A transparent polyethylene film with stable friction performance and a preparation method thereof

Abstract

This invention discloses a transparent polyethylene film with stable frictional properties and its preparation method. The film is prepared from the following raw materials: 100 parts by weight of linear low-density polyethylene, 0.025-0.055 parts by weight of a compounded opening agent, 0.05-0.20 parts by weight of a slip agent, and 0.05-0.20 parts by weight of an antioxidant. The compounded opening agent is obtained by compounding silane-modified silica with a cyclic olefin polymer, and the mass ratio of silica to cyclic olefin polymer is 1:1 to 6:1. The slip agent is erucamide, and the melt flow rate of the cyclic olefin polymer at 230°C and 2.16 kg is 3 g / 10 min to 10 g / 10 min. By using two compounded opening agents, this invention significantly reduces the amount of silica used compared to the prior art using silica alone. At the same addition amount, it exhibits better opening and transparency compared to the prior art, and also has good friction coefficient stability.

Description

Technical Field

[0001] This invention belongs to the field of polyolefin film technology, specifically relating to a transparent polyethylene film with stable frictional properties and its preparation method. Background Technology

[0002] Due to their high coefficient of surface friction, plastic films tend to self-adhere and adhere to equipment surfaces during processing. To facilitate the processing of these films into finished packaging products or for shaping, feeding, and sealing, slip agents, anti-sticking agents, and opening agents must be added to the plastic films (sheets). Extrusion molding without these agents will result in adhesion to the rollers, causing wrinkles, an uneven surface, and even rendering the product unusable in subsequent processes.

[0003] Linear low-density polyethylene (LLDPE) exhibits superior puncture and tear resistance, and its processing performance and gloss are better than high-density polyethylene (HDPE). Its puncture resistance, tear strength, and environmental stress cracking resistance are also better than ordinary LLDPE. Due to its lower production cost, LLDPE has experienced rapid growth in recent years, with production capacity increasing for five consecutive years, totaling 15.6 million tons. LLDPE is primarily used to produce films and sheets, accounting for 79.9% of total consumption. It is widely used in agriculture, industry, and packaging. LLDPE film materials can be classified into three types based on their opening characteristics: unopened, open, and highly open. Non-opening LLDPE mainly includes products such as Shanghai SECCO LL0220AA, Dushanzi Petrochemical DFDA-7042, and Guoneng Ningxia Coal Industry DFDA-7042, primarily used in fields such as agricultural mulch film and stretch film. Opening LLDPE mainly includes products such as DFDA-7042 developed by Fushun Petrochemical and Lanzhou Petrochemical, primarily used for inner lining bags on automated production lines. High-opening LLDPE mainly includes products such as Zhenhai Refining & Chemical DFDC-7050H, Shanghai SECCO LL0220KJ, and Lanzhou Petrochemical DFDC-7042H, primarily used in high-speed automated packaging films for packaging food, hygiene products, textiles, magazines, etc., on high-speed production lines. However, during the blown film process, linear low-density polyethylene (LLDPE) is prone to adhesion between film layers, making them difficult to separate. Combined with the pressure roller extrusion, this further exacerbates adhesion between the films, a problem also encountered in the production of cast films.

[0004] LLDPE is also commonly used as the surface layer of composite films for packaging food (e.g., vegetables and similar products), pharmaceuticals, etc., and comes into direct contact with powders, granules, and lumps. To prevent the packaged product from sticking, the slip properties of LLDPE are particularly important. For example, reduced membrane-to-membrane and membrane-to-metal friction makes it easier to feed the film into automated conversion and packaging equipment. Films with low slippage are difficult to handle and prone to wrinkling, leading to high conversion losses. Adding an opening agent to LLDPE helps overcome adhesion during production and prevents adhesion during storage, especially in summer when adhesion is highly likely. This ensures the film material is easy to produce, use, and store, and prevents the LLDPE film surface from sticking to the packaged product.

[0005] Slip agents, anti-sticking agents, and opening agents can facilitate secondary processing and downstream packaging operations by reducing friction between films and between films and equipment. They also effectively prevent film adhesion and adhesion to the packaged goods. Existing opening agents are either inorganic or organic. Inorganic opening agents include silica, calcium carbonate, clay, kaolin, or talc, as well as synthetic silicates. Based on 100 parts of LLDPE, the dosage of silica, calcium carbonate, clay, kaolin, or talc is generally between 0.05 and 0.2 parts, while the dosage of synthetic silicates is generally between 0.05 and 1.25 parts. Organic opening agents are stearates. Inorganic opening agents can be used alone or in combination, and they can also be combined with organic opening agents.

[0006] Patent CN101012322 discloses an antistatic, anti-adhesion, slip-resistant linear low-density polyethylene composition: using LLDPE as a base material, and adding an opening agent, a slip agent, an antistatic agent, and an antioxidant. The opening agent is synthetic silica, prepared by adding it during the granulation stage after mixing the additives with LLDPE as the base material; or by pre-preparing the additives into a masterbatch, metering it into the masterbatch during the granulation stage, and then producing a special material. The proportions of various additives in the masterbatch are: 4-80 parts LLDPE powder, 4-16 parts opening agent, 4-24 parts slip agent, 4-24 parts antistatic agent, 4-16 parts antioxidant, and 4-16 parts zinc stearate. This invention meets the requirements of general production and application; however, the addition of 4-80 parts LLDPE powder during the masterbatch manufacturing process results in a low content of effective components in the masterbatch, requiring a large amount to be added during industrial production, which poses certain difficulties in production.

[0007] Patent CN101052675A discloses a melt-blended polyethylene / cyclic olefin polymer (COP) composition suitable for preparing optically transparent films with a low coefficient of friction, wherein the cyclic olefin polymer is melt-blended into the composition as an opening agent. Based on 100 parts of LLDPE, the amount of opening agent added is 2 to 33 parts. Films made from this composition have a low-friction surface compared to films made from polyethylene resin alone, and also exhibit a haze value comparable to films without an opening agent, but at a higher amount.

[0008] The literature “Development of Special Resins for LLDPE Film” (Synthetic Resins and Plastics, 2009, 26(3): 56-61) introduces that Daqing Petrochemical, while keeping the existing process unchanged, added 0.075 to 0.175 parts of opening agent silica as a basis of 100 parts of LLDPE to improve the opening performance of LLDPE film, but the transparency of the film decreased.

[0009] The literature “Development of special resin for linear low-density polyethylene film” (Refining and Chemical Industry, 2010, (1): 19-21) states that the SiO2 dosage range should be 75-175 μg / g, the optimal dosage of the lubricant is 30-90 μg / g, the developed resin has a haze of 14%, and the opening performance is easy to peel off. Therefore, specific data on the friction performance of the film are not mentioned, and the haze is relatively high.

[0010] In the literature “Research and Application of Easy-to-Open, High-Transparency Linear Low-Density Polyethylene” (Elastomers, 2010, 20(5): 60-63), the opening agent is a mixture of inorganic opening agent dicalcium phosphate and organic opening agent stearamide. The ratio of organic opening agent to inorganic opening agent is 3-2 (mass ratio). The best compounding effect is achieved when the amount added is 0.10%. However, in order to increase transparency, a transparency enhancer was added during the experiment. After the transparency enhancer was added, it was easy to produce an odor, which is not good for the packaging film.

[0011] The literature “Application of slip agents and anti-stick opening agents in plastic films” (Plastic Additives, 2017, (3): 19-22) details the application and function of slip agents, anti-stick and opening agents in plastic films, including amide slip agents, non-migratory slip and anti-stick agents, inorganic anti-stick and opening agents, and organic anti-stick and opening agents, but does not provide specific performance data.

[0012] In the existing technology, the opening agent is either inorganic or organic. Inorganic opening agents include silica, calcium carbonate, clay, kaolin, or talc, as well as synthetic silicates. Based on 100 parts of LLDPE, the dosage of silica, calcium carbonate, clay, kaolin, or talc is generally between 0.05 and 0.2 parts, while the dosage of synthetic silicates is generally between 0.05 and 1.25 parts. Organic opening agents are stearates. Inorganic opening agents can be used alone or in combination, and they can also be used in combination with organic opening agents.

[0013] The market demand for LLDPE, which combines good openness and slip properties with high transparency, is approximately 300,000 tons per year.

[0014] Existing literature mainly focuses on improving the opening and slip properties of films, primarily using opening agents and slip agents. The earliest opening agents were inorganic talc and diatomaceous earth, while later developments included organic oleic acid amines, erucic acid amines, and their derivatives. Currently, synthetic silica is also widely used as an opening agent in films. All these additives have side effects to varying degrees. Organic opening agents produce a large amount of precipitates on the film surface, affecting the film's printability, heat-sealing properties, and color. Furthermore, excessive precipitates can compromise slip properties. The dispersion of inorganic opening agents has always been a challenge in production. Adding lubricants and organic dispersants to the formulation also produces precipitates, both of which can severely contaminate the packaged goods, especially in food, liquid, and pharmaceutical packaging. Moreover, precipitates reduce frictional properties, resulting in unsatisfactory opening performance. Furthermore, while improving the opening and smoothness, it reduces the transparency of the product. There are also studies on using transparent nucleating agents to increase transparency, but this invisibly increases the amount of additives required, raising production costs. In addition, the addition of nucleating agents can easily produce odors, which is detrimental to the packaging film.

[0015] The coefficient of friction is an important indicator for evaluating plastic packaging films. It is also a key indicator of the production efficiency of flexible plastic packaging materials. The coefficient of friction has a significant impact on the physical properties of composite film flexible packaging materials, such as opening performance, slip properties, and material uniformity, and is crucial for quality control. The coefficient of friction of the film surface depends on the film surface adhesion (surface tension and crystallinity), additives (slip agents, pigments, etc.), and surface polishing. Ensuring good stability of the film's coefficient of friction is also a crucial consideration during film preparation. Summary of the Invention

[0016] The purpose of this invention is to provide a transparent polyethylene film with stable frictional properties and its preparation method, so as to solve the problems of excessive amount of opening agent, poor frictional properties and easy film adhesion in the prior art.

[0017] To achieve the above objectives, the present invention provides a transparent polyethylene film with stable frictional properties, prepared from the following raw materials: 100 parts by weight of linear low-density polyethylene, 0.025 to 0.055 parts by weight of a compounded opening agent, 0.05 to 0.20 parts by weight of a slip agent, and 0.05 to 0.20 parts by weight of an antioxidant. The compounded opening agent is obtained by compounding silane-modified silica with a cyclic olefin polymer, wherein the mass ratio of silica to cyclic olefin polymer is 1:1 to 6:1, preferably 4:1. The slip agent is erucamide, and the melt flow rate of the cyclic olefin polymer at 230°C and 2.16 kg is 3 g / 10 min to 10 g / 10 min.

[0018] The tribologically stable transparent polyethylene film of the present invention is prepared by the following method: mixing silica, cyclic olefin polymer and silane coupling agent, stirring at 80-100°C to obtain the compound opening agent. In the present invention, the stirring time is not specifically limited, as long as the materials are fully mixed, preferably for 10-25 minutes.

[0019] The transparent polyethylene film with stable frictional properties of the present invention has a mass ratio of silicon dioxide to silane coupling agent of 100:1 to 3.

[0020] The tribologically stable transparent polyethylene film of the present invention comprises linear low-density polyethylene with a density of 0.915–0.921 g / cm³. 3 Measured according to ISO 1183-2:2004.

[0021] The transparent polyethylene film with stable frictional properties of the present invention uses an antioxidant that is a hindered phenolic antioxidant or a mixture of a hindered phenolic antioxidant and a phosphite antioxidant. The hindered phenolic antioxidant is a commonly used substance in the art, such as 1010 or 1076; the phosphite antioxidant is a commonly used substance in the art, such as 168.

[0022] The transparent polyethylene film with stable frictional properties described in this invention has a silica particle size of 900-2000 mesh.

[0023] The tribologically stable transparent polyethylene film of the present invention comprises a cyclic olefin polymer, which is a polymer of monocyclic or polycyclic olefins, such as a polymer of cycloene, dicyclic olefin, tricyclic olefin or tetracyclic olefin.

[0024] The transparent polyethylene film with stable frictional properties described in this invention comprises a monocyclic or polycyclic olefin that is a monosubstituted or polysubstituted cyclic olefin.

[0025] The tribologically stable transparent polyethylene film of the present invention comprises a cyclic olefin polymer that is a copolymer of monocyclic or polycyclic olefins and acyclic olefins; the acyclic olefin is one or more of ethylene, propylene and butene; and the cyclic olefin is norbornene.

[0026] To achieve the above objectives, the present invention also provides a method for preparing the above-described transparent polyethylene film with stable frictional properties, comprising the following steps:

[0027] S1, mix linear low-density polyethylene, compound opening agent, slip agent and antioxidant evenly;

[0028] S2, the uniformly mixed mixture is granulated in a twin-screw extruder to obtain a special material for polyethylene film;

[0029] S3, blow the polyethylene film material into a film.

[0030] The method for preparing a transparent polyethylene film with stable frictional properties according to the present invention includes the following steps: Step S1 involves mixing at 10–50°C for 2–5 min; Step S2 involves granulation at 170–230°C; and Step S3 involves blowing at 170–200°C.

[0031] Beneficial effects of this invention:

[0032] This invention uses two opening agents in combination, which significantly reduces the amount of silica used compared to the prior art using silica alone. At the same amount added, it has better opening and transparency than the prior art, and has good friction coefficient stability. This invention is easier to implement for continuous industrial production than general blending modification methods. Detailed Implementation

[0033] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0034] The raw materials used in the experiment and their sources are as follows:

[0035] LLDPE: Model DFDA7042: Powder material from Lanzhou Petrochemical Company's ethylene plant, density 0.918 g / cm³ 3 .

[0036] Cyclic olefin polymer: Polyplastics 8007F-600, 230℃, 2.16KG melt mass flow rate 10g / 10min.

[0037] Silica: Shanghai Liangjiang Titanium Dioxide Chemical Products Co., Ltd., particle size 1300 mesh.

[0038] Erucamide: Shandong Alinda Chemical Co., Ltd.

[0039] Oleamide: Shandong Jiahong Chemical Co., Ltd.

[0040] Antioxidant: Compound antioxidant AT-215, Jin Hai Ya Bao.

[0041] Silane coupling agent KH-550: Nanjing Shuguang Chemical Group Co., Ltd.

[0042] Talc powder: Qingdao Lukuang Talc Powder Co., Ltd.

[0043] Analysis method:

[0044] The haze was measured using a Yokosuka HGM-2DP haze meter from Japan.

[0045] Friction coefficient: Tested using the E-2 friction coefficient tester from the Italian company CEAST.

[0046] Friction coefficient change rate: The friction coefficient was tested after being placed in a TR240 oven of Nabertech Industrial Furnace GmbH, Germany, at 55°C for 24 hours and 48 hours respectively. The friction coefficient change rate was calculated as (friction coefficient after placement - initial friction coefficient) / initial friction coefficient × 100%. Specific implementation examples:

[0048] Example 1

[0049] Preparation of silane-modified silica and cyclic olefin polymer compound opening agent: Silica and cyclic olefin polymer are compounded at a ratio of 4:1. 1000 parts of dry silica and 250 parts of cyclic olefin polymer are weighed and placed in a high-speed mixer. Then, 20 parts of silane coupling agent KH-550 are added and stirred at 80℃ for 20 min to obtain the silane-modified silica and cyclic olefin polymer compound opening agent.

[0050] 100 parts of LLDPE resin DFDA7042, 0.025 parts of silane-modified silica and cyclic olefin polymer compound opening agent, 0.19 parts of erucamide and 0.19 parts of antioxidant B561 were added to a high-speed mixer and mixed at 25°C for 2 min. The mixed material was then granulated in a twin-screw extruder at a temperature of 170–230°C to obtain polyethylene film special material. Finally, the polyethylene film special material was blown into a film at a temperature of 170–200°C, labeled as film 1, with a film thickness of 30 μm. The film haze is shown in Table 1, and the frictional performance changes are shown in Table 2.

[0051] Example 2

[0052] Other conditions are the same as in Example 1, except that the amount of antioxidant added is 0.10 parts, the amount of silane-modified silica and cycloolefin polymer compound opening agent added is 0.04 parts, labeled as film 2, film haze is shown in Table 1, and friction performance changes are shown in Table 2.

[0053] Example 3

[0054] Other conditions are the same as in Example 1, except that the amount of antioxidant added is 0.15 parts, the amount of silane-modified silica and cyclic olefin polymer compound opening agent added is 0.05 parts, the amount of slip agent added is 0.1 parts, labeled as film 3, the haze of the film is shown in Table 1, and the change in friction performance is shown in Table 2.

[0055] Example 4

[0056] Other conditions are the same as in Example 1, except that the amount of antioxidant added is 0.05 parts, the amount of silane-modified silica and cyclic olefin polymer compound opening agent added is 0.055 parts, the amount of slip agent added is 0.05 parts, labeled as film 4, the haze of the film is shown in Table 1, and the change in friction performance is shown in Table 2.

[0057] Example 5

[0058] Other conditions are the same as in Example 3, except that silica and cyclic olefin polymer are compounded in a 1:1 ratio during the preparation of the compound opening agent. The amount of each raw material used in the preparation of the compound opening agent is: 600 parts silica, 600 parts cyclic olefin polymer, and 18 parts silane coupling agent KH-550, labeled as film 5. The haze of the film is shown in Table 1, and the change in friction performance is shown in Table 2.

[0059] Example 6

[0060] Other conditions are the same as in Example 3, except that silica and cyclic olefin polymer are compounded in a 6:1 ratio during the preparation of the compound opening agent. The amount of each raw material used in the preparation of the compound opening agent is: 600 parts silica, 100 parts cyclic olefin polymer, and 6 parts silane coupling agent KH-550, labeled as film 6. Film haze is shown in Table 1, and friction performance changes are shown in Table 2.

[0061] Comparative Example 1

[0062] Other conditions were the same as in Example 1, except that 0.02 parts of silane-modified silica and cyclic olefin polymer were used to formulate an opening agent, which was labeled as control sample 1. The film properties are shown in Table 1, and the changes in friction properties are shown in Table 2.

[0063] Comparative Example 2

[0064] Other conditions were the same as in Example 3, except that no composite opening agent was prepared during the preparation of the polyethylene film special material. Instead, 0.05 parts of cyclic olefin polymer were added as the opening agent and labeled as control sample 2. The film haze is shown in Table 1 and the changes in friction properties are shown in Table 2.

[0065] Comparative Example 3

[0066] Other conditions were the same as in Example 3, except that no composite opening agent was prepared during the preparation of the polyethylene film special material. Instead, 0.05 parts of silica were used as the opening agent, and the sample was labeled as control sample 3. The film haze is shown in Table 1, and the changes in friction properties are shown in Table 2.

[0067] Comparative Example 4

[0068] Other conditions are the same as in Example 3, except that the opening agent is not modified in the preparation of polyethylene film special material. A mixture of silica and cyclic olefin polymer with a mass ratio of 4:1 is used as the compound opening agent, which is labeled as control sample 4. The film haze is shown in Table 1, and the change in friction performance is shown in Table 2.

[0069] Comparative Example 5

[0070] Other conditions were the same as in Example 3, except that silica and cyclic olefin polymer were mixed in a 7:1 ratio during the preparation of the compound opening agent, and this was designated as control sample 5. The haze of the film is shown in Table 1, and the changes in frictional properties are shown in Table 2.

[0071] Comparative Example 6

[0072] Other conditions were the same as in Example 3, except that talc powder was used as the opening agent and was labeled as control sample 6. The film haze is shown in Table 1 and the changes in friction performance are shown in Table 2.

[0073] Comparative Example 7

[0074] Other conditions were the same as in Example 3, except that the slip agent was selected as oleic acid amide, which was labeled as control sample 7. The film haze is shown in Table 1, and the changes in friction performance are shown in Table 2.

[0075] Comparative Example 8

[0076] Other conditions were the same as in Example 3, except that a cyclic olefin polymer with a melt flow rate of 14 g / 10 min at 230 °C and a mass of 2.16 kg was used, which was labeled as control sample 8. The film haze is shown in Table 1, and the changes in friction properties are shown in Table 2.

[0077] Table 1

[0078]

[0079]

[0080] Table 2

[0081]

[0082]

[0083] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A transparent polyethylene film with stable frictional properties, characterized in that, The product is prepared from the following raw materials: 100 parts by weight of linear low-density polyethylene, 0.025 to 0.055 parts by weight of compound opening agent, 0.05 to 0.20 parts by weight of slip agent and 0.05 to 0.20 parts by weight of antioxidant. The compound opening agent is obtained by compounding silane-modified silica with cyclic olefin polymer. The mass ratio of silica to cyclic olefin polymer is 1:1 to 6:

1. The slip agent is erucamide. The melt flow rate of the cyclic olefin polymer at 230°C and 2.16 kg is 3 g / 10 min to 10 g / 10 min.

2. The tribologically stable transparent polyethylene film according to claim 1, characterized in that, The preparation method of the compound opening agent is as follows: mix silica, cyclic olefin polymer and silane coupling agent, stir at 80-100°C to obtain the compound opening agent.

3. The tribologically stable transparent polyethylene film according to claim 2, characterized in that, The mass ratio of silicon dioxide to silane coupling agent is 100:1 to 3.

4. The tribologically stable transparent polyethylene film according to claim 1, characterized in that, The linear low density polyethylene has a density of 0.915 to 0.921 g / cm 3 .

5. The tribologically stable transparent polyethylene film according to claim 1, characterized in that, The antioxidant is a hindered phenolic antioxidant, or a mixture of a hindered phenolic antioxidant and a phosphite antioxidant.

6. The tribologically stable transparent polyethylene film according to claim 1, characterized in that, The silica has a particle size of 900–2000 mesh.

7. The tribologically stable transparent polyethylene film according to claim 1, characterized in that, The cyclic olefin polymer is a polymer of monocyclic or polycyclic olefins.

8. The tribologically stable transparent polyethylene film according to claim 7, characterized in that, The monocyclic or polycyclic olefins are monosubstituted or polysubstituted cyclic olefins.

9. The tribologically stable transparent polyethylene film according to claim 7, characterized in that, The cyclic olefin polymer is a copolymer of monocyclic or polycyclic olefins and acyclic olefins; the acyclic olefin is one or more of ethylene, propylene and butene; the cyclic olefin is norbornene.

10. A method for preparing a tribologically stable transparent polyethylene film according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1, mix linear low-density polyethylene, compound opening agent, slip agent and antioxidant evenly; S2, the uniformly mixed mixture is granulated in a twin-screw extruder to obtain a special material for polyethylene film; S3, blow the polyethylene film material into a film.

11. The method for preparing a tribologically stable transparent polyethylene film according to claim 10, characterized in that, The mixing in step S1 is carried out at 10-50°C for 2-5 minutes; the granulation temperature in step S2 is 170-230°C; and the film blowing temperature in step S3 is 170-200°C.

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