What causes peeling when switching to water-based paint? The difference in pre-treatment.
The rise in thinner prices is accelerating the switch to water-based paints. This explains the reasons why switching while keeping the same pre-treatment can lead to peeling, as well as the points to check during the transition.
The thinner prices have risen significantly, so we switched to water-based paint. However, peeling that had never occurred before has started to appear. In spring 2026, major paint manufacturers raised thinner prices by more than 50% and up to 75%. ────────────── ■ Cause of Occurrence Water-based paints are weaker than solvent-based paints in their ability to dissolve oils on the surface of materials. The lack of degreasing that could be compensated for by solvent-based paints directly leads to poor adhesion. ■ The Truth The problem is not with the paint itself, but with not reviewing the pre-treatment during the switch. Water-based paints are also more susceptible to humidity during drying, and may not fully dry under the same furnace conditions. ■ Improvement Measures During the switch, we will recheck the degreasing conditions and water drainage drying. We will conduct adhesion tests on trial paint boards and redefine the curing conditions before entering mass production. Eiwa Kogei can proceed to mass production after confirming the conditions with testing equipment. Please download and utilize the materials summarizing the confirmation points in the process.
basic information
Theme: Poor adhesion during paint switching. Management items: Degreasing conditions, water drainage drying, humidity during painting, curing conditions, adhesion testing. Background: Thinner price increase in spring 2026.
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Applications/Examples of results
A metal parts manufacturer considering switching from solvent-based paint to water-based paint. Materials switching decisions by the purchasing department, change management by the quality control department, and training materials for new employees.
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We are not just a "subcontracted painting factory." Established in 1958, our company has a foundation of painting technology and also specializes in chemical treatment, stripping, and cleaning, functioning as the "external surface treatment department" in your organizational chart. Based on our philosophy of "preparation is eight-tenths of the work," we emphasize participation from the "upstream process" before the drawings are finalized. We conduct test painting on a wide range of metals and difficult materials, and we produce the entire process from assembly, packaging, to delivery, thereby reducing your management workload. Additionally, by being able to perform zinc phosphate treatment in-house, we achieve stable painting quality. Furthermore, our micro-heating stripping technology, which does not use chemicals, maintains the electrical state of the "jigs (hangers)" that influence painting quality. Our approach of "pre-treatment determines painting quality" ensures the stability of the paint film during mass production. Rather than simply "applying specified standards," we work backwards to achieve optimal painting specifications and prevent scratches during transportation, sparing no effort in thorough discussions from the outset. This diligent preparation is the shortest path to preventing rework and minimizing total costs. From the development stage, please utilize the expertise of our specialists as part of your production line.