Crosslinked polyolefin thermal shrinkage film and preparation process thereof

Abstract

The invention discloses a cross-linked polyolefin thermal shrinkage film and a preparation process thereof, and relates to the technical field of preparation of thin film materials. Comprising the following steps: step 1, respectively extruding raw materials of an outer layer, an inner layer and a core layer in a single-screw extruder, then converging in a three-layer co-extrusion die head, carrying out co-extrusion molding, and cooling to obtain a multi-layer composite sheet; and 2, the multi-layer composite sheet is pulled to a stretching drying oven to be subjected to two-way synchronous stretching, and then the finished product is obtained after air ring cooling, halving, rolling and slitting. The preparation method has the beneficial effects that the specific inorganic nano material and the organic heat-resistant agent are synthesized, the surface of the inorganic nano material is modified, the ratio of the inorganic nano material to the organic heat-resistant agent is accurately controlled, and the compatibility of the inorganic nano material and the organic heat-resistant agent is remarkably improved. The improvement not only enhances the thermal stability of the cross-linked polyolefin thermal shrinkage film, but also improves the mechanical properties of the cross-linked polyolefin thermal shrinkage film.

Description

Technical Field

[0001] The invention relates to the technical field of film material preparation, in particular to a cross-linked polyolefin heat shrinkable film and a preparation process thereof. Background Art

[0002] As an important packaging material, heat shrink film is widely used in food, beverage, medicine, electronics and other fields. Among them, cross-linked polyolefin heat shrink film has become a hot spot for research and application in recent years due to its excellent mechanical properties, heat resistance, transparency and environmental protection. However, traditional cross-linked polyolefin heat shrink film still has some defects, which limits its further application. Among them, the existing heat shrink film has insufficient shrinkage rate at high temperature, which makes it difficult to tightly wrap objects with complex shapes, affecting the packaging effect and product appearance; some cross-linked polyolefin heat shrink films have insufficient mechanical properties such as tensile strength and tear strength, which are prone to damage during transportation and storage, affecting the product protection performance.

[0003] At present, in order to improve the performance of polyolefin heat shrinkable film, inorganic and organic heat resistant agents are usually added. However, these additives have some problems: inorganic materials have poor compatibility with organic polymer matrices, are easy to agglomerate, form stress concentration points, and affect the uniformity and mechanical properties of the material; the interface bonding force is weak, and interface peeling is easy to occur when stressed, reducing the strength and toughness of the material. Organic heat resistant agents may migrate to the surface of the material, affecting the appearance and performance. In addition, inorganic and organic heat resistant agents have poor compatibility when mixed, which is easy to cause phase separation, further affecting the uniformity and overall performance of the material.

[0004] In summary, in order to solve the above problems, the present invention provides a preparation process of a cross-linked polyolefin heat shrinkable film. Summary of the invention

[0005] The object of the present invention is to provide a cross-linked polyolefin heat shrinkable film and a preparation process thereof, so as to solve the problems raised in the prior art.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A preparation process of a cross-linked polyolefin heat shrinkable film comprises the following steps:

[0008] Step 1: The outer layer, inner layer and core layer raw materials are extruded separately in a single screw extruder, and then merged in a three-layer co-extrusion die head, co-extruded and cooled to obtain a multi-layer composite sheet;

[0009] Step 2: The multi-layer composite sheet is pulled into a stretching oven for bidirectional synchronous stretching, then cooled by an air ring, split and rolled up, and cut to obtain a finished product.

[0010] More optimally, the outer layer and inner layer materials are the same, including the following substances: by weight, 100-110 parts of terpolymer polypropylene, 10-12 parts of anti-sticking agent, 3-4 parts of heat-resistant agent, 0.1-0.2 parts of initiator; the core layer materials include the following substances: by weight, 70-80 parts of low-density polyethylene, 5-8 parts of heat-resistant agent, 0.1-0.2 parts of initiator, and 2-3 parts of lubricant.

[0011] More optimally, the heat-resistant agent comprises a modified inorganic nanomaterial and an organic heat-resistant agent in a mass ratio of (3-4):1.

[0012] More optimally, the preparation process of the modified inorganic nanomaterial is:

[0013] S1: adding illite to a sodium hydroxide solution, heating to 40-50°C, stirring and soaking for 1-2 hours, filtering and washing with deionized water until neutral; then transferring to a hydrochloric acid solution, stirring and soaking for 1-2 hours at room temperature, filtering and washing with deionized water until neutral, and drying to obtain pretreated illite;

[0014] S2: Mix the pretreated illite with deionized water, heat to 70-80°C, add hydrochloric acid, adjust the pH to 2-3, then slowly add anhydrous ethanol solution of titanium tetrachloride, continue to react for 2-3 hours after the addition is complete, cool, wash, dry, transfer to a muffle furnace and calcine at 500-550°C for 2-3 hours to obtain a composite inorganic substance;

[0015] S3: dissolve the composite inorganic material in anhydrous ethanol, ultrasonically disperse for 30-40 minutes, add hydrochloric acid to adjust the pH to 3-4, add a mixed solution of 3-aminopropyltriethoxysilane and ethanol, stir for 30-40 minutes, react at 60-70°C for 3-4 hours, cool to room temperature, wash with anhydrous ethanol, vacuum dry, ultrasonically disperse in deionized water, add a mixed solution of 3-mercaptopropyltriethoxysilane and methanol and an alkaline solution, heat to 70-80°C, react for 5-8 hours, wash, and dry to obtain a modified inorganic nanomaterial.

[0016] More optimally, the mass ratio of 3-aminopropyltriethoxysilane to 3-mercaptopropyltriethoxysilane is 1:(2-3).

[0017] Preferably, the pretreated illite comprises the following substances: by weight, 20-30 parts of illite, 244-250 parts of sodium hydroxide solution, and 210-215 parts of hydrochloric acid solution; wherein the mass fraction of the sodium hydroxide solution is 20-25%, and the mass fraction of the hydrochloric acid solution is 10-15%;

[0018] The composite inorganic material comprises the following substances: by weight, 25-30 parts of pretreated illite, 260-280 parts of deionized water, and 42-45 parts of anhydrous ethanol solution of titanium tetrachloride.

[0019] More optimally, the preparation process of the organic heat-resistant agent is as follows: 2-amino-4-pentenoic acid and calcium carbonate are added to tetrahydrofuran, ultrasonically dispersed for 30-40 minutes, then placed in an ice water bath at 0°C, and a benzene solution of 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride is slowly added dropwise. After the addition is complete, the temperature is raised to 50-60°C, and the reaction is carried out at a constant temperature for 20-25 hours. After cooling to room temperature, the mixture is filtered, washed, and dried to obtain the organic heat-resistant agent.

[0020] More optimally, the organic heat-resistant agent raw material includes the following components: by weight, 11-12 parts of 2-amino-4-pentenoic acid, 200-220 parts of calcium carbonate, 250-180 parts of tetrahydrofuran, and 18-20 parts of 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride in a benzene solution.

[0021] More optimally, the extrusion temperature of the outer layer and the inner layer in the single screw extruder is 180-190°C; the extrusion temperature of the core layer in the single screw extruder is 170-180°C.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention synthesizes specific inorganic nanomaterials and organic heat-resistant agents, and modifies the surface of the inorganic nanomaterials to precisely control the ratio of the inorganic nanomaterials and the organic heat-resistant agents, thereby significantly improving the compatibility of the two. This improvement not only enhances the thermal stability of the cross-linked polyolefin heat shrinkable film, but also improves its mechanical properties. The details are as follows:

[0024] First: In the scheme, by controlling the mass ratio of modified inorganic nanomaterials to organic heat-resistant agents at (3-4):1, the compatibility of the two can be effectively balanced. The thiol group and amino group on the modified inorganic nanomaterial can react with the vinyl and carboxyl groups of the organic heat-resistant agent to reduce the migration of the organic heat-resistant agent. However, if the proportion of inorganic nanomaterials is too high, they may agglomerate in the organic polymer matrix to form stress concentration points, thereby affecting the uniformity and mechanical properties of the film; conversely, if the proportion is too low, the thermal stability of the heat shrinkable film will be significantly reduced. Similarly, too much organic heat-resistant agent may cause phase separation inside the film, affecting the uniformity and overall performance of the film; and when the proportion of organic heat-resistant agent is too low, the antioxidant properties and flexibility of the film will decrease, causing the performance of the film to rapidly decrease in high temperature and oxidative environments, affecting its service life;

[0025] Second: In the scheme, by using aminosilane coupling agent and mercaptosilane coupling agent to modify the composite inorganic material and controlling the ratio of the two to 1: (2-3), a combination reaction of multiple groups can be achieved. Among them, the mercapto group can react with the vinyl group in the organic heat-resistant agent to form a stable thioether bond; the amino group can react with the carboxyl group in the organic heat-resistant agent to form a stable amide bond. This multi-group combination reaction can further improve the overall performance of the material; however, if too much aminosilane coupling agent is grafted, due to the hygroscopicity of the amide bond, the resulting heat shrinkable film may absorb moisture in a humid environment, thereby affecting its use scenario; on the contrary, if too much mercaptosilane coupling agent is grafted, the thermal stability of the material may be reduced;

[0026] Third: The multilayer illite used in the scheme has good interlayer bonding force and mechanical strength, providing a good dispersion platform for inorganic nanomaterials and organic heat-resistant agents. This structure can effectively inhibit the thermal shrinkage of the material at high temperature and ensure the dimensional stability of the film in a high temperature environment. DETAILED DESCRIPTION

[0027] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

[0028] It should be noted that the following parts are parts by weight, and the purchase manufacturers of all raw materials involved in the present invention are not subject to any special restrictions and are exemplified as follows: in the following embodiments, 2-amino-4-pentenoic acid CAS is 16338-48-0; 3-aminopropyltriethoxysilane CAS is 919-30-2; 3-mercaptopropyltriethoxysilane CAS is 14814-09-6.

[0029] Embodiment 1: A process for preparing a cross-linked polyolefin heat shrinkable film, comprising the following steps:

[0030] Step 1: 100 parts of terpolymer polypropylene, 10 parts of paraffin wax, 3 parts of heat-resistant agent, and 0.1 parts of diisopropylbenzene peroxide are mixed as the raw materials for the outer layer and the inner layer; 70 parts of low-density polyethylene, 5 parts of heat-resistant agent, 0.1 parts of diisopropylbenzene peroxide, and 2 parts of calcium stearate are mixed as the raw materials for the core layer; wherein the heat-resistant agent comprises a modified inorganic nanomaterial and an organic heat-resistant agent in a mass ratio of 3:1;

[0031] Step 2: Extruding the outer layer and the inner layer in a single screw extruder at 180° C.; extruding the core layer in a single screw extruder at 170° C., and then merging in a three-layer co-extrusion die, co-extruding and cooling to obtain a multi-layer composite sheet;

[0032] Step 3: The multi-layer composite sheet is pulled into a stretching oven for bidirectional synchronous stretching, then cooled by an air ring, split and rolled up, and cut to obtain a finished product;

[0033] Among them, the preparation process of modified inorganic nanomaterials is:

[0034] S1: adding 20 parts of illite to 244 parts of 25wt% sodium hydroxide solution, heating to 40°C, stirring and soaking for 1 hour, filtering and washing with deionized water until neutral; then transferring to 210 parts of 15wt% hydrochloric acid solution, stirring and soaking for 1 hour at room temperature, filtering and washing with deionized water until neutral, and drying to obtain pretreated illite;

[0035] S2: 25 parts of pretreated illite and 260 parts of deionized water were mixed, the temperature was raised to 70-80°C, hydrochloric acid was added dropwise, the pH was adjusted to 2, and then 42 parts of anhydrous ethanol solution of titanium tetrachloride were slowly added dropwise. After the addition was complete, the reaction was continued for 2 hours, cooled, washed, dried, and transferred to a muffle furnace and calcined at 500°C for 2 hours to obtain a composite inorganic material;

[0036] S3: Dissolve 10 parts of the composite inorganic material in anhydrous ethanol, ultrasonically disperse for 30 minutes, add hydrochloric acid to adjust the pH to 3, then add a mixed solution of 3-aminopropyltriethoxysilane and ethanol, stir for 30 minutes, react at 60°C for 3 hours, cool to room temperature, wash with anhydrous ethanol, vacuum dry, transfer to deionized water, add a mixed solution of 3-mercaptopropyltriethoxysilane and methanol and an alkaline solution, heat to 70°C, react for 5 hours, wash, and dry to obtain a modified inorganic nanomaterial; wherein the mass ratio of 3-aminopropyltriethoxysilane to 3-mercaptopropyltriethoxysilane is 1:2;

[0037] Among them, the preparation process of the organic heat-resistant agent is: add 11 parts of 2-amino-4-pentenoic acid and 200 parts of calcium carbonate to 250 parts of tetrahydrofuran, ultrasonically disperse for 30 minutes, then place in an ice water bath at 0°C, slowly add 18 parts of 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride benzene solution, after the addition is completed, heat to 50°C, react at a constant temperature for 20 hours, cool to room temperature, filter, wash, and dry to obtain the organic heat-resistant agent.

[0038] Embodiment 2: A process for preparing a cross-linked polyolefin heat shrinkable film, comprising the following steps:

[0039] Step 1: 110 parts of terpolymer polypropylene, 12 parts of paraffin wax, 4 parts of heat-resistant agent, and 0.2 parts of diisopropylbenzene peroxide are mixed as raw materials for the outer layer and the inner layer; 80 parts of low-density polyethylene, 8 parts of heat-resistant agent, 0.2 parts of diisopropylbenzene peroxide, and 3 parts of calcium stearate are mixed as raw materials for the core layer; wherein the heat-resistant agent comprises a modified inorganic nanomaterial and an organic heat-resistant agent in a mass ratio of 4:1;

[0040] Step 2: Extruding the outer layer and the inner layer in a single screw extruder at 190° C.; extruding the core layer in a single screw extruder at 180° C., and then merging in a three-layer co-extrusion die, co-extruding and cooling to obtain a multi-layer composite sheet;

[0041] Step 3: The multi-layer composite sheet is pulled into a stretching oven for bidirectional synchronous stretching, then cooled by an air ring, split and rolled up, and cut to obtain a finished product;

[0042] Among them, the preparation process of modified inorganic nanomaterials is:

[0043] S1: 30 parts of illite are added to 250 parts of 25wt% sodium hydroxide solution, heated to 50°C, stirred and soaked for 2 hours, filtered and washed with deionized water until neutral; then transferred to 215 parts of 15wt% hydrochloric acid solution, stirred and soaked for 2 hours at room temperature, filtered and washed with deionized water until neutral, and dried to obtain pretreated illite;

[0044] S2: 30 parts of pretreated illite were mixed with 280 parts of deionized water, the temperature was raised to 80°C, hydrochloric acid was added dropwise, the pH was adjusted to 3, and then 45 parts of anhydrous ethanol solution of titanium tetrachloride were slowly added dropwise. After the addition was complete, the reaction was continued for 3 hours, cooled, washed, dried, and transferred to a muffle furnace for calcination at 550°C for 3 hours to obtain a composite inorganic material;

[0045] S3: Dissolve 20 parts of the composite inorganic material in anhydrous ethanol, ultrasonically disperse for 40 minutes, add hydrochloric acid to adjust the pH to 4, then add a mixed solution of 3-aminopropyltriethoxysilane and ethanol, stir for 40 minutes, react at 70°C for 4 hours, cool to room temperature, wash with anhydrous ethanol, vacuum dry, transfer to deionized water, add a mixed solution of 3-mercaptopropyltriethoxysilane and methanol and an alkaline solution, heat to 80°C, react for 8 hours, wash, and dry to obtain a modified inorganic nanomaterial; wherein the mass ratio of 3-aminopropyltriethoxysilane to 3-mercaptopropyltriethoxysilane is 1:3;

[0046] Among them, the preparation process of the organic heat-resistant agent is: add 12 parts of 2-amino-4-pentenoic acid and 220 parts of calcium carbonate to 280 parts of tetrahydrofuran, ultrasonically disperse for 40 minutes, then place in an ice water bath at 0°C, slowly add 20 parts of 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride benzene solution, after the addition is complete, heat to 60°C, react at a constant temperature for 25 hours, cool to room temperature, filter, wash, and dry to obtain the organic heat-resistant agent.

[0047] Embodiment 3: A process for preparing a cross-linked polyolefin heat shrinkable film, comprising the following steps:

[0048] Step 1: 108 parts of terpolymer polypropylene, 11 parts of paraffin wax, 3.5 parts of heat-resistant agent, and 0.15 parts of dicumyl peroxide are mixed as the raw materials for the outer layer and the inner layer; 75 parts of low-density polyethylene, 6 parts of heat-resistant agent, 0.15 parts of dicumyl peroxide, and 2.5 parts of calcium stearate are mixed as the raw materials for the core layer; wherein the heat-resistant agent includes modified inorganic nanomaterials and organic heat-resistant agent in a mass ratio of 3.5:1;

[0049] Step 2: Extruding the outer layer and the inner layer in a single screw extruder at 185° C.; extruding the core layer in a single screw extruder at 175° C., and then merging in a three-layer co-extrusion die, co-extruding and cooling to obtain a multi-layer composite sheet;

[0050] Step 3: The multi-layer composite sheet is pulled into a stretching oven for bidirectional synchronous stretching, then cooled by an air ring, split and rolled up, and cut to obtain a finished product;

[0051] Among them, the preparation process of modified inorganic nanomaterials is:

[0052] S1: adding 25 parts of illite to 248 parts of 25wt% sodium hydroxide solution, heating to 45°C, stirring and soaking for 1.5h, filtering and washing with deionized water until neutral; then transferring to 212 parts of 15wt% hydrochloric acid solution, stirring and soaking for 1.5h at room temperature, filtering and washing with deionized water until neutral, and drying to obtain pretreated illite;

[0053] S2: 28 parts of pretreated illite were mixed with 270 parts of deionized water, the temperature was raised to 75°C, hydrochloric acid was added dropwise, the pH was adjusted to 3, and then 45 parts of anhydrous ethanol solution of titanium tetrachloride were slowly added dropwise. After the addition was complete, the reaction was continued for 3 hours, cooled, washed, dried, and transferred to a muffle furnace and calcined at 550°C for 3 hours to obtain a composite inorganic material;

[0054] S3: Dissolve 15 parts of the composite inorganic material in anhydrous ethanol, ultrasonically disperse for 35 minutes, add hydrochloric acid to adjust the pH to 3, then add a mixed solution of 3-aminopropyltriethoxysilane and ethanol, stir for 30 minutes, react at 60°C for 3 hours, cool to room temperature, wash with anhydrous ethanol, vacuum dry, transfer to deionized water, add a mixed solution of 3-mercaptopropyltriethoxysilane and methanol and an alkaline solution, heat to 75°C, react for 5.5 hours, wash, and dry to obtain a modified inorganic nanomaterial; wherein the mass ratio of 3-aminopropyltriethoxysilane to 3-mercaptopropyltriethoxysilane is 1:2.5;

[0055] Among them, the preparation process of the organic heat-resistant agent is: add 11.5 parts of 2-amino-4-pentenoic acid and 210 parts of calcium carbonate to 260 parts of tetrahydrofuran, ultrasonically disperse for 35 minutes, then place in an ice water bath at 0°C, slowly add 20 parts of 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride benzene solution, after the addition is completed, heat to 55°C, react at a constant temperature for 23 hours, cool to room temperature, filter, wash, and dry to obtain the organic heat-resistant agent.

[0056] Comparative Example 1: No organic heat-resistant agent is added, and the rest is the same as Example 3, specifically as follows:

[0057] Step 1: 108 parts of terpolymer polypropylene, 11 parts of paraffin wax, and 3.5 parts of modified inorganic nanomaterials are mixed as raw materials for the outer layer and inner layer; 75 parts of low-density polyethylene, 6 parts of modified inorganic nanomaterials, and 2.5 parts of calcium stearate are mixed as raw materials for the core layer;

[0058] Step 2: Extruding the outer layer and the inner layer in a single screw extruder at 185° C.; extruding the core layer in a single screw extruder at 175° C., and then merging in a three-layer co-extrusion die, co-extruding and cooling to obtain a multi-layer composite sheet;

[0059] Step 3: The multi-layer composite sheet is pulled into a stretching oven for bidirectional synchronous stretching, then cooled by an air ring, split and rolled up, and cut to obtain a finished product;

[0060] Among them, the preparation process of modified inorganic nanomaterials is:

[0061] S1: adding 25 parts of illite to 248 parts of 25wt% sodium hydroxide solution, heating to 45°C, stirring and soaking for 1.5h, filtering and washing with deionized water until neutral; then transferring to 212 parts of 15wt% hydrochloric acid solution, stirring and soaking for 1.5h at room temperature, filtering and washing with deionized water until neutral, and drying to obtain pretreated illite;

[0062] S2: 28 parts of pretreated illite were mixed with 270 parts of deionized water, the temperature was raised to 75°C, hydrochloric acid was added dropwise, the pH was adjusted to 3, and then 45 parts of anhydrous ethanol solution of titanium tetrachloride were slowly added dropwise. After the addition was complete, the reaction was continued for 3 hours, cooled, washed, dried, and transferred to a muffle furnace and calcined at 550°C for 3 hours to obtain a composite inorganic material;

[0063] S3: Dissolve 15 parts of the composite inorganic material in anhydrous ethanol, ultrasonically disperse for 35 minutes, add hydrochloric acid to adjust the pH to 3, then add a mixed solution of 3-aminopropyltriethoxysilane and ethanol, stir for 30 minutes, react at 60°C for 3 hours, cool to room temperature, wash with anhydrous ethanol, vacuum dry, transfer to deionized water, add a mixed solution of 3-mercaptopropyltriethoxysilane and methanol and an alkaline solution, heat to 75°C, react for 5.5 hours, wash, and dry to obtain a modified inorganic nanomaterial; wherein the mass ratio of 3-aminopropyltriethoxysilane to 3-mercaptopropyltriethoxysilane is 1:2.5.

[0064] Comparative Example 2: No modified inorganic nanomaterial is added, and the rest is the same as Example 3, specifically as follows:

[0065] Step 1: Mix 108 parts of terpolymer polypropylene, 11 parts of paraffin wax, and 3.5 parts of organic heat-resistant agent as the raw materials for the outer layer and inner layer; mix 75 parts of low-density polyethylene, 6 parts of organic heat-resistant agent, and 2.5 parts of calcium stearate as the raw materials for the core layer;

[0066] Step 2: Extruding the outer layer and the inner layer in a single screw extruder at 185° C.; extruding the core layer in a single screw extruder at 175° C., and then merging in a three-layer co-extrusion die, co-extruding and cooling to obtain a multi-layer composite sheet;

[0067] Step 3: The multi-layer composite sheet is pulled into a stretching oven for bidirectional synchronous stretching, then cooled by an air ring, split and rolled up, and cut to obtain a finished product;

[0068] Among them, the preparation process of the organic heat-resistant agent is: add 11.5 parts of 2-amino-4-pentenoic acid and 210 parts of calcium carbonate to 260 parts of tetrahydrofuran, ultrasonically disperse for 35 minutes, then place in an ice water bath at 0°C, slowly add 20 parts of 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride benzene solution, after the addition is completed, heat to 55°C, react at a constant temperature for 23 hours, cool to room temperature, filter, wash, and dry to obtain the organic heat-resistant agent.

[0069] Comparative Example 3: An excessive amount of modified inorganic nanomaterial was added, and the rest was the same as in Example 3, specifically as follows:

[0070] Step 1: 108 parts of terpolymer polypropylene, 11 parts of paraffin wax, 3.5 parts of heat-resistant agent, and 0.15 parts of dicumyl peroxide are mixed as the raw materials for the outer layer and the inner layer; 75 parts of low-density polyethylene, 6 parts of heat-resistant agent, 0.15 parts of dicumyl peroxide, and 2.5 parts of calcium stearate are mixed as the raw materials for the core layer; wherein the heat-resistant agent comprises a modified inorganic nanomaterial and an organic heat-resistant agent in a mass ratio of 5:1;

[0071] Step 2: Extruding the outer layer and the inner layer in a single screw extruder at 185° C.; extruding the core layer in a single screw extruder at 175° C., and then merging in a three-layer co-extrusion die, co-extruding and cooling to obtain a multi-layer composite sheet;

[0072] Step 3: The multi-layer composite sheet is pulled into a stretching oven for bidirectional synchronous stretching, then cooled by an air ring, split and rolled up, and cut to obtain a finished product.

[0073] Comparative Example 4: The amount of mercaptosilane coupling agent used was increased, and the rest was the same as Example 3, as follows:

[0074] Step 1: 108 parts of terpolymer polypropylene, 11 parts of paraffin wax, 3.5 parts of heat-resistant agent, and 0.15 parts of dicumyl peroxide are mixed as the raw materials for the outer layer and the inner layer; 75 parts of low-density polyethylene, 6 parts of heat-resistant agent, 0.15 parts of dicumyl peroxide, and 2.5 parts of calcium stearate are mixed as the raw materials for the core layer; wherein the heat-resistant agent includes modified inorganic nanomaterials and organic heat-resistant agent in a mass ratio of 3.5:1;

[0075] Step 2: Extruding the outer layer and the inner layer in a single screw extruder at 185° C.; extruding the core layer in a single screw extruder at 175° C., and then merging in a three-layer co-extrusion die, co-extruding and cooling to obtain a multi-layer composite sheet;

[0076] Step 3: The multi-layer composite sheet is pulled into a stretching oven for bidirectional synchronous stretching, then cooled by an air ring, split and rolled up, and cut to obtain a finished product;

[0077] Among them, the preparation process of modified inorganic nanomaterials is:

[0078] S1: adding 25 parts of illite to 248 parts of 25wt% sodium hydroxide solution, heating to 45°C, stirring and soaking for 1.5h, filtering and washing with deionized water until neutral; then transferring to 212 parts of 15wt% hydrochloric acid solution, stirring and soaking for 1.5h at room temperature, filtering and washing with deionized water until neutral, and drying to obtain pretreated illite;

[0079] S2: 28 parts of pretreated illite were mixed with 270 parts of deionized water, the temperature was raised to 75°C, hydrochloric acid was added dropwise, the pH was adjusted to 3, and then 45 parts of anhydrous ethanol solution of titanium tetrachloride were slowly added dropwise. After the addition was complete, the reaction was continued for 3 hours, cooled, washed, dried, and transferred to a muffle furnace and calcined at 550°C for 3 hours to obtain a composite inorganic material;

[0080] S3: Dissolve 15 parts of the composite inorganic material in anhydrous ethanol, ultrasonically disperse for 35 minutes, add hydrochloric acid to adjust the pH to 3, then add a mixed solution of 3-aminopropyltriethoxysilane and ethanol, stir for 30 minutes, react at 60°C for 3 hours, cool to room temperature, wash with anhydrous ethanol, vacuum dry, transfer to deionized water, add a mixed solution of 3-mercaptopropyltriethoxysilane and methanol and an alkaline solution, heat to 75°C, react for 5.5 hours, wash, and dry to obtain a modified inorganic nanomaterial; wherein the mass ratio of 3-aminopropyltriethoxysilane to 3-mercaptopropyltriethoxysilane is 1:5.

[0081] Performance test: (1) The finished products obtained in the embodiment and the comparative example were tested for tensile strength according to the provisions of GB / T1040.3; (2) The finished products obtained in the embodiment and the comparative example were tested for shrinkage at different temperatures; the results are shown in the following table:

[0082]

[0083]

[0084] Table 1

[0085] Conclusion: Example 3 of the present invention is the best example. By precisely controlling the ratio of modified inorganic nanomaterials and organic heat-resistant agents, the tensile strength and shrinkage rate of the cross-linked polyolefin heat shrinkable film are significantly improved. Moreover, the synergistic effect of the two is crucial to improving the material performance. If any one of the components is missing (such as Comparative Examples 1 and 2), the material performance will be significantly reduced. At the same time, the ratio of each component needs to be strictly controlled. Excessive modified inorganic nanomaterials (such as Comparative Example 3) and mercaptosilane coupling agents (such as Comparative Example 4) will lead to a decrease in material performance.

[0086] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A process for preparing a cross-linked polyolefin heat shrinkable film, characterized in that: The following steps are involved: Step 1: The outer layer, inner layer and core layer raw materials are extruded separately in a single screw extruder, and then merged in a three-layer co-extrusion die head, co-extruded and cooled to obtain a multi-layer composite sheet; Step 2: The multi-layer composite sheet is pulled into a stretching oven for bidirectional synchronous stretching, then cooled by an air ring, split and rolled up, and cut to obtain a finished product.

2. The process for preparing a cross-linked polyolefin heat shrinkable film according to claim 1, characterized in that: The outer layer and the inner layer have the same raw materials, including the following substances: by weight, 100-110 parts of terpolymer polypropylene, 10-12 parts of anti-sticking agent, 3-4 parts of heat-resistant agent, and 0.1-0.2 parts of initiator; the core layer has the following raw materials: by weight, 70-80 parts of low-density polyethylene, 5-8 parts of heat-resistant agent, 0.1-0.2 parts of initiator, and 2-3 parts of lubricant.

3. The process for preparing a cross-linked polyolefin heat shrinkable film according to claim 2, characterized in that: The heat-resistant agent comprises a modified inorganic nano material and an organic heat-resistant agent in a mass ratio of (3-4):

1.

4. The process for preparing a cross-linked polyolefin heat shrinkable film according to claim 3, characterized in that: The preparation process of the modified inorganic nanomaterial is: S1: adding illite to a sodium hydroxide solution, heating to 40-50°C, stirring and soaking for 1-2 hours, filtering and washing with deionized water until neutral; then transferring to a hydrochloric acid solution, stirring and soaking for 1-2 hours at room temperature, filtering and washing with deionized water until neutral, and drying to obtain pretreated illite; S2: Mix the pretreated illite with deionized water, heat to 70-80°C, add hydrochloric acid, adjust the pH to 2-3, then slowly add anhydrous ethanol solution of titanium tetrachloride, continue to react for 2-3 hours after the addition is complete, cool, wash, dry, transfer to a muffle furnace and calcine at 500-550°C for 2-3 hours to obtain a composite inorganic substance; S3: dissolve the composite inorganic material in anhydrous ethanol, ultrasonically disperse for 30-40 minutes, add hydrochloric acid to adjust the pH to 3-4, add a mixed solution of 3-aminopropyltriethoxysilane and ethanol, stir for 30-40 minutes, react at 60-70°C for 3-4 hours, cool to room temperature, wash with anhydrous ethanol, vacuum dry, ultrasonically disperse in deionized water, add a mixed solution of 3-mercaptopropyltriethoxysilane and methanol and an alkaline solution, heat to 70-80°C, react for 5-8 hours, wash, and dry to obtain a modified inorganic nanomaterial.

5. The process for preparing a cross-linked polyolefin heat shrinkable film according to claim 4, characterized in that: The mass ratio of the 3-aminopropyltriethoxysilane to the 3-mercaptopropyltriethoxysilane is 1:(2-3).

6. The process for preparing a cross-linked polyolefin heat shrinkable film according to claim 4, characterized in that: The pretreated illite comprises the following materials: by weight, 20-30 parts of illite, 244-250 parts of sodium hydroxide solution, and 210-215 parts of hydrochloric acid solution; The mass fraction of the sodium hydroxide solution is 20-25%, and the mass fraction of the hydrochloric acid solution is 10-15%; The composite inorganic material comprises the following substances: by weight, 25-30 parts of pretreated illite, 260-280 parts of deionized water, and 42-45 parts of anhydrous ethanol solution of titanium tetrachloride.

7. The process for preparing a cross-linked polyolefin heat shrinkable film according to claim 3, characterized in that: The preparation process of the organic heat-resistant agent is as follows: 2-amino-4-pentenoic acid and calcium carbonate are added to tetrahydrofuran, ultrasonically dispersed for 30-40 minutes, then placed in an ice water bath at 0°C, and a benzene solution of 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride is slowly added dropwise, and after the addition is completed, the temperature is raised to 50-60°C, and the reaction is carried out at a constant temperature for 20-25 hours. After cooling to room temperature, the organic heat-resistant agent is filtered, washed, and dried to obtain the organic heat-resistant agent.

8. The process for preparing a cross-linked polyolefin heat shrinkable film according to claim 7, characterized in that: The organic heat-resistant agent raw material comprises the following components: by weight, 11-12 parts of 2-amino-4-pentenoic acid, 200-220 parts of calcium carbonate, 250-180 parts of tetrahydrofuran, and 18-20 parts of a benzene solution of 3,5-bis(tert-butyl)-4-hydroxyphenylpropionyl chloride.

9. The process for preparing a cross-linked polyolefin heat shrinkable film according to claim 1, characterized in that: The extrusion temperature of the outer layer and the inner layer in the single screw extruder is 180-190°C; the extrusion temperature of the core layer in the single screw extruder is 170-180°C.

10. The finished product obtained according to the preparation process of a cross-linked polyolefin heat shrinkable film according to any one of claims 1 to 9.

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