Three Influencing Factors of Weak Adhesion of TPE Package
Source：德创化工Time：2020-06-07Hits：2163
Plastic wrapping can be said to be common and ubiquitous in the current plastic product processing and manufacturing industry. Toothbrushes, shower heads, screwdriver handles and so on in daily life are all typical cases of plastic encapsulation. Although the plastic coating process has been very mature in the industry, it is not uncommon for some users who have little contact with TPE coating materials to suffer from the problem that TPE plastic coating is not firm during the preliminary mold opening and testing process. The author makes a brief analysis here, hoping to be helpful to everyone.
Analysis of Influencing Factors of Unsecured Package
I didn't find the right factor
Cause Analysis of the Problem: Some users have just come into contact with a new TPE-coated product, have not used TPE before, and have not learned about the TPE materials through the Internet or other channels, so they directly take any TPE materials from their acquaintances (usually some plastic traders who are not very professional in TPE materials). It turned out that it could not be wrapped up.
Suggestion: For first contact with TPE rubber-coated materials, it is better to make preliminary technical consultation with TPE manufacturers with production and research strength.
Knowledge popularization:
1 Simple Analysis on Difficulty of Plastic Coating
Commonly used plastics include ABS,PP,PC,PA, PS,POM, etc. Each kind of plastic basically has the corresponding brand of TPE coating material. Relatively speaking, PP is best coated. PS, ABS, PC, PC+ABS, PE plastic encapsulation followed, but the encapsulation technology is also very mature, it is not difficult to achieve a firm encapsulation; Nylon PA is more difficult to encapsulate, but in recent years great progress has been made in technology. TPE-coated nylon is no longer the patent of imported TPE manufacturers, and at least several TPE manufacturers in China can provide TPE brand of firmly-coated nylon; As for the encapsulation of polyoxymethylene (POM steel), it is still a difficult problem in the industry. At present, the imported German rubber treasure TCXH series can be encapsulated. Home-made Guangdong jiejia, TSE-ADM series can achieve good coating.
2. The hardness range of TPE coated by main plastics
PP encapsulation: hardness range 10~95A;
ABS, PC, PC+ABS Encapsulation: Hardness Range 30~90A;
PS encapsulation: hardness range 20-95A;
Nylon PA Encapsulation: Hardness Range 40~80A;
POM (polyoxymethylene steel) encapsulation: hardness range TCXH series 50~80A,TSE-ADM series 60~85A.
Factor 2: Mold and Product Structure
A product structure-coating thickness and area
The greater the product coating thickness and area, the longer the TPE flow in the mold cavity to complete the coating, but the longer the time, the greater the temperature drop of the rubber during the flow in the mold cavity, and the lower the temperature is not conducive to the adhesive bonding.
B product structure-flow length ratio
The greater the flow length ratio, the more difficult it is to encapsulate. For general overmolding die design, it is recommended that the flow length ratio be below 1:150. For example, the coating thickness is 0.5mm, and the maximum coating length (flow direction) of the coating is recommended to be below 75 mm. The larger the ratio of coating flow length, the higher the requirements on the fluidity and melt strength of TPE materials.
Die Design-Runner and Gate Design
For some products with large encapsulation area or flow length, the design of flow interface size, gate location and number should be considered. The core of the TPE coating process is: coating while it is hot, so some designs should be conducive to the rapid completion of TPE coating.
Mold Design-Hot Runner
For complex product coating structure, if conditions permit, hot runner mold will be used to realize hot coating, thus obtaining better coating effect.
Factor 3: overmolding process
A forming temperature
The overmolding temperature is low, and TPE cannot form a cladding interface erosion layer with the plastic to be clad. If the material selection is no problem and the encapsulation effect is not good, an appropriate increase in the overmolding temperature can be tried.
For general PP coating, it is recommended that the overmolding temperature be 180 ~ 250℃.
Including ABS,PC,PC+ABS, the recommended coating temperature is 180~230℃. The temperature of PC is higher than that of ABS.
The molding temperature of nylon is 210~280℃, PA66 is higher than PA6D, and the coating temperature of nylon with fiber and good heat resistance is higher. For nylon encapsulation, the corresponding TPE brand should be matched according to the temperature resistance of nylon.
For POM,TSE-ADM series, the recommended coating temperature given by supplier Jie Jia company is 175~195℃.
The specific molding temperature should be adjusted appropriately according to different products and mold structures. In addition, different injection molding machine models should also choose and adjust the appropriate molding temperature.
B TPE baking material
For the encapsulation of ABS, PC, PC+ABS, PA and other plastics, we suggest to bake TPE before overmolding. Drying time is 2 hours, drying temperature is 60~80℃ (TPE with high hardness, higher drying temperature is recommended).
C plastic parts baking
For secondary injection molding of nylon parts by common injection molding machine, it is recommended to preheat and bake nylon parts before coating. Nylon material has strong water absorption and high molding temperature is required for overmolding. Preheating before coating can remove moisture, which is conducive to rapid hot coating.
D mode temperature control
The mold temperature for overmolding is generally controlled at 30~50℃, but for some TPE brands with stronger crystallinity, the mold temperature can be appropriately raised at 60~70℃, which is favorable for bonding and can obtain a more glossy coated surface.
Analysis on the Causes of Covering Other Common Problems
1. Peel the glue inlet layer by layer
The problem of material A (improving TPE compatibility);
B injection speed is fast and pressure is high (reduce injection speed and pressure appropriately)
C gate is too small (appropriately increase the gate size)
2. The encapsulation is not good for demoulding.
A. material issues-
Countermeasures: Change TPE Material
B. mold is too smooth-
Countermeasures: Drying Patterns on Mould
3. The surface of the encapsulated product is white-haired and sticky.
Precipitation of Small Molecular Additives in TPE Compounding Agent
Countermeasures: Pay attention to the addition of additives
4 deformation of hard plastic parts
A the hard plastic parts are thin, the temperature is high during the secondary injection molding, softening and deforming;
B the thickness of soft rubber coating is relatively large, and the shrinkage causes the hard plastic part to be pulled and deformed.
Countermeasures: Adopt lower injection temperature, reduce injection speed, properly strengthen pressure keeping, and make the mold into reinforcement structure when necessary.
