A low-crystallization-point polyethylene-based packaging film, preparation method and application

Abstract

The present invention relates to the technical field of low-crystallization point packaging films, and discloses a low-crystallization point polyethylene-based packaging film, a preparation method and an application, including: synthesizing a four-armed alkyl long-chain hindered phenolic antioxidant; using the four-armed alkyl long-chain hindered phenolic antioxidant to modify polyethylene resin to prepare a low-crystallization point polyethylene masterbatch; using the low-crystallization point polyethylene masterbatch as a raw material and adopting an upward blowing film blowing process to prepare a low-crystallization point polyethylene-based packaging film. This film product not only significantly reduces the number of crystal points per unit area of the polyethylene-based film, but also significantly improves the mechanical properties of the polyethylene-based film and can be applied in the packaging field.

Description

Technical Field

[0001] The present invention relates to the technical field of low-crystallization point packaging films, and particularly 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 a stress concentration point. The existence of too many crystallization points will have a serious adverse impact on the appearance, mechanical properties and service life of the polyethylene packaging film.

[0003] The raised crystallization point region 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 chain transfer occurs to the polyethylene carbon chain to cause a chain reaction, resulting in a multiple increase in the relative molecular weight of some polyethylene resins and 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 the crystallization points of polyethylene films. This is because antioxidants can capture the active free radicals generated during the processing of polyethylene resin, generate non-active 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 dosage 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, 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 out or extracted from the matrix under the action of heat, 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:

[0008] 97-99 parts of low-density polyethylene resin;

[0009] 0.3-1.5 parts of a four-armed alkyl long-chain hindered phenolic antioxidant;

[0010] 0.1-0.5 part of an ultraviolet absorber;

[0011] 0.1-0.5 part of an antistatic agent;

[0012] 0.1-0.5 part of an antiblocking agent;

[0013] Among them, the general chemical structure formula of the four-armed alkyl long-chain hindered phenolic antioxidant is:

[0014] .

[0015] Preferably, the preparation method of the four-armed alkyl long-chain hindered phenolic antioxidant is as follows:

[0016] An amine-ene addition reaction occurs between the -NH2 functional group of the diamine monomer and the alkenyl functional group of methyl acrylate to generate intermediate 1;

[0017] An transesterification reaction occurs between the ester functional group of intermediate 1 and the hydroxyl functional group of 5-hydroxypentanal to generate intermediate 2;

[0018] A Mannich condensation reaction occurs between intermediate 2 and 3,5-di-tert-butyl-4-hydroxyacetophenone containing α-H and N-dodecylmethylamine to generate a four-armed alkyl long-chain hindered phenolic antioxidant.

[0019] Preferably, the diamine monomer is one of 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, and 1,8-octanediamine.

[0020] Preferably, the ultraviolet absorber is one of ultraviolet absorber UV-329, ultraviolet absorber UV-326, and ultraviolet absorber UV-531.

[0021] Preferably, the antistatic agent is antistatic agent AT.

[0022] Preferably, the antiblocking agent is octadecyl erucamide or stearic acid amide.

[0023] A preparation method of a low-crystallization-point polyethylene-based packaging film, comprising the following steps:

[0024] Step 1: According to the formula of the low-crystallization-point polyethylene-based packaging film, ingredients are prepared, and each raw material is added to a high-speed mixer and mixed evenly, then extruded and granulated by a twin-screw extruder, and dried to obtain a low-crystallization-point polyethylene masterbatch;

[0025] Step 2: The low-crystallization-point polyethylene masterbatch is added to a single-screw extrusion blown film machine, and blown into a film by the upward blowing method to obtain a low-crystallization-point polyethylene-based packaging film.

[0026] 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.

[0027] Preferably, the process parameters of the single-screw extrusion blown film 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 blown film machine is 60-70 mm, and the blow-up ratio is 2.5-2.9.

[0028] An application of a low-crystallization-point polyethylene-based packaging film in the packaging field.

[0029] 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 a raw material, a low-crystallization-point polyethylene-based packaging film was prepared by an upward blowing film blowing process;

[0030] 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;

[0031] And it is found that the low-crystallization-point polyethylene-based packaging film prepared by the present invention also has a beneficial technical effect of significant improvement in mechanical properties. Specific embodiments

[0032] Aiming at the problems commonly existing in hindered phenol antioxidants, such as low molecular weight, strong polarity, poor compatibility with polymer materials, and easy migration and precipitation, the present invention designs and synthesizes a four-armed alkyl long-chain hindered phenol 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:

[0033] Using diamine monomers, methyl acrylate, 5-hydroxypentanal, 3,5-di-tert-butyl-4-hydroxyacetophenone, and N-dodecylmethylamine as raw materials, through amine-ene addition reaction, transesterification reaction, and Mannich condensation reaction, a four-armed alkyl long-chain hindered phenol antioxidant (tetraamine-bridged four-armed alkyl long-chain hindered phenol antioxidant, pentaamine-bridged four-armed alkyl long-chain hindered phenol antioxidant, hexaamine-bridged four-armed alkyl long-chain hindered phenol antioxidant, heptaamine-bridged four-armed alkyl long-chain hindered phenol antioxidant, octaamine-bridged four-armed alkyl long-chain hindered phenol antioxidant) is prepared, and its preparation process is as follows:

[0034] The first step: Through the amine-ene addition reaction between the -NH2 functional group of the diamine monomer and the alkenyl functional group of methyl acrylate, intermediate 1 is generated, and its chemical structural formula is:

[0035] ;

[0036] The second step: Through the transesterification reaction between the ester functional group of intermediate 1 and the hydroxyl functional group of 5-hydroxypentanal, intermediate 2 is generated, and its chemical structural formula is:

[0037] ;

[0038] The third step: Through the Mannich condensation reaction of intermediate 2 with 3,5-di-tert-butyl-4-hydroxyacetophenone containing α-H and N-dodecylmethylamine, a four-armed alkyl long-chain hindered phenol antioxidant is generated, and its chemical structural formula is:

[0039] ;

[0040] Among them, the diamine monomer can be selected from the following raw materials:

[0041] 1,4-Butanediamine: ;

[0042] 1,5-Pentanediamine: ;

[0043] 1,6-Hexanediamine: ;

[0044] 1,7-Heptanediamine: ;

[0045] 1,8 - octanediamine: ;

[0046] Using the method for synthesizing tetra - armed alkyl - long - chained hindered phenolic antioxidants, when 1,6 - hexanediamine is used as the diamine monomer, the hexanediamine - bridged tetra - armed alkyl - long - chained hindered phenolic antioxidant is synthesized, and its chemical structure is:

[0047] ;

[0048] The specific experimental steps for preparing the hexanediamine - bridged tetra - armed alkyl - long - chained hindered phenolic antioxidant are as follows:

[0049] Add 4.0 g of methyl acrylate and 40 mL of methanol into a three - necked flask, stir at room temperature until completely dissolved, then dropwise add 10 mL of a methanol solution containing 1.1 g of 1,6 - hexanediamine into the three - necked flask, stir and mix at room temperature for 10 min, raise the temperature to 40 °C for stirring reaction, monitor by thin - layer chromatography (the developing agent is petroleum ether, ethyl acetate and methanol, and their volume ratio is 3:1:10), after stirring reaction for 10 h, the composition of the reaction solution no longer changes significantly, rotary evaporate to remove the excess methyl acrylate and methanol solvents, and dry under vacuum to obtain intermediate 1;

[0050] Under the protection of nitrogen, add 2.3 g of intermediate 1, 2.5 g of 5 - hydroxypentanal and 50 mL of cyclohexane into a three - necked flask, stir at room temperature until completely dissolved, add 0.8 mL of tetra - isopropyl titanate into the three - necked flask, raise the temperature to 90 °C for stirring and reflux reaction, continuously distill out the methanol generated in the reaction, monitor by thin - layer chromatography (the developing agent is dichloromethane, methanol and ammonia water, and their volume ratio is 9.5:1:1), after stirring reaction 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 60 °C deionized water, rotary evaporate to remove the solvent, and dry under vacuum to obtain intermediate 2;

[0051] Under the protection of nitrogen, add 1.8 g of intermediate 2, 2.5 g of 3,5 - di - tert - butyl - 4 - hydroxyphenylethanone, 2.0 g of N - dodecylmethylamine and 50 mL of absolute ethanol into a three - necked flask, slowly drop 5 drops of concentrated hydrochloric acid into the three - necked flask under mechanical stirring, raise the temperature to 85 °C for reflux reaction for 8 h, cool to room temperature, rotary evaporate to remove the solvent, and dry under vacuum to obtain the hexanediamine - bridged tetra - armed alkyl - long - chained hindered phenolic antioxidant;

[0052] The nuclear magnetic resonance hydrogen spectrum characterization of the hexanediamine - bridged tetra - armed alkyl - long - chained hindered phenolic antioxidant is: 11H NMR (CDCl3, 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);

[0053] Using the method for synthesizing tetra - armed alkyl - long - chained hindered phenolic antioxidants, 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 hexanediamine - bridged tetra - armed alkyl - long - chained hindered phenolic antioxidants, tetra - armed alkyl - long - chained hindered phenolic antioxidants bridged by butanediamine, tetra - armed alkyl - long - chained hindered phenolic antioxidants bridged by pentanediamine, tetra - armed alkyl - long - chained hindered phenolic antioxidants bridged by heptanediamine, and tetra - armed alkyl - long - chained hindered phenolic antioxidants bridged by octanediamine are successively prepared. Example Two:

[0054] A low - crystallization - point polyethylene - based packaging film I, comprising the following raw materials in parts by weight:

[0055] 98.2 parts of low - density polyethylene resin, with the brand LD 150DW and a melt mass - flow rate (MFR) of 0.3 g / 10 min (220 °C, 2 kg);

[0056] 0.8 part of hexanediamine - bridged tetra - armed alkyl - long - chained hindered phenolic antioxidant;

[0057] 0.5 part of ultraviolet absorber UV - 329;

[0058] 0.3 part of antistatic agent AT;

[0059] 0.2 part of octadecyl erucamide. Example Three:

[0060] A preparation method of the low - crystallization - point polyethylene - based packaging film I, comprising the following steps:

[0061] Step 1: According to the formula of the low - crystallization - point polyethylene - based packaging film I, proportion the raw materials, add each raw material into a high - speed mixer and mix evenly, extrude and pelletize through a twin - screw extruder, and dry in vacuum at 80 °C for 6 h to obtain the low - crystallization - point polyethylene masterbatch I;

[0062] 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;

[0063] Step 2: Add the low-crystallinity polyethylene masterbatch Ⅰ into a single-screw extrusion blow molding machine, and blow it into a film by the upward blowing method to obtain a 100-μm low-crystallinity polyethylene-based packaging film Ⅰ;

[0064] 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 4:

[0065] A low-crystallinity polyethylene-based packaging film Ⅱ, the difference in its raw material composition from the low-crystallinity polyethylene-based packaging film Ⅰ in Example 1 is only that: 97.5 parts of low-density polyethylene resin and 1.5 parts of hexamethylenediamine-bridged tetra-armed alkyl long-chain hindered phenolic antioxidant;

[0066] The preparation method of the low-crystallinity polyethylene-based packaging film Ⅱ is the same as that of the low-crystallinity polyethylene-based packaging film Ⅰ in Example 2. Example 5:

[0067] A low-crystallinity polyethylene-based packaging film Ⅲ, the difference in its raw material composition from the low-crystallinity polyethylene-based packaging film Ⅰ in Example 1 is only that: 98.7 parts of low-density polyethylene resin and 0.3 parts of hexamethylenediamine-bridged tetra-armed alkyl long-chain hindered phenolic antioxidant;

[0068] The preparation method of the low-crystallinity polyethylene-based packaging film Ⅲ is the same as that of the low-crystallinity polyethylene-based packaging film Ⅰ in Example 2.

[0069] Comparative Example 1:

[0070] Prepare a polyethylene-based film a, the difference in its raw material composition from the low-crystallinity polyethylene-based packaging film Ⅰ in Example 1 is only that: use a commercial antioxidant 264 (dibutylhydroxytoluene) to replace the hexamethylenediamine-bridged tetra-armed alkyl long-chain hindered phenolic antioxidant;

[0071] The preparation method of the polyethylene-based film a is the same as that of the low-crystallinity polyethylene-based packaging film Ⅰ in Example 2.

[0072] Comparative Example 2:

[0073] Prepare a polyethylene-based film b: compared with the low-crystallinity polyethylene-based packaging film Ⅰ, the difference is only that: use low-density polyethylene resin to replace the low-crystallinity polyethylene masterbatch Ⅰ.

[0074] Performance test:

[0075] (1)Measurement of the number of crystal points: According to Method 1 in Section 6.10.2 of the standard GB / T 11115-2009, the number of fisheyes with major axis 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 of the film sample was measured respectively;

[0076] (2)Mechanical property test: The mechanical properties of the film sample were tested using an Instron 5565 universal tensile testing machine in accordance with GB / T 1040.3-2006 (sampling along the film blowing direction), and the longitudinal tensile strength and longitudinal elongation at break of the sample were recorded; among them, the sample size was 150 mm × 20 mm (length × width), and the test speed was 50 mm / min;

[0077] The results of the above performance experiments are shown in Table 1 below.

[0078] Table 1 Experimental results of the properties of low-crystal-point polyethylene-based packaging film

[0079]

[0080] Based on the comprehensive analysis of the above experimental results, the following conclusions can be drawn:

[0081] Conclusion 1: Compared with the polyethylene-based film without using antioxidant or using commercial small-molecule antioxidants, the polyethylene-based film prepared by using the self-developed four-armed alkyl long-chain hindered phenolic antioxidant in the present invention can significantly reduce the number of crystal points per unit area and belongs to the low-crystal-point polyethylene-based packaging film;

[0082] Conclusion 2: The low-crystal-point polyethylene-based packaging film prepared in the present invention also has the beneficial technical effect of significant improvement in mechanical properties.

Claims

1. A low-crystallization-point polyethylene-based packaging film, characterized in that, The composition 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 anti-blocking agent; Among them, the general chemical structure formula of the four-arm alkyl long-chain hindered phenol antioxidant is: 。 2. The low-crystallization-point polyethylene-based packaging film according to claim 1, wherein 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. The low-crystallization-point polyethylene-based packaging film according to claim 2, wherein, 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. A low-crystallization-point polyethylene-based packaging film according to claim 1, characterized in that, The antistatic agent is antistatic agent AT.

6. The low-crystallization-point polyethylene-based packaging film according to claim 1, wherein, The opening agent is octadecyl erucamide or stearamide.

7. A method for preparing a low-crystallization-point polyethylene-based packaging film according to any one of claims 1-6, 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 all 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 adopt the upward blowing method to blow the film to obtain a low crystal point polyethylene-based packaging film.

8. The preparation method of a low-crystallization-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, and 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 the low-crystallinity polyethylene-based packaging film according to any one of claims 1 to 6 in the field of packaging.

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