Common problems and solutions for the production of PET bottle preform
Common problems and solutions for the production of PET bottle preform
PET bottles are bottles containing a plastic material, called polyethyleneterephthalate, or PET for short, which is made of p-phenylene diene.
PET plastics are light, transparent, impact resistant and unbreakable.
PET bottles are used in a wide range of applications, from household goods to daily chemical packaging. From mould processing.The machines and equipment are extremely selective, easy to start with but difficult to perfect.
PET bottles are re-processed by blow moulding to form plastic bottles, including bottles for cosmetics, medicine, health care, beverages, mineral water, reagents, etc. This method of bottle making is called dipping.
The quality of PET bottles depends on the quality of the supplied preforms.
The common problems in the production of PET bottles, and the corresponding solutions according to many years of experience.
| Defects | Reasons | Exclusion methods |
| White bottom of PET bottle preform | 1. Insufficient hot runner temperature 2. Insufficient material temperature | 1. Enhanced insulation measures
2. Increase the temperature of the hot nozzle at this location 3. Raise the material temperature appropriately 4. Accelerated injection rate 5. Reduced holding pressure 6. Slow down the cooling water flow rate |
| Pet bottle preform are
opaque |
1. insufficient drying of raw materials 2. insufficient plasticisation of raw materials 3. excessive wall thickness or insufficient cooling of pp>bottles 4. mixing with other plastics 5. too low material temperature | 1 Ensure drying for at least four hours
2. Raising the material temperature 3. Increase screw speed 4. Check if the drying temperature of the material is too small or the injection volume does not match, you must ensure that the raw material is dried at 165 degrees until the moisture content is less than 0.02%. 5. Enhanced cooling, thinner wall thickness |
| PET bottle preform from
transparent to opaque |
De-filming temperature too high | 1. Enhanced cooling water
2. 2. Extended cooling time 3. Change of injection time |
| Foggy shadow on one side of the PET preform | 1. too high holding pressure 2. eccentric bottom film gate hole | 1. Reduced pressure 2. Corrected mould |
| pet bottle preform with
silvering or yellowing |
Plastic decomposition | 1. lower the drying temperature and extend the drying time 2. adjust the injection speed 3. lower the material temperature 4. lower the hot nozzle temperature |
| PET bottle preform with
air bubbles |
Insufficient drying | 1. Enhanced drying
2. Increase the material temperature 3. Reduced screw speed |
| Irregular ring grooves in PET bottle preform | Water vapour condensation in the core cavity | 1. Strengthening workshop drying
2. Increase the cooling water temperature 3. Dry the mould |
| PET preform pulling at
the spout |
1. hot runner gate and gate not centred 2. gate upside down 3. gate area too hot | 1. Correction moulds
2. Gating correction 3. Extended cooling time 4. Increase the injection rate or injection time 5. Reinforced sprues insulation |
| The mouth of the bottle
is not fully filled or has a dissolution pattern |
1. poor venting 2. eccentric injection | 1. Enlarge the exhaust tank
2. clean the lip mould 3. reduce the injection rate 4. Correction of the bottom mould sprue hole |
| PET bottle prefrom with
thick and pliable edges |
1. poor mould manufacture 2. off-set gate holes 3. high injection pressure 4. displaced cores | 1. Modification of the mould 2. Increase of the material temperature 3. Reduction of the pressure 4. Use of high strength and high precision moulds with adjustable core structure |
| Denting of the surface of the preform | 1. too high material temperature 2. too short injection rate 3. too short holding pressure 4. too short injection time 5. insufficient cooling | 1. lower the material temperature 2. lower the injection rate 3. increase the holding pressure 4. increase the injection time 5. increase the water pressure |
| Preform sprues drawing | 1. poor insulation 2. insufficient cooling 3. pressure in the heat flow 4. poor screw stop 5. too low holding pressure | 1. ensure insulation of the gate 2. increase cooling 3. strengthen the backing 4. clean the screw nozzle 5. increase pressure retention |
| Bending of the preform
after release |
1. eccentric gating hole 2. uneven cooling | 1. correct the mould 2. reduce the holding pressure 3. increase the injection rate 4. extend the cooling 5. clean the waterway 6. increase the cooling water pressure |
| Bending of the preform
after warming |
1. Eccentricity of the preform 2. Eccentricity of the thermoregulation hole or seat 3. Inconsistent density of the preform | 1. correction of the mould 2. correction of the thermoregulated positioning parts 3. reduction of the thermoregulation temperature, especially in the bending part |
| Partial whitening of PET blow bottles | Inadequate temperature regulation of the preform | Increased temperature and internal and external homogeneity of PET preforms |
| White after the bottle is warmed | Too high a temperature for the blanks in the whitening section | Guaranteed PET preforms at 80 to 110 degrees pp>blown bottles |
| PET bottles don’t blow up | 1. Insufficient air pressure 2. Insufficient temperature regulation of the bottle preform 3. Defective injection of the bottle preform | 1. Increase the air pressure 2. Increase the embryo temperature 2. Check the PET bottle embryo with 100 degree boiling water to see if it is softening evenly |
| Pulling through the
embryo bottom |
1. Embryo bottom temperature too high 2. Embryo body temperature too low 3. Severe plastic degradation | 1. adjusting the embryo temperature 2. replacing the embryo and the raw material in La Cha, and enhancing drying |
| Preform eccentricity | 1. Blowing too early
2. too high wind pressure 3. misalignment between the stretching bar and the bottom of the bottle 4. severe eccentricity of the bottle preform 5. too slow speed of the stretching bar 6. stretching bar more than 1.5 mm from the bottom mould 7. too high bottom temperature of the bottle preform |
1. slow down the delayed blowing time 2. reduce the air pressure 3. correct the installation state 4. check and correct the condition of the bottle 5. adjust the tensioning cylinder pressure 6. correct the end of the tensioning rod to the bottom die 1-1.5 mm 7. reduce the temperature of the lower end of the tempering |
| Bottle not blown full in the vertical direction | 1. dissatisfied with the temperature of part of the preform too high 2. dissatisfied with the cold block of part of the preform 3. insufficient air pressure and air volume 4. poor exhaust of the blowing mould 5. too high temperature of the blowing mould 6. too thin wall of the preform 7. insufficient longitudinal stretch ratio of the bottle | 1. adjust the temperature of the PET bottle embryo 2. do not touch the heated embryo, check whether the cold hard block has touched 3. increase the storage air pressure gas volume 4. increase the exhaust 5. add cooling water in the blowing mould 6. correct the mould 7. increase the stretching ratio (longitudinal) |
| Uneven wall thickness
around the circumference of the PET bottle |
1. eccentric bottle preform 2. uneven temperature regulation 3. poor venting | 1. improve the preform mould 2. improve the temperature control equipment 3. reduce the temperature of the defective part of the pet preform 4. increase the exhaust air |
| The bottle has a ‘crater’ shaped bulge at the
bottom |
The bottom of the bottle is too cold or the rest of the bottle is too hot | Earlier blowing time and adjustment of regulating temperature |
| Partial whitening of the bottle after blowing | 1. insufficient local temperature regulation 2. too large local stretch ratio 3. water in the compressed air | 1. increase the temperature of the preform 2. check the design of the preform 3. strengthen the water and oil filtration |
| Poor vertical load
carrying capacity of bottles |
1. uneven wall thickness 2. too high heating temperature of the preform 3. bad shape of the bottle | 1. improve the uniformity of the bottle wall thickness 2. try to form the bottle at low temperature and high pressure 3. improve the bottle design |
| Bottles are easy to break | 1. Bottom wall thickness not properly stretched 2. High temperature degradation of plastic | 1. improve the bottom stretch ratio 2. enhance the drying of the raw material before injection 3. reduce the production temperature |
| Pockmarked, white mist
inside the bottle |
1. incoming unclean air 2. high air humidity | 1. Installation of air filtration devices 2. Reduction in humidity of the air blown in |
| Bottle too soft | 1. Poor design
2. Processing temperature too high |
1. Improved design 2. Injection and blow moulding at low temperatures where possible |
| Burnt odour after blowing | 1. too high heating 2. poor compressed air 3. use of poor quality raw materials | 1. reduce blowing temperature 2. sort out compressors and filters 3. use regular materials |
| Water tastes bad for a
while after the bottle is filled |
1. high acetaldehyde content in the bottle 2. inappropriate ingredients | 1. use low temperature injection and blowing 2. check the acetaldehyde content of raw materials before processing to exclude poor quality raw materials |
PET bottle mold and injection molding process requirements
PET bottle mold is a kind of special mold in plastic molds,Mold in the design, processing, adjustment process has a lot of attention.
- The treatment of plastics
Because PET macromolecules contain lipid groups,With a certain degree of hydrophilicity,Granular materials are sensitive to water at high temperature,When the moisture content exceeds the limit,The molecular weight of PET decreased during processing,Products with color, brittle.Therefore, before processing,The material must be dried,The drying temperature is 150 °C,More than 4 hours,when 170 ° C for 3-4 hours.The air-jet method can be used to check whether the material is completely dry.The proportion of recycled PET preform should not exceed 25%,The recycled material should be dried thoroughly.
- Injection machine option
PET has a short stabilization time after melting point,And the melting point is higher,Therefore need to choose more temperature control section,plasticizing self-friction less heat of the injection system.And the actual weight of the product (containing water mouth material) can not be less than 2/3 of the inject weight.
- Mold and gate design
PET bottle preform, generally with hot runner mold molding,There should be a heat shield between the mould and the mould plate of the injection molding machine,thickness is about 12 mm,And the heat shield must be able to withstand high pressure,Exhaust must be sufficient to avoid local overheating or fragmentation,The depth of exhaust port should not exceed 0.03 mm, otherwise it is easy to produce flash.
- Melt temperature
Available air-launched measurements ranging from 275 ° C to 295 ° C,The enhanced grade GF-PET can be set to 295-315 ° C,
- Speed of injection
Generally the injection speed must be quick, may prevent when the injection is too early to solidify,But too fast, high shear rate, so that the material fragile,The injection is usually completed in 4 seconds.
- Back pressure
The lower the better to avoid wear and tear,Generally not more than 100 bar, usually do not need to use
- Retention time
Do not use prolonged retention time to prevent molecular weight loss,Avoid temperatures above 300 °C,If the machine is less than 15 minutes,Only air-blast treatment is required;If more than 15 minutes, then use viscosity PE cleaning,And the barrel temperature down to PE temperature, until the boot up.
- Notice points.
- recycling material can not be too big, otherwise, easy to produce in the next material“Bridge” and impact on plasticization;
- If the mold temperature control is not good, or material temperature control is not appropriate, easy to produce“Fog” and opaque;The mould temperature is low and uniform, the cooling speed is fast, the crystallization is few, then the product is transparent.
