Transparent plastic must have high transparency, certain strength and wear resistance, impact resistance, better heat resistance, better chemical resistance, and lower water absorption. Only in this way can it meet the requirements of transparency in use and remain unchanged for a long time. , the commonly used transparent plastics are:

1. Polymethyl methacrylate (commonly known as acrylic or plexiglass, codenamed PMMA),

2. Polycarbonate (code name PC),

3. Polyethylene terephthalate (code-named PET),

4. Transparent nylon, ABS

5.AS (acrylonitrile-styrene copolymer),

6. Polysulfone (code PSF)

1) Performance comparison

Transparent plastic must have high transparency, certain strength and wear resistance, impact resistance, better heat resistance, better chemical resistance, and lower water absorption. Only in this way can it meet the requirements of transparency in use and remain unchanged for a long time. , the commonly used transparent plastics are:

1. Polymethyl methacrylate (commonly known as acrylic or plexiglass, codenamed PMMA),

2. Polycarbonate (code name PC),

3. Polyethylene terephthalate (code-named PET),

4. Transparent nylon, ABS

5.AS (acrylonitrile-styrene copolymer),

6. Polysulfone (code PSF)

1) Performance comparison

Material\Properties

Transparency J/m2

Hot shape temperature °C

Shrinkage

PMMA

92 95 0.5
PC

90 137 0.6
PET

86 120 2
The products generally required are still mainly made of PMMA, while PET is mostly used in packaging and containers because it needs to be stretched to obtain good mechanical properties.

2) Process characteristics during injection molding

i. Process characteristics of PMMA

PMMA has high viscosity and poor fluidity, so it must be injected with high material temperature and high injection pressure. The influence of injection temperature is greater than that of injection pressure, but the increase of injection pressure is conducive to improving the shrinkage rate of the product. The injection temperature range is wide, the melting temperature is 160 ° C, and the decomposition temperature is 270 ° C, so the material temperature adjustment range is wide, and the processability is good. Therefore, to improve the fluidity, the injection temperature can be started. Poor impact resistance, poor wear resistance, easy to scratch, easy to brittle, so the mold temperature should be increased to improve the condensation process to overcome these defects.

ii. Process characteristics of PC

PC has high viscosity, high melting temperature and poor fluidity. In this case, it must be injected at a higher temperature (between 270-320T). Relatively speaking, the material temperature adjustment range is narrow, and the processability is not as good as PMMA. The injection pressure has little effect on the fluidity, but due to the high viscosity, the injection pressure is still large. Correspondingly, in order to prevent the internal stress, the pressure holding time should be as short as possible. The shrinkage rate is large and the size is stable, but the internal stress of the product is large and it is easy to crack. Therefore, it is advisable to increase the temperature instead of the pressure to improve the fluidity, and to increase the mold temperature, improve the mold structure and post-treatment to reduce the possibility of cracking. When the injection speed is low, the gate is prone to corrugation and other defects. The temperature of the radiation nozzle should be con trolled separately, the mold temperature should be high, and the resistance of the runner and gate should be small.

iii. Process characteristics of PET

The PET molding temperature is high, and the material temperature adjustment range is narrow (260-300 ° C), but after melting, the fluidity is good, so the processability is poor, and an anti-spreading device is often added to the nozzle . The mechanical strength and performance are not high after injection, and the performance must be improved by stretching and modification. The mold temperature is accurately controlled to prevent warping. Deformation is an important factor, so it is recommended to use a hot runner mold. The mold temperature is high, otherwise it will cause poor surface gloss and difficult demolding.

3) Defects and solutions of transparent plastic parts

i. Silver streak: Influenced by the anisotropy of internal stress during the filling and condensation process, the stress generated in the vertical direction causes the resin to be oriented on the flow, and the refractive index of the resin is different from the non-flow orientation, resulting in shiny silk streaks. After expansion, cracks may appear in the product. In addition to paying attention to the injection molding process and mold, it is best to anneal the product. For example, the PC material can be heated to above 160 °C for 3-5 minutes, and then cooled naturally.

ii. Bubbles: "vacuum bubbles" are formed due to the condensation of the condensation surface too fast due to the inability of the water vapor and other gases in the resin to be discharged, or due to insufficient mold filling.

iii. Poor surface gloss: Mainly due to the large roughness of the mold, on the other hand, the premature condensation makes the resin unable to copy the state of the mold surface, all of which make the surface uneven and make the product lose its luster.

iv. Vibration pattern: refers to the dens

e corrugations formed from the sprue as the center. The reason is that the melt viscosity is too large, the front end material has been condensed in the cavity, and then the material breaks through the condensation surface, resulting in the appearance of vibration pattern on the surface.

v. Whitening, halo: mainly caused by dust falling into the raw material in the air or the water content of the raw material is too large.

vi. White smoke, black spots: mainly due to the decomposition or deterioration of the resin in the barrel due to local overheating of the plastic in the barrel

Specific selection of transparent plastics

1. Daily transparent materials:

1. Transparent films: PE PP PS PVC and PET for packaging, PE PVC and PET for agricultural use;

2. Transparent sheet: use PP PVC PET PMMA and PC, etc.;

3. Transparent pipes: PVC PA, etc.

4. Transparent bottles: use PVC PET PP PS and PC, etc.

2. Lighting equipment materials:

Mainly used as lampshade, commonly used PS modified PS AS PMMA and PC, etc.

3. Optical instrument materials

1. The hard lens body mainly uses CR-39 and J.D.

2. HEMA is commonly used in contact lenses

4. Glass materials

1. Two kinds of traffic glass are commonly used: PMMA and PC

2. PVF and PET are commonly used in architectural glass.

5. Solar materials: commonly used PMMA PC GF-UP FEP PVF and SI, etc.

6. Optical fiber material: PMMA or PC for the core layer, fluorine-containing olefin polymer for the cladding layer, fluorine-containing methyl methacrylate

7. Disc material: commonly used PC PMMA

8. Transparent packaging materials

Surface hardened PMMA FEP EVA EMA PVB etc.

The products generally required are still mainly made of PMMA, while PET is mostly used in packaging and containers because it needs to be stretched to obtain good mechanical properties.

2) Process characteristics during injection molding

i. Process characteristics of PMMA

PMMA has high viscosity and poor fluidity, so it must be injected with high material temperature and high injection pressure. The influence of injection temperature is greater than that of injection pressure, but the increase of injection pressure is conducive to improving the shrinkage rate of the product. The injection temperature range is wide, the melting temperature is 160 ° C, and the decomposition temperature is 270 ° C, so the material temperature adjustment range is wide, and the processability is good. Therefore, to improve the fluidity, the injection temperature can be started. Poor impact resistance, poor wear resistance, easy to scratch, easy to brittle, so the mold temperature should be increased to improve the condensation process to overcome these defects.

ii. Process characteristics of PC

PC has high viscosity, high melting temperature and poor fluidity. In this case, it must be injected at a higher temperature (between 270-320T). Relatively speaking, the material temperature adjustment range is narrow, and the processability is not as good as PMMA. The injection pressure has little effect on the fluidity, but due to the high viscosity, the injection pressure is still large. Correspondingly, in order to prevent the internal stress, the pressure holding time should be as short as possible. The shrinkage rate is large and the size is stable, but the internal stress of the product is large and it is easy to crack. Therefore, it is advisable to increase the temperature instead of the pressure to improve the fluidity, and to increase the mold temperature, improve the mold structure and post-treatment to reduce the possibility of cracking. When the injection speed is low, the gate is prone to corrugation and other defects. The temperature of the radiation nozzle should be controlled separately, the mold temperature should be high, and the resistance of the runner and gate should be small.

iii. Process characteristics of PET

The PET molding temperature is high, and the material temperature adjustment range is narrow (260-300 ° C), but after melting, the fluidity is good, so the processability is poor, and an anti-spreading device is often added to the nozzle. The mechanical strength and performance are not high after injection, and the performance must be improved by stretching and modification. The mold temperature is accurately controlled to prevent warping. Deformation is an important factor, so it is recommended to use a hot runner mold. The mold temperature is high, otherwise it will cause poor surface gloss and difficult demolding.

3) Defects and solutions of transparent plastic parts

i. Silver streak: Influenced by the anisotropy of internal stress during the filling and condensation process, the stress generated in the vertical direction causes the resin to be oriented on the flow, and the refractive index of the resin is different from the non-flow orientation, resulting in shiny silk streaks. After expansion, cracks may appear in the product. In addition to paying attention to the injection molding process and mold, it is best to anneal the product. For example, the PC material can be heated to above 160 °C for 3-5 minutes, and then cooled naturally.

ii. Bubbles: "vacuum bubbles" are formed due to the condensation of the condensation surface too fast due to the inability of the water vapor and other gases in the resin to be discharged, or due to insufficient mold filling.

iii. Poor surface gloss: Mainly due to the large roughness of the mold, on the other hand, the premature condensation makes the resin unable to copy the state of the mold surface, all of which make the surface uneven and make the product lose its luster.

iv. Vibration pattern: refers to the dense corrugations formed from the sprue as the center. The reason is that the melt viscosity is too large, the front end material has been condensed in the cavity, and then the material breaks through the condensation surface, resulting in the appearance of vibration pattern on the surface.

v. Whitening, halo: mainly caused by dust falling into the raw material in the air or the water content of the raw material is too large.

vi. White smoke, black spots: mainly due to the decomposition or deterioration of the resin in the barrel due to local overheating of the plastic in the barrel

Specific selection of transparent plastics

1. Daily transparent materials:

1. Transparent films: PE PP PS PVC and PET for packaging, PE PVC and PET for agricultural use;

2. Transparent sheet: use PP PVC PET PMMA and PC, etc.;

3. Transparent pipes: PVC PA, etc.

4. Transparent bottles: use PVC PET PP PS and PC, etc.

2. Lighting equipment materials:

Mainly used as lampshade, commonly used PS modified PS AS PMMA and PC, etc.

3. Optical instrument materials

1. The hard lens body mainly uses CR-39 and J.D.

2. HEMA is commonly used in contact lenses

4. Glass materials

1. Two kinds of traffic glass are commonly used: PMMA and PC

2. PVF and PET are commonly used in architectural glass.

5. Solar materials: commonly used PMMA PC GF-UP FEP PVF and SI, etc.

6. Optical fiber material: PMMA or PC for the core layer, fluorine-containing olefin polymer for the cladding layer, fluorine-containing methyl methacrylate

7. Disc material: commonly used PC PMMA

8. Transparent packaging materials

Surface hardened PMMA FEP EVA EMA PVB etc.