Anti-extrusion bopp white label film and preparation method thereof

Abstract

The present application relates to a kind of anti-extraction BOPP white label film and its preparation method, belong to label film technical field.The anti-extraction BOPP white label film includes the printable surface layer, the upper surface layer, the core layer, the lower surface layer and the tackiness coating surface layer sequentially arranged;Printable surface layer includes random copolymer polypropylene and 3-7wt% ethylene vinyl alcohol grafting propylene-benzonorbornene copolymer;Upper surface layer, lower surface layer all include homopolymer polypropylene, 1-3wt% ethylene vinyl alcohol grafting homopolymer polypropylene and 1-5wt% titanium dioxide white masterbatch;Core layer includes homopolymer polypropylene and 28-38wt% calcium carbonate masterbatch;Tackiness coating surface layer includes homopolymer polypropylene and 5-10wt% saponified ethylene-vinyl acetate copolymer.The anti-extraction BOPP white label film, without adding antistatic agent, can make film have certain antistatic property, the surface tension of printable surface layer is high and good durability, and the tackiness coating surface layer has good glue performance.

Description

Technical Field

[0001] This invention relates to the field of label film technology, and in particular to an anti-precipitation BOPP white label film and its preparation method. Background Technology

[0002] Among numerous BOPP film products, white BOPP label film has garnered significant attention and become a market favorite due to its unique visual effect and wide range of applications. While retaining the excellent performance of BOPP film, white BOPP label film achieves an opaque effect by adding titanium dioxide white masterbatch, making it highly sought after. The emergence of white BOPP label film not only enriches the variety of packaging materials but also enhances the aesthetics and practicality of packaging. The layered structure of white BOPP label film is generally a five-layer structure. The two outermost layers are typically composed of homopolymer polypropylene and an anti-blocking agent, the two sub-layers are typically composed of homopolymer polypropylene and titanium dioxide, and the core layer is typically composed of homopolymer polypropylene and calcium carbonate.

[0003] Titanium dioxide and calcium carbonate, as inorganic materials, are added in the form of masterbatches (white titanium dioxide masterbatch and calcium carbonate masterbatch). During the preparation of calcium carbonate masterbatch or white titanium dioxide masterbatch, calcium carbonate or titanium dioxide is typically coated with a low-molecular-weight dispersant (such as stearic acid) to improve their dispersion in homopolymer polypropylene. When the aforementioned calcium carbonate masterbatch or white titanium dioxide masterbatch is added to BOPP white label film, over time, the low-molecular-weight dispersant in these masterbatches gradually migrates to the film surface and precipitates, affecting the surface tension of the film surface layer (e.g., the printable surface layer) and the adhesion between the film's other surface layer (e.g., the tackifying coating layer) and the adhesive.

[0004] In addition, the gravure printing and oil coating processes in the post-processing of white BOPP label film usually contain organic solvents, which are extremely sensitive to static electricity. To ensure the universality of post-processing, traditional small molecule antistatic agents are generally not added to white BOPP label film (to exert antistatic effects by migrating to the film surface through traditional small molecule antistatic agents). This results in the static electricity generated during processing not being able to be discharged in time, thus affecting the processing quality of the product. Summary of the Invention

[0005] Based on this, the purpose of this invention is to provide an anti-exudation BOPP white label film and its preparation method, which has the characteristics of reducing exudation and low exudation, and is not adversely affected by the migration of low molecular weight dispersants on the printable surface. The printable surface has high surface tension and good durability, thus ensuring the printability of inks. At the same time, the film has certain antistatic properties without the need to add additional antistatic agents, and also takes into account the adhesion between the tackifying coating surface and the adhesive, thereby helping to ensure a firm bond between the film and the substrate during subsequent processing and application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides an anti-exudation BOPP white label film, comprising, in sequence, a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive-coated surface layer; the printable surface layer comprises random copolymer polypropylene and 3-7 wt% ethylene alcohol-grafted propylene-benzonorbornene copolymer, wherein the grafting rate of ethylene alcohol in the ethylene alcohol-grafted propylene-benzonorbornene copolymer is 5-9%; the top surface layer and the bottom surface layer each comprise homopolymer polypropylene, 1-3 wt% ethylene alcohol-grafted homopolymer polypropylene, and 1-5 wt% titanium dioxide white masterbatch; the grafting rate of ethylene alcohol in the ethylene alcohol-grafted homopolymer polypropylene is 2-6%; the core layer comprises homopolymer polypropylene and 28-38 wt% calcium carbonate masterbatch; the adhesive-coated surface layer comprises homopolymer polypropylene and 5-10 wt% saponified ethylene-vinyl acetate copolymer; the degree of saponification of the saponified ethylene-vinyl acetate copolymer is 15-25%.

[0008] The anti-exudation BOPP white label film of the present invention is designed with a printable surface layer, on which ink can be printed in subsequent applications. The present invention adds 3-7 wt% of ethylene alcohol-grafted propylene-benzonorbornene copolymer to the printable surface layer: (1) In a first aspect, the ethylene alcohol in the ethylene alcohol-grafted propylene-benzonorbornene copolymer helps the printable surface layer to maintain a high surface tension without corona treatment, and the ethylene alcohol in the ethylene alcohol-grafted propylene-benzonorbornene copolymer can react with "low molecular weight dispersants (e.g., stearic acid) that migrate from the calcium carbonate masterbatch of the core layer or from the titanium dioxide white masterbatch of the previous and next surface layers (e.g.) (e.g., stearic acid) forms hydrogen bonds, reducing the migration and precipitation of low molecular weight dispersants to the outside of the printable surface, thus reducing the adverse effects of low molecular weight dispersants migrating to the surface of the printable surface on the printing performance, which is beneficial to the stability of the printable surface's printing performance during storage; (2) Secondly, the hydroxyl groups in the ethylene alcohol in the ethylene alcohol-propene-benzonorbornene copolymer have water absorption properties on the outside of the printable surface. This water absorption property can adsorb moisture in the air, which is beneficial to the formation of a conductive network on the outside of the printable surface, playing a role similar to a nonionic antistatic agent, reducing the anti-precipitation BOP. The static electricity generation and accelerated dissipation of the P white label film can give the anti-deposition BOPP white label film a certain antistatic property even without the addition of an antistatic agent; (3) In addition, the benzonorbornene in the vinyl alcohol grafted propylene-benzonorbornene copolymer has a six-membered ring structure. Compared with the structure of norbornene, the structure of benzonorbornene has a greater ring strain. After corona treatment, the six-membered ring structure of benzonorbornene reduces the orientation of polar groups and the movement and migration of macromolecular chains on the surface of the printable surface, and slows down the surface tension of the printable surface. The force decay rate, combined with the effect of hydroxyl groups, helps to maintain a high surface tension of the printable surface layer; (4) Furthermore, the ethylene alcohol grafted propylene-benzonorbornene copolymer can also play a certain barrier role (by means of the hydrogen bond network formed by it and the six-membered ring structure of benzonorbornene), which can reduce the penetration of external substances such as water vapor in the environment from the outside of the printable surface layer into the inside of the film, which is beneficial to the adhesion of the anti-exudation BOPP white label film to the adhesive surface layer and the glue in subsequent applications, thereby facilitating the firm adhesion of the anti-exudation BOPP white label film to the substrate.

[0009] This invention limits the amount of the ethylene alcohol-grafted propylene-benzonorbornene copolymer added to the printable surface layer to 3-7 wt%. If the amount of the ethylene alcohol-grafted propylene-benzonorbornene copolymer added to the printable surface layer is too low, it cannot sufficiently inhibit the migration of low molecular weight dispersants to the surface of the printable surface layer, nor can it effectively play an antistatic role. If the amount of the ethylene alcohol-grafted propylene-benzonorbornene copolymer added to the printable surface layer is too high, due to the difference in polarity, the ethylene alcohol-grafted propylene-benzonorbornene copolymer cannot be effectively co-extruded, resulting in thick, incompatible sheets. This leads to film breakage during stretching and causes an excessively large polarity difference between the printable surface layer and the previous surface layer, which is not conducive to ensuring interlayer bonding and may cause delamination during stretching.

[0010] This invention limits the grafting rate of ethylene alcohol in the ethylene alcohol-grafted propylene-benzonorbornene copolymer to 5-9%. If the grafting rate of ethylene alcohol in the ethylene alcohol-grafted propylene-benzonorbornene copolymer is too low, it cannot sufficiently inhibit the migration of low molecular weight dispersants to the printable surface, nor can it effectively play an antistatic role. If the grafting rate of ethylene alcohol in the ethylene alcohol-grafted propylene-benzonorbornene copolymer is too high, the high content of polar groups (hydroxyl groups) and the excessive hydrogen bonding forces between molecular chains will cause the printable surface to be too brittle, which is not conducive to biaxial stretching and is prone to delamination during stretching. Furthermore, if the grafting rate of ethylene alcohol in the ethylene alcohol-grafted propylene-benzonorbornene copolymer is too high, it will easily lead to excessive surface tension of the printable surface, which is not conducive to the smoothness of film unwinding (unwinding between the printable surface and the tackifying coating surface in the roll film).

[0011] The anti-exudation BOPP white label film of the present invention is made by adding 1-3 wt% ethylene alcohol-grafted homopolymer polypropylene to the upper and lower surface layers: (1) On the one hand, the upper and lower surface layers have a certain polarity, thereby ensuring the interlayer bonding force between the upper surface layer and the printable surface layer and the interlayer bonding force between the lower surface layer and the tackifying coating surface layer, and preventing delamination; (2) On the other hand, the ethylene alcohol in the ethylene alcohol-grafted homopolymer polypropylene can form hydrogen bond interactions with the migrating low molecular weight dispersant, reducing the migration of low molecular weight dispersant to the printable surface layer or the tackifying coating surface layer, and further ensuring the printability of the printable surface layer and the coating performance of the tackifying coating surface layer of the anti-exudation BOPP white label film in subsequent applications.

[0012] This invention limits the content of the ethylene alcohol-grafted homopolymer polypropylene in the upper and lower surface layers to 1-3 wt%, and limits the grafting rate of ethylene alcohol in the ethylene alcohol-grafted homopolymer polypropylene to 2-6%. If the content of the ethylene alcohol-grafted homopolymer polypropylene in the upper and lower surface layers is too low, and / or if the grafting rate of ethylene alcohol in the ethylene alcohol-grafted homopolymer polypropylene is too low, delamination may easily occur between the upper surface layer and the printable surface layer, and between the lower surface layer and the tackifying coating surface layer, due to polarity differences during film preparation. If the content of the ethylene alcohol-grafted homopolymer polypropylene in the upper and lower surface layers is too high, and / or if the grafting rate of ethylene alcohol in the ethylene alcohol-grafted homopolymer polypropylene is too high, delamination may easily occur between the upper surface layer and the core layer, and between the lower surface layer and the core layer, due to polarity differences during film preparation.

[0013] The anti-exudation BOPP white label film of this invention features a tackifying coating surface layer. In subsequent applications, an adhesive (commonly acrylic or hot melt adhesives) is applied to this tackifying coating surface layer to facilitate bonding and fixation with the substrate. This invention incorporates 5-10 wt% saponified ethylene-vinyl acetate copolymer into the tackifying coating surface layer. The degree of saponification of the saponified ethylene-vinyl acetate copolymer is designed to be 15-25%. This saponified ethylene-vinyl acetate copolymer is obtained by alcoholysis of ethylene-vinyl acetate copolymer, in which some ester groups are converted to hydroxyl groups through alcoholysis. This facilitates the formation of hydrogen bonds with migrating low-molecular-weight dispersants, reducing the migration and exudation of low-molecular-weight dispersants to the tackifying coating surface layer and minimizing their adverse effects on coating performance. Simultaneously, the saponified ethylene-vinyl acetate copolymer retains some ester groups, which enhances the adhesion between the tackifying coating surface layer and the adhesive. In addition, the hydroxyl groups in the saponified ethylene-vinyl acetate copolymer can adsorb moisture in the air, which is beneficial to the formation of a conductive network on the outside of the adhesive coating layer. It plays a role similar to a non-ionic antistatic agent, and works in conjunction with the printable surface layer to further reduce the static electricity generation of the anti-deposition BOPP white label film and accelerate the dissipation of static electricity.

[0014] This invention limits the content of the saponified ethylene-vinyl acetate copolymer in the tackifying coating layer to 5-10 wt%, and limits the saponification degree of the saponified ethylene-vinyl acetate copolymer to 15-25%. If the content of the saponified ethylene-vinyl acetate copolymer in the tackifying coating layer is too low, and / or if the saponification degree of the saponified ethylene-vinyl acetate copolymer is too low, the tackifying coating layer cannot effectively play an antistatic role, and the coating performance of the tackifying coating layer is poor, with low adhesion to the adhesive. If the content of the saponified ethylene-vinyl acetate copolymer in the tackifying coating layer is too high, and / or if the saponification degree of the saponified ethylene-vinyl acetate copolymer is too high, the film preparation process may result in roller sticking, and the prepared film has poor winding and unwinding smoothness.

[0015] Furthermore, the preparation method of the ethylene alcohol-grafted propylene-benzonorbornene copolymer is as follows: using propylene-benzonorbornene copolymer as raw material, BPO as initiator, and ethylene-vinyl acetate as grafting monomer, a solid-phase suspension grafting reaction is carried out to obtain ethylene-vinyl acetate-grafted propylene-benzonorbornene copolymer, and then the ethylene-vinyl acetate-grafted propylene-benzonorbornene copolymer is subjected to an alcoholysis reaction to obtain the ethylene alcohol-grafted propylene-benzonorbornene copolymer.

[0016] Furthermore, the molar content of benzonorbornene in the propylene-benzonorbornene copolymer is 18-22 mol%. Through the above limitations, during the film manufacturing process, on the one hand, it helps the printable surface layer maintain a high surface tension after corona treatment; on the other hand, it gives the printable surface layer higher stiffness, reducing the adhesion between the inner and outer layers of the film (i.e., between the printable surface layer and the tackifying coating layer), which helps ensure smooth winding and unwinding during film production and application.

[0017] Furthermore, the ethylene alcohol-grafted propylene-benzonorbornene copolymer has a melt index of 1-2 g / 10 min at 230°C and a load of 2.16 kg. Adding the ethylene alcohol-grafted propylene-benzonorbornene copolymer with the above melt index to the printable surface layer improves its melt compatibility with other components in the printable surface layer, resulting in a suitable thick sheet for biaxial stretching and ensuring the smoothness of the biaxial stretching process.

[0018] Furthermore, the random copolymer polypropylene has a melt index of 5-10 g / 10 min at 230°C and a load of 2.16 kg, and a melting point of 120-150°C. Preferably, the random copolymer polypropylene is selected from one or two of ethylene-propylene copolymer polypropylene and ethylene-propylene-butene copolymer polypropylene.

[0019] Furthermore, the titanium dioxide white masterbatch comprises homopolymer polypropylene and 50-70 wt% titanium dioxide coated with a low-molecular-weight dispersant. Adding the titanium dioxide white masterbatch to the upper and lower surface layers provides excellent light-blocking properties for the anti-exudation BOPP white label film. Preferably, the particle size D50 of the titanium dioxide in the titanium dioxide white masterbatch is 400-800 nm. By limiting the particle size of the titanium dioxide in the titanium dioxide white masterbatch, the light-blocking effect of the upper and lower surface layers is more uniform.

[0020] Furthermore, the calcium carbonate masterbatch comprises homopolymer polypropylene and 65-75 wt% calcium carbonate coated with a low-molecular-weight dispersant. Adding calcium carbonate masterbatch to the core layer provides a good pearlescent effect for the anti-precipitation BOPP white label film. Preferably, the particle size D50 of the calcium carbonate in the calcium carbonate masterbatch is 1.0-1.5 μm. Limiting the particle size of the calcium carbonate in the masterbatch facilitates effective dispersion of the calcium carbonate masterbatch in the core layer, achieving a relatively uniform "cavitation" effect and ensuring the pearlescent effect of the film.

[0021] Furthermore, the saponified ethylene-vinyl acetate copolymer of the present invention is preferably obtained by alcoholysis of an unsaponified ethylene-vinyl acetate copolymer. The unsaponified ethylene-vinyl acetate copolymer contains 15-18 wt% vinyl acetate monomer, and the melt index of the unsaponified ethylene-vinyl acetate copolymer at 190°C and a load of 2.16 kg is 10-20 g / 10 min. The saponified ethylene-vinyl acetate copolymer prepared by the above method of the present invention is beneficial to its melt compatibility with the homopolymer polypropylene in the tackifying coating layer, resulting in suitable thick sheets for biaxial stretching and ensuring the smoothness of the biaxial stretching process.

[0022] Furthermore, the tackifying coating surface layer also includes 0.1-0.2 wt% (i.e., 1000-2000 ppm) of an anti-blocking agent. By adding the anti-blocking agent to the tackifying coating surface layer, the benzo[a]bornene cyclic structure with a hardening convexity in the printable surface layer's vinyl alcohol-grafted propylene-benzo[a]bornene copolymer jointly ensures the smooth winding and unwinding of the anti-exudation BOPP white label film. Preferably, the anti-blocking agent is silica.

[0023] Furthermore, the homopolymer polypropylene in the upper surface layer, the lower surface layer, the core layer, and the tackifying coating layer all has a melt index of 2.8-3.8 g / 10 min at 230°C and a load of 2.16 kg, and the melting point of the homopolymer polypropylene in the upper surface layer, the lower surface layer, the core layer, and the tackifying coating layer is 160-180°C. Selecting homopolymer polypropylene with appropriate melt index and melting point is beneficial to the overall heat resistance and mechanical properties of the film. An excessively low melt index will reduce the material's ductility, making effective biaxial stretching difficult and increasing the risk of problems such as film breakage and poor stretching.

[0024] Furthermore, the total thickness of the anti-exudation BOPP white label film is 30-70 μm; wherein, the thickness of the printable surface layer is 1-2 μm, the thickness of the upper surface layer and the lower surface layer are 4-6 μm respectively, and the thickness of the tackifying coating surface layer is 1-1.5 μm.

[0025] The present invention also provides a method for preparing any of the above-mentioned anti-exudation BOPP white label films, comprising the following steps: adding each layer of raw material into the extruder of the corresponding layer to form a homogenized melt; the melt is filtered and then co-extruded through a die in multiple layers; then casting and cooling into a thick sheet according to the flat film method; the thick sheet is made into a biaxially stretched film by a biaxial stretching method of first longitudinal and then transverse or longitudinal and transverse simultaneously; the film is cooled and then subjected to corona treatment, and then wound into a master roll; the master roll is subjected to aging treatment and then slit into finished products.

[0026] Furthermore, in the above process flow: the melt extrusion temperature of the printable surface layer and the tackifying coating surface layer is 200-260℃; the melt extrusion temperature of the core layer is 230-260℃; the melt extrusion temperature of the upper surface layer and the lower surface layer is 230-260℃; the temperature of the quench water and the quench roller is 20-40℃; the temperature of the longitudinal stretching zone is 100-130℃; the temperature of the transverse stretching zone is 140-180℃; the longitudinal stretching ratio is 4.5-5.5 times; and the transverse stretching ratio is 8-10 times. Detailed Implementation

[0027] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0028] In the following embodiments or comparative examples:

[0029] (1) In the printable surface layer:

[0030] Random copolymer polypropylene: Specifically, (random) ethylene-propylene copolymer polypropylene, with a melt index of 6 g / 10 min and a melting point of 140℃ at 230℃ and a load of 2.16 kg.

[0031] The ethylene alcohol-grafted propylene-benzonorbornene copolymer has a melt index of 2 g / 10 min at 230℃ and a load of 2.16 kg. The preparation method of the ethylene alcohol-grafted propylene-benzonorbornene copolymer is as follows: using propylene-benzonorbornene copolymer as raw material, BPO as initiator, and ethylene-vinyl acetate as grafting monomer, a solid-phase suspension grafting reaction is carried out to obtain ethylene-vinyl acetate-grafted propylene-benzonorbornene copolymer. Then, the ethylene-vinyl acetate-grafted propylene-benzonorbornene copolymer is subjected to an alcoholysis reaction to obtain the ethylene alcohol-grafted propylene-benzonorbornene copolymer. The molar content of benzonorbornene in the propylene-benzonorbornene copolymer is 28 mol.

[0032] (2) Between the previous surface layer and the next surface layer:

[0033] Homopolymer polypropylene: The melt index is 3.5 g / 10 min at 230℃ and 2.16 kg load.

[0034] Titanium dioxide white masterbatch: consists of homopolymer polypropylene and 62wt% titanium dioxide coated with a low molecular weight dispersant (stearic acid); the particle size D50 of titanium dioxide in the titanium dioxide white masterbatch is 500nm.

[0035] (3) In the core layer:

[0036] Homopolymer polypropylene: The melt index is 3.5 g / 10 min at 230℃ and 2.16 kg load.

[0037] Calcium carbonate masterbatch: includes homopolymer polypropylene and 65wt% calcium carbonate coated with a low molecular weight dispersant (stearic acid); the particle size D50 of calcium carbonate in the calcium carbonate masterbatch is 1.5μm; the melt index of homopolymer polypropylene in the calcium carbonate masterbatch is 6g / 10min at 230℃ and 2.16kg load.

[0038] (4) In the tackifying adhesive surface layer:

[0039] Homopolymer polypropylene: The melt index is 3.5 g / 10 min at 230℃ and 2.16 kg load.

[0040] Saponified ethylene-vinyl acetate copolymer: obtained by alcoholysis of unsaponified ethylene-vinyl acetate copolymer.

[0041] Unsaponified ethylene-vinyl acetate copolymer: melt index of 10 g / 10 min at 190 °C and 2.16 kg load, with a vinyl acetate monomer content of 15 wt%.

[0042] Anti-blocking agent: specifically silicon dioxide.

[0043] Example 1

[0044] This embodiment provides an anti-exudation BOPP white label film, comprising, in sequence, a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive-coated surface layer. The components and contents of each layer are shown in Table 1 and the following:

[0045] Printable surface layer: 97wt% random copolymer polypropylene and 3wt% ethylene alcohol-grafted propylene-benzonorbornene copolymer (ethylene alcohol grafting rate is 9%).

[0046] Top layer: 94wt% homopolymer polypropylene, 3wt% ethylene alcohol-grafted homopolymer polypropylene (ethylene alcohol grafting rate 6%) and 3wt% titanium dioxide white masterbatch;

[0047] Core layer: 70wt% homopolymer polypropylene and 30wt% calcium carbonate masterbatch;

[0048] Next surface layer: 94wt% homopolymer polypropylene, 3wt% ethylene alcohol-grafted homopolymer polypropylene (ethylene alcohol grafting rate 6%) and 3wt% titanium dioxide white masterbatch;

[0049] Tackifying coating surface: 94.8 wt% homopolymer polypropylene, 5 wt% saponified ethylene-vinyl acetate copolymer (saponification degree of 15%) and 0.2 wt% antiblocking agent.

[0050] The preparation method of the anti-precipitation BOPP white label film in this embodiment includes the following steps:

[0051] Each layer of raw material is added to the corresponding extruder to form a homogenized melt. The melt is then filtered and co-extruded through a die in multiple layers. The melt is then cast into a thick sheet using the flat film method and then chilled. The thick sheet is then stretched into a biaxially oriented film using a biaxial stretching method, first longitudinally and then laterally. The film is cooled and then subjected to corona treatment (corona power factor of 25 W·min / m). It is then wound into a master roll, which is then aged and slit into finished products.

[0052] In the above process flow: the melt extrusion temperature of the printable surface layer and the tackifying coating surface layer is 230℃; the melt extrusion temperature of the core layer is 240℃; the melt extrusion temperature of the upper surface layer and the lower surface layer is 240℃; the temperature of the quench water and the quench roller is 40℃; the temperature of the longitudinal stretching zone is 110℃; the temperature of the transverse stretching zone is 150℃; the longitudinal stretching ratio is 5 times; and the transverse stretching ratio is 9 times.

[0053] In this embodiment, the total thickness of the anti-exudation BOPP white label film is 50 μm; wherein, the thickness of the printable surface layer is 2 μm, the thickness of the upper surface layer and the lower surface layer are 4 μm respectively, and the thickness of the tackifying coating surface layer is 1.5 μm.

[0054] Example 2

[0055] This embodiment provides an anti-exudation BOPP white label film, comprising, in sequence, a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive-coated surface layer. The components and contents of each layer are shown in Table 1 and the following:

[0056] Printable surface layer: 95wt% random copolymer polypropylene and 5wt% ethylene alcohol-grafted propylene-benzonorbornene copolymer (ethylene alcohol grafting rate 7%).

[0057] Top layer: 95wt% homopolymer polypropylene, 2wt% ethylene alcohol-grafted homopolymer polypropylene (ethylene alcohol grafting rate 4%) and 3wt% titanium dioxide white masterbatch;

[0058] Core layer: 70wt% homopolymer polypropylene and 30wt% calcium carbonate masterbatch;

[0059] Next surface layer: 95wt% homopolymer polypropylene, 2wt% ethylene alcohol-grafted homopolymer polypropylene (ethylene alcohol grafting rate 4%) and 3wt% titanium dioxide white masterbatch;

[0060] Tackifying coating surface: 91.8 wt% homopolymer polypropylene, 8 wt% saponified ethylene-vinyl acetate copolymer (saponification degree of 20%) and 0.2 wt% antiblocking agent.

[0061] The preparation method of the anti-exudation BOPP white label film in this embodiment is the same as that in Example 1.

[0062] The total thickness and the thickness of each layer of the anti-exudation BOPP white label film in this embodiment are the same as those in Example 1.

[0063] Example 3

[0064] This embodiment provides an anti-exudation BOPP white label film, comprising, in sequence, a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive-coated surface layer. The components and contents of each layer are shown in Table 1 and the following:

[0065] Printable surface layer: 93wt% random copolymer polypropylene and 7wt% ethylene alcohol-grafted propylene-benzonorbornene copolymer (ethylene alcohol grafting rate 5%).

[0066] Top layer: 96wt% homopolymer polypropylene, 1wt% ethylene alcohol-grafted homopolymer polypropylene (ethylene alcohol grafting rate 2%) and 3wt% titanium dioxide white masterbatch;

[0067] Core layer: 70wt% homopolymer polypropylene and 30wt% calcium carbonate masterbatch;

[0068] Next surface layer: 96wt% homopolymer polypropylene, 1wt% ethylene alcohol-grafted homopolymer polypropylene (ethylene alcohol grafting rate of 2%) and 3wt% titanium dioxide white masterbatch;

[0069] Tackifying coating surface: 89.8 wt% homopolymer polypropylene, 10 wt% saponified ethylene-vinyl acetate copolymer (saponification degree of 25%) and 0.2 wt% antiblocking agent.

[0070] The preparation method of the anti-exudation BOPP white label film in this embodiment is the same as that in Example 1.

[0071] The total thickness and the thickness of each layer of the anti-exudation BOPP white label film in this embodiment are the same as those in Example 1.

[0072] Comparative Example 1

[0073] This comparative example provides a BOPP white label film, comprising, in sequence, a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive coating layer. The components and contents of each layer are shown in Table 1 and the following: The components and contents are essentially the same as in Example 2, except that the printable surface layer does not contain vinyl alcohol-grafted propylene-benzonorbornene copolymer, i.e.:

[0074] Printable surface layer: 100wt% random copolymer polypropylene.

[0075] The preparation method of the BOPP white label film in this comparative example is the same as that in Example 1.

[0076] The total thickness and the thickness of each layer of the BOPP white label film in this comparative example are the same as those in Example 1.

[0077] Comparative Example 2

[0078] This comparative example provides a BOPP white label film, comprising, in sequence, a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive-coated surface layer. The components and contents of each layer are shown in Table 1 and the following: The components and contents are essentially the same as in Example 2, except that saponified ethylene-vinyl acetate copolymer is not added to the adhesive-coated surface layer, i.e.:

[0079] Tackifying coating: 99.8 wt% homopolymer polypropylene and 0.2 wt% antiblocking agent.

[0080] The preparation method of the BOPP white label film in this comparative example is the same as that in Example 1.

[0081] The total thickness and the thickness of each layer of the BOPP white label film in this comparative example are the same as those in Example 1.

[0082] Comparative Example 3

[0083] This comparative example provides a BOPP white label film, comprising, in sequence, a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive coating layer. The components and contents of each layer are shown in Table 1 and the following: The components and contents are basically the same as in Example 2, except that vinyl alcohol-grafted homopolymer polypropylene is not added to the top and bottom surface layers, i.e.:

[0084] Top layer: 97wt% homopolymer polypropylene and 3wt% titanium dioxide white masterbatch;

[0085] Next surface layer: 97wt% homopolymer polypropylene and 3wt% titanium dioxide white masterbatch.

[0086] The preparation method of the BOPP white label film in this comparative example is the same as that in Example 1.

[0087] The total thickness and the thickness of each layer of the BOPP white label film in this comparative example are the same as those in Example 1.

[0088] Comparative Example 4

[0089] This comparative example provides a BOPP white label film, comprising a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive coating layer arranged sequentially. The components and contents of each layer are shown in Table 1 and the following: The components and contents are basically the same as in Example 2, except that the amount of vinyl alcohol-grafted propylene-benzonorbornene copolymer added to the printable surface layer is excessively high, i.e.:

[0090] Printable surface layer: 88wt% random copolymer polypropylene and 12wt% ethylene alcohol-grafted propylene-benzonorbornene copolymer (ethylene alcohol grafting rate 7%).

[0091] The preparation method of the BOPP white label film in this comparative example is the same as that in Example 1.

[0092] The total thickness and the thickness of each layer of the BOPP white label film in this comparative example are the same as those in Example 1.

[0093] Comparative Example 5

[0094] This comparative example provides a BOPP white label film, comprising, in sequence, a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive-coated surface layer. The components and contents of each layer are shown in Table 2 and the following: The components and contents are basically the same as in Example 2, except that the amount of saponified ethylene-vinyl acetate copolymer added to the adhesive-coated surface layer is excessively high, i.e.:

[0095] Tackifying coating surface: 84.8 wt% homopolymer polypropylene, 15 wt% saponified ethylene-vinyl acetate copolymer (saponification degree of 20%) and 0.2 wt% antiblocking agent.

[0096] The preparation method of the BOPP white label film in this comparative example is the same as that in Example 1.

[0097] The total thickness and the thickness of each layer of the BOPP white label film in this comparative example are the same as those in Example 1.

[0098] Comparative Example 6

[0099] This comparative example provides a BOPP white label film, comprising, in sequence, a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive coating layer. The components and contents of each layer are shown in Table 2 and the following: The components and contents are basically the same as in Example 2, except that the amount of vinyl alcohol-grafted homopolymer polypropylene added in the top and bottom surface layers is excessively high, i.e.:

[0100] Top layer: 92wt% homopolymer polypropylene, 5wt% ethylene alcohol-grafted homopolymer polypropylene (ethylene alcohol grafting rate 4%) and 3wt% titanium dioxide white masterbatch;

[0101] Next surface layer: 92wt% homopolymer polypropylene, 5wt% ethylene alcohol-grafted homopolymer polypropylene (ethylene alcohol grafting rate 4%) and 3wt% titanium dioxide white masterbatch.

[0102] The preparation method of the BOPP white label film in this comparative example is the same as that in Example 1.

[0103] The total thickness and the thickness of each layer of the BOPP white label film in this comparative example are the same as those in Example 1.

[0104] Comparative Example 7

[0105] This comparative example provides a BOPP white label film, comprising a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive coating layer arranged sequentially. The components and contents of each layer are shown in Table 2 and the following: The components and contents are basically the same as in Example 2, except that the grafting rate of ethylene alcohol in the ethylene alcohol-grafted propylene-benzonorbornene copolymer added to the printable surface layer is too low, i.e.:

[0106] Printable surface layer: 95wt% random copolymer polypropylene and 5wt% ethylene alcohol-grafted propylene-benzonorbornene copolymer (ethylene alcohol grafting rate 2%).

[0107] The preparation method of the BOPP white label film in this comparative example is the same as that in Example 1.

[0108] The total thickness and the thickness of each layer of the BOPP white label film in this comparative example are the same as those in Example 1.

[0109] Comparative Example 8

[0110] This comparative example provides a BOPP white label film, comprising, in sequence, a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive coating layer. The components and contents of each layer are shown in Table 2 and the following: The components and contents are basically the same as in Example 2, except that the grafting rate of ethylene alcohol in the ethylene alcohol-grafted propylene-benzonorbornene copolymer added to the printable surface layer is excessively high, i.e.:

[0111] Printable surface layer: 95wt% random copolymer polypropylene and 5wt% ethylene alcohol-grafted propylene-benzonorbornene copolymer (ethylene alcohol grafting rate is 15%).

[0112] The preparation method of the BOPP white label film in this comparative example is the same as that in Example 1.

[0113] The total thickness and the thickness of each layer of the BOPP white label film in this comparative example are the same as those in Example 1.

[0114] Comparative Example 9

[0115] This comparative example provides a BOPP white label film, comprising, in sequence, a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive-coated surface layer. The components and contents of each layer are shown in Table 2 and the following: The components and contents are basically the same as in Example 2, except that the saponification level of the saponified ethylene-vinyl acetate copolymer added to the adhesive-coated surface layer is too low, i.e.:

[0116] Tackifying coating surface: 91.8 wt% homopolymer polypropylene, 8 wt% saponified ethylene-vinyl acetate copolymer (saponification degree of 10%) and 0.2 wt% antiblocking agent.

[0117] The preparation method of the BOPP white label film in this comparative example is the same as that in Example 1.

[0118] The total thickness and the thickness of each layer of the BOPP white label film in this comparative example are the same as those in Example 1.

[0119] Comparative Example 10

[0120] This comparative example provides a BOPP white label film, comprising, in sequence, a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive-coated surface layer. The components and contents of each layer are shown in Table 2 and the following: The components and contents are basically the same as in Example 2, except that the saponification level of the saponified ethylene-vinyl acetate copolymer added to the adhesive-coated surface layer is too high, i.e.:

[0121] Tackifying coating surface: 91.8 wt% homopolymer polypropylene, 8 wt% saponified ethylene-vinyl acetate copolymer (saponification degree of 30%) and 0.2 wt% antiblocking agent.

[0122] The preparation method of the BOPP white label film in this comparative example is the same as that in Example 1.

[0123] The total thickness and the thickness of each layer of the BOPP white label film in this comparative example are the same as those in Example 1.

[0124] Comparative Example 11

[0125] This comparative example provides a BOPP white label film, comprising, in sequence, a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive coating layer. The components and contents of each layer are shown in Table 2 and the following: The components and contents are basically the same as in Example 2, except that the ethylene alcohol grafting rate in the ethylene alcohol-grafted homopolymer polypropylene added to the bottom surface layer is excessively high, i.e.:

[0126] Next surface layer: 95wt% homopolymer polypropylene, 2wt% ethylene alcohol-grafted homopolymer polypropylene (ethylene alcohol grafting rate 8%) and 3wt% titanium dioxide white masterbatch.

[0127] The preparation method of the BOPP white label film in this comparative example is the same as that in Example 1.

[0128] The total thickness and the thickness of each layer of the BOPP white label film in this comparative example are the same as those in Example 1.

[0129] Table 1. Composition of each layer of the thin film in Examples 1-3 and Comparative Examples 1-4

[0130]

[0131] Table 2. Composition of each layer of the thin film in Comparative Examples 5-11

[0132]

[0133] Comparative Example 12

[0134] This comparative example provides a BOPP white label film, comprising a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive coating layer arranged sequentially. The components and contents of each layer are as follows: The components and contents are basically the same as in Example 2, except that the vinyl alcohol-grafted propylene-benzobornene copolymer in the printable surface layer is replaced with vinyl alcohol-grafted propylene-norbornene copolymer, i.e.:

[0135] Printable surface layer: 93wt% random copolymer polypropylene and 7wt% ethylene alcohol-grafted propylene-norbornene copolymer (ethylene alcohol grafting rate 5%).

[0136] The preparation method of the BOPP white label film in this comparative example is the same as that in Example 1.

[0137] The total thickness and the thickness of each layer of the BOPP white label film in this comparative example are the same as those in Example 1.

[0138] Comparative Example 13

[0139] This comparative example provides a BOPP white label film, comprising, in sequence, a printable surface layer, a top surface layer, a core layer, a bottom surface layer, and an adhesive coating layer. The components and contents of each layer are as follows: They are essentially the same as those in Example 2, except that the saponified ethylene-vinyl acetate copolymer in the adhesive coating layer is replaced with unsaponified ethylene-vinyl acetate copolymer, i.e.:

[0140] Tackifying coating surface: 91.8 wt% homopolymer polypropylene, 8 wt% unsaponified ethylene-vinyl acetate copolymer and 0.2 wt% antiblocking agent.

[0141] The preparation method of the BOPP white label film in this comparative example is the same as that in Example 1.

[0142] The total thickness and the thickness of each layer of the BOPP white label film in this comparative example are the same as those in Example 1.

[0143] Performance Evaluation

[0144] The following performance tests were performed on the BOPP white label films of Examples 1-3 and Comparative Examples 1-13 respectively:

[0145] 1. Antistatic properties (surface resistance): The surface resistance of the printable surface and the adhesive coating surface of the BOPP white label film of Examples 1-3 and Comparative Examples 1-13 were tested in accordance with GB / T 31838.3-2019. The testing instrument was a surface resistance meter (SIMCO, Japan, model: ST-4).

[0146] 2. Surface tension and surface tension durability: Tests were conducted in accordance with GB / T 14216-2008. The BOPP white label films of Examples 1-3 and Comparative Examples 1-13 were subjected to aging treatment for 0 days, 30 days, 60 days and 90 days, respectively, and the surface tension of the printable surface of the film was tested.

[0147] 3. Evaluation of the adhesion performance (peel force) between the tackifying coating and the adhesive: Hot melt adhesive (ethylene-vinyl acetate copolymer, VA content of 18wt%, melt index of 15g / 10min) was applied to the surface of the BOPP white label film of Examples 1-3 and Comparative Examples 1-13, respectively. The coating thickness was 8μm. After coating, the film was kept at 25℃ for 5 minutes to form a hot melt adhesive layer on the tackifying coating of the BOPP white label film, thus obtaining the sample. The sample was cut into strips with a width of 15mm and a length of 15cm. The interlayer peel test was performed using 3M adhesive tape. The peel force required to peel the tackifying coating from the hot melt adhesive layer was recorded. The greater the peel force, the stronger the bond between the tackifying coating and the hot melt adhesive layer.

[0148] Please refer to Table 3 for the test results:

[0149] Table 3 Performance test results of the thin films of Examples 1-3 and Comparative Examples 1-13

[0150]

[0151] Referring to Table 3, the anti-exudation BOPP white label film of Examples 1-3 of the present invention has the characteristics of reduced exudation and low exudation. It is not adversely affected by the migration of low molecular weight dispersants on the printable surface. The printable surface has high surface tension and good durability, thus ensuring the printability of ink. At the same time, the film has certain antistatic properties without the need to add additional antistatic agents. It also takes into account the adhesion between the tackifying coating surface and the adhesive, thus helping to ensure a firm bond between the film and the substrate in subsequent applications.

[0152] The BOPP white label film of Comparative Example 1 did not contain ethylene alcohol-grafted propylene-benzonorbornene copolymer in its printable surface layer. As a result, the surface tension of the printable surface layer was low and its surface tension durability was poor. The surface resistance of the printable surface layer was high, and it could not effectively play an antistatic role.

[0153] In Comparative Example 2, the BOPP white label film did not contain saponified ethylene-vinyl acetate copolymer in its tackifying coating layer. The peel strength between the tackifying coating layer and the hot melt adhesive layer was low (i.e., the adhesion between the tackifying coating layer and the adhesive was relatively poor). The surface resistance of the tackifying coating layer was high, and it could not effectively play an antistatic role.

[0154] In Comparative Example 3, no vinyl alcohol-grafted homopolymer polypropylene was added to either the upper or lower surface layer. During the film preparation process, delamination occurred between the upper and printable surface layer and between the lower and tackifying coating surface layer. Furthermore, the surface tension and durability of the printable surface layer were reduced.

[0155] In Comparative Example 4, the BOPP white label film had an excessive amount of ethylene alcohol-grafted propylene-benzonorbornene copolymer added to its printable surface layer, which easily led to film breakage during film preparation.

[0156] In Comparative Example 5, the amount of saponified ethylene-vinyl acetate copolymer added to the tackifying coating layer was too high, resulting in sticking to the rollers during film preparation and poor winding and unwinding smoothness of the prepared film.

[0157] In Comparative Example 6, the amount of ethylene alcohol-grafted homopolymer polypropylene added to both the upper and lower surface layers was too high, resulting in delamination between the upper and core layers and between the lower and core layers during film preparation.

[0158] In Comparative Example 7, the BOPP white label film has a low grafting rate of ethylene alcohol in the ethylene alcohol-grafted propylene-benzonorbornene copolymer added to its printable surface, which cannot adequately inhibit the migration of low molecular weight dispersants to the printable surface. The printable surface has low surface tension and poor surface tension persistence. In addition, the surface resistance of the printable surface is relatively high, which cannot effectively play an antistatic role.

[0159] In Comparative Example 8, the BOPP white label film has an excessively high grafting rate of ethylene alcohol in the ethylene alcohol-grafted propylene-benzonorbornene copolymer added to its printable surface layer. Due to the high content of polar groups (hydroxyl groups), the film is prone to breakage during the film preparation process.

[0160] Compared with the BOPP white label film of Comparative Example 9, the saponification of the saponified ethylene-vinyl acetate copolymer added to the tackifying coating layer is too low, the peel strength between the tackifying coating layer and the hot melt adhesive layer is relatively low (i.e. the adhesion between the tackifying coating layer and the adhesive is relatively poor); the surface resistance of the tackifying coating layer is relatively high, and it cannot effectively play an antistatic role.

[0161] In Comparative Example 10, the BOPP white label film had an excessively high saponification level in the added saponified ethylene-vinyl acetate copolymer in the tackifying coating layer, which caused the film to stick to the rollers during film preparation and resulted in poor winding and unwinding smoothness.

[0162] In Comparative Example 11, the BOPP white label film had a high grafting rate of ethylene alcohol in the ethylene alcohol-grafted homopolymer polypropylene added to the second surface layer, resulting in delamination between the second surface layer and the core layer during film preparation.

[0163] The BOPP white label film of Comparative Example 12 uses ethylene alcohol-grafted propylene-norbornene copolymer instead of the ethylene alcohol-grafted propylene-benzonorbornene copolymer of the present invention in its printable surface layer. The surface tension of its printable surface layer decays faster, and the smoothness of the film prepared is worse than that of Examples 1-3 of the present invention.

[0164] In Comparative Example 13, the BOPP white label film uses unsaponified ethylene-vinyl acetate copolymer instead of the saponified ethylene-vinyl acetate copolymer of the present invention in its tackifying coating surface layer. The peel strength between the tackifying coating surface layer and the hot melt adhesive layer is low (i.e., the adhesion between the tackifying coating surface layer and the adhesive is relatively poor); the surface resistance of the tackifying coating surface layer is high, and it cannot effectively play an antistatic role.

[0165] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and the present invention also intends to include these modifications and variations.

Claims

1. An anti-extruded BOPP white label film characterized in that: The anti-settlement BOPP white label film comprises, in sequence, a printable surface layer, an upper surface layer, a core layer, a lower surface layer and an adhesive coating surface layer. The printable surface layer comprises random copolymerized polypropylene and 3-7 wt% of ethylene-vinyl alcohol grafted propylene-benzonorbornene copolymer, the grafting rate of ethylene-vinyl alcohol in the ethylene-vinyl alcohol grafted propylene-benzonorbornene copolymer being 5-9%; the ethylene-vinyl alcohol grafted propylene-benzonorbornene copolymer is prepared by solid-phase suspension grafting reaction using propylene-benzonorbornene copolymer as raw material, BPO as initiator and ethylene-vinyl acetate as grafting monomer to obtain ethylene-vinyl acetate grafted propylene-benzonorbornene copolymer, and then alcoholysis of the ethylene-vinyl acetate grafted propylene-benzonorbornene copolymer to obtain the ethylene-vinyl alcohol grafted propylene-benzonorbornene copolymer; The upper surface layer and the lower surface layer each comprise homopolymerized polypropylene, 1-3 wt% of ethylene-vinyl alcohol grafted homopolymerized polypropylene and 1-5 wt% of titanium dioxide white masterbatch, the grafting rate of ethylene-vinyl alcohol in the ethylene-vinyl alcohol grafted homopolymerized polypropylene being 2-6%; The core layer comprises homopolymerized polypropylene and 28-38 wt% of calcium carbonate masterbatch; The adhesive coating surface layer comprises homopolymerized polypropylene and 5-10 wt% of saponified ethylene-vinyl acetate copolymer, the saponification degree of the saponified ethylene-vinyl acetate copolymer being 15-25%.

2. The anti -precipitation BOPP white label film according to claim 1, characterized in that: The molar content of benzonorbornene in the propylene-benzonorbornene copolymer is 18-22 mol%.

3. The anti -precipitation BOPP white label film according to claim 1, characterized in that: The melt index of the ethylene-vinyl alcohol grafted propylene-benzonorbornene copolymer under a load of 2.16 kg at 230℃ is 1-2 g / 10 min.

4. The anti -precipitation BOPP white label film according to claim 1, characterized in that: The titanium dioxide white masterbatch comprises homopolymerized polypropylene and 50-70 wt% of low-molecular dispersant coated titanium dioxide.

5. The anti -precipitation BOPP white label film according to claim 1, characterized by: The calcium carbonate masterbatch comprises homopolymerized polypropylene and 65-75 wt% of low-molecular dispersant coated calcium carbonate.

6. The anti -precipitation BOPP white label film according to claim 1, characterized by: The saponified ethylene-vinyl acetate copolymer is obtained by alcoholysis of unsaponified ethylene-vinyl acetate copolymer; the content of vinyl acetate monomer in the unsaponified ethylene-vinyl acetate copolymer is 15-18 wt%, and the melt index of the unsaponified ethylene-vinyl acetate copolymer under a load of 2.16 kg at 190℃ is 10-20 g / 10 min.

7. The anti -precipitation BOPP white label film according to claim 1, characterized by: The adhesive coating surface layer further comprises 0.1-0.2 wt% of anti-blocking agent.

8. The anti -precipitation BOPP white label film according to claim 1, characterized by: The total thickness of the anti-settlement BOPP white label film is 30-70 μm; the thickness of the printable surface layer is 1-2 μm, the thickness of the upper surface layer and the lower surface layer is 4-6 μm respectively, and the thickness of the adhesive coating surface layer is 1-1.5 μm.

9. A process for the preparation of the anti-pop-out BOPP white label film as claimed in any one of claims 1 to 8, characterized by: The method comprises the following steps: adding raw materials of each layer into corresponding extruders respectively to prepare homogenized melt, and then multi-layer co-extruding the melt through a die after passing through a filter; then, according to the flat film method, casting a thick sheet after chilling, and then stretching the thick sheet in the longitudinal direction first and then in the transverse direction or stretching the thick sheet in the longitudinal direction and the transverse direction simultaneously to prepare a biaxially stretched film; after cooling, the film is subjected to corona treatment, and then is wound to prepare a mother roll, which is subjected to aging treatment, and then is cut to prepare a finished product.

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