阅读说明：本技术 基于电子辐照交联的聚乙烯收缩薄膜及其制备方法 (Polyethylene shrink film based on electron irradiation crosslinking and preparation method thereof ) 是由 焦逸清 于 2021-08-25 设计创作，主要内容包括：本发明涉及聚乙烯收缩薄膜技术领域,具体地说,涉及基于电子辐照交联的聚乙烯收缩薄膜及其制备方法。其包括两个表层和一个中间层组成；表层至少包括茂金属线性低密度聚乙烯、高密度聚乙烯、交联敏化剂和增强剂组成；中间层至少包括茂金属线性低密度聚乙烯、高密度聚乙烯、低密度聚乙烯、交联敏化剂和共聚树脂组成,该基于电子辐照交联的聚乙烯收缩薄膜及其制备方法中,通过重新设计聚乙烯收缩膜的配方,并且使用电子束对优化配方设计的聚乙烯收缩膜进行交联强化,可以显著的提高聚乙烯收缩膜的各项物理机械性能,从而提高聚乙烯收缩膜的适用性,在相同的性能要求下,可以显著地降低薄膜的厚度。(The invention relates to the technical field of polyethylene shrink films, in particular to a polyethylene shrink film based on electron irradiation crosslinking and a preparation method thereof. It comprises two surface layers and a middle layer; the surface layer at least comprises metallocene linear low-density polyethylene, high-density polyethylene, a crosslinking sensitizer and a reinforcing agent; the middle layer at least comprises metallocene linear low-density polyethylene, high-density polyethylene, low-density polyethylene, a crosslinking sensitizer and copolymer resin, and in the polyethylene shrink film based on electron irradiation crosslinking and the preparation method thereof, various physical and mechanical properties of the polyethylene shrink film can be remarkably improved by redesigning the formula of the polyethylene shrink film and using electron beams to crosslink and strengthen the polyethylene shrink film designed by the optimized formula, so that the applicability of the polyethylene shrink film is improved, and the thickness of the film can be remarkably reduced under the same performance requirement.)

1. The polyethylene shrink film based on electron irradiation crosslinking is characterized by comprising two surface layers and a middle layer;

the surface layer at least comprises the following raw materials: 78-82% of metallocene linear low-density polyethylene, 18-22% of high-density polyethylene, 0.5-2.5% of crosslinking sensitizer and 1-5% of reinforcing agent;

the intermediate layer at least comprises the following raw materials: 58 to 62 percent of metallocene linear low-density polyethylene, 18 to 22 percent of high-density polyethylene, 18 to 22 percent of low-density polyethylene, 0.5 to 2.5 percent of crosslinking sensitizer and 0.5 to 3 percent of copolymer resin;

the crosslinking sensitizer is at least one selected from trimethylolpropane triacrylate, triallyl cyanurate, triallyl isocyanurate, pentaerythritol triacrylate and trimethylolpropane triacrylate.

2. The electron irradiation crosslinked based polyethylene shrink film according to claim 1, characterized in that: the reinforcing agent is selected from various mixtures of calcium carbonate, mica powder and sodium silicate.

3. The electron irradiation crosslinked based polyethylene shrink film according to claim 1, characterized in that: the copolymer resin is selected from epoxy resin.

4. A method for preparing a polyethylene shrink film based on electron irradiation crosslinking, comprising the polyethylene shrink film based on electron irradiation crosslinking of claim 1, and comprising the following steps:

s1, adding metallocene linear low-density polyethylene, high-density polyethylene, a crosslinking sensitizer and a reinforcing agent into a double-screw extruder, and granulating after blending to obtain a surface layer material;

s2, adding metallocene linear low-density polyethylene, high-density polyethylene, low-density polyethylene, a crosslinking sensitizer and copolymer resin into a double-screw extruder, and granulating after blending to obtain an intermediate layer material;

s3, adding two parts of surface layer materials and one part of middle layer material into a three-layer co-extrusion film blowing machine for extrusion to obtain a semi-finished shrink film;

and S4, carrying out electron irradiation crosslinking on the polyethylene shrink film through an electron accelerator, and finally obtaining the polyethylene shrink film.

5. The method for preparing the electron irradiation crosslinking-based polyethylene shrink film according to claim 4, wherein: in the step S3, the thickness of the semi-finished shrink film is 58-62 um.

6. The method for preparing the electron irradiation crosslinking-based polyethylene shrink film according to claim 4, wherein: in S4, the energy level of the electron accelerator is 75-500 Kev.

7. The method for preparing the electron irradiation crosslinking-based polyethylene shrink film according to claim 4, wherein: in the S4, the irradiation dose is 25-75 Kev.

8. The method for preparing the electron irradiation crosslinking-based polyethylene shrink film according to claim 4, wherein: in the S4, the thickness of the polyethylene shrink film is 18-22 um.

Technical Field

The invention relates to the technical field of polyethylene shrink films, in particular to a polyethylene shrink film based on electron irradiation crosslinking and a preparation method thereof.

Background

PE shrink film is a special packaging material, mainly used for protecting and securing products, commonly used for beverages, cans, health products and daily chemicals etc., and can be transparent or colored, with or without printing, and has a film thickness of from 20 to 150 um. The production process of the PE shrink film comprises the steps of plasticizing and melting different resin raw materials through an extruder, extruding through a co-extrusion die, cooling and shaping, rolling, and then printing or cutting according to requirements;

the main defects of the existing PE shrink film are as follows:

1. the product strength is not enough, and although the PE shrink film generally uses polyethylene material with lower melt index, the strength of the conventional polyethylene still needs to be improved, and the defect is more obvious particularly on the package of some heavy objects. Generally, thicker packaging materials are required when packaging heavy products.

2. The product has poor adaptability, and different shrink films are required to be used for packaging different contents. For example, heavier products, and products with sharp corners typically require thicker packaging material to protect.

3. The appearance performance is poor, and the thicker the thickness of the packaging film, the more opaque the film appears (the higher the haze), and the poorer the appearance experience of the packaged goods.

Disclosure of Invention

The invention aims to provide a polyethylene shrink film based on electron irradiation crosslinking and a preparation method thereof, so as to solve the problems in the background technology.

In order to achieve the above objects, in one aspect, the present invention provides a polyethylene shrink film based on electron irradiation crosslinking, comprising two skin layers and an intermediate layer;

the surface layer at least comprises the following raw materials: 78-82% of metallocene linear low-density polyethylene, 18-22% of high-density polyethylene and 0.5-2.5% of crosslinking sensitizer;

the intermediate layer at least comprises the following raw materials: 58 to 62 percent of metallocene linear low-density polyethylene, 18 to 22 percent of high-density polyethylene, 18 to 22 percent of low-density polyethylene and 0.5 to 2.5 percent of crosslinking sensitizer;

the crosslinking sensitizer is at least one selected from trimethylolpropane triacrylate, triallyl cyanurate, triallyl isocyanurate, pentaerythritol triacrylate and trimethylolpropane triacrylate, the number of functional groups of the multifunctional monomer is significantly different from that of the radiation promoting effect, the trifunctional monomer is most effective, the difunctional monomer is next, and the monofunctional monomer is worst.

As a further improvement of the technical scheme, the reinforcing agent is selected from various mixtures of calcium carbonate, mica powder and sodium silicate and is used for reinforcing the toughness and strength of the surface layer.

As a further improvement of the technical scheme, the copolymerized resin is selected from epoxy resin, and the epoxy resin is added to enhance the viscosity of the middle layer, so that the surface layer and the middle layer have better adhesiveness, and the prepared film has better quality.

In another aspect, the present invention provides a method for preparing a polyethylene shrink film based on electron irradiation crosslinking, comprising any one of the above polyethylene shrink films based on electron irradiation crosslinking, the method comprising the following steps:

s1, adding metallocene linear low-density polyethylene, high-density polyethylene, a crosslinking sensitizer and a reinforcing agent into a double-screw extruder, and granulating after blending to obtain a surface layer material;

s2, adding metallocene linear low-density polyethylene, high-density polyethylene, low-density polyethylene, a crosslinking sensitizer and copolymer resin into a double-screw extruder, and granulating after blending to obtain an intermediate layer material;

s3, adding two parts of surface layer materials and one part of middle layer material into a three-layer co-extrusion film blowing machine for extrusion to obtain a semi-finished shrink film;

and S4, carrying out electron irradiation crosslinking on the polyethylene shrink film through an electron accelerator, and finally obtaining the polyethylene shrink film.

Preferably, in S3, the thickness of the semi-finished shrink film is 58-62 um.

Preferably, in S4, the electron accelerator has an energy level of 75 to 500 Kev.

Preferably, in the step S4, the irradiation dose is 25 to 75 Kev.

Preferably, in S4, the polyethylene shrink film has a thickness of 16-22 um.

In the invention, when the epoxy resin reacts with polyethylene, the acidic substance of the crosslinking sensitizer is used for catalysis, so that the resin has better fusibility and stronger viscosity; and when the surface layer and the middle layer are bonded, the reinforcing agent in the surface layer is dispersed through the acid substance applied in the crosslinking sensitizer under the action of high temperature, and the dispersed metal substance is fused into the middle layer, so that the toughness of the middle layer is enhanced, and the quality of the shrink film is further improved.

Compared with the prior art, the invention has the beneficial effects that:

according to the polyethylene shrink film based on electron irradiation crosslinking and the preparation method thereof, the formula of the polyethylene shrink film is redesigned, and the polyethylene shrink film designed by the optimized formula is subjected to crosslinking reinforcement by using electron beams, so that various physical and mechanical properties of the polyethylene shrink film can be remarkably improved, the applicability of the polyethylene shrink film is improved, the thickness of the film can be remarkably reduced under the same performance requirement, the consumption of raw material resin is reduced, and the low-carbon environmental protection and sustainable development of a packaging material are realized.

Drawings

FIG. 1 is an overall flow diagram of the present invention;

FIG. 2 is a schematic view of the high-energy electron beam cross-linked polyethylene of the present invention;

FIG. 3 is a diagram illustrating the energy level and penetration depth of an electron accelerator according to the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.

Example 1 a polyethylene shrink film crosslinked based on electron irradiation and a method for preparing the same, comprising:

preparation of modified resin

Adding 78% of metallocene linear low-density polyethylene, 22% of high-density polyethylene, 0.5% of crosslinking sensitizer and 1% of reinforcing agent into a double-screw extruder, and granulating after blending to prepare a surface layer material for later use; adding 58% of metallocene linear low-density polyethylene, 22% of high-density polyethylene, 20% of low-density polyethylene, 0.5% of crosslinking sensitizer and 0.5% of copolymer resin into a double-screw extruder, and granulating after blending to prepare an intermediate layer material for later use;

preparation of shrink film

Adding two parts of surface layer materials and one part of middle layer material into a three-layer co-extrusion film blowing machine for extrusion to prepare a semi-finished product shrink film with the thickness of 62 um; carrying out electron irradiation crosslinking on the polyethylene shrink film by an electron accelerator, wherein the energy level of the electron accelerator is 200Kev, and the irradiation dose is 50Kev, and finally preparing the polyethylene shrink film with the thickness of 22 um;

the electron irradiation can modify the polyethylene, the high-energy electron beam and the polyethylene polymer act to open the original chemical bond to generate free radicals, and the free radicals react with each other to form a new chemical bond, so that the polyethylene molecules are linked together and changed into a body structure from a linear structure;

the energy level of the electron accelerator determines the accelerated speed of the electron beam, so that the penetration depth of the electron beam is influenced, if the energy level is too low, the electron beam cannot penetrate through a material, the cross-linking radiation is not uniform, and if the energy level is too high, a large amount of energy is wasted;

the irradiation dose determines the degree of crosslinking of the material, thereby affecting the overall performance of the material. The irradiation dose is too low, the crosslinking degree is low, the material performance modification is not obvious, the irradiation dose is too high, not only can a large amount of energy be wasted, but also the material can be degraded and aged due to excessive irradiation, the performance is not increased and inversely reduced, and therefore, the proper irradiation dose is of great importance.

Example 2 a polyethylene shrink film crosslinked based on electron irradiation and a method for preparing the same, comprising:

preparation of modified resin

Adding 79% of metallocene linear low-density polyethylene, 21% of high-density polyethylene, 1% of crosslinking sensitizer and 2% of reinforcing agent into a double-screw extruder, and granulating after blending to prepare a surface layer material for later use; 59% of metallocene linear low-density polyethylene, 20% of high-density polyethylene and 21% of low-density polyethylene. Adding 1% of crosslinking sensitizer and 1% of copolymer resin into a double-screw extruder, blending and granulating to prepare an intermediate layer material for later use;

preparation of shrink film

Adding two parts of surface layer materials and one part of middle layer material into a three-layer co-extrusion film blowing machine for extrusion to obtain a semi-finished product shrink film with the thickness of 59 um; and (3) carrying out electron irradiation crosslinking on the polyethylene shrink film by an electron accelerator, wherein the energy level of the electron accelerator is 200Kev, and the irradiation dose is 50Kev, and finally preparing the polyethylene shrink film with the thickness of 19 um.

Example 3 a polyethylene shrink film crosslinked based on electron irradiation and a method for preparing the same, comprising:

preparation of modified resin

Adding 80% of metallocene linear low-density polyethylene, 20% of high-density polyethylene, 1.5% of crosslinking sensitizer and 3% of reinforcing agent into a double-screw extruder, and granulating after blending to prepare a surface layer material for later use; adding 60% of metallocene linear low-density polyethylene, 20% of high-density polyethylene, 20% of low-density polyethylene, 1.5% of crosslinking sensitizer and 1.5% of copolymer resin into a double-screw extruder, and granulating after blending to prepare an intermediate layer material for later use;

preparation of shrink film

Adding two parts of surface layer materials and one part of middle layer material into a three-layer co-extrusion film blowing machine for extrusion to prepare a semi-finished product shrink film with the thickness of 58 um; and (3) carrying out electron irradiation crosslinking on the polyethylene shrink film by an electron accelerator, wherein the energy level of the electron accelerator is 200Kev, and the irradiation dose is 50Kev, and finally preparing the polyethylene shrink film with the thickness of 18 um.

Example 4 a polyethylene shrink film crosslinked based on electron irradiation and a method for preparing the same, comprising:

preparation of modified resin

Adding 81% of metallocene linear low-density polyethylene, 19% of high-density polyethylene, 2% of crosslinking sensitizer and 4% of reinforcing agent into a double-screw extruder, and granulating after blending to prepare a surface layer material for later use; adding 61% of metallocene linear low-density polyethylene, 21% of high-density polyethylene, 18% of low-density polyethylene, 2% of crosslinking sensitizer and 2% of copolymer resin into a double-screw extruder, and granulating after blending to obtain an intermediate layer material for later use;

preparation of shrink film

Adding two parts of surface layer materials and one part of middle layer material into a three-layer co-extrusion film blowing machine for extrusion to prepare a semi-finished product shrink film with the thickness of 60 mu m; and (3) carrying out electron irradiation crosslinking on the polyethylene shrink film by an electron accelerator, wherein the energy level of the electron accelerator is 200Kev, and the irradiation dose is 50Kev, and finally preparing the polyethylene shrink film with the thickness of 20 um.

Example 5 polyethylene shrink film crosslinked based on electron irradiation and a method for preparing the same, comprising:

preparation of modified resin

Adding 82% of metallocene linear low-density polyethylene, 18% of high-density polyethylene, 2.5% of crosslinking sensitizer and 5% of reinforcing agent into a double-screw extruder, and granulating after blending to prepare a surface layer material for later use; adding 62% of metallocene linear low-density polyethylene, 19% of high-density polyethylene, 19% of low-density polyethylene, 2.5% of crosslinking sensitizer and 3% of copolymer resin into a double-screw extruder, and granulating after blending to prepare an intermediate layer material for later use;

preparation of shrink film

Adding two parts of surface layer materials and one part of middle layer material into a three-layer co-extrusion film blowing machine for extrusion to prepare a semi-finished product shrink film with the thickness of 61 um; and (3) carrying out electron irradiation crosslinking on the polyethylene shrink film by an electron accelerator, wherein the energy level of the electron accelerator is 200Kev, and the irradiation dose is 50Kev, and finally preparing the polyethylene shrink film with the thickness of 21 um.

In the above examples 1 to 5, the crosslinking sensitizer is selected from at least one of trimethylolpropane triacrylate, triallyl cyanurate, triallyl isocyanurate, pentaerythritol triacrylate and trimethylolpropane triacrylate, the number of functional groups of the multifunctional monomer is significantly different from that of the irradiation promoting effect, the trifunctional monomer is most effective, the bifunctional monomer is next to the bifunctional monomer, and the least the monofunctional monomer is to be the monofunctional monomer;

the reinforcing agent is selected from various mixtures of calcium carbonate, mica powder and sodium silicate and is used for enhancing the toughness and strength of the surface layer;

the copolymer resin is selected from epoxy resin, and the epoxy resin is added to enhance the viscosity of the middle layer, so that the surface layer and the middle layer have better adhesion, and the prepared film has better quality;

in the invention, when the epoxy resin reacts with polyethylene, the acidic substance of the crosslinking sensitizer is used for catalysis, so that the resin has better fusibility and stronger viscosity; and when the surface layer and the middle layer are bonded, the reinforcing agent in the surface layer is dispersed through the acid substance applied in the crosslinking sensitizer under the action of high temperature, and the dispersed metal substance is fused into the middle layer, so that the toughness of the middle layer is enhanced, and the quality of the shrink film is further improved.

The relevant indexes of the polyethylene shrink film based on electron irradiation crosslinking prepared by the invention are shown in the table 1:

TABLE 1

	Tensile strength (Mpa)	Puncture strength (N)	Falling label impact strength (g)
				Example 1	49.7	14.9	309
Example 2	53.5	15.2	341
				Example 3	55.3	15.6	387
Example 4	52.8	15.0	339
				Example 5	50.2	15.3	302

As shown in Table 1, the polyethylene shrink films prepared in examples 1-5 of the present invention based on electron irradiation crosslinking all have better tensile strength, puncture strength and dart impact strength, wherein the polyethylene shrink film has the best physical and mechanical properties when the surface layer material amount is 80% of metallocene linear low density polyethylene, 20% of high density polyethylene, 1.5% of crosslinking sensitizer and 3% of reinforcing agent, and the middle layer material amount is 60% of metallocene linear low density polyethylene, 20% of high density polyethylene, 20% of low density polyethylene, 1.5% of crosslinking sensitizer and 1.5% of copolymer resin in example 3.

Comparative example 1 a polyethylene shrink film and a method for preparing the same, comprising:

preparation of modified resin

Adding 80% of metallocene linear low-density polyethylene, 20% of high-density polyethylene and 3% of reinforcing agent into a double-screw extruder, and granulating after blending to prepare a surface layer material for later use; adding 60% of metallocene linear low-density polyethylene, 20% of high-density polyethylene, 20% of low-density polyethylene and 1.5% of copolymer resin into a double-screw extruder, and granulating after blending to prepare an intermediate layer material for later use;

preparation of shrink film

Adding two parts of surface layer materials and one part of middle layer materials into a three-layer co-extrusion film blowing machine for extrusion to prepare a semi-finished product shrink film; and (3) carrying out electron irradiation crosslinking on the polyethylene shrink film by an electron accelerator, wherein the energy level of the electron accelerator is 200Kev, and the irradiation dose is 50Kev, and finally preparing the polyethylene shrink film with the thickness of 16 um.

Comparative example 2 a polyethylene shrink film and a method for preparing the same, comprising:

preparation of modified resin

Adding 80% of metallocene linear low-density polyethylene, 20% of high-density polyethylene, 1.5% of crosslinking sensitizer and 3% of reinforcing agent into a double-screw extruder, and granulating after blending to prepare a surface layer material for later use; adding 60% of metallocene linear low-density polyethylene, 20% of high-density polyethylene, 20% of low-density polyethylene, 1.5% of crosslinking sensitizer and 1.5% of copolymer resin into a double-screw extruder, and granulating after blending to prepare an intermediate layer material for later use;

preparation of shrink film

And adding two parts of surface layer materials and one part of middle layer material into a three-layer co-extrusion film blowing machine for extrusion to obtain the polyethylene shrink film.

Comparative example 3 a polyethylene shrink film and a method for preparing the same, comprising:

preparation of modified resin

Adding 80% of metallocene linear low-density polyethylene, 20% of high-density polyethylene and 3% of reinforcing agent into a double-screw extruder, and granulating after blending to prepare a surface layer material for later use; adding 60% of metallocene linear low-density polyethylene, 20% of high-density polyethylene, 20% of low-density polyethylene and 1.5% of copolymer resin into a double-screw extruder, and granulating after blending to prepare an intermediate layer material for later use;

preparation of shrink film

And adding two parts of surface layer materials and one part of middle layer material into a three-layer co-extrusion film blowing machine for extrusion to obtain the polyethylene shrink film.

The polyethylene shrink film based on electron irradiation crosslinking prepared by the invention has better physical and mechanical properties, low cost consumption and lower thickness, has a larger relationship with the added crosslinking sensitizer used and electron irradiation crosslinking, and in order to verify the related technical scheme, the applicant performs the following tests:

comparative examples 1 to 3: by adopting the method of example 3, after the steps of crosslinking by the crosslinking sensitizer and electron irradiation crosslinking are removed, the indexes related to the prepared polyethylene shrink film are detected, which are specifically shown in table 2:

TABLE 2

	Tensile strength (Mpa)	Puncture strength (N)	Falling label impact strength (g)	Thickness (um)
					Comparative example 1	48.8	13.5	215	23
Comparative example 2	50.1	13.7	221	23
					Comparative example 3	47.7	13	193	23
Example 3	55.3	15.6	387	18

According to the table 2, after the crosslinking step of the crosslinking sensitizer and the electron irradiation crosslinking step are removed, the thickness of the polyethylene shrink film is increased, but the tensile strength, puncture strength and falling mark impact strength of the polyethylene shrink film are reduced to different degrees, so that it can be seen that the crosslinking step of the crosslinking sensitizer and the electron irradiation crosslinking step are important factors for changing the physical and mechanical properties of the polyethylene shrink film.

The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and the preferred embodiments of the present invention are described in the above embodiments and the description, and are not intended to limit the present invention. The scope of the invention is defined by the appended claims and equivalents thereof.