Polyethylene film with stable friction coefficient as well as preparation method and application thereof

Abstract

The invention relates to the field of packaging, in particular to a polyethylene film with a stable friction coefficient and a preparation method and application thereof. The polyethylene film comprises a corona layer, a middle layer and a heat sealing layer which are sequentially compounded, the corona layer is composed of linear low-density polyethylene and low-density polyethylene, the middle layer is composed of high-density polyethylene and low-density polyethylene, and the heat sealing layer is composed of metallocene polyethylene, low-density polyethylene and an anti-blocking agent; wherein the corona layer is made of linear low-density polyethylene with the Dow chemical mark of 2038.68 G, and the heat sealing layer is made of metallocene high-density polyethylene with the Dow chemical mark of 5408. The polyethylene film is excellent in stiffness, the friction coefficient of the film is very stable due to the use of the special resin, the phenomenon that the slipping agent is migrated to the surface of the corona layer is avoided, the friction coefficient of the inner-layer film is not greatly changed along with time, and the high-speed packaging requirement can be met.

Description

Technical Field

[0001] The invention belongs to the technical field of packaging, and in particular relates to a polyethylene film with a stable friction coefficient and a preparation method and application thereof. Background Art

[0002] With the development of the packaging industry and the upgrading of packaging equipment, higher requirements are placed on packaging efficiency and production capacity. How to maximize packaging efficiency is one of the main development goals.

[0003] Polyethylene (PE) film is the most commonly used inner heat-sealing material in the packaging industry. In order to make the ordinary PE film roll neatly, the winding tension is generally large, and the surface tension of the heat-sealing layer is smaller than that of the corona layer. As time goes by or the temperature changes, the additives added in the heat-sealing layer will slowly precipitate and migrate to the surface of the corona layer, causing the friction coefficient of the PE film to change, resulting in a decrease in the matching of the unwinding speed and the machine when packaging the PE film. During the automatic packaging process, problems such as the film cannot be pulled, the machine is abnormal, and the machine is stuck may occur, affecting the packaging efficiency and packaging quality.

[0004] Therefore, a stable coefficient of friction (COF) is very important for the packaging industry and automatic packaging equipment. In the prior art, the friction coefficient is generally controlled by adding silicone additives and adjusting the film aging time. For example, patent CN105667011A discloses a composite film with a stable friction coefficient and inkjet-able and a preparation method thereof. A silicone lubricant is added to the heat-sealing layer to improve the stability of the friction coefficient of the inner surface of the film, but the addition of silicone lubricants has a certain effect on the heat-sealing properties of the film. The paper "Zhao Sufen, Liu Mengliang, Liu Xiaoyan, et al. Analysis and application of friction coefficient performance of solvent-free composite PE film [J]. Plastics, 2019, 48(03): 16-18." The friction coefficient is reduced by controlling the amount of lubricating masterbatch and the aging temperature, thereby controlling the degree of change in the friction coefficient, but the friction coefficient of the film finally prepared is not very uniform and stable.

[0005] Therefore, providing a polyethylene film with a stable friction coefficient to meet the needs of high-speed packaging is a technical problem that needs to be solved urgently. Summary of the invention

[0006] In order to solve the problems in the prior art, one of the objects of the present invention is to provide a polyethylene film with a stable friction coefficient.

[0007] The present invention adopts the following technical solutions:

[0008] A polyethylene film with a stable friction coefficient, the polyethylene film comprises a corona layer, an intermediate layer and a heat-sealing layer which are compounded in sequence, and the formulas of the layers are respectively:

[0009] Corona layer: 75wt% linear low-density polyethylene, 25wt% low-density polyethylene;

[0010] Middle layer: 75wt% high-density polyethylene, 25wt% low-density polyethylene;

[0011] Heat sealing layer: 79wt% metallocene polyethylene, 20wt% low-density polyethylene, 1wt% anti-blocking agent;

[0012] The linear low-density polyethylene in the corona layer is a linear low-density polyethylene with a grade of Dow Chemical 2038.68G, and the metallocene polyethylene in the heat-sealing layer is a metallocene high-density polyethylene with a grade of Dow Chemical 5408.

[0013] Preferably, the low-density polyethylene is BASF-YPC brand 2420H, and the high-density polyethylene is PTT brand HD3355F.

[0014] Preferably, the opening agent is Aaron brand AB-20LD opening agent.

[0015] Preferably, the total thickness of the polyethylene film is 70 μm, and the thickness ratio of the corona layer, the intermediate layer and the heat-sealing layer is 3:8:3.

[0016] A second object of the present invention is to provide a method for preparing the polyethylene film having a stable friction coefficient as described above, comprising the following steps:

[0017] S1. According to the formula composition of the corona layer, the middle layer and the heat sealing layer, weigh the required weight portions of the component particles and add them into the barrel of the film blowing equipment respectively;

[0018] S2. The component particles in the barrel are mixed and melted to form a tube billet. After the tube billet is stretched, compressed air is blown out from the center of the extruder die head to form a film bubble. The film bubble is cooled and shaped by an air ring to obtain the desired polyethylene film.

[0019] Preferably, during extruder blow molding, the barrel temperature of the corona layer is 175°C / 180°C / 180°C / 180°C / 180°C / 180°C, the barrel temperature of the intermediate layer is 175°C / 180°C / 180°C / 180°C / 180°C / 180°C, and the barrel temperature of the heat sealing layer is 170°C / 175°C / 175°C / 175°C / 175°C / 175°C.

[0020] Preferably, when the extruder is blowing film, the die head temperature in the extruder is 180°C.

[0021] Preferably, after the film bubble is cooled and shaped by an air ring, it also has a winding process, and the winding tension is 45N.

[0022] A third object of the present invention is to provide a polyethylene film with a stable friction coefficient as described above for use in product packaging.

[0023] The beneficial effects of the present invention are:

[0024] The polyethylene film of the present invention adopts a special formula, and the heat sealing layer uses a special metallocene resin 5408, without adding any additional lubricant, which can greatly improve the heat sealing strength. At the same time, the resin is embedded with a non-migratable opening agent and a lubricant, which can not only provide the film with good opening and lubricity, but also maintain high stability under high temperature and high humidity conditions.

[0025] The composite layer and middle layer of the film are made of linear low-density polyethylene (LLDPE) which has a relatively high density (density of 0.935) in LDPE. While ensuring the composite strength, the film has excellent stiffness and can be wound with a smaller winding tension, thus avoiding the migration of the heat-sealing layer additive to the composite layer surface when the film is wound, which would affect the friction coefficient of the film.

[0026] If the film winding tension is too high, the migration of the additives will be accelerated under high temperature and high humidity conditions. The general film winding tension needs to be around 70N. The film of the present application has excellent stiffness and can reduce the winding tension of the A / B side, avoiding excessive winding of the film while ensuring that the film is neatly wound, further reducing the migration rate of the additives and improving the stability of the film friction coefficient.

[0027] The test results under high temperature environment show that the internal / internal friction coefficient of the film of the present application is very stable over time, basically maintained at about 0.2. However, the friction coefficient of ordinary PE varies greatly over time and the friction coefficient at the initial off-machine, and has poor stability.

[0028] The polyethylene film of the present application has excellent stiffness, and the use of special resin makes the film friction coefficient very stable, and the phenomenon of lubricant migration to the surface of the corona layer will not occur. Therefore, the COF of the inner film will not change significantly over time, and the stability is very good, which is suitable for high-speed packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the layered structure of the polyethylene film provided by the present invention.

[0030] The meanings of the symbols in the figure are as follows:

[0031] 10-corona layer 20-middle layer 30-heat sealing layer DETAILED DESCRIPTION

[0032] The technical solution of the present invention is described below in conjunction with embodiments to facilitate understanding by those skilled in the art.

[0033] A polyethylene film with a stable friction coefficient comprises a corona layer 10, an intermediate layer 20 and a heat-sealing layer 30 which are laminated in sequence. The total thickness of the polyethylene film is 70 μm, and the thickness ratio of the corona layer 10, the intermediate layer 20 and the heat-sealing layer 30 is 3:8:3. In the film:

[0034] The corona layer 10 is composed of two raw materials, 75wt% linear low-density polyethylene and 25wt% low-density polyethylene. The linear low-density polyethylene is selected from Dow Chemical's linear low-density polyethylene of grade 2038.68G, which does not contain additives and has a density of 0.935. Compared with the ordinary LLDPE with a minimum density of 0.915, it can provide PE film with high composite strength and very good stiffness; the low-density polyethylene is selected from Yangba Petrochemical's low-density polyethylene of grade 2420H, which can greatly improve the processing performance of the film.

[0035] The middle layer 20 is made of 75wt% high-density polyethylene and 25wt% low-density polyethylene. The high-density polyethylene is HD3355F from PTT Thailand, which has a density of 0.962 and can provide good stiffness for the film; the low-density polyethylene is 2420H from Yangba Petrochemical, which can greatly improve the processing performance of the film.

[0036] The heat seal layer 30 is composed of three raw materials: 79wt% metallocene polyethylene, 20wt% low-density polyethylene and 1wt% opening agent. The metallocene polyethylene uses metallocene high-density polyethylene of Dow Chemical brand 5408, which is polymerized from 8C polyethylene monomers. A certain amount of non-migrating inorganic opening agent and lubricant are embedded in its ethylene monomer, making the film friction coefficient very stable, and the problem of unstable friction coefficient caused by the migration of lubricants will not occur. The low-density polyethylene uses low-density polyethylene of Yangba Petrochemical brand 2420H, which can greatly improve the processing performance of the film; the opening agent uses Aaron brand AB-20LD opening agent, whose main component is silicon dioxide, which will not migrate in a high temperature and high humidity environment to affect the friction coefficient of the film.

[0037] The processing method of the above film comprises the following steps:

[0038] S1. According to the formula composition of the corona layer 10, the intermediate layer 20 and the heat sealing layer 30, the required weight portions of the component particles are weighed and added into the barrel of the film blowing equipment respectively;

[0039] S2. The component particles in the barrel are mixed and melted to form a tube billet. After the tube billet is stretched, compressed air is blown out from the center of the extruder die head to form a film bubble. The film bubble is cooled and shaped by an air ring to obtain the desired polyethylene film.

[0040] The detailed processing technology in this step is shown in Table 1:

[0041] Table 1 Film blowing process

[0042]

[0043]

[0044] Generally, the winding tension of the film needs to be around 70N, but too much winding tension will accelerate the migration of additives under high temperature and high humidity conditions. In this application, since the film has excellent stiffness, the winding tension of the A / B side can be reduced to 45±10N, which will not make the film too tight while ensuring that the film is neatly wound, which is conducive to maintaining a stable friction coefficient of the film.

[0045] According to the formulation of the present application, Examples 1 and 2 were prepared respectively, and placed together with the comparative example in a high temperature environment to test the friction coefficient. The formulation is shown in Table 2, and the test results are shown in Table 3.

[0046] Table 2 Experimental film formulations

[0047]

[0048]

[0049] Table 3 Test results

[0050]

[0051] As can be seen from Table 3, the film prepared by the formula of the present application has a small elongation at break, and the change of the heat seal layer formula has little effect on the elongation at break. In a high temperature environment, as time goes by, the friction coefficient inside / outside the film of Example 1 of the present application is very stable, basically maintained at around 0.2. The friction coefficient of the films of Examples 2, 3 and Comparative Example 1 gradually increases with the passage of time, wherein the difference in friction coefficient between Example 2 and the initial off-machine time is 0.07, and the friction coefficient between Example 3 and the initial off-machine time is 0.13, indicating that the heat seal layer formula is the key to affecting the dynamic friction coefficient, and the addition amount of 5408 has a significant effect on the film material coefficient. When the addition amount of 5408 is 79%, the film effect is the best, while the final friction coefficient of Comparative Example 1 is very different from the initial off-machine time, reaching 0.28, and the friction coefficient is unstable, which will affect the effect on the packaging machine.

[0052] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A polyethylene film with a stable friction coefficient, characterized in that: The polyethylene film comprises a corona layer, an intermediate layer and a heat-sealing layer which are compounded in sequence, and the formulas of the layers are respectively: Corona layer: 75wt% linear low-density polyethylene, 25wt% low-density polyethylene; Middle layer: 75wt% high-density polyethylene, 25wt% low-density polyethylene; Heat sealing layer: 79wt% metallocene polyethylene, 20wt% low-density polyethylene, 1wt% anti-blocking agent; The linear low-density polyethylene in the corona layer is a linear low-density polyethylene with a grade of Dow Chemical 2038.68G, and the metallocene polyethylene in the heat-sealing layer is a metallocene high-density polyethylene with a grade of Dow Chemical 5408.

2. The polyethylene film with a stable friction coefficient according to claim 1, characterized in that: The low-density polyethylene is 2420H, a brand of Yangba Petrochemical, and the high-density polyethylene is HD3355F, a brand of PTT.

3. The polyethylene film with a stable friction coefficient according to claim 1, characterized in that: The opening agent is the Aaron brand AB-20LD opening agent.

4. The polyethylene film with a stable friction coefficient according to claim 1, characterized in that: The total thickness of the polyethylene film is 70 μm, and the thickness ratio of the corona layer, the middle layer and the heat-sealing layer is 3:8:

3.

5. A method for preparing a polyethylene film with a stable friction coefficient according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. According to the formula composition of the corona layer, the middle layer and the heat sealing layer, weigh the required weight portions of the component particles and add them into the barrel of the film blowing equipment respectively; S2. The component particles in the barrel are mixed and melted to form a tube billet. After the tube billet is stretched, compressed air is blown out from the center of the extruder die head to form a film bubble. The film bubble is cooled and shaped by an air ring to obtain the desired polyethylene film.

6. The method for preparing a polyethylene film having a stable friction coefficient according to claim 5, characterized in that: During extruder blow molding, the barrel temperature of the corona layer is 175℃ / 180℃ / 180℃ / 180℃ / 180℃ / 180℃, the barrel temperature of the intermediate layer is 175℃ / 180℃ / 180℃ / 180℃ / 180℃ / 180℃ / 180℃, and the barrel temperature of the heat sealing layer is 170℃ / 175℃ / 175℃ / 175℃ / 175℃ / 175℃ / 175℃.

7. The method for preparing a polyethylene film having a stable friction coefficient according to claim 6, characterized in that: When the extruder is used for film blowing, the die head temperature of the extruder is 180°C.

8. The method for preparing a polyethylene film having a stable friction coefficient according to claim 5, characterized in that: After the film bubble is cooled and shaped by the air ring, it also has a winding process, and the winding tension is 45N.

9. Use of the polyethylene film with a stable friction coefficient as claimed in any one of claims 1 to 4 in product packaging.

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