Low-precipitation polyethylene film for clothing packaging and preparation method of low-precipitation polyethylene film

Abstract

The invention discloses a low-precipitation polyethylene film for clothing packaging and a preparation method thereof, and relates to the technical field of clothing packaging bags. The low-precipitation polyethylene film is prepared from the following raw materials in parts by mass: 50 to 70 parts of low-density polyethylene, 20 to 30 parts of linear low-density polyethylene, 5 to 10 parts of polyisobutene, 0.1 to 0.5 part of antioxidant, 0.2 to 1 part of slipping agent and 1 to 3 parts of nano silicon dioxide. According to the preparation method, a twin-screw partitioned temperature control extrusion and rotary die head film blowing process is adopted, the thickness of the obtained film is 20-50 microns, the longitudinal tensile strength is greater than or equal to 22 MPa, the moisture permeability is less than or equal to 4.8 g / (m < 2 >. 24 h), the tensile retention rate is greater than 85% after light aging for 1000 h, and the precipitation amount of the antioxidant is reduced by 92% compared with that of a traditional product. The film has the advantages of high barrier property, long-acting oxidation resistance and excellent flexibility, and can meet the strict requirements of high-end clothing packaging on the cleanliness and durability of materials.

Description

Technical Field

[0001] The present invention relates to the technical field of clothing packaging bags, in particular to a low-precipitation polyethylene film for clothing packaging and a preparation method thereof. Background Art

[0002] In the field of clothing packaging, polyethylene film is widely used due to its good flexibility, transparency and cost advantages. However, in actual use, it has the problem of oxidation and aging, which seriously affects the film performance and packaging effect.

[0003] Oxidative aging is a key factor in the degradation of polyethylene film. During production, storage, and use, the film is exposed to ambient oxygen, ultraviolet light, and high temperatures, which can break carbon-carbon and carbon-hydrogen bonds in the molecular chain, triggering free radical reactions. These free radicals combine with oxygen to form peroxides, which in turn trigger a chain oxidation reaction, breaking or crosslinking the polyethylene molecular chains. This can lead to a decrease in the film's mechanical properties, including tensile strength and elongation at break. The film becomes brittle and prone to cracking, compromising packaging integrity. This is particularly prone to damage during transportation and stacking of garments, increasing the risk of contamination.

[0004] Oxidative aging also alters the film's surface chemical structure, changing its surface energy and affecting the adhesion of printing inks and adhesives. This can cause printed patterns on packaging to fade and blur, and reduce the adhesive bond at the seal, affecting the packaging's appearance and sealability. Furthermore, low-molecular-weight products produced by oxidation may precipitate onto the film's surface, forming oil mist or particles that can contaminate clothing, affecting both quality and the consumer experience.

[0005] While existing technologies have slowed oxidation by adding antioxidants, these agents are prone to precipitation and are ineffective in inhibiting oxidative aging after long-term use. Furthermore, maintaining antioxidant properties is even more difficult during high-temperature processing and with decreasing film thickness. Therefore, developing a method for preparing polyethylene films with low precipitation and high antioxidant properties is crucial for improving the quality of clothing packaging and extending its shelf life. Summary of the Invention

[0006] The purpose of the present invention is to provide a low precipitation, high efficiency and anti-oxidation polyethylene film for clothing packaging and a preparation method thereof in view of the problems existing in the prior art.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a low-precipitation polyethylene film for clothing packaging, comprising the following raw materials in parts by weight: 50-70 parts of low-density polyethylene (LDPE), 20-30 parts of linear low-density polyethylene (LLDPE), 5-10 parts of polyisobutylene, 0.1-0.5 parts of antioxidant, 0.2-1 parts of lubricant, and 1-3 parts of nano-silica;

[0008] The antioxidant has a structure shown in Formula 1:

[0009] Formula 1;

[0010] The D represents deuterium;

[0011] Said Z1 is selected from: O, N-R1, S, CH2;

[0012] R1 is selected from the group consisting of: H, methyl, ethyl, tert-butyl, and phenyl.

[0013] Furthermore, the density of the low-density polyethylene (LDPE) is in the range of 0.910-0.940 g / cm 3 , tensile strength is 10-20MPa, crystallinity is 45%-60%, and transmittance is 85%-90%.

[0014] Furthermore, the density of the linear low-density polyethylene (LLDPE) is in the range of 0.915-0.925 g / cm 3 , tensile strength is 20-30MPa, crystallinity is 55%-70%, and transmittance is 80%-85%.

[0015] Furthermore, the antioxidant has both antioxidant and antibacterial effects.

[0016] Furthermore, the antibacterial effect is the inhibition of Escherichia coli growth.

[0017] Furthermore, the mass ratio of the low-density polyethylene to the linear low-density polyethylene is 3-5 parts:1 part.

[0018] Furthermore, the lubricant includes erucamide and / or oleamide.

[0019] Furthermore, the antioxidant includes any one of the compounds shown in the following structures:

[0020] ;

[0021] ;

[0022] .

[0023] Furthermore, the thickness of the low-elution polyethylene film for clothing packaging is 20-50 μm.

[0024] Furthermore, the low precipitation polyethylene film for clothing packaging has a longitudinal tensile strength of ≥20MPa, a transverse tensile strength of ≥18MPa, and a water vapor permeability of ≤5g / (m 2 ·24h).

[0025] A method for preparing a low-elution polyethylene film for clothing packaging comprises the following steps:

[0026] S1. The low-density polyethylene, linear low-density polyethylene and polyisobutylene are dried at 100-110 ℃ for 2-4 hours to obtain a dried material;

[0027] S2. The dried material and the antioxidant, lubricant and nano-silica were mixed at a speed of 300-500r / min for 10-20 minutes to obtain a mixture;

[0028] S3. The mixture was melt extruded and granulated, the melt extrusion granulation temperature was controlled at 160-190 ℃, the screw speed during the melt extrusion granulation process was 150-250r / min to obtain pellets;

[0029] S4. The pellets are blown into a film at a melt temperature of 180-220 ° C, the blow ratio is controlled at 2.5-3.5: 1, and the pulling speed is 10-20m / min;

[0030] S5. After cooling through an air ring, a low-precipitation polyethylene film with a thickness of 20-50 μm for clothing packaging is obtained.

[0031] Furthermore, the melt extrusion granulation in S3 adopts a twin-screw extruder, and the barrel temperature is controlled in zones: zone 1 160-170°C, zone 2 170-180°C, zone 3 180-190°C, and the die head temperature is controlled at 185-195°C.

[0032] Furthermore, the film blowing in S4 adopts a rotary die head, the die lip gap is adjusted to 0.8-1.2 mm, and the melt pressure is maintained at 12-18 MPa.

[0033] Furthermore, the air ring in S5 is cooled to a cooling temperature of 10°C.

[0034] The antioxidant described in this invention integrates key functional groups such as hydroxyl, amino, benzene ring conjugated system and long-chain alkyl groups into its molecular structure, forming a diversified antioxidant pathway. The hydroxyl (-OH) and benzene ring conjugation stabilize the intermediate product after free radical capture through the electron delocalization effect, significantly prolonging the antioxidant effect and avoiding the defect of traditional phenolic antioxidants that are deactivated by a single reaction. The electronic effect of the amino group, the lone pair of electrons can neutralize the active oxygen free radicals (such as O2 - ), while also enhancing the adsorption stability of molecules in polar environments (such as film surfaces) through protonation. The hydrophobic anchoring of the long-chain alkyl groups and the hydrophobic interaction of the terminal butyl chains embed into the amorphous regions of polyethylene, reducing the tendency of molecular migration and mitigating the risk of precipitation at the source.

[0035] The antioxidant of the present invention has a benzofuran ring whose function can be adjusted by replacing heteroatoms (O, N or S). When Z1 is an oxygen atom, the electron-rich property of the furan ring can preferentially bind to the Fe in the active center of the bacterial metalloenzyme. 3+ , inhibiting enzyme catalytic activity; if it is an amino group (-N-R1), it enhances interfacial compatibility with the polyethylene matrix through a hydrogen bonding network. The rigid structure of the furan ring restricts the disordered diffusion of molecules in the polyethylene matrix, synergizing with the physical barrier effect of nano-silica to further inhibit precipitation.

[0036] The branched structure of low-density polyethylene provides anchoring points for the antioxidant, while the linear structure of LLDPE enhances mechanical strength through the ordered arrangement of its molecular chains. The two blend together to form a dynamic hydrophobic network that restricts the migration of small molecules. Nanosilica forms hydrogen bonds with the amino / hydroxyl groups of the antioxidant, improving dispersion uniformity. The "maze effect" of the nanoparticles also extends the permeation path for oxygen and water vapor, synergistically reducing the oxidation rate. Erucamide forms a uniform lubricating layer on the film surface, reducing the localized accumulation of antioxidants caused by friction and maintaining the long-term distribution stability of the functional molecules.

[0037] The polyisobutylene described in this invention, as an elastomer, can effectively enhance the film's flexibility and tear resistance. Its long-chain molecular structure forms a physical crosslinking network with polyethylene (LDPE / LLDPE), absorbing impact energy and preventing brittle fracture during packaging or transportation. The addition of polyisobutylene can reduce melt viscosity and improve processing fluidity. In particular, during blown film molding (S4), the lubricating effect of polyisobutylene helps stabilize melt flow, reduce surface defects such as sharkskin, and ensure uniform film thickness. Polyisobutylene itself has low air permeability, which can help reduce the film's oxygen transmission rate, slow the oxidation reaction, and synergize with antioxidants to extend the film's service life. Polyisobutylene significantly improves film performance through multi-scale synergy with nano-silica, antioxidants and polyethylene matrix: its long hydrophobic chain combines with the physical barrier effect of nanoparticles to form a composite barrier to reduce moisture / oxygen permeability; at the same time, it anchors antioxidants through hydrophobic interaction and hydrogen bond network, inhibiting the migration and precipitation of functional molecules; and complements the branched / linear structure of polyethylene to balance the flexibility and tensile strength of the film, ultimately achieving an integrated design of low-precipitation, high-durability packaging film.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. Long-lasting antioxidant and low precipitation properties: Through molecular structure design, the antioxidant has both free radical capture and physical anchoring functions, forming a stable dispersion system in the polyethylene matrix, significantly delaying the oxidative aging process, and reducing the molecular mobility by more than 90%, avoiding the problem of traditional antioxidants easily precipitating and contaminating clothing.

[0040] 2. Synergistic improvement of mechanical properties and weather resistance: Nano-silica and polyisobutylene synergistically enhance the mechanical strength of the film, with longitudinal tensile strength ≥20MPa and moisture permeability ≤5g / (m 2 ·24h), and the tensile strength retention rate after 1000h of light aging is greater than 80%, achieving a balance between high barrier and durability.

[0041] 3. Optimized processing adaptability: Through twin-screw zone temperature control and rotary die head film blowing process, the high-temperature processing stability of the antioxidant is ensured, the film thickness deviation is less than ±1.5μm, and the surface roughness Ra≤0.12μm, meeting the homogenization requirements of ultra-thin packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The antioxidant 1 prepared in Preparation Example 1 of the present invention 1 HNMR spectrum.

[0043] Figure 2 These are the structures of the antioxidants synthesized in Preparation Examples 2 to 6 and their corresponding MS [MS+1].

[0044] Figure 3 This is the ABTS clearance result graph.

[0045] Figure 4 It is a performance test chart. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0047] Preparation Example 1

[0048] Synthesis of antioxidant 1:

[0049] ;

[0050] Step 1: Under nitrogen, 20.00 g of raw material 1 and 24.91 g of AlCl₃ were added to 150 g of dichloromethane. A solution of 20.24 g of raw material 2 dissolved in 80 g of dichloromethane was then slowly added dropwise. The mixture was added at -20°C, with the reaction temperature not exceeding 10°C. The reaction was allowed to proceed at room temperature for 6 h. After completion of the reaction, the pH was adjusted to neutral with 0.1 mol / L HCl at 0°C. 100 g of water was added, and the mixture was stirred for 30 min. The mixture was allowed to stand for separation, and the organic phase was retained. The aqueous phase was washed three times with 50 ml of dichloromethane. The combined organic phases were dried over 20 g of anhydrous magnesium sulfate, filtered, and spin-dried. Purification by silica gel column chromatography using petroleum ether and ethyl acetate as eluents yielded 28.40 g of intermediate 1. MS[MS+1]: 358.

[0051] Step 2: Under nitrogen, 28.40 g of Intermediate 1, 8.29 g of hydroxylamine hydrochloride, and 13.04 g of sodium acetate were added to 300 g of tetrahydrofuran. The mixture was reacted at 70°C for 12 h. The reaction solution was added to 1000 ml of water, incubated at 0°C overnight, and filtered to obtain a powdery solid. Purification by silica gel column chromatography using petroleum ether and ethyl acetate as eluents afforded 24.67 g of Intermediate 2. MS [MS+1]: 373.

[0052] Step 3: Under nitrogen protection, 24.67g of intermediate 2 and 250g of ultra-dry tetrahydrofuran were cooled to -70°C, and 4.50g of n-butyl lithium was added dropwise. After the addition was complete, the mixture was stirred for 1h. 18.70g of triisopropyl borate was added dropwise. After the addition was complete, the temperature was naturally raised to 25°C, and the reaction was carried out for 12h. The solvent was spin-dried to obtain 18.82g of intermediate 3.

[0053] Step 4: Under nitrogen, 18.82 g of intermediate 3, 32.44 g of starting material 3, 15.43 g of anhydrous potassium carbonate, 1.94 g of tetrakis(triphenylphosphine)palladium, and 200 g of a mixture of toluene, ethanol, and water (volume ratio 2:1:1) were heated to 75°C and refluxed for 10 hours. The mixture was then turned off, cooled to room temperature, and allowed to stand for separation. The aqueous phase was extracted twice with ethyl acetate. The combined organic phases were washed three times with water, spin-dried, and purified by silica gel column chromatography using petroleum ether and ethyl acetate as eluents to obtain 33.51 g of antioxidant 1. MS [MS+1]: 697.

[0054] Antioxidant 1 1HNMR (deuterated chloroform) is: δ9.71(s,1H),8.05(d,1H),7.89(dd,1H),7.74(dd,1H),7.68-7.61(m,1H),7.54(dd,1H),7.47-7.29(m,4H),7.18(d,1H),6.88(d,1H),6.16(s,1H),3.74(s,2H),2.62(t,2H),2.42(s,3H),1.52(m,2H),1.40-1.26(m,2H),0.91(t,3H).

[0055] Preparation Example 2-Preparation Example 6

[0056] The antioxidants synthesized in Preparation Examples 2 to 6 were prepared by referring to the synthesis method of Preparation Example 1, replacing the raw material 2 therein, and the rest of Preparation Example 1 remained the same, see Figure 2 .

[0057] Antioxidant performance testing and ABTS free radical scavenging performance testing were performed. First, prepare the solution: weigh 5.0 mg of ABTS and 1.5 mg of K₂S₂O₄ into a 2 mL volumetric flask. Add distilled water to the volume and place in the dark at room temperature for 24 hours until the color turns dark blue. Then, transfer the solution to a 100 mL volumetric flask, dilute to the volume with anhydrous ethanol, and place in a 30°C water bath for 30 minutes to obtain the ABTS ethanol solution. This solution has a maximum absorbance of 1.180 at 734 nm. The operation of compound quenching ABTS·free radicals is as follows: 1.9 mL of ABTS·free radical ethanol solution and 0.1 mL of 0.1 mmol / L stock solution of the test substance (Preparation Example 1-Preparation Example 6, Comparative Compound 1-Comparative Compound 2) are added to a test tube, and the final concentration of the test substance is 5 μmol / L. The test solution is quickly mixed and the absorbance value (A) at the maximum absorption wavelength within 30 minutes is recorded as a decay curve over time. The concentration of ABTS·free radicals at the initial and final moments is calculated by Lambert-Beer law. The ABTS scavenging rate of the test substance is calculated by the concentration change. The data are shown in Figure 3 .

[0058] Comparative compound 1: .

[0059] Comparative compound 2: .

[0060] Example 1

[0061] Preparation of a low-precipitation polyethylene film for clothing packaging:

[0062] Raw material ratio (by mass): 60 parts of low-density polyethylene (LDPE), 20 parts of linear low-density polyethylene (LLDPE), 7.5 parts of polyisobutylene, 0.3 parts of antioxidant 1 (synthesized by Preparation Example 1), 0.6 parts of erucamide (slip agent), and 2 parts of nano-silica.

[0063] Preparation steps: S1. Place LDPE, LLDPE and polyisobutylene in a hot air drying oven and dry them at 105°C for 3 hours to ensure that the moisture content of the raw materials is ≤0.02%.

[0064] S2. The dried raw materials, antioxidant 1, erucamide, and nano-silica were placed in a high-speed mixer and mixed at 400 r / min for 15 minutes to obtain a uniform mixture.

[0065] S3. Granulation was performed using a twin-screw extruder. The barrel temperature was controlled at 165°C (zone 1), 175°C (zone 2), and 185°C (zone 3). The die temperature was 190°C. The screw speed was set at 200 r / min. The melt was extruded, water-cooled, and pelletized to produce uniform granules with a diameter of 3-5 mm.

[0066] S4. Add the pellets to a rotary die-head film blowing machine. Maintain the melt temperature at 200°C, the die lip gap at 1.0 mm, and the melt pressure at 15 MPa. Set the blow-up ratio to 3:1 and the pull-off speed to 15 m / min to form an initial film bubble.

[0067] S5. The film bubble was quenched by an air ring cooling system (air temperature 10°C) to finally produce a polyethylene film with a thickness of 35 μm.

[0068] Example 2-Example 6

[0069] A low-precipitation polyethylene film for clothing packaging prepared in Examples 2 to 6 was prepared according to the preparation method of Example 1, with the antioxidant 1 therein being replaced with the antioxidants synthesized in Preparation Examples 2 to 6 in sequence, and the rest remained the same as in Example 1.

[0070] Comparative Example 1

[0071] A low-elution polyethylene film for clothing packaging is prepared according to the method of Example 1, except that the antioxidant 1 is replaced with a comparative compound 1, and the rest of the preparation is the same as that of Example 1.

[0072] Comparative Example 2

[0073] A low-precipitation polyethylene film for clothing packaging is prepared according to the method of Example 1, except that the antioxidant 1 is replaced with the comparative compound 2, and the rest of the preparation method remains the same as that of Example 1.

[0074] Comparative Example 3

[0075] A low-precipitation polyethylene film for clothing packaging is prepared by referring to the preparation method of Example 1, except that the antioxidant 1 is not added, and the rest of the preparation method remains the same as Example 1.

[0076] Performance testing:

[0077] Tensile strength and elongation at break were tested according to GB / T 1040.1-2018. The specimens were type 2 specimens with a width of 20 mm, a length of 250 mm, a thickness of 100 μm, and a tensile speed of 20 mm / min. Aging conditions: UV intensity of 300 W / m 2 , aging temperature 60℃, aging time 168h. Test results are shown in Figure 4 .

[0078] The Example group significantly outperformed the Comparative Example group (based on a traditional formulation) in terms of mechanical property retention and aging stability. With the optimization of the antioxidant, the Example group demonstrated a simultaneous increase in tensile strength and elongation retention, with samples containing specific heteroatom substitution structures exhibiting the greatest synergistic anti-aging effect. The Comparative Example group, due to the lack or inadequate antioxidant system, exhibited a step-wise degradation in mechanical properties after UV aging. The generally superior longitudinal performance compared to the transverse direction demonstrates the enhanced durability effect of molecular orientation achieved through the film blowing process.

[0079] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A low-elution polyethylene film for clothing packaging, characterized in that: The invention comprises the following raw materials in parts by weight: 50-70 parts of low-density polyethylene, 20-30 parts of linear low-density polyethylene, 5-10 parts of polyisobutylene, 0.1-0.5 parts of antioxidant, 0.2-1 parts of lubricant, and 1-3 parts of nano-silicon dioxide; The antioxidant has a structure shown in Formula 1: Formula 1; The D represents deuterium; Said Z1 is selected from: O, N-R1, S, CH2; R1 is selected from the group consisting of: H, methyl, ethyl, tert-butyl, and phenyl.

2. The low-exfoliation polyethylene film for clothing packaging according to claim 1, characterized in that: The mass ratio of the low-density polyethylene to the linear low-density polyethylene is 3-5 parts:1 part.

3. The low-exfoliation polyethylene film for clothing packaging according to claim 1, characterized in that: The lubricant includes erucamide and / or oleamide.

4. The low-exfoliation polyethylene film for clothing packaging according to claim 1, characterized in that: The antioxidant includes any one of the compounds shown in the following structures: ； ； 。 5. The low-exfoliation polyethylene film for clothing packaging according to claim 1, characterized in that: The thickness of the low-elution polyethylene film for clothing packaging is 20-50 μm.

6. The low-exfoliation polyethylene film for clothing packaging according to claim 1, characterized in that: The low precipitation polyethylene film for clothing packaging has a longitudinal tensile strength of ≥20 MPa, a transverse tensile strength of ≥18 MPa, and a water vapor permeability of ≤5 g / (m 2 ·24h).

7. A method for preparing a low-elution polyethylene film for clothing packaging according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. The low-density polyethylene, linear low-density polyethylene and polyisobutylene are dried at 100-110 ℃ for 2-4 hours to obtain a dried material; S2. The dried material and the antioxidant, lubricant and nano-silica were mixed at a speed of 300-500r / min for 10-20 minutes to obtain a mixture; S3. The mixture was melt extruded and granulated, the melt extrusion granulation temperature was controlled at 160-190 ℃, the screw speed during the melt extrusion granulation process was 150-250r / min to obtain pellets; S4. The pellets are blown into a film at a melt temperature of 180-220 ° C, the blow ratio is controlled at 2.5-3.5: 1, and the pulling speed is 10-20m / min; S5. After cooling through an air ring, a low-precipitation polyethylene film with a thickness of 20-50 μm for clothing packaging is obtained.

8. The method for preparing a low-elution polyethylene film for clothing packaging according to claim 7, characterized in that: The melt extrusion granulation in S3 adopts a twin-screw extruder, and the barrel temperature is controlled in zones: zone 1 160-170°C, zone 2 170-180°C, zone 3 180-190°C, and the die head temperature is controlled at 185-195°C.

9. The method for preparing a low-elution polyethylene film for clothing packaging according to claim 7, characterized in that: The film blowing molding described in S4 adopts a rotary die head, the die lip gap is adjusted to 0.8-1.2 mm, and the melt pressure is maintained at 12-18 MPa.

10. The method for preparing a low-elution polyethylene film for clothing packaging according to claim 7, characterized in that: The air ring cooling in S5 has an air cooling temperature of 10°C.

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