阅读说明：本技术 一种利用双泡法制备非交联双向拉伸pe热收缩膜的工艺 (Process for preparing non-crosslinked biaxially oriented PE (polyethylene) heat shrinkable film by using double-bubble method ) 是由 刘秋贵 刘焜 刘新 于 2020-12-18 设计创作，主要内容包括：本发明提供了一种利用双泡法制备非交联双向拉伸PE热收缩膜的工艺包括如下步骤：将聚乙烯原料分别经挤出机加热熔融后,共挤得到复合圆形管坯,同时通过内外冷却系统对所述复合圆形管坯进行冷却；将复合圆形管坯经牵引装置牵引至加热烘箱顶部；在牵引装置的驱动下,将所述圆形管坯从顶部向下依次经过加热烘箱,分段加热保温；对处理后的复合圆形管坯进行二次吹胀。采用本发明技术方案制备的PE热收缩膜,解决了纯PE作为原料生产热收缩膜过程中,膜体表面易破裂的问题,产品力学性能高于传统POF膜,接近交联热缩膜,使用过程中无有害物质渗漏,可应用于食品、生鲜等产品的包装,具有良好的稳定性和安全性,且纯PE膜有利于产品的循环利用。(The invention provides a process for preparing a non-crosslinked biaxially oriented PE heat shrinkable film by using a double-bubble method, which comprises the following steps: respectively heating and melting polyethylene raw materials through an extruder, co-extruding to obtain a composite round pipe blank, and cooling the composite round pipe blank through an internal and external cooling system; drawing the composite round pipe blank to the top of a heating oven through a drawing device; under the drive of a traction device, the circular tube blank sequentially passes through a heating oven from the top to the bottom, and is heated and insulated in sections; and carrying out secondary blowing on the treated composite round pipe blank. The PE heat shrinkable film prepared by the technical scheme solves the problem that the surface of a film body is easy to crack in the process of producing the heat shrinkable film by taking pure PE as a raw material, the mechanical property of the product is higher than that of the traditional POF film, the product is close to that of a cross-linked heat shrinkable film, no harmful substance leaks in the use process, the PE heat shrinkable film can be applied to the packaging of products such as food, fresh food and the like, the PE heat shrinkable film has good stability and safety, and the pure PE film is favorable for recycling the products.)

1. A process for preparing a non-crosslinked biaxially oriented PE heat shrinkable film by using a double-bubble method is characterized by comprising the following steps of:

step (1): respectively heating and melting polyethylene raw materials through an extruder, co-extruding to obtain a composite round pipe blank, and cooling the composite round pipe blank through an internal and external cooling system;

step (2): drawing the composite round pipe blank obtained in the step (1) to the top of a heating oven through a drawing device;

and (3): under the drive of a traction device, the circular tube blank sequentially passes through a heating oven from the top to the bottom, and is heated and insulated in sections;

and (4): and (4) performing secondary blowing on the composite round tube blank treated in the step (3), and cooling after blowing to obtain the heat shrinkable film.

2. The process for preparing non-crosslinked biaxially oriented PE heat shrinkable film according to claim 1, wherein the polyethylene raw material in step (1) comprises: at least one of linear low density polyethylene, low density polyethylene and high density polyethylene.

3. The process for preparing a non-crosslinked biaxially oriented PE heat shrinkable film according to claim 2, wherein the linear low density polyethylene has a melt index of 0.5 to 2g/10min and a density of 0.900 to 0.920g/cm³(ii) a The low density polyethylene has a melt index of 0.25-5 g/10min and a density of 0.910-0.925 g/cm³(ii) a The high-density polyethylene has a melt index of 0.35-8 g/10min and a density of 0.952-0.964 g/cm³。

4. The process for preparing a non-crosslinked biaxially oriented PE heat shrinkable film according to claim 3, wherein the linear low density polyethylene has a density of 0.912 to 0.913g/cm³。

5. The process for preparing the non-crosslinked biaxially oriented PE heat shrinkable film according to claim 1, wherein the heating temperature in the step (1) is 190 to 200 ℃.

6. The process for preparing the non-crosslinked biaxially oriented PE heat shrinkable film according to claim 1, wherein the drawing height difference in the step (2) is 12 to 20 m.

7. The process for preparing a non-crosslinked biaxially stretched PE heat shrinkable film according to claim 1, wherein the heating oven in the step (3) comprises 4 to 6 temperature sections from top to bottom, the temperature range is 195 to 250 ℃, and the gradient of each temperature section is 5 to 10 ℃.

8. The process for preparing a non-crosslinked biaxially oriented PE heat shrinkable film according to claim 1, wherein the blow-up ratio of the secondary blow-up in the step (4) is 4 to 6 times.

9. The process for preparing a non-crosslinked biaxially stretched PE heat shrinkable film according to claim 1, wherein in the step (4), the heat shrinkable film comprises 3 to 7 layers.

10. The process for preparing a non-crosslinked biaxially stretched PE heat shrinkable film according to claim 1, wherein the thickness of the heat shrinkable film in the step (4) is 10 to 30 um.

Technical Field

The invention relates to the technical field of plastic film packaging, in particular to a process for preparing a non-crosslinked biaxially oriented PE heat shrinkable film by using a double-bubble method.

Background

A heat shrinkable film is a thermoplastic film that is oriented by stretching in the machine direction and the transverse direction of the film during production and shrinks by heat during use. The heat shrinkability of films was used as early as 1936, and originally rubber films were primarily used for shrink-wrapping perishable foods. Nowadays, the heat-shrinkable technology has been developed to almost use plastic shrink films to package various commodities, and has wide applications in the fields of food and beverage, electronic products, automobile products, daily chemicals, stationery, medicine, and the like.

Along with the improvement of the requirements of consumers on health, environmental protection, green and the like, the heat shrinkable film is developed towards the direction of non-toxicity, degradability, convenient recycling and improvement of recycling rate. Polyethylene (PE) is one of the base materials commonly used as a heat shrinkable film, and low density polyethylene (ldpe) has received attention from packaging industry personnel because of its high impact strength, tear strength, stretch resilience, and thermal stability.

The thermal shrinkage film is usually processed by a double-bubble method, the physical principle of the double-bubble process is that when a high polymer is in a high elastic state, the high polymer is stretched and oriented, then the high polymer is quenched to be below the glass transition temperature, the molecular orientation is frozen, when an object is heated in the packaging process, the molecules are sent out due to the stress generated by the thermal motion of the molecules, and the molecules are recovered to the original state to generate shrinkage. In the traditional processing process of the double-bubble method, in order to ensure the stability of the blown film, a cross-linking reaction is needed to be carried out after the raw material tube blank is formed so as to improve the mechanical property of the polymer, thereby ensuring the stability of a film layer during the two-bubble blowing, but the cross-linking reaction can change the molecular form of the raw material, and even if a single olefin material is adopted, the cross-linked product cannot be recycled after being used.

At present, in the process of producing the heat shrinkable film by using pure PE as a raw material, due to the influence of the material quality of the PE material, even after the film blowing performance of the PE is improved by adopting a crosslinking method, the surface of a film body is still easy to crack in the second bubble film blowing process, and the PE heat shrinkable film with good mechanical property is difficult to stably produce.

Disclosure of Invention

The invention mainly aims to provide a process for preparing a non-crosslinked biaxially oriented PE heat shrinkable film by using a double-bubble method, and aims to solve the problem that the PE heat shrinkable film with good mechanical property is difficult to stably produce due to easy cracking of the film body surface in the process of producing the heat shrinkable film by using pure PE as a raw material at present.

In order to realize the purpose, the invention provides a process for preparing a non-crosslinked biaxially oriented PE heat shrinkable film by using a double-bubble method, which comprises the following steps:

step (1): respectively heating and melting polyethylene raw materials through an extruder, co-extruding to obtain a composite round pipe blank, and cooling the composite round pipe blank through an internal and external cooling system;

step (2): drawing the composite round pipe blank obtained in the step (1) to the top of a heating oven through a drawing device;

and (3): under the drive of a traction device, the circular tube blank sequentially passes through a heating oven from the top to the bottom, and is heated and insulated in sections;

and (4): and (4) performing secondary blowing on the composite round tube blank treated in the step (3), and cooling after blowing to obtain the heat shrinkable film.

Preferably, the polyethylene feedstock in step (1) comprises: at least one of linear low density polyethylene, low density polyethylene and high density polyethylene.

Preferably, the linear low density polyethylene has a melt index of 0.5 to 2g/10min and a density of 0.900 to 0.920g/cm³(ii) a The low density polyethylene has a melt index of 0.25-5 g/10min and a density of 0.910-0.925 g/cm³(ii) a The high-density polyethylene has a melt index of 0.35-8 g/10min and a density of 0.952-0.964 g/cm³。

Preferably, the density of the linear low-density polyethylene is 0.912-0.913 g/cm³。

Preferably, the heating temperature in the step (1) is 190-200 ℃.

Preferably, the traction height difference in the step (2) is 12-20 m.

Preferably, the heating oven in the step (3) comprises 4-6 temperature sections from top to bottom, the temperature range is 195-250 ℃, and the gradient of each temperature section is 5-10 ℃.

Preferably, the blow-up ratio of the secondary blow-up in the step (4) is 4 to 6 times.

Preferably, the heat shrinkable film in the step (4) comprises 3-7 layers.

Preferably, the thickness of the heat shrinkable film in the step (4) is 10um to 30 um.

According to the technical scheme, the polyethylene is used as the raw material, no other functional auxiliary agent is added, the prepared PE heat shrinkable film can be directly recycled, the utilization rate of the raw material is greatly improved, and the PE heat shrinkable film has a remarkable environmental protection value. According to the technical scheme, the polyethylene heat shrinkage film is processed by a double-bubble method process, the heating temperature in the first-bubble process and the second-bubble process is precisely controlled to be adapted to the melt index of different layers in a raw material polyethylene multilayer tube blank, and the synchronization of the induction temperature of polyethylene in different layers to heat radiation is ensured, so that the surface of the polyethylene film layer between different layers is synchronously stretched and blown, and the phenomenon of film layer breakage in the blowing process is avoided.

The PE heat shrinkable film prepared by the technical scheme of the invention has the mechanical property between that of the traditional POF film and that of the cross-linked heat shrinkable film, and has stable performance. And because no functional auxiliary agent is added, no harmful substance leaks in the using process of the product, the packaging film can be applied to the packaging of products such as food, fresh food and the like, and has good stability and safety.

Detailed Description

The technical solutions in the embodiments of the present invention are described clearly and completely below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Preparation of three-layer non-crosslinked biaxially oriented PE heat shrinkable film

The preparation method comprises the following steps: heating polyethylene raw materials to 190-200 ℃ through three extruders respectively, and then carrying out co-extrusion to obtain a composite round tube blank;

step (2) drawing the composite round pipe blank obtained in the step (1) to the top of a heating oven through a drawing device, wherein the drawing height is 12-20 m;

under the drive of a traction device, the round pipe blank sequentially passes through 5 heating ovens from the top to the bottom, and is heated and insulated in sections at the temperatures of 195 ℃, 200 ℃, 210 ℃, 215 ℃ and 220 ℃;

and (4) carrying out secondary blowing on the composite round tube blank treated in the step (3), wherein the blowing ratio is 5.2, the composite round tube blank is cooled after blowing to obtain the heat shrinkable film, and the thickness of the prepared heat shrinkable film is 10-20 microns.

Raw material ratio of three-layer non-crosslinked biaxially oriented PE heat shrinkable film

Example 1

The raw materials were selected as shown in the following table.

Example 2

The raw materials were selected as shown in the following table.

Example 3

The raw materials were selected as shown in the following table.

Example 4

The raw materials were selected as shown in the following table.

To better illustrate the beneficial effects of the examples of the present invention, a commercially available POF heat shrinkable film was used as comparative example 1, a commercially available crosslinked heat shrinkable film was used as comparative example 2, and the commercially available POF heat shrinkable film, the commercially available crosslinked heat shrinkable film, and the non-crosslinked biaxially oriented PE heat shrinkable films of examples 1 to 4 were subjected to performance tests, and the test results are shown in Table 1.

TABLE 1 Performance test results for comparative example 1 and examples 1-4

The results in table 1 show that, under a specific raw material ratio, the tensile strength and elongation at break of the three-layer non-crosslinked biaxially oriented PE heat shrinkable film prepared by the technical scheme of the present invention are between those of the commercially available POF heat shrinkable film and crosslinked heat shrinkable film, and the tear strengths of the three films are not greatly different from each other.

Example 5

This example differs from example 1 in that: and (3) under the drive of a traction device, sequentially passing the circular tube blank through 4 heating ovens from the top to the bottom, and carrying out sectional heating and heat preservation at the temperatures of 195 ℃, 205 ℃, 215 ℃ and 220 ℃.

Example 6

This example differs from example 1 in that: and (3) under the drive of a traction device, sequentially passing the circular tube blank through 6 heating ovens from the top to the bottom, and carrying out sectional heating and heat preservation at the temperatures of 195 ℃, 200 ℃, 205 ℃, 210 ℃, 215 ℃ and 220 ℃.

Example 7

This example differs from example 1 in that: and (3) under the drive of a traction device, sequentially passing the circular tube blank through 4 heating ovens from the top to the bottom, and carrying out sectional heating and heat preservation at the temperatures of 195 ℃, 205 ℃, 215 ℃ and 220 ℃.

Comparative example 2

This example differs from example 1 in that: and (3) under the drive of a traction device, sequentially passing the circular tube blank through 3 heating ovens from the top to the bottom, and carrying out sectional heating and heat preservation at the temperatures of 195 ℃, 210 ℃ and 220 ℃. The temperature rise process of the embodiment is rapid, so that the tube blank is soft collapsed and broken in the secondary bubble blowing process, and the finished product cannot be blown out.

The performance test of the non-crosslinked biaxially oriented PE heat shrinkable films prepared in example 1 and examples 5 to 7 is shown in Table 2.

Table 2 Performance test results of example 1 and examples 5 to 7

The results in table 2 show that the film body cracking phenomenon in the second-stage blowing process can be avoided by strictly controlling the heating gradient in the second stage, and the good mechanical properties of the non-crosslinked biaxially oriented PE heat shrinkable film can be maintained.

Preparation of five-layer non-crosslinked biaxially oriented PE heat shrinkable film

The preparation method comprises the following steps: heating polyethylene raw materials to 190-200 ℃ through five extruders respectively, and then carrying out co-extrusion to obtain a composite round tube blank;

step (2) drawing the composite round pipe blank obtained in the step (1) to the top of a heating oven through a drawing device, wherein the drawing height is 12-20 m;

under the drive of a traction device, the round pipe blank sequentially passes through 5 heating ovens from the top to the bottom, and is heated and insulated in sections at the temperatures of 195 ℃, 200 ℃, 210 ℃, 215 ℃ and 220 ℃;

and (4) carrying out secondary blowing on the composite round tube blank treated in the step (3), wherein the blowing ratio is 5.2, the composite round tube blank is cooled after blowing to obtain the heat shrinkable film, and the thickness of the prepared heat shrinkable film is 13-25 microns.

Raw material ratio of five-layer non-crosslinked biaxially oriented PE heat shrinkable film

Example 8

The raw materials were selected as shown in the following table.

Example 9

The raw materials were selected as shown in the following table.

Example 10

The raw materials were selected as shown in the following table.

Example 11

The raw materials were selected as shown in the following table.

The performance test of the non-crosslinked biaxially oriented PE heat shrinkable films prepared in examples 8 to 11 was performed, and the test results are shown in Table 3.

TABLE 3 Performance test results of examples 8 to 11

The results in table 3 show that the mechanical properties of the five-layer non-crosslinked biaxially oriented PE heat shrinkable film prepared by the technical scheme of the present invention are not much different from those of the three-layer non-crosslinked biaxially oriented PE heat shrinkable film in a specific raw material ratio, which indicates that the non-crosslinked biaxially oriented PE heat shrinkable film prepared by the present invention has good stability and controllability.

Preparation of seven-layer non-crosslinked biaxially oriented PE heat shrinkable film

The preparation method comprises the following steps: heating polyethylene raw materials to 190-200 ℃ through seven extruders respectively, and then carrying out co-extrusion to obtain a composite round tube blank;

step (2) drawing the composite round pipe blank obtained in the step (1) to the top of a heating oven through a drawing device, wherein the drawing height is 12-20 m;

under the drive of a traction device, the round pipe blank sequentially passes through 5 heating ovens from the top to the bottom, and is heated and insulated in sections at the temperatures of 195 ℃, 200 ℃, 210 ℃, 215 ℃ and 220 ℃;

and (4) carrying out secondary blowing on the composite round tube blank treated in the step (3), wherein the blowing ratio is 5.2, the composite round tube blank is cooled after blowing to obtain the heat shrinkable film, and the thickness of the prepared heat shrinkable film is 20-30 microns.

Raw material ratio of seven-layer non-crosslinked biaxially oriented PE heat shrinkable film

Example 12

The raw materials were selected as shown in the following table.

Example 13

The raw materials were selected as shown in the following table.

The performance tests of the non-crosslinked biaxially oriented PE heat shrinkable films prepared in examples 12 and 13 are shown in Table 4.

TABLE 4 results of the Performance test of examples 12 and 13

From the results in table 4, it can be seen that, under a specific raw material ratio, the seven-layer non-crosslinked biaxially oriented PE heat shrinkable film prepared by the technical scheme of the present invention has improved tensile strength, tear strength and elongation at break compared to three-layer or five-layer non-crosslinked biaxially oriented PE heat shrinkable film, which may be related to the film thickness, and the higher the thickness is, the corresponding mechanical properties are slightly improved.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the present specification and directly/indirectly applied to other related technical fields within the spirit of the present invention are included in the scope of the present invention.