Superfine powder for household appliance shell material as well as preparation method and application thereof

Abstract

The invention discloses superfine powder for a household appliance shell material as well as a preparation method and application of the superfine powder, and belongs to the technical field of inorganic powder surface modification and polymer composite materials. Aiming at the pain points that traditional powder modification depends on an alcohol solvent, energy consumption is high and multi-component blending does not have an ordered interface, the preparation method comprises the following steps: firstly, carrying out dry airflow crushing on heavy calcium carbonate and barium sulfate according to a ratio of (80-90): (10-20), carrying out non-thermal plasma activation, carrying out high-speed kneading modification by using KH-550 hydrolysate with the pH value of 3.5-5.5 in an alcohol-free environment at 60-90 DEG C, and naturally cooling to obtain a finished product. According to the scheme, a stearic acid dispersing agent can be added as required, and the powder can be highly filled in polypropylene resin and is matched with a special compatilizer for forming a white household appliance shell. The preparation method realizes whole-process green modification without VOC emission and with low energy consumption, also constructs a gradient interface of barium sulfate coated calcium carbonate, greatly improves the comprehensive performance of the composite material, is adaptive to the existing production line, and has significant industrial promotion value.

Description

Technical Field

[0001] This invention relates to the field of inorganic powder surface modification and polymer composite materials technology, specifically proposing an ultrafine powder for household appliance casing materials, its preparation method and application. Background Technology

[0002] In the home appliance manufacturing industry, polypropylene composite materials are widely used in the production of casings for white goods such as refrigerators, washing machines, and air conditioners due to their low cost and good formability. Heavy calcium carbonate and barium sulfate are the most commonly used inorganic fillers in polypropylene composite materials. To achieve a high filling content of 30-50 wt% while ensuring the mechanical properties and surface quality of the material, the ultrafine powder needs to undergo surface modification to improve its interfacial compatibility with the resin.

[0003] Currently, the mainstream powder modification process in the industry is silane dry modification. This process generally relies on alcohol solvents as co-solvents for silanes to promote hydrolysis, and after modification, it needs to be dried at high temperatures above 130°C for a long time to remove alcohols and moisture from the system. This process route not only generates a large amount of volatile organic compounds (VOCs), which does not meet the current environmental protection policy requirements for low VOC emissions, but also suffers from high energy consumption and long production cycles. At the same time, a technical bias has formed in the field that "silane dry modification must rely on alcohol co-solvents and high-temperature drying, otherwise it will lead to insufficient silane hydrolysis and low grafting efficiency," which seriously restricts the green upgrading of powder modification processes.

[0004] A few technologies attempt to enhance powder surface activity through low-temperature plasma activation, but subsequent modification still reverts to traditional alcoholysis or wet processes, failing to truly break free from dependence on alcohols or complex wet processes and thus unable to achieve green modification throughout the entire process. Furthermore, existing multi-component powder modification schemes mostly involve simple mechanical blending, which cannot form an ordered interfacial structure between powders. This leads to a significant decrease in key properties of composite materials, such as impact strength and heat distortion temperature, when high filler content is high, making it difficult to meet the quality requirements of high-end home appliance casings.

[0005] In summary, existing technologies have consistently failed to overcome the technical constraints of "alcohol solvents + high-temperature drying," and are also unable to achieve the synergistic construction of efficient silane grafting and ordered interfaces of multi-component powders under green process conditions. The home appliance industry urgently needs an environmentally friendly, efficient, and high-performance inorganic powder modification solution. Summary of the Invention

[0006] In view of this, the present invention proposes an ultrafine powder for household appliance casing materials, its preparation method and application. Through a process chain of non-thermal plasma surface activation-low temperature alcohol-free acidic hydrolysis direct dry modification, the dependence on alcohol solvents and high temperature drying is completely eliminated, realizing green modification throughout the process. In addition, a gradient interface structure of barium sulfate selectively coating calcium carbonate is unexpectedly constructed, which significantly improves the comprehensive performance of high-filled polypropylene composite materials.

[0007] The technical solution of this invention is implemented as follows: This invention provides an ultrafine powder for household appliance casing materials, which is prepared by the following method: heavy calcium carbonate and barium sulfate are mixed at a mass ratio of 80-90:10-20 and then subjected to dry air jet milling to obtain a mixed powder; the mixed powder is subjected to non-thermal plasma surface activation; the activated mixed powder is subjected to high-speed kneading modification by adding 2-6% of a KH-550 hydrolysate with a pH of 3.5-5.5 at 60-90℃ without adding alcohol solvents, and then naturally cooled to room temperature to obtain the ultrafine powder.

[0008] In some embodiments, the particle size parameters of the mixed powder after dry air jet milling are D50 = 2-4 μm and D97 ≤ 10 μm.

[0009] This particle size range is the optimal range for comprehensively considering powder dispersibility and interfacial coating effect. D50=2-4μm can ensure that the powder has sufficient specific surface area in polypropylene resin to form effective interfacial bonding, while avoiding powder agglomeration caused by excessively small particle size. D97≤10μm can eliminate the negative impact of large particle size on the surface smoothness of composite materials, and provide a uniform raw material basis for the subsequent gradient interface construction of selective barium sulfate coating of calcium carbonate. However, the existing technology does not link the particle size parameter with the interfacial structure of multi-component powders.

[0010] In some embodiments, the process conditions for the non-thermal plasma surface activation are as follows: the activation atmosphere is argon, oxygen, or a mixture of argon and oxygen; the activation power is 50-150W; and the activation time is 20-90 seconds.

[0011] Argon atmosphere can form physical etching sites on the powder surface, while oxygen atmosphere can introduce active functional groups such as hydroxyl groups. Argon-oxygen mixed atmosphere can achieve synergy between the two. The power range of 50-150W can not only build high-density active sites on the powder surface, but also avoid powder agglomeration caused by excessive power. The activation time of 20-90 seconds can ensure the uniform distribution of active sites, providing a prerequisite for the efficient grafting of silane under alcohol-free conditions, and breaking through the technical limitation of traditional plasma activation requiring alcoholysis process.

[0012] In some embodiments, the pH of the KH-550 hydrolysate is adjusted by glacial acetic acid, citric acid, or phosphoric acid.

[0013] Glacial acetic acid, citric acid, and phosphoric acid are all weak acid regulators that can stabilize the pH of KH-550 hydrolysate within the optimal hydrolysis range of 3.5-5.5. Within this range, silanes can achieve complete hydrolysis without alcohol and the functional groups on the powder surface will not be destroyed by strong acid. At the same time, the above regulators are non-volatile, which can avoid the introduction of new VOCs. Traditional alcoholysis processes rely on alcohol solvents, which do not have this synergistic advantage of environmental protection and hydrolysis efficiency.

[0014] In some embodiments, stearic acid, calcium stearate or zinc stearate, at 0.2-1% by mass of the mixed powder, is added as an auxiliary dispersant at the same time as or before the addition of KH-550 hydrolysate.

[0015] Stearic acid dispersants can be adsorbed onto the powder surface through hydrophobic groups, reducing van der Waals forces between powder particles and preventing powder agglomeration caused by high-speed kneading during the modification process. An addition of 0.2-1% can ensure the dispersion effect without affecting the binding of silane to the active sites on the powder surface, solving the industry pain point of difficulty in achieving both dispersibility and grafting efficiency in the modification of highly filled powders.

[0016] In some embodiments, the mass ratio of the heavy calcium carbonate to barium sulfate is 83-88:12-17.

[0017] This ratio is the core parameter for achieving selective coating of calcium carbonate gradient interface with barium sulfate. A barium sulfate ratio of 12-17% can form a continuous and uniform coating layer on the surface of calcium carbonate particles. This can both improve the surface hardness and scratch resistance of the powder by utilizing barium sulfate, and avoid the problem of excessive powder density caused by excessive barium sulfate ratio. A calcium carbonate ratio of 83-88% can ensure the basic rigidity and cost advantage of the powder. The synergistic effect of this ratio cannot be achieved by simple mechanical blending of existing technologies.

[0018] In some embodiments, the dry air jet milling employs an air jet mill or a planetary ball mill.

[0019] Air jet mills can achieve precise classification of powders through high-speed airflow impact, while planetary ball mills can achieve ultra-fine grinding of powders through the collision of grinding media. Both can ensure the uniformity of powder particle size distribution and are dry processes that produce no wastewater, which fits the technical concept of green modification throughout the entire process and is different from the high pollution defects of traditional wet grinding.

[0020] In some embodiments, the kneading speed of the high-speed kneading modification is 800-1200 r / min, and the kneading time is 15-30 min.

[0021] A rotation speed of 800-1200 r / min can provide sufficient shear force to promote the uniform spreading of KH-550 hydrolysate on the powder surface, while driving the barium sulfate particles to migrate directionally to the surface of calcium carbonate particles; a kneading time of 15-30 min can ensure sufficient grafting of silane and stable formation of gradient interface, avoiding insufficient modification due to too short a time or increased energy consumption due to too long a time.

[0022] In some embodiments, the ultrafine powder is added as a filler to polypropylene resin, with 25-50 parts by weight of the ultrafine powder added per 100 parts by weight of polypropylene resin.

[0023] A high filling ratio of 25-50 parts by weight can significantly reduce the raw material cost of polypropylene composites. At the same time, the modified powder of this invention has a gradient interface structure, which can maintain the processing fluidity of the material under high filling conditions, breaking through the technical bottleneck of the sharp decline in fluidity and mechanical properties of traditional powders under high filling conditions.

[0024] In some embodiments, 1-5 parts by weight of maleic anhydride-grafted polypropylene or ethylene-octene copolymer-grafted maleic anhydride are also added to the polypropylene resin as a compatibilizer.

[0025] The anhydride groups of maleic anhydride-grafted compatibilizers can form chemical bonds with the amino groups of silanes on the powder surface. At the same time, their polypropylene or ethylene-octene segments can form molecular chain entanglements with the polypropylene resin matrix, further strengthening the interfacial bonding between the powder and the resin and ensuring the mechanical property stability of the highly filled composite material.

[0026] In some embodiments, polypropylene resin with the added ultrafine powder is used for injection molding or extrusion molding of refrigerator / freezer compartment shells, washing machine outer drum shells, or air conditioner indoor unit shells.

[0027] The polypropylene composite material prepared by the modified powder of this invention has excellent mechanical properties, heat distortion temperature and surface scratch resistance. It can be adapted to the molding process and usage environment of white goods such as refrigerators, washing machines and air conditioners, and meet the customized needs of the home appliance industry for high-performance green materials.

[0028] In some embodiments, the specific preparation method of the KH-550 hydrolysate is as follows: KH-550 silane coupling agent and deionized water are mixed at a mass ratio of 1:8 to 1:12, and then glacial acetic acid, citric acid or phosphoric acid are added dropwise to adjust the pH to 3.5-5.5. The mixture is stirred at room temperature for 15-20 minutes to obtain a stable alcohol-free KH-550 hydrolysate. This ratio can ensure that the silane is fully hydrolyzed and that the alcohol-free system will not introduce VOCs.

[0029] The present invention has the following advantages over the prior art: This invention possesses significant and diverse technological and industrial advantages over existing technologies: Compared to traditional silane dry modification processes that rely on alcohol solvents and high-temperature drying, this invention completely eliminates the use of alcohol additives and the high-temperature drying process, achieving a fully green modification process with no volatile organic compound emissions and no wastewater generation. Simultaneously, it significantly reduces production energy consumption, fundamentally solving the environmental and high-energy-consumption pain points of traditional processes. Furthermore, it breaks the industry's technical prejudice that silane grafting efficiency cannot be guaranteed without alcohol solvents and high-temperature drying above 130°C. Compared to conventional methods involving simple mechanical blending of multi-component powders, this invention, through the synergistic effect of non-thermal plasma activation and alcohol-free low-temperature modification, not only achieves… The efficient grafting of silane onto the powder surface unexpectedly constructs a gradient interface structure in which barium sulfate selectively coats calcium carbonate, effectively improving the comprehensive performance of polypropylene composites under high-filling conditions. This solves the industry problem of the difficulty in simultaneously achieving mechanical properties, thermal deformation capacity, and surface scratch resistance when using traditional blended powders with high filling. In terms of production applications, the process of this invention does not require additional dedicated production equipment and can be scaled up using existing production lines. The overall production cost is comparable to that of traditional processes, and the modified powder has excellent compatibility with polypropylene resin, which can directly meet the injection molding or extrusion molding requirements of mainstream white goods such as refrigerators, washing machines, and air conditioners. It has outstanding industrial promotion value and practical application prospects. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] General Raw Materials and Equipment Raw materials: Heavy calcium carbonate (industrial grade), barium sulfate (industrial grade), KH-550 silane coupling agent (industrial grade), glacial acetic acid (analytical grade), phosphoric acid (analytical grade), calcium stearate (industrial grade), zinc stearate (industrial grade), polypropylene resin (PP, homopolymer grade), maleic anhydride grafted polypropylene compatibilizer (industrial grade). Equipment: Air jet mill (flat type, classifier wheel speed 12000r / min), non-thermal plasma activator (dielectric barrier discharge type, discharge gap 2mm), high-speed kneader (Z-type blade, volume 50L), injection molding machine (horizontal screw, clamping force 1200kN), silane grafting rate tester, notched impact tester, heat distortion temperature tester, scratch resistance tester, VOC detector.

[0032] Example 1 Step 1: Mix heavy calcium carbonate and barium sulfate evenly at a mass ratio of 85:15, and put them into an air jet mill for dry air jet milling. Control the particle size of the powder to D50=3μm and D97=8μm to obtain mixed powder. Step 2: Place the mixed powder into a non-thermal plasma activator and activate it for 60 seconds under an argon-oxygen mixed atmosphere (argon:oxygen = 7:3) and a power of 100W. Step 3: Pre-preparation of KH-550 hydrolysate: Mix KH-550 silane and deionized water at a mass ratio of 1:10, add glacial acetic acid to adjust the pH to 4.5, stir at room temperature for 20 minutes, and set aside. Transfer the activated mixed powder to a high-speed kneader, heat to 75°C, and add 4% of the mass of KH-550 hydrolysate (pH=4.5, adjusted by glacial acetic acid) without adding any alcohol solvent. Adjust the kneading speed to 1000 r / min and continue kneading for 20 minutes. Step 4: After kneading, allow it to cool naturally to room temperature to obtain the ultrafine powder for appliance casings.

[0033] Example 2 Step 1: Mix heavy calcium carbonate and barium sulfate evenly at a mass ratio of 86:14, and put them into an air jet mill for dry air jet milling. Control the particle size of the powder to D50=3μm and D97=8μm to obtain mixed powder. Step 2: Place the mixed powder into a non-thermal plasma activator and activate it for 60 seconds under an argon-oxygen mixed atmosphere (argon:oxygen = 7:3) and a power of 100W. Step 3: Transfer the activated mixed powder to a high-speed kneader, heat it to 75°C, and without adding any alcohol solvent, first add 0.5% calcium stearate dispersant by weight of the mixed powder, then add 4% KH-550 hydrolysate (pH=4.5, adjusted by glacial acetic acid) by weight of the mixed powder, adjust the kneading speed to 1000 r / min, and continue kneading for 20 minutes; Step 4: After kneading, allow it to cool naturally to room temperature to obtain the ultrafine powder for appliance casings.

[0034] Example 3 Step 1: Mix heavy calcium carbonate and barium sulfate evenly at a mass ratio of 80:20, and put them into an air jet mill for dry air jet milling. Control the particle size of the powder to D50=2μm and D97=10μm to obtain mixed powder. Step 2: Place the mixed powder into a non-thermal plasma activator and activate it for 90 seconds under a pure oxygen atmosphere and a power of 50W. Step 3: Transfer the activated mixed powder to a high-speed kneader, heat it to 60°C, and without adding any alcohol solvent, first add 0.2% zinc stearate dispersant by weight of the mixed powder, then add 2% KH-550 hydrolysate (pH=3.5, adjusted by phosphoric acid) by weight of the mixed powder, adjust the kneading speed to 800 r / min, and continue kneading for 30 minutes; Step 4: After kneading, allow it to cool naturally to room temperature to obtain the ultrafine powder for appliance casings.

[0035] Comparative Example 1 Step 1: Same as Step 1 in Example 1; Step 2: Omit the plasma activation step; Step 3: Same as step 3 in Example 1; Step 4: Same as Step 4 in Example 1.

[0036] Comparative Example 2 Step 1: Same as Step 1 in Example 1; Step 2: Same as Step 2 in Example 1; Step 3: Transfer the activated mixed powder to a high-speed kneader, heat it to 130°C, add 4% of the mass of the mixed powder in an alcoholysis-type KH-550 solution (ethanol:water = 1:1), adjust the kneading speed to 1000 r / min, knead for 20 minutes, and then continue to dry at 130°C for 2 hours. Step 4: After drying, cool to room temperature to obtain the powder.

[0037] Comparative Example 3 Step 1: Mix heavy calcium carbonate and barium sulfate at a mass ratio of 70:30 until homogeneous, and follow the same procedure as in Step 1 of Example 1. Step 2: Same as Step 2 in Example 1; Step 3: Same as step 3 in Example 1; Step 4: Same as Step 4 in Example 1.

[0038] Comparative Example 4 Step 1: Same as Step 1 in Example 1; Step 2: Same as Step 2 in Example 1; Step 3: Transfer the activated mixed powder to a high-speed kneader, heat it to 75°C, and add 4% of the mass of KH-550 hydrolysate (pH=2.5, adjusted by hydrochloric acid) without adding any alcohol solvent. The rest is the same as step 3 in Example 1. Step 4: Same as Step 4 in Example 1.

[0039] Comparative Example 5 Step 1: Mix heavy calcium carbonate and barium sulfate mechanically at a mass ratio of 85:15 until homogeneous, without air jet milling, plasma activation, or silane modification; Step 2: Discharge directly to obtain mixed powder.

[0040] Performance verification 1. Sample preparation: 40 parts by weight of the ultrafine powder obtained in each example / comparative example were added to 100 parts by weight of polypropylene resin, and 3 parts by weight of maleic anhydride grafted polypropylene compatibilizer were added simultaneously. After being mixed evenly by a high-speed mixer, the sample was prepared into a standard test strip by injection molding machine. 2. Silane grafting rate test: The grafting rate was calculated after the powder sample was extracted and dried using the Soxhlet extraction method. 3. Notched impact strength test: The notched impact strength of the specimen in a simply supported beam was tested at 23℃ according to GB / T1843-2008 standard. 4. Heat distortion temperature test: The heat distortion temperature of the specimen was tested under a load of 0.45 MPa according to GB / T1634.2-2004 standard. 5. Scratch resistance rating test: The scratch resistance rating is evaluated by gradient load scratch test according to GB / T31402-2015 standard (rated from 1 to 5, with higher ratings indicating better scratch resistance). 6. VOC emission test: The modified powder is placed in a sealed chamber, and the concentration of volatile organic compounds in the chamber is measured using a VOC detector; 7. Microstructure testing: The surface morphology of the powder was observed using a scanning electron microscope (SEM), and elemental surface scanning was performed using an energy dispersive spectroscopy (EDS) instrument to analyze the distribution characteristics of Ca and S elements and determine the coating of barium sulfate on calcium carbonate. 8. UV resistance test: According to GB / T 16422.3-2014, the sample was placed in a xenon lamp aging chamber (irradiation intensity 340nm / 0.71W / m). 2 Aging at 65℃ and 50% RH for 1000 hours, and testing the yellowing index Δb (≤1.5 is acceptable); 9. Damp heat cycling test: According to GB / T 2423.4-2008, the specimen is cycled 50 times in an environment of 40℃ / 90% RH, and the impact strength retention rate of the test specimen is tested (≥85% is qualified).

[0041] Performance verification results

[0042] microstructure

[0043] Aging resistance

[0044] The data shows that all performance indicators of Examples 1-3 are excellent and there are no VOC emissions, demonstrating the synergistic effect of the core technical features. However, the performance of each comparative example is significantly inferior due to the lack or replacement of key technical features. Comparative example 1 has a significantly reduced grafting rate and mechanical properties due to the lack of plasma activation. Comparative example 2 has a grafting rate close to that of the examples but has high VOC emissions and poor scratch resistance. Comparative example 3 cannot form an effective gradient interface due to deviation in the ratio. Comparative example 4 has damaged the functional groups on the powder surface due to improper pH. Comparative example 5 has the worst performance without modification treatment. This fully proves that the key technical features of the present invention are irreplaceable and cannot be achieved by simple combination of existing technologies.

[0045] SEM and EDS data from Example 1 show that barium sulfate formed a continuous coating layer with a thickness of about 50-80 nm on the surface of calcium carbonate. However, Comparative Example 3 failed to form this structure due to a deviation in the ratio, and Comparative Example 5 failed to form this structure due to no modification treatment. This directly proves the regulatory effect of the process of the present invention on the gradient interface.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An ultrafine powder for use in household appliance casings, characterized in that, The ultrafine powder is prepared by the following method: heavy calcium carbonate and barium sulfate are mixed at a mass ratio of 80-90:10-20 and then subjected to dry air jet milling to obtain a mixed powder; the mixed powder is then subjected to non-thermal plasma surface activation; the activated mixed powder is then subjected to high-speed kneading modification by adding 2-6% of a KH-550 hydrolysate with a pH of 3.5-5.5 at 60-90℃ without adding alcohol solvents, followed by natural cooling to room temperature to obtain the ultrafine powder.

2. The ultrafine powder for appliance casings according to claim 1, characterized in that, The particle size parameters of the mixed powder after dry air jet milling are D50 = 2-4 μm and D97 ≤ 10 μm.

3. The ultrafine powder for appliance casings according to claim 1, characterized in that, The process conditions for non-thermal plasma surface activation are as follows: the activation atmosphere is argon, oxygen, or a mixture of argon and oxygen; the activation power is 50-150W; and the activation time is 20-90 seconds.

4. The ultrafine powder for appliance casings according to claim 1, characterized in that, The pH of the KH-550 hydrolysate was adjusted using glacial acetic acid, citric acid, or phosphoric acid.

5. The ultrafine powder for appliance casings according to claim 1, characterized in that, At the same time as or before adding KH-550 hydrolysate, add 0.2-1% by weight of stearic acid, calcium stearate or zinc stearate as an auxiliary dispersant to the mixed powder.

6. The ultrafine powder for appliance casings according to claim 1, characterized in that, The mass ratio of heavy calcium carbonate to barium sulfate is 83-88:12-17.

7. A method for preparing ultrafine powder for household appliance casings according to any one of claims 1-6, characterized in that, The dry air jet milling process employs an air jet mill or a planetary ball mill, and the high-speed kneading modification involves a kneading speed of 800-1200 r / min and a kneading time of 15-30 min.

8. The application of the ultrafine powder for appliance casings according to any one of claims 1-6, characterized in that, The ultrafine powder is added to polypropylene resin as a filler, with 25-50 parts by weight of the ultrafine powder added per 100 parts by weight of polypropylene resin.

9. The application according to claim 8, characterized in that, The polypropylene resin also contains 1-5 parts by weight of maleic anhydride-grafted polypropylene or ethylene-octene copolymer-grafted maleic anhydride as a compatibilizer.

10. The application according to claim 8 or 9, characterized in that, Polypropylene resin with added ultrafine powder is used for injection molding or extrusion molding of refrigerator / freezer compartment shells, washing machine drum shells, or air conditioner indoor unit shells.

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