Toughened polyethylene cast film and preparation method thereof

Abstract

The invention provides a toughened polyethylene cast film and a preparation method thereof, and relates to the technical field of films. The polyethylene cast film is prepared by compounding the multi-element polyethylene base material and introducing the toughening resin, the melt flowability and the film forming uniformity are improved by adding the metallocene polyethylene, and the melt viscoelasticity can be adjusted by the toughening resin, so that the casting process stability is improved; the toughened resin, the high-density polyethylene and the metallocene polyethylene synergistically toughen the polyethylene cast film, so that the comprehensive performance of the polyethylene cast film is improved, and the polyethylene cast film has relatively high toughness and tensile strength and keeps proper rigidity and puncture resistance at the same time.

Description

Technical Field

[0001] This invention relates to the field of thin film technology, and in particular to a toughened polyethylene cast film and its preparation method. Background Technology

[0002] Polyethylene cast film, also known as unstretched polyethylene film (CPE), is a type of non-stretched, non-oriented flat-extruded film primarily produced by rapidly cooling molten polyethylene during casting. Polyethylene cast films are available in single-layer and multi-layer forms. The casting method for preparing flat-extruded polyethylene films offers significant advantages such as high production speed, high product quality, and high processing efficiency. The resulting films exhibit superior transparency, gloss, smoothness, and uniformity. Furthermore, polyethylene cast films possess a suitable coefficient of friction, good tensile strength, and excellent compatibility. Whether used alone or in combination with other film materials, polyethylene cast films have a wide range of applications in the packaging industries for food, pharmaceuticals, daily necessities, and decorative products.

[0003] my country only began using the casting method to prepare thin films in the 1980s. Despite a late start and relatively weak foundational capabilities, the industry has developed very rapidly. These films can be widely used in medical, hygiene products, and food packaging. With the continuous improvement of people's living standards, the demand for various multifunctional, high-quality, and high-performance film products is becoming increasingly urgent. Polyethylene cast film possesses excellent material properties and has considerable vitality and broad growth potential in the future, with particularly huge market potential.

[0004] Existing polyethylene cast films have low tear resistance, puncture resistance, and tensile strength, making them prone to breakage when packaging heavy objects or subjected to external impacts. Toughening technology mainly involves adding POE, TPU, and other types of polyolefin elastomers for blending modification to improve the toughness of the cast film. Although the toughness of the polyethylene cast film is improved after introducing these elastomers for modification, such as increasing the elongation at break, it also leads to a decrease in the strength of the cast film, resulting in shortcomings and limitations in its application fields.

[0005] Introducing HDPE into polyethylene cast film can improve rigidity, stiffness, tensile strength, and puncture resistance. However, HDPE is highly shear-sensitive, and its addition can easily disrupt the overall structure of the film. HDPE's high rigidity sacrifices toughness, which can lead to a decrease in the film's elongation at break. As a result, it is difficult for polyethylene cast film to simultaneously possess high toughness, elongation at break, strength, and puncture resistance. Summary of the Invention

[0006] To address the challenge that existing polyethylene cast films containing HDPE, prepared using elastomers such as TPU, EVA, and POE, often lack the ability to simultaneously achieve high toughness, elongation at break, strength, and puncture resistance, this application provides a toughened polyethylene cast film and its preparation method.

[0007] Technical solution:

[0008] In a first aspect, this application provides a toughened polyethylene cast film, comprising, by weight, 5-50 parts of low-density polyethylene, 5-90 parts of linear low-density polyethylene, 1-45 parts of high-density polyethylene, 1-50 parts of metallocene linear low-density polyethylene, and 0.5-15 parts of toughening resin.

[0009] The toughening resin is any one or a combination of several of the following: polyolefin elastomer, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, ultra-low density polyethylene, and phenoxy resin.

[0010] Furthermore, the composition includes 10-25 parts of low-density polyethylene, 45-85 parts of linear low-density polyethylene, 5-25 parts of high-density polyethylene, 5-15 parts of metallocene linear low-density polyethylene, and 1-10 parts of phenoxy resin.

[0011] Further, the composition includes 10-25 parts of low-density polyethylene (LDPE), 45-85 parts of linear low-density polyethylene (LLDPE), 5-10 parts of high-density polyethylene (HDPE), 5-15 parts of metallocene linear low-density polyethylene (mLLDPE), and 1-10 parts of phenoxy resin.

[0012] Preferably, the composition comprises 15-20 parts of low-density polyethylene, 60-70 parts of linear low-density polyethylene, 5-10 parts of high-density polyethylene, 5-10 parts of metallocene linear low-density polyethylene, and 1-10 parts of phenoxy resin.

[0013] More preferably, the low-density polyethylene is 15-20 parts, linear low-density polyethylene is 60-70 parts, high-density polyethylene is 5-10 parts, metallocene linear low-density polyethylene is 5-8 parts, and phenoxy resin is 2.5-10 parts.

[0014] Furthermore, the weight ratio of the high-density polyethylene to phenoxy resin is 0.5-12.5.

[0015] Furthermore, the weight ratio of the high-density polyethylene to phenoxy resin is 0.5-4.

[0016] Furthermore, the weight-average molecular weight (MW) of the phenoxy resin is 30,000-90,000.

[0017] Furthermore, the weight-average molecular weight (MW) of the phenoxy resin is 50,000-70,000.

[0018] Furthermore, the density of LDPE is 0.910-0.925 g / cm³, the density of LLDPE is 0.915-0.925 g / cm³, the density of HDPE is 0.941-0.965 g / cm³, and the density of mLLDPE is 0.890-0.970 g / cm³.

[0019] Secondly, this application provides a method for preparing the toughened polyethylene cast film of this application.

[0020] Beneficial effects: 1. Introducing HDPE into polyethylene cast film can improve rigidity, stiffness, tensile strength and puncture resistance. However, HDPE has high shear sensitivity. The addition of HDPE can easily destroy the overall structure of the film. The high rigidity of HDPE will sacrifice toughness and easily lead to a decrease in the elongation at break of the film. As a result, it is difficult for polyethylene cast film to have high toughness, elongation at break, strength and puncture resistance at the same time.

[0021] This application uses phenoxy resin containing benzene rings, which has good heat resistance, to improve the toughness of the cast film. Simultaneously, the use of mLLDPE not only complements the performance of HDPE but also reduces the HDPE content and shear sensitivity, thus decreasing the possibility of melt fracture, while maintaining performance. The hydroxyl groups (-OH) of the phenoxy resin and the small amount of vinyl groups at the ends of the HDPE chain... The formation of weak hydrogen bonds (C=C···H—O) reduces phase separation, and the aromatic ring structure of phenoxy resin can provide a certain degree of rigidity; the use of phenoxy resin in combination with HDPE, especially under the condition of high HDPE content, not only improves tensile strength and impact strength, but also improves elongation at break.

[0022] 2. Further, optimize the content of HDPE, metallocene polyethylene and toughening resin to further improve the stability of the casting process; the toughening resin and metallocene polyethylene synergistically toughen the polyethylene casting film, reduce the shear sensitivity of HDPE, and improve the comprehensive performance of the polyethylene casting film, so that the polyethylene casting film has excellent toughness and tensile strength, while maintaining appropriate rigidity and puncture resistance. Detailed Implementation

[0023] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0024] Example 1: A toughened polyethylene cast film, using raw materials as shown in Table 1, and its preparation process includes the following steps:

[0025] Polyethylene raw materials are premixed in a specific ratio and then fed into a feeding hopper for single-screw melt co-extrusion. The extruder temperature zones are set as follows: Zone 1: 190±5℃, Zone 2: 200±5℃, Zone 3: 210±5℃, Zone 4: 240±5℃, and Zone 5: 255±5℃. The melt is extruded through a coat hanger-type T-die with a die temperature set at 260±5℃ (in other embodiments, the temperature can be set to 235-260℃ according to actual needs). The main machine speed is 50Hz, and the melt pump is synchronously adjusted to 48±2Hz for stable feeding. After casting, the film is quickly shaped by a 20±5℃ cooling roller with a traction speed of 18Hz and a winding speed of 22±2Hz. Finally, the edges are trimmed, cleaned, and the film is wound to obtain a homogeneous polyethylene cast film with a thickness of 44μm±5μm.

[0026] The following are the optional performance parameters:

[0027] Low-density polyethylene (LDPE) density: 0.910~0.925 g / cm³, linear low-density polyethylene (LLDPE) density: 0.915~0.925 g / cm³, high-density polyethylene (HDPE) density: 0.941~0.965 g / cm³, metallocene linear low-density polyethylene (mLLDPE) density: 0.890~0.970 g / cm³.

[0028] In this embodiment, the raw material performance parameters are as follows:

[0029] LDPE density: 0.915 g / cm³, LLDPE density: 0.920 g / cm³, HDPE density: 0.958 g / cm³, mLLDPE density: 0.930 g / cm³, and the weight-average molecular weight (MW) of phenoxy resin is 50,000.

[0030] Examples 2 to 5 and Comparative Examples 1 to 4 describe a toughened polyethylene cast film, which differs from Example 1 in that it uses different types of raw materials, as detailed in Table 1.

[0031] Table 1: List of raw materials used in the toughened polyethylene cast films of Examples 1 to 5 and Comparative Examples 1 to 4

[0032] project LDPE / portion LLDPE / portion HDPE / piece mLLDPE / serving Phenoxy resin / part POE / copy EVA / serving HDPE percentage HDPE / Phenoxy resin weight ratio Example 1 20 65 10 5 2.5 0 0 9.76% 4.0 Example 2 20 65 10 5 1 0 0 9.90% 12.5 Example 3 20 65 10 5 1.5 0 0 9.85% 6.7 Example 4 20 65 10 5 5 0 0 9.52% 2.0 Example 5 20 65 5 5 10 0 0 4.76% 0.5 Comparative Example 1 20 65 0 5 5 0 0 0.00% 0.0 Comparative Example 2 20 65 5 5 0 0 0 5.26% - Comparative Example 3 25 65 0 5 0 3 0 0.00% - Comparative Example 4 25 65 10 0 0 0 5 9.52% -

[0033] Performance testing:

[0034] 1. Gram weight shall be tested according to ASTM D3776-20: sample size 200mm x 250mm.

[0035] 2. Breaking strength and elongation were tested in accordance with ISO 527:2019.

[0036] 3. Bursting strength shall be tested in accordance with ISO 13938-1:2019.

[0037] 4. Puncture resistance shall be tested according to ASTM F1306.

[0038] 5. Softness shall be tested in accordance with ASTM D2923.

[0039] The test results are shown in Table 2 below:

[0040] Table 2: Experimental data list of toughened polyethylene cast films of Examples 1 to 5 and Comparative Examples 1 to 4

[0041] Test Project gram Tensile strength - MD Elongation - MD Tensile Strength - CD Elongation - CD Bursting strength puncture Hand-O-meter softness unit <![CDATA[g / m 2 ]]> N / 25mm % N / 25mm % Kpa N mN Example 1 36.6 16.8 543 16.3 816 It doesn't burst when it expands. 4.8 55 Example 2 36.2 15.1 531 14.2 820 It doesn't burst when it expands. 4.7 36 Example 3 36 15.9 572 14.7 827 It doesn't burst when it expands. 4.9 40 Example 4 36.5 17.5 558 15.8 859 It doesn't burst when it expands. 5.2 72 Example 5 36.5 18.3 583 17.2 851 It doesn't burst when it expands. 6.1 87 Comparative Example 1 36.2 16.1 562 14.5 819 It doesn't burst when it expands. 4.8 70 Comparative Example 2 36 13.3 445 12.3 717 41.2 4.6 33 Comparative Example 3 36.3 11.2 580 9.7 892 It doesn't burst when it expands. 4.5 27 Comparative Example 4 36.4 16.7 511 15.3 750 It doesn't burst when it expands. 4.6 31

[0042] Examples 1 to 5 all included the addition of phenoxy resin. Compared with Comparative Example 2 without the addition of phenoxy resin, the tensile strength was significantly improved, and the elongation at break was increased by about 25%.

[0043] In the experimental data of Examples 1 to 5, the tensile strength increased with the increase of the addition ratio of phenoxy resin. However, high content of phenoxy resin is not recommended, mainly because although the mechanical properties are improved, the film becomes harder (the hardness of the film is generally characterized by a softness tester, and the larger the mN, the harder it is). At the same time, the cost will also increase, which is not conducive to production and use.

[0044] As can be seen from Example 4 and Comparative Example 1, the effective combination of HDPE and phenoxy resin can significantly improve its mechanical properties while maintaining a good elongation at break.

[0045] Example 5, by adjusting and increasing the amount of phenoxy resin added, i.e., increasing the proportion of phenoxy resin added, significantly improved the tensile strength, elongation at break, and puncture resistance compared to Comparative Example 2. However, the softness value also increased at the same time. Within an acceptable range, as the amount of phenoxy resin continues to increase, the softness value will increase, the hardness will be greater, the use will be limited, and the cost will also increase rapidly.

[0046] Comparative Example 3 did not use HDPE. Although the elongation at break was improved, the tensile strength was reduced, which limited its application scenarios.

[0047] Although comparative example 4 uses high-strength HDPE but not mLLDPE and phenoxy resin, although the tensile strength is high, the elongation at break and puncture resistance are reduced, which limits its application scenarios.

[0048] The aforementioned beneficial effects may be attributed to the following: HDPE exhibits high shear sensitivity; excessively high content can disrupt the overall structure of the film. HDPE's high rigidity sacrifices toughness, easily leading to a decrease in the film's elongation at break. Phenoxy resins containing benzene rings, which possess better heat resistance, can improve the processing performance of HDPE, reduce its shear sensitivity, and decrease the likelihood of melt fracture. The hydroxyl groups (-OH) in phenoxy resins interact with the small amount of vinyl groups at the ends of HDPE chains. The formation of weak hydrogen bonds (C=C···H—O) reduces phase separation, and the aromatic ring structure of phenoxy resin can provide a certain degree of rigidity; the use of phenoxy resin in combination with HDPE, especially under the condition of high HDPE content, not only improves tensile strength and impact strength, but also improves elongation at break.

[0049] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A toughened polyethylene cast film, characterized in that, By weight, it includes 5-50 parts of low-density polyethylene, 5-90 parts of linear low-density polyethylene, 1-45 parts of high-density polyethylene, 1-50 parts of metallocene linear low-density polyethylene, and 0.5-15 parts of toughening resin. The toughening resin is any one or a combination of several of the following: polyolefin elastomer, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, ultra-low density polyethylene, and phenoxy resin.

2. The toughened polyethylene cast film according to claim 1, characterized in that, The composition includes 10-25 parts of low-density polyethylene, 45-85 parts of linear low-density polyethylene, 5-25 parts of high-density polyethylene, 5-15 parts of metallocene linear low-density polyethylene, and 1-10 parts of phenoxy resin.

3. A toughened polyethylene cast film according to claim 1 or 2, characterized in that, The composition includes 15-20 parts of low-density polyethylene, 60-70 parts of linear low-density polyethylene, 5-10 parts of high-density polyethylene, 5-10 parts of metallocene linear low-density polyethylene, and 1-10 parts of phenoxy resin.

4. The toughened polyethylene cast film according to claim 3, characterized in that, The composition includes 15-20 parts of low-density polyethylene, 60-70 parts of linear low-density polyethylene, 5-10 parts of high-density polyethylene, 5-8 parts of metallocene linear low-density polyethylene, and 2.5-10 parts of phenoxy resin.

5. The toughened polyethylene cast film according to claim 3, characterized in that, The weight ratio of high-density polyethylene to phenoxy resin is 0.5-12.

5.

6. The toughened polyethylene cast film according to claim 5, characterized in that, The weight ratio of high-density polyethylene to phenoxy resin is 0.5-4.

7. The toughened polyethylene cast film according to claim 3, characterized in that, The weight-average molecular weight (MW) of the phenoxy resin is 30,000-90,000.

8. The toughened polyethylene cast film according to claim 7, characterized in that, The weight-average molecular weight (MW) of the phenoxy resin is 50,000-70,000.

9. A toughened polyethylene cast film according to any one of claims 1, 2, 4-8, characterized in that, The density of the low-density polyethylene is 0.910-0.925 g / cm³, the density of the linear low-density polyethylene is 0.915-0.925 g / cm³, the density of the high-density polyethylene is 0.941-0.965 g / cm³, and the density of the metallocene linear low-density polyethylene is 0.890-0.970 g / cm³.

10. A method for preparing a toughened polyethylene cast film according to any one of claims 1-9.