Stability Of PVC Foam Board

Author: admin / 2022-11-11

  PVC foam board is a widely used closed-cell structure board. Good melt plasticizing performance is the premise of producing PVC foam board products. In addition to ensuring that the melt does not degrade during extrusion, the stabilizer also plays an important role in regulating the decomposition temperature of the blowing agent. If the stabilizer is too much or too little, the decomposition temperature of the blowing agent is too low or too high, which is not conducive to foaming. The stabilizer should be adjusted according to the resin grade, such as type 8 resin, the plasticizing temperature is low, and the stabilizer should be appropriately increased to make the plasticizing temperature of the material consistent with the decomposition temperature of the foaming agent. However, if too much stabilizer is added or the melt temperature is too high, the blowing agent will decompose in advance in the extruder, and the foaming gas will escape from the feed hole and vacuum hole, making the foam incomplete.

  ​​  Solution: During the extrusion operation, in addition to ensuring good plasticization of the melt, the melt temperature in the extruder must be lower than the decomposition temperature of the blowing agent to prevent the blowing agent from decomposing prematurely in the machine; The melting temperature of the outlet mold must reach the decomposition temperature range of the blowing agent to promote adequate foaming. The setting and control of the extrusion temperature should also be adjusted in time according to the material of the vacuum hole and the forming form of the melt at startup. Ensure that the material is orange peel when passing through the vent, and there should be no powder flow at the bottom of the screw; when the melt is extruded from the die, its surface should be smooth and elastic, and it should not sag or sag as soon as it leaves the die. Crystallized with a rough cross-section.

  Generally speaking, the polymerization method of PVC foam board can be divided into emulsion polyvinyl chloride, suspension polyvinyl chloride, and bulk polyvinyl chloride. When producing rigid PVC foamed products, such as emulsion-type PVC resins, products with uniform cells and smooth surfaces can be obtained, but the dimensional stability of the products is difficult to control; Vinyl chloride resin, the appearance quality and cell uniformity of the product are slightly worse. From the perspective of comprehensive technology, price and performance, it is appropriate to mix the two in a certain ratio, and the ratio can be between 80/20-20/80. Solution: The production of PVC foam board should try to use sc-7 resin, sc-8 resin, or sc-8 resin mixed with sc-5 or sc-6 resin.

  The production of PVC foam board generally adopts three different foaming agents: heating type, endothermic type, or endothermic and exothermic composite balance type. Ammonium azodicarboxylate, also called ac, is an azo catalyst. The decomposition temperature of the Ac blowing agent is high, up to 232 ° C, far exceeding the processing temperature of PVC, and is used to reduce the decomposition temperature.

  ​  The foaming rate of the foaming agent is high, about 190-260ml/g, the decomposition speed is fast, and the calorific value is large, but the foaming time is short, and the rupture force is strong. Therefore, when the amount of AC foaming agent is too large, the amount of air generated will rapidly increase the pressure inside the bubble, the size of the bubble will increase, the gas will be released rapidly, the structure of the bubble will be destroyed, and the size of the bubble will be uneven. Even open-cell structures can form, creating larger bubbles and voids in this area. Some time ago, we also talked about the production process of PVC foam board, so the foaming agent ac cannot be used alone in the production of foam plastic products. It should be used in combination with an endothermic blowing agent or compound chemical blowing agent to balance heat release and heat release. Inorganic foaming agent sodium bicarbonate is an endothermic foaming agent, although the foaming speed is slow, the foaming time is long, and mixed with ac foaming agent, it can play a complementary and balancing role. The exothermic foaming agent can improve the gas-generating capacity of the endothermic foaming agent. The endothermic foaming agent can cool the endothermic foaming agent, stabilize its decomposition and balance the release of gas, inhibit the overheating degradation inside the thick plate, and reduce the sedimentation of residues. , has a whitening effect.