Knowledge of PVC formula design
Pure belong to a class of strongly polar polymer polyvinyl chloride (PVC) resin, the larger molecular inter-atomic forces, leading to a PVC softening temperature and melt temperature is higher, generally need to 160 ~ 210 ℃ to processing. Additional PVC molecules containing some to replace the chlorine easy to cause the dehydrochlorination of PVC resin reaction, thus cause the degradation of PVC reaction, so the PVC on the thermal unstable, temperature rise will greatly promote the PVC HCL reaction, pure PVC have begun to take off the HCL reaction at 120 ℃, thereby resulting in the degradation of PVC. In view of the above two aspects of defects, VC in the processing needs to add additives, in order to be able to produce a variety of soft, hard, transparent, good electrical insulation, foaming and other products to meet the needs of people. When selecting the variety and dosage of additives, it is necessary to consider all aspects of factors, such as physical-chemical properties, flow properties, molding properties, and finally establish the ideal formula. In addition, we also need to choose the resin model according to different USES and processing methods. The PVC resin of different model and all sorts of auxiliary agent match combination way, it is the PVC recipe design that we often say. So how do you do that? The following will be through the choice of raw and auxiliary materials to explain the way to explain, I hope to be of benefit to you.
One, the choice of resin
Viscosity or K values are commonly used in industry to indicate average molecular weight (or average degree of polymerization). The molecular weight of the resin is related to the physical and mechanical properties of the product. The higher the molecular weight, the higher the tensile strength, impact strength and elastic modulus of the product, but the fluidity and plasticity of the resin melt decreased. At the same time, different synthesis processes lead to different shapes of the resin. The most common loose resin produced by suspension method is SG resin, commonly known as SG resin, which has loose structure, irregular surface shape and reticular transport porosity. Therefore, SG resin absorption plasticizer, plasticizing speed is fast. The main USES of suspension resin are shown in the table below. Emulsion resin suitable for PVC paste, production of artificial leather. PVC resin suspension method model and main use model level main use SG1 level A high electrical insulating materials SG2 level electrical insulating materials, film grade B, secondary general soft products SG3 level A electrical insulating materials, agricultural film, artificial leather surface film level 1, level 2 B all plastic sandals SG4 grade industrial and civilian film grade B, secondary hose, PVC leather, high strength pipe SG5 level 1 level 1, level 2 B A transparent products hard pipe, plate, monofilament, pipe, profile SG6 level A record and transparent slice of level 1, level 2 B hard board, welding rod and fiber SGG7 grade A bottle, transparent sheet grade A B, grade ii hard injection pipe fittings, PVC resin
Ii. Plasticizer system
The addition of plasticizer, can reduce the force between PVC molecular chain, make PVC plastic vitrification temperature, flow temperature and microcrystalline melting point are reduced, plasticizer can improve the plasticity of resin, make products soft, good resistance to low temperature performance. Plasticizer is in 10 when the influence of the following to mechanical strength is not apparent, when adding 5 or so plasticizer, mechanical strength is the highest instead, it is so-called reverse plasticizing phenomenon. It is generally believed that the reverse plasticizing phenomenon is that after adding a small amount of plasticizer, the activity ability of macromolecular chain increases and the molecular ordering produces the effect of microcrystalline. The impact strength of hard products with a small amount of plasticizer is smaller than that without addition. However, when the amount of plasticizer is increased to a certain dose, the impact strength increases with the increase of dosage and satisfies the universal law. In addition, increase plasticizer, the heat-resisting property of the product and corrosion-resisting all have drop, every increase plasticizer, Martin heat-resisting drops 2~3. Accordingly, general hardware does not add plasticizer or add plasticizer less. Sometimes a few plasticizers are added to improve the flow of processing. And soft product needs to add a lot of plasticizer, plasticizer quantity is bigger, the product is softer. Plasticizer kinds of phthalic acid esters, aliphatic ester, epoxy, phosphate ester, etc., its comprehensive performance, DOP is one of the better varieties, and can be used for all kinds of PVC products formula, aliphatic esters such as DOS is a hardy plasticizer, long used in agricultural films, it has good compatibility with PVC, is no more than eight copies, epoxy plasticizer besides good cold resistance, but also has heat resistance, light fastness, especially with the metal soap stabilizer and synergies from time to tome, general dosage of epoxy plasticizer for 3 ~ 5. Wire, cable products should have flame retardant, and should choose relatively good performance of electricity plasticizer. PVC itself has flame retardant, but after plasticizing soft products are mostly flammable, in order to make soft PVC products with flame retardant, flame retardant plasticizer should be added such as phosphate ester and chlorinated paraffin, the electrical performance of these two types of plasticizer is also better than other plasticizer, but with the increase in the amount of plasticizer, the electrical performance of the overall trend of decline. For non - toxic PVC products, non - toxic plasticizer such as epoxy soybean oil should be used. As to plasticizer gross amount, should ask to the softness degree of the product and use, craft and use environment are different and different. General rolling process produces PVC film, the total amount of plasticizer in about 50. Blow molding film slightly lower, generally in 45~50.
PVC plasticizer is mainly dioctyl phthalate (DOP), sometimes to reduce costs, often add white oil, chlorinated paraffin, soybean oil and other auxiliary agents. There is a great relationship between the growth efficiency of plasticizer and its chemical structure, which is mainly reflected as follows:
(1) under the same molecular weight of plasticizer, plasticizer with more polar groups or ring structure inside the molecule has poor plasticizing efficiency.
(2) in ester plasticizers, the alkyl chain length increases and the plasticizing efficiency decreases.
(3) the introduction of chlorine substituents into alkyl or aryl groups reduces the growth efficiency.
(4) plasticizer plasticizer efficiency is also related to plasticizer viscosity, with the series of plasticizer equivalent dosage increases with viscosity.
White oil: colorless, transparent, oily liquid with no odor. 0.831 ~ 0.883, the flash point (open) 164 ~ 223 ℃, the movement viscosity (5.7 ~ 26 was 50 ℃)/s, the acid value of 0.05 or less. Stable to acid, light and heat, insoluble in ethanol, soluble in ether, benzene, petroleum ether, etc., and soluble with most fat oil. Is a mixture of liquid hydrocarbons, the main components of which are n-isomeric alkanes (saturated cycloalkanes and paraffin alkanes) of c16-c31. Depending on viscosity and other properties, white oil products can be divided into 7#, 11#, 15#, 18#, 24#, 48#, 64#, 100# and other models. White oil is colorless, odorless, chemically inert and has good photostability. Its basic composition is saturated hydrocarbon structure, and aromatic hydrocarbon, nitrogen, oxygen, sulfur and other substances are nearly zero. Due to this super refining depth, it is difficult to implement the heavy distillate in the actual manufacturing process, so the molecular weight of white oil is usually within the range of 250-450.
White oil belongs to the external lubricant, if the use of too much will cause the product plasticization is not good, or even not plasticized, the product is very easy to become brittle.
Chlorinated paraffin is a chlorinated derivative of paraffin hydrocarbon, which has the advantages of low volatility, flame retardant, good electrical insulation, low price, etc., and can be used as flame retardant and PVC plasticizer. Widely used in the production of cable materials, floor materials, hose, artificial leather, rubber and other products. And additives used in paints, lubricants and so on.
Chlorinated paraffin wax 42 # is a yellowish viscous liquid. Freezing point - 30 ℃, relative density 1.16 (25/25 ℃), insoluble in water, soluble in organic solvents and various kinds of mineral oil.
Chlorinated paraffin wax plasticizing efficiency is low and easy to precipitate, too much use will reduce the toughness of products, and the viscosity of chlorinated paraffin wax is larger. But the price of chlorinated paraffin is lower, adding chlorinated paraffin as plasticizer can reduce the cost.
Epoxidized soybean oil: at room temperature for light yellow viscous, oily liquid, formula C57H106O10, molecular weight is about 1000, pour point - 3 ℃, boiling point 150 ℃ (0.5 Kpa), viscosity of 325 mpa. S, refractive index of 1.473 (25 ℃), in the water solubility of < 0.01 (25 ℃), water solubility in the product this 0.55% (25 ° C), soluble in hydrocarbons, esters, ketones, higher alcohols, such as organic solvent, slightly soluble in alcohol. This product is one of the most widely used PVC non-toxic plasticizer and stabilizer. Good compatibility with PVC resin, low volatility, low mobility. With excellent thermal stability and light stability, water and oil resistance is also good, can give products good mechanical strength, weather resistance and electrical properties, and non-toxic, is internationally recognized for food packaging materials chemical process additives. This product can be used in all PVC products.
Iii. Stabilizer system
PVC processed at high temperature, easy to release HCL, forming an unstable polyene structure. At the same time, HCL has an autocatalytic effect, which will further degrade PVC. In addition, the presence of oxygen or plasma of iron, aluminum, zinc, tin, copper and cadmium can catalyze the degradation of PVC and accelerate its aging. Accordingly plastic will appear all sorts of undesirable phenomenon, if change color, be out of shape, crack, mechanical strength drops, electrical insulation property drops, hair is brittle wait. In order to solve these problems, stabilizers, especially thermal stabilizers, must be added to the formula. Stabilizers for PVC include heat stabilizers, antioxidants, ultraviolet absorbers and chelators. Formula design according to the requirements of product use and processing technology requirements to choose different varieties, different quantities of stabilizer.
(1) heat stabilizer
Heat stabilizer must be able to capture the self-catalytic HCL released by PVC resin, or be able to react with the unstable polyene structure generated by PVC resin to prevent or reduce the decomposition of PVC resin. In general, the characteristics, functions and requirements of the heat stabilizer selected in the formulation are considered. For example: lead salt stabilizers are mainly used in hard products. Lead salt stabilizers are characterized by good thermal stabilizers, excellent electrical properties and low price. But its toxicity is bigger, easy to pollute the product, can only produce opaque products. In recent years, composite stabilizers have appeared in large quantities, and the single-component stabilizers are in danger of being replaced. Composite stabilizer is characterized by strong specificity, small pollution, processing enterprises simple ingredients and other advantages. However, there is no uniform standard, so the compound stabilizers vary greatly.
Barium cadmium stabilizer is a kind of better thermal stabilizer. It is widely used in PVC agricultural film. Barium, cadmium and zinc are usually combined with organic phosphite esters and antioxidants.
Calcium and zinc stabilizer can be used as non-toxic stabilizer, used in food packaging and medical equipment, drug packaging, but its stability is relatively low, calcium stabilizer dosage is poor transparency, easy to spray frost. Calcium and zinc stabilizers generally use polyols and antioxidants to improve their performance, recently, there have been used for hard pipe calcium and zinc composite stabilizers appear. Shenzhen senderi plastic additives co., ltd. has successfully developed CZX series of non-toxic calcium and zinc stabilizer, which can meet the production of hard pipe and pipe fittings, and is used in bulk by liansu and other pipe manufacturers.
Organic tin thermal stabilizer performance is good, is used for PVC hard products and transparent products of a better variety, especially octyl tin almost become non-toxic packaging products indispensable stabilizer, but its price is more expensive.
Epoxy stabilizers are usually used as auxiliary stabilizers. When combined with barium, cadmium, calcium and zinc stabilizers, the stabilizer can improve the stability of light and heat. Also used as an auxiliary stabilizer are polyols and organic phosphite esters.
In recent years, rare earth stabilizers and hydrotalcite stabilizers have also appeared. The main characteristics of rare earth stabilizers are excellent processing performance, while hydrotalcite is a non-toxic stabilizer.
PVC products in the process of processing and use, because of the role of heat, uv oxidation, oxidation degradation and the production of free radicals. The main antioxidants are chain breaking termination agents or free radical elimination agents. Its main function is to combine with the free radical to form A stable compound and terminate the chain reaction. The main antioxidant used for PVC is generally bisphenol A. There are also auxiliary antioxidants or hydrogen peroxide decomposition agent, PVC auxiliary antioxidants for the phosphite triphenyl ester and biiso-octyl phosphite. The combination of main and auxiliary antioxidants can play a synergistic role.
(3) ultraviolet absorbent
Outdoor use of PVC products, due to its sensitive wavelength range of ultraviolet radiation, PVC molecules into an excited state, or its chemical bonds are broken, causing free chain reaction, PVC degradation and aging. Ultraviolet absorbers are often added to improve the ability to resist ultraviolet rays. PVC commonly used UV absorbers are triazine-5, uv-9, uv-326, TBS, BAD, OBS. Triazine-5 has the best effect, but the film is slightly yellow due to its yellow color, and a small amount of phthalocyanine blue can be added to improve it. Uv-9 is commonly used in PVC agricultural film, with a general dosage of 0.2~0.5. TBS, BAD and OBS, which belong to salicylic acid, have mild effects and can be used together with antioxidants to obtain good aging resistance. For non-transparent products, generally by adding shading rutile titanium dioxide to improve the weather resistance, at this time, if the addition of ultraviolet absorber, it requires a large amount, not very cost-effective.
(4) chelating agents
In the stable system of PVC plastic, phosphite ester is not only an auxiliary antioxidant, but also ACTS as a chelating agent. It can generate metal complex and substance with the harmful metal ion that urges PVC to dehcl. The commonly used phosphite esters are triphenyl phosphite, diisooctyl phosphite and diphenyl octyl phosphite. In PVC agricultural film, the general amount is 0.5~1 portion, when used alone in the early stage is easy to color, thermal stability is not good, generally with metal soap and four, lubricants lubricants function is to reduce the friction between the polymer and equipment, as well as the internal friction between polymer molecular chain. The former is called external lubrication and the latter is called internal lubrication. Those with external lubrication such as silicone oil, paraffin, etc., and those with internal lubrication such as monoglycerides, stearols and esters, etc. As for metallic soaps, they are both. To be sure, other internal and external lubrication is just our a habit, and no obvious boundaries, some lubricant in different role in different conditions, such as stearic acid, at the time of low temperature or a few, can the lubrication effect, but when the temperature or increase dosage, the advantage of its external lubrication gradually, and there is a special case is calcium stearate, it separately when used as lubricant, but when it hard lead and paraffin and became promote plasticizing lubricant inside.
In hard PVC plastic, excessive lubricant will lead to reduced strength, but also affect the process operation. For injection products, peeling may occur, especially near the gate. For injection products, the total amount of stearic acid and paraffin is generally 0.5~1 portion: extruded products generally do not exceed 1 portion. In the formulation of soft products, too much lubricant will cause frost and affect the strength of products and high frequency welding and printing. And lubricants too little will stick to the roll, for blowing film, lubricants too little will stick to the mouth mold, easy to make plastic coking in the mold. At the same time, in order to improve the stickiness of blowing film, it is advisable to add a small amount of internal lubricant monoglyceride. When producing PVC soft products, the lubricant is generally less than 1 part. 5, processing agent ACR PVC processing agent ACR is the abbreviation of acrylate copolymer, because of the cost of styrene and other raw materials, also known as A.