Stretch-resistant polyethylene blown film and its preparation process

Abstract

The invention relates to the technical field of polyethylene films, and specifically discloses a stretch-resistant polyethylene blown film and a preparation process thereof. The preparation process of the stretch-resistant polyethylene blown film comprises the following steps: mixing low-density polyethylene, metallocene polyethylene, a modified polyethylene mixture, a montmorillonite modified nucleating agent, a defoaming agent and an antioxidant in a mass ratio of 100:45-55:7-12:3-5:0.1-0.3:0.3-0.5 in a high-speed mixer, transferring the mixed materials to a twin-screw extruder after uniform mixing, blending, extruding, granulating through a die and a pelletizer to obtain pellets, blowing the pellets through a blow molding machine, discharging the pellets to obtain the stretch-resistant polyethylene blown film, and the polyethylene blown film is easy to stretch and not easy to break, and the raw materials have excellent dispersibility and compatibility, excellent tensile strength and puncture resistance, and excellent comprehensive performance.

Description

Technical Field

[0001] The invention relates to the technical field of polyethylene films, in particular to a stretch-resistant polyethylene blown film and a preparation process thereof. Background Art

[0002] Polyethylene (PE) is a colorless, tasteless, odorless thermoplastic with good chemical stability, water resistance, hot viscosity, low temperature resistance and excellent processing performance. Due to the fast crystallization rate and high crystallinity of polyethylene, it is currently mainly produced by blow molding or cast film process. Blow molding is a common process for producing polyethylene film. The molten polyethylene resin is extruded into a film blank through an extruder, and the film blank is blown into a polyethylene film using compressed air. The resulting polyethylene blown film can maintain high strength and ductility and is not easy to break. It has a wide range of applications in packaging, agriculture, construction and other fields, especially in packaging products, which occupy an increasing share in the market.

[0003] During the production process of the blow molding process, due to factors such as the distribution of airflow and cooling speed, the thickness distribution of the film may not be uniform, and at the same time, the raw material melt index, fluidity and other performance requirements are relatively high. Chinese patent application CN109081990A discloses a durable plastic packaging bag film, which is composed of the following raw materials by weight: 20-30 parts of linear low-density polyethylene, 60-80 parts of high-density polyethylene, 10-20 parts of metallocene polyethylene, 15-25 parts of glass fiber, 4-6 parts of nano zinc oxide, 4-6 parts of nano titanium dioxide, 0.5-1.5 parts of compatibilizer, 1-2 parts of coupling agent, and 1-2 parts of antioxidant. The plastic packaging bag film has the advantages of chemical stability, electrical resistance, thermal stability, super hydrophilicity, non-migration, etc., but the nano inorganic particles are prone to agglomeration and will precipitate after a period of use, resulting in performance degradation. Chinese patent application CN113087985A discloses a polyethylene blown film for packaging, which contains 5-10% high-density polyethylene, 20-40% low-density polyethylene, 20-40% linear low-density polyethylene, 10-20% ethylene-acrylate copolymer resin and 5-15% ethylene-vinyl acetate copolymer by mass, and the polyethylene blown film has good heat sealing performance, stable sealing, and will not have delamination and drawing problems. Chinese patent application CN105254988A discloses a polyethylene film for packaging, which is composed of the following components by weight: 3-4 parts of dodecyl trimethyl ammonium chloride, 4-5 parts of oxidized polyethylene wax, 1-2 parts of impact-resistant polystyrene, 2-3 parts of nano-magnesium hydroxide, 1-2 parts of dibutyl sebacate, 4-5 parts of calcium stearate, 24 parts of polyethylene micropowder, 1-2 parts of lauryl trimethyl ammonium chloride, and 2-3 parts of titanium dioxide. The polyethylene film for packaging has good transparency and heat resistance and is not easy to wrinkle. However, the above films all have the problem of poor tensile properties and poor dispersibility between the raw materials. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In order to solve the above technical problems, the present invention provides a stretch-resistant polyethylene blown film and a preparation process thereof, which solves the problems of poor tensile properties of the polyethylene film and poor dispersibility between raw materials.

[0006] (II) Technical solution

[0007] In order to achieve the above object, the present invention discloses a preparation process of a stretch-resistant polyethylene blown film, comprising the following steps:

[0008] Step 1, activating montmorillonite to obtain activated montmorillonite, adding the activated montmorillonite to anhydrous toluene, adding 1,8-diisocyanate in a nitrogen atmosphere, stirring and mixing, heating, reacting, cooling after the reaction, filtering, washing with anhydrous ethanol, and vacuum drying at 50° C. for 12 hours to obtain modified montmorillonite;

[0009] Step 2: Evenly mix 1,3-2,4-di(p-methylbenzylidene)sorbitol and N-methylpyrrolidone, then add modified montmorillonite and dibutyltin dilaurate, stir and mix, heat and react, filter after the reaction, wash with methanol, and vacuum dry at 50° C. for 12 hours to obtain a montmorillonite modified nucleating agent;

[0010] Step 3, polyethylene, polypropylene, acetone, maleic anhydride and dicumyl peroxide are uniformly mixed, and after the acetone is volatilized, the mixture is transferred to a twin-screw extruder for melt blending. After the melt blending is completed, the mixture is extruded and cooled to obtain a maleic anhydride grafted blend;

[0011] Step 4: Evenly mix polyvinyl alcohol and dimethyl sulfoxide, then add maleic anhydride grafted blend, dicyclohexylcarbodiimide and 4-dimethylaminopyridine, stir and mix in a nitrogen atmosphere to react, and after the reaction is completed, cool, wash with deionized water, filter, and vacuum dry at 50° C. for 12 hours to obtain a modified polyethylene mixture;

[0012] Step 5: Place low-density polyethylene, metallocene polyethylene, modified polyethylene mixture, montmorillonite modified nucleating agent, defoaming agent and antioxidant in a high-speed mixer, mix at 70-80°C for 15-18 minutes, transfer to a twin-screw extruder after mixing evenly, perform blending, extrude, granulate through a die and a pelletizer to obtain pellets, and then blow film through a blow molding machine, discharge the material, and obtain a stretch-resistant polyethylene blow film.

[0013] Preferably, the specific steps of the activation treatment of montmorillonite in step 1 are as follows: add montmorillonite into a three-necked flask, heat it up in a nitrogen atmosphere, activate it, the activation temperature is 280° C., the activation time is 2 h, and activated montmorillonite is obtained.

[0014] Preferably, in the step 1, the mass ratio of activated montmorillonite, anhydrous toluene and 1,8-diisocyanate is 100:2000-2100:102-120, the reaction temperature is 85-95° C., and the reaction time is 2-5 h.

[0015] Preferably, in step 2, the mass ratio of 1,3-2,4-di(p-methylbenzylidene)sorbitol, N-methylpyrrolidone, modified montmorillonite and dibutyltin dilaurate is 58-75:950-1200:100:0.5-1.2, the reaction temperature is 60-70° C., and the reaction time is 4-6 h.

[0016] Preferably, in step three, the mass ratio of polyethylene, polypropylene, acetone, maleic anhydride and dicumyl peroxide is 100:78-105:200-240:12-18:3-5.

[0017] Preferably, the temperature of melt blending in step 3 is 180-190° C., and the time of melt blending is 10-15 min.

[0018] Preferably, in step 4, the mass ratio of polyvinyl alcohol, dimethyl sulfoxide, maleic anhydride grafted blend, dicyclohexylcarbodiimide and 4-dimethylaminopyridine is 32-45:4500-6500:100:12-25:3-7.

[0019] Preferably, the reaction temperature in step 4 is 95-105° C., and the reaction time is 18-24 h.

[0020] Preferably, in the step five, the mass ratio of low-density polyethylene, metallocene polyethylene, modified polyethylene mixture, montmorillonite modified nucleating agent, defoaming agent and antioxidant is 100:45-55:7-12:3-5:0.1-0.3:0.3-0.5.

[0021] Preferably, in step five, the extrusion temperature is 160-180° C., the blow molding temperature is 170-190° C., and during the blow molding process, the blow ratio is 2.2-2.6.

[0022] Preferably, the defoaming agent in step five is polyoxyethylene.

[0023] Preferably, the antioxidant in step five is 2,6-di-tert-butyl-p-cresol.

[0024] A stretch-resistant polyethylene blown film prepared by adopting the preparation process of the stretch-resistant polyethylene blown film.

[0025] 3. Beneficial technical effects

[0026] Low-density polyethylene has the characteristics of high impact resistance, low temperature resistance and heat resistance, and good moisture resistance. Metallocene polyethylene has excellent chemical stability and excellent mechanical properties, which can enhance the firmness of the matrix. Metallocene polyethylene has excellent elongation at break and impact strength, which significantly improves the tensile properties of the blown film. Polypropylene is a colorless, tasteless, and odorless resin with excellent chemical resistance, heat resistance and mechanical strength, which can improve the rigidity and stiffness of the blown film. Polyvinyl alcohol is a water-soluble polymer material containing polyhydroxy groups. It has excellent film-forming properties, elasticity, high tensile strength, transparency and gloss. At the same time, it has good tensile properties and good barrier properties. It has excellent barrier effects on gas and moisture. Adding it to the polyethylene matrix can significantly improve the barrier properties of the blown film, which is particularly suitable for packaging fields that require high barrier properties.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) In the present invention, montmorillonite is activated, and then 1,8-diisocyanate is used to modify the montmorillonite, and alkyl long chains and isocyanate groups are introduced on the surface of the montmorillonite to obtain modified montmorillonite. The isocyanate groups on the surface of the modified montmorillonite and the hydroxyl groups on 1,3-2,4-di(p-methylbenzylidene)sorbitol react under the action of the catalyst dibutyltin dilaurate to obtain a montmorillonite modified nucleating agent. The montmorillonite used is cheap and can reduce the cost of raw materials to a certain extent. It also has a layered structure and excellent mechanical and thermodynamic properties. It is grafted onto 1,3-2,4-di(p-methylbenzylidene)sorbitol by a grafting method, which effectively avoids the agglomeration of montmorillonite, can be evenly dispersed in the matrix to form a network structure, and avoids the precipitation of 1,3-2,4-di(p-methylbenzylidene)sorbitol. When subjected to external force, it can effectively eliminate stress and improve the mechanical properties of the matrix. Furthermore, 1,3-2,4-di(p-methylbenzylidene) sorbitol has excellent thermal stability, biocompatibility and degradability. The flexible long chain introduced during the reaction process can effectively improve the toughness of the matrix. At the same time, it contains a large number of active groups, which improves the compatibility and dispersibility between the raw materials. When subjected to external forces, it can effectively improve the mechanical properties of the matrix. Montmorillonite is closely combined with the matrix, which effectively improves the dimensional stability of the matrix, can improve production efficiency and processing performance, and 1,3-2,4-di(p-methylbenzylidene) sorbitol can change the crystal structure of polyethylene, refine the grain structure size, increase crystallinity, and accelerate the crystallization rate. As nucleating agents, the two work synergistically to help improve the overall performance of polyethylene blown film.

[0029] (2) In the present invention, polyethylene and polypropylene are polymerized with maleic anhydride under the action of dicumyl peroxide as an initiator to obtain a maleic anhydride grafted blend, anhydride groups are introduced into the blend, and the anhydride groups on the maleic anhydride grafted blend react with polyvinyl alcohol to obtain a modified polyethylene mixture, which has excellent dispersibility and compatibility, can obtain a cross-linked mechanical network structure, and has excellent mechanical properties. During the reaction, the regularity of the continuous phase matrix is ​​destroyed, the amorphous area increases, and a sea island type microstructure is presented, which makes the molecular chain segments easier to move. The modified polyethylene can absorb more energy, and the induced shear band is blocked and turned, which effectively inhibits the silver streaks from developing to a deeper level, and has excellent mechanical properties.

[0030] (3) In the present invention, low-density polyethylene, metallocene polyethylene, modified polyethylene mixture, montmorillonite modified nucleating agent, defoaming agent, and antioxidant are uniformly mixed by a high-speed mixer, and blown by melt blending, extrusion, granulation, and a blow molding machine to obtain a stretch-resistant polyethylene blown film. The addition of the modified polyethylene mixture can improve the melt fluidity, the melt strength is higher, which is beneficial to the stability of the blown film, and at the same time can improve the processing performance and make the blown film process smoother. The addition of the modified polyethylene mixture and the montmorillonite modified nucleating agent greatly improves the volume expansion performance, heat resistance and weather resistance. The various active groups help to form a better interface with other materials, improve the overall performance of the blown film, and greatly improve the durability of the blown film. The obtained stretch-resistant polyethylene blown film has excellent tensile elastic modulus and puncture resistance, is easy to stretch, not easy to break, has strong tension resistance, and has strong puncture resistance. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Example 1

[0032] A process for preparing a stretch-resistant polyethylene blown film comprises the following steps:

[0033] (1) activating montmorillonite to obtain activated montmorillonite, adding the activated montmorillonite to anhydrous toluene, adding 1,8-diisocyanate in a nitrogen atmosphere, stirring and mixing, wherein the mass ratio of activated montmorillonite, anhydrous toluene and 1,8-diisocyanate is 100:2000:102, heating, reacting at 85°C for 5 hours, cooling after the reaction, filtering, washing with anhydrous ethanol, and vacuum drying at 50°C for 12 hours to obtain modified montmorillonite;

[0034] (2) 1,3-2,4-di(p-methylbenzylidene)sorbitol and N-methylpyrrolidone are mixed evenly, and then modified montmorillonite and dibutyltin dilaurate are added, and stirred to mix, wherein the mass ratio of 1,3-2,4-di(p-methylbenzylidene)sorbitol, N-methylpyrrolidone, modified montmorillonite and dibutyltin dilaurate is 58:950:100:0.5, and the temperature is raised to react at 60°C for 6 hours. After the reaction is completed, the mixture is filtered, washed with methanol, and vacuum dried at 50°C for 12 hours to obtain a montmorillonite modified nucleating agent;

[0035] (3) Polyethylene, polypropylene, acetone, maleic anhydride and dicumyl peroxide in a mass ratio of 100:78:200:12:3 were mixed evenly, and after the acetone was volatilized, the mixture was transferred to a twin-screw extruder and melt-blended at 180° C. for 15 min. After the melt-blending was completed, the mixture was extruded and cooled to obtain a maleic anhydride grafted blend;

[0036] (4) Polyvinyl alcohol and dimethyl sulfoxide are mixed evenly, and then maleic anhydride grafted blend, dicyclohexylcarbodiimide and 4-dimethylaminopyridine are added, wherein the mass ratio of polyvinyl alcohol, dimethyl sulfoxide, maleic anhydride grafted blend, dicyclohexylcarbodiimide and 4-dimethylaminopyridine is 32:4500:100:12:3, and the mixture is stirred and mixed in a nitrogen atmosphere, and reacted at 95°C for 24 hours. After the reaction is completed, the mixture is cooled, washed with deionized water, filtered, and vacuum dried at 50°C for 12 hours to obtain a modified polyethylene mixture;

[0037] (5) Low-density polyethylene, metallocene polyethylene, modified polyethylene mixture, montmorillonite modified nucleating agent, defoaming agent polyethylene oxide, and antioxidant 2,6-di-tert-butyl-p-cresol in a mass ratio of 100:45:7:3:0.1:0.3 were placed in a high-speed mixer, mixed at 70°C for 18 minutes, and after being evenly mixed, transferred to a twin-screw extruder for blending, extruded at 160°C, and granulated through a die and a pelletizer to obtain pellets, which were then blown into film by a blow molding machine, wherein the blowing temperature was 170°C and the blowing ratio was 2.2. The material was discharged to obtain a stretch-resistant polyethylene blow film. Example 2

[0038] A process for preparing a stretch-resistant polyethylene blown film comprises the following steps:

[0039] (1) Activating montmorillonite to obtain activated montmorillonite, adding the activated montmorillonite to anhydrous toluene, adding 1,8-diisocyanate in a nitrogen atmosphere, stirring and mixing, wherein the mass ratio of activated montmorillonite, anhydrous toluene and 1,8-diisocyanate is 100:2050:115, heating, reacting at 90°C for 4 hours, cooling after the reaction, filtering, washing with anhydrous ethanol, and vacuum drying at 50°C for 12 hours to obtain modified montmorillonite;

[0040] (2) 1,3-2,4-di(p-methylbenzylidene)sorbitol and N-methylpyrrolidone are mixed evenly, and then modified montmorillonite and dibutyltin dilaurate are added, and stirred to mix, wherein the mass ratio of 1,3-2,4-di(p-methylbenzylidene)sorbitol, N-methylpyrrolidone, modified montmorillonite and dibutyltin dilaurate is 65:1050:100:0.8, and the temperature is raised to react at 65°C for 5 hours. After the reaction is completed, the mixture is filtered, washed with methanol, and vacuum dried at 50°C for 12 hours to obtain a montmorillonite modified nucleating agent;

[0041] (3) Polyethylene, polypropylene, acetone, maleic anhydride and dicumyl peroxide in a mass ratio of 100:90:215:15:4 were mixed evenly, and after the acetone was volatilized, the mixture was transferred to a twin-screw extruder and melt-blended at 185° C. for 12 min. After the melt-blending was completed, the mixture was extruded and cooled to obtain a maleic anhydride grafted blend;

[0042] (4) Polyvinyl alcohol and dimethyl sulfoxide are mixed evenly, and then maleic anhydride grafted blend, dicyclohexylcarbodiimide and 4-dimethylaminopyridine are added, wherein the mass ratio of polyvinyl alcohol, dimethyl sulfoxide, maleic anhydride grafted blend, dicyclohexylcarbodiimide and 4-dimethylaminopyridine is 38:5200:100:18:5, and the mixture is stirred and mixed in a nitrogen atmosphere, and reacted at 100° C. for 20 hours. After the reaction is completed, the mixture is cooled, washed with deionized water, filtered, and vacuum dried at 50° C. for 12 hours to obtain a modified polyethylene mixture;

[0043] (5) Low-density polyethylene, metallocene polyethylene, modified polyethylene mixture, montmorillonite modified nucleating agent, defoaming agent polyethylene oxide, and antioxidant 2,6-di-tert-butyl-p-cresol in a mass ratio of 100:48:9:3.5:0.25:0.4 were placed in a high-speed mixer, mixed at 75°C for 16 minutes, and after being evenly mixed, transferred to a twin-screw extruder for blending, extruded at 170°C, and granulated through a die and a pelletizer to obtain pellets, which were then blown into film by a blow molding machine, wherein the blowing temperature was 175°C and the blowing ratio was 2.5. The material was discharged to obtain a stretch-resistant polyethylene blow film. Example 3

[0044] A process for preparing a stretch-resistant polyethylene blown film comprises the following steps:

[0045] (1) 1,3-2,4-di(p-methylbenzylidene)sorbitol and N-methylpyrrolidone are mixed evenly, and then modified montmorillonite and dibutyltin dilaurate are added, and stirred to mix, wherein the mass ratio of 1,3-2,4-di(p-methylbenzylidene)sorbitol, N-methylpyrrolidone, modified montmorillonite and dibutyltin dilaurate is 72:1150:100:1, and the temperature is raised to react at 65°C for 5 hours. After the reaction is completed, the mixture is filtered, washed with methanol, and vacuum dried at 50°C for 12 hours to obtain a montmorillonite modified nucleating agent;

[0046] (2) Low-density polyethylene, metallocene polyethylene, modified polyethylene mixture, montmorillonite modified nucleating agent, defoaming agent polyethylene oxide, and antioxidant 2,6-di-tert-butyl-p-cresol in a mass ratio of 100:48:9:3.5:0.25:0.4 were placed in a high-speed mixer, mixed at 75°C for 16 minutes, and after being evenly mixed, transferred to a twin-screw extruder for blending, extruded at 170°C, and granulated through a die and a pelletizer to obtain pellets, which were then blown into film by a blow molding machine, wherein the blowing temperature was 175°C and the blowing ratio was 2.5. The material was discharged to obtain a stretch-resistant polyethylene blow film.

[0047] The preparation method of the modified montmorillonite is the same as the preparation method of the modified montmorillonite in Example 2.

[0048] The preparation method of the modified polyethylene mixture is the same as the preparation method of the modified polyethylene mixture in Example 2. Example 4

[0049] A process for preparing a stretch-resistant polyethylene blown film comprises the following steps:

[0050] (1) Polyvinyl alcohol and dimethyl sulfoxide are mixed evenly, and then maleic anhydride grafted blend, dicyclohexylcarbodiimide and 4-dimethylaminopyridine are added, wherein the mass ratio of polyvinyl alcohol, dimethyl sulfoxide, maleic anhydride grafted blend, dicyclohexylcarbodiimide and 4-dimethylaminopyridine is 42:6000:100:24:6, and the mixture is stirred and mixed in a nitrogen atmosphere, and reacted at 100° C. for 22 hours. After the reaction is completed, the mixture is cooled, washed with deionized water, filtered, and vacuum dried at 50° C. for 12 hours to obtain a modified polyethylene mixture;

[0051] (2) Low-density polyethylene, metallocene polyethylene, modified polyethylene mixture, montmorillonite modified nucleating agent, defoaming agent polyethylene oxide, and antioxidant 2,6-di-tert-butyl-p-cresol in a mass ratio of 100:48:9:3.5:0.25:0.4 were placed in a high-speed mixer, mixed at 75°C for 16 minutes, and after being evenly mixed, transferred to a twin-screw extruder for blending, extruded at 170°C, and granulated through a die and a pelletizer to obtain pellets, which were then blown into film by a blow molding machine, wherein the blowing temperature was 175°C and the blowing ratio was 2.5. The material was discharged to obtain a stretch-resistant polyethylene blow film.

[0052] The preparation method of the montmorillonite modified nucleating agent is the same as the preparation method of the montmorillonite modified nucleating agent in Example 2.

[0053] The preparation method of the maleic anhydride grafted blend is the same as the preparation method of the maleic anhydride grafted blend in Example 2. Example 5

[0054] A process for preparing a stretch-resistant polyethylene blown film comprises the following steps:

[0055] (1) Low-density polyethylene, metallocene polyethylene, modified polyethylene mixture, montmorillonite modified nucleating agent, defoaming agent polyethylene oxide, and antioxidant 2,6-di-tert-butyl-p-cresol in a mass ratio of 100:52:10:4.5:0.25:0.4 were placed in a high-speed mixer, mixed at 75°C for 16 minutes, and after being uniformly mixed, transferred to a twin-screw extruder for blending, extruded at 175°C, and granulated through a die and a pelletizer to obtain pellets, which were then blown by a blow molding machine, wherein the blowing temperature was 185°C, and the blowing ratio was 2.5 during the blow molding process, and the material was discharged to obtain a stretch-resistant polyethylene blown film.

[0056] The preparation methods of the modified polyethylene mixture and the montmorillonite modified nucleating agent are the same as those of the modified polyethylene mixture and the montmorillonite modified nucleating agent in Example 4. Example 6

[0057] A process for preparing a stretch-resistant polyethylene blown film comprises the following steps:

[0058] (1) activating montmorillonite to obtain activated montmorillonite, adding the activated montmorillonite to anhydrous toluene, adding 1,8-diisocyanate in a nitrogen atmosphere, stirring and mixing, wherein the mass ratio of activated montmorillonite, anhydrous toluene and 1,8-diisocyanate is 100:2100:120, heating, reacting at 95°C for 2 hours, cooling after the reaction, filtering, washing with anhydrous ethanol, and vacuum drying at 50°C for 12 hours to obtain modified montmorillonite;

[0059] (2) 1,3-2,4-di(p-methylbenzylidene)sorbitol and N-methylpyrrolidone are mixed evenly, and then modified montmorillonite and dibutyltin dilaurate are added, and stirred to mix, wherein the mass ratio of 1,3-2,4-di(p-methylbenzylidene)sorbitol, N-methylpyrrolidone, modified montmorillonite and dibutyltin dilaurate is 58:950:100:0.5, and the temperature is raised to react at 60°C for 6 hours. After the reaction is completed, the mixture is filtered, washed with methanol, and vacuum dried at 50°C for 12 hours to obtain a montmorillonite modified nucleating agent;

[0060] (3) Polyethylene, polypropylene, acetone, maleic anhydride and dicumyl peroxide in a mass ratio of 100:105:240:18:5 were mixed uniformly, and after the acetone was volatilized, the mixture was transferred to a twin-screw extruder and melt-blended at 190° C. for 10 min. After the melt-blending was completed, the mixture was extruded and cooled to obtain a maleic anhydride grafted blend;

[0061] (4) Polyvinyl alcohol and dimethyl sulfoxide are mixed evenly, and then maleic anhydride grafted blend, dicyclohexylcarbodiimide and 4-dimethylaminopyridine are added, wherein the mass ratio of polyvinyl alcohol, dimethyl sulfoxide, maleic anhydride grafted blend, dicyclohexylcarbodiimide and 4-dimethylaminopyridine is 45:6500:100:25:7, and the mixture is stirred and mixed in a nitrogen atmosphere, and reacted at 105° C. for 18 hours. After the reaction is completed, the mixture is cooled, washed with deionized water, filtered, and vacuum dried at 50° C. for 12 hours to obtain a modified polyethylene mixture;

[0062] (5) Low-density polyethylene, metallocene polyethylene, modified polyethylene mixture, montmorillonite modified nucleating agent, defoaming agent polyethylene oxide, and antioxidant 2,6-di-tert-butyl-p-cresol in a mass ratio of 100:55:12:5:0.3:0.5 were placed in a high-speed mixer, mixed at 80°C for 15 minutes, and after being evenly mixed, transferred to a twin-screw extruder for blending, extruded at 180°C, and granulated through a die and a pelletizer to obtain pellets, which were then blown into film by a blow molding machine, wherein the blowing temperature was 190°C and the blowing ratio was 2.6. The material was discharged to obtain a stretch-resistant polyethylene blow film. Comparative Example 1

[0063] A process for preparing a stretch-resistant polyethylene blown film comprises the following steps:

[0064] (1) Low-density polyethylene, metallocene polyethylene, modified polyethylene mixture, 1,3-2,4-di(p-methylbenzylidene) sorbitol, montmorillonite, defoaming agent polyethylene oxide, and antioxidant 2,6-di-tert-butyl-p-cresol in a mass ratio of 100:52:10:1.9:2.6:0.25:0.4 were placed in a high-speed mixer, mixed at 75°C for 16 minutes, and after being uniformly mixed, transferred to a twin-screw extruder for blending, extruded at 175°C, granulated through a die and a pelletizer to obtain pellets, and then passed through a blow molding machine for film blowing, wherein the blowing temperature was 185°C, and the blow ratio was 2.5 during the blow molding process, and the material was discharged to obtain a stretch-resistant polyethylene blow film.

[0065] The preparation method of the modified polyethylene mixture is the same as the preparation method of the modified polyethylene mixture in Example 4. Comparative Example 2

[0066] A process for preparing a stretch-resistant polyethylene blown film comprises the following steps:

[0067] (1) Low-density polyethylene, metallocene polyethylene, polyvinyl alcohol, polyethylene, polypropylene, montmorillonite-modified nucleating agent, defoaming agent polyoxyethylene, and antioxidant 2,6-di-tert-butyl-p-cresol in a mass ratio of 100:52:3:3.7:3.3:4.5:0.25:0.4 were placed in a high-speed mixer, mixed at 75°C for 16 minutes, and after being uniformly mixed, transferred to a twin-screw extruder for blending, extruded at 175°C, and granulated through a die and a pelletizer to obtain pellets, which were then blown into film by a blow molding machine, wherein the blowing temperature was 185°C, and the blow ratio was 2.5 during the blow molding process. The material was discharged to obtain a stretch-resistant polyethylene blown film.

[0068] The preparation method of the montmorillonite modified nucleating agent is the same as the preparation method of the montmorillonite modified nucleating agent in Example 4. Comparative Example 3

[0069] A process for preparing a stretch-resistant polyethylene blown film comprises the following steps:

[0070] (1) Low-density polyethylene, metallocene polyethylene, polyvinyl alcohol, polyethylene, polypropylene, 1,3-2,4-di(p-methylbenzylidene) sorbitol, montmorillonite, defoaming agent polyoxyethylene, and antioxidant 2,6-di-tert-butyl-p-cresol in a mass ratio of 100:52:3:3.7:3.3:1.9:2.6:0.25:0.4 were placed in a high-speed mixer, mixed at 75°C for 16 minutes, and after being uniformly mixed, transferred to a twin-screw extruder for blending, extruded at 175°C, and granulated through a die and a pelletizer to obtain pellets, which were then blown into film by a blow molding machine, wherein the blowing temperature was 185°C, and the blow ratio was 2.5 during the blow molding process, and the material was discharged to obtain a stretch-resistant polyethylene blown film.

[0071] The specific steps of the activation treatment of montmorillonite in the embodiments and comparative examples of the present invention are as follows: montmorillonite is added into a three-necked flask, heated in a nitrogen atmosphere, and activated at a temperature of 280° C. for 2 h to obtain activated montmorillonite.

[0072] The polyethylene in the examples and comparative examples of the present invention is low-density polyethylene.

[0073] The CAS number of 1,8-diisocyanate used in the embodiments and comparative examples of the present invention is 10124-86-4, purchased from San Chemical Technology (Shanghai) Co., Ltd.; the montmorillonite is nano-montmorillonite purchased from Zhejiang Baina Chemical Co., Ltd., with a particle size of 50-100 nm; polyvinyl alcohol was purchased from Tianjin Alfa Aesar Co., Ltd., with a number average molecular weight of 60,000; low-density polyethylene was purchased from Sinopec Yangzi Petrochemical Co., Ltd., model 2426K; metallocene polyethylene was purchased from Dongguan Mingyuan Plastic Co., Ltd., brand: Dow, grade NG5401B; polypropylene was purchased from PetroChina Daqing Petrochemical Company, model T30S; other raw materials and reagents are commercially available.

[0074] The polyethylene blown films in Examples 1-6 and Comparative Examples 1-3 were used as samples for performance testing. The samples were made into polyethylene blown films with a thickness of 20 μm. The test standard of GB / T 6672-2001 "Mechanical measurement method for the determination of thickness of plastic films and sheets" was adopted. The relevant performance tests are as follows:

[0075] (1) The puncture resistance of the samples was tested using the test standard of GB / T 10004-2008 "Plastic composite film for packaging, dry composite and extrusion composite of bags". The tensile strength and elongation at break of the samples were tested using a BJDW universal testing machine. The test standard was based on the test standard of GB / T 4456-2008 "Polyethylene blown film for packaging". The above test results are shown in Table 1:

[0076]

[0077] According to the test results in Table 1, the polyethylene blown film of the present invention has excellent puncture resistance and mechanical properties, is not easy to break, has strong tensile strength, strong puncture resistance, excellent tensile strength in both the transverse and longitudinal directions, and high elongation at break.

[0078] Although the embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that all equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A process for preparing a stretch-resistant polyethylene blown film, characterized in that: The steps include: Step 1, activating montmorillonite to obtain activated montmorillonite, adding the activated montmorillonite to anhydrous toluene, adding 1,8-diisocyanate in a nitrogen atmosphere, stirring and mixing, heating, reacting, cooling after the reaction, filtering, washing, and vacuum drying at 50° C. for 12 hours to obtain modified montmorillonite; Step 2: Evenly mix 1,3-2,4-di(p-methylbenzylidene)sorbitol and N-methylpyrrolidone, then add modified montmorillonite and dibutyltin dilaurate, stir and mix, heat and react, filter, wash and vacuum dry at 50° C. for 12 h to obtain a montmorillonite modified nucleating agent after the reaction is completed; Step 3, polyethylene, polypropylene, acetone, maleic anhydride and dicumyl peroxide are uniformly mixed, and after the acetone is volatilized, the mixture is transferred to a twin-screw extruder for melt blending. After the melt blending is completed, the mixture is extruded and cooled to obtain a maleic anhydride grafted blend; Step 4: Evenly mix polyvinyl alcohol and dimethyl sulfoxide, then add maleic anhydride grafted blend, dicyclohexylcarbodiimide and 4-dimethylaminopyridine, stir and mix in a nitrogen atmosphere to react, and after the reaction is completed, cool, wash, filter, and vacuum dry at 50° C. for 12 hours to obtain a modified polyethylene mixture; Step 5, placing low-density polyethylene, metallocene polyethylene, modified polyethylene mixture, montmorillonite modified nucleating agent, defoaming agent, and antioxidant in a high-speed mixer, mixing at 70-80° C. for 15-18 minutes, transferring to a twin-screw extruder after uniform mixing, blending, extruding, granulating through a die and a pelletizer to obtain pellets, and then blowing through a blow molding machine to obtain a stretch-resistant polyethylene blown film; In the step 1, the mass ratio of activated montmorillonite, anhydrous toluene and 1,8-diisocyanate is 100:2000-2100:102-120, the reaction temperature is 85-95° C., and the reaction time is 2-5 h; In the step 2, the mass ratio of 1,3-2,4-di(p-methylbenzylidene)sorbitol, N-methylpyrrolidone, modified montmorillonite, and dibutyltin dilaurate is 58-75:950-1200:100:0.5-1.2, the reaction temperature is 60-70°C, and the reaction time is 4-6h; In the step 3, the mass ratio of polyethylene, polypropylene, acetone, maleic anhydride and dicumyl peroxide is 100:78-105:200-240:12-18:3-5; In the step 4, the mass ratio of polyvinyl alcohol, dimethyl sulfoxide, maleic anhydride grafted blend, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 32-45:4500-6500:100:12-25:3-7; In the step 5, the mass ratio of low-density polyethylene, metallocene polyethylene, modified polyethylene mixture, montmorillonite modified nucleating agent, defoaming agent and antioxidant is 100:45-55:7-12:3-5:0.1-0.3:0.3-0.

5.

2. The process for preparing a stretch-resistant polyethylene blown film according to claim 1, characterized in that: The temperature of melt blending in step 3 is 180-190° C., and the time of melt blending is 10-15 min.

3. The process for preparing a stretch-resistant polyethylene blown film according to claim 1, characterized in that: The reaction temperature in step 4 is 95-105° C., and the reaction time is 18-24 hours.

4. The process for preparing a stretch-resistant polyethylene blown film according to claim 1, characterized in that: The extrusion temperature in step 5 is 160-180° C., the blow molding temperature is 170-190° C., and during the blow molding process, the blow ratio is 2.2-2.

6.

5. A stretch-resistant polyethylene blown film prepared by the process for preparing a stretch-resistant polyethylene blown film according to any one of claims 1 to 4.

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