CN114643698A - Method for molding milk plastic bottle - Google Patents

Abstract

The invention discloses a method for molding a milk plastic bottle, which comprises the following steps: after die assembly, preprocessing the heated plastic bottle blank; then carrying out high-pressure blow molding crystallization molding on the plastic bottle blank; and carrying out post-treatment on the plastic bottle after molding. Wherein the high pressure blow molding crystallization comprises: s1, blowing air at high pressure for the first time until a plastic bottle blank is crystallized and preformed; s2, discharging a small amount of gas, and blowing gas at high pressure for the second time until the plastic bottle blank is crystallized and molded; and S3, blowing high-pressure cold air while exhausting air for the third time so as to crystallize and shape the plastic bottle blank. The invention solves the problems of no high temperature resistance and poor thermal stability of the existing milk plastic bottle, and has the advantages of low production cost, high production efficiency, simple process, high finished product quality and the like.

Description

Method for molding milk plastic bottle

Technical Field

The invention relates to the technical field of plastic bottle forming, in particular to a process method for forming a milk plastic bottle.

Background

With the change of petrochemical industry, the advantages of plastic raw materials compared with traditional raw materials are more obvious. For the bottle-making industry, the plastic bottle has the advantages of low cost, easy recovery, convenient disinfection and easy decoration, so that the plastic bottle can greatly replace the traditional glass packaging container, and the body image of the plastic bottle can be seen in various hot, cold and carbonated beverages and medical saline bottles. At present, plastic raw materials commonly used in the field of bottle making comprise PE, PP, PVC and the like, and are expanded to polyethylene terephthalate (PET), and the strong market demand makes the full-automatic rotary bottle blowing machine PMRB become the mainstream of a plastic bottle blowing machine. However, plastic bottles generally have poor heat resistance and cannot be used for filling hot liquids, for example, plastic containers with liquid temperatures higher than 65 ℃ are irreversibly deformed, which results in useless container bodies, and therefore, plastic bottles are generally used for filling cold-filled (i.e., cold-filled) beverages such as drinking water and soft drinks; in the case of fruit juice, sugar-containing beverages (without steam) or fruit, vegetable, cream, etc., hot-filling must be used in order to prevent bacterial growth and spoilage in sealed containers, so that the containers can withstand 98 ℃ to meet the need for sterilization, and therefore traditionally glass bottles are used for hot-filling or cold-filling only after preservatives are added. But the glass bottle has the defects of heavy weight and frangibility, and the excessive consumption of the preservative is harmful to human bodies; of course, the plastic container after being formed is specially treated and processed to make it suitable for high-temperature hot filling, but the processing procedure is complex, the production cost is high and the production speed is slow. Can a method be found for producing hot-fill plastic bottles with good heat resistance, material savings, and deformation not exceeding the allowable range?

At present, the existing bottle blowing process is one-step high-pressure blow molding crystallization molding, i.e. preheated plastic bottle blank is sent into a blow molding die to be directly blow molded by high-pressure gas. The internal molecular structure characteristics of the blown plastic bottle body are unstable, so that the milk plastic bottle is not high in temperature resistance and poor in thermal stability. The bottle body is deformed when filled with hot liquid. In order to produce a container bottle with good heat resistance and high heat stability.

Disclosure of Invention

The invention aims to provide a blowing process method for plastic, in particular PET (polyethylene terephthalate) material hot-filling plastic bottles, which has high thermal stability, no bottle deformation exceeding an allowable value at a high temperature of 95 ℃ and light gram weight.

A milk plastic bottle forming process method is designed according to the problems to be solved, and comprises the following steps: after die assembly, firstly pretreating a plastic bottle blank, then carrying out high-pressure blow molding crystallization molding on the plastic bottle blank, and carrying out post-treatment on the plastic bottle after molding, wherein the high-pressure blow molding crystallization molding is as follows:

s1, blowing air at high pressure for the first time until a plastic bottle blank is crystallized and preformed;

s2, discharging a small amount of gas, and blowing gas at high pressure for the second time until the plastic bottle blank is crystallized and molded;

and S3, blowing high-pressure cold air while exhausting air for the third time until the plastic bottle blank is crystallized and shaped, and thus obtaining the milk plastic bottle.

The pretreatment before the high-pressure blow molding crystallization molding is to stretch the plastic bottle blank longitudinally and stretch the plastic bottle blank transversely by preblowing. The pretreated plastic bottle blank is close to the film wall of the blow molding die, which is beneficial to the next step of blow molding crystallization molding. The post-treatment after the pressure blow molding crystallization molding comprises the steps of discharging high-pressure gas, cooling, opening the mold and taking out the bottle.

The gas pressure intensity adopted by the pre-blowing is 0.8-1.2 MPA, and the gas pressure intensity adopted by the blow molding crystallization molding is 3.5-4 MPa.

The time used in the whole process flow of the invention is 4s, wherein the time parameters of each stage are as follows: the time of longitudinal stretching is 850ms, the time of pre-blowing is 50ms, the time of first high-pressure air blowing is 1750ms, the time of discharging a small amount of gas is 100ms, the time of second high-pressure air blowing is 120ms, the time of third air discharging and air blowing is 500ms, the time of discharging high-pressure gas after forming is 100ms, the time of cooling is 30ms, the time of opening the die and taking out the bottle is 500ms, and the total time of the whole process flow is 4 s.

The temperature of the blow molding die is 145-170 ℃.

The invention carries out three times of high-pressure blow molding crystallization molding on the plastic bottle blank, prolongs the heat preservation time of producing the milk plastic bottle and improves the heat resistance of the milk plastic bottle. Wherein, the heated gas is continuously discharged, and new cold gas is blown in, which is beneficial to strengthening the crystallinity of the plastic bottle and the reasonable distribution of the crystallinity; the blowing process is characterized in that one-time high-pressure blowing and one-time exhaust are added in the traditional blowing process, namely three-time high-pressure blowing and three-time exhaust are carried out in a circulating mode, the pressure maintaining time is prolonged as much as possible, in the pressure maintaining period, the more heat-exchanging air pressure is discharged, new cold air is injected into the mold, the crystallinity of the plastic bottle is enhanced, the cooling efficiency of the plastic bottle is accelerated, and the reason is also the main reason for heat resistance of the finished bottle. The invention effectively solves the problems of no high temperature resistance and poor thermal stability of the existing milk plastic bottle. When the blown milk plastic bottle is filled with liquid with the temperature of more than 95 ℃, the bottle body is hardly deformed, and the heat resistance and the heat stability are obviously improved. And on the basis that the deformation of the bottle body does not exceed the allowable period, the material consumption of a single bottle can be reduced by about 7 percent, and the production cost is reduced. The time of the whole process for producing a single bottle is 4s, and compared with the time of 6s in the prior art, the time of the whole process for producing a single bottle obviously improves the production efficiency.

Detailed Description

The invention will be explained in more detail below by way of example for the production of PET milk plastic bottles.

A milk plastic bottle forming process method comprises the following steps: firstly, PET plastic bottle blanks heated to about 110 ℃ are fed into a blow molding die at 145-170 ℃. After die assembly, the plastic bottle blank is longitudinally stretched through a stretching mechanism, and then is transversely stretched by blowing gas with the pressure of 0.8-1.2 MPa. And then, carrying out primary high-pressure air blowing on the plastic bottle blank to enable the plastic bottle blank to be tightly attached to a high-temperature mold for crystallization and preforming. And (3) discharging a small amount of hot gas after preforming, wherein the plastic bottle has slight shrinkage deformation, and injecting high-pressure gas for the second time to enable the plastic bottle to be tightly attached to a high-temperature mold again for crystallization molding. And thirdly, discharging heated gas and blowing high-pressure cold air simultaneously to crystallize and shape the plastic bottle blank, thus obtaining the PET milk plastic bottle. Then discharging high-pressure blow molding gas, cooling, opening the mold and taking out the bottle.

On a production line for producing PET milk plastic bottles, the injection mold completes the whole process flow by rotating for one circle, and the time of one cycle is 4 s.

The time of longitudinal stretching is 850ms, and the rotation angle of the die is 76 degrees; the pre-blowing time is 50ms, and the rotation angle of the die is 5 degrees; the time of the first high-pressure air blowing is 1750ms, and the rotation angle of the die is 158 degrees; the time for exhausting a small amount of gas is 100ms, and the rotation angle of the die is 10 degrees; the time of the second high-pressure air blowing is 120ms, and the rotation angle of the die is 11 degrees; the time of high-pressure air blowing for the third time is 500ms, and the rotation angle of the die is 45 degrees; the time for exhausting high-pressure gas after molding is 100ms, and the rotation angle of the mold is 9 degrees; the cooling time is 30ms, and the rotation angle of the die is 2 degrees; the time for opening the mold and taking out the bottle is 500ms, and the rotation angle of the mold is 45 degrees. In the whole process flow, the blow mold rotates 360 degrees, namely a period from mold closing to mold opening to bottle taking, and the blow mold returns to the original point. Thus, the next PET plastic bottle blank can be received, and the plastic bottle blank is subjected to blow molding crystallization molding after the die is closed.

The invention carries out three times of high pressure blow molding crystallization molding on the PET plastic bottle blank, prolongs the heat preservation time of producing the milk plastic bottle and improves the heat resistance of the milk plastic bottle. Wherein the heated gas is continuously discharged and new cold gas is blown in, which is beneficial to strengthening the crystallinity of the plastic bottle and the reasonable distribution of the crystallinity. The invention effectively solves the problems of no high temperature resistance and poor thermal stability of the existing milk plastic bottle. When the blown PET milk plastic bottle is filled with liquid with the temperature of more than 95 ℃, the bottle body is hardly deformed, and the heat resistance and the heat stability are obviously improved. And on the basis that the deformation of the bottle body does not exceed the permitted period, the material consumption of a single bottle is reduced by about 7 percent, and the production cost is reduced. And the time of the whole process for producing a single bottle is 4s, compared with the time of 6s in the prior art, the production efficiency is obviously improved.

The above description is only a non-limiting embodiment of the present invention, and the material of the milk plastic bottle, the time of each stage, and the change in the rotation angle of the blow mold do not substantially affect the present invention, and are not exemplified many times. Furthermore, the blow mold does not need to be rotated to complete the entire process.

Claims (5)

1. A method for forming a milk plastic bottle comprises the following steps:

after die assembly, firstly pretreating a plastic bottle blank, then carrying out high-pressure blow molding crystallization molding on the plastic bottle blank, and carrying out post-treatment on the plastic bottle after molding, and the method is characterized in that:

high pressure blow molding crystallization molding is as follows:

s1, blowing air at high pressure for the first time until a plastic bottle blank is crystallized and preformed;

s2, discharging a small amount of gas, and blowing gas at high pressure for the second time until the plastic bottle blank is crystallized and molded;

s3, blowing high-pressure cold air for the third time while exhausting air until the plastic bottle blank is crystallized and shaped, and thus obtaining the milk plastic bottle;

the pretreatment before the high-pressure blow molding crystallization molding is to stretch the plastic bottle blank longitudinally and stretch the plastic bottle blank transversely by preblowing.

2. A method of forming milk plastic bottles according to claim 1, characterised in that: the post-treatment after the high-pressure blow molding crystallization molding comprises the steps of discharging high-pressure gas, cooling, opening the mold and taking out the bottle.

3. A method of forming milk plastic bottles according to claim 2, characterised in that: the gas pressure intensity adopted by the pre-blowing is 0.8-1.2 MPA, and the gas pressure intensity adopted by the high-pressure blow molding crystallization molding is 3.5-4 MPa.

4. A method of forming milk plastic bottles according to claim 3, characterised in that: the time used in the whole process flow is 4s, wherein the time parameters of each stage are as follows: the time of longitudinal stretching is 850ms, the time of pre-blowing is 50ms, the time of first high-pressure air blowing is 1750ms, the time of discharging a small amount of gas is 100ms, the time of second high-pressure air blowing is 120ms, the time of third air discharging and air blowing is 500ms, the time of discharging high-pressure gas after forming is 100ms, the time of cooling is 30ms, and the time of opening the die and taking out the bottle is 500 ms.

5. A method of forming milk plastic bottles according to claim 4, characterised in that: the temperature of the blow molding die is 145-170 ℃.