China Plastic Molding


Transparent Plastic Part Injection Molding

In modern industry and daily life, Chinese people prefer to use transparent plastic parts instead of glass for optical instruments and packaging usage. But since for those areas, the material should be of high transparency, good impact and abrasion resistance, thus we need to pay much attention to the selection and design of plastic components, molding technique, facility, mould etc.

Sino Moldings Co., Ltd is one of the most professional companies for transparent plastic parts injection molding in China. With about20 years’ experience in the plastic mould industry, Sino Moldings Co. always keep on continuous research and development for different transparent plastic part molding solutions. We have special design for transparent part molding, and the steel is also different to work out the transparent parts with high-quality surface. Apart from that, because of the material difference, we need to adopt different way in each step. Following is our general conclusion for the property and molding technology for the four main transparent plastic materials.

PS Transparent Molding

1. PS transparent molding property

• PS has low water absorption rate of 0.02%~0.03%, thus not necessary for material drying before production
• PS is good for flow ability which can mold complex plastic parts; meanwhile it will cause flash easily.
• De-molding angle for PS parts should be designed more than 2 °to make sure the ejection force is even to avoid the part broken and deformed during ejection.
• PS is of low shrinkage rate 0.2%~0.8% for molding the plastic products of high precision
• PS has high inner stress, so better to offer heat treatment after de-moulding. And also because of the high inner stress and fragility, it is not a good choice to do the inserts over moulding unless the inserts are preheated.
• Quick cooling, so no need for long holding time after injection.

2. PS transparent molding condition

• Barrel temperature: 140~260℃,nozzle temperature:170~190℃
• Mould temperature: mould temperature should be even with a tolerance of below 3~6℃, and the mould temperature can be controlled between 40~60℃
• Injection pressure: 30~120Mpa. A suitable injection pressure can reduce the inner stress and the fragility for easier de-moulding.

PC Transparent Molding

1. PC transparent molding property

• PC has low water absorption rate, but it will degrade even with small percentage of water. So the PC material should be dried before production if the material contains more than 0.2% water.
• PC has bad flow ability, and the flow rate is greatly affected by the temperature change. In addition, the cooling speed is very fast.
• PC plastic parts should be with even thickness and avoid too much inner stress caused by sharp edge, gap and metal inserts. And the metal inserts should be preheated to 110~130℃。
• PC melt will stick to metal easily, so after the production, the barrel and nozzle should be cleaned carefully.
• PC has high inner stress, so it should be with strict molding condition, and heat treatment is necessary after remolding.
• Heating device is required in the loader part for PC products production to make sure the material temperate is over 100℃
• PC melt is not corrosive to the steel, so the mould can be without chrome, but the mould should be with enough strength intensity and abrasive resistance.

2. PC transparent molding condition

• Barrel temperature: 230~310℃. The barrel temperature will greatly affect the PC transparent parts quality and the molding result.
• Mould temperature: normally, the temperature can be between 80~120℃。 And for thinwall part, the temperature is better around 80~100℃while 100~120℃for thicker parts. If it rises over 120℃, the parts cool slow, easy deformation and difficult for remolding.
• Injection pressure: 70~140Mpa.

PET Transparent Molding

1. PET transparent molding property

• PET has high water absorption rate, the material must be dried before production
• PET shrinkage rate: 1.8%
• PET parts should be heated after molding to remove the inner stress.
• PET part moulding can be with less than 20% recycled PET material which should also be dried.
• PET material has the obvious melting point of 270~290℃, the material will degrade if the temperature is over 300℃.
• Since PET melt cools fast, so the injection should be high speed to fill the cavity soon quickly.
• PET melt has very good flow ability, pin point gate and submarine gate are available for PET parts.

2. PET transparent molding condition
• Barrel temperature: 240~280℃. The barrel temperature will greatly affect the PET transparent parts performance, quality and the molding result.
• Mould temperature: 100~140℃。
• Injection pressure: 80~140Mpa.

PMMA Transparent Molding

1. PMMA transparent molding property

• PMMA has high water absorption rate of 0.3~0.4%, the material must be dried for 4~5 hours under 80~85℃before production.
• PMMA has high stickiness and quick cooling rate, the parts need to be treated after moulding.
• Low shrinkage rate: 0.5~0.8%, it can keep the parts with high precision.
• Bad flow ability, big size injection gate is required for PMMA molding.
• By increasing the molding stress and material temperature, the PMMA melt stickiness will be reduced to get better melt material flow.

2. PMMA transparent molding condition

• Barrel temperature: 180~230℃.
• Mould temperature: 40~80℃。
• Injection pressure: 80~120Mpa. Holding pressure: 40~60Mpa.


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