Polyvinyl chloride (PVC) plastic has many advantages and characteristics, its wood windows and steel corrosion resistance than aluminum windows and windows; sealing, sound insulation, heat insulation performance is good, and exquisite appearance, easy maintenance, modelling diversity, harmony with all kinds of buildings. However, the hard PVC as the external window sash especially when the profiles need long-term exposure to outdoor, year-round to withstand wind, sun and rain, environmental pollution and atmospheric environmental erosion, suffered environmental damage factors are complex, there are optional and products of resins and additives in raw materials and molding process problems. The weather has become an important indicator of the quality assessment of people PVC plastic window.
1 The influence factors of pvc plastic windows's weatherability and measures to prevent the aging
PVC weatherability mainly refers to the problem of aging. PVC is a synthetic polymer material. The causes of the aging of polymer materials are not only the two aspects of internal and external causes. The internal cause mainly refers to the molecular structure state of polymer materials, including the chemical structure and physical structure, and the properties and proportions of components in polymer material system. The structure state and composition of polymer materials determine the aging resistance of the material to a great extent. External factors refer to the environmental factors of the outside world.
1.1 The internal factors to effect the pvc plastic window's weatherability
PVC molecule structure weakness is mainly affected due to its weather resistance. Under normal circumstances, the molecular structure of PVC is a regular linear chain formed by vinyl chloride monomer in the first and the last way. Chlorine and hydrogen atoms are only combined with secondary carbon atoms, which is relatively stable. However, in actual production, especially when the polymerization temperature is high, irregular connections and double bonds and branched chains may be generated. In addition, the presence of initiators and impurities will also affect the molecular structure and purity of PVC.
"Head" and "tail, and irregular structure connected to the thermal stability of PVC variation, easy out of hydrogen chloride (HCL).
The existence of double bonds, especially the unsaturated double bonds formed at the ends of molecular chains, is also a structural weakness. They are easy to oxidize, break chain and so on.
When branched exists, tertiary chlorine atom or tertiary hydrogen atom branching point on the aging reaction of vulnerable parts of the chain, because they are low, especially tertiary chlorine chain more easy activation reaction. The TERT chloride at the branching point can even release HCl from the adjacent H action at the time of polymerization, and then produces a double bond structure in the molecular chain.
When the PVC polymerization process using peroxide as initiator or presence of oxygen, can make the molecular chain containing -OH or -0 group, also one of the factors of later easy aging and reduced performance.
1.2 The external factors to effect the pvc plastic window's weatherability
PVC weatherability effects include light (wavelength, intensity), radiation, heat, force and power and energy factors, air, gas, oxygen, ozone, the activity of H2S, SO2, HCI, water, organic solvents, microbial hazards and insect damage and other environmental factors, these factors are main factors causing aging of PVC polymer materials during storage or use. From the main mechanism of PVC aging, the aging of light, heat and oxygen is the main factor affecting the weatherability of PVC.
(1) the effect of ultraviolet radiation
Weatherability of mainly refers to the damage caused by light. Photoaging is mainly caused by the short wavelength and high energy ultraviolet (UV) damage to polymer materials. Has a great influence on weather resistance of UV irradiation on PVC windows. The wavelength of UV is 200 ~ 380nm, which has enough energy to cause the breaking of the PVC molecular chemical bonds and the generation of free radicals.
(2) influence of temperature, humidity and oxygen
Temperature on the aging process of PVC the heat sensitive plastics also plays an important role in attenuation and place of use of the temperature dependent properties of PVC. PVC plastic surface temperature of outdoor use is not high (near ground temperature), not enough to cause the PVC immediately. But because PVC plastic absorb sunlight in the infrared into heat, so that the surface temperature is higher, especially the mutual effects of light, oxygen and other factors make the heat of PVC plastic aging acceleration effect, the higher the temperature, the faster degradation of light. The test shows that the degradation rate is 1 times as fast as the temperature rises 10 degrees C. This involves the light and thermal stability of colored and dark colored special-shaped materials. The different colors of the plastic window in the same temperature under the surface temperature difference is large, light and heat stability will be significantly different.
PVC is easily decomposed by heat, and is more intense if there is oxygen.
Humidity is also an important factor affecting PVC plastic aging.
In addition, aging properties of geographical location and other conditions such as wind, dust and air pollution on the PVC series also have effect.
2 some measures to prevent the aging of PVC plastic window
Selection of impact modifier
Currently applies to the PVC window (door) profile of the excellent weatherability impact modifier can be divided into 3 types, namely chlorinated polyethylene (PE-C), (ethylene vinyl acetate) copolymers (E/VAC) and acrylate copolymer (ACR).
PE-C modified PVC was first used, but the processing of the product range is narrow, will cause the product yellowing phenomenon, a decreasing trend in the market.
E/VAC the annual amount in the 3 largest impact modifier, accounting for more than 55%, but due to the extrusion temperature range is narrow, and VEKA will reduce the softening temperature, consumption began to decrease.
ACR has the advantages of low melting temperature, good processability, processing temperature and a wide range of products, the appearance of white color, smooth and fine, with excellent impact strength and durability. The ACR modifier is an effective way to improve the weatherability of PVC plastic window.
2.2 selection of stable system
Stabilizer in PVC plastic profile formula in addition to bear the thermal stability, but also has good weatherability and machinability. The most commonly used thermal stability systems are mainly 3 kinds of lead salts, barium cadmium and organotin. They are all ideal heat stabilizers for PVC, some of them are also strong in light and heat stabilization.
Lead salt stabilizer. The best effect and low price, and metal soap and lubricant with good processability, thermal stability and aging resistance, occupies a large proportion in the processing of PVC at home and abroad. It has a good stability effect for PE-C modified PVC.
The thermal stability of barium, light stability of cadmium, barium cadmium stable system for both light and heat stability, suitable for outdoor use. If the lead and barium cadmium stabilizer are used together, the photothermal stability and weatherability can be further improved, and the whitening degree of products can be reduced, but the toxicity of cadmium is large.
Organic tin stabilizer, the thermal stability of mercaptide is better, but poor weather resistance. The best weatherability in tin system is two lauteric acid, two butyl tin and tin maleate.
2.3 Selection of coloring agents
For many years at home and abroad use experience shows that the white plastic doors and windows can be used as the durability of building materials. Rutile TiO has cubic structure. Its density is high, crystal structure is stable, refractive index is large, it can effectively scatter light, and has high optical stability, excellent protection effect for materials. It is suitable for outdoor use. Rutile TiO2 is the most ideal white plastic colorant, with both UV shielding and scattering effect.
In the general climate condition of China's manufacturing PVC plastic window profiles with 4-6 TiO2 can, in the light of strong radiation, high temperature area can be increased with the amount of. If the organotin stabilizer system is used, 12~15 copies of Ti02 are needed.
For colored PVC plastic profile, the resistance to high temperature above 200 DEG, strong light (7 ~ 8), acid (> 4) and migration resistance (more than 5) pigment as colouring agent. Can also be used in CO extrusion process with PMMA thin layer or film extrusion profiles in the white surface, can be used after color processing method.
2.4 The selection of ultraviolet absorbents and antioxidants
In PVC plastic profile formula if the choice of good light and heat stability of the system, such as the stability of the system in two lead phosphite lead, not only have good thermal stability, and UV shielding effect, and has the function of antioxidant system, and also can shield and scattering ultraviolet Ti02, so in general can no longer add ultraviolet absorbent and antioxidant. But in areas with hot weather and strong light radiation, in order to further improve weatherability, a proper amount of ultraviolet absorbent UV-531 or UV-9 can be added. However, it is worth noting that the matching of these auxiliaries with other auxiliaries has a strong selectivity.
A lot of factors PVC plastics window, in the quality of the products must be guaranteed internal conditions, effects of weather resistant PVC plastic window depends on the atmosphere. The factor of atmospheric environment is a variable, which changes with the change of season and time, and at the same time changes with the different geographical conditions. Ultraviolet light is the main factor that causes the aging of PVC materials, and the co action of heat and * * also degrades the PVC material. At the same time by the PVC material aging mechanism show that the aging process of PVC frame section is mainly the process of polymer chain in the comprehensive effect of light, heat, oxygen, discoloration, fracture that cross-linking strength decreased, in the manufacture of PVC plastic profile in the process, the selection of modifier, stabilizer, coloring agent, ultraviolet absorbent and antioxidant. That is to prevent PVC plastic aging, improve the measures of the main PVC plastics window.