阅读说明：本技术 一种超高温蒸煮食品包装薄膜及其制备方法 (Ultrahigh-temperature steamed food packaging film and preparation method thereof ) 是由 苏壮 盛金华 于 2019-09-26 设计创作，主要内容包括：本发明提供一种超高温蒸煮食品包装薄膜及其制备方法,包括由不同物理性能的聚丙烯和含辛烯共聚单体金属线性聚乙烯塑胶原料颗粒共混、并采用三层共挤吹膜机上吹风冷法吹制成膜形成三层共挤层,三层共挤层由内层基膜、中层基膜、外层基膜组成,内层基膜为热封层,外层基膜为电晕处理层或复合层；制备时,首先,通过三层共挤吹膜机对各层料筒温度、风冷温度、吹胀比和冷凝线参数进行设置,然后采用三层共挤上吹法制备内层基膜、中层基膜和外层基膜,得到多层结构复合且综合性能优异的食品包装薄膜,有效的达到超高温蒸煮级别,在超高温蒸煮条件下,包装的食品能耐135℃蒸煮1小时和145℃可蒸煮10分钟,可应用于各种肉类、禽类的135℃/60min和145℃/10min蒸煮。(The invention provides an ultrahigh-temperature steamed food packaging film and a preparation method thereof, wherein the ultrahigh-temperature steamed food packaging film comprises three co-extruded layers formed by blending polypropylene and metal linear polyethylene plastic raw material particles containing octene comonomer with different physical properties and blowing the mixture into a film by adopting an upper blowing cold method of a three-layer co-extrusion film blowing machine, wherein the three co-extruded layers comprise an inner-layer base film, a middle-layer base film and an outer-layer base film, the inner-layer base film is a heat-sealing layer, and the outer-layer base film is a corona treatment layer or a composite; when the film is prepared, firstly, the temperature, the air cooling temperature, the blowing ratio and the condensation line parameters of each charging barrel are set through a three-layer co-extrusion film blowing machine, then the inner-layer base film, the middle-layer base film and the outer-layer base film are prepared through a three-layer co-extrusion up-blowing method, the food packaging film with a composite multilayer structure and excellent comprehensive performance is obtained, the ultra-high temperature cooking level is effectively achieved, the packaged food can be cooked for 1 hour at 135 ℃ and cooked for 10 minutes at 145 ℃ under the ultra-high temperature cooking condition, and the film can be applied to 135 ℃/60min and 145 ℃/10min cooking of various meats and poultry.)

1. The ultrahigh-temperature steamed food packaging film is characterized by comprising three co-extrusion layers, wherein each co-extrusion layer consists of an inner-layer base film, a middle-layer base film and an outer-layer base film, the inner-layer base film is a heat-sealing layer, and the outer-layer base film is a corona treatment layer or a composite layer;

the inner base film, the middle base film and the outer base film of the three co-extrusion layers respectively comprise the following components in percentage by mass:

the inner base film accounts for 30% of the total thickness, and the inner base film comprises the following components in percentage by mass:

block copolymerized polypropylene: the content of the active ingredients is 98 percent,

metallocene linear polyethylene containing octene comonomer: 2 percent;

the middle base film accounts for 40% of the total thickness, and the middle base film comprises the following components in percentage by mass:

random copolymerized polypropylene: the content of the active ingredients is 98 percent,

metallocene linear polyethylene containing octene comonomer: 2 percent;

the outer base film accounts for 30% of the total thickness, and the outer base film comprises the following components in percentage by mass:

block copolymerized polypropylene: the content of the active ingredients is 98 percent,

metallocene linear polyethylene containing octene comonomer: 2 percent.

2. The ultrahigh-temperature retort food packaging film according to claim 1, wherein the three co-extruded layers are formed by blending polypropylene and metal linear polyethylene plastic raw material granules containing octene comonomer with different physical properties and blowing the blended materials into a film by a three-layer co-extrusion film blowing machine.

3. The ultrahigh temperature retort food packaging film according to claim 1 or 2, wherein the three co-extruded layers are blown into a film by a three co-extrusion up-blowing method.

4. The ultrahigh-temperature steamed food packaging film according to claim 1, wherein the block copolymer polypropylene is a raw material BC918CF produced by northern Europe chemical industry, and the physical melting point of the block copolymer polypropylene is 3 g/10 min and the melting point of the block copolymer polypropylene is 166 ℃.

5. The ultrahigh-temperature steamed food packaging film according to claim 1, wherein the octene-containing comonomer metallocene linear polyethylene is MLLDPE 1327CA which is produced by Exxon chemistry and contains octene comonomer and has physical melting point of 1.3 g/10 min and melting point of 122 ℃.

6. The ultrahigh-temperature steamed food packaging film according to claim 1, wherein the random copolymer polypropylene is a raw material RB707CF produced by northern Europe chemical industry, and the physical melting point of the random copolymer polypropylene is 1.5 g/10 min and the melting point of the random copolymer polypropylene is 143-147 ℃.

7. The preparation method of the ultrahigh-temperature steamed food packaging film is characterized in that the film is prepared by adopting a three-layer co-extrusion up-blowing method, and comprises the following steps:

1) and three-layer co-extrusion film blowing machine parameter setting

a) Selecting the temperature, wherein the temperature of an inner layer screw material cylinder of the three-layer co-extrusion film blowing machine is 210-215 ℃, the temperature of a middle layer screw material cylinder is 195-200 ℃, the temperature of an outer layer screw material cylinder is 210-215 ℃, and the temperature of a die head runner is 210 ℃;

b) selecting air cooling temperature, wherein the air cooling temperature is 5-13 ℃;

c) selecting a blow-up ratio, and selecting a proportion range of the blow-up ratio: 1: 1.5-1: 1.3;

d) selecting a condensation line, wherein the condensation line is selected within the range of 300mm to 350 mm;

2) preparing the inner layer film

Uniformly mixing raw material particles of block copolymerization polypropylene and metallocene linear polyethylene containing an octene comonomer according to a preparation ratio of 49: 1, adding the mixture into an inner layer hopper of a three-layer co-extrusion film blowing machine, setting the temperature of a screw barrel corresponding to the inner layer hopper to be 210-215 ℃, and extruding the mixture into an inner layer base film of the three-layer co-extrusion layer through a screw;

3) preparing the middle layer film

Uniformly mixing raw material particles of random copolymerization polypropylene and metallocene linear polyethylene containing an octene comonomer according to a preparation ratio of 49: 1, adding the raw material particles into a middle layer hopper of a three-layer co-extrusion film blowing machine, setting the temperature of a screw barrel corresponding to the middle layer hopper to be 195-200 ℃, and extruding the mixture by a screw to form a middle layer base film of the three-layer co-extrusion layer;

4) preparing an outer film

Uniformly mixing raw material particles of block copolymerization polypropylene and metallocene linear polyethylene containing an octene comonomer according to a preparation ratio of 49: 1, adding the mixture into an outer layer hopper of a three-layer co-extrusion film blowing machine, setting the temperature of a screw barrel corresponding to the outer layer hopper to be 210-215 ℃, and extruding the mixture into an outer layer base film of the three-layer co-extrusion layer through a screw;

5) the inner base film, the middle base film and the outer base film are extruded and blown to form a finished film through the die heads of the three-layer co-extrusion film blowing machine under the action of the screw rod, and the die head temperature of the three-layer co-extrusion film blowing machine is set to be 210 ℃.

8. The method for preparing the ultrahigh-temperature steamed food packaging film according to claim 7, wherein the block copolymer polypropylene in the steps 2) and 4) is a raw material BC918CF produced by northern Europe chemical industry, and the physical melting point of the block copolymer polypropylene is 3 g/10 min and the melting point of the block copolymer polypropylene is 166 ℃.

9. The method for preparing the ultrahigh-temperature-steamed food packaging film according to claim 7, wherein the octene-containing comonomer metallocene linear polyethylene in the steps 2), 3) and 4) is MLLDPE 1327CA (MLLDPE 1327CA with octene-containing comonomer as a raw material produced by Exxon chemical technology, and the physical melting point is 1.3 g/10 min and the melting point is 122 ℃.

10. The preparation method of the ultrahigh-temperature steamed food packaging film according to claim 7, wherein in the step 3), the random copolymer polypropylene is a raw material RB707CF produced by northern Europe chemical industry, and the physical melting point of the random copolymer polypropylene is 1.5 g/10 min and the melting point of the random copolymer polypropylene is 143-147 ℃.

[ technical field ] A method for producing a semiconductor device

The invention relates to a food packaging film technology, in particular to an ultrahigh-temperature steamed food packaging film and a preparation method thereof.

[ background of the invention ]

As is well known, the common bacteria causing food spoilage are pseudomonas and vibrio, both of which are not heat resistant; intestinal bacteria die after being heated at 60 ℃ for 30 minutes, and some lactic acid bacteria can resist being heated at 65 ℃ for 30 minutes; the bacillus can generally resist the heating of 95-100 ℃ for several minutes, and a few bacillus can resist the heating of 20 minutes at 120 ℃; in addition to bacteria, a large number of fungi, including mucor, yeast, etc., are present in food products; in addition, light, oxygen, temperature, moisture, pH, etc. can cause spoilage of food, but the main factor is microorganisms. Therefore, the killing of microorganisms by high-temperature cooking is an important method for long-term preservation of food.

The existing food sterilization includes pasteurization at 72 ℃/30min, boiling sterilization at 100 ℃/30min, high-temperature cooking sterilization at 121 ℃/30min, high-temperature cooking sterilization at 135 ℃/10min and ultrahigh-temperature instant sterilization at 145 ℃/5 sec according to the temperature; however, in the prior art, the ultra-high temperature cooking film for preparing the packaging bag basically adopts polypropylene raw materials, and most of film-making processes of the polypropylene raw materials can only be limited to two processing modes of flow casting extrusion or downward blowing water cooling and air cooling, and the two extrusion modes are relatively easy to prepare when producing the high temperature cooking film, but have the defects that the prepared film can not reach the ultra-high temperature cooking level and is not suitable for the use of high temperature cooking packaging food.

[ summary of the invention ]

The invention provides the ultrahigh-temperature steamed food packaging film which reaches the ultrahigh-temperature steaming level and is suitable for being prepared by a three-layer co-extrusion upward blowing method and the preparation method thereof by selecting the polypropylene raw material and the metal linear polyethylene containing the octene comonomer.

In order to achieve the purpose, the technical scheme is as follows:

the ultrahigh-temperature steamed food packaging film comprises three co-extrusion layers, wherein each co-extrusion layer consists of an inner-layer base film, a middle-layer base film and an outer-layer base film, the inner-layer base film is a heat sealing layer, and the outer-layer base film is a corona treatment layer or a composite layer;

the inner base film, the middle base film and the outer base film of the three co-extrusion layers respectively comprise the following components in percentage by mass:

the inner base film accounts for 30% of the total thickness, and the inner base film comprises the following components in percentage by mass:

block copolymerized polypropylene: the content of the active ingredients is 98 percent,

metallocene linear polyethylene containing octene comonomer: 2 percent;

the middle base film accounts for 40% of the total thickness, and the middle base film comprises the following components in percentage by mass:

random copolymerized polypropylene: the content of the active ingredients is 98 percent,

metallocene linear polyethylene containing octene comonomer: 2 percent;

the outer base film accounts for 30% of the total thickness, and the outer base film comprises the following components in percentage by mass:

block copolymerized polypropylene: the content of the active ingredients is 98 percent,

metallocene linear polyethylene containing octene comonomer: 2 percent.

Further, the three-layer co-extrusion layer is formed by blending polypropylene with different physical properties and metal linear polyethylene plastic raw material particles containing octene comonomer and blowing the mixture by a three-layer co-extrusion film blowing machine.

Further, the three-layer co-extrusion layer is blown into a film by a three-layer co-extrusion up-blowing method.

Furthermore, the block copolymerization polypropylene is a raw material BC918CF produced by northern Europe chemical industry, and the physical melting point of the block copolymerization polypropylene is 3 g/10 min and the melting point of the block copolymerization polypropylene is 166 ℃.

Furthermore, the metallocene linear polyethylene containing the octene comonomer is MLLDPE 1327CA which is produced by Exxon chemistry and is used as a raw material and contains the octene comonomer, and the physical properties of the product are 1.3 g/10 min and the melting point of the product is 122 ℃.

Further, the random copolymerization polypropylene is a raw material RB707CF produced by northern Europe chemical industry, and the physical melting point of the random copolymerization polypropylene is 1.5 g/10 min and 143-147 ℃.

A preparation method of a superhigh temperature steamed food packaging film adopts a three-layer coextrusion up-blowing method to prepare the film, and comprises the following steps:

1) and three-layer co-extrusion film blowing machine parameter setting

a) Selecting the temperature, wherein the temperature of an inner layer screw material cylinder of the three-layer co-extrusion film blowing machine is 210-215 ℃, the temperature of a middle layer screw material cylinder is 195-200 ℃, the temperature of an outer layer screw material cylinder is 210-215 ℃, and the temperature of a die head runner is 210 ℃;

b) selecting air cooling temperature, wherein the air cooling temperature is 5-13 ℃;

c) selecting a blow-up ratio, and selecting a proportion range of the blow-up ratio: 1: 1.5-1: 1.3;

d) selecting a condensation line, wherein the condensation line is selected within the range of 300mm to 350 mm;

2) preparing the inner layer film

Uniformly mixing raw material particles of block copolymerization polypropylene and metallocene linear polyethylene containing an octene comonomer according to a preparation ratio of 49: 1, adding the mixture into an inner layer hopper of a three-layer co-extrusion film blowing machine, setting the temperature of a screw barrel corresponding to the inner layer hopper to be 210-215 ℃, and extruding the mixture into an inner layer base film of the three-layer co-extrusion layer through a screw;

3) preparing the middle layer film

Uniformly mixing raw material particles of random copolymerization polypropylene and metallocene linear polyethylene containing an octene comonomer according to a preparation ratio of 49: 1, adding the raw material particles into a middle layer hopper of a three-layer co-extrusion film blowing machine, setting the temperature of a screw barrel corresponding to the middle layer hopper to be 195-200 ℃, and extruding the mixture by a screw to form a middle layer base film of the three-layer co-extrusion layer;

4) preparing an outer film

Uniformly mixing raw material particles of block copolymerization polypropylene and metallocene linear polyethylene containing an octene comonomer according to a preparation ratio of 49: 1, adding the mixture into an outer layer hopper of a three-layer co-extrusion film blowing machine, setting the temperature of a screw barrel corresponding to the outer layer hopper to be 210-215 ℃, and extruding the mixture into an outer layer base film of the three-layer co-extrusion layer through a screw;

5) the inner base film, the middle base film and the outer base film are extruded and blown to form a finished film through the die heads of the three-layer co-extrusion film blowing machine under the action of the screw rod, and the die head temperature of the three-layer co-extrusion film blowing machine is set to be 210 ℃.

Furthermore, the block copolymerization polypropylene in the step 2) and the step 4) is a raw material BC918CF produced by northern Europe chemical industry, and the physical melting point refers to a product with the melting point of 3 g/10 min and the melting point of 166 ℃.

Further, the octene-containing comonomer metallocene linear polyethylene in the step 2), the step 3) and the step 4) is MLLDPE 1327CA which is produced by Exxon chemistry and contains octene comonomer, and the physical properties refer to 1.3 g/10 min and the melting point is 122 ℃.

Further, in the step 3), the random copolymerization polypropylene is a raw material RB707CF produced by northern Europe chemical industry, and the physical melting point of the random copolymerization polypropylene is 1.5 g/10 min and the melting point of the random copolymerization polypropylene is 143-147 ℃.

The invention has the advantages that:

the invention adopts a three-layer coextrusion upwind blowing method, aims at the phenomenon that the temperature is a key control point when polypropylene raw materials are upblown, the film bubble is unstable when the temperature is high, the temperature is not enough when the temperature is low, the temperature is calculated according to the melt index, the invention selects the appointed polypropylene raw materials and the metallocene linear polyethylene containing octene comonomer through a plurality of tests, wherein the polypropylene raw materials are block copolymerization polypropylene and random copolymerization polypropylene, the block copolymerization polypropylene selects the raw material BC918CF produced by northern Europe chemical industry, the physical property melt index refers to 3 g/10 min and the product with the melting point of 166 ℃, the random copolymerization polypropylene selects the raw material RB707CF produced by the northern Europe chemical industry, the physical property melt index refers to 1.5 g/10 min and the product with the melting point of 143-147 ℃, and the metallocene linear polyethylene containing octene comonomer selects the LDPE 1327CA produced by the Exxon chemical, the physical melting refers to a product with the melting point of 122 ℃ of 1.3 g/10 min, and the prepared film effectively reaches the ultra-high temperature cooking level and is suitable for packaging various ultra-high temperature cooked foods.

Moreover, each layer of the high-temperature cooking film prepared by the three-layer co-extrusion up-blowing cold method in the structural form is made of special raw materials, and the specific thickness proportion requirement is adopted among the layers, wherein the inner-layer base film accounts for 30% of the total thickness, the middle-layer base film accounts for 40% of the total thickness, and the outer-layer base film accounts for 30% of the total thickness; the prepared food packaging film can resist boiling at 135 ℃ for 1 hour and 145 ℃ for 10 minutes under the condition of ultrahigh-temperature boiling, and can be used for boiling various meats and poultry at 135 ℃/60min and 145 ℃/10 min.

[ detailed description ] embodiments

The present invention will be further described with reference to the following specific examples.

A food packaging film cooked at ultrahigh temperature comprises polypropylene and metal linear polyethylene plastic raw material particles containing octene comonomer which have different physical properties, are blended and blown into a film by a three-layer coextrusion up-blowing method by a three-layer coextrusion film blowing machine to form a three-layer coextrusion layer, wherein the three-layer coextrusion layer consists of an inner-layer base film, a middle-layer base film and an outer-layer base film, the inner-layer base film is a heat sealing layer, and the outer-layer base film is a corona treatment layer or a composite layer;

the inner base film, the middle base film and the outer base film of the three co-extrusion layers respectively comprise the following components in percentage by mass:

the inner base film accounts for 30% of the total thickness, and the inner base film comprises the following components in percentage by mass:

block copolymerized polypropylene: the content of the active ingredients is 98 percent,

linear metallocene octene-containing comonomer (C8): 2 percent;

the middle base film accounts for 40% of the total thickness, and the middle base film comprises the following components in percentage by mass:

random copolymerized polypropylene: the content of the active ingredients is 98 percent,

linear metallocene octene-containing comonomer (C8): 2 percent;

the outer base film accounts for 30% of the total thickness, and the outer base film comprises the following components in percentage by mass:

block copolymerized polypropylene: the content of the active ingredients is 98 percent,

linear metallocene octene-containing comonomer (C8): 2 percent.

Wherein, the block copolymerization polypropylene is a raw material BC918CF produced by northern Europe chemical industry, the physical compatibility refers to a product with the melting point of 166 ℃ of 3 g/10 min, the metallocene linear polyethylene containing octene comonomer adopts the MLLDPE 1327CA produced by Exxon chemistry as the raw material containing octene comonomer, and the physical compatibility refers to a product with the melting point of 122 ℃ of 1.3 g/10 min; the random copolymerization polypropylene is a raw material RB707CF in northern Europe chemical production, and the physical melting point of the random copolymerization polypropylene is 1.5 g/10 min and the melting point of the random copolymerization polypropylene is 143-147 ℃.

The preparation method of the ultrahigh-temperature steamed food packaging film adopts a three-layer coextrusion up-blowing method to prepare the film, and comprises the following steps:

1) and three-layer co-extrusion film blowing machine parameter setting

a) Selecting the temperature, namely selecting the temperature of an inner layer screw cylinder of a three-layer co-extrusion film blowing machine to be 210-215 ℃, the temperature of a middle layer screw cylinder to be 195-200 ℃, the temperature of an outer layer screw cylinder to be 210-215 ℃ and the temperature of a die head runner to be 210 ℃, wherein in the step, the temperature of the inner layer screw is the same as that of the outer layer screw, and the temperature of the middle layer screw is 15 ℃ lower than that of the inner layer screw and that of the outer layer screw;

b) selecting air cooling temperature, wherein the air cooling temperature is 5-13 ℃, the energy consumption is high when the air cooling temperature is lower than the lower limit temperature by 5 ℃, and the cooling effect is poor when the air cooling temperature is higher than the upper limit temperature by 13 ℃;

c) selecting a blowing-up ratio, wherein the ratio range of the blowing-up ratio is 1: 1.5-1: 1.3;

d) selecting a condensation line, wherein the condensation line is selected within the range from 300mm to 350mm, the transparency of the film is deteriorated when the condensation line is lower than the lower limit value by 300mm, the bubble is unstable when the condensation line is higher than the upper limit value by 350mm, and the range from 300mm to 350mm is selected as a result of multiple experimental verifications;

2) preparing the inner layer film

Uniformly mixing raw material particles of block copolymerization polypropylene and metallocene linear polyethylene containing an octene comonomer according to a preparation ratio of 49: 1, adding the mixture into an inner layer hopper of a three-layer co-extrusion film blowing machine, setting the temperature of a screw barrel corresponding to the inner layer hopper to be 210-215 ℃, and extruding the mixture into an inner layer base film of the three-layer co-extrusion layer through a screw;

3) preparing the middle layer film

Uniformly mixing raw material particles of random copolymerization polypropylene and metallocene linear polyethylene containing an octene comonomer according to a preparation ratio of 49: 1, adding the raw material particles into a middle layer hopper of a three-layer co-extrusion film blowing machine, setting the temperature of a screw barrel corresponding to the middle layer hopper to be 195-200 ℃, and extruding the mixture by a screw to form a middle layer base film of the three-layer co-extrusion layer;

4) preparing an outer film

Uniformly mixing raw material particles of block copolymerization polypropylene and metallocene linear polyethylene containing an octene comonomer according to a preparation ratio of 49: 1, adding the mixture into an outer layer hopper of a three-layer co-extrusion film blowing machine, setting the temperature of a screw barrel corresponding to the outer layer hopper to be 210-215 ℃, and extruding the mixture into an outer layer base film of the three-layer co-extrusion layer through a screw;

5) the inner base film, the middle base film and the outer base film are extruded and blown to form a finished film through the die heads of the three-layer co-extrusion film blowing machine under the action of the screw rod, and the die head temperature of the three-layer co-extrusion film blowing machine is set to be 210 ℃.

Wherein, the block copolymerization polypropylene in the step 2) and the step 4) is a raw material BC918CF produced by northern Europe chemical industry, and the physical melting refers to a product with the melting point of 3 g/10 min and the melting point of 166 ℃; the octene-containing comonomer (C8) metallocene linear polyethylene in the steps 2), 3) and 4) is MLLDPE 1327CA which is produced by Exxon chemistry and contains octene comonomer, and the physical compatibility is 1.3 g/10 min and is a product with the melting point of 122 ℃; and in the step 3), the random copolymerization polypropylene is a raw material RB707CF produced by northern Europe chemical industry, and the physical melting point of the random copolymerization polypropylene is 1.5 g/10 min and the melting point of the random copolymerization polypropylene is 143-147 ℃.

In the specific embodiment, the friction coefficient of the inner base film in the three co-extrusion layers is less than or equal to 0.3, the heat sealing temperature range is 180-185 ℃, and the lower limit temperature value of 180 ℃ can cause poor extrusion temperature plasticization, uneven film thickness and the like; the extrusion bubble may be unstable when the temperature is higher than the upper limit value of 185 ℃; the shrinkage rate of the middle base film in the three co-extrusion layers is less than or equal to 1-2%; the corona surface corona treatment value of the outer base film in the three co-extrusion layers is 32-38 dynes; the tensile strength of the finished film is more than or equal to 35MPa in the transverse direction, the tensile strength of the finished film is more than or equal to 30MPa in the longitudinal direction, the drop hammer impact is more than or equal to 150g, the puncture resistance is more than or equal to 2.5J, and the value less than the value of the tensile strength can cause bag breakage in the process of flat stacking, high boxing and transportation of the finished bags made of the film.

When the polypropylene raw material is prepared by a blown film up-blowing cold method, the polypropylene raw material and the metallocene linear polyethylene containing the octene comonomer (C8) are designed by proportioning and extrusion temperature, so that the compatibility between the polypropylene raw material and the metallocene linear polyethylene is effectively realized on the premise of ensuring the fluidity, and the surface of the film is smooth and has no particles which are not completely melted.

Meanwhile, the transparency of the polypropylene raw material to the film is tested to be the maximum by the up-blowing method, the water cooling of the polypropylene raw material is extremely transparent, but the air cooling of the polypropylene raw material by the up-blowing method is basically dull or matte, in the embodiment, the extrusion temperature and the raw material ratio of the polypropylene raw material and the metallocene linear polyethylene containing the octene comonomer (C8) are controlled, the condensation line height is selected to be within the range of 300mm to 350mm, and multiple times of experiments prove that the transparency of the polypropylene raw material and the metallocene linear polyethylene containing the octene comonomer (C8) during mixed extrusion is effectively ensured, wherein the transparency of the film is deteriorated when the condensation line is lower than the lower limit value by 300mm, and the bubble is unstable when the condensation line is higher than the upper limit value by 350 mm.

The polypropylene raw material is blown on the three-layer co-extrusion film blowing machine, because the tensile strength of the pure polypropylene raw material after film forming is lower, the metallocene linear polyethylene containing the octene comonomer (C8) is added in the preparation formula and is respectively mixed in the inner layer, the middle layer and the outer layer, the tensile strength of the blown film is ensured, and the ratio range of the blow-up ratio is selected to be 1: 1.5-1: 1.3 through multiple experiments according to the tensile strength of the polypropylene raw material and the metallocene linear polyethylene containing the octene comonomer (C8) after film forming by mixing in the inner layer, the middle layer and the outer layer, so that the tensile film forming of each layer is effectively ensured.

In addition, by selecting octene-containing comonomer (C8) metallocene linear polyethylene as the connecting resin and controlling the raw material proportion and the extrusion temperature, the adhesiveness of the extruded film layers of the inner layer, the middle layer and the outer layer can be effectively ensured when the polypropylene raw material is prepared by a blown film up-blowing cold method, and the interlayer delamination is avoided.

The invention adopts a three-layer coextrusion upward blowing method, aims at the condition that the temperature is a key control point when polypropylene raw materials are blown upward, the film bubble is unstable when the temperature is high, and the temperature is insufficient when the temperature is low, the temperature is not accurate at all according to the melt index, through a plurality of tests, the appointed polypropylene raw materials and metallocene linear polyethylene containing octene comonomer are selected, and the raw material proportion and the extrusion temperature of the polypropylene raw materials and the metallocene linear polyethylene containing octene comonomer (C8) are controlled, wherein the polypropylene raw materials are block copolymerization polypropylene and random copolymerization polypropylene, the temperature resistance of the inner layer, the middle layer and the outer layer after being extruded into films is effectively improved, and the prepared film effectively reaches the ultrahigh temperature cooking level and is suitable for packaging various ultrahigh temperature cooking foods.

In addition, the high-temperature cooking film prepared by the three-layer co-extrusion up-blowing cold method in the structural form is prepared by adopting special raw materials for each layer structure, and the specific thickness proportion requirement is adopted among the layers, wherein the inner-layer base film accounts for 30% of the total thickness, the middle-layer base film accounts for 40% of the total thickness, and the outer-layer base film accounts for 30% of the total thickness; the prepared food packaging film can resist boiling at 135 ℃ for 1 hour and 145 ℃ for 10 minutes under the condition of ultrahigh-temperature boiling, and can be used for boiling various meats and poultry at 135 ℃/60min and 145 ℃/10 min.

The above-mentioned embodiments are only preferred embodiments of the present invention, and the scope of the present invention is not limited by these embodiments, except for the cases listed in the specific embodiments; all equivalent variations of the methods and principles of the present invention are intended to be within the scope of the present invention.