Analysis of PET Injection Molding in Cosmetic Packaging

01 PET material characteristics

PET raw material is a milky white or light yellow highly crystalline polymer with smooth and glossy surface. PET raw material has creep resistance, fatigue resistance, abrasion resistance, good dimensional stability, small abrasion and high hardness. It has the largest toughness among thermoplastics. It has good electrical insulation performance, little affected by temperature, but poor corona resistance. It’s non-toxic, weather resistant, has good chemical stability, low water absorption rate, resistant to weak acids and organic solvents, but not resistant to heat and water immersion, not resistant to alkali. Therefore, it is widely used in the packaging of beauty and cosmetic industries.

 

02 Mould characteristics

1. According to the project volume, the number of cavities of the bottle embryo mold ranges from one out of one to one out of ninety-six. The mold plate uses pre-hardening processed P20 steel. The core, cavity and screws are made of S136H high strength and corrosion resistant stainless steel. The mold plate is finished by one machining to ensure the concentricity of the molding hole and guide bush and to ensure the compact structure of the mold.
2. Exclusive spiral cooling water tank design for every single core and cavity helps to shorten cycle time, improve productivity and save cost. The opening and closing plates are of bearing sliding type, giving the preforms a reliable structure, a highly integrated slider, push plate and ejector process. All sliding parts are surface inlaid with self-lubricating copper alloy to ensure low friction efficiency and strong wear resistance.
3. Each cavity is individually self-locking to ensure high precision, reduce defects and also facilitate disassembly.
4. Hot runner system: heating temperature is uniform, it can prevent white defects of bottle embryos and improve the quality of plastic products.

 

03 Mold design points

The cooling system is especially important when the mold is designed. The injection molding cycle of the product is shortened, which greatly improves the efficiency of the product, the size and surface effect of the plastic mold are more stable, and the quality of the product is improved. The main points of water transportation design:

1、Water transportation in the front mold of the bottle embryo mold, as shown in the following figure.

①bottle blast mold gate use cooling water jacket independent cooling, cavity use spiral cooling to provide good mold temperature control. ②the import and export of each cooling water channel need to be connected separately, not in series with each other, so as not to reduce the cooling series of the mold.

2、Water transportation for the mold core of the bottle blast mold, as shown in the following figure.

①Bottle blast mold core adopts water transportation needle. ②Water runs from the mouth to the top of the spray well way as cooling cycle. Uniform cooling method can make the product cool down quickly and improve the production efficiency and quality of the product.

 

04 Preform injection molding

1、Pre-treatment of the original plastic  When the water content exceeds the limit, the molecular weight of PET will drop during processing, and the products will become colorful and brittle. In this case, the material must be dried before processing, and the drying temperature is 150℃ for more than 4 hours, usually 170℃ for 3-4 hours. Available air injection method can tests whether the material is completely dry.

2、Cautions ①The recovery material can not be too large, otherwise it is easy to occur a “bridge” in the material injection place and affect the plasticization. ②If the mold temperature control is not good or material temperature control is not appropriate, easy to occur “white mist” and the product will not be transparent. With low and uniform mold temperature, fast cooling speed, less crystallization, then the finished product is bright.

 

05 Stretch blowing bottle

1、Two-step blowing method, the heating of the bottle embryo is done by the heating oven, its temperature is automatically adjusted by manual setting, the oven is heated by the lamp to the bottle embryo, the bottle embryo in the oven forward movement at the same time self-rotation, so that the bottle embryo is heated evenly.

2、The heat in the oven is controlled by the opening number of lamps, the overall temperature setting, the power of the drying environment and the heating ratio of each section together, and the temperature adjustment should be adjusted in combination with the pre-blown effect bottles.

3、After finishing the heating of the bottle embryo, it is transported to the blow molding mold by the drive system of the blow molding machine for the blow molding process.

4、During the blow molding process, the mold is kept in a cool state. When the blow molding is set then to the transmission system drive to the packaging table to complete the packaging process.

 

06 The progress and state of environmental protection material application

1、Nowadays environmental protection is being paid more and more attention to, marine recycling material R-PET (PCR) has been used in large quantities, from trace addition to 100% application. R-PET (PCR) material testing and production have already formed a mature technical system.

2, PLA from corn starch has also been tested and produced in multiple batches, because of the high cost, the current overall volume is not large for the time being.