissolves the reaction product (A) and the cyanate resin (B) and does not inhibit the curing reaction. Specifically, toluene, cyclohexanone, propylene glycol monomethyl ether acetate, etc. are mentioned, for example.

  Examples of a method for producing a prepreg using the obtained varnish-like resin composition include a method in which a fibrous base material is impregnated with the resin composition and then dried.

  Specific examples of the fibrous base material include glass cloth, aramid cloth, polyester cloth, glass nonwoven fabric, aramid nonwoven fabric, polyester nonwoven fabric, pulp paper, and linter paper. When a glass cloth is used, a laminate having excellent mechanical strength can be obtained, and a flat glass processed glass cloth is particularly preferable. Specifically, the flattening processing can be performed, for example, by continuously pressing a glass cloth with a press roll at an appropriate pressure and compressing the yarn flatly. In addition, as a thickness of the said fibrous base material, the thing of 0.04-0.3 mm can generally be used, for example.

  The impregnation is performed by dipping or coating. The impregnation can be repeated a plurality of times as necessary. At this time, it is also possible to repeat the impregnation using a plurality of solutions having different compositions and concentrations, and finally adjust to a desired composition and resin amount.

  The fibrous base material impregnated with the resin composition is heated at a desired heating condition, for example, 80 to 170 ° C. for 1 to 10 minutes to obtain a semi-cured (B stage) prepreg.

  As a method for producing a metal-clad laminate using the prepreg thus obtained, one or a plurality of the prepregs are stacked, and a metal foil such as a copper foil is stacked on both upper and lower surfaces or one surface thereof. By heating and pressing to laminate and integrate, a double-sided metal foil-clad laminate or a single-sided metal foil-clad laminate can be produced. The heating and pressing conditions can be appropriately set depending on the thickness of the laminate to be produced, the type of the resin composition of the prepreg, etc. For example, the temperature is 170 to 220 ° C., the pressure is 3 to 4 MPa, and the time is 60 to 150. Can be minutes.

  The resin composition is excellent in heat resistance and flame retardancy of a cured product while maintaining the excellent dielectric properties of polyphenylene ether. For this reason, the metal-clad laminated board using the prepreg obtained using the said resin composition is excellent in a dielectric property, heat resistance, and a flame retardance. Moreover, since the polyphenylene ether contained in the resin composition has a low molecular weight, the resin composition has a low viscosity and a high fluidity. Therefore, the obtained prepreg is excellent in reliability capable of suppressing the occurrence of molding defects when manufacturing a metal-clad laminate or a printed wiring board using the metal-clad laminate.

  Moreover, a printed wiring board can be manufactured using a prepreg. Specifically, for example, by forming a circuit by etching the metal foil on the surface of the produced laminate, a printed wiring board having a conductor pattern as a circuit on the surface of the laminate can be obtained. Is. The printed wiring board thus obtained has excellent dielectric properties and has high heat resistance and flame retardancy.

  The present invention will be described more specifically with reference to the following examples. However, the scope of the present invention is not limited to these examples.

[Preparation of reaction product]
In this example, each component used in preparing the reaction product will be described.

(Polyphenylene ether)
PPE1: polyphenylene ether (polyphenylene ether synthesized by the method described in International Publication No. 2008/0667669, number average molecular weight Mn 1800, Mw / Mn = 2.5, functional group equivalent 1000)
PPE2: Polyphenylene ether obtained by reducing the molecular weight of a high molecular weight polyphenylene ether by a known molecular weight reduction method (molecular rearrangement method) (number average molecular weight Mn1800, Mw / Mn = 4.0, functional group equivalent 1000)
(Epoxy resin)
Epoxy resin 1: bisphenol F-type epoxy resin (Epiclon 830S manufactured by DIC Corporation, number average molecular weight Mn400, functional group equivalent 170, average number of epoxy groups 2)
Epoxy resin 2: bisphenol A type epoxy resin (Epiclon 850S manufactured by DIC Corporation, number average molecular weight Mn420, functional group equivalent 190, average number of epoxy groups 2)
Epoxy resin 3: bisphenol A type epoxy resin (Epiclon 1050 manufactured by DIC Corporation, number average molecular weight Mn1050, functional group equivalent 500, average number of epoxy groups 2)
Epoxy resin 4: biphenyl type epoxy resin (Nippon Kayaku Co., Ltd. NC3000H, number average molecular weight Mn980, functional group equivalent 258, average number of epoxy groups 3.4)
Epoxy resin 5: Naphthalene type epoxy resin (Epiclon HP-5000 manufactured by DIC Corporation, number average molecular weight Mn700, functional group equivalent 250, average number of epoxy groups 2.8)
Epoxy resin 6: Cresol novolak-type epoxy resin (EOCN103S manufactured by Nippon Kayaku Co., Ltd., number average molecular weight Mn1200, functional group equivalent 210, average number of epoxy groups 6)
(Catalyst during pre-react)
2E4MZ: 2-ethyl-4-imidazole (manufactured by Shikoku Kasei Kogyo Co., Ltd.)
DBU: 1,8-diazabicyclo [5.4.0] undecene-7 (manufactured by Nacalai Tesque)
TPP: Triphenylphosphine (made by Hokuko Chemical Co., Ltd.)
[Preparation method]
After adding each component to toluene so that it may become the mixture ratio of Table 1, it was made to stir at 100 degreeC for 6 hours. By doing so, the reaction product was prepared by reacting (prereacting) the low molecular weight polyphenylene ether and the epoxy resin in advance.

[Result of pre-react (reaction amount)]
When the total number of hydroxyl groups of the low molecular weight polyphenylene ether before reacting with the epoxy resin is 1, the reaction amount due to prereact was measured. That is, the number of hydroxyl groups decreased by reacting with the epoxy group of the epoxy resin when the total number of hydroxyl groups of the low molecular weight polyphenylene ether before the reaction with the epoxy resin was set to 1. Specifically, a solution of a low molecular weight polyphenylene ether before reacting with an epoxy resin and a solution of low molecular weight polyphenylene ether after reacting with an epoxy resin were converted into an ultraviolet absorptiometer (UVmini-1240 manufactured by Shimadzu Corporation). ) At a measurement wavelength of 318 nm. The ratio of the absorbance of the low molecular weight polyphenylene ether solution after the reaction with the epoxy resin when the absorbance of the low molecular weight polyphenylene ether solution before the reaction with the epoxy resin was taken as 1 was measured.

[Preparation of resin composition]
In this example, each component used when preparing the resin composition will be described.

(Cyanate resin)
Cyanate resin: Badcy made by Lonza Japan Co., Ltd., number average molecular weight Mn280, functional group equivalent 139, average number of cyanate groups 2)
(Curing accelerator)
Fatty acid metal salt: zinc octoate (manufactured by DIC Corporation)
(Other ingredients)
Phosphinate flame retardant: Aluminum dialkylphosphinate (OP935 manufactured by Clariant Japan KK)
Cyclic phosphazene compound: SPB-100 manufactured by Otsuka Chemical Co., Ltd.
Silica particles: Silica particles (SC2500-SEJ manufactured by Admatechs Co., Ltd.)
[Preparation method]
By heating the obtained reaction product solution to 80 ° C. so that the blending ratio shown in Table 1 is reached, and adding the cyanate resin and the curing accelerator thereto, stirring for 30 minutes, It was completely dissolved. Further, other components such as phosphinate flame retardant, cyclic phosphazene compound and silica particles were added and dispersed by a ball mill to obtain a varnish-like resin composition (resin varnish).

  Next, the obtained resin varnish was impregnated into a glass cloth (# 2116 type, WEA116E, E glass manufactured by Nitto Boseki Co., Ltd.) and then heated and dried at 150 ° C. for about 3 to 8 minutes to obtain a prepreg. . In that case, it adjusted so that content (resin content) of resin components, such as a polyphenylene ether, an epoxy resin, and a hardening | curing agent, may be 40-45 mass%.

  And 4 sheets of each obtained prepreg were laminated | stacked and laminated | stacked, and the evaluation board | substrate of thickness 0.4mm was obtained by heat-pressing on the conditions of temperature 200 degreeC, 2 hours, and pressure 3MPa.

  In addition, when not performing a pre-react, the raw material of a pre-react was prepared similarly to the said preparation method except having mix | blended simultaneously so that it might become a mixture ratio of Table 1, and the evaluation board | substrate was obtained.

  Each prepreg and evaluation substrate prepared as described above were evaluated by the following method.

[Glass transition temperature (Tg)]
The Tg of the prepreg was measured using a viscoelastic spectrometer “DMS100” manufactured by Seiko Instruments Inc. At this time, dynamic viscoelasticity measurement (DMA) was performed with a bending module at a frequency of 10 Hz, and the temperature at which tan α was maximized when the temperature was increased from room temperature to 280 ° C. at a temperature increase rate of 5 ° C./min was Tg. did.

[Dielectric properties (dielectric constant and dielectric loss tangent)]
The dielectric constant and dielectric loss tangent of the evaluation board | substrate in 1 GHz were measured by the method based on IPC-TM650-2.5.5.9. Specifically, the dielectric constant and dielectric loss tangent of the evaluation board | substrate in 1 GHz were measured using the impedance analyzer (RF impedance analyzer HP4291B by Agilent Technologies).

[Heat-resistant]
The heat resistance was measured by a method based on JIS C 6481. Specifically, the evaluation board is subjected to a pressure cooker test (PCT) of 121 ° C., 2 atm (0.2 MPa), and 1 hour for each sample, and the number of samples is 5 for 20 seconds in a solder bath at a predetermined temperature. It was immersed and visually observed for the occurrence of abnormalities such as measling and swelling. The maximum temperature at which no abnormality was confirmed was measured.

[Flame retardance]
A test piece having a length of 125 mm and a width of 12.5 mm was cut out from the evaluation substrate. Then, this test piece was evaluated according to "Test for Flammability of Plastic Materials-UL 94" of Underwriters Laboratories.

[Varnish Life]
First, the gel time at 180 ° C. (time until reaching a predetermined torque) of the obtained resin varnish was measured using an automatic curing time measuring device manufactured by Cyber Inc. The measured gel time is taken as the initial gel time.

  And the obtained resin varnish was stored at room temperature, and the gel time was measured by said method for every predetermined time. The number of days that the gel time was shortened by 20% with respect to the initial gel time was evaluated as the varnish life.

[Copper foil adhesion strength (copper foil peel strength)]
First, copper foils (1 oz, 3EC-III manufactured by Mitsui Mining & Smelting Co., Ltd., thickness 35 μm) are arranged on both outer layers of the evaluation substrate, respectively, and heated and pressed under the conditions of a temperature of 220 ° C. and a pressure of 3 MPa to obtain a thickness of 0. A 4 mm copper clad laminate was obtained. The peel strength (copper foil adhesion strength) of the copper foil on the surface of the obtained copper-clad laminate was measured according to JIS C 6481. At this time, a pattern having a width of 10 mm and a length of 100 mm is formed on a test piece having a width of 20 mm and a length of 100 mm, and the copper foil is peeled off at a speed of 50 mm / min by a tensile tester. cm) was measured as copper foil adhesion strength.

[Chloroform resistance (chloroform extraction degree)]
The evaluation substrate was frozen with liquid nitrogen and then finely pulverized with a mill. The pulverized product was immersed in chloroform so as to be about 8 g and 10% by mass. And it extracted with refluxing chloroform for 3 hours (hot chloroform extraction). The extract obtained by this extraction was dried at room temperature (room temperature) for 24 hours to obtain a solid content (eluting component) contained in the extract. The eluted component was weighed using an electronic balance. And the mass ratio (elution component / pulverized product) of the eluted component to the pulverized product immersed in chloroform was calculated as chloroform resistance (chloroform extraction degree) (mass%).

[Flowability of prepreg (resin flowability)]
The flowability (resin flowability) of each prepreg was measured by a method according to JIS C 6521.

  These results are shown in Table 2.

  As can be seen from Tables 1 and 2, the low molecular weight polyphenylene comprising a low molecular weight polyphenylene ether having a number average molecular weight of 500 to 3000 and a ratio of the weight average molecular weight to the number average molecular weight of 1 to 3, and an epoxy resin, A reaction product (A) obtained by reacting part or all of the hydroxyl groups of ether with the epoxy group of the epoxy resin in advance and a cyanate resin (B) having an average of two or more cyanate groups in one molecule ) And a curing accelerator (C), the epoxy resin having a number average molecular weight of 600 or less and having an average of 1.5 to 2.4 epoxy groups in one molecule, When a resin composition that is a second epoxy resin having an average number of molecular weight of 1000 or less and having an average of 2.5 to 4.4 epoxy groups in one molecule is used (Example 1). 9), as compared with Comparative Examples 1 to 4 that do not satisfy either while maintaining excellent dielectric characteristics possessed by PPE, high flowability of the prepreg was excellent in heat resistance of the cured product.

Claims (13)

A low molecular weight polyphenylene ether having a number average molecular weight of 500 to 3000 and a ratio of the weight average molecular weight to the number average molecular weight of 1 to 3, and an epoxy resin, wherein at least part of the hydroxyl groups of the low molecular weight polyphenylene ether A reaction product (A) obtained by pre-reaction with an epoxy group of an epoxy resin;
A cyanate resin (B) having an average of 2 or more cyanate groups in one molecule;
A curing accelerator (C),
The epoxy resin has a number average molecular weight of 600 or less, a first epoxy resin having an average of 1.5 to 2.4 epoxy groups in one molecule, and a number average molecular weight of 1000 or less in average. A resin composition, which is a second epoxy resin having 2.5 to 4.4 epoxy groups.   The resin composition according to claim 1, wherein the epoxy resin is one of a bisphenol A type epoxy resin and a bisphenol F type epoxy resin.   The reaction product (A) is a product in which half or more of the total hydroxyl groups of the low molecular weight polyphenylene ether before the epoxy resin is reacted with the epoxy groups of the epoxy resin. 2. The resin composition according to 2.   The resin composition according to any one of claims 1 to 3, comprising a phosphorus-containing compound. The resin composition according to any one of claims 1 to 4, wherein the low molecular weight polyphenylene ether is a compound represented by the following general formula (1).

(In Formula (1), m shows 0-20, n shows 0-20, and the sum total of m and n shows 1-30.)   The resin composition according to any one of claims 1 to 5, wherein the epoxy resin has 1 to 4 epoxy groups per hydroxyl group of the low molecular weight polyphenylene ether.   The resin composition according to any one of claims 1 to 6, wherein the epoxy group of the reaction product (A) is 0.5 to 1 per cyanate group of the cyanate resin. By heating a mixture of a low molecular weight polyphenylene ether having a number average molecular weight of 500 to 3000 and a ratio of the weight average molecular weight to the number average molecular weight of 1 to 3, and an epoxy resin, at least the hydroxyl groups of the low molecular weight polyphenylene ether Reacting a portion with an epoxy group of the epoxy resin;
The reaction product obtained by the reaction comprises a step of blending a cyanate resin having an average of two or more cyanate groups in one molecule and a curing accelerator,
The epoxy resin has a number average molecular weight of 600 or less, a first epoxy resin having an average of 1.5 to 2.4 epoxy groups in one molecule, and a number average molecular weight of 1000 or less in average. The manufacturing method of the resin composition characterized by using the 2nd epoxy resin which has 2.5-4.4 epoxy groups.   A resin varnish containing the resin composition according to any one of claims 1 to 7 and a solvent.   The resin varnish according to claim 9, wherein the solvent is at least one selected from the group consisting of toluene, cyclohexanone, and propylene glycol monomethyl ether acetate.   A prepreg obtained by impregnating a fibrous base material with the resin varnish according to claim 9 or 10.   A metal-clad laminate obtained by laminating a metal foil on the prepreg according to claim 11 and heating and pressing.   A printed wiring board produced using the prepreg according to claim 11.