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. The invention comprises the following steps: synthesizing a low-surface-energy compound, monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane; grafting the monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane onto an EVA main chain based on a free radical melt grafting method to prepare a low-surface-energy EVA; compounding the low-surface-energy EVA with EVA to form granules, blow-molding the mixture into a film, and hot-pressing a template to form a rough structure to prepare a superphobic EVA film. The film can be used as an inner layer material of a liquid food packaging cover film. The cover film product prepared in this manner achieves the beneficial technical effect of significantly reducing the adhesion rate of viscous liquid food yogurt. At the same time, the cover film product has a smooth peeling mark without undesirable phenomena such as delamination, stringing, and residue, has excellent comprehensive performance, and can be used in the field of viscous liquid food packaging.

Description

Technical Field

[0001] The present 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 method of sealing food packaging, using the heat-dependent adhesion between the film and the edge of the cup body to seal the food. Currently, commercialized film seals consist of an outer layer of polyester, an intermediate layer of aluminum foil, and an inner layer of EVA (ethylene-vinyl acetate copolymer, a copolymer of ethylene E and vinyl acetate VA). The primary function of the inner layer of EVA is to seal the bottle. Studies have shown that EVA films exhibit adhesion to viscous liquid foods such as yogurt, juice, and honey. Actual application results have also confirmed that viscous liquid foods adhere to the sealing film. Therefore, research on 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. A low-surface-energy substance is grafted onto the molecular backbone of EVA, and a micron-scale rough structure is constructed on the surface of the obtained low-surface-energy EVA film through a template hot-pressing method to produce a new EVA film product with superphobic properties. This technical improvement significantly improves the adhesion performance of traditional EVA film products to viscous liquid foods.

[0005] A process for preparing a liquid food packaging cover film comprises the following steps:

[0006] Step 1, synthesizing a low surface energy compound monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane;

[0007] 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;

[0008] Step 3: The low surface energy EVA and EVA are fed into a granulation device at a mass ratio of 1: (1.5-4) to prepare a masterbatch, the masterbatch is used to prepare a low surface energy EVA film by a blown film process, and a micron-scale rough structure is constructed on the low surface energy EVA film by a template hot pressing method to prepare a superphobic EVA film;

[0009] Step 4: Using the superphobic EVA film as the inner layer, the middle layer of aluminum foil and the outer layer of PET film are composited to produce a liquid food packaging cover film.

[0010] Preferably, the preparation method of the monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane is:

[0011] Octave-vinyl-POSS and octadecyldimethylsilane are used as raw materials, and an addition reaction occurs between the alkenyl functional group of octavinyl-POSS and the Si-H functional group of octadecyldimethylsilane, and the molar ratio of the octavinyl-POSS to the octadecyldimethylsilane is controlled to be 1:(8.01-8.09) to generate octa(octadecyl) cage-type polysilsesquioxane.

[0012] Octa-octadecyl caged polysilsesquioxane was used as raw material and tetraethylammonium hydroxide was used as opening agent to synthesize hepta-octadecyl trisilanol incompletely condensed caged polysilsesquioxane by the vertex-opening method.

[0013] Monoalkenyl heptadecanyl cage polysilsesquioxane was synthesized by the vertex-capping method using heptadecanyl trisilanol incomplete condensation cage polysilsesquioxane as raw material and 7-octenyltrimethoxysilane as capping reagent.

[0014] Preferably, the amount of monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane in the low surface energy EVA is 0.5-2 wt % of the amount of EVA.

[0015] Preferably, the granulation equipment in step 3 is a twin-screw extruder;

[0016] 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.

[0017] Preferably, the process equipment used in the film blowing process in step 3 is a single-screw extruder film blowing machine;

[0018] Preferably, 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.

[0019] Preferably, the process parameters of the template hot pressing method in step three are set to: temperature 90-110° C., pressure 1-3 MPa, and time 2-5 min.

[0020] Preferably, the process parameters of the compounding process in step 4 are set as follows: 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.

[0021] The liquid food packaging cover film prepared according to the above process consists 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.

[0022] 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;

[0023] 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

[0024] Using octavinyl-POSS, octadecyldimethylsilane and 7-octenyltrimethoxysilane as raw materials, the cage-type siloxane skeleton was modified with long alkyl chains with low surface energy 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 to prepare the low surface energy compound monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane.

[0025] A low-surface-energy EVA was prepared by free-radical melt grafting of monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane onto the EVA backbone. The product was then compounded and granulated, blown into a film, and subjected to template hot pressing to create a rough structure. This new EVA film reduced the adhesion rate of viscous liquid foods such as yogurt to below 6%. This indicates that the new EVA film prepared by the present invention exhibits superphobic properties for viscous liquid foods such as yogurt.

[0026] 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 when peeled off, and has no undesirable phenomena such as delamination, drawing, and residue. It has excellent comprehensive performance and can be used in the field of viscous liquid food packaging. DETAILED DESCRIPTION Example 1:

[0027] A liquid food packaging cover film, the product structure of which is the following layers arranged in sequence: a polyethylene terephthalate resin PET (brand VR-8863) layer, an aluminum foil Al (model 8011) layer, and a superphobic EVA layer;

[0028] The liquid food packaging cover film is made of a 30μm thick PET layer, a 20μm thick aluminum foil Al layer and a 40μm thick superphobic EVA layer using a high-speed solvent-free composite process with an ethylene-acrylic acid copolymer EAA adhesive (grade 5050).

[0029] Among them, the superphobic EVA layer is one of superphobic EVA layer I, superphobic EVA layer II and superphobic EVA layer III. Example 2:

[0030] The superphobic EVA film I used in the superphobic EVA layer I includes the following raw materials in parts by weight:

[0031] 60 parts of EVA (brand APPEEL 53007);

[0032] 30 parts of low surface energy EVA;

[0033] 2 parts polyethylene wax;

[0034] 1 part zinc stearate;

[0035] Among them, the preparation steps of low surface energy EVA are as follows:

[0036] Step 1: prepare monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane, and the preparation process is as follows:

[0037] Step S1: Octa-vinyl-POSS and octadecyldimethylsilane are used as raw materials, and an addition reaction occurs between the alkenyl functional group of octa-vinyl-POSS and the Si-H functional group of octadecyldimethylsilane, and the molar ratio of the octa-vinyl-POSS and octadecyldimethylsilane participating in the reaction is controlled to be 1:8.05 to generate octadecyl cage-type polysilsesquioxane, whose chemical formula is:

[0038] ;

[0039] Step S2: Octa-octadecyl cage-type polysilsesquioxane is used as a raw material and tetraethylammonium hydroxide is used as an opening reagent to synthesize hepta-octadecyl trisilanol-based incompletely condensed cage-type polysilsesquioxane by a vertex-opening method, the chemical structure of which is:

[0040] ;

[0041] Step S3: Using hepta(octadecyl)trisilanol-based incompletely condensed cage-type polysilsesquioxane as raw material and 7-octenyltrimethoxysilane as a capping agent, a monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane is synthesized by a vertex-capping method, and its chemical structure is:

[0042] ;

[0043] The specific experimental steps for preparing monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane are as follows:

[0044] Under nitrogen protection, 3.2 g of octavinyl-POSS (CAS No. 69655-76-1) and 30 mL of tetrahydrofuran were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, 70 mL of a tetrahydrofuran solution containing 12.5 g of octadecyldimethylsilane and 8 drops of Custer's catalyst were added to the three-necked flask. The temperature was raised to 75°C and stirred under reflux for 10 h. The mixture was cooled to room temperature and the tetrahydrofuran was removed by rotary evaporation. The mixture was washed with ethanol and deionized water in sequence and dried in vacuo to obtain octadecyl cage-type polysilsesquioxane.

[0045] 7.8 g of octadecyl cage-type polysilsesquioxane and 80 mL of tetrahydrofuran were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, 10 mL of a 40 wt% tetraethylammonium hydroxide aqueous solution was added to the three-necked flask, the temperature was raised to 70° C., and the mixture was stirred and refluxed for 5 h. The mixture was cooled to room temperature, the pH was adjusted to neutral using 0.1 mol / L dilute hydrochloric acid, the tetrahydrofuran was removed by rotary evaporation, and the mixture was dissolved in ether. The mixture was dried over anhydrous magnesium sulfate, filtered, and the ether was removed by rotary evaporation. The mixture was dried in vacuo to obtain a cage-type polysilsesquioxane containing incomplete condensation of heptadecyl trisilanol groups.

[0046] Under nitrogen protection, 4.6 g of hepta(octadecyl)trisilanol incomplete condensation cage-type polysilsesquioxane and 50 mL of tetrahydrofuran were added to a three-necked flask, stirred at room temperature until completely dissolved, and then placed in an ice-water bath. 0.5 mL of 7-octenyltrimethoxysilane was added dropwise to the three-necked flask, and the reaction was stirred in an ice-water bath for 1 h, after which the ice-water bath was removed. The reaction was continued by stirring at room temperature for 8 h, and the tetrahydrofuran was removed by rotary evaporation. The solution was concentrated to a saturated solution and dried in vacuo to obtain a monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane.

[0047] The nuclear magnetic resonance hydrogen spectrum of the monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane is characterized as follows: 1 H NMR (CDCl3, 400MHz) 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);

[0048] Step 2: preparing low surface energy EVA: using a free radical melt grafting method, generating free radicals through the action of a peroxide initiator during the EVA melt processing, utilizing the alkenyl functional group of the monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane to couple with the free radicals in the EVA to achieve graft modification treatment of the EVA, and extruding and granulating through a twin-screw extruder to prepare low surface energy EVA;

[0049] The peroxide initiator is one of dicumyl peroxide (DCP), tert-butyl hydroperoxide (TBHP), dibenzoyl peroxide (BPO), tert-butyl perbenzoate (TBPB), and lauroyl peroxide (LPO); in this embodiment, dicumyl peroxide (DCP) is selected;

[0050] The specific experimental steps for preparing low-surface-energy EVA are as follows: first, EVA (brand APPEEL 53007) was dried in a vacuum drying oven at 60°C for 12 hours. Then, 10 g of the dried EVA, 1.2 g of monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane, and 0.1 g of dicumyl peroxide initiator were added to a high-speed mixer and mixed evenly. The mixture was then melted, extruded, and granulated using a twin-screw extruder to obtain low-surface-energy EVA.

[0051] Among them, the process parameters of the twin-screw extruder are set as: preheating temperature 150°C, temperatures of zones 1-6 are 150°C, 155°C, 160°C, 170°C, 170°C, and 180°C respectively, rotation speed is 60r / min, and melting processing time is 20min. Example 3:

[0052] The preparation process of the superphobic EVA film I in Example 2 comprises the following steps:

[0053] Step 1: Prepare ingredients according to the formula of superphobic EVA film I, add all raw materials into a high-speed mixer and mix evenly, extrude granules through a twin-screw extruder, and vacuum dry at 80°C for 6 hours to obtain low surface energy EVA masterbatch I;

[0054] 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 400 r / min;

[0055] Step 2: Add low surface energy EVA masterbatch I into a single screw extruder film blowing machine, use the upward blowing method to blow the film, and then use the template hot pressing method to construct a rough structure on the film surface. Cut the film with an area of ​​25cm 2The 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 2 The double-layer Teflon cloth was hot-pressed at 100°C and 2 MPa for 3 minutes to ensure that the microarray structure was replicated on the film surface. After cooling and peeling, the superphobic EVA film I was obtained.

[0056] 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 blow-up ratio is 2.5. Example 4:

[0057] 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;

[0058] The preparation process of the superphobic EVA film II is the same as the preparation process of the superphobic EVA film I in Example 3. Embodiment 5:

[0059] 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;

[0060] 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. Example 6:

[0061] Preparation of liquid food packaging cover film: Using a high-speed solvent-free laminating machine, a PET layer, an Al layer, and a superphobic EVA layer are sequentially bonded together using an ethylene-acrylic acid copolymer (EAA) adhesive to obtain a liquid food packaging cover film;

[0062] The process parameters of the high-speed solvent-free laminating machine are set as follows: laminating speed 300 m / min, laminating temperature 40°C, cooling temperature 25°C, laminating pressure 0.45 MPa, and gluing pressure 0.5 MPa.

[0063] When the superphobic EVA layer is superphobic EVA layer I, the prepared film product is recorded as liquid food packaging cover film I;

[0064] When the superphobic EVA layer is superphobic EVA layer II, the prepared film product is recorded as liquid food packaging cover film II;

[0065] When the superphobic EVA layer is superphobic EVA layer III, the prepared film product is recorded as liquid food packaging cover film III.

[0066] Comparative Example:

[0067] The conventional EVA film used to prepare the conventional EVA layer has a raw material formula that differs from that of the superphobic EVA film I in Example 2 only in that EVA (brand APPEEL 53007) is used instead of the low surface energy EVA, and the preparation process thereof differs from that of the superphobic EVA film I in Example 3 only in that the template hot pressing process is not performed.

[0068] A conventional cover film is prepared, which differs from the liquid food packaging cover film I only in that a conventional EVA layer is used to replace the superphobic EVA layer I.

[0069] Performance testing:

[0070] (1) Superphobicity test: The superphobicity of liquid food (taking yogurt as an example) was analyzed by testing its residual rate on the cover film sample. The specific test steps are as follows: a circular cover film sample with a diameter of 10 cm (mass m0g) was fixed on a plywood, yogurt (Yili original fermented milk, mass Mg) was dropped on the EVA layer surface of the cover film sample, and the cover film sample was placed at a 45° angle to the horizontal plane. After the yogurt flowed down, it was left to stand for 30 seconds. The weight of the cover film sample at this time, m1g, was recorded, and the residual rate was calculated. The specific method is as follows:

[0071] Residual rate (%) = [(m1-m0) / M] × 100%;

[0072] The above experimental results are shown in Table 1 below;

[0073] Table 1 Performance test results of liquid food packaging cover film

[0074] Product Type Residual rate (%) Liquid food packaging cover film Ⅰ 3.5 Liquid food packaging cover film Ⅱ 5.8 Liquid food packaging cover film Ⅲ 3.2 Comparative Example 37.6

[0075] By analyzing the experimental results in Table 1, the following conclusions can be drawn: the liquid food packaging cover film product prepared by the present invention has achieved the beneficial technical effect of significantly reducing the amount of liquid food residue and exhibits excellent superphobic properties;

[0076] (2) Sealing strength test: The cover film sample was laminated with the PP cup body using an HSG-C heat sealer, with a sealing area of ​​15 cm × 1 cm, a heat sealing temperature of 160 °C, a heat sealing pressure of 0.1 MPa, and a heat sealing time of 2.0 s.

[0077] The sealing performance of heat-sealed samples was tested according to QB / T 2358-1998 "Test method for heat-sealed strength of plastic film packaging bags" at a test speed of 200 mm / min and a clamp spacing of 50 mm. The sealing strength of the samples was recorded.

[0078] (3) Easy-to-peel performance test: The cover film sample was laminated with the PP cup body using an HSG-C 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). The cover film sample was then peeled off from the PP cup body and the peeling marks were observed.

[0079] The above experimental results are shown in Table 2 below;

[0080] Table 2 Performance test results of liquid food packaging cover film II

[0081] Product Type Sealing strength (N / 15mm) Uncover the traces Liquid food packaging cover film Ⅰ 15.7 No delamination, smooth peeling marks, no drawing, no residue Liquid food packaging cover film Ⅱ 16.2 No delamination, smooth peeling marks, no drawing, no residue Liquid food packaging cover film Ⅲ 15.4 No delamination, smooth peeling marks, no drawing, no residue

[0082] By comprehensively analyzing the above experimental results, the following conclusions can be drawn:

[0083] The sealing strength of the liquid food packaging cover film prepared by the present invention is greater than the technical requirement of JB / T 9086-2007 "Plastic Bag Hot Press Sealing Machine" on sealing strength ≥15N (material thickness R, 0.08mm≤R<0.18mm), and the peeling mark after peeling off the PP cup body is smooth without delamination, drawing, residue and other undesirable phenomena, meeting the use requirements of the cover film, having practical application value, and being applicable to the field of viscous liquid food packaging.

Claims

1. A process for preparing a liquid food packaging cover 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: The low surface energy EVA and EVA are fed into a granulation device at a mass ratio of 1: (1.5-4) to prepare a masterbatch, the masterbatch is used to prepare a low surface energy EVA film by a blown film process, and a micron-scale rough structure is constructed on the low surface energy EVA film by a template hot pressing method to prepare 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 are composited to produce a liquid food packaging cover film.

2. The process for preparing a liquid food packaging cover film according to claim 1, characterized in that: The preparation method of the monoalkenyl hepta(octadecyl) cage-type polysilsesquioxane is as follows: Octave-vinyl-POSS and octadecyldimethylsilane are used as raw materials, and an addition reaction occurs between the alkenyl functional group of octavinyl-POSS and the Si-H functional group of octadecyldimethylsilane, and the molar ratio of the octavinyl-POSS to the octadecyldimethylsilane is controlled to be 1:(8.01-8.09) to generate octa(octadecyl) cage-type polysilsesquioxane. Octa-octadecyl caged polysilsesquioxane was used as raw material and tetraethylammonium hydroxide was used as opening agent to synthesize hepta-octadecyl trisilanol incompletely condensed caged polysilsesquioxane by the vertex-opening method. Monoalkenyl heptadecanyl cage polysilsesquioxane was synthesized by the vertex-capping method using heptadecanyl trisilanol incomplete condensation cage polysilsesquioxane as raw material and 7-octenyltrimethoxysilane as capping reagent.

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

4. The process for preparing a liquid food packaging cover 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 process for preparing a liquid food packaging cover film according to claim 1, characterized in that: The process equipment used in the film blowing process in step 3 is a single-screw extruder 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 process for preparing a liquid food packaging cover film according to claim 1, characterized in that: The process parameters of the template hot pressing method in step 3 are set as follows: temperature 90-110° C., pressure 1-3 MPa, and time 2-5 min.

7. The process for preparing a liquid food packaging cover film according to claim 1, characterized in that: The process parameters of the compounding process in step 4 are set as follows: 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 cover film prepared by the process according to any one of claims 1 to 7, characterized in that: The liquid food packaging cover film consists 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 cover film according to claim 8, characterized in that: 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.

10. The liquid food packaging cover film according to claim 9, characterized in that: The composite auxiliary agent includes 0.5-3 parts by weight of polyethylene wax and 0.5-3 parts by weight of zinc stearate.

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