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EP-4737524-A1 - INKJET INK, SOLDER RESIST, PRINTED WIRING BOARD, METHOD FOR FORMING COATING FILM, AND DEVICE FOR FORMING COATING FILM

EP4737524A1EP 4737524 A1EP4737524 A1EP 4737524A1EP-4737524-A1

Abstract

This inkjet ink comprises a polymerizable monomer, a blocked isocyanate, and a photopolymerization initiator, and has a water content, as determined by the Karl Fischer method, in the range of 0.05-0.60 mass% relative to the total mass of the inkjet ink.

Inventors

  • NAKAHARA ISSEI
  • KATSUDA AI

Assignees

  • Konica Minolta, Inc.

Dates

Publication Date
20260506
Application Date
20240605

Claims (12)

  1. An inkjet ink containing: a polymerizable monomer; a blocked isocyanate; and a photopolymerization initiator, wherein a water content of the inkjet ink measured by a Karl Fischer method is within a range of 0.05% to 0.60% by mass relative to a total mass of the inkjet ink.
  2. The inkjet ink according to claim 1, wherein the ink is configured to be ejected at a temperature of 40°C or higher.
  3. The inkjet ink according to claim 1, wherein the blocked isocyanate has an aromatic ring structure.
  4. The inkjet ink according to claim 1, wherein the blocked isocyanate has an isocyanurate structure.
  5. The inkjet ink according to claim 1, wherein the inkjet ink contains, relative to the inkjet ink, 30% by mass or more of the polymerizable monomer having an octanol/water partition coefficient (ClogP) value in a range of 2.0 to 7.0.
  6. The inkjet ink according to claim 1, wherein the polymerizable monomer contains a polymerizable monomer having at least one bisphenol A structure.
  7. The inkjet ink according to claim 1, wherein a sum of a hydroxy value of a compound contained in the inkjet ink is 60 mg KOH/g or less, the compound having a hydroxy group.
  8. The inkjet ink according to claim 1, wherein the inkjet ink is contained in a container having a water vapor transmission rate within a range of 0.05 to 1.50 g/m 2 ·day·atm under conditions of 40°C and 90% RH.
  9. A solder resist containing the inkjet ink according to any one of claims 1 to 8.
  10. A printed wiring board comprising the solder resist according to claim 9.
  11. A method for forming a coating film, comprising: using the inkjet ink according to any one of claims 1 to 8; and heating the inkjet ink to 40°C or higher in a channel for supplying the inkjet ink to an inkjet head of a coating film forming apparatus.
  12. A coating film forming apparatus comprising: the inkjet ink according to any one of claims 1 to 8; and a means for heating the inkjet ink to 40°C or higher in a channel for supplying the inkjet ink to an inkjet head of the coating film forming apparatus.

Description

Technical Field The present invention relates to an inkjet ink, a solder resist, a printed wiring board, a method for forming a coating film, and a coating film forming apparatus. In particular, the present invention relates to an inkjet ink and the like that can provide good ejection property, stable curability, and coating film performance even when an inkjet ink containing a blocked isocyanate is used. Background Art On a printed wiring board in a printed circuit board (PCB), an ink is applied and cured to form an insulating film (solder resist film) for the purpose of protecting a circuit pattern. Conventionally, the solder resist has been patterned to match the wiring of the PCB by using silk screen printing, a photographic development method, a direct exposure machine, or the like. On the other hand, in recent years, a method for applying a solder resist film by an inkjet method has been studied from the viewpoints of material loss and environmental regulations. For example, it has already been proposed to form a solder resist on a copper-clad laminate for a printed wiring board with an inkjet printer using an inkjet ink containing a thermosetting agent (see, for example, Patent Documents 1 to 3). The inkjet method can greatly reduce the number of steps and labor as compared with photolithography, which requires a photomask, and a screen printing method using resist ink or marking ink, which requires a screen. Furthermore, the inkjet method can reduce consumables such as a developing solution, various inks, and a cleaning solvent, and also reduce wastewater, which is expected to lead to a cleaner environment. However, in an ink containing the thermosetting agent, in particular a blocked isocyanate, water or a hydroxy group contained in the ink reacts with the blocked isocyanate to generate a solid. Therefore, there is a problem in that curing or ejection failure easily occurs in the inkjet printer. In particular, curable ink is usually heated to reduce the ink viscosity before ejection in order to increase the inkjet ejection performance, but the heating further accelerates the generation of solids. Therefore, a method for suppressing the water content to be as low as 500 ppm at the time of producing an ink containing an isocyanate group has been proposed (for example, see Patent Document 4). However, the method of limiting the water content to 500 ppm is difficult to achieve in practice because of the large production load, difficulty in maintenance and storage, and the resulting increase in costs. In addition, the above method is based on the premise that the ink is used immediately after production. Citation List Patent Literature Patent Document 1: Japanese Patent No. 06069300Patent Document 2: Japanese Unexamined Patent Application Publication No. 2011-043565Patent Document 3: Japanese Patent No. 05969208Patent Document 4: Japanese Unexamined Patent Application Publication No. 2014-201593 Summary of Invention Technical Problem The present invention has been made in consideration of the above-mentioned problems and situations. A problem to be solved by the present invention is to suppress generation of solids in a coating film forming apparatus when an inkjet ink containing a blocked isocyanate is used. As a result, it is an object of the present invention to provide an inkjet ink, a solder resist, a printed wiring board, a method for forming a coating film, and a coating film forming apparatus, with which good ejection property, stable curability, and coating film performance can be obtained. Note that hereinafter, the term "inkjet ink" is also referred to simply as "ink". Solution to Problem In order to solve the above-described problem, the present inventors have defined the water content of an inkjet ink containing a blocked isocyanate in the course of investigating the cause and the like of the above-described problem. As a result, the present inventors have found that it is possible to provide an inkjet ink or the like that can suppress the generation of cured products or solids in a coating film forming apparatus and can obtain good ejection property, stable curability, and coating film performance. This has led to the present invention. 1. An inkjet ink containing: a polymerizable monomer; a blocked isocyanate; and a photopolymerization initiator, wherein a water content of the inkjet ink measured by a Karl Fischer method is within a range of 0.05 to 0.60% by mass relative to a total mass of the inkjet ink.2. The inkjet ink according to item 1, wherein the ink is configured to be ejected at a temperature of 40°C or higher.3. The inkjet ink according to item 1, wherein the blocked isocyanate has an aromatic ring structure.4. The inkjet ink according to item 1, wherein the blocked isocyanate has an isocyanurate structure.5. The inkjet ink according to item 1, wherein the inkjet ink contains, relative to the inkjet ink, 30% by mass or more of the polymerizable monomer having an octanol/water