Liquid food packaging cover film and preparation process

Abstract

The invention relates to the technical field of functional sealing cover film materials, and discloses a liquid food packaging cover film and a preparation process thereof, and the preparation process comprises the following steps: synthesizing a low-surface-energy compound monoalkenyl hepta (octadecyl) cage type polysilsesquioxane; on the basis of a free radical melt grafting method, monoalkenyl hepta (octadecyl) cage type polysilsesquioxane is grafted to an EVA main chain, and low surface energy type EVA is prepared; low-surface-energy EVA and EVA are subjected to compounding granulation, blow molding film forming and template hot pressing to form a rough structure, the super-hydrophobic EVA film is prepared, the film can be used as an inner layer material of a liquid food packaging cover film, the prepared cover film product has the beneficial technical effect of remarkably reducing the adhesion rate of viscous liquid food yoghourt, meanwhile, the uncovering trace is smooth, and the film is not prone to falling off. The adhesive is free of delamination, wiredrawing, residues and other undesirable phenomena, excellent in comprehensive performance and capable of being applied to the field of viscous liquid food packaging.

Description

Technical Field

[0001] The invention relates to the technical field of functional sealing cover film materials, in particular to a liquid food packaging cover film and a preparation process thereof. Background Art

[0002] Film sealing is a common sealing method in food packaging. It uses the heat-adhesive bonding between the film and the edge of the cup body to seal the food, thereby achieving a sealing effect. The current commercial film structure is an outer layer of polyester, a middle layer of aluminum foil and an inner layer of EVA (its Chinese name is: ethylene-vinyl acetate copolymer, which is copolymerized by ethylene E and vinyl acetate VA). The main function of the inner layer of EVA is to seal the bottle body. Studies have found that EVA film has adhesion properties for viscous liquid foods such as yogurt, juice and honey. Actual application results also confirm that viscous liquid foods adhere to the sealing film. Therefore, the study of superphobic sealing films has important application value for viscous liquid food packaging.

[0003] Currently, there are two main ways to prepare superphobic functional materials. One is to construct a rough structure on the surface of low surface energy materials; the other is to modify low surface energy substances on the rough surface. Summary of the invention

[0004] The present invention adopts a technical route of constructing a rough structure on the surface of a low surface energy material to prepare a superphobic material, grafts a low surface energy substance onto the molecular main chain of EVA, and constructs a micron-level rough structure on the surface of the obtained low surface energy EVA film by a template hot pressing method, thereby obtaining a new EVA film product with superphobic properties. This technical improvement method significantly improves the adhesion performance of traditional EVA film products to viscous liquid foods.

[0005] A preparation process for a liquid food packaging cover film comprises the following steps: Step 1, synthesizing a low surface energy compound monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane; Step 2: Based on the free radical melt grafting method, monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane is grafted onto the EVA main chain to prepare low surface energy EVA; Step 3, feeding the low surface energy EVA and EVA in a mass ratio of 1: (1.5-4) into a granulation device to prepare a masterbatch, preparing a low surface energy EVA film by a blow molding film forming process, constructing a micron-scale rough structure on the low surface energy EVA film by a template hot pressing method, and preparing a superphobic EVA film; Step 4: Using the superphobic EVA film as the inner layer, the middle layer of aluminum foil and the outer layer of PET film through a composite process to obtain a liquid food packaging cover film.

[0006] Preferably, the preparation method of the monoalkenyl hepta(octadecyl)cage-type polyhedral oligomeric silsesquioxane is as follows: Using octavinyl-POSS and octadecyl dimethylsilane as raw materials, an addition reaction occurs between the alkenyl functional groups of octavinyl-POSS and the Si-H functional groups of octadecyl dimethylsilane, and the molar ratio of octavinyl-POSS and octadecyl dimethylsilane participating in the reaction is controlled to be 1:(8.01 - 8.09) to produce octa(octadecyl)cage-type polyhedral oligomeric silsesquioxane; Using octa(octadecyl)cage-type polyhedral oligomeric silsesquioxane as the raw material, tetraethylammonium hydroxide is used as the opening reagent, and hepta(octadecyl)trisilanol group incompletely condensed cage-type polyhedral oligomeric silsesquioxane is synthesized by the vertex-opening method; Using hepta(octadecyl)trisilanol group incompletely condensed cage-type polyhedral oligomeric silsesquioxane as the raw material, 7-octenyltrimethoxysilane is used as the capping reagent, and monoalkenyl hepta(octadecyl)cage-type polyhedral oligomeric silsesquioxane is synthesized by the vertex-capping method.

[0007] Preferably, the dosage of the monoalkenyl hepta(octadecyl)cage-type polyhedral oligomeric silsesquioxane in the low surface energy type EVA is 0.5 - 2 wt% of the EVA dosage.

[0008] Preferably, the granulation equipment in step three is a twin-screw extruder; Preferably, the process parameters of the twin-screw extruder are set as follows: the temperatures of zones 1 - 6 are 115 - 125 °C, 130 - 145 °C, 140 - 160 °C, 150 - 160 °C, 150 - 170 °C, and 160 - 180 °C respectively.

[0009] Preferably, the process equipment used in the blown film forming process in step three is a single-screw extrusion blown film machine; Preferably, the process parameters of the single-screw extrusion blown film machine are set as follows: the temperatures of zones 1 - 3 are 110 - 130 °C, 140 - 160 °C, and 160 - 180 °C respectively.

[0010] Preferably, the process parameters of the template hot pressing method in step three are set as follows: temperature 90 - 110 °C, pressure 1 - 3 MPa, and time 2 - 5 min.

[0011] Preferably, the process parameters of the composite process in step four are set as follows: composite speed 250 - 400 m / min, composite temperature 40 - 50 °C, cooling temperature 20 - 25 °C, composite pressure 0.4 - 0.5 Mpa, and sizing pressure 0.4 - 0.6 Mpa.

[0012] A liquid food packaging lid film prepared according to the above process is composed of a PET film with a thickness of 20 - 40 μm, an aluminum foil with a thickness of 15 - 25 μm, and a superhydrophobic EVA film with a thickness of 30 - 50 μm.

[0013] Preferably, the formula of the superphobic EVA film is: 50-70 parts of EVA, 15-40 parts of low surface energy EVA and 1-5 parts of composite additives; Preferably, the composite auxiliary agent includes 0.5-3 parts by weight of polyethylene wax and 0.5-3 parts by weight of zinc stearate. Beneficial Effects

[0014] Octaveenyl-POSS, octadecyldimethylsilane and 7-octenyltrimethoxysilane were used as raw materials, and a long alkyl chain with low surface energy was modified on the cage-type siloxane skeleton by utilizing the hydrosilylation reaction mechanism. The cage-type siloxane skeleton was opened by the vertex opening method, and then closed again by the vertex capping method, thereby obtaining a low surface energy compound, monovinyl heptadecanyl cage-type polysilsesquioxane. A low surface energy EVA is prepared by free radical melt grafting of monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane onto the main chain of EVA, and the mixture is granulated, blown into a film, and the template is hot-pressed to form a rough structure to obtain a new EVA film product, which reduces the adhesion rate of viscous liquid food yogurt to less than 6%, that is, the new EVA film prepared by the present invention exhibits superphobic properties for viscous liquid foods such as yogurt; The new EVA film prepared by the present invention can be used as the inner layer material of the liquid food packaging cover film. The cover film product prepared thereby has smooth marks after being peeled off, has no delamination, drawing, residue and other undesirable phenomena, has excellent comprehensive performance, and can be used in the field of viscous liquid food packaging. DETAILED DESCRIPTION Embodiment 1:

[0015] A liquid food packaging cover film, the product structure of which is the following layers arranged in sequence: a polyethylene terephthalate resin PET (brand name VR-8863) layer, an aluminum foil Al (model 8011) layer, and a superphobic EVA layer; The liquid food packaging cover film is made of a PET layer with a thickness of 30 μm, an aluminum foil Al layer with a thickness of 20 μm and a superphobic EVA layer with a thickness of 40 μm, which is compounded by a high-speed solvent-free compounding process using an ethylene-acrylic acid copolymer EAA adhesive (grade 5050); Among them, the superphobic EVA layer is one of superphobic EVA layer I, superphobic EVA layer II and superphobic EVA layer III. Embodiment 2:

[0016] The superphobic EVA film I used in the superphobic EVA layer I includes the following raw materials in parts by weight: 60 parts of EVA (grade APPEEL 53007); 30 parts of low surface energy EVA; 2 parts of polyethylene wax; 1 part of zinc stearate; Among them, the preparation steps of the low surface energy type EVA are as follows: Step 1: Prepare monoalkenyl hepta(octadecyl)cage polyhedral oligomeric silsesquioxane, and its preparation process is as follows: Step S1: Using octavinyl-POSS and octadecyl dimethylsilane as raw materials, through the addition reaction of the alkenyl functional group of octavinyl-POSS and the Si-H functional group of octadecyl dimethylsilane, and controlling the molar ratio of octavinyl-POSS and octadecyl dimethylsilane participating in the reaction to be 1:8.05, octa(octadecyl)cage polyhedral oligomeric silsesquioxane is generated, and its chemical structural formula is: ; Step S2: Using octa(octadecyl)cage polyhedral oligomeric silsesquioxane as the raw material, using tetraethylammonium hydroxide as the opening reagent, and synthesizing hepta(octadecyl)trisilanol group incompletely condensed cage polyhedral oligomeric silsesquioxane by the vertex-opening method, and its chemical structural formula is: ; Step S3: Using hepta(octadecyl)trisilanol group incompletely condensed cage polyhedral oligomeric silsesquioxane as the raw material, using 7-octenyltrimethoxysilane as the capping reagent, and synthesizing monoalkenyl hepta(octadecyl)cage polyhedral oligomeric silsesquioxane by the vertex-capping method, and its chemical structural formula is: ; The specific experimental steps for preparing monoalkenyl hepta(octadecyl)cage polyhedral oligomeric silsesquioxane are as follows: Under the protection of nitrogen, add 3.2 g of octavinyl-POSS (CAS number 69655-76-1) and 30 mL of tetrahydrofuran to a three-necked flask, stir at room temperature until completely dissolved, then successively add 70 mL of a tetrahydrofuran solution containing 12.5 g of octadecyl dimethylsilane and 8 drops of Karstedt catalyst to the three-necked flask, heat up to 75 °C and stir and reflux for 10 h, cool to room temperature, rotate and evaporate to remove tetrahydrofuran, wash successively with ethanol and deionized water, and dry in vacuum to obtain octa(octadecyl)cage polyhedral oligomeric silsesquioxane; Add 7.8 g of octa(octadecyl)cage polyhedral oligomeric silsesquioxane and 80 mL of tetrahydrofuran to a three-necked flask, stir at room temperature until completely dissolved, then add 10 mL of 40 wt% tetraethylammonium hydroxide aqueous solution to the three-necked flask, heat up to 70 °C and stir and reflux for 5 h, cool to room temperature, adjust the pH to neutral with 0.1 mol / L dilute hydrochloric acid, rotate and evaporate to remove tetrahydrofuran, dissolve in ether, dry with anhydrous magnesium sulfate, filter, rotate and evaporate to remove ether, and dry in vacuum to obtain hepta(octadecyl)trisilanol group incompletely condensed cage polyhedral oligomeric silsesquioxane; Under nitrogen protection, 4.6 g of incompletely condensed heptakis(octadecyl) silsesquioxane with trihydroxyl groups and 50 mL of tetrahydrofuran were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, it was placed in an ice-water bath, and 0.5 mL of 7-octenyltrimethoxysilane was added dropwise to the three-necked flask. After stirring and reacting in the ice-water bath for 1 h, the ice-water bath was removed, and the reaction was continued to stir at room temperature for 8 h. Tetrahydrofuran was removed by rotary evaporation and concentrated to a saturated solution, and then dried in vacuo to obtain monoalkenyl heptakis(octadecyl) silsesquioxane; The 1H NMR characterization of monoalkenyl heptakis(octadecyl) silsesquioxane is as follows: 1 H NMR(CDCl3, 400 MHz) δ: 0.06(s, 42H), 0.75 - 0.90(m, 37H), 1.08 - 1.55(m, 244H), 1.69 - 1.79(m, 16H), 2.09 - 2.14(m, 2H), 4.94 - 4.97(d, 2H), 5.76 - 5.86(m, 1H); Step 2, preparation of low surface energy EVA: Using the method of free radical melt grafting, free radicals are generated by the action of a peroxide initiator during the melt processing of EVA. The alkenyl functional groups of monoalkenyl heptakis(octadecyl) silsesquioxane react with the free radicals in EVA to achieve graft modification of EVA, and then it is extruded and pelletized by a twin-screw extruder to obtain low surface energy EVA; Among them, the peroxide initiator is one of dicumyl peroxide (DCP), tert-butyl hydroperoxide (TBHP), benzoyl peroxide (BPO), tert-butyl perbenzoate (TBPB), lauroyl peroxide (LPO); In this example, dicumyl peroxide (DCP) is selected for use; The specific experimental steps for preparing low surface energy EVA are as follows: First, EVA (grade APPEEL 53007) is placed in a vacuum drying oven at 60 °C and dried for 12 h. Then, 10 g of the dried EVA, 1.2 g of monoalkenyl heptakis(octadecyl) silsesquioxane, and 0.1 g of dicumyl peroxide initiator are added to a high-speed mixer and mixed evenly, and then melted, extruded, and pelletized by a twin-screw extruder to obtain low surface energy EVA; Among them, the process parameters of the twin-screw extruder are set as follows: the preheating temperature is 150 °C, the temperatures of zones 1 - 6 are 150 °C, 155 °C, 160 °C, 170 °C, 170 °C, 180 °C respectively, the rotation speed is 60 r / min, and the melt processing time is 20 min. Example 3:

[0017] The preparation process of the superhydrophobic EVA film Ⅰ in Example 2 includes the following steps: Step 1: Prepare ingredients according to the formula of superphobic EVA film I, add all raw materials into a high-speed mixer and mix them evenly, extrude and granulate them through a twin-screw extruder, and vacuum dry them at 80°C for 6 hours to obtain low surface energy EVA masterbatch I; The process parameters of the twin-screw extruder were set as follows: the temperatures of zones 1-6 were 120°C, 140°C, 150°C, 155°C, 160°C, and 170°C, respectively, and the rotation speed was 400r / min; Step 2: Add low surface energy EVA masterbatch I into a single screw extruder film blowing machine, use the upward blowing method to blow film, and then use the template hot pressing method to construct a rough structure on the film surface. Cut the area of 25cm 2 The film was placed between a template with a microarray structure on the surface (purchased from Beijing Huidexin Technology Co., Ltd., the template material is aluminum plate, the diameter of the array protrusion is 100 μm) with an area of 100 cm in the middle. 2 The double-layer Teflon cloth was hot-pressed at 100°C and 2MPa for 3 minutes to ensure that the microarray structure was replicated on the film surface. After being taken out and cooled, it was peeled off to obtain superphobic EVA film I. Among them, the process parameters of the single-screw extrusion film blowing machine are set as follows: the temperatures of zones 1-3 are 120°C, 150°C, and 170°C, respectively; the rotation speed is 60r / min; the traction speed is 5m / min; the die head diameter of the film blowing machine is 60mm; and the blowing ratio is 2.5. Embodiment 4:

[0018] The raw material formula of the superphobic EVA film II used in the superphobic EVA layer II in Example 1 is different from that of the superphobic EVA film I in Example 2 only in that the amount of low surface energy EVA is 15 parts by weight; The preparation process of superphobic EVA film II is the same as the preparation process of superphobic EVA film I in Example 3. Embodiment five:

[0019] The raw material formula of the superphobic EVA film III used in the superphobic EVA layer III in Example 1 is different from that of the superphobic EVA film I in Example 2 only in that the amount of low surface energy EVA is 40 parts by weight; The preparation process of the superphobic EVA film III is the same as the preparation process of the superphobic EVA film I in Example 3. Embodiment six:

[0020] Preparation of liquid food packaging cover film: using a high-speed solvent-free laminating machine to sequentially bond a PET layer, an Al layer and a superphobic EVA layer together through an ethylene-acrylic acid copolymer EAA adhesive to obtain a liquid food packaging cover film; Among them, the process parameters of the high-speed solventless laminator are set as follows: laminating speed 300 m / min, laminating temperature 40 °C, cooling temperature 25 °C, laminating pressure 0.45 Mpa, and glue application pressure 0.5 Mpa; When the superhydrophobic EVA layer is the superhydrophobic EVA layer I, the prepared film product is denoted as the liquid food packaging lid film I; When the superhydrophobic EVA layer is the superhydrophobic EVA layer II, the prepared film product is denoted as the liquid food packaging lid film II; When the superhydrophobic EVA layer is the superhydrophobic EVA layer III, the prepared film product is denoted as the liquid food packaging lid film III. Comparative example:

[0021] The conventional EVA film used to prepare the conventional EVA layer only differs from the superhydrophobic EVA film I in Example II in the following part of the raw material formula: using EVA (grade APPEEL 53007) to replace the low surface energy type EVA. The difference in its preparation process from the preparation process of the superhydrophobic EVA film I in Example III is only that: the template hot pressing method treatment is not carried out; The conventional lid film is prepared, and the difference from the liquid food packaging lid film I is only that: using the conventional EVA layer to replace the superhydrophobic EVA layer I. Performance test:

[0022] (1) Superhydrophobic performance test: Analyze its superhydrophobic performance by testing the residue rate of liquid food (taking yogurt as an example) on the lid film sample. The specific test steps are as follows: Fix a circular lid film sample with a diameter of 10 cm (mass m0 g) on the clamping plate, drop yogurt (Yili original fermented milk, mass M g) on the EVA layer surface of the lid film sample, place the lid film sample at an angle of 45° to the horizontal plane, wait for the yogurt to flow down and then stand still for 30 s, record the weight m1 g of the lid film sample at this time, and calculate the residue rate. The specific method is as follows: Residue rate (%) = [(m1 - m0) / M] × 100%; The above experimental results are shown in Table 1 below; Table 1 Experimental results of the performance of the liquid food packaging lid film I Product type Residual rate (%) Liquid food packaging lid film Ⅰ 3.5 Liquid food packaging lid film Ⅱ 5.8 Liquid food packaging lid film Ⅲ 3.2 Control example 37.6 By analyzing the experimental results in Table 1, the following conclusion can be drawn: The liquid food packaging lid film product prepared by the present invention has achieved the beneficial technical effect of significantly reducing the residue amount of liquid food and exhibits excellent superhydrophobic performance; (2) Sealing strength test: Use an HSG-C type heat sealer to laminate the lid film sample with the PP cup body. The sealing knife area is 15 cm × 1 cm, the heat sealing temperature is 160 °C, the heat sealing pressure is 0.1 MPa, and the heat sealing time is 2.0 s; The sealing performance of the heat-sealed samples was tested in accordance with QB / T 2358-1998 "Test Method for Heat Seal Strength of Plastic Film Packaging Bags". The test speed was 200 mm / min, the fixture spacing was 50 mm, and the sealing strength of the samples was recorded. (3)Easily peelable performance test: The lid film sample was laminated with the PP cup body using an HSG-C type heat sealer (the heat sealing temperature was 160 °C, the heat sealing pressure was 0.1 MPa, and the heat sealing time was 2.0 s). Then, the lid film sample was peeled off from the PP cup body, and the peeling marks were observed. The above experimental results are shown in Table 2 below. Table 2 Performance test results of the lid film for liquid food packaging II Product type Sealing strength (N / 15mm) Peeling trace Liquid food packaging lid film Ⅰ 15.7 No delamination, smooth peeling trace, no wire drawing, no residue Liquid food packaging lid film Ⅱ 16.2 No delamination, smooth peeling trace, no wire drawing, no residue Liquid food packaging lid film Ⅲ 15.4 No delamination, smooth peeling trace, no wire drawing, no residue The following conclusions can be drawn through comprehensive analysis of the above experimental results: The sealing strength of the lid film for liquid food packaging prepared by the present invention is greater than the technical requirement of JB / T 9086-2007 "Plastic Bag Hot Press Sealing Machine" for the sealing strength ≥ 15 N (material thickness R, 0.08 mm ≤ R < 0.18 mm). After being peeled off from the PP cup body, the peeling marks are smooth, and there are no adverse phenomena such as delamination, wire drawing, and residue, meeting the usage requirements of the lid film, having practical application value, and being applicable in the field of viscous liquid food packaging.

Claims

1. A preparation process for a liquid food packaging lid film, characterized in that, The following steps are involved: Step 1, synthesize a low surface energy compound monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane, the chemical structure of which is: ； Step 2: Based on the free radical melt grafting method, monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane is grafted onto the EVA main chain to prepare low surface energy EVA; Step 3, feeding the low surface energy EVA and EVA in a mass ratio of 1: (1.5-4) into a granulation device to prepare a masterbatch, preparing a low surface energy EVA film by a blow molding film forming process, constructing a micron-scale rough structure on the low surface energy EVA film by a template hot pressing method, and preparing a superphobic EVA film; Step 4: Using the superphobic EVA film as the inner layer, the middle layer of aluminum foil and the outer layer of PET film through a composite process to obtain a liquid food packaging cover film.

2. The preparation process of a liquid food packaging lid film according to claim 1, characterized in that, The preparation method of the monoalkenyl heptadecanyl cage-type polysilsesquioxane is as follows: Octaveenyl-POSS and octadecyldimethylsilane are used as raw materials, an alkenyl functional group of octavinyl-POSS is reacted with a Si-H functional group of octadecyldimethylsilane by addition reaction, and the molar ratio of octavinyl-POSS and octadecyldimethylsilane participating in the reaction is controlled to be 1:(8.01-8.09), thereby generating octa(octadecyl) cage-type polysilsesquioxane; Octa(octadecyl) cage-type polysilsesquioxane was used as raw material and tetraethylammonium hydroxide was used as an opening agent to synthesize hepta(octadecyl) trisilanol group incompletely condensed cage-type polysilsesquioxane by vertex-opening method. Monoalkenyl heptadecanyl cage polysilsesquioxane was synthesized by vertex-capping method using heptadecanyl trisilanol incomplete condensation cage polysilsesquioxane as raw material and 7-octenyl trimethoxysilane as capping agent.

3. The preparation process of a liquid food packaging lid film according to claim 1, characterized in that, The amount of monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane in the low surface energy EVA is 0.5-2wt% of the amount of EVA.

4. The preparation process of a liquid food packaging lid film according to claim 1, characterized in that, The granulation equipment in step 3 is a twin-screw extruder; The process parameters of the twin-screw extruder are set as follows: the temperatures of zones 1-6 are 115-125° C., 130-145° C., 140-160° C., 150-160° C., 150-170° C., and 160-180° C., respectively.

5. The preparation process of a liquid food packaging lid film according to claim 1, characterized in that, The process equipment used in the film blowing process in step 3 is a single screw extrusion film blowing machine; The process parameters of the single screw extrusion film blowing machine are set as follows: the temperatures of zones 1-3 are 110-130° C., 140-160° C., and 160-180° C., respectively.

6. The preparation process of a liquid food packaging lid film according to claim 1, characterized in that, The process parameters of the template hot pressing method in step three are set as follows: temperature 90-110° C., pressure 1-3 MPa, and time 2-5 min.

7. The preparation process of a liquid food packaging lid film according to claim 1, characterized in that, The process parameters of the compounding process in step 4 are set as: compounding speed 250-400 m / min, compounding temperature 40-50° C., cooling temperature 20-25° C., compounding pressure 0.4-0.5 MPa, and gluing pressure 0.4-0.6 MPa.

8. A liquid food packaging lid film prepared by the process according to any one of claims 1-7, characterized in that, The liquid food packaging cover film is composed of a PET film with a thickness of 20-40 μm, an aluminum foil with a thickness of 15-25 μm, and a superphobic EVA film with a thickness of 30-50 μm.

9. The liquid food packaging lid film according to claim 8, characterized in that, The formulation of the superhydrophobic EVA film is as follows: 50 - 70 parts of EVA, 15 - 40 parts of low surface energy EVA, and 1 - 5 parts of composite additives.

10. A liquid food packaging lid film according to claim 9, characterized in that, The composite additives include 0.5 - 3 parts by weight of polyethylene wax and 0.5 - 3 parts by weight of zinc stearate.

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