What is PET blowing moulding?
PET is short for polyethylene terephthalate. PET blowing
mouldingmeans use PET material Injection molding or blow molding into the required products, It has the following characteristics:
- Excellent gas barrier
- Pressure and creep resistance
- Impact resistance
Transparent, shiny surface
- Food safety
- Easy to shape and beautiful
It has been widely used in various food containers.
PET bottle production process
- Direct blowing: The molten PET plastic is blown into the cavity and blown, and the common blow molding machine is blow molded in this way.
- Injection Molding and blowing: PET preforms are re-processed by blow molding to form plastic bottles, including bottles for cosmetics, medicine, health care, beverages, mineral water, reagents, etc. This bottle making method is called a two-step method, that is, forming preforms by injection molding, again Method for forming PET plastic bottle by blow molding
Injection molding is divided into two types: thermal type embryo method and cold type embryo method.
The hot type embryo method, also known as the one-step method, can be used only from one molding machine from the beginning of the preforming to the blow molding.
The preformed preform is cooled to a temperature lower than the crystallization temperature, but remains in a thermoelastic state. Blowing into a bottle.
The cold embryo type method, also known as the two-step method, is that after the pre-forming and the blow molding are respectively performed by different machines
The preforms are firstly formed by the injection molding machine, and the preforms are cooled to a solidification temperature, and are taken out and cooled to room temperature
When the bottle is to be blown, it is sent to the hollow molding machine to heat the preform to the blowing temperature, and then blown and cooled.
The origin of PET preforms
PET materials were first used in eye drops in Japan in 1975.
PET materials have been developed for more than 35 years, and their application has been widely used in canned containers around the world.
Such as mineral water, tea drinks, sodas. Containers such as edible oils, cosmetics, detergents, and candy can, and have widely replaced containers such as PVC bottles or glass bottles.
Advantages of PET preforms
Because PET (polyethylene terephthalate) has good mechanical properties, heat-resistant filling and re-use, it is widely used:
- PET plastics are light in weight, high in transparency, resistant to impact and easy to break. They also prevent carbon dioxide gas and keep the soda air.
- Good mechanical properties: including gas barrier, transparency, gloss, impact resistance, toughness, light weight, chemical resistance, and easy processing.
- Heat-resistant filling: PET can be filled at 70~90 °C, and it also increases gas barrier
- Reusable: In 1984, the Continental Can Company requested Coca-Cola to develop PET containers by replacing glass bottles with PET. The life of PET can be reused 20 times. Nowadays, PET is recycled and then woven into silk to make other kinds of products, such as clothing, bag, etc.
Characteristics of PET materials
PET is a hygroscopic material.
If the water content is too high, hydrolysis will occur under high-temperature processing, and the PET molecular chain will be broken and thermally decomposed to produce acetaldehyde.
The physical and mechanical properties will be reduced, the crystallization rate will be increased, and the bottle will be produced when the preform is injected.
The part of the embryo is crystallized and white, which affects the quality of the product.
Before the preform is injection molded, the PET pellets must be dried to a moisture content of 0.005% or less, in order to produce a good amorphous transparent preform.
The dew point temperature must be between -29 ° C (-200 ° F) and -40 ° C (-400 ° F). The temperature of the dryer is set between 177 degrees and 182 degrees and dried for about four hours.
PET bottle production equipment
In the whole preform processing equipment, in addition to the injection molding machine, other interface equipment is required.
Such as hot runner mold, plastic dryer, mold chiller, perform removal robot, perform conveyor belt and injection environment control air conditioner dehumidifier Etc.
These interface devices are all in line with the action of the injection machine, so the injection molding machine is the most important role in the production of preforms.
China’s plastic injection molding machine manufacturing industry has developed PET special machines for PET manufacturers to use the products produced in the bottle, from:
- 350cc to 2000cc (bottle mouth diameter 28~30mm)
- The cavity number from 16~48 points
- 5000cc (bottle The caliber is 48mm)
- The number of cavities is from 4 to 16 cavities
- The wide-mouth bottle (bottle opening is 63, 90, 120 mm)
- The number of cavities is from 4 to 8 cavities.
PET preform cooling method
The cooling mode of the preform can be divided into two modes:
- in-mold cooling
- external cooling
The main difference is that the cooling time can be used when the cooling time is shorter or the same, and the cooling time is longer or shorter than the feeding time.
Throughout the molding cycle time, the mold can be cooled after the pressure is maintained to shorten the cycle time.
The development trend of PET molding
Due to its light weight and good preservation, the technical trend of emphasizing heat resistance and pressure resistance has made PET bottles the mainstream of today’s drinking packaging.
PET bottles have become the mainstay of packaging materials for drinking products.
Due to its low environmental pollution and energy consumption
PET bottles have gradually replaced traditional packaging materials in today’s environmental awareness.
With its functions of heat resistance and pressure resistance, it has recently replaced various PVC bottles, bags, aluminum cans, iron cans, glass bottles, etc., and has become the packaging material with the most growth potential.