Easy-to-tear PE film composite material and preparation method thereof

Abstract

The invention discloses an easy-to-tear PE film composite material and a preparation method thereof. The method comprises the following steps: providing a connecting film, wherein the connecting film comprises a PE base material and a plurality of carbon nanotubes dispersed in the PE base material; applying a first high-frequency induction electric field to perform primary pressing to obtain a first assembly; applying a mechanical external force to re-layer the first combination; applying a second high-frequency induction electric field for secondary pressing to obtain a second assembly; and carrying out hot-pressing treatment on the easily-torn PE film composite material. According to the invention, a connecting film compounded with a carbon nanotube is used as a connecting medium layer, a microscopic concave-convex structure is constructed in a local area of the carbon nanotube in cooperation with a mode of induction local heating and secondary fusion after stripping, and the two ends of the carbon nanotube extending out of a connecting layer are implanted into a middle layer or a hot melting layer; firm anchoring between the layers is achieved, the situation that layering or tearing occurs in a non-hot-melting area in the uncovering process after the thin film is subjected to hot-melting sealing is avoided, and the tearing success rate and the use experience are improved.

Description

Technical Field

[0001] The invention relates to the technical field of polymer packaging materials, and in particular to an easy-to-peel PE film composite material and a preparation method thereof. Background Art

[0002] Easy-to-peel materials are usually in the form of films. They are widely used in the packaging of food, medicine, and industrial products. They are an indispensable type of material in the operation of modern society.

[0003] Among many materials, polyethylene film is non-toxic and tasteless and has good low temperature resistance, moisture resistance, moisture permeability resistance and aging resistance. It is one of the plastic films with the largest production volume in my country. Common polyethylene processing and molding processes include: inflation method, cast film method, and biaxial stretching method. Among them, since the cast film polyethylene film is a flat extruded film, subsequent processes such as printing and lamination are extremely convenient. Compared with single-layer polyethylene cast film, multi-layer polyethylene cast film has high barrier, high stability and high adaptability, and is widely used in food, medical and other fields.

[0004] However, when using traditional cast film processing technology to prepare easy-to-peel film materials, it is usually necessary to co-extrude multiple layers and then blow them. The bonding between the layers in this preparation method only relies on melt bonding. After hot-melt packaging, for example, when the package is sealed, the layers of the film will form a tighter bond with the hot-melt bonding area of ​​the seal, but the suspended area is not affected by the hot melt and maintains the original bonding performance. Therefore, when peeling off, it is easy to cause delamination or tearing caused by stress concentration in the suspended area, which ultimately leads to tearing failure or inability to completely tear off. This phenomenon is very common in the food field. For example, when jelly packaging is peeled off, the sealing film often delaminates or tears in the middle area. Summary of the invention

[0005] In view of the deficiencies in the prior art, the object of the present invention is to provide an easy-to-remove PE film composite material and a preparation method thereof.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes:

[0007] The first aspect of the present invention provides a method for preparing an easy-to-peel PE film composite material, which comprises the following steps:

[0008] A bonding film is provided, wherein the bonding film comprises a PE substrate and a plurality of carbon nanotubes dispersed in the PE substrate, and the average length of the carbon nanotubes is more than 1 times the thickness of the PE substrate; the bonding film used in this step mainly functions to tightly bond the hot-melt layer and the middle layer to provide uniform bonding ability, and the carbon nanotubes with a longer length in the bonding film mainly function to be implanted into the hot-melt layer and the middle layer for microscopic bonding in subsequent steps.

[0009] Under the condition of a first temperature and application of a first high-frequency induced electric field, the hot-melt layer film and the intermediate layer film are respectively attached to the two opposite sides of the connecting film and pressed once to obtain a first assembly, wherein the first temperature is lower than the softening temperatures of the hot-melt layer film, the connecting film and the intermediate layer film; this step is a relatively critical step, and the first temperature below the softening point is used as a basis, and the first high-frequency induced electric field is combined to heat the conductive carbon nanotubes, causing the material near the carbon nanotubes to soften or even melt, so that the carbon nanotubes can move in the connecting film, and softening areas or hot-melt areas are formed near the carbon nanotubes, and these areas are combined with the films on both sides.

[0010] Applying a mechanical external force causes the first combination to be re-stratified; specifically, applying a tearing force for stratification causes the three-layer film to be re-stratified. Since there is no adhesion in the area without carbon nanotubes, and the area with carbon nanotubes softens or even melts when heated, a local adhesion protruding micro-nano structure will be formed under the pulling of the mechanical external force during tearing, and the carbon nanotubes will be pulled away from the center of the film, so that part of the carbon nanotubes are exposed on the top or side surfaces of the protruding micro-nano structure, forming subsequent connection conditions. It should be noted that this step should be performed when the induced electric field exists or immediately after leaving the induced electric field to prevent the local temperature from cooling and causing separation to be impossible.

[0011] Under the condition of a second temperature and application of a second high-frequency induced electric field, the separated hot melt layer film, the connecting film and the intermediate layer film are pressed again to obtain a second assembly, wherein the second temperature is higher than the softening temperature of the hot melt layer film, the connecting film and the intermediate layer film and is lower than the fusion temperature of the hot melt layer film, the connecting film and the intermediate layer film. This step reuses a slightly higher base temperature in combination with an induced electric field to heat the raised micro-nano structure where the carbon nanotubes are located, so that the three-layer film is pre-assembled, and the temperature at the position of the raised micro-nano structure is higher, and the combination is tighter, thereby achieving the effect of locally implanting carbon nanotubes into the hot melt layer and the intermediate layer.

[0012] Finally, the second assembly is subjected to a first heat pressing treatment at a third temperature, so that the intermediate film, the tie film and the hot-melt film are sequentially fused to each other to form an easy-to-peel PE film composite material consisting of at least an intermediate layer, a tie layer and a hot-melt layer. This step is the final heat pressing step, so that the three films are completely fused into a multi-layer film.

[0013] Furthermore, the preparation method further comprises:

[0014] While the first heat-pressing treatment is being performed, the surface layer film is covered on the side of the intermediate layer film facing away from the connecting film, and heat-pressing and fusing are simultaneously performed to form the surface layer.

[0015] Alternatively, after the first heat pressing treatment, a second heat pressing treatment is performed to cover the surface layer film, so that the surface layer film covers the side of the intermediate layer film facing away from the connecting film and fuses to form a surface layer. The surface layer has protective, isolating and decorative functions, but how to set the specific surface layer is not the focus of the present invention, and the above methods are only examples of some implementation methods.

[0016] Furthermore, the preparation method further comprises:

[0017] The step of stretching and thinning the obtained composite film consisting of at least the intermediate layer, the bonding layer and the hot-melt layer.

[0018] Furthermore, the stretching and thinning is performed by hot melt inflation, and the inflation ratio is below 2. If the inflation ratio is too large, the three-layer carbon nanotubes implanted vertically or with a certain inclination along the thickness direction may be flattened in the plane direction, resulting in a decrease in anchoring ability.

[0019] Of course, it is also possible to use other methods for stretching and thinning. Even if the thickness of the original film meets the requirements, stretching and thinning may not be performed.

[0020] Furthermore, the material of the intermediate layer includes metallocene medium density polyethylene and linear low density polyethylene; the PE substrate includes linear low density polyethylene; and the material of the hot melt layer includes high density polyethylene, polybutylene and polypropylene.

[0021] Further regarding specific process conditions, the first temperature is 80-100° C., the frequency of the first high-frequency induced electric field is 40-200 kHz, the power is 500-1000w, and the pressure of the first pressing is 0.5-2MPa.

[0022] Furthermore, the second temperature is 150-170° C., the frequency of the first high-frequency induced electric field is 40-200 kHz, the power is 500-1000w, and the pressure of the secondary pressing is 0.5-3MPa.

[0023] Furthermore, the third temperature is 190-220°C.

[0024] Furthermore, in the connecting film, the mass fraction of the carbon nanotubes is 1-3%.

[0025] Furthermore, the thickness of the PE substrate is 10-20 μm, and the average length of the carbon nanotubes is 20-40 μm.

[0026] Furthermore, the thickness of the hot-melt layer film is 20-40 μm, and the thickness of the intermediate layer film is 40-80 μm.

[0027] The second aspect of the present invention also provides an easy-to-peel PE film composite material obtained by the above preparation method.

[0028] Corresponding to the process and microscopic changes of the above-mentioned preparation method, further, the easy-to-remove PE film composite material includes a hot-melt layer film, a connecting film and an intermediate layer film which are sequentially stacked and fused with each other, both sides of the connecting film have a protruding structure, and carbon nanotubes are embedded in the connecting film, and the carbon nanotubes extend out of the connecting film from the protruding structure;

[0029] The hot-melt layer film and the intermediate layer film cover and surround the protruding structure, and the ends of the carbon nanotubes are located within the hot-melt layer film or the intermediate layer film.

[0030] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention at least include:

[0031] The easy-to-peel PE film composite material and the preparation method thereof provided by the present invention utilize a connecting film composited with a certain amount of carbon nanotubes whose length exceeds a certain multiple of the film thickness as a connecting medium layer for the hot-melt layer and the middle layer, and cooperate with induction local heating and secondary fusion after peeling to construct a microscopic concave-convex structure in the local area of ​​the carbon nanotubes, and make the carbon nanotubes extend out of the connecting layer and the two ends are implanted in the middle layer or the hot-melt layer, thereby realizing a firm anchoring between the layers, avoiding the delamination or tearing in the non-hot-melt area during the peeling process after the film is hot-melt sealed, thereby improving the peeling success rate and the use experience, and increasing the added value of the product.

[0032] The above description is only an overview of the technical solution of the present invention. In order to enable those skilled in the art to more clearly understand the technical means of the present application and implement them according to the contents of the specification, the following is a description of the preferred embodiments of the present invention in conjunction with detailed drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the structure of some products of the preparation process of the easy-to-peel PE film composite material provided by a typical implementation case of the present invention;

[0034] Figure 2 It is a schematic diagram of the structure of some products of the preparation process of the easy-to-peel PE film composite material provided by a typical implementation case of the present invention;

[0035] Figure 3 It is a schematic diagram of the structure of some products of the preparation process of the easy-to-peel PE film composite material provided by a typical implementation case of the present invention;

[0036] Figure 4It is a schematic diagram of the structure of some products of the preparation process of an easy-to-peel PE film composite material provided by a typical implementation case of the present invention. DETAILED DESCRIPTION

[0037] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle will be further explained as follows.

[0038] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0039] Moreover, relational terms such as “first” and “second” are merely used to distinguish one component or method step from another with the same name, but do not necessarily require or imply any such actual relationship or order between these components or method steps.

[0040] The embodiment of the present invention provides a method for preparing an easy-to-peel PE film composite material, which comprises:

[0041] See also Figure 1 As shown, a bonding film is provided, the bonding film comprising a PE substrate and a plurality of carbon nanotubes dispersed in the PE substrate, and the average length of the carbon nanotubes is more than 1 times the thickness of the PE substrate;

[0042] See also Figure 2 As shown, under the condition of a first temperature and a first high-frequency induced electric field, the hot-melt layer film and the intermediate layer film are respectively attached to the two opposite sides of the connecting film and pressed once to obtain a first assembly, wherein the first temperature is lower than the softening temperatures of the hot-melt layer film, the connecting film and the intermediate layer film;

[0043] See also Figure 3 As shown, applying a mechanical external force causes the first assembly to be re-stratified;

[0044] See also Figure 4 As shown, under the condition of a second temperature and a second high-frequency induced electric field, the separated hot-melt layer film, the connecting film and the intermediate layer film are pressed together for a second time to obtain a second assembly, wherein the second temperature is higher than the softening temperature of the hot-melt layer film, the connecting film and the intermediate layer film and lower than the fusion temperature at which the hot-melt layer film, the connecting film and the intermediate layer film are combined with each other;

[0045] Continue to see Figure 4As shown, the second assembly is subjected to a first heat pressing treatment at a third temperature so that the intermediate layer film, the connecting film and the hot-melt layer film are sequentially fused with each other to form an easy-to-peel PE film composite material consisting of at least an intermediate layer, a connecting layer and a hot-melt layer.

[0046] An embodiment of the present invention also provides an easy-to-peel PE film composite material obtained by the above-mentioned preparation method, which includes a hot-melt layer film, a connecting film and an intermediate layer film that are stacked in sequence and fused with each other, both sides of the connecting film have a protruding structure, and carbon nanotubes are embedded in the connecting film, and the carbon nanotubes extend out of the connecting film from the protruding structure; the hot-melt layer film and the intermediate layer film cover and surround the protruding structure, and the ends of the carbon nanotubes are inside the hot-melt layer film or the intermediate layer film.

[0047] The technical solution of the present invention is further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only used to illustrate the present invention, and do not limit the scope of the present invention.

[0048] Example 1

[0049] This embodiment prepares an easy-to-peel PE film composite material, and the specific process is as follows:

[0050] Using a melt extruder, 98wt% LLDPE (linear low-density polyethylene, Mobil) and 2wt% carbon nanotube powder are co-extruded and compounded at least three times, and then blown into a film to obtain a connected film with a film thickness ranging from 10-20μm. The carbon nanotubes used are multi-walled powders with an average tube length of 20μm.

[0051] Commercially available hot-melt layer films with a thickness of 30 μm (HDPE, PP, PB1, a composite film product in a mass ratio of 1:1:1) and intermediate layer films with a thickness of 60 μm (metallocene medium density polyethylene, linear low density polyethylene, a composite film product in a mass ratio of 1:1).

[0052] The film is passed through a pressure roller (ceramic + rubber material, avoid using conductive metal and other materials) continuously and is placed in a cavity at 100°C. A high-frequency induction electric field with a frequency of 100kHz and a power of 1000w is applied to the cavity. The pressure is estimated to be about 1MPa based on the contact area for pressing.

[0053] Three different collecting rollers are used to immediately and continuously separate, tear off and wind up the film after it passes through the pressure roller.

[0054] Then the films on the three different collecting rollers were pressed again under the induced electric field for the second time, using the same non-conductive pressing roller pressing method. The temperature was set to 160°C, the induced electric field frequency and power remained unchanged, and the estimated pressure was also around 1 MPa.

[0055] Finally, the pre-bonded film obtained in the previous step is further subjected to thorough hot pressing at 210° C. using a hot pressing roller to obtain a composite film of a certain thickness.

[0056] Of course, if the film is considered too thick later, it can be thinned by hot stretching or inflation, but the stretching ratio or inflation ratio should not be too large, and the surface layer can be covered on the middle layer in the last step or in an additional separate design step. The specific method can be adjusted appropriately.

[0057] Comparative Example 1

[0058] This comparative example is substantially the same as Example 1, except that:

[0059] The connecting film is omitted, and there is no step of pressing once and then tearing off and then pressing again. Instead, a hot pressing roller is directly used for overall hot pressing.

[0060] Comparative Example 2

[0061] This comparative example is substantially the same as Example 1, except that:

[0062] The commercial easy-to-peel PE film purchased also has a structure of hot-melt layer-middle layer-surface layer, but this film is produced by extrusion blowing.

[0063] The composite films provided in the above-mentioned Example 1 and Comparative Examples 1-2 were subjected to a hot melt tearing test. The test conditions were as follows: a cup-shaped packaging material with a diameter of 3 cm and a 4 mm hot melt flange on its edge was used. The hot melt temperature was set to 210°C and the pressure was set to 3 kg for packaging. The packaging time was 5 s. 100 packaged samples were prepared for the film samples provided in each example. Then, a manual peeling experiment was carried out to calculate the peeling problem rate (corner residue, film delamination, and tearing in the middle of the film are all peeling problems).

[0064] None of the 100 samples provided in Example 1 had any peeling failure, while 4 and 3 packaging samples had peeling failure among the 100 samples provided in Comparative Example 1 and Comparative Example 2, respectively.

[0065] Example 2

[0066] This embodiment is substantially the same as Embodiment 1, and the main difference is that:

[0067] The process conditions were adjusted so that the mass ratio of carbon nanotubes in the bonding film was 1%, the thickness of the hot-melt layer film was 40 μm, and the thickness of the intermediate layer film was 80 μm;

[0068] The temperature of the first pressing is 80°C, the frequency of the induced electric field is 200kHz, the power is 500w, and the pressure is 3MPa. The temperature of the second pressing is 170°C, the frequency of the induced electric field is 200kHz, the power is 500w, and the pressure is 3MPa.

[0069] The temperature of the hot press fusion was adjusted to 220°C.

[0070] Example 3

[0071] This embodiment is substantially the same as Embodiment 1, and the main difference is that:

[0072] The process conditions were adjusted so that the mass ratio of carbon nanotubes in the bonding film was 3%, the thickness of the hot-melt layer film was 20 μm, and the thickness of the intermediate layer film was 40 μm;

[0073] The temperature of the first pressing is 90°C, the frequency of the induced electric field is 40kHz, the power is 800w, and the pressure is 0.5MPa. The temperature of the second pressing is 150°C, the frequency of the induced electric field is 40kHz, the power is 800w, and the pressure is 0.5MPa.

[0074] The temperature of the hot press fusion was adjusted to 190°C.

[0075] The above-mentioned embodiments 2 and 3 can still obtain a composite film with equivalent peeling performance, which will not be described in detail here.

[0076] Based on the above embodiments and comparative examples, it can be clearly seen that the easy-to-remove PE film composite material and the preparation method thereof provided in the embodiments of the present invention utilize a connecting film composited with a certain amount of carbon nanotubes whose length exceeds a certain multiple of the film thickness as a connecting medium layer for the hot melt layer and the intermediate layer, and cooperates with induction local heating and secondary fusion after peeling to construct a microscopic concave-convex structure in the local area of ​​the carbon nanotubes, and the carbon nanotubes extending out of the connecting layer are implanted at both ends in the intermediate layer or the hot melt layer, thereby achieving firm anchoring between the layers, avoiding delamination or tearing in the non-hot melt area during the peeling process after the film is hot-melt sealed, thereby improving the tearing success rate and usage experience, and increasing the added value of the product.

[0077] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing an easy-to-peel PE film composite material, characterized in that: include: Providing a bonding film, the bonding film comprising a PE substrate and a plurality of carbon nanotubes dispersed in the PE substrate, wherein the average length of the carbon nanotubes is more than 1 times the thickness of the PE substrate; Under the condition of a first temperature and a first high-frequency induced electric field, the hot-melt layer film and the intermediate layer film are respectively attached to the two opposite sides of the connecting film and pressed once to obtain a first assembly, wherein the first temperature is lower than the softening temperatures of the hot-melt layer film, the connecting film and the intermediate layer film; Applying mechanical external force to re-stratify the first assembly; Under the condition of a second temperature and a second high-frequency induction electric field, the separated hot-melt layer film, the connecting film and the intermediate layer film are pressed together again to obtain a second assembly, wherein the second temperature is higher than the softening temperature of the hot-melt layer film, the connecting film and the intermediate layer film and lower than the fusion temperature at which the hot-melt layer film, the connecting film and the intermediate layer film are combined with each other; The second assembly is subjected to a first heat pressing treatment at a third temperature so that the intermediate layer film, the connecting film and the hot-melt layer film are sequentially fused with each other to form an easy-to-peel PE film composite material consisting of at least an intermediate layer, a connecting layer and a hot-melt layer.

2. The preparation method according to claim 1, characterized in that: Also includes: During the first heat-pressing treatment, the surface layer film is covered on the side of the intermediate layer film facing away from the connecting film, and heat-pressing and fusing are simultaneously performed to form a surface layer; Alternatively, after the first heat pressing treatment, a second heat pressing treatment is performed to cover the surface layer film, so that the surface layer film covers the side of the intermediate layer film facing away from the connecting film and fuses to form a surface layer.

3. The preparation method according to claim 1 or 2, characterized in that: Also includes: The step of stretching and thinning the obtained composite film consisting of at least the intermediate layer, the connecting layer and the hot-melt layer.

4. The preparation method according to claim 3, characterized in that: The stretching and thinning is carried out by hot melt blowing, and the blowing ratio is less than 2.

5. The preparation method according to claim 1, characterized in that: The material of the intermediate layer includes metallocene medium-density polyethylene and linear low-density polyethylene; the PE substrate includes linear low-density polyethylene; and the material of the hot-melt layer includes high-density polyethylene, polybutylene and polypropylene.

6. The preparation method according to claim 1, characterized in that: The first temperature is 80-100° C., the frequency of the first high-frequency induced electric field is 40-200 kHz, the power is 500-1000w, and the pressure of the first pressing is 0.5-2MPa; And / or, the second temperature is 150-170° C., the frequency of the first high-frequency induced electric field is 40-200 kHz, the power is 500-1000w, and the pressure of the secondary pressing is 0.5-3MPa; And / or, the third temperature is 190-220°C.

7. The preparation method according to claim 1, characterized in that: In the bonding film, the mass fraction of the carbon nanotubes is 1-3%.

8. The preparation method according to claim 1, characterized in that: The thickness of the PE substrate is 10-20 μm, and the average length of the carbon nanotubes is 20-40 μm; And / or, the thickness of the hot-melt layer film is 20-40 μm, and the thickness of the intermediate layer film is 40-80 μm.

9. An easy-to-peel PE film composite material obtained by the preparation method according to any one of claims 1 to 8.

10. The easy-to-peel PE film composite material according to claim 9, characterized in that: It comprises a hot-melt layer film, a connecting film and an intermediate layer film which are sequentially stacked and fused with each other, both sides of the connecting film have a convex structure, and carbon nanotubes are embedded in the connecting film, and the carbon nanotubes extend out of the connecting film from the convex structure; The hot-melt layer film and the intermediate layer film cover and surround the protruding structure, and the ends of the carbon nanotubes are located within the hot-melt layer film or the intermediate layer film.

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