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CN-121973423-A - Extrusion blow molding injection molding composite forming process for food packaging plastic bottle

CN121973423ACN 121973423 ACN121973423 ACN 121973423ACN-121973423-A

Abstract

The invention relates to the technical field of high polymer material processing and plastic molding, and discloses an extrusion blow molding injection molding composite molding process of a food packaging plastic bottle. The process comprises the steps of extruding a pre-oriented tubular parison, performing primary inflation shaping to obtain a bottle body with uniform wall thickness, directly performing injection molding on a high-precision threaded bottle opening in a closed die, performing secondary inflation finishing to compensate local shrinkage, cooling, demolding, and performing online detection on the size and sealing performance. The whole process is integrated in a clean environment without intermediate transfer. The process obviously improves the structural precision, sealing reliability and surface smoothness of the bottle body, enhances the compression resistance and the falling performance, improves the production efficiency and the material utilization rate, and ensures that the finished product meets the food contact safety standard.

Inventors

  • LI MUSEN

Assignees

  • 青岛森丰塑胶包装制品有限公司

Dates

Publication Date
20260505
Application Date
20260309

Claims (10)

  1. 1. An extrusion blow molding injection molding composite molding process of a plastic bottle for food packaging is characterized by comprising the following steps: step 1, preparing a thermoplastic parison, namely heating food-grade polyethylene terephthalate particles to a preset melting temperature range, continuously extruding the food-grade polyethylene terephthalate particles through an extruder to form a tubular parison, wherein the parison has preset outer diameter and wall thickness, and synchronously applying axial stretching force to pre-orient a molecular chain structure in the extrusion process; Step 2, performing primary inflation shaping, namely introducing the thermoplastic parison into a blow molding die preheated to a preset temperature, introducing clean compressed air to perform primary inflation, enabling the parison to be attached to the inner cavity of the die to form a main body outline of the bottle body, and controlling the inflation ratio within a preset range to ensure that the deviation of the uniformity of the distribution of the wall thickness of the bottle body is smaller than a preset threshold value; step 3, injection molding the bottle mouth, namely injecting a homogeneous or heterogeneous thermoplastic material at a preset melting temperature into a bottle mouth molding cavity through an injection molding unit integrated on an upper die of the blow molding die in a closed state of the blow molding die, and directly integrally molding a high-precision threaded bottle mouth on the top of the preliminarily molded bottle body; Step 4, secondary inflation finishing, namely maintaining the mold to be closed after the injection molding of the bottle mouth is completed, and introducing compressed air again to perform secondary inflation to compensate local stress concentration and volume shrinkage caused by the injection molding of the bottle mouth, so that the overall dimensional stability of the bottle body is improved, and the surface finish reaches the preset roughness requirement; And 5, cooling, demolding and online detection, namely cooling the product to be below a preset temperature through a circulating cooling water channel arranged in the mold, automatically taking out the product by a mechanical arm after opening the mold, and synchronously carrying out non-contact optical detection on the size of the bottle mouth, the flatness of the sealing surface and the perpendicularity of the bottle body, wherein the detected qualified product enters the next process, and the unqualified product is automatically removed.
  2. 2. The extrusion-blow-molding injection-molding composite molding process of the plastic food packaging bottle according to claim 1, wherein the extruder in the step 1 is provided with a double-stage venting screw structure, has a preset length-diameter ratio and a preset compression ratio, the fluctuation of the melt temperature is controlled within a preset error range, the extrusion rate is precisely matched with the subsequent blow-molding beat, and the matching error is smaller than a preset threshold value.
  3. 3. The extrusion-blow-molding injection-molding composite molding process of the plastic bottles for food packaging according to claim 1, wherein the surface of the inner cavity of the blow-molding die in the step 2 is subjected to mirror polishing treatment, the surface roughness reaches the preset requirement, a zonal temperature control system is arranged, the surface is divided into an upper independent temperature control zone, a middle independent temperature control zone and a lower independent temperature control zone along the height direction of the bottle body, the temperature of each zone can be independently adjusted, and the adjustment precision meets the preset control requirement.
  4. 4. The extrusion-blow-molding injection molding composite molding process of the plastic bottles for food packages according to claim 1, wherein the injection unit in the step 3 adopts a precision injection molding mechanism driven by a servo motor, the response time of the injection speed is smaller than a preset threshold value, and a hot runner valve needle is arranged at the communication part between the injection runner and the inside of the bottle body, so that the backflow of the melt can be cut off immediately after the injection molding is finished.
  5. 5. The extrusion-blow-molding injection-molding composite molding process of the plastic food packaging bottle according to claim 1, wherein in the step 3, a high-hardness stainless steel insert is embedded in the bottle opening forming cavity, the surface hardness is larger than a preset hardness value, a micro cooling channel is integrated in the insert, and the flow speed of the cooling medium is in a preset range.
  6. 6. The process of claim 1, wherein the compressed air used for secondary inflation in step 4 is subjected to multistage filtration and drying, the dew point temperature is lower than a preset low temperature threshold, and the oil content is lower than a preset cleanliness standard.
  7. 7. The extrusion-blow-molding injection-molding composite molding process of the plastic food packaging bottle according to claim 1, wherein the non-contact optical detection system in the step 5 comprises a line laser scanner and a high-resolution industrial camera, the sampling frequency is a preset high-frequency value, and the tolerance of the external diameter of the bottle mouth, the flatness error of the sealing surface and the perpendicularity deviation of the bottle body can be measured in real time.
  8. 8. The extrusion blow molding and injection molding composite molding process of the food packaging plastic bottle according to claim 1, wherein the process is completed in a closed clean workshop in the whole process, the environmental cleanliness level is not lower than a preset cleanliness level, all equipment parts in contact with materials are made of food-grade stainless steel, and the surfaces of the equipment parts are subjected to electrolytic polishing treatment.
  9. 9. The process of claim 1, wherein the extrusion, blow molding and injection molding steps are performed continuously on the same integrated molding apparatus without intermediate transfer and secondary heating, and the single product molding cycle is within a predetermined period of time.
  10. 10. The process for extrusion blow molding and injection molding of plastic bottles for food packages according to claim 1 wherein said thermoplastic material is polyethylene terephthalate, polypropylene or blends thereof, wherein the intrinsic viscosity of the polyethylene terephthalate is within a predetermined range and the acetaldehyde content is less than a preset safety limit.

Description

Extrusion blow molding injection molding composite forming process for food packaging plastic bottle Technical Field The invention relates to the technical field of high polymer material processing and plastic molding, in particular to an extrusion blow molding injection molding composite molding process of a food packaging plastic bottle. Background With the continuous development of the food packaging industry, plastic bottles have become the main stream container for storing and transporting liquid foods due to the advantages of light weight, corrosion resistance, low cost and the like. In many molding processes, extrusion blow molding, injection molding and blow molding each have specific application scenes and are widely applied to the production of packaging products with different structure and performance requirements. The manufacturing of plastic bottles generally needs to consider the strength, the tightness, the appearance precision and the production efficiency of the bottle body, and therefore, higher requirements are put on the integration and the refinement of the forming process. However, it is difficult for the conventional single molding process to simultaneously satisfy the above multiple performance indexes. For example, extrusion blow molding is suitable for mass production of hollow containers, but has low bottle opening precision and difficult realization of high sealing performance, injection molding can ensure bottle opening size precision, but has limitations in bottle body uniformity and material utilization rate, and conventional blow molding process is limited by parison control capability, thus uneven wall thickness distribution is easy to cause, and mechanical property and appearance consistency of products are affected. In addition, the existing composite forming process is mostly connected by adopting step-by-step working procedures, the transfer and reheating processes among the working procedures not only reduce the production efficiency, but also easily introduce thermal degradation and dimensional deviation of materials, and are difficult to meet the severe standards of food-grade packaging on cleanliness and stability. Therefore, a composite molding process capable of efficiently fusing the advantages of extrusion, blow molding and injection molding is needed to realize the cooperative optimization of the food packaging plastic bottle in terms of structural precision, material performance and production efficiency. Disclosure of Invention The invention aims to provide an extrusion blow molding injection molding composite molding process for a food packaging plastic bottle, which can effectively solve the problems in the background technology. In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: An extrusion blow molding injection molding composite molding process for a plastic bottle for food packaging comprises the following specific steps of 1, preparing a thermoplastic parison, namely heating food-grade polyethylene terephthalate particles to a preset melting temperature range, continuously extruding the food-grade polyethylene terephthalate particles through an extruder to form a tubular parison, wherein the parison has a preset outer diameter and a preset wall thickness, and synchronously applying axial stretching force in the extrusion process to pre-orient a molecular chain structure; step 2, one-time inflation shaping, namely, introducing the thermoplastic parison into a blow molding die preheated to a preset temperature, introducing clean compressed air with the pressure of a preset value to perform primary inflation, enabling the parison to be attached to the inner cavity of the die to form the outline of the bottle body, controlling the inflation ratio within a preset range, simultaneously, ensuring that the uniformity deviation of the thickness distribution of the bottle body wall is smaller than a preset threshold value, step 3, injection molding the bottle mouth, namely, injecting a homogeneous or heterogeneous thermoplastic material at the preset melting temperature into the bottle mouth molding cavity through an injection molding unit integrated on the upper die in the closed state of the blow molding die, wherein the injection pressure is the preset value, the dwell time is the preset time period, directly integrally molding a high-precision threaded bottle mouth at the top of the bottle body which is preliminarily shaped, step 4, performing secondary inflation finishing, namely, maintaining the die closure, introducing the compressed air with the pressure of the preset value again to perform secondary inflation, compensating the local stress concentration and volume shrinkage caused by the bottle mouth injection molding, improving the integral size stability of the bottle mouth, enabling the surface finish to reach the roughness requirement of the bottle mouth, and step 5, cooling and detecting, namely, au