Low-crystal-point polyethylene composite protective film and preparation method thereof

Abstract

The invention discloses a low-crystal-point polyethylene composite protective film which is a co-extruded film and comprises an outer layer, a middle layer and an inner layer which are sequentially laminated from outside to inside and have the layer thickness ratio of (18-22): (42-50): (32-38), the main raw materials of the outer layer comprise first low-density polyethylene and a fluorine-containing auxiliary agent in a mass ratio of 100: (1-3); the middle layer comprises the following main raw materials: second low-density polyethylene, metallocene linear low-density polyethylene and a fluorine-containing auxiliary agent in a mass ratio of 100: (20-30): (1-3); the main raw materials of the inner layer comprise third low-density polyethylene and a fluorine-containing auxiliary agent in a mass ratio of 100: (1-3); and the fluorine-containing polymer content of the fluorine-containing auxiliary agent is 3%-5%. By controlling the melt index, the density and the thickness ratio of the three layers of polyethylene raw materials of the outer layer, the middle layer and the inner layer to be matched with corresponding processes and combining the optimization of the raw materials of each layer, the mechanical property and the optical property of the protective film are improved, and the generation of crystal points is controlled.

Description

Technical Field

[0001] The invention relates to the technical field of protective films, and in particular to a low-crystal-point polyethylene composite protective film and a preparation method thereof. Background Art

[0002] As a surface protective film, polyethylene protective film can protect products from damage during transportation and processing. When the protective film is retained on the surface of the product, it is not only required to have few crystal points to meet the optical performance, to ensure that the product's appearance quality or optical performance test is not affected; but also to have good mechanical properties, such as anti-punching, tensile strength, etc.

[0003] Therefore, it is necessary to improve the polyethylene protective film in the prior art. Summary of the invention

[0004] One of the purposes of the present invention is to overcome the defects existing in the prior art and provide a low crystal point polyethylene composite protective film. Under the condition of no nitrogen protection, the melt index, density and layer thickness ratio of the outer layer, middle layer and inner layer polyethylene raw materials are controlled to match with the corresponding process, combined with the optimization of the raw materials of each layer, so as to improve the mechanical properties, optical properties and control the generation of crystal points of the protective film.

[0005] In order to achieve the above process effect, the technical solution of the present invention is: a low crystal point polyethylene composite protective film, which is a co-extruded film, including an outer layer, a middle layer and an inner layer stacked in sequence from the outside to the inside;

[0006] The main raw materials of the outer layer include a first low-density polyethylene and a fluorine-containing auxiliary agent in a mass ratio of 100:(1-3);

[0007] The main raw materials of the middle layer include a second low-density polyethylene, a metallocene linear low-density polyethylene and a fluorine-containing additive in a mass ratio of 100: (20-30): (1-3);

[0008] The main raw materials of the inner layer include a third low-density polyethylene and a fluorine-containing additive in a mass ratio of 100:(1-3);

[0009] The first low-density polyethylene and the second low-density polyethylene have a melt index of 1.7 to 2.2 g / 10 min and a density of 0.920 to 0.926 g / cm 3 ;

[0010] The third low-density polyethylene has a melt index of 2.2 to 2.6 g / 10 min and a density of 0.920 to 0.925 g / cm 3 ;

[0011] The metallocene linear low-density polyethylene has a melt index of 1.87 to 1.92 g / 10 min and a density of 0.920 to 0.925 g / cm 3 ;

[0012] The fluorine-containing polymer content of the fluorine-containing auxiliary agent is 3% to 5%;

[0013] The thickness ratio of the outer layer, the middle layer and the inner layer is (18-22): (42-50): (32-38).

[0014] The preferred technical solution is that the main raw material of the fluorine-containing additive is linear low-density polyethylene, the melt index of the fluorine-containing additive is 1.5-4g / 10min, and the density is 0.924-0.928g / cm 3 .

[0015] The second purpose of the present invention is to overcome the defects existing in the prior art and provide a method for preparing a low-crystal-point polyethylene composite protective film, comprising the following steps: the raw materials of the outer layer, the middle layer and the inner layer are respectively penetrated into the outer layer extruder, the middle layer extruder and the inner layer extruder for melting and plasticization, the obtained sol is filtered and transported to the die head, the film is extruded and blown to form film bubbles and blown out from the die mouth, the blown film bubbles are cooled by the automatic air ring at the die mouth to obtain the above-mentioned low-crystal-point polyethylene composite protective film, and the wind temperature of the automatic air ring cooling is 8°C to 12°C.

[0016] The preferred technical solution is that the outer layer extruder, the middle layer extruder and the inner layer extruder are all provided with five heating zones, which are recorded as zones 1 to 5 in the order of feeding, and the die head is provided with four heating zones, which are recorded as zones 1 to 4 in the order of feeding;

[0017] The temperature of the outer layer extruder in zone 1 is 135°C to 145°C, the temperature of zone 2 is 150°C to 160°C, the temperature of zone 3 is 150°C to 160°C, the temperature of zone 4 is 145°C to 155°C, and the temperature of zone 5 is 145°C to 155°C;

[0018] The temperature of the first zone of the middle layer extruder is 135°C to 145°C, the temperature of the second zone is 150°C to 160°C, the temperature of the third zone is 150°C to 160°C, the temperature of the fourth zone is 145°C to 155°C, and the temperature of the fifth zone is 145°C to 155°C;

[0019] The temperature of the first zone of the inner layer extruder is 135°C to 145°C, the temperature of the second zone is 150°C to 160°C, the temperature of the third zone is 150°C to 160°C, the temperature of the fourth zone is 145°C to 155°C, and the temperature of the fifth zone is 145°C to 155°C;

[0020] The temperature of the first zone of the die head is 145°C to 155°C, the temperature of the second zone is 145°C to 155°C, the temperature of the third zone is 145°C to 155°C, and the temperature of the fourth zone is 155°C to 165°C.

[0021] The preferred technical solution is that the outer layer extruder, the middle layer extruder and the inner layer extruder are all provided with a sol filter mesh, and the filter mesh is arranged between the first zone and the second zone, the second zone and the third zone, the third zone and the fourth zone, the fourth zone and the fifth zone, and the fifth zone and the die head of each layer of the extruder, and the holes per inch of the filter mesh are set to 200 mesh, 300 mesh, 400 mesh, 500 mesh, and 300 mesh in sequence according to the feeding order.

[0022] A preferred technical solution is that the extrusion pressures of the outer layer extruder, the middle layer extruder and the inner layer extruder are 30 to 45 MPa.

[0023] A preferred technical solution is that the blowing ratio of the film bubble is 1.1 to 1.3.

[0024] The advantages and beneficial effects of the present invention are:

[0025] The low-crystal-point polyethylene composite protective film optimizes the mechanical properties and optical properties of the protective film and controls the generation of crystal points by controlling the melt index, density and thickness ratio of the polyethylene raw materials of the outer layer, middle layer and inner layer, and then matching them with the corresponding processes; the generation of crystal points is further reduced by combining the metallocene linear low-density polyethylene contained in the middle layer raw material and the fluorine-containing processing aids in each layer. DETAILED DESCRIPTION

[0026] The specific implementation of the present invention is further described below in conjunction with the examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, and cannot be used to limit the protection scope of the present invention.

[0027] model

[0028] The first low-density polyethylene is Huizhou Zhonghai Shell 2420H;

[0029] The second low-density polyethylene is Huizhou Zhonghai Shell 2420H;

[0030] The third low-density polyethylene is Qatar Petrochemical FD0274;

[0031] The metallocene linear low-density polyethylene is Japan Prime sp2320;

[0032] The fluorine-containing additive was from Jiaxing Jinjiacai Plastic Co., Ltd. and the brand name was M8001.

[0033] Outer Layer

[0034] Using LDPE raw materials without opening agents can reduce the number of crystal points; the molecular structure of LDPE contains more long-chain branches, which lead to irregular arrangement between polymer chains, thereby reducing the formation of crystal areas and increasing the proportion of amorphous areas, making the LDPE film have better transparency; good tensile strength; the obtained outer layer is easy to corona to improve adhesion.

[0035] Middle level

[0036] The addition of metallocene linear low-density polyethylene (mLLDPE) further increases the strength of the base film while improving the elongation of the base film, so that it maintains a certain deformation rate during the stamping process and is not easy to damage the base film and the sheet. mLLDPE has a highly regular molecular structure and a low degree of branching, which may lead to the formation of smaller and more uniform crystals in the blend, thereby reducing visible crystal points. The addition of mLLDPE can improve the crystallization behavior of LDPE, reduce crystal points, and enhance the optical transparency of the film. The low viscosity of mLLDPE may make the blend easier to process, increase the extrusion speed and film quality. Too little mLLDPE addition will result in poor stamping strength and easy fragmentation of the protective film; too much addition will cause stamping film peeling, and the stamping strength will increase and it will not be easy to break, but the cost is high.

[0037] Inner Layer

[0038] The use of LDPE containing an opening agent in the inner layer is beneficial to the smoothness of the base film preparation and rolling. Bubbles are easily discharged to make the surface of the base film roll smoothly, reduce the friction coefficient of the protective film surface, and it is not easy to break the protective film and damage the sheet when the protective film is deformed during the stamping process.

[0039] Example 1

[0040] The low crystal point polyethylene composite protective film is a co-extruded film with a total film thickness of 45 μm. It includes an outer layer, a middle layer and an inner layer stacked in sequence from the outside to the inside, with the outer layer having a thickness of 9 μm, the middle layer having a thickness of 20.25 μm and the inner layer having a thickness of 13.75 μm.

[0041] The raw material components of each layer are as follows:

[0042] The outer layer is made of LDPE CNOOC Shell 2420H and fluorinated additive M8001 in a mass ratio of 100:2;

[0043] The raw materials of the middle layer are LDPE CNOOC Shell 2420H, mLLDPE Japan Prime sp2320 and fluorine-containing additive M8001 in a mass ratio of 100:25:2;

[0044] The raw materials of the inner layer are LDPE Qatar Petrochemical FD0274 and fluorine-containing additive M8001 in a mass ratio of 100:2.

[0045] The preparation method of the low crystal point polyethylene composite protective film comprises the following steps:

[0046] The raw materials of the outer layer, middle layer and inner layer are respectively passed through the outer layer extruder, the middle layer extruder and the inner layer extruder for melting and plasticization. The obtained sol is filtered and then transported to the die head, extruded and blown to form film bubbles to be blown out of the die mouth. The blown film bubbles are cooled by the automatic air ring at the die mouth to obtain the above-mentioned low crystal point polyethylene composite protective film. The wind temperature of the automatic air ring cooling is 10°C. There is no need to produce in a nitrogen environment.

[0047] The outer layer extruder, the middle layer extruder and the inner layer extruder are all provided with five heating zones, which are recorded as zones 1 to 5 in the order of feeding, and the die head is provided with four heating zones, which are recorded as zones 1 to 4 in the order of feeding;

[0048] The temperature of the outer layer extruder zone 1 is 140°C, the temperature of zone 2 is 155°C, the temperature of zone 3 is 155°C, the temperature of zone 4 is 150°C, and the temperature of zone 5 is 150°C;

[0049] The temperature of the middle layer extruder zone 1 is 140°C, the temperature of zone 2 is 155°C, the temperature of zone 3 is 155°C, the temperature of zone 4 is 150°C, and the temperature of zone 5 is 150°C;

[0050] The temperature of the inner layer extruder zone 1 is 140°C, the temperature of zone 2 is 155°C, the temperature of zone 3 is 155°C, the temperature of zone 4 is 150°C, and the temperature of zone 5 is 150°C;

[0051] The temperature of the first zone of the die is 150°C, the temperature of the second zone is 150°C, the temperature of the third zone is 150°C, and the temperature of the fourth zone is 160°C.

[0052] The outer layer extruder, the middle layer extruder and the inner layer extruder are all provided with sol filter meshes, which are arranged between the first and second zones, the second and third zones, the third and fourth zones, the fourth and fifth zones, and the fifth zone and the die head of each layer of the extruder, and the holes per inch of the filter meshes are set to 200 meshes, 300 meshes, 400 meshes, 500 meshes, and 300 meshes in sequence according to the feeding order.

[0053] Example 2

[0054] Example 2 is based on Example 1, except that the raw materials of the middle layer are LDPE CNOOC Shell 2420H, mLLDPE Japan Prime sp2320 and fluorine-containing additive M8001 in a mass ratio of 100:20:2. The preparation method of the low crystal point polyethylene composite protective film remains unchanged.

[0055] Example 3

[0056] Example 3 is based on Example 1, except that the raw materials of the middle layer are LDPE CNOOC Shell 2420H, mLLDPE Japan Prime sp2320 and fluorine-containing additive M8001 in a mass ratio of 100:30:2. The preparation method of the low crystal point polyethylene composite protective film remains unchanged.

[0057] Example 4

[0058] Example 4 is based on Example 1, except that the thickness ratio of the outer layer, the middle layer and the inner layer is 30:35:35. The preparation method of the low crystal point polyethylene composite protective film remains unchanged.

[0059] Example 5

[0060] Example 5 is based on Example 1, except that the temperature of zone 1 of the die is 160°C, the temperature of zone 2 is 160°C, the temperature of zone 3 is 160°C, and the temperature of zone 4 is 170°C.

[0061] Example 6

[0062] Example 6 is based on Example 1, with the difference that the outer layer extruder, the middle layer extruder and the inner layer extruder are all provided with sol filter meshes, and the filter meshes are arranged between the first and second zones, the second and third zones, the third and fourth zones, the fourth and fifth zones, and the fifth zone and the die head of each layer of the extruder, and the number of holes per inch of the filter meshes is set to 200 mesh, 300 mesh, 400 mesh, 300 mesh, and 200 mesh in sequence according to the feeding order.

[0063] Example 7

[0064] Example 7 is based on Example 1, except that the outer layer extruder, the middle layer extruder and the inner layer extruder are all provided with sol filter meshes, and the filter meshes are arranged between the first and second zones, the second and third zones, the third and fourth zones, the fourth and fifth zones, and the fifth zone and the die head of each layer of the extruder, and the number of holes per inch of the filter meshes is set to 200 mesh, 300 mesh, 300 mesh, 300 mesh, and 200 mesh according to the feeding order.

[0065] Comparative Example 1

[0066] Comparative Example 1 is based on Example 1, except that the raw material of the outer layer is only LDPE CNOOC Shell 2420H, the raw material of the inner layer is only LDPE Qatar Petrochemical FD0274, and no fluorine-containing additive is added to the outer layer and the inner layer. The raw material composition of the middle layer remains unchanged. The preparation method of the low crystal point polyethylene composite protective film remains unchanged.

[0067] Comparative Example 2

[0068] Comparative Example 2 is based on Example 1, except that the raw materials of the outer layer are LDPE CNOOC Shell 2420H, mLLDPE Japan Prime sp2320 and fluorine-containing additive M8001 in a mass ratio of 100:25:2;

[0069] The raw materials of the middle layer are LDPE CNOOC Shell 2420H and fluorinated additive M8001 in a mass ratio of 100:2;

[0070] The raw materials of the inner layer are LDPE Qatar Petrochemical FD0274 and fluorine-containing additive M8001 in a mass ratio of 100:2.

[0071] The thickness ratio of the outer layer, the middle layer and the inner layer remains unchanged; the processing conditions remain unchanged.

[0072] Comparative Example 3

[0073] Comparative Example 3 is based on Example 1, except that the raw materials of the outer layer are LDPE CNOOC Shell 2420H and mLLDPE Japan Prime sp2320 in a mass ratio of 100:25;

[0074] The raw materials of the middle layer are LDPE CNOOC Shell 2420H and mLLDPE Japan Prime sp2320 in a mass ratio of 100:25;

[0075] The raw materials of the inner layer are LDPE Qatar Petrochemical FD0274 and mLLDPE Japan Prime sp2320 in a mass ratio of 100:25.

[0076] The thickness ratio of the outer layer, the middle layer and the inner layer remains unchanged; the processing conditions remain unchanged.

[0077] Performance Testing

[0078] 1. Determination of tensile strength and elongation at break: according to the test standard GB / T1040.3-2006;

[0079] 2. Transmittance and haze determination: according to the test standard GB / T2410-2008;

[0080] 3. Crystal point test: Cut a 20m long film sample from the prepared protective film, and then cut a 1m×1m sample every 5m, take three pieces in total, observe with the naked eye first, circle the crystal points with a ballpoint pen if there are any, and measure the number of crystal points with a 10x magnifying glass.

[0081] The performance test results of the embodiments and comparative examples are as follows:

[0082]

[0083] Compared with Example 1, the low content of metallocene linear low-density polyethylene, the main raw material of the middle layer, in Example 2 and Example 3 has a negative impact on the mechanical properties; although the mechanical properties are improved when the content is high, the cost is also increased.

[0084] In Example 4, compared with Example 1, the reduction in the thickness of the middle layer has a negative impact on the mechanical properties of the protective film.

[0085] Compared with Example 1, the die head temperature in each zone of Example 5 is too high, which can easily lead to the breakage of the polyethylene molecular chain or the generation of cross-linking, and has a negative impact on the mechanical properties of the protective film; it causes overheating in some areas, and the polymer in this area quickly cools and crystallizes to form more crystal points, and the growth rate of the crystal nucleus is accelerated, and it is also easy to form larger crystal points.

[0086] Compared with Example 1, the two filters with different hole settings in Example 6 and Example 7 did not completely filter large impurities, and the control of the crystal points of the protective film fluctuated. The hole setting of the filter needs to ensure that the raw materials are continuously output under a stable pressure state, thereby controlling the amount and generation of crystal points. If the pressure of the raw materials passing through the filters with different hole settings deviates or fluctuates too much, it is easy to cause more crystal points.

[0087] Compared with Example 1, in Comparative Example 1, the main raw materials of the outer layer and the inner layer do not include fluorine-containing processing aids, which easily leads to crystal points in the protective film.

[0088] Compared with Example 1, the middle layer of Comparative Example 2 does not contain metallocene linear low-density polyethylene, which has a negative impact on the mechanical properties of the protective film.

[0089] Compared with Example 1, the outer layer, middle layer and inner layer of Comparative Example 3 all contain metallocene linear low-density polyethylene, which improves the mechanical and optical properties of the protective film, but increases the cost. Since it does not contain fluorine-containing processing aids, the protective film is prone to produce crystal points.

[0090] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A low crystal point polyethylene composite protective film, which is a co-extruded film, characterized in that: From the outside to the inside, it includes an outer layer, a middle layer and an inner layer stacked in sequence; The main raw materials of the outer layer include a first low-density polyethylene and a fluorine-containing additive in a mass ratio of 100:(1-3); The main raw materials of the middle layer include a second low-density polyethylene, a metallocene linear low-density polyethylene and a fluorine-containing additive in a mass ratio of 100: (20-30): (1-3); The main raw materials of the inner layer include a third low-density polyethylene and a fluorine-containing additive in a mass ratio of 100: (1-3); The first low-density polyethylene and the second low-density polyethylene have a melt index of 1.7-2.2 g / 10 min and a density of 0.920-0.926 g / cm 3 ; The third low-density polyethylene has a melt index of 2.2-2.6 g / 10 min and a density of 0.920-0.925 g / cm 3 ; The metallocene linear low-density polyethylene has a melt index of 1.87-1.92 g / 10 min and a density of 0.920-0.925 g / cm 3 ; The fluorine-containing polymer content of the fluorine-containing additive is 3% to 5%; The thickness ratio of the outer layer, the middle layer and the inner layer is (18-22): (42-50): (32-38).

2. The low crystal point polyethylene composite protective film according to claim 1, characterized in that: The main raw material of the fluorine-containing additive is linear low-density polyethylene. The melt index of the fluorine-containing additive is 1.5-4 g / 10 min, and the density is 0.924-0.928 g / cm 3 .

3. A method for preparing a low crystal point polyethylene composite protective film, characterized in that: The method comprises the following steps: respectively passing the raw materials of the outer layer, the middle layer and the inner layer into the outer layer extruder, the middle layer extruder and the inner layer extruder for melting and plasticizing, filtering the obtained sol and conveying it to the die head, extruding and blowing the film to form film bubbles and blowing them out from the die mouth, cooling the blown film bubbles through the automatic air ring at the die mouth, and obtaining the low crystal point polyethylene composite protective film according to claims 1-2, wherein the wind temperature of the automatic air ring cooling is 8°C-12°C.

4. The method for preparing the low crystal point polyethylene composite protective film according to claim 3, characterized in that: The outer layer extruder, the middle layer extruder and the inner layer extruder are all provided with five heating zones, which are recorded as zones 1 to 5 in the order of feeding, and the die head is provided with four heating zones, which are recorded as zones 1 to 4 in the order of feeding; The temperature of the outer layer extruder in zone 1 is 135°C to 145°C, the temperature of zone 2 is 150°C to 160°C, the temperature of zone 3 is 150°C to 160°C, the temperature of zone 4 is 145°C to 155°C, and the temperature of zone 5 is 145°C to 155°C; The temperature of the first zone of the middle layer extruder is 135°C to 145°C, the temperature of the second zone is 150°C to 160°C, the temperature of the third zone is 150°C to 160°C, the temperature of the fourth zone is 145°C to 155°C, and the temperature of the fifth zone is 145°C to 155°C; The temperature of the first zone of the inner layer extruder is 135°C to 145°C, the temperature of the second zone is 150°C to 160°C, the temperature of the third zone is 150°C to 160°C, the temperature of the fourth zone is 145°C to 155°C, and the temperature of the fifth zone is 145°C to 155°C; The temperature of zone one of the die head is 145°C to 155°C, the temperature of zone two is 145°C to 155°C, the temperature of zone three is 145°C to 155°C, and the temperature of zone four is 155°C to 165°C.

5. The method for preparing the low crystal point polyethylene composite protective film according to claim 3 or 4, characterized in that: The outer layer extruder, the middle layer extruder and the inner layer extruder are all provided with sol filter meshes, and the filter meshes are arranged between the first zone and the second zone, the second zone and the third zone, the third zone and the fourth zone, the fourth zone and the fifth zone, and the fifth zone and the die head of each layer of the extruder, and the holes per inch of the filter meshes are set to 200 meshes, 300 meshes, 400 meshes, 500 meshes, and 300 meshes in sequence according to the feeding order.

6. The method for preparing the low crystal point polyethylene composite protective film according to claim 5, characterized in that: The extrusion pressures of the outer layer extruder, the middle layer extruder and the inner layer extruder are 30-45 MPa.

7. The method for preparing the low crystal point polyethylene composite protective film according to claim 3, characterized in that: The blowing ratio of the film bubble is 1.1-1.3.

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