An easy-to-unroll and roll-up paper-plastic composite film, its preparation method and application

Abstract

The present invention relates to an easily rewound paper-plastic composite film, its preparation method and application, belonging to the field of paper-plastic laminating. The easily rewound paper-plastic composite film described in the present invention includes a surface layer, a support layer, a hot melt adhesive layer and a roughened hot melt adhesive layer arranged in sequence; the hot melt adhesive layer is composed of a first hot melt adhesive copolymer, and the melting point of the first hot melt adhesive copolymer is 80-90 °C; the roughened hot melt adhesive layer is composed of a second hot melt adhesive copolymer, and the melting point of the second hot melt adhesive copolymer is 70-75 °C. The easily rewound paper-plastic composite film prepared by the present invention using a specific method will not have the problem of difficult rewinding, and will not easily produce visible snowflake points due to insufficient compaction after paper-plastic lamination.

Description

Technical Field

[0001] The present invention relates to the technical field of paper-plastic laminating, and particularly to an easily unwindable and rewound paper-plastic composite film, a preparation method thereof, and an application thereof. Background Art

[0002] Paper-plastic laminating is generally carried out by thermally pressing and laminating a film on the printed surface of a printed paper product (obtained by printing a paper product). Paper-plastic laminating generally has the following functions: (1) preventing the printed paper product from being affected by moisture and reducing its mechanical strength; (2) protecting the printed ink on the printed paper product from being scratched; (3) preventing the printed ink on the printed paper product from being oxidized by air and changing color.

[0003] At present, the film used for paper-plastic laminating is usually called a paper-plastic composite film. The paper-plastic composite film generally includes an instant-coated paper-plastic composite film and a pre-coated paper-plastic composite film, and the pre-coated paper-plastic composite film is divided into an on-line pre-coated paper-plastic composite film and an off-line pre-coated paper-plastic composite film. Due to cost reasons, in the prior art, many users choose the on-line pre-coated paper-plastic composite film for paper-plastic laminating.

[0004] Please refer to Figure 2 , the on-line pre-coated paper-plastic composite film generally includes a surface layer 1, a support layer 2, and a hot melt adhesive layer 3 arranged in sequence. The production process of the on-line pre-coated paper-plastic composite film is to laminate a layer of hot melt adhesive layer 3 on the surface of the support layer 2 by a one-step forming method, and finally form a paper-plastic composite film with a hot melt adhesive layer 3. Its production process generally includes co-extrusion and lamination through an extrusion-casting process to form a three-layer structure casting sheet, and then through a longitudinal stretching process, a transverse stretching process, a traction-thickness measurement-corona treatment-winding process and other processes to form a film semi-finished product, and then through an aging-slitting process, and finally form a film finished product, that is, an on-line pre-coated paper-plastic composite film.

[0005] However, although the existing on-line pre-coated paper-plastic composite film has the advantage of one-step forming, it also has the following problems:

[0006] (1) In the longitudinal stretching process of the production process, the hot melt adhesive layer needs to be in contact with the heating roller; therefore, the melting point of the hot melt adhesive copolymer used in the hot melt adhesive layer cannot be too low. If the melting point is too low, it is easy to cause problems such as scalding or poor stretching of the hot melt adhesive layer in the biaxial stretching process, affecting the appearance of the paper-plastic laminating finished product during subsequent paper-plastic laminating; and in order to meet the subsequent paper-plastic laminating requirements, the melting point of the hot melt adhesive copolymer used in the hot melt adhesive layer cannot be too high. If the melting point is too high, the processing window of paper-plastic laminating is too narrow, and the production speed of paper-plastic laminating will be reduced. Therefore, the selection of the melting point of the hot melt adhesive layer of the on-line pre-coated paper-plastic composite film needs to take into account both the production process of the film and the subsequent application process.

[0007] (2)The hot melt adhesive copolymer used in the hot melt adhesive layer has room temperature bonding characteristics, and the hot melt adhesive layer of the traditional online pre-coated paper-plastic composite film is smooth. When winding, the hot melt adhesive layer is in close contact with the surface layer, resulting in difficulties in winding and unwinding during the production and use of the online pre-coated paper-plastic composite film. During the winding and unwinding process, it is extremely easy to produce wrinkling, causing abnormal appearance, and the unwinding sound is relatively loud, affecting the health of production employees. Especially when the surface opposite to the surface of the hot melt adhesive layer (i.e., the surface of the surface layer) is corona-treated, it will be further difficult to achieve normal winding and unwinding work.

[0008] (3)For paper-plastic laminating, usually, the hot melt adhesive layer of the paper-plastic composite film is first adhered to the printed surface of the printed paper product, and then the paper-plastic composite film and the printed paper product are laminated together through a hot pressing process to form a paper-plastic laminated finished product. In the hot pressing process, the heat transfer method is generally from the outside to the inside, that is, the heat is first transferred to the surface layer through the heating roller, then passes through the support layer, and then gradually transfers to the hot melt adhesive layer. The total thickness of the surface layer and the support layer is generally 10 - 15 μm, and the thickness of the hot melt adhesive layer is generally 5 - 10 μm. After the heat is transferred through the above path, the hot melt adhesive layer receives the least heat. If the high-speed lamination (that is, the lamination speed is too fast) is easy to produce the phenomenon of insufficient compaction. The phenomenon of insufficient compaction means that the paper-plastic laminated finished product after paper-plastic lamination has visible snowflake points to the naked eye (the main reason for the insufficient compaction is that the hot melt adhesive copolymer used in the hot melt adhesive layer cannot be fully melted, resulting in that the hot melt adhesive layer cannot be fully adhered to the printed surface of the printed paper product, and there are micro voids, resulting in abnormal appearance). Summary of the Invention

[0009] Based on this, the purpose of the present invention is to provide an easily unwindable paper-plastic composite film, its preparation method and application. The easily unwindable paper-plastic composite film prepared by the specific method of the present invention is not easy to produce scalding or poor stretching during the longitudinal stretching process of the production process, will not have difficulties in winding and unwinding, and is not easy to produce visible snowflake points on the paper-plastic laminated finished product due to insufficient compaction when used for paper-plastic lamination.

[0010] To achieve the above purpose, the present invention adopts the following technical solutions:

[0011] The first object of the present invention is to provide a preparation method of an easily unwindable paper-plastic composite film. The easily unwindable paper-plastic composite film includes a surface layer, a support layer, a hot melt adhesive layer, and a roughened hot melt adhesive layer arranged in sequence. The hot melt adhesive layer is composed of a first hot melt adhesive copolymer, and the melting point of the first hot melt adhesive copolymer is 80 - 90 °C. The roughened hot melt adhesive layer is composed of a second hot melt adhesive copolymer, and the melting point of the second hot melt adhesive copolymer is 70 - 75 °C. The preparation method of the easily unwindable paper-plastic composite film includes the following steps:

[0012] Grind the raw materials of the roughened hot melt adhesive layer into a powder form to obtain the roughened hot melt adhesive layer powder. Through the high-voltage tip discharge process, make the surface of the roughened hot melt adhesive layer powder obtain an electrostatic charge of - / + (25 - 30) KV for standby (this step can be completed before the roughening treatment process, and there is no sequence limit);

[0013] Send the raw materials of the surface layer, support layer, and hot melt adhesive layer into the extruders corresponding to each layer respectively, and form a cast sheet through the extrusion-casting process;

[0014] The cast sheet undergoes a longitudinal stretching process to form a thick sheet;

[0015] The thick sheet undergoes a roughening treatment process: make the roughened hot melt adhesive layer powder adsorb and weld on the surface of the hot melt adhesive layer of the thick sheet to form a roughened thick sheet;

[0016] The roughened thick sheet undergoes a transverse stretching process and a traction-thickness measurement-corona-reeling process to obtain a film semi-finished product;

[0017] The film semi-finished product undergoes an aging-slitting process to obtain a film finished product, that is, the easily unrolled paper-plastic composite film.

[0018] The preparation method of the easily unrolled paper-plastic composite film of the present invention is as follows: After melting the raw materials of the surface layer, support layer, and hot melt adhesive layer through an extruder respectively, they are co-extruded and quenched into a cast sheet with a three-layer laminated structure (i.e., surface layer - support layer - hot melt adhesive layer) integrated in the extrusion-casting process. After the cast sheet undergoes a longitudinal stretching process, a thick sheet with a longitudinally stretched three-layer laminated structure is obtained. In the present invention, the raw materials of the roughened hot melt adhesive layer are ground into the roughened hot melt adhesive layer powder in powder form in advance. Through the high-voltage tip discharge process, the surface of the roughened hot melt adhesive layer powder obtains an electrostatic charge of - / + (25 - 30) KV. In the roughening treatment process, using the electrostatic charge on the surface of the roughened hot melt adhesive layer powder, the roughened hot melt adhesive layer powder is adsorbed onto the surface of the hot melt adhesive layer of the thick sheet and welded together to form a roughened thick sheet together with the thick sheet. After the roughened thick sheet undergoes a transverse stretching process, the roughened hot melt adhesive layer powder is further welded together with the hot melt adhesive layer, further reducing the protrusion height of the roughened hot melt adhesive layer powder on the surface of the hot melt adhesive layer, and the gap between the roughened hot melt adhesive layer powders will increase due to transverse stretching, and finally a roughened hot melt adhesive layer with an uneven surface texture is formed on the surface of the hot melt adhesive layer; then it undergoes a traction-thickness measurement-corona-reeling process to obtain a film semi-finished product. The film semi-finished product undergoes an aging-slitting process to obtain a film finished product, that is, the easily unrolled paper-plastic composite film.

[0019] The hot melt adhesive layer of the present invention is composed of a first hot melt adhesive copolymer with a relatively high melting point (80 - 90 °C), which makes the hot melt adhesive layer not prone to generate defective stripes during the longitudinal stretching process and is not prone to scalding; the roughened hot melt adhesive layer is designed to be composed of a second hot melt adhesive copolymer with a relatively low melting point (70 - 75 °C), and this design is beneficial for the roughened hot melt adhesive layer powder to be welded to the hot melt adhesive layer and not prone to falling off. In addition, the present invention makes the roughened hot melt adhesive layer powder adsorbed on the surface of the hot melt adhesive layer through the roughening treatment process. After the transverse stretching process, the gap between the roughened hot melt adhesive layer powders will increase, and finally a roughened hot melt adhesive layer with an uneven surface texture is formed on the surface of the hot melt adhesive layer. This roughened hot melt adhesive layer effectively reduces the effective contact area between the hot melt adhesive layer and the surface layer after the film is wound, greatly reduces the normal temperature adhesion between the hot melt adhesive layer and the surface layer, reduces the difficulty of winding and unwinding the film, and also avoids the wrinkling phenomenon and noise pollution generated during the winding and unwinding process, and will not have problems with difficult winding and unwinding due to the normal temperature adhesion of the hot melt adhesive layer and the corona treatment on both sides of the film. The easily unwindable paper-plastic composite film of the present invention uses a hot melt adhesive layer copolymer with an even lower melting point based on the roughened hot melt adhesive layer, and less heat is required to melt during paper-plastic film laminating. Thus, the problem of insufficient compaction feeling can be improved, and high-speed lamination can be achieved during paper-plastic film laminating and it is not prone to visible snowflake points due to insufficient compaction feeling.

[0020] In the preparation method of the easily unwindable paper-plastic composite film of the present invention, the surface of the roughened hot melt adhesive layer powder is given an electrostatic charge of - / + (25 - 30) KV through a high-voltage tip discharge process. In the roughening treatment process, by using the electrostatic charge on the surface of the roughened hot melt adhesive layer powder, the roughened hot melt adhesive layer powder can be adsorbed on the surface of the hot melt adhesive layer of the thick sheet. After the subsequent transverse stretching process, the gap between the roughened hot melt adhesive layer powders will increase, and a roughened hot melt adhesive layer with an uneven surface texture is formed on the surface of the hot melt adhesive layer. If the electrostatic charge value obtained on the surface of the roughened hot melt adhesive layer powder is lower than 25 KV, the electrostatic adsorption force between the roughened hot melt adhesive layer powder and the hot melt adhesive layer of the thick sheet is too low, resulting in the roughened hot melt adhesive layer powder not being fully adsorbed on the surface of the hot melt adhesive layer of the thick sheet, resulting in a decrease in the roughness of the prepared easily unwindable paper-plastic composite film and being not easily unwindable; if the electrostatic charge value obtained on the surface of the roughened hot melt adhesive layer powder exceeds 30 KV, there will be a risk of electrostatic injury during the film preparation process, causing a safety hazard.

[0021] As a preferred solution, the roughening process includes the following steps: applying a high-voltage tip discharge process to the surface of the hot melt adhesive layer of the thick sheet so that the surface of the hot melt adhesive layer of the thick sheet obtains + / - (25-30) KV static electricity; utilizing the mechanism of attraction between positive and negative charges to adsorb a layer of roughened hot melt adhesive layer powder on the surface of the hot melt adhesive layer of the thick sheet, and utilizing the residual heat of the thick sheet after the longitudinal stretching process to fuse the roughened hot melt adhesive layer powder and the hot melt adhesive layer of the thick sheet together to form the roughened thick sheet. The present invention uses a high-voltage tip discharge process to apply - / + (25-30) KV static electricity to the surface of the roughened hot melt adhesive layer powder before the roughening process, and uses a high-voltage tip discharge process to apply + / - (25-30) KV static electricity to the surface of the hot melt adhesive layer of the thick sheet during the roughening process. When the thick sheet passes through the roughened hot melt adhesive layer powder, the mechanism of attraction between positive and negative charges is utilized to neutralize the charges so that the surface of the hot melt adhesive layer of the thick sheet adsorbs a layer of roughened hot melt adhesive layer powder. At the same time, due to the residual heat after the longitudinal stretching process, the roughened hot melt adhesive layer powder is adsorbed on the surface of the hot melt adhesive layer of the thick sheet. The surface of the hot melt adhesive layer of the thick sheet has a relatively high residual temperature (it is well known to those skilled in the art that the surface of the hot melt adhesive layer of the thick sheet obtained after the longitudinal stretching process will have a relatively high residual temperature, which is generally 80-90°C, and the melting point of the hot melt adhesive copolymer used in the roughened hot melt adhesive layer is 70-75°C). The residual temperature on the surface of the hot melt adhesive layer of the thick sheet is used to weld the powder of the roughened hot melt adhesive layer to the hot melt adhesive layer of the thick sheet, so that the powder of the roughened hot melt adhesive layer is difficult to fall off and prevent failure, and together with the thick sheet, form a roughened thick sheet.

[0022] As a preferred embodiment, the transverse stretching ratio in the transverse stretching step is 7-10. The roughened hot melt adhesive powder on the roughened thick sheet obtained after the roughening step is fused to the surface of the hot melt adhesive layer. By controlling the transverse stretching to 7-10 times in the transverse stretching step, the gaps between the roughened hot melt adhesive powder are increased, which facilitates the formation of a roughened hot melt adhesive layer with an uneven surface texture on the surface of the hot melt adhesive layer of the thick sheet.

[0023] As a preferred embodiment, after the longitudinal stretching process, the surface temperature of the hot melt adhesive layer of the thick sheet is 80-90°C. The present invention controls the surface temperature of the hot melt adhesive layer of the thick sheet to 80-90°C after the longitudinal stretching process, so that during the roughening process, after the roughened hot melt adhesive layer powder is adsorbed on the surface of the hot melt adhesive layer of the thick sheet, the residual heat of the hot melt adhesive layer of the thick sheet can cause the roughened hot melt adhesive layer powder (melting point 70-75°C) to be fused to the hot melt adhesive layer of the thick sheet.

[0024] As a preferred solution, the preparation method of the roughened hot melt adhesive layer powder is as follows: the raw materials of the roughened hot melt adhesive layer (in the form of resin particles with an average particle size of 4 - 5 mm) are cooled with liquid nitrogen and then placed in a grinding machine for grinding, and then screened by a screening vibrator into powder with an average particle size of 4 - 6 µm, thus obtaining the roughened hot melt adhesive layer powder. By making the raw materials of the roughened hot melt adhesive layer into roughened hot melt adhesive layer powder with an average particle size of 4 - 6 µm, it is convenient for the roughened hot melt adhesive layer powder to be effectively adsorbed on the surface of the hot melt adhesive layer under the action of electrostatic adsorption force during the roughening process. In addition, after the thick sheet undergoes the transverse stretching process in the roughening process, the protrusion height of the roughened hot melt adhesive layer on the surface of the hot melt adhesive layer will decrease from 4 - 6 µm to 0.4 - 0.6 µm. Preferably, the average particle size of the roughened hot melt adhesive layer powder is 5 µm.

[0025] As a preferred solution, after obtaining the roughened hot melt adhesive layer powder, the roughened hot melt adhesive layer powder is placed in a powder tank, and then a high-voltage tip discharge process is performed on the roughened hot melt adhesive layer powder in the powder tank, so that the surface of the roughened hot melt adhesive layer powder in the powder tank obtains an electrostatic charge of - / +(25 - 30) KV.

[0026] As a preferred solution, during the roughening process, the powder tank is placed between the longitudinal stretching process and the transverse stretching process. After the surface of the hot melt adhesive layer of the thick sheet obtains an electrostatic charge of + / -(25 - 30) KV, the thick sheet is passed through the powder tank, and the distance between the hot melt adhesive layer of the thick sheet and the roughened hot melt adhesive layer powder in the powder tank is 10 - 20 mm. In this way, by controlling the distance between the hot melt adhesive layer of the thick sheet and the roughened hot melt adhesive layer powder in the powder tank to be 10 - 20 mm, a layer of roughened hot melt adhesive layer powder can be quickly and effectively adsorbed on the surface of the hot melt adhesive layer of the thick sheet.

[0027] Further, the first hot melt adhesive copolymer is at least one of ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), ethylene-acrylic acid copolymer (EAA), ethylene-α-olefin copolymer, maleic anhydride grafted ethylene-α-olefin copolymer, ethylene-vinyl chloride copolymer, propylene-α-olefin copolymer, and ethylene-vinyl acetate-vinyl alcohol terpolymer with a melting point of 80-90°C; the second hot melt adhesive copolymer is at least one of ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), ethylene-acrylic acid copolymer (EAA), ethylene-α-olefin copolymer, maleic anhydride grafted ethylene-α-olefin copolymer, ethylene-vinyl chloride copolymer, propylene-α-olefin copolymer, and ethylene-vinyl acetate-vinyl alcohol terpolymer with a melting point of 70-75°C. The hot melt adhesive layer uses a hot melt adhesive copolymer with a high melting point (80-90°C), and the roughened hot melt adhesive layer uses a hot melt adhesive copolymer with a low melting point (70-75°C). Preferably, due to the excellent adhesion performance, large production volume, and low price of ethylene-vinyl acetate copolymer, for commercial considerations, the present invention preferably uses ethylene-vinyl acetate copolymer as the hot melt adhesive copolymer, that is, the hot melt adhesive layer uses ethylene-vinyl acetate copolymer with a melting point of 80-90°C as the first hot melt adhesive copolymer, and the roughened hot melt adhesive layer uses ethylene-vinyl acetate copolymer with a melting point of 70-75°C as the second hot melt adhesive copolymer.

[0028] As a preferred embodiment of the surface layer, the surface layer comprises homopolypropylene and 0.3-1.5 wt% of an anti-blocking agent. By adding the anti-blocking agent to the surface layer, the anti-blocking effect of the surface layer can be improved, and film adhesion can be prevented.

[0029] Further, the homopolypropylene in the surface layer has a melt index of 2.8-3.2 g / min (230°C, 2.16 kg), an isotacticity of 95-97%, and a melting point temperature of 160-168°C.

[0030] Further, the anti-blocking agent is at least one of silica and polymethyl methacrylate, and the average particle size of the anti-blocking agent is 4-5 µm.

[0031] As another preferred embodiment of the surface layer, the surface layer comprises high density polyethylene and propylene-ethylene copolymer.

[0032] Further, the high density polyethylene has a melt index of 8-10 g / min (190°C, 21.6 kg) and a melting point temperature of 130-136°C.

[0033] Furthermore, the melt index of the propylene-ethylene copolymer is 7-9 g / min (230 °C, 2.16 kg), the melting point temperature is 135-145 °C, and the ethylene content is 3.5-4.5 wt%.

[0034] As a preferred embodiment of the support layer, the support layer comprises homopolypropylene and 0.4-1.5 wt% antistatic agent.

[0035] Furthermore, the melt index of the homopolypropylene in the support layer is 2.8-3.2 g / min (230 °C, 2.16 kg), the isotacticity is 95-97%, and the melting point temperature is 160-168 °C.

[0036] Furthermore, the antistatic agent is at least one of glycerol monostearate, ethoxylated alkylamine, N,N-dihydroxyethyl lauramide, ethoxylated alcohol, alkyl sulfonate, alkyl phosphate, tetraalkyl quaternary ammonium salt, trialkyl benzyl quaternary ammonium salt, alkyl betaine.

[0037] Another object of the present invention is to provide an easily unwindable paper-plastic composite film prepared by the preparation method described in any one of the above.

[0038] Another object of the present invention is to provide an application of the easily unwindable paper-plastic composite film in paper-plastic laminating. The application process specifically includes the following steps: unwind the easily unwindable paper-plastic composite film and the printed paper product respectively, and make the roughened hot melt adhesive layer of the easily unwindable paper-plastic composite film adhere to the printed surface of the printed paper product; then through a hot pressing process, the easily unwindable paper-plastic composite film and the printed paper product are laminated together to form a finished paper-plastic laminated product.

[0039] Furthermore, in the hot pressing process, the processing temperature is 100-140 °C, and the processing pressure is 12-15 MPa. Under the above high temperature and high pressure conditions, the hot melt adhesive layer and the roughened hot melt adhesive layer can be melted and flattened, and the roughened texture will not affect the appearance of the laminate.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] (1) The easily unwindable paper-plastic composite film of the present invention is designed for the hot melt adhesive layer and the roughened hot melt adhesive layer and prepared by a specific preparation method, so that the easily unwindable paper-plastic composite film of the present invention is not prone to scalding or poor stretching during the longitudinal stretching process in the production process, and there will be no difficulty in unwinding and rewinding. When used for paper-plastic laminating, it is not easy to produce visible snowflakes in the finished paper-plastic laminated product due to insufficient compaction, so that the film can be laminated at high speed in the application of paper-plastic laminating, thereby improving the processing efficiency.

[0042] (2) The easy-to-wind-and-unwind paper-plastic composite film of the present invention has a roughened hot melt adhesive layer laminated on the basis of the hot melt adhesive layer, effectively reducing the effective contact area between the hot melt adhesive layer and the surface layer, greatly reducing the normal temperature adhesion force between the hot melt adhesive layer and the surface layer, reducing the difficulty of the winding and unwinding process, and avoiding wrinkling and noise pollution.

[0043] 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

[0044] Figure 1 It is a schematic structural diagram of an easy-to-wind-and-unwind paper-plastic composite film of the present invention;

[0045] Figure 2 It is a schematic structural diagram of a traditional online pre-coated paper-plastic composite film;

[0046] Figure 3 It is a process flow diagram of the production of an easy-to-wind-and-unwind paper-plastic composite film of the present invention;

[0047] Figure 4 It is a process flow diagram of the paper-plastic composite application of an easy-to-wind-and-unwind paper-plastic composite film of the present invention;

[0048] In the figure: 1, surface layer; 2, support layer; 3, hot melt adhesive layer; 4, roughened hot melt adhesive layer; A, raw material; B, cast sheet; C, thick sheet; D, roughened thick sheet; E, film semi-finished product; F, film finished product; G, extrusion-casting process; H, longitudinal stretching process; I, roughening process; J, transverse stretching process; K, traction-thickness measurement-corona-winding process; L, aging-slitting process; M, paper-plastic laminating semi-finished product; N, paper-plastic laminating finished product; P, printed paper product; Q, hot pressing process. Specific Embodiments

[0049] For ease 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.

[0050] The present invention provides an easy-to-wind-and-unwind paper-plastic composite film. Please refer to Figure 1 , which is a four-layer structure, including a surface layer 1, a support layer 2, a hot melt adhesive layer 3, and a roughened hot melt adhesive layer 4 arranged in sequence.

[0051] Among them, the raw material formulas of each layer are as follows:

[0052] Surface layer 1: homopolypropylene and anti-blocking agent; or high-density polyethylene and propylene-ethylene copolymer;

[0053] Support layer 2: homopolypropylene and antistatic agent;

[0054] Hot melt adhesive layer 3: one of ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), ethylene-acrylic acid copolymer (EAA), ethylene-α-olefin copolymer, maleic anhydride grafted ethylene-α-olefin copolymer, ethylene-vinyl chloride copolymer, propylene-α-olefin copolymer, and ethylene-vinyl acetate-vinyl alcohol terpolymer, with a melting point of 80-90°C; melt index of 10-25 g / 10 min (190°C, 21.6 kg);

[0055] Roughened hot melt adhesive layer 4: one of ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), ethylene-acrylic acid copolymer (EAA), ethylene-α-olefin copolymer, maleic anhydride grafted ethylene-α-olefin copolymer, ethylene-vinyl chloride copolymer, propylene-α-olefin copolymer, and ethylene-vinyl acetate-vinyl alcohol terpolymer with a melting point of 70-75°C; a melt index of 10-25 g / 10 min (190°C, 21.6 kg).

[0056] In the easy-to-retract and unroll paper-plastic composite film of the present invention, please refer to Figure 1 A roughened hot melt adhesive layer 4 having an uneven surface pattern is formed on the surface of the hot melt adhesive layer 3 to facilitate winding and unwinding.

[0057] The present invention also provides a method for preparing an easily retractable paper-plastic composite film. Figure 3, including the following steps: Premix the raw materials A of the screened surface layer 1, support layer 2, and hot melt adhesive layer 3 according to the designed formula respectively, stir evenly, and after weighing and calculating the input ratio, send them into the extruders corresponding to each layer, and form a cast sheet B after the extrusion-casting process G; the cast sheet B forms a thick sheet C after the longitudinal stretching process H, and after the longitudinal stretching process H, the surface temperature of the hot melt adhesive layer 3 of the thick sheet C reaches 80-90 °C; the thick sheet C undergoes a roughening treatment process I: on the surface of the hot melt adhesive layer 3 of the thick sheet C, through the high-voltage tip discharge process, the surface of the hot melt adhesive layer 3 of the thick sheet C obtains static electricity of + / -(25-30) KV, and then the above-mentioned thick sheet C passes through a powder trough filled with roughened hot melt adhesive layer powder (the powder trough is pre-treated by the high-voltage tip discharge process to make the surface of the roughened hot melt adhesive layer powder in it obtain static electricity of - / +(25-30) KV, and the roughened hot melt adhesive layer powder is obtained by cooling the raw materials of the roughened hot melt adhesive layer (resin particles with an average particle size of 4-5 mm) with liquid nitrogen and then placing them in a grinding machine for grinding and sieving into powder with an average particle size of 5 µm), where the distance between the hot melt adhesive layer of the thick sheet C and the roughened hot melt adhesive layer powder in the powder trough is 10-20 mm. Through the mechanism of attraction between positive and negative charges, a layer of roughened hot melt adhesive layer powder is adsorbed on the surface of the hot melt adhesive layer 3 of the thick sheet C by neutralizing the charges. At the same time, because the surface temperature of the hot melt adhesive layer 3 of the thick sheet C after the longitudinal stretching process reaches 80-90 °C, the remaining temperature on the surface of the hot melt adhesive layer 3 of the thick sheet C is used to fuse the hot melt adhesive layer 3 of the thick sheet C with the roughened hot melt adhesive layer powder together, so that the roughened hot melt adhesive layer powder is difficult to fall off and prevent failure, and a roughened treated thick sheet D is obtained; the roughened treated thick sheet D first undergoes a transverse stretching process J. After the roughened treated thick sheet D undergoes the transverse stretching process J (the transverse stretching ratio is controlled at 7-10), the roughened hot melt adhesive layer powder is further fused with the hot melt adhesive layer 3 together. The protruding height of the roughened hot melt adhesive layer powder on the surface of the hot melt adhesive layer 3 drops from 5 µm to 0.5 µm, and the gap between the roughened hot melt adhesive layer powders will increase, and finally a roughened hot melt adhesive layer 4 with an uneven surface texture is formed on the surface of the hot melt adhesive layer 3; then through the traction-thickness measurement-corona-winding process K, a film semi-finished product E (a large-width master roll) is obtained, and the film semi-finished product E finally undergoes an aging-slitting process L to obtain a film finished product F, that is, the easily unwound paper-plastic composite film.

[0058] The equipment used in the high-voltage tip discharge process is: an induction discharge rod (operating voltage: 0 - 50 KV), model: SC-1, manufacturer: Jiangxi Senmu Electronics Co., Ltd. In the method for preparing the easily unwindable paper-plastic composite film of the present invention, the high-voltage tip discharge voltage is: 25 - 30 KV. If it is lower than 25 KV, the electrostatic adsorption force is too low, resulting in the powder of the roughened hot melt adhesive layer not being fully adsorbed on the surface of the hot melt adhesive layer of the thick sheet, making it difficult to unwind and rewind the film. After testing by the inventor, when the discharge voltage is set at 25 - 30 KV, the powder of the roughened hot melt adhesive layer can be effectively adsorbed on the surface of the hot melt adhesive layer of the thick sheet. If it exceeds 30 KV, there will be a risk of electrostatic shock, causing a safety hazard.

[0059] The production equipment is mainly a flat film process biaxially oriented polypropylene production line provided by BRUECKNER of Germany, and a powder tank is added between the transverse stretching process and the longitudinal stretching process. The temperatures of the extruder, flow channel, pipeline, filter, and die head used in the above production line are controlled at 230 - 260 °C, and the quenching temperature is controlled at 25 - 40 °C; the process temperature of the surface layer 1 in the longitudinal stretching process (heated by a heat conduction roller) is controlled at 138 - 140 °C, and the process temperature of the hot melt adhesive layer 3 in the longitudinal stretching process (heated by a heat conduction roller) is controlled at 80 - 90 °C; the longitudinal stretching process consists of a preheating process, a stretching process, and a shaping process (the temperatures of the heating rollers passed by the surface layer 1: preferably set at 140 °C in the preheating process, 138 °C in the stretching process, and 140 °C in the shaping process, and the temperatures of the heating rollers passed by the hot melt adhesive layer 3: preferably set at 90 °C in the preheating process, 80 °C in the stretching process, and 90 °C in the shaping process); the process temperature of the transverse stretching process (heated by air) is controlled at 150 - 180 °C, and the transverse stretching process consists of a preheating process, a stretching process, a shaping process, and a cooling process. Preferably, the preheating process is set at 165 - 170 °C, the stretching process is set at 155 - 160 °C, the shaping process is set at 165 - 175 °C, and the cooling process is set at room temperature. 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.

[0060] The present invention also provides an application of the easily unwindable paper-plastic composite film in paper-plastic laminating. Please refer to Figure 4 , and its application process is specifically as follows: Unwind the film finished product F (i.e., the easily unwindable paper-plastic composite film of the present invention) and the printed paper product P respectively, and make the roughened hot melt adhesive layer 4 of the film finished product F fit with the printed surface of the printed paper product; then pass through the hot pressing process Q to compound the film finished product F and the printed paper product P together to form a laminated finished product N. Among them: In the hot pressing process Q, the processing temperature is 100 - 140 °C, and the processing pressure is 12 - 15 MPa.

[0061] Example 1

[0062] This embodiment provides an easily collectible and unrolled paper-plastic composite film. Please refer to Figure 1 , which has a four-layer structure, including a surface layer 1, a support layer 2, a hot melt adhesive layer 3, and a roughened hot melt adhesive layer 4 arranged in sequence.

[0063] Among them, the raw material formulations of each layer are as follows:

[0064] Surface layer 1: 99.5wt% homopolypropylene (isotacticity is 95%, density is 0.905 g / cm 3 , melting point is 163 °C, melt index is 3 g / 10 min, melt index test conditions: melting temperature is 230 °C, load weight is 2.16 kg) and 0.5wt% silica (average particle size is 5 µm);

[0065] Support layer 2: 99.5wt% homopolypropylene (isotacticity is 95%, density is 0.905 g / cm 3 , melting point is 163 °C, melt index is 3 g / 10 min, melt index test conditions: melting temperature is 230 °C, load weight is 2.16 kg) and 0.5wt% glycerol monostearate;

[0066] Hot melt adhesive layer 3: 100wt% ethylene-vinyl acetate copolymer (vinyl acetate content is 18wt%, density is 0.940 g / cm 3 , melting point is 86 °C, melt index is 15 g / 10 min, melt index test conditions: melting temperature is 190 °C, load weight is 2.16 kg);

[0067] Roughened hot melt adhesive layer 4: 100wt% ethylene-vinyl acetate copolymer (vinyl acetate content is 26wt%, density is 0.949 g / cm 3 , melting point is 73 °C, melt index is 15 g / 10 min, melt index test conditions: melting temperature is 190 °C, load weight is 2.16 kg).

[0068] This embodiment also provides a preparation method for the easily collectible and unrolled paper-plastic composite film, including the following steps:

[0069] (1) Grind the raw materials of the roughened hot melt adhesive layer 4 into a powder form, that is, cool the raw materials of the roughened hot melt adhesive layer 4 (ethylene-vinyl acetate copolymer, average particle size is 4 - 5 mm) with liquid nitrogen for 30 minutes, then use a grinder to grind them into a powder, and obtain ethylene-vinyl acetate copolymer powder with an average particle size of 5 µm through a sieve shaker; place the ethylene-vinyl acetate copolymer powder in a powder tank, and then through the high-voltage tip discharge process, make the surface of the ethylene-vinyl acetate copolymer powder in the powder tank obtain an electrostatic charge of -28 KV for standby;

[0070] (2) Please refer toFigure 2 The raw materials A of each layer of the screened surface layer 1, support layer 2, and hot melt adhesive layer 3 are premixed according to the designed formula respectively, stirred evenly, and sent into each extruder after being weighed and calculated for the input ratio. After the extrusion-casting process G, a cast sheet B is formed. After the longitudinal stretching process H, the cast sheet B is formed into a thick sheet C, and the surface temperature of the hot melt adhesive layer 3 of the thick sheet C reaches 80-90°C. The thick sheet C undergoes a roughening treatment process: on the surface of the hot melt adhesive layer 3 of the thick sheet C, through the high-voltage tip discharge process, the surface of the hot melt adhesive layer 3 of the thick sheet C obtains a static electricity of +28 KV. Then the above-mentioned thick sheet passes through a powder tank, and the distance between the hot melt adhesive layer of the thick sheet and the ethylene-vinyl acetate copolymer powder in the powder tank is 10 mm. Through the mechanism of the attraction of positive and negative charges, the thick sheet adsorbs a layer of ethylene-vinyl acetate copolymer powder by neutralizing the charges. At the same time, because the surface temperature of the hot melt adhesive layer of the thick sheet reaches 80-90°C after the longitudinal stretching process, the hot melt adhesive layer 3 of the thick sheet and the ethylene-vinyl acetate copolymer powder are fused together by the residual temperature of the thick sheet, so that the ethylene-vinyl acetate copolymer powder is difficult to fall off and prevent failure, and a roughened thick sheet D is obtained. Then after the roughened thick sheet D undergoes the transverse stretching process J, the gap between the ethylene-vinyl acetate copolymer powders will increase, and the ethylene-vinyl acetate copolymer powder will be further fused with the hot melt adhesive layer 3 of the thick sheet due to the temperature of the transverse stretching process J. The surface protrusion height drops from 5 µm to 0.5 µm, and finally a roughened hot melt adhesive layer 4 with an uneven surface texture is formed on the surface of the hot melt adhesive layer 3. Then through the traction-thickness measurement-corona-winding process K, a film semi-finished product E is obtained. The film semi-finished product E finally undergoes the aging-slitting process L to obtain a film finished product F, that is, the easy-to-unwind paper-plastic composite film of this embodiment.

[0071] Among them, the main production equipment is a flat film method biaxially oriented polypropylene production line provided by BRUECKNER of Germany, and a powder tank is added between the transverse stretching process and the longitudinal stretching process. The screw of the main extruder (for the support layer 2) is a single-screw extruder with a diameter of 150 mm and a length-diameter ratio of 33:1. The 2 auxiliary extruders (for the surface layer 1 and the hot melt adhesive layer 3 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, 250 °C in other sections, 250 °C in the filter, runner and die head sections, and 30 °C in the quenching (cast film) temperature. In the longitudinal stretching process H, the corresponding temperatures of the preheating zone, stretching zone and shaping zone passed by the surface layer 1 are 140 °C, 138 °C and 140 °C, and the corresponding temperatures of the preheating zone, stretching zone and shaping zone passed by the hot melt adhesive layer 3 are 90 °C, 80 °C and 90 °C, and the longitudinal stretching ratio is 5.0. In the transverse stretching process J, the corresponding temperatures of the preheating zone, stretching zone and shaping zone passed by are 170 °C, 157 °C and 175 °C, the transverse stretching ratio is 8.5, and the production speed is 300 m / min. The corona strength on the surface of the surface layer 1 is 30 W·min / m 2 。

[0072] The total thickness of the easily unwound and rewound paper-plastic composite film in this embodiment is 15.5 μm, the thickness of the surface layer 1 is 1 μm, the thickness of the support layer 2 is 9 μm, the thickness of the hot melt adhesive layer 3 is 5 μm, and the thickness of the roughened hot melt adhesive layer 4 is 0.5 μm.

[0073] This embodiment also provides an application of the easily unwound and rewound paper-plastic composite film in paper-plastic laminating. Please refer to Figure 4 , and its application process is specifically as follows: Unwind the film finished product F and the printed paper product P respectively, and make the roughened hot melt adhesive layer 4 of the film finished product F fit with the printed surface of the printed paper product; then pass through the hot pressing process Q to make the film finished product F and the printed paper product P composite together to form a laminated finished product N. Among them: In the hot pressing process Q, the processing temperature (electromagnetic heating) is 135 °C, the processing pressure (hydraulic pressure) is 14 MPa, and the composite speed is 120 m / min.

[0074] Comparative Example 1

[0075] This comparative example provides a traditional online pre-coated paper-plastic composite film. Please refer to Figure 2 , which includes a surface layer 1, a support layer 2 and a hot melt adhesive layer 3 arranged in sequence, and does not contain a roughened hot melt adhesive layer 4. Among them, the raw material formulas of the surface layer 1, the support layer 2 and the hot melt adhesive layer 3 are the same as those in Example 1.

[0076] This comparative example also provides a method for preparing a traditional online pre-coated paper-plastic composite film, which is basically the same as the method for preparing the easy-to-unwind paper-plastic composite film in Example 1, except that: the method for preparing the traditional online pre-coated paper-plastic composite film in this comparative example does not include step (1) of Example 1, and does not include the roughening treatment process I and the roughened thick sheet D in step (2) of Example 1; that is, for the method for preparing the traditional online pre-coated paper-plastic composite film in this comparative example, after obtaining the thick sheet C, the transverse stretching process J and other subsequent processes are directly carried out.

[0077] The total thickness of the traditional online pre-coated paper-plastic composite film in this comparative example is 15 μm, the thickness of the surface layer 1 is 1 μm, the thickness of the support layer 2 is 9 μm, and the thickness of the hot melt adhesive layer 3 is 5 μm.

[0078] This comparative example also provides an application of a traditional online pre-coated paper-plastic composite film in paper-plastic laminating. Its application process is basically the same as that of the easy-to-unwind paper-plastic composite film in Example 1. Since the traditional online pre-coated paper-plastic composite film in this comparative example does not contain a roughened hot melt adhesive layer, the same operations can be carried out after the hot melt adhesive layer is adhered to the printed paper product.

[0079] Example 2

[0080] This example provides an easy-to-unwind paper-plastic composite film. Please refer to Figure 1 , which includes a surface layer 1, a support layer 2, a hot melt adhesive layer 3, and a roughened hot melt adhesive layer 4 arranged in sequence.

[0081] Among them, the raw material formulas of each layer are as follows:

[0082] Surface layer 1: The same as the surface layer 1 in Example 1;

[0083] Support layer 2: The same as the support layer 2 in Example 1;

[0084] Hot melt adhesive layer 3: 100 wt% ethylene-vinyl acetate copolymer (vinyl acetate content is 15 wt%, density is 0.938 g / cm 3 , melting point is 90 °C, melt index is 15 g / 10 min, melt index test conditions: melting temperature is 190 °C, load weight is 2.16 kg);

[0085] Roughened hot melt adhesive layer 4: The same as the roughened hot melt adhesive layer 4 in Example 1.

[0086] This example also provides a method for preparing an easy-to-unwind paper-plastic composite film, which is the same as Example 1.

[0087] The total thickness and the thickness of each layer of the easy-to-unwind paper-plastic composite film in this example are the same as those in Example 1.

[0088] This embodiment also provides an application of the easily collectible and unrolled paper-plastic composite film in paper-plastic laminating, and its application process is the same as that of Embodiment 1.

[0089] Comparative Example 2

[0090] This comparative example provides a paper-plastic composite film. Please refer to Figure 1 , which includes a surface layer 1, a support layer 2, a hot melt adhesive layer 3, and a roughened hot melt adhesive layer 4 arranged in sequence.

[0091] Among them, the raw material formulas of each layer are as follows:

[0092] Surface layer 1: the same as the surface layer 1 of Embodiment 1;

[0093] Support layer 2: the same as the support layer 2 of Embodiment 1;

[0094] Hot melt adhesive layer 3: 100 wt% ethylene-vinyl acetate copolymer (vinyl acetate content is 12 wt%, density is 0.936 g / cm 3 , melting point is 94 °C, melt index is 15 g / 10 min, melt index test conditions: melting temperature is 190 °C, load weight is 2.16 kg);

[0095] Roughened hot melt adhesive layer 4: the same as the roughened hot melt adhesive layer 4 of Embodiment 1.

[0096] This comparative example also provides a preparation method of the easily collectible and unrolled paper-plastic composite film, which is the same as that of Embodiment 1.

[0097] The total thickness of the paper-plastic composite film of this comparative example and the thickness of each layer are the same as those of Embodiment 1.

[0098] This comparative example also provides an application of the paper-plastic composite film in paper-plastic laminating, and its application process is the same as that of Embodiment 1.

[0099] Embodiment 3

[0100] This embodiment provides an easily collectible and unrolled paper-plastic composite film. Please refer to Figure 1 , which includes a surface layer 1, a support layer 2, a hot melt adhesive layer 3, and a roughened hot melt adhesive layer 4 arranged in sequence.

[0101] Among them, the raw material formulas of each layer are as follows:

[0102] Surface layer 1: the same as the surface layer 1 of Embodiment 1;

[0103] Support layer 2: the same as the support layer 2 of Embodiment 1;

[0104] Hot melt adhesive layer 3: 100 wt% ethylene-vinyl acetate copolymer (vinyl acetate content is 23 wt%, density is 0.945 g / cm 3, with a melting point of 80 °C and a melt index of 15 g / 10 min. Melt index test conditions: melting temperature is 190 °C, load weight is 2.16 kg);

[0105] Roughened hot melt adhesive layer 4: The same as the roughened hot melt adhesive layer 4 in Example 1.

[0106] This example also provides a method for preparing an easily unwound and rewound paper-plastic composite film, which is the same as that in Example 1.

[0107] The total thickness and the thickness of each layer of the easily unwound and rewound paper-plastic composite film in this example are the same as those in Example 1.

[0108] This example also provides an application of the easily unwound and rewound paper-plastic composite film in paper-plastic laminating, and its application process is the same as that in Example 1.

[0109] Comparative Example 3

[0110] This comparative example provides a paper-plastic composite film. Please refer to Figure 1 , which includes a surface layer 1, a support layer 2, a hot melt adhesive layer 3, and a roughened hot melt adhesive layer 4 arranged in sequence.

[0111] Among them, the raw material formula of each layer is as follows:

[0112] Surface layer 1: The same as the surface layer 1 in Example 1;

[0113] Support layer 2: The same as the support layer 2 in Example 1;

[0114] Hot melt adhesive layer 3: 100 wt% ethylene-vinyl acetate copolymer (vinyl acetate content is 28 wt%, density is 0.946 g / cm 3 , with a melting point of 71 °C and a melt index of 15 g / 10 min. Melt index test conditions: melting temperature is 190 °C, load weight is 2.16 kg);

[0115] Roughened hot melt adhesive layer 4: The same as the roughened hot melt adhesive layer 4 in Example 1.

[0116] This comparative example also provides a method for preparing a paper-plastic composite film, which is the same as that in Example 1.

[0117] The total thickness and the thickness of each layer of the paper-plastic composite film in this comparative example are the same as those in Example 1.

[0118] This comparative example also provides an application of the paper-plastic composite film in paper-plastic laminating, and its application process is the same as that in Example 1.

[0119] Example 4

[0120] This example provides an easily unwound and rewound paper-plastic composite film. Please refer to Figure 1, including a surface layer 1, a support layer 2, a hot melt adhesive layer 3, and a roughened hot melt adhesive layer 4 arranged in sequence.

[0121] Among them, the raw material formulas of each layer are as follows:

[0122] Surface layer 1: The same as the surface layer 1 in Example 1;

[0123] Support layer 2: The same as the support layer 2 in Example 1;

[0124] Hot melt adhesive layer 3: The same as the hot melt adhesive layer 3 in Example 1;

[0125] Roughened hot melt adhesive layer 4: 100wt% ethylene-vinyl acetate copolymer (vinyl acetate content is 25wt%, density is 0.947g / cm 3 , melting point is 75°C, melt index is 15g / 10min, melt index test conditions: melting temperature is 190°C, load weight is 2.16kg).

[0126] This example also provides a preparation method of an easily unwound and rewound paper-plastic composite film, which is the same as that in Example 1.

[0127] The total thickness and the thickness of each layer of the easily unwound and rewound paper-plastic composite film in this example are the same as those in Example 1.

[0128] This example also provides an application of the easily unwound and rewound paper-plastic composite film in paper-plastic laminating, and its application process is the same as that in Example 1.

[0129] Comparative Example 4

[0130] This comparative example provides a paper-plastic composite film. Please refer to Figure 1 , including a surface layer 1, a support layer 2, a hot melt adhesive layer 3, and a roughened hot melt adhesive layer 4 arranged in sequence.

[0131] Among them, the raw material formulas of each layer are as follows:

[0132] Surface layer 1: The same as the surface layer 1 in Example 1;

[0133] Support layer 2: The same as the support layer 2 in Example 1;

[0134] Hot melt adhesive layer 3: The same as the hot melt adhesive layer 3 in Example 1;

[0135] Roughened hot melt adhesive layer 4: 100wt% ethylene-vinyl acetate copolymer (vinyl acetate content is 23wt%, density is 0.945g / cm 3 , melting point is 80°C, melt index is 15g / 10min, melt index test conditions: melting temperature is 190°C, load weight is 2.16kg).

[0136] This comparative example also provides a method for preparing a paper-plastic composite film, which is the same as that in Example 1.

[0137] The total thickness of the paper-plastic composite film in this comparative example and the thickness of each layer are the same as those in Example 1.

[0138] This comparative example also provides an application of a paper-plastic composite film in paper-plastic laminating, and its application process is the same as that in Example 1.

[0139] Example 5

[0140] This example provides an easily unwindable and rewound paper-plastic composite film. Please refer to Figure 1 , which includes a surface layer 1, a support layer 2, a hot melt adhesive layer 3, and a roughened hot melt adhesive layer 4 arranged in sequence.

[0141] Among them, the raw material formulations of each layer are as follows:

[0142] Surface layer 1: The same as the surface layer 1 in Example 1;

[0143] Support layer 2: The same as the support layer 2 in Example 1;

[0144] Hot melt adhesive layer 3: The same as the hot melt adhesive layer 3 in Example 1;

[0145] Roughened hot melt adhesive layer 4: 100 wt% ethylene-vinyl acetate copolymer (vinyl acetate content is 28 wt%, density is 0.946 g / cm 3 , melting point is 71 °C, melt index is 15 g / 10 min, melt index test conditions: melting temperature is 190 °C, load weight is 2.16 kg).

[0146] This example also provides a method for preparing an easily unwindable and rewound paper-plastic composite film, which is the same as that in Example 1.

[0147] The total thickness of the easily unwindable and rewound paper-plastic composite film in this example and the thickness of each layer are the same as those in Example 1.

[0148] This example also provides an application of an easily unwindable and rewound paper-plastic composite film in paper-plastic laminating, and its application process is the same as that in Example 1.

[0149] Comparative Example 5

[0150] This comparative example provides a paper-plastic composite film. Please refer to Figure 1 , which includes a surface layer 1, a support layer 2, a hot melt adhesive layer 3, and a roughened hot melt adhesive layer 4 arranged in sequence.

[0151] Among them, the raw material formulations of each layer are as follows:

[0152] Surface layer 1: The same as the surface layer 1 in Example 1;

[0153] Support layer 2: The same as the support layer 2 in Example 1;

[0154] Hot melt adhesive layer 3: The same as the hot melt adhesive layer 3 in Example 1;

[0155] Roughened hot melt adhesive layer 4: 100 wt% ethylene-vinyl acetate copolymer (vinyl acetate content is 33 wt%, density is 0.955 g / cm 3 , melting point is 62 °C, melt index is 15 g / 10 min, melt index test conditions: melting temperature is 190 °C, load weight is 2.16 kg).

[0156] This comparative example also provides a method for preparing a paper-plastic composite film, which is the same as that in Example 1.

[0157] The total thickness and the thickness of each layer of the paper-plastic composite film in this comparative example are the same as those in Example 1.

[0158] This comparative example also provides an application of the paper-plastic composite film in paper-plastic laminating, and its application process is the same as that in Example 1.

[0159] Example 6

[0160] This example provides an easily unwindable paper-plastic composite film. Please refer to Figure 1 , which includes a surface layer 1, a support layer 2, a hot melt adhesive layer 3, and a roughened hot melt adhesive layer 4 arranged in sequence.

[0161] Among them, the raw material formula of each layer is as follows:

[0162] Surface layer 1: 55 wt% propylene-ethylene copolymer (ethylene content is 4.2 wt%, melting point is 140 °C, melt index is 8 g / min, melt index test conditions: melting temperature is 230 °C, load weight is 2.16 kg) and 45 wt% high-density polyethylene (melting point is 134 °C, melt index is 9 g / min, melt index test conditions: melting temperature is 190 °C, load weight is 21.6 kg);

[0163] Support layer 2: The same as the support layer 2 in Example 1;

[0164] Hot melt adhesive layer 3: The same as the hot melt adhesive layer 3 in Example 1;

[0165] Roughened hot melt adhesive layer 4: The same as the roughened hot melt adhesive layer 4 in Example 1.

[0166] This example also provides a method for preparing an easily unwindable paper-plastic composite film, which is the same as that in Example 1.

[0167] The total thickness and the thickness of each layer of the easily unwindable paper-plastic composite film in this example are the same as those in Example 1.

[0168] This embodiment also provides an application of the easy-to-collect and unwind paper-plastic composite film in paper-plastic laminating, and its application process is the same as that of Embodiment 1.

[0169] Performance evaluation

[0170] The following performance evaluations were respectively carried out on the paper-plastic composite films (film products) or laminated products of Examples 1-6 and Comparative Examples 1-5:

[0171] Roughness: According to the national standard GB / T 14234-1993, the surface roughness of the roughened hot-melt adhesive layer 4 or the hot-melt adhesive layer 3 (i.e., the other surface of the paper-plastic composite film opposite to the surface of the surface layer 1) of the paper-plastic composite film was measured. The measuring instrument was a surface roughness meter (manufactured by Mitutoyo Corporation, Japan, model: SJ-210).

[0172] Normal temperature bonding strength: Two paper-plastic composite films were stacked together and clamped with a silicone rubber sheet to form a silicone rubber sheet / / film / / film / / silicone rubber sheet structure. The contact method between the two films was as follows: The roughened hot-melt adhesive layer 4 (or the hot-melt adhesive layer 3) of one film was in contact with the surface layer 1 of the other film. The surface tension of the silicone rubber sheet was only 21-22 mN / m, and the film was too thin. Using the silicone rubber sheet as a gasket could make the films in full contact, which was convenient for taking out the adhered films after hot pressing. A 10 kg weight was used to press the above four-layer structure, and then it was placed in an oven at 60 °C for 30 min to simulate the summer container transportation conditions. Finally, the bonding strength between the two films was measured by a film bonding strength tester (manufactured by Dynisco, USA, model: D9047).

[0173] Light transmittance: According to the national standard GB / T 2410-2008, the light transmittance of the paper-plastic composite film was measured. The measuring instrument was a direct-reading haze meter (manufactured by Diffusion, UK, model: EEL 57D).

[0174] Glossiness of the bonding surface: According to the national standard GB / T 8807-1988, the glossiness of the bonding surface of the paper-plastic composite film was measured (the bonding surface of Comparative Example 1 was the surface of the hot-melt adhesive layer; the bonding surfaces of Examples 1-6 and Comparative Examples 2-5 were the surfaces composed of the hot-melt adhesive layer and the roughened hot-melt adhesive layer). The measuring instrument was a 45° glossiness meter (manufactured by BYK, Germany, model: 4454).

[0175] Adhesion strength: The paper-plastic composite film and the printed paper product were bonded by an adhesion strength tester under the conditions of 135 °C, 1 second, and 0.18 MPa, and the adhesion strength was measured. The measuring instrument was an adhesion strength tester (manufactured by Bruger Feinmechanlk GmbH, Germany, model: HSG-C).

[0176] Coated film appearance: Visually inspect whether there are obvious snowflake spots or other appearance abnormalities (such as scalding, poor stretching) on the appearance of the paper-plastic coated finished product.

[0177] Unwinding noise: Test the noise during the unwinding of the paper-plastic composite film according to the national standard GB 12348-2008. The test instrument is a digital noise meter (produced by Biaozhi, model GM-1356).

[0178] For the formulation compositions of each layer and the test results of relevant properties of the paper-plastic composite films of Examples 1-6 and Comparative Examples 1-5, please refer to Tables 1-6 respectively.

[0179] Table 1 Formulation compositions of each layer and test results of properties of the paper-plastic composite films of Example 1 and Comparative Example 1

[0180]

[0181] Table 2 Formulation compositions of each layer and test results of properties of the paper-plastic composite films of Example 2 and Comparative Example 2

[0182]

[0183] Table 3 Formulation compositions of each layer and test results of properties of the paper-plastic composite films of Example 3 and Comparative Example 3

[0184]

[0185] Table 4 Formulation compositions of each layer and test results of properties of the paper-plastic composite films of Example 4 and Comparative Example 4

[0186]

[0187] Table 5 Formulation compositions of each layer and test results of properties of the paper-plastic composite films of Example 5 and Comparative Example 5

[0188]

[0189] Table 6 Formulation compositions of each layer and test results of properties of the paper-plastic composite film of Example 6

[0190]

[0191] In the preparation method of the easily unwindable paper-plastic composite film of Examples 1-6 of the present invention, it is prepared by designing and adopting a specific preparation method for the hot melt adhesive layer and the roughened hot melt adhesive layer, so that the easily unwindable paper-plastic composite film of the present invention is not prone to scalding or poor stretching during the longitudinal stretching process in the production process, does not have difficulties in unwinding and rewinding, and is not prone to visible snowflake spots on the paper-plastic coated finished product due to insufficient compaction when used for paper-plastic coating.

[0192] The paper-plastic composite film of Comparative Example 1 is a traditional on-line pre-coated paper-plastic composite film, which does not include the roughened hot-melt adhesive layer of the present invention. The traditional on-line pre-coated paper-plastic composite film of Comparative Example 1 has a low roughness, a high normal-temperature bonding strength, is not easy to unwind and rewind, and has a large unwinding noise. Moreover, due to the smooth hot-melt adhesive layer of the paper-plastic composite film of Comparative Example 1, the bonding surface has a high gloss. The paper-plastic composite film of Comparative Example 1 used for paper-plastic laminating shows a slight snowflake appearance on the surface of the paper-plastic laminated product, and the bonding strength between the traditional on-line pre-coated paper-plastic composite film of Comparative Example 1 and the printed paper product is relatively low.

[0193] For the paper-plastic composite film of Comparative Example 2, the melting point of the ethylene-vinyl acetate copolymer used in the hot-melt adhesive layer is too high. The paper-plastic laminated product formed by paper-plastic laminating shows a slight snowflake appearance on the surface, and the bonding strength between the paper-plastic composite film of Comparative Example 2 and the printed paper product is low.

[0194] For the paper-plastic composite film of Comparative Example 3, the melting point of the ethylene-vinyl acetate copolymer used in the hot-melt adhesive layer is too low, resulting in slight scalding and poor longitudinal stretching on the surface of the hot-melt adhesive layer during the longitudinal stretching process in the preparation process. Furthermore, the paper-plastic laminated product formed by paper-plastic laminating shows a slight scalding and poor longitudinal stretching appearance. And because the melting point of the ethylene-vinyl acetate copolymer used in the hot-melt adhesive layer is too low, it has a certain impact on the normal-temperature bonding strength and unwinding noise of the paper-plastic composite film of Comparative Example 3.

[0195] For the paper-plastic composite film of Comparative Example 4, the melting point of the ethylene-vinyl acetate copolymer used in the roughened hot-melt adhesive layer is too high. Although it can reduce the normal-temperature bonding strength of the paper-plastic composite film, the paper-plastic laminated product formed by paper-plastic laminating shows a slight snowflake appearance on the surface, and the bonding strength between the paper-plastic composite film of Comparative Example 4 and the printed paper product is relatively low.

[0196] For the paper-plastic composite film of Comparative Example 5, the melting point of the ethylene-vinyl acetate copolymer used in the roughened hot-melt adhesive layer is too low. The paper-plastic composite film of Comparative Example 5 has a high normal-temperature bonding strength, is not easy to unwind and rewind, and has a large unwinding noise.

[0197] The above-described embodiments only represent several implementation manners of the present invention. The description 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 deformations.

Claims

1. A preparation method of an easily rewound paper-plastic composite film, characterized in that: The easily rewound paper-plastic composite film comprises a surface layer, a support layer, a hot melt adhesive layer and a roughened hot melt adhesive layer arranged in sequence; the hot melt adhesive layer is composed of a first hot melt adhesive copolymer, and the melting point of the first hot melt adhesive copolymer is 80-90 °C; the roughened hot melt adhesive layer is composed of a second hot melt adhesive copolymer, and the melting point of the second hot melt adhesive copolymer is 70-75 °C; The preparation method of the easily rewound paper-plastic composite film comprises the following steps: Grind the raw material of the roughened hot melt adhesive layer into a powder form to obtain the roughened hot melt adhesive layer powder. Through the high-voltage tip discharge process, the surface of the roughened hot melt adhesive layer powder is obtained with static electricity of - / + (25-30) KV and reserved; Respectively feed the raw materials of the surface layer, the support layer and the hot melt adhesive layer into the extruders corresponding to each layer, and form a cast sheet through the extrusion-casting process; The cast sheet forms a thick sheet through the longitudinal stretching process; The thick sheet undergoes a roughening treatment process: making the roughened hot melt adhesive layer powder adsorb and weld on the surface of the hot melt adhesive layer of the thick sheet to form a roughened thick sheet; wherein, the roughening treatment process comprises the following steps: on the surface of the hot melt adhesive layer of the thick sheet through the high-voltage tip discharge process, the surface of the hot melt adhesive layer of the thick sheet is obtained with static electricity of + / -(25-30) KV; utilize the mechanism of attraction between positive and negative charges to make a layer of roughened hot melt adhesive layer powder adsorb on the surface of the hot melt adhesive layer of the thick sheet, and utilize the residual temperature of the thick sheet after the longitudinal stretching process to make the roughened hot melt adhesive layer powder and the hot melt adhesive layer of the thick sheet weld together to form the roughened thick sheet; The roughened thick sheet undergoes a transverse stretching process, a traction-thickness measurement-corona-winding process to obtain a film semi-finished product; The film semi-finished product undergoes an aging-slitting process to obtain a film finished product, that is, the easily rewound paper-plastic composite film.

2. The preparation method of the easily collectible and unrolled paper-plastic composite film according to claim 1, wherein: In the transverse stretching process, the transverse stretching ratio is 7-10.

3. The preparation method of the easily collapsible and unrolled paper-plastic composite film according to claim 1, characterized in that: After the longitudinal stretching process, the temperature on the surface of the hot melt adhesive layer of the thick sheet is 80-90 °C.

4. The preparation method of the easy-to-collect and unwind paper-plastic composite film according to claim 1, wherein: The preparation method of the roughened hot melt adhesive layer powder is: cool the raw material of the roughened hot melt adhesive layer with liquid nitrogen and then place it in a grinding machine for grinding, and then screen it through a sieve shaker into a powder with an average particle size of 4-6 µm to obtain the roughened hot melt adhesive layer powder.

5. According to the preparation method of the easily rewound paper-plastic composite film as claimed in claim 1, characterized in that: After obtaining the roughened hot melt adhesive layer powder, place the roughened hot melt adhesive layer powder in a powder tank, and then perform the high-voltage tip discharge process on the roughened hot melt adhesive layer powder in the powder tank; In the roughening treatment process, make the thick sheet pass through the powder tank, wherein the distance between the hot melt adhesive layer of the thick sheet and the roughened hot melt adhesive layer powder in the powder tank is 10-20 mm.

6. According to the preparation method of the easily rewound paper-plastic composite film as claimed in claim 1, characterized in that: The first hot-melt adhesive copolymer is at least one of ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-α-olefin copolymer, maleic anhydride grafted ethylene-α-olefin copolymer, ethylene-vinyl chloride copolymer, propylene-α-olefin copolymer, and ethylene-vinyl acetate-vinyl alcohol terpolymer with a melting point of 80-90 °C; The second hot-melt adhesive copolymer is at least one of ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-α-olefin copolymer, maleic anhydride grafted ethylene-α-olefin copolymer, ethylene-vinyl chloride copolymer, propylene-α-olefin copolymer, and ethylene-vinyl acetate-vinyl alcohol terpolymer with a melting point of 70-75 °C.

7. The method for preparing the easily unwinding and rewinding paper-plastic composite film according to claim 1, wherein: The surface layer comprises homopolypropylene and an anti-blocking agent; or the surface layer comprises high-density polyethylene and a propylene-ethylene copolymer; The support layer comprises homopolypropylene and an antistatic agent.

8. A paper-plastic composite film that is easy to collect and unwind, characterized in that: Prepared by the method for preparing the easily unwinding and rewinding paper-plastic composite film according to any one of claims 1-7.

9. An application of the easily unwinding and rewinding paper-plastic composite film according to claim 8 in paper-plastic laminating.

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