EP-4737130-A1 - COATING FILM FORMING METHOD

Abstract

A coating film forming method according to the present invention is a coating film forming method employing an inkjet head, wherein an inkjet ink contains a polymerizable monomer, a blocked isocyanate, and a photopolymerization initiator, and the method includes: a dewatering step for the ink; and a heating step for bringing the temperature of the ink ejected from the inkjet head to 40°C or higher.

Inventors

• TANABE ITARU
• KURAMOCHI SHOUHEI
• KATSUDA AI
• NAKAHARA ISSEI

Assignees

• Konica Minolta, Inc.

Dates

Publication Date

20260506

Application Date

20240606

Claims (7)

1. A coating film forming method using an inkjet head, wherein an inkjet ink contains a polymerizable monomer, a blocked isocyanate, and a photopolymerization initiator, the method comprising the steps of: dehydrating the inkjet ink; and heating the inkjet ink such that a temperature of the inkjet ink to be ejected from the inkjet head becomes 40°C or higher.
2. The coating film forming method according to claim 1, wherein the heating step includes heating the inkjet ink in an ink supply path for supplying the inkjet ink to the inkjet head.
3. The coating film forming method according to claim 1, wherein the dehydration step includes injecting a dry gas having a moisture content reduced by a dryer into an ink supply path for supplying the inkjet ink to the inkjet head.
4. The coating film forming method according to claim 3, wherein the dehydration step includes making the dry gas by using a membrane filter or activated carbon.
5. The coating film forming method according to claim 1, further comprising a step of degassing the inkjet ink after the dehydration step.
6. The coating film forming method according to claim 5, wherein the degassing step includes using a hollow fiber or an ultrasonic wave.
7. The coating film forming method according to claim 2, further comprising, after the dehydration step, a step of second heating in the ink supply path for supplying the inkjet ink to the inkjet head, in addition to the heating step.

Description

Technical Field The present invention relates to a coating film forming method. The present invention particularly relates to a coating film forming method in which the generation of solid matter in an apparatus and the clogging of a head nozzle are suppressed, and satisfactory ejection properties and stable curability are obtained. Background Art Conventionally, photolithography and screen printing methods have been used for forming etching resists, solder resists, and markings on printed wiring boards. As an application of the inkjet method to a method for producing a printed wiring board, for example, an inkjet ink containing a thermal curing agent is used for a copper-clad laminate for a printed wiring board. Furthermore, it has already been proposed to form a solder resist with an inkjet printer (see, for example, Patent Documents 1 to 3). The inkjet method can greatly reduce the number of steps and time and effort as compared with photolithography, which requires a photomask, or screen printing methods using resist ink or marking ink, which require a screen plate. In addition, the inkjet method can reduce the amount of consumables such as developers, various inks, and cleaning solvents, and can also reduce waste water, which can be expected to lead to a cleaner environment. However, in ink containing the thermal curing agent, in particular, a blocked isocyanate, water or a hydroxy group contained in the ink reacts with the blocked isocyanate to generate solid matter. For this reason, when the ink is ejected from a head by an inkjet method, there is a problem that clogging occurs in a nozzle, which easily causes ejection failure. In particular, curable ink is usually heated to reduce the ink viscosity before ejection in order to increase the ejection performance of the inkjet, but heating may further accelerate the generation of solid matter. Therefore, a method of suppressing the water content rate to as low as 500 ppm during the production of ink containing an isocyanate group has been proposed (see, for example, Patent Document 4). However, the method of suppressing the water content rate to 500 ppm has a large production load, is difficult to maintain and store, and leads to increased 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: JP 06069300Patent Document 2: JP 2011-043565 APatent Document 3: JP 05969208Patent Document 4: JP 2014-201593 A Summary of Invention Technical Problem The present invention has been conceived in consideration of the above problems and circumstances. An object of the present invention is to provide a coating film forming method in which the generation of solid matter in an apparatus and the clogging of a head nozzle are suppressed, and satisfactory ejection properties and stable curability are obtained. Note that, hereinafter, the term "inkjet ink" is also simply referred to as "ink". Solution to Problem To solve the above problems, the present inventors have investigated the causes of the above problems and the like. The present inventors have found that even when ink containing a blocked isocyanate is used, it is possible to suppress the generation of solid matter in a coating film forming apparatus by ejecting the ink after performing an ink dehydration step. In other words, the above-described problems according to the present invention are solved by the following means. 1. A coating film forming method using an inkjet head, wherein an inkjet ink contains a polymerizable monomer, a blocked isocyanate, and a photopolymerization initiator, the method including the steps of: dehydrating the inkjet ink; andheating the inkjet ink such that the temperature of the inkjet ink to be ejected from the inkjet head becomes 40°C or higher.2. The coating film forming method according to item 1, wherein the heating step is performed in an ink supply path that supplies the inkjet ink to the inkjet head.3. The coating film forming method according to item 1, wherein in the dehydration step, a dry gas having a moisture content reduced by a dryer is injected into an ink supply path that supplies the inkjet ink to the inkjet head.4. The coating film forming method according to item 3, wherein in the dehydration step, a membrane filter or activated carbon is used for making the dry gas.5. The coating film forming method according to item 1, further including a step of degassing the inkjet ink after the dehydration step.6. The coating film forming method according to item 5, wherein the degassing step uses a hollow fiber or an ultrasonic wave.7. The coating film forming method according to item 2, further including, after the dehydration step, a step of second heating in the ink supply path that supplies the inkjet ink to the inkjet head, in addition to the heating step. Advantageous Effects of Invention By the above-described means of the present invention, it is possible to p