Aging-resistant high-whiteness bopp matt white label film and preparation method thereof

Abstract

The application relates to an anti-aging high-whiteness BOPP matt white label film and a preparation method thereof, and belongs to the technical field of white label films. The anti-aging high-whiteness BOPP matt white label film comprises a matt layer, a core layer and a smooth layer arranged in sequence; the matt layer comprises random copolymerized polypropylene, 40-45 wt% high-density polyethylene, 2-4 wt% ethylene-2-allyl benzene methyl ether random copolymer and 0.1-0.5 wt% antioxidant; the core layer comprises homopolymerized polypropylene and 10-20 wt% white masterbatch, the white masterbatch comprises homopolymerized polypropylene, 5-10 wt% ultrahigh molecular weight polyethylene and 50-70 wt% surface-modified titanium white powder, and the organic coating agent used in the surface-modified titanium white powder is bis[(3-methyl dimethoxy silyl) propyl] polyoxypropylene. The label film has the advantages of anti-aging, high whiteness, good matt uniformity and good whiteness uniformity.

Description

Technical Field

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

[0002] Biaxially oriented polypropylene (BOPP) matte white label film is a functional BOPP matte film designed specifically for label applications. It presents a white, opaque appearance and a unique matte texture, and is widely used in beverage bottle wrap labels, daily chemical product labels, and high-end product markings.

[0003] BOPP matte white label film evolved from BOPP film (BOPP glossy film) and BOPP matte film. BOPP film, primarily made of polypropylene, suffers from degradation due to the presence of tertiary carbon atoms in its main chain and the low CH bond energy (≈350 kJ / mol). This makes it 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 degradation makes the polypropylene film prone to aging, especially at the two ends of the film roll, which are directly exposed to light, high temperatures, or oxidizing environments, severely impacting its appearance and lifespan. BOPP matte film typically consists of a matte layer and a core layer. The core layer suffers from the aging problems present in BOPP film. The matte layer imparts a rough, matte surface structure, increasing the surface area exposed to air, moisture, and ultraviolet radiation, leading to environmental stress accumulation and accelerating oxidation and chalking. Furthermore, the high proportion of amorphous regions in the matte layer makes it more susceptible to free radical attack. Therefore, BOPP matte film is more prone to aging than ordinary BOPP film (BOPP glossy film), which will affect subsequent processing and applications.

[0004] BOPP matte white label film is based on BOPP matte film, but with the addition of a certain amount of white masterbatch (the effective component being rutile titanium dioxide (TiO2), i.e., titanium dioxide) to the core layer. This gives the film the advantages of high whiteness and strong hiding power, making BOPP matte white label film a core material for beverage bottle wrap labels, daily chemical labels, and high-end markings. However, this type of BOPP matte white label film introduces more prominent and complex aging defects on top of the aging problems of ordinary BOPP matte film. The aging process is faster, and the damage to the film's appearance and whiteness is more significant, severely limiting its application in harsh environments such as outdoor, high-temperature, and high-humidity conditions.

[0005] On the one hand, rutile TiO2, i.e., titanium dioxide, is excited under ultraviolet irradiation, producing hydroxyl radicals (·OH) and superoxide anion radicals (·O2). -The photocatalytic oxidation of rutile TiO2 directly attacks the polypropylene backbone, causing the film to degrade at a faster rate than ordinary matte films, becoming the core cause of accelerated aging. This aging directly exacerbates the deterioration of the film's whiteness and its appearance: under the dual effects of polypropylene degradation caused by rutile TiO2 photocatalysis and the easy oxidation degradation of polypropylene by heat / light / oxygen, the film rapidly exhibits problems such as decreased whiteness, obvious yellowing, graying, color difference, and spots, making it difficult to maintain high whiteness and appearance stability.

[0006] On the other hand, to prevent uneven dispersion or easy high-temperature agglomeration of titanium dioxide, it is generally necessary to modify the surface of titanium dioxide before using it in films. Existing surface-modified titanium dioxide is usually obtained through a gradient coating process, first inorganically coating the titanium dioxide and then organically coating it. Currently, the commonly used organic coating agents are small-molecule silane coupling agents (general formula RSiX3). Although these can form chemical bonds with the titanium dioxide surface, during the actual coating process, some molecules are adsorbed onto the titanium dioxide surface through weaker forces such as van der Waals forces or hydrogen bonds. These molecules are prone to desorption in subsequent processing or usage environments. In particular, the high-temperature melt extrusion and high shear forces in BOPP film production processes can destroy these weakly bonded adsorption "structures" and even some chemically bonded "structures," leading to the migration and precipitation of some silane coupling agents. This affects the uniform dispersion of titanium dioxide in the film layer, resulting in a decrease in the overall whiteness uniformity of the film.

[0007] Therefore, developing a BOPP matte white label film with strong aging resistance, high whiteness, and stability is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] Based on this, the purpose of the present invention is to provide an aging-resistant, high-whiteness BOPP matte white label film and its preparation method. The aging-resistant, high-whiteness BOPP matte white label film has the advantages of aging resistance and high whiteness, and also has good matte uniformity and whiteness uniformity.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] This invention provides an aging-resistant, high-whiteness BOPP matte white label 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, and 0.1-0.5 wt% antioxidant, wherein the content of 2-allyl anisole in the ethylene-2-allyl anisole random copolymer is 14-30 mol. The core layer comprises homopolymer polypropylene and 10-20 wt% white masterbatch, wherein the white masterbatch comprises homopolymer polypropylene, 5-10 wt% ultra-high molecular weight polyethylene (UHMWPE), and 50-70 wt% surface-modified titanium dioxide. The surface-modified titanium dioxide is obtained by gradient coating treatment of titanium dioxide first by inorganic coating and then by organic coating, wherein the organic coating agent used is bis[(3-methyldimethoxysilyl)propyl]polyoxypropylene.

[0011] This invention relates to a high-whiteness, matte white BOPP label film with aging resistance. The matte layer comprises a marine phase of random copolymer polypropylene and an island phase of high-density polyethylene, forming a rough structure with a matte surface. This invention, by adding an antioxidant to the matte layer, can inhibit its aging to a certain extent. Furthermore, considering the potential for thermal decomposition and thermal migration of the antioxidant, which could affect the film's appearance, this invention adds a certain amount of ethylene-2-allyl anisole random copolymer to the matte layer. This synergistic effect with the antioxidant improves the film's aging resistance, ensuring uniform matting and stable appearance. The antioxidant used 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.

[0012] In the ethylene-2-allyl anisole random copolymer, the comonomer 2-allyl anisole has the following structural formula: ; On the one hand, the ethylene-2-allyl anisole random copolymer 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 is an 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.

[0013] The present invention limits the addition amount of the ethylene-2-allyl anisole random copolymer in the matte layer to 2-4 wt%. If the addition amount of the ethylene-2-allyl anisole random copolymer 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 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 will easily lead to film breakage during the subsequent biaxial stretching process, affecting the smoothness of production.

[0014] This invention limits the molar content of 2-allyl anisole in the ethylene-2-allyl anisole random copolymer to 14-30 mol%. The ethylene-2-allyl anisole random copolymer 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 to 14-30 mol% ensures that the ethylene-2-allyl anisole random copolymer can effectively inhibit antioxidant migration; on the other hand, it ensures that the ethylene-2-allyl anisole random copolymer 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.

[0015] The present invention relates to an aging-resistant, high-whiteness BOPP matte white label film. The white masterbatch in the core layer is selected from "surface-modified titanium dioxide that has undergone specific coating treatment". At the same time, a certain amount of ultra-high molecular weight polyethylene is added to the white masterbatch matrix resin, which is beneficial to improving the aging resistance of the film and ensuring the uniformity of whiteness and appearance stability.

[0016] The aging-resistant, high-whiteness BOPP matte white label film of the present invention, wherein the surface-modified titanium dioxide in the white masterbatch of the core layer is obtained by first inorganically coating titanium dioxide and then organically coating it, wherein the organic coating agent used for organic coating is bis[(3-methyldimethoxysilyl)propyl]polyoxypropylene.

[0017] The general structural formula of the bis[(3-methyldimethoxysilyl)propyl]polyoxypropylene is (CH3O)2(CH3)Si-CH2CH2CH2O-[CH2CH(CH3)O] n -CH2CH2CH2-Si(CH3)(OCH3)2, where n is the number of repeating units. The following is a schematic structural formula when n equals 1: ; This invention uses bis[(3-methyldimethoxysilyl)propyl]polyoxypropylene instead of the commonly used silane coupling agent as the organic coating agent. The bis[(3-methyldimethoxysilyl)propyl]polyoxypropylene forms Si-O-Ti chemical bonds with titanium dioxide and inorganic coating layer (i.e., inorganic matter) through the silanes at both ends, which are firmly anchored. Furthermore, its polyoxypropylene segments are similar in structure and have matching solubility parameters with homopolymer polypropylene, which is beneficial to improving the dispersibility and interfacial bonding of white masterbatch in homopolymer polypropylene matrix, improving the coating stability under high temperature and high shear in biaxial stretching process, making it less prone to desorption, migration, and precipitation, and providing good whiteness and dispersion stability, thus ensuring the whiteness uniformity of the film.

[0018] In addition, a certain amount of ultra-high molecular weight polyethylene (UHMWPE) is added to the matrix resin of the white masterbatch. This means the matrix resin of the white masterbatch is composed of homopolymer polypropylene and ultra-high molecular weight polyethylene, rather than a single homopolymer polypropylene. The ultra-high molecular weight polyethylene has extremely high crystallinity, extremely low polarity, and no active hydrogen, enabling it to synergistically construct a dense matrix with homopolymer polypropylene. This hinders the penetration of oxygen, moisture, and TiO2 photogenerated free radicals, reducing the risk of photodegradation, further improving the film's aging resistance, and ensuring the film's whiteness. This invention controls the addition amount of ultra-high molecular weight polyethylene in the white masterbatch to be 5-10 wt%. If the addition amount of ultra-high molecular weight polyethylene is too high, due to the difference in crystal structure and number-average molecular weight between ultra-high molecular weight polyethylene and homopolymer polypropylene (the number-average molecular weight of homopolymer polypropylene is usually below 1 million, while that of ultra-high molecular weight polyethylene is usually in the millions), excessive addition may lead to micro-phase separation after the core layer is blended, preventing the formation of a completely homogeneous system and negatively impacting the dispersion uniformity of the surface-modified titanium dioxide. If the amount of ultra-high molecular weight polyethylene added to the white masterbatch is too low, the ultra-high molecular weight polyethylene cannot synergistically construct a dense matrix with homopolymer polypropylene, thus failing to effectively inhibit TiO2 photocatalytic degradation and having little effect on improving the film's aging resistance.

[0019] 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.

[0020] Further, the preparation method of the ethylene-2-allyl anisole random copolymer 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; 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. Preferably, the molar ratio of 2-allyl anisole to the catalyst titanium dichlorophenoxyacetate is 1000:1.

[0021] Furthermore, the preparation method of the white masterbatch in the core layer includes the following steps: adding the components of the white masterbatch to a continuous internal mixer in proportion, extruding it through a single-screw extruder, and then drawing, pelletizing, and drying the extruded melt to obtain the white masterbatch. Preferably, the processing temperature of the single-screw extruder is set to 170-190℃, and a vacuum is applied at the end to remove volatiles.

[0022] Furthermore, in the core layer, the ultra-high molecular weight polyethylene in the white masterbatch has a number average molecular weight of 2-3 million and a crystallinity of 85-95%, which is beneficial to maintaining the stability of melt extrusion processing performance and synergistically constructing a dense matrix with homopolymer polypropylene, hindering the penetration of oxygen, moisture and TiO2 photogenerated free radicals, reducing the risk of photodegradation, and further improving the film's aging resistance.

[0023] Furthermore, in the core layer, the ultra-high molecular weight polyethylene (UHMWPE) in the white masterbatch has a particle size D50 of 30-100 μm. Powder-grade UHMWPE (with a particle size D50 of 30-100 μm) is preferred to ensure that the UHMWPE can be fully and completely melted during the preparation of the white masterbatch, making it easier to uniformly disperse with the surface-modified titanium dioxide and homopolymer polypropylene.

[0024] Further, in the core layer, the particle size D50 of the surface-modified titanium dioxide in the white masterbatch is 0.2-0.4 μm. More preferably, the particle size D50 of the surface-modified titanium dioxide is 0.25-0.35 μm.

[0025] Furthermore, the preparation method of the surface-modified titanium dioxide (gradient coating treatment method) includes the following steps: inorganically coating titanium dioxide to form an inorganic coating layer on the titanium dioxide, obtaining inorganic coated titanium dioxide; organically coating the inorganic coated titanium dioxide with the organic coating agent (i.e., bis[(3-methyldimethoxysilyl)propyl]polyoxypropylene) to form an organic coating layer on the inorganic coated titanium dioxide, obtaining the surface-modified titanium dioxide (inorganic-organic composite double-layer coated modified titanium dioxide). Because titanium dioxide is rich in hydroxyl groups on its surface, it has poor compatibility with non-polar polypropylene, easily agglomerates, and disperses unevenly. Furthermore, uncoated (i.e., unmodified) titanium dioxide generates strong oxidizing free radicals when excited by ultraviolet light, easily initiating photodegradation, yellowing, and embrittlement of polypropylene. Therefore, gradient coating is necessary to improve compatibility and inhibit photocatalytic activity. The surface-modified titanium dioxide of this invention is obtained by first subjecting titanium dioxide to inorganic coating and then to organic coating in a gradient coating process. The inorganic coating forms a dense barrier layer (i.e., an inorganic coating layer), physically blocking the leakage of photogenerated electrons and holes, thereby reducing the photocatalytic activity of titanium dioxide at the source and decreasing the erosion of polypropylene by free radicals. The subsequent organic coating process enables the titanium dioxide surface to undergo a functional transformation from hydrophilic to oleophilic.

[0026] Furthermore, the titanium dioxide is rutile titanium dioxide, i.e., rutile titanium dioxide; the inorganic coating layer includes one or both of silicon dioxide and aluminum oxide, and the coating amount of the inorganic coating layer is 0.5-2.0 wt% of the titanium dioxide (i.e., the unmodified titanium dioxide); the organic coating layer is bis[(3-methyldimethoxysilyl)propyl]polyoxypropylene, and the coating amount of the organic coating layer is 0.8-1.2 wt% of the titanium dioxide (i.e., the unmodified titanium dioxide).

[0027] Furthermore, the glossy layer comprises homopolymer polypropylene and 1-5 wt% antiblocking masterbatch.

[0028] 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.

[0029] Furthermore, the melt flow index of the homopolymer polypropylene in the core layer, the homopolymer polypropylene in the white masterbatch, the homopolymer polypropylene in the glossy layer, and the homopolymer polypropylene in the antiblocking agent masterbatch, measured under test conditions of 230℃ and 2.16kg, is 3-6g / 10min.

[0030] Furthermore, the total thickness of the aging-resistant high-whiteness BOPP matte white label film is 30-50μm; wherein the thickness of the matte layer is 1.5-3.5μm, and the thickness of the glossy layer is 1.5-3.5μm.

[0031] The present invention also provides a method for preparing any of the above-mentioned anti-aging high whiteness BOPP matte white label films, comprising the following steps: feeding the dried raw materials of each layer to the extruder of each layer according to the proportion, heating and melting and fully plasticizing the melt of each layer to form a co-extrusion die, the co-extruded melt to obtain a thick sheet after rapid cooling, the thick sheet is first stretched longitudinally, then stretched laterally, then shaped and cooled, then measured and corona treated, after corona treatment, the film roll is wound up to obtain a master roll and subjected to aging treatment and slitting to obtain the finished film roll.

[0032] Furthermore, in the above preparation method, the melt extrusion temperature of the matte layer is 240-260℃, the melt extrusion temperature of the core layer and the glossy layer is 220-270℃, and the quenching temperature is 15-40℃; the longitudinal stretching temperature is 110-130℃, and the longitudinal stretching ratio is 4.5-5.7 times; the transverse stretching temperature is 150-160℃, and the transverse stretching ratio is 7.5-10 times; the corona power factor is 20-40W•min / m. Detailed Implementation

[0033] 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.

[0034] The raw materials used in the following examples or comparative examples: (1) Random copolymer polypropylene: melt index is 6.8 g / 10min (test conditions: 230℃, 2.16kg).

[0035] (2) High-density polyethylene: melt index is 11.6 g / 10 min (test conditions: 190℃, 21.6 kg).

[0036] (3) Ethylene-2-allyl anisole random copolymer: 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 pipeline using a three-way stopcock. Ethylene (1 atm) was introduced into the system, and the solution was stirred until 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 an ethylene-2-allyl anisole random copolymer.

[0037] This ethylene-2-allyl anisole random copolymer, using deuterated chloroform as a solvent, through... 1 H NMR analysis showed that the content of 2-allyl anisole in the ethylene-2-allyl anisole random copolymer was 20.89 mol.

[0038] (4) Antioxidant: Antioxidant 1010.

[0039] (5) Homopolymer polypropylene: melt index is 4.5 g / 10 min (test conditions: 230℃, 2.16 kg).

[0040] (6) Ultra-high molecular weight polyethylene: grade B-0340GK, manufacturer: Yanshan Petrochemical, crystallinity is about 90%, number average molecular weight is 2 million, particle size is 30μm.

[0041] (7) Surface-modified titanium dioxide: ① Surface-modified titanium dioxide A: First, an inorganic silica coating layer is formed, with a coating amount of 1 wt% of the titanium dioxide; then, an organic bis[(3-methyldimethoxysilyl)propyl]polyoxypropylene coating layer is formed, with a coating amount of 1 wt% of the titanium dioxide; the particle size D50 of the surface-modified titanium dioxide A after coating is 0.3 μm.

[0042] The specific preparation method of surface-modified titanium dioxide A is as follows: S1. Using rutile titanium dioxide as raw material, titanium dioxide and deionized water are mixed at a mass ratio of 1:4 to form an aqueous slurry with a solid content of 20wt%. Sodium hexametaphosphate, accounting for 0.5wt% of the titanium dioxide mass, is added to the aqueous slurry as a dispersant. The slurry is then dispersed at a high speed of 3000 r / min for 45 min to fully deagglomerate the particles. The initial pH of the slurry is then adjusted to 4.0~4.5 using dilute sulfuric acid. S2. Subsequently, the above slurry is heated to 75°C for inorganic coating: a suitable volume of sodium silicate solution (modulus 3.3, effective SiO2 concentration approximately 28wt%) is slowly added dropwise to the slurry, wherein: the total amount of sodium silicate solution added is 1wt% of the mass of titanium dioxide based on SiO2 (i.e., the SiO2 addition is controlled to be 1wt% of the mass of titanium dioxide), dilute sulfuric acid is used throughout the process to maintain the pH of the system stable at 8.8~9.2, the dropping time is controlled at 2 h, and the system is kept at this temperature for 1.5 hours for curing. h is used to ensure uniform deposition of silicate ions and uniform coating thickness, so that the final actual coating rate, calculated as SiO2, is infinitely close to 1 wt% of the titanium dioxide mass. After the coating reaction, the slurry is washed with deionized water until the conductivity of the filtrate is below 50 μS / cm to remove soluble impurities such as sodium ions and sulfate ions. The solid filter cake is obtained by plate and frame filtration and dried at 150℃ until the moisture content is below 1% (at this point, the material coated on the titanium dioxide is converted into silicon dioxide, which serves as an inorganic coating layer). Finally, the titanium dioxide is pulverized and classified by air jet milling, controlling the particle size D50 to be around 0.3 μm, to obtain inorganic coated titanium dioxide.

[0043] S3. Then, a dry high-speed mixing process is used for surface organic coating: First, the above-mentioned inorganic coated titanium dioxide is put into a high-speed mixer, the mixing speed is set to 2500 r / min, and the heating temperature is raised to 150℃. The powder is preheated and kept at this temperature for 15 minutes to completely remove the surface adsorbed moisture and residual trace moisture, so as to avoid powder agglomeration at high temperature. Then, the organic coating agent (bis[(3-methyldimethoxysilyl)propyl]polyoxypropylene, KANEKA MS Polymer S303H from Zhongyuan Chemical) is added evenly to the mixing chamber in 3-4 portions, with a 5-minute interval between each addition. The mixture is stirred at a constant temperature and high speed for 60 minutes. The mixture is subjected to strong mechanical shearing to ensure uniform spreading and adsorption onto the surface of titanium dioxide particles, thereby forming a stable chemical bond between bis[(3-methyldimethoxysilyl)propyl]polyoxypropylene and the inorganic coating layer. This results in a uniform and dense coated modified titanium dioxide. After mixing, the mixture is slowly cooled to room temperature to prevent the powder from agglomerating due to sudden cooling. Once the material is loose and dry, it is discharged and then subjected to pulverization and grading to control the particle size D50 at 0.3 μm. Finally, inorganic-organic composite double-layer coated modified titanium dioxide, namely surface-modified titanium dioxide A, is obtained.

[0044] ② Surface-modified titanium dioxide B is first coated with an inorganic silica layer, with a coating amount of 1.0 wt% of titanium dioxide, and then coated with an organic layer of small molecule silane coupling agent KH570, with a coating amount of 1.0 wt% of titanium dioxide. The particle size D50 of the coated surface-modified titanium dioxide is 0.3 μm.

[0045] The preparation method of surface-modified titanium dioxide B is basically the same as that of surface-modified titanium dioxide A, except that the small molecule silane coupling agent KH570 is used instead of bis[(3-methyldimethoxysilyl)propyl]polyoxypropylene.

[0046] (8) White masterbatch: ① White Masterbatch A: Composed of 30wt% homopolymer polypropylene, 10wt% ultra-high molecular weight polyethylene and 60wt% surface-modified titanium dioxide A; The preparation method of white masterbatch A is as follows: each component is added to a continuous internal mixer in proportion and then extruded through a single-screw extruder. The processing temperature of the single-screw extruder is set to 180℃. At the same time, a vacuum is drawn at the end to remove volatiles. The extruded melt is then stretched, pelletized and dried to obtain the finished product.

[0047] ② White Masterbatch B: Composed of 32wt% homopolymer polypropylene, 8wt% ultra-high molecular weight polyethylene and 60wt% surface-modified titanium dioxide A; the preparation method of white masterbatch B is the same as that of white masterbatch A.

[0048] ③ White Masterbatch C: Composed of 35wt% homopolymer polypropylene, 5wt% ultra-high molecular weight polyethylene and 60wt% surface-modified titanium dioxide A; the preparation method of white masterbatch C is the same as that of white masterbatch A.

[0049] ④ White Masterbatch D: Composed of 40wt% homopolymer polypropylene and 60wt% surface-modified titanium dioxide A; the preparation method of white masterbatch D is basically the same as that of white masterbatch A: the difference is that ultra-high molecular weight polyethylene is not added.

[0050] ⑤ White Masterbatch E: Composed of 20wt% homopolymer polypropylene, 20wt% ultra-high molecular weight polyethylene and 60wt% surface-modified titanium dioxide A; the preparation method of white masterbatch E is the same as that of white masterbatch A.

[0051] ⑥ White Masterbatch F: Composed of 32wt% homopolymer polypropylene, 8wt% ultra-high molecular weight polyethylene and 60wt% surface-modified titanium dioxide B; the preparation method of white masterbatch F is the same as that of white masterbatch A.

[0052] (9) Anti-blocking agent 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.

[0053] 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

[0054] Specifically, the white masterbatch in Example 1 is white masterbatch A; the white masterbatch in Example 2, Comparative Example 1, and Comparative Example 2 is white masterbatch B; the white masterbatch in Example 3 is white masterbatch C; the white masterbatch in Comparative Example 3 is white masterbatch D; the white masterbatch in Comparative Example 4 is white masterbatch E; and the white masterbatch in Comparative Example 5 is white masterbatch F.

[0055] The following description uses specific examples and comparative models for illustration.

[0056] Example 1 This embodiment provides an aging-resistant, high-whiteness BOPP matte white label 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 and 0.2 wt% antioxidant; Core layer: 85wt% homopolymer polypropylene and 15wt% white masterbatch A; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0057] The preparation method of the aging-resistant high-whiteness BOPP matte white label film in this embodiment includes the following steps: the raw materials of each layer after drying are transported to the extruder of each layer according to the ratio, the melt of each layer formed by heating and melting and fully plasticizing is co-extruded through the co-extrusion die, the co-extruded melt is cooled to obtain a thick sheet, the thick sheet is first stretched longitudinally, then stretched laterally, then shaped and cooled, then the thickness is measured and corona treatment is performed, after the corona treatment, the roll is wound to obtain a master roll and subjected to master aging treatment and slitting to obtain the finished roll of the aging-resistant high-whiteness BOPP matte white label film.

[0058] The melt extrusion temperature of the matte layer is 250℃, the melt extrusion temperature of the core layer and the glossy layer is 260℃, and the quenching temperature is 30℃; the longitudinal stretching temperature is 110℃, and the longitudinal stretching ratio is 5.0 times; the transverse stretching temperature is 155℃, and the transverse stretching ratio is 8 times; the corona power factor is 25W•min / m.

[0059] The aging-resistant, high-whiteness BOPP matte white label film of this embodiment has a total thickness of 35μm; wherein, the thickness of the matte layer is 2.0μm, the thickness of the core layer is 30μm, and the thickness of the glossy layer is 3.0μm.

[0060] Example 2 This embodiment provides an aging-resistant, high-whiteness BOPP matte white label 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 and 0.2wt% antioxidant; Core layer: 85wt% homopolymer polypropylene and 15wt% white masterbatch B; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0061] The preparation method of the aging-resistant, high-whiteness BOPP matte 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 aging-resistant, high-whiteness BOPP matte white label film in this embodiment are the same as those in Example 1.

[0063] Example 3 This embodiment provides an aging-resistant, high-whiteness BOPP matte white label 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 and 0.2wt% antioxidant; Core layer: 85wt% homopolymer polypropylene and 15wt% white masterbatch C; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0064] The preparation method of the aging-resistant, high-whiteness BOPP matte white label film in this embodiment is the same as that in Example 1.

[0065] The total thickness and the thickness of each layer of the aging-resistant, high-whiteness BOPP matte white label film in this embodiment are the same as those in Example 1.

[0066] Comparative Example 1 This comparative example provides a BOPP matte white label film, which is basically the same as the aging-resistant high-whiteness BOPP matte white label film of Example 2, except that: no ethylene-2-allyl anisole random copolymer is added to the matte layer.

[0067] Specifically, the BOPP matte white label film of this comparative example includes a matte layer, a core layer, and a glossy layer arranged in sequence; 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: 85wt% homopolymer polypropylene and 15wt% white masterbatch B; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0068] The preparation method of the BOPP matte white label film in this comparative example is the same as that in Example 1.

[0069] The total thickness and the thickness of each layer of the BOPP matte white label film in this comparative example are the same as those in Example 1.

[0070] Comparative Example 2 This comparative example provides a BOPP matte white label film, which is basically the same as the aging-resistant high-whiteness BOPP matte white label film of Example 2, except that: an excessive amount of ethylene-2-allyl anisole random copolymer is added to the matte layer.

[0071] Specifically, the BOPP matte white label film of this comparative example includes a matte layer, a core layer, and a glossy layer arranged in sequence; 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 and 0.2 wt% antioxidant; Core layer: 85wt% homopolymer polypropylene and 15wt% white masterbatch B; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0072] The preparation method of the BOPP matte white label film in this comparative example is the same as that in Example 1.

[0073] The total thickness and the thickness of each layer of the BOPP matte white label film in this comparative example are the same as those in Example 1.

[0074] Comparative Example 3 This comparative example provides a BOPP matte white label film, which is basically the same as the aging-resistant high-whiteness BOPP matte white label film of Example 2, except that: this comparative example uses white masterbatch D instead of white masterbatch B of Example 2.

[0075] Specifically, the BOPP matte white label film of this comparative example includes a matte layer, a core layer, and a glossy layer arranged in sequence; 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 and 0.2wt% antioxidant; Core layer: 85wt% homopolymer polypropylene and 15wt% white masterbatch D; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0076] The preparation method of the BOPP matte white label film in this comparative example is the same as that in Example 1.

[0077] The total thickness and the thickness of each layer of the BOPP matte white label film in this comparative example are the same as those in Example 1.

[0078] Comparative Example 4 This comparative example provides a BOPP matte white label film, which is basically the same as the aging-resistant high-whiteness BOPP matte white label film of Example 2, except that: this comparative example uses white masterbatch E instead of white masterbatch B of Example 2.

[0079] Specifically, the BOPP matte white label film of this comparative example includes a matte layer, a core layer, and a glossy layer arranged in sequence; 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 and 0.2wt% antioxidant; Core layer: 85 wt% homopolymer polypropylene and 15 wt% white masterbatch E; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

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

[0082] Comparative Example 5 This comparative example provides a BOPP matte white label film, which is basically the same as the aging-resistant high-whiteness BOPP matte white label film of Example 2, except that: this comparative example uses white masterbatch F instead of white masterbatch B of Example 2.

[0083] Specifically, the BOPP matte white label film of this comparative example includes a matte layer, a core layer, and a glossy layer arranged in sequence; 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 and 0.2wt% antioxidant; Core layer: 85 wt% homopolymer polypropylene and 15 wt% white masterbatch F; Smooth surface layer: 98wt% homopolymer polypropylene and 2wt% antiblocking masterbatch.

[0084] The preparation method of the BOPP matte white label film in this comparative example is the same as that in Example 1.

[0085] The total thickness and the thickness of each layer of the BOPP matte white label film in this comparative example are the same as those in Example 1.

[0086] Performance testing The following performance tests were performed on the films of Examples 1-3 and Comparative Examples 1-5 respectively: (1) Whiteness: The whiteness of the film is tested according to GB 2913-1982 "Test Method for Whiteness of Plastics".

[0087] (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.

[0088] (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".

[0089] The specific testing method is as follows: Select a label film with a white end face as a standard sample, place it end-up on the ground, and calibrate it by placing the colorimeter probe stably on the end face. After calibration, test the end face of the sample (i.e., the film roll of each embodiment or comparative example), and confirm the end face color through the ▲E color difference value. The larger the ▲E, the greater the color change. Compare the end 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.

[0090] (4) Appearance - uniformity of whiteness and uniformity of matting: The test was conducted in accordance with GB / T 32021-2015 "Biaxially oriented polypropylene matte film" (6.3 Appearance).

[0091] The specific testing method is as follows: Whiteness uniformity: With the matte layer of the film facing upwards, observe with the naked eye under both natural light and 45° oblique flashlight conditions to check for unevenness in whiteness, color spots, or uneven whiteness. Uniformity of matting: With the matting layer of the film facing upwards, visually inspect it under natural light and under a 45° angled flashlight to check for bright spots, dark spots, uneven matting, frost, and agglomeration.

[0092] 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

[0093] As can be seen from the results in Table 2, the aging-resistant high-whiteness BOPP matte white label films of Examples 1-3 of the present invention have high whiteness, long oxidation induction time, small color difference (i.e., aging resistance), good whiteness uniformity and matte uniformity, and good film production smoothness.

[0094] Comparative Example 1, a BOPP matte white label film, lacks the addition of ethylene-2-allyl anisole random copolymer to its matte layer. The BOPP matte white label film of Comparative Example 1 exhibits a shorter oxidation induction time and greater color difference, indicating that it is prone to aging. Furthermore, the matte uniformity of the BOPP matte white label film of Comparative Example 1 is poor. Comparative Example 1 demonstrates that the absence of ethylene-2-allyl anisole random copolymer in the matte layer hinders the formation of a uniform and dense surface matte structure, thus negatively impacting the film's aging resistance.

[0095] In Comparative Example 2, the BOPP matte white label film contained too much ethylene-2-allyl anisole random copolymer 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 white label film in Comparative Example 2 was too large, resulting in the thick film exhibiting an "incompatible state" and causing film breakage during production.

[0096] In Comparative Example 3, the BOPP matte white label film used in the core layer consisted of 40 wt% homopolymer polypropylene and 60 wt% surface-modified titanium dioxide, without the addition of ultra-high molecular weight polyethylene. The BOPP matte white label film of Comparative Example 3 had a shorter oxidation induction time, larger color difference, and poor aging resistance. The reason for the above performance results is that, since ultra-high molecular weight polyethylene was not added, it could not work with homopolymer polypropylene to form a dense matrix, thus failing to effectively inhibit the photocatalytic degradation caused by titanium dioxide, resulting in poor aging resistance of the film.

[0097] In Comparative Example 4, the BOPP matte white label film used in the core layer consisted of 20 wt% homopolymer polypropylene, 20 wt% ultra-high molecular weight polyethylene, and 60 wt% surface-modified titanium dioxide. The addition of ultra-high molecular weight polyethylene was too high, resulting in film breakage during the production of the BOPP matte white label film in Comparative Example 4. The produced film had poor whiteness uniformity and relatively large color difference. This is because ultra-high molecular weight polyethylene and homopolymer polypropylene have different crystal structures and number-average molecular weights. Adding too much ultra-high molecular weight polyethylene may cause micro-phase separation after the core layer components are blended, making it impossible to form a completely homogeneous system, which is not conducive to the uniform dispersion of surface-modified titanium dioxide.

[0098] In Comparative Example 5, the BOPP matte white label film uses white masterbatch F and surface-modified titanium dioxide B in its core layer. The titanium dioxide is organically coated using the conventional small-molecule silane coupling agent KH570 as the organic coating agent. Comparative Example 5 exhibits poor whiteness uniformity and significant color variation in its BOPP matte white label film. This is because the small-molecule silane coupling agent KH570 is prone to desorption, migration, and precipitation, leading to poor dispersion stability of the titanium dioxide, resulting in poor whiteness uniformity and affecting the color variation of the film.

[0099] 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. A high-whiteness, age-resistant BOPP matte white label 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, and 0.1-0.5 wt% antioxidant; the content of 2-allyl anisole in the ethylene-2-allyl anisole random copolymer is 14-30 mol%; 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; The core layer comprises homopolymer polypropylene and 10-20 wt% white masterbatch, wherein the white masterbatch comprises homopolymer polypropylene, 5-10 wt% ultra-high molecular weight polyethylene and 50-70 wt% surface-modified titanium dioxide; the surface-modified titanium dioxide is obtained by gradient coating treatment of titanium dioxide first inorganically and then organically, wherein the organic coating agent used for organic coating is bis[(3-methyldimethoxysilyl)propyl]polyoxypropylene.

2. The aging-resistant, high-whiteness BOPP matte white label 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, high-whiteness BOPP matte white label film according to claim 1, characterized in that, The preparation method of the ethylene-2-allyl anisole random copolymer 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; 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, high-whiteness BOPP matte white label film according to claim 1, characterized in that, The preparation method of the white masterbatch includes the following steps: adding each component to a continuous internal mixer in proportion, extruding it through a single screw extruder, and then drawing, pelletizing and drying the extruded melt to obtain the white masterbatch.

5. The aging-resistant, high-whiteness BOPP matte white label film according to claim 1, characterized in that, The number average molecular weight of the ultra-high molecular weight polyethylene is 2-3 million; the crystallinity of the ultra-high molecular weight polyethylene is 85-95%; and the particle size D50 of the ultra-high molecular weight polyethylene is 30-100 μm.

6. The aging-resistant, high-whiteness BOPP matte white label film according to claim 1, characterized in that, The particle size D50 of the surface-modified titanium dioxide is 0.2-0.4 μm.

7. The aging-resistant, high-whiteness BOPP matte white label film according to claim 1, characterized in that, The preparation method of the surface-modified titanium dioxide includes the following steps: Inorganic coating treatment is performed on titanium dioxide to form an inorganic coating layer on the titanium dioxide, thereby obtaining inorganic coated titanium dioxide; wherein the coating amount of the inorganic coating layer is 0.5-2.0 wt% of the titanium dioxide, and the inorganic coating layer includes one or two of silicon dioxide and aluminum oxide; The inorganic coated titanium dioxide is subjected to organic coating treatment with the organic coating agent to form an organic coating layer on the inorganic coated titanium dioxide, thereby obtaining the surface-modified titanium dioxide; wherein the coating amount of the organic coating layer is 0.8-1.2 wt% of the titanium dioxide.

8. The aging-resistant, high-whiteness BOPP matte white label film according to claim 1, characterized in that, The total thickness of the aging-resistant, high-whiteness BOPP matte white label film is 30-50 μm; wherein, the thickness of the matte layer is 1.5-3.5 μm, and the thickness of the glossy layer is 1.5-3.5 μm.

9. A method for preparing an aging-resistant, high-whiteness BOPP matte white label film as described in any one of claims 1-8, characterized in that, Includes the following steps: According to the formula, the dried raw materials of each layer are transported to the extruder of each layer. The melt of each layer is heated, melted and fully plasticized and then co-extruded through the co-extrusion die. The co-extruded melt is cooled to obtain a thick sheet. The thick sheet is first stretched longitudinally and then stretched laterally. Then it is shaped and cooled. Next, it is measured and corona treated. After corona treatment, it is wound up to obtain a master roll and then aged and cut to obtain the finished film roll.

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