White masterbatch for high-rigidity and high-heat-resistance bopp film and preparation method and application thereof

Abstract

The application relates to a white master batch for high-stiffness high-heat-resistance BOPP film, a preparation method and application thereof, and belongs to the technical field of white master batches. The white master batch for high-stiffness high-heat-resistance BOPP film comprises polypropylene, 60-70 wt% titanium white powder, 3-7 wt% boehmite and 0.15-0.35 wt% aluminum-titanium bimetallic composite coupling agent; the aluminum-titanium bimetallic composite coupling agent is obtained by reacting acrylic acid polymer with butyl titanate and polyaluminum chloride-propylene glycol complex, wherein the number average molecular weight of the acrylic acid polymer is 3000-5000, the molar ratio of the carboxyl in the acrylic acid polymer to the butyl titanate is 1:(1.05-1.1), and the mass ratio of the butyl titanate to the polyaluminum chloride-propylene glycol complex is (1.4-2):1. The BOPP film prepared from the white master batch for high-stiffness high-heat-resistance BOPP film has the characteristics of high stiffness and high heat resistance.

Description

Technical Field

[0001] This invention relates to the field of white masterbatch technology, and in particular to a white masterbatch for high stiffness and high heat resistance BOPP film, its preparation method and application. Background Technology

[0002] White labels are a common application of biaxially oriented polypropylene (BOPP) film. By adding white masterbatch to BOPP film, it is given high whiteness and low transmittance, resulting in printed BOPP film with distinct colors and clearly visible text or patterns, thus producing white labels that fully showcase product brands or various information.

[0003] In existing technologies, the white masterbatch added to BOPP films is typically composed of 60-70 wt% titanium dioxide and 30-40 wt% polypropylene, making it a polypropylene composite material with a high proportion of inorganic fillers. In industrial production, twin-screw extruders are mostly used to fully disperse and mix the titanium dioxide and polypropylene before granulation to obtain the white masterbatch.

[0004] Current technologies primarily focus on whether white masterbatches can be uniformly dispersed when used in the preparation of BOPP films and whether the final BOPP film meets the requirements for high whiteness and low light transmittance. No new white masterbatches have been developed to address other needs of BOPP films. The addition of white masterbatches to BOPP films is typically for white labels. For white labels to effectively convey information and ensure good visual appeal, post-processing steps such as printing on the BOPP film are necessary. Furthermore, in addition to traditional processing methods, the emerging in-mold labeling process places higher demands on the stiffness and heat resistance of these BOPP films, beyond just the basic appearance and printing quality of white labels. Moreover, even with traditional processing methods, to optimize production efficiency and cost, these BOPP films must maintain excellent mechanical properties even as they become thinner. Therefore, the addition of white masterbatches to BOPP films must consider not only their uniform dispersion and whether the final BOPP film meets the requirements for high whiteness and low light transmittance, but also whether the addition of white masterbatches improves the stiffness and heat resistance of the BOPP film.

[0005] Therefore, developing a white masterbatch specifically for BOPP film (especially BOPP film used for white labels) that can improve the stiffness and heat resistance of BOPP film is a problem worth exploring. Summary of the Invention

[0006] Based on this, the purpose of this invention is to provide a white masterbatch for high stiffness and high heat resistance BOPP film, its preparation method, and its application. When used to prepare BOPP film, the white masterbatch for high stiffness and high heat resistance can impart high stiffness (high mechanical strength) and high heat resistance to the BOPP film. The high stiffness (high mechanical strength) refers to the fact that, under the same thickness and the same amount of titanium dioxide, the tensile modulus of the BOPP film with the addition of the white masterbatch for high stiffness and high heat resistance of this invention is significantly higher than that of the BOPP film with the addition of ordinary white masterbatch, under the same test conditions and with the same thickness and the same amount of titanium dioxide. The high heat resistance refers to the fact that, under the same test conditions, the warpage of the BOPP film with the addition of the white masterbatch for high stiffness and high heat resistance of this invention is significantly lower than that of the BOPP film with ordinary white masterbatch, under the same test conditions and with the same thickness and the same amount of titanium dioxide.

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

[0008] This invention provides a white masterbatch for high stiffness and high heat resistance BOPP film, comprising polypropylene, 60-70 wt% titanium dioxide, 3-7 wt% boehmite (γ-crystalline hydrated alumina), and 0.15-0.35 wt% aluminum-titanium bimetallic composite coupling agent; the aluminum-titanium bimetallic composite coupling agent is obtained by reacting an acrylic polymer with tetrabutyl titanate and a polyaluminum chloride-propylene glycol complex, wherein the number average molecular weight of the acrylic polymer is 3000-5000, the molar ratio of the carboxyl groups in the acrylic polymer to the tetrabutyl titanate is 1:(1.05-1.1), and the mass ratio of the tetrabutyl titanate to the polyaluminum chloride-propylene glycol complex is (1.4-2):1.

[0009] This invention uses polypropylene as the base resin of the white masterbatch for high stiffness and high heat resistance BOPP film, which allows the white masterbatch for high stiffness and high heat resistance BOPP film to have a certain fluidity, which is beneficial to ensuring the adaptability of the white masterbatch for high stiffness and high heat resistance BOPP film in BOPP film, and to ensuring that the components in the white masterbatch for high stiffness and high heat resistance BOPP film are fully mixed with the base resin (polypropylene) of BOPP film.

[0010] This invention adds 60-70 wt% titanium dioxide to the white masterbatch for high-stiffness and high-heat-resistant BOPP film to provide the high whiteness and low light transmittance required for BOPP film. If the content of titanium dioxide in the white masterbatch for high-stiffness and high-heat-resistant BOPP film is too low, an excessive amount of the white masterbatch needs to be added to ensure that the white masterbatch for high-stiffness and high-heat-resistant BOPP film achieves the desired high whiteness and low light transmittance when used to prepare BOPP film, which is detrimental to the flexibility of BOPP film formulation design. If the content of titanium dioxide in the white masterbatch for high stiffness and high heat resistance BOPP film is too high, the titanium dioxide will have poor dispersibility in the matrix resin (i.e., polypropylene) of the white masterbatch, resulting in poor flowability of the white masterbatch itself. When the white masterbatch for high stiffness and high heat resistance BOPP film is used to prepare BOPP film, it will be difficult for the white masterbatch for high stiffness and high heat resistance BOPP film to flow smoothly in the casting process during BOPP film production, thus failing to disperse evenly in the thick sheet. It may even cause the extruder die head to become clogged or the film to break during BOPP film production.

[0011] This invention improves the stiffness and heat resistance of BOPP films by adding 3-7 wt% boehmite (γ-crystalline hydrated alumina) to a white masterbatch for high stiffness and high heat resistance. Specifically, when this white masterbatch is used to prepare BOPP films, the high hardness (Mohs hardness 3.5) of boehmite contributes to improved stiffness, while its extremely high thermal decomposition temperature (>400℃) enhances the heat resistance of the BOPP film. If the boehmite content in the white masterbatch for high stiffness and high heat resistance BOPP film is too low, when the white masterbatch for high stiffness and high heat resistance BOPP film is used to prepare BOPP film, its contribution to the tensile modulus and heat resistance temperature of BOPP film is insufficient, and the performance improvement is not significant. If the boehmite content in the white masterbatch for high stiffness and high heat resistance BOPP film is too high, it is not conducive to the uniformity of boehmite dispersion. Moreover, since boehmite itself has a certain aspect ratio and is not a spherical inorganic material, too high a content can easily cause damage to the BOPP film, and may even cause film breakage during the biaxial stretching preparation process.

[0012] This invention further considers that boehmite is a highly polar inorganic material with a surface rich in hydroxyl groups. The polarity difference between boehmite and the matrix resin polypropylene in the white masterbatch is significant, and boehmite is highly prone to agglomeration. To ensure that boehmite is uniformly dispersed in the matrix resin polypropylene without agglomeration, this invention introduces a self-made "amphiphilic substance" as a bridge "connecting" the highly polar inorganic material (i.e., boehmite) and the non-polar organic material (i.e., polypropylene). This invention coats the boehmite by adding a self-made high-molecular-weight aluminum-titanium bimetallic composite coupling agent, fully utilizing the role of the aluminum-titanium bimetallic composite coupling agent as an "amphiphilic substance" to connect boehmite and polypropylene, thereby improving the uniform dispersion of boehmite in polypropylene without agglomeration. This invention specifies that the aluminum-titanium bimetallic composite coupling agent is obtained by reacting an acrylic polymer with a number average molecular weight of 3000-5000 with tetrabutyl titanate and the polyaluminum chloride-propylene glycol complex. The molar ratio of carboxyl groups in the acrylic polymer to tetrabutyl titanate is specified as 1:(1.05-1.1), and the mass ratio of tetrabutyl titanate to the polyaluminum chloride-propylene glycol complex is specified as (1.4-2):1. Through these specifications, during the reaction, tetrabutyl titanate reacts with all carboxyl groups in the acrylic polymer, and then the polyaluminum chloride-propylene glycol complex further reacts with the groups formed by the reaction of tetrabutyl titanate and carboxyl groups on the acrylic polymer molecular chain, thereby obtaining the high molecular weight aluminum-titanium bimetallic composite coupling agent of this invention. The present invention further incorporates the aluminum-titanium bimetallic composite coupling agent at 0.15-0.35 wt% of the white masterbatch for high stiffness and high heat resistance BOPP film, wherein the aluminum-titanium bimetallic composite coupling agent has a group on one end (e.g., -(OC4H) introduced by tetrabutyl titanate). 9) The chlorine introduced by the polyaluminum chloride-propylene glycol complex can react with the hydroxyl groups on the surface of boehmite and be fixed on the surface of boehmite. The polymer segment of the acrylic polymer at the "other end" of the aluminum-titanium bimetallic composite coupling agent can be compatible with polypropylene. This allows the boehmite to be uniformly dispersed in the polypropylene (matrix resin) in the BOPP film when the white masterbatch for high stiffness and high heat resistance of BOPP film is used to prepare BOPP film. This can both give full play to the heat resistance effect of adding boehmite from the white masterbatch for high stiffness and high heat resistance of BOPP film to BOPP film and avoid the film breakage caused by the agglomeration of boehmite during the production of BOPP film.

[0013] Furthermore, compared to common aluminate or titanate coupling agents with fewer than 10 carbon atoms in the alkane segment, the high molecular weight aluminum-titanium bimetallic composite coupling agent of this invention has a longer alkane chain, a larger molecular weight, and better thermal stability. It is less prone to precipitation or migration during the processing and transportation of the finished product, making BOPP films containing the high-stiffness, high-heat-resistant white masterbatch for BOPP films better suited for various white label applications. This invention selects an acrylic polymer with a number-average molecular weight of 3000-5000 to prepare the aluminum-titanium bimetallic composite coupling agent to ensure the reactivity and compatibility with polypropylene of the prepared high molecular weight aluminum-titanium bimetallic composite coupling agent. When the number average molecular weight of the acrylic polymer is less than 3000, the difference between the alkane chain length of the polymer in the prepared aluminum-titanium bimetallic composite coupling agent and the alkane chain length of the polypropylene in the BOPP film is too large, resulting in poor compatibility between the aluminum-titanium bimetallic composite coupling agent and the polypropylene in the BOPP film, which is not conducive to the dispersion of boehmite in the matrix resin after coating. When the number average molecular weight of the acrylic polymer exceeds 5000, the mobility of the finally synthesized aluminum-titanium bimetallic composite coupling agent will decrease, making it difficult to interact effectively with boehmite, resulting in poor coating effect on boehmite. This invention specifies that the aluminum-titanium bimetallic composite coupling agent is prepared by reacting the acrylic polymer with a molar ratio of carboxyl groups to tetrabutyl titanate of 1:(1.05-1.1) and a mass ratio of tetrabutyl titanate to the polyaluminum chloride-propylene glycol complex of (1.4-2):1. This ensures that the carboxyl groups in the acrylic polymer react completely, making the performance and quality of the prepared aluminum-titanium bimetallic composite coupling agent controllable and avoiding the presence of unstable carboxyl groups in the aluminum-titanium bimetallic composite coupling agent, which could lead to other adverse reactions during subsequent processing. This invention limits the content of the aluminum-titanium bimetallic composite coupling agent in the white masterbatch for high stiffness and high heat resistance BOPP film to 0.15-0.35 wt%. If the content of the aluminum-titanium bimetallic composite coupling agent in the white masterbatch for high stiffness and high heat resistance BOPP film is too low, the effect of improving the stiffness and heat resistance of the film will not be significant; if the content of the aluminum-titanium bimetallic composite coupling agent in the white masterbatch for high stiffness and high heat resistance BOPP film is too high, the aluminum-titanium bimetallic composite coupling agent is prone to precipitation, affecting the surface printing performance of the BOPP film.

[0014] Furthermore, the polypropylene in the white masterbatch for high stiffness and high heat resistance BOPP film is homopolymer polypropylene, which has a melt index of 2-5 g / 10min at 230℃ and a load of 2.16 kg. By selecting the above-mentioned polypropylene as the matrix resin of the white masterbatch for high stiffness and high heat resistance BOPP film, the adaptability of the white masterbatch for high stiffness and high heat resistance BOPP film in the biaxial stretching production process of BOPP film can be guaranteed when the white masterbatch for high stiffness and high heat resistance BOPP film is used to prepare BOPP film; if the melt index of polypropylene is too high, it will lead to insufficient melt strength, which will not meet the production requirements of BOPP film.

[0015] Furthermore, the surface of the titanium dioxide is coated with both inorganic and organic materials, and the average particle size D50 of the titanium dioxide is 200-300 nm. During the preparation process, titanium dioxide may have lattice defects on its surface. These defects are typically addressed by coating it with inorganic materials such as alumina or zirconium oxide to block light contact, reduce its photoactivity, and ensure its weather resistance. In addition, since titanium dioxide is an inorganic material with a significant difference in polarity from polypropylene, an organic layer such as a silane coupling agent is usually coated on its surface to help it disperse uniformly in polypropylene resin. This invention uses commercially available general-purpose plastic-specific titanium dioxide, whose surface has both inorganic and organic coatings. Furthermore, by adding titanium dioxide with an average particle size D50 in the range of 200-300 nm, visible light can be effectively scattered, ensuring high whiteness and low light transmittance in the film product.

[0016] As a specific implementation, the titanium dioxide surface has a 1 wt% inorganic coating. Commonly used inorganic materials are alumina and / or zirconium oxide, which can compensate for lattice defects in titanium dioxide, forming a "protective film" on the titanium dioxide surface. This shields the photoactivity of the titanium dioxide, preventing yellowing and degradation of polypropylene. The content of this inorganic material is usually controlled at around 1 wt% because most plastics are not used in environments with prolonged outdoor exposure, and the requirements for weather resistance are relatively low. Adding 1 wt% is sufficient to meet the weather resistance requirements in most application scenarios. Excessive addition would result in performance overkill and increased costs, which is something commercially available products should avoid as much as possible. The titanium dioxide surface of this invention also has approximately 0.5 wt% organic coating, typically using a silane coupling agent. These organic materials have high reactivity and good coating effect, helping the titanium dioxide to disperse uniformly in polypropylene. Furthermore, titanium dioxide primarily achieves its white visual effect by effectively reflecting visible light from its surface. Therefore, while the organic coating on the titanium dioxide surface should meet dispersion requirements, excessive organic coating is not advisable to avoid creating an overly thick organic coating layer, which would impair effective reflection of visible light and ultimately affect its white visual effect. It should also be noted that the titanium dioxide in the white masterbatch added to the BOPP film is generally a general-purpose plastic-specific titanium dioxide that has undergone both inorganic and organic coating. This invention does not impose specific limitations on the content of inorganic or organic coatings on its surface; those skilled in the art can select specific general-purpose plastic-specific titanium dioxide according to actual conditions.

[0017] Furthermore, the average particle size D50 of the boehmite is 1.5-3.5 μm. When the white masterbatch for high stiffness and high heat resistance BOPP film is used to prepare BOPP film, the relatively large average particle size D50 (1.5-3.5 μm) of the boehmite causes a cavitation effect during the biaxial stretching process of the BOPP film, scattering the visible light entering the BOPP film, further ensuring the light-shielding ability of the final BOPP film, and working in conjunction with titanium dioxide to meet the high whiteness and low light transmittance required by the BOPP film. This invention selects commercially available boehmite with an average particle size D50 ranging from 1.5 to 3.5 μm. If the average particle size D50 of the boehmite is too small, the white masterbatch for high stiffness and high heat resistance of BOPP film will not adequately improve the tensile modulus and heat resistance of the BOPP film when used to prepare the BOPP film. At the same time, it will not be able to form a cavitation structure in the BOPP film, thus affecting the scattering effect of visible light entering the BOPP film and failing to effectively achieve the light-blocking effect. If the average particle size D50 of the boehmite is too large, the white masterbatch for high stiffness and high heat resistance of BOPP film (generally used in the non-surface layer of BOPP film) will easily affect the interlayer bonding force of the BOPP film, and will also easily lead to the formation of protrusions on the surface of the BOPP film, affecting the film quality. It will also easily form stress concentration points during the biaxial stretching process of the BOPP film, causing film breakage.

[0018] Furthermore, the synthesis method of the acrylic polymer includes the following steps: adding an organic solvent to a reaction vessel, purging with nitrogen, raising the temperature to 60-70°C under mechanical stirring, then adding acrylic monomers, followed by adding a free radical initiator and reacting for 2-4 hours, filtering, and drying to obtain the acrylic polymer. By adopting the above scheme, acrylic polymers with a number average molecular weight of 3000-5000 can be prepared. Those skilled in the art will readily understand that the number average molecular weight of acrylic polymers is mainly controlled by the reaction temperature and reaction time; if the reaction temperature is too low and the reaction time is too short, the monomer reactivity is insufficient, polymerization is not easy to occur or the degree of polymerization is low, resulting in a lower number average molecular weight of the obtained acrylic polymer; if the reaction temperature is too high and the reaction time is too long, explosive polymerization is likely to occur, resulting in a higher number average molecular weight of the obtained acrylic polymer.

[0019] Further, the preparation method of the polyaluminum chloride-propylene glycol complex includes the following steps: adding polyaluminum chloride and water into a reaction vessel, and after the polyaluminum chloride dissolves, adding methanol and heating to reflux at 75-85°C, then adding 1,2-propanediol, refluxing reaction, filtering, and drying to obtain the polyaluminum chloride-propylene glycol complex.

[0020] Further, the preparation method of the aluminum-titanium bimetallic composite coupling agent includes the following steps: adding the acrylic polymer to a reaction vessel, then adding 1,2-propanediol to dissolve the acrylic polymer, then adding the tetrabutyl titanate, and reacting at 100-110°C; then adding the polyaluminum chloride-propylene glycol complex, and reacting at 100-110°C, the resulting pale yellow solid is the aluminum-titanium bimetallic composite coupling agent. During the reaction, the tetrabutyl titanate reacts with some of the carboxyl groups in the acrylic polymer, and then the polyaluminum chloride-propylene glycol complex further reacts with the "groups formed by the reaction of tetrabutyl titanate and carboxyl groups" on the acrylic polymer molecular chain, thereby obtaining the high molecular weight aluminum-titanium bimetallic composite coupling agent of the present invention.

[0021] Furthermore, the white masterbatch for high-stiffness and high-heat-resistant BOPP film also includes 0.05-0.25 wt% antioxidant. The addition of antioxidant protects the polypropylene and reduces thermo-oxidative degradation during processing. Preferably, the antioxidant is a composite antioxidant (i.e., a combination of primary and secondary antioxidants) commonly used in polypropylene processing, avoiding the cumbersome steps of adding primary and secondary antioxidants separately. Additionally, the white masterbatch for high-stiffness and high-heat-resistant BOPP film of this invention is produced using internal mixing at a relatively low processing temperature; therefore, most of the antioxidant remains in the white masterbatch, eliminating the need for separate addition of antioxidants during subsequent BOPP film production.

[0022] The present invention also provides a method for preparing a white masterbatch for high stiffness and high heat resistance BOPP film as described above, comprising the following steps: adding each component in proportion to a continuous internal mixer, and extruding and granulating the mixture through a single screw extruder to obtain the finished product.

[0023] This invention also provides the application of any of the above-described high-stiffness, high-heat-resistant BOPP film white masterbatches in high-stiffness, high-heat-resistant BOPP films. When the high-stiffness, high-heat-resistant BOPP film white masterbatch of this invention is used to prepare BOPP films, the prepared BOPP films can have the characteristics of high stiffness (high mechanical strength) and high heat resistance, that is, a high-stiffness, high-heat-resistant BOPP film is obtained.

[0024] As a preferred embodiment, the high-stiffness, high-heat-resistant BOPP film comprises, in sequence, an upper surface layer, a lower surface layer, a core layer, a lower surface layer, and a bottom surface layer; both the upper and lower surface layers comprise polypropylene and 5 wt% anti-blocking masterbatch; the thickness of both the upper and lower surface layers is 3 μm; both the lower and upper surface layers comprise polypropylene and 25 wt% of any of the aforementioned high-stiffness, high-heat-resistant BOPP film white masterbatch; the thickness of the lower and upper surface layers is 5 μm; the core layer comprises polypropylene and 50 wt% pearlescent masterbatch; the thickness of the core layer is 44 μm. The above embodiment represents only one specific method, and those skilled in the art can select and adjust it according to actual circumstances.

[0025] Furthermore, the polypropylene in the upper surface layer, the upper sub-surface layer, the core layer, the lower sub-surface layer, and the lower surface layer is homopolymer polypropylene, preferably the same as the polypropylene in the white masterbatch for high stiffness and high heat resistance BOPP film; the pearlescent masterbatch is composed of 60wt% calcium carbonate and 40wt% polypropylene, and the polypropylene in the pearlescent masterbatch is homopolymer polypropylene, preferably the same as the polypropylene in the white masterbatch for high stiffness and high heat resistance BOPP film. Detailed Implementation

[0026] 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.

[0027] In the following embodiments or comparative examples:

[0028] Polypropylene: Guangxi Petrochemical Polypropylene L5D98C;

[0029] Titanium dioxide: Chemours titanium dioxide R-104;

[0030] Boehmite: Yishitong hydrated alumina BG-403;

[0031] Aluminate coupling agent: Hangzhou Jessica Chemical Aluminate Coupling Agent HY-980;

[0032] Titanate coupling agent: Hangzhou Jessica Chemical Titanate Coupling Agent HY-130;

[0033] Antioxidant: Lianlong Antioxidant B215;

[0034] Aluminum-titanium bimetallic composite coupling agent:

[0035] The preparation method of the (self-made) aluminum-titanium bimetallic composite coupling agent in the embodiments or comparative examples of the present invention includes the following steps:

[0036] (1) The specific method for synthesizing acrylic polymer is as follows:

[0037] 500 mL of n-hexane was added to a 1 L three-necked flask as a solvent, and nitrogen gas was introduced for protection. The system temperature was raised to 65 °C under mechanical stirring. After the temperature stabilized, 100 mL of acrylic acid monomer was added, and stirring continued for 10 minutes. Then, 0.5 mL of azobisisobutyronitrile (AIBN) free radical initiator was added dropwise over 5 minutes. Stirring continued for 3 hours, followed by filtration and drying to obtain an acrylic polymer with a specific molecular weight. It should be noted that the number-average molecular weight of the acrylic polymer used in the preparation of the aluminum-titanium bimetallic coupling agent in each example or comparative example should be specifically referred to in each example, comparative example, and Table 1. Those skilled in the art can control the molecular weight of the acrylic polymer, mainly by adjusting the reaction temperature and reaction time, which will not be elaborated here.

[0038] The chemical reaction formula for the above-mentioned synthesis of acrylic polymer can be simplified as follows:

[0039]

[0040] (2) The specific method for preparing polyaluminum chloride-propylene glycol complex is as follows:

[0041] Add 45 g of polymeric aluminum chloride (industrial grade) and 30 mL of water to a three-necked flask, add mechanical stirring, and install a reflux condenser. After the polymeric aluminum chloride is fully dissolved, add 120 mL of methanol, heat to reflux at 80 °C, then add 10.2 mL of 1,2-propanediol, reflux for 1 h, filter, and dry to obtain the desired aluminum alkoxide complex (average molecular weight 236 g / mol).

[0042] The chemical reaction formula for preparing the polyaluminum chloride-propylene glycol complex is simplified as follows:

[0043]

[0044] (3) Preparation of aluminum-titanium bimetallic composite coupling agent:

[0045] Weigh out an acrylic polymer containing 1 mol of carboxyl groups and add it to a three-necked flask. Then add 100 mL of 1,2-propanediol and let it dissolve completely. Then slowly add 1.05 mol (357 g) of tetrabutyl titanate. After reacting at 105 °C for 50 min, add 247.8 g of the polyaluminum chloride-propanediol complex from step (2) and continue to react at 105 °C for 2 h. The resulting pale yellow solid is the aluminum-titanium bimetallic composite coupling agent.

[0046] During the reaction, the tetrabutyl titanate reacts with some of the carboxyl groups in the acrylic polymer, and then the polyaluminum chloride-propylene glycol complex further reacts with the "groups formed by the reaction of tetrabutyl titanate and carboxyl groups" on the acrylic polymer molecular chain to obtain an aluminum-titanium bimetallic composite coupling agent.

[0047] The chemical reaction formula for preparing the aluminum-titanium bimetallic composite coupling agent described above is simplified as follows (wherein, the product formed after each carboxyl group on the acrylic polymer reacts completely with tetrabutyl titanate is then reacted with the polyaluminum chloride-propylene glycol complex to finally obtain the aluminum-titanium bimetallic composite coupling agent):

[0048]

[0049] The following formula illustrates the reaction between the aluminum-titanium bimetallic composite coupling agent and boehmite. The aluminum-titanium bimetallic composite coupling agent reacts with the hydroxyl groups on the surface of the boehmite, allowing the coupling agent to coat the surface of the boehmite, ultimately forming a layer of "aluminum-titanium bimetallic composite coupling agent" on the surface of the boehmite. Furthermore, the acrylic polymer segments in the aluminum-titanium bimetallic composite coupling agent within the scope of this invention are compatible with the matrix resin (polypropylene), resulting in uniform dispersion of the boehmite.

[0050]

[0051] Based on the above information, the following embodiments and comparative examples are further described below:

[0052] Example 1

[0053] This embodiment provides a white masterbatch for high stiffness and high heat resistance BOPP film. Please refer to Table 1. It includes the following components: 29.5 wt% homopolymer polypropylene, 65 wt% titanium dioxide, 5 wt% boehmite, 0.25 wt% aluminum-titanium bimetallic composite coupling agent (the number average molecular weight of the acrylic polymer used in the preparation is 4000) and 0.25 wt% antioxidant.

[0054] The preparation method of the white masterbatch for high stiffness and high heat resistance BOPP film in this embodiment includes the following steps: adding each component to a continuous internal mixer in proportion, setting the processing temperature to 180°C, and extruding and granulating the mixture through a single screw extruder to obtain the finished product.

[0055] Example 2

[0056] This embodiment provides a white masterbatch for high stiffness and high heat resistance BOPP film. Please refer to Table 1. It includes the following components: 31.6 wt% homopolymer polypropylene, 65 wt% titanium dioxide, 3 wt% boehmite, 0.15 wt% aluminum-titanium bimetallic composite coupling agent (the number average molecular weight of the acrylic polymer used in the preparation is 3000) and 0.25 wt% antioxidant.

[0057] The preparation method of the white masterbatch for high stiffness and high heat resistance BOPP film in this embodiment is the same as that in Example 1.

[0058] Example 3

[0059] This embodiment provides a white masterbatch for high stiffness and high heat resistance BOPP film. Please refer to Table 1. It includes the following components: 27.4 wt% homopolymer polypropylene, 65 wt% titanium dioxide, 7 wt% boehmite, 0.35 wt% aluminum-titanium bimetallic composite coupling agent (the number average molecular weight of the acrylic polymer used in the preparation is 5000) and 0.25 wt% antioxidant.

[0060] The preparation method of the white masterbatch for high stiffness and high heat resistance BOPP film in this embodiment is the same as that in Example 1.

[0061] Comparative Example 1

[0062] This comparative example provides a white masterbatch, as shown in Table 1, comprising the following components: 29.5 wt% homopolymer polypropylene, 65 wt% titanium dioxide, 5 wt% boehmite, 0.25 wt% aluminum-titanium bimetallic composite coupling agent (the number average molecular weight of the acrylic polymer used in preparation is 1500), and 0.25 wt% antioxidant.

[0063] The preparation method of the white masterbatch in this comparative example is the same as that in Example 1.

[0064] Comparative Example 2

[0065] This comparative example provides a white masterbatch, as shown in Table 1, comprising the following components: 29.5 wt% homopolymer polypropylene, 65 wt% titanium dioxide, 5 wt% boehmite, 0.25 wt% aluminum-titanium bimetallic composite coupling agent (the number average molecular weight of the acrylic polymer used in the preparation is 6000), and 0.25 wt% antioxidant.

[0066] The preparation method of the white masterbatch in this comparative example is the same as that in Example 1.

[0067] Comparative Example 3

[0068] This comparative example provides a white masterbatch, as shown in Table 1, comprising the following components: 24.5 wt% homopolymer polypropylene, 65 wt% titanium dioxide, 10 wt% boehmite, 0.25 wt% aluminum-titanium bimetallic composite coupling agent (the number average molecular weight of the acrylic polymer used in preparation is 4000), and 0.25 wt% antioxidant.

[0069] The preparation method of the white masterbatch in this comparative example is the same as that in Example 1.

[0070] Comparative Example 4

[0071] This comparative example provides a white masterbatch, as shown in Table 1, comprising the following components: 33.5 wt% homopolymer polypropylene, 65 wt% titanium dioxide, 1 wt% boehmite, 0.25 wt% aluminum-titanium bimetallic composite coupling agent (the number average molecular weight of the acrylic polymer used in preparation is 4000), and 0.25 wt% antioxidant.

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

[0073] Comparative Example 5

[0074] This comparative example provides a white masterbatch, as shown in Table 1, comprising the following components: 28.75 wt% homopolymer polypropylene, 65 wt% titanium dioxide, 5 wt% boehmite, 1 wt% aluminum-titanium bimetallic composite coupling agent (the number average molecular weight of the acrylic polymer used in preparation is 4000), and 0.25 wt% antioxidant.

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

[0076] Comparative Example 6

[0077] This comparative example provides a white masterbatch, as shown in Table 2, comprising the following components: 34.75 wt% homopolymer polypropylene, 65 wt% titanium dioxide, and 0.25 wt% antioxidant.

[0078] The preparation method of the white masterbatch in this comparative example is the same as that in Example 1.

[0079] Comparative Example 7

[0080] This comparative example provides a white masterbatch, as shown in Table 2, comprising the following components: 29.75 wt% homopolymer polypropylene, 65 wt% titanium dioxide, 5 wt% boehmite, and 0.25 wt% antioxidant.

[0081] The preparation method of the white masterbatch in this comparative example is the same as that in Example 1.

[0082] Comparative Example 8

[0083] This comparative example provides a white masterbatch, as shown in Table 2, comprising the following components: 29.5 wt% homopolymer polypropylene, 65 wt% titanium dioxide, 5 wt% boehmite, 0.25 wt% aluminate coupling agent, and 0.25 wt% antioxidant.

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

[0085] Comparative Example 9

[0086] This comparative example provides a white masterbatch, as shown in Table 2, comprising the following components: 29.5 wt% homopolymer polypropylene, 65 wt% titanium dioxide, 5 wt% boehmite, 0.25 wt% titanate coupling agent, and 0.25 wt% antioxidant.

[0087] The preparation method of the white masterbatch in this comparative example is the same as that in Example 1.

[0088] Table 1. Composition of white masterbatch in Examples 1-3 and Comparative Examples 1-5

[0089]

[0090] Table 2. Composition of white masterbatch in Comparative Examples 6-9

[0091]

[0092] Performance Evaluation

[0093] The white masterbatches from Examples 1-3 and Comparative Examples 1-9 were subjected to the following performance tests:

[0094] (1) Filterability test: Take 1 kg of white masterbatch and measure the filtration value under a 1200 mesh filter according to ISO 787-5 (determination of filtration value of pigments and fillers) standard;

[0095] (2) Precipitation resistance: Take an appropriate amount of white masterbatch and weigh it as M1. Soak it in ethyl acetate solution, reflux and heat for 2 hours, remove the solvent, weigh the white masterbatch again and record it as M2. The mass difference between M1 and M2 is the content of precipitate. The precipitation resistance is evaluated by the content of precipitate.

[0096] To more intuitively demonstrate the performance of the white masterbatch, the white masterbatch from Examples 1-3 and Comparative Examples 1-9 were further used to prepare BOPP film samples:

[0097] The BOPP film sample comprises, in sequence, an upper surface layer, a lower surface layer, a core layer, a lower surface layer, and a bottom surface layer; both the upper and lower surface layers comprise polypropylene and 5 wt% anti-blocking masterbatch; the thickness of both the upper and lower surface layers is 3 μm; both the lower and upper surface layers comprise polypropylene and 25 wt% of any one of the white masterbatch from Examples 1-3 and Comparative Examples 1-9; the thickness of both the lower and upper surface layers is 5 μm; the core layer comprises polypropylene and 50 wt% pearlescent masterbatch (the pearlescent masterbatch consists of 60 wt% calcium carbonate and 40 wt% polypropylene); the thickness of the core layer is 44 μm.

[0098] The preparation method of the film sample is as follows: using a five-layer co-extrusion test line, the formula of each layer is weighed and put into each extruder. After multi-layer co-extrusion through the die head, the film is cast and then chilled into a thick sheet according to the flat film method. The thick sheet is then stretched in both longitudinal and transverse directions to make a biaxially stretched film sample.

[0099] After preparing thin film samples from the white masterbatches of Examples 1-3 and Comparative Examples 1-9 respectively according to the above method, the following performance tests were performed:

[0100] (3) Whiteness and transmittance: The whiteness of the film sample was tested according to GB 2913-82, and the transmittance was tested according to GBT 2410-2008;

[0101] (4) Wetting tension: The wetting tension of the upper surface layer of the film sample was tested according to GB / T 14216-2008;

[0102] (5) Heat resistance: The film sample was stored at 120℃ for 10 minutes, and the warpage height was tested to evaluate its heat resistance.

[0103] (6) Tensile modulus: The tensile modulus of the film sample is tested according to GBT 1040.3-2006 to evaluate its mechanical strength (stiffness).

[0104] Please refer to Table 3 for the test results:

[0105] Table 3 Performance test results of Examples 1-3 and Comparative Examples 1-9

[0106]

[0107] Please refer to Table 3. The high stiffness and high heat resistance BOPP film of Examples 1-3 of the present invention uses white masterbatch added to BOPP film, which can make BOPP film have the characteristics of high stiffness (high mechanical strength) and high heat resistance, that is, to form high stiffness and high heat resistance BOPP film.

[0108] The number-average molecular weight of the acrylic polymer used in the preparation of the aluminum-titanium bimetallic composite coupling agent in the white masterbatch of Comparative Example 1 was too low, resulting in an excessively low number-average molecular weight of the prepared aluminum-titanium bimetallic composite coupling agent. Consequently, the white masterbatch of Comparative Example 1 contained a relatively large amount of precipitates and had poor resistance to precipitation. When the white masterbatch of Comparative Example 1 was used to prepare BOPP film, it resulted in a large warpage height and insufficient heat resistance of the BOPP film.

[0109] In Comparative Example 2, the number-average molecular weight of the acrylic polymer used to prepare the aluminum-titanium bimetallic composite coupling agent was too high. This resulted in an excessively high number-average molecular weight of the prepared aluminum-titanium bimetallic composite coupling agent. When the white masterbatch of Comparative Example 2 was used to prepare BOPP film, the mobility of the aluminum-titanium bimetallic composite coupling agent decreased, making it difficult to effectively interact with boehmite. This led to poor coating effect on boehmite, affecting its dispersibility. Consequently, the BOPP film exhibited a large warpage height, insufficient heat resistance, and a relatively low transverse tensile modulus, resulting in an insignificant effect on improving the mechanical strength of the BOPP film.

[0110] The white masterbatch of Comparative Example 3 had an excessive amount of boehmite added, and the white masterbatch itself had an excessively high filtration pressure value, which was not conducive to dispersion in BOPP film. Furthermore, when the white masterbatch of Comparative Example 3 was used to prepare BOPP film, the transverse tensile modulus of the BOPP film was too high (too rigid), which was not conducive to stretching and forming.

[0111] In Comparative Example 4, the amount of boehmite added to the white masterbatch was too low. When the white masterbatch of Comparative Example 4 was used to prepare BOPP film, the BOPP film had low mechanical strength and poor heat resistance.

[0112] In Comparative Example 5, the amount of aluminum-titanium bimetallic coupling agent added was too high, resulting in severe precipitation when the white masterbatch of Comparative Example 5 was used to prepare BOPP film.

[0113] The white masterbatch of Comparative Example 6, without the addition of boehmite or the aluminum-titanium bimetallic composite coupling agent of the present invention, resulted in BOPP films with low mechanical strength and poor heat resistance when used to prepare BOPP films.

[0114] The white masterbatch of Comparative Example 7, without the addition of the aluminum-titanium bimetallic composite coupling agent of the present invention, did not significantly improve the strength and heat resistance of BOPP film when used to prepare BOPP film.

[0115] The white masterbatch of Comparative Example 8 contains a common aluminate coupling agent with less than 10 carbon atoms in the alkane segment, rather than the high molecular weight aluminum-titanium bimetallic composite coupling agent of this invention. When the white masterbatch of Comparative Example 8 is used to prepare BOPP film, the BOPP film has low mechanical strength and poor heat resistance, and more precipitation occurs.

[0116] In Comparative Example 9, a common alkane segment with less than 10 carbon atoms, a titanate coupling agent, was added instead of the high molecular weight aluminum-titanium bimetallic composite coupling agent of the present invention. When the white masterbatch of Comparative Example 9 was used to prepare BOPP film, the BOPP film had low mechanical strength and poor heat resistance, and a lot of precipitation occurred.

[0117] 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 white masterbatch for high stiffness and high heat resistance BOPP film, characterized in that: The mixture comprises polypropylene, 60-70 wt% titanium dioxide, 3-7 wt% boehmite, and 0.15-0.35 wt% aluminum-titanium bimetallic composite coupling agent. The aluminum-titanium bimetallic composite coupling agent is obtained by reacting an acrylic polymer with tetrabutyl titanate, followed by the addition of a polyaluminum chloride-propylene glycol complex. The acrylic polymer has a number-average molecular weight of 3000-5000, the molar ratio of carboxyl groups in the acrylic polymer to tetrabutyl titanate is 1:(1.05-1.1), and the mass ratio of tetrabutyl titanate to the polyaluminum chloride-propylene glycol complex is (1.4-2):

1.

2. The white masterbatch for high stiffness and high heat resistance BOPP film according to claim 1, characterized in that: The polypropylene is homopolymer polypropylene, and the melt index of the polypropylene at 230℃ and 2.16kg load is 2-5 g / 10min.

3. The white masterbatch for high stiffness and high heat resistance BOPP film according to claim 1, characterized in that: The surface of the titanium dioxide is coated with inorganic and organic materials, and the average particle size D50 of the titanium dioxide is 200-300 nm.

4. The white masterbatch for high stiffness and high heat resistance BOPP film according to claim 1, characterized in that: The average grain size D50 of the boehmite is 1.5-3.5 μm.

5. The white masterbatch for high stiffness and high heat resistance BOPP film according to claim 1, characterized in that: The method for synthesizing the acrylic polymer includes the following steps: adding an organic solvent to a reaction vessel, purging with nitrogen, raising the temperature to 60-70°C under mechanical stirring, then adding acrylic monomer, then adding a free radical initiator and reacting for 2-4 hours, filtering, drying, and obtaining the acrylic polymer.

6. The white masterbatch for high stiffness and high heat resistance BOPP film according to claim 1, characterized in that: The preparation method of the polyaluminum chloride-propylene glycol complex includes the following steps: adding polyaluminum chloride and water into a reaction vessel, and after the polyaluminum chloride dissolves, adding methanol and heating to reflux at 75-85°C, then adding 1,2-propanediol, refluxing, filtering, and drying to obtain the polyaluminum chloride-propylene glycol complex.

7. The white masterbatch for high stiffness and high heat resistance BOPP film according to claim 1, characterized in that: The preparation method of the aluminum-titanium bimetallic composite coupling agent includes the following steps: adding the acrylic polymer to a reaction vessel, then adding 1,2-propanediol to dissolve the acrylic polymer, then adding the tetrabutyl titanate, and reacting at 100-110℃; then adding the polyaluminum chloride-propylene glycol complex, and reacting at 100-110℃, the resulting pale yellow solid is the aluminum-titanium bimetallic composite coupling agent.

8. The white masterbatch for high stiffness and high heat resistance BOPP film according to any one of claims 1-7, characterized in that: The white masterbatch for high stiffness and high heat resistance BOPP film also includes 0.05-0.25 wt% antioxidant.

9. A method for preparing a white masterbatch for high stiffness and high heat resistance BOPP film as described in any one of claims 1-8, characterized in that: Includes the following steps: The components are added to a continuous internal mixer in proportion and then extruded and granulated by a single screw extruder to obtain the finished product.

10. The application of a white masterbatch for high stiffness and high heat resistance BOPP film as described in any one of claims 1-8 in high stiffness and high heat resistance BOPP film.

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