Surface-Treated Metal Sheet Adhesion via Primer Layer
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Solution Overview
Problem
Existing methods for bonding metal sheets to plastics during injection molding face challenges with adhesive strength, particularly when using heat-sensitive crosslinking agents, which are not suitable for short high-temperature contacts, leading to inefficient processing and reduced adhesive strength in metal-sheet-resin composite molded articles.
Innovation Solution
A surface-treated metal sheet with a laminate structure comprising a metal substrate, a chemical conversion coating film containing colloidal silica and a thermosetting resin, and an adhesive layer, where a primer layer is included between the chemical conversion coating film and the adhesive layer, using water-based urethane, acrylic-modified epoxy, or phenolic resins, and a crosslinking agent to enhance adhesive properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a heat-sensitive crosslinking agent is used in the resin coating film to increase adhesive strength between the metal sheet and the coating film, then adhesive strength is improved, but the process is not suitable for injection molding because the contact time at high temperature is too short for the crosslinking agent to react
Solution Approach 1:
The patent changes the type of crosslinking agent from heat-sensitive to room-temperature crosslinking agent, fundamentally altering the reaction conditions. This allows the crosslinking reaction to proceed at lower temperatures where the injection-molded plastic can maintain contact long enough for complete reaction, resolving the time-temperature conflict
Solution Approach 2:
The patent introduces a primer layer as an intermediary between the metal sheet and the adhesive layer. This primer layer provides a surface that enhances adhesion while allowing the room-temperature crosslinking agent to form a strong bond without requiring high-temperature heating, thus compatible with injection molding processes
2Reliability
If the temperature of the plastic is increased to facilitate the reaction of the heat-sensitive crosslinking agent, then the crosslinking reaction can occur, but a longer period of time is required to cool and solidify the plastic, losing the advantage of efficient injection molding
Solution Approach 1:
The patent changes the reaction temperature parameter from high temperature to room temperature by selecting a room-temperature crosslinking agent. This eliminates the need to increase plastic temperature, thereby maintaining short cooling times and high injection molding productivity while ensuring complete crosslinking reaction
3Adaptability or versatility
If a polar group-containing thermoplastic resin layer is formed on the metal sheet surface to join the metal sheet to a glass fiber-reinforced resin, then adhesive properties are improved, but the adhesive strength between the resin layer and the metal sheet is insufficient
Solution Approach 1:
The patent creates a composite structure with multiple layers: metal sheet, chemical conversion coating, primer layer, and adhesive layer. Each layer contributes specific properties - the chemical conversion coating provides surface activation, the primer layer provides bonding interface, and the adhesive layer with room-temperature crosslinking agent provides strong final bond, achieving both adaptability and strength
Solution Approach 2:
The patent introduces a primer layer as an intermediary between the metal sheet and the adhesive layer. This primer layer acts as a bonding mediator that chemically bonds to both the metal substrate and the adhesive layer, significantly improving the adhesive strength that was insufficient when using only a polar group-containing thermoplastic resin layer
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a metal-sheet-resin composite molded article with high adhesive strength, suitable for injection molding, offering improved efficiency and durability in applications like automotive components and office automation equipment.
Implementation Method 1
a chemical conversion coating film which contains colloidal silica and a thermosetting resin
Implementation Method 2
the thermosetting resin is a water-based urethane resin, a water-based acrylic-modified epoxy resin or a water-based phenolic resin, or a combination of a water-based carboxyl group-containing acrylic resin and a crosslinking agent which is able to react with a carboxyl group
Implementation Method 3
a primer layer is provided between the chemical conversion coating film and the adhesive layer
Implementation Method 4
injecting a molten plastic and then solidifying the plastic by cooling
Data Source
AI summary
Provided are: a surface-treated metal sheet that is useful when integrating a molded plastic (resin) article and a metal sheet during injection molding; and a metal sheet-resin composite molded article in which the metal sheet and a resin molded article are integrated. The surface-treated metal sheet consists of a laminate having a metal substrate, a chemical conversion coating film and an adhesive layer in order, and is characterized in that the chemical conversion coating film contains colloidal silica and a thermosetting resin.