JP7821873B2 - Curable resin composition, cured product, and printed wiring board - Google Patents

Description

The present invention relates to a curable resin composition, particularly a curable resin composition that is suitable for use in filling holes in printed wiring boards and smoothing gaps between circuits. Furthermore, the present invention relates to a cured product of the curable resin composition and a printed wiring board comprising the cured product, particularly a printed wiring board smoothed by the cured product.

As electronic devices have become smaller and more functional in recent years, there is an increasing need for finer printed wiring board patterns, smaller mounting areas, and higher-density component mounting. This has led to the use of multilayer printed wiring boards, such as double-sided boards with through-holes, or through-holes, that electrically connect different wiring layers to each other, and build-up wiring boards, in which insulating layers and conductor circuits are sequentially formed on a core substrate and interconnected by via holes or other means. In such printed wiring boards, gaps (recesses) between conductor circuits on the surface and holes such as through holes and via holes with wiring layers formed on their inner walls are typically filled and smoothed with a curable resin filler (see, for example, Patent Documents 1 to 3). The curable resin filler typically comprises a thermosetting resin composition containing an epoxy resin as a curable resin component, an epoxy resin curing agent, and an inorganic filler (see, for example, Patent Document 4).

In the manufacture of electronic devices, halogen-containing compounds, including resin materials, are widely used. Because these halogen-containing compounds generate harmful gases when burned, various efforts, including legal restrictions, have been made to prevent the generation of harmful gases.

Epoxy resins, which are used as the main component of thermosetting resin compositions, generally contain a large amount of chlorine because the raw material typically used in their synthesis, epichlorohydrin, contains a large amount of chlorine. In the manufacture of electronic devices, epoxy resins are almost always used in a chlorine-containing state. Therefore, when thermosetting resin fillers containing such epoxy resins are burned, harmful gases containing large amounts of chlorine are released, placing a significant burden on the environment. To address this issue, attempts have been made to reduce the chlorine content by cleaning (purifying) the epoxy resin or by using epoxy resins synthesized without epichlorohydrin. However, these approaches require significant time and financial costs, making them impractical.

In addition, brominated epoxy resins are sometimes used as thermosetting resin fillers. Furthermore, the colorants, particularly pigments, used in thermosetting resin fillers may contain bromine. When such brominated epoxy resins or thermosetting resin fillers containing bromine-containing colorants are burned, harmful gases containing bromine are released, posing a significant environmental burden, similar to the thermosetting resin fillers containing chlorine-containing epoxy resins mentioned above.

Japanese Patent Application Laid-Open No. 2001-15909 Japanese Patent Application Laid-Open No. 2007-49106 Japanese Patent Application Laid-Open No. 2004-75967 JP 2013-76002 A

Accordingly, an object of the present invention is to provide a curable resin composition that reduces the amount of halogen-containing substances released during combustion. Another object of the present invention is to provide a cured product obtained by curing the curable resin composition, and a printed wiring board comprising the cured product.

The inventors have discovered that the amount of halogen-containing substances released during combustion can be reduced by using a specific component as a filler in a curable resin composition containing an epoxy resin, an epoxy resin curing agent, and a filler. The present invention is based on this discovery. The gist of the present invention is as follows:

[1] an epoxy resin,
A curable resin composition comprising an epoxy resin curing agent and a filler,
the filler comprises at least one selected from the group consisting of magnesium carbonate, magnesium oxide, hydrotalcite, and aluminum hydroxide;
A curable resin composition characterized in that the amount of halogen measured by a quartz tube combustion method is 100 to 1000 ppm.
[2] The curable resin composition according to [1], wherein the total content of the filler is 50 to 300 parts by mass per 100 parts by mass of the epoxy resin.
[3] The curable resin composition according to [1] or [2], wherein the total content of the magnesium carbonate, magnesium oxide, hydrotalcite, and aluminum hydroxide is 10 to 250 parts by mass per 100 parts by mass of the epoxy resin.
[4] The curable resin composition according to any one of [1] to [3], wherein the total content of the magnesium carbonate, magnesium oxide, hydrotalcite, and aluminum hydroxide is 4 to 100 mass% relative to the total content of the filler.
[5] The curable resin composition according to any one of [1] to [4], wherein the epoxy resin contains an epoxy resin having a tertiary amine.
[6] The curable resin composition according to any one of [1] to [5], wherein the content of the epoxy resin is 10 to 60 parts by mass per 100 parts by mass of the curable resin composition.
[7] The curable resin composition according to any one of [1] to [6], having a viscosity of 200 to 1000 dPa·s when rotated at a rotation speed of 5 rpm at 25°C for 30 seconds.
[8] The curable resin composition according to any one of [1] to [7], which is used for plugging holes in a printed wiring board or filling gaps between circuits in a printed wiring board.
[9] A cured product of the curable resin composition according to any one of [1] to [8].
[10] A printed wiring board comprising the cured product according to [9].

The present invention makes it possible to realize a curable resin composition that reduces the amount of halogen-containing substances released during combustion. Furthermore, by using the curable resin composition, it is possible to realize a cured product that reduces the amount of halogen-containing substances released during combustion, and a printed wiring board that includes the cured product.

[Curable resin composition]
The curable resin composition of the present invention contains an epoxy resin, an epoxy resin curing agent, and a filler as essential components. The curable resin composition of the present invention can be used to form a solder resist layer on a printed wiring board, as an interlayer insulating material, and as a hole-filling material, and is particularly suitable for use as a hole-filling material for filling holes such as through-holes and via holes on a printed wiring board, and gaps (recesses) between circuits, and as a filler for filling gaps between circuits on a printed wiring board. The curable resin composition of the present invention can suppress the release of halogen-containing substances during combustion by using a specific component as a filler.

Traditionally, epoxy resins have mainly been synthesized using epichlorohydrin, which contains chlorine atoms, so the synthesized epoxy resin contains a large amount of chlorine derived from the epichlorohydrin. Therefore, when such epoxy resins are used in the production of curable resin compositions, unless the epoxy resin is subjected to treatment such as washing (purification), a large amount of chlorine will inevitably be contained in the curable resin composition.

In addition, in the production of curable resin compositions, brominated epoxy resins or components containing bromine may be used as epoxy resins. In particular, colorants such as pigments often contain bromine. When such brominated epoxy resins or components containing bromine are used in the production of curable resin compositions, bromine will be included in the curable resin composition.

Therefore, when a cured product of such a halogen-containing curable resin composition is burned, compounds containing these halogens, i.e., halogen-containing substances, are released as components of the gas generated by combustion of the cured product. Many halogen-containing substances are harmful, including elemental halogens such as chlorine and bromine, hydrogen halides such as hydrogen chloride, and organic halogen compounds such as dioxins and brominated dioxins (brominated dioxins). Many of these halogen-containing substances are designated as harmful substances or pollutants under various environmental standards. Therefore, when curable resin compositions produced using the halogen-containing components described above are burned, the release of large amounts of halogen-containing substances is an inseparable problem.

While it is unclear why the use of a specific filler in a curable resin composition produced using a halogen-containing component reduces the amount of halogen-containing substances released during combustion of the cured product, the reason for this is believed to be as follows: The specific filler used in the present invention is believed to retain liberable anions within the filler. Therefore, it is believed that the halogen in the halogen-containing component contained in the curable resin composition is liberated to form halide ions, and that these halide ions are exchanged or substituted with the anions retained in the filler, thereby forming a chemical or physical bond between the halogen and the filler (e.g., the metal species constituting the filler). This retains the halide ions in the filler, which is believed to result in reduced amounts of halogen-containing substances released during combustion of the cured product of the curable resin composition.

The curable resin composition of the present invention has a halogen content of 100 to 1,000 ppm, preferably 100 to 700 ppm, and more preferably 100 to 650 ppm, as measured by the quartz tube combustion method. In this specification, "halogen" refers to chlorine and bromine. Furthermore, in this specification, the terms "amount" and "content" refer to the total amount of chlorine and bromine, respectively. For example, "amount of halogen of 100 to 1,000 ppm" means that the total amount of chlorine and bromine is in the range of 100 to 1,000 ppm. While there are currently no regulations regarding "halogen-free," standards established by the Japan Electronics Packaging and Circuits Association (JPCA) and the International Electrotechnical Commission (IEC) stipulate that copper-clad laminates used in electrical and electronic devices can be labeled "halogen-free" if their chlorine and bromine contents are 900 ppm or less each and their total content is 1,500 ppm or less. The curable resin composition of the present invention has a total halogen (chlorine and bromine) content of 1,000 ppm or less as measured by the quartz tube combustion method. Therefore, when the chlorine and bromine contents are both 900 ppm or less, the composition can be used to produce "halogen-free" cured products and printed wiring boards. Therefore, the curable resin composition of the present invention preferably has a chlorine and bromine content of 900 ppm or less. On the other hand, the lower the halogen content in the curable resin composition, the higher the reactivity of the curable resin composition. Therefore, if the halogen content in the curable resin composition is too low, the viscosity of the curable resin composition tends to be excessively high, causing problems during use. Therefore, when the halogen content in the curable resin composition of the present invention is 100 ppm or more as measured by the quartz tube combustion method, such problems can be avoided.

The amount of halogen (amount of chlorine and bromine) in a cured product of a curable resin composition using the quartz tube combustion method can be measured in accordance with standard IEC 62321-3-2 established by the International Electrotechnical Commission (IEC). Specifically, the measurement can be performed according to the following procedure. First, 0.1 g of the curable resin composition to be measured is combusted using an automatic sample combustion device AQF-2100H manufactured by Nitto Seiko Analytech Co., Ltd., and the gas components are collected. Next, the collected gas components are absorbed in an absorption liquid (hydrogen peroxide solution), and the chlorine and bromine in the obtained absorption liquid are quantified by ion chromatography using an ion chromatography system Thermo Scientific Dionex ICS-1100, Thermo Scientific Dionex AERS 500 suppressor, and Dionex IonPac AS12A column manufactured by Thermo Fisher Scientific.

Each component of the curable resin composition of the present invention will be described in detail below.
(epoxy resin)
The curable resin composition of the present invention contains an epoxy resin. Any known epoxy resin can be used as the epoxy resin. The epoxy resin may be monofunctional or polyfunctional.

Epoxy resins include epoxidized vegetable oils; bisphenol A epoxy resins; hydroquinone epoxy resins; bisphenol epoxy resins; thioether epoxy resins; brominated epoxy resins; novolac epoxy resins; phenol novolac epoxy resins; biphenol novolac epoxy resins; bisphenol F epoxy resins; hydrogenated bisphenol A epoxy resins; glycidylamine epoxy resins; hydantoin epoxy resins; alicyclic epoxy resins; trihydroxyphenylmethane epoxy resins; bixylenol or biphenol epoxy resins, or mixtures thereof. Examples of epoxy resins that can be used include, but are not limited to, epoxy resins such as epoxy resins of bisphenol S type, bisphenol A novolac type, tetraphenylolethane type, heterocyclic epoxy resins, diglycidyl phthalate resins, tetraglycidyl xylenoylethane resins, naphthalene group-containing epoxy resins, epoxy resins having a dicyclopentadiene skeleton, glycidyl methacrylate copolymer epoxy resins, cyclohexylmaleimide and glycidyl methacrylate copolymer epoxy resins, epoxy-modified polybutadiene rubber derivatives, CTBN-modified epoxy resins, and brominated epoxy resins. These epoxy resins may be used alone or in combination of two or more.

Epoxy resins preferably include epoxy resins containing tertiary amines and epoxy resins containing bisphenol skeletons. In this specification, "epoxy resins containing tertiary amines" refers to epoxy resins containing two or more epoxy groups and one or more tertiary amine groups per molecule. These epoxy resins may be aliphatic or aromatic. Aromatic epoxy resins are preferred from the viewpoints of heat resistance, electrical insulation, water absorption, and other properties. Furthermore, these epoxy resins are liquid. In this context, "liquid" refers to a liquid state that is fluid at 20°C. When using the above-mentioned epoxy resins, particularly epoxy resins containing tertiary amines, the crosslink density increases when the curable resin composition is cured, resulting in sufficient curing and the production of a cured product with good heat resistance (high glass transition temperature Tg) and a low coefficient of linear expansion (CTE). On the other hand, epoxy resins having tertiary amines generally have a high chlorine content because many raw materials containing chlorine are used in the synthesis process to impart functional groups to the molecules, which poses a problem in terms of an increase in the amount of chlorine-containing substances released during combustion. In the present invention, the use of a specific component as a filler can solve this problem while providing the above-mentioned advantages, and therefore epoxy resins having tertiary amines are preferably used.

Examples of epoxy resins containing tertiary amines include N,N,N',N'-tetraglycidylaminodiphenylmethane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, triglycidyl-p-aminophenol, N,N-diglycidylaniline, and N,N-diglycidyl-o-toluidine. Commercially available epoxy resins containing tertiary amines include jER (registered trademark) 630 (para-aminophenol type epoxy resin) and jER (registered trademark) 604 (diaminodiphenylmethane type epoxy resin) manufactured by Mitsubishi Chemical Corporation, ELM-100 (para-aminophenol type epoxy resin) manufactured by Sumitomo Chemical Co., Ltd., GAN (diglycidyl aniline) manufactured by Nippon Kayaku Co., Ltd., GOT (diglycidyl orthotoluidine) manufactured by Nippon Kayaku Co., Ltd., Sumiepoxy (registered trademark) ELM-434 manufactured by Sumitomo Chemical Co., Ltd., and TETRAD (registered trademark)-X manufactured by Mitsubishi Gas Chemical Company, Inc.

Examples of epoxy resins having a bisphenol skeleton include bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol E (AD) epoxy resins, and bisphenol S epoxy resins. From the viewpoints of the electrical insulation properties of the cured product of the curable resin composition and adhesion to conductive and insulating parts, bisphenol A epoxy resins, bisphenol F epoxy resins, and bisphenol E (AD) epoxy resins are preferably used. From the viewpoint of the filling properties of the curable resin composition, epoxy resins having a bisphenol skeleton are preferably liquid. Note that the term "liquid" in relation to epoxy resins having a bisphenol skeleton refers to the same as that described in the explanation of epoxy resins having tertiary amines. Commercially available epoxy resins having a bisphenol skeleton include, for example, jER (registered trademark) 828, jER (registered trademark) 834, and jER (registered trademark) 1001 (all bisphenol A-type epoxy resins), jER (registered trademark) 807, and jER (registered trademark) 4004P (all bisphenol F-type epoxy resins) manufactured by Mitsubishi Chemical Corporation, and R710 (bisphenol E-type epoxy resin) manufactured by Air Water Inc. One type of epoxy resin having a bisphenol skeleton may be used alone, or two or more types may be used in combination, but it is particularly preferable to use a combination of a bisphenol A-type epoxy resin and a bisphenol F-type epoxy resin.

The content of epoxy resin in the curable resin composition is not particularly limited as long as the effects of the present invention are achieved, but it can be preferably 10 to 60 parts by mass, and more preferably 25 to 50 parts by mass, in solids content terms, per 100 parts by mass of the curable resin composition.

(epoxy resin curing agent)
The curable resin composition of the present invention contains an epoxy resin curing agent for curing the above-mentioned epoxy resin. As the epoxy resin curing agent, a known curing agent generally used for curing epoxy resins can be used. Examples of the epoxy resin curing agent include amines, imidazoles, polyfunctional phenols, acid anhydrides, isocyanates, and polymers containing these functional groups. The epoxy resin curing agent may be used alone or in combination of two or more.

Among the epoxy resin curing agents mentioned above, amines and imidazoles are particularly preferred from the viewpoints of adhesion to conductive and insulating parts, storage stability, heat resistance, etc. Examples of amines include adduct compounds of aliphatic polyamines such as alkylenediamines having 2 to 6 carbon atoms, polyalkylenepolyamines having 2 to 6 carbon atoms, and aromatic ring-containing aliphatic polyamines having 8 to 15 carbon atoms; adduct compounds of alicyclic polyamines such as isophoronediamine and 1,3-bis(aminomethyl)cyclohexane; and mixtures of the above aliphatic polyamine adduct compounds and the above alicyclic polyamine adduct compounds. In particular, curing agents whose main component is an adduct compound of xylylenediamine or isophoronediamine are preferred.

Preferred adduct compounds of the above aliphatic polyamines are those obtained by subjecting the aliphatic polyamines to an addition reaction with an aryl glycidyl ether (particularly phenyl glycidyl ether or tolyl glycidyl ether) or an alkyl glycidyl ether. Furthermore, preferred adduct compounds of the above alicyclic polyamines are those obtained by subjecting the alicyclic polyamines to an addition reaction with n-butyl glycidyl ether, bisphenol A diglycidyl ether, or the like.

Examples of aliphatic polyamines include alkylenediamines having 2 to 6 carbon atoms, such as ethylenediamine and propylenediamine; polyalkylenepolyamines having 2 to 6 carbon atoms, such as diethylenetriamine and triethylenetriamine; and aromatic ring-containing aliphatic polyamines having 8 to 15 carbon atoms, such as xylylenediamine. Commercially available examples of modified aliphatic polyamines include FXE-1000, FXR-1020, Fujicure FXR-1030, Fujicure FXR-1080, and FXR-1090M2 manufactured by T&K TOKA Corporation; and Ancamine 2089K, Sanmaid P-117, Sanmaid X-4150, Ancamine 2422, Surwet R, Sanmaid TX-3000, and Sanmaid A-100 manufactured by Evonik Japan Co., Ltd.

Examples of alicyclic polyamines include isophoronediamine, 1,3-bis(aminomethyl)cyclohexane, bis(4-aminocyclohexyl)methane, norbornenediamine, 1,2-diaminocyclohexane, and laromine. Commercially available modified alicyclic polyamines include, for example, Ancamine 1618, Ancamine 2074, Ancamine 2596, Ancamine 2199, Sanmaid IM-544, Sanmaid I-544, Ancamine 2075, Ancamine 2280, Ancamine 1934, and Ancamine 2228, all manufactured by Evonik Japan Co., Ltd.; Daitoclar F-5197 and Daitoclar B-1616, all manufactured by Daito Sangyo Co., Ltd.; Fujicure FXD-821 and Fujicure 4233, all manufactured by T&K TOKA Corporation; jER (registered trademark) Cure 113, all manufactured by Mitsubishi Chemical Corporation; and Laromine C-260, all manufactured by BASF Japan Ltd.

Examples of imidazole compounds include 2-methylimidazole, 4-methyl-2-ethylimidazole, 2-phenylimidazole, 4-methyl-2-phenylimidazole, 1-benzyl-2-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, and 1-cyanoethyl-2-undecylimidazole. Commercially available imidazole compounds include imidazoles such as 2E4MZ, C11Z, C17Z, and 2PZ, imidazole azine compounds such as 2MZ-A and 2E4MZ-A, imidazole isocyanurates such as 2MZ-OK and 2PZ-OK, and imidazole hydroxymethyl compounds such as 2PHZ and 2P4MHZ, all manufactured by Shikoku Chemical Industry Co., Ltd. Commercially available imidazole latent curing agents include Cureduct P-0505, manufactured by Shikoku Chemical Industry Co., Ltd.

The content of the epoxy resin curing agent in the curable resin composition is not particularly limited as long as the effects of the present invention are achieved, but it can be preferably 1 to 30 parts by mass, more preferably 4 to 20 parts by mass, per 100 parts by mass of the above-mentioned epoxy resin.

Furthermore, when imidazoles are used in combination with at least one of polyamines and imidazole-type latent curing agents, the content ratio of imidazoles to polyamines and imidazole-type latent curing agents is preferably 1:99 to 99:1 by mass, and more preferably 10:90 to 90:10.

(filler)
The curable resin composition of the present invention contains a filler. The filler contains at least one selected from the group consisting of magnesium carbonate, magnesium oxide, hydrotalcite, and aluminum hydroxide. In the present invention, the term "hydrotalcite" is a concept that also encompasses so-called hydrotalcite-like compounds.

Hydrotalcite is a type of clay mineral that can be obtained naturally or artificially. It is a generic name for a layered inorganic compound represented by the following general formula: It has a base layer mainly composed of positively charged [Mg _1−X Al _X (OH) ₂ ] ^{X +} and an intermediate layer mainly composed of negatively charged [(CO ₃ ) _X/2 ·mH ₂ O] X−.
[In the formula,
^M1 represents a divalent metal cation such as Mg ²⁺ , Fe ²⁺ , Zn ²⁺ , Ca ²⁺ , Li ²⁺ , Ni ²⁺ , Co ²⁺ , or Cu ²⁺ ;
^M2 represents a trivalent metal cation such as Al3 ⁺ , Fe3 ⁺ , or Mn3 ⁺ ;
A ^n- represents an n-valent anion such as CO ₃ ^2- , Cl ^- , or NO ^3- ;
X represents any number satisfying 0<X≦0.33;
m represents an arbitrary number satisfying 0≦m.

Specific examples of hydrotalcites include Indigirite Mg ₂ Al ₂ [(CO ₃ ) ₄ (OH) ₂ ]·15H ₂ O, Fe ²⁺ ₄ Al ₂ [(OH) ₁₂ CO ₃ ]·3H ₂ O, Quintinite Mg ₄ Al ₂ (OH) ₁₂ CO ₃ ·H ₂ O, Manasseite Mg ₆ Al ₂ [(OH) ₁₆ CO ₃ ]·4H ₂ O, SjOegrenite Mg ₆ Fe ³⁺ ₂ [(OH) ₁₆ CO ₃ ]·4H ₂ O, Zaccagnaite Zn ₄ Al ₂ (CO ₃ ) (OH) ₁₂ ·3H ₂ O, and Desautelsite. Mg ₆ Mn ³⁺ ₂ [(OH) ₁₆ CO ₃ ]・4H ₂ O, Hydrotalcite Mg ₆ Al ₂ [(OH) ₁₆ CO ₃ ]・4H ₂ O, Pyroaurite Mg ₆ Fe ³⁺ ₂ [(OH) ₁₆ CO ₃ ]・4H ₂ O, Reevesite Ni ₆ Fe ³⁺ ₂ [(OH) ₁₆ CO ₃ ]・4H ₂ O, Stichtite Mg ₆ Cr ₂ [(OH) ₁₆ CO ₃ ]・4H ₂ O, Takovite Ni ₆ Examples include Al ₂ [(OH) ₁₆ CO ₃ ]·4H ₂ O and the like. Commercially available hydrotalcites include, for example, Alkamiser (registered trademark), DHT-4A (registered trademark), Kyoward (registered trademark) 500, and Kyoward (registered trademark) 1000 manufactured by Kyowa Chemical Industry Co., Ltd., and STABIACE (registered trademark) series HT-1, HT-7, and HT-P manufactured by Sakai Chemical Industry Co., Ltd. As the hydrotalcite, one containing magnesium and aluminum as the main components, that is, the above-mentioned hydrotalcite in which M ¹ is Mg ²⁺ and M ² is Al ³⁺ , is preferably used.

Commercially available magnesium carbonate products include, for example, GP-30 manufactured by Konoshima Chemical Co., Ltd. Commercially available magnesium oxide products include, for example, the SMO series manufactured by Sakai Chemical Industry Co., Ltd. and RF-50-FC manufactured by Ube Material Industries, Ltd. Commercially available aluminum hydroxide products include, for example, C-305 manufactured by Hayashi Kasei Co., Ltd., C-310 manufactured by Sumitomo Chemical Co., Ltd., and BF-013 manufactured by Nippon Light Metal Co., Ltd. Fillers including hydrotalcite are not limited to the commercially available products listed above; other commercially available products may also be used, or appropriately adjusted products may be used.

In addition to the above-mentioned magnesium carbonate, magnesium oxide, hydrotalcite, and aluminum hydroxide, the filler may also include other known fillers, particularly inorganic fillers, used in conventional resin compositions. Examples of such inorganic fillers include non-metallic fillers such as silica, barium sulfate, calcium carbonate, silicon nitride, aluminum nitride, boron nitride, alumina, magnesium hydroxide, titanium oxide, mica, talc, and organic bentonite, with silica and calcium carbonate being preferred. The other fillers may be used alone or in combination of two or more.

The shape of the filler is not particularly limited, and examples include spherical, needle-like, plate-like, scaly, hollow, irregular, hexagonal, cubic, and flaky shapes, but spherical shapes are preferred from the perspective of increasing the filler content.

Taking into consideration the dispersibility of the filler, its ability to fill holes, and the smoothness when forming a wiring layer in the filled holes, the average particle size of the filler is preferably 0.1 μm to 25 μm, more preferably 0.1 μm to 15 μm, and even more preferably 1 μm to 10 μm. The "average particle size" of the filler refers to the average primary particle size, and the average particle size (D50) can be measured using a laser diffraction/scattering method.

The filler content in the curable resin composition is not particularly limited as long as the effects of the present invention are achieved. However, the total content of magnesium carbonate, magnesium oxide, hydrotalcite, and aluminum hydroxide per 100 parts by mass of epoxy resin is not particularly limited as long as the effects of the present invention are achieved. However, it is preferably adjusted to 10 to 250 parts by mass, more preferably 10 to 150 parts by mass, and even more preferably 20 to 100 parts by mass per 100 parts by mass of epoxy resin. By adjusting the total amount of magnesium carbonate, magnesium oxide, hydrotalcite, and aluminum hydroxide relative to the epoxy resin within the above-mentioned range, it is possible to sufficiently suppress the amount of halogen-containing substances released upon combustion of a cured product of the curable resin composition, while at the same time adjusting the viscosity of the curable resin composition to a range suitable for use (e.g., application to a substrate, etc.). Furthermore, when the filler contains the other fillers described above, the filler content in the curable resin composition is adjusted so that the total amount of magnesium carbonate, magnesium oxide, hydrotalcite, and aluminum hydroxide is within the above-mentioned range, and the total amount of all fillers is preferably 50 to 300 parts by mass, more preferably 100 to 250 parts by mass, per 100 parts by mass of epoxy resin. By adjusting the filler content relative to the epoxy resin within the above-mentioned range, a composition with good printability suitable for filling holes in printed wiring boards and gaps between circuits can be obtained, and the cured product can also achieve the good solder heat resistance required. In this specification, the term "filler content" refers to the total content of the magnesium carbonate, magnesium oxide, hydrotalcite, and aluminum hydroxide described above, plus the other fillers.

In the curable resin composition, the total content of magnesium carbonate, magnesium oxide, hydrotalcite, and aluminum hydroxide is not particularly limited as long as the effects of the present invention are achieved, but is preferably 4 to 100% by mass, more preferably 10 to 100% by mass, and even more preferably 20 to 100% by mass relative to the total content of filler. By adjusting the ratio of the total content of magnesium carbonate, magnesium oxide, hydrotalcite, and aluminum hydroxide relative to the total content of filler within the above-mentioned range, the amount of halogen-containing substances released during combustion of the curable resin composition can be suppressed and maintained within the above-mentioned range.

(solvent)
The curable resin composition of the present invention preferably does not contain a solvent. Generally, most solvents (dilution solvents) used to adjust the viscosity of a curable resin composition volatilize during curing of the curable resin composition. However, the volatilized solvent can cause voids to form in the cured product of the curable resin composition. For example, when the curable resin composition of the present invention is used as a filler, the presence of voids in the cured product of the curable resin composition may impair the properties required of the filler. In order to avoid impairing the properties of the cured product of the curable resin composition, the curable resin composition preferably does not contain a solvent.

(Other ingredients)
The curable resin composition of the present invention may further contain, as necessary, components such as colorants, elastomers, mercapto compounds, urethanization catalysts, thixotropic agents, adhesion promoters, block copolymers, chain transfer agents, polymerization inhibitors, copper inhibitors, antioxidants, rust inhibitors, thickeners such as organic bentonite and montmorillonite, at least one of silicone-based, fluorine-based, and polymer-based antifoaming agents and leveling agents, imidazole-based, thiazole-based, and triazole-based silane coupling agents, and flame retardants such as phosphinates, phosphate ester derivatives, and phosphorus compounds such as phosphazene compounds. These may be known in the field of electronic materials.

The viscosity of the curable resin composition is not particularly limited as long as the effects of the present invention are achieved. However, the viscosity measured using a rotational viscometer, i.e., the viscosity when rotated at 5 rpm for 30 seconds at 25°C, is preferably 200 to 1,000 dPa·s, and more preferably 200 to 800 dPa·s. Having the viscosity of the curable resin composition within the above range allows for good shape retention (suppression of dripping) and embeddability of the curable resin composition. The viscosity of the curable resin composition can be measured using a cone-plate viscometer (e.g., TV-30 model, manufactured by Toki Sangyo Co., Ltd., rotor 3° x R9.7) consisting of a cone rotor and plate as described in JIS Z 8803.

The curable resin composition of the present invention can be used to fill, for example, through-holes and gaps between circuits (recesses with bottoms) in multilayer printed wiring boards using known patterning methods such as screen printing and vacuum printing. Preferably, the curable resin composition of the present invention is filled so that the through-holes and gaps between circuits are flat (having a uniform height). By filling the curable resin composition in this manner, a cured product with a smooth surface can be formed on the printed wiring board after curing. The curable resin composition is preferably filled completely, with a small amount of excess beyond the holes and recesses. The multilayer printed wiring board with the holes and recesses filled with the curable resin composition is heated, for example, at 80 to 160°C for approximately 30 to 180 minutes, to cure the curable resin composition and form a cured product. To prevent bubbles from forming during printing, two-stage curing may be used. That is, the curable resin composition may be pre-cured at a lower temperature, followed by full curing (finish curing). The pre-curing conditions are preferably heating at 80 to 110°C for about 30 to 90 minutes. Because the hardness of the pre-cured product is relatively low, unnecessary portions protruding from the substrate surface can be easily removed by physical polishing, resulting in a smooth surface. The product is then heated for full curing. The pre-curing conditions are preferably heating at 130 to 160°C for about 30 to 180 minutes. The hardness of the pre-cured product can be controlled by changing the heating time and temperature for pre-curing.

After curing the curable resin composition as described above, if necessary, unnecessary portions of the cured product of the printed wiring board are removed and smoothed using a known physical polishing method, and the surface wiring layer is then patterned into the desired pattern to form the desired circuit pattern. If necessary, the surface of the cured product may be roughened using an aqueous potassium permanganate solution or the like, and then a wiring layer may be formed on the cured product using electroless plating or the like.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" are all by mass unless otherwise specified.

[Preparation of Curable Resin Composition]
The components shown in Table 1 below were mixed in the amounts shown in the table, pre-mixed using a mixer, and then kneaded using a three-roll mill to prepare the curable resin compositions of Examples 1 to 11 and Comparative Examples 1 to 4. Details of each component in Table 1 are as follows. In Table 1, all values without units represent parts by mass.
Epoxy resin 1 (epoxy resin having a tertiary amine): p-aminophenol-type liquid epoxy resin (jER (registered trademark) 630, manufactured by Mitsubishi Chemical Corporation)
Epoxy resin 2 (epoxy resin having a tertiary amine): N,N,N',N'-tetraglycidyl-m-xylylenediamine Epoxy resin 3 (epoxy resin having a tertiary amine): p-aminophenol-type liquid epoxy resin (jER (registered trademark) 604, manufactured by Mitsubishi Chemical Corporation)
Epoxy resin 4 (epoxy resin having a bisphenol skeleton): bisphenol A type epoxy resin (jER (registered trademark) 828, manufactured by Mitsubishi Chemical Corporation)
Epoxy resin 5 (epoxy resin having a bisphenol skeleton): bisphenol F type epoxy resin (jER (registered trademark) 806H, manufactured by Mitsubishi Chemical Corporation)
Epoxy resin curing agent: 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine (Curesol 2MZA-PW, manufactured by Shikoku Chemicals Corporation)
Filler 1: calcium carbonate Filler 2: silica Filler 3: synthetic hydrotalcite Filler 4: aluminum hydroxide Filler 5: magnesium oxide Filler 6: magnesium carbonate Antifoaming agent: silicone resin (KS-66, manufactured by Shin-Etsu Chemical Co., Ltd.)

[Measurement of halogen content by quartz tube combustion method]
The amounts of chlorine and bromine released when each of the curable resin compositions of the Examples and Comparative Examples was burned were measured according to the following procedure.
First, 0.1 g of each curable resin composition was combusted using an automatic sample combustion apparatus AQF-2100H manufactured by Nitto Seiko Analytech Co., Ltd., and the gas components were collected. Next, the collected gas components were absorbed in an absorption liquid (hydrogen peroxide solution), and the chlorine and bromine contents of the resulting absorption liquid were quantified by ion chromatography using an ion chromatograph system Thermo Scientific Dionex ICS-1100 manufactured by Thermo Fisher Scientific, a Thermo Scientific Dionex AERS 500 suppressor, and a Dionex IonPac AS12A column. The halogen content of each curable resin composition in the examples and comparative examples was evaluated according to the following criteria. The measurement results and evaluation results of the halogen content (total amount of chlorine and bromine) are shown in Table 1.
⊚: The amount of halogen is 500 ppm or less, and the amount of halogen-containing substances released is extremely well suppressed.
Good: The amount of halogen is more than 500 ppm and not more than 1000 ppm, and the amount of halogen-containing substances released is well suppressed.
×: The amount of halogen exceeds 1000 ppm, and the amount of halogen-containing substances released is not sufficiently suppressed.

[Evaluation of Printing Properties]
The printability of each of the curable resin compositions of the Examples and Comparative Examples was evaluated according to the following procedure.
Each of the curable resin compositions of the Examples and Comparative Examples was filled into a 1 mm thick glass epoxy substrate, which had previously been formed with through holes of 500 μm diameter by panel plating, using a screen printing method under the following printing conditions: The glass epoxy substrate filled with each curable resin composition was placed in a hot air circulation drying oven and held horizontally at 180°C for 1 hour to cure each curable resin composition, thereby obtaining each evaluation substrate.
(Printing conditions)
Squeegee: Squeegee thickness 20 mm, hardness 70°, angled grinding: 23°
Plate: PET 100 mesh bias plate Printing pressure: 60 kgf/cm ²
Squeegee speed: 5 cm/sec Squeegee angle: 80°

For each evaluation substrate, the degree of filling of the cured product of the curable resin composition in the through-holes was visually observed, and the printability of each curable resin composition of the Examples and Comparative Examples was evaluated according to the following criteria. The evaluation results are shown in Table 1.
◎: Completely filled and hardened.
○: Not completely filled but sufficiently filled and hardened.
×: Difficult to fill.

[Evaluation of solder heat resistance]
The solder heat resistance of each of the curable resin compositions of the Examples and Comparative Examples was evaluated according to the following procedure.
First, the same evaluation substrates as those used in the polishing evaluation described above were prepared. The surface of each evaluation substrate, on which the curable resin composition was applied, was physically polished using a polishing machine with a single axis of a resin polishing buff equivalent to #320. Next, each evaluation substrate after physical polishing was immersed in a solder solution at 288°C for 10 seconds three times and then allowed to cool to room temperature. Next, each evaluation substrate was cut at the through-hole portion, and the cross section was observed with an optical microscope to count the number of cracks in 100 through-holes. Based on the number of cracks, the solder heat resistance of each curable resin composition of the Examples and Comparative Examples was evaluated according to the following criteria. The evaluation results are shown in Table 1.
◯: 0 cracks.
△: 1 to 5 cracks.
×: Six or more cracks.

The evaluation results shown in Table 1 reveal that the amount of halogen emitted by each of the curable resin compositions of the Examples, measured by the quartz tube combustion method, is low, at 1,000 ppm or less. The amount of halogen measured by the quartz tube combustion method is considered to be the amount of halogen derived from various halogen-containing substances released during combustion. Therefore, it can be said that the amount of halogen-containing substances released during combustion is suppressed in each of the curable resin compositions of the Examples. It can also be seen that each of the curable resin compositions of the Examples exhibits good printability and good solder heat resistance, making it suitable for use in filling holes in printed wiring boards and smoothing gaps between circuits. On the other hand, it can be seen that the amount of halogen emitted by each of the curable resin compositions of the Comparative Examples, at over 1,000 ppm, during combustion is high. Therefore, it can be said that the amount of halogen-containing substances released during combustion is not sufficiently suppressed in each of the curable resin compositions of the Comparative Examples.

Claims (8)

epoxy resin,
A curable resin composition comprising an epoxy resin curing agent and a filler,
the filler comprises hydrotalcite ;
the total content of the filler is 50 parts by mass or more and less than 250 parts by mass relative to 100 parts by mass of the epoxy resin,
The content of the hydrotalcite is 4 to 100 mass% based on the total content of the filler,
A curable resin composition characterized in that the amount of halogen measured by a quartz tube combustion method is 100 to 1000 ppm. The curable resin composition according to claim 1 , wherein the content of the hydrotalcite is 10 parts by mass or more and less than 250 parts by mass per 100 parts by mass of the epoxy resin. The curable resin composition according to claim 1 or 2, wherein the epoxy resin comprises an epoxy resin having a tertiary amine. The curable resin composition according to claim 1 or 2, wherein the content of the epoxy resin is 10 to 60 parts by mass per 100 parts by mass of the curable resin composition. The curable resin composition according to claim 1 or 2, which has a viscosity of 200 to 1,000 dPa·s when rotated at 25°C at a rotation speed of 5 rpm for 30 seconds. The curable resin composition according to claim 1 or 2, which is used to plug holes in printed wiring boards or fill gaps between circuits on printed wiring boards. A cured product of the curable resin composition according to claim 1 or 2. A printed wiring board comprising the cured product according to claim 7 .