Polyamide fresh-keeping composite film with oxygen absorption function and preparation method thereof

Abstract

The invention discloses a polyamide fresh-keeping composite film with an oxygen absorption function. The polyamide fresh-keeping composite film sequentially comprises a polyamide surface layer, a first oxygen absorption layer, a barrier core layer, a second oxygen absorption layer and a polyamide heat sealing layer from top to bottom, wherein the polyamide surface layer is prepared from the following raw materials in percentage by mass: 93-99% of PA6, 0.5-3.5% of a slipping agent and 0.5-3.5% of an anti-blocking agent; the first oxygen uptake layer and the second oxygen uptake layer are prepared from the following raw materials in percentage by mass: 10-38% of PA6, 60-80% of MXD6 and 2.0-10% of a modified oxygen uptake blocking agent; the modified oxygen uptake blocking agent is layered inorganic particles loaded with an oxygen uptake agent; the barrier core layer is made of 100% EVOH (ethylene vinyl alcohol); the polyamide heat sealing layer is prepared from the following raw materials in percentage by mass: 87 to 99 percent of copolymer nylon, 0.25 to 2 percent of an anti-blocking agent, 0.25 to 1 percent of a slipping agent and 0.5 to 10 percent of a water absorbent. Through the arrangement of the first oxygen absorption layer and the second oxygen absorption layer, the oxygen content in the package can be effectively reduced, the freshness of contents is kept through the synergistic effect of all the layers, the deterioration reaction of the contents caused by oxygen is slowed down, and the freshness locking effect is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of polyamide films, and in particular relates to a polyamide fresh-locking composite film with oxygen absorption function and a preparation method thereof. Background Art

[0002] During packaging or storage, food is easily affected by oxygen and deteriorates, such as corruption and discoloration, which affects food quality and even affects the health of consumers. In addition, nutrients in food are prone to deterioration in a high-oxygen environment. For example, fats will deteriorate in a high-oxygen environment, and pigments in food will also change color or fade under the influence of oxygen, thus affecting the color and flavor of the food. Most aerobic bacteria and facultative anaerobic bacteria can grow well in an aerobic environment. Even if the oxygen content is as low as 2-3%, they can still grow and biochemical reactions can still proceed.

[0003] Modified atmosphere packaging and vacuum packaging are currently the main methods used to reduce the oxygen content in packaging bags, but there will still be a small amount (0.1-2.0%) of residual oxygen remaining in the packaging container in the packaging environment.

[0004] Oxygen-absorbing packaging can absorb oxygen that penetrates into the package from the inside and outside environment, keeping the oxygen environment inside the package at a low level, preventing oxidation and deterioration of the package contents, maintaining the freshness of the contents, and extending their shelf life.

[0005] Iron-based bagged oxygen absorbers are the most widely used oxygen absorbers on the market. They are made by putting iron powder oxygen absorbers into small bags and then putting them into food packaging bags. When the water activity in the packaging is high, the iron powder can actively absorb the oxygen in the packaging bag, thereby reducing the oxygen content in the packaging bag. However, this type of bagged oxygen absorber has the risk of accidental ingestion and leakage, and because its main oxygen-absorbing component is iron or ferrous salt, it cannot pass the metal detector on the packaging line, posing a safety hazard.

[0006] In view of the above-mentioned problems with bagged iron-based oxygen absorbers, people began to try to add organic oxygen absorbers to resins to prepare oxygen-absorbing films. Compared with bagged iron-based oxygen absorbers, oxygen-absorbing films have broader market application prospects.

[0007] The Chinese patent application with application number CN201811399199.4 discloses a high oxygen barrier film and its preparation method and application. The high oxygen barrier film includes, from outside to inside, the following: outer layer A; adhesive layer B1; oxygen absorbing layer C1; adhesive layer B2; barrier layer D, including intermediate layer D2 and transition layers D1 and D3 on both sides of intermediate layer D2; adhesive layer B3; oxygen absorbing layer C2 and heat sealing layer E. The oxygen absorbing layers C1 and C2 are composed of oxygen absorbers and polyolefin resins, and the main components of the oxygen absorbers are methyl ethacrylate and / or cyclohexene acrylic acid terpolymers. The high oxygen barrier film of the invention introduces an oxygen absorbing layer composed of oxygen absorbers and polyolefin resins, wherein the oxygen absorbers can generate free radicals when irradiated with ultraviolet rays before packaging. The free radicals combine with oxygen to achieve the effect of oxygen absorption, effectively blocking oxygen transmission, and greatly improving the oxygen barrier performance of the film. However, the film has many layers, and the preparation process requires multiple processes to be carried out simultaneously, which is relatively cumbersome. Therefore, it is urgent to develop a polyamide fresh-keeping composite film with oxygen absorption function. Summary of the invention

[0008] In order to solve the above problems, the present invention provides a polyamide fresh-keeping composite film with oxygen absorption function and a preparation method thereof. The present invention endows the film with good oxygen barrier properties by arranging a barrier core layer, and effectively reduces the oxygen content in the package by arranging a first oxygen absorption layer and a second oxygen absorption layer. The synergistic effect of each layer is utilized to maintain the freshness of the contents, slow down the deterioration reaction caused by oxygen, and achieve the effect of locking in freshness.

[0009] The technical solution of the present invention is as follows:

[0010] One of the purposes of the present invention is to provide a polyamide fresh-keeping composite film with oxygen absorption function, wherein the polyamide fresh-keeping composite film with oxygen absorption function comprises, from top to bottom, a polyamide surface layer, a first oxygen absorption layer, a barrier core layer, a second oxygen absorption layer and a polyamide heat-sealing layer;

[0011] Wherein, the polyamide surface layer is composed of the following raw materials in percentage by mass: 93-99% PA6, 0.5-3.5% lubricant, and 0.5-3.5% anti-blocking agent;

[0012] The first oxygen absorbing layer and the second oxygen absorbing layer are composed of the following raw materials in percentage by mass: 10-38% PA6, 60-80% MXD6, and 2.0-10% modified oxygen absorbing barrier; the modified oxygen absorbing barrier is layered inorganic particles loaded with oxygen absorbing agent;

[0013] The barrier core layer is 100% EVOH;

[0014] The polyamide heat-sealing layer is composed of the following raw materials in percentage by mass: 87-99% copolymerized nylon, 0.25-2% opening agent, 0.25-1% lubricant, and 0.5-10% water absorbent.

[0015] Furthermore, in the modified oxygen absorption barrier, the layered inorganic particles are one or a combination of nano-silicon dioxide, nano-mica, nano-montmorillonite, layered double hydroxide, kaolin, and nano-alumina.

[0016] Furthermore, in the modified oxygen absorbing barrier, the oxygen absorber is one or a combination of ascorbic acid-based oxygen absorbers, unsaturated fatty acid-based oxygen absorbers, and phenolic hydroxyl-based oxygen absorbers.

[0017] Furthermore, in the polyamide surface layer and the polyamide heat-sealing layer, the lubricant is one or a combination of erucamide, oleamide, ethylene bisstearamide, silicone powder, silicone oil, polyethylene wax, and oxidized polyethylene wax.

[0018] Furthermore, in the polyamide surface layer and the polyamide heat-sealing layer, the anti-blocking agent is one or a combination of silicon dioxide, talc, kaolin, calcium carbonate, clay, magnesium carbonate, barium carbonate, calcium phosphate, aluminum oxide, and titanium dioxide.

[0019] Furthermore, in the barrier core layer, the ethylene molar content of EVOH is 20-40% mol / L.

[0020] Furthermore, in the polyamide heat-sealing layer, the water absorbent is one or a combination of calcium oxide and calcium hydroxide.

[0021] Furthermore, the total thickness of the composite film is 30-90 μm, wherein the thickness ratio of the polyamide surface layer, the first oxygen absorbing layer, the barrier core layer, the second oxygen absorbing layer and the heat sealing layer is 1:2:(1-2):2:(0.5-1).

[0022] The second object of the present invention is to provide a method for preparing a polyamide fresh-keeping composite film with oxygen absorption function, comprising the following steps:

[0023] S1: Weigh each raw material according to the set ratio, mix each layer of raw materials separately, and disperse them evenly through a high-speed mixer;

[0024] S2: The raw materials of each layer are melted and extruded through their respective extruders, flow out through a T-die, and are cooled on a chilled roller to form an unstretched sheet;

[0025] S3: After the unstretched sheet is passed through a water tank for humidity adjustment, it is heated for synchronous transverse stretching;

[0026] S4: performing heat setting treatment on the stretched film to obtain the polyamide fresh-keeping composite film with oxygen absorption function.

[0027] Furthermore, in step S3, the stretching temperature is 160-210° C., and the stretching ratio is 2.5*2.5-3.2*3.2.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention provides a polyamide fresh-keeping composite film with oxygen absorption function. The arrangement and coordination of each layer structure of the composite film can help maintain the freshness of the package contents and effectively extend the shelf life of the contents. Among them, the arrangement of the first oxygen absorption layer and the second oxygen absorption layer can absorb the original oxygen in the package and the oxygen that penetrates into the package from the outside, effectively reduce the oxygen content in the package, and slow down the deterioration reaction caused by oxygen. In addition, the organic oxygen absorber used in the oxygen absorption layer also has a certain antibacterial effect, which can inhibit the occurrence of corruption reactions caused by microorganisms. And the modified oxygen absorption barrier in the first oxygen absorption layer and the second oxygen absorption layer of the present invention is a layered inorganic particle loaded with an oxygen absorber. The layered inorganic particle can not only improve the thermal stability of the oxygen absorber, but also form a "tortuous path" to extend the permeation path of the gas, hinder the diffusion of the gas in the matrix, and improve the gas barrier property of the film. The raw materials MXD6 and EVOH of the first oxygen absorbing layer and the second oxygen absorbing layer of the present invention both have good oxygen barrier properties, but the barrier property of EVOH is negatively correlated with humidity, and the barrier property of MXD6 does not change with changes in humidity. The MXD6 in the oxygen absorbing layer allows the film to maintain good oxygen barrier properties in different humidity environments after the oxygen absorber loses its effectiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic structural diagram of a polyamide fresh-keeping composite film with oxygen absorption function provided by the present invention.

[0031] In the figure, 1, polyamide surface layer; 2, first oxygen absorbing layer; 3, barrier core layer; 4, second oxygen absorbing layer; 5, polyamide heat sealing layer. DETAILED DESCRIPTION

[0032] The following is in conjunction with the preferred embodiment and with reference to the attached Figure 1 , the present invention is further described. The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values; for numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein; the materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels; the experimental methods in the following examples, unless otherwise specified, are all conventional methods.

[0033] Example 1

[0034] This embodiment provides a polyamide fresh-keeping composite film with oxygen absorption function, and the polyamide fresh-keeping composite film with oxygen absorption function comprises, from top to bottom, a polyamide surface layer, a first oxygen absorption layer, a barrier core layer, a second oxygen absorption layer and a polyamide heat-sealing layer;

[0035] Wherein, the polyamide surface layer is composed of the following raw materials in percentage by mass: 95% PA6, 2.5% lubricant, and 2.5% anti-blocking agent;

[0036] The first oxygen absorbing layer and the second oxygen absorbing layer are composed of the following raw materials in percentage by weight: 30% PA6, 60%

[0037] MXD6, 10% modified oxygen absorbing barrier agent; the modified oxygen absorbing barrier agent is layered inorganic particles loaded with oxygen absorbing agent;

[0038] The barrier core layer is 100% EVOH;

[0039] The polyamide heat-sealing layer is composed of the following raw materials in percentage by mass: 95% copolymerized nylon, 2% anti-blocking agent, 1% lubricating agent, and 2% water absorbent.

[0040] In this embodiment, the modified oxygen absorbing barrier is a cinnamic acid modified layered metal oxide, wherein the layered inorganic particles are zinc-aluminum-based LDHs, and the oxygen absorber is cinnamic acid.

[0041] In this embodiment, in the polyamide surface layer and the polyamide heat-sealing layer, the lubricant is erucic acid amide, and the opening agent is a combination of silicon dioxide and talcum powder. In the barrier core layer, the ethylene molar content of EVOH is 30% mol / L. In the polyamide heat-sealing layer, the water absorbent is calcium oxide. The total thickness of the composite film is 40 μm, wherein the thickness ratio of the polyamide surface layer, the first oxygen absorption layer, the barrier core layer, the second oxygen absorption layer, and the heat-sealing layer is 1:2:2:2:1.

[0042] This embodiment also provides a method for preparing a polyamide fresh-keeping composite film with oxygen absorption function, comprising the following steps:

[0043] S1: Weigh each raw material according to the set ratio, mix each layer of raw materials separately, and disperse them evenly through a high-speed mixer;

[0044] S2: The raw materials of each layer are melted and extruded through their respective extruders, flow out through a T-die, and are cooled on a chilled roller to form an unstretched sheet;

[0045] S3: After the unstretched sheet is passed through a water tank for humidity adjustment, it is heated for synchronous transverse stretching;

[0046] S4: performing heat setting treatment on the stretched film to obtain the polyamide fresh-keeping composite film with oxygen absorption function.

[0047] In step S3 of this embodiment, the stretching temperature is 200° C. and the stretching ratio is 3.0*3.0.

[0048] Example 2

[0049] This embodiment provides a polyamide fresh-keeping composite film with oxygen absorption function, and the polyamide fresh-keeping composite film with oxygen absorption function comprises, from top to bottom, a polyamide surface layer, a first oxygen absorption layer, a barrier core layer, a second oxygen absorption layer and a polyamide heat-sealing layer;

[0050] The polyamide surface layer is composed of the following raw materials in percentage by mass: 93% PA6, 3.5% lubricant, and 3.5% anti-blocking agent;

[0051] The first oxygen absorbing layer and the second oxygen absorbing layer are composed of the following raw materials in percentage by weight: 38% PA6, 60%

[0052] MXD6, 2% modified oxygen absorbing barrier agent; the modified oxygen absorbing barrier agent is layered inorganic particles loaded with oxygen absorbing agent;

[0053] The barrier core layer is 100% EVOH;

[0054] The polyamide heat-sealing layer is composed of the following raw materials in percentage by mass: 99% copolymerized nylon, 0.25% anti-blocking agent, 0.25% lubricating agent, and 0.5% water absorbent.

[0055] In this embodiment, the modified oxygen absorbing barrier is gallic acid modified nano-montmorillonite, wherein the layered inorganic particles are nano-montmorillonite and the oxygen absorbing agent is gallic acid.

[0056] In this embodiment, in the polyamide surface layer and the polyamide heat-sealing layer, the lubricant is a combination of oleic acid amide and silicone oil, and the opening agent is kaolin. In the barrier core layer, the ethylene molar content of EVOH is 20% mol / L. In the polyamide heat-sealing layer, the water absorbent is calcium oxide. The total thickness of the composite film is 40 μm, wherein the thickness ratio of the polyamide surface layer, the first oxygen absorption layer, the barrier core layer, the second oxygen absorption layer, and the heat-sealing layer is 1:2:2:2:1.

[0057] This embodiment also provides a method for preparing a polyamide fresh-keeping composite film with oxygen absorption function, comprising the following steps:

[0058] S1: Weigh each raw material according to the set ratio, mix each layer of raw materials separately, and disperse them evenly through a high-speed mixer;

[0059] S2: The raw materials of each layer are melted and extruded through their respective extruders, flow out through a T-die, and are cooled on a chilled roller to form an unstretched sheet;

[0060] S3: After the unstretched sheet is passed through a water tank for humidity adjustment, it is heated for synchronous transverse stretching;

[0061] S4: performing heat setting treatment on the stretched film to obtain the polyamide fresh-keeping composite film with oxygen absorption function.

[0062] In step S3 of this embodiment, the stretching temperature is 160° C. and the stretching ratio is 2.5*2.5.

[0063] Example 3

[0064] This embodiment provides a polyamide fresh-keeping composite film with oxygen absorption function, and the polyamide fresh-keeping composite film with oxygen absorption function comprises, from top to bottom, a polyamide surface layer, a first oxygen absorption layer, a barrier core layer, a second oxygen absorption layer and a polyamide heat-sealing layer;

[0065] Wherein, the polyamide surface layer is composed of the following raw materials in percentage by mass: 99% PA6, 0.5% lubricant, and 0.5% anti-blocking agent;

[0066] The first oxygen absorbing layer and the second oxygen absorbing layer are composed of the following raw materials in percentage by weight: 15% PA6, 80%

[0067] MXD6, 5% modified oxygen absorbing barrier agent; the modified oxygen absorbing barrier agent is layered inorganic particles loaded with oxygen absorbing agent;

[0068] The barrier core layer is 100% EVOH;

[0069] The polyamide heat-sealing layer is composed of the following raw materials in percentage by mass: 87% copolymerized nylon, 2% anti-blocking agent, 1% lubricating agent, and 10% water absorbent.

[0070] In this embodiment, the modified oxygen-absorbing barrier agent is tea polyphenol-modified layered metal oxide, wherein the layered inorganic particles are magnesium-aluminum-based LDHs, and the oxygen absorber is tea polyphenol.

[0071] In this embodiment, in the polyamide surface layer and the polyamide heat-sealing layer, the lubricant is polyethylene wax, and the opening agent is a combination of calcium carbonate and clay. In the barrier core layer, the ethylene molar content of EVOH is 40% mol / L. In the polyamide heat-sealing layer, the water absorbent is calcium oxide. The total thickness of the composite film is 40 μm, wherein the thickness ratio of the polyamide surface layer, the first oxygen absorption layer, the barrier core layer, the second oxygen absorption layer, and the heat-sealing layer is 1:2:2:2:1.

[0072] This embodiment also provides a method for preparing a polyamide fresh-keeping composite film with oxygen absorption function, comprising the following steps:

[0073] S1: Weigh each raw material according to the set ratio, mix each layer of raw materials separately, and disperse them evenly through a high-speed mixer;

[0074] S2: The raw materials of each layer are melted and extruded through their respective extruders, flow out through a T-die, and are cooled on a chilled roller to form an unstretched sheet;

[0075] S3: After the unstretched sheet is passed through a water tank for humidity adjustment, it is heated for synchronous transverse stretching;

[0076] S4: performing heat setting treatment on the stretched film to obtain the polyamide fresh-keeping composite film with oxygen absorption function.

[0077] In step S3 of this embodiment, the stretching temperature is 210° C. and the stretching ratio is 3.2*3.2.

[0078] Example 4

[0079] This embodiment provides a polyamide fresh-keeping composite film with oxygen absorption function, and the polyamide fresh-keeping composite film with oxygen absorption function comprises, from top to bottom, a polyamide surface layer, a first oxygen absorption layer, a barrier core layer, a second oxygen absorption layer and a polyamide heat-sealing layer;

[0080] The polyamide surface layer is composed of the following raw materials in percentage by mass: 93% PA6, 3.5% lubricant, and 3.5% anti-blocking agent;

[0081] The first oxygen absorbing layer and the second oxygen absorbing layer are composed of the following raw materials in percentage by weight: 10% PA6, 80%

[0082] MXD6, 10% modified oxygen absorbing barrier agent; the modified oxygen absorbing barrier agent is layered inorganic particles loaded with oxygen absorbing agent;

[0083] The barrier core layer is 100% EVOH;

[0084] The polyamide heat-sealing layer is composed of the following raw materials in percentage by mass: 98% copolymerized nylon, 0.5% anti-blocking agent, 0.5% lubricating agent, and 1% water absorbent.

[0085] In this embodiment, the modified oxygen absorbing barrier is a gallic acid-modified layered metal oxide, wherein the layered inorganic particles are zinc-aluminum-based LDHs, and the oxygen absorbing agent is gallic acid.

[0086] In this embodiment, in the polyamide surface layer and the polyamide heat-sealing layer, the lubricant is a combination of two types of oxidized polyethylene wax, and the opening agent is kaolin. In the barrier core layer, the ethylene molar content of EVOH is 30% mol / L. In the polyamide heat-sealing layer, the water absorbent is calcium oxide. The total thickness of the composite film is 40 μm, wherein the thickness ratio of the polyamide surface layer, the first oxygen absorption layer, the barrier core layer, the second oxygen absorption layer, and the heat-sealing layer is 1:2:1:2:0.5.

[0087] This embodiment also provides a method for preparing a polyamide fresh-keeping composite film with oxygen absorption function, comprising the following steps:

[0088] S1: Weigh each raw material according to the set ratio, mix each layer of raw materials separately, and disperse them evenly through a high-speed mixer;

[0089] S2: The raw materials of each layer are melted and extruded through their respective extruders, flow out through a T-die, and are cooled on a chilled roller to form an unstretched sheet;

[0090] S3: After the unstretched sheet is passed through a water tank for humidity adjustment, it is heated for synchronous transverse stretching;

[0091] S4: performing heat setting treatment on the stretched film to obtain the polyamide fresh-keeping composite film with oxygen absorption function.

[0092] In step S3 of this embodiment, the stretching temperature is 160° C. and the stretching ratio is 2.5*2.5.

[0093] Example 5

[0094] The method is basically the same as Example 1, except that in this embodiment, the water absorbent of the polyamide heat-sealing layer is a combination of calcium oxide and calcium hydroxide. The total thickness of the polyamide fresh-keeping composite film of this embodiment is 30 μm, wherein the thickness ratio of the polyamide surface layer, the first oxygen-absorbing layer, the barrier core layer, the second oxygen-absorbing layer, and the heat-sealing layer is 1:2:1.5:2:0.8.

[0095] Example 6

[0096] The method is basically the same as Example 1, except that in this embodiment, the water absorbent of the polyamide heat-sealing layer is calcium hydroxide. The total thickness of the polyamide fresh-keeping composite film in this embodiment is 90 μm.

[0097] In this embodiment, in the modified oxygen-absorbing barrier agent, the layered inorganic particles can also be selected from one or more combinations of nano-silicon dioxide, nano-mica, nano-montmorillonite, layered double hydroxide, kaolin, and nano-alumina, and the oxygen absorber can also be selected from one or more combinations of ascorbic acid-based oxygen absorbers, gallic acid-based oxygen absorbers, unsaturated fatty acid-based oxygen absorbers, and naturally classified oxygen absorbers; in the polyamide surface layer and the polyamide heat-sealing layer, the lubricant can also be selected from one or more combinations of erucic acid amide, oleic acid amide, ethylene bisstearamide, silicone powder, silicone oil, polyethylene wax, and oxidized polyethylene wax, and the opening agent can also be selected from one or more combinations of silicon dioxide, talc, kaolin, calcium carbonate, clay, magnesium carbonate, barium carbonate, calcium phosphate, alumina, and titanium dioxide.

[0098] Comparative Example 1

[0099] The difference from Example 1 is that in the first oxygen absorption layer and the second oxygen absorption layer of this comparative example, the oxygen absorption barrier agent is not modified with cinnamic acid.

[0100] Comparative Example 2

[0101] The difference from Example 1 is that the first oxygen absorbing layer and the second oxygen absorbing layer of this comparative example do not contain a modified oxygen absorbing barrier agent.

[0102] The first oxygen absorbing layer and the second oxygen absorbing layer of this comparative example are composed of the following raw materials in percentage by mass: 30% PA6 and 70% MXD6.

[0103] Implementation effect evaluation

[0104] The following is a specific test of the composite membranes prepared in Examples 1-6 and Comparative Examples 1-2 to further illustrate the excellent effects achieved by the present invention:

[0105] Tensile strength and elongation at break: tested in accordance with the relevant standards of GB / T 1040;

[0106] Oxygen transmission rate: tested according to the relevant standards of ASTM D3985;

[0107] Freshness-locking property: It is evaluated by the sensory evaluation method. After the film is made into bags, a certain amount of fresh garlic paste is filled in and sealed. After storing in a cool place for one week, the appearance and flavor of the garlic paste are observed and compared. The freshness-locking property of ○ is excellent, □ is good, △ is average, and × is poor.

[0108] The test results are shown in the table below:

[0109] Table 1 Performance test results statistics

[0110]

[0111] It can be seen from the test results of Example 1 and Comparative Example 1 that, compared with Example 1, the unmodified layered inorganic particles in Comparative Example 1 have poor dispersibility in the polymer matrix, resulting in reduced mechanical properties of the film, and do not have oxygen absorption barrier function, resulting in poor film barrier properties.

[0112] It can be seen from the test results of Example 1 and Comparative Example 2 that, compared with Example 1, Comparative Example 2 does not contain layered inorganic particles and has poor barrier properties.

[0113] From the test results of Example 1 and the common BOPA / CPP composite film on the market, it can be seen that compared with the common BOPA / CPP composite film on the market, the polyamide surface layer, the first oxygen absorption layer, the barrier core layer, the second oxygen absorption layer, and the polyamide heat-sealing layer contained in Example 1 make the composite film have good barrier and freshness-locking properties, which can help maintain the freshness of the packaged contents and effectively extend its shelf life.

[0114] The above is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A polyamide fresh-keeping composite film with oxygen absorption function, characterized in that: The polyamide fresh-keeping composite film with oxygen absorption function comprises, from top to bottom, a polyamide surface layer, a first oxygen absorption layer, a barrier core layer, a second oxygen absorption layer and a polyamide heat-sealing layer; The polyamide surface layer is composed of the following raw materials in percentage by mass: 93-99% PA6, 0.5-3.5% Slip agent, 0.5-3.5% anti-blocking agent; The first oxygen absorbing layer and the second oxygen absorbing layer are composed of the following raw materials in percentage by mass: 10-38% PA6, 60-80% MXD6, 2.0-10% modified oxygen absorbing barrier agent; the modified oxygen absorbing barrier agent is loaded with oxygen absorbing Layered inorganic particles of an oxidizing agent; The barrier core layer is 100% EVOH; The polyamide heat-sealing layer is composed of the following raw materials in percentage by mass: 87-99% copolymerized nylon, 0.25-2% opening agent, 0.25-1% lubricant, and 0.5-10% water absorbent.

2. The polyamide fresh-keeping composite film with oxygen absorption function according to claim 1, characterized in that: In the modified oxygen absorption barrier, the layered inorganic particles are one or a combination of nano silicon dioxide, nano mica, nano montmorillonite, layered double hydroxide, kaolin, and nano alumina.

3. The polyamide fresh-keeping composite film with oxygen absorption function according to claim 1, characterized in that: In the modified oxygen absorbing barrier, the oxygen absorber is one or a combination of ascorbic acid oxygen absorbers, unsaturated fatty acid oxygen absorbers, and phenolic hydroxyl oxygen absorbers.

4. The polyamide fresh-keeping composite film with oxygen absorption function according to claim 1, characterized in that: In the polyamide surface layer and the polyamide heat-sealing layer, the lubricant is one or a combination of erucamide, oleamide, ethylenebisstearamide, silicone powder, silicone oil, polyethylene wax, and oxidized polyethylene wax.

5. The polyamide fresh-keeping composite film with oxygen absorption function according to claim 1, characterized in that: In the polyamide surface layer and the polyamide heat-sealing layer, the anti-blocking agent is one or a combination of silicon dioxide, talc, kaolin, calcium carbonate, clay, magnesium carbonate, barium carbonate, calcium phosphate, aluminum oxide, and titanium dioxide.

6. The polyamide fresh-keeping composite film with oxygen absorption function according to claim 1, characterized in that: In the barrier core layer, the ethylene molar content of EVOH is 20-40% mol / L.

7. The polyamide fresh-keeping composite film with oxygen absorption function according to claim 1, characterized in that: In the polyamide heat-sealing layer, the water absorbent is one or a combination of calcium oxide and calcium hydroxide.

8. The polyamide fresh-keeping composite film with oxygen absorption function according to claim 1, characterized in that: The total thickness of the composite film is 30-90 μm, wherein the thickness ratio of the polyamide surface layer, the first oxygen absorbing layer, the barrier core layer, the second oxygen absorbing layer and the heat sealing layer is 1:2:(1-2):2:(0.5-1).

9. The method for preparing a polyamide fresh-keeping composite film with oxygen absorption function according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1: Weigh each raw material according to the set ratio, mix each layer of raw materials separately, and disperse them evenly through a high-speed mixer; S2: The raw materials of each layer are melted and extruded through their respective extruders, flow out through a T-die, and are cooled on a chilled roller to form an unstretched sheet; S3: After the unstretched sheet is passed through a water tank for humidity adjustment, it is heated for synchronous transverse stretching; S4: performing heat setting treatment on the stretched film to obtain the polyamide fresh-keeping composite film with oxygen absorption function.

10. The method for preparing a polyamide fresh-keeping composite film with oxygen absorption function according to claim 9, characterized in that: In step S3, the stretching temperature is 160-210°C, and the stretching ratio is 2.5*2.5-3.2*3.2.

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