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 PC+GF is popular material in plastic molded products, and there are some issues to be clarified with the transparent PC+GF, hope we can help you with that.

Transparent PC + GF products have high light transmittance, so it has high requirements on the surface. There are not any defects such as streaks, stomata, whitening, haze, black spots, discoloration, poor gloss, etc. Therefore, we must pay great attention to and put forward strict and special requirements on the design of raw materials and products.

In addition, the PC + GF mostly have high melting points and poor fluidity, we required higher temperatures in order to ensure the surface quality. The process parameters such as injection pressure and speed must also be fine-tuned to fill the mold, but will not produce internal stress and cause deformation and cracking.

Therefore, strict operations are required from the raw material preparation, mold requirements to injection molding process and raw material processing.

1. Preparation and drying of raw materials

Since any impurities contained in PC + GF plastic may affect the transparency of the product.It is necessary to pay attention to sealing during storage, transportation and feeding to ensure raw materials cleaness.

If the raw material contains moisture, which will cause deterioration after heating, so it must be dried. The feeding must use a dry hopper while injection molding. The input air should preferably be filtered and dehumidified to ensure that it will not contaminate during the drying process.

2. Cleaning of barrel, screw and accessories

In order to prevent contaminating PC + GF and old materials or impurities in the recess of the screw and accessories, especially in the resin with poor thermal stability, the screw cleaning agent should be used to clean each piece before use and after shutdown. Impurities are sticky. When no screw cleaning agent is available, we can use PE and PS to clean the screw.

When temporarily stopping, in order to prevent the raw materials from staying at high temperature for too long and causing degradation, the temperature of the dryer and the barrel should be reduced. For example, the barrel temperature of PC + GF, PMMA, etc. must be lowered below 160 ° C (hopper temperature For PC it should be reduced below 100 ° C).

3. Problems to be noticed in mold design

In order to prevent poor flow of raw materials or uneven cooling caused by poor plastic molding, resulting in surface defects and deterioration, generally the following points should be noted when designing the mold:

The wall thickness should be as uniform as possible, and the draft angle should be large enough;

The transition part should be smooth and gradually transition to prevent sharp corners and sharp edges, especially PC + GF products must not have gaps;

The gate and runner should be as wide and stubby as possible, and the position of the gate should be set according to the contraction and condensation process, and a cold material well should be added if necessary;

The surface of the mold should be smooth and low in roughness (preferably less than 0.8);

The exhaust holes and grooves must be sufficient to timely discharge air and gases from the melt; except for PET, the wall thickness should not be too thin, generally it should not be less than 1 mm.

4. Problems to be noticed in injection processing

In order to reduce internal stress and surface quality defects, the following issues should be noted in the injection molding process:

Injection pressure: Generally higher to overcome the defect of high melt viscosity, but too high pressure will cause internal stress and cause difficulty in demolding and deformation;

Injection speed: In the case of filling the mold, generally it should be low, it is best to use slow-fast-slow multi-stage injection.

Holding time and molding cycle: in the case of filling the product without dents or bubbles; it should be as short as possible to minimize the time that the melt stays in the barrel;

Screw speed and back pressure: under the premise of meeting the plasticization quality, it should be as low as possible to prevent the possibility of degradation;

Mold temperature: The cooling of the product has a great impact on the quality, so the mold temperature must be able to accurately control the process. If possible, the mold temperature should be higher.

5. Other problems

In order to prevent the deterioration, mold release agents should be used as little as possible. It should not be greater than 20% when using regrind.

Products should be post-processed to eliminate internal stress. PMMA should be dried in hot air circulation at 70-8 0t for 4 hours; PC should be heated in clean air, glycerin or liquid paraffin at 110-135 ° C. The time depends on the products, up to 10 hours.

 

If you want to make a high-quality plastic mold with good material or know more knowledge about precision mold,

You are welcome to contact by wfcxm1028@vip.163.com

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