New wood substitute PVC foam board
DATE：2022/3/16 8:41:24 / READ： / SOURCE：This station
New wood substitute PVC foam board
1. Material selection and formula design(1) PVC resin PVC resin is the main component of the board. Its model plays a leading role in the physical and mechanical properties and processing properties of the board, and also has a great impact on the foaming process. The resin viscosity is too high, the foaming process is not good, the cell structure is poor, the plate density is high, the hardness is large, the surface is not smooth, and the processing is difficult; The resin viscosity is too low. Although it is easy to process, the foaming is not good, and the physical and mechanical properties of the plate are poor. Generally, S-700 PVC resin with K value of 58 ~ 60 is the most suitable. S-800 PVC resin shall be selected for plates with low surface quality requirements.
(2) The main parts of the machine are ammonia carbonate and sodium bicarbonate; Organic foaming agents mainly include Azodicarbonamide (AC) and butyronitrile. Using AC foaming agent, its decomposition degree is high, generally at 195-200 degrees, foaming agent, AC foaming agent easily dispersed in PVC melt, resulting in uniform and dense bubbles, suitable for mesh foam. The amount of AC is directly related to the density and quality of the plate. Generally, the density of plate decreases with the increase of AC dosage. However, if the gas pressure in the body is greater than the melt strength, some gas will break through the bubble wall and escape, resulting in the increase of plate density and the decrease of plate quality. Generally, the dosage of AC should be 0.3 ~ 0.5 phr. (3) from the foaming process, foaming agent is required to obtain uniform and dense closed cell foam structure. First, the gelation of the resin must take place before the decomposition of the foaming agent. Secondly, the melt must have enough strength and elasticity to ensure that the gas does not break through the bubble wall. Because PVC does not have these characteristics, it must be modified by adding a certain amount of foaming regulator zb-530 (acrylic acid).
The solubility parameter of zb-530 is 9.2, which is close to that of PVC, indicating that zb-530 is easy to disperse in PVC. After the use of ZB-530, the plasticization time of PVC is obviously shortened, and its gelation is promoted, so that the gas produced by the decomposition of AC can be dissolved in PVC melt as soon as possible. In addition, the acrylic elastomer in zb-530 runs through the whole PVC melt and is intertwined with the PVC molecular chain, which greatly improves the strength and elasticity of the PVC melt, so that the melt can have the strength and elongation corresponding to the expansion gas, so as to ensure that the gas forms small, dense and independent bubbles in the expansion process, so as to reduce the density of the product and make the melt under high extrusion rate, The plate surface is smooth and the bubble structure is uniform.
In production, how to control the balance between melt strength and viscosity and the decomposition and expansion pressure of foaming agent is the key to ensure the plate density and cell structure. Generally, the melt strength and viscosity increase with the increase of zb-530 dosage. However, if the amount of zb-530 is too large, the melt strength will be too high, so as to hinder foaming and cause too high plate density. At the same time, if the amount of zb-530 is too large, the melt viscosity will be too large, resulting in too large extrusion torque. The materials are very easy to adhere to the screw and die, resulting in paste shortly after the beginning of production. The dosage of zb-530 is generally 4 ~ 8 parts.
(4) Stabilizer and stabilizer are added to inhibit the damage of PVC caused by external factors. The researchers used tribasic lead sulfate and dibasic lead sulfate. Its initial 211
It can make the surface of products bright and clean, has the ability of anti-oxidation and shielding ultraviolet rays, has superior weather performance, and has the functions of processing modification and lubrication. But in PVC system, due to
The dosage should be larger, usually 4-6 portions. It will react with metal salts to form metal hydroxylate, which will reduce the stability of the system
(5) for its friction and adhesion to the equipment, reduce the internal friction of materials and improve the surface roughness of products, the internal lubricant and external lubricant need to be added to the raw material formula. The researchers choose stearic acid as the internal lubricant and paraffin as the external lubricant. If the amount of lubricant is too small, the materials are easy to adhere to the equipment surface and produce paste; if the amount is too large, it will affect the plasticization efficiency, prolong the plasticization time and cause the plasticization of materials Poor and the surface of the plate is not smooth. Its dosage is generally 2 ~ 3 parts.
(6) The filler can improve the molding performance of PVC and reduce its molding cost. The researchers selected light calcium carbonate, which has the advantages of low cost, non toxicity and high whiteness. In addition, the smaller the particle size of light calcium carbonate, the better the filling effect. Its dosage is generally 5 ~ 7 parts.
(7) Adding 1 ~ 2 parts of epoxy soybean oil to the formula of other additives is conducive to improve the elasticity of melt and the flexibility of bubble wall, and has the function of stabilizer. Adjust the proportion of colorants, antistatic agents, flame retardants, repellents and other additives according to different products and different requirements.
(8) Formula (parts by mass): PVC 100 foaming agent AC 0.3 ~ 0.5 foaming regulator 4-8 stabilizer 4 ~ 6 lubricant 2 ~ 3 light CaCOs 5-7 epoxy soybean oil 1-2
2. Main equipment
Kmd-125 PVC free foaming sheet extrusion production line produced by Breyer company in Germany.
3. Preparation process
(1) The process flow of rigid PVC free foaming extrusion plate production line is shown in Figure 2-12.
(2) Setting of process conditions
1) Mixing process. The mixing of materials is usually carried out in high-strength turbine mixer and cold mixing unit. The mixing effect of materials has a great influence on the extrusion molding and the appearance quality of plates
Author：admin