Aging-resistant bopp matt film and preparation method thereof

Abstract

This invention relates to an aging-resistant BOPP matte film and its preparation method, belonging to the field of matte film technology. The aging-resistant BOPP matte film includes a matte layer, a core layer, and a glossy layer arranged sequentially. The matte layer comprises random copolymer polypropylene, 40-45 wt% high-density polyethylene, 2-4 wt% ethylene-2-allyl anisole random copolymer A, and 0.1-0.5 wt% antioxidant. The core layer comprises homopolymer polypropylene, 5-8 wt% ethylene-2-allyl phenol random copolymer, and 0.05-0.1 wt% auxiliary antioxidant. Through the synergistic design of the matte layer and the core layer, the aging-resistant BOPP matte film can effectively extend the service life of the BOPP matte film, improve the problem of yellowing due to aging, and enhance the weather resistance and aesthetics of the film product.

Description

Technical Field

[0001] This invention relates to the field of matte film technology, and in particular to an aging-resistant BOPP matte film and its preparation method. Background Technology

[0002] BOPP matte film is a type of BOPP film characterized by high haze and low gloss, exhibiting a matte diffuse reflection effect on its surface. BOPP matte film generally consists of a matte layer and a core layer. The core layer is primarily made of polypropylene, while the matte layer achieves matte finish by giving the film a rough surface structure.

[0003] In practical applications, especially when exposed to long-term light, high temperature, or oxidizing environments, BOPP matting films are prone to degradation due to the low CH bond energy (≈350 kJ / mol) of the polypropylene main chain, which contains tertiary carbon atoms. This makes the core layer susceptible to free radical chain oxidation triggered by heat, light, and oxygen, leading to chain breakage, cross-linking, and carbonyl formation in the polypropylene main chain. This, in turn, causes degradation of the polypropylene and makes the film prone to aging. The end faces of the film roll, being directly exposed to light, high temperature, or oxidizing environments, are particularly vulnerable, severely impacting the film's appearance and lifespan. Furthermore, the rough surface structure of the matting layer increases the contact area between the BOPP matting film and air, moisture, and ultraviolet radiation, easily accumulating environmental stress and accelerating surface oxidation and chalking. Additionally, the high proportion of amorphous regions in the matting layer makes it more susceptible to free radical attack.

[0004] Currently, the method to inhibit the aging of BOPP matte film is to add compound antioxidants to the core layer. Although this method can inhibit yellowing of the film to some extent by preventing thermo-oxidative aging, the large polymer molecules in the film degrade under prolonged exposure to ultraviolet light, leading to the inactivation of antioxidants and making the film prone to aging and yellowing. In addition, the molecular weight of the compound antioxidants currently available is relatively low, resulting in poor compatibility with the large polymer matrix and uneven dispersion in the film matrix, which affects the anti-aging effect. Under long-term use or heating conditions, these antioxidants are prone to migrate to the film surface, forming "frost" or spots, affecting the appearance and transparency of the film.

[0005] Therefore, developing a BOPP matte film with strong aging resistance is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] Based on this, the purpose of the present invention is to provide an aging-resistant BOPP matte film and its preparation method. The aging-resistant BOPP matte film, through the synergistic design of the matte layer and the core layer, can effectively extend the service life of the BOPP matte film, improve the problem of yellowing due to aging, and enhance the weather resistance and aesthetics of the film product.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides an aging-resistant BOPP matte film, comprising a matte layer, a core layer, and a glossy layer arranged sequentially. The matte layer comprises random copolymer polypropylene, 40-45 wt% high-density polyethylene, 2-4 wt% ethylene-2-allyl anisole random copolymer A, and 0.1-0.5 wt% antioxidant, wherein the ethylene-2-allyl anisole random copolymer A contains 14-30 mol of 2-allyl anisole. The core layer comprises homopolymer polypropylene, 5-8 wt% ethylene-2-allyl phenol random copolymer, and 0.05-0.1 wt% auxiliary antioxidant, wherein the ethylene-2-allyl phenol random copolymer is obtained by hydroxylating the methoxy group of ethylene-2-allyl anisole random copolymer B using a hydroxylation agent, and the ethylene-2-allyl anisole random copolymer B contains 2.5-3.0 mol of 2-allyl anisole.

[0009] The present invention relates to an aging-resistant BOPP matte film, wherein the matte layer comprises random copolymer polypropylene as the marine phase and high-density polyethylene as the island phase, forming a rough structure with a matte surface. The present invention, by adding an antioxidant to the matte layer, can inhibit the aging of the matte layer to a certain extent. Furthermore, considering the potential for thermal decomposition and migration of the antioxidant, which could affect the film's appearance, the present invention adds a certain amount of ethylene-2-allyl anisole random copolymer A to the matte layer, synergistically with the antioxidant, to improve the film's aging resistance and ensure uniform matting and stable appearance. The antioxidant is a commonly used antioxidant in the art; it can be a single hindered phenolic antioxidant or a compound antioxidant with a hindered phenolic antioxidant as the main antioxidant and a phosphite antioxidant as an auxiliary antioxidant.

[0010] In the ethylene-2-allyl anisole random copolymer A, the comonomer 2-allyl anisole has the following structural formula: ; On the one hand, the ethylene-2-allyl anisole random copolymer A contains a polar methoxy group (-OCH3) introduced by the comonomer 2-allyl anisole, which contains lone pair electrons. This allows it to form hydrogen bonds with the -OH group of hindered phenolic antioxidants (such as antioxidant 1010 and antioxidant BHT) and to generate dipole attraction with the PO group of phosphite antioxidants. This can reduce the migration of the antioxidants to the film surface due to thermal decomposition, thus reducing the formation of "frost" or spots. On the other hand, the main chain of the ethylene-2-allyl anisole random copolymer A is ethylene segment. It has good compatibility with marine random copolymer polypropylene and island phase high-density polyethylene in the matting layer, which is conducive to forming a more uniform and dense surface matting structure. This reduces the contact area between the matting layer and air, moisture, and ultraviolet rays to a certain extent, and reduces the probability of free radical attack on the amorphous region, thereby improving the aging resistance of the film.

[0011] This invention limits the addition amount of the ethylene-2-allyl anisole random copolymer A in the matte layer to 2-4 wt%. If the addition amount of the ethylene-2-allyl anisole random copolymer A in the matte layer is too low, it will not effectively reduce the migration of the antioxidant, nor will it be conducive to forming a uniform and dense surface matte structure. If the addition amount of the ethylene-2-allyl anisole random copolymer A in the matte layer is too high, the thick sheet will appear "incompatible" due to the large viscosity difference between the matte layer and the adjacent core layer during the multilayer co-extrusion process of film production. This can easily lead to film breakage during the subsequent biaxial stretching process, affecting the smoothness of production.

[0012] This invention limits the molar content of 2-allyl anisole in the ethylene-2-allyl anisole random copolymer A to 14-30 mol%. The ethylene-2-allyl anisole random copolymer A exhibits suitable melt flowability and can produce significant flexible deformation under biaxial stretching stress, which is beneficial for adapting to biaxial stretching processes. Furthermore, controlling the molar content of 2-allyl anisole in the ethylene-2-allyl anisole random copolymer A to 14-30 mol% ensures that the ethylene-2-allyl anisole random copolymer A can effectively inhibit antioxidant migration; on the other hand, it ensures that the ethylene-2-allyl anisole random copolymer A has suitable melt flowability, matching the viscosity of adjacent core layers, improving the lateral distribution of the co-extruded melt at the die, and facilitating the formation of suitable biaxially stretched film thicknesses.

[0013] The anti-aging BOPP matte film of the present invention incorporates an ethylene-2-allylphenol random copolymer into the core layer, synergistically enhancing the film's antioxidant degradation resistance while ensuring smooth production. The ethylene-2-allylphenol random copolymer of the present invention is obtained by hydroxylating the methoxy groups of ethylene-2-allyl anisole random copolymer B using a hydroxylation agent. The ethylene-2-allylphenol random copolymer contains phenolic hydroxyl groups, which have low OH bond dissociation energy. These hydroxyl groups can rapidly donate hydrogen atoms to the peroxide radicals generated during the high-temperature processing of the core layer's main raw material (homopolymer polypropylene), forming hydroperoxide ROOH and phenoxy radicals ArO·, terminating the chain growth reaction. Furthermore, relying on the π-π conjugation effect of the ortho-allyl group, single electrons are delocalized and dispersed on the benzene ring and allyl double bond, forming resonantly stable radicals (single electrons delocalized to the benzene ring and allyl double bond). The activity of ArO· is significantly reduced, making it difficult to initiate new oxidation chains and avoiding the formation of secondary oxidation chains. This further inhibits the chain oxidation reaction of homopolymer polypropylene, protecting it from further degradation and improving the overall aging resistance of the film. In addition, the ethylene-2-allylphenol random copolymer is a macromolecular polymer with an ethylene segment as its main chain. Compared to low-molecular-weight antioxidants, it has better dispersibility in the core layer, does not migrate, and thus exerts a more effective antioxidant effect. Furthermore, the addition of the ethylene-2-allylphenol random copolymer ensures good interlayer bonding between the core layer and the matte layer, preventing delamination during preparation. Simultaneously, the invention incorporates a certain amount of auxiliary antioxidant in the core layer to further decompose hydroperoxide (ROOH), and the macromolecular phenol captures free radicals, forming a complete antioxidant system, further improving processing stability and long-term aging performance. Preferably, the auxiliary antioxidant is a phosphite or a thioether.

[0014] This invention limits the addition amount of the ethylene-2-allylphenol random copolymer in the core layer to 5-8 wt%. If the addition amount of the ethylene-2-allylphenol random copolymer in the core layer is too low, the improvement in antioxidant effect will not be significant; if the addition amount of the ethylene-2-allylphenol random copolymer in the core layer is too high, due to the difference in polarity with homopolymer polypropylene, it will lead to uneven dispersion in the core layer, and even thick incompatible sheets, which can easily cause film breakage during subsequent biaxial stretching, affecting production smoothness. The ethylene-2-allylphenol random copolymer is obtained by hydroxylating the methoxy group of ethylene-2-allyl anisole random copolymer B. This invention limits the content of 2-allyl anisole in ethylene-2-allyl anisole random copolymer B to 2.5-3.0 mol%, which is beneficial to achieve a balance between the antioxidant degradation effect on the film and production smoothness of the obtained ethylene-2-allylphenol random copolymer. If the content of 2-allyl anisole in the ethylene-2-allyl anisole random copolymer B is too high, the resulting ethylene-2-allylphenol random copolymer will be too polar, resulting in poor compatibility with homopolymer polypropylene. This will lead to uneven dispersion in the core layer, or even thick, incompatible sheets, which may cause film breakage during subsequent biaxial stretching, affecting production smoothness. If the content of 2-allyl anisole in the ethylene-2-allyl anisole random copolymer B is too low, the resulting ethylene-2-allylphenol random copolymer will not significantly improve the antioxidant effect of the film, and will also affect the interlayer bonding between the core layer and the matte layer, potentially causing delamination.

[0015] Furthermore, in the matte layer, the melt index of the random copolymer polypropylene measured at 230°C and 2.16 kg is 6-8 g / 10 min, and the melt index of the high-density polyethylene measured at 190°C and 21.6 kg is 9-20 g / 10 min.

[0016] Further, the preparation method of the ethylene-2-allyl anisole random copolymer A in the matting layer includes the following steps: adding triisobutylaluminum to a toluene solution containing 2-allyl anisole to remove impurities; then placing it in a water bath at 10-25°C and introducing ethylene, adding a mixture containing the catalyst dichlorodicyclopentadiene and the co-catalyst [Ph3C][B(C6F5)4], reacting for 150-200 minutes, adding methanol, cooling to precipitate, filtering and collecting, washing, and drying to obtain the ethylene-2-allyl anisole random copolymer A; wherein, the molar ratio of 2-allyl anisole to the catalyst dichlorodicyclopentadiene is (500-1000):1, and the molar ratio of the catalyst dichlorodicyclopentadiene to the co-catalyst [Ph3C][B(C6F5)4] is 1:1. Under the above reaction conditions, ethylene and 2-allyl anisole copolymerizes in the presence of the catalyst titanium dichlorophenoxyacetate and the co-catalyst [Ph3C][B(C6F5)4] to obtain the ethylene-2-allyl anisole random copolymer A. Preferably, the molar ratio of 2-allyl anisole to the catalyst titanium dichlorophenoxyacetate is 1000:1.

[0017] Further, the preparation method of the ethylene-2-allylphenol random copolymer in the core layer includes the following steps: under a nitrogen atmosphere, dissolving the ethylene-2-allyl anisole random copolymer B in 1,2,4-trichlorobenzene, then placing it in an ice bath and adding a hydroxylation agent; after the addition is complete, removing the ice bath and reacting at room temperature for 20-28 hours; subsequently cooling in the ice bath and adding ice water, stirring for 20-40 minutes to precipitate the precipitate; then removing the ice bath, restoring to room temperature, collecting the precipitate by filtration, washing, and drying to obtain the ethylene-2-allylphenol random copolymer; wherein, the molar ratio of the ethylene-2-allyl anisole random copolymer B to the hydroxylation agent is 1:(1.5-3). Through the above preparation method, the methoxy groups on the ethylene-2-allyl anisole random copolymer B are hydroxylated to phenolic hydroxyl groups, thereby obtaining the ethylene-2-allylphenol random copolymer. Preferably, the molar ratio of the ethylene-2-allyl anisole random copolymer B to the hydroxylation agent is 1:2.

[0018] Furthermore, the hydroxylation agent is preferably boron tribromide.

[0019] Furthermore, the melting point of the ethylene-2-allyl anisole random copolymer B is 110-115℃, which helps to ensure that the processing performance of the ethylene-2-allylphenol random copolymer prepared from the ethylene-2-allyl anisole random copolymer B can match the processing temperature of the main resin homopolymer polypropylene and the biaxial stretching process, thus ensuring smooth production.

[0020] Further, the preparation method of the ethylene-2-allyl anisole random copolymer B includes the following steps: adding triisobutylaluminum to a toluene solution containing 2-allyl anisole to remove impurities; then placing it in a water bath at 10-25°C and introducing ethylene, adding a mixture containing the catalyst dichlorodicyclopentadiene and the co-catalyst [Ph3C][B(C6F5)4], reacting for 20-40 minutes, adding methanol, cooling to precipitate, filtering and collecting, washing, and drying to obtain the ethylene-2-allyl anisole random copolymer B; wherein, the molar ratio of 2-allyl anisole to the catalyst dichlorodicyclopentadiene is (90-120):1, and the molar ratio of the catalyst dichlorodicyclopentadiene to the co-catalyst [Ph3C][B(C6F5)4] is 1:1. Under the above reaction conditions, ethylene and 2-allyl anisole copolymerizes in the presence of the catalyst titanium dichlorophenoxyacetate and the co-catalyst [Ph3C][B(C6F5)4] to obtain the ethylene-2-allyl anisole random copolymer B. Preferably, the molar ratio of 2-allyl anisole to the catalyst titanium dichlorophenoxyacetate is 100:1.

[0021] Furthermore, the glossy layer comprises homopolymer polypropylene and 1-5 wt% antiblocking agent masterbatch.

[0022] Furthermore, the anti-blocking agent in the anti-blocking masterbatch is at least one of silica, talc, and plexiglass microspheres, with a particle size D50 of 3-7 μm. The carrier resin in the anti-blocking agent masterbatch is homopolymer polypropylene. Controlling the particle size D50 of the anti-blocking agent to 3-7 μm ensures the formation of an effective surface anti-blocking microstructure and inhibits anti-blocking agent migration loss caused by localized stress concentration, thereby significantly reducing the risk of detachment under high-speed winding conditions. Preferably, the effective content of the anti-blocking agent in the anti-blocking agent masterbatch is 5 wt%. The anti-blocking agent prevents adhesion between films, which is beneficial to the smoothness of film production and winding / unwinding.

[0023] Furthermore, the melt flow index of the homopolymer polypropylene in the core layer, the homopolymer polypropylene in the glossy layer, and the homopolymer polypropylene in the antiblocking masterbatch, measured under test conditions of 230°C and 2.16 kg, is 3-6 g / 10 min.

[0024] Furthermore, the total thickness of the aging-resistant BOPP matte film is 10-20 μm; wherein the thickness of the matte layer is 1-2 μm, and the thickness of the glossy layer is 1-3 μm.

[0025] The present invention also provides a method for preparing the aging-resistant BOPP matte film as described above, comprising the following steps: mixing the raw materials of each layer according to the proportion and adding them into each extruder respectively; after being metered by a metering pump, the melt of each extruder is merged into a thick sheet at the T-die; the thick sheet is cooled by a chilling roller and then enters a chilling water tank and a blowing chamber; then it is stretched longitudinally, and then enters a transverse stretching area for transverse stretching to obtain a film; the film is shaped, corona treated and then wound up; then it is subjected to aging treatment and slitting to obtain the aging-resistant BOPP matte film.

[0026] Furthermore, in the above preparation method, the quenching temperature is 15-40℃; the extrusion temperature of the matte layer is 235-250℃, and the extrusion temperatures of the core layer and the glossy layer are 245-250℃; during longitudinal stretching, the longitudinal stretching ratio is 4.5-5.7 times, the preheating temperature of the matte layer is 130-135℃, the stretching temperature is 126-132℃, the preheating temperature of the glossy layer is 135-140℃, and the stretching temperature is 130-135℃; during transverse stretching, the transverse stretching ratio is 7.5-10 times, the preheating temperature is 168-172℃, the stretching temperature is 160-165℃, and the setting temperature is 163-168℃; the corona power factor is 20-40 W•min / m. 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] The raw materials used in the following examples or comparative examples: (1) Random copolymer polypropylene: melt index is 6.8 g / 10 min (test conditions: 230℃, 2.16 kg).

[0029] (2) High-density polyethylene: melt index is 11.6 g / 10 min (test conditions: 190℃, 21.6 kg).

[0030] (3) Random copolymer of ethylene-2-allyl anisole: ① Ethylene-2-allyl anisole random copolymer A: The content of 2-allyl anisole is 20.89 mol%. The preparation method is as follows: In a glove box, 25 ml of toluene solution containing 40 mmol of 2-allyl anisole monomer was added to a three-necked flask with a magnetic stir bar (to form a mixture), and triisobutylaluminum (2 mmol) was added to remove impurities; 1 ml of toluene solution containing the co-catalyst [Ph3C][B(C6F5)4] (0.04 mmol) was added dropwise to 1 ml of toluene solution containing the catalyst dichlorodicyclopentadiene (0.04 mmol), and the mixture was transferred to a two-necked flask, and the flask neck was sealed with silicone grease. The three-necked flask was removed and placed in a water bath (20°C), and connected to a clean Schlenk ethylene line using a three-way stopcock. Ethylene (1 atm) was introduced into the system, and the mixture was stirred until the solution was saturated. Subsequently, under an ethylene atmosphere, the mixture in the two-necked flask was transferred to the three-necked flask described above. Timing was started, and the reaction was stirred for 180 minutes. After the reaction was completed, methanol (150 mL) was added, and the mixture was cooled to 5°C to allow the copolymer to precipitate. The copolymer was collected by filtration, washed with methanol, and dried under vacuum at 60°C to a fixed weight to obtain ethylene-2-allyl anisole random copolymer A.

[0031] ② Ethylene-2-allyl anisole random copolymer B: The molar content of 2-allyl anisole is 2.85 mol%, and the melting point is 114 °C. The preparation method is as follows: In a glove box, 50 ml of toluene solution containing 4 mmol of 2-allyl anisole monomer is added to a three-necked flask with a magnetic stir bar (to form a mixture), and triisobutylaluminum (2 mmol) is added to remove impurities. 1 ml of toluene solution containing the co-catalyst [Ph3C][B(C6F5)4] (0.04 mmol) is added dropwise to 1 ml of toluene solution containing the catalyst dichlorodicyclopentadiene (0.04 mmol), and both are transferred to a two-necked flask, which is then sealed with silicone grease. The three-necked flask is removed and placed in a water bath (20 °C). A three-way stopcock is used to connect to a cleaned Schlenk ethylene line, and ethylene (1 atm) is introduced into the system. The mixture is stirred until the solution is saturated. Subsequently, under an ethylene atmosphere, the mixture in the two-necked flask was transferred to the three-necked flask described above. Timing was started, and the reaction was stirred for 30 minutes. After the reaction was completed, methanol (150 mL) was added, and the mixture was cooled to 5°C to allow the copolymer to precipitate. The copolymer was collected by filtration, washed with methanol, and dried under vacuum at 60°C to a fixed weight to obtain ethylene-2-allyl anisole random copolymer B.

[0032] For the above-mentioned ethylene-2-allyl anisole random copolymer A or ethylene-2-allyl anisole random copolymer B, using deuterated chloroform or deuterated 1,1,2,2-tetrachloroethane as a solvent, through... 1¹H NMR analysis revealed that the content of 2-allyl anisole in ethylene-2-allyl anisole random copolymer A was 20.89 mol, and the content of 2-allyl anisole in ethylene-2-allyl anisole random copolymer B was 2.85 mol. Furthermore, differential scanning calorimetry (DSC) analysis of ethylene-2-allyl anisole random copolymer B showed a melting point of 114 °C.

[0033] (4) Antioxidant: Antioxidant 1010 and antioxidant 168 are compounded in a mass ratio of 1:1.

[0034] (5) Homopolymer polypropylene: melt index is 4.5 g / 10 min (test conditions: 230℃, 2.16 kg).

[0035] (6) The preparation method of ethylene-2-allylphenol random copolymer is as follows: Under a nitrogen atmosphere, ethylene-2-allyl anisole random copolymer B (1 eq.) was dissolved in 1,2,4-trichlorobenzene (concentration of 0.3 mol / L), placed in an ice bath (0℃), and boron tribromide (2 eq.) was added dropwise over 30 minutes. After the addition was complete, the ice bath was removed, and the mixture was reacted at room temperature for 24 hours. Subsequently, the mixture was cooled in an ice bath (0℃), and ice water was slowly added dropwise while stirring for 30 minutes. As the fumes dissipated, a precipitate gradually formed. The ice bath was then removed, and the mixture was slowly restored to room temperature. The precipitate was collected by filtration, washed with water and methanol, and the resulting white powder was dried in a vacuum drying oven at 80℃ for 12 hours to obtain ethylene-2-allylphenol random copolymer. The disappearance of the methoxyl characteristic peak at 3.76 ppm in the 1H NMR spectrum, replaced by a hydroxyl signal peak at 4.5 ppm, indicates that the ethylene-2-allyl anisole random copolymer B has been completely hydroxylated and transformed into ethylene-2-allylphenol random copolymer.

[0036] (7) Auxiliary antioxidant: Antioxidant 168.

[0037] (8) Anti-blocking masterbatch: The matrix resin is homopolymer polypropylene, the active ingredient is silicon dioxide, the effective content is 5wt%, and the particle size D50 of silicon dioxide is 4.0μm.

[0038] The table below shows the components of each layer of the film and their proportions in each embodiment and comparative example: Table 1. Components and content percentages (wt%) of each layer of the films in Examples 1-3 and Comparative Examples 1-5

[0039] Example 1 This embodiment provides an aging-resistant BOPP matte film, comprising a matte layer, a core layer, and a glossy layer arranged sequentially; wherein, please refer to Table 1, the specific formulation of each layer is as follows: Matte layer: 52.8 wt% random copolymer polypropylene, 45 wt% high-density polyethylene, 2 wt% ethylene-2-allyl anisole random copolymer A and 0.2 wt% antioxidant; Core layer: 91.9 wt% homopolymer polypropylene, 8 wt% ethylene-2-allylphenol random copolymer and 0.1 wt% auxiliary antioxidant; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0040] The preparation method of the aging-resistant BOPP matte film in this embodiment includes the following steps: the raw materials of each layer are mixed according to the ratio and then added to each extruder. After being metered by the metering pump, the melt of each extruder is merged into a thick sheet at the T-die. The thick sheet is cooled by the quenching roller and then enters the quenching water tank and the blowing chamber. Then it is stretched longitudinally and then stretched laterally in the transverse stretching area to obtain a film. After the film is shaped and corona treated, it is wound up and then subjected to aging treatment and slitting to obtain the aging-resistant BOPP matte film.

[0041] In the above preparation method, the quenching temperature is 30℃; the extrusion temperature of the matte layer is 240℃, and the extrusion temperature of the core layer and the glossy layer is 250℃; during longitudinal stretching, the longitudinal stretching ratio is 5.0 times, the preheating temperature of the matte layer is 130℃, the stretching temperature is 132℃, and the preheating temperature and stretching temperature of the glossy layer are 135℃ and 135℃; during transverse stretching, the transverse stretching ratio is 8.0 times, the preheating temperature is 168℃, the stretching temperature is 165℃, and the setting temperature is 165℃; the corona power factor is 25 W•min / m.

[0042] The aging-resistant BOPP matte film of this embodiment has a total thickness of 12μm; wherein the thickness of the matte layer is 1μm, the thickness of the core layer is 9μm, and the thickness of the glossy layer is 2μm.

[0043] Example 2 This embodiment provides an aging-resistant BOPP matte film, comprising a matte layer, a core layer, and a glossy layer arranged sequentially; wherein, please refer to Table 1, the specific formulation of each layer is as follows: Matte layer: 51.8wt% random copolymer polypropylene, 45wt% high-density polyethylene, 3wt% ethylene-2-allyl anisole random copolymer A and 0.2wt% antioxidant; Core layer: 93.4 wt% homopolymer polypropylene, 6.5 wt% ethylene-2-allylphenol random copolymer and 0.1 wt% auxiliary antioxidant; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0044] The preparation method of the aging-resistant BOPP matte film in this embodiment is the same as that in Example 1.

[0045] The total thickness and the thickness of each layer of the aging-resistant BOPP matte film in this embodiment are the same as those in Embodiment 1.

[0046] Example 3 This embodiment provides an aging-resistant BOPP matte film, comprising a matte layer, a core layer, and a glossy layer arranged sequentially; wherein, please refer to Table 1, the specific formulation of each layer is as follows: Matte layer: 50.8wt% random copolymer polypropylene, 45wt% high-density polyethylene, 4wt% ethylene-2-allyl anisole random copolymer A and 0.2wt% antioxidant; Core layer: 94.9 wt% homopolymer polypropylene, 5 wt% ethylene-2-allylphenol random copolymer and 0.1 wt% auxiliary antioxidant; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0047] The preparation method of the aging-resistant BOPP matte film in this embodiment is the same as that in Example 1.

[0048] The total thickness and the thickness of each layer of the aging-resistant BOPP matte film in this embodiment are the same as those in Embodiment 1.

[0049] Comparative Example 1 This comparative example provides a BOPP matte film, comprising a matte layer, a core layer, and a glossy layer arranged sequentially; wherein, please refer to Table 1, the specific formulation of each layer is as follows: Matte layer: 54.8 wt% random copolymer polypropylene, 45 wt% high-density polyethylene and 0.2 wt% antioxidant; Core layer: 99.9 wt% homopolymer polypropylene and 0.1 wt% auxiliary antioxidant; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0050] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0051] The total thickness and the thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0052] Comparative Example 2 This comparative example provides a BOPP matte film, comprising a matte layer, a core layer, and a glossy layer arranged sequentially; wherein, please refer to Table 1, the specific formulation of each layer is as follows: Matte layer: 54.8 wt% random copolymer polypropylene, 45 wt% high-density polyethylene and 0.2 wt% antioxidant; Core layer: 93.4 wt% homopolymer polypropylene, 6.5 wt% ethylene-2-allylphenol random copolymer and 0.1 wt% auxiliary antioxidant; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0053] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0054] The total thickness and the thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0055] Comparative Example 3 This comparative example provides a BOPP matte film, comprising a matte layer, a core layer, and a glossy layer arranged sequentially; wherein, please refer to Table 1, the specific formulation of each layer is as follows: Matte layer: 44.8 wt% random copolymer polypropylene, 45 wt% high-density polyethylene, 10 wt% ethylene-2-allyl anisole random copolymer A and 0.2 wt% antioxidant; Core layer: 93.4 wt% homopolymer polypropylene, 6.5 wt% ethylene-2-allylphenol random copolymer and 0.1 wt% auxiliary antioxidant; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0056] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0057] The total thickness and the thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0058] Comparative Example 4 This comparative example provides a BOPP matte film, comprising a matte layer, a core layer, and a glossy layer arranged sequentially; wherein, please refer to Table 1, the specific formulation of each layer is as follows: Matte layer: 51.8wt% random copolymer polypropylene, 45wt% high-density polyethylene, 3wt% ethylene-2-allyl anisole random copolymer A and 0.2wt% antioxidant; Core layer: 99.9 wt% homopolymer polypropylene and 0.1 wt% auxiliary antioxidant; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0059] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0060] The total thickness and the thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0061] Comparative Example 5 This comparative example provides a BOPP matte film, comprising a matte layer, a core layer, and a glossy layer arranged sequentially; wherein, please refer to Table 1, the specific formulation of each layer is as follows: Matte layer: 51.8wt% random copolymer polypropylene, 45wt% high-density polyethylene, 3wt% ethylene-2-allyl anisole random copolymer A and 0.2wt% antioxidant; Core layer: 84.9 wt% homopolymer polypropylene, 15 wt% ethylene-2-allylphenol random copolymer and 0.1 wt% auxiliary antioxidant; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0062] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0063] The total thickness and the thickness of each layer of the BOPP matte film in this comparative example are the same as those in Example 1.

[0064] Performance testing The following performance tests were performed on the films of Examples 1-3 and Comparative Examples 1-5 respectively: (1) Haze: The haze of the film was tested according to GB / T2410-2008 "Determination of light transmittance and haze of transparent plastic".

[0065] (2) Oxidation induction time (OIT): The oxidation induction time of the film was tested according to GB / T 19466.6-2009 "Differential scanning calorimetry (DSC) for plastics - Part 6: Determination of oxidation induction time (isothermal OIT) and oxidation induction temperature (dynamic OIT)". Test conditions: Under N2 (50 mL / min), the temperature was increased to 200℃ at a rate of 20℃ / min; the temperature was held constant for 5 min (thermal equilibrium); the temperature was then switched to O2 (50 mL / min), and the timing was started; the temperature was maintained at 200℃ until a significant exothermic oxidation peak appeared; the time when a significant exothermic oxidation peak appeared was the oxidation induction time.

[0066] (3) Color difference ▲E: The total color difference ▲E of the film roll end face was measured using a colorimeter: the test was conducted in accordance with GB / T 7921-2008 "Uniform Color Space and Color Difference Formula" and GB / T 3978-2008 "Standard Illuminators and Geometric Conditions".

[0067] The specific testing method is as follows: Select a white matte film as the standard sample, place it face up on the ground, and calibrate it by placing the colorimeter probe stably on the face. After calibration, test the face of the sample (i.e., the film rolls of each embodiment or comparative example) and confirm the face color through the ▲E color difference value. The larger the ▲E, the greater the color change. Compare the face color changes by immediate testing, curing (40℃±2℃, constant temperature chamber) for 24 hours, and room temperature for 15, 30, 60, and 90 days.

[0068] (4) Appearance - uniformity of matting and film surface quality: The test was conducted in accordance with GB / T 32021-2015 "Biaxially oriented polypropylene matte film" (6.3 Appearance).

[0069] The specific method is as follows: Extinction uniformity: With the surface of the film's extinction layer facing upwards, visually inspect for any uneven extinction under both natural light and 45° oblique flashlight illumination.

[0070] Film quality: Visually inspect for bright spots, dark spots, frost, and agglomeration.

[0071] The test results are shown in the table below: Table 2. Test results of thin film performance in Examples 1-3 and Comparative Examples 1-5

[0072] As shown in Table 2, the aging-resistant BOPP matte films of Examples 1-3 of the present invention have a long oxidation induction time, small color difference (aging resistance), good matte uniformity and film surface quality, and good film production smoothness.

[0073] In Comparative Example 1, the BOPP matte film did not contain ethylene-2-allyl anisole random copolymer A in the matte layer, nor did it contain ethylene-2-allyl phenol random copolymer in the core layer. The BOPP matte film in Comparative Example 1 had a short oxidation induction time and a large color difference, indicating that the BOPP matte film in Comparative Example 1 was prone to aging. Furthermore, the BOPP matte film in Comparative Example 1 had poor matte uniformity.

[0074] In Comparative Example 2, the BOPP matte film, without the addition of ethylene-2-allyl anisole random copolymer A to the matte layer, exhibited a relatively shorter oxidation induction time and a relatively larger color difference, indicating that the BOPP matte film of Comparative Example 2 is relatively prone to aging. Furthermore, the matte uniformity of the BOPP matte film of Comparative Example 2 is poor. Comparative Example 2 demonstrates that the absence of ethylene-2-allyl anisole random copolymer A in the matte layer is detrimental to the formation of a uniform and dense surface matte structure, thus hindering the improvement of the film's aging resistance.

[0075] In Comparative Example 3, the BOPP matte film contained too much ethylene-2-allyl anisole random copolymer A in the matte layer. During the multilayer co-extrusion process, the viscosity difference between the matte layer and the adjacent core layer of the BOPP matte film in Comparative Example 3 was too large, resulting in the thick film exhibiting an "incompatible state". This led to film breakage during production, and the surface quality of the produced film was poor.

[0076] In Comparative Example 4, the BOPP matte film did not contain ethylene-2-allylphenol random copolymer in the core layer. The oxidation induction time of the BOPP matte film in Comparative Example 4 was relatively short and the color difference change was relatively large, indicating that the BOPP matte film in Comparative Example 4 was relatively easy to age. In addition, since no ethylene-2-allylphenol random copolymer was added to the core layer, the interlayer bonding force between the core layer and the matte layer was generally weak, and the film smoothness was also generally weak.

[0077] In Comparative Example 5, the BOPP matte film had an excessive amount of ethylene-2-allylphenol random copolymer in the core layer. Due to the polarity difference between the ethylene-2-allylphenol random copolymer and the homopolymer polypropylene, the ethylene-2-allylphenol random copolymer was unevenly dispersed in the core layer, resulting in thick, incompatible sheets. This led to film breakage during the subsequent biaxial stretching process, affecting production smoothness.

[0078] 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 aging-resistant BOPP matte film, characterized in that, This includes a matte layer, a core layer, and a glossy layer arranged in sequence; The matte layer comprises random copolymer polypropylene, 40-45 wt% high-density polyethylene, 2-4 wt% ethylene-2-allyl anisole random copolymer A, and 0.1-0.5 wt% antioxidant, wherein the content of 2-allyl anisole in ethylene-2-allyl anisole random copolymer A is 14-30 mol%. The core layer comprises homopolymer polypropylene, 5-8 wt% ethylene-2-allylphenol random copolymer, and 0.05-0.1 wt% auxiliary antioxidant. The ethylene-2-allylphenol random copolymer is obtained by hydroxylating the methoxy group of ethylene-2-allyl anisole random copolymer B with a hydroxylating agent. The content of 2-allyl anisole in ethylene-2-allyl anisole random copolymer B is 2.5-3.0 mol.

2. The aging-resistant BOPP matte film according to claim 1, characterized in that, The random copolymer polypropylene had a melt index of 6-8 g / 10 min measured under test conditions of 230°C and 2.16 kg, and the high-density polyethylene had a melt index of 9-20 g / 10 min measured under test conditions of 190°C and 21.6 kg.

3. The aging-resistant BOPP matte film according to claim 1, characterized in that, The preparation method of the ethylene-2-allyl anisole random copolymer A includes the following steps: adding triisobutylaluminum to a toluene solution containing 2-allyl anisole to remove impurities; then placing it in a water bath at 10-25°C and introducing ethylene, adding a mixture containing the catalyst dichlorodicyclopentadiene and the co-catalyst [Ph3C][B(C6F5)4], reacting for 150-200 minutes, adding methanol, cooling to precipitate, filtering and collecting, washing, and drying to obtain the ethylene-2-allyl anisole random copolymer A; wherein, the molar ratio of 2-allyl anisole to the catalyst dichlorodicyclopentadiene is (500-1000):1, and the molar ratio of the catalyst dichlorodicyclopentadiene to the co-catalyst [Ph3C][B(C6F5)4] is 1:

1.

4. The aging-resistant BOPP matte film according to claim 1, characterized in that, The antioxidant is a hindered phenolic antioxidant, or the antioxidant is a compound antioxidant with hindered phenolic antioxidant as the main antioxidant and phosphite antioxidant as the auxiliary antioxidant.

5. The aging-resistant BOPP matte film according to claim 1, characterized in that, The preparation method of the ethylene-2-allylphenol random copolymer includes the following steps: under a nitrogen atmosphere, ethylene-2-allyl anisole random copolymer B is dissolved in 1,2,4-trichlorobenzene, and then placed in an ice bath, and a hydroxylation agent is added; after the addition is complete, the ice bath is removed, and the reaction is carried out at room temperature for 20-28 hours; then the mixture is cooled in an ice bath, and ice water is added, and the mixture is stirred for 20-40 minutes to precipitate the precipitate; then the ice bath is removed, the mixture is restored to room temperature, and the precipitate is collected by filtration, washed, and dried to obtain the ethylene-2-allylphenol random copolymer; wherein, the molar ratio of the ethylene-2-allyl anisole random copolymer B to the hydroxylation agent is 1:(1.5-3).

6. The aging-resistant BOPP matte film according to claim 1, characterized in that, The preparation method of the ethylene-2-allyl anisole random copolymer B includes the following steps: adding triisobutylaluminum to a toluene solution containing 2-allyl anisole to remove impurities; then placing it in a water bath at 10-25℃ and introducing ethylene, adding a mixture containing the catalyst dichlorodicyclopentadiene and the co-catalyst [Ph3C][B(C6F5)4], reacting for 20-40 minutes, adding methanol, cooling to precipitate, filtering and collecting, washing, and drying to obtain the ethylene-2-allyl anisole random copolymer B; wherein, the molar ratio of 2-allyl anisole to the catalyst dichlorodicyclopentadiene is (90-120):1, and the molar ratio of the catalyst dichlorodicyclopentadiene to the co-catalyst [Ph3C][B(C6F5)4] is 1:

1.

7. The aging-resistant BOPP matte film according to claim 1, characterized in that, The auxiliary antioxidant is a phosphite antioxidant or a thioether antioxidant.

8. The aging-resistant BOPP matte film according to claim 1, characterized in that: The smooth layer comprises homopolymer polypropylene and 1-5 wt% anti-blocking agent masterbatch.

9. The aging-resistant BOPP matte film according to claim 1, characterized in that: The total thickness of the aging-resistant BOPP matte film is 10-20 μm; wherein, the thickness of the matte layer is 1-2 μm, and the thickness of the glossy layer is 1-3 μm.

10. A method for preparing an aging-resistant BOPP matte film as described in any one of claims 1-9, characterized in that, Includes the following steps: After the raw materials of each layer are mixed according to the formula, they are added to each extruder. After being metered by the metering pump, the melt of each extruder is combined into a thick sheet at the T-die. The thick sheet is cooled by the cooling roller and then enters the cooling water tank and the blowing chamber. Then it is stretched longitudinally and then stretched laterally in the transverse stretching area to obtain a film. After the film is shaped and corona treated, it is wound up, then aged and slit to obtain the aging resistant BOPP matte film.

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