Highly-dispersible multifunctional composite powder, and preparation method and application thereof

Abstract

This invention provides a highly dispersible multifunctional composite powder, its preparation method, and its applications, belonging to the field of functional inorganic non-metallic mineral filler processing technology. The highly dispersible multifunctional composite powder of this invention has a three-layer ordered coating structure: an inner deagglomeration layer, a middle activation layer, and an outer spatial isolation layer. The inner deagglomeration layer is obtained by covalent bonding between a silane coupling agent and the silanol groups on the surface of talc. The middle activation layer is obtained by coordination bonding between a metal coordination coupling agent and the calcium-magnesium active sites on the surface of dolomite and natural magnesium carbonate. The outer spatial isolation layer is obtained by melting a steric hindrance dispersant into a film. This invention can achieve precise layered coating of ternary symbiotic minerals, effectively improving the compatibility and melt dispersibility of the filler with PVC resin, and preparing a highly dispersible multifunctional composite powder that can completely replace traditional calcium-based composite fillers, thereby improving the overall performance of semi-rigid PVC calendered films.

Description

Technical Field

[0001] This invention relates to the field of functional inorganic non-metallic mineral filler processing technology, and in particular to a highly dispersible multifunctional composite powder, its preparation method, and its application. Background Technology

[0002] Currently, the semi-rigid PVC calendered film industry commonly uses nano-calcium carbonate combined with ultrafine heavy calcium carbonate as the mainstream inorganic filler system. This traditional filler system has several inherent defects: First, during the preparation of nano-calcium carbonate, unsaturated fatty acids need to be added for saponification modification, leaving free fatty acids on the powder surface. These fatty acids are easily precipitated and migrated during the high-temperature calendering process of PVC, causing problems such as blooming, fisheyes, and surface defects on the film surface, which seriously affect the appearance and performance of the film. Second, the particle size control of ultrafine heavy calcium carbonate powder on the market is inconsistent, with a wide distribution of coarse and fine particles. Under high filling conditions, the powder itself agglomerates significantly, ultimately leading to a decrease in the mechanical strength of the film, obvious whitening defects, and a decline in product yield.

[0003] Natural magnesium carbonate-dolomite-talc ternary symbiotic primary ore is an integrated intercalated mineral raw material. Each particle simultaneously contains talc silanol sites, dolomite, and natural magnesium carbonate calcium magnesium metal active sites, possessing multiple advantages such as talc reinforcement, carbonate cost reduction, smoke suppression, and heat resistance. It can replace the traditional nano-calcium carbonate + heavy calcium carbonate composite filler system and is suitable for PVC calendered film processing. However, the surface active sites of this ternary symbiotic mineral are complex. Single coupling agent, conventional one-step dry modification, and two-step isothermal modification processes all encounter problems such as site competition of modifiers, uneven coating, inability to dissociate powder agglomerates after the first agglomeration, and rebound of secondary agglomeration during storage and processing. The filler has poor dispersibility in the PVC matrix and cannot give full play to the composite functional advantages of the primary symbiotic mineral.

[0004] Therefore, it is of great significance to provide a highly dispersible multifunctional composite powder that can achieve precise layered coating of ternary symbiotic minerals, effectively improve the compatibility and melt dispersibility of fillers and PVC resins, and thus enhance the overall performance of semi-rigid PVC calendered films, as well as its preparation method and application. Summary of the Invention

[0005] The purpose of this invention is to provide a highly dispersible multifunctional composite powder, its preparation method, and its application, in order to solve the technical problems of uneven coating, competitive active sites by additives, severe secondary agglomeration of powder, and numerous defects in film processing in existing conventional mineral filler modification processes.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a highly dispersible multifunctional composite powder, wherein the composite powder has a three-layer ordered coating structure consisting of an inner deagglomeration layer, a middle activation layer, and an outer spatial isolation layer; The inner deagglomeration layer is obtained by covalent bonding of a silane coupling agent with silanol groups on the surface of talc. The middle activation layer is obtained by coordination binding of a metal coordination coupling agent with the calcium and magnesium active sites on the surface of dolomite and natural magnesium carbonate; The outer spatial isolation layer is obtained by melting and forming a film from a steric hindrance dispersant.

[0007] Furthermore, the silane coupling agent includes one or more of aminosilanes, epoxysilanes, and alkylsilanes; The metal coordination coupling agent includes one or more of titanate, aluminate, phosphate and borate esters; The steric hindrance dispersant includes one or more of polycarboxylic acid dispersants, polyester dispersants, and modified inorganic phosphate dispersants.

[0008] This invention provides a method for preparing the highly dispersible multifunctional composite powder, comprising the following steps: 1) The natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder is preheated. After preheating, a silane coupling agent is added and mixed. After uniform mixing, targeted modification is performed to obtain powder with an inner deagglomeration layer. 2) Add a metal coordination coupling agent to the powder with an inner deagglomeration layer and mix. After mixing evenly, perform graft modification to obtain a powder with an inner deagglomeration layer and a middle activation layer. 3) Add a steric hindrance dispersant to the powder with an inner deagglomeration layer and a middle activation layer and mix. After mixing evenly, perform isolation modification to obtain a powder with an inner deagglomeration layer, a middle activation layer and an outer steric isolation layer. 4) After the isolation modification is completed, air cooling is performed to obtain a highly dispersible multifunctional composite powder.

[0009] Furthermore, the natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder meets the following physicochemical properties: median particle size D 50 The thickness is 1.2~2.0μm; Based on the total mass of the ternary symbiotic ultrafine powder, the content of talc is 22~40wt%, the content of dolomite is 40~62wt%, the content of natural magnesium carbonate is 10~22wt%, and the total proportion of the three minerals is ≥96wt%.

[0010] Furthermore, the amount of the silane coupling agent added is 0.25~0.35 wt% of the mass of the natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder; The amount of the metal coordination coupling agent added is 0.45~0.55 wt% of the mass of the natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder; The amount of the steric dispersant added is 0.35~0.45wt% of the mass of the natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder.

[0011] Furthermore, the preheating temperature is 80~100℃; In step 1), the targeted modification temperature is 80~100℃ and the targeted modification time is 3~5min.

[0012] Furthermore, in step 2), the grafting modification temperature is 80~100℃, and the grafting modification time is 3~4min.

[0013] Furthermore, in step 3), the temperature for isolation modification is 110~130℃, and the time for isolation modification is 5~6 minutes.

[0014] Furthermore, in steps 1) and 2), the mixing is carried out by stirring, and the stirring speed is independently 200~500 r / min; In step 3), the mixing is carried out by stirring at a speed of 500~800 r / min.

[0015] The present invention also provides an application of the highly dispersible multifunctional composite powder in semi-rigid PVC calendered film. When preparing semi-rigid PVC calendered film, based on 100 parts of PVC resin, the mass parts of DOTP are 20-24 parts, the mass parts of stabilizer are 2-6 parts, and the mass parts of composite powder are 40-60 parts.

[0016] The beneficial effects of this invention are: 1) This invention utilizes a three-stage gradient temperature stepwise dry modification process to address the differentiated reaction requirements between talc silanol groups and the active sites of calcium and magnesium in dolomite and natural magnesium carbonate. By controlling the temperature in stages and adding silane coupling agents, metal coordination coupling agents, and steric hindrance dispersants in specific temperature zones, a three-layer ordered coating structure of "inner layer deagglomeration, middle layer activation, and outer layer spatial isolation" is successfully constructed. This achieves precise and complete coverage of the active sites on the powder surface, resulting in a modified powder that combines the advantages of high activation and low oil absorption.

[0017] 2) This invention relies on the covalent bonding of the inner silane coupling agent to dissociate the primary agglomeration of talc sheets, and then uses the outer dispersant to form a dense spatial isolation layer through high-temperature melting. This effectively inhibits the secondary agglomeration rebound of powder during storage and processing, optimizes the interfacial compatibility and stress transfer effect between the filler and PVC resin, and significantly improves the overall performance of semi-rigid PVC calendered film. This invention utilizes the in-situ reinforcing effect of the ternary symbiotic mineral talc, combined with a complete layered coating structure to enhance interfacial bonding, solving the problem of film strength attenuation after high filler loading in traditional fillers; it can effectively dissociate primary agglomerates and block secondary agglomeration during processing, allowing the powder to achieve nanoscale uniform dispersion in the PVC melt; the three-layer ordered coating structure optimizes the stress transfer at the filler and resin interface, eliminates micro-voids caused by bending, and significantly improves the bending weather resistance and appearance performance of the film.

[0018] 3) This invention abandons the fatty acid saponification modification system used in traditional nano-calcium and adopts silane / metal coupling agent covalent bonding and coordination modification. After modification, there are no free low-molecular-weight easily migrating additives on the powder surface, eliminating the high-temperature blooming defect of the film from the root. At the same time, the three-stage gradient temperature stepwise dry modification process of this invention has wide compatibility with various industry-general modifiers such as aminosilane / epoxysilane, titanate / aluminate / phosphate ester, polycarboxylic acid / polyester dispersant. Moreover, the whole process can be completed by relying on the existing general high-speed mixer in the PVC industry without adding new equipment. It realizes the complete replacement of nano-calcium carbonate + heavy calcium carbonate two artificial compound fillers by a single ternary symbiotic mineral, significantly reducing the overall cost of raw materials and making it highly industrializable. Detailed Implementation

[0019] This invention provides a highly dispersible multifunctional composite powder, wherein the composite powder has a three-layer ordered coating structure consisting of an inner deagglomeration layer, a middle activation layer, and an outer spatial isolation layer; The inner deagglomeration layer is obtained by covalent bonding of a silane coupling agent with silanol groups on the surface of talc. The middle activation layer is obtained by coordination binding of a metal coordination coupling agent with the calcium and magnesium active sites on the surface of dolomite and natural magnesium carbonate; The outer spatial isolation layer is obtained by melting and forming a film from a steric hindrance dispersant.

[0020] In this invention, the silane coupling agent includes one or more of aminosilane, epoxysilane and alkylsilane, preferably aminosilane and / or epoxysilane, and more preferably aminosilane.

[0021] In this invention, the metal coordination coupling agent includes one or more of titanate, aluminate, phosphate and borate, preferably one or more of titanate, phosphate and borate, and more preferably titanate and / or phosphate.

[0022] In this invention, the steric hindrance dispersant includes one or more of polycarboxylic acid dispersants, polyester dispersants, and modified inorganic phosphate dispersants, preferably polycarboxylic acid dispersants and / or polyester dispersants, and more preferably polycarboxylic acid dispersants.

[0023] This invention provides a method for preparing the highly dispersible multifunctional composite powder, comprising the following steps: 1) The natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder is preheated. After preheating, a silane coupling agent is added and mixed. After uniform mixing, targeted modification is performed to obtain powder with an inner deagglomeration layer. 2) Add a metal coordination coupling agent to the powder with an inner deagglomeration layer and mix. After mixing evenly, perform graft modification to obtain a powder with an inner deagglomeration layer and a middle activation layer. 3) Add a steric hindrance dispersant to the powder with an inner deagglomeration layer and a middle activation layer and mix. After mixing evenly, perform isolation modification to obtain a powder with an inner deagglomeration layer, a middle activation layer and an outer steric isolation layer. 4) After the isolation modification is completed, air cooling is performed to obtain a highly dispersible multifunctional composite powder.

[0024] In this invention, the natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder meets the following physicochemical properties: median particle size D of the powder. 50 The thickness is 1.2~2.0μm, preferably 1.2~2.0μm, and even more preferably 1.2~2.0μm.

[0025] In this invention, based on the total mass of the ternary symbiotic ultrafine powder, the content of talc is 22~40wt%, the content of dolomite is 40~62wt%, the content of natural magnesium carbonate is 10~22wt%, and the total proportion of the three minerals is ≥96wt%.

[0026] Preferably, based on the total mass of the ternary symbiotic ultrafine powder, the content of talc is 24~38wt%, the content of dolomite is 42~60wt%, the content of natural magnesium carbonate is 12~20wt%, and the total proportion of the three minerals is ≥96.5wt%.

[0027] More preferably, based on the total mass of the ternary symbiotic ultrafine powder, the content of talc is 26~35wt%, the content of dolomite is 44~55wt%, the content of natural magnesium carbonate is 14~18wt%, and the total proportion of the three minerals is ≥97wt%.

[0028] In this invention, the amount of the silane coupling agent added is 0.25~0.35 wt% of the mass of the natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder, preferably 0.27~0.32 wt%, and more preferably 0.3 wt%. The amount of the metal coordination coupling agent added is 0.45~0.55 wt% of the mass of the natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder, preferably 0.47~0.52 wt%, and more preferably 0.5 wt%. The amount of the steric hindrance dispersant added is 0.35~0.45wt% of the mass of the natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder, preferably 0.37~0.42wt%, and more preferably 0.4wt%.

[0029] In this invention, the preheating temperature is 80~100℃, preferably 85~95℃, and more preferably 90℃.

[0030] In this invention, in step 1), the temperature for targeted modification is 80~100℃, preferably 85~95℃, and more preferably 90℃; the time for targeted modification is 3~5min, preferably 3.5~4.5min, and more preferably 4min.

[0031] In this invention, in step 2), the grafting modification temperature is 80~100℃, preferably 85~95℃, and more preferably 90℃; the grafting modification time is 3~4min, preferably 3.2~3.8min, and more preferably 3.4~3.6min.

[0032] In this invention, in step 3), the temperature for isolation modification is 110~130℃, preferably 115~125℃, and more preferably 120℃; the time for isolation modification is 5~6min, preferably 5.2~5.8min, and more preferably 5.5min.

[0033] In this invention, in steps 1) and 2), the mixing is carried out by stirring, and the stirring speed is independently 200~500 r / min, preferably 250~450 r / min, and more preferably 300~400 r / min; In step 3), the mixing is carried out by stirring, and the stirring speed is 500~800 r / min, preferably 550~750 r / min, and more preferably 600~700 r / min.

[0034] The present invention also provides an application of the highly dispersible multifunctional composite powder in semi-rigid PVC calendered film. When preparing semi-rigid PVC calendered film, based on 100 parts of PVC resin, the mass parts of DOTP are 20-24 parts, the mass parts of stabilizer are 2-6 parts, and the mass parts of composite powder are 40-60 parts.

[0035] Preferably, in preparing semi-rigid PVC calendered film, the mass fraction of DOTP is 21-23 parts per 100 parts of PVC resin, the mass fraction of stabilizer is 3-5 parts per 10 ...

[0036] More preferably, in the preparation of semi-rigid PVC calendered film, the mass fraction of DOTP is 22 parts per 100 parts of PVC resin, the mass fraction of stabilizer is 4 parts per 4 parts per 4 parts per 50 ...

[0037] In this invention, the core mechanism is as follows: the silane coupling agent only covalently bonds with the silanol groups (Si-OH) on the surface of talc (forming Si-O-Si), and does not act on the calcium and magnesium sites of dolomite and magnesium carbonate, because it does not have condensable hydroxyl groups and cannot form stable bonds thermodynamically. In the first step of the process, it is added separately to ensure that the silane specifically targets talc and achieves directional deagglomeration; the metal coordination coupling agent preferentially chelates and coordinates with the active sites of calcium and magnesium, and has extremely low reactivity with silanol groups; and the inner silane has saturated and deactivated the silanol groups on the surface of talc and formed a spatial shield, so the metal coupling agent only acts on dolomite / magnesium carbonate and does not cross-react with the silane layer.

[0038] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0039] Example 1

[0040] D of natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder 50 =1.8μm; oil absorption value 32mL / 100g; based on the total mass of the ternary symbiotic ultrafine powder, the content of talc is 32wt%, the content of dolomite is 53wt%, the content of natural magnesium carbonate is 13wt%, and the total proportion of the three minerals is 98wt%; the powder has not been calcined at high temperature, and the moisture content is 0.17%; 400 kg of natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder was preheated to 85°C. After preheating, 1.2 kg of aminosilane coupling agent was added and stirred at 300 r / min. After mixing evenly, the powder was targeted modified at 85°C for 4 min to obtain powder with an inner deagglomeration layer. Add 2 kg of titanate coupling agent to the powder with an inner deagglomeration layer and stir at 300 r / min. After mixing evenly, perform graft modification at 85℃ for 4 min to obtain powder with an inner deagglomeration layer and a middle activation layer. 1.6 kg of polyester dispersant (SS-310R purchased from Shanghai Songshan New Material Technology Co., Ltd.) was added to the powder with an inner deagglomeration layer and a middle activation layer. The mixture was stirred at 600 r / min and mixed evenly. The powder was then subjected to isolation modification at 115℃ for 5 min to obtain a powder with an inner deagglomeration layer, a middle activation layer and an outer spatial isolation layer. After isolation and modification, the powder is air-cooled to below 40°C to obtain a highly dispersible multifunctional composite powder.

[0041] Example 2

[0042] Compared with Example 1, the difference is that the preheating, targeted modification and grafting modification temperatures in Example 2 are all 90°C; and the steric hindrance dispersant is a polycarboxylic acid dispersant.

[0043] Example 3

[0044] The difference between Example 2 and Example 3 is that the metal coordination coupling agent is an aluminate.

[0045] Example 4

[0046] The difference between Example 4 and Example 2 is that the silane coupling agent in Example 4 is an epoxy silane coupling agent.

[0047] Example 5

[0048] The difference between Example 2 and Example 5 is that the metal coordination coupling agent is a phosphate ester.

[0049] Comparative Example 1

[0050] Comparative Example 1 uses the natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder from Example 1.

[0051] Comparative Example 2

[0052] Compared with Example 2, the difference is that in Comparative Example 2, silane coupling agents, metal coordination coupling agents and steric hindrance dispersants were added simultaneously.

[0053] Comparative Example 3

[0054] Compared with Example 2, the difference is that Comparative Example 3 only involves two steps of isothermal modification, without the addition of polycarboxylic acid dispersant for isolation modification.

[0055] Comparative Example 4

[0056] Compared with Example 2, the difference is that Comparative Example 4 uses a three-step isothermal modification, and the temperature of the isolation modification is 90°C.

[0057] Comparative Example 5

[0058] Comparative Example 5 used artificially compounded nano-calcium CCR from Guangxi Huana New Materials Co., Ltd.

[0059] The performance of the composite powders prepared in Examples 1-5 and Comparative Examples 1-5 was tested: The oil absorption value test method is as follows: Weigh 5g of product (accurate to 0.01) and place it on a glass plate. While mixing the product with a spatula, add dioctyl phthalate (DOP) dropwise. Continue stirring until the added DOP completely binds the product together, that is, until saturation is reached. Record the volume of DOP consumed.

[0060] The formula for calculating oil absorption is: oil absorption = v / m × 100, where m is the weight of the product (in g), v is the volume of DOP consumed (in mL); the unit of oil absorption is mL / 100g.

[0061] The activation degree test method is as follows: Weigh 5g of product (accurate to 0.01g) into a separatory funnel, add 200mL of water, shake repeatedly at a speed of 120 times / min for 1min, gently place it on the funnel rack and let it stand for 30min until obvious stratification occurs. Then, put the settled calcium carbonate into a glass sand crucible that has been dried to constant mass at 105℃ in one go, filter to remove water, and place the filter residue in an electric thermostatic drying oven to dry to constant mass at 105℃. Calculate the activation degree.

[0062] The degree of activation is expressed as a mass fraction ω, with the value expressed as a percentage (%), and is calculated according to Equation 1: Formula 1, Where: ω is the activation degree (in %); m2 is the weight of the crucible and the settled calcium carbonate after drying (in grams). m1 is the weight of the crucible (in grams); m is the weight of the sample (in grams).

[0063] The test results are shown in Table 1.

[0064] Table 1 Performance test results of Examples 1-5 and Comparative Examples 1-5

[0065] As shown in Table 1, the activation degree of the product obtained by the present invention is 96.6-97.9%, which is 8-12.7 percentage points higher than that of the comparative example (85.2-88.6%), and more than 10 percentage points higher than that of commercially available nano-calcium (86.1%). This result proves that the three-stage layered coating process can achieve full coverage of the mineral surface without exposing any hydrophilic active sites, and the compatibility of the product with PVC resin is significantly better than that of existing processes. The oil absorption value of the product of this invention is only 20~23mL / 100g, which is 9~12 units lower than the blank raw powder and traditional nano calcium, and 4~9 units lower than Comparative Example 2. The lower the oil absorption value, the less plasticizer is consumed during processing and the better the melt flow, which can effectively solve the problems of stickiness and high mixing resistance of high-filled PVC film.

[0066] The composite powders prepared in Examples 1-5 and Comparative Examples 1-5 were used as fillers to prepare semi-rigid PVC calendered films. The specific method was as follows: PVC resin (SG-5): 100 parts, DOTP: 22 parts, stabilizer: 4 parts, filler: 50 parts. Each raw material was accurately weighed according to the above formula, thoroughly mixed, and then rolled on a two-roll mill at 170°C. After uniform rolling, a 0.2 mm thick film was drawn, and simultaneously, a 4 mm thick sample was pressed into the mixed material. Tensile properties were tested after pneumatic sampling. The test method was as follows: Tensile properties: tested according to GB / T 528-2009 using a Chengde Jinjian UTM-1422 electronic universal testing machine; Test method for fisheye effect on thin film: Cut a 0.2mm thin film into 200mm pieces. The number of fish eyes in a 200mm sample was observed under a white light source. Based on industry standards, fisheye condition is classified into 1-5 levels according to the following criteria. The lower the level, the better the dispersibility and the better the film appearance. The fisheye condition classification is shown in Table 2.

[0067] Table 2 Classification of Fisheye Condition

[0068] Thin film precipitation test method: Cut a 0.2 mm thin film into 100 mm pieces. After a 100mm sample was placed in an 80℃ electric oven for 72 hours, the film surface was visually inspected under natural light; the surface condition of the sample was evaluated in conjunction with the surface condition of the mixture processed on the open mill. Based on industry standards, the precipitation condition is divided into 1-5 levels according to the following criteria. The lower the level, the better the adhesion and the better the ink absorption performance of the film. The classification of film precipitation condition levels is shown in Table 3.

[0069] Table 3 Classification of Thin Film Precipitation Status

[0070] Evaluation method for the whitening performance of thin films: Cut a 0.2mm film into 150mm pieces. For a 50mm sample, fold the sample 180° along its length and then fold it back 180° in the opposite direction to complete one reciprocating bend. Repeat this bending process 20 times. After bending, flatten the film and visually observe the degree and width of whitening along the center line of the bend under natural light. Based on industry standards, the whitening resistance is classified into 1-5 levels according to the following criteria. The lower the level, the better the whitening resistance and the superior film performance. The classification of film whitening performance levels is shown in Table 4.

[0071] Table 4 Classification of Film Whitening Performance Grades

[0072] The performance test results of the prepared semi-rigid PVC calendered film are shown in Table 5.

[0073] Table 5 Performance test results of the prepared semi-rigid PVC calendered film

[0074] As shown in Table 5, the tensile strength of the film of this invention reaches 33.14~34.37 MPa, which is 22%~26.6% higher than that of mainstream nano-calcium (27.15 MPa) in the industry, and 10%~17% higher than that of defect modification process (29.31~29.98 MPa). This is due to the in-situ reinforcing effect of talc in ternary symbiotic minerals and the enhanced interfacial bonding force brought about by complete layered coating, which effectively solves the problem of film strength decay under high filling of traditional fillers.

[0075] In most embodiments of this invention, the fisheye grade is grade 1 (no visible white gel spots), with the worst embodiment 5 being only grade 2; while all comparative examples (including commercially available nano-calcium) have a fisheye grade of grade 3 or higher, indicating the presence of a large number of agglomerated gel particles. This demonstrates that the three-stage gradient temperature stepwise modification effectively dissociates the primary agglomerates and blocks secondary agglomeration during processing, enabling the powder to achieve uniform nanoscale dispersion in the PVC melt.

[0076] In this invention, the precipitation grade is 1-2, with a clean film surface free of oil film and white bloom. Traditional nano-calcium, due to residual free fatty acids, has a precipitation grade of 2-3, and the one-step / two-stage modification process achieves a precipitation grade of 3, with the film surface becoming noticeably white after 72 hours of high-temperature aging. This invention abandons the traditional calcium salt fatty acid saponification modification system, and the powder surface is free of free low-molecular-weight, easily migrating additives, thus eliminating the high-temperature blooming defect of the film at its source.

[0077] In the embodiments of this invention, the whitening level is grade 1, with no whitening marks after 20 cycles of bending; all comparative examples have a whitening level of grade 2-3, showing obvious stress whitening after bending. The three-layer ordered coating structure optimizes the stress transfer at the filler-resin interface, eliminates micro-voids generated by bending, and significantly improves the bending weather resistance and appearance of the film.

[0078] As can be seen from the above embodiments, the present invention provides a highly dispersible multifunctional composite powder, its preparation method, and its application. The highly dispersible multifunctional composite powder has a three-layer ordered coating structure consisting of an inner deagglomeration layer, a middle activation layer, and an outer spatial isolation layer. The inner deagglomeration layer is obtained by covalent bonding between a silane coupling agent and the silanol groups on the surface of talc. The middle activation layer is obtained by coordination bonding between a metal coordination coupling agent and the calcium-magnesium active sites on the surface of dolomite and natural magnesium carbonate. The outer spatial isolation layer is obtained by melting a steric hindrance dispersant into a film. The present invention can achieve precise layered coating of ternary symbiotic minerals, effectively improve the compatibility and melt dispersibility of fillers and PVC resins, and prepare highly dispersible multifunctional composite powders that can completely replace traditional calcium-based composite fillers, thereby improving the overall performance of semi-rigid PVC calendered films.

[0079] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A highly dispersible, multifunctional composite powder, characterized in that, The composite powder has a three-layer ordered coating structure consisting of an inner deagglomeration layer, a middle activation layer, and an outer spatial isolation layer. The inner deagglomeration layer is obtained by covalent bonding of a silane coupling agent with silanol groups on the surface of talc. The middle activation layer is obtained by coordination binding of a metal coordination coupling agent with the calcium and magnesium active sites on the surface of dolomite and natural magnesium carbonate; The outer spatial isolation layer is obtained by melting and forming a film from a steric hindrance dispersant.

2. The highly dispersible multifunctional composite powder according to claim 1, characterized in that, The silane coupling agent includes one or more of aminosilanes, epoxysilanes and alkylsilanes; The metal coordination coupling agent includes one or more of titanate, aluminate, phosphate and borate esters; The steric hindrance dispersant includes one or more of polycarboxylic acid dispersants, polyester dispersants, and modified inorganic phosphate dispersants.

3. A method for preparing the highly dispersible multifunctional composite powder according to claim 1 or 2, characterized in that, Includes the following steps: 1) The natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder is preheated. After preheating, a silane coupling agent is added and mixed. After uniform mixing, targeted modification is performed to obtain powder with an inner deagglomeration layer. 2) Add a metal coordination coupling agent to the powder with an inner deagglomeration layer and mix. After mixing evenly, perform graft modification to obtain a powder with an inner deagglomeration layer and a middle activation layer. 3) Add a steric hindrance dispersant to the powder with an inner deagglomeration layer and a middle activation layer and mix. After mixing evenly, perform isolation modification to obtain a powder with an inner deagglomeration layer, a middle activation layer and an outer steric isolation layer. 4) After the isolation modification is completed, air cooling is performed to obtain a highly dispersible multifunctional composite powder.

4. The method for preparing highly dispersible multifunctional composite powder according to claim 3, characterized in that, The natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder meets the following physicochemical properties: median particle size D of the powder 50 The thickness is 1.2~2.0μm; Based on the total mass of the ternary symbiotic ultrafine powder, the content of talc is 22~40wt%, the content of dolomite is 40~62wt%, the content of natural magnesium carbonate is 10~22wt%, and the total proportion of the three minerals is ≥96wt%.

5. The method for preparing highly dispersible multifunctional composite powder according to claim 4, characterized in that, The amount of the silane coupling agent added is 0.25~0.35 wt% of the mass of the natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder; The amount of the metal coordination coupling agent added is 0.45~0.55 wt% of the mass of the natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder; The amount of the steric dispersant added is 0.35~0.45wt% of the mass of the natural magnesium carbonate-dolomite-talc ternary symbiotic ultrafine powder.

6. The method for preparing highly dispersible multifunctional composite powder according to claim 4 or 5, characterized in that, The preheating temperature is 80~100℃; In step 1), the targeted modification temperature is 80~100℃ and the targeted modification time is 3~5min.

7. The method for preparing highly dispersible multifunctional composite powder according to claim 6, characterized in that, In step 2), the grafting modification temperature is 80~100℃ and the grafting modification time is 3~4min.

8. The method for preparing highly dispersible multifunctional composite powder according to claim 7, characterized in that, In step 3), the temperature for isolation modification is 110~130℃, and the time for isolation modification is 5~6 minutes.

9. The method for preparing highly dispersible multifunctional composite powder according to claim 7 or 8, characterized in that, In steps 1) and 2), the mixing is carried out by stirring, and the stirring speed is independently 200~500 r / min; In step 3), the mixing is carried out by stirring at a speed of 500~800 r / min.

10. The application of the highly dispersible multifunctional composite powder as described in claim 1 or 2 in semi-rigid PVC calendered films, characterized in that, When preparing semi-rigid PVC calendered film, based on 100 parts of PVC resin, the mass fraction of DOTP is 20-24 parts, the mass fraction of stabilizer is 2-6 parts, and the mass fraction of composite powder is 40-60 parts.

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