Integrally formed easily recyclable in-mold labeling film for high-density polyethylene bottles, its preparation method and application

Abstract

The present invention relates to an integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles, its preparation method and application, belonging to the technical field of functional polypropylene films. The integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles of the present invention comprises a surface layer, a coloring layer, a foaming support layer, a connecting layer and a hot melt adhesive layer arranged in sequence; the surface layer comprises polypropylene and an anti-blocking agent; the coloring layer comprises polypropylene and 5-30 wt% titanium dioxide; the foaming support layer comprises polypropylene and 5-30 wt% calcium carbonate; the connecting layer comprises polypropylene and 30-50 wt% maleic anhydride grafted polypropylene; the hot melt adhesive layer is composed of 40-60 wt% propylene-butene copolymer and ethylene-butene copolymer. The integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles of the present invention can not only meet the bonding fastness requirements for labeling, but also peel the in-mold label film from the high-density polyethylene bottle by peeling, which is beneficial to the recycling of single materials.

Description

Technical Field

[0001] The present invention relates to the technical field of functional polypropylene films, and particularly to an integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles, its preparation method and application. Background Art

[0002] The so-called in-mold label is to directly place the printed trademark label image sheet (with hot melt adhesive on the back) into a plastic mold, and through the blow molding process, the label and the plastic container are combined together to form a complete plastic product. The biggest feature of this technology is that the label and the bottle body of the plastic container are on the same surface, making the label color graphics and texts seem to be directly printed on the surface of the bottle body of the plastic container. As a novel label packaging form, in-mold labels have been popular in some developed countries for many years. In recent years, with the increasing demand for innovative packaging technologies in the domestic market, in-mold labels have also been favored by more and more printing substrate suppliers, label producers and end consumers in China. In-mold labels play an important role in aspects such as food logistics, anti-counterfeiting, and identification.

[0003] Although in-mold labels have the above advantages, there are also some limitations. The plastic products to which in-mold labels are applied are generally mainly made of high-density polyethylene materials. However, the general in-mold label film materials are mainly made of polypropylene. Although these two materials are both polyolefin materials, phase separation occurs when they are mixed, showing an incompatible state and being difficult to recycle as a single material.

[0004] In addition, for the in-mold label film in related technologies, after being applied to high-density polyethylene bottles, one of the main problems is that after the in-mold label film is adhered to the high-density polyethylene bottle, it is difficult to separate the in-mold label from the high-density polyethylene bottle, resulting in the label base film and its surface ink being brought into the recycling of high-density polyethylene bottles, thereby coloring the recycled particles and affecting the recycling and reuse of high-density polyethylene bottles. In particular, the recycling of such transparent high-density polyethylene bottles is particularly difficult. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to provide an integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles, its preparation method and application. The integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles can not only meet the required adhesion strength for label sticking during in-mold labeling, but also be cleanly peeled off from the high-density polyethylene bottle by peeling during recycling, which is beneficial to the recycling and reuse of single materials.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions.

[0007] An integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles, comprising a surface layer, a coloring layer, a foaming support layer, a connecting layer, and a hot-melt adhesive layer arranged in sequence; the surface layer comprises polypropylene and an anti-blocking agent; the coloring layer comprises polypropylene and titanium dioxide, and the addition ratio of the titanium dioxide in the coloring layer is 5-30 wt%; the foaming support layer comprises polypropylene and calcium carbonate, and the addition ratio of the calcium carbonate in the foaming support layer is 5-30 wt%; the connecting layer comprises polypropylene and maleic anhydride grafted polypropylene, and the content of the maleic anhydride grafted polypropylene in the connecting layer is 30-50 wt%; the hot-melt adhesive layer is composed of an ethylene-propylene copolymer and an ethylene-butene copolymer; the content of the ethylene-propylene copolymer in the hot-melt adhesive layer is 40-60 wt%.

[0008] For the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles of the present invention, through the cooperation of the structures of each layer and the design of the components of each layer, the adhesion strength between the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles and the high-density polyethylene bottle not only meets the requirements of in-mold labeling, but also can peel off the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles from the surface of the high-density polyethylene bottle cleanly by peeling during recycling, realizing the separation of the high-density polyethylene bottle and the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles, and classifying and recycling them as single materials respectively, avoiding the problem of the recycling pollution of the high-density polyethylene bottle caused by the materials of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles itself and the ink on the surface.

[0009] The surface layer is used for surface printing, and the ink can be printed on the surface of the surface layer. By adding an anti-blocking agent to the surface layer, the anti-blocking effect of the surface layer can be improved to prevent adhesion. The coloring layer is a white layer, which serves as a white background. The coloring layer uses polypropylene and 5-30 wt% titanium dioxide, so that the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles can exist in the product form of a white label film, and can be used as the white background when printing on the surface of the surface layer, reducing the process of applying a white background during surface printing and saving printing costs; the addition ratio of the titanium dioxide in the coloring layer is 5-30 wt%; if the addition ratio of the titanium dioxide in the coloring layer is higher than 30 wt%, on the one hand, the titanium dioxide used in the coloring layer is expensive and the product cost is high, on the other hand, it is easy to cause peeling and delamination between the surface layer and the coloring layer and between the coloring layer and the foaming support layer, affecting the bonding strength between layers; if the addition ratio of the titanium dioxide in the coloring layer is lower than 5 wt%, the coloring layer cannot achieve the coloring effect, and the light transmittance is significantly improved, and it cannot effectively serve as the white background for surface printing on the surface layer.

[0010] The foamed support layer plays a role in mechanical support and cavitation. The foamed support layer is made of polypropylene and 5 - 30 wt% calcium carbonate. Due to the addition of calcium carbonate, when the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles is stretched (during the preparation process), it causes pore formation during stretching, resulting in a cavitation effect. When the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles is subjected to in-mold labeling, since the temperature of in-mold labeling is usually relatively high (the in-mold labeling temperature is generally 170 - 190 °C, and the melting point temperature of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this invention is 160 - 165 °C), the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles will melt, and cavitation collapse occurs during melting, resulting in an orange peel-like uneven morphology on the surface of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles, meeting the appearance requirements after the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles is formed on high-density polyethylene bottles. The addition ratio of calcium carbonate in the foamed support layer is 5 - 30 wt%. If the addition ratio of calcium carbonate in the foamed support layer is lower than 5 wt%, it is not easy to form an orange peel-like uneven morphology on the surface of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles when applied to high-density polyethylene bottles. If the addition ratio of calcium carbonate in the foamed support layer is higher than 30 wt%, it is easy to peel and delaminate between the coloring layer and the foamed support layer, and between the foamed support layer and the connection layer, affecting the bonding strength between layers.

[0011] The connection layer is used to connect the foamed support layer and the hot melt adhesive layer. The connection layer uses two resins, polypropylene and maleic anhydride grafted polypropylene, to connect the foamed support layer and the hot melt adhesive layer. Through the interlocking of polymer chains and the interfacial adhesion between maleic anhydride grafted polypropylene and inorganic fillers, the bonding strength of the foamed support layer, the connection layer, and the hot melt adhesive layer is improved, preventing peeling and delamination. Among them, the maleic anhydride grafted polypropylene in the connection layer bonds with the calcium carbonate in the foamed support layer, enhancing the bonding strength between the connection layer and the foamed support layer; the polypropylene in the connection layer can interlock with the propylene-butene copolymer in the hot melt adhesive layer. Through the entanglement of polymer molecular chains and the interlocking of local propylene chain segments, the bonding strength between the connection layer and the hot melt adhesive layer is improved. The content of maleic anhydride grafted polypropylene in the connection layer is 30 - 50 wt%. If the content of maleic anhydride grafted polypropylene is lower than 30 wt%, the bonding strength between the connection layer and the foamed support layer is poor and it is easy to delaminate. If the content of maleic anhydride grafted polypropylene is higher than 50 wt%, the cost is too high.

[0012] The hot melt adhesive layer is composed of an ethylene-propylene copolymer and an ethylene-butene copolymer. The ethylene-propylene copolymer is an ethylene-propylene copolymer with propylene as the main body and butene as the copolymerization unit; the ethylene-butene copolymer is an ethylene-butene copolymer with ethylene as the main body and butene as the copolymerization unit. The ethylene-butene copolymer is conducive to heat bonding during in-mold forming with a high-density polyethylene bottle mold. The hot melt adhesive layer is composed of an ethylene-propylene copolymer and an ethylene-butene copolymer. On the one hand, through the intermolecular chain interlocking between the ethylene-propylene copolymer and the polypropylene in the connecting layer, the bonding strength between the hot melt adhesive layer and the connecting layer is strengthened; on the other hand, the ethylene-propylene copolymer and the ethylene-butene copolymer can achieve synergistic interlocking. After the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles is applied to a high-density polyethylene bottle, during peeling, due to the intermolecular chain interlocking between the ethylene-propylene copolymer in the hot melt adhesive layer and the polypropylene in the connecting layer, and the synergistic interlocking with the ethylene-butene copolymer, it is difficult for the ethylene-butene copolymer to remain on the surface of the high-density polyethylene bottle, avoiding the problem of high-density polyethylene bottle recycling pollution caused by the residue of the self-material of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles. On the other hand, for the ethylene-propylene copolymer and the ethylene-butene copolymer, by introducing the copolymerization monomer butene, the melting point of the copolymer is reduced, so that the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles can be in-mold labeled at the processing temperature of the blow molding process without generating bubbles. The content of the ethylene-propylene copolymer in the hot melt adhesive layer is 40-60wt%. If the content of the ethylene-propylene copolymer is less than 40wt%, the content of the ethylene-butene copolymer is relatively high. Since the hot melt adhesive layer is mainly heat-bonded to the high-density polyethylene bottle through the ethylene-butene copolymer, it may lead to too high a bonding strength between the hot melt adhesive layer and the high-density polyethylene bottle, resulting in some materials remaining on the high-density polyethylene bottle during peeling and recycling. If the content of the ethylene-propylene copolymer is higher than 60wt%, the content of the ethylene-butene copolymer is relatively low, and the hot melt adhesive layer cannot be firmly bonded to the high-density polyethylene bottle, resulting in poor labeling between the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles and the high-density polyethylene bottle.

[0013] Further, the polypropylene in the surface layer, the coloring layer, the foaming support layer and the connecting layer is all homopolypropylene, with a melt index of 2.5-3.5 g / 10 min (melt index test conditions: 230 °C, 2.16 KG), and an isotacticity of 95-97%.

[0014] Further, in the connecting layer, the grafting rate of maleic anhydride in the maleic anhydride grafted polypropylene is 0.5-1 wt%, and the melt index of the maleic anhydride grafted polypropylene is 2.5-3.5 g / 10 min (melt index test condition: 230 °C, 2.16 KG). If the grafting rate of maleic anhydride in the maleic anhydride grafted polypropylene is too low, the bonding strength between the connecting layer and the foamed support layer is insufficient, and delamination is likely to occur. The melt index of the maleic anhydride grafted polypropylene is selected to be 2.5-3.5 g / 10 min (melt index test condition: 230 °C, 2.16 KG), which is close to the melt index of the polypropylene in the connecting layer and the foamed support layer. On the one hand, it ensures the mechanical strength, and on the other hand, it ensures better dispersion and mutual melting of the maleic anhydride grafted polypropylene with the polypropylene in the connecting layer and the foamed support layer.

[0015] Further, in the hot melt adhesive layer, the content of butene in the propylene-butene copolymer is 4-10 wt%, the melting point of the propylene-butene copolymer is 75-100 °C, and the melt index is 3-15 g / 10 min (melt index test condition: 230 °C, 2.16 KG). If the content of butene in the propylene-butene copolymer is less than 4 wt%, and / or the melting point of the propylene-butene copolymer is higher than 100 °C, when the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles is used for in-mold labeling on high-density polyethylene bottles, it is likely to have poor adhesion and cause bubble problems; if the content of butene in the propylene-butene copolymer is higher than 10 wt%, and / or the melting point of the propylene-butene copolymer is lower than 75 °C, the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles not only easily causes sticking roller breakage during longitudinal stretching in the preparation process, affecting the appearance of the film surface, but also has room temperature tackiness due to too low melting point during storage at room temperature, resulting in label sticking together.

[0016] Further, in the hot melt adhesive layer, the content of butene in the ethylene-butene copolymer is 5-25 wt%, the melting point of the ethylene-butene copolymer is 75-100 °C, and the melt index is 3-15 g / 10 min (melt index test conditions: 230 °C, 2.16 KG). If the content of butene in the ethylene-butene copolymer is less than 5 wt%, and / or the melting point of the ethylene-butene copolymer is higher than 100 °C, when the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles is subjected to in-mold labeling, it is easy to have poor adhesion and cause bubble problems. Moreover, the interlocking ability between the polymer chains of the ethylene-butene copolymer and the propylene-butene copolymer is weakened, resulting in too strong adhesion between the ethylene-butene copolymer and the high-density polyethylene bottle and remaining on the surface of the high-density polyethylene bottle. If the content of butene in the ethylene-butene copolymer is higher than 25 wt%, and / or the melting point of the propylene-butene copolymer is lower than 75 °C, the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles not only easily causes sticking roller breakage during longitudinal stretching in the preparation process, affecting the appearance of the film surface, but also has room temperature tackiness due to too low melting point during storage at room temperature, resulting in label sticking together phenomenon.

[0017] Further, the addition ratio of the anti-blocking agent in the surface layer is 0.1-1 wt%, the anti-blocking agent is silica or polymethyl methacrylate, and the average particle size is 4-5 μm. By adding 0.1-1 wt% of the anti-blocking agent in the surface layer, the anti-blocking effect of the surface layer is improved. Using silica or polymethyl methacrylate as the anti-blocking agent, and the average particle size of the anti-blocking agent is 4-5 μm, so that it can protrude from the surface layer to achieve the anti-blocking effect. This is a conventional technical means in the art and will not be elaborated here.

[0018] Further, in the coloring layer, the average particle size of the titanium dioxide is 0.2-0.4 μm, and the synthesis process of the titanium dioxide is the chlorination process. The titanium dioxide with an average particle size of 0.2-0.4 μm synthesized by the chlorination process can improve the coloring effect of the coloring layer.

[0019] Further, in the foaming support layer, the average particle size of the calcium carbonate is 0.9-2 μm. By using calcium carbonate with an average particle size of 0.9-2 μm, it is convenient for the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles to be stretched into "holes" of appropriate size during the preparation process, which is beneficial to cavitation; and when the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles is subjected to in-mold labeling, cavitation collapse occurs, forming an orange peel uneven morphology.

[0020] Furthermore, the connecting layer further includes an antistatic agent, and the content of the antistatic agent in the connecting layer is 0.5-1 wt%, and the antistatic agent is glycerol monostearate or ethylamine. By adding 0.5-1 wt% of the antistatic agent to the connecting layer, it is beneficial to improve the antistatic effect of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles.

[0021] Furthermore, the thickness of the surface layer is 1-1.5 μm; the thickness of the coloring layer is 2-10 μm; the thickness of the foaming support layer is 50-80 μm; the thickness of the connecting layer is 5-10 μm; the thickness of the hot melt adhesive layer is 3-10 μm.

[0022] The present invention further designs the thickness of each layer. The thickness of the surface layer is 1 - 1.5 μm, and the average particle size of the anti-blocking agent is 4 - 5 μm. If the thickness of the surface layer is less than 1 μm, the anti-blocking agent is likely to fall off from the surface layer, contaminating the guide roller and causing the one-piece formed and easily recyclable in-mold label film for high-density polyethylene bottles to be easily scratched during the preparation process. If the thickness of the surface layer is greater than 1.5 μm, the height of the anti-blocking agent protruding from the surface layer is insufficient, resulting in the one-piece formed and easily recyclable in-mold label film for high-density polyethylene bottles being prone to adhesion and reducing the anti-blocking effect. The thickness of the coloring layer is 2 - 10 μm. If the thickness of the coloring layer is greater than 10 μm, the product cost is high. If the thickness of the coloring layer is less than 2 μm, the coloring effect cannot be achieved either, and the light transmittance is significantly increased, making the coloring layer unable to effectively serve as the white background for surface printing on the surface. The thickness of the foamed support layer is 50 - 80 μm. If the thickness of the foamed support layer is less than 50 μm, the stiffness of the one-piece formed and easily recyclable in-mold label film for high-density polyethylene bottles is too low, resulting in the label not being able to stand upright single-sheet and affecting the label feeding effect. If the thickness of the foamed support layer is greater than 80 μm, the strength of the one-piece formed and easily recyclable in-mold label film for high-density polyethylene bottles is too high, and after being applied to high-density polyethylene bottles, it is likely to cause the high-density polyethylene bottles to deform (since there will be a post-shrinkage phenomenon after the high-density polyethylene bottles are formed, when the strength of the one-piece formed and easily recyclable in-mold label film for high-density polyethylene bottles is much higher than the shrinkage stress, it will cause the high-density polyethylene bottles to deform). The connecting layer specifically selects two resins, polypropylene and maleic anhydride grafted polypropylene, and controls the layer thickness to connect the foamed layer (polypropylene and calcium carbonate) and the hot melt adhesive layer (propylene-butene copolymer and ethylene-butene copolymer). The thickness of the connecting layer is 5 - 10 μm. If the thickness of the connecting layer is less than 5 μm, the foamed support layer and the hot melt adhesive layer are likely to delaminate. If the thickness of the connecting layer is greater than 10 μm, the film cost increases. The thickness of the hot melt adhesive layer is 3 - 10 μm. If the thickness of the hot melt adhesive layer is on the high side, based on the low melting point and high shrinkage rate of the hot melt adhesive layer, it is likely to cause the one-piece formed and easily recyclable in-mold label film for high-density polyethylene bottles to be uneven. If the thickness of the hot melt adhesive layer is on the low side, the bonding strength of the hot melt adhesive layer is low, easily resulting in poor bonding.

[0023] The present invention also provides a preparation method for the one-piece formed and easily recyclable in-mold label film for high-density polyethylene bottles described in any one of the above, adopting an integrated forming process, including the following steps:

[0024] After melting each layer of raw materials through an extruder respectively, they are converged at a co-extrusion die head to form an integrally formed thick sheet, and then through processes such as sheet casting, longitudinal stretching, transverse stretching, traction corona winding, aging treatment, slitting, and die pressing, the one-piece formed and easily recyclable in-mold label film for high-density polyethylene bottles is formed.

[0025] The present invention also provides an application of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles as described in any one of the above in high-density polyethylene bottles.

[0026] Integrate the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles as described in any one of the above with the high-density polyethylene bottle to form a high-density polyethylene bottle with an in-mold label. As a preferred solution, the application of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in high-density polyethylene bottles is specifically as follows: After melting high-density polyethylene at 170-190 °C, extrude it through an annular die to form a cylindrical blank. Then, place it in a mold with the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles as described in any one of the above. After cutting the blank and inserting a blowing rod, after ventilation (blowing pressure 0.4-0.5 MPa), the blank expands, and the residual heat of the blank melts the hot melt adhesive layer of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles as described in any one of the above. Finally, after cooling, the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles as described in any one of the above is integrated with the plastic part to form a high-density polyethylene bottle with an in-mold label.

[0027] When the high-density polyethylene bottle with an in-mold label needs to be recycled after use, the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles can be easily torn off from the high-density polyethylene bottle by peeling. There is no residual label material on the surface of the high-density polyethylene bottle. In this way, the in-mold label film with ink and the high-density polyethylene bottle can be classified and recycled, which is beneficial to the single-material recycling and reuse, especially suitable for this transparent high-density polyethylene bottle.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) One of the innovative points of the present invention is that by adjusting the structure, component and thickness of each layer of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles, after the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles is applied to the blow-molded product high-density polyethylene bottle, its adhesion fastness not only meets the requirements of in-mold labeling, but also can cleanly peel the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles from the surface of the high-density polyethylene bottle by peeling during recycling, realizing the classified recycling of the high-density polyethylene bottle and the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles, and avoiding the recycling pollution problem caused by the material of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles itself and the ink on its surface.

[0030] (2) The second innovation point of the present invention is that an integrally formed easy-to-recycle in-mold label film for high-density polyethylene bottles is prepared by an integrally formed processing method, specifically realized through a co-extrusion and biaxial stretching process, replacing the method of off-line coating with hot melt adhesive. The integrally formed processing method of the present invention is beneficial to increasing the bonding strength between the foaming support layer and the hot melt adhesive layer through the connecting layer, preventing delamination between the foaming support layer and the hot melt adhesive layer.

[0031] (3) The third innovation point of the present invention is that a connecting layer is provided between the foaming support layer and the hot melt adhesive layer. By using the intermolecular interlocking effect of polymer chains and the interfacial adhesion effect of maleic anhydride grafted polypropylene-inorganic filler, the bonding strength between the foaming support layer and the hot melt adhesive layer is improved through the connecting layer, preventing film peeling and delamination.

[0032] For better understanding and implementation, the present invention will be described in detail below with reference to the accompanying drawings. Brief Description of the Drawings

[0033] Figure 1 It is a schematic diagram of the five-layer structure of an integrally formed easy-to-recycle in-mold label film for high-density polyethylene bottles according to the present invention;

[0034] Figure 2 It is a schematic diagram of the production process flow of an integrally formed easy-to-recycle in-mold label film for high-density polyethylene bottles according to the present invention;

[0035] Figure 3 It is a schematic diagram of the application process flow of an integrally formed easy-to-recycle in-mold label film for high-density polyethylene bottles according to the present invention;

[0036] Figure 4 It is a schematic diagram of the recycling of an integrally formed easy-to-recycle in-mold label film for high-density polyethylene bottles according to the present invention. Detailed Description of the Embodiments

[0037] For the convenience of understanding the present invention, the present invention will be described more comprehensively below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

[0038] As an embodiment of the integrally formed easy-to-recycle in-mold label film for high-density polyethylene bottles described in the present invention, please refer to Figure 1 , which is a five-layer structure, including a surface layer 1, a coloring layer 2, a foaming support layer 3, a connecting layer 4, and a hot melt adhesive layer 5 arranged in sequence.

[0039] The main components of each layer are as follows:

[0040] Surface layer 1: Polypropylene and anti-blocking agent;

[0041] Coloring layer 2: Polypropylene and titanium dioxide;

[0042] Foaming support layer 3: Polypropylene and calcium carbonate;

[0043] Connection layer 4: Polypropylene, maleic anhydride grafted polypropylene and antistatic agent;

[0044] Hot melt adhesive layer 5: Propylene-butene copolymer and ethylene-butene copolymer.

[0045] The integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles of the present invention can adopt a biaxial stretching film-forming process, a casting film-forming process, and a blown film-forming process, and preferably selects the biaxial stretching film-forming process.

[0046] Specifically, an integrally formed processing method is adopted, specifically realized by a co-extrusion-biaxial stretching process, including the following steps: After each layer of raw materials are melted by an extruder respectively, they are converged at a co-extrusion die head to form an integrally formed thick sheet, and through processes such as sheet casting, longitudinal stretching, transverse stretching, traction corona winding, aging treatment, slitting, and molding pressing, the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles is formed.

[0047] Please refer to Figure 2 , A is the raw material, B is the melt, C is the thick sheet, D is the film master roll, E is the film finished product, F is the film molding finished product, G is the extrusion process of the extruder, H is the quenching process, I is the biaxial stretching process, J is the corona-winding process, K is the aging and slitting process, and L is the molding pressing process.

[0048] The specific production process is as follows: Each layer of raw materials A after screening is premixed according to the designed formula, stirred evenly, and after calculating the input ratio by weighing, it is sent into each extruder, and is plasticized into a melt B in the extrusion process G of the extruder. The melt is transported through a pipeline and filtered by a filter, and is distributed to the die head through a runner for co-extrusion. Then, the melt B forms a thick sheet C through the quenching process H of the chill roll. The thick sheet C forms a film through the biaxial stretching process I. The biaxial stretching process can be a step-by-step biaxial stretching process of first longitudinal stretching and then transverse stretching, or a synchronous biaxial stretching process of simultaneous longitudinal and transverse stretching. After the film is cooled, trimmed on both sides, traction thickness measurement, and corona-winding process J, the film master roll D is obtained. After the film master roll D undergoes the aging and slitting process K, the film finished product E is formed. Then, the molding pressing process L is carried out on the hot melt adhesive layer of the film finished product E, and finally the film molding finished product F is formed.

[0049] The temperatures of the extruder, flow channel, pipeline, filter, and die head used in the above method are controlled at 230 - 260 °C, the quenching temperature is controlled at 25 - 40 °C. In the stepwise stretching process, the process temperatures for longitudinal and transverse stretching are controlled at 60 - 180 °C, the longitudinal stretching ratio is controlled at 4.0 - 6.0 times, and the transverse stretching ratio is controlled at 7.0 - 10.0 times; in the synchronous stretching process, the process temperatures for longitudinal and transverse stretching are controlled at 150 - 180 °C, the longitudinal stretching ratio is controlled at 4.0 - 10.0 times, and the transverse stretching ratio is controlled at 4.0 - 10.0 times. After the two-way stretching process H, the film can be cooled at room temperature. After trimming both sides and traction thickness measurement, it is wound into a film master roll D. The above-mentioned film D is then molded at 110 - 150 °C and 40 - 80 m / min to finally obtain the molded film product F, that is, the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles.

[0050] The application process flow of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles with a five-layer structure of the present invention:

[0051] Please refer to Figure 3 , according to the common general knowledge in the art, the molded film product F first undergoes a printing process P, which includes but is not limited to common processes such as rotary printing, offset printing, flexographic printing, etc., to obtain a semi-finished product M. Then, it undergoes a die-cutting process Q to obtain single in-mold labels N. The in-mold labels N are stacked together and placed on a label rack. Through a negative pressure label feeding process R and an in-mold labeling process S, finally, a high-density polyethylene bottle O with an in-mold label is obtained.

[0052] The recycling method of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles of the present invention:

[0053] Please refer to Figure 4 , the high-density polyethylene bottle O with an in-mold label is separated from the in-mold label by manual peeling. After separation, no in-mold label material remains on the surface of the high-density polyethylene bottle, realizing the classified recycling of the two materials and facilitating secondary utilization.

[0054] In the following examples or comparative examples:

[0055] Note 1: Method for measuring the heat seal strength between the in-mold label film and the high-density polyethylene film:

[0056] This test simulates the adhesion strength between the in-mold label film and the high-density polyethylene bottle after in-mold labeling. Through the casting process, a 100-μm high-density polyethylene film is obtained. Then, using a heat sealer, the in-mold label film and the high-density polyethylene film are heat-sealed under the conditions of 135 °C, 0.18 MPa, and 1 second. After standing in the test environment for 3 minutes, the sample is cut into strips with a width of 15 mm and a length of 15 cm. Finally, the heat-sealed interface is peeled off, and the heat-sealing strength is measured using a universal tensile machine.

[0057] Description 2: Method for determining the interlayer bonding strength:

[0058] This test calibrates the difficulty of peeling the hot-melt adhesive layer of the in-mold label film. Through off-line corona treatment on the hot-melt adhesive layer of the in-mold label film, the surface tension of the hot-melt adhesive layer reaches 40 mN / m. Then, a high-viscosity tape is compounded with the surface of the hot-melt adhesive layer of the in-mold label film, and a pressure roller is used to roll back and forth on the film surface three times at a speed of about 12 cm / s under its own weight of 2.5 kg. It is required that there are no bubbles between the in-mold label film and the high-viscosity tape. After placing in the test environment for 3 minutes, the sample is cut into strips with a width of 15 mm and a length of 15 cm. Finally, the in-mold label film and the high-viscosity tape are peeled off, and the peeling force is measured using a universal tensile machine. If the peeling force ≥ 10 N / 15 mm and the in-mold label film still does not delaminate, it is evaluated as "non-delaminating"; if the peeling force < 10 N / 15 mm and the in-mold label film shows delamination, it is evaluated as "delaminating", and hereby the difficulty of delamination of the in-mold label film is evaluated.

[0059] Example 1

[0060] This embodiment provides an integrally formed recyclable in-mold label film for high-density polyethylene bottles. For its specific structure, please refer to Figure 1 which includes a surface layer 1, a coloring layer 2, a foaming support layer 3, a connecting layer 4, and a hot-melt adhesive layer 5 arranged in sequence.

[0061] Among them:

[0062] The component of the surface layer 1 is: 99.5 wt% isotactic polypropylene (isotacticity is 97%, density is 0.905 g / cm 3 , melt index is 3 g / 10 min, melt index test conditions: melting temperature is 230 °C, load weight is 2.16 kg) and 0.5 wt% silica (average particle size is 5 μm);

[0063] The component of the coloring layer 2 is: 85 wt% isotactic polypropylene (isotacticity is 97%, density is 0.905 g / cm 3, with a melt index of 3 g / 10 min, melt index test conditions: melt temperature of 230 °C, load weight of 2.16 kg) and 15 wt% titanium dioxide (chlorination process, rutile type, average particle size of 0.3 μm);

[0064] The foaming support layer 3 is composed of: 85 wt% isotactic polypropylene (isotacticity of 97%, density of 0.905 g / cm 3 , with a melt index of 3 g / 10 min, melt index test conditions: melt temperature of 230 °C, load weight of 2.16 kg) and 15 wt% calcium carbonate (average particle size 1.2 μm);

[0065] The connecting layer 4 is composed of: 50 wt% isotactic polypropylene (isotacticity of 97%, density of 0.905 g / cm 3 , with a melt index of 3 g / 10 min, melt index test conditions: melt temperature of 230 °C, load weight of 2.16 kg), 49.5 wt% maleic anhydride grafted polypropylene (maleic anhydride grafting rate of 1 wt%, density of 0.905 g / cm 3 , with a melt index of 3 g / 10 min, melt index test conditions: melt temperature of 230 °C, load weight of 2.16 kg) and 0.5 wt% glycerol monostearate;

[0066] The hot melt adhesive layer 5 is composed of: 50 wt% propylene-butene copolymer (butene content of 9%, density of 0.879 g / cm 3 , with a melt index of 8 g / 10 min, melt index test conditions: melt temperature of 230 °C, load weight of 2.16 kg) and 50 wt% ethylene-butene copolymer (butene content of 18 wt%, density of 0.905 g / cm 3 , with a melt index of 7.5 g / 10 min, melt index test conditions: melt temperature of 230 °C, load weight of 2.16 kg).

[0067] This embodiment also provides a preparation method for an integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles. Please refer to Figure 2, the specific production process is as follows: Premix the selected raw materials A of each layer according to the designed formula, stir evenly, and after weighing and calculating the input ratio, send them into each extruder, and plasticize them into melt B in the extrusion process G of the extruder. The melt is transported through pipelines and filtered by filters, and then distributed to the die head through the flow channel for co-extrusion. After that, melt B forms a thick sheet C through the quenching process H of the chill roll. The thick sheet C forms a film through the biaxial stretching process I, where the biaxial stretching process is a step-by-step double stretching process of first longitudinal stretching and then transverse stretching. The film is shaped, cooled, trimmed on both sides, traction thickness measurement, traction thickness measurement, corona treatment, and mother roll winding J to obtain the film mother roll D. After the film mother roll D undergoes the aging and slitting process K, the film finished product E is formed. Then, the die pressing process L is carried out on the hot melt adhesive layer of the film finished product E, and finally the die-pressed film finished product F is formed.

[0068] Among them, the production equipment is a flat film method step-by-step biaxial stretching polypropylene production line provided by BRUECKNER Company in Germany. The screw of the main extruder (for the foaming support layer 3) is a single-screw extruder with a diameter of 150 mm and a length-diameter ratio of 33:1. The 4 auxiliary extruders (for the surface layer 1, coloring layer 2, connecting layer 4, and hot melt adhesive layer 5 respectively) are single-screw extruders with a screw diameter of 120 mm and a length-diameter ratio of 30:1. The temperature of the extruder is 80 °C in the feeding section, and 250 °C in other sections. The temperature of the filter, flow channel, and die head in each section is 250 °C, and the quenching (cast film) temperature is 30 °C; the corresponding temperatures of the preheating zone, stretching zone, and shaping zone passed through in the longitudinal stretching process are 140 °C, 135 °C, and 140 °C respectively, and the stretching ratio is 5.0; the corresponding temperatures of the preheating zone, stretching zone, and shaping zone passed through in the transverse stretching process are 176 °C, the stretching zone is 157 °C, and the shaping zone is 168 °C, and the stretching ratio is 8.5. The production speed is 300 m / min, and the corona strength on the surface of the surface layer is 30 W·min / m 2 . After the film slitting is completed, then die pressing is carried out under the conditions of 130 °C and 60 m / min, and finally the die-pressed film finished product is obtained.

[0069] The total thickness of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this embodiment is 105 μm, the thickness of the surface layer 1 is 1 μm, the thickness of the coloring layer 2 is 10 μm, the thickness of the foaming layer 3 is 79 μm, the thickness of the connecting layer 4 is 10 μm, and the thickness of the hot melt adhesive layer is 5 μm.

[0070] In the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this embodiment, the heat seal strength between the in-mold label film and the high-density polyethylene film is 3.2 N / 15 mm, and the determination of the interlayer bonding fastness: no delamination.

[0071] The application process of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this embodiment: Please refer to Figure 3, the in-mold label film F first undergoes a printing process P, which includes but is not limited to common processes such as rotary printing, offset printing, flexographic printing, etc., to obtain a semi-finished product M. Then, through a die-cutting process Q, single in-mold labels N are obtained. The in-mold labels N are stacked together and placed on a label rack. Through a negative pressure label feeding process R and an in-mold labeling process S, finally, a high-density polyethylene bottle O with an in-mold label is obtained.

[0072] The recycling process of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this embodiment: Please refer to Figure 4 , the high-density polyethylene bottle O with an in-mold label is separated from the in-mold label by manual peeling. After separation, no in-mold label material remains on the surface of the high-density polyethylene bottle, realizing the classified recycling of the two materials and facilitating secondary utilization. Based on the determination of the interlayer bonding fastness without delamination, it shows that the interlayer bonding strength ≥ 10 N / 15 mm, which is much higher than the heat-sealing strength of 3.2 N / 15 mm between the in-mold label film and the high-density polyethylene film. The in-mold label film can be torn off from the surface of the high-density polyethylene bottle without delamination, and no label material remains on the surface of the high-density polyethylene bottle.

[0073] For convenient comparison, the differences in performance of the formulations of each layer are designed based on Example 1, only changing the proportion of materials, and are systematically compared in the form of a list below. Specifically as follows:

[0074] Example 2

[0075] This embodiment is basically the same as Example 1, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this embodiment, the hot melt adhesive layer 5 is composed of 40 wt% propylene-butene copolymer and 60 wt% ethylene-butene copolymer. Please refer to Table 1 for details.

[0076] Comparative Example 1

[0077] This comparative example is basically the same as Example 1, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this comparative example, the hot melt adhesive layer 5 is composed of 30 wt% propylene-butene copolymer and 70 wt% ethylene-butene copolymer. Please refer to Table 1 for details.

[0078] Comparative Example 2

[0079] This comparative example is basically the same as Example 1, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this comparative example, the hot melt adhesive layer 5 is composed of 70 wt% propylene-butene copolymer and 30 wt% ethylene-butene copolymer. Please refer to Table 1 for details.

[0080] Table 1 Composition of each layer in Examples 1-2 and Comparative Examples 1-2

[0081]

[0082]

[0083] Example 3

[0084] This example is basically the same as Example 1, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this example, the content of butene in the propylene-butene copolymer used in the hot melt adhesive layer 5 is 4 wt%, and the content of butene in the ethylene-butene copolymer is 5 wt%. For details, please refer to Table 2.

[0085] Example 4

[0086] This example is basically the same as Example 1, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this example, the content of butene in the propylene-butene copolymer used in the hot melt adhesive layer 5 is 10 wt%, and the content of butene in the ethylene-butene copolymer is 25 wt%. For details, please refer to Table 2.

[0087] Table 2 Composition of each layer in Examples 3-4

[0088]

[0089]

[0090] Comparative Example 3

[0091] This comparative example is basically the same as Example 1, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this comparative example, the content of butene in the ethylene-butene copolymer used in the hot melt adhesive layer 5 is 2 wt%. For details, please refer to Table 3.

[0092] Comparative Example 4

[0093] This comparative example is basically the same as Example 1, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this comparative example, the content of butene in the ethylene-butene copolymer used in the hot melt adhesive layer 5 is 30 wt%. For details, please refer to Table 3.

[0094] Table 3 Composition of each layer in Comparative Examples 3-4

[0095]

[0096]

[0097] Comparative Example 5

[0098] This comparative example is basically the same as Example 1, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this comparative example, the content of butene in the propylene-butene copolymer used in the hot melt adhesive layer 5 is 2 wt%. For details, please refer to Table 4.

[0099] Comparative Example 6

[0100] This comparative example is basically the same as Example 1, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this comparative example, the content of butene in the propylene-butene copolymer used in the hot melt adhesive layer 5 is 15 wt%. For details, please refer to Table 4.

[0101] Table 4 Formulation compositions of each layer of Comparative Examples 5-6

[0102]

[0103]

[0104] Example 5

[0105] This example is basically the same as Example 1, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this example, the content of polypropylene in the coloring layer 2 is 70 wt% and the content of titanium dioxide is 30 wt%. For details, please refer to Table 5.

[0106] Comparative Example 7

[0107] This comparative example is basically the same as Example 1, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this comparative example, the content of polypropylene in the coloring layer 2 is 60 wt% and the content of titanium dioxide is 40 wt%. For details, please refer to Table 5.

[0108] Example 6

[0109] This example is basically the same as Example 1, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this example, the content of polypropylene in the foaming support layer 3 is 70 wt% and the content of calcium carbonate is 30 wt%. For details, please refer to Table 5.

[0110] Comparative Example 8

[0111] This comparative example is basically the same as Example 1, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this comparative example, the content of polypropylene in the foaming support layer 3 is 60 wt%, and the content of calcium carbonate is 40 wt%. For details, please refer to Table 5.

[0112] Table 5 Composition of each layer of Examples 5-6 and Comparative Examples 7-8

[0113]

[0114] Example 7

[0115] This example is basically the same as Example 5, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this example, the content of polypropylene in the connecting layer 4 is 69.5 wt%, and the content of maleic anhydride grafted polypropylene is 30 wt%. For details, please refer to Table 6.

[0116] Comparative Example 9

[0117] This comparative example is basically the same as Example 7, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this comparative example, the content of polypropylene in the connecting layer 4 is 79.5 wt%, and the content of maleic anhydride grafted polypropylene is 20 wt%. For details, please refer to Table 6.

[0118] Example 8

[0119] This example is basically the same as Example 7, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this example, the grafting rate of maleic anhydride in the maleic anhydride grafted polypropylene used in the connecting layer 4 is 0.5 wt%. For details, please refer to Table 6.

[0120] Comparative Example 10

[0121] This comparative example is basically the same as Example 7, except that in the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in this comparative example, the grafting rate of maleic anhydride in the maleic anhydride grafted polypropylene used in the connecting layer 4 is 0.2 wt%. For details, please refer to Table 6.

[0122] Table 6 Composition of each layer and performance test results of Examples 7-8 and Comparative Examples 9-10

[0123]

[0124] Please refer to Tables 1 - 6. For the integrally formed and easily recyclable in - mold label film for high - density polyethylene bottles of the present invention, through the design of each layer structure, composition and thickness, after the integrally formed and easily recyclable in - mold label film for high - density polyethylene bottles is applied to the blow - molded product, i.e., high - density polyethylene bottles, its adhesion fastness not only meets the requirements of in - mold labeling, but also can be cleanly peeled off from the surface of high - density polyethylene bottles by peeling during recycling, realizing the classified recycling of high - density polyethylene bottles and the integrally formed and easily recyclable in - mold label film for high - density polyethylene bottles, and avoiding the recycling pollution problem caused by the material of the integrally formed and easily recyclable in - mold label film for high - density polyethylene bottles itself and the ink on its surface.

[0125] In the hot - melt adhesive layer 5 of the integrally formed and easily recyclable in - mold label film for high - density polyethylene bottles of Comparative Example 1, the content of propylene - butene copolymer is on the low side and the content of ethylene - butene copolymer is on the high side. After the integrally formed and easily recyclable in - mold label film for high - density polyethylene bottles of Comparative Example 1 is applied to high - density polyethylene bottles and peeled off, there is a trace amount of material remaining on the high - density polyethylene bottles, and it cannot be effectively recycled as a single material.

[0126] In the hot - melt adhesive layer 5 of the integrally formed and easily recyclable in - mold label film for high - density polyethylene bottles of Comparative Example 2, the content of propylene - butene copolymer is on the high side and the content of ethylene - butene copolymer is on the low side. The integrally formed and easily recyclable in - mold label film for high - density polyethylene bottles of Comparative Example 2 has a problem of poor labeling firmness when applied to high - density polyethylene bottles.

[0127] In the hot - melt adhesive layer 5 of the integrally formed and easily recyclable in - mold label film for high - density polyethylene bottles of Comparative Example 3, the content of butene in the ethylene - butene copolymer is on the low side. When the integrally formed and easily recyclable in - mold label film for high - density polyethylene bottles of Comparative Example 3 is applied to high - density polyethylene bottles, it is easy to have poor adhesion and generate bubbles during in - mold labeling. Moreover, the inter - locking ability between the polymer chains of ethylene - butene copolymer and propylene - butene copolymer is weakened, resulting in too high adhesion fastness between the ethylene - butene copolymer and high - density polyethylene bottles, and a trace amount of material remaining on the high - density polyethylene bottles, and it cannot be effectively recycled as a single material.

[0128] In the hot - melt adhesive layer 5 of the integrally formed and easily recyclable in - mold label film for high - density polyethylene bottles of Comparative Example 4, the content of butene in the ethylene - butene copolymer is on the high side. During the preparation process, it is easy to have sticky roller breakage during longitudinal stretching, affecting the appearance of the film surface.

[0129] In the hot melt adhesive layer 5 of the integrally formed and easily recyclable in-mold labeling film for high-density polyethylene bottles of Comparative Example 5, the content of butene in the propylene-butene copolymer is relatively low. When the integrally formed and easily recyclable in-mold labeling film for high-density polyethylene bottles of Comparative Example 5 is applied to high-density polyethylene bottles, it is likely to be poorly adhered during in-mold labeling, resulting in the generation of bubbles. When peeled off for recycling, a small amount of material remains on the high-density polyethylene bottles, and it cannot be effectively recycled as a single material.

[0130] In the hot melt adhesive layer 5 of the integrally formed and easily recyclable in-mold labeling film for high-density polyethylene bottles of Comparative Example 6, the content of butene in the propylene-butene copolymer is relatively high. During the preparation process, it is prone to sticking roller breakage during longitudinal stretching, affecting the appearance of the film surface.

[0131] In the coloring layer 2 of the integrally formed and easily recyclable in-mold labeling film for high-density polyethylene bottles of Comparative Example 7, the content of titanium dioxide is relatively high, resulting in high production costs. Moreover, delamination easily occurs between the surface layer 1 and the coloring layer 2, and between the coloring layer 2 and the foaming support layer 3. After the integrally formed and easily recyclable in-mold labeling film for high-density polyethylene bottles of Comparative Example 7 is applied to high-density polyethylene bottles and peeled off for recycling, a large amount of material remains on the high-density polyethylene bottles, and it cannot be effectively recycled as a single material.

[0132] In the foaming support layer 3 of the integrally formed and easily recyclable in-mold labeling film for high-density polyethylene bottles of Comparative Example 8, the content of calcium carbonate is relatively high. Delamination easily occurs between the coloring layer 2 and the foaming support layer 3, and between the foaming support layer 3 and the connecting layer 4. After the integrally formed and easily recyclable in-mold labeling film for high-density polyethylene bottles of Comparative Example 8 is applied to high-density polyethylene bottles and peeled off for recycling, a large amount of material remains on the high-density polyethylene bottles, and it cannot be effectively recycled as a single material.

[0133] In the foaming connecting layer 4 of the integrally formed and easily recyclable in-mold labeling film for high-density polyethylene bottles of Comparative Example 9, the content of maleic anhydride grafted polypropylene is relatively low, and the adhesion between maleic anhydride grafted polypropylene and calcium carbonate in the foaming support layer 3 is insufficient, resulting in poor bonding strength between the connecting layer and the foaming support layer and easy delamination. After the integrally formed and easily recyclable in-mold labeling film for high-density polyethylene bottles of Comparative Example 9, which is prone to delamination, is applied to high-density polyethylene bottles and peeled off for recycling, a large amount of material remains on the high-density polyethylene bottles, and it cannot be effectively recycled as a single material.

[0134] In the foamed connecting layer 4 of the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in Comparative Example 10, the grafting rate of maleic anhydride in maleic anhydride-grafted polypropylene is relatively low, and the bonding strength between the connecting layer and the foamed support layer is insufficient, resulting in easy delamination. After the integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles in Comparative Example 10 is applied to high-density polyethylene bottles and peeled off for recycling, a large amount of material remains on the high-density polyethylene bottles and cannot be effectively recycled as a single material.

[0135] The above embodiments only represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and the present invention also intends to include these modifications and improvements.

Claims

1. An integrated and easily recyclable in-mold label film for high-density polyethylene bottles, characterized in that: It includes a surface layer, a coloring layer, a foaming support layer, a connecting layer and a hot melt adhesive layer which are arranged in sequence; The surface layer includes polypropylene and an anti-blocking agent; The coloring layer comprises polypropylene and titanium dioxide, and the addition ratio of the titanium dioxide in the coloring layer is 5-30wt%; The foaming support layer comprises polypropylene and calcium carbonate, and the calcium carbonate is added to the foaming support layer in an amount of 5-30 wt %; The connecting layer comprises polypropylene and maleic anhydride grafted polypropylene, wherein the content of the maleic anhydride grafted polypropylene in the connecting layer is 30-50wt%; and the grafting rate of maleic anhydride in the maleic anhydride grafted polypropylene is 0.5-1wt%; The hot melt adhesive layer is composed of propylene-butene copolymer and ethylene-butene copolymer; the content of the propylene-butene copolymer in the hot melt adhesive layer is 40-60wt%; the content of butene in the propylene-butene copolymer is 4-10wt%; the content of butene in the ethylene-butene copolymer is 5-25wt%.

2. The one-piece easily recyclable in-mold label film for high-density polyethylene bottles according to claim 1, characterized in that: The polypropylene in the surface layer, the coloring layer, the foaming support layer and the connecting layer are all homopolymer polypropylene, with a melt index of 2.5-3.5 g / 10 min and an isotacticity of 95-97%.

3. The one-piece easily recyclable in-mold label film for high-density polyethylene bottles according to claim 1, characterized in that: In the connecting layer, the maleic anhydride grafted polypropylene has a melt index of 2.5-3.5 g / 10 min.

4. The one-piece easily recyclable in-mold label film for high-density polyethylene bottles according to claim 1, characterized in that: In the hot melt adhesive layer, the melting point of the propylene-butene copolymer is 75-100° C., and the melt index is 3-15 g / 10 min; in the hot melt adhesive layer, the melting point of the ethylene-butene copolymer is 75-100° C., and the melt index is 3-15 g / 10 min.

5. The one-piece easily recyclable in-mold label film for high-density polyethylene bottles according to claim 1, characterized in that: The anti-adhesive agent is added to the surface layer in a proportion of 0.1-1 wt %. The anti-adhesive agent is silicon dioxide or polymethyl methacrylate, and has an average particle size of 4-5 μm.

6. The one-piece easily recyclable in-mold label film for high-density polyethylene bottles according to claim 1, characterized in that: In the coloring layer, the average particle size of the titanium dioxide is 0.2-0.4 μm; in the foaming support layer, the average particle size of the calcium carbonate is 0.9-2 μm.

7. The one-piece easily recyclable in-mold label film for high-density polyethylene bottles according to claim 1, characterized in that: The connecting layer further comprises an antistatic agent, the content of which in the connecting layer is 0.5-1 wt %, and the antistatic agent is glyceryl monostearate or ethylamine.

8. The one-piece easily recyclable in-mold label film for high-density polyethylene bottles according to claim 1, characterized in that: The thickness of the surface layer is 1-1.5 μm; the thickness of the coloring layer is 2-10 μm; the thickness of the foaming support layer is 50-80 μm; the thickness of the connecting layer is 5-10 μm; and the thickness of the hot melt adhesive layer is 3-10 μm.

9. A method for preparing an integrally formed and easily recyclable in-mold label film for high-density polyethylene bottles according to any one of claims 1 to 8, characterized in that: The one-piece molding process includes the following steps: The raw materials of each layer are melted in an extruder and gathered at a co-extrusion die to form an integrally formed thick sheet, which is then subjected to sheet casting, longitudinal stretching, transverse stretching, traction corona winding, aging treatment, slitting and molding processes to form the integrally formed easily recyclable in-mold label film for high-density polyethylene bottles.

10. Use of the one-piece easily recyclable in-mold label film for high-density polyethylene bottles according to any one of claims 1 to 8 in high-density polyethylene bottles.

Images