The PVC Formula Design Summary

The PVC Formula Design Summary
Pure polyvinyl chloride (PVC) resin belongs to a class of strong polar polymer, its intermolecular force is large, which leads to high PVC softening temperature and melting temperature, generally need 160~210℃ to process.In addition, the substituted chlorine group contained in PVC molecules can easily lead to hydrogen dechlorination of pvc resin, thus causing PVC degradation reaction, so PVC is unstable to thermal pole, temperature will greatly promote PVC HCL reaction, pure PVC began to remove HCL reaction at 120℃, which leads to PVC degradation.In view of the above two aspects, PVC needs to add additives in the processing, in order to make a variety of soft, hard, transparent, good electrical insulation, foam and other products to meet people’s needs.When choosing the variety and dosage of additives, all factors, such as physical-chemical properties, fluidity energy and molding performance, and finally establish the ideal formula.In addition, according to different uses and processing ways, we also need to make a choice of the resin model.Different models of PVC resin and various kinds of additives to match the combination, is what we often say PVC formula design.So how to design the specific formula?The following will be explained through the choice of raw materials to explain, I hope to be beneficial to you.

1, the choice of resin
一、Industrial common viscosity or K value indicates the average molecular weight (or average 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 decrease.At the same time, the synthesis process is different, leading to the different shape of the resin, our common is the loose resin produced by suspension method, commonly known as SG resin, its loose tissue, irregular surface shape, section transport porous mesh.Therefore, the SG type resin absorbs the plasticizer quickly, and the plasticizers are fast.The main uses of the suspension method resin are shown in the table below.Emulsion method resin is suitable for PVC paste to produce artificial leather.
Model and main use of suspension method PVC resin

Model level main use
SG1 level A advanced electric insulation material
SG2 level A electric insulation material, film SG2 level B, secondary general soft products
SG3 level A electric insulation materials, agricultural film, artificial leather mask SG3 level B, secondary all plastic sandals
SG4 level A industrial and civil film SG4 level B, secondary hose, artificial leather, high strength pipe
SG5 grade A transparent products SG5 level B, secondary hard pipe, hard chip, single wire, catheter, profile
SG6 level A record, transparent sheet SG6 class B, class 2 hard plate, welding rod, fiber
SG7 class A bottle, transparent sheet SG7 class B, class 2 hard injection pipe fittings, overvinyl chloride resin
  2, the plasticizer system
The addition of plasticizer can reduce the force between PVC molecular chains, reduce the glass temperature, flow temperature and the melting point of microcrystals, plasticizer can improve the plasticity of resin, make the products soft and low temperature resistance is good.
The effect of plasticizer on the mechanical strength is not obvious, when adding about 5 parts of plasticizer, the mechanical strength is the highest, is the so-called antiplasticizer phenomenon.It is generally believed that the antiplasticizer phenomenon is that after the addition of a small amount of plasticizer, the activity ability of the macromolecular chain increases, so that the molecular order produces the effect of microcrystals.Add a small amount of plasticizer of hard products, its impact strength is smaller than no overtime, but increased to a certain dose, its impact strength will increase with the increase of the dosage, to meet the universal rule.In addition, increasing the plasticizer, the product heat resistance and corrosion resistance have decreased, each addition of plasticizer, Martin heat resistance decreased 2~3. Therefore, the general hard products do not add plasticizer or add less plasticizer.Sometimes only a few parts of plasticizer are added to improve the processing mobility.And soft products need to add a large number of plasticizer, the larger the amount of plasticizer, the softer the product.
Plastic plasticizer phthalates, straight ester, epoxy, phosphate, etc., on its comprehensive performance, DOP is a good variety, can be used in a variety of PVC products formula, straight ester such as DOS is cold plasticizer, long in agricultural film, it is not compatible with PVC, generally not more than 8, epoxy plasticizer in addition to cold resistance, also has heat resistance, light resistance, especially with metal soap stabilizer and synergistic effect, epoxy plasticizer general dosage is 3~5.Wire and cable products should have flame retardant, and should choose a relatively excellent electrical performance of plasticizer.PVC itself has flame retardant, but most of the soft products after plasticizer are flammable. In order to make soft PVC products flame retardant, flame retardant plasticizer such as phosphate and chlorofaffin should be added. The electrical properties of these two types of plasticizers are also better than other plasticizers, but with the increase of plasticizer dosage, the electrical performance shows an overall downward trend.For PVC products used for non-toxic use, non-toxic plasticizer such as epoxy soybean oil should be used.As for the total amount of plasticizer, it should be different according to the softness requirements, use, process and use environment of the product.The general rolling process produces PVC film, and the total amount of plasticizer is about 50 parts.Blow-blown plastic film is slightly lower, generally in 45~50 parts.
3, the stabilizer system
PVC is processed at high temperature, easy to release HCL, forming an unstable polyene structure.Meanwhile, HCL is autocatalytic for PVC further degradation.In addition, if the presence of aerobic or iron, aluminum, zinc, tin, copper and cadmium plasma presence, it will catalyze the role of PVC degradation and accelerate its aging.Therefore, plastic will appear a variety of bad phenomena, such as discoloration, deformation, cracking, mechanical strength decline, electrical insulation performance decline, brittle, and so on.To solve these problems, stabilizers must be added to the formulation, especially thermal stabilizers are essential.Stabilizers used for PVC include thermal stabilizers, antioxidants, UV absorbers, and chelators.Different varieties and different quantities of stabilizer are selected according to the requirements of product use and processing process.
(1) Thermal stabilizer A thermal stabilizer must be able to capture the autocatalytic HCL released by pvc resin, or can add it to the unstable polyene structure produced by PVC resin to prevent or reduce the decomposition of PVC resin.Generally, consider the characteristics, functions and product requirements of the heat stabilizer selected in the formula.for instance:
Lead-salt stabilizers are mainly used in hard products.Lead-salt stabilizer has the characteristics of good thermal stabilizer, excellent electric performance and low price.But its is more toxic, easy to pollute products, can only produce opaque products.In recent years, compound stabilizers have appeared in large numbers, and single-component stabilizers are in danger of being replaced.Compound stabilizer is characterized by strong specificity, small pollution, and simple ingredients in processing enterprises.However, because there is no uniform standard, the compound stabilizer varies very much.
Barium cadmium stabilizer is a kind of thermal stabilizer.It was widely used in the PVC agricultural film.Usually barium cadmium zinc and organophosphate and antioxidants.
Calcium and zinc stabilizer can be used as a non-toxic stabilizer, used in food packaging, medical devices, drug packaging, but its stability is relatively low, calcium stabilizer dosage is large when the transparency is poor, easy to spray frost.Calcium and zinc stabilizers are generally used with polyols and antioxidants to improve their performance. Recently, calcium and zinc composite stabilizers have been used in hard pipes in China.A company in Shenzhen has successfully developed XXX series non-toxic calcium and zinc stabilizer, which can meet the production of hard pipe and pipe fittings, and use it in joint plastic and other pipe manufacturers.
Organic tin thermal stabilizer performance is good, is used in PVC hard products and transparent products better varieties, especially Xinji tin has almost become an indispensable stabilizer of non-toxic packaging products, but its price is more expensive, have a bad smell.
As an emerging type of Chinese characteristics, rare earth stabilizer will represent the trend of stabilizer selection with the increasing improvement of environmental protection requirements, which is especially reflected in the national “12th Five-Year Plan”.At present, the market is also with many mixed brands, and the WWP series rare earth compound stabilizer developed by Guangdong Willina has been relatively high recognition, and has been used in conch, gu di and other leading enterprises for many years.
The reason why rare earth composite stabilizer has been widely recognized inseparable from its excellent performance characteristics:

1. Good thermal stability.Long-term heat resistance is better than lead salt and calcium, barium soap stabilizer, the initial colorism is similar to zinc soap, transparency and similar to organic tin;
2. Non-toxic and odorless;
3. Proper lubricity, good dispersion, precipitation resistance and good plasticizing effect;
4. With the coupling effect, the amount of inorganic filler can be appropriately increased;
5. Improve the toughness and processing properties of PVC.Can reduce the amount of impulse resistance modification agent and processing additives;
6. Products with light stability and suitable for outdoor use;
   Epoxy stabilizers usually act as auxiliary stabilizers.This kind of stabilizer agent and barium cadmium calcium and zinc stabilizer can improve the stability of light and heat, its disadvantage is easy permeability.Also used as auxiliary stabilizers are polyols, organic phosphate esters.
   In recent years, the water slide system stabilizer has also appeared, which is mainly characterized by non-toxic stabilizer.
   (2) In the process of processing and use, antioxidant PVC products are oxidized due to the action of heat and ultraviolet light, and their oxidative degradation is related to the production of free radicals.The main antioxidant is a strand break terminator or a free radical scavenger.Its main effect is to bind to free groups to form stable compounds and terminate the linkage reaction, and PVC is usually bisphenol A.There are also auxiliary antioxidants or hydrogen peroxide decomposants, which PVC is triphenyl phosphate and phenyldiisoctyl phosphate.Main and auxiliary antioxidant agents can play a synergistic effect.
   (3) PVC products used by ultraviolet absorbent in outdoor, due to ultraviolet radiation in its sensitive wavelength range, PVC molecules into an excited state, or its chemical bonds are destroyed, causing free base chain reaction, and promote PVC degradation and aging.In order to improve the ability to resist ultraviolet light, ultraviolet absorber is often added.The UV absorbers commonly used in PVC are triazine-5, UV-9, UV-326, TBS, BAD, and OBS.Triazine-5 has the best effect, but because the film slightly yellow, adding a small amount of phthalocyanine blue can improve.UV-9 is commonly used in PVC film, with the general dosage of 0.2 to 0.5 copies.TBS, BAD and OBS of salicylic acid have moderate effect, and the use combined with antioxidant will get good aging resistance effect.For non-transparent products, generally by adding the shading of rutile titanium dioxide to improve the weather resistance, then if you add ultraviolet absorbent, it needs a large amount of use, not very economical.
   (4) Chelator In the PVC plastic stability system, the phosphate esters often added are not only auxiliary antioxidants, but also play the role of chelator.It can generate metal complexes and objects with harmful metal ions that promote PVC to remove HCL.Commonly used phosphate esters are triphenyl phosphate, benzene diisocecl phosphate and bisphosphate.In PVC agricultural film, the general amount is 0.5~1, used alone when the early easy to color, thermal stability is not good, generally used with metal soap
   4, lubricant
   The lubricant reduces the friction between the polymer and the device, as well as the internal friction between the chains of polymer molecules.The former is called external lubrication, while the latter is called internal lubrication.With external lubrication effect such as silicone oil, paraffin, with internal lubrication effect such as monoglyceride, stearol and esters.As for metal soap, there are both.Also need to explain that internal and external lubrication is just a habit of our name, there is no obvious boundary, some lubricant in different conditions play different roles, such as stearic acid, at low temperature or a small amount, can play internal lubrication effect, but when the temperature rises or dosage increases, its external lubrication effect gradually advantage, there is calcium stearate, it is used alone as external lubricant, but when it and hard lead and paraffin and used to promote plastic internal lubricant.
   In hard PVC plastics, excessive lubricant results in reduced strength and also affects process operation.For injection products, especially peeling near the gate.For injection products, the total amount of stearic acid and paraffin used is generally 0.5~1: extrusion products are generally not more than 1.
   In the soft system
   5、plugging compound
   Some inorganic fillers are added to PVC as incremental agents to reduce costs, while improving certain physical and mechanical properties (such as hardness, thermal deformation temperature, dimensional stability and reduced shrinkage), and increase electrical insulation and flame resistance.In recent years, it has been a hot topic to nano inorganic fillers into plastics as a modifying agent, and some research results such as nano calcium carbonate toughness and enhanced PVC. The important problem to be solved is how to evenly disperse nano products in plastics.
   In the hard extrusion molding process, PVC products are generally filled with calcium carbonate and barium sulfate.For injection plastic products, require good fluidity and toughness, generally appropriate with titanium dioxide and calcium carbonate.The packing quantity of hard products within 10 parts has little impact on the performance of the products, in recent years, we in order to reduce the cost, hard to add packing, which is unfavorable to the performance of the products.
   In terms of soft products, adding the right amount of filler will make the film have good elasticity, dry but not bright, and high thermal pressure resistance and permanent shape and small advantages.In soft products formula commonly used to talc powder, barium sulfate, calcium carbonate, titanium dioxide and clay and other fillers.Talc powder has less effect on transparency.Production of thin film is, the filler volume can be up to 3 parts, more than affect the performance.At the same time, we should pay attention to the filler fineness, otherwise easy to form a rigid block, so that the plastic fracture.Calcium carbonate is mainly added to ordinary auxiliary cables; calcined clay can improve plastic heat resistance and electrical insulation.In addition, antimony trioxide can also be added as a filler to improve the flame resistance.
   In particular, it is proposed that the current general calcium and zinc stabilizers will have different color reactions to highly filled calcium carbonate, mainly redness, which is often not the insufficient stability of calcium and zinc stabilizer, but the influence of some impurity in calcium carbonate.It is recommended that when selecting materials, try to choose good white, without active ingredients of ultra-fine light calcium carbonate powder as filler, it can reduce adverse reactions.
   6、colorant
   The colorants used in PVC plastics are mainly organic and inorganic pigments.PVC plastics have high requirements for pigments, such as high temperature resistance during processing, not affected by HCL, no migration during processing, light resistance, etc.Commonly used are: (1) red is mainly soluble azo pigment, cadmium red inorganic pigment, iron oxide red pigment, phthalocyanine red, etc.; (2) yellow mainly chromium yellow, cadmium yellow and fluorescent yellow; (3) blue mainly phthalocyanine blue (4) green; (5) white mainly with titanium dioxide; (6) purple is mainly plastic purple RL; (7) black is mainly carbon black.In addition, fluorescent whitening agent is used for whitening, gold powder, silver powder is used for color printing, pearl powder makes plastic have pearl like astigmatism.
   7、foaming agent
   The foaming agent used in PVC are mainly ADC foaming agent, azodiisoonitrile and inorganic foaming agent.In addition, lead salt and cadmium salt also contribute to the foaming effect, which can reduce the decomposition temperature of AC foaming agent to about 150~180℃.The amount of foaming agent is determined according to the foaming doubling rate.
   8、fire retardant
   Plastics used for building materials, electrical equipment, automobiles and aircraft are required to be flame retardant.Generally containing halogen, antimony, boron, phosphorus, nitrogen and other compounds have flame retardant effect, can be used as flame retardant.
   Hard PVC plastic because of the high chlorine content, itself has flame retardant, for PVC cable, decorative walls and plastic curtains mixed with flame retardant, can increase its flame resistance.Often used chlorine paraffin, antimony trioxide (2~5 parts), phosphate and other flame retardants.Phosphates and chlorine-containing plasticizers are also flame-retardant