Hardware package adhesive has the distinction between true package and false package. True encapsulation is to use the compatibility of soft glue and hard glue in softening and melting to form a layer of bonding layer on the interface between hard glue and soft glue, which greatly improves the bonding between TPE soft glue and hard plastic. False encapsulation hardly involves the compatibility of two kinds of materials. The encapsulation of materials is through mechanical force, through the design of dies and products and surface treatment, through the hoop effect, the soft glue and hard glue can be joined together.
Processing Technology of Hardware Package Adhesive Injection
Hardware package adhesive injection generally adopts secondary injection molding process, which fixes the hard plastic parts that have beer on the plastic package mould, and then injects TPE soft rubber into the hard rubber parts at the appropriate temperature, and then gets the products by cooling. The injection temperature of the adhesive-coated injection depends on the hard rubber material. Because the temperature should take into account that hard rubber and TPE soft rubber should be softened, in order to promote the two materials to achieve a certain compatibility at the contact surface. In order to achieve the effect of true encapsulation, usually the injection temperature of hardware encapsulated PP material is about 170-190 degrees Celsius; encapsulated ABS material is about 220-220 degrees Celsius; encapsulated PC material is slightly higher than that of encapsulated ABS; encapsulated PA nylon, the injection temperature is about 240 degrees Celsius.
Common metal package adhesive materials
TPE is used in adhesive-coated injection bonding. TPE soft rubber is used as the outer layer of soft rubber. The common hard materials are plastics, metals and fabrics. TPE and woven fabric jet bonding are mainly used in luggage products. Like metal bonding, TPE and woven fabric jet bonding are generally false bonding. True-encapsulated adhesives are commonly used in secondary and double-color injection moulding, that is, the main material of metal-encapsulated adhesives is plastic. TPE can adhere firmly to some common plastics such as PP, GPPS, HIPS, ABS and engineering plastics such as PC, PC/ABS, PA and their modified materials. The adhesion between TPE and POM polyformaldehyde is still a difficult problem in the elastomer industry. Because the solubility parameter SP (22.6) of POM is far different from that of TPE (7.2-7.6), the two materials are not compatible. At present, there is no suitable compatibilizer to promote the good adhesion between them in China.
Problems needing attention in adhesive injection moulding of hardware packages
1. The compatibility of TPE and hard gel structures should be matched, and the molecular solubility is close, so the molecular compatibility is better.
2. In order to ensure good contact between TPE and hard rubber parts and improve bonding effect, sharp corners should be avoided as far as possible in design.
3. To avoid the gas in the mould cavity by proper exhaust;
4. Keep the temperature of TPE melt to ensure the bonding effect.
5. Balance the thickness of TPE with the expected tactile sensation.
6. The TPE coating process needs to be baked to reduce the surface watermarks and achieve uniform surface color.
7. The carrier resin of the selected masterbatch is compatible with TPE and structural materials.
8. Special treatment should be given to smooth surfaces, with the aim of increasing the bonding contact surface between soft and hard adhesives and enhancing the bonding effect.
9. TPE should have good fluidity. Because the thickness-to-size ratio of metal cladding layer is very small, TPE usually needs to flow through a long path and thin-walled area to fill the die.
10. The flow length/product thickness ratio of TPE is less than 150:1.
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