A cpp cast film and a method of making the same

Abstract

This invention relates to the field of polymer materials technology, and proposes a CPP cast film and its preparation method. The CPP cast film, from top to bottom, comprises a corona layer, a core layer, and a heat-sealing layer. The corona layer comprises the following raw materials in parts by weight: 50-70 parts copolymer polypropylene, 10-15 parts of a first ethylene-vinyl acetate copolymer, and 0.1-0.3 parts anti-blocking agent. The core layer comprises the following raw materials in parts by weight: 60-80 parts homopolymer polypropylene and 0.1-0.3 parts slip agent. The heat-sealing layer comprises the following raw materials in parts by weight: 40-50 parts copolymer polypropylene, 15-20 parts metallocene polypropylene, 10-15 parts of a second ethylene-vinyl acetate copolymer, 0.1-0.5 parts slip agent, and 0.2-0.5 parts anti-blocking agent. This technical solution solves the problem of poor low-temperature resistance of CPP cast films in related technologies.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a CPP cast film and its preparation method. Background Technology

[0002] With the rapid development of the packaging industry, the demand for high-performance packaging materials is increasing. Among many packaging materials, plastic film has become one of the most widely used due to its good flexibility, barrier properties, and processing performance. In the field of plastic film, polypropylene (CPP) cast film has gradually gained an important position due to its unique performance advantages. Early packaging films were mostly traditional blown films, but blown films have limitations in terms of flatness, thickness uniformity, and optical properties. As the market's requirements for packaging film quality continue to increase, cast film technology has emerged. Cast films have uniform thickness, high flatness, and good transparency, meeting the stringent quality requirements of the high-end packaging market. However, polypropylene's low-temperature resistance is not ideal. In cold winters, packaging films made of polypropylene may become brittle and crack during handling or storage due to low temperatures, failing to effectively protect the contents. 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] This invention proposes a CPP cast film and its preparation method, which solves the problem of poor low-temperature resistance of CPP cast films in related technologies.

[0004] The technical solution of the present invention is as follows:

[0005] This invention proposes a CPP cast film, which comprises, from top to bottom, a corona layer, a core layer, and a heat-sealing layer. The corona layer comprises the following raw materials in parts by weight: 50-70 parts of copolymer polypropylene, 10-15 parts of first ethylene-vinyl acetate copolymer, and 0.1-0.3 parts of anti-blocking agent.

[0006] The core layer comprises the following raw materials in parts by weight: 60-80 parts homopolymer polypropylene and 0.1-0.3 parts slip agent;

[0007] The heat-sealing layer comprises the following raw materials in parts by weight: 40-50 parts of copolymer polypropylene, 15-20 parts of metallocene polypropylene, 10-15 parts of second ethylene-vinyl acetate copolymer, 0.1-0.5 parts of slip agent, and 0.2-0.5 parts of anti-blocking agent.

[0008] 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 19wt%~33wt%.

[0009] In this invention, by limiting the vinyl acetate content of the first ethylene-vinyl acetate copolymer and the second ethylene-vinyl acetate copolymer to 19wt%~33wt% independently, the low-temperature resistance of the CPP cast film is further improved.

[0010] As a further technical solution, the vinyl acetate content of the first ethylene-vinyl acetate copolymer is 19wt%; the vinyl acetate content of the second ethylene-vinyl acetate copolymer is 33wt%.

[0011] In this invention, by limiting the vinyl acetate content of the first ethylene-vinyl acetate copolymer to 19 wt% and the vinyl acetate content of the second ethylene-vinyl acetate copolymer to 33 wt%, the impact resistance of the CPP cast film is improved.

[0012] As a further technical solution, the core layer also includes 8-12 parts of polybutyl acrylate.

[0013] In this invention, by adding polybutyl acrylate to the core layer, the adhesion between the core layer, the corona layer, and the heat-sealing layer can be enhanced, thereby improving the impact resistance of the CPP cast film.

[0014] As a further technical solution, the copolymerized polypropylene is one or both of binary copolymerized polypropylene and ternary copolymerized polypropylene.

[0015] In this invention, copolymer polypropylene is used as the substrate in the heat-sealing layer and the corona layer because it has good heat-sealing performance, toughness and impact strength, thereby improving the heat-sealing strength and toughness of the CPP cast film.

[0016] As a further technical solution, the homopolymer polypropylene has a melt index of 25~35g / 10min at 230℃ and 2.16kg.

[0017] As a further technical solution, the mass ratio of the corona layer, core layer, and heat-sealing layer is 1:3:2~3.

[0018] As a further technical solution, the slip agent includes one or both of oleamide and erucamide.

[0019] In this invention, the addition of a slip agent can improve the friction between the CPP cast film and the equipment, thereby improving processing performance and surface gloss.

[0020] As a further technical solution, the anti-adhesion agent includes one or more of diatomaceous earth, talc, and calcium carbonate.

[0021] In this invention, by adding an anti-blocking agent, a tiny rough surface can be formed on the surface of the CPP cast film to prevent the films from sticking together.

[0022] This invention also proposes a method for preparing CPP cast film, comprising the following steps:

[0023] S1. The raw materials of the corona layer, core layer and heat-sealing layer are melted, co-extruded, cast and cooled to obtain a cast film semi-finished product;

[0024] S2. The corona layer of the cast film semi-finished product is subjected to corona treatment to obtain CPP cast film.

[0025] The working principle and beneficial effects of this invention are as follows:

[0026] In this invention, the CPP cast film consists of a corona layer, a core layer, and a heat-sealing layer. The corona layer and heat-sealing layer use copolymer polypropylene as the substrate, combined with ethylene-vinyl acetate copolymer, which improves the flexibility and low-temperature resistance of the corona layer and heat-sealing layer. The heat-sealing layer also incorporates metallocene polypropylene, which, due to its narrow molecular weight distribution and excellent processing performance, promotes compatibility with other components and enhances the overall performance of the heat-sealing layer. The core layer uses homopolymer polypropylene as the substrate, providing a certain supporting strength for the CPP cast film. The addition of a slip agent reduces frictional resistance between films, preventing film rupture due to stress concentration at low temperatures and improving the low-temperature stability of the CPP cast film. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] In the following embodiments and comparative examples:

[0029] Homopolymer polypropylene PP 519A, melt index at 230℃ and 2.16kg: 35g / 10min; homopolymer polypropylene PP5780P, melt index at 230℃ 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 14wt%; ethylene-vinyl acetate copolymer EVA VS430, vinyl acetate content 19wt%; ethylene-vinyl acetate copolymer EVA VA810, vinyl acetate content 33wt%; ethylene-vinyl acetate copolymer EVA EV 40W, vinyl acetate content 41wt%.

[0030] Example 1

[0031] A method for preparing a CPP cast film includes the following steps:

[0032] S1. The raw materials for the corona layer, core layer and heat-sealing layer are added to the extruder in a mass ratio of 1:3:2. The three layers are then melt-extruded, cast and cooled to obtain a cast film semi-finished product.

[0033] S2. The corona layer of the cast film semi-finished product is subjected to corona treatment to obtain CPP cast film;

[0034] 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;

[0035] Core layer raw materials: 60 parts homopolymer polypropylene PP 519A, 0.1 parts oleamide;

[0036] 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 oleamide, and 0.2 parts of diatomaceous earth.

[0037] Example 2

[0038] A method for preparing a CPP cast film includes the following steps:

[0039] S1. The raw materials of the corona layer, core layer and heat-sealing layer are added to the extruder in a mass ratio of 1:3:3. The three layers are melt-extruded, cast and cooled to obtain a cast film semi-finished product.

[0040] S2. The corona layer of the cast film semi-finished product is subjected to corona treatment to obtain CPP cast film;

[0041] Corona layer raw materials: 70 parts of ternary copolymer polypropylene, 15 parts of ethylene-vinyl acetate copolymer EVA 14J2, and 0.3 parts of talc;

[0042] Core layer raw materials: 80 parts of homopolymer polypropylene PP 519A, 0.3 parts of erucamide;

[0043] Heat-sealing layer raw materials: 50 parts of ternary copolymer 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.

[0044] Example 3

[0045] The only difference between this embodiment and Embodiment 2 is that the ethylene-vinyl acetate copolymer EVA 14J2 in both the corona layer and the heat-sealing layer is replaced with an equal amount of ethylene-vinyl acetate copolymer EVA EV 40W.

[0046] Example 4

[0047] The only difference between this embodiment and Embodiment 2 is that the ethylene-vinyl acetate copolymer EVA 14J2 in both the corona layer and the heat-sealing layer is replaced with an equal amount of ethylene-vinyl acetate copolymer EVA VS430.

[0048] Example 5

[0049] The only difference between this embodiment and Embodiment 2 is that the ethylene-vinyl acetate copolymer EVA 14J2 in both the corona layer and the heat-sealing layer is replaced with an equal amount of ethylene-vinyl acetate copolymer EVA VA810.

[0050] Example 6

[0051] The only difference between this embodiment and Embodiment 4 is that the ethylene-vinyl acetate copolymer EVAVS430 in the corona layer is replaced with an equal amount of ethylene-vinyl acetate copolymer EVAVA810.

[0052] Example 7

[0053] The only difference between this embodiment and Embodiment 4 is that the ethylene-vinyl acetate copolymer EVAVS430 in the heat-sealing layer is replaced with an equal amount of ethylene-vinyl acetate copolymer EVAVA810.

[0054] Example 8

[0055] The only difference between this embodiment and Example 7 is that 2 parts of polybutyl acrylate are added to the core layer raw material.

[0056] Example 9

[0057] The only difference between this embodiment and Example 7 is that 15 parts of polybutyl acrylate are added to the core layer raw material.

[0058] Example 10

[0059] The only difference between this embodiment and Example 7 is that 8 parts of polybutyl acrylate are added to the core layer raw material.

[0060] Example 11

[0061] The only difference between this embodiment and Example 7 is that 12 parts of polybutyl acrylate are added to the core layer raw material.

[0062] Comparative Example 1

[0063] The only difference between this comparative example and Example 1 is that the ethylene-vinyl acetate copolymer EVA14J2 is not added to the corona layer.

[0064] Comparative Example 2

[0065] The only difference between this comparative example and Example 1 is that the ethylene-vinyl acetate copolymer EVA14J2 is not added to the heat-sealing layer.

[0066] Comparative Example 3

[0067] The only difference between this comparative example and Example 1 is that ethylene-vinyl acetate copolymer EVA 14J2 is not added to either the corona layer or the heat-sealing layer.

[0068] Experimental Example 1

[0069] The CPP cast films prepared in Examples 1-5 and Comparative Examples 1-3 were tested for longitudinal tensile strength according to the method in GB / T 27740-2011 "Cast Polypropylene (CPP) Films", and the longitudinal tensile strength after being placed at -40℃ for 24 hours was also tested. The test results are shown in Table 1.

[0070] Table 1 Tensile strength test of CPP cast film

[0071]

[0072] As shown in Table 1, the longitudinal tensile strength of the CPP cast films prepared in Examples 1-5 after being placed at -40℃ for 24 hours changed less than that in Comparative Examples 1-3, indicating that adding ethylene-vinyl acetate copolymer to the corona layer and heat-sealing layer can improve the low-temperature resistance of the CPP cast film. Comparing Examples 2-5, it was found that when the vinyl acetate content in the ethylene-vinyl acetate copolymer is 19wt%~33wt%, the low-temperature resistance of the CPP cast film can be further improved.

[0073] Experiment Example 2

[0074] The CPP cast films prepared in Examples 4-11 were tested for impact fracture mass according to the method in GB / T 9639.1-2008 "Test methods for impact resistance of plastic films and sheets - free-falling dart method - Part 1: step method". The sample thickness was 70 μm. The test results are shown in Table 2.

[0075] Table 2 Impact Resistance Test Results of CPP Cast Film

[0076]

[0077] As shown in Table 2, the impact breakage quality of the CPP cast film prepared in Example 7 is higher than that in Examples 4-6, 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.

[0078] Comparing Examples 8-11, it was found that the impact breakage quality of the CPP cast film prepared in Examples 10-11 was higher than that in Examples 8-9, indicating that adding 8-12 parts of polybutyl acrylate to the core layer can further improve the impact resistance of the CPP cast film.

[0079] Experimental Example 3

[0080] The CPP cast film prepared in Example 1 was tested for water vapor transmission rate, 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.

[0081] Table 3. Test results of water vapor transmission rate, initial heat sealing temperature and wetting tension of CPP cast film

[0082]

[0083] As shown in Table 3, the CPP cast film prepared by this invention has the required water vapor transmission rate, initial heat sealing temperature, and wetting tension, which meet the stringent requirements of the high-end packaging market for film quality.

[0084] The above are merely 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 within the protection scope of the present invention.

Claims

1. A CPP cast film, characterized in that, From top to bottom, it includes a corona layer, a core layer, and a heat-sealing layer. The corona layer comprises the following raw materials in parts by weight: 50-70 parts of copolymer polypropylene, 10-15 parts of first ethylene-vinyl acetate copolymer, and 0.1-0.3 parts of anti-blocking agent. The core layer comprises the following raw materials in parts by weight: 60-80 parts of homopolymer polypropylene, 0.1-0.3 parts of slip agent, and 8-12 parts of polybutylene acrylate; The heat-sealing layer comprises the following raw materials in parts by weight: 40-50 parts of copolymer polypropylene, 15-20 parts of metallocene polypropylene, 10-15 parts of second ethylene-vinyl acetate copolymer, 0.1-0.5 parts of slip agent, and 0.2-0.5 parts of anti-blocking agent. The first ethylene-vinyl acetate copolymer has a vinyl acetate content of 19 wt%; the second ethylene-vinyl acetate copolymer has a vinyl acetate content of 33 wt%.

2. The 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.

3. The 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℃ and 2.16 kg.

4. The CPP cast film according to claim 1, characterized in that, The mass ratio of the corona layer, core layer, and heat seal layer is 1:3:2~3.

5. A CPP cast film according to claim 1, characterized in that, The slip agent includes one or both of oleamide and erucamide.

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

7. A method for preparing a CPP cast film according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. The raw materials of the corona layer, core layer and heat-sealing layer are melted, co-extruded, cast and cooled to obtain a cast film semi-finished product; S2. The corona layer of the cast film semi-finished product is subjected to corona treatment to obtain CPP cast film.

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