PVC skinned foamed bar
DATE：2022/3/24 9:01:31 / READ： / SOURCE：This station
PVC skinned foamed bar
1. Material selection and formula design(1) PVC resin and its modifier PVC resin used in the production of skin foaming products is based on homopolymer with low k value. Because this material system has the characteristics of fast absorption of additives, easy plasticization and rapid melting in the processing process, it can ensure that its materials have been melted and plasticized at the decomposition temperature of foaming agent. Therefore, loose (XS) PVC resin produced by suspension method is selected, with an average degree of polymerization of 700 ~ 1000K and a value of 61 ~ 68. EVA film production line www.handler.com com
From the process of producing PVC skinned foaming bar, in order to obtain uniform and fine closed cell foaming structure, the melt should have sufficient strength and elasticity to ensure that the gas will not break through the bubble wall. Because PVC resin does not have these characteristics. It must be modified. The commonly used modifiers are CPE, ACR and MBS, among which CPE and MBS have a great improvement on the impact properties of products, while ACR has a great improvement on the processing properties. ACR hard, high friction heat and large-scale superheat transmission and selection can promote the plasticization of PVC resin. Moreover, ACR is intertwined with molecules in the whole body to increase the melt strength and elasticity, which is conducive to obtaining products with uniform cell structure, flat and smooth surface and good mechanical properties. Therefore, the modifier of hair wood is selected ACR can be cr201, ACR 401 and zb530. Zb530 has high relative molecular weight and is more suitable for foamed products. The dosage of ACR is generally 3 ~ 6 phr.
(2) And foaming agent, peeling hair material, chemical hair method. Azodicarbonamide (AC) is a common chemical foaming agent for extrusion foaming molding, and it is also one of the largest output. It has the characteristics of controllable decomposition reaction, fast gas release and easy dispersion in VC melt. It is more suitable for foaming extrusion. EVA film production line www.handler.com com
According to the requirements of PVC crust foaming production process, the decomposition temperature of foaming agent should be within the temperature range of polymer melt. The decomposition temperature of foaming agent is not only related to the molecular structure, but also affected by other chemicals in the system. Selecting appropriate chemicals can adjust the decomposition temperature of foaming agent. In fact, in the PVC crust foaming formula, the metal soap stabilizer added will reduce the decomposition temperature of the foaming agent by tens of degrees, which can meet the processing requirements. Therefore, these metal soap stabilizers also act as foaming AIDS. EVA film production line www.handler.com com
By adjusting the amount of foaming agent and foaming aid, foaming materials with different densities can be obtained. If the amount of AC is too large, the air pressure in the melt will be too high, the shear heat of the material will increase, and the material is easy to degrade and paste, making it difficult to form. The determination of the amount of foaming agent is closely related to the heat stabilizer, lubricant and nucleating agent in the PVC formula system. The dosage is generally 0.3 ~ 0.5 phr, which is more suitable.
(3) Stabilizer PVC skinned foamed bar production adopts the stabilizer of lead salt system, which is not only used to prevent the degradation and deterioration of PVC in the processing process, but also has a good activation effect on AC foaming agent due to the presence of metal ions, which can reduce the AC decomposition temperature to about 160 ℃, so as to meet the requirements of PVC processing. The order of the activation effect of stabilizer on AC foaming agent is 3PbO · PbSO4 · 2h, O > PBST > BST > cdst, The amount of stabilizer added to the formula of PVC skinned foamed bar is 4 ~ 7 parts. EVA film production line www.handler.com com
(4) The importance of lubricant. When the amount of lubricant is small, the friction between materials and equipment is large, which is prone to die sticking and the surface quality of products is reduced; If there is too much lubricant, the lubrication is excessive, the materials slip in the extruder, it is difficult to generate shear heat, and the AC decomposition temperature cannot be reached, or the decomposed gas is difficult to keep due to the decline of plasticization performance, so the product is not foamed or the foaming ratio is low. Therefore, the amount of lubricant should not be excessive, which is generally controlled at 1 ~ 2 parts.
(5) The filler and pigment added in the formula of VC crust foaming material produced by nucleating agent can not only control the appearance quality of products and reduce the cost of products, but also play the role of nucleating agent in the foaming process. Therefore, the particle size of fillers and pigments should not be too coarse. Ultra fine light calcium carbonate can be used, and its dosage can be added by 5 ~ 10 parts. EVA film production line www.handler.com com
Author：admin