Highly transparent polyethylene blown film for industrial packaging and method for its production

Abstract

The application discloses a kind of high-transparency polyethylene blown film for industrial packaging and preparation method thereof, belong to packaging film technical field, characterized by: film body is from outside to inside sequentially by outer layer, middle layer and inner layer;Outer layer is made of 6-9 mass fraction metallocene linear low density polyethylene, 1.5-2.5 mass fraction first low density polyethylene and 0.3-0.7 mass fraction PPA, middle layer is made of 8-11 mass fraction matte linear low density polyethylene, inner layer is made of 5.5-8.5 mass fraction metallocene linear low density polyethylene, 1.5-2.5 mass fraction first low density polyethylene, 0.3-0.7 mass fraction PPA and 0.3-0.7 mass fraction opening smooth agent.This film is through raw material ratio, not only maintains higher mechanical property, but also can greatly improve the stability of film bubble, the packaging film of thickness uniformity and width stability is prepared, but also can improve the plasticity of raw material, improve melt flow rate, reduce the generation of crystal point, eliminate the water ripples generated by melt rupture on film surface, so as to improve the transparency of film body.

Description

Technical Field

[0001] This invention belongs to the field of packaging film preparation technology, specifically relating to a high-permeability polyethylene blown film for industrial packaging and its preparation method. Background Technology

[0002] Polyethylene film plays a vital role in packaging materials and is highly favored in the food, pharmaceutical, and various industrial product packaging industries. Because industrial products are significantly heavier than food and pharmaceutical products—sometimes thousands of times heavier—the polyethylene packaging film for industrial products requires higher mechanical properties. This necessitates the use of metallocene linear low-density polyethylene (MDPE), a material with a relatively high molecular weight, as the primary raw material for industrial polyethylene packaging films. While meeting usage requirements, this also reduces the film's transparency, limiting it to only 85%.

[0003] With the increasing convenience of people's lives and work habits, higher requirements have been placed on the transparency of polyethylene packaging films in order to observe the condition of packaged goods through the packaging film. This creates an irreconcilable contradiction between this requirement and high mechanical properties. To address this, invention patent CN102476491A discloses a method and process for manufacturing a high-transparency composite plastic film. This method involves applying an anti-reflection layer to the outside of a polyamide / polyethylene (PA / PE) composite layer. The anti-reflection layer is made of polypropylene (PP), biaxially oriented polypropylene (BOPP), low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), or polyvinyl chloride (PVC). While this film utilizes the principle that thin-film interference can significantly reduce the intensity of reflected light, thereby enhancing transmitted light and improving the film's transparency, it can only be formed through biaxial stretching. This not only reduces production efficiency but also weakens the film's mechanical properties, thus failing to meet the requirements for high mechanical performance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a high-transparency polyethylene blown film for industrial packaging and its preparation method, which can greatly reduce the haze of the packaging film and improve its transparency while meeting the mechanical properties required for industrial packaging.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is: to design a high-permeability polyethylene blown film for industrial packaging, comprising a film body, wherein the film body is composed of an outer layer, a middle layer and an inner layer from the outside to the inside; characterized in that:

[0006] The outer layer is made of the following raw materials in parts by weight:

[0007] 6-9 parts of metallocene linear low-density polyethylene

[0008] First, 1.5 to 2.5 parts of low-density polyethylene.

[0009] PPA 0.3-0.7 parts

[0010] The intermediate layer is made from the following parts by weight of raw materials:

[0011] 8-11 parts of matte linear low-density polyethylene

[0012] The surface gloss of matte linear low-density polyethylene is 12-15%, and its haze is 70-75%.

[0013] The inner layer is made of the following raw materials in parts by weight:

[0014] Metallocene linear low-density polyethylene, 5.5–8.5 parts

[0015] First, 1.5 to 2.5 parts of low-density polyethylene.

[0016] PPA 0.3-0.7 parts

[0017] Opening slip agent 0.3-0.7 parts

[0018] The opening slip agent is made from the following raw materials in the following weight percentages:

[0019] Erucamide 3-7%

[0020] Microcrystalline glass 12-18%

[0021] Secondary low-density polyethylene 76-84%

[0022] The metallocene polyethylene is graded SP1520, and the first low-density polyethylene is graded 105BR.

[0023] Preferably, the outer layer is made of the following raw materials in parts by weight:

[0024] 7.5 parts of metallocene linear low-density polyethylene

[0025] Two parts of the first low-density polyethylene

[0026] 0.5 parts PPA

[0027] The intermediate layer is made from the following parts by weight of raw materials:

[0028] 9.5 parts of matte linear low-density polyethylene

[0029] The inner layer is made of the following raw materials in parts by weight:

[0030] 7 parts of metallocene linear low-density polyethylene

[0031] Two parts of the first low-density polyethylene

[0032] 0.5 parts PPA

[0033] 0.5 parts of opening slip agent

[0034] The opening slip agent is made from the following raw materials in the following weight percentages:

[0035] 5% erucamide

[0036] 15% of microcrystalline glass

[0037] Second, low-density polyethylene 80%.

[0038] Preferably, the grade of matte linear low-density polyethylene is FB2230.

[0039] Preferably, the thickness of the membrane body is 50–100 μm.

[0040] Preferably, the thickness ratio of the outer layer, the middle layer, and the inner layer is 2:1:2.

[0041] This invention also provides a method for preparing a high-permeability polyethylene blown film for industrial packaging, characterized by comprising the following steps:

[0042] (1) Preparation of the first special material: Mix 6-9 parts by weight of metallocene linear low-density polyethylene, 1.5-2.5 parts by weight of first low-density polyethylene and 0.3-0.7 parts by weight of PPA to obtain the first mixture;

[0043] (2) Preparation of the second special material: Mix 5.5 to 8.5 parts by weight of metallocene linear low-density polyethylene, 1.5 to 2.5 parts by weight of first low-density polyethylene, 0.3 to 0.7 parts by weight of PPA and 0.3 to 0.7 parts by weight of opening slip agent to obtain the second mixture;

[0044] The opening slip agent is made of erucamide, microcrystalline glass, and second low-density polyethylene. The mass percentage of erucamide in the opening slip agent is 3-7%, the mass percentage of microcrystalline glass is 12-18%, and the mass percentage of second low-density polyethylene is 76-84%.

[0045] (3) Co-extrusion blown film: The first mixture obtained in step (1), matte linear low-density polyethylene and the second mixture obtained in step (2) are co-extruded and blown in multiple layers to form an outer layer, a middle layer and an inner layer of packaging film arranged from the outside to the inside;

[0046] The metallocene polyethylene is graded SP1520, the first low-density polyethylene is graded 105BR, and the matte linear low-density polyethylene has a surface gloss of 12-15% and a haze of 70-75%.

[0047] Preferably, in step (1), the first mixture is composed of 7.5 parts by mass of metallocene linear low-density polyethylene, 2 parts by mass of first low-density polyethylene and 0.5 parts by mass of PPA;

[0048] In step (2), the second mixture is composed of 7 parts by mass of metallocene linear low-density polyethylene, 2 parts by mass of first low-density polyethylene, 0.5 parts by mass of PPA and 0.5 parts by mass of opening slip agent; the mass percentage of erucamide in the opening slip agent is 5%, the mass percentage of microcrystalline glass in the opening slip agent is 15%, and the mass percentage of second low-density polyethylene in the opening slip agent is 80%.

[0049] Preferably, the grade of the first low-density polyethylene is the same as that of the second low-density polyethylene.

[0050] Preferably, the first mixture in step (1) and the second mixture in step (2) are both granulated before entering step (3).

[0051] Preferably, in step (3), the extrusion temperature of the outer and inner layers is 165-175°C, and the extrusion temperature of the middle layer is 160-170°C.

[0052] Preferably, in step (3), the thickness ratio of the outer layer, the middle layer and the inner layer is 2:1:2.

[0053] Preferably, in step (3), the thickness of the packaging film is 50 to 100 μm.

[0054] Preferably, the grade of PPA is PEA-3S, the grade of matte linear low-density polyethylene is FB2230, and the grade of the opening slip agent is SAB-957.

[0055] Compared with the prior art, the beneficial effects of the present invention are:

[0056] 1. The raw material ratio of each layer of the present invention not only maintains the high mechanical properties of the packaging film, but also greatly improves the stability of the film bubble, thereby producing a packaging film with uniform thickness and stable width. It can also improve the plasticity of the raw materials, improve the melt flow rate, reduce the generation of crystal points, eliminate water ripples caused by melt rupture on the film surface, thereby improving the transparency of the film.

[0057] 2. Those skilled in the art generally believe that matte materials, due to their high surface roughness or microstructure, produce a matte effect and reduce the light transmittance of the film. Therefore, they are generally not used to enhance the light transmittance of the film. However, this application cleverly uses matte linear low-density polyethylene as the intermediate layer, and uses highly transparent metallocene linear low-density polyethylene and low-density polyethylene on both sides. When light passes through the transparent outer layer, it undergoes a certain degree of scattering and refraction, resulting in the light reaching the intermediate layer having a strong directionality. The microstructure of matte linear low-density polyethylene can reduce the scattering and refraction of light out of the intermediate layer, thereby enhancing its light transmittance.

[0058] 3. Matte linear low-density polyethylene with grade FB2230 also has excellent toughness and high melt strength, which helps to improve the tensile and tear resistance of packaging films, thus resulting in better strength and toughness.

[0059] 4. The opening slip agent of the present invention not only does not affect the haze of the packaging film, but also helps to maintain or improve its transparency; it also reduces exudation, which helps to maintain the longevity of the film performance and reduces the contamination of the packaged goods by the exudate.

[0060] 5. This invention can enhance the compatibility between various materials, so that each layer is thermally fused together, thereby enhancing the overall performance of the membrane.

[0061] 6. This invention has a unique concept. By improving the raw material formula, the film can reduce haze and increase transparency while meeting excellent mechanical properties, thus meeting more needs in the packaging field and facilitating its promotion and application in the industry. Detailed Implementation

[0062] The present invention will now be described in further detail with reference to specific embodiments.

[0063] When the present invention is in use, the side closer to the packaged item is defined as the inner side, and the side farther away from the packaged item is defined as the outer side. Example 1

[0064] High-permeability polyethylene film for industrial packaging is prepared by the following steps:

[0065] (1) Preparation of the first special material: 7.5 parts by mass of metallocene linear low-density polyethylene, 2 parts by mass of first low-density polyethylene and 0.5 parts by mass of PPA are mixed to obtain the first mixture. The first mixture is granulated to obtain the first special material.

[0066] (2) Preparation of the second special material: 7 parts by mass of metallocene linear low-density polyethylene, 2 parts by mass of first low-density polyethylene, 0.5 parts by mass of PPA and 0.5 parts by mass of opening slip agent are mixed to obtain the second mixture. The second mixture is granulated to obtain the second special material.

[0067] The opening slip agent used is made of erucamide, microcrystalline glass, and second low-density polyethylene. The mass percentage of erucamide in the opening slip agent is 5%, the mass percentage of microcrystalline glass in the opening slip agent is 15%, and the mass percentage of second low-density polyethylene in the opening slip agent is 80%.

[0068] (3) Co-extrusion blown film: The first special material obtained in step (1), matte linear low-density polyethylene, and the second special material obtained in step (2) are co-extruded and blown in multiple layers to produce a packaging film with a thickness of 80 μm. The first special material, matte linear low-density polyethylene, and the second special material are arranged sequentially to form the outer layer, middle layer, and inner layer of the packaging film from the outside to the inside. The thickness ratio of the outer layer, middle layer, and inner layer is 2:1:2. The extrusion temperature of the outer layer and inner layer is 170℃, and the extrusion temperature of the middle layer is 165℃.

[0069] The metallocene polyethylene and the first low-density polyethylene used are both existing purchased products. The metallocene polyethylene is MLLDPE from Mitsui Chemicals of Japan, with the grade SP1520; the first low-density polyethylene is LDPE from ExxonMobil of the United States, with the grade 105BR. Furthermore, the first low-density polyethylene and the second low-density polyethylene in the opening slip agent can be of the same grade or different grades, as long as the carrier of the opening slip agent is low-density polyethylene, and there are no specific requirements for its specific grade.

[0070] The aforementioned matte linear low-density polyethylene (LLDPE) specifically uses Borouge's FB2230 grade LLDPE. Other grades of matte linear LLDPE can also be used, as long as their surface gloss is 12-15% and haze is 70-75%, they can all achieve the effect of enhancing transparency. Experiments have shown that using ExxonMobil's 105BR grade LDPE can enhance the strength and toughness of the packaging film. PPA is a processing aid that can eliminate sharkskin and watermarks caused by melt fracture, reduce crystal points caused by equipment and raw material factors, and improve the gloss and smoothness of the film surface. PPA-3S, a processing aid from Huayi-Weiba Packaging Additives Co., Ltd., can be used. Opening slip agents are also available as finished products, such as SAB-957 from Huayi-Weiba Packaging Additives Co., Ltd. Example 2

[0071] The difference between this embodiment and Embodiment 1 is that:

[0072] In step (1), the first mixture consists of 6 parts by mass of metallocene linear low-density polyethylene, 1.5 parts by mass of first low-density polyethylene and 0.3 parts by mass of PPA.

[0073] In step (2), the second mixture consists of 5.5 parts by mass of metallocene linear low-density polyethylene, 1.5 parts by mass of first low-density polyethylene, 0.3 parts by mass of PPA and 0.3 parts by mass of opening slip agent; the mass percentage of erucamide in the opening slip agent is 3%, the mass percentage of microcrystalline glass in the opening slip agent is 13%, and the mass percentage of second low-density polyethylene in the opening slip agent is 84%.

[0074] In step (3), the thickness of the packaged film is 50 μm, the extrusion temperature of the outer and inner layers is 165 °C, and the extrusion temperature of the middle layer is 160 °C.

[0075] The rest are the same as in Example 1. Example 3

[0076] The difference between this embodiment and Embodiment 1 is that:

[0077] In step (1), the first mixture consists of 9 parts by mass of metallocene linear low-density polyethylene, 2.5 parts by mass of first low-density polyethylene and 0.7 parts by mass of PPA.

[0078] In step (2), the second mixture consists of 8.5 parts by mass of metallocene linear low-density polyethylene, 2.5 parts by mass of first low-density polyethylene, 0.7 parts by mass of PPA and 0.7 parts by mass of opening slip agent; the mass percentage of erucamide in the opening slip agent is 7%, the mass percentage of microcrystalline glass in the opening slip agent is 17%, and the mass percentage of second low-density polyethylene in the opening slip agent is 76%.

[0079] In step (3), the thickness of the packaged film is 100 μm, the extrusion temperature of the outer and inner layers is 175 °C, and the extrusion temperature of the middle layer is 170 °C.

[0080] The rest are the same as in Example 1. Example 4

[0081] The difference between this embodiment and Embodiment 1 is that:

[0082] In step (1), the first mixture consists of 6 parts by mass of metallocene linear low-density polyethylene, 2.5 parts by mass of first low-density polyethylene and 0.4 parts by mass of PPA.

[0083] In step (2), the second mixture consists of 5.5 parts by mass of metallocene linear low-density polyethylene, 2.5 parts by mass of first low-density polyethylene, 0.6 parts by mass of PPA and 0.4 parts by mass of opening slip agent; the mass percentage of erucamide in the opening slip agent is 6%, the mass percentage of microcrystalline glass in the opening slip agent is 12%, and the mass percentage of second low-density polyethylene in the opening slip agent is 82%.

[0084] In step (3), the thickness of the packaged film is 60 μm, the extrusion temperature of the outer and inner layers is 170 °C, and the extrusion temperature of the middle layer is 165 °C.

[0085] The rest are the same as in Example 1. Example 5

[0086] The difference between this embodiment and Embodiment 1 is that:

[0087] In step (1), the first mixture consists of 9 parts by mass of metallocene linear low-density polyethylene, 1.5 parts by mass of first low-density polyethylene and 0.6 parts by mass of PPA.

[0088] In step (2), the second mixture consists of 8.5 parts by mass of metallocene linear low-density polyethylene, 1.5 parts by mass of first low-density polyethylene, 0.4 parts by mass of PPA and 0.6 parts by mass of opening slip agent; the mass percentage of erucamide in the opening slip agent is 4%, the mass percentage of microcrystalline glass in the opening slip agent is 18%, and the mass percentage of second low-density polyethylene in the opening slip agent is 78%.

[0089] In step (3), the thickness of the packaged film is 90 μm, the extrusion temperature of the outer and inner layers is 165 °C, and the extrusion temperature of the middle layer is 170 °C.

[0090] The rest are the same as in Example 1.

[0091] Comparative Example

[0092] The difference between this embodiment and Embodiment 1 is that:

[0093] The matte linear low-density polyethylene of the intermediate layer is replaced by a first special material; that is, the outer and intermediate layers of the packaging film are made of the first special material, and the extrusion temperature of the intermediate layer is the same as that of the outer layer. Everything else is the same as in Example 1.

[0094] The packaging films prepared in the above embodiments were subjected to performance tests in terms of thickness, tensile strength, tear strength, elongation, planar dart impact resistance, light transmittance, and haze, and were compared with those prepared in the comparative example. The tensile strength test was conducted according to ASTM standard D 882-02, Test method for tensile properties of plastic sheets; the tear strength test was conducted according to ASTM standard D 1004-13, American Standard for Materials and Testing; the planar dart impact test was conducted according to national standard GB / T9639.1-2008, Test method for impact resistance of plastic films and sheets, free-falling dart method; and the light transmittance and haze tests were conducted according to national standard GB / T2410-2008, Determination of light transmittance and haze of transparent plastics. The test results are as follows:

[0095]

[0096] As can be seen, compared with the comparative example, the packaging film prepared by the present invention, under the premise of the same thickness, number of layers and thickness of each layer, can maintain or slightly improve the mechanical properties such as tensile strength, tear strength, elongation and dart drop, while greatly reducing the haze of the packaging film, significantly improving the light transmittance, enhancing its transparency, and allowing the inner packaging to be clearly seen through the packaging film.

[0097] In this invention, the closed-form expression of raw material composition refers to the main raw material, that is, the raw material accounting for more than 99.5% of the total mass of the raw materials, and may also include other trace excipients. That is to say, based on the closed-form expression of raw material composition of this invention, if the proportion of added excipients in the total mass of the raw materials does not exceed 0.5%, it still falls within the protection scope of this invention.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A high-permeability polyethylene blown film for industrial packaging, comprising a film body, wherein the film body is composed of an outer layer, a middle layer, and an inner layer from the outside to the inside; characterized in that: The outer layer is made of the following raw materials in parts by weight: 6-9 parts of metallocene linear low-density polyethylene First, 1.5 to 2.5 parts of low-density polyethylene. PPA 0.3-0.7 parts The intermediate layer is made from the following parts by weight of raw materials: 8-11 parts of matte linear low-density polyethylene The surface gloss of matte linear low-density polyethylene is 12-15%, and its haze is 70-75%. The inner layer is made of the following raw materials in parts by weight: Metallocene linear low-density polyethylene, 5.5–8.5 parts First, 1.5 to 2.5 parts of low-density polyethylene. PPA 0.3-0.7 parts Opening slip agent 0.3-0.7 parts The opening slip agent is made from the following raw materials in the following weight percentages: Erucamide 3-7% Microcrystalline glass 12-18% Secondary low-density polyethylene 76-84% The metallocene linear low-density polyethylene is graded SP1520, the first low-density polyethylene is graded 105BR, the PPA is graded PEA-3S, and PAA is a processing aid.

2. The high-permeability polyethylene blown film for industrial packaging according to claim 1, characterized in that: The outer layer is made of the following raw materials in parts by weight: 7.5 parts of metallocene linear low-density polyethylene Two parts of the first low-density polyethylene 0.5 parts PPA The intermediate layer is made from the following parts by weight of raw materials: 9.5 parts of matte linear low-density polyethylene The inner layer is made of the following raw materials in parts by weight: 7 parts of metallocene linear low-density polyethylene Two parts of the first low-density polyethylene 0.5 parts PPA 0.5 parts of opening slip agent The opening slip agent is made from the following raw materials in the following weight percentages: 5% erucamide 15% of microcrystalline glass Second, low-density polyethylene 80%.

3. The high-permeability polyethylene blown film for industrial packaging according to claim 2, characterized in that: The grade of matte linear low-density polyethylene is FB2230.

4. The high-permeability polyethylene blown film for industrial packaging according to any one of claims 1 to 3, characterized in that: The thickness of the membrane body is 50–100 μm.

5. The high-permeability polyethylene blown film for industrial packaging according to claim 4, characterized in that: The thickness ratio of the outer layer, middle layer and inner layer is 2:1:

2.

6. A method for preparing a high-permeability polyethylene blown film for industrial packaging, characterized in that: Includes the following steps: (1) Preparation of the first special material: Mix 6-9 parts by weight of metallocene linear low-density polyethylene, 1.5-2.5 parts by weight of first low-density polyethylene and 0.3-0.7 parts by weight of PPA to obtain the first mixture; (2) Preparation of the second special material: Mix 5.5 to 8.5 parts by weight of metallocene linear low-density polyethylene, 1.5 to 2.5 parts by weight of first low-density polyethylene, 0.3 to 0.7 parts by weight of PPA and 0.3 to 0.7 parts by weight of opening slip agent to obtain the second mixture; The opening slip agent is made of erucamide, microcrystalline glass, and second low-density polyethylene. The mass percentage of erucamide in the opening slip agent is 3-7%, the mass percentage of microcrystalline glass is 12-18%, and the mass percentage of second low-density polyethylene is 76-84%. (3) Co-extrusion blown film: The first mixture obtained in step (1), matte linear low-density polyethylene and the second mixture obtained in step (2) are co-extruded and blown in multiple layers to form an outer layer, a middle layer and an inner layer of packaging film arranged from the outside to the inside; The metallocene linear low-density polyethylene is graded SP1520, the first low-density polyethylene is graded 105BR, the matte linear low-density polyethylene has a surface gloss of 12-15% and a haze of 70-75%, the PPA is graded PEA-3S, and PAA is a processing aid.

7. The method for preparing high-permeability polyethylene blown film for industrial packaging according to claim 6, characterized in that: In step (1), the first mixture is composed of 7.5 parts by mass of metallocene linear low-density polyethylene, 2 parts by mass of first low-density polyethylene and 0.5 parts by mass of PPA; In step (2), the second mixture is composed of 7 parts by mass of metallocene linear low-density polyethylene, 2 parts by mass of first low-density polyethylene, 0.5 parts by mass of PPA and 0.5 parts by mass of opening slip agent; the mass percentage of erucamide in the opening slip agent is 5%, the mass percentage of microcrystalline glass in the opening slip agent is 15%, and the mass percentage of second low-density polyethylene in the opening slip agent is 80%.

8. The method for preparing a high-permeability polyethylene blown film for industrial packaging according to claim 6 or 7, characterized in that: The grade of the first low-density polyethylene is the same as that of the second low-density polyethylene.

9. The method for preparing high-permeability polyethylene blown film for industrial packaging according to claim 8, characterized in that: The first mixture in step (1) and the second mixture in step (2) are both granulated before entering step (3).

10. The method for preparing high-permeability polyethylene blown film for industrial packaging according to claim 9, characterized in that: In step (3), the extrusion temperature of the outer and inner layers is 165-175℃, and the extrusion temperature of the middle layer is 160-170℃.

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