Method for forming cured coating film

Abstract

The object of the present invention is to provide a method for forming a cured coating film, which can prevent leakage of a photosensitive resin composition to the back side of a substrate through a through hole even if a substrate is provided with a through hole, and can make the thickness of the coating film uniform. The method for forming a cured coating film comprises: a step of applying a first photosensitive resin composition having a viscosity of 150 to 1500 mPa·s at 25°C to at least the through hole portion of the substrate by an inkjet method, thereby forming a filler in the through hole; a step of applying a second photosensitive resin composition on the first main surface of the substrate and on the surface of the filler on the first main surface side, thereby forming a coating film; a step of curing the coating film to form a cured coating film, wherein in the step of applying the first photosensitive resin composition, at least the peripheral portion of the through hole in the second main surface of the substrate, which is the surface opposite to the first main surface, is brought into a non-contact state.

Description

Technical Field

[0001] The present invention relates to a method for forming a cured coating film by coating a photosensitive resin composition on a substrate using an inkjet method. Background Art

[0002] Conventionally, when a coating (e.g., an insulating coating such as a solder resist) is formed on a substrate such as a printed wiring board having a desired circuit pattern, a photosensitive resin composition is applied by screen printing, pre-dried, and a negative film having a pattern other than the pads of the circuit pattern to be light-transmissive is bonded to the coating of the photosensitive resin composition, and active energy rays (ultraviolet rays) are irradiated therefrom, and non-exposed areas corresponding to the pads are removed with a dilute alkaline aqueous solution, the coating is developed, and post-cured (Patent Document 1).

[0003] However, sometimes a through hole is provided in the printed wiring board. In this case, if the screen printing method is used, the applied photosensitive resin composition leaks through the through hole to the back side of the printed wiring board, so the photosensitive resin composition applied at the peripheral edge of the through hole shrinks. Therefore, a thin portion of the coating film is generated at the peripheral edge of the through hole, and there is a problem that the thickness of the coating film cannot be fully uniformed.

[0004] In particular, when the surface (back side) of the substrate opposite to the surface coated with the photosensitive resin composition contacts the coating stage, the capillary force generated at the interface between the coating stage surface and the back side of the substrate may promote leakage of the photosensitive resin composition to the back side of the printed wiring board through the through hole.

[0005] Depending on the use conditions of the substrate, etc., it may be required to prevent such a problem.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2002-293882 Summary of the invention

[0009] Problems to be solved by the invention

[0010] In view of the above-mentioned actual situation, an object of the present invention is to provide a method for forming a cured coating film, which can prevent the photosensitive resin composition from leaking to the back side of the substrate through the through-hole even if the substrate is provided with a through-hole, and can make the thickness of the coating film uniform.

[0011] Means for solving problems

[0012] An embodiment of the present invention is a method for forming a cured coating film, which comprises: a step of applying a first photosensitive resin composition having a viscosity of 150 to 1500 mPa·s at 25° C. to at least a through-hole portion of a substrate by an inkjet method, thereby forming a filler in the through-hole; a step of applying a second photosensitive resin composition on a first main surface of the substrate and on a surface on the first main surface side of the filler, thereby forming a coating film; and a step of curing the coating film, thereby forming a cured coating film, wherein in the step of applying the first photosensitive resin composition, at least the peripheral portion of the through-hole in the second main surface of the substrate, which is the surface opposite to the first main surface, is brought into a non-contact state.

[0013] In the above embodiment, the through hole is filled with the first photosensitive resin composition applied by the inkjet method, and the second photosensitive resin composition is further applied on the filled first photosensitive resin composition by a desired coating method including the inkjet method, and at least the applied second photosensitive resin composition is cured. It should be noted that applying the second photosensitive resin composition on the first main surface of the substrate and the surface on the first main surface side of the filler includes the following cases: the case where the second photosensitive resin composition is directly applied on the first main surface of the substrate and the surface on the first main surface side of the filler; the case where a resin composition other than the second photosensitive resin composition (including the first photosensitive resin composition) is applied on the first main surface of the substrate and the surface on the first main surface side of the filler, and then the second photosensitive resin composition is applied thereon.

[0014] An embodiment of the present invention is a method for forming a cured coating film, wherein the first photosensitive resin composition includes a non-reactive diluent having a surface tension of 30 mN / m or less at 25° C.

[0015] An embodiment of the present invention is a method for forming a cured coating film, wherein the non-reactive diluent includes diethylene glycol diethyl ether.

[0016] An embodiment of the present invention is a method for forming a cured coating film, wherein the coating method of the second photosensitive resin composition is screen printing, inkjet, roller coating, rod coating, spray coating, curtain flow coating, squeegee, applicator, blade coating, knife coating or gravure coating.

[0017] An embodiment of the present invention is a method for forming a cured coating film, wherein the second photosensitive resin composition is applied to the surface of the filler on the first main surface side by a coating method other than an inkjet method.

[0018] An embodiment of the present invention is a method for forming a cured coating film, wherein the other coating method is screen printing, roller coating, rod coating, spraying, curtain coating, roll printing, applicator, blade coating, knife coating or gravure coating.

[0019] An embodiment of the present invention is a method for forming a cured coating film, wherein the viscosity of the first photosensitive resin composition at 25° C. is 180 to 1000 mPa·s.

[0020] An embodiment of the present invention is a method for forming a cured coating film, wherein the viscosity of the second photosensitive resin composition at 25° C. is 120 to 60,000 mPa·s.

[0021] An embodiment of the present invention is a method for forming a cured coating film, wherein the first photosensitive resin composition is the same photosensitive resin composition as the second photosensitive resin composition.

[0022] An embodiment of the present invention is a method for forming a cured coating film, wherein the curing treatment is an exposure treatment using active energy rays and / or a heat treatment.

[0023] An embodiment of the present invention is a method for forming a cured coating film, wherein the exposure amount of the exposure treatment using active energy rays is 30 to 500 mJ / cm 2 .

[0024] Effects of the Invention

[0025] According to an embodiment of the present invention, before applying the second photosensitive resin composition by a desired coating method, first, the first photosensitive resin composition having a viscosity of 150 to 1500 mPa·s at 25° C. is applied by an inkjet method to fill the through-holes of the substrate. During the filling, the peripheral edge of the through-holes on the second main surface (back side) is made non-contact, thereby preventing the generation of capillary force at the interface between the coating stage surface and the back side of the substrate. By preventing the generation of capillary force, the first photosensitive resin composition can be prevented from leaking to the back side of the substrate through the through-holes, so that the through-holes can be reliably filled with the first photosensitive resin composition.

[0026] As can be seen from the above, even if a through hole is provided in the substrate as the coating object, the following situation can be prevented: the second photosensitive resin composition coated on the peripheral portion of the through hole leaks to the back side of the substrate through the through hole, and the second photosensitive resin composition shrinks, resulting in a thinner thickness of the coating film. In addition, the following situation can also be prevented: the through hole cannot be reliably filled with the first photosensitive resin composition, so that a depression remains at the through hole trace, causing the second photosensitive resin composition coated on the peripheral portion of the through hole to invade the depression. Therefore, even if the second photosensitive resin composition is coated on the peripheral portion of the through hole, the thickness of the coating film can be uniform.

[0027] According to an embodiment of the present invention, by making the first photosensitive resin composition contain a non-reactive diluent having a surface tension of 30 mN / m or less at 25° C., the first photosensitive resin composition can be reliably prevented from leaking to the back side of the substrate through the through hole, and the through hole can be more reliably filled with the first photosensitive resin composition. In addition, even if a coating film is formed using the first photosensitive resin composition, the thickness of the coating film can be made more uniform.

[0028] According to the embodiment of the present invention, by setting the viscosity of the first photosensitive resin composition at 25° C. to 150 to 1500 mPa·s, the through-holes can be reliably filled and the thickness of the cured coating film can be further uniformed.

[0029] According to an embodiment of the present invention, by setting the exposure amount of the exposure process using active energy rays to 30 to 500 mJ / cm 2 , thereby shortening the exposure time. Therefore, even if the coating of the first photosensitive resin composition and the coating of the second photosensitive resin composition are included, productivity can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 FIG. (a) is an explanatory diagram of filling a through hole by applying a first photosensitive resin composition by an inkjet method in a method for forming a cured coating film according to an embodiment of the present invention, Figure 1 FIG. (b) is an explanatory diagram of applying a second photosensitive resin composition in the method for forming a cured coating film according to an embodiment of the present invention, Figure 1 FIG. (c) is an explanatory diagram of curing treatment by exposure in the method for forming a cured coating film according to an embodiment of the present invention, Figure 1 FIG. (d) is an explanatory diagram of the state of the cured coating film after development.

[0031] Figure 2 It is a plan view for explaining a printed wiring board having a cured coating film formed by the method for forming a cured coating film according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] Next, an embodiment of the method for forming a cured coating film of the present invention is described using the accompanying drawings. The method for forming a cured coating film of the present invention is to form a cured coating film on a substrate (e.g., a circuit substrate such as a printed wiring board or a flexible printed wiring board) having through holes. Figure 1 FIG. (a) is an explanatory diagram of filling a through hole by applying a first photosensitive resin composition by an inkjet method in a method for forming a cured coating film according to an embodiment of the present invention, Figure 1 FIG. (b) is an explanatory diagram of a second photosensitive resin composition applied in a method for forming a cured coating film according to an embodiment of the present invention, Figure 1 FIG. (c) is an explanatory diagram of curing treatment by exposure in the method for forming a cured coating film according to an embodiment of the present invention, Figure 1 FIG. (d) is an explanatory diagram of the state of the cured coating film after development. Figure 2 It is a plan view for explaining a printed wiring board having a cured coating film formed in the method for forming a cured coating film according to an embodiment of the present invention.

[0033] like Figure 1 As shown in (a), in the method for forming a cured coating film according to an embodiment of the present invention, first, an inkjet method ( Figure 1 In the method, for example, using an inkjet method using a jet dispenser 4, a predetermined amount of the first photosensitive resin composition 1 is applied to the through hole 31 of the substrate 3, thereby filling the through hole 31 with the first photosensitive resin composition 1 and completely filling the through hole 31.

[0034] Of the two main surfaces (first main surface 21 and second main surface 22) of the substrate 3, the second main surface 22 corresponding to the back side of the substrate 3 has a peripheral portion of the through hole 31 that is not in contact with the coating station 100. Therefore, a gap 101 is provided between the second main surface 22 and the surface of the coating station 100. Figure 1 In (a), the spacer 20 is provided on the surface of the coating station 100 , and the substrate 3 is placed on the spacer 20 so that the peripheral edge of the through hole 31 of the second main surface 22 is not in contact with the coating station 100 .

[0035] By making the peripheral edge of the through hole 31 of the second main surface 22 in a non-contact state, it is possible to prevent the capillary force from being generated at the interface between the surface of the coating station 100 and the second main surface 22 of the substrate 3. By preventing the generation of the capillary force, it is possible to prevent the first photosensitive resin composition 1 from leaking from the first main surface 21 of the substrate 3 to the second main surface 22 through the through hole 31, so that the first photosensitive resin composition 1 can be reliably and sufficiently filled in the through hole 31. The height of the gap 101 is not particularly limited, and is, for example, 1.0 mm to 10 mm.

[0036] The viscosity of the first photosensitive resin composition 1 at 25°C is adjusted to 150 to 1500 mPa·s using a non-reactive diluent. By setting the lower limit of the viscosity at 25°C to 150 mPa·s, when the first photosensitive resin composition 1 is applied to the through-hole 31 by an inkjet method, it is possible to prevent the first photosensitive resin composition 1 from leaking to the back side of the substrate 3 through the through-hole 31 during application. As a result, the through-hole 31 can be filled with the first photosensitive resin composition 1. In addition, by setting the upper limit of the viscosity at 25°C to 1500 mPa·s, when the first photosensitive resin composition 1 is applied by an inkjet method, it is possible to prevent the first photosensitive resin composition 1 from being applied in a convex shape, and the thickness of the cured coating film can be made uniform.

[0037] The viscosity of the first photosensitive resin composition 1 at 25° C. is not particularly limited as long as it is in the range of 150 to 1500 mPa·s. The lower limit thereof is preferably 180 mPa·s, and particularly preferably 300 mPa·s, from the perspective of reliably preventing the first photosensitive resin composition 1 from leaking to the back side of the substrate 3 through the through hole 31. In addition, the upper limit of the viscosity at 25° C. is preferably 1000 mPa·s, more preferably 900 mPa·s, and particularly preferably 700 mPa·s, from the perspective of reliably preventing the first photosensitive resin composition 1 from being applied in a convex shape. It should be noted that the size of the through hole 31 is not particularly limited, and for example, the inner diameter is 50 to 200 μm and the depth is 50 to 200 μm.

[0038] The non-reactive diluent for adjusting the viscosity of the first photosensitive resin composition 1 at 25°C is not particularly limited. From the perspective of reliably preventing the first photosensitive resin composition 1 from leaking to the back side of the substrate 3 through the through hole 31 and more reliably filling the through hole 31 with the first photosensitive resin composition 1, a non-reactive diluent having a surface tension of 30 mN / m or less at 25°C is more preferred, and a non-reactive diluent having a surface tension of 27 mN / m or less at 25°C is particularly preferred. As a non-reactive diluent having a surface tension of 30 mN / m or less at 25°C, for example, diethylene glycol diethyl ether (surface tension of 25 mN / m at 25°C) is preferred.

[0039] Next, if Figure 1 As shown in (b), the second photosensitive resin composition 2 is applied on the first photosensitive resin composition 1 filled in the through hole 31 by a desired coating method. Figure 1In (b), the second photosensitive resin composition 2 is applied to the entire first main surface 21 of the substrate 3. The time interval from the completion of the application of the first photosensitive resin composition 1 to the start of the application of the second photosensitive resin composition 2 is not particularly limited, but is preferably 72 hours or less from the perspective of preventing oxidation of the first main surface 21 of the substrate 3 and the surface of the first photosensitive resin composition 1.

[0040] There is no particular limitation on the coating method of the second photosensitive resin composition 2, and all methods used in the past can be used. Specifically, for example, screen printing, inkjet (for example, inkjet using a jet dispenser, etc.), roller coating, rod coating, spray coating, curtain coating, roll printing, applicator, scraper coating, blade coating, gravure coating, etc. can be cited. The coating method of the second photosensitive resin composition 2 can be the same coating method as the coating method of the first photosensitive resin composition 1 (that is, inkjet), or it can be a coating method other than inkjet. Among them, screen printing is preferred from the perspective of ease of coating the entire first main surface 21 of the substrate 3.

[0041] The second photosensitive resin composition 2 may be a resin composition composed of the same components as the first photosensitive resin composition 1, or may be a resin composition composed of different components. In addition, the viscosity of the second photosensitive resin composition 2 at 25°C may be the same as or different from the viscosity of the first photosensitive resin composition 1 at 25°C. The viscosity of the second photosensitive resin composition 2 at 25°C can also be adjusted using a non-reactive diluent. The viscosity of the second photosensitive resin composition 2 at 25°C depends on the coating method used. For example, as for its lower limit, from the perspective of coating to a specified film thickness, it is preferably 120 mPa·s. When screen printing is used as the coating method, from the perspective of reliably coating to a specified film thickness, it is more preferably 10000 mPa·s, and particularly preferably 12000 mPa·s. The upper limit of the viscosity at 25° C. is preferably 60,000 mPa·s from the perspective of coating properties, more preferably 50,000 mPa·s when screen printing is used as the coating method, and particularly preferably 30,000 mPa·s from the perspective of leveling properties.

[0042] The film thickness of the second photosensitive resin composition 2 when applied can be appropriately selected according to the use of the substrate 3 , and for example, when applied to a circuit board having a circuit pattern of a conductor such as copper foil formed thereon as the substrate 3 , the film thickness can be 10 to 100 μm.

[0043] Next, if Figure 1As shown in (c), the applied first photosensitive resin composition 1 and second photosensitive resin composition 2 are subjected to curing treatment 5 to form a cured coating film 12. Examples of the curing treatment 5 include exposure treatment using active energy rays and heat treatment using a heater.

[0044] exist Figure 1 In (c), a light-transmitting negative film (photomask) 102 other than the pads of the circuit pattern consisting of the through hole 31 and the copper foil 32 as a conductor is bonded to the second photosensitive resin composition 2, and is photocured by irradiating it with active energy rays, thereby performing curing treatment 5.

[0045] The conditions for the exposure treatment using active energy rays are not particularly limited as long as they are conditions for photocuring at least the second photosensitive resin composition 2. For example, the lower limit of the exposure to ultraviolet rays (e.g., wavelength 240 to 420 nm) is preferably 10 mJ / cm2 from the perspective of reliably photocuring the composition. 2 , more preferably 25 mJ / cm 2 , particularly preferably 30 mJ / cm 2 On the other hand, the upper limit of the ultraviolet exposure is not particularly limited from the perspective of photocuring, but is preferably 2000 mJ / cm from the perspective of shortening the exposure time and improving productivity. 2 , particularly preferably 500 mJ / cm 2 The light source of ultraviolet rays is not particularly limited, and examples thereof include metal halide lamps, ultrahigh pressure mercury lamps, xenon lamps, UV-LEDs, and the like.

[0046] Next, if Figure 1 As shown in (d), after the second photosensitive resin composition 2 is photocured, the non-exposed area corresponding to the above-mentioned through hole 31 and the pad is removed by using a dilute alkali aqueous solution, thereby developing the coating film. In the above-mentioned development method, for example, a spray method, a shower method, etc. are used. The dilute alkali aqueous solution used is not particularly limited, and for example, a 0.5 to 5% by mass sodium carbonate aqueous solution can be listed. By development, the first photosensitive resin composition 1 filled in the through hole 31 is removed, and the through hole 31 is exposed. After development, post-curing is performed at 130 to 170°C for 20 to 80 minutes using a hot air circulation dryer, so that it can be as shown. Figure 2 As shown in FIG. 2 , a target cured coating film 12 is formed on the first main surface 21 of the substrate 3 .

[0047] In the case where the second photosensitive resin composition 2 contains a non-reactive diluent, after applying the second photosensitive resin composition 2, in order to volatilize the non-reactive diluent and form a non-tack coating film, the composition may be pre-dried using a dryer or the like, and then subjected to a curing treatment 5. Pre-drying conditions include, for example, heating at a temperature of about 60 to 80° C. for about 15 to 60 minutes.

[0048] In the case of heat treatment, the curing treatment 5 is not particularly limited as long as the conditions are conditions for thermal curing of the second photosensitive resin composition 2 , and examples thereof include 60 to 170° C. and 15 to 80 minutes.

[0049] By performing the curing treatment 5, a cured coating film 12 having a desired pattern can be formed on the first main surface 21 of the substrate 3. It should be noted that in the above-mentioned embodiment, no curing treatment such as exposure treatment and heat treatment is performed after the first photosensitive resin composition is applied and before the second photosensitive resin composition is applied, but as required, the first photosensitive resin composition can be cured after the first photosensitive resin composition is applied and before the second photosensitive resin composition is applied. In addition, in the above-mentioned embodiment, after the first photosensitive resin composition is applied and before the second photosensitive resin composition is applied, other resin compositions including the first photosensitive resin composition can be further applied on the first photosensitive resin composition as required.

[0050] As can be seen from the above, even if the through hole 31 is provided in the substrate 3 to be coated, the second photosensitive resin composition 2 coated on the peripheral portion of the through hole 31 leaks to the second main surface 22 of the substrate 3 through the through hole 31, thereby preventing the second photosensitive resin composition coated on the first main surface 21 from shrinking and causing the thickness of the cured coating film 12 to become thinner. In addition, the through hole 31 cannot be reliably filled with the first photosensitive resin composition 1, so that a depression remains at the trace of the through hole 31, causing the second photosensitive resin composition 2 coated on the peripheral portion of the through hole 31 to intrude into the depression. Therefore, even if the second photosensitive resin composition 2 is coated on the peripheral portion of the through hole 31, the thickness of the cured coating film 12 can be made uniform.

[0051] Next, the first photosensitive resin composition and the second photosensitive resin composition (hereinafter sometimes the first photosensitive resin composition and the second photosensitive resin composition are collectively referred to as "photosensitive resin composition") are described. As a cured coating of the photosensitive resin composition, for example, an insulating film (for example, a solder resist film, etc.) formed on a circuit substrate such as a printed wiring board can be cited. As a photosensitive resin composition, for example, the following components can be included.

[0052] Photosensitive resin

[0053] As the photosensitive resin, for example, a photosensitive resin containing a carboxyl group can be cited. The photosensitive resin containing a carboxyl group is not particularly limited, and for example, a resin having one or more, preferably two or more, photosensitive unsaturated double bonds can be cited. As the photosensitive resin containing a carboxyl group, for example, a polyacid-modified free radical polymerizable unsaturated monocarboxylic acid epoxy resin such as polyacid-modified epoxy (meth) acrylate can be cited, and the polyacid-modified epoxy (meth) acrylate is obtained as follows: a free radical polymerizable unsaturated monocarboxylic acid such as acrylic acid, methacrylic acid (hereinafter sometimes referred to as "(meth) acrylic acid") is reacted with at least a part of the epoxy group of a multifunctional epoxy resin having two or more epoxy groups in one molecule to obtain a free radical polymerizable unsaturated monocarboxylic acid epoxy resin such as epoxy (meth) acrylate, and the polyacid or its anhydride is reacted with the generated hydroxyl group.

[0054] The chemical structure of the multifunctional epoxy resin is not particularly limited as long as it is a bifunctional or higher epoxy resin. The epoxy equivalent of the multifunctional epoxy resin is not particularly limited, but is preferably 3,000 or less, more preferably 1,000 or less, and particularly preferably 100 to 500. Among the multifunctional epoxy resins, for example, aralkyl epoxy resins, biphenyl aralkyl epoxy resins, biphenyl epoxy resins, naphthalene epoxy resins, dicyclopentadiene epoxy resins, ε-caprolactone modified epoxy resins, bisphenol A type, bisphenol F type, bisphenol AD ​​type and other phenol novolac epoxy resins, o-cresol novolac type and other cresol novolac type epoxy resins, bisphenol A novolac type epoxy resins, cyclic aliphatic epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, heterocyclic epoxy resins, bisphenol modified novolac type epoxy resins, multifunctional modified novolac type epoxy resins, condensate type epoxy resins of phenols and aromatic aldehydes having phenolic hydroxyl groups, etc. These epoxy resins can be used alone or in combination of two or more.

[0055] The radical polymerizable unsaturated monocarboxylic acid is not particularly limited, and examples thereof include (meth)acrylic acid, crotonic acid, cinnamic acid, etc. These radical polymerizable unsaturated monocarboxylic acids may be used alone or in combination of two or more.

[0056] The reaction method of the polyfunctional epoxy resin and the radically polymerizable unsaturated monocarboxylic acid is not particularly limited. For example, the polyfunctional epoxy resin and the radically polymerizable unsaturated monocarboxylic acid can be reacted by heating them in an appropriate diluent.

[0057] The polyacid or polyacid anhydride reacts with the hydroxyl group generated by the reaction of the epoxy resin and the free radical polymerizable unsaturated monocarboxylic acid, thereby introducing a free carboxyl group into the photosensitive resin. The polyacid or its anhydride is not particularly limited, and saturated or unsaturated polyacids or their anhydrides can be used. Among the polyacids, for example, succinic acid, maleic acid, adipic acid, citric acid, phthalic acid, tetrahydrophthalic acid, 3-methyltetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, 3-ethyltetrahydrophthalic acid, 4-ethyltetrahydrophthalic acid, hexahydrophthalic acid, 3-methylhexahydrophthalic acid, 4-methylhexahydrophthalic acid, 3-ethylhexahydrophthalic acid, 4-ethylhexahydrophthalic acid, methyltetrahydrophthalic acid, methylhexahydrophthalic acid, methylenetetrahydrophthalic acid, methylmethylenetetrahydrophthalic acid, trimellitic acid, pyromellitic acid and diglycolic acid can be listed, and as the polyacid anhydride, the anhydrides of the above-mentioned polyacids can be listed. These compounds can be used alone or in combination of two or more.

[0058] The above-mentioned polyacid-modified unsaturated monocarboxylic acid-modified epoxy resin can also be used as a photosensitive resin containing a carboxyl group. If necessary, a glycidyl compound having one or more free radical polymerizable unsaturated groups and an epoxy group can be reacted with the carboxyl group of the above-mentioned polyacid-modified unsaturated monocarboxylic acid-modified epoxy resin to further introduce free radical polymerizable unsaturated groups into the above-mentioned polyacid-modified unsaturated monocarboxylic acid-modified epoxy resin, thereby preparing a photosensitive resin containing a carboxyl group with further improved sensitivity to active energy lines.

[0059] The photosensitive resin containing a carboxyl group that further improves the sensitivity to active energy lines is further combined with a free radical polymerizable unsaturated group in the side chain of the polyacid-modified unsaturated monocarboxylic epoxy resin skeleton through the reaction of the above-mentioned glycidyl compound, thereby improving the photopolymerization reactivity (photocurability) and being able to have excellent photosensitivity. As compounds having one or more free radical polymerizable unsaturated groups and epoxy groups, for example, glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, pentaerythritol triacrylate monoglycidyl ether, etc. can be listed. It should be noted that multiple glycidyl groups can be present in one molecule. The above-mentioned compounds having one or more free radical polymerizable unsaturated groups and epoxy groups can be used alone, or two or more can be used in combination.

[0060] Photopolymerization initiator

[0061] The photopolymerization initiator is not particularly limited as long as it is a commonly used photopolymerization initiator, and examples thereof include ethyl ketone, oxime initiators such as 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]-1-(O-acetyl oxime), benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butyl ether, benzoin isobutyl ether, acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropane-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1-one, 4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)ketone, benzophenone, p-phenylbenzophenone, 4,4′-diethylaminobenzophenone, dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 2-aminoanthraquinone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzyl dimethyl ketal, acetophenone dimethyl ketal, ethyl p-dimethylaminobenzoate, etc. The above-mentioned photopolymerization initiators may be used alone or in combination of two or more. The amount of the photopolymerization initiator is not particularly limited, but is preferably 5 to 20 parts by mass relative to 100 parts by mass of the photosensitive resin containing a carboxyl group.

[0062] Epoxides

[0063] Epoxy compounds are used to increase the crosslinking density of the cured coating film to obtain a cured coating film with sufficient strength. As epoxy compounds, for example, epoxy resins can be listed. As epoxy resins, there is no particular limitation, for example, bisphenol A type epoxy resins, aralkyl type epoxy resins, biphenyl aralkyl type epoxy resins, novolac type epoxy resins (phenol novolac type epoxy resins, o-cresol novolac type epoxy resins, p-tert-butylphenol novolac type epoxy resins, etc.), bisphenol F type epoxy resins obtained by reacting epichlorohydrin with bisphenol F and bisphenol S, bisphenol S type epoxy resins, alicyclic epoxy resins with cyclohexenyl oxide, tricyclodecyl oxide, cyclopentenyl oxide, etc., isocyanuric acid tris (2,3-epoxypropyl) ester, triglycidyl tris (2-hydroxyethyl) isocyanurate, triglycidyl isocyanurate, dicyclopentadiene type epoxy resins, adamantane type epoxy resins with triazine rings. These compounds can be used alone or in combination of two or more. The amount of the epoxy compound is not particularly limited, but is preferably 10 to 50 parts by mass, particularly preferably 20 to 40 parts by mass, relative to 100 parts by mass of the photosensitive resin containing the carboxyl group, in order to obtain a coating film having sufficient strength after curing.

[0064] Non-reactive diluent

[0065] The non-reactive diluent is used to adjust the viscosity of the photosensitive resin composition and, if necessary, to adjust the drying property. Examples of the non-reactive diluent include organic solvents. Examples of organic solvents include ketones such as methyl ethyl ketone and cyclohexanone; aromatic hydrocarbons such as toluene and xylene; alcohols such as methanol, isopropyl alcohol, and cyclohexanol; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; petroleum solvents such as naphtha; cellosolves such as cellosolves and butyl cellosolves; carbitols such as carbitol and butyl carbitol; esters such as ethyl acetate, butyl acetate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, ethyl diglycol acetate, and ethylene glycol acetate; ethers such as diethylene glycol diethyl ether, and the like. Among them, a non-reactive diluent (organic solvent) having a surface tension of 35 mN / m or less at 25°C is preferred, a non-reactive diluent having a surface tension of 30 mN / m or less at 25°C is more preferred, and a non-reactive diluent having a surface tension of 27 mN / m or less at 25°C is particularly preferred. As a non-reactive diluent having a surface tension of 35 mN / m or less at 25°C, for example, diethylene glycol diethyl ether (surface tension at 25°C: 25 mN / m) and ethylene glycol acetate (surface tension at 25°C: 31 mN / m) are preferred. As a non-reactive diluent having a surface tension of 30 mN / m or less at 25°C, for example, diethylene glycol diethyl ether (surface tension at 25°C: 25 mN / m) is preferred.

[0066] In addition, in the photosensitive resin composition, carbamate (meth) acrylate can be added as needed. Carbamate (meth) acrylate helps to obtain a cured coating film with flexibility. Carbamate (meth) acrylate is obtained by reacting a carbamate compound with (meth) acrylic acid as a free radical polymerizable unsaturated monocarboxylic acid. Carbamate is obtained by reacting a compound having two or more isocyanate groups in one molecule with a polyol compound having two or more hydroxyl groups in one molecule.

[0067] The compound having two or more isocyanate groups in one molecule is not particularly limited, and examples thereof include diisocyanate compounds such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), methylene diisocyanate (MDI), methylenebiscyclohexyl isocyanate, trimethylhexamethylene diisocyanate, hexane diisocyanate, hexamethylamine diisocyanate, methylenebiscyclohexyl isocyanate, toluene diisocyanate, 1,2-diphenylethane diisocyanate, 1,3-diphenylpropane diisocyanate, diphenylmethane diisocyanate, and dicyclohexylmethyl diisocyanate. These compounds may be used alone or in combination of two or more.

[0068] The polyol compound having two or more hydroxyl groups in one molecule is not particularly limited, and examples thereof include ethylene glycol, propylene glycol, trimethylene glycol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, neopentyl glycol, 1,6-hexanediol, 2,2-diethyl-1,3-propanediol, 3,3-dihydroxymethylheptane, 2-ethyl-2-butyl-1,3-propanediol, 1,12-dodecanediol, 1,18-octadecanediol, and the like. 2 -C 22 Alkanediols; aliphatic diols such as olefin diols such as 2-butene-1,4-diol and 2,6-dimethyl-1-octene-3,8-diol; alicyclic diols such as 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol; aliphatic triols such as glycerol, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2,4-dihydroxy-3-hydroxymethylpentane, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2,4-dihydroxy-3-(hydroxymethyl)pentane, and 2,2-bis(hydroxymethyl)-3-butanol; polyols having four or more hydroxyl groups such as tetramethylolmethane, pentaerythritol, dipentaerythritol, and xylitol, etc. These compounds may be used alone or in combination of two or more.

[0069] The amount of urethane (meth) acrylate is not particularly limited, but its lower limit is preferably 5 parts by mass, particularly preferably 10 parts by mass, relative to 100 parts by mass of the photosensitive resin containing the carboxyl group, from the perspective of improving the flexibility of the cured coating film. On the other hand, its upper limit is preferably 50 parts by mass, from the perspective of preventing the photosensitivity from decreasing.

[0070] In addition, the photosensitive resin composition may further contain various additives such as a colorant, an extender pigment, a latent curing agent, a defoaming agent, a flame retardant, and the like, as required.

[0071] Example

[0072] Next, examples of the present invention will be described, but the present invention is not limited to these examples unless the gist of the present invention is exceeded.

[0073] Examples 1 to 4, Comparative Examples 1 to 4

[0074] The components shown in Table 1 below were mixed in the proportions shown in Table 1 below, and mixed and dispersed at room temperature using a triple roll to prepare a resin composition, and a predetermined amount of a diluting solvent (non-reactive diluent) was further added to the resin composition to prepare photosensitive resin compositions used in Examples 1 to 4 and Comparative Examples 1 to 4. Then, the prepared photosensitive resin composition was applied as described below to prepare a test piece.

[0075] Base plate: with inner diameter Substrate with a through hole of 70 μm in depth

[0076] Substrate surface (corresponding to the first main surface) treatment: acid treatment (5 mass % sulfuric acid aqueous solution)

[0077] After the surface treatment of the substrate, a jet dispenser (manufactured by Nordson Advantest Technology Corporation, platform body Quantum Q-6800, DispenseJet Valve DJ-9500) is used to apply the photosensitive resin composition prepared as described above one by one for Examples 1 to 4 and Comparative Examples 2 to 4, and the photosensitive resin composition (corresponding to the first photosensitive resin composition) is filled only in the through-holes of the substrate, and the through-holes are completely buried. At this time, in Examples 1 to 4 and Comparative Examples 3 and 4, a spacer is used to make the back side of the substrate (corresponding to the second main surface) 1.6 mm away from the surface of the coating platform, so that the peripheral portion of the through-hole is in a non-contact state. On the other hand, in Comparative Example 2, the back side of the substrate is placed directly on the surface of the coating platform, so that the peripheral portion of the through-hole is in contact with the surface of the coating platform.

[0078] Then, for Examples 1 to 4 and Comparative Examples 2 to 4, the above-mentioned jet dispenser was further used to apply the photosensitive resin composition prepared as described above (corresponding to the first photosensitive resin composition) to the entire surface of the substrate with a film thickness of 50 μm. Then, for Examples 1 to 4 and Comparative Examples 1 to 4, the photosensitive resin composition prepared as described above (corresponding to the second photosensitive resin composition) was applied to the entire surface of the substrate by screen printing on the first photosensitive resin composition applied to the entire surface of the substrate. It should be noted that the viscosity of the photosensitive resin composition of Examples 1 to 4 and Comparative Examples 1 to 4 during screen printing was adjusted to 15000 mPa·s.

[0079] Dry film thickness of screen printing: 20~23μm

[0080] Pre-drying: 80℃, 20 minutes

[0081] Exposure (curing): wavelength 250-450nm (light source: metal halide lamp), 250mJ / cm 2(Orc Manufacturing Co., Ltd., HMW-680GW)

[0082] Development: 1 mass % sodium carbonate aqueous solution, 60 seconds, spray pressure 0.2 MPa

[0083] Post-curing: 150°C, 30 minutes

[0084] It should be noted that the dry film thickness of screen printing was measured at a location where coating was not performed using a jet dispenser. In Comparative Example 1, coating was not performed using a jet dispenser, and the back side of the substrate was directly placed on the surface of the coating table, so that only screen printing was performed in a state where the peripheral edge of the through hole was in contact with the surface of the coating table.

[0085] Evaluation Project

[0086] (1) Viscosity (mPa·s)

[0087] The photosensitive resin compositions of Examples 1 to 4 and Comparative Examples 1 to 4 were measured for viscosity at 25° C. at 50 rpm using an E-type viscometer.

[0088] (2) Through-hole filling

[0089] 100 through holes provided in the test piece having the cured coating film formed thereon were observed using an optical microscope (×40 times) to see whether the photosensitive resin compositions of Examples 1 to 4 and Comparative Examples 1 to 4 were filled and completely buried, and the number of buried through holes was counted.

[0090] ○: 100

[0091] △: 99 to 80

[0092] ×: Less than 79

[0093] (3) Leakage to the back side of the substrate

[0094] The photosensitive resin compositions of Examples 1 to 4 and Comparative Examples 1 to 4 were observed using an optical microscope (×40 times) to see whether they leaked to the back side of the substrate through 100 through holes provided in the test piece on which the cured coating film was formed.

[0095] (4) Film thickness uniformity

[0096] The cross section of the cured coating film between the wiring patterns having through holes of the test piece on which the cured coating film was formed was sealed and polished, and then observed with a microscope at N=9 to measure the film thickness of the portion coated by the jet dispenser.

[0097] ○: The difference between the maximum and minimum film thicknesses is less than 3 μm.

[0098] △: The difference between the maximum and minimum film thicknesses is 3 μm or more and less than 5 μm.

[0099] ×: The difference between the maximum and minimum film thicknesses is 5 μm or more.

[0100] (5) Gap

[0101] The cross section of the test piece on which the cured coating film was formed was sealed and polished, and then observed with a microscope to evaluate the presence or absence of voids.

[0102] The evaluation results are shown in Table 1 below.

[0103] [Table 1]

[0104]

[0105] As shown in Table 1, in Examples 1 to 4, the first photosensitive resin composition having a viscosity of 200 to 800 mPa·s at 25° C. is applied to the through hole by the inkjet method while the peripheral portion of the through hole is in a non-contact state, thereby filling the through hole with the first photosensitive resin composition, so that the through hole filling property is excellent and leakage to the back side of the substrate is prevented. In addition, in Examples 1 to 4, since the film thickness uniformity of the portion applied by the jet dispenser is excellent, the film thickness uniformity of the cured coating of the second photosensitive resin composition applied by screen printing is also excellent. In addition, in Examples 1 to 4, no voids are generated, and the properties of the cured coating are also excellent.

[0106] In addition, from the comparison between Example 1 and Example 4, it can be seen that when a non-reactive diluent, namely diethylene glycol diethyl ether, having a surface tension of 25 mN / m at 25° C. is used as a dilution solvent, the film thickness uniformity is further improved compared with a non-reactive diluent, namely ethylene glycol acetate, having a surface tension of 31 mN / m at 25° C. In addition, from the comparison between Example 2 and Examples 1, 3, and 4, it can be seen that when a first photosensitive resin composition having a viscosity of 400 to 800 mPa·s at 25° C. is used, leakage to the back side of the substrate can be more reliably prevented compared with a first photosensitive resin composition having a viscosity of 200 mPa·s at 25° C.

[0107] On the other hand, in Comparative Example 1 in which only screen printing was performed, Comparative Example 2 in which the peripheral edge of the through hole was in contact, and Comparative Example 4 in which the viscosity at 25°C was 100 mPa·s, through-hole filling was not achieved, leakage to the back side of the substrate was observed, and film thickness uniformity was not achieved. In addition, in Comparative Example 3 in which the viscosity at 25°C was 2000 mPa·s, film thickness uniformity was not achieved, and voids were generated.

[0108] Industrial Applicability

[0109] The method for forming a cured coating film of the present invention can prevent the photosensitive resin composition from leaking to the back side of the substrate through the through-holes even when the substrate has through-holes, and can make the thickness of the coating film uniform. Therefore, it has high utilization value in the field of insulating films of circuit substrates having through-holes, for example.

[0110] Description of Reference Numerals

[0111] 1. First photosensitive resin composition

[0112] 2. Second photosensitive resin composition

[0113] 3 substrate

[0114] 4 Spray dispenser

[0115] 5. Curing

[0116] 12 Curing coating

Claims

1. A method for forming a cured coating film, comprising: The step of applying a first photosensitive resin composition containing a non-reactive diluent and having a viscosity of 150 to 1500 mPa·s at 25° C. to at least the through-hole portion of the substrate by an inkjet method to form a filler in the through-hole, a step of forming a coating film by applying a second photosensitive resin composition containing a non-reactive diluent on the first main surface of the substrate and on the surface of the filler on the first main surface side by screen printing, inkjet, roll coating, rod coating, spray coating, curtain coating, roll printing, applicator, blade coating, knife coating or gravure coating, and a step of curing the coating film to form a cured coating film, The curing treatment is not performed after applying the first photosensitive resin composition and before applying the second photosensitive resin composition, In the step of applying the first photosensitive resin composition, at least the peripheral edge of the through hole in the second main surface of the substrate opposite to the first main surface is placed in non-contact with a coating stage. The second main surface is the back surface of the substrate.

2. The method for forming a cured coating film according to claim 1, wherein: The first photosensitive resin composition includes a non-reactive diluent having a surface tension of 30 mN / m or less at 25° C.

3. The method for forming a cured coating film according to claim 2, wherein: The non-reactive diluent comprises diethylene glycol diethyl ether.

4. The method for forming a cured coating film according to any one of claims 1 to 3, wherein: The coating method of the second photosensitive resin composition is screen printing, roller coating, rod coating, spray coating, curtain coating, roll printing, applicator coating, blade coating, knife coating or gravure coating.

5. The method for forming a cured coating film according to any one of claims 1 to 3, wherein: The viscosity of the first photosensitive resin composition at 25° C. is 180 to 1000 mPa·s.

6. The method for forming a cured coating film according to any one of claims 1 to 3, wherein: The viscosity of the second photosensitive resin composition at 25° C. is 120 to 60,000 mPa·s.

7. The method for forming a cured coating film according to any one of claims 1 to 3, wherein: The first photosensitive resin composition has the same components as those of the second photosensitive resin composition.

8. The method for forming a cured coating film according to any one of claims 1 to 3, wherein: The curing treatment is an exposure treatment using active energy rays and / or a heat treatment.

9. The method for forming a cured coating film according to claim 8, wherein: The exposure amount of the active energy ray exposure treatment using a wavelength of 240 to 420 nm is 30 to 500 mJ / cm 2 .

10. The method for forming a cured coating film according to any one of claims 1 to 3, wherein: The first photosensitive resin composition contains a non-reactive diluent having a surface tension of 27 mN / m or less at 25° C., and the second photosensitive resin composition contains a non-reactive diluent having a surface tension of 27 mN / m or less at 25° C.

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