Heat-resistant plastic film and preparation method thereof

Abstract

The invention relates to the technical field of packaging plastic films, and particularly discloses a heat-resistant plastic film and a preparation method thereof. The heat-resistant plastic film is prepared from the following raw materials in parts by mass: 100 parts of polypropylene, 5-10 parts of activated calcium carbonate, 1-3 parts of an antioxidant, 1-2 parts of calcium stearate, 5-10 parts of zein, 1-2 parts of polyfructose, 1-4 parts of nano silicon dioxide and 1-2 parts of carboxyl-terminated polyamidoamine. The obtained film has good steaming and boiling resistance (can resist steaming and boiling at the high temperature of 135 DEG C) and processability, has good physical and mechanical properties, can meet the requirements of the market for the packaging materials, and is low in preparation cost, simple in preparation method and suitable for large-scale popularization and production.

Description

Technical Field

[0001] The invention relates to the technical field of packaging plastic films, in particular to a heat-resistant plastic film and a preparation method thereof. Background Art

[0002] High temperature cooking resistant packaging is commonly used for meat, bean products and other food packaging forms, generally using vacuum packaging, can be sterilized by high temperature (121-135 ℃), and stored at room temperature. Foods in cooking resistant packaging are easy to carry, ready to eat after opening the bag, hygienic and convenient, and can well maintain the flavor of the food, and are deeply loved by consumers.

[0003] Depending on the sterilization process and packaging materials, the shelf life of retort-resistant packaging products ranges from half a year to two years. The packaging process of retort food is bag making, bagging, vacuuming, heat sealing, inspection, retort heating sterilization, drying and cooling, and packaging. However, the molecular chain movement of packaging bags made of polymer materials-plastics intensifies after heating, the physical properties of the materials are prone to thermal decay, odor may occur after retorting, and the solvent residue of the packaging material exceeds the standard, or the material selection is improper. If PE film is used as a high-temperature retort bag above 120°C, the PE film is very likely to have a bad smell at high temperatures.

[0004] Existing high-temperature cooking bags often use RCPP. RCPP is a high-temperature cooking resistant polypropylene film, mainly produced by cast extrusion process, with good anti-pollution heat sealing performance, able to withstand high temperatures of 135°C, and has the advantage of no leakage. Therefore, RCPP film is widely used as packaging material for food, daily necessities and electronic products.

[0005] However, the existing RCPP film is not only too hard, but also has poor heat sealing strength and impact strength, which needs to be improved urgently. Summary of the invention

[0006] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a heat-resistant plastic film and a preparation method thereof.

[0007] A heat-resistant plastic film comprises the following raw materials by mass: 100 parts of polypropylene, 5-10 parts of activated calcium carbonate, 1-3 parts of antioxidant, 1-2 parts of calcium stearate, 5-10 parts of zein, 1-2 parts of polyfructose, 1-4 parts of nano silicon dioxide and 1-2 parts of carboxyl-terminated polyamidoamine.

[0008] Preferably, the polypropylene has a melt flow rate of 7.2-8.6 g / 10 min at 230° C. and 2.16 kg, and an isotacticity of 94%-96%.

[0009] Preferably, the antioxidant comprises: a primary antioxidant and an auxiliary antioxidant, and the auxiliary antioxidant is a phosphite antioxidant.

[0010] Preferably, the main antioxidant is at least one of antioxidant BHT, antioxidant TNP, antioxidant TPP, antioxidant 1010, antioxidant 1076, and antioxidant 168.

[0011] Preferably, the phosphite antioxidant is at least one of trioctyl phosphite, tridecyl phosphite, tri(dodecanol) phosphite and tri(hexadecanol) phosphite.

[0012] Preferably, the activated calcium carbonate is prepared by the following specific operation: adding nano calcium carbonate to an ethanol aqueous solution and stirring evenly, adding stearic acid thereto, stirring at 70-80° C. for 1-2 hours, and spray drying.

[0013] Preferably, the mass ratio of nano calcium carbonate to stearic acid is 5-10:1-2.

[0014] The method for preparing the heat-resistant plastic film comprises the following steps: S1. Powdered polypropylene, activated calcium carbonate, antioxidant and calcium stearate are mixed evenly, melted and granulated at 200-215°C, cooled, and extruded and cast into a film; 60 A pretreated film is obtained by irradiation treatment with a Co γ-ray source; S2. Add zein to ethanol aqueous solution and stir evenly, add polyfructose, nano-silica and carboxyl-terminated polyamidoamine thereto and stir for 10-20 minutes, apply to the surface of the pretreated film, heat treat at 130-140° C. for 5-10 minutes, cool to room temperature and dry.

[0015] Preferably, in S1, the irradiation dose of the irradiation treatment is 20-30 kGy.

[0016] Preferably, in S1, during the extrusion casting process, the extruder temperature is 220-230°C, the die head temperature is 235-245°C, and the casting machine temperature is 30-40°C.

[0017] Beneficial effects: The invention adopts stearic acid to treat the surface of nano calcium carbonate, and then mixes it with polypropylene, which can not only significantly enhance the dispersibility of nano calcium carbonate in polypropylene, but also make the obtained film have high thermal deformation temperature and excellent impact resistance; after irradiation treatment, free radicals can be generated on the surface and active groups such as peroxyl groups and hydroxyl groups can be formed, but it is very easy to cause the hardness of the film to become higher and the impact resistance to be greatly reduced.

[0018] The present invention further adopts a compound of zein and polyfructose, and coats them on the surface of the pretreated film. After high-temperature heat treatment, they are combined on the surface of the film to form a three-dimensional network structure, which can not only enhance the toughness of the film and effectively solve the problem of a significant decrease in the impact resistance of the film due to radiation treatment, but also cooperate with nano-silicon dioxide and terminal carboxyl polyamide amine. The two are bonded and combined into the three-dimensional network structure, so that the obtained film has good heat-sealing strength, excellent high-temperature resistance, high-temperature cooking resistance, and excellent high-temperature sealing.

[0019] The premix used in the present invention has a high bonding strength with the film, which can not only effectively form a barrier layer and increase the sealing performance, but also has a high coating stability, is difficult for oxygen and water to pass through, has excellent barrier performance, is durable and not easy to break.

[0020] The film obtained by the present invention has good resistance to cooking (can withstand high-temperature cooking at 135°C) and processing performance, and has good physical and mechanical properties, which can meet the market demand for this type of packaging material. At the same time, the preparation cost is low, the preparation method is simple, and it is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a comparison chart of the longitudinal tensile strength and transverse tensile strength of the plastic films obtained in Example 5 and Comparative Examples 1-2.

[0022] Figure 2 This is a comparison chart of the impact strength of the plastic films obtained in Example 5 and Comparative Examples 1-2 and the oxygen permeability after being steamed at 135° C. for 30 minutes.

[0023] Figure 3 This is a comparison chart of the heat sealing strength at 190°C before and after the plastic films obtained in Example 5 and Comparative Examples 1-2 were cooked at 135°C for 30 minutes.

[0024] Figure 4 This is a comparison chart of the heat seal strength retention rate of the plastic films obtained in Example 5 and Comparative Examples 1-2 before and after being steamed at 135° C. for 30 minutes. DETAILED DESCRIPTION

[0025] The present invention will be further explained below in conjunction with specific embodiments.

[0026] The grade of polypropylene used in the following is Shanghai Petrochemical PP F800E, the melt flow rate (230°C, 2.16kg) is 8.0g / 10min, and the isotacticity is 94%. The zein used in the following is purchased from Shijiazhuang Mouyuan Starch Co., Ltd.

[0027] Example 1 A heat-resistant plastic film, whose raw materials include: 1000g of polypropylene, 50g of activated calcium carbonate, 10g of antioxidant, 10g of calcium stearate, 50g of zein, 10g of polyfructose, 10g of nano silicon dioxide, and 10g of 2.0-generation carboxyl-terminated polyamidoamine.

[0028] The antioxidant is composed of antioxidant BHT and trioctyl phosphite in a mass ratio of 1:0.1. The activated calcium carbonate is prepared by the following specific operation: 50g of nano calcium carbonate is added to 300g of 40% ethanol aqueous solution and stirred evenly, 10g of stearic acid is added thereto, stirred at a temperature of 70°C for 1h, and spray dried.

[0029] The method for preparing the heat-resistant plastic film comprises the following steps: S1. Powdered polypropylene, activated calcium carbonate, antioxidant and calcium stearate are mixed evenly, and sent to a twin-screw extruder for melt granulation, with a melting temperature of 200°C and a screw speed of 100 r / min. The mixture is cooled, extruded and cast into a film with a thickness of 60 μm; 60 Co γ-ray source irradiation treatment, the irradiation dose is 20kGy, to obtain a pretreated film; During the extrusion casting process, the extruder temperature was 220°C, the die temperature was 235°C, and the casting machine temperature was 30°C; S2. Add zein to 300 g of 70% ethanol solution and stir evenly. Add polyfructose, nano-silica and carboxyl-terminated polyamide amine and stir for 10 minutes. Apply to the surface of the pretreated film by a coating machine, heat treat at 130°C for 5 minutes, cool to room temperature and dry.

[0030] Example 2 A heat-resistant plastic film comprises the following raw materials: 1000g of polypropylene, 100g of activated calcium carbonate, 30g of antioxidant, 20g of calcium stearate, 100g of zein, 20g of polyfructose, 40g of nano silicon dioxide and 20g of 2.0-4.0 generation carboxyl-terminated polyamidoamine.

[0031] The antioxidant is composed of antioxidant 1076 and tris(hexadecanol) phosphite in a mass ratio of 2:0.5. The activated calcium carbonate is prepared by the following specific operation: 100g of nano calcium carbonate is added to 600g of 60% ethanol aqueous solution and stirred evenly, 20g of stearic acid is added thereto, stirred at a temperature of 80°C for 2h, and spray dried.

[0032] The method for preparing the heat-resistant plastic film comprises the following steps: S1. Powdered polypropylene, activated calcium carbonate, antioxidant and calcium stearate are mixed evenly, and sent to a twin-screw extruder for melt granulation, with a melting temperature of 215°C and a screw speed of 150 r / min. The mixture is cooled, extruded and cast into a film with a thickness of 70 μm; 60 Co γ-ray source irradiation treatment, the irradiation dose is 30kGy, to obtain a pretreated film; During the extrusion casting process, the extruder temperature was 230°C, the die temperature was 245°C, and the casting machine temperature was 40°C; S2. Add zein to 500 g of 80% ethanol solution and stir evenly. Add polyfructose, nano-silica and carboxyl-terminated polyamide amine and stir for 20 minutes. Apply the solution to the surface of the pretreated film using a coating machine. Heat treat at 140°C for 10 minutes, cool to room temperature and dry.

[0033] Example 3 A heat-resistant plastic film, whose raw materials include: 1000g of polypropylene, 70g of activated calcium carbonate, 25g of antioxidant, 13g of calcium stearate, 90g of zein, 12g of polyfructose, 30g of nano silicon dioxide and 14g of 3.0-generation carboxyl-terminated polyamidoamine.

[0034] The antioxidant is composed of antioxidant 168 and tris(dodecanol) phosphite in a mass ratio of 1.7:0.2. The activated calcium carbonate is prepared by the following specific operation: 90g of nano calcium carbonate is added to 400g of 55% ethanol aqueous solution and stirred evenly, 13g of stearic acid is added thereto, stirred at a temperature of 77°C for 80min, and spray dried.

[0035] The method for preparing the heat-resistant plastic film comprises the following steps: S1. Powdered polypropylene, activated calcium carbonate, antioxidant and calcium stearate are mixed evenly, and sent to a twin-screw extruder for melt granulation, with a melt temperature of 210°C and a screw speed of 110 r / min. The mixture is cooled, extruded and cast into a film with a thickness of 65 μm; 60 Co γ-ray source irradiation treatment, the irradiation dose is 28kGy, to obtain a pre-treated film; During the extrusion casting process, the extruder temperature was 222°C, the die temperature was 242°C, and the casting machine temperature was 33°C; S2. Add zein to 450 g of 73% ethanol solution and stir evenly. Add polyfructose, nano-silica and carboxyl-terminated polyamide amine and stir for 18 minutes. Apply the solution to the surface of the pretreated film by a coating machine. Heat treat at 133°C for 9 minutes, cool to room temperature and dry.

[0036] Example 4 A heat-resistant plastic film, whose raw materials include: 1000g of polypropylene, 90g of activated calcium carbonate, 15g of antioxidant, 17g of calcium stearate, 70g of zein, 18g of polyfructose, 20g of nano silicon dioxide and 16g of 3.0-generation carboxyl-terminated polyamidoamine.

[0037] The antioxidant is composed of antioxidant TPP and tris(dodecyl)phosphite in a mass ratio of 1.3:0.4. The activated calcium carbonate is prepared by the following specific operation: 70g of nano calcium carbonate is added to 500g of 45% ethanol aqueous solution and stirred evenly, 17g of stearic acid is added thereto, stirred at a temperature of 73°C for 100min, and spray dried.

[0038] The method for preparing the heat-resistant plastic film comprises the following steps: S1. Powdered polypropylene, activated calcium carbonate, antioxidant and calcium stearate are mixed evenly, and sent to a twin-screw extruder for melt granulation, with a melting temperature of 205°C and a screw speed of 130 r / min. The mixture is cooled, extruded and cast into a film with a thickness of 65 μm; 60 Co γ-ray source irradiation treatment, the irradiation dose is 22kGy, to obtain a pre-treated film; During the extrusion casting process, the extruder temperature was 228°C, the die temperature was 238°C, and the casting machine temperature was 37°C; S2. Add zein to 350 g of 77% ethanol solution and stir evenly. Add polyfructose, nano-silica and carboxyl-terminated polyamide amine and stir for 12 minutes. Apply the solution to the surface of the pretreated film by a coating machine. Heat treat at 137°C for 7 minutes, cool to room temperature and dry.

[0039] Example 5 A heat-resistant plastic film, whose raw materials include: 1000g of polypropylene, 80g of activated calcium carbonate, 20g of antioxidant, 15g of calcium stearate, 80g of zein, 15g of polyfructose, 25g of nano silicon dioxide and 15g of 3.0-generation carboxyl-terminated polyamidoamine.

[0040] The antioxidant is composed of antioxidant 1010 and tridecyl phosphite in a mass ratio of 1.5:0.3. The activated calcium carbonate is prepared by the following specific operation: 80g of nano calcium carbonate is added to 450g of 50% ethanol aqueous solution and stirred evenly, 15g of stearic acid is added thereto, stirred at a temperature of 75°C for 90min, and spray dried.

[0041] The method for preparing the heat-resistant plastic film comprises the following steps: S1. Powdered polypropylene, activated calcium carbonate, antioxidant and calcium stearate are mixed evenly, and sent to a twin-screw extruder for melt granulation, with a melting temperature of 208°C and a screw speed of 120 r / min. The mixture is cooled, extruded and cast into a film with a thickness of 65 μm; 60 Co γ-ray source irradiation treatment, the irradiation dose is 25kGy, to obtain a pre-treated film; During the extrusion casting process, the extruder temperature was 225°C, the die temperature was 240°C, and the casting machine temperature was 35°C; S2. Add zein to 400 g of 75% ethanol solution and stir evenly. Add polyfructose, nano-silica and carboxyl-terminated polyamide amine and stir for 15 minutes. Apply the solution to the surface of the pretreated film by a coating machine. Heat treat at 135°C for 8 minutes, cool to room temperature and dry.

[0042] Comparative Example 1 A heat-resistant plastic film, whose raw materials include: 1000g of polypropylene, 80g of activated calcium carbonate, 20g of antioxidant, 15g of calcium stearate, 80g of zein, 15g of polyfructose, 25g of nano silicon dioxide and 15g of 3.0-generation carboxyl-terminated polyamidoamine.

[0043] The antioxidant is composed of antioxidant 1010 and tridecyl phosphite in a mass ratio of 1.5:0.3. The activated calcium carbonate is prepared by the following specific operation: 80g of nano calcium carbonate is added to 450g of 50% ethanol aqueous solution and stirred evenly, 15g of stearic acid is added thereto, stirred at a temperature of 75°C for 90min, and spray dried.

[0044] The method for preparing the heat-resistant plastic film comprises the following steps: S1. Powdered polypropylene, activated calcium carbonate, antioxidant and calcium stearate are mixed evenly, and sent to a twin-screw extruder for melt granulation, with a melt temperature of 208°C and a screw speed of 120 r / min, and then cooled and extruded and cast into a film with a thickness of 65 μm; During the extrusion casting process, the extruder temperature was 225°C, the die temperature was 240°C, and the casting machine temperature was 35°C; S2. Add zein to 400 g of 75% ethanol solution and stir evenly. Add polyfructose, nano-silica and carboxyl-terminated polyamide amine and stir for 15 minutes. Apply to the film surface by a coating machine, heat treat at 135°C for 8 minutes, cool to room temperature and dry.

[0045] Comparative Example 2 A heat-resistant plastic film comprises the following raw materials: 1000g of polypropylene, 80g of activated calcium carbonate, 20g of antioxidant, 15g of calcium stearate, 80g of zein, 15g of polyfructose and 25g of nano silicon dioxide.

[0046] The antioxidant is composed of antioxidant 1010 and tridecyl phosphite in a mass ratio of 1.5:0.3. The activated calcium carbonate is prepared by the following specific operation: 80g of nano calcium carbonate is added to 450g of 50% ethanol aqueous solution and stirred evenly, 15g of stearic acid is added thereto, stirred at a temperature of 75°C for 90min, and spray dried.

[0047] The method for preparing the heat-resistant plastic film comprises the following steps: S1. Powdered polypropylene, activated calcium carbonate, antioxidant and calcium stearate are mixed evenly, and sent to a twin-screw extruder for melt granulation, with a melting temperature of 208°C and a screw speed of 120 r / min. The mixture is cooled, extruded and cast into a film with a thickness of 65 μm; 60 Co γ-ray source irradiation treatment, the irradiation dose is 25kGy, to obtain a pre-treated film; During the extrusion casting process, the extruder temperature was 225°C, the die temperature was 240°C, and the casting machine temperature was 35°C; S2. Add zein to 400 g of 75% ethanol solution and stir evenly. Add polyfructose and nano-silicon dioxide and stir for 15 minutes. Apply the solution to the surface of the pretreated film using a coating machine. Heat treat at 135°C for 8 minutes, cool to room temperature, and dry.

[0048] The longitudinal tensile strength and transverse tensile strength of the plastic films obtained in Example 5 and Comparative Examples 1-2 were measured with reference to GB / T 1040.3-2006 “Determination of tensile properties of plastics Part 3: Test conditions for thin plastics and sheets”.

[0049] like Figure 1 As shown, the longitudinal / transverse tensile strength of the plastic film obtained in Example 5 is higher than that of Comparative Examples 1-2 (P < 0.05).

[0050] The impact strength of the plastic films obtained in Example 5 and Comparative Examples 1-2 was measured with reference to GB / T 8809-2015 "Test Method for Pendulum Impact Resistance of Plastic Films". The plastic films obtained in Example 5 and Comparative Examples 1-2 were steamed at 135°C for 30 min, and then the oxygen transmission rate was tested at 23°C and 80% RH according to "ASTM F1927".

[0051] like Figure 2 As shown, the impact strength and oxygen permeability after cooking of the plastic film obtained in Example 5 are higher than those of Comparative Examples 1-2 (P < 0.05).

[0052] The plastic films obtained in Example 5 and Comparative Examples 1-2 were then steamed at 135°C for 30 min, and then the heat seal strength at 190°C before and after steaming was tested with reference to QB / T2358-1998 "Test Method for Heat Seal Strength of Plastic Film Packaging Bags", and the heat seal strength retention rate before and after steaming was calculated.

[0053] Heat seal strength retention rate = heat seal strength after cooking / heat seal strength before cooking × 100% like Figure 3 and Figure 4 As shown, the heat sealing strength of the plastic film obtained in Example 5 before and after steaming is higher than that of Comparative Examples 1-2 (P < 0.05), and the heat sealing strength retention rate of the plastic film obtained in Example 5 is also higher than that of Comparative Examples 1-2 (P < 0.05).

[0054] The applicant believes that this is because the present invention uses stearic acid to treat the surface of nano calcium carbonate, and then cooperates with polypropylene, which can not only significantly enhance the dispersibility of nano calcium carbonate in polypropylene, but also make the heat deformation temperature of the obtained film high and excellent in impact resistance; after irradiation treatment, it can promote the generation of free radicals on the surface and form active groups such as peroxy and hydroxyl groups, but it is very easy to cause the film hardness to become high and the impact resistance to drop significantly. The present invention further uses zein and polyfructose to compound, and coat them on the surface of the pretreated film, and after high-temperature heat treatment, it is combined on the surface of the film to form a three-dimensional network structure, which can not only enhance the toughness of the film, effectively solve the problem of the film's impact resistance to drop significantly due to irradiation treatment, but also cooperate with nano silicon dioxide and carboxyl-terminated polyamide amine, the two are bonded and combined into the three-dimensional network structure, so that the obtained film has good heat sealing strength, excellent high temperature resistance, and high temperature resistance to boiling, and excellent high temperature sealing. The premix used in the present invention has a high bonding strength with the film, which can not only effectively form a barrier layer and increase the sealing performance, but also has a high coating stability, is difficult for oxygen and water to pass through, has excellent barrier performance, is durable and not easy to break.

[0055] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A heat-resistant plastic film, characterized in that: The raw materials include, by mass, 100 parts of polypropylene, 5-10 parts of activated calcium carbonate, 1-3 parts of antioxidant, 1-2 parts of calcium stearate, 5-10 parts of zein, 1-2 parts of polyfructose, 1-4 parts of nano silicon dioxide and 1-2 parts of carboxyl-terminated polyamidoamine.

2. The heat-resistant plastic film according to claim 1, characterized in that: The melt flow rate of polypropylene at 230°C and 2.16 kg is 7.2-8.6 g / 10 min, and the isotacticity is 94%-96%.

3. The heat-resistant plastic film according to claim 1, characterized in that: Antioxidants include: Main antioxidant and auxiliary antioxidant, the auxiliary antioxidant is a phosphite antioxidant.

4. The heat-resistant plastic film according to claim 3, characterized in that: The main antioxidant is at least one of antioxidant BHT, antioxidant TNP, antioxidant TPP, antioxidant 1010, antioxidant 1076, and antioxidant 168.

5. The heat-resistant plastic film according to claim 3, characterized in that: The phosphite antioxidant is at least one of trioctyl phosphite, tridecyl phosphite, tri(dodecanol) phosphite and tri(hexadecanol) phosphite.

6. The heat-resistant plastic film according to claim 1, characterized in that: The activated calcium carbonate is prepared by the following specific operation: adding nano calcium carbonate to ethanol aqueous solution and stirring evenly, adding stearic acid thereto, stirring at 70-80° C. for 1-2 hours, and spray drying.

7. The heat-resistant plastic film according to claim 6, characterized in that: The mass ratio of nano calcium carbonate to stearic acid is 5-10:1-2.

8. A method for preparing a heat-resistant plastic film according to any one of claims 1 to 7, characterized in that: The steps include: S1. Powdered polypropylene, activated calcium carbonate, antioxidant and calcium stearate are mixed evenly, melted and granulated at 200-215°C, cooled, and extruded and cast into a film; 60 A pretreated film is obtained by irradiation treatment with a Co γ-ray source; S2. Add zein to ethanol aqueous solution and stir evenly, add polyfructose, nano-silica and carboxyl-terminated polyamidoamine thereto and stir for 10-20 minutes, apply to the surface of the pretreated film, heat treat at 130-140° C. for 5-10 minutes, cool to room temperature and dry.

9. The method for preparing the heat-resistant plastic film according to claim 8, characterized in that: In S1, the irradiation treatment has an irradiation dose of 20-30 kGy.

10. The method for preparing a heat-resistant plastic film according to claim 8, characterized in that: In S1, during the extrusion casting process, the extruder temperature is 220-230°C, the die head temperature is 235-245°C, and the casting machine temperature is 30-40°C.

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