An easy-to-peel film, its preparation method and application

Abstract

The application provides an easy-to-peel film, a preparation method and application thereof. The easy-to-peel film comprises a corona layer, a base layer, an intermediate layer and a heat-seal layer arranged in sequence, wherein the intermediate layer comprises 100 parts of polyethylene resin A, 5-30 parts of flaky filler and 0.5-1 part of processing aid; the heat-seal layer comprises 100 parts of polyethylene resin B, 1-15 parts of polybutene resin and 0-1 part of processing aid; wherein the density ρ A > of the polyethylene resin A in the intermediate layer is greater than the density ρ B > of the polyethylene resin B in the heat-seal layer, and the polyethylene resin B comprises metallocene polyethylene. By adding polybutene in the heat-seal layer to reduce the peeling force of the film, then adding an intermediate layer containing flaky filler between the heat-seal layer and the base layer, and specifically matching the base of the heat-seal layer and the intermediate layer, an easy-to-peel film with excellent performance can be prepared.

Description

Technical Field

[0001] This invention relates to the field of food packaging film materials technology, and in particular to an easy-peel film, its preparation method, and its application. Background Technology

[0002] With technological advancements and improved living standards, consumers are increasingly focusing on product packaging while demanding higher quality. The aesthetics, convenience, and practicality of packaging have become important factors for consumers when choosing products. For products of similar quality, a better opening experience and a smoother tearing motion are more appealing to consumers, especially for liquids, powders, and pastes that are prone to spillage. Therefore, businesses are placing greater emphasis on the packaging of their products.

[0003] The traditional approach to solving this problem is to reduce the peel force of the material, allowing the outer packaging to be peeled off with less force. For example, Chinese patent CN112549712A discloses an easy-open cup lid film prepared by a multi-layer co-blowing method. This composite film has the characteristics of low peel force, good tearability, and no burrs. However, compared with traditional heat-sealing films, the packaging material prepared by this method has reduced the peel force, but the initial force of the material is still relatively high and has large fluctuations. Patent CN112874087A discloses a co-extruded film with barrier properties and easy opening. This method focuses on the barrier effect of the material and reducing the problem of material stringing. However, this method is prone to poor sealing, which can lead to product deterioration or damage to the packaging due to compression, drops, etc.

[0004] Furthermore, for some products with complex and irregular structures, significant differences in force in different directions when tearing open the packaging can easily lead to a poor consumer experience. Some studies (such as patent CN108026297A) have used bimodal polyethylene as a matrix to prepare isotropic films through biaxial stretching. However, the high content of low molecular weight polyethylene in the bimodal polyethylene matrix reduces the cohesive strength of the film. When applied to easy-open heat-sealable films, cohesive failure rather than interfacial failure is more likely to occur during peeling, resulting in poor peel performance.

[0005] Therefore, there is a need to develop an easy-peel packaging film with the same peel strength in all directions. Summary of the Invention

[0006] The purpose of this invention is to address the problem of significant differences in peel force in different directions in existing easy-open packaging films, and to provide an easy-open film with uniform peel force in all directions. This invention reduces the peel force of the film by adding polybutene to the heat-sealing layer, then adding an intermediate layer containing sheet-like filler between the heat-sealing layer and the substrate layer, and specifically combining the substrate of the heat-sealing layer and the intermediate layer, thus producing an easy-open film with excellent performance.

[0007] Another object of the present invention is to provide a method for preparing the easy-peel film.

[0008] Another object of the present invention is to provide the application of the easy-open film in the field of packaging.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] An easy-peel film includes a corona layer, a substrate layer, an intermediate layer, and a heat-sealing layer arranged sequentially:

[0011] The intermediate layer comprises 100 parts of polyethylene resin A, 5 to 30 parts of sheet filler, and 0.5 to 1 part of processing aid;

[0012] The heat-sealing layer comprises 100 parts of polyethylene resin B, 1 to 15 parts of polybutene resin, and 0 to 1 part of processing aids;

[0013] The density ρ of the polyethylene resin A in the intermediate layer is... A The density ρ of polyethylene resin B in the heat-sealing layer B Furthermore, the polyethylene resin B contains metallocene polyethylene.

[0014] In this invention, all "parts" in the dosage refers to parts by weight.

[0015] In the easy-peel film of the present invention: the addition of polybutene (PB) can reduce the peel strength of the heat-sealing layer; the sheet filler can reduce the difference in peel force in different directions. Because the sheet filler is randomly dispersed in the resin matrix, the sheet structure of the sheet filler is randomly arranged. During the peeling process, there is a certain stress buffering performance between the sheets. Therefore, the sheet structure randomly arranged in different directions can alleviate the tensile stress buffering in different directions. Thus, the difference in peel force in different directions during the peeling process of the film can be reduced.

[0016] However, the inventors of this invention discovered during their research that, since polyolefin material is a crystalline resin, directly adding the aforementioned sheet filler to the heat-sealing layer would increase the crystallinity of the heat-sealing matrix, leading to a significant difference in film thickness after heat sealing compared to before heat sealing, resulting in poor heat-sealing stability. It would also cause variations in peel strength at different points on the film, potentially leading to uneven sealing. Therefore, to better control the actual heat-sealing thickness and improve the uniformity of peel strength and thermal stability, this invention adds an intermediate layer between the heat-sealing layer and the matrix layer, incorporating the sheet filler into the intermediate layer. This not only improves the barrier properties of the film itself but also, by enhancing the isotropy of the heat-sealing film, makes the actual film thickness involved in heat sealing more controllable and uniform, thereby reducing fluctuations in its anisotropic peel force.

[0017] Furthermore, through further research, the inventors discovered that by specifically selecting and combining the substrates of the heat-sealing layer and the intermediate layer, the heat-sealing strength can be further controlled: 1) The present invention selects metallocene polyethylene and low-density polyethylene as the heat-sealing layer substrate, which can achieve a better heat-sealing effect, thereby ensuring the sealing of the packaging; 2) Because the intermediate layer uses high-density polyethylene, it reduces or prevents melt recrystallization during the heat-sealing process. The intermediate layer filled with inorganic fillers works synergistically with the polybutene in the heat-sealing layer to reduce and precisely control the peel strength of the film after heat sealing. In the present invention, the corona layer and the substrate layer include 100 parts of matrix resin and 0-2 parts of processing aids. The matrix resin can be selected from conventional polyethylene resins in the art, and the polyethylene resin can be at least one of high-density polyethylene, low-density polyethylene, and linear low-density polyethylene. The melt flow rate of the matrix resin at 190°C and 2.16 kg is 0.5-2.5 g / 10 min, and the test standard is GB / T 3682.1-2018. The polyethylene at this melt flow rate has excellent processing performance.

[0018] Preferably, the density difference ρ between polyethylene resin A in the intermediate layer and polyethylene resin B in the heat-sealing layer is... A -ρ B ≥0.007g / cm 3 As the density difference between the two layers of polyethylene resin increases, the heat-sealing stability of the resulting heat-sealable film improves. However, once the density difference reaches a certain value, further increases in the density difference do not significantly change the heat-sealing stability. Furthermore, the heat-sealed sealing layer contains some intermediate layer masterbatch. Due to the large density difference between the two resins, the compatibility deteriorates, leading to a certain decline in the sealing performance of the resulting polyethylene. Therefore, to further improve the overall performance of the film, the density difference ρ... A -ρ B A further preferred value is 0.007–0.030 g / cm³. 3 .

[0019] In this invention, the polyethylene resin A is selected from at least one of high-density polyethylene, low-density polyethylene, and linear low-density polyethylene; the polyethylene resin B may contain at least one of high-density polyethylene, low-density polyethylene, and linear low-density polyethylene in addition to metallocene polyethylene.

[0020] In the heat-sealing layer, the amount of metallocene polyethylene used is 50 to 100 parts, preferably 100 parts, relative to 100 parts of polyethylene resin B.

[0021] Preferably, the melt flow rate (also known as melt index, abbreviated as MFR) of the polyethylene resin A and polyethylene resin B at 190°C and 2.16 kg is independently 0.5–2.5 g / 10 min, and the test standard is GB / T3682.1-2018. Polyethylene with this melt index exhibits excellent processing properties.

[0022] Preferably, the densities of polyethylene resin A and polyethylene resin B are each independently 0.910-0.94 g / cm³. 3 .

[0023] Preferably, in the easy-peel film, the thickness ratio of the corona layer, substrate layer, intermediate layer, and heat-sealing layer is corona layer: substrate layer: intermediate layer: heat-sealing layer = 1:(2-4):(1-2):1. The intermediate layer is slightly thicker than the heat-sealing layer. If the intermediate layer is too thin, the heat-sealing performance will still be relatively unstable; if the intermediate layer is too thick, it will easily lead to film cohesion failure during peeling, affecting peeling performance. Within the above thickness ratio range, the obtained heat-sealing easy-peel film has good heat-sealing and peeling performance. The thickness of the heat-sealing easy-peel film can be 30-100 μm.

[0024] Preferably, the thickness of the intermediate layer in the easy-peel film is 4–35 μm.

[0025] Conventional sheet fillers can be used in this invention, including but not limited to at least one of talc, mica, or kaolin.

[0026] Optionally, the processing aids in the corona layer, substrate layer, intermediate layer and heat seal layer are independently selected from at least one of opening agents, slip agents, dispersants or antioxidants.

[0027] The opening agent includes, but is not limited to, at least one of silica, diatomaceous earth, or aluminum silicate.

[0028] The slip agent includes, but is not limited to, at least one of oleamide or erucamide.

[0029] The antioxidants include, but are not limited to, at least one of antioxidant 1010 or antioxidant 168.

[0030] This invention also protects the method for preparing the above-mentioned easy-peel film, comprising the following steps:

[0031] S1. After the raw materials of the corona layer, matrix layer, intermediate layer and heat seal layer are mixed evenly, they are melt extruded and cooled to obtain the raw materials for co-extrusion of each layer;

[0032] S2. The raw materials for co-extrusion of each layer obtained in step S1 are fed into different feed ports, and the easy-to-peel film is obtained by multi-layer co-extrusion and blow molding.

[0033] Preferably, the temperature of the melt extrusion in step S1 is 120-220°C.

[0034] Preferably, the extrusion temperature of the multilayer co-extrusion in step S2 is 150-210°C.

[0035] The application of the aforementioned easy-open film in the packaging field is also within the scope of protection of this invention.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] This invention reduces the peel strength of the film by adding polybutene to the heat-sealing layer, then adding an intermediate layer containing sheet-like filler between the heat-sealing layer and the substrate layer, and specifically matching the substrate of the heat-sealing layer and the intermediate layer, thus producing an easy-to-peel film with excellent performance. The heat-sealing strength of the film after heat sealing is below 10N; the ratio of transverse to longitudinal heat-sealing strength is below 1.5, and can be as low as 1.0; and the sealing performance is excellent. Detailed Implementation

[0038] To better illustrate the purpose, technical solution, and advantages of this invention, specific embodiments will be used to further describe the invention below. However, these embodiments do not limit the invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this invention are commercially available.

[0039] The following raw materials are selected in the embodiments of the present invention:

[0040] Polyethylene resin matrix:

[0041] PE-1: 4201G, density 0.912g / cm³ 3 The MFR at 190℃ and 2.16kg was 1.0g / 10min, purchased from Dow Chemical.

[0042] PE-2: 1002YB, density 0.918 g / cm³ 3 The MFR at 190℃ and 2.16kg was 2.0g / 10min, purchased from ExxonMobil;

[0043] PE-3: 2036P, density 0.935 g / cm³ 3 The MFR at 190℃ and 2.16kg was 2.5g / 10min, purchased from Dow Chemical.

[0044] PE-4: 4606g, density 0.911g / cm³ 3 The MFR at 190℃ and 2.16kg was 3.3g / 10min, purchased from Dow Chemical.

[0045] PE-5: 132g, density 0.921g / cm³ 3 The MFR at 190℃ and 2.16kg was 0.25g / 10min, purchased from Dow Chemical.

[0046] PE-6: Metallocene polyethylene, AT 6101, density 0.905 g / cm³ 3 The MFR at 190℃ and 2.16kg was 0.8g / 10min, purchased from Dow Chemical.

[0047] PE-7: Metallocene polyethylene, 2018MA, density 0.918 g / cm³ 3 The MFR at 190℃ and 2.16kg was 2.0g / 10min, purchased from ExxonMobil;

[0048] PE-8: 4203G, density 0.905g / cm³ 3 The MFR at 190℃ and 2.16kg was 0.8g / 10min, purchased from Dow Chemical.

[0049] Flake packing:

[0050] Talc powder: AH-51210, 3000 mesh talc powder, purchased from Liaoning Aihai;

[0051] Mica: TR003, purchased from Sanbao Mica in Shantou City;

[0052] Kaolin: CMP-1, purchased from China Kaolin Co., Ltd.;

[0053] Polybutene resin (PB-1): PB8640M, purchased from LyondellBasell;

[0054] Processing aids:

[0055] Opening agent: SYLOBLOC 45, commercially available;

[0056] Slip agent: WK2680, commercially available;

[0057] Dispersant: A-C6A, commercially available;

[0058] Antioxidant: SONOX 1010, commercially available;

[0059] Antioxidant: SONOX 168, commercially available.

[0060] Unless otherwise specified, the processing aids used in the following examples and comparative examples were all commercially available, and the same processing aids were used in the parallel experiments.

[0061] Examples 1-12, Comparative Examples 1-4

[0062] This invention provides a series of polyethylene heat-sealable easy-peel films, the preparation method of which includes the following steps:

[0063] S1. Preparation of raw materials for co-extrusion of each layer

[0064] According to the raw material formulas in Tables 1-3, the corona layer raw material, matrix layer raw material, intermediate layer raw material, and heat-sealing layer raw material are added to a high-speed mixer and mixed at 800 rpm for 2 minutes at 80°C. After uniform mixing, the mixture is fed into a 75D co-rotating twin-screw extruder for melt extrusion granulation, drying, and cooling to obtain the raw materials for extrusion of the above layers. The temperature of the twin-screw extruder from the feeding section to the die head is 120°C, 180°C, 20 ...

[0065] S2. Preparation of heat-sealable polyethylene easy-peel film

[0066] The raw materials for co-extrusion obtained in step S1 are fed into different feed ports of the co-extruder. After multi-layer co-extrusion and blow molding, the corona layer is corona treated to obtain a heat-sealable polyethylene easy-peel film with a thickness of 50μm. The temperatures of each zone from the feed port to the die head in the multi-layer co-extrusion are 150℃, 180℃, 190℃, 190℃, and 190℃. The specific process parameters for blow molding are: blow ratio of 2 to 3 and blow film temperature of 18 to 22℃.

[0067] Table 1. Formulations (parts by weight) of polyethylene heat-sealable films in Examples 1-7

[0068]

[0069]

[0070] Note: In Table 1 and subsequent tables, ρ A ρ is the density of the polyethylene resin in the intermediate layer. B This represents the density of the polyethylene resin in the heat-sealing layer.

[0071] Table 2. Formulations (parts by weight) of the polyethylene heat-sealable films in Examples 8-12.

[0072]

[0073]

[0074] Table 3 shows the formulations (parts by weight) of polyethylene heat-sealable films for Comparative Examples 1-4.

[0075]

[0076] Note: The formulations of corona layer I and substrate layer II, which are not listed in the table, are the same as in Example 1.

[0077] Performance testing

[0078] The performance of the polyethylene heat-sealing films prepared in the above embodiments and comparative examples was tested. The specific test items and test methods are as follows:

[0079] 1. Peel strength test: The above-mentioned polyethylene heat-sealing film was heat-sealed with PE at 110℃ and 0.3MPa for 2s to obtain a heat-sealing film sample. Then, the test was carried out according to the method described in standard GB / T 2792-2014. The 90° peel strength (N / 15mm) in the X direction (transverse) and Y direction (longitudinal) was tested respectively. The peel speed was 30mm / min. The degree of cohesion (or interface) damage was recorded at the same time as the peel strength.

[0080] 2. Shrinkage rate: Cut the prepared heat-sealing film into 10cm×10cm square film samples along the longitudinal and transverse directions, place them in a 90℃ water bath for 1min to test their longitudinal dimension, and calculate their shrinkage rate: Shrinkage rate (%) = |10-l| / 10×100%, where l is the longitudinal dimension of the square film sample after water bath;

[0081] The test results are detailed in Table 4.

[0082] Table 4 Performance Test Results

[0083]

[0084] The results above show that:

[0085] The polyethylene heat-sealing films prepared according to the various embodiments of the present invention have excellent peel performance, wherein the heat-sealing strength of the film after heat sealing is 6 to 10 N, which is within the range of good peel performance and sealing performance; the ratio of the heat-sealing strength in the transverse direction to the longitudinal direction is below 1.3, and can be as low as 1.0; and the heat shrinkage rate is within 10%.

[0086] The results of Examples 1 to 3 show that, within the dosage range described above in this invention, an easy-to-peel film with excellent peeling performance can be obtained.

[0087] The results of Examples 1, 4-7, and Comparative Examples 1 and 3 show that as the density difference between the polyethylene resin matrix in the intermediate layer and the heat-sealing layer increases, the thickness fluctuation (i.e., shrinkage rate) and longitudinal and transverse differences of the obtained heat-sealing film are smaller (i.e., it tends to be isotropic). However, when the density difference reaches a certain value, further increasing the density difference (e.g., increasing it to 0.013 g / cm³) will reduce its effectiveness. 3The heat-sealing stability did not change significantly, but the density difference between the two resins was too large (for example, the density difference reached 0.03 g / cm³ in Example 4). 3 The compatibility deteriorates, leading to a decrease in the sealing performance (i.e., peel strength) of the resulting polyethylene. Simultaneously, as the melt index of the matrix polyethylene in the interlayer increases, the peel strength of the resulting heat-sealable easy-peel film shows a trend of first increasing and then decreasing. In Comparative Example 1, the polyethylene densities in the interlayer and heat-seal layer are similar; in Comparative Example 3, the density of the interlayer is lower than that of the heat-seal layer, resulting in increased fluctuations in the peel strength of the resulting heat-sealable film.

[0088] The results of Examples 1, 8-9 show that the thickness of the intermediate layer is slightly thicker than that of the heat-sealing layer, and when the thickness is too thin, the peel strength fluctuation is relatively large. Within the above thickness ratio range, the heat-sealing performance and peel performance of the obtained heat-sealing film are both good.

[0089] The results of Examples 1 and 10-11 show that conventional sheet packings can be used in this invention.

[0090] The results of Examples 1 and 12 show that after adding non-metallocene polyethylene to the matrix of the heat-sealing layer, the peel performance can still meet the requirements, but the peel strength will decrease.

[0091] In Comparative Example 2, a non-metallocene polyethylene matrix was used for the heat-sealing layer. This resulted in a significant decrease in the peel strength of the heat-sealing easy-peel film, leading to its easy peeling under relatively low peel force. Consequently, it could be easily broken due to compression during transportation, resulting in significantly poorer sealing performance. In Comparative Example 4, no intermediate layer was added. Although the resulting heat-sealing film exhibited good peel performance, its heat-sealing stability was significantly worse.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An easy-peel film, comprising a corona layer, a substrate layer, an intermediate layer, and a heat-sealing layer arranged sequentially, characterized in that: The intermediate layer comprises 100 parts of polyethylene resin A, 5-30 parts of sheet filler, and 0.5-1 part of processing aid; The heat-sealing layer comprises 100 parts of polyethylene resin B, 1-15 parts of polybutene resin and 0-1 parts of processing aids; All "parts" in the dosage refers to parts by weight; The density ρ of the polyethylene resin A in the intermediate layer is... A The density ρ of polyethylene resin B in the heat-sealing layer B Furthermore, the polyethylene resin B contains metallocene polyethylene; The density difference ρ between polyethylene resin A in the intermediate layer and polyethylene resin B in the heat-sealing layer A -ρ B The value is 0.007~0.030 g / cm³. 3 .

2. The easy-peel film according to claim 1, characterized in that, The thickness ratio of the corona layer, the substrate layer, the intermediate layer and the heat seal layer is corona layer: substrate layer: intermediate layer: heat seal layer = 1: (2~4): (1~2):

1.

3. The easy-peel film according to claim 1, characterized in that, The sheet-like filler is at least one of talc, mica, or kaolin.

4. The easy-peel film according to claim 1, characterized in that, The melt flow rates of polyethylene resin A and polyethylene resin B at 190℃ and 2.16kg are independently 0.5~2.5g / 10min, and the test standard is GB / T 3682.1-2018.

5. The easy-peel film according to claim 4, characterized in that, The polyethylene resin A is selected from at least one of high-density polyethylene, low-density polyethylene, and linear low-density polyethylene.

6. The easy-peel film according to claim 1, characterized in that, The processing aids in the corona layer, substrate layer, intermediate layer and heat seal layer are independently selected from at least one of opening agents, slip agents, dispersants or antioxidants.

7. The method for preparing the easy-peel film according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. After the raw materials of the corona layer, matrix layer, intermediate layer and heat-sealing layer are mixed evenly, they are melt-extruded and cooled and granulated by a twin-screw extruder to obtain the raw materials for co-extrusion of each layer. S2. The raw materials for co-extrusion of each layer obtained in step S1 are fed into different feed ports, and the easy-to-peel film is obtained by multi-layer co-extrusion and blow molding.

8. The application of the easy-open film according to any one of claims 1 to 6 in the packaging field.

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