EVOH / polyamide recycled composite film containing recycled materials and preparation method thereof

Abstract

The present invention belongs to the technical field of film packaging, and specifically discloses an EVOH / polyamide recycled composite film containing recycled materials and a preparation method thereof, wherein the EVOH / polyamide recycled composite film includes a five-layer structure, which is, from top to bottom, a first polyamide surface layer, a first polyamide recycled layer, an EVOH barrier layer, a second polyamide recycled layer, and a second polyamide surface layer; wherein the components of the first polyamide surface layer and the second polyamide surface layer include 95-97wt% of polyamide and 3-5wt% of polyamide anti-sticking masterbatch; the components of the first polyamide recycled layer and the second polyamide recycled layer include 60-90wt% of polyamide and 10-40wt% of EVOH / polyamide recycled material; and the component of the EVOH barrier layer includes 100wt% of EVOH resin. The present invention can receive polyamide / EVOH recycled material generated during the film production process without affecting the barrier, surface printing and compounding of the film.

Description

Technical Field

[0001] The invention belongs to the technical field of film packaging, and particularly relates to an EVOH / polyamide recycled composite film containing recycled materials and a preparation method thereof. Background Art

[0002] Ethylene-vinyl alcohol copolymer (EVOH) is a new polymer synthetic material that combines the processability of ethylene polymers with the gas barrier properties of vinyl alcohol polymers. It has excellent gas barrier, water resistance, and oil resistance. In the 1950s, DuPont in the United States first produced EVOH resin by copolymerizing ethylene with vinyl acetate (VAc) and then alcoholyzing it. The oxygen permeability of polyvinyl alcohol in dry state is less than 10cc / m -2 ﹒ d﹒ 0.1Mpa, a typical high-barrier material. However, EVOH is difficult to process thermoplastically due to the close proximity between its decomposition point and melting point: its melting point is 220-240°C, while its decomposition temperature is around 200°C. This means it decomposes before melting, carbonizing and turning yellow. Commercial EVOH is typically treated with lubricants during the polymerization process to raise its melting point to around 160-180°C, thus meeting thermoplastic processing requirements. However, single-layer EVOH films have poor mechanical properties, making them difficult to meet the requirements of packaging film applications.

[0003] BOPA film is made from polyamide 6 (nylon 6). Compared to other films, BOPA film has higher strength than PE and BOPP films. Polyamide also has excellent compatibility with ethylene-vinyl alcohol copolymers. This has led to the emergence of PA / EVOH / PA biaxially oriented coextruded film. PA / EVOH / PA biaxially oriented coextruded film is produced by melting the film using different extruders at their respective processing temperatures. After a brief convergence in a T-die, the film is melt-bonded, rapidly cooled, and then biaxially stretched. This production process inevitably produces scrap and waste film. The melting point of polyamide 6 is around 220°C, and processing temperatures typically reach 250°C. EVOH easily decomposes and carbonizes at these processing temperatures, making it difficult to recycle scrap and waste film back into the PA / EVOH / PA biaxially oriented coextruded film, significantly increasing costs. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the prior art and provide an EVOH / polyamide recycled composite film containing recycled materials and a preparation method thereof.

[0005] In order to achieve the above objectives, the technical solution of the present invention is: an EVOH / polyamide recycled composite film containing recycled materials, including a five-layer structure, from top to bottom, a first polyamide surface layer, a first polyamide recycled layer, an EVOH barrier layer, a second polyamide recycled layer, and a second polyamide surface layer; wherein, the components of the first polyamide surface layer and the second polyamide surface layer include 95-97wt% of polyamide and 3-5wt% of polyamide anti-sticking masterbatch; the components of the first polyamide recycled layer and the second polyamide recycled layer include 60-90wt% of polyamide and 10-40wt% of EVOH / polyamide recycled materials; the components of the EVOH barrier layer include 100wt% EVOH resin.

[0006] In a preferred embodiment of the present invention, the polyamide is polyamide 6.

[0007] In a preferred embodiment of the present invention, the components of the EVOH / polyamide recycled material include 97-98.8wt% of EVOH / polyamide recycled composite film crushed material, 1-2wt% of lubricant, 0.1-0.5wt% of hydroxyl end-capping agent and 0.1-0.5wt% of antioxidant.

[0008] Further preferably, the EVOH content in the EVOH / polyamide recycled composite film crushed material is ≤30 wt%.

[0009] Further preferably, the lubricant is one or a combination of dicarboxylic acid esters, fatty acid esters of glycerol and other short-chain alcohols, oligomeric fatty acid esters, polar polyolefin waxes and their derivatives, non-polar polyolefin waxes, natural and synthetic paraffin waxes.

[0010] More preferably, the hydroxyl end-capping agent is one or a combination of fatty acid, fatty acid amide, montanic acid and metal salts thereof.

[0011] More preferably, the antioxidant is one or a combination of phenolic antioxidants, organophosphorus antioxidants and sulfate antioxidants.

[0012] In a preferred embodiment of the present invention, the total thickness of the EVOH / polyamide recycled composite film layer is 15-35 μm, the thickness of the EVOH barrier layer is 3-6 μm, the thickness of the first polyamide surface layer and the second polyamide surface layer is 1-2 μm, and the thickness of the first polyamide recycled layer and the second polyamide recycled layer is 2.5-15 μm.

[0013] A method for preparing an EVOH / polyamide recycled composite film containing recycled materials comprises the following steps:

[0014] (1) Preparation of EVOH / polyamide recycled material: The scraps and waste films generated during the production of EVOH / polyamide recycled composite films are crushed to obtain crushed EVOH / polyamide recycled composite film, which is then mixed evenly with lubricant, hydroxyl end-capping agent, and antioxidant according to the component ratio, and granulated by a twin-screw extruder to obtain EVOH / polyamide recycled material;

[0015] (2) Preparation of each film layer of the EVOH / polyamide recycled composite film: polyamide and polyamide anti-sticking masterbatch are fed into an extruder according to a component ratio to prepare a first polyamide surface layer and a second polyamide surface layer, respectively; the EVOH / polyamide recycled material and polyamide obtained in step (1) are fed into an extruder according to a component ratio to prepare a first polyamide recycled layer and a second polyamide recycled layer, respectively; EVOH resin is fed into an extruder to prepare an EVOH barrier layer;

[0016] (3) Preparation of EVOH / polyamide recycled composite film: The film layers prepared in step (2) are rapidly cooled, and then humidified, cleaned, and the surface moisture is removed, and then biaxially stretched using the LISIM synchronous stretching method to obtain the EVOH / polyamide recycled composite film.

[0017] In a preferred embodiment of the present invention, the temperature of the twin-screw extruder in step (1) is controlled between 165-185° C., and the rotation speed is controlled between 150-300 r / min.

[0018] In a preferred embodiment of the present invention, in step (2), the extruder temperature of the first polyamide surface layer and the second polyamide surface layer and the temperature of the T-die thereof are controlled between 210-250°C, the extruder temperature of the first polyamide regenerated layer and the second polyamide regenerated layer and the temperature of the T-die thereof are controlled between 180-220°C, and the extruder temperature of the EVOH barrier layer and the temperature of the T-die thereof are controlled between 160-190°C.

[0019] In a preferred embodiment of the present invention, in step (3), the humidity adjustment temperature is 60-80°C, the stretching temperature is 160-190°C, the setting temperature is 180-210°C, and the stretching ratio is 3.0*3.0-3.8*3.8.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. A high content of lubricant is added to the EVOH / polyamide recycled material of the present invention to prevent the EVOH from melting, decomposing, carbonizing and yellowing due to excessively high processing temperature during the regeneration and backfilling process; a hydroxyl end-capping agent is added to cap the hydroxyl groups of EVOH and the terminal amino and carboxyl groups of polyamide in a molten state to avoid cross-linking of the hydroxyl groups with the terminal amino and carboxyl groups by hot melt reaction; and an antioxidant is added to prevent the EVOH and polyamide from being thermally degraded during multiple processing steps, thereby affecting the processing and subsequent application of the film.

[0022] 2. The present invention can receive polyamide / EVOH recycled materials generated during the film production process without affecting the barrier properties, surface printing and lamination of the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the layer structure of the EVOH / polyamide recycled composite film of Example 1-4;

[0024] Among them, 10 is the first polyamide surface layer, 20 is the first polyamide recycled layer, 30 is the EVOH barrier layer, 40 is the second polyamide recycled layer, and 50 is the second polyamide surface layer. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is described in more detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0026] The terms "upper" and "lower" are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, they should not be understood as limiting the present invention.

[0027] It should be noted that if no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in this field or the product instructions shall be followed. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0028] Example 1

[0029] An EVOH / polyamide recycled composite film containing recycled materials, comprising a five-layer structure, from top to bottom, a first polyamide surface layer 10, a first polyamide recycled layer 20, an EVOH barrier layer 30, a second polyamide recycled layer 40, and a second polyamide surface layer 50; wherein the components of the first polyamide surface layer 10 and the second polyamide surface layer 50 include polyamide 6 96wt% and polyamide anti-sticking masterbatch 4wt%; the components of the first polyamide recycled layer 20 and the second polyamide recycled 40 include polyamide 670wt% and EVOH / polyamide recycled material 30wt%; the components of the EVOH barrier layer 30 include 100wt% EVOH resin; the components of the EVOH / polyamide recycled material include EVOH / polyamide recycled composite film crushed material (wherein the EVOH content is 26.67wt%) 98wt%, polyethylene wax 1.5wt%, stearic acid 0.3wt% and antioxidant 1680.2wt%, including EVOH content in the EVOH / polyamide recycled composite film crushed material is 26.67wt%.

[0030] Prepared by the following method, comprising the following steps:

[0031] (1) Preparation of EVOH / polyamide recycled material: The scraps and waste films generated during the production of EVOH / polyamide recycled composite films are crushed to obtain crushed EVOH / polyamide recycled composite film, which is then mixed evenly with lubricant, hydroxyl end-capping agent, and antioxidant according to the component ratio, and granulated by a twin-screw extruder to obtain EVOH / polyamide recycled material;

[0032] (2) Preparation of each film layer of EVOH / polyamide recycled composite film: polyamide and polyamide anti-sticking masterbatch are put into an extruder according to the component ratio to prepare a first polyamide surface layer and a second polyamide surface layer respectively; the EVOH / polyamide recycled material and polyamide obtained in step (1) are put into an extruder according to the component ratio to prepare a first polyamide recycled layer and a second polyamide recycled layer respectively; EVOH resin is put into an extruder to prepare an EVOH barrier layer; wherein the extruder temperature of the first polyamide surface layer and the second polyamide surface layer and the temperature of the T-die thereof are controlled between 210-250°C, the extruder temperature of the first polyamide recycled layer and the second polyamide recycled layer and the temperature of the T-die thereof are controlled between 180-220°C, and the extruder temperature of the EVOH barrier layer and the temperature of the T-die thereof are controlled between 160-190°C;

[0033] (3) Preparation of EVOH / polyamide recycled composite film: The film layers prepared in step (2) were rapidly cooled, and then humidified and cleaned in a 60°C hot steamer. After removing the surface moisture with hot air, the film layers were biaxially stretched using the LISIM synchronous stretching method. The stretching temperature was 185°C, the setting temperature was 205°C, and the stretching ratio was 3.0*3.1. EVOH / polyamide recycled composite film was obtained.

[0034] Example 2

[0035] A recycled EVOH / polyamide composite film comprising recycled materials comprises a five-layer structure, comprising, from top to bottom, a first polyamide surface layer 10, a first polyamide recycled layer 20, an EVOH barrier layer 30, a second polyamide recycled layer 40, and a second polyamide surface layer 50. The first polyamide surface layer 10 and the second polyamide surface layer 50 are composed of 95 wt% polyamide 6 and 5 wt% polyamide anti-sticking masterbatch; the first polyamide recycled layer 20 and the second polyamide recycled layer 40 are composed of 60 wt% polyamide and 40 wt% EVOH / polyamide recycled materials; the EVOH barrier layer 30 is composed of 100 wt% EVOH resin; and the recycled materials of the EVOH / polyamide composite film are composed of 97 wt% EVOH / polyamide composite film crushed material (including 26.67 wt% EVOH), 2 wt% polypropylene wax, 0.5 wt% erucamide, and 0.5 wt% antioxidant 10. The preparation method is the same as in Example 1.

[0036] Example 3

[0037] A recycled EVOH / polyamide composite film comprises a five-layer structure, comprising, from top to bottom, a first polyamide surface layer 10, a first polyamide recycled layer 20, an EVOH barrier layer 30, a second polyamide recycled layer 40, and a second polyamide surface layer 50. The first polyamide surface layer 10 and the second polyamide surface layer 50 are composed of 97 wt% polyamide 6 and 3 wt% polyamide anti-sticking masterbatch; the first polyamide recycled layer 20 and the second polyamide recycled layer 40 are composed of 90 wt% polyamide 6 and 10 wt% EVOH / polyamide recycled material; the EVOH barrier layer 30 is composed of 100 wt% EVOH resin; and the recycled material of the EVOH / polyamide composite film comprises 97-98.8 wt% EVOH / polyamide composite film crushed material (including 26.67 wt% EVOH), 1 wt% paraffin, 0.1 wt% montanic acid, and 0.1 wt% antioxidant 264. The preparation method is the same as in Example 1.

[0038] Comparative Example 1

[0039] Commercially available 15μm biaxially oriented EVOH / nylon co-extruded film.

[0040] Comparative Example 2

[0041] A recycled EVOH / polyamide composite film comprises a five-layer structure, comprising, from top to bottom, a first polyamide surface layer 10, a first polyamide recycled layer 20, an EVOH barrier layer 30, a second polyamide recycled layer 40, and a second polyamide surface layer 50. The first polyamide surface layer 10 and the second polyamide surface layer 50 are composed of 96% polyamide and 4% polyamide anti-sticking masterbatch; the first polyamide recycled layer and the second polyamide recycled layer are composed of 70% polyamide 6 and 30% EVOH / polyamide recycled material; the EVOH barrier layer 30 is composed of 100% EVOH resin; and the recycled material of the EVOH / polyamide composite film comprises 100% EVOH / polyamide composite film crushed material (including 26.67% EVOH). The preparation method is the same as in Example 1.

[0042] The films of Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests, and the test standards were as follows:

[0043] (1) Thickness: GB / T 20220-2006 Average thickness of plastic film and sheet samples, average thickness of rolls and unit mass area;

[0044] (2) Surface tension: Surface tension of films was tested according to GB / T 14216-2008;

[0045] (3) Hygroscopic elongation: The film size is initially L0. After being placed in a 23°C / 50% humidity environment for 48 hours, the size becomes L1. The film size unchanged rate is measured as [(L1-L0) / L0]*100%;

[0046] (4) Thermal shrinkage: GB / T12027-2004 Test method for dimensional change of plastic film and sheeting upon heating;

[0047] (5) Oxygen barrier: Test according to GB / T19789-2005 “Plastic film and sheeting for packaging materials - Oxygen permeability test - Coulometric test method”.

[0048] (6) Nucleated crystal points: Use a 10cm*10cm thick piece and count the number of points with an outer diameter greater than 1mm under the oblique illumination of a flashlight.

[0049] The film performance test evaluation results are shown in Table 1:

[0050] Table 1 Test results of film properties of Examples 1-3 and Comparative Examples 1-2

[0051]

[0052] As can be seen from Table 1, the EVOH / polyamide recycled composite films prepared in Examples 1-3 have good oxygen barrier properties, and their dimensional stability and apparent quality are comparable to those of the film in Comparative Example 1 without adding recycled material.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An EVOH / polyamide recycled composite film containing recycled materials, characterized in that: The invention comprises a five-layer structure, which comprises, from top to bottom, a first polyamide surface layer, a first polyamide recycled layer, an EVOH barrier layer, a second polyamide recycled layer, and a second polyamide surface layer; wherein, the components of the first polyamide surface layer and the second polyamide surface layer include 95-97 wt% of polyamide and 3-5 wt% of polyamide anti-sticking masterbatch; the components of the first polyamide recycled layer and the second polyamide recycled layer include 60-90 wt% of polyamide and 10-40 wt% of EVOH / polyamide recycled material; the components of the EVOH barrier layer include 100 wt% EVOH resin; the components of the EVOH / polyamide recycled material include 97-98.8 wt% of EVOH / polyamide recycled composite film crushed material, 1-2 wt% of lubricant, 0.1-0.5 wt% of hydroxyl end-capping agent and 0.1-0.5 wt% of antioxidant. wt%; the lubricant is one or more combinations of dicarboxylic acid esters, fatty acid esters of glycerol and other short-chain alcohols, oligomeric fatty acid esters, polar polyolefin waxes and their derivatives, non-polar polyolefin waxes, natural and synthetic paraffin waxes; the hydroxyl end-capping agent is one or more combinations of fatty acids, fatty acid amides and montanic acid and their metal salts; the antioxidant is one or more combinations of phenolic antioxidants, organophosphorus antioxidants and sulfate antioxidants.

2. The EVOH / polyamide recycled composite film containing recycled materials according to claim 1, characterized in that: The polyamide is polyamide 6.

3. The EVOH / polyamide recycled composite film containing recycled materials according to claim 1, characterized in that: The EVOH content in the EVOH / polyamide recycled composite film crushed material is ≤30 wt%.

4. The EVOH / polyamide recycled composite film containing recycled materials according to claim 1, characterized in that: The total thickness of the EVOH / polyamide recycled composite film layer is 15-35 μm, the thickness of the EVOH barrier layer is 3-6 μm, the thickness of the first polyamide surface layer and the second polyamide surface layer is 1-2 μm, and the thickness of the first polyamide recycled layer and the second polyamide recycled layer is 2.5-15 μm.

5. A method for preparing an EVOH / polyamide recycled composite film containing recycled materials according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Preparation of EVOH / polyamide recycled materials: The scraps and waste films generated during the production of EVOH / polyamide recycled composite films are crushed to obtain EVOH / polyamide recycled composite film crushed materials, which are then mixed evenly with lubricants, hydroxyl end-capping agents, and antioxidants according to the component ratios, and granulated using a twin-screw extruder to obtain EVOH / polyamide recycled materials; (2) Preparation of each film layer of EVOH / polyamide recycled composite film: polyamide and polyamide anti-sticking masterbatch are fed into an extruder according to a component ratio to prepare a first polyamide surface layer and a second polyamide surface layer respectively; the EVOH / polyamide recycled material and polyamide obtained in step (1) are fed into an extruder according to a component ratio to prepare a first polyamide recycled layer and a second polyamide recycled layer respectively; EVOH resin is fed into an extruder to prepare an EVOH barrier layer; (3) Preparation of EVOH / polyamide recycled composite film: The film layers prepared in step (2) are rapidly cooled, and then humidified, cleaned, and the surface moisture is removed, and then biaxially stretched using the LISIM synchronous stretching method to obtain the EVOH / polyamide recycled composite film.

6. The method for preparing the EVOH / polyamide recycled composite film containing recycled materials according to claim 5, characterized in that: In the step (1), the temperature of the twin-screw extruder is controlled between 165-185° C., and the rotation speed is controlled between 150-300 r / min.

7. The method for preparing the EVOH / polyamide recycled composite film containing recycled materials according to claim 5, characterized in that: In the step (2), the extruder temperature of the first polyamide surface layer and the second polyamide surface layer and the temperature of the T-die thereof are controlled between 210-250° C., the extruder temperature of the first polyamide regenerated layer and the second polyamide regenerated layer and the temperature of the T-die thereof are controlled between 180-220° C., and the extruder temperature of the EVOH barrier layer and the temperature of the T-die thereof are controlled between 160-190° C.

8. The method for preparing the EVOH / polyamide recycled composite film containing recycled materials according to claim 5, characterized in that: In the step (3), the humidity adjustment temperature is 60-80°C, the stretching temperature is 160-190°C, the shaping temperature is 180-210°C, and the stretching ratio is 3.0*3.0-3.8*3.8.

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