A high-strength, high-impact, high-barrier multilayer EVOH composite sheet and a preparation method and application thereof

Abstract

This invention relates to the field of polymer sheets, and discloses a high-strength, high-impact, and high-barrier multilayer EVOH composite sheet, its preparation method, and its applications. The multilayer EVOH composite sheet comprises two outer layers A and multiple stacked core layers B located between the two outer layers A, having AB1B2…B m Structure A; m is an integer not less than 2; the two outer layers A are the same or different, each containing a polyolefin composition A; the core layers B each contain composition B, which are the same or different, and each contains EVOH; the preparation process of the core layer B includes a stretching step, with a stretching ratio of 1-15 times. This multilayer EVOH composite sheet not only has high gas barrier properties, but also high tensile strength and impact strength. Furthermore, this multilayer EVOH composite sheet also has high peel strength.

Description

Technical Field

[0001] This invention relates to the field of polymer sheets, and more specifically, to a high-strength, high-impact, high-barrier multilayer EVOH composite sheet, its preparation method, and its applications. Background Technology

[0002] Ethylene-vinyl alcohol copolymer (EVOH) is one of the best gas barrier resins among synthetic resins to date. In addition to its excellent gas barrier properties, EVOH also exhibits good oil and organic solvent resistance and printability. Due to its thermal stability resulting from its bond with ethylene, multilayer containers containing EVOH barrier layers are completely reusable. These characteristics allow EVOH-barrier plastic containers to replace many glass and metal containers in food packaging.

[0003] With the implementation of plastic reduction policies both domestically and internationally in recent years, there is a growing demand for increased strength to reduce packaging material thickness (weight) and improved barrier properties to extend shelf life. Therefore, a higher strength and better barrier properties of EVOH material are needed. Patent document CN109705248A utilizes a blend of Group IIA metals with EVOH to obtain a composition with higher glass transition temperature, mechanical properties, and barrier properties. Patent document CN113698695A discloses a composition consisting of EVOH, manganese, boron, alkali metals, etc., which, by controlling the content of each component, strengthens intermolecular hydrogen bonds, ionic bonds, and other interactions, ultimately enhancing the gas barrier properties and gelation behavior of the EVOH composition. Patent document CN111993732A discloses a high-flatness, high-barrier, high-strength, retortable stretch film. From top to bottom, it consists of an outer layer, a first outer layer, a second outer layer, a first adhesive layer, a first PA layer, a high-barrier layer, a second PA layer, a second adhesive layer, a second heat-sealing layer, a first heat-sealing layer, and a heat-sealing layer. The outer layer, the first outer layer, and the second outer layer are all made of PP. The first adhesive layer and the second adhesive layer are both made of maleic anhydride-modified polyethylene resin. The first PA layer and the second PA layer are both made of PA. The high-barrier layer is made of EVOH. The second heat-sealing layer, the first heat-sealing layer, and the heat-sealing layer are all made of PE. The product structure is PP / PP / PP / TIE / PA / EVOH / PA / TIE / PE / PE / PE. In the product structure, EVOH provides high barrier function, and nylon provides high strength function.

[0004] From the perspective of existing technology, most methods to improve the barrier properties of EVOH are blending modification, while methods to improve the mechanical strength of EVOH involve introducing other materials such as nylon and polyamide for multilayer composite. These methods have relatively complex production processes and have limited improvement on the strength, barrier properties and other performance of EVOH materials.

[0005] Therefore, how to provide a high-strength, high-impact, and high-barrier EVOH material remains a technical problem that needs to be solved in this field. Summary of the Invention

[0006] To further address the technical issues of barrier properties and mechanical strength of EVOH materials, the present invention aims to provide a high-strength, high-impact, and high-barrier multilayer EVOH composite sheet, its preparation method, and its application. This multilayer EVOH composite sheet not only possesses high gas barrier properties but also high tensile strength and impact strength. Furthermore, it also exhibits high peel strength.

[0007] In a first aspect, the object of the present invention is to provide a multilayer EVOH composite sheet comprising two outer layers A and a plurality of stacked core layers B located between the two outer layers A, having AB1B2…B m Structure A; m is an integer not less than 2; the two outer layers A are the same or different, each containing a polyolefin composition A; the core layers B each contain composition B, the compositions B are the same or different, each containing EVOH; the preparation process of the core layer B includes a stretching step, with a stretching ratio of 1-15 times.

[0008] According to the present invention, the melting point of the composition B can be selected within a wide range. In a preferred embodiment of the present invention, the melting point of each composition B is 150-210°C, preferably 160-200°C.

[0009] According to a preferred embodiment of the present invention, the core layer B contains only EVOH, that is, composition B is EVOH.

[0010] According to the present invention, the selection range of EVOH is relatively wide. In a preferred embodiment of the present invention, the ethylene content in the EVOH is 15-50 mol%, preferably 21-49 mol%.

[0011] In a preferred embodiment of the present invention, the melt flow rate of the EVOH at 190°C and 2.16 kg load is 1-50 g / 10 min, preferably 1-20 g / 10 min.

[0012] According to the present invention, the number of layers m of the core layer B can be selected from a wide range. Preferably, m is 2-200, and more preferably 4-100.

[0013] In a preferred embodiment of the present invention, the multilayer EVOH composite sheet has AB1B2…B i …B n …B i…B2B1A layered structure, where i and n are both integers not less than 2, and i≤n, n is 2-100, preferably 2-50.

[0014] According to the present invention, the multilayer EVOH composite sheet has AB1B2…B m Structure A, B1B2…B m The melting points can be the same or different, and the technical effects of this invention can be achieved in either case.

[0015] Through research, the inventors of this invention unexpectedly discovered that when B1B2…B m When the melting points are the same or arranged according to a specific melting point gradient, the resulting multilayer EVOH composite sheets are superior to those of B1B2…B m Arrangement that does not follow a specific melting point gradient pattern yields superior technical results. Preferably, composition B... i Melting point ≥ composition B i+1 Its melting point.

[0016] More preferably, composition B i Melting point > Composition B i+1 The melting point of B1B2……B m When the melting points are arranged according to a specific melting point gradient, compared to B1B2……B m Having the same melting point, it offers further and superior technical effects. In particular, if the EVOH layer undergoes the specific melting point gradient lamination hot-pressing treatment of this invention, the peel strength between the EVOH layers can be significantly improved. Even more preferably, composition B... i With composition B i+1 The melting point difference is 5-15℃.

[0017] According to the present invention, the stretch ratio can be selected within a wide range. In a preferred embodiment of the present invention, the stretch ratio is 2-15 times.

[0018] According to the present invention, preferably, the stretching method is a combination of one or more of the following: free stretching, solid-phase stretching, and multi-stage stretching.

[0019] In a more preferred embodiment of the present invention, the stretching conditions in the preparation step of the core layer B include: the core layer B is prepared by extruding EVOH, casting or calendering, and stretching.

[0020] More preferably, the stretching conditions include: a stretching temperature of 140-185°C, preferably 150-175°C; and a stretching ratio of 2-15 times.

[0021] This invention does not limit the thickness of the high-strength, high-impact, and high-barrier composite sheet, and it can be selected within a wide range according to its actual application field. In a preferred embodiment of this invention, the thickness of the multilayer EVOH composite sheet is 5-1000 μm, preferably 5-500 μm, and more preferably 5-300 μm.

[0022] According to the present invention, the total thickness of all core layers B can be selected within a wide range as a percentage of the thickness of the multilayer EVOH composite sheet. In a preferred embodiment of the present invention, taking the total thickness of the multilayer EVOH composite sheet as 100%, the total thickness of all core layers B accounts for 10%-90% of the total thickness of the multilayer EVOH composite sheet.

[0023] The thickness of the outer layer A on both sides of the core layer B can be the same or different, preferably the same.

[0024] According to the present invention, the thickness of layer A and layer B can be controlled by the extruder melt pump during the processing.

[0025] According to the present invention, the placement angle of the core layer B can be selected within a wide range. In a preferred embodiment of the present invention, the core layer B is stacked from top to bottom in a 0-90° interval between the warp and the warp.

[0026] The outer layer A mainly serves to protect the core layer BB. Because EVOH is relatively easy to absorb moisture, the outer composite layer A can effectively improve the service life. The material selection of layer A in this invention is not strictly limited. According to this invention, the two outer layers A may be the same or different, each containing a polyolefin composition A. In a preferred embodiment of this invention, the polyolefin composition A contains polyolefin a and thermal bonding enhancer b.

[0027] According to the present invention, the contents of polyolefin a and thermal bonding reinforcing agent b can be selected within a wide range. In a preferred embodiment of the present invention, the total weight of the polyolefin composition A is 100 wt%, and the polyolefin composition A contains 70-99 wt% polyolefin a and 1-30 wt% thermal bonding reinforcing agent b; preferably, the polyolefin composition A comprises 80-99 wt% polyolefin a and 1-20 wt% thermal bonding reinforcing agent b.

[0028] According to the present invention, polyolefin a can be selected from a wide range of materials. In a preferred embodiment of the present invention, the polyolefin a is selected from one or more of polypropylene, polyethylene, and ethylene-vinyl acetate.

[0029] According to the present invention, the thermal bonding reinforcing agent b can be selected from a wide range. In a preferred embodiment of the present invention, the thermal bonding reinforcing agent b is selected from one or more of the following: anhydride-modified polypropylene, anhydride-modified polyethylene, anhydride-modified ethylene-vinyl acetate, glycidyl methacrylate (GMA)-modified polypropylene, glycidyl methacrylate-modified polyethylene (i.e., GMA-modified polyethylene), glycidyl methacrylate-modified ethylene-vinyl acetate (i.e., GMA-modified ethylene-vinyl acetate), and maleic anhydride copolymer.

[0030] According to the present invention, the high-strength, high-impact, and high-barrier multilayer EVOH composite sheet can be prepared by various methods. In a preferred embodiment of the present invention, the multilayer EVOH composite sheet is prepared by sequentially stacking an outer layer A, multiple core layers B, and another outer layer A, and then laminating them.

[0031] In a more preferred embodiment of the present invention, the lamination method is hot pressing followed by cooling and shaping; more preferably, the multilayer EVOH composite sheet is prepared by extruding, casting or calendering, stretching and slitting the raw materials forming the outer layer A and the raw materials forming the core layer B respectively to obtain the corresponding sheet, and then stacking, hot pressing and cooling the corresponding sheet according to the corresponding structural sequence.

[0032] The multilayer EVOH composite sheet of the present invention has at least one of the following characteristics:

[0033] The tensile strength of the multilayer EVOH composite sheet is 50-350 MPa, preferably 150-350 MPa;

[0034] The drop hammer impact strength of the multilayer EVOH composite sheet is 50-200J, preferably 100-200J;

[0035] The interlayer peel strength of the multilayer EVOH composite sheet is 1-2 N / mm, preferably 1.2-2 N / mm;

[0036] The oxygen permeability of the multilayer EVOH composite sheet is 0.1-20*10. -3 cm 3 / m 2 • 24h, preferably 0.1-10*10 -3 cm 3 / m 2 ·24h.

[0037] All parameters were obtained by directly testing the composite sheets in the corresponding embodiments and comparative examples according to the corresponding standards.

[0038] The methods for detecting the above parameters include, but are not limited to, the methods described in the specific embodiments of this invention.

[0039] The second aspect of the present invention is to provide a method for preparing the multilayer EVOH composite sheet described in the first aspect, comprising preparing the raw materials for forming the outer layer A and the raw materials for forming the core layer B into corresponding sheets A and sheet B, respectively, and then stacking the corresponding sheets in a corresponding structural order, hot pressing, and cooling for shaping; wherein the preparation process of sheet B includes a stretching step, with a stretching ratio of 1-15 times.

[0040] In a preferred embodiment of the present invention, the step of preparing sheet A includes: melting and blending the raw materials forming the outer layer A, preferably by extrusion molding, and then casting or calendering, stretching, and slitting to obtain sheet A; the conditions and equipment for melting and blending the raw materials forming the outer layer A are the same as those for melting and blending polyolefins in the prior art, and preferably, the equipment is a twin-screw extruder.

[0041] The extrusion molding and casting temperature range of the outer layer A of the present invention is relatively wide. In a preferred embodiment of the present invention, the temperatures of co-extrusion molding and casting are independently selected from 200-250°C; the calendering temperature is 50-70°C.

[0042] The range of conditions for stretching the outer layer A is relatively wide. In a preferred embodiment of the present invention, the stretching conditions include: the stretching method is free stretching, and / or solid-phase stretching, and / or multi-stage stretching, preferably solid-phase stretching, and / or multi-stage stretching, more preferably multi-stage stretching; the stretching temperature is 90-165℃, preferably 90-140℃; the stretching ratio is preferably 1-20 times, preferably 2-15 times.

[0043] In a preferred embodiment of the present invention, the step of preparing the core layer B includes: extruding the raw material to form the core layer B, and then casting or calendering, stretching, and slitting to obtain sheet B.

[0044] In a more preferred embodiment of the present invention, the preparation conditions of sheet B include: the extrusion molding temperature and the casting temperature are independently selected from 200-260°C; the calendering temperature is 50-90°C.

[0045] According to the present invention, the preparation process of the core layer B includes a stretching step, with a stretching ratio of 1-15 times. For the stretching method, various methods can be selected. Preferably, the stretching method of sheet B is a combination of one or more of free stretching, solid-state stretching, and multi-stage stretching; more preferably, the stretching method is a combination of one or two of solid-state stretching and multi-stage stretching. The inventors have found that solid-state stretching, in addition to further improving mechanical strength, also helps to further improve barrier properties.

[0046] The stretching conditions of sheet B can be selected within a wide range. Preferably, the stretching temperature is 140-185℃, more preferably 150-175℃; the stretching ratio is 1-15 times, more preferably 2-15 times.

[0047] In a preferred embodiment of the present invention, the stacking method includes: the sheet A and sheet B are stacked sequentially from top to bottom with the warp direction at an angle of 0-90° between them.

[0048] The inventors have discovered that EVOH exhibits significantly improved mechanical strength and barrier properties after tensile reinforcement. After multilayer EVOH films are stacked, their respective barrier properties are maintained in directions perpendicular to the film. In directions parallel to the film, due to the 0-90° angle between the warp and weft directions and the gradient of melting points, the multilayer EVOH films can be easily bonded together via hot pressing. This results in a substantial improvement in the tensile strength, impact strength, peel strength, and other mechanical properties of the multilayer EVOH.

[0049] In a preferred embodiment of the present invention, the hot pressing temperature is 135-190°C, preferably 150-190°C.

[0050] In a preferred embodiment of the present invention, the hot pressing pressure is 2-10 MPa.

[0051] In a preferred embodiment of the present invention, the preheating time is 5-600s, and / or the hot pressing time is 1-600s, preferably 10-500s.

[0052] In a preferred embodiment of the present invention, the cooling and shaping conditions include: a cooling pressure of 2-8 MPa and / or a cooling time of 30-700 s.

[0053] In a more preferred embodiment of the present invention, the hot pressing conditions include: the hot pressing temperature is 135-190°C, preferably 150-190°C; and / or, the hot pressing pressure is 2-10 MPa; and / or, the preheating time is 5-600 s, and / or, the hot pressing time is 1-600 s, preferably 10-500 s; and / or, the cooling and shaping conditions include: the cooling pressure is 2-8 MPa, and / or, the cooling time is 30-700 s.

[0054] Thirdly, the purpose of this invention is to provide an application of the multilayer EVOH composite sheet described in the first aspect or the multilayer EVOH composite sheet obtained by the preparation method described in the second aspect in the fields of packaging, mechanical parts, and industrial and agricultural film materials.

[0055] When the composite sheet of the present invention is used in film packaging, it can be further processed, such as stamping, vacuum forming, etc. The composite sheet of the present invention can be subjected to secondary forming processing according to application requirements.

[0056] As mentioned earlier, while the current gas barrier properties and strength of EVOH are sufficient for current applications, these fundamental properties need further improvement as people's living standards improve. Conventionally, increasing the thickness of EVOH can improve gas barrier properties, but the increase in tensile strength and impact strength is minimal. In particular, current packaging applications generally require relatively thin packaging materials, and increasing the thickness of EVOH to enhance gas barrier properties contradicts the principle of reducing thickness. Furthermore, conventional methods of multi-layering EVOH often result in multi-layered composites that are prone to peeling, introducing new defects into the composite material.

[0057] The multilayer EVOH composite sheet of this invention controls the aggregated structure of the material by physically altering the molding and processing conditions (the preparation process of the core layer B includes a stretching step with a stretching ratio of 1-15 times), thereby achieving an intrinsic reinforcing effect and significantly improving the mechanical properties of the material. The multilayer EVOH composite sheet of this invention is prepared using a hot-pressing method. During hot pressing, the surface of the multilayer sheet softens, and they bond together through intermolecular forces, providing interfacial adhesion. Through research, the inventors of this invention have surprisingly discovered that the multilayer EVOH composite sheet of this invention has AB1B2…B i …B n …B i …B2B1 sheet structure, preferably in the thin film layer B i The melting point of B is ≥ B i+1 The melting point of the multilayer EVOH composite sheet, which is hot-pressed through the above-mentioned layering, not only has high gas barrier properties, but also high tensile strength and impact strength. Moreover, the multilayer EVOH composite sheet also has high peel strength.

[0058] In summary, compared with the prior art, the beneficial effects of the present invention are as follows:

[0059] (1) Compared with traditional single-layer or same-thickness EVOH composite materials, the composite sheet prepared by the present invention has higher mechanical strength and gas barrier properties (the smaller the oxygen permeability value, the better).

[0060] (2) The composite sheet of the present invention can change the number of layers according to application requirements. Through the preferred unique melting point gradient setting, the hot pressing temperature of the composite sheet can be selected more widely, the interlayer adhesion of different EVOH layers is strong, and the outer polyolefin can maintain the water resistance and boiling resistance of the composite sheet.

[0061] (3) The high-strength, high-impact, and high-barrier composite sheet of the present invention can be produced using existing equipment, the process is mature, and it has important application value. Detailed Implementation

[0062] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0063] In the following embodiments and comparative examples:

[0064] The extrusion calender and solid phase stretching equipment were purchased from Tianjin Hengrui Company, and the model is HRPC-800 three-layer co-extrusion plastic stretching sheet production line.

[0065] The performance of the composite sheet was tested according to the following methods:

[0066] (1) Melt mass flow rate (MFR): The test shall be performed in accordance with the method specified in GB / T 3682-2000, wherein the test temperature is 230℃ and the load is 2.16kg;

[0067] (2) Tensile strength: determined according to the method specified in GB / T1040.1-2018;

[0068] (3) Hammer impact strength: determined according to the method specified in GB / T14153-1993;

[0069] (4) Oxygen permeability: determined according to the method specified in GB / T19789-2005;

[0070] (5) Interlayer peel strength: The test shall be conducted in accordance with the method specified in QB / T2358-1998.

[0071] The parameters in Table 1 were obtained by direct testing of the composite sheets in the corresponding embodiments and comparative examples.

[0072] In the following examples, the sources of some raw materials are described in the examples, and the remaining raw materials are commercially available products unless otherwise specified.

[0073] Example 1

[0074] High-strength, high-impact, and high-barrier multilayer EVOH composite sheets are prepared according to the following steps:

[0075] (1) Preparation of polyolefin composition film layer A:

[0076] Polyolefin A is Shanghai Petrochemical's low-density polyethylene Q281D, with a melt index of 2.8 g / 10 min and a density of 0.925 g / cm³. 3 The heat-bonding reinforcing agent b is Mitsui ADMER NF528 from Japan.

[0077] The components are weighed and mixed according to the formula, wherein component a has a mass fraction Wa of 95 parts by weight and component b has a mass fraction Wb of 5 parts by weight. The mixture is added to a high-speed mixer and mixed evenly. The mixed material is then added to the feeder of a twin-screw extruder manufactured by W&P. The material enters the twin screw through the feeder. During the processing, the screw temperature is maintained between 180-210℃. After being melted and mixed evenly by the screw, extruded, granulated and dried, polyethylene composition granules are obtained.

[0078] After the above-mentioned polyethylene composition granules are added to the extrusion casting machine and flow out, they pass through the calendering roller and the traction roller in sequence, and then undergo solid phase stretching, edge trimming and winding to obtain the polyolefin composition film layer A.

[0079] The extrusion casting temperature is 215℃, and the calendering roll temperature is 55℃. The solid-phase stretching process is carried out at a temperature of 120℃, a stretching rate of 2m / min, and a stretching ratio of 7 times.

[0080] (2) Preparation of EVOH thin film layer B:

[0081] EVOH (Kuraray Corporation, Japan, F171B, ethylene content 32%, melting point 183℃, melt index 1.6g / 10min at 190℃ / 2.16kg) is added to an extrusion casting machine and flows out, then passes through calendering rollers and traction rollers in sequence, followed by solid-phase stretching, edge trimming and winding to obtain the EVOH film layer B.

[0082] The extrusion casting temperature is 220℃, and the calendering roll temperature is 55℃. The solid-phase stretching process is carried out at a temperature of 170℃, a stretching rate of 2m / min, and a stretching ratio of 7 times.

[0083] (3) Preparation of multilayer EVOH composite sheets:

[0084] Four layers of EVOH film B were stacked at 90° angles between the warp and weft directions. A polyolefin film layer A was placed on the outermost layer of the EVOH layers (i.e., the structure is ABBBA). After hot pressing and cooling, composite sheet S1 was obtained. The hot pressing conditions were: temperature 170℃, hot pressing pressure 5MPa, preheating time 180s, hot pressing time 180s, and cooling time 600s. The thickness of the resulting composite sheet S1 was 100μm, of which the thickness of the EVOH film layer B accounted for 80% of the total sheet thickness.

[0085] Comparative Example 1

[0086] Multilayer EVOH composite sheets are prepared according to the following steps:

[0087] (1) Same as step (1) in Example 1;

[0088] (2) EVOH is not subjected to solid-phase stretching, but by controlling the die of the casting machine and the spacing of the calendering rolls, the resulting EVOH film layer B is made to have the same thickness as in Example 1;

[0089] (3) Same as step (3) in Example 1, the resulting composite sheet is D1.

[0090] The resulting composite sheet has a thickness of 100 μm, in which the thickness of the EVOH thin film layer Bi accounts for 80% of the total sheet thickness.

[0091] Example 2

[0092] Multilayer EVOH composite sheets are prepared according to the following steps:

[0093] Steps (1) and (2) are the same as steps (1) and (2) in Example 1;

[0094] Except for step (3), in which the four EVOH film layers B are stacked with the warp direction at 0° to the warp direction, the rest is the same as step (3) of Example 1, and the resulting composite sheet is S2.

[0095] Example 3

[0096] Multilayer EVOH composite sheets are prepared according to the following steps:

[0097] Step (1) is the same as step (1) in Example 1;

[0098] Step (2) The material selection is the same as step (2) of Example 1. The difference is that after solid-phase stretching (stretching rate of 2m / min, stretching ratio of 7 times), EVOH is subjected to a second stage of free stretching, with a stretching rate of 0.5m / min and a stretching ratio of 2 times.

[0099] Step (3) is the same as step (3) in Example 1. The resulting composite sheet is S3 with a thickness of 62 μm, wherein the thickness of the EVOH thin film layer Bi accounts for 52% of the total thickness of the sheet.

[0100] Example 4

[0101] Multilayer EVOH composite sheets are prepared according to the following steps:

[0102] Steps (1) and (2) are the same as steps (1) and (2) in Example 1;

[0103] In step (3), except that the number of EVOH film layer B is changed to 7 layers, the rest is the same as step (3) of Example 1. The resulting composite sheet is S4 with a thickness of 160 μm, wherein the thickness of EVOH film layer B accounts for 87% of the total thickness of the sheet.

[0104] Example 5

[0105] Multilayer EVOH composite sheets are prepared according to the following steps:

[0106] Step (1) is the same as step (1) in Example 1;

[0107] Step (2) Preparation of EVOH thin film layer B:

[0108] EVOH (represented by: Kuraray Corporation, Japan, M100B, ethylene content 25%, melting point 195℃, corresponding to B1);

[0109] L171B, ethylene content 27%, melting point 190℃, corresponds to B2;

[0110] F171B, ethylene content 32%, melting point 183℃, corresponds to B3;

[0111] H171B, with an ethylene content of 38% and a melting point of 172°C (corresponding to B4), is added to an extrusion casting machine and flows out sequentially through calendering rollers and traction rollers, followed by solid-phase stretching, edge trimming, and winding to obtain the EVOH film layers B1, B2, B3, and B4.

[0112] The extrusion casting temperature was 220°C, and the calendering roll temperature was 55°C. The solid-phase stretching process was carried out at a temperature of 170°C, a stretching rate of 2 m / min, and a stretching ratio of 7 times. The thickness of each film layer Bi was the same as that of film layer B in Example 1.

[0113] (3) Preparation of composite sheets:

[0114] 7-layer EVOH thin film layer B i The layers are stacked at 90° intervals between the warp and weft directions, with the following stacking pattern from top to bottom: B1 / B2 / B3 / B4 / B3 / B2 / B1. A polyolefin film layer A is placed on the outermost layer of EVOH, resulting in a structure of AB1 / B2 / B3 / B4 / B3 / B2 / B1A. The hot-pressing conditions are the same as in Example 1, resulting in composite sheet S5 with a thickness of 160 μm. The thickness of the EVOH film layer Bi accounts for 87% of the total thickness of the sheet.

[0115] Example 6

[0116] Multilayer EVOH composite sheets are prepared according to the following steps:

[0117] Steps (1) and (2) are the same as step (1) in Example 1;

[0118] Step (3) The Bi layer is laid up from top to bottom as follows: B4 / B3 / B2 / B1 / B2 / B3 / B4, and the rest is the same as in Example 5, to obtain composite sheet S6 with a thickness of 160 μm, wherein the thickness of the EVOH thin film layer Bi accounts for 87% of the total thickness of the sheet.

[0119] The properties of the composite sheets prepared in the above embodiments and comparative examples are shown in Table 1.

[0120] Table 1

[0121]

[0122]

[0123] As can be seen from the comparison between Examples 1-6 of the present invention and Comparative Example 1, after solid-phase stretching, the tensile strength, impact strength and oxygen barrier properties of EVOH are significantly improved.

[0124] As can be seen from Example 1 and Comparative Example 1, the tensile strength, impact strength and oxygen barrier properties of the laminated composite sheet are all increased exponentially. This is because the EVOH is placed at 90° between the warp and weft directions, and the composite sheet has a reinforcing effect in both the transverse and longitudinal directions after being subjected to external force.

[0125] The multilayer EVOH composite sheet of this invention has AB1B2…B m Structure A, B1B2……B m The melting points can be the same or different, and the technical effects of this invention can be achieved in either case.

[0126] Through research, the inventors of this invention unexpectedly discovered that when B1B2…B m When the melting points are the same or arranged according to a specific melting point gradient, the resulting multilayer EVOH composite sheets are superior to those of B1B2…B m Arrangement that does not follow a specific melting point gradient has a better technical effect, as specifically seen in Examples 4, 5 and 6.

[0127] And when B1B2…B m When the melting points are arranged according to a specific melting point gradient, compared to B1B2…B m With the same melting point, it offers further superior technical effects. See the comparison between Examples 4 and 5 for details. In particular, if the EVOH layer undergoes the specific melting point gradient lamination hot-pressing treatment of this invention, the peel strength between the EVOH layers can be significantly improved.

[0128] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

[0129] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0130] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0131] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values; such ranges or values ​​should be understood to include values ​​close to them. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0132] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

[0133] Furthermore, any implementation described herein can be freely combined with one or more other implementations described herein, and the resulting technical solutions or technical ideas shall be regarded as part of the original disclosure or original record of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider the combination to be obviously unreasonable.

Claims

1. A multilayer EVOH composite sheet, comprising two outer layers A and a plurality of stacked core layers B located between the two outer layers A; the multilayer EVOH composite sheet having AB1B2…B i …B n …B i …B2B1A layered structure, where i and n are both integers not less than 2, and i≤n, where n is 2-100; The two outer layers A may be the same or different, each containing a polyolefin composition A; the core layers B each contain composition B, which may be the same or different, each containing EVOH; composition B i Melting point ≥ composition B i+1 The melting point; The preparation process of the core layer B includes a stretching step, with a stretching ratio of 1-15 times.

2. The multilayer EVOH composite sheet according to claim 1, characterized in that: The melting points of each of the compositions B are 150-210°C; and / or, The composition B is EVOH; and / or, The ethylene content in the EVOH is 15-50 mol.

3. The multilayer EVOH composite sheet according to claim 1, characterized in that: The melting points of each of the compositions B are 160-200°C; and / or, The ethylene content in the EVOH is 21-49 mol.

4. The multilayer EVOH composite sheet according to claim 1, characterized in that: n is 2-50; and / or, Composition B i Melting point > Composition B i+1 Its melting point.

5. The multilayer EVOH composite sheet according to claim 1, characterized in that: Composition B i With composition B i+1 The melting point difference is 5-15℃.

6. The multilayer EVOH composite sheet according to claim 1, characterized in that: The stretching ratio is 2-15 times; and / or the stretching method is one or more of the following: free stretching, solid-phase stretching, and multi-stage stretching.

7. The multilayer EVOH composite sheet according to claim 1, characterized in that: The stretching conditions in the preparation steps of the core layer B include: the core layer B is prepared by extruding EVOH, casting or calendering, and stretching.

8. The multilayer EVOH composite sheet according to claim 6, characterized in that: The conditions for stretching include: The stretching temperature is 140-185℃; the stretching ratio is 2-15 times.

9. The multilayer EVOH composite sheet according to claim 6, characterized in that: The conditions for stretching include: The stretching temperature is 150-175℃; the stretching ratio is 2-15 times.

10. The multilayer EVOH composite sheet according to claim 1, characterized in that: The thickness of the multilayer EVOH composite sheet is 5-1000 μm; and / or, Taking the total thickness of the multilayer EVOH composite sheet as 100%, the total thickness of all core layers B accounts for 10%-90% of the total thickness of the multilayer EVOH composite sheet; and / or, The core layer B is stacked from top to bottom in a 0-90° arrangement between the warp and weft directions.

11. The multilayer EVOH composite sheet according to claim 1, characterized in that: The thickness of the multilayer EVOH composite sheet is 5-500 μm.

12. The multilayer EVOH composite sheet according to claim 1, characterized in that: The thickness of the multilayer EVOH composite sheet is 5-300 μm.

13. The multilayer EVOH composite sheet according to any one of claims 1-12, characterized in that: The polyolefin composition A contains polyolefin a and thermal bonding enhancer b.

14. The multilayer EVOH composite sheet according to claim 13, characterized in that: The total weight of the polyolefin composition A is 100 wt%, and the polyolefin composition A contains 70-99 wt% polyolefin a and 1-30 wt% thermal bonding enhancer b.

15. The multilayer EVOH composite sheet according to claim 13, characterized in that: The total weight of the polyolefin composition A is 100 wt%, and the polyolefin composition A comprises 80-99 wt% polyolefin a and 1-20 wt% thermal bonding enhancer b.

16. The multilayer EVOH composite sheet according to claim 13, characterized in that: The polyolefin a is selected from one or more of polypropylene, polyethylene, and ethylene-vinyl acetate; and / or, The thermal bonding reinforcing agent b is selected from one or more of the following: anhydride-modified polypropylene, anhydride-modified polyethylene, anhydride-modified ethylene-vinyl acetate, glycidyl methacrylate-modified polypropylene, glycidyl methacrylate-modified polyethylene, glycidyl methacrylate-modified ethylene-vinyl acetate, and maleic anhydride copolymer.

17. The multilayer EVOH composite sheet according to any one of claims 1-12, characterized in that: The multilayer EVOH composite sheet is prepared by sequentially stacking outer layer A, multiple core layers B, and outer layer A, and then laminating them.

18. The multilayer EVOH composite sheet according to claim 17, characterized in that: The lamination process involves hot pressing followed by cooling and shaping.

19. The multilayer EVOH composite sheet according to claim 17, characterized in that: The multilayer EVOH composite sheet is prepared by extruding, casting or calendering, stretching and slitting the raw materials forming the outer layer A and the raw materials forming the core layer B to obtain the corresponding sheets, and then stacking, hot pressing and cooling the corresponding sheets in the corresponding structural order.

20. A method for preparing a multilayer EVOH composite sheet according to any one of claims 1-19, comprising respectively preparing the raw materials for forming the outer layer A and the raw materials for forming the core layer B into corresponding sheets A and B, and then stacking, hot-pressing, and cooling the corresponding sheets according to their corresponding structural order; wherein, The preparation process of sheet B includes a stretching step, with a stretching ratio of 1-15 times.

21. The preparation method according to claim 20, characterized in that: The steps for preparing sheet A include: melting and blending the raw materials that form the outer layer A, and then casting or calendering, stretching, and slitting to obtain sheet A.

22. The preparation method according to claim 20, characterized in that: The steps for preparing sheet A include: extruding the raw material that forms the outer layer A, and then casting or calendering, stretching, and slitting to obtain sheet A.

23. The preparation method according to claim 22, characterized in that: The preparation conditions for sheet A include: The extrusion and casting temperatures are independently selected from 200-250°C; the calendering temperature is 50-70°C; and / or, The stretching method is a combination of one or more of the following: free stretching, solid-phase stretching, and multi-stage stretching.

24. The preparation method according to claim 22, characterized in that: The stretching temperature is 90-165℃; the stretching ratio is 1-20 times.

25. The preparation method according to claim 22, characterized in that: The stretching temperature is 90-140℃; the stretching ratio is 1-20 times.

26. The preparation method according to claim 20, characterized in that: The steps for preparing core layer B include: extruding the raw material that forms core layer B, and then casting or calendering, stretching, and slitting to obtain sheet B.

27. The preparation method according to claim 26, characterized in that: The preparation conditions for sheet B include: The extrusion and casting temperatures are independently selected from 200-260°C; the calendering temperature is 50-90°C; and / or, The stretching method is a combination of one or more of the following: free stretching, solid-phase stretching, and multi-stage stretching.

28. The preparation method according to claim 26, characterized in that: The stretching temperature is 140-185℃; the stretching ratio is 1-15 times.

29. The preparation method according to claim 26, characterized in that: The stretching temperature is 150-175℃; the stretching ratio is 2-15 times.

30. The preparation method according to claim 26, characterized in that: The stretching method is one or a combination of two of the following: solid-phase stretching and multi-stage stretching.

31. The preparation method according to any one of claims 20-30, characterized in that: The stacking method includes: from top to bottom, sheet A and sheet B are stacked sequentially with their warp directions at an angle of 0-90°; and / or, The hot pressing conditions include: the hot pressing temperature is 135-190℃; and / or, the hot pressing pressure is 2-10MPa; and / or, the preheating time is 5-600s; and / or, the hot pressing time is 1-600s. And / or, the conditions for cooling and shaping include: a cooling pressure of 2-8 MPa, and / or a cooling time of 30-700 s.

32. The preparation method according to any one of claims 20-30, characterized in that: The hot pressing conditions include: the hot pressing temperature is 150-190℃; and / or the hot pressing time is 10-500s.

33. The application of a multilayer EVOH composite sheet according to any one of claims 1-19 or a multilayer EVOH composite sheet prepared by any one of claims 20-32 in the fields of packaging, mechanical parts, and industrial and agricultural film materials.

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