CPP cast film and preparation method thereof

Abstract

The invention relates to the technical field of high polymer materials, and provides a CPP cast film and a preparation method thereof. The CPP cast film sequentially comprises a corona layer, a core layer and a heat sealing layer from top to bottom, and the corona layer comprises the following raw materials in parts by weight: 50-70 parts of co-polypropylene, 10-15 parts of a first ethylene-vinyl acetate copolymer and 0.1-0.3 part of an anti-adhesion agent; the core layer is prepared from the following raw materials in parts by weight: 60 to 80 parts of homo-polypropylene and 0.1 to 0.3 part of slipping agent; the heat sealing layer is prepared from the following raw materials in parts by weight: 40 to 50 parts of co-polypropylene, 15 to 20 parts of metallocene polypropylene, 10 to 15 parts of second ethylene-vinyl acetate copolymer, 0.1 to 0.5 part of slipping agent and 0.2 to 0.5 part of anti-adhesion agent. According to the technical scheme, the problem of poor low temperature resistance of the CPP cast film in the prior art is solved.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to a CPP cast film and a preparation method thereof. Background Art

[0002] With the rapid development of the packaging industry, the demand for high-performance packaging materials is growing. Among many packaging materials, plastic film has become one of the most widely used packaging materials due to its good flexibility, barrier properties and processing properties. In the field of plastic films, polypropylene (CPP) cast film has gradually occupied an important position with its unique performance advantages. Early packaging films were mainly traditional blown films, but there were certain limitations in terms of flatness, thickness uniformity and optical properties of blown films. With the continuous improvement of market requirements for packaging film quality, cast film technology came into being. Cast film has uniform thickness, high flatness and good transparency, which meets the strict requirements of the high-end packaging market for film quality. However, the low temperature resistance of polypropylene is not ideal. In winter in cold areas, packaging films made of polypropylene materials may become brittle and cracked due to low temperatures during transportation or storage, and cannot effectively protect the items in the package. Therefore, it is necessary to develop a CPP cast film with good low temperature resistance to solve the problem of its brittleness at low temperatures. Summary of the invention

[0003] The invention provides a CPP cast film and a preparation method thereof, which solves the problem of poor low temperature resistance of the CPP cast film in the related art.

[0004] The technical solution of the present invention is as follows: The present invention provides a CPP cast film, which comprises a corona layer, a core layer and a heat sealing layer from top to bottom, wherein the corona layer comprises the following raw materials in parts by weight: 50-70 parts of copolymerized polypropylene, 10-15 parts of a first ethylene-vinyl acetate copolymer, and 0.1-0.3 parts of an anti-blocking agent; The core layer comprises the following raw materials in parts by weight: 60-80 parts of homopolypropylene and 0.1-0.3 parts of lubricant; The heat-sealing layer comprises the following raw materials in parts by weight: 40-50 parts of copolymerized polypropylene, 15-20 parts of metallocene polypropylene, 10-15 parts of a second ethylene-vinyl acetate copolymer, 0.1-0.5 parts of a lubricant, and 0.2-0.5 parts of an anti-blocking agent.

[0005] As a further technical solution, the vinyl acetate content of the first ethylene-vinyl acetate copolymer and the second ethylene-vinyl acetate copolymer is independently 19 wt % to 33 wt %.

[0006] In the present invention, by limiting the vinyl acetate content of the first ethylene-vinyl acetate copolymer and the second ethylene-vinyl acetate copolymer to 19 wt % to 33 wt % respectively, the low temperature resistance of the CPP cast film is further improved.

[0007] As a further technical solution, the vinyl acetate content of the first ethylene-vinyl acetate copolymer is 19wt%; and the vinyl acetate content of the second ethylene-vinyl acetate copolymer is 33wt%.

[0008] In the present invention, the impact resistance of the CPP cast film is improved by limiting the vinyl acetate content of the first ethylene-vinyl acetate copolymer to 19wt% and the vinyl acetate content of the second ethylene-vinyl acetate copolymer to 33wt%.

[0009] As a further technical solution, the core layer further comprises 8 to 12 parts of polybutyl acrylate.

[0010] In the present invention, by adding polybutyl acrylate into the core layer, the adhesion between the core layer, the corona layer and the heat sealing layer can be enhanced, and the impact resistance of the CPP cast film can be improved.

[0011] As a further technical solution, the copolymerized polypropylene is one or both of binary copolymerized polypropylene and ternary copolymerized polypropylene.

[0012] In the present invention, copolymer polypropylene has good heat sealing performance, toughness and impact strength, so copolymer polypropylene is used as the base material in the heat sealing layer and the corona layer, thereby improving the heat sealing strength and toughness of the CPP cast film.

[0013] As a further technical solution, the homopolymer polypropylene has a melt index of 25-35 g / 10 min at 230° C. and 2.16 kg.

[0014] As a further technical solution, the mass ratio of the corona layer, the core layer and the heat sealing layer is 1:3:2~3.

[0015] As a further technical solution, the lubricant includes one or both of oleamide and erucamide.

[0016] In the present invention, the friction between the CPP cast film and the equipment can be improved by adding a lubricant, thereby improving the processing performance and surface glossiness.

[0017] As a further technical solution, the anti-adhesion agent includes one or more of diatomaceous earth, talcum powder, and calcium carbonate.

[0018] In the present invention, a micro rough surface can be formed on the surface of the CPP cast film by adding an anti-blocking agent to prevent adhesion between films.

[0019] The present invention also provides a method for preparing a CPP cast film, comprising the following steps: S1, the raw materials of the corona layer, the core layer and the heat sealing layer are subjected to three-layer melt co-extrusion, casting and cooling to obtain a cast film semi-finished product; S2, subjecting the corona layer of the semi-finished cast film to corona treatment to obtain a CPP cast film.

[0020] The working principle and beneficial effects of the present invention are: In the present invention, the CPP cast film consists of a corona layer, a core layer and a heat-sealing layer, wherein the corona layer and the heat-sealing layer use copolymerized polypropylene as a base material and are used in combination with ethylene-vinyl acetate copolymer to improve the flexibility and low-temperature resistance of the corona layer and the heat-sealing layer; metallocene polypropylene is also added to the heat-sealing layer, which has a narrow molecular weight distribution and excellent processing performance, can promote compatibility with other components and enhance the overall performance of the heat-sealing layer; the core layer uses homopolymerized polypropylene as a base material to provide a certain support strength for the CPP cast film, and the addition of a lubricant can reduce the friction resistance between the films, prevent the film from being broken due to stress concentration at low temperatures, and improve the low-temperature stability of the CPP cast film. DETAILED DESCRIPTION

[0021] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] In the following embodiments and comparative examples: Homopolymer polypropylene PP 519A, melt index at 230°C and 2.16kg: 35g / 10min, homopolymer polypropylene PP5780P, melt index at 230°C and 2.16kg: 25g / 10min; polybutyl acrylate, MW 90,000~100,000; binary copolymer polypropylene, model: C4608; ternary copolymer polypropylene, model: DY-W725EF; metallocene polypropylene, model: MR4025; ethylene-vinyl acetate copolymer EVA 14J2, vinyl acetate content is 14wt%; ethylene-vinyl acetate copolymer EVA VS430, vinyl acetate content is 19wt%; ethylene-vinyl acetate copolymer EVA VA810, vinyl acetate content is 33wt%; ethylene-vinyl acetate copolymer EVA EV 40W, vinyl acetate content is 41wt%.

[0023] Example 1 A method for preparing a CPP cast film comprises the following steps: S1, adding the raw materials of the corona layer, the core layer and the heat sealing layer into the extruder at a mass ratio of 1:3:2, and obtaining a cast film semi-finished product by melt three-layer co-extrusion, casting and cooling; S2, corona treating the corona layer of the semi-finished cast film to obtain a CPP cast film; Corona layer raw materials: 50 parts of binary copolymer polypropylene, 10 parts of ethylene-vinyl acetate copolymer EVA 14J2, and 0.1 parts of diatomaceous earth; Core layer materials: 60 parts of homopolymer polypropylene PP 519A, 0.1 parts of oleic acid amide; Heat sealing layer raw materials: 40 parts of binary copolymer polypropylene, 15 parts of metallocene polypropylene, 10 parts of ethylene-vinyl acetate copolymer EVA14J2, 0.1 parts of oleic acid amide, and 0.2 parts of diatomaceous earth.

[0024] Example 2 A method for preparing a CPP cast film comprises the following steps: S1, adding the raw materials of the corona layer, the core layer and the heat sealing layer into the extruder at a mass ratio of 1:3:3, and obtaining a cast film semi-finished product by melt three-layer co-extrusion, casting and cooling; S2, corona treating the corona layer of the semi-finished cast film to obtain a CPP cast film; Corona layer raw materials: 70 parts of terpolymer polypropylene, 15 parts of ethylene-vinyl acetate copolymer EVA 14J2, and 0.3 parts of talc; Core layer materials: 80 parts of homopolymer polypropylene PP 519A, 0.3 parts of erucamide; Heat sealing layer raw materials: 50 parts of terpolymer polypropylene, 20 parts of metallocene polypropylene, 15 parts of ethylene-vinyl acetate copolymer EVA14J2, 0.5 parts of erucamide, and 0.5 parts of talc.

[0025] Example 3 The only difference between this embodiment and embodiment 2 is that the ethylene-vinyl acetate copolymer EVA 14J2 in the corona layer and the heat-sealing layer is replaced by an equal amount of ethylene-vinyl acetate copolymer EVA EV 40W.

[0026] Example 4 The only difference between this embodiment and embodiment 2 is that the ethylene-vinyl acetate copolymer EVA 14J2 in the corona layer and the heat-sealing layer is replaced by an equal amount of ethylene-vinyl acetate copolymer EVA VS430.

[0027] Example 5 The only difference between this embodiment and embodiment 2 is that the ethylene-vinyl acetate copolymer EVA 14J2 in the corona layer and the heat-sealing layer is replaced by an equal amount of ethylene-vinyl acetate copolymer EVA VA810.

[0028] Example 6 The only difference between this embodiment and embodiment 4 is that the ethylene-vinyl acetate copolymer EVA VS430 in the corona layer is replaced by an equal amount of ethylene-vinyl acetate copolymer EVA VA810.

[0029] Example 7 The only difference between this embodiment and embodiment 4 is that the ethylene-vinyl acetate copolymer EVA VS430 in the heat-sealing layer is replaced by an equal amount of ethylene-vinyl acetate copolymer EVA VA810.

[0030] Example 8 The only difference between this embodiment and embodiment 7 is that 2 parts of polybutyl acrylate are added to the core layer raw material.

[0031] Example 9 The only difference between this embodiment and embodiment 7 is that 15 parts of polybutyl acrylate are added to the core layer raw material.

[0032] Example 10 The only difference between this embodiment and embodiment 7 is that 8 parts of polybutyl acrylate are added to the core layer raw material.

[0033] Embodiment 11 The only difference between this embodiment and embodiment 7 is that 12 parts of polybutyl acrylate are added to the core layer raw material.

[0034] Comparative Example 1 The only difference between this comparative example and Example 1 is that ethylene-vinyl acetate copolymer EVA14J2 is not added to the corona layer.

[0035] Comparative Example 2 The only difference between this comparative example and Example 1 is that ethylene-vinyl acetate copolymer EVA14J2 is not added to the heat sealing layer.

[0036] Comparative Example 3 The only difference between this comparative example and Example 1 is that ethylene-vinyl acetate copolymer EVA 14J2 is not added to the corona layer and the heat-sealing layer.

[0037] Experimental Example 1 The CPP cast films prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were tested for longitudinal tensile strength according to the method in GB / T 27740-2011 "Cast Polypropylene (CPP) Film", and the longitudinal tensile strength was tested after being placed at -40°C for 24 hours. The test results are shown in Table 1.

[0038] Table 1 CPP cast film tensile strength test

[0039] As can be seen from Table 1, the change in longitudinal tensile strength of the CPP cast film prepared in Examples 1 to 5 after being placed at -40°C for 24 hours is lower than that in Comparative Examples 1 to 3, indicating that the addition of ethylene-vinyl acetate copolymer to the corona layer and the heat sealing layer can improve the low temperature resistance of the CPP cast film; by comparing Examples 2 to 5, it is found that when the content of vinyl acetate in the ethylene-vinyl acetate copolymer is 19wt%~33wt%, the low temperature resistance of the CPP cast film can be further improved.

[0040] Experimental Example 2 The CPP cast films prepared in Examples 4 to 11 were tested for impact damage quality according to the method in GB / T 9639.1-2008 "Test method for impact resistance of plastic film and sheeting - Free-fall dart method - Part 1: Step method", with a sample thickness of 70 μm. The test results are shown in Table 2.

[0041] Table 2 CPP cast film impact resistance test results

[0042] As shown in Table 2, the impact damage quality of the CPP cast film prepared in Example 7 is higher than that of Examples 4 to 6, indicating that when the vinyl acetate content of the ethylene-vinyl acetate copolymer in the corona layer is 19wt% and the vinyl acetate content of the ethylene-vinyl acetate copolymer in the heat sealing layer is 33wt%, the impact resistance of the CPP cast film can be improved; By comparing Examples 8 to 11, it is found that the impact damage quality of the CPP cast film prepared in Examples 10 to 11 is higher than that in Examples 8 to 9, indicating that adding 8 to 12 parts of polybutyl acrylate to the core layer can further improve the impact resistance of the CPP cast film.

[0043] Experimental Example 3 The CPP cast film prepared in Example 1 was tested for water vapor permeability, initial heat sealing temperature, and wetting tension according to the method in GB / T 27740-2011 "Cast Polypropylene (CPP) Film". The test results are shown in Table 3.

[0044] Table 3 Water vapor permeability, initial heat sealing temperature and wetting tension test results of CPP cast film

[0045] As can be seen from Table 3, the water vapor permeability, initial heat sealing temperature and wetting tension of the CPP cast film prepared in the present invention meet the use requirements and meet the strict requirements of the high-end packaging market for film quality.

[0046] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A CPP cast film, characterized in that: The invention comprises a corona layer, a core layer and a heat-sealing layer in order from top to bottom, wherein the corona layer comprises the following raw materials in parts by weight: 50-70 parts of copolymerized polypropylene, 10-15 parts of a first ethylene-vinyl acetate copolymer and 0.1-0.3 parts of an anti-blocking agent; The core layer comprises the following raw materials in parts by weight: 60-80 parts of homopolypropylene and 0.1-0.3 parts of lubricant; The heat-sealing layer comprises the following raw materials in parts by weight: 40-50 parts of copolymerized polypropylene, 15-20 parts of metallocene polypropylene, 10-15 parts of a second ethylene-vinyl acetate copolymer, 0.1-0.5 parts of a lubricant, and 0.2-0.5 parts of an anti-blocking agent.

2. A CPP cast film according to claim 1, characterized in that: The vinyl acetate content of the first ethylene-vinyl acetate copolymer and the second ethylene-vinyl acetate copolymer is independently 19 wt % to 33 wt %.

3. A CPP cast film according to claim 2, characterized in that: The vinyl acetate content of the first ethylene-vinyl acetate copolymer is 19 wt %; and the vinyl acetate content of the second ethylene-vinyl acetate copolymer is 33 wt %.

4. A CPP cast film according to claim 1, characterized in that: The core layer also includes 8 to 12 parts of polybutyl acrylate.

5. A CPP cast film according to claim 1, characterized in that: The copolymerized polypropylene is one or both of binary copolymerized polypropylene and ternary copolymerized polypropylene.

6. A CPP cast film according to claim 1, characterized in that: The homopolymer polypropylene has a melt index of 25-35 g / 10 min at 230° C. and 2.16 kg.

7. A CPP cast film according to claim 1, characterized in that: The mass ratio of the corona layer, the core layer and the heat sealing layer is 1:3:2-3.

8. A CPP cast film according to claim 1, characterized in that: The lubricant includes one or both of oleamide and erucamide.

9. A CPP cast film according to claim 1, characterized in that: The anti-adhesion agent includes one or more of diatomaceous earth, talc, and calcium carbonate.

10. The method for preparing a CPP cast film according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1, the raw materials of the corona layer, the core layer and the heat sealing layer are subjected to three-layer melt co-extrusion, casting and cooling to obtain a cast film semi-finished product; S2, subjecting the corona layer of the semi-finished cast film to corona treatment to obtain a CPP cast film.

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