how to make a plastic bottle

- Sep 18, 2020-

 

The development status of plastic water cups
Plastic water cups have changed from disposable water cups to today's green plastic cups. All kinds of plastic cups appear in our lives. Various plastic cups have appeared in our lives. During this period, the shape of plastic water cups has also changed from the original monotonous shape to the present  shape colorful and beautiful, it embodies the combination of craft and art. Until now, in addition to its basic functions, the production of plastic cups must also consider health, non-toxicity, and beauty.

Plastic water cups are usually divided into two categories: disposable and reusable. Because the plastic water cup is easy to use and uses less materials, Generally very cheap. And half of the disposable plastic water cups use PET (polyethylene terephthalate). This plastic cannot hold hot water. Heat resistant to 70°C,For reusable water cups, high-temperature resistant and non-toxic high-performance plastics are generally used, such as PP plastic cups commonly sold in the general market.This resin itself does not contain harmful substances and is safer to use. There are also good sales in the market.


With the development of the times, people began to pursue individualization and humanization. Because of the changeable shape, bright colors, and the characteristics of not afraid of being beaten, plastic drinking cups are loved by many people. With the continuous progress of plastic water cup materials, with the promotion of non-toxic and harmless environmentally friendly materials. Plastic water cups have made considerable progress in the past five years.
Common plastic water cups mainly include four parts: cup lid, cup body, sealing ring and handle. The following mainly introduces the forming process of each cup according to raw material selection, formula design and processing technology.

1. Reasons for choosing polymers and additives
PP is polypropylene and PC is polycarbonate. First of all, in theory, both are non-toxic, but in terms of aging resistance and weather resistance, PP is more suitable for water cups. Secondly, from the perspective of synthesis method, PC is generally synthesized by bisphenol A type method. The molecule contains benzene ring. Although PC itself has good heat resistance, as a polymer material, it still contains some low molecular substances. Substances will volatilize and decompose when exposed to heat and light, and most of them are carcinogenic. Therefore, PP cups are usually safer. But why are there so many PC material water cups on the market? This is because the transparency of PC is better, and more glassy texture, so in order to please consumers, businesses will also produce PC cups.


(1) The pp polypropylene material has a catalyst, and if the molecular mass regulator is made into a water cup, add pigment. The transparent agent is best not to add the transparent agent of inorganic salt.

Use characteristics: resistant to high temperature of 130 ℃, poor transparency, reusable.

Strength, stiffness, hardness and heat resistance are better than low-pressure polyethylene, and can be used at about 100°C. But it becomes brittle at low temperature, not wear-resistant, and easy to age.  

PP needs to add metal deactivator and antioxidant additives during processing, these additives are not good for the human body. But compared with other plastics, PP is non-toxic, and the added additives are the least harmful to people. In addition, PP can be boiled and disinfected in water below 110°C.

Hazard analysis: It is the only plastic container that can be placed in a microwave oven to heat food and can be reused after cleaning.

Special reminder: The body of some microwave oven lunch boxes is made of 05PP, but the lid is made of 06PS, which is not resistant to high temperature. Never put the microwave oven together with the box to heat food.


(2) PC polycarbonate generally contains a small amount of bisphenol A, but the hardness, transparency and temperature resistance of PC are very good.

Usage characteristics: Reusable, but avoid using damaged or aging containers

Polycarbonate resin is a kind of thermoplastic engineering plastic with heat resistance, cold resistance and good mechanical properties. Due to its odorless, oil-resistant, and non-contaminated characteristics, polycarbonate resin is mainly used in the manufacture and processing of food molds(such as biscuits, chocolate molds, etc.), baby bottles, and food processing PC polycarbonate: one A new type of thermoplastic, with a transparency of 90%, it is known as a transparent metal. It is rigid and tough, has high impact strength, high dimensional stability and a wide range of operating temperatures, good heat resistance and non-toxicity. PC has excellent thermal properties, can be used for a long time between -100°C and 130°C, and the embrittlement temperature is below -100°C. Widely used, including: medical equipment: cups, tubes, bottles and dental equipment, medicine containers and surgical instruments that can be used for medical purposes, and even as artificial kidneys, artificial lungs and other artificial organs for daily use as feeding bottles, tableware, Toys and models, etc.   In terms of materials, PC should be better, and the price of PC is higher than that of PP. Machinery and other food containers and food processing equipment with impact resistance and certain transparency requirements.

Hygiene problem: Polycarbonate resin itself is nontoxic, but phenol is produced as an intermediate when bisphenol A and diphenyl carbonate are transesterified. Phenol not only has certain toxicity, but also produces peculiar smell, which affects the sensory properties of food. The weight and tensile strength of polycarbonate resin soaked in 50% and 100% ethylene glycol solution for 30 days have significantly decreased. Therefore, in accordance with the provisions of GB13116-9 1 "Sanitary Standards for Polycarbonate Molded Products for Food Containers and Packaging Materials", the content of free phenol in polycarbonate resins for food containers, packaging materials and molded products should be controlled at 0.05 mg/l  ,The following, and should not be exposed to high concentration ethanol solution
 Hazard analysis: Because a small amount of bisphenol A is not completely converted into the plastic structure of PC during the production of PC products, it may be released into food or beverages. The remaining bisphenol A accelerates its release with increasing temperature. Therefore cannot hold hot water. If the container is damaged, it must be stopped to prevent bacterial contamination.
(3) PET polyester, not enough temperature resistance, can be used as cold water cup. The temperature resistance is 70 degrees.
PET (polyethylene terephthalate)
Product use: pure water, mineral water, carbonated beverage bottles.
Use characteristics: Can not holdl hot water. Heat resistant to 70°C. It can only be used once.
Glycol acid ester (commonly known as polyester) has good physical and mechanical properties such as high strength and toughness, high gas barrier, high transparency, and is resistant to acid, alkali, solvent and heat (film). Therefore, polyethylene terephthalate is mainly used to make films (as raw materials for composite food packaging bags), beverage bottles, oil bottles and other condiment bottles. Polyethylene terephthalate resin is non-toxic. Because polyethylene terephthalate resin uses antimony (usually antimony trioxide or antimony acetate) as a catalyst ,Therefore, there may be residual antimony in the resin. Antimony is a moderately acutely toxic metal that can damage the myocardium,Catalysts are also used abroad. Therefore, in accordance with the provisions of GB1314-91 "Hygienic Standards for Polyethylene Terephthalate Molded Products for Food Containers and Packaging Materials"Hygienic Standard for Polyethylene Terephthalate Molded Products for Food Containers and Packaging Materials", the antimony The content should be controlled below 1.5mg and 0.05mg/l. Hazard analysis: the body of the hot liquid or heating bottle will be deformed and harmful substances can be melted. After 10 months of continuous use, it may release carcinogens that are toxic to humans. It must be discarded after use. Do not use it as a water cup or as a storage container for liquids such as acid solution or grease.
2. Basic formula
The substance that controls the molecular weight of the polymer is essentially a chain transfer agent. The chain transfer constant and the amount of molecular weight regulator are important factors to control the molecular weight, such as dibenzoyl peroxide, di-tert-butyl peroxide, di-tert-butane peroxide, dicumyl peroxide and so on. The molecular weight regulator can be added directly, or it can be added in the form of masterbatch after making it into a masterbatch. ), lubricants (commonly used lubricants include stearic acid, butyl stearate, oleamide, ethylene bis-stearamide and so on.
  Many paraffin waxes can be used as lubricants, such as natural paraffin, liquid paraffin (white oil), microcrystalline paraffin, etc., but their effects are different. Natural paraffin wax is mostly used for external lubrication. It can be used as a lubricant and release agent for a variety of plastics. The general dosage is 0.2~1phr, but its compatibility, thermal stability and dispersibility are not very good. The dosage should not be too large, preferably with Internal lubricants are used together; while white oil is mostly used as internal lubricants for PVC and PS, which has good lubrication performance and thermal stability. The general dosage is 0.5phr. They are all drug-free and can be used for food packaging. There is also a kind of microcrystalline paraffin wax: it is also used as a lubricant in plastic processing, the amount is 1~2Phr, and its thermal stability and lubricity are better than ordinary paraffin wax.
Low molecular weight polymers are also widely used as lubricants, such as polyethylene wax and low molecular weight polypropylene, which have good internal and external lubricity and are non-toxic. Polyethylene wax is suitable for extrusion and calendering processing of PVC and other materials. The dosage is generally 0.1~1phr, which can improve processing efficiency, prevent film adhesion, and improve the dispersion of fillers or pigments. The compatibility and transparency are not very good; irregular Structure low molecular weight polypropylene can be used as a lubricant for rigid PVC and PE. It has excellent performance and can improve the dispersibility of other additives. The dosage (0.05~0.5phr.), antioxidant (according to chemical structure can be divided into phenols, There are five categories of amines, phosphorus-containing compounds, sulfur-containing compounds and organic metal salts. According to different mechanisms of action, phenols and amines are also called primary antioxidants, and phosphorus and sulfur-containing compounds are also called secondary antioxidants. Transparent agent.), transparent agent (plastic transparent agent is usually called nucleating agent, a crystal nucleating transparent agent. The characteristics of this product are to improve the transparency, surface gloss, rigidity and flexural modulus of the product. This series of products are suitable It is used in blow molding, injection molding and extrusion molding products such as PP sheets, beverage cups, and instrument casings.
There are usually two ways to apply nucleating transparent agent in plastic processing: one is to add the nucleating transparent agent to the resin for direct mixing or extrusion molding; the other is to mix the nucleating transparent agent with resin and other additives. A certain amount of transparent masterbatch is then blended with ordinary polyolefin to achieve transparency.
Plastic transparent agent product application: Add 0.2-0.4% of this product to the corresponding material to achieve the desired anti-reflection effect. The addition of the nucleating transparent agent can improve the mechanical properties of the material. It is suitable for manufacturing transparent plastic products, and is also widely used on transparent polypropylene sheets and transparent polypropylene tubes. Not only can it be used directly by dry blending with polypropylene, but it can also be used after making 2.5-5% masterbatch.
3. Process flow and reasons for its choice
Different blow molding methods have different advantages in processing different products due to differences in raw materials, processing requirements, output and costs.
Here we introduce the characteristics of blow molding from a macro perspective. Blow molding of hollow products includes three main methods: extrusion blow molding: mainly used for processing unsupported parisons; injection blow molding: mainly used for processing parisons supported by metal cores; stretch blow molding: including Extrusion-stretching-blow molding and injection-stretching-blow molding can process biaxially oriented products, greatly reducing production costs and improving product performance. In addition, there are multilayer blow molding, compression blow molding, dip coating blow molding, foam blow molding, three-dimensional blow molding and so on.
However, 75% of blow-molded products are extrusion blow molding, 24% are injection blow molding, and 1% are other blow molding; of all blow-molded products, 75% are biaxially stretched products. The advantages of extrusion blow molding are high production efficiency, low equipment cost, wide selection of molds and machinery. Extrusion blow molding is one of the main molding methods for the production of plastic hollow parts, suitable for PE, PP, PVC, and thermoplastic engineering Plastics, thermoplastic elastomers and other polymers and various blends are mainly used for forming packaging containers, storage tanks and vats, and also for forming industrial parts such as the automobile industry. Extrusion blow molding is the same as other plastic hollow molding. Its main advantages are low product cost, simple process and high efficiency, but its outstanding disadvantage is that the product wall thickness and uniformity are difficult to control.
Extrusion blow molding is to place the extruded semi-molten plastic tube (parison) in a mold of various shapes while it is hot, and immediately blow compressed air into the tube to inflate it, so that It is formed close to the wall of the mold cavity, and the thermoforming process of the hollow part is obtained after cooling and demolding. Its entire forming process can be divided into three stages: parison formation, parison inflation, cooling and solidification.
(1). Parison forming
Parison formation refers to obtaining a semi-molten plastic tube (parison) by extrusion molding. As the geometry of hollow blow molded parts becomes more and more complex, a well-designed preform is of great significance for obtaining the required wall thickness distribution and structurally stable parts with minimal material consumption. In the blank forming stage, the wall thickness distribution shape of the parison is adjusted to make the wall thickness distribution of the blow molded product tend to be uniform.
(2). Parison inflation
Parison inflation means that the plastic tube blank is placed in the mold while it is hot, and compressed air is immediately blown into the tube blank to inflate it, and it is formed close to the cavity wall. The molding at this stage directly affects the shape of the product , Wall thickness uniformity and product performance are the key links in the entire molding process.
(3). Product cooling and solidification
Product cooling and solidification refers to the process in which the parison is inflated and closely adhered to the mold wall by means of a mold with a higher thermal diffusivity and compressed air for cooling, after cooling to a certain temperature, the mold is opened, and then cooled in air. Generally include external cooling (convection heat transfer between the outer surface of the product and the mold cavity), internal cooling (convection heat transfer between the inner surface of the product and cooling air or other media) and cooling after opening the mold (the internal and external surfaces of the product and air or other media Natural convection heat transfer).
The experimental research of the product cooling and solidification stage is mainly to measure the transient temperature, shrinkage rate and warpage of the product.


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