Low-crystal-point polyethylene-based packaging film as well as preparation method and application thereof

Abstract

The invention relates to the technical field of low-crystal-point packaging films, and discloses a low-crystal-point polyvinyl packaging film, and a preparation method and application thereof, and the preparation method comprises the following steps: synthesizing a four-arm alkyl long-chain hindered phenol antioxidant; the preparation method comprises the following steps: carrying out modification treatment on polyethylene resin by using a four-arm alkyl long-chain hindered phenol antioxidant to prepare a low-crystal-point polyethylene master batch; the low-crystal-point polyethylene-based packaging film is prepared by taking the low-crystal-point polyethylene master batch as a raw material and adopting an up-blowing blow molding film forming process, and the film product not only remarkably reduces the number of crystal points in unit area of the polyethylene-based film, but also remarkably improves the mechanical property of the polyethylene-based film, and can be applied to the field of packaging.

Description

Technical Field

[0001] The present invention relates to the technical field of low-crystallization point packaging films, and specifically relates to a low-crystallization point polyethylene-based packaging film, a preparation method and an application thereof. Background Art

[0002] Polyethylene films have many advantages such as high impact strength, excellent chemical stability, low temperature resistance, high transparency, easy heat sealing and high cost performance, and are widely used in the packaging material fields of food, medicine, electronic products, etc. During the processing of polyethylene packaging films, small raised particles often appear on the film surface, and this defect is called a crystallization point (also called a fish eye). The position of the crystallization point is often the stress concentration point. The existence of too many crystallization points will have serious adverse effects on the appearance, mechanical properties and service life of the polyethylene packaging film.

[0003] The raised crystallization point area of the polyethylene film is usually composed of polyethylene chain segments with relatively high molecular weights. The polyethylene resin contains cross-linked high molecular polymers, which cannot be uniformly melted and dispersed during the addition process, and form a film prior to the surrounding polymers, resulting in the appearance of crystallization points. Among them, the reason for the generation of cross-linked high molecular polymers in the polyethylene resin is that during the processing of the polyethylene resin, due to the action of high temperature and high shear stress, the C-H bonds or C-C bonds of some polyethylene chain segments are broken to generate free radicals. These free radicals are very active and can generate peroxide free radicals in the presence of trace amounts of oxygen, and transfer to the polyethylene carbon chain to occur a chain reaction, resulting in the relative molecular weight of some polyethylene resins increasing several times, leading to the generation of cross-linked high molecular polymers.

[0004] Research has found that adding antioxidants to polyethylene resin is one of the effective methods to eliminate crystallization points of polyethylene films. This is because antioxidants can capture the active free radicals generated during the processing of polyethylene resin, generate inactive free radicals, terminate the chain reaction, delay the oxidation process of polyethylene, and ensure the smooth progress of the processing process.

[0005] Hindered phenol antioxidants have the advantages of low toxicity, non-coloring, high efficiency and environmental protection, and are one of the antioxidants with the largest consumption and the widest application at present, and are widely used in polymer materials such as polyethylene. However, most of the commonly used phenolic antioxidants are small molecule substances, which are easily volatilized and lost when heated during the processing process, reducing the actual effective components of the antioxidants in the polymer. In addition, during the use of the polymer, small molecule antioxidants are easily migrated or extracted from the matrix under the action of heat, fire, solvents, etc., resulting in a decrease in the use performance of the material. A large number of studies and practices have shown that increasing the molecular weight of antioxidants can effectively improve the migration resistance and thermal stability of antioxidants, and avoid the volatilization of antioxidants due to heat or the extraction due to the action of solvents. Summary of the Invention

[0006] The present invention uses a self-developed four-armed alkyl long-chain hindered phenolic antioxidant as a modification component for polyethylene resin, and a low-crystallization-point polyethylene-based packaging film is prepared by extrusion blow molding. This film product not only significantly reduces the number of crystallization points per unit area of the polyethylene-based film, but also significantly improves the mechanical properties of the polyethylene-based film.

[0007] A low-crystallization-point polyethylene-based packaging film, comprising the following raw materials in parts by weight: 97-99 parts of low-density polyethylene resin; 0.3-1.5 parts of four-armed alkyl long-chain hindered phenolic antioxidant; 0.1-0.5 part of ultraviolet absorber; 0.1-0.5 part of antistatic agent; 0.1-0.5 part of antiblocking agent; Among them, the chemical structural general formula of the four-armed alkyl long-chain hindered phenolic antioxidant is: .

[0008] Preferably, the preparation method of the four-armed alkyl long-chain hindered phenolic antioxidant is as follows: Through the amino group -NH 2 of the diamine monomer and the alkenyl functional group of methyl acrylate to carry out an amino-ene addition reaction to generate intermediate 1; Through the ester functional group of intermediate 1 and the hydroxyl functional group of 5-hydroxypentanal to carry out a transesterification reaction to generate intermediate 2; Through intermediate 2 and 3,5-di-tert-butyl-4-hydroxyacetophenone containing α-H and N-dodecylmethylamine to carry out a Mannich condensation reaction to generate a four-armed alkyl long-chain hindered phenolic antioxidant.

[0009] Preferably, the diamine monomer is one of 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine.

[0010] Preferably, the ultraviolet absorber is one of ultraviolet absorber UV-329, ultraviolet absorber UV-326, ultraviolet absorber UV-531.

[0011] Preferably, the antistatic agent is antistatic agent AT.

[0012] Preferably, the antiblocking agent is octadecyl erucamide or stearamide.

[0013] A preparation method of a low-crystallization-point polyethylene-based packaging film, comprising the following steps: Step 1: Weigh the ingredients according to the formula of the low-crystallization-point polyethylene-based packaging film, add each raw material into a high-speed mixer and mix evenly, then extrude and pelletize through a twin-screw extruder, and obtain the low-crystallization-point polyethylene masterbatch after drying. Step 2: Add the low-crystallization-point polyethylene masterbatch into a single-screw extrusion blow molding machine, and blow and mold it into a film by the upward blowing method to obtain the low-crystallization-point polyethylene-based packaging film.

[0014] Preferably, the process parameters of the twin-screw extruder are set as follows: the temperatures of zones 1-6 are 140-160 °C, 155-165 °C, 160-170 °C, 160-180 °C, 160-180 °C, 175-185 °C respectively, and the rotation speed is 200-400 r / min.

[0015] Preferably, the process parameters of the single-screw extrusion blow molding machine are set as follows: the temperatures of zones 1-3 are 140-160 °C, 160-180 °C, 180-190 °C respectively, the rotation speed is 40-60 r / min, the traction speed is 5-7 m / min, the die head diameter of the blow molding machine is 60-70 mm, and the blow-up ratio is 2.5-2.9.

[0016] An application of a low-crystallization-point polyethylene-based packaging film in the packaging field.

[0017] Based on the mechanisms of amine-ene addition reaction, transesterification reaction and Mannich condensation reaction, the present invention designed and synthesized a four-armed alkyl long-chain hindered phenolic antioxidant, used it to modify polyethylene resin, and prepared a low-crystallization-point polyethylene masterbatch; using the low-crystallization-point polyethylene masterbatch as the raw material, a low-crystallization-point polyethylene-based packaging film was prepared by the upward blowing film-forming process. The experimental results show that: compared with the polyethylene-based film without using an antioxidant or using a conventional small molecule antioxidant, the polyethylene-based film prepared by the present invention can significantly reduce the number of crystal points per unit area and belongs to a low-crystallization-point polyethylene-based packaging film. And it is found that the low-crystallization-point polyethylene-based packaging film prepared by the present invention also has the beneficial technical effect of significant improvement in mechanical properties. Detailed Embodiments

[0018] Aiming at the problems commonly existing in hindered phenolic antioxidants, such as low molecular weight, strong polarity, poor compatibility with polymer materials and easy migration and precipitation, the present invention designed and synthesized a four-armed alkyl long-chain hindered phenolic antioxidant. The alkyl long chain has lipophilicity and can physically entangle with the molecular chain segments of polyethylene, effectively enhancing the interfacial compatibility between the antioxidant and polyethylene, thereby avoiding the migration and precipitation of the antioxidant in the polyethylene system. Example 1:

[0019] Using diamine monomers, methyl acrylate, 5-hydroxypentanal, 3,5-di-tert-butyl-4-hydroxyacetophenone and N-dodecylmethylamine as raw materials, tetra-armed alkyl long-chain hindered phenolic antioxidants (tetra-armed alkyl long-chain hindered phenolic antioxidants bridged by butanediamine, tetra-armed alkyl long-chain hindered phenolic antioxidants bridged by pentanediamine, tetra-armed alkyl long-chain hindered phenolic antioxidants bridged by hexanediamine, tetra-armed alkyl long-chain hindered phenolic antioxidants bridged by heptanediamine, tetra-armed alkyl long-chain hindered phenolic antioxidants bridged by octanediamine) are prepared through amine-ene addition reaction, transesterification reaction and Mannich condensation reaction. The preparation process is as follows: Step 1: Through the -NH 2 functional group of the diamine monomer and the alkenyl functional group of methyl acrylate to carry out an amine-ene addition reaction to generate Intermediate 1, whose chemical structural formula is: ; Step 2: Through the ester group functional group of Intermediate 1 and the hydroxyl group functional group of 5-hydroxypentanal to carry out a transesterification reaction to generate Intermediate 2, whose chemical structural formula is: ; Step 3: Through Intermediate 2 and 3,5-di-tert-butyl-4-hydroxyacetophenone containing α-H and N-dodecylmethylamine to carry out a Mannich condensation reaction to generate a tetra-armed alkyl long-chain hindered phenolic antioxidant, whose chemical structural formula is: ; Among them, the diamine monomer can be selected from the following raw materials: 1,4-Butanediamine: ; 1,5-Pentanediamine: ; 1,6-Hexanediamine: ; 1,7-Heptanediamine: ; 1,8-Octanediamine: ; Using the method for synthesizing tetra-armed alkyl long-chain hindered phenolic antioxidants, when 1,6-hexanediamine is used as the diamine monomer, the hexanediamine-bridged tetra-armed alkyl long-chain hindered phenolic antioxidant is synthesized, and its chemical structure is: ; The specific experimental steps for preparing the hexanediamine-bridged tetra-armed alkyl long-chain hindered phenolic antioxidant are as follows: Add 4.0 g of methyl acrylate and 40 mL of methanol to a three-necked flask, stir at room temperature until completely dissolved, then add dropwise to the three-necked flask a methanol solution containing 1.1 g of 1,6-hexanediamine. Stir and mix at room temperature for 10 min, then raise the temperature to 40 °C and carry out a stirring reaction. Monitor using thin-layer chromatography (the developing agent is petroleum ether, ethyl acetate and methanol, and their volume ratio is 3:1:10). After stirring and reacting for 10 h, the composition of the reaction solution no longer changes significantly. Rotate and evaporate to remove the excess methyl acrylate and methanol solvents, and dry in vacuo to obtain Intermediate 1; Under the protection of nitrogen, add 2.3 g of Intermediate 1, 2.5 g of 5-hydroxypentanal and 50 mL of cyclohexane to a three-necked flask, stir at room temperature until completely dissolved, add 0.8 mL of titanium tetraisopropoxide to the three-necked flask, raise the temperature to 90 °C and carry out a stirring reflux reaction, continuously distill out the methanol generated in the reaction, monitor using thin-layer chromatography (the developing agent is dichloromethane, methanol and ammonia water, and their volume ratio is 9.5:1:1). After stirring and reacting for 4 h, the composition of the reaction solution no longer changes significantly. Cool to 60 °C, add 2 mL of deionized water, stir and react for 20 min, filter while it is hot, wash with deionized water at 60 °C, rotate and evaporate to remove the solvent, and dry in vacuo to obtain Intermediate 2; Under the protection of nitrogen, add 1.8 g of Intermediate 2, 2.5 g of 3,5-di-tert-butyl-4-hydroxyacetophenone, 2.0 g of N-dodecylmethylamine and 50 mL of absolute ethanol to a three-necked flask. While stirring mechanically, slowly add 5 drops of concentrated hydrochloric acid to the three-necked flask, raise the temperature to 85 °C and carry out a reflux reaction for 8 h. Cool to room temperature, rotate and evaporate to remove the solvent, and dry in vacuo to obtain a hexanediamine-bridged four-armed alkyl long-chain hindered phenolic antioxidant; The nuclear magnetic resonance hydrogen spectrum characterization of the hexanediamine-bridged four-armed alkyl long-chain hindered phenolic antioxidant is as follows: 1 H NMR(CDCl 3 , 400 MHz) δ: 0.86 - 0.90 (t, 12H), 1.18 - 1.69 (m, 184H), 2.37 (s, 12H), 2.44 - 2.48 (t, 4H), 2.56 - 2.59 (t, 8H), 2.70 - 2.74 (t, 8H), 2.88 - 2.89 (d, 8H), 3.04 - 3.08 (t, 8H), 3.28 - 3.35 (m, 4H), 4.07 - 4.11 (t, 8H), 7.60 (s, 8H); Method for synthesizing tetra-armed alkyl long-chain hindered phenolic antioxidant. When diamine monomers are respectively 1,4-butanediamine, 1,5-pentanediamine, 1,7-heptanediamine, and 1,8-octanediamine, referring to the specific experimental steps for preparing hexamethylenediamine-bridged tetra-armed alkyl long-chain hindered phenolic antioxidant, tetra-armed alkyl long-chain hindered phenolic antioxidant bridged by butanediamine, tetra-armed alkyl long-chain hindered phenolic antioxidant bridged by pentanediamine, tetra-armed alkyl long-chain hindered phenolic antioxidant bridged by heptanediamine, and tetra-armed alkyl long-chain hindered phenolic antioxidant bridged by octanediamine are successively prepared. Example Two:

[0020] A low-crystallization-point polyethylene-based packaging film I, comprising the following raw materials in parts by weight: 98.2 parts of low-density polyethylene resin, with the trade name LD 150DW and a melt mass flow rate (MFR) of 0.3 g / 10 min (220 °C, 2 kg); 0.8 part of hexamethylenediamine-bridged tetra-armed alkyl long-chain hindered phenolic antioxidant; 0.5 part of ultraviolet absorber UV-329; 0.3 part of antistatic agent AT; 0.2 part of octadecyl erucamide. Example Three:

[0021] A preparation method of a low-crystallization-point polyethylene-based packaging film I, comprising the following steps: Step 1: Weigh the ingredients according to the formula of the low-crystallization-point polyethylene-based packaging film I, add each raw material to a high-speed mixer and mix evenly, extrude and pelletize through a twin-screw extruder, and vacuum dry at 80 °C for 6 h to obtain the low-crystallization-point polyethylene masterbatch I; Among them, the process parameters of the twin-screw extruder are set as follows: the temperatures of zones 1-6 are 150 °C, 160 °C, 165 °C, 170 °C, 170 °C, and 180 °C respectively, and the rotation speed is 300 r / min; Step 2: Add the low-crystallization-point polyethylene masterbatch I to a single-screw extrusion blow molding machine, and blow and mold it into a film by the upward blowing method to obtain a 100-μm low-crystallization-point polyethylene-based packaging film I; Among them, the process parameters of the single-screw extrusion blow molding machine are set as follows: the temperatures of zones 1-3 are 150 °C, 170 °C, and 185 °C respectively, the rotation speed is 50 r / min, the traction speed is 6 m / min, the die head diameter of the blow molding machine is 65 mm, and the blow-up ratio is 2.8. Example Four:

[0022] A low-crystallization-point polyethylene-based packaging film II, the difference in its raw material composition from the low-crystallization-point polyethylene-based packaging film I in Example One is only: 97.5 parts of low-density polyethylene resin and 1.5 parts of hexamethylenediamine-bridged tetra-armed alkyl long-chain hindered phenolic antioxidant; The preparation method of the low-crystallization-point polyethylene-based packaging film II is the same as that of the low-crystallization-point polyethylene-based packaging film I in Example 2. Example 5:

[0023] A low-crystallization-point polyethylene-based packaging film III, the difference in its raw material composition from the low-crystallization-point polyethylene-based packaging film I in Example 1 is only that: 98.7 parts of low-density polyethylene resin and 0.3 part of hexamethylenediamine-bridged tetra-armed alkyl long-chain hindered phenolic antioxidant; The preparation method of the low-crystallization-point polyethylene-based packaging film III is the same as that of the low-crystallization-point polyethylene-based packaging film I in Example 2. Comparative Example 1:

[0024] Prepare a polyethylene-based film a, the difference in its raw material composition from the low-crystallization-point polyethylene-based packaging film I in Example 1 is only that: use commercial antioxidant 264 (dibutylhydroxytoluene) to replace hexamethylenediamine-bridged tetra-armed alkyl long-chain hindered phenolic antioxidant; The preparation method of the polyethylene-based film a is the same as that of the low-crystallization-point polyethylene-based packaging film I in Example 2. Comparative Example 2:

[0025] Prepare a polyethylene-based film b: compared with the low-crystallization-point polyethylene-based packaging film I, the difference is only that: use low-density polyethylene resin to replace the low-crystallization-point polyethylene masterbatch I. Performance test:

[0026] (1) Crystallization point number test: According to Method 1 in Section 6.10.2 of the GB / T 11115-2009 standard, the number of fish eyes with major diameters less than 0.2 mm, 0.2 mm - 0.4 mm, 0.4 mm - 0.8 mm, and greater than 0.8 mm in each 1 m 2 film sample was measured respectively; (2) Mechanical property test: Use an Instron 5565 universal tensile testing machine to test the mechanical properties of the film sample according to GB / T 1040.3-2006 (sampling along the blown film direction), and record the longitudinal tensile strength and longitudinal elongation at break of the sample; among them, the sample size is 150 mm × 20 mm (length × width), and the test speed is 50 mm / min; The results of the above performance experiments are shown in Table 1 below.

[0027] Table 1 Performance experiment results of the low-crystallization-point polyethylene-based packaging film

[0028] Through comprehensive analysis of the above experimental results, the following conclusions can be drawn: Conclusion 1: Compared with the polyvinyl films without using antioxidants or using commercial small molecule antioxidants, the polyvinyl films prepared by using the self-developed four-armed alkyl long-chain hindered phenolic antioxidant of the present invention can significantly reduce the number of crystal points per unit area and belong to low-crystal-point polyvinyl packaging films; Conclusion 2: The low-crystal-point polyvinyl packaging film prepared by the present invention also achieves a beneficial technical effect of significant improvement in mechanical properties.

Claims

1. A low crystal point polyethylene-based packaging film, characterized in that: The invention comprises the following raw materials in parts by weight: 97-99 parts of low density polyethylene resin; 0.3-1.5 parts of four-arm alkyl long-chain hindered phenol antioxidant; 0.1-0.5 parts of anti-ultraviolet agent; 0.1-0.5 parts of antistatic agent; 0.1-0.5 parts of opening agent; Among them, the general chemical structure formula of the four-arm alkyl long-chain hindered phenol antioxidant is: 。 2. A low crystal point polyethylene-based packaging film according to claim 1, characterized in that: The preparation method of the four-arm alkyl long-chain hindered phenol antioxidant is: The -NH2 functional group of the diamine monomer and the alkenyl functional group of methyl acrylate undergo an amine-ene addition reaction to generate intermediate 1; The ester functional group of intermediate 1 and the hydroxyl functional group of 5-hydroxyvaleraldehyde undergo an ester exchange reaction to generate intermediate 2; The intermediate 2 undergoes a Mannich condensation reaction with α-H-containing 3,5-di-tert-butyl-4-hydroxyacetophenone and N-dodecylmethylamine to generate a four-arm alkyl long-chain hindered phenol antioxidant.

3. A low crystal point polyethylene-based packaging film according to claim 2, characterized in that: The diamine monomer is one of 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine and 1,8-octanediamine.

4. The low crystal point polyethylene-based packaging film according to claim 1, characterized in that: The anti-ultraviolet agent is one of the anti-ultraviolet agent UV-329, the anti-ultraviolet agent UV-326 and the anti-ultraviolet agent UV-531.

5. The low crystal point polyethylene-based packaging film according to claim 1, characterized in that: The antistatic agent is antistatic agent AT.

6. The low crystal point polyethylene-based packaging film according to claim 1, characterized in that: The opening agent is octadecyl erucamide or stearic acid amide.

7. A method for preparing a low crystal point polyethylene-based packaging film according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: Prepare ingredients according to the formula of low crystal point polyethylene-based packaging film, add various raw materials into a high-speed mixer and mix them evenly, extrude and granulate them through a twin-screw extruder, and obtain low crystal point polyethylene masterbatch after drying; Step 2: Add the low crystal point polyethylene masterbatch into a single screw extruder film blowing machine, and use the upward blowing method to blow the film to obtain a low crystal point polyethylene-based packaging film.

8. The method for preparing a low crystal point polyethylene-based packaging film according to claim 7, characterized in that: The process parameters of the twin-screw extruder are set as follows: the temperatures of zones 1-6 are 140-160°C, 155-165°C, 160-170°C, 160-180°C, 160-180°C, 175-185°C, respectively, and the rotation speed is 200-400r / min.

9. The method for preparing a low crystal point polyethylene-based packaging film according to claim 7, characterized in that: The process parameters of the single screw extrusion film blowing machine are set as follows: the temperatures of zones 1-3 are 140-160° C., 160-180° C., and 180-190° C., respectively; the rotation speed is 40-60 r / min; the traction speed is 5-7 m / min; the die head diameter of the film blowing machine is 60-70 mm; and the blow-up ratio is 2.5-2.

9.

10. Use of a low crystal point polyethylene-based packaging film according to any one of claims 1 to 6 in the field of packaging.

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