PVC (polyvinyl chloride) chemical and physical properties Rigid PVC is one of the most widely used plastic materials.

Basic introduction

Polyvinylchloridepolymer=PVC

PVC material is a non-crystalline material. In actual use, stabilizers, lubricants, auxiliary processing agents, colorants, impact agents and other additives are often added to PVC materials. PVC materials are non-flammable, high-strength, resistant to climate changes and have excellent geometric stability. PVC has strong resistance to oxidants, reducing agents and strong acids. However, it can be corroded by concentrated oxidizing acids such as concentrated sulfuric acid and concentrated nitric acid and is not suitable for contact with aromatic hydrocarbons and chlorinated hydrocarbons. The melting temperature of PVC is a very important process parameter during processing. If this parameter is improper, it will lead to the problem of material decomposition. The flow characteristics of PVC are quite poor and its process range is very narrow. In particular, high molecular weight PVC materials are more difficult to process (this material usually needs to add lubricants to improve the flow characteristics), so low molecular weight PVC materials are usually used. The shrinkage rate of PVC is quite low, generally 0.2~0.6%.

Injection mold process conditions

Drying treatment: Drying treatment is usually not required.

Melt temperature: 185~205CMold temperature: 20~50C

Injection pressure: Can be as high as 1500barHolding pressure: Can be as high as 1000barInjection speed: To avoid material degradation, a corresponding injection speed is generally used.

Runners and gates: All conventional gates can be used. If processing smaller parts, it is best to use a pinpoint gate or a submerged gate; for thicker parts, it is best to use a fan gate. The minimum diameter of a pinpoint gate or a submerged gate should be 1mm; the thickness of a fan gate cannot be less than 1mm.

Classification of packaging films

1. Photocatalytic inorganic antibacterial film

Antibacterial mechanism: The current photocatalytic antibacterial agent is mainly TiO2, which can produce a large number of hydroxyl groups and oxygen groups on the surface under the action of light. These two groups have strong chemical activity and can cause various microorganisms to undergo organic decomposition, thus having antibacterial properties.

Application of photocatalytic inorganic antibacterial film. Since photocatalytic preparations were first launched in Japan in 1995, one of the current widely used fields is food packaging.

2. Natural and polymer antibacterial film

Other antibacterial films include natural antibacterial film and polymer antibacterial film. Their antibacterial mechanism is to inhibit the reproduction of microorganisms through the charge on the molecular chain, thereby inhibiting the reproduction of microorganisms and playing an antibacterial role. Currently, chitosan, sorbic acid, and curcuminol are mainly used for food packaging.

3. Composite antimicrobial film

The effects of composite antimicrobial film are mainly reflected in the following aspects: extending the antimicrobial cycle; producing antimicrobial properties at low concentrations; broadening the antimicrobial spectrum, inhibiting more microorganisms than any single antimicrobial film.

4. Inorganic antimicrobial film

Inorganic antimicrobial agents are antimicrobial agents made by using the bactericidal and antibacterial abilities of metals such as silver, copper, zinc, titanium and their ions. In the early 1980s, Japanese scientists began to add silver compounds directly to resins, and for the first time used inorganic antimicrobial agents to make antibacterial plastic films. Antimicrobial mechanism: Since inorganic antimicrobial agents are dissolution contact antimicrobial agents, the antibacterial effect of inorganic antimicrobial film is passive. There are currently two explanations for the antibacterial mechanism of metal ions. One is the contact reaction mechanism. The metal ions in the inorganic antimicrobial film come into contact with microorganisms, destroying the protein structure of the microorganisms, causing the death of the microorganisms or dysfunction. One is the active oxygen mechanism. The micro-metal ions distributed on the surface of the inorganic antimicrobial film can absorb energy from the environment, activate oxygen in the air and water adsorbed on the surface of the packaging film, and produce hydroxyl groups and active oxygen ions. They have strong redox ability and can destroy the reproduction ability of bacterial cells, inhibit or kill bacteria, and produce antibacterial effects.

5. Organic antimicrobial film

Antibacterial mechanism: The main mechanism of action of organic antimicrobial agents is to gradually enter the cells by combining with anions on the surface of microbial cell membranes, or react with groups such as sulfhydryl groups on the cell surface, destroying the synthesis system of proteins and cell membranes, and inhibiting the reproduction of microorganisms.

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