A polyolefin composite film, a preparation method thereof, and a pre-cooked food sealing aluminum foil cover film and a lunch box

Abstract

The application belongs to the technical field of plastic packaging, and relates to a polyolefin composite film, a preparation method thereof, and a pre-prepared sealing aluminum foil sealing cover film for dishes and a lunch box. The application discloses a polyolefin composite film, which comprises a composite layer, an intermediate easy-cutting layer and an easy-peeling heat-sealing layer. The raw material of the easy-peeling heat-sealing layer comprises, in weight fractions, 50-60 parts of an easy-peeling resin, 20-30 parts of a maleic anhydride modified polypropylene resin and 20-30 parts of a polyolefin elastomer resin. The application further discloses a preparation method of the polyolefin composite film. The application also discloses a pre-prepared sealing aluminum foil sealing cover film for dishes and a lunch box.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of plastic packaging and relates to a polyolefin composite film, a preparation method thereof and a pre-prepared meal sealing aluminum foil sealing cover film and a meal box. BACKGROUND

[0002] With the continuous expansion of the domestic pre-prepared meal market, more and more pre-prepared meal products begin to be packaged in aluminum foil meal boxes. In order to prolong the shelf life of pre-prepared meal products, all pre-prepared meal products need to be subjected to high-temperature sterilization treatment after packaging and then circulated to the market for sale. The cover film used in the market is prone to poor sealing and poor easy-to-uncover effect after sterilization, and part of the cover film is also prone to poor cutting. SUMMARY

[0003] The purpose of the application is to solve the above problems existing in the prior art, and a polyolefin composite film resistant to cooking, easy to cut and easy to uncover is provided, and the polyolefin composite film is dry-combined with soft aluminum foil to be used as a sealing cover film for a pre-prepared meal sealing aluminum foil meal box.

[0004] The purpose of the application can be achieved by the following technical solutions:

[0005] A polyolefin composite film, the polyolefin composite film comprising a composite layer, an intermediate easy-to-cut layer and an easy-to-uncover heat-sealing layer.

[0006] The raw material of the easy-to-uncover heat-sealing layer comprises, by weight fraction, 50-60 parts of an easy-to-peel resin, 20-30 parts of a maleic anhydride modified polypropylene resin and 20-30 parts of a polyolefin elastomer resin.

[0007] Preferably, the thickness of the composite layer is 5-15 microns, the thickness of the intermediate easy-to-cut layer is 15-30 microns, and the thickness of the easy-to-uncover heat-sealing layer is 10-30 microns.

[0008] Further preferably, the thickness of the easy-to-uncover heat-sealing layer accounts for 25-45% of the thickness of the polyolefin composite film.

[0009] Preferably, the raw material of the composite layer comprises, by weight fraction, 40-60 parts of a copolymerized polypropylene resin and 40-70 parts of a metallocene catalyzed polypropylene resin.

[0010] Preferably, the raw material of the intermediate easy-to-cut layer comprises, by weight fraction, 20-40 parts of a copolymerized polypropylene resin, 20-30 parts of a metallocene catalyzed polypropylene resin, 20-30 parts of a cyclic olefin polymer resin and 10-20 parts of a maleic anhydride modified polypropylene resin.

[0011] The raw materials of the composite layer and the intermediate easy cutting layer both contain metallocene catalyzed polypropylene resin, so that the two layers have better cross-linking and ensure the function of resisting cooking sterilization; the raw materials of the intermediate easy cutting layer and the easy peel heat sealing layer both contain maleic anhydride modified polypropylene resin, which is beneficial to the dispersion of components while increasing the compatibility of the two layers.

[0012] Preferably, the content of the easy peel resin in the raw material of the easy peel heat sealing layer is 52-57%, and the mass ratio of the maleic anhydride modified polypropylene resin and the polyolefin elastomer resin is (0.8-1.1):1.

[0013] Further preferably, the easy peel resin is DuPont Easy Open 55010, the melt index is 2.0 g / 10 min (190℃ / 21.6 kg), and the density is 0.92 g / cm 3 (ASTM D792).

[0014] The application further discloses a preparation method of the polyolefin composite film, which comprises the following steps: pretreating the raw materials of the intermediate easy cutting layer and the easy peel heat sealing layer respectively, and then adding the pretreated intermediate easy cutting layer particles and the pretreated easy peel heat sealing layer particles into corresponding barrels of an extruder respectively, and performing segmented heating and pressurizing plasticization and blowing.

[0015] Preferably, the pretreatment comprises mixing the raw materials of the intermediate easy cutting layer and the easy peel heat sealing layer by closed mixing, shearing and compressing after segmented heating by a double-screw extruder, and extruding after segmented heating by a single-screw extruder, and then modifying and granulating.

[0016] Further preferably, the closed mixing temperature in the pretreatment is 90-110℃.

[0017] Further preferably, the segmented heating temperature of the double-screw extruder in the pretreatment is 120-220℃; the first heating temperature is 120-140℃, the second heating temperature is 150-160℃, the third heating temperature is 180-200℃, and the fourth heating temperature is 205-220℃.

[0018] Further preferably, the segmented heating temperature of the single-screw extruder in the pretreatment is 150-200℃; the first heating temperature is 180-200℃, the second heating temperature is 180-200℃, the third heating temperature is 165-180℃, and the fourth heating temperature is 150-160℃.

[0019] Preferably, the segmented heating temperature of the pretreated intermediate easy cutting layer particles in the extruder is 70-210℃; the first heating temperature is 70℃, the second heating temperature is 185℃, and the heating temperature of the third to seventh segments is 205℃.

[0020] Preferably, the pretreated easy-to-peel heat-sealing particles are heated in stages in the extruder at temperatures ranging from 60 to 190°C; the first stage is heated at 60°C, the second stage at 175°C, and the third to seventh stages at 185°C.

[0021] Preferably, the composite layer material is heated in stages in the extruder at the same temperature as the pretreated easy-to-peel heat-seal layer material.

[0022] This invention also discloses a pre-made food sealing aluminum foil capping film, which is a composite film made by dry lamination of a PET layer, a soft aluminum foil, and a polyolefin composite film.

[0023] Preferably, the soft aluminum foil is in contact with the composite layer in the polyolefin composite film.

[0024] Further optimization involves applying a corona treatment to the composite layer in the soft aluminum foil and polyolefin composite film before lamination.

[0025] The present invention further discloses a pre-prepared food sealed aluminum foil lunch box, which is made by heat-sealing a pre-prepared food sealed aluminum foil lunch box sealing film to the lunch box body.

[0026] Preferably, the polyolefin composite film side of the sealing cap film is in contact with the main body of the pre-prepared food sealing aluminum foil lunch box; the heat sealing temperature between the sealing cap film and the main body of the lunch box is 180-200℃.

[0027] Preferably, the main body of the lunchbox is made of AL / RCPP.

[0028] As a preferred option, pre-prepared food sealed aluminum foil lunch boxes (bags) can be made by heat-sealing two easy-to-open heat-seal layers of polyolefin composite films together.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The polyolefin composite film of the present invention comprises a composite layer, an intermediate easy-to-cut layer, and an easy-to-open heat-seal layer in sequence, which can ensure easy opening while preventing poor sealing.

[0031] 2. Maleic anhydride-modified polypropylene resin is added to the raw materials of the middle easy-to-cut layer and the easy-to-remove heat-sealable layer of the polyolefin composite film of the present invention to improve compatibility and avoid interlayer delamination.

[0032] 3. When the polyolefin composite film of the present invention is used in the sealing aluminum foil cap film for pre-prepared dishes, it can ensure effective heat sealing with the main body of the food container. After heat sealing and high-temperature sterilization, the peeling strength is controlled at 10-20 N / 15 mm. Detailed Implementation

[0033] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0034] Unless otherwise specified, the raw materials used in this invention are common commercially available products, and the preparation method is a conventional technique.

[0035] The raw materials used in this invention include:

[0036] Copolymer polypropylene resin: Produced by Borouge, grade RB707CF, melt index 1.5 g / 10 min, density 0.905 g / cm³ 3 ;

[0037] Metallocene-catalyzed polypropylene resin: manufactured by Total, grade MR10MX0, melt index 10 g / 10 min, density 0.902 g / cm³ 3 ;

[0038] Cyclic olefin polymer resin: Produced by Polyplastics Inc., Japan, grade 8007F-600, melt index 2.0 g / 10 min, density 1.01 g / cm³ 3 ;

[0039] Maleic anhydride modified polypropylene resin: Manufactured by Mitsui Chemicals, Japan, grade QF500T, melt flow index 3.0 g / 10 min, density 0.901 g / cm³ 3 ;

[0040] Easy-peel resin: Manufactured by Dow Chemical, grade 55010, melt index 2.0 g / 10 min, density 0.92 g / cm³ 3 ;

[0041] Polyolefin elastomer resin: manufactured by LyondellBasell, grade C200F, melt index 6.0 g / 10 min, density 0.89 g / cm³. 3 ;

[0042] Aluminum foil (soft state), AL, 50μm thickness, manufactured by Hangzhou Wuxing;

[0043] Polyester film: PET film, 12μm thick, produced by Hefei Pengfei Packaging Materials Co., Ltd.

[0044] High-temperature boiling polyurethane adhesive, YH3166A / YH3166B, manufactured by Beijing Gaomeng.

[0045] Example 1

[0046] The polyolefin composite film in this embodiment includes: a composite layer with a thickness of 10 μm, an intermediate easy-to-cut layer with a thickness of 20 μm, and an easy-to-peel heat-seal layer with a thickness of 20 μm.

[0047] The raw materials for the composite layer, by weight, include 50 parts copolymer polypropylene resin and 50 parts metallocene-catalyzed polypropylene resin.

[0048] The raw materials for the easily cut intermediate layer, by weight, include 35 parts copolymer polypropylene resin, 27 parts metallocene-catalyzed polypropylene resin, 23 parts cyclic olefin polymer resin, and 15 parts maleic anhydride-modified polypropylene resin.

[0049] The raw materials for the easy-peel heat-sealable layer, by weight, include 55 parts of easy-peel resin, 22 parts of maleic anhydride-modified polypropylene resin, and 23 parts of polyolefin elastomer resin.

[0050] The preparation process of polyolefin composite films includes:

[0051] Weigh the raw materials for the easily cut intermediate layer according to the specified ratio, put them into a high-speed mixer and mix evenly. Then, put them into a plastic internal mixer and mix at a high temperature of 100°C. Then, feed them into a conical twin-screw feeding device for segmented heating, with the first stage heating temperature being 125°C, the second stage heating temperature being 158°C, the third stage heating temperature being 190°C, and the fourth stage heating temperature being 210°C. Next, feed them into a single-screw extruder and extrude them after segmented heating, with the first stage heating temperature being 195°C, the second stage heating temperature being 195°C, the third stage heating temperature being 175°C, and the fourth stage heating temperature being 160°C. After extrusion, allow them to cool naturally to obtain pretreated easily cut intermediate layer particles.

[0052] Weigh the raw materials for the easy-open heat-sealable layer according to the specified proportions, put them into a high-speed mixer and mix evenly. Then, put them into a plastic internal mixer and mix at a high temperature of 100°C. Next, feed them into a conical twin-screw feeding device for segmented heating, with the first stage heating temperature being 125°C, the second stage heating temperature being 158°C, the third stage heating temperature being 190°C, and the fourth stage heating temperature being 210°C. Then, feed them into a single-screw extruder and extrude them after segmented heating, with the first stage heating temperature being 195°C, the second stage heating temperature being 195°C, the third stage heating temperature being 175°C, and the fourth stage heating temperature being 160°C. After extrusion, allow them to cool naturally to obtain pretreated easy-open heat-sealable layer particles.

[0053] The pretreated intermediate easy-to-cut layer particles and pretreated easy-to-open heat-seal layer particles, along with the composite layer raw material, are added to the corresponding barrels of the extruder, and the extruder is subjected to segmented heating and pressurization plasticization. The segmented heating temperatures set for the composite layer material and the easy-to-open heat-seal layer material are: 60℃ for the first segment, 175℃ for the second segment, and 185℃ for the third to seventh segments; the segmented heating temperatures set for the intermediate easy-to-cut layer material are: 70℃ for the first segment, 185℃ for the second segment, and 205℃ for the third to seventh segments.

[0054] After extrusion, all particles are filtered, pressurized and plasticized, and then mixed evenly in the blown film head channel, heated and kept warm. The temperatures of each zone of the die head are as follows: Zone 1 heating temperature 195℃, Zones 2 to 9 heating temperatures 205℃, Zone 10 heating temperature 190℃, initially inflating into a plastic tubular film shape. By adjusting the internal and external cooling air volume and traction speed, the initially inflated tubular film is blown to the set thickness and width, and then cooled by rotary traction (40℃), edge trimming, annealing device cooling, online slitting, and finally wound into a roll film by the winding device.

[0055] Preparation of sealing film:

[0056] The prepared polyolefin composite film is dry-laminated with soft aluminum foil and PET film to form a sealing cap film. The polyolefin composite film needs to be corona-treated before lamination. The adhesive used for dry lamination is YH3166A / YH3166B with a weight ratio of 20:3.5, the dry adhesive coating amount is 4.3 gsm, and the curing time is 50℃ / 72H.

[0057] The sealing film was cut into 80mm*160mm single sheets on a bag making machine. A total of 500 sheets were cut continuously, and the cutting effect was observed. The number of sheets that stuck together or could not be cut was counted. Every 50 sheets were counted in one round. The results are shown in Table 1.

[0058] Preparation of sealed aluminum foil lunch boxes for pre-cooked meals:

[0059] After heat-sealing the sealing film to the main body of the food container (AL / RCPP), it was sterilized by high-temperature steaming at 121℃ for 30min. The heat-sealing conditions were: pressure 0.2Mpa, time 1S, upper heating plate temperature adjusted, and lower heating plate 190℃. The comparison results of the opening strength (N / 15mm) before and after high-temperature steaming sterilization with the upper heating plate temperature are shown in Table 2.

[0060] Example 2

[0061] The polyolefin composite film in this embodiment includes: a composite layer with a thickness of 10 μm, an intermediate easy-to-cut layer with a thickness of 25 μm, and an easy-to-peel heat-seal layer with a thickness of 15 μm.

[0062] The raw materials for the composite layer, by weight, include 55 parts copolymer polypropylene resin and 45 parts metallocene-catalyzed polypropylene resin.

[0063] The raw materials for the easily cut intermediate layer, by weight, include 30 parts copolymer polypropylene resin, 25 parts metallocene-catalyzed polypropylene resin, 25 parts cyclic olefin polymer resin, and 20 parts maleic anhydride-modified polypropylene resin.

[0064] The raw materials for the easy-peel heat-sealable layer, by weight, include 53 parts of easy-peel resin, 23 parts of maleic anhydride-modified polypropylene resin, and 24 parts of polyolefin elastomer resin.

[0065] Polyolefin composite film, sealing cap film, and pre-prepared sealed aluminum foil lunch box for food were prepared according to the method described in Example 1; the properties are shown in Table 1 and Table 2.

[0066] Example 3

[0067] Compared with Example 1, the difference is that the polyolefin composite film includes: a composite layer with a thickness of 15 μm, an intermediate easy-to-cut layer with a thickness of 25 μm, and an easy-to-peel heat-seal layer with a thickness of 10 μm.

[0068] Polyolefin composite film, sealing cap film, and pre-made sealed aluminum foil lunch box for food were prepared according to the raw materials and methods described in Example 1; the properties are shown in Table 1 and Table 2.

[0069] Example 4

[0070] Compared with Example 1, the difference is that the polyolefin composite film includes: a composite layer with a thickness of 10 μm, an intermediate easy-to-cut layer with a thickness of 15 μm, and an easy-to-peel heat-seal layer with a thickness of 25 μm.

[0071] Polyolefin composite film, sealing cap film, and pre-made sealed aluminum foil lunch box for food were prepared according to the raw materials and methods described in Example 1; the properties are shown in Table 1 and Table 2.

[0072] Example 5

[0073] Compared with Example 1, the difference lies in the raw materials of the intermediate easily cut layer, which, by weight, include 40 parts of copolymer polypropylene resin, 30 parts of metallocene-catalyzed polypropylene resin, and 30 parts of cyclic olefin polymer resin.

[0074] Polyolefin composite film, sealing cap film, and pre-made sealed aluminum foil lunch box for food were prepared according to the raw materials and methods described in Example 1; the properties are shown in Table 1 and Table 2.

[0075] Example 6

[0076] Compared with Example 1, the difference is that neither the intermediate easy-to-cut layer nor the easy-to-peel heat-seal layer contains maleic anhydride-modified polypropylene resin.

[0077] The raw materials for the intermediate easily cut layer, by weight, include 40 parts copolymer polypropylene resin, 30 parts metallocene-catalyzed polypropylene resin, and 30 parts cyclic olefin polymer resin.

[0078] The raw materials for the easy-peel heat-sealable layer, by weight, include 65 parts of easy-peel resin and 35 parts of polyolefin elastomer resin.

[0079] Polyolefin composite film, sealing cap film, and pre-made sealed aluminum foil lunch box for food were prepared according to the raw materials and methods described in Example 1; the properties are shown in Table 1 and Table 2.

[0080] Example 7

[0081] Compared to Example 1, the difference is that the pre-prepared food sealed aluminum foil lunch box is made only of sealing film material. Two pieces of sealing film material are joined together to form a pre-prepared food sealed aluminum foil lunch bag, which can be easily separated.

[0082] Comparative Example 1

[0083] Compared with Example 1, the difference is that the polyolefin composite film consists only of a composite layer and an easy-to-cut layer.

[0084] The properties of the polyolefin composite film are shown in Table 1. After the polyolefin composite film is made according to the method described in Example 1, it is directly dry-laminated with soft aluminum foil to obtain a sealing cap film and then made into a pre-made sealed aluminum foil lunch box for food. It is extremely difficult to open before and after high-temperature cooking sterilization.

[0085] Comparative Example 2

[0086] Compared with Example 1, the difference is that the easy-to-peel heat-sealable layer of the polyolefin composite film does not contain an easy-to-peel resin; the specific raw materials include: 50 parts maleic anhydride modified polypropylene and 50 parts polyolefin elastomer.

[0087] Polyolefin composite film, sealing cap film, and pre-made sealed aluminum foil lunch box for food were prepared according to the raw materials and methods described in Example 1; the properties are shown in Table 2.

[0088] Comparative Example 3

[0089] Compared with Example 1, the difference is that random copolymer polypropylene is used instead of easy-peel resin in the heat-sealing layer of the polyolefin composite film;

[0090] The specific raw materials include: 55 parts random copolymer polypropylene, 25 parts maleic anhydride modified polypropylene, and 20 parts polyolefin elastomer.

[0091] Polyolefin composite film, sealing cap film, and pre-made sealed aluminum foil lunch box for food were prepared according to the raw materials and methods described in Example 1; the properties are shown in Table 2.

[0092] Comparative Example 4

[0093] Compared with Example 1, the difference lies in the specific raw materials in the heat-sealing layer of the polyolefin composite film, which include: 78 parts of random copolymer polypropylene, 11 parts of polyolefin elastomer, and 11 parts of lubricant.

[0094] Polyolefin composite film, sealing cap film, and pre-made sealed aluminum foil lunch box for food were prepared according to the raw materials and methods described in Example 1; the properties are shown in Table 1 and Table 2.

[0095] Comparative Example 5

[0096] Compared with Example 1, the difference lies in the raw materials of the easy-peel heat-sealing layer, which, by weight, include 40 parts of easy-peel resin, 25 parts of maleic anhydride modified polypropylene resin, and 35 parts of polyolefin elastomer resin.

[0097] Polyolefin composite film, sealing cap film, and pre-made sealed aluminum foil lunch box for food were prepared according to the raw materials and methods described in Example 1; the properties are shown in Table 2.

[0098] Comparative Example 6

[0099] Compared with Example 1, the difference lies in the raw materials of the easy-peel heat-sealing layer, which, by weight, include 70 parts of easy-peel resin, 15 parts of maleic anhydride modified polypropylene resin, and 15 parts of polyolefin elastomer resin.

[0100] Polyolefin composite film, sealing cap film, and pre-made sealed aluminum foil lunch box for food were prepared according to the raw materials and methods described in Example 1; the properties are shown in Table 2.

[0101] Comparative Example 7

[0102] Compared to Example 1, the difference lies in that the sealing cap film is made by dry lamination of commercially available easy-open film and soft aluminum foil.

[0103] Polyolefin composite film, sealing cap film, and pre-made sealed aluminum foil lunch box for food were prepared according to the raw materials and methods described in Example 1; the properties are shown in Table 1 and Table 2.

[0104] Table 1. Cutting Test Results

[0105]

[0106] Table 2. Comparison of heat seal opening strength before and after high-temperature steam sterilization.

[0107]

[0108]

[0109] (Note: When the heat seal peel strength exceeds 30N / 15mm, the sealing film is not easy to peel off.)

[0110] As can be seen from Tables 1 and 2 above, the polyolefin composite film of the present invention has good cutting properties; the sealing cap film and the pre-prepared food sealing aluminum foil lunch box have good resistance to steaming and boiling, easy cutting and easy opening properties.

[0111] In Example 3, the easy-open heat-sealable layer of the polyolefin composite film was too thin, resulting in normal easy-openability at low temperatures but difficulty in opening at high temperatures. In Example 4, the easy-open heat-sealable layer of the polyolefin composite film was too thick, resulting in a slight decrease in cutability and excessive cost. In Example 5, the absence of maleic anhydride-modified polypropylene resin in the cutting layer led to a decrease in the dispersion of raw materials in the cutting layer and a decrease in compatibility with the easy-open heat-sealable layer, which may cause interlayer delamination. In Example 6, the absence of maleic anhydride-modified polypropylene resin in both the cutting layer and the easy-open heat-sealable layer further reduced the degree of crosslinking between the two layers, resulting in interlayer delamination.

[0112] In Comparative Example 1, the polyolefin composite film omitted the easy-peel heat-sealing layer, resulting in difficulty in peeling it off. In Comparative Example 2, the easy-peel heat-sealing layer did not contain easy-peel resin, leading to an increase in heat-seal peel strength before and after sterilization. In Comparative Example 3, the easy-peel heat-sealing layer used random copolymer polypropylene instead of easy-peel resin, resulting in greater heat-seal peel strength after sterilization, making it difficult to peel off. In Comparative Example 4, the easy-peel heat-sealing layer used a formula of random copolymer polypropylene, polyolefin elastomer, and lubricant, but lacked maleic anhydride-modified polypropylene resin and easy-peel resin, resulting in poor heat-seal peel strength after high-temperature sterilization. In Comparative Example 5, the easy-peel heat-sealing layer contained less easy-peel resin, leading to a decrease in easy-peel performance. In Comparative Example 6, the easy-peel heat-sealing layer contained more easy-peel resin, resulting in poor sealing. In Comparative Example 7, a commercially available ordinary easy-peel film was used, resulting in poor heat-seal peel strength after high-temperature sterilization.

[0113] In summary, the polyolefin composite film of the present invention comprises a composite layer, an intermediate easy-to-cut layer, and an easy-to-open heat-seal layer, which can ensure easy opening while preventing poor sealing. Furthermore, the addition of maleic anhydride-modified polypropylene resin to the raw materials of the intermediate easy-to-cut layer and the easy-to-open heat-seal layer of the polyolefin composite film of the present invention aims to improve compatibility and avoid interlayer delamination. The addition of metallocene-catalyzed polypropylene resin to the raw materials of the composite layer and the intermediate easy-to-cut layer aims to improve heat resistance.

[0114] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A polyolefin composite film, characterized in that, The polyolefin composite film includes a composite layer, an intermediate easy-to-cut layer, and an easy-to-peel heat-seal layer; The raw materials for the easy-open heat-sealable layer, by weight, include 50-60 parts of easy-peel resin, 20-30 parts of maleic anhydride-modified polypropylene resin, and 20-30 parts of polyolefin elastomer resin; wherein the easy-peel resin is DuPont Easy-Open Cap 55010, with a melt index of 2.0 g / 10 min at 190°C and 21.6 kg, and a density of 0.92 g / cm³. 3 ; The thickness of the composite layer is 5~15μm, the thickness of the middle easy-to-cut layer is 15~30μm, and the thickness of the easy-to-peel heat-sealable layer is 10~30μm; The raw materials for the composite layer, by weight, include 40-60 parts copolymer polypropylene resin and 40-70 parts metallocene catalyzed polypropylene resin. The raw materials for the intermediate easily cut layer, by weight, include 20-40 parts copolymer polypropylene resin, 20-30 parts metallocene-catalyzed polypropylene resin, 20-30 parts cyclic olefin polymer resin, and 10-20 parts maleic anhydride-modified polypropylene resin.

2. The polyolefin composite film according to claim 1, characterized in that, The thickness of the easily peelable heat-sealing layer accounts for 25-45% of the thickness of the polyolefin composite film.

3. The polyolefin composite film according to claim 1, characterized in that, The amount of easily peelable resin added to the raw material of the easy-to-peel heat-sealable layer is 52-57%, and the mass ratio of maleic anhydride modified polypropylene resin to polyolefin elastomer resin is (0.8-1.1):

1.

4. A method for preparing a polyolefin composite film as described in claim 1, characterized in that, The preparation method includes: pre-treating the raw materials of the intermediate easy-to-cut layer and the easy-to-open heat-sealable layer respectively, and then adding the pre-treated intermediate easy-to-cut layer particles, the pre-treated easy-to-open heat-sealable layer particles, and the composite layer raw materials into the corresponding barrels of the extruder and performing segmented heating, pressurizing, plasticizing, and blowing of the extruder.

5. The method for preparing the polyolefin composite film according to claim 4, characterized in that, The pretreatment includes mixing the raw materials of the easily cut and easily heat-sealed intermediate layers, followed by shearing and compression after segmented heating with a twin-screw extruder, and extrusion after segmented heating with a single-screw extruder, followed by modification and granulation.

6. A sealing aluminum foil capping film for pre-prepared dishes, characterized in that, The pre-prepared food sealing aluminum foil capping film is a composite film made by sequentially dry laminating a PET layer, a soft aluminum foil, and a polyolefin composite film as described in any one of claims 1 to 3.

7. The pre-prepared food sealing aluminum foil capping film according to claim 6, characterized in that, The soft aluminum foil is in contact with the composite layer in the polyolefin composite film.

8. The pre-prepared food sealing aluminum foil capping film according to claim 6, characterized in that, The composite layer in the polyolefin composite film needs to be corona treated before being laminated with the soft aluminum foil.

9. A pre-prepared food container with sealed aluminum foil, characterized in that, The pre-prepared food sealed aluminum foil lunch box is made by heat-sealing the sealing film of the pre-prepared food sealed aluminum foil lunch box as described in any one of claims 6 to 8 to the lunch box body.

10. The pre-prepared food sealing aluminum foil lunch box according to claim 9, characterized in that, The polyolefin composite film side of the sealing cap film is in contact with the main body of the pre-prepared food sealing aluminum foil lunch box; the heat sealing temperature between the sealing cap film and the main body of the lunch box is 180~200℃.

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