Moisture absorbing packaging composite film and process for preparing the same

Abstract

The application relates to the technical field of development of moisture-proof and moisture-absorbing packaging materials, and discloses a moisture-absorbing packaging composite film and a preparation process thereof, which comprises the following steps: preparing a tricarboxypyridyl s-triazine type ligand; preparing a MOF type moisture absorber through a coordination reaction between the tricarboxypyridyl s-triazine type ligand and metal ions; functionally modifying low-density polyethylene resin by using the MOF type moisture absorber to prepare a moisture-absorbing polyethylene; and preparing a moisture-absorbing packaging composite film by using the moisture-absorbing polyethylene as raw material to form an inner layer and adopting a nine-layer co-extrusion blow molding film process, wherein the composite film has excellent moisture-absorbing performance and moisture-proof performance and can be used in the packaging field.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of development of moisture-proof and moisture-absorbing packaging materials, in particular to a moisture-absorbing packaging composite film and a preparation process thereof. BACKGROUND

[0002] At present, most moisture-proof packaging in the market uses a desiccant as a moisture absorber, so as to achieve the purpose of moisture-proof by using the desiccant to absorb the moisture in the packaging. However, such packaging has some problems, for example, the moisture absorber is easy to be missed or eaten by mistake during the packaging process, and the moisture absorber occupies a certain packaging space and increases the weight of products, in addition, the purchase of the desiccant needs to be additionally increased, and the packaging cost is increased, and the development and application of the packaging material with the moisture-proof and moisture-absorbing functions can well solve a series of problems.

[0003] Metal-organic framework (MOF) is a kind of porous crystalline material formed by self-assembly of metal ions and organic ligands through coordination bonds, has the characteristics of large surface area, super-high porosity and more than 90% of pore space, and has excellent moisture absorption activity, and there is a report in the prior art that the MOF material is used as a moisture absorber to be applied in food preservation. SUMMARY

[0004] The application independently develops a new type of MOF type moisture absorber, and the MOF type moisture absorber is used to simultaneously improve the moisture absorption performance and the moisture-proof performance of the nine-layer co-extrusion film, so that a moisture-absorbing packaging composite film is prepared, and the moisture-absorbing packaging composite film can be used to manufacture the packaging material with the moisture-proof and moisture-absorbing functions.

[0005] A preparation process of a moisture-absorbing packaging composite film comprises the following steps:

[0006] Step one: preparing a tricarboxypyridyl s-triazine type ligand;

[0007] Step two: preparing the MOF type moisture absorber by the coordination reaction of the tricarboxypyridyl s-triazine type ligand and metal ions; wherein the metal ions are one of Ag + , Cu 2+ , Ca 2+ , Ti 2+ , Zn 2+ ;

[0008] Step three: modifying the low-density polyethylene resin by using the MOF type moisture absorber to prepare the moisture-absorbing polyethylene;

[0009] Step five: generating the inner layer by using the moisture-absorbing polyethylene as the raw material, and preparing the moisture-absorbing packaging composite film by using the nine-layer co-extrusion blow molding process.

[0010] Preferably, the preparation method of the tricarboxypyridyl s-triazine type ligand is as follows:

[0011] Step S2-1: 5-(methylamino)nicotinic acid methyl ester is used as a nucleophile, and a nucleophilic substitution reaction occurs between the secondary amine function of 5-(methylamino)nicotinic acid methyl ester and the chlorine function of cyanuric chloride, to generate a triester pyridyl s-triazine type monomer;

[0012] Step S2-2: In the presence of sodium hydroxide, the ester function of the triester pyridyl s-triazine type monomer undergoes a hydrolysis reaction to generate a tricarboxy pyridyl s-triazine type ligand.

[0013] Preferably, the preparation method of the moisture-absorbing packaging composite film is as follows:

[0014] Step S4-1: The moisture-absorbing packaging composite film is set to be a nine-layer co-extruded film, and the film structure is as follows:

[0015] First layer: low-density polyethylene resin layer, 10-25 parts by weight;

[0016] Second layer: low-density polyethylene resin layer, 3-10 parts by weight;

[0017] Third layer: low-density polyethylene resin layer, 5-15 parts by weight;

[0018] Fourth layer: maleic anhydride grafted low-density polyethylene resin layer, 3-8 parts by weight;

[0019] Fifth layer: ethylene-vinyl alcohol copolymer resin layer, 10-25 parts by weight;

[0020] Sixth layer: maleic anhydride grafted low-density polyethylene resin layer, 3-8 parts by weight;

[0021] Ninth layer: low-density polyethylene resin layer, 5-15 parts by weight;

[0022] Eighth layer: low-density polyethylene resin layer, 3-10 parts by weight;

[0023] Ninth layer: moisture-absorbing polyethylene layer, 10-30 parts by weight

[0024] Step S4-2: The raw materials in step S4-1 are respectively fed into a nine-layer co-extruded film blowing machine, melted and extruded, converged at the die of the nine-layer die through their respective flow channels, and then blown and formed, with a blowing ratio controlled at 2.5-2.9, to prepare the moisture-absorbing packaging composite film.

[0025] Preferably, the mass ratio of the MOF type moisture-absorbing agent to the low-density polyethylene resin in the moisture-absorbing polyethylene is 1:(3-15).

[0026] The moisture-absorbing packaging composite film prepared according to the above process has a thickness of 50-150 μm.

[0027] Preferably, the moisture absorption rate of the moisture absorption packaging composite film is (0.4-0.5) %, the water vapor transmission amount is (1.0-1.5) g / (m 2 ·24h).

[0028] Advantages:

[0029] The present application designs and synthesizes a novel tricarboxypyridyl s-triazine type ligand, based on metal coordination, a MOF type moisture absorber is prepared, the MOF type moisture absorber is used for functional modification of polyethylene resin to obtain a moisture absorption type polyethylene, the moisture absorption type polyethylene is used as raw material to form an inner layer, and a nine-layer co-extrusion blow molding process is adopted to prepare a moisture absorption packaging composite film.

[0030] Through experiments, it is found that the novel composite film developed by the present application has achieved significant improvement in moisture absorption and moisture-proof performance, and can be used in the packaging field. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is the chemical structural formula of the tricarboxypyridyl s-triazine type monomer;

[0032] Figure 2 is the chemical structural formula of the tricarboxypyridyl s-triazine type ligand;

[0033] Figure 3 is the performance test result of the moisture absorption packaging composite film. DETAILED DESCRIPTION

[0034] Example 1:

[0035] The MOF type moisture absorber is prepared, and the preparation steps are as follows:

[0036] Step one: preparing a tricarboxypyridyl s-triazine type ligand;

[0037] Step two: preparing a MOF type moisture absorber by coordination reaction of the tricarboxypyridyl s-triazine type ligand and metal ions;

[0038] The metal ion is one of Ag + , Cu 2+ , Ca 2+ , Ti 2+ , Zn 2+ In this embodiment, Cu 2+ is selected;

[0039] The specific experimental steps for preparing the MOF type moisture absorber are as follows:

[0040] (1) preparing a tricarboxypyridyl s-triazine type ligand, and the preparation process is as follows:

[0041] Preparation of triester pyridyl s-triazine monomer: using 5-(methylamino) nicotinic acid methyl ester as a nucleophile, a nucleophilic substitution reaction between the secondary amine function of 5-(methylamino) nicotinic acid methyl ester and the chlorine function of cyanuric chloride was carried out to generate triester pyridyl s-triazine monomer, the chemical structural formula of which is shown in Figure 1 The specific experimental steps are as follows: 1.8 g of cyanuric chloride, 0.7 g of anhydrous potassium carbonate and 5.0 g of 5-(methylamino) nicotinic acid methyl ester were sequentially added to a three-necked flask, which was placed in an ice water bath under the protection of nitrogen for 30 min, then 40 mL of anhydrous tetrahydrofuran and 20 mL of anhydrous 1,4-dioxane were sequentially injected into the three-necked flask, and the reaction was stirred for 2 h under the ice water bath condition, then the ice water bath was removed, the reaction was stirred for 4 h at room temperature, the temperature was increased to 100 ℃ for reflux reaction for 4 h, the solvent was removed by distillation under reduced pressure, and then the product was washed with ethanol and deionized water sequentially until neutral, and then dried in vacuum to obtain the triester pyridyl s-triazine monomer.

[0042] Preparation of tricarboxy pyridyl s-triazine ligand: under the condition of the presence of sodium hydroxide, the ester function of the triester pyridyl s-triazine monomer was hydrolyzed to generate the tricarboxy pyridyl s-triazine ligand, the chemical structural formula of which is shown in Figure 2 The specific experimental steps are as follows: 2.9 g of the triester pyridyl s-triazine monomer, 2.0 g of sodium hydroxide, 10 mL of 1,4-dioxane and 40 mL of deionized water were added to a three-necked flask, and the reaction was stirred for 2 h at 70 ℃, then the pH of the solution was adjusted to 2 using concentrated hydrochloric acid, and then the solution was cooled to room temperature, washed with deionized water and dried in vacuum to obtain the tricarboxy pyridyl s-triazine ligand.

[0043] The nuclear magnetic resonance hydrogen spectrum of the tricarboxy pyridyl s-triazine ligand is shown in 1 H NMR (CDCl3, 400 MHz) δ: 3.79 (s, 9H), 7.83 (s, 3H), 8.41 (s, 3H), 8.77 (s, 3H); the active hydrogen in the carboxyl function of the tricarboxy pyridyl s-triazine ligand does not peak in the CDCl3 solvent;

[0044] (2) Preparation of MOF type moisture absorbent: 5.3 g of the tricarboxy pyridyl s-triazine ligand and 4.5 g of copper nitrate were dissolved in 100 mL of N,N-dimethylformamide, and then the solution was sealed in a Teflon-lined stainless steel autoclave and ultrasonically treated for 30 min, and then the solution was heated to 100 ℃ for reaction for 48 h, and then the solution was cooled to room temperature, centrifuged at 8000 r / min for 15 min, redispersed with N,N-dimethylformamide, centrifuged and dried to obtain the MOF type moisture absorbent.

[0045] Example 2:

[0046] Preparation of moisture-absorbing polyethylene: 10 g of low-density polyethylene resin and 2 g of MOF type moisture absorber were added to a twin-screw extruder, and were blended, melted, extruded and pelletized by the twin-screw extruder to obtain moisture-absorbing polyethylene;

[0047] The process parameters of the twin-screw extruder were set as follows: the temperatures of zones 1-3 were 120℃, 150℃ and 180℃ respectively, and the rotation speed was 40 r / min.

[0048] The low-density polyethylene resin was purchased from China Offshore Shell Petrochemical Co., Ltd., and had a specification of 2420H, Mn ~ 180000 and MFR 2.0-2.5 g / 10 min.

[0049] Example 3:

[0050] (1) Preparation of moisture-absorbing packaging composite film, comprising the following steps:

[0051] Step one: the moisture-absorbing packaging composite film was set as a nine-layer co-extruded film, and the film structure was as follows:

[0052] First layer: low-density polyethylene resin layer, 20 parts by weight;

[0053] Second layer: low-density polyethylene resin layer, 5 parts by weight;

[0054] Third layer: low-density polyethylene resin layer, 10 parts by weight;

[0055] Fourth layer: maleic anhydride grafted low-density polyethylene resin layer, 5 parts by weight;

[0056] Fifth layer: ethylene-vinyl alcohol copolymer resin layer, 20 parts by weight;

[0057] Sixth layer: maleic anhydride grafted low-density polyethylene resin layer, 5 parts by weight;

[0058] Ninth layer: low-density polyethylene resin layer, 10 parts by weight;

[0059] Eighth layer: low-density polyethylene resin layer, 5 parts by weight;

[0060] Ninth layer: moisture-absorbing polyethylene layer, 20 parts by weight;

[0061] Step two: each raw material in step one was respectively put into a nine-layer co-extruded film blowing machine, melted and extruded, converged at the die orifice of the nine-layer die through the respective flow channels, and then blow molded, with a blow-up ratio controlled at 2.7, cooled and wound up to obtain a moisture-absorbing packaging composite film with a thickness of 80 μm;

[0062] The process parameters of the screw extruder corresponding to the moisture-absorbing polyethylene layer and the low-density polyethylene resin layer are set as follows: the temperatures of zones 1-3 are 120 DEG C, 150 DEG C, and 180 DEG C respectively, the flow channel temperature is 175 DEG C, and the rotating speed is 30 r / min;

[0063] The process parameters of the screw extruder corresponding to the maleic anhydride grafted polyethylene resin layer are set as follows: the temperatures of zones 1-3 are 125 DEG C, 150 DEG C, and 165 DEG C respectively, the flow channel temperature is 160 DEG C, and the rotating speed is 15 r / min;

[0064] The process parameters of the screw extruder corresponding to the ethylene-vinyl alcohol copolymer resin layer are set as follows: the temperatures of zones 1-3 are 180 DEG C, 200 DEG C, and 210 DEG C respectively, the flow channel temperature is 205 DEG C, and the rotating speed is 40 r / min.

[0065] The ethylene-vinyl alcohol copolymer resin is purchased from Dongguan Kaisili Plastic Raw Material Co., Ltd., and has a specification of E105B, Mn ~ 10000, and ethylene content of 44%; the maleic anhydride grafted low-density polyethylene resin is purchased from Dongguan Tao Tao Plastic Raw Material Co., Ltd., and has a specification of 4288, Mn ~ 130000, and grafting rate of 4.5%.

[0066] (2) Preparation of the composite film: referring to the preparation steps and experimental conditions of the moisture-absorbing packaging composite film, the difference between the preparation experiment of the moisture-absorbing packaging composite film and the composite film is that the low-density polyethylene resin is used to replace the moisture-absorbing polyethylene, and the composite film is prepared as a comparative example.

[0067] Performance test:

[0068] (1) Moisture absorption performance test: a 60 mm x 60 mm (length x width) sample is dried in a 55 DEG C oven for 4 h, weighed, and recorded as the initial weight. The dried sample is completely immersed in distilled water for 24 h, taken out with tweezers, and the water on the surface of the sample is absorbed with water-absorbing filter paper, weighed, and recorded as the weight after moisture absorption. The moisture absorption rate of the sample is calculated, and the specific method is as follows:

[0069] Moisture absorption rate (%) = (weight of sample after moisture absorption-initial weight of sample) / initial weight of sample x 100%;

[0070] (2) Moisture resistance performance test: the water vapor transmission amount of the sample is tested according to GB / T 1037-2021 "Plastic films and sheets-determination of water vapor transmission-weighing and weighing method", and a 30 cm circular sample is placed in a glass desiccator with anhydrous calcium chloride as the desiccant at an environmental temperature of 25 DEG C for 72 h. Then, the moisture resistance performance is tested using a W3 / 060 type water vapor transmission tester.

[0071] (3)Mechanical property test: according to GB / T 13022-1991 "Plastic film tensile property test method", the tensile strength of the sample was tested, and the 30mm*5mm sample was fixed on the Instron 5565 universal tensile testing machine, and the tensile test was carried out at a tensile rate of 5mm / min, and the tensile strength in the longitudinal and transverse directions was recorded respectively;

[0072] The above experimental results are shown in Table 1 and Figure 1 .

[0073] Table 1 Performance test results of moisture absorption packaging composite film

[0074]

[0075] Through comprehensive analysis of the above experimental results, the following conclusions can be drawn:

[0076] The new composite film developed by the application has achieved significant improvement in moisture absorption and moisture-proof performance.

Claims

1. A process for the production of a moisture-absorbing packaging composite film, characterized by, It comprises the following steps: Step one: preparing a tricarboxypyridyl s-triazine type ligand, whose chemical structural formula is: ； Step two: a MOF type moisture absorbent is prepared by coordination reaction between a tricarboxypyridyl s-triazine type ligand and a metal ion; wherein the metal ion is one of Ag + , Cu 2+ , Ca 2+ , Ti 2+ , Zn 2+ . Step three: using the MOF type moisture absorbent to modify the low-density polyethylene resin, and preparing a moisture-absorbing polyethylene; Step five: using the moisture-absorbing polyethylene as raw material to form an inner layer, and using a nine-layer co-extrusion blow molding process to prepare a moisture-absorbing packaging composite film.

2. The process for preparing a moisture absorbing packaging composite film according to claim 1, characterized by, The preparation method of the tricarboxypyridyl s-triazine type ligand is: Step S2-1: using 5-(methylamino)nicotinic acid methyl ester as a nucleophile, and generating a triester pyridyl s-triazine type monomer through a nucleophilic substitution reaction between the secondary amine functional group of the 5-(methylamino)nicotinic acid methyl ester and the chlorine functional group of cyanuric chloride; Step S2-2: in the presence of sodium hydroxide, the ester functional group of the triester pyridyl s-triazine type monomer undergoes a hydrolysis reaction to generate a tricarboxypyridyl s-triazine type ligand.

3. The process for preparing a moisture absorbing packaging composite film according to claim 1, characterized by, The preparation method of the moisture-absorbing packaging composite film is: Step S4-1: setting the moisture-absorbing packaging composite film as a nine-layer co-extrusion film, and the film structure is in turn: The first layer: a low-density polyethylene resin layer, 10-25 parts by weight; The second layer: a low-density polyethylene resin layer, 3-10 parts by weight; The third layer: a low-density polyethylene resin layer, 5-15 parts by weight; The fourth layer: a maleic anhydride grafted low-density polyethylene resin layer, 3-8 parts by weight; The fifth layer: an ethylene-vinyl alcohol copolymer resin layer, 10-25 parts by weight; The sixth layer: a maleic anhydride grafted low-density polyethylene resin layer, 3-8 parts by weight; The ninth layer: a low-density polyethylene resin layer, 5-15 parts by weight; The eighth layer: a low-density polyethylene resin layer, 3-10 parts by weight; The ninth layer: a moisture-absorbing polyethylene layer, 10-30 parts by weight Step S4-2: putting each raw material in step S4-1 into a nine-layer co-extrusion film blowing machine, melting and extruding, converging at the die of the nine-layer die head through their own flow channels, and then blow molding, with a blow-up ratio controlled at 2.5-2.9, to prepare a moisture-absorbing packaging composite film.

4. The process for preparing a moisture absorbing packaging composite film according to claim 3, characterized by, The mass ratio of the MOF type moisture absorbent to the low-density polyethylene resin in the moisture-absorbing polyethylene is 1:(3-15).

5. A moisture absorbing packaging composite film prepared by the process according to any one of claims 1 to 4, characterized in that, The thickness of the moisture-absorbing packaging composite film is 50-150 μm.

6. A moisture absorbing packaging composite film according to claim 5, characterized in that The moisture absorption rate of the moisture absorption packaging composite film is (0.4-0.5)%, the water vapor transmission amount is (1.0-1.5) g / (m 2 •24h).

7. A moisture absorbing packaging composite film prepared by the process according to any one of claims 1 to 4, characterized by, The application of the moisture-absorbing packaging composite film in the packaging field.

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