Hot-bending stamping protective film as well as preparation method and application thereof

Abstract

The invention relates to the technical field of protective films, and provides a hot-bending stamping protective film as well as a preparation method and application thereof. The preparation raw materials of the outer layer of the hot-bending stamping protective film comprise metallocene low-density polyethylene and a polyolefin plastomer, the preparation raw materials of the middle layer comprise first polypropylene and low-density polyethylene, and the preparation raw materials of the inner layer comprise second polypropylene and third polypropylene. The preparation raw materials and the ratio of the outer layer, the middle layer and the inner layer of the hot-bending stamping protective film are strictly controlled, so that the high-temperature resistance of the hot-bending stamping protective film can be improved, and the viscosity stability and the mechanical strength are improved. When the protective film is applied to the PET hot bending punch forming process, the phenomena of difficult film tearing, high-temperature melting and the like are avoided, and the protective film is not broken by punching.

Description

Technical Field

[0001] The present invention relates to the technical field of protective films, and in particular to a hot-bending stamping protective film and a preparation method and application thereof. Background Art

[0002] Polyethylene terephthalate (PET) has good chemical stability and is widely used in packaging, electronic appliances and household products industries.

[0003] The hot bending and stamping process of PET is to heat the PET substrate and then stamp it into shape to prepare a product with a certain curvature. For example, in the current preparation process of electronic equipment casings, it is necessary to use the hot bending and stamping process to form a 2D sheet into a 3D sheet with a curved surface effect to meet different design and functional requirements; in addition, the preparation of food or medicine packaging boxes, various lamps and lampshades also involve the hot bending and stamping process of PET.

[0004] In order to avoid damage to the PET sheet during hot bending and stamping, it is generally necessary to cover the sheet with a protective film before forming. However, hot bending and stamping need to be carried out under high temperature conditions. The viscosity of the existing protective film increases under high temperature conditions, making it difficult to tear the film. Some will even melt at high temperatures and stick to the surface of the product. Summary of the invention

[0005] In view of this, the present invention provides a heat bending and stamping protective film and a preparation method and application thereof. The heat bending and stamping protective film provided by the present invention has good high temperature resistance, stable viscosity, high strength and elongation at break, and is not broken by stamping.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A hot bending and stamping protective film comprises an outer layer, a middle layer and an inner layer; the outer layer is prepared from raw materials comprising, by weight: 40 to 80 parts of metallocene low-density polyethylene and 20 to 60 parts of polyolefin plastomer;

[0008] In terms of weight, the raw materials for preparing the middle layer include: 30 to 90 parts of first polypropylene and 10 to 60 parts of low-density polyethylene;

[0009] In parts by weight, the raw materials for preparing the inner layer include: 30 to 80 parts of the second polypropylene and 20 to 50 parts of the third polypropylene;

[0010] The first polypropylene and the second polypropylene have a melt index of 1 to 3 g / 10 min and a density of 0.89 to 0.91 g / cm 3 The third polypropylene has a melt index of 0.5 to 1 g / 10 min and a density of 0.89 to 0.91 g / cm 3.

[0011] Preferably, the metallocene low-density polyethylene has a melt index of 2 to 4 g / 10 min and a density of 0.915 to 0.920 g / cm 3 The melt index of the polyolefin plastomer is 3 to 4 g / 10 min and the density is 0.870 to 0.900 g / cm 3 .

[0012] Preferably, the low-density polyethylene has a melt index of 1.5 to 3.0 g / 10 min and a density of 0.920 to 0.930 g / cm 3 .

[0013] Preferably, the grade of the metallocene low-density polyethylene is 3518CB; the grade of the polyolefin plastomer is KC8852G;

[0014] The grades of the first polypropylene and the second polypropylene are RB707CF; the grade of the low-density polyethylene is 450E; and the grade of the third polypropylene is HJ340F.

[0015] Preferably, taking the total mass of the outer layer, the middle layer and the inner layer as 100%, the mass fraction of the outer layer is 10-30%, the mass fraction of the middle layer is 40-80%, and the mass fraction of the inner layer is 10-50%.

[0016] The present invention also provides a method for preparing the hot bending stamping protective film described in the above scheme, comprising the following steps:

[0017] The raw materials for the outer layer, the middle layer and the inner layer are co-extruded to obtain the hot bending and stamping protective film.

[0018] Preferably, the three-layer co-extrusion comprises: feeding the raw materials for the outer layer, the middle layer and the inner layer into the outer layer, the middle layer and the inner layer extruders respectively for melting and plasticizing, conveying the obtained glue solution to the die head, extruding and blowing the film to obtain a film bubble, and after the film bubble is air-cooled, passing through a stabilizing ring and a herringbone arrangement to be pulled upward for rotation, and after the film bubble is flattened, it is inspected, trimmed, destaticized and rolled to obtain the hot bending and stamping protective film.

[0019] Preferably, the outer layer extruder, the middle layer extruder and the inner layer extruder are all provided with 5 heating zones, which are recorded as zones 1 to 5 in the order in which the raw materials pass; the temperature of zone 1 of the outer layer extruder is 170-180°C, the temperature of zone 2 is 185-195°C, the temperature of zone 3 is 185-195°C, the temperature of zone 4 is 185-195°C, and the temperature of zone 5 is 185-195°C; the temperature of zone 1 of the middle layer extruder is The temperature of zone 1 of the inner layer extruder is 190-200°C, the temperature of zone 2 is 200-220°C, the temperature of zone 3 is 200-220°C, the temperature of zone 4 is 200-220°C, and the temperature of zone 5 is 200-220°C; the temperature of zone 1 of the inner layer extruder is 190-200°C, the temperature of zone 2 is 200-220°C, the temperature of zone 3 is 200-220°C, the temperature of zone 4 is 200-220°C, and the temperature of zone 5 is 200-220°C;

[0020] The die head is provided with 4 heating zones, which are respectively recorded as zones 1 to 4 according to the order in which the raw materials pass through; the temperature of zone 1 of the die head is 190-210°C, the temperature of zone 2 is 200-220°C, the temperature of zone 3 is 200-220°C, and the temperature of zone 4 is 200-220°C.

[0021] Preferably, the extrusion pressure of the outer layer extruder is 250-600 bar, the extrusion pressure of the middle layer extruder is 250-600 bar, and the extrusion pressure of the inner layer extruder is 250-600 bar.

[0022] The present invention also provides the use of the hot bending stamping protective film described in the above scheme or the hot bending stamping protective film prepared by the preparation method described in the above scheme in PET hot bending stamping molding.

[0023] The present invention provides a hot bending stamping protective film, comprising an outer layer, a middle layer and an inner layer; in parts by weight, the raw materials for preparing the outer layer include: 40 to 80 parts of metallocene low-density polyethylene and 20 to 60 parts of polyolefin plastomer; in parts by weight, the raw materials for preparing the middle layer include: 30 to 90 parts of first polypropylene and 10 to 60 parts of low-density polyethylene; in parts by weight, the raw materials for preparing the inner layer include: 30 to 80 parts of second polypropylene and 20 to 50 parts of third polypropylene; the melt index of the first polypropylene and the second polypropylene is 1 to 3 g / 10 min, and the density is 0.89 to 0.91 g / cm 3 The third polypropylene has a melt index of 0.5 to 1 g / 10 min and a density of 0.89 to 0.91 g / cm 3. The present invention strictly controls the raw materials and proportions of the outer layer, middle layer and inner layer of the hot bending and stamping protective film, wherein the outer layer can provide stable adhesion, the middle layer provides higher strength and elongation at break, and the inner layer provides better temperature resistance, thereby obtaining a hot bending and stamping protective film that is resistant to high temperatures, has good viscosity stability, high strength and high elongation at break. When the protective film of the present invention is applied to the PET hot bending and stamping forming process, there will be no difficulty in tearing the film, melting at high temperatures, etc., and it will not break when stamped. DETAILED DESCRIPTION

[0024] The present invention provides a hot bending stamping protective film, comprising an outer layer, a middle layer and an inner layer; in terms of weight, the raw materials for preparing the outer layer include: 40 to 80 parts of metallocene low-density polyethylene and 20 to 60 parts of polyolefin plastomer;

[0025] In terms of weight, the raw materials for preparing the middle layer include: 30 to 90 parts of first polypropylene and 10 to 60 parts of low-density polyethylene;

[0026] In parts by weight, the raw materials for preparing the inner layer include: 30 to 80 parts of the second polypropylene and 20 to 50 parts of the third polypropylene;

[0027] The first polypropylene and the second polypropylene have a melt index of 1 to 3 g / 10 min and a density of 0.89 to 0.91 g / cm 3 The third polypropylene has a melt index of 0.5 to 1 g / 10 min and a density of 0.89 to 0.91 g / cm 3 .

[0028] In parts by weight, the raw materials for preparing the outer layer include 40 to 80 parts of metallocene low-density polyethylene, specifically 50 parts, 60 parts or 70 parts; the melt index of the metallocene low-density polyethylene is preferably 2 to 4 g / 10 min, more preferably 3 to 3.5 g / 10 min, and the density is preferably 0.915 to 0.920 g / cm 3 , more preferably 0.916 to 0.918 g / cm 3 In a specific embodiment of the present invention, the metallocene low-density polyethylene is 3518CB, manufactured by Exxon, with a melt index of 3.5 g / 10 min and a density of 0.918 g / cm 3 The metallocene low-density polyethylene used in the present invention is a metallocene ethylene-ethane copolymer, which has excellent tensile properties, impact resistance and puncture resistance.

[0029] Based on the weight percentage of the metallocene low-density polyethylene used in the outer layer, the raw material for preparing the outer layer includes 20 to 60 parts of polyolefin plastomer (POP), specifically 30 parts, 40 parts or 50 parts; the melt index of the polyolefin plastomer is preferably 3 to 4 g / 10 min, more preferably 3.5 to 3.8 g / 10 min, and the density is preferably 0.870 to 0.900 g / cm 3 , more preferably 0.875 to 0.880 g / cm 3 In a specific embodiment of the present invention, the POP is KC8852G, manufactured by Dow Chemical, has a melt index of 3.5 g / 10 min, and a density of 0.875 g / cm 3 The POP used in the present invention has high self-adhesiveness and excellent toughness.

[0030] In parts by weight, the raw material for preparing the middle layer includes 30 to 90 parts of the first polypropylene, specifically 40 parts, 50 parts, 60 parts, 70 parts, 80 parts or 90 parts; the melt index of the first polypropylene is 1 to 3 g / 10min, preferably 1.5 to 2 g / 10min, and the density is 0.89 to 0.91 g / cm 3 , preferably 0.9 to 0.905 g / cm 3 In a specific embodiment of the present invention, the first polypropylene is RB707CF, produced by Borouge Chemical, with a melt index of 1.5g / 10min and a density of 0.9g / cm 3 The first polypropylene used in the present invention has good processability.

[0031] Based on the weight percentage of the first polypropylene used in the middle layer, the raw material for preparing the middle layer includes 10 to 60 parts of low-density polyethylene, specifically 10 parts, 30 parts, 40 parts or 50 parts; the melt index of the low-density polyethylene is preferably 1.5 to 3.0 g / 10min, more preferably 2 to 2.5 g / 10min, and the density is preferably 0.920 to 0.930 g / cm 3 , more preferably 0.923 to 0.925 g / cm 3 In a specific embodiment of the present invention, the grade of the low-density polyethylene is 450E, the manufacturer is Dow Chemical, the melt index is 2g / 10min, and the density is preferably 0.923g / cm 3 The low-density polyethylene used in the present invention has the characteristics of low crystal point and easy processing.

[0032] In parts by weight, the raw material for preparing the inner layer includes 30 to 80 parts of the second polypropylene, specifically 40 parts, 50 parts, 60 parts, 70 parts or 80 parts. In the present invention, the melt index of the second polypropylene is 1 to 3 g / 10min, preferably 1.5 to 2 g / 10min, and the density is 0.89 to 0.91 g / cm 3 , preferably 0.9 to 0.905 g / cm 3 In a specific embodiment of the present invention, the second polypropylene is RB707CF, produced by Borouge Chemical, has a melt index of 1.5g / 10min, and a density of 0.9g / cm 3 The second polypropylene used in the present invention has good processability.

[0033] Based on the weight of the second polypropylene used in the inner layer, the raw material for preparing the inner layer includes 20 to 50 parts of the third polypropylene, specifically 30 or 40 parts. In the present invention, the melt index of the third polypropylene is 0.5 to 1 g / 10 min, preferably 0.7 to 0.9 g / 10 min, and the density is 0.89 to 0.91 g / cm 3 , preferably 0.9 to 0.905 g / cm 3 In a specific embodiment of the present invention, the third polypropylene is of grade HJ340F, manufactured by Exxon, with a melt index of 0.9 g / 10 min and a density of 0.9 g / cm 3 The third polypropylene used in the present invention is a specially designed polypropylene block copolymer having very high impact strength and excellent optical properties.

[0034] In the present invention, taking the total mass of the outer layer, the middle layer and the inner layer as 100%, the mass fraction of the outer layer is preferably 10-30%, more preferably 20%, the mass fraction of the middle layer is 40-80%, more preferably 60%, and the mass fraction of the inner layer is 10-50%, more preferably 20%.

[0035] In the present invention, the longitudinal tensile strength of the hot-bending stamping protective film is 36-50 MPa, the transverse tensile strength is 28-30 MPa, the longitudinal elongation at break is 440-580%, the transverse elongation at break is 710-720%, the viscosity at room temperature is 0.075-0.088N, and the viscosity at 120°C is 0.096-0.11N.

[0036] The present invention also provides a method for preparing the hot bending stamping protective film described in the above scheme, comprising the following steps:

[0037] The raw materials for the outer layer, the middle layer and the inner layer are co-extruded to obtain the hot bending and stamping protective film.

[0038] In the present invention, the three-layer co-extrusion preferably includes: feeding the raw materials for the outer layer, the middle layer and the inner layer into the outer layer, the middle layer and the inner layer extruders respectively for melting and plasticization, conveying the obtained glue solution to the die head, extruding and blowing the film to obtain a film bubble, and after the film bubble is air-cooled, passing through a stabilizing ring and a herringbone arrangement to be pulled upward for rotation, and after the film bubble is flattened, it is inspected, trimmed, destaticized and rolled to obtain the hot bending and stamping protective film.

[0039] In the present invention, the outer layer extruder, the middle layer extruder and the inner layer extruder are preferably provided with 5 heating zones, which are sequentially recorded as zones 1 to 5 according to the order in which the raw materials pass; the temperature of zone 1 of the outer layer extruder is preferably 170 to 180°C, more preferably 175°C, the temperature of zone 2 is preferably 185 to 195°C, more preferably 190°C, the temperature of zone 3 is preferably 185 to 195°C, more preferably 190°C, the temperature of zone 4 is preferably 185 to 195°C, more preferably 190°C, and the temperature of zone 5 is preferably 185 to 195°C, more preferably 190°C; the temperature of zone 1 of the middle layer extruder is preferably 180 to 190°C, more preferably 185°C, and the temperature of zone 2 is preferably 185 to 195°C, more preferably 190°C. The temperature of zone 1 of the inner layer extruder is preferably 190-200°C, more preferably 195°C, the temperature of zone 2 is preferably 200-220°C, more preferably 210°C, the temperature of zone 3 is preferably 200-220°C, more preferably 210°C, the temperature of zone 4 is preferably 200-220°C, more preferably 210°C, and the temperature of zone 5 is preferably 200-220°C, more preferably 210°C.

[0040] In the present invention, the die head is preferably provided with 4 heating zones, which are sequentially recorded as zones 1 to 4 according to the order in which the raw materials pass; the temperature of zone 1 of the die head is preferably 190-210°C, more preferably 200°C, the temperature of zone 2 is preferably 200-220°C, more preferably 210°C, the temperature of zone 3 is preferably 200-220°C, more preferably 210°C, and the temperature of zone 4 is preferably 200-220°C, more preferably 210°C.

[0041] In the present invention, the extrusion pressure of the outer layer extruder is preferably 250-600 bar, more preferably 300-355 bar, the extrusion pressure of the middle layer extruder is preferably 250-600 bar, more preferably 300-330 bar, and the extrusion pressure of the inner layer extruder is preferably 250-600 bar, more preferably 400-425 bar.

[0042] In the present invention, the detection is preferably performed by a crystal point defect detector to detect the appearance and crystal points of the film; after the detection is completed, the edges are trimmed, and then the single sheets are separated by the lower traction roller and enter the static electricity removal device for static electricity removal, and then rolled up by the front and rear winding devices to obtain the hot bending stamping protective film of the present invention.

[0043] The present invention also provides the use of the hot bending stamping protective film described in the above scheme or the hot bending stamping protective film prepared by the preparation method described in the above scheme in PET hot bending stamping molding.

[0044] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions 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.

[0045] Example 1

[0046] A hot bending stamping protective film is made of a three-layer co-extruded blown film of an outer layer, a middle layer and an inner layer. The weight percentages of the raw materials of the outer layer, the middle layer and the inner layer are respectively: 20% for the outer layer, 60% for the middle layer and 20% for the inner layer. The amount of raw materials used for each layer is shown in Table 1.

[0047] Table 1 Amount of raw materials used in each layer of the hot bending stamping protective film in Example 1

[0048]

[0049] The preparation method is as follows: the raw materials of the outer layer, the middle layer and the inner layer are mixed in proportion by an automatic batching system, and then sent to the outer layer, the middle layer and the inner layer extruders; the raw materials of the outer layer, the middle layer and the inner layer are melted and plasticized and then sent to the die head for extrusion and film blowing; and then cooled by air cooling, and the film is flattened by the upper traction rotation through a stabilizing ring and a herringbone arrangement; and the film cooled by the guide roller enters the crystal point defect detector to detect the appearance and crystal points of the film, and then the trimming is separated into single sheets by the lower traction roller and enters the static elimination device and the front and rear winding devices for winding, so as to obtain a hot bending stamping protective film with a thickness of 35 μm; the extrusion pressure and the temperature of each zone of the outer layer, the middle layer and the inner layer extruders are shown in Table 2.

[0050] Table 2 Extrusion pressure and temperature of each zone of the outer layer, middle layer and inner layer extruder

[0051] temperature Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Pressure(bar) Outer Layer 180 190 190 190 190 355 Middle level 190 200 200 200 200 330 Inner Layer 200 210 210 210 210 425 Die head 200 210 210 210 / /

[0052] Example 2

[0053] A hot bending stamping protective film is made of a three-layer co-extruded blown film of an outer layer, a middle layer and an inner layer. The weight percentages of the raw materials of the outer layer, the middle layer and the inner layer are respectively: 20% for the outer layer, 60% for the middle layer and 20% for the inner layer. The amount of raw materials used for each layer is shown in Table 3. The thickness of the protective film is 35 μm.

[0054] Table 3 Amount of raw materials used in each layer of the hot bending stamping protective film in Example 2

[0055]

[0056] The preparation method is the same as that in Example 1.

[0057] Example 3

[0058] A hot bending stamping protective film is made of a three-layer co-extruded blown film of an outer layer, a middle layer and an inner layer. The weight percentages of the raw materials of the outer layer, the middle layer and the inner layer are respectively: 20% for the outer layer, 60% for the middle layer and 20% for the inner layer. The amount of raw materials used for each layer is shown in Table 4. The thickness of the protective film is 35 μm.

[0059] Table 4 Amount of raw materials used in each layer of the hot bending stamping protective film in Example 3

[0060]

[0061] The preparation method is the same as that in Example 1.

[0062] Comparative Example 1

[0063] A hot bending stamping protective film is made of a three-layer co-extruded blown film of an outer layer, a middle layer and an inner layer. The weight percentages of the raw materials of the outer layer, the middle layer and the inner layer are respectively: 20% for the outer layer, 60% for the middle layer and 20% for the inner layer. The amount of raw materials used for each layer is shown in Table 5. The thickness of the protective film is 35 μm.

[0064] Table 5 The amount of raw materials used in each layer of the hot bending stamping protective film in comparative example 1

[0065]

[0066]

[0067] The preparation method is the same as that in Example 1.

[0068] Comparative Example 2

[0069] A hot bending stamping protective film is made of a three-layer co-extruded blown film of an outer layer, a middle layer and an inner layer. The weight percentages of the raw materials of the outer layer, the middle layer and the inner layer are respectively: 20% for the outer layer, 60% for the middle layer and 20% for the inner layer. The amount of raw materials used for each layer is shown in Table 6. The thickness of the protective film is 35 μm.

[0070] Table 6 Amount of raw materials used in each layer of the hot bending stamping protective film in comparative example 2

[0071]

[0072] The preparation method is the same as that in Example 1.

[0073] Performance Testing:

[0074] The tensile strength, elongation at break, viscosity at room temperature and viscosity at 120°C of the protective films prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were tested. The test methods and test results are shown in Table 7, wherein the temperature resistance was tested by a hot stamping experiment. The temperature of the hot stamping test was 500°C and the hot stamping time was 3s. If it does not melt during the hot stamping process, it is heat-resistant, otherwise it is not heat-resistant.

[0075] Table 7 Performance test results

[0076]

[0077] According to the data in Table 1, it can be seen that the hot bending stamping protective film prepared by the present invention has high tensile strength and elongation at break, and the higher elongation at break makes it difficult to be broken during the stamping process; and the viscosity of the hot bending stamping protective film prepared by the present invention at high temperature does not change much compared with the viscosity at room temperature, indicating that it has good viscosity stability, will not melt during the hot stamping process, has good temperature resistance, and is suitable for the hot bending stamping molding process of PET; the protective films prepared in Comparative Examples 1 and 2 are not temperature resistant, will melt during the hot bending stamping process, especially Comparative Example 2 has severe viscosity increase at high temperature and poor mechanical properties.

[0078] 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 principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A hot-bending stamping protective film, characterized in that: It comprises an outer layer, a middle layer and an inner layer; the raw materials for preparing the outer layer comprise, by weight: 40 to 80 parts of metallocene low-density polyethylene and 20 to 60 parts of polyolefin plastomer; In terms of weight, the raw materials for preparing the middle layer include: 30 to 90 parts of first polypropylene and 10 to 60 parts of low-density polyethylene; In parts by weight, the raw materials for preparing the inner layer include: 30 to 80 parts of the second polypropylene and 20 to 50 parts of the third polypropylene; The first polypropylene and the second polypropylene have a melt index of 1 to 3 g / 10 min and a density of 0.89 to 0.91 g / cm 3 The third polypropylene has a melt index of 0.5 to 1 g / 10 min and a density of 0.89 to 0.91 g / cm 3 .

2. The heat-bending stamping protective film according to claim 1, characterized in that: The metallocene low-density polyethylene has a melt index of 2 to 4 g / 10 min and a density of 0.915 to 0.920 g / cm 3 The melt index of the polyolefin plastomer is 3 to 4 g / 10 min and the density is 0.870 to 0.900 g / cm 3 .

3. The heat-bending stamping protective film according to claim 1, characterized in that: The low-density polyethylene has a melt index of 1.5 to 3.0 g / 10 min and a density of 0.920 to 0.930 g / cm 3 .

4. The heat-bending stamping protective film according to claim 1, characterized in that: The grade of the metallocene low-density polyethylene is 3518CB; the grade of the polyolefin plastomer is KC8852G; The grades of the first polypropylene and the second polypropylene are RB707CF; the grade of the low-density polyethylene is 450E; and the grade of the third polypropylene is HJ340F.

5. The heat-bending stamping protective film according to claim 1, characterized in that: Taking the total mass of the outer layer, the middle layer and the inner layer as 100%, the mass fraction of the outer layer is 10-30%, the mass fraction of the middle layer is 40-80%, and the mass fraction of the inner layer is 10-50%.

6. The method for preparing the hot bending stamping protective film according to any one of claims 1 to 5, characterized in that: The following steps are involved: The raw materials for the outer layer, the middle layer and the inner layer are co-extruded to obtain the hot bending and stamping protective film.

7. The preparation method according to claim 6, characterized in that: The three-layer co-extrusion comprises: feeding the raw materials for the outer layer, the middle layer and the inner layer into the outer layer, the middle layer and the inner layer extruders respectively for melting and plasticizing, conveying the obtained glue liquid to the die head, extruding and blowing the film to obtain a film bubble, cooling the film bubble with air, passing through a stabilizing ring and a herringbone arrangement to be pulled up for rotation, flattening the film bubble, and then conducting inspection, trimming, removing static electricity and winding to obtain the hot bending and stamping protective film.

8. The preparation method according to claim 6, characterized in that: The outer layer extruder, the middle layer extruder and the inner layer extruder are all provided with 5 heating zones, which are respectively recorded as zones 1 to 5 according to the order in which the raw materials pass through; the temperature of zone 1 of the outer layer extruder is 170-180°C, the temperature of zone 2 is 185-195°C, the temperature of zone 3 is 185-195°C, the temperature of zone 4 is 185-195°C, and the temperature of zone 5 is 185-195°C; the temperature of zone 1 of the middle layer extruder is 18 0~190℃, the temperature of zone 2 is 190~210℃, the temperature of zone 3 is 190~210℃, the temperature of zone 4 is 190~210℃, and the temperature of zone 5 is 190~210℃; the temperature of zone 1 of the inner layer extruder is 190~200℃, the temperature of zone 2 is 200~220℃, the temperature of zone 3 is 200~220℃, the temperature of zone 4 is 200~220℃, and the temperature of zone 5 is 200~220℃; The die head is provided with 4 heating zones, which are respectively recorded as zones 1 to 4 according to the order in which the raw materials pass through; the temperature of zone 1 of the die head is 190-210°C, the temperature of zone 2 is 200-220°C, the temperature of zone 3 is 200-220°C, and the temperature of zone 4 is 200-220°C.

9. The preparation method according to claim 8, characterized in that: The extrusion pressure of the outer layer extruder is 250-600 bar, the extrusion pressure of the middle layer extruder is 250-600 bar, and the extrusion pressure of the inner layer extruder is 250-600 bar.

10. Use of the hot bending and stamping protective film according to any one of claims 1 to 5 or the hot bending and stamping protective film prepared by the preparation method according to any one of claims 6 to 9 in PET hot bending and stamping molding.

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