Bonding TechnologyK＆K

  • HOME
  • Bonding Technology: K＆K

Polyplatics-Evonik’s adhesive technology

One of the advantage technologies in Polyplastics-Evonik is "adhesion".
By using bonding technology with multiple materials, you can achieve the following benefits:

  • Weight reduction of products
  • Improving the efficiency of the manufacturing process
  • Expansion of design flexibility

On this page, we will first introduce the advantages of adhesive bonding compared to mechanical bonding. After that, we will introduce some of Polyplastics-Evonik's bonding technologies.
The opposite of adhesive bonding, which our company specializes in, is mechanical joining using screws and bolts. The general advantages and disadvantages of mechanical and adhesive bonding are summarized in Table 1.

Table 1: Advantages and disadvantages of mechanical and adhesive bonding.
Figure 1: Difference in stress concentration at the joint between mechanical and adhesive joints

In Table 1, one of the characteristics of mechanical bonding is the stress concentration at the joint. A simplified example of this is shown in Figure 1. Adhesive bonds allow the substrate to be captured by a "plane", thus avoiding the stress concentration at the joint that appears in mechanical joints.

Case Study of Adhesive Technology 1: Direct Bonding Technology between Polyamide and Rubber

This technology is an adhesive technology that forms a cross-linked layer of plastic and rubber at the interface between plastic and rubber. There is no need for surface treatment before bonding, as is the case when using adhesives, or post-processing such as solvent drying after application, and if an appropriate cross-linking agent is selected, bonding is possible without being too concerned about the affinity between resin and rubber. It has already been used in automotive applications in Europe and in Japan for sealing materials for low-voltage electronics. The main reasons for adopting these are cost reduction through process simplification and improved component performance through direct bonding.
We applied this technology to polyamide films with low melting points, such as PA12 and PEBA, and launched a film called R-COMPO®, which is a composite of polyamide film and rubber (Fig. 2). R-COMPO® is used in the soles of sports shoes.
In addition to being lighter than rubber soles, R-COMPO® is characterized by a high grip.

Figure 2: Example of R-COMPO® = Composite sheet of Polyamide film and rubber

Case Study of Adhesive Technology 2: Direct Bonding Technology between Polyamide and TPU

A derivative of the bonding technology between polyamide and rubber is the bonding of polyamide-based resins to thermoplastic polyurethane elastomers (TPUs). Since it uses the reaction at the interface rather than the conventional bond with affinity, you can enjoy the following performance advantages.

  • High adhesive strength
  • Adhesive strength does not decrease even in high-temperature environments.

In addition, there are advantages in terms of application techniques, such as:

  • No need to use solvents such as primers
  • No need for complicated operations before gluing
  • Polyamide can be molded first, inserted, and TPU can be molded later.
Figure 3: Peel strength between TPU and PEBA (either conventional PEBA or Daiamid® E62K2).
Left: conventional PEBA. Right: Daiamid® E62K2

These features also lead to a high degree of freedom in application techniques. The degree of freedom in the application techniques also leads to the simplification of mold design, and the effect of cost reduction is also significant. In addition, it also increases the degree of freedom in design. For example, it is possible to make the shape of the studs of the shoe simpler.
The peel strength data is shown below. Figure 3 shows a comparison between conventional PEBA (polyamide elastomer) and our special PEBA, Daiamid® E62K2. Both materials have a Shore hardness of about 60D. The comparison focuses on the storage time and bond strength between TPU and PEBA (either conventional PEBA or Daiamid® E62K2). The upper two graphs are the data when the inserted material is TPU, and the bottom two are the data when the inserted material is PEBA, and both of the graphs on the right are for E62K2.
E62K2 outperforms conventional PEBA in insert molding processes, whether inserted material is TPU or PEBA. It consistently demonstrates stronger and more stable bond strength, regardless of storage time before insert-molded.