1. Characteristics of PVC plastic bags
PVC (PVC) chemical and physical properties of rigid PVC are one of the most widely used plastics. PVC material is a kind of non-crystalline material. PVC material is often used in the actual use of stabilizers, lubricants, auxiliary processing agents, color materials, anti-impact agents and other additives.
The PVC material has non-flammability, high strength, resistance to climate change and excellent geometric stability. PVC has a strong resistance to oxidants, reductants and strong acids. However, it can be corroded by concentrated oxidizing acid such as concentrated sulfuric acid, concentrated nitric acid, and is not suitable for contact with aromatic hydrocarbons and chlorinated hydrocarbons.
The melting temperature of PVC is a very important technological parameter in the process of processing. If this parameter is improper, it will cause the problem of material decomposition. The flow characteristics of PVC are quite poor and its process is very narrow. In particular, the large molecular weight of PVC material is more difficult to process (this material usually has to be lubricants to improve the flow characteristics), so it is usually used for small molecular weight of PVC material. The shrinkage rate of PVC is quite low, generally 0.2~ 0.6%.
Injection molding process conditions
Melting temperature: 185 ~ 205 ℃ mold temperature: 20 ~ 50 ℃
Injection pressure: can be large to 1500bar pressure pressure: can be large to 1000bar injection speed: to avoid material degradation, it is generally used to give a considerable injection speed.
Runner and gate: all regular sprue can be used. If you are working with smaller parts, it is better to use a needle gate or a submerged gate. For thicker parts, it is best to use a fan gate. The minimum diameter of needle-pointed gate or submerged gate should be 1mm; The thickness of the fan gate should not be less than 1mm.
Typical use of water supply pipeline, household pipe, housing wall board, commercial machine housing, electronic packaging, medical equipment, food packaging, etc.
2. Classification of PVC plastic bags
PVC can be divided into soft PVC and hard PVC. Hard PVC accounts for about 2/3 of the market, and soft PVC accounts for 1/3. Commonly used in soft PVC floor, ceiling, and the surface of leather, but because of the soft PVC contains softening agent (which is the difference between the soft PVC and hard PVC), easy to brittle, not easy to save, so its use range was limited. Hard PVC contains no softener, so it is flexible and easy to form. It is not brittle. It is not toxic and pollution-free. It has a long preservation time. Therefore, it has great development and application value. The following is referred to as PVC. The essence of PVC is a vacuum plastic film, which is used in the surface packing of all kinds of panels, so it is also called decorative film and adhesive film, which is used in many industries such as building materials, packaging and medicine. The building materials industry accounts for the largest proportion of 60%, followed by packaging industry, and a number of other small-scale applications.
Performance and identification
The combustion characteristics of polyvinyl chloride are difficult to ignite, the flame is extinguished, the flame is yellow, white smoke, and the plastic is soft when burned.
PVC resin is a kind of multi-component plastic, according to the different USES can join different additives, so as the composition of different, its products can present different physical and mechanical properties, such as to join or not join plasticizer can make it a hard and soft products. In general, PVC products have the advantages of chemical stability, self-extinguishing, wear-resisting, acoustic shock absorption, high strength, good electrical insulation, wide source of cheap materials, good gas and tightness, etc. The disadvantage is that the thermal stability performance is poor, and the light, heat and oxygen are susceptible to aging. Polyvinyl chloride resin itself is non-toxic, if the non-toxic plasticizer, stabilizer and other auxiliary materials are made from the products, it is harmless to human animals. However, most of the plasticizers and stabilizers used in the products of polyvinyl chloride products in the market are toxic, so no food is used for food, except for products with no toxic formula.
Thermoplastic plastic with amorphous structure of polyvinyl chloride resin. In ultraviolet light, hard PVC produces light blue or violet white fluorescence, soft PVC emits blue or blue-white fluorescence. When the temperature was 20 ℃ refractive index is 1.544, specific gravity of 1.40, and products with plasticizer and filler added density is usually in the range of 1.15 ~ 2.00, soft PVC foam density is 0.08 ~ 0.48, rigid foam is 0.03 ~ 0.08. PVC water absorption rate is not greater than 0.5%.
The physical mechanical properties of polyvinyl chloride are dependent on the molecular weight of resin, plasticizer and the content of filler. The greater the molecular weight of resin, the higher the mechanical property, cold resistance and thermal stability, but the processing temperature also requires high, which is difficult to form. Low molecular weight is the opposite of the above. The packing content increases, the tensile strength decreases.
2. Thermal performance
The softening point of polyvinyl chloride resin is close to the decomposition temperature. It has started to decompose in 140 ℃, and at 170 ℃ break down more quickly. In order to ensure the normal operation of the forming process, the two most important technological indexes of polyvinyl chloride resin are defined, namely decomposition temperature and thermal stability. The temperature at which the so-called decomposition temperature is a large amount of released hydrogen chloride, the so-called thermal stability is in a certain temperature conditions (usually 190 ℃) is not a large amount of released hydrogen chloride. Polyvinyl chloride (PVC) plastic long-term exposure to under 100 ℃, unless add alkali stabilizer, otherwise will decompose, if more than 180 ℃ the rapid decomposition.
Most of polyvinyl chloride (PVC) plastic products use for a long time temperature should not be more than 55 ℃, but special formula of polyvinyl chloride (PVC) plastic can be long-term use of temperature of 90 ℃. Low temperature soft polyvinyl chloride products will harden. Polyvinyl chloride molecules contain chlorine atoms, so it has a copolymer that can be resistant to flammability, self-extinguishing, and drip-free.
Stability of 3.
Polyvinyl chloride resin is a relatively unstable polymer, which can degrade under the action of light and heat. The process is to release hydrogen chloride and change the structure, but it is relatively light. At the same time, the decomposition of mechanical force, oxygen, odor, HCl and certain active metal ions can be accelerated.
When polyvinyl chloride resin is removed from HCl, the conjugate double chain is produced in the main chain, and the color changes. As the number of hydrogen chloride breaks up, polyvinyl chloride resins change from white to yellow, rose, red, brown and black.
The electrical performance of PVC depends on the number of residues in the polymer, the type and number of additives in the formula. PVC electrical is related with the heating: when heating decompose PVC, due to the presence of chloride ions and reduce its electricity insulativity, if produce large amounts of chloride ions can't by alkali stabilizer (such as lead salt) and, to cause a decline in its electrical insulating performance obviously. Unlike non-polar polymers such as polyethylene and polypropylene, the electrical properties of PVC are varying with frequency and temperature, such as the dielectric constant decreases with increasing frequency.
Polyvinyl chloride has excellent chemical stability and is valuable as an anticorrosive material.
PVC is stable to most inorganic acids and bases and is divided into hydrogen chloride by means of heat. The unsaturated product of brown refractory with potassium hydroxide. The solubility of PVC is related to molecular weight and polymerization methods. In general, solubility decreases with the increase of molecular weight of polymer, and the solubility of emulsion is worse than that of suspension. It can be dissolved in ketones (such as ketone, cyclohexanone), aromatic solvents (such as toluene, xylene), dimethyl formyl, tetrahydrofuran. At normal temperature, polyvinyl chloride resin is almost insoluble in plasticizers, and in high temperature, it is swelling and even dissolving.
PVC is the amorphous polymer, no obvious melting point, heating to 120 ~ 150 ℃ plasticity. Due to its poor thermal stability, it contains a small amount of HCl in this temperature, which causes it to further decompose, so it is necessary to add alkaline stabilizer and HCl to inhibit its catalytic cracking reaction. Pure PVC rigid products, need to add the right amount of plasticizer can make the soft for different products still need to join, such as ultraviolet absorbent, fillers, lubricants, pigment, the use of fertilizer to become good PVC products such as mould inhibitor performance. Like other plastics, resin performance determines the quality and processing conditions of the products. For PVC, the properties of resin are: particle size, thermal stability, molecular weight, fisheye, loose density, purity and foreign impurity and porosity. The viscosity and gelatinization properties of PVC paste and paste should be determined to control the processing conditions and the quality of products.
It was modified by copolymerization
The polymerization of the monomer in the main chain of vinyl chloride is derived from the new polymer consisting of two monomers, known as copolymer. At present, the main varieties and properties of the copolymer of vinyl chloride and other monomers are as follows:
: (1) vinyl chloride - vinyl acetate copolymer of vinyl acetate monomer introduction can have the effect of plasticizer commonly, also referred to as the "internal plasticization, can avoid general plasticizer volatilization of shortcomings, such as pump, migration and can also reduce the melt viscosity, lower processing temperature, improve the processing performance. The content of vinyl acetate in general copolymer is 3 ~ 14%.
The main disadvantages of vinyl chloride - vinyl acetate copolymer are tensile strength, thermal deformation temperature, wear resistance, chemical stability and thermal stability.
Perchloroethylene-vinylidene chloride copolymer: the plasticization, softening temperature, solubility of the copolymer and the plasticization of the molecule are basically the same as that of chloroethylene-vinyl acetate copolymer. It is characterized by low water and gas transmittance, high solubility in the solvents of ketone and the dilution of aromatic hydrocarbons, which can effectively be used for coating. In addition, it is used to make thin film. Due to the difference of heat and light stability than vinyl chloride - vinyl acetate copolymer, monomer cost is higher, so it is not widely used in application of chloroethyl-vinyl acetate.
(3) vinyl chloride - acrylate copolymer, the internal plasticizing effect of the copolymer and vinyl chloride, vinyl acetate, better thermal stability, can be used in the manufacture of hard and soft products, improve the processability and impact resistance and cold resistance, etc. It can also be used for coating and bonding.
Polyvinyl chloride - maleate copolymer: the content of this copolymer is about 15%, and the inner plasticizing effect is similar to that of chloroethylene-acrylate. Good machining performance. The physical mechanical properties are lower and the heat resistance is higher than the general copolymer.
Polyvinyl chloride - olefin copolymer: polymerization of olefin monomers such as ethylene and propylene can be produced with excellent copolymer resin such as fluidity, thermal stability, impact resistance, transparency and heat resistance.
The modification was made by mixing
It is a simple and effective modification method to mix and import heterogeneous macromolecular polymer in polyvinyl chloride phase, and has accumulated experience in actual production. A mixture of two or more different polymers can be prepared with a mixture of these high polymer properties.
In order to improve the fluidity and impact performance of rigid polyvinyl chloride, the commonly used copolymer is: acrylonitrile-butadiene - styrene (ABS), which mainly increases the impact strength. Methyl methacrylate (mma) - butadiene - styrene (MBS), in addition to the climate resistance, the rest of the various performance is close to ideal, especially the impact strength, just add a small amount can be greatly improved. Chlorinated polyethylene (CPE) can improve the impact strength. If 20% dosage is added, the impact strength can be very high. Ethylene - vinyl acetate (EVA) can enhance impact strength.
In order to improve soft polyvinyl chloride (PVC) in the process of using the volatilization of plasticizer, migration, and take the commonly used blending polymer are: nitrile rubber (NBR), chlorinated polyethylene (CPE), vinyl chloride - acrylate and maleic acid double dioctyl, ethylene - vinyl acetate copolymer (EVA), ethylene - vinyl acetate - vinyl chloride copolymer, etc.
Graft reaction polymerization
The modification is called grafting reaction polymerization by importing other monomer on the side chain of polyvinyl chloride or by importing the chain of vinyl chloride on the side chain of the heterogeneous high polymer.
Changing the arrangement of chains in the main chain of PVC, or changing the arrangement of the polyvinyl chloride chains to change the polymerization method, this modification is called low temperature polymerization.