PVC plastic doors and windows have been widely used due to their excellent heat preservation, noise reduction, and sealing properties. Especially in cold areas and sandstorm-prone areas in northern my country, it has fully demonstrated its incomparable superiority. However, PVC plastic windows have also exposed certain weaknesses after years of use, such as poor low-temperature impact resistance, cracking, aging and discoloration.
Application of impact modifiers at home and abroad
Since my country introduced PVC plastic door and window manufacturing technology in the 1980s, impact modifiers have basically been CPE, and my country has strong production capacity and large output, and there is a trend of oversupply. Therefore, it is very common for domestic enterprises to produce PVC plastic window profiles to use CPE as an impact modifier. Due to the fierce market competition among companies producing CPE, individual manufacturers win by quantity and ignore product quality, which affects the stability of product quality of some PVC plastic window profile manufacturers. For example, the heat distortion temperature drops, the process is unstable, and the impact performance fluctuates due to the quality of CPE, which directly affects the quality of PVC plastic windows. Although many professional and technical personnel have noticed the low-temperature impact resistance of PVC plastic windows in the formulation design, they always focus on CPE as a modifier to improve the low-temperature impact resistance, so the actual effect is not obvious. With the advancement of technology, the emergence of the new domestic impact modifier ACR has significantly improved the low-temperature impact resistance of PVC plastic windows and other issues after trials. After the 1990s, with the increase in the production of acrylic ester (ACR) in my country, the cost fell, and more PVC plastic window profiles production plants used it. The superiority of ACR shows more and more the effect of improving the low-temperature impact resistance of PVC, reducing cracking, and improving the aging and discoloration problems. At present, the impact modifiers used abroad, especially in Europe, are mainly ACR, whose performance is significantly better than CPE and other modifier products. Therefore, the application of ACR is an important way to improve and improve the performance of PVC plastic windows.
The choice of impact modifier
The choice of impact modifier should pay attention to the following aspects:
1. The compatibility with PVC resin should be moderate. If the compatibility is too large, the two are completely mixed at the molecular level. The impact modifier may act as a plasticizer and adhere closely to the PVC molecules, causing impact The force acts directly on the PVC chain, and cannot improve the impact resistance. On the contrary, if the compatibility of the two is too small to achieve uniform dispersion, the adhesion to PVC will be lost, and the impact force will not be absorbed.
2. The glass transition temperature should be low, which can improve the impact resistance of PVC at low temperatures.
3. The molecular weight should be high, and light cross-linking is best if necessary to improve the reinforcement effect.
4. It has no obvious influence on the performance and physical properties of PVC.
5. Good weather resistance and low mold release expansion.
6. Blending with PVC has good manufacturability.
7. Heat resistance (deformation resistance, thermal stability) is better.
The characteristics and application of acrylate series impact modifiers
Because acrylate is a "core-shell" structural elastomer, it gives it a series of advantages for modification:
Excellent impact resistance
The impact resistance of the "core-shell" structure is better than that of the network structure polymer (CPE, EVA). As far as the glass transition temperature is concerned, CPE is -10℃～-20℃, and acrylate can reach -56℃, so the low temperature impact performance is obviously better than CPE. The newly developed TAE-858 has a glass transition temperature of over -60℃, which has a significant effect on improving the low-temperature impact performance of the profile.
Wide range of processing technology, stable operation technology
The processing temperature range of CPE is narrow, because the structure of chlorinated polyethylene is close to that of PVC, the temperature is high (185°C), the blending property is good, the network structure is easily destroyed, and the impact resistance is reduced. If the temperature is low, the plasticization is not good, the dispersion is poor, and it will also affect the impact, appearance and other properties. However, the acrylic impact modifier does not have the above problems, the processing temperature is wide, the operation is easy, the yield is high, and the production is stable. Good sex.
Low thermal shrinkage, dimensional stability
P V C profiles that use AC R impact modifiers generally have a low shrinkage rate at 100°C for 60 minutes, generally below 1.5%. The CPE is higher, generally above 1.5% (standard requirements ≤ 2.5%). The practical significance of this project is to test the longitudinal stress of the P V C profile. The influencing factors of the longitudinal stress are the degree of plasticized gelation and the speed of process traction. Therefore, the residual stress between the molecules is too large, and the local is more concentrated, which is the main reason for the stress cracking of the P V C profile. The use of ACR impact modifier has a significant effect on improving the stress cracking of the profile, and there is less cracking in the low temperature assembly.
is suitable for high-speed extrusion of profiles and has the function of flow modifier
ACR impact modifier has reasonable physical structure, so it has a wide processing range, fast extrusion speed, adapts to higher shear speed, and is suitable for high-speed extrusion. The melting temperature is low, and the fluidity is good, which can omit the AC R flow modifier and reduce the cost.
The surface gloss of the product is good
Because ACR is easy to plasticize, the melt strength is low, and the gel degree is high, so the surface gloss of the product is high. Experiments show that the general glossiness of CPE modification is between 20% and 40%, but after A C R modification, the glossiness can reach 40% to 65%, the product is smooth and delicate, and the hand feels good.
Improve the fillet strength
Because of the improved plasticization performance after the application of ACR, the performance of the PVC profile body is improved. In addition, due to the wide processing temperature and strong adaptability, the welding strength is improved, so the welding angle strength is significantly improved.
Improved the weather resistance of PVC profiles
At present, the domestic PVC profiles using CPE impact system have different degrees of graying and yellowing, which is directly related to CPE. After CPE is irradiated with ultraviolet light, the whiteness changes greatly, which can reach 50%, while the ACR changes only 30%. Therefore, it seriously affects the appearance and color changes of PVC profiles. The use of AC R is an important way to improve weather resistance and resistance to light aging and discoloration.