Natural color is yellowish translucent, shiny. Transparency is better than polyethylene, polypropylene, worse than polystyrene, with the amount of different additives, divided into soft, hard polyvinyl chloride, soft soft and tough, feel sticky, hard hardness is higher than low-density polyethylene, And lower than the polypropylene, in the inflection will appear whitening phenomenon. Common products: sheet, pipe, soles, toys, doors and windows, wire sheath, stationery and so on. Is a polymer material that uses a chlorine atom to replace one of the hydrogen atoms in polyethylene.
First, the characteristics of pvc plastic bags
PVC (polyvinyl chloride) chemical and physical properties Rigid PVC is one of the most widely used plastic materials. PVC material is a non-crystalline material. PVC materials in the actual use of often added stabilizers, lubricants, auxiliary processing agents, colorants, impact agents and other additives.
PVC material with non-flammability, high strength, weather resistance and excellent geometric stability. PVC has a strong resistance to oxidants, reducing agents and strong acids. However, it can be concentrated oxide acid such as concentrated sulfuric acid, concentrated nitric acid corrosion and does not apply with aromatic hydrocarbons, chlorinated hydrocarbons in contact with the occasion.
PVC melting temperature during processing is a very important process parameters, if this parameter will lead to improper decomposition of the material. PVC flow characteristics are quite poor, the process range is very narrow. In particular, large molecular weight PVC materials are more difficult to process (this material is usually added to the lubricant to improve the flow characteristics), so are usually used are small molecular weight PVC material. PVC shrinkage is quite low, generally 0.2 to 0.6%.
Injection molding process conditions
Melting temperature: 185 to 205 ° C Mold temperature: 20 to 50 ° C
Injection pressure: up to 1500bar Holding pressure: up to 1000bar Injection speed: In order to avoid material degradation, generally use a considerable injection speed.
Runners and gates: All conventional gates are available. If smaller parts are machined, it is advisable to use needle tip gates or submersible gates; for thicker parts, it is best to use fan-shaped gates. The minimum diameter of the needle tip or submersible gate shall be 1 mm; the thickness of the fan gate shall not be less than 1 mm.
Typical use of water supply pipes, household pipes, housing wall panels, commercial machine shell, electronic products packaging, medical equipment, food packaging.
Second, the classification of pvc plastic bags
PVC can be divided into soft PVC and hard PVC. Which accounted for about 2/3 of the hard PVC market, soft PVC accounted for 1/3 Soft PVC is generally used for the floor, ceiling and leather surface, but because the soft PVC contains softeners (which is the difference between soft PVC and hard PVC), easy to become brittle, easy to save, so its use has been limited. Hard PVC does not contain softener, so flexible, easy to shape, not brittle, non-toxic and pollution-free, long storage time, so it has great development and application value. Hereinafter referred to as PVC. The essence of PVC is a vacuum plastic film, used for all kinds of panel surface packaging, it is also known as decorative film, with film, used in building materials, packaging, medicine and many other industries. Which accounted for the largest proportion of building materials industry, 60%, followed by the packaging industry, there are several other small-scale application of the industry.
Performance and identification
PVC combustion characteristics, flame retardant, from the fire that is off, the flame was yellow, white smoke, burning green when the plastic issued a stimulating taste of chlorine.
Polyvinyl chloride resin is a multi-component plastic, depending on the application can be added to different additives, so with the composition of different products can show different physical and mechanical properties, such as adding or without adding plasticizer can make it There are hard and soft products of the points. In general, PVC products are resistant to chemical stability, flame self-extinguishing, wear, muffler shock, high strength, good electrical insulation, low cost and wide material source, good air tightness and so on. The shortcomings of poor thermal stability, by the light, heat, the role of oxygen easy to aging. Polyvinyl chloride resin itself is non-toxic, if the use of non-toxic plasticizers, stabilizers and other auxiliary materials made of products, harmless to humans and animals. However, generally seen in the market of PVC products used plasticizers, stabilizers are mostly toxic, so in addition to marked non-toxic formula products, can not be used to dress food.
⒈ physical properties
Polyvinyl chloride resin is an amorphous structure of thermoplastics. In the ultraviolet light, hard PVC produce light blue or purple white fluorescence, soft PVC is issued blue or blue and white fluorescence. The temperature at 20 ℃ when the refractive index of 1.544, the specific gravity of 1.40, and add plasticizer and filler products density is usually in the range of 1.15 ~ 2.00, soft PVC foam density of 0.08 ~ 0.48, rigid foam 0.03 ~ 0.08. PVC water absorption of not more than 0.5%.
The physical and mechanical properties of polyvinyl chloride depend on the molecular weight of the resin, the content of the plasticizer and the filler. The larger the molecular weight of the resin, the higher the mechanical properties, the cold resistance and the thermal stability, but the processing temperature is also high and the molding is difficult; the low molecular weight is opposite to the above. Increased filler content, reduced tensile strength.
⒉ thermal performance
The softening point of the polyvinyl chloride resin is close to the decomposition temperature. It begins to decompose at 140 ° C and decomposes more rapidly at 170 ° C. In order to ensure the normal processing of forming, PVC resin provides two of the most important process indicators, namely, decomposition temperature and thermal stability. The so-called decomposition temperature is a large number of hydrogen chloride release temperature, the so-called thermal stability is a certain temperature conditions (usually 190 ℃) is not a lot of time to release hydrogen chloride. Polyvinyl chloride plastic long-term exposure to 100 ℃, unless the addition of alkaline stabilizer, otherwise it will break down, if more than 180 ℃ rapid decomposition.
Most of the long-term use of polyvinyl chloride plastic products should not exceed the temperature of 55 ℃, but the special formula of polyvinyl chloride plastic long-term use of up to 90 ℃. Low temperature soft PVC products will become hard. PVC molecules due to the chlorine atoms, so it and its copolymer is generally flame resistant flame, with self-extinguishing, no drip.
Polyvinyl chloride resin is a less stable polymer, in the role of light and heat will be degraded, the process is to release hydrogen chloride, the structure changes, but the degree of light. At the same time in the mechanical force, oxygen, odor, HCl and some active metal ions in the presence of accelerated decomposition.
After the PVC resin has been removed from the HCl, a conjugated double strand is produced in the main chain and the color is changed. With the increase in the amount of hydrogen chloride decomposition, the polyvinyl chloride resin from the original white to yellow, rose, red, brown or black.
⒋ electrical performance
The electrical properties of PVC depend on the amount of residue in the polymer, the type and amount of the various additives in the formulation. The electrical properties of PVC are also related to the heat conditions: when heating to PVC decomposition, due to the presence of chloride ions to reduce its electrical insulation, if a large number of chloride ions can not be alkaline stabilizers (such as lead salt) It will lead to its electrical insulation performance decreased significantly. PVC is not like polyethylene, polypropylene, such non-polar polymer, its electrical properties vary with frequency and temperature, such as dielectric constant decreases with increasing frequency.
Polyvinyl chloride has a very good chemical stability, used as a preservative material is extremely valuable.
PVC for most of the inorganic acid and alkali is stable, heat does not dissolve and decomposition of the release of hydrogen chloride. And potassium hydroxide azeotropy to produce brown insoluble unsaturated products. The solubility of PVC is related to the molecular weight and polymerization method. In general, the solubility decreases with the increase of the molecular weight of the polymer, and the emulsion resin is less soluble than the suspension resin. It can be dissolved in ketones (such as methyl hexanone, cyclohexanone), aromatic solvents (such as toluene, xylene), dimethyl formyl, tetrahydrofuran. At room temperature, polyvinyl chloride resin is almost insoluble in plasticizers, high temperature swelling, or even dissolved.
⒍ processing performance
PVC is amorphous polymer, no significant melting point, heated to 120 ~ 150 ℃ with plasticity. Because of its poor thermal stability, at this temperature containing a small amount of HCl release, to further decomposition, it must be added to the basic stabilizer and HCl and inhibit its catalytic cracking reaction. Pure PVC is a hard product, need to add the right amount of plasticizer to make it soft for different products need to add such as UV absorbers, fillers, lubricants, pigments, fungicides and other additives to Zhen good PVC products Use performance. As with other plastics, the performance of the resin determines the quality of the product and processing conditions. For PVC, the resin properties related to processing are: particle size, thermal stability, molecular weight, fish eyes, bulk density, purity and foreign impurities, porosity. PVC paste and paste viscosity and gelling properties, etc., should be determined to determine, easy to grasp the processing conditions and product quality.
⒈ copolymerization reaction modification
The introduction of the monomer copolymerization in the vinyl chloride backbone resulted in a novel polymer comprising two monomer chains, which are referred to as copolymers. The main varieties and properties of copolymers of vinyl chloride and other monomers are as follows:
⑴ vinyl chloride - vinyl acetate copolymer: the introduction of vinyl acetate monomer can play the role of the general plasticizer, that is, the so-called "plastic", to avoid the general plasticizer evaporation, migration, extraction and other shortcomings , Can also reduce the melt viscosity, reduce processing temperature, improve processing performance. The vinyl acetate content of the general copolymer is 3 to 14%.
The main drawbacks of the vinyl chloride-vinyl acetate copolymer are the reduced tensile strength, heat distortion temperature, abrasion resistance, chemical stability and thermal stability.
(2) vinyl chloride - vinylidene chloride copolymer: the copolymer of plasticity, softening temperature, solubility and molecular plasticization and vinyl chloride - vinyl acetate copolymer is basically the same. Its biggest feature is the water and gas permeability is small, in the ketone solvent solubility and resistance to aromatic dilution, which can be effectively used for coating. In addition, it is also used to make shrink film. Due to the heat resistance, the light stability is worse than that of the vinyl chloride-vinyl acetate copolymer, the monomer cost is high, so there is no wide application of vinyl chloride-vinyl acetate in the application.
⑶ vinyl chloride - acrylate copolymer: the copolymer of the plasticization of the role of vinyl chloride - vinyl acetate equivalent, good thermal stability, can be used to manufacture hard and soft products, improve the workability, impact resistance And cold resistance and so on. Can also be used for coating, bonding and so on.
⑷ vinyl chloride - maleate copolymer: the copolymer of maleic acid ester content of about 15%, within the plasticization and vinyl chloride - acrylic similar. With good processing performance. Physical and mechanical properties to reduce smaller, heat resistance than the average copolymer.
(5) Vinyl chloride-olefin copolymer: Copolymerization of olefin monomers such as ethylene and propylene to obtain copolymer resins excellent in flowability, thermal stability, impact resistance, transparency, heat resistance and the like can be obtained.
⒉ miscible modified
The introduction of heterogeneous polymer phase-polymer blends in the PVC phase is a simple and effective method for modification, and has accumulated experience in practical production. Generally, when two or more different polymers are blended, a mixture of these high polymer properties can be prepared.
In order to improve the mobility and impact properties of rigid polyvinyl chloride, the commonly used blends of polymers are: acrylonitrile-butadiene-styrene (ABS), which is mainly to improve the impact strength. Methyl methacrylate - butadiene - styrene (MBS), in addition to weather resistance, the rest of the performance are almost ideal, especially the impact strength, as long as a small amount can be greatly improved. Chlorinated polyethylene (CPE) can improve the impact strength, if the amount of 20%, the impact strength can be very high. Ethylene-vinyl acetate (EVA) can improve the impact strength.
In order to improve the soft polyvinyl chloride in the course of the use of plasticizer volatile, migration, extraction and other commonly used blends are: nitrile rubber (NBR), chlorinated polyethylene (CPE), vinyl chloride - acrylate , Dioctyl maleate and the like, ethylene-vinyl acetate (EVA), ethylene-vinyl acetate-vinyl chloride copolymer, and the like.
⒊ graft polymerization polymerization
The introduction of other monomers on the side chain of polyvinyl chloride or the introduction of vinyl chloride chains on the side chains of the heteropolymers, which is called graft polymerization.
⒋ low temperature polymerization
Change the arrangement of the chain of PVC chain, or change the arrangement of PVC chain that changes the polymerization method, this modification called low temperature polymerization.