Key points of process operation
DATE：2022/10/12 8:44:53 / READ： / SOURCE：This station
Key points of process operation
① The plasticizing heating temperature of raw materials in the barrel shall be gradually increased from the feeding section to the mold mouth; The temperature control shall be stable with small fluctuation.② If the melt temperature is controlled normally, the melt will be decomposed. At this time, check the fit clearance between the inner circle of the barrel and the outer diameter of the screw; The fit clearance between the barrel and the screw is too large, the molten material stays in the barrel for too long, and the PVC molten material is easy to decompose. The decomposition of PVC raw materials will release hydrogen chloride gas, which is harmful to human health, and indoor ventilation should be carried out in time.
③ The mandrel type molding die is the most suitable for PVC resin extrusion blow molding film. The molten material stays in the mold for a short time to avoid frequent decomposition of molten material due to high temperature in the mold body.
④ 60 mesh stainless steel wire filter screen shall be used for filtering the melt extrusion blown film.
⑤ The lip clearance of the mold for molten material forming film blank is within the range of 0.5~1.2mm. When adjusting the clearance, pay attention to loosen the adjusting screw on the small side of the clearance, and then tighten the adjusting screw on the large side of the clearance to avoid damage to the mold parts and the adjusting screw. The die lip clearance shall be uniform throughout the circumference of the die.
⑥ The distance between the wind ring and the die mouth is about 100mm, and it can be adjusted up and down. If the diameter of membrane blank tube is large, the distance shall be smaller, otherwise, the larger value shall be taken. The air pressure and air volume blown out by the air ring shall be stable to ensure the stable operation of the blown film bubble cylinder and good cooling effect. The height of condensation line on the membrane bubble shall be controlled at about 300mm.
⑦ Air flow is not allowed in the working environment of film bubble cooling.
⑧ The blowing ratio of PVC melt should be about 2, and a small blowing ratio will reduce the working strength of membrane products; The traction ratio of membrane bubble should be about 5. Pay attention that the difference between the blowing ratio and the traction ratio should not be too large to avoid excessive difference in the longitudinal and transverse strength of the membrane products.
⑨ The temperature of PVC plasticizing melt shall not exceed 200 ℃ to avoid decomposition of melt.
6.4.2 PVC agricultural film extrusion blow molding
The thickness of formed agricultural film is 0.08mm by up blowing method.
(1) Suspension PVC resin SG3 is selected as the raw material, and the combined formula with auxiliary materials is shown in Table 4-4.
(2) Equipment conditions Raw material preparation: use a three roll grinder, a high-speed mixer (200L), and a pelleting extruder (L/D>10:1, and the screws are of equal spacing and unequal depth gradual type). The specifications of the extruder for extrusion blow molding agricultural film shall be selected according to the conditions in Table 6-1.
(3) The molding process is the same as that of PVC film extrusion blow molding in 6.41.
(4) Quality requirements The quality of PVC agricultural film (extrusion blown agricultural film) shall comply with the provisions of QB1257-91 standard (see Table 6-41~Table 6-43), and the appearance quality shall comply with the provisions of Table 6-44.
6.4.3 Extrusion blow molding of PVC rigid transparent film
The thickness of hard PVC film formed by extrusion blow molding is generally 0015~006mm. The main performance characteristics of PVC hard transparent film are: high tensile strength and light transmittance, as well as kinking performance, similar to traditional cellophane
(1) The raw material is SG6 resin in suspension PVC (the residual amount of vinyl chloride monomer in the material is required to be no more than 5mg/kg). The combination formula with auxiliary materials is as follows (quality).
100 portions of polyvinyl chloride (PVC SG6), 6 portions of methacrylate butadiene styrene copolymer (MBS), 1.5 portions of bis (isooctyl thioglycolate) dimethyl tin, 0.5 portions of di-n-octyl tin dilaurate, 0.5 portions of n-butyl stearate, 1.5 portions of acrylic acid processing modifier, 0.3 portions of stearyl alcohol, and appropriate amount of blue pigment.
(2) The equipment parts and equipment are the same as those in Chapter 6 Plastic Film Extrusion Molding Preparation of 41PV Plastic Film Molding Equipment. If the screw diameter is 100mm, the die diameter of the forming die can be selected as 250mm, and the die clearance is 1.3mm; There are anti-static low temperature heat sealing treatment tanks in the production line.
(3) Forming process
① The pre production preparation of PVC hard transparent film forming materials is the same as that of PVC soft blown film materials, which can be operated according to Chapter 4. The production process sequence is as follows.
PVC resin sieving (40 mesh screen) - metering 7 - high-speed mixing → cooling mixing - mixing and grinding of other additives in the extrusion plasticizing formula → metering "
Forming the film blank → blowing the film blank, cooling and setting → anti-static, heat sealing and coating treatment, cutting and inspection → packaging and warehousing
② Process temperature
a. The material temperature is about 100 ℃, and the mixture is stirred in a high-speed mixer for 5-8 minutes; After mixing, the material temperature drops below 45 ℃, and then it is put into the extruder for production.
b. Barrel process temperature (from feeding section to homogenizing section): 130~140 ℃, 150~160 ℃, 170~180 ℃. Temperature of connecting neck between mold and barrel: 180~190 ℃. Mold temperature: 190~210 ℃.
(4) Key points of process operation
① The blowing ratio of the membrane bubble is about 25, and the stretching ratio is slightly larger than the blowing ratio.
② When the food packaging film is packed manually, the production process of anti-static and heat sealing coating treatment is not required.
③ For cigarette packaging film, if automatic heat sealing packaging is required, the finished film must go through the production process of anti-static and heat sealing coating to prevent electrostatic dust absorption and fire caused by film surface friction.
6.4.4 Extrusion blow molding of PVC heat shrinkable film
The thickness of PVC film is 0.04mm, and the packaging heating temperature is greater than 100 ℃; It is produced by extrusion horizontal blowing method.
(1) SG5 suspension PVC resin is selected as raw material, and heat shrinkable PVC film is preferred. For example, EB106 of Shanghai Chlor Alkali Group Chemical Co., Ltd. and TH-400 PVC resin produced by Tianjin Chemical Co., Ltd.
-441 -- 440-Plastic extrusion molding technologist's manual (quantity). PVC suspension resin SG5100 shares, methacrylate butadiene styrene copolymer (MBS) 4 shares, dioctyl phthalate (DOP) 4 shares, dibutyl phthalate (DBP) 3 shares, C-102 organic tin (DBTL) 2 shares, epoxy octyl stearate (ED) 2 shares, chelating agent 0.5 shares, stearic acid (HSt) 0.2 shares, calcium carbonate (CaCO3) 0.2 shares.
(2) The single screw extruder is selected as the equipment condition. The screw is of equal spacing and unequal depth progressive type, with a diameter of+30mm, a length diameter ratio of 25:1, and a compression ratio of 3. The die is of cross flat blow type, and the die clearance is adjustable between 0.4~0.7mm. The diameter of the heating stretching setting sleeve shall be consistent with the diameter of the membrane bubble. The stretching setting sleeve shall be made of stainless steel pipe, and the surface shall be drilled with ф There are many holes with a diameter of 2mm, which are evenly distributed on the pipe surface to facilitate hot water spraying from the hole diameter to heat the film bubble. The contact surface between the setting sleeve and the film must be smooth and flat. The cooling and temperature setting sleeve shall be able to cool and shape the film with cold water.
(3) Forming process ① Production process sequence
PVC resin is sieved with 40 mesh screen → measurement I
Plasticizer filtration (100 meshes) → metering I>high-speed mixing → uniform mixing → powder cooling
Mixing of other additives → metering I
Lower the temperature to 40~50 ℃ → extrude and plasticize → extrude the membrane tube from the molding die → blow air into the membrane tube (the membrane bubble is slightly inflated to prevent adhesion) → lower the temperature in the air and pull it slowly → heat the membrane tube to stretch the setting sleeve → cool down and set the setting → roll it
② The raw material mixing is the same as the production of ordinary PVC film (refer to Chapter 4).
③ Process temperature: barrel process temperature (from feeding section to homogenizing section): 140~150 ℃, 160~170 ℃, 180~190 ℃.
Forming mold temperature: 170~190 ℃. Water spraying temperature of hot stretching set sleeve: 85~95 ℃. Temperature of cooling setting water: 15~25 ℃
(4) Key points of process operation: the blowing ratio for heat shrinkable film forming is about 4, which is better; Pay attention to the uniformity of the film thickness to ensure the equilibrium of the film shrinkage rate when heated. The PVC resin used for food packaging film molding shall comply with GB4803-94 health standard, and various additives shall comply with - 442 Plastic Extrusion Molding Technician Manual
For example, QG 7555 of Sinopec Qilu Petrochemical Company, GPPS-350 of Shanghai Secco Petrochemical Co., Ltd. and 158K165H of Yangzi BASF Styrene Series Co., Ltd. can be used to extrude film (sheet) products.
② Equipment condition The equipment for polystyrene resin extrusion forming film (sheet) is usually a universal single screw extruder. The length diameter ratio L/D of the screw is 20~25, and the compression ratio is 2~2.5. When extruding the membrane, the coat hanger type molding die can be used to cool and shape the membrane with the three rollers in the process route shown in Figure 1-2. If the film is extruded and blown, the air cooling type shall be used to cool the film bubble.
③ Process temperature
a. The barrel temperature is 130~160 ℃, 160~180 ℃, 180~200 ℃.
b. The temperature of the forming die (coat hanger or manifold structure) is 200 ℃ in the middle and 210 ℃ at the ends on both sides.
c. When the temperature of the three rolls for cooling and setting is in accordance with the sheet feeding mode in Figure 6-3, the lower roll is 90 ℃, the middle roll is 85 ℃, and the upper roll is 80 ℃.
(4) Key points of process operation
① The extruded polystyrene film (sheet) shall be made of general grade polystyrene (GPPS) resin and high impact grade polystyrene (HIPS) resin. In order to obtain better product appearance quality, it is better to heat the resin for 1h at a temperature of about 70 ℃ before putting it into production.
② Extrude the plasticized polystyrene resin. The screw structure has no special requirements. The gradual change screw structure is used. The length diameter ratio is (20~25): 1, and the compression ratio is about 2.5- 444-
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