JP4093216B2 - Prepreg and method for producing prepreg - Google Patents

Description

  The present invention relates to a prepreg used when manufacturing a printed wiring board such as a multilayer printed wiring board, and a laminated board for electrical and electronic parts formed using the prepreg.

  Laminated boards used in the manufacture of printed wiring boards are desired to have a constant dielectric constant and dielectric loss tangent, and preferably a low dielectric loss tangent, in a wide high frequency range, wide temperature range and wide humidity range. In such applications, laminates using an epoxy resin composition containing an epoxy resin and a polyphenylene ether resin (hereinafter sometimes referred to as PPE as appropriate) are used.

  Conventionally, as a laminated board using an epoxy resin composition containing this epoxy resin and PPE, a cured product of epoxy resin and PPE using an epoxy resin composition simply blended with an epoxy resin and PPE is chemically independent. In addition, a laminated board made of a cured product obtained by crosslinking PPE and an epoxy resin by reacting an epoxy group of an epoxy resin with a terminal hydroxyl group of PPE has been studied.

  Of these, the former laminate, when immersed in alkali or chloroform and performing an alkali resistance test or a solvent resistance test, has a problem that delamination occurs due to insufficient bonding between the epoxy resin and PPE, In the latter laminate, when the used PPE has a high molecular weight, the reactivity between the terminal phenolic hydroxyl group of PPE and the epoxy group of the epoxy resin is low, and unreacted PPE not involved in the crosslinked structure is present in the cured product. Due to the presence of a large amount, there is a problem that the interlayer adhesion strength is low, and when a solvent resistance test is performed, it is superior to the former laminate, but there is still a problem that delamination still occurs.

  Therefore, by modifying a high molecular weight PPE and a phenolic compound in the presence of a radical reaction initiator such as a peroxide, a modified number average molecular weight of 1,000 to 1,000 which is lower than the number average molecular weight of the PPE used. It has been studied to produce 3,000 modified phenolic compounds and to produce a laminate having excellent solvent resistance using an epoxy resin composition in which the modified phenolic compound and an epoxy resin are blended (for example, patents) Reference 1). In the case of the laminate of Patent Document 1, PPE is taken into the cross-linked structure in the cured product by the reaction between the phenolic hydroxyl group of the modified phenolic compound and the epoxy group of the epoxy resin, so that the solvent resistance is considered excellent. Yes.

  However, in recent years, due to the space saving of personal computers and the popularization of mobile phones and PDAs (personal digital assistants), semiconductor packages to be mounted are rapidly becoming smaller and thinner. At the same time, board materials for forming printed wiring boards used in the above equipment are also required to be lighter, and by switching from the mainstream ceramic package to the laminate package, weight reduction and workability are achieved. Improvements are being made.

In order to reduce the size of the laminated board, it can be stacked in the height direction to make a multilayer structure, and the circuit extending in the plane direction can be extended in the height direction. At this time, the through hole formed for connecting the front and back Also plays the role of establishing connections between each layer. For this reason, the number of through-holes has increased dramatically compared to the conventional case, and the hole density has increased, so that it is demanded that the through-holes have a small diameter. In order to form such a small-diameter through hole, good workability with a small-diameter drill of about 0.05 to 0.3 mmφ has been required.
Patent No. 3339301

  However, when a small-diameter through-hole is produced in a laminated plate produced using a prepreg having a modified phenolic compound as a substrate material as in Patent Document 1 above, problems with drill breakage, drill life, and rough inner wall of the drilled through-hole It has been found that deterioration of surface (roughness) occurs.

  Further, when the hole density increases, the distance between the walls of adjacent through holes approaches. Therefore, it has been clarified that when the inside of the through hole is plated, copper migration (CAF) is likely to occur, and the reliability is further lowered due to the surface roughness of the inner wall.

  An object of the present invention is to provide a prepreg capable of forming fine through holes in a laminated board by drilling while suppressing occurrence of drill breakage, drill wear rate and deterioration of inner wall roughness of through holes. .

  Another object of the present invention is to provide a highly reliable laminate that can suppress the occurrence of CAF even when a small-diameter through hole with a short distance between walls is formed.

The present invention is produced by impregnating and drying a resin varnish containing a phenol-modified polyphenylene ether compound having a number average molecular weight of 1,000 to 3,000, (B) an epoxy resin, and (C) a curing agent. In the method for producing a prepreg, a step of preparing a resin mixed solution by adding the (B) epoxy resin to a solution of the phenol-modified polyphenylene ether compound (A), and an aggregate precipitated in the resin mixed solution, It comprises a resin varnish preparation step having a dispersion treatment step and a step of adding the curing agent (C) after the dispersion treatment step .

This onset Ming as described above, the modified phenolic compound having a low molecular weight, epoxy resin, and the resin composition comprising a curing agent, since the maximum particle size using the following modified phenol compounds 15 [mu] m, thereby homogenizing the resin composition Therefore, by forming a laminate using the prepreg of the present invention, even when a small-diameter drill is used, the occurrence of drill breakage, the deterioration of the drill wear rate, and the deterioration of the inner wall roughness of the hole can be suppressed. It is possible to form smooth fine holes on the inner wall surface by drilling.

The present onset Ming, when using the glass cloth subjected to flattening treatment process is one which can prevent deterioration of the wall roughness of the drill wear rates and holes.

This onset Ming, so formed by laminating the above prepreg and a metal foil, a reliable laminate which suppresses the occurrence of CAF by suppressing the deterioration of occurrence or a drill wear rates and hole wall roughness of the drill breakage A board can be obtained.

And according to the onset bright, by providing the re-dispersion treatment of the modified phenolic compound at a given manufacturing process, it is possible to miniaturization of aggregates to produce a homogeneous prepreg achieved.

  The present invention will be specifically described below.

  The resin composition used in the present invention contains a low molecular weight modified phenolic compound (A) having a number average molecular weight of 1,000 to 3,000 as a constituent component.

  The above modified phenol compound further redisperses a modified phenol compound obtained by redistributing a polyphenylene ether resin having a number average molecular weight of 10,000 to 30,000 and a phenolic compound in the presence of a radical reaction initiator. Can be obtained.

  PPE used for the production of the modified phenolic compound is also called polyphenylene oxide resin, and an example thereof is poly (2,6-dimethyl-1,4-phenylene oxide).

  When the number average molecular weight of the modified phenolic compound used in the present invention is less than 1,000, the heat resistance of the laminate is lowered. As a result, the melt viscosity increases, and as a result, the peel strength of the metal foil of the laminate, the solder heat resistance, and the plating penetration performance are impaired.

  Examples of a method for producing such a modified phenol compound include a method described in US Pat. No. 4,059,568.

  Examples of the phenolic compound used for the production of the modified phenol compound include bisphenol A, bisphenol F, phenol novolak, cresol novolak, and the like. In addition, it is preferable to use phenols having two or more phenolic hydroxyl groups in the molecule. The upper limit of the number of phenolic hydroxyl groups of these phenols is not particularly limited, but those having 30 or less in the molecule are generally used. In addition, the quantity of a phenolic compound is 1-20 mass parts with respect to 100 mass parts of PPE.

  Examples of the radical reaction initiator used for the production of the modified phenol compound include benzoyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-di- -T-butylperoxyhexyne-3,2,5-dimethyl-2,5-di-t-butylperoxyhexane, α, α'-bis (t-butylperoxy-m-isopropyl) benzene, etc. Peroxides. Moreover, although it is not a peroxide, the brand name "Biscumyl" (one minute half temperature 330 degreeC) by Nippon Oil & Fats Co., Ltd. which is a commercially available radical reaction initiator can also be used. Use of benzoyl peroxide is preferable because of excellent reactivity. The amount of the radical reaction initiator used is 1 to 20 parts by mass with respect to 100 parts by mass of PPE.

  And when manufacturing a modified phenol compound, said PPE and a phenolic compound are redistributed in presence of a radical reaction initiator in an organic solvent, and a molecular weight lower than the number average molecular weight of used PPE. A modified phenolic compound is produced. As conditions for the redistribution reaction, for example, the PPE, the phenolic compound, and the radical reaction initiator are stirred and heated at 80 to 120 ° C. for about 10 to 100 minutes. Examples of the organic solvent to be used include aromatic hydrocarbon solvents such as toluene, benzene and xylene.

  When a PPE having a number average molecular weight of 10,000 to 30,000 is reacted with a phenolic compound in the presence of a radical reaction initiator, it is considered that PPE is first radicalized and a redistribution reaction in which a straight chain is cleaved. Advances to lower the molecular weight of PPE, and the phenolic compound is denatured by the reduced molecular weight PPE.

  And the structure of the obtained modified phenol compound is considered to be a structure in which a phenolic compound is bonded to one or both terminal portions of PPE having a reduced molecular weight, and one or both terminals have a phenolic hydroxyl group. For this reason, it is considered that this phenolic hydroxyl group at the terminal reacts with the epoxy group of the epoxy resin and is strongly crosslinked with the epoxy resin.

  In the prepreg of the present invention, the low molecular weight modified phenol compound (A) obtained as described above is mixed in a solvent together with (B) an epoxy resin and (C) a curing agent, and the base material is impregnated with the resin varnish. , Dried to produce.

  When mixing each of the above resin components, the epoxy resin of (B) is previously dissolved in a solvent and the modified phenolic compound of (A) is added thereto, or the modified phenolic compound of (A) and (B) There is also a method in which the epoxy resin is added to the solvent at the same time and mixed, but considering the solubility of the modified phenolic compound (A) and the epoxy resin (B), the solution of the modified phenolic compound (A) is prepared in advance. In addition, the method of adding the epoxy resin (B) is preferable. In addition, since it is convenient for production to synthesize the modified phenolic compound of (A) as described above and use the obtained solution as it is, the solution for preparing the modified phenolic compound of (A) is prepared. After that, it is preferable to add the epoxy resin (B). In addition, although it does not restrict | limit especially as temperature which mixes the said (A) modified phenolic compound and (B) epoxy resin, It is more preferable to carry out at 20-60 degreeC, respectively.

  According to the study of the present invention, when the step of adding the epoxy resin (B) to the solution of the low molecular weight modified phenolic compound (A) as described above is adopted, the solution becomes semi-turbid and the mixed solution has It has become clear that the above-described problems occur in a laminate made of a prepreg produced using a resin varnish prepared by adding a predetermined arbitrary component or a curing agent (C).

  The semi-turbidity at the time of mixing the above epoxy resin is dissolved in the solvent of the modified phenolic compound of (A) and is precipitated from the difference in solubility by adding the epoxy resin of (B). It has been found that the particle size is generated as an aggregate having a size of several tens of μm. Since the laminate produced using the solution containing the aggregated modified phenolic compound is present in the prepreg in a state where the aggregate is scattered, the processing characteristics of the drill differ from the other resin portions in the aggregated portion. Therefore, it was thought that problems such as drill wear would occur. In addition, in the case of a small-diameter through hole having a high hole density, there is a high probability of drilling a spot where scattered aggregates exist. Therefore, if the aggregate is present in the drilled part, the aggregates fall off at that part. It was thought that the inner wall roughness deteriorated due to this.

  In the present invention, in order to reduce aggregation of the modified phenolic compound, the (A) epoxy resin is added to the modified phenolic compound solution prepared by mixing the modified phenolic compound with a solvent, and then the (C) Before the curing agent is mixed, the (A) modified phenol compound is redispersed to a maximum particle size of 15 μm or less, whereby the agglomerates are refined to produce a homogeneous prepreg. And since the laminated board laminated | stacked using the prepreg does not contain the aggregate of a large particle size, it can improve the drill life at the time of drilling using a small diameter drill, and is smooth also as a small diameter through hole. Since it can be used as an inner wall surface, a highly reliable laminated plate capable of reducing CAF and the like is obtained.

  The maximum particle size of the modified phenol compound is not particularly limited as long as it is 15 μm or less, but the aggregate is finer as the maximum particle size is smaller, more preferably 12 μm or less, and most preferably 8 μm or less. is there. The maximum particle size is measured with a laser diffraction particle size distribution measuring device.

  The redispersion treatment after the addition of the epoxy resin (B) and before the blending of the curing agent (C) is not particularly limited as long as the maximum particle size of the aggregate of the modified phenolic compound can be 15 μm or less. In consideration of the properties, it is preferable to provide a mechanical shearing process using a mill, a disper, a mixer or the like. In the redispersion step, the shear rate is preferably 100 [1 / second] or more and 1,000 [1 / second] or less, and is 500 [1 / second] or more and 1,000 [1 / second] or less. It is more preferable. By setting the shear rate to 100 [1 / second] or more, it is possible to efficiently refine the aggregate to have a maximum particle size of 15 μm or less, and by setting the shear rate to 1,000 [1 / second] or less, The significant cooling load of a typical shearing device can be suppressed. In addition, the shearing time should just be sufficient time to make a maximum particle size into 15 micrometers or less, and is 120-240 minutes normally.

  In addition, even if the redispersion treatment is performed, it is reaggregated if it is left as it is. Therefore, it is preferable to impregnate the base material within 120 minutes after the redispersion treatment as long as such reaggregation does not occur.

  The epoxy resin blended in the resin composition of the present invention may be an epoxy resin having two or more epoxy groups in the molecule, such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, Hydantoin type epoxy resins, alicyclic epoxy resins, biphenyl type epoxy resins, epoxy resins obtained by halogenating these resins, triphenylmethane type epoxy resins, tetraphenyl glycidyl ether ethane (tetrafunctional epoxy resins), various novolacs Type epoxy resin, modified epoxy resin modified with halogen, and the like, and two or more types may be used in combination. An epoxy resin having one epoxy group in the molecule can be used in combination. The ratio of the epoxy resin and the modified phenol compound is such that the modified phenol compound is 20 to 100 parts by mass, preferably 30 to 60 parts by mass with respect to 100 parts by mass of the epoxy resin.

  Examples of epoxy resin curing agents blended in the resin composition include amide curing agents such as dicyandiamide and aliphatic polyamide, and amine curing agents such as diaminodiphenylmethane, metaphenylenediamine, ammonia, triethylamine, and diethylamine, Examples thereof include phenolic curing agents such as bisphenol A, bisphenol F, phenol novolac resin, cresol novolac resin, p-xylene-novolac resin, and acid anhydrides, and two or more kinds may be used in combination.

  The ratio of the epoxy resin and the curing agent is usually 0.1 to 5 parts by mass, preferably 1 to 2 parts by mass with respect to 100 parts by mass of the epoxy resin. In addition, as temperature at the time of mixing a hardening | curing agent, 30-50 degreeC is preferable.

  In order to accelerate the curing reaction, it is also preferable to add a curing accelerator if necessary to the resin composition of the present invention. Examples of the curing accelerator include imidazoles such as 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1,8-diaza-bicyclo [5.4.0] undecene-7, Examples include tertiary amines such as ethylenediamine and benzyldimethylamine, organic phosphines such as tributylphosphine and triphenylphosphine, and tetraphenylboron salts such as tetraphenylphosphonium tetraphenylborate and triphenylphosphinetetraphenylborate. You may use the above together.

  The ratio of the epoxy resin and the curing agent accelerator is usually 0.1 to 5 parts by mass, preferably 0.3 to 1 part by mass of the epoxy resin curing agent accelerator with respect to 100 parts by mass of the epoxy resin. good.

  Moreover, an inorganic filler etc. can also be mix | blended with the resin composition of this invention as needed. Examples of the inorganic filler include silica powder, glass fiber, talc and the like, and two or more kinds may be used in combination. The particle size of the inorganic filler is preferably in the range of 0.2 to 3.0 μm. By making the particle size of the inorganic filler to be added 3.0 μm or less, the drill wear rate and breakage can be improved as compared with the case of adding a large particle size, and the particle size is set to 0.2 μm or more. As a result, good flowability of the resin composition can be obtained, and blurring during molding can be reduced. The blending amount is preferably 240 parts by mass or less with respect to 100 parts by mass of the resin component (the total of the resin, the curing agent, and the curing accelerator). By setting the blending amount of the inorganic filler within the above range, scum and voids can be reduced during the formation of the laminate. The inorganic filler is preferably added after the epoxy resin and before the curing agent.

  Examples of the solvent used for producing the resin varnish of the present invention include organic solvents such as aromatic hydrocarbons such as toluene, xylene, and benzene, ketones, and alcohols. These organic solvents can be used alone or in combination of two or more.

  As solid content concentration in the said resin varnish of this invention, it is preferable to set it as 40-70 mass%, and it is more preferable to set it as 50-60 mass%.

  The prepreg of the present invention is redispersed as described above, and a resin varnish is prepared by blending an optional component such as a curing agent (C) and, if desired, an effect accelerator, etc., and using this as a base material. It can be produced by impregnating and then heating and semi-curing the resin composition in the substrate to a B-stage state by heating.

  The heating conditions for drying and semi-curing can be appropriately set depending on the composition of the resin composition, etc., and can be, for example, 150 to 170 ° C. for 4 to 7 minutes. Moreover, what is necessary is just to set the resin content rate of the prepreg of this invention suitably according to the thickness of a base material, and its intended purpose, For example, it can be 45-65 mass%.

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

  The electrical laminate (substrate material) of the present invention is formed using the above prepreg and metal foil such as copper foil. One or a plurality of prepregs can be used, and after a metal foil is stacked on one or both sides of this prepreg, the resin composition of the prepreg is cured by heating and pressing to form an insulating layer. In addition, a single-sided or double-sided metal foil-clad laminate can be formed by integrating the metal foil and the insulating layer by curing the resin composition. The heating and pressing conditions during the above-described lamination molding can be appropriately set depending on the thickness of the laminate to be produced, the type of the prepreg resin composition, and the like. The time can be 120-150 minutes.

  The laminated board thus obtained is a laminated board having excellent high-frequency characteristics such as dielectric characteristics, solder heat resistance, adhesive strength and the like because the characteristics of the epoxy resin and the modified phenol compound are not impaired.

  The use form of the resin composition of the present invention is not limited to the form in which the prepreg is produced by impregnating and drying the base material. For example, a sheet not containing the base material is prepared by casting, and this sheet is used as the prepreg. It can be substituted. This casting method is performed by, for example, applying a resin composition to a thickness of 5 to 700 μm on a sheet insoluble in a solvent contained in the resin composition, such as a polyester film or a polyimide film, and after drying, peeling the sheet. The resin composition is manufactured by heat melting or extrusion molding. In the case of the method of producing by applying to a sheet, the sheet can be easily produced at a relatively low temperature as compared with the extrusion molding method. In addition, since the sheet | seat which apply | coats a resin composition uses the sheet | seat surface-treated with the mold release agent, since peeling becomes easy, it is excellent in productivity and preferable.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1
A resin composition was prepared with the formulation shown in Table 1. The resin component is a resin, a curing agent, and a curing accelerator. Moreover, the modified phenolic compound and the epoxy resin were used as resin. The modified phenolic compound is composed of 30 parts by mass (hereinafter referred to as “parts”) of polymer polyphenylene ether (manufactured by GE Plastics, number average molecular weight: 15,000, product number 640-111) and 1.2 parts of bisphenol A (phenolic compound). ) In a toluene solvent at 60-70 ° C. and mixed, and then 1.5 parts of benzoyl peroxide (a radical initiator made by NOF Corporation) is blended to combine the polymer polyphenylene ether and bisphenol A. It adjusted by making it react, The solution of the modified phenolic compound whose number average molecular weight is 2,800 was obtained with the gel permeation chromatograph.

  48 parts brominated bisphenol A type epoxy resin (“EPPN501H” manufactured by Nippon Kayaku Co., Ltd.) and 18 parts phenol novolac type epoxy resin (“EPN1182” manufactured by Asahi Ciba) are used as the epoxy resin in the modified phenol compound solution. Added at 45 ° C.

  After the solution becomes semi-turbid due to the mixing of the epoxy resin, the temperature is maintained at 20 to 50 ° C. using a Henschel mixer until the maximum particle size of the aggregated modified phenol compound becomes 15 μm, and the shear rate is 500 [1 / second]. Redispersion was performed for 120 minutes.

  The maximum particle size was confirmed to be 15 μm using a laser diffraction particle size distribution analyzer (SALD-2100 manufactured by Shimadzu Corporation).

  Next, 1 part of diaminodiphenylmethane (“Ecure” manufactured by Yuka Shell) as a curing agent and 0.3 part of 2-ethyl-4-methyl-imidazole (manufactured by Shikoku Kasei) as a curing accelerator were added to the above solution and stirred. .

  Then, 100 parts of the above resin solution is dissolved in 90 parts of toluene to prepare a resin varnish, the resin varnish is impregnated into a glass cloth that has not been flattened, and then the glass cloth impregnated with the resin varnish. Was dried and the resin composition in the glass cloth was semi-cured by heating to form a prepreg having a resin content of 50%.

  Next, four prepregs are overlaid and a copper foil having a thickness of 18 μm is laminated on both outer sides of these prepregs, and this is heated and pressed under conditions of a temperature of 200 ° C., a pressure of 3.5 MPa, and a time of 120 minutes. Thus, a double-sided copper-clad laminate having a thickness of 0.4 mm was formed.

Example 2
In the production of the resin varnish of Example 1, using the composition shown in Table 1, using a glass cloth that has been flattened, the redispersion condition is 180 minutes at a shear rate of 1,000 [1 / second], A prepreg and a double-sided copper-clad laminate were formed in the same manner as in Example 1 except that the modified phenol compound redispersed to a maximum particle size of 8 μm was used.

Example 3
In the production of the resin varnish of Example 1, the prepreg and the prepreg were prepared in the same manner as in Example 1 except that the composition shown in Table 1 was used, and a resin composition containing an inorganic filler was added after the epoxy resin was added and before the curing agent was added. A double-sided copper-clad laminate was formed. As the inorganic filler, silica (Admartex synthetic silica having a substantially spherical particle shape and an average particle diameter of 0.5 μm) was used.

Comparative Example 1
In preparing the resin varnish of Example 1, a prepreg and a double-sided copper-clad laminate were formed in the same manner as in Example 1 except that the redispersion treatment was not performed. In the adjustment of the resin varnish of Comparative Example 1, the maximum particle size of the aggregate of the modified phenol compound when the epoxy resin was mixed was 20 μm.

Comparative Example 2
In preparing the resin varnish of Example 3, a prepreg and a double-sided copper-clad laminate were formed in the same manner as in Example 3 except that the redispersion treatment was not performed. In the adjustment of the resin varnish of Comparative Example 2, the maximum particle size of the aggregate of the modified phenol compound when the epoxy resin was mixed was 20 μm.

  About the double-sided copper clad laminated board of said Examples 1-3 and Comparative Examples 1-2, the following drill wear rates and the evaluation of the inner wall roughness of a drill hole were performed. The results are shown in Table 1.

[Drill wear rate]
With respect to the drill wear rate, 2000 holes were drilled with a drill bit having a diameter of 0.075 mm on the obtained double-sided copper-clad laminate, and the wear rate of the subsequent drill bit was measured.

[Inner wall roughness]
The inner wall roughness is determined by applying desmearing to the drilled double-sided copper-clad laminate, plating the hole inner wall, and observing the hole cross section with a microscope. It was measured.

As shown in Table 1, after (B) the epoxy resin is blended in the solution in which the low molecular weight modified phenolic compound of the present invention is dispersed, (C) the epoxy resin is added before mixing the curing agent. By redispersing the agglomerated modified phenolic resin to a maximum particle size of 15 μm or less, the drill wear rate can be reduced and the inner wall roughness can be improved even if through holes are made using a small diameter drill. I understand.

Claims (3)

Phenol-modified polyphenylene ether (A) a compound of a number average molecular weight of 1,000 to 3,000, (B) an epoxy resin, and, (C) impregnating the base material a resin varnish containing a curing agent, dried and manufactured in concrete In the manufacturing method of the prepreg to be performed ,
Adding the (B) epoxy resin to the solution of the phenol-modified polyphenylene ether compound (A) to prepare a resin mixed solution;
A step of dispersing the aggregate precipitated in the resin mixed solution;
(C) adding the curing agent after the dispersion treatment step.
A method for producing a prepreg comprising a resin varnish preparation step .   The method for producing a prepreg according to claim 1, wherein the base material is impregnated with the resin varnish within 120 minutes after the redispersion treatment. A prepreg obtained by the production method according to claim 1 or 2.