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Proposed Applications for Metal-Resin Bonding Technology

Proposed Applications for Metal-Resin Bonding Technology in Polyplastics Products

1. Introduction

Engineering plastics have contributed to weight reduction in automotive parts, electronics and electrical products, and many other industrial products, by being used in place of metal materials. Today rather than simply replacing metal materials, many metal- resin composite materials are manufactured which still have some metal materials, and replace the rest with engineering plastics. Metal- resin composite materials deliver the advantage of simultaneously using both the properties of metal materials (such as high rigidity, electrical conductivity, etc.) and the properties of engineering plastics (such as low density, electrical insulation, etc.). However, since there is a bond interface between the two materials, it presents a higher level of technical difficulty when bonding force and airtightness are required.

Past methods used to produce metal-resin composite materials include simple insert molding, as well as physical joining through caulking or screw tightening, bonding with adhesives, and sealing with potting agent. However, simple insert molding, caulking and screw tightening often did not provide enough functionality because they provide poor airtightness. Bonding with adhesives and sealing with potting agent involve large numbers of parts and extensive procedures, making high costs inevitable.

In order to resolve this problem, technologies appeared from the year 2000 onward which give the bond interface of the metal and resin properties of bonding force and airtightness with injection molding alone by giving the metal surface physical texture and chemical affinity in advance and making it into insert molding. However, since many factors (metal parts, resin materials, mold structure, injection molding conditions, etc.) in this method have an effect on bonding, it does not provide stable bonding. As a result, there are still not many examples of this going into mass production. Thus here we will introduce some points to keep in mind to get metal-resin bonding capability with injection molding alone.

  Pattern (1) Pattern (2) Pattern (3)
Conventional technology Outsert molding, adhesion, screw tightening Adhesion, radiation sheets O-rings
Benefits of metal adhesion Better appearance
(better strength, design)
Better functionality
(better heat release)
Added functionality
(Added water resistance)
Application examples

Resin boss bonding to metals

Release of heat to heat

sink of heating elements

Water resistance for mobile device connectors

Figure 1-1. Benefits gained from metal-resin bonding technology

2. Points for successful metal adhesion

Figure 2-1 shows the process of direct metal-resin bonding with metal insert molding.

Direct metal-resin bonding is a process which produces parts in which metal parts and resins are firmly bonded by introducing molten resin through injection molding to metal parts which have already undergone sufficient surface treatment, and the resin then cools and solidifies. Since there are many influential factors in this process, all of the factors shown in figure 2-1 (metal parts, resin materials, metal mold structure, injection molding conditions, etc.) have to be optimized in order to produce a stable bond. Below are the points to keep in mind for each of these different factors.

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16th May 2018