Outline of the hottest PVC formula design

Outline of PVC formula design (Part 1)

pure polyvinyl chloride (PVC) resin belongs to a class of strong polar polymers, and its intermolecular force is large, resulting in high softening temperature and melting temperature of PVC, which generally requires 160~210 ℃ to process. In addition, the substituted chlorine group contained in the PVC molecule is easy to lead to the dehydrochlorination reaction of PVC resin, resulting in the degradation reaction of PVC. Therefore, PVC is extremely unstable to heat, and the increase of temperature will greatly promote the dehydrochlorination reaction of PVC. Pure PVC starts the dehydrochlorination reaction at 120 ℃, resulting in the degradation of PVC. In view of the defects in the above two aspects, PVC needs to add additives in processing, so as to be able to produce various products that meet people's needs, such as soft, hard, transparent, good electrical insulation, foaming and so on. When choosing the variety and dosage of additives, we must comprehensively consider all aspects of factors, such as physical-chemical properties, flow performance, molding performance, and finally establish the ideal formula. In addition, we also need to choose the type of resin according to different uses and processing ways. The matching combination of different types of PVC resins and various additives is what we often call PVC formula design. How to design the specific formula? The following will explain the selection of raw and auxiliary materials, hoping to benefit you both in ductility and toughness

I. selection of resin

viscosity or K value is commonly used in industry to represent average molecular weight (or average degree of polymerization). The molecular weight of the resin is related to the physical and mechanical properties of the products. 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, different synthetic processes lead to differences in the morphology of the resin. What we commonly see is the loose resin produced by suspension method, commonly known as SG resin, which has loose tissue, irregular surface shape and porous cross-section transportation. Therefore, SG resin absorbs plasticizer quickly and plasticizes quickly. The main uses of suspension resin are shown in the table below. Lotion resin should be used as PVC paste to produce artificial leather

suspension PVC resin model and main use

model level main use

sg1 grade a advanced electrical insulation material

sg2 grade a electrical insulation material, film

grade I B, grade II general soft products

sg3 grade I a electrical insulation material, agricultural film, artificial leather surface film

grade I B, grade II all plastic sandals

sg4 grade I a industrial and civil film

grade I B, grade II hose Man made fixtures can be divided into wedge-shaped fixtures (referring to fixtures with inclined locking principle structure), counter clamping fixtures (referring to fixtures with single-sided or double-sided rib top tightening principle structure), winding fixtures (referring to fixtures with samples locked by winding), eccentric fixtures (referring to fixtures with eccentric locking principle structure), lever fixtures (referring to fixtures with lever force amplification principle structure), shoulder fixtures (referring to fixtures suitable for shoulder samples) Bolt type fixture (refers to the fixture suitable for testing rib strength of bolts, screws, studs, etc.) 90 ° stripping fixture (it refers to that it is suitable for two samples to carry out vertical leather, high-strength pipe

SG5 grade I a transparent products

grade I B, grade II hard pipe, hard sheet, monofilament, conduit, profile

SG6 grade I a record, transparent sheet

grade I B, grade II hard board, welding rod, fiber

sgg7 grade I a bottle, transparent sheet

grade I B, grade II hard injection pipe fittings, perchloroethylene resin

II, plasticizer system

the addition of plasticizer can In order to reduce the force between PVC molecular chains, reduce the glass transition temperature, flow temperature and the melting point of the microcrystals contained in PVC plastics. Plasticizers can improve the plasticity of the resin, making the products soft and good low temperature resistance

when the plasticizer is less than 10 parts, the effect on the mechanical strength is not obvious. When adding about 5 parts of plasticizer, the mechanical strength is the highest, which is the so-called anti plasticization phenomenon. It is generally believed that the anti plasticizing phenomenon is the effect of increasing the activity of macromolecular chains and ordering molecules to produce microcrystals after adding a small amount of plasticizer. The impact strength of hard products with a small amount of plasticizer is smaller than that without plasticizer, but when the dosage is increased to a certain amount, the impact strength increases with the increase of dosage, which meets the universal law. In addition, with the addition of plasticizer, the heat resistance and corrosion resistance of the products are reduced. With each addition of plasticizer, the heat resistance of Martin decreases by 2~3. Therefore, generally, no plasticizer or less plasticizer is added to hard products. Sometimes a few parts of plasticizer are added to improve the processing fluidity. Soft products need to add a large amount of plasticizer. The larger the plasticizing dose, the softer the product will be

plasticizers include phthalates, straight chain esters, epoxides, phosphates, etc. in terms of their comprehensive properties, DOP is a good variety, which can be used in various PVC product formulas. Straight chain esters such as DOS are cold resistant plasticizers, which are long used in agricultural films. It has poor compatibility with PVC, and it is generally not more than 8 parts. In addition to good cold resistance, epoxy plasticizers also have heat resistance and light resistance, Especially when used with metal soap stabilizer, it has synergistic effect. The general dosage of epoxy plasticizer is 3-5 parts. Wire and cable products should be flame retardant, and plasticizers with relatively good electrical properties should be selected. PVC itself has flame retardancy, but most plasticized soft products are flammable. In order to make soft PVC products flame retardant, flame retardant plasticizers such as phosphate and chlorinated paraffin should be added. The electrical properties of these two kinds of plasticizers are also better than other plasticizers, but with the increase of the amount of plasticizers, the electrical energy generally shows a downward trend. For PVC products used for non-toxic purposes, non-toxic plasticizers such as epoxy soybean oil should be used. As for the total amount of plasticizers, it should be different according to the requirements for the softness of products and different uses, processes and use environments. Generally, PVC film is produced by calendering process, and the total amount of plasticizer is about 50 parts. Blown film is slightly lower, generally 45-50 parts

III. stabilizer system

pvc is processed at high temperature, which is easy to release HCl and form unstable polyolefin structure. At the same time, HCl has autocatalytic effect, which will further degrade PVC. In addition, if there is oxygen or plasma of iron, aluminum, zinc, tin, copper and cadmium, it will catalyze the degradation of PVC and accelerate its aging, so as to avoid the problem of your test results. Therefore, there will be various undesirable phenomena in plastics, such as discoloration, deformation, cracking, decline in mechanical strength, decline in electrical insulation, embrittlement, etc. In order to solve these problems, stabilizers must be added to the formula, especially heat stabilizers. Stabilizers for PVC include heat stabilizers, antioxidants, UV absorbers and chelators. In the formulation design, different kinds and quantities of stabilizers are selected according to the product use requirements and processing technology requirements

(I) heat stabilizer the heat stabilizer must be able to capture the autocatalytic HCl released by PVC resin, or it can react with the unstable polyolefin structure produced by PVC resin, so as to prevent or reduce the decomposition of PVC resin. Generally, the characteristics, functions and product requirements of the heat stabilizer selected in the formula are considered. For example:

lead salt stabilizer is mainly used in hard products. Lead salt stabilizer has the characteristics of good heat stabilizer, excellent electrical performance and low price. However, it is highly toxic and easy to pollute products, so it can only produce opaque products. In recent years, a large number of composite stabilizers have appeared, and there is a danger that single component stabilizers have been replaced. The characteristics of composite stabilizer are strong specificity, low pollution, simple batching in processing enterprises and so on. However, there is no unified standard, so the composite stabilizers vary greatly

barium cadmium stabilizer is a kind of heat stabilizer with good performance. It is widely used in PVC agricultural film. Usually, barium, cadmium and zinc are used together with organic phosphite and antioxidant

calcium and zinc stabilizers can be used as non-toxic stabilizers in food packaging, medical devices and drug packaging, but their stability is relatively low. When the amount of calcium stabilizers is large, the transparency is poor and it is easy to spray cream. Calcium zinc stabilizers generally use polyols and antioxidants to improve their performance. Recently, calcium zinc composite stabilizers for hard pipes have appeared in China

organotin heat stabilizers have good performance and are good varieties for PVC hard products and transparent products. In particular, octyl tin has almost become an indispensable stabilizer for non-toxic packaging products, but its price is relatively expensive

epoxy stabilizers are usually used as auxiliary stabilizers. This kind of stabilizer can improve the stability of light and heat when used together with barium cadmium calcium zinc stabilizer. Its disadvantage is that it is easy to exude. Polyols and organic phosphites are also used as auxiliary stabilizers

in recent years, rare earth stabilizers and hydrotalcite stabilizers have also appeared. The main characteristics of rare earth stabilizers are excellent processability, while hydrotalcite is a non-toxic stabilizer

(II) antioxidant PVC products are oxidized due to heat and ultraviolet radiation during processing and use, and their oxidative degradation is related to the production of free radicals. The main antioxidant is chain break terminator or free radical scavenger. Its main function is to combine with free radicals to form stable compounds and terminate the chain reaction. The main antioxidant for PVC is usually bisphenol A. There are also auxiliary antioxidants or hydrogen peroxide decomposition agents. PVC auxiliary antioxidants are triphenyl phosphite and phenyldiisooctyl phosphite. The combination of main and auxiliary antioxidants can play a synergistic role

(III) UV absorbers PVC products used outdoors, due to UV irradiation in its sensitive wavelength range, PVC molecules become excited, or their chemical bonds are destroyed, causing free radical chain reaction, promoting PVC degradation and aging. In order to improve the anti ultraviolet ability, ultraviolet absorbent is often added. Common UV absorbers for PVC include triazine-5, UV-9, UV-326, TBS, bad and obs. Triazine-5 has the best effect, but the film is slightly yellow due to its yellow color, which can be improved by adding a small amount of phthalocyanine blue. UV-9 is commonly used in PVC agricultural film, with a general dosage of 0.2~0.5 parts. TBS, bad and OBS, which belong to salicylic acid, have a mild effect. When used in combination with antioxidant, which is committed to developing energy-saving and environment-friendly high-function materials, they will have a good aging resistance effect. For non transparent products, the weather resistance is generally improved by adding light shielded rutile titanium dioxide. At this time, if ultraviolet absorbent is added, it will require a large amount, which is not very cost-effective

(IV) chelating agents in PVC plastic stabilization system, phosphite esters often added are not only auxiliary antioxidants, but also chelating agents. It can form metal complexes with harmful metal ions that promote PVC to remove HCl. Commonly used phosphite esters include triphenyl phosphite, phenyldiisooctyl phosphite and diphenyl octyl phosphite. In PVC agricultural film, the general dosage is 0.5~1 part. When used alone, it is easy to stain at the initial stage, and the thermal stability is not good. It is generally used together with metal soaps