Microwave-assisted treatment of decorative metal wood and method of making the same

Abstract

A microwave-assisted treatment method for decorative metallic wood and its preparation includes: subjecting wood to constant humidity treatment and microwave irradiation treatment; adding surface-modified nano-copper to a molten low-melting-point metal at a temperature 20-30°C higher than the alloy melting point to obtain a composite metal; subjecting the composite metal to high-speed shear emulsification to obtain a composite emulsion containing metal composite droplets; causing in-situ condensation on the surface of the composite droplets to form urea-formaldehyde resin microcapsule wall material, thereby obtaining metal microcapsules constituting a microencapsulated low-melting-point metal / nano-copper composite; adding the metal microcapsules to a KH550 aqueous impregnation solution to prepare a metal microcapsule impregnation solution; immersing the microwave-irradiated wood in the metal microcapsule impregnation solution for impregnation treatment; and subjecting the impregnated wood to microwave irradiation to induce microcapsule rupture and directional release of metal, thereby obtaining microwave-assisted treated decorative metallic wood. This yields decorative metallic wood with controllable metallic luster, uniform distribution, and strong adhesion.

Description

Technical Field

[0001] This invention relates to the field of wood functionalization and decorative materials technology, specifically to microwave-assisted treatment of decorative metal wood and its preparation method. Background Technology

[0002] As people's demands for the aesthetics and comfort of indoor environments increase, decorative wood not only needs to possess excellent physical and mechanical properties, but also requires rich colors and textures. Traditional wood staining methods mostly employ paint coatings and surface films, but the colors are superficial and obscure the natural grain of the wood. Introducing composite materials with a metallic sheen into the wood, allowing them to work synergistically with the wood's natural grain to create an "endogenous" decorative effect, is a new approach to expanding the field of wood decoration.

[0003] Low-melting-point metals exhibit a silvery-white metallic luster after solidification. However, the color of a single low-melting-point metal tends to be cool white, lacking warm tones, making it difficult to meet diverse decorative needs.

[0004] In addition, existing methods for preparing metal-wood mainly involve direct pressure impregnation or microwave treatment of wood to create large cracks before impregnation. However, these methods are difficult to solve problems such as uneven distribution of metal within the wood, weak interfacial bonding, uncontrollable impregnation content, and limited color options. Summary of the Invention

[0005] This invention was developed in view of the above problems, with the aim of providing decorative metal wood with controllable metallic luster, uniform distribution and strong bonding, and its preparation method.

[0006] This invention specifically provides a method for preparing decorative metal wood through microwave synergistic treatment. Using wood as a substrate, a low-melting-point metal is composited with nano-copper and microencapsulated through microwave pretreatment and microwave-triggered curing synergistic technology, and then directionally enriched inside the wood to prepare wood that combines metallic texture decoration and thermal management.

[0007] The preparation method includes: Step 1: The wood with a thickness of 2-20mm is subjected to constant humidity treatment. After adjusting the moisture content of the wood to 15-30%, it is subjected to intermittent irradiation treatment using microwaves with a frequency of 2450MHz and a power density of 3.0-5.0kW / kg under the condition of argon gas introduction. Step 2: Mix bismuth, lead, tin and indium in parts by mass of 50-58, 24-27, 25-48 and 50-52, respectively, to form low-melting-point metals with melting points of 62-118°C. Step 3: Disperse copper nanoparticles with an average particle size of 20-60 nm in a mixture of stearic acid and anhydrous ethanol at a mass ratio of (1-3):100. After ultrasonic dispersion for 30-60 min, perform solid-liquid separation, collect the precipitate and dry it to obtain surface-modified copper nanoparticles. Step 4: Add the surface-modified nano-copper to molten low-melting-point metal at a temperature 20–30°C higher than the alloy's melting point. Stir at 500–800 rpm for 15–45 minutes under nitrogen protection, then perform ultrasonic dispersion to obtain the low-melting-point metal / nano-copper composite metal. Surface-modified nano-copper accounts for 2–15% of the total mass of the composite metal. The ultrasonic dispersion process involves a power of 100–300W, a frequency of 20–40kHz, and a time of 5–10min. Step 5: The composite metal is added to an aqueous phase containing emulsifiers and nucleating agents and subjected to high-speed shear emulsification to obtain a composite emulsion containing metal composite droplets with a particle size of 2–10 μm. The high-speed shearing process involves a rotation speed of 8000–15000 rpm and a time of 5–20 minutes. Urea and formaldehyde in a molar ratio of 1:1.5 to 1:2.0 were added to a composite emulsion, along with melamine, where the melamine accounted for 5% to 20% of the urea mass. The pH was adjusted to 4.0 to 5.5, and the temperature was raised to 60 to 90°C and reacted for 2 to 4 hours. This allowed for in-situ condensation polymerization on the surface of the composite droplets, forming urea-formaldehyde resin microcapsule wall material. After cooling and neutralization to pH 7 to 8, the microcapsules were centrifuged, washed, and dried to obtain microencapsulated low-melting-point metal / nano-copper composite metal microcapsules with an average particle size of 3 to 15 μm and a wall thickness of 50 to 300 nm. The core material content of the low-melting-point metal / nano-copper composite is 60-85% by mass; Step 6: Prepare a 3-5% (w / w) KH550 aqueous impregnation solution. The solvent is a mixture of deionized water and anhydrous ethanol in a volume ratio of 2:(8-10), and adjust the pH to 4-5. Add the metal microcapsules to the KH550 aqueous impregnation solution, ultrasonically disperse for 3-5 minutes, and continue stirring for 30-60 minutes to obtain a metal microcapsule impregnation solution, wherein the solid content of the metal microcapsules is 2-15%. Step 7: Place the wood treated in Step 1 into the metal microcapsule impregnation solution, vacuum-treat it under a vacuum of -0.1 to -0.05 MPa for 10 to 30 minutes, then pressurize it to 0.2 to 1.2 MPa and maintain it for 30 to 60 minutes, remove the wood and dry it; Step 8: The impregnated wood is subjected to microwave irradiation treatment at a power density of 2.0-5.0 kW / kg and a frequency of 2450 MHz for 2-10 minutes to obtain microwave-co-treated decorative metal wood.

[0008] Adjusting the mass ratio of surface-modified nano-copper in the composite metal from 2% to 15% controls the variation of decorative colors from light gold, rose gold, red copper to purple copper.

[0009] Surface-modified nano-copper accounts for 2-5% of the total mass of the composite metal.

[0010] Surface-modified nano-copper accounts for 5-15% of the total mass of the composite metal.

[0011] The proportion of surface-modified nano-copper in the total mass of the composite metal is selected from any one of 2-3%, 3-5%, 5-8%, 8-12%, and 12-15%.

[0012] Intermittent irradiation treatment lasts for 30-50 seconds per session, repeated 2-4 times.

[0013] According to the present invention, wood is used as a substrate. The internal channels of the wood are opened by microwave pretreatment. The metal composite is impregnated and enriched in the wood by resin microencapsulation. Microwave-induced microcapsule rupture causes the metal composite to melt and flow, forming a continuous metal network inside the wood to form a physical interlocking and chemical bonding interface. It works in conjunction with the wood texture to form different colors of metal and luster, thus obtaining controllable metallic luster decorative wood for use in interior decorative wood products. Attached Figure Description

[0014] Figure 1 This is a scanning electron microscope image of the decorative metal wood of Embodiment 1 of the present invention.

[0015] Figure 2 This is an elemental distribution diagram of the decorative metal wood of Embodiment 1 of the present invention.

[0016] Figure 3 This is a physical image of the decorative metal and wood product according to Embodiment 1 of the present invention. Detailed Implementation

[0017] The process description of this invention will include numerical values ​​related to temperature or pressure, process change rate, etc. For example, regarding temperature, those skilled in the art should understand that when mentioning a reaction taking place at a certain temperature, the actual meaning is that the temperature control is not absolutely constant, but may, and often will, fluctuate to some extent. This fluctuation may exceed one degree or even more in some cases, as long as the objective is achieved. The magnitude of temperature changes and the precision of temperature control are based on what those skilled in the art can understand.

[0018] Furthermore, the temperature defined in this article can be an input for temperature control on the equipment used. In actual operation, the temperature at a certain point in time depends on the specific characteristics of the equipment and the conditions at the time of the reaction. The defined temperature can also be a target command from the operator. In actual control, this may involve a time period for temperature changes, or even a process of repeated fluctuations. For example, when the detected temperature is below the defined temperature, the reactor is heated; when it is above the defined temperature, the reactor is cooled, thereby maintaining the commanded temperature overall.

[0019] In this invention, if some processes do not specify a temperature or room temperature limit, they should generally be considered to be carried out at room temperature or room temperature. Those skilled in the art can control the process conditions without special knowledge, unless specifically indicated or understood by those skilled in the art. In addition, unless otherwise stated, the numerical range "A to B" in this invention refers to A or above (greater than or equal to A) and B or below (less than or equal to B).

[0020] This invention utilizes a synergistic technique of microwave pretreatment and microwave-triggered curing to composite and microencapsulate low-melting-point metals with nano-copper, thereby directionally enriching them within wood. This achieves stable loading of the metal within the wood and controllable microwave release, resulting in the preparation of wood-based panels that combine metallic texture decoration with thermal management.

[0021] Copper and its alloys possess a unique metallic luster and exhibit excellent thermal, electrical, and antibacterial properties. Nano-copper particles not only retain the color of copper but are also easily dispersed in polymer or metal matrices. This invention combines low-melting-point metals with nano-copper to achieve a range of warm-toned metallic lusters, from silver-white and pink-gold to bronze, greatly enriching the color expression of decorative wood. However, nano-copper has high surface energy, is prone to aggregation, and its interfacial compatibility with low-melting-point metals needs to be addressed. This invention provides a specific solution to further overcome the new problems encountered in the low-melting-point metal / nano-copper compounding process.

[0022] The specific technical solution is as follows: 1. Apply constant humidity treatment to wood with a thickness of 2-20mm. Place the wood in a constant temperature treatment chamber to adjust the moisture content of the wood to 15-30%. After constant humidity treatment, treat the wood with microwave radiation. Under the condition that the mechanical properties of the wood are not affected, argon gas is introduced into the microwave reactor (flow rate 120-150 sccm), and microwaves with a frequency of 2450MHz and a power density of 3.0-5.0kW / kg are used for intermittent irradiation treatment (30-50 seconds per session, 2-4 cycles). This causes cracks to form in the tracheids and thin-walled cells inside the wood, enriching the impregnation channels of the wood without reducing the mechanical properties of the wood.

[0023] Timber specifically refers to boards made from logs, and there are no restrictions on the type; it can be any type such as eucalyptus, pine, or poplar.

[0024] By coordinating the configuration of moisture content and microwave irradiation parameters, not only is the mechanical property not affected, but an optimized structural window is also provided for subsequent capsule impregnation, directional enrichment, and metallization fixation. Excessive moisture content leads to excessively large cracks, affecting the subsequent metallization effect.

[0025] 2. Prepare low-melting-point metals with melting points of 62–118℃ by compounding different metal elements such as 50–58% bismuth (Bi), 24–27% lead (Pb), 25–48% tin (Sn), and 50–52% indium (In). The content of different metal elements is selected according to the melting point requirements. The prepared low-melting-point metals are the main core materials for microencapsulation.

[0026] The mixture should be thoroughly mixed, but it is not limited to this step.

[0027] The following provides examples of compound formulations, which are selected for use in the embodiments below, but those skilled in the art can replace the component schemes according to the actual situation.

[0028] Formula 1 (melting point approximately 62°C) · Bismuth (Bi): 50 parts Lead (Pb): 24 parts Tin (Sn): 48 parts • Indium (In): 52 parts Formula 2 (melting point approximately 72°C) · Bismuth (Bi): 58 parts Lead (Pb): 27 parts Tin (Sn): 25 parts • Indium (In): 50 parts Formula 3 (melting point approximately 82℃) · Bismuth (Bi): 55 parts Lead (Pb): 25 parts Tin (Sn): 35 parts • Indium (In): 51 parts Formula 4 (melting point approximately 92°C) · Bismuth (Bi): 52 parts • Lead (Pb): 26 parts Tin (Sn): 30 parts • Indium (In): 50 parts Formula 5 (melting point approximately 103°C) · Bismuth (Bi): 50 parts Lead (Pb): 27 parts Tin (Sn): 40 parts • Indium (In): 51 parts Formula 6 (melting point approximately 112℃) · Bismuth (Bi): 58 parts Lead (Pb): 24 parts Tin (Sn): 42 parts • Indium (In): 52 parts Formula 7 (melting point approximately 118℃) · Bismuth (Bi): 56 parts Lead (Pb): 25 parts Tin (Sn): 48 parts • Indium (In): 50 parts 3. Select spherical or near-spherical nano-copper powder with an average particle size of 20-60 nm, disperse it in anhydrous ethanol containing stearic acid (1-3% by mass), ultrasonically disperse for 30-60 min, centrifuge and dry to obtain surface-modified nano-copper, thereby improving the dispersion stability of nano-copper in low-melting-point metals.

[0029] The ratio of nano-copper powder to anhydrous ethanol is 1:20 to 1:100 g / mL.

[0030] After mixing nano-copper powder, stearic acid, and anhydrous ethanol, the agglomerated nano-copper is dispersed by ultrasonication, while stearic acid molecules are adsorbed onto the copper surface to form a uniform suspension.

[0031] After ultrasonic dispersion, the suspension is centrifuged to separate solids and liquids. Under centrifugal force, the surface-modified nano-copper precipitates to the bottom. The supernatant is removed and the precipitate is collected.

[0032] The nano-copper precipitate obtained by centrifugation is placed in a vacuum drying oven or a forced-air drying oven and dried at 50-70°C for more than 6 hours to remove residual solvent, thereby obtaining dry, surface-modified nano-copper powder.

[0033] 4. Add the surface-modified nano-copper to the molten low-melting-point metal at a ratio of 2-15% of the total mass of the composite metal core (temperature 20-30°C higher than the alloy melting point). Mechanically stir (500-800 rpm, 15-45 min) under nitrogen protection and supplement with ultrasonic dispersion (100-300 W power, 20-40 kHz frequency, 5-10 min) to make the nano-copper uniformly suspended in the liquid low-melting-point metal, forming a uniformly distributed low-melting-point metal / nano-copper composite metal.

[0034] Stearic acid has a melting point of 69–71°C. In metal melts at 82–148°C, stearic acid would theoretically melt / decompose. However, this invention unexpectedly discovered that stearic acid molecules adsorbed on the surface of nano-copper form a dense protective shield. Even if the temperature exceeds its melting point, strong van der Waals forces between molecules maintain an ordered arrangement. This "thermal hysteresis effect" allows stearic acid to still play a dispersing role in low-melting-point metal melts.

[0035] 5. The decorative color can be controlled by adjusting the nano copper content. When the nano copper content is selected from 0.1% to 5%, the composite metal will appear silver, light gold to rose gold as the content increases. When the nano copper content is 5% to 15%, it will appear red copper to purple copper.

[0036] The nano-copper content is 0.1%, it is silvery-white, with an L* value of 85, an a* value of 2, and a b* value of 5. The nano-copper content is 1%, exhibiting micro-gold properties, with an L* value of 82, an a* value of 6, and a b* value of 12. The nano-copper content is 2%, it is light gold in color, with an L* value of 78, an a* value of 10, and a b* value of 18. It contains 3% nano-copper, is rose gold in color, has an L* value of 72, an a* value of 18, and a b* value of 16. The nano copper content is 5%, and it has a reddish-copper color with a rose-like hue. The L* value is 66, the a* value is 23, and the b* value is 13. The nano-copper content is 8%, and it is red copper in appearance. The L* value is 60, the a* value is 26, and the b* value is 11. The nano-copper content is 12%, and it is light purple copper with an L* value of 54, an a* value of 27, and a b* value of 9. The nano-copper content is 15%, and it is in the form of purple copper. The L* value is 48, the a* value is 28, and the b* value is 8.

[0037] Where L* value represents lightness, a* value represents red-green hue, and b* value represents yellow-blue hue.

[0038] 6. Add the prepared composite metals of different colors to the aqueous phase containing emulsifier and nucleating agent, and emulsify by high-speed shearing (8000-15000 rpm, 5-20 min) to obtain an emulsion with a composite droplet size of 2-10 μm. Urea and formaldehyde (molar ratio 1:1.5–1:2.0) were added to the emulsion, along with melamine, accounting for 5–20% of the mass of urea (melamine to formaldehyde molar ratio 1:2.5–3). The pH was adjusted to 4.0–5.5, and the temperature was raised to 60–90°C. The reaction was carried out for 2–4 hours, during which urea-formaldehyde resin microcapsule wall material was formed by in-situ condensation on the surface of the composite droplets. The mixture was then cooled and neutralized to pH 7–8, followed by centrifugation, washing, and drying (at 50–70°C for more than 6 hours) to obtain a microencapsulated low-melting-point metal / nano-copper composite with an average particle size of 3–15 μm, a capsule wall thickness of 50–300 nm, and a core material content of 60–85%.

[0039] The aqueous phase is a liquid system containing emulsifiers and nucleating agents, with water as the continuous phase. The mass ratio of the composite metal to the aqueous phase is 1:2 to 1:10. The emulsifier can be Tween 80, Span 80, or a mixture of both, and the amount of emulsifier is 0.5% to 5% of the mass of the aqueous phase. The nucleating agent can be sodium chloride or polyvinyl alcohol, and the amount of nucleating agent is 0.1% to 2% of the mass of the aqueous phase.

[0040] The total mass ratio of urea and formaldehyde to the mass ratio of the composite metals in the emulsion is 1:1.5 to 1:6.

[0041] For adjusting the pH to 4.0–5.5, the pH adjuster can be one or more of acetic acid, citric acid, dilute hydrochloric acid, or dilute sulfuric acid, preferably a 10–30% aqueous solution of acetic acid, which is added slowly dropwise under stirring.

[0042] For example, under stirring conditions, slowly add a 10-30% aqueous acetic acid solution to the emulsion to adjust the pH to 4.0-5.5. The adding rate should be controlled at 1-2 drops / second to avoid localized excessively low pH levels that could lead to rapid polymerization.

[0043] When the pH is adjusted to 4.0–5.5 and the temperature is raised to 60–90°C, hydroxymethyl urea and hydroxymethyl melamine in the aqueous phase undergo a condensation reaction, removing water molecules to form methylene bridges, thus generating urea-formaldehyde resin-melamine modified wall material in situ on the surface of the composite metal droplets. Controlling the pH within this range serves to accelerate the condensation reaction through acidic catalysis, while preventing excessive cross-linking that could lead to an overly brittle wall material. Maintaining the temperature at 60–90°C provides the activation energy to complete the condensation reaction within 2–4 hours, while preventing excessive temperature from causing the composite metal to melt and overflow or resulting in rapid polymerization. A reaction time of 2–4 hours allows the wall material to reach the ideal degree of cross-linking, forming a dense and complete three-dimensional network structure, with a wall thickness controlled at 50–300 nm.

[0044] For the process of cooling and neutralizing to pH 7-8, after the reaction is complete, the reaction system is naturally cooled to room temperature (about 20-25°C), or cooled to room temperature using a water bath. Then, under stirring, a 10-20% sodium hydroxide aqueous solution is slowly added dropwise to the cooled system to adjust the pH to 7-8.

[0045] For the centrifugal separation after cooling and neutralization, the reaction solution is centrifuged at 8000-15000 rpm for 5-20 minutes, the supernatant is discarded, the precipitate is collected, deionized water or ethanol aqueous solution is added to the precipitate, it is redispersed and centrifuged again, and the washing is repeated 2-3 times.

[0046] 7. Preparation of Metal Microcapsule Impregnation Solution: First, prepare a 3% KH550 aqueous impregnation solution (KH550 is selected to improve the interfacial crosslinking strength between metal, resin, and wood). The solvent is a mixture of deionized water and anhydrous ethanol (water:ethanol = 2:8), with a pH of 4–5. Then, add the metal microcapsules to the KH550 aqueous impregnation solution, ultrasonically disperse for 3–5 min, and then mechanically stir for 30–60 min to form the metal microcapsule impregnation solution. The solid content of the metal microcapsules is 2–15%.

[0047] Deionized water and anhydrous ethanol were mixed at a volume ratio of 2:8. KH550 was then added under stirring to achieve a KH550 mass fraction of 3%. While continuing stirring, glacial acetic acid (or a 10% aqueous acetic acid solution) was slowly added dropwise to the solution, and the pH was adjusted to 4–5 using a pH meter.

[0048] The purpose of adjusting the pH to 4–5 is to ensure that the hydrolysis rate of KH550 is moderate under weakly acidic conditions, allowing for sufficient generation of active silanols (Si-OH) before impregnation. Simultaneously, this pH condition effectively inhibits the condensation reaction between silanols, preventing KH550 self-polymerization and precipitation, and maintaining the clarity and stability of the impregnation solution. If the pH is below 4, KH550 hydrolyzes too quickly and is prone to self-polymerization and inactivation; if the pH is above 5, hydrolysis is insufficient, resulting in inadequate coupling activity. Therefore, pH 4–5 is the optimal window for achieving stable activation of KH550 and ensuring subsequent chemical bonding at the metal-resin-wood interface.

[0049] 8. Place the microwave-pretreated wood with micro-cracks into the metal microcapsule impregnation solution and vacuum it for 10 to 30 minutes under a vacuum of -0.1 to -0.05 MPa. Then pressurize it to 0.2 to 1.2 MPa and maintain it for 30 to 60 minutes to allow the metal microcapsules to fully penetrate into the internal cell cavities of the wood through the micro-crack network. Remove the impregnated wood and dry it.

[0050] The impregnated wood is then dried at 50–80°C for 6–12 hours, or vacuum dried to constant weight.

[0051] 9. Place the impregnated wood in a microwave treatment device and irradiate it for 2 to 10 minutes at a power density of 2.0 to 5.0 kW / kg and 2450 MHz to finally obtain decorative metal wood.

[0052] Microwave-induced self-assembly allows microcapsules to be directionally enriched along the wood's vessels, triggering partial microcapsule wall rupture at temperatures above their melting points. This causes the metal composite to melt and flow, releasing a low-melting-point metal / nano-copper core to form a three-dimensional metal network. Simultaneously, microwave irradiation promotes complexation reactions between urea-formaldehyde resin, metal ions, and active functional groups such as hydroxyl and carboxyl groups on the wood cell walls, achieving metallization and fixation within the wood, resulting in metallic luster in various shades.

[0053] 10. The density range of the prepared metal composite decorative wood is 0.80–2.6 g / cm³. 3 The impregnation weight gain is 80-500%, the thermal conductivity is 0.31-2.6 W / (m·K), and the bending strength is 150.3-205.4 MPa. It can be used for decorative wall panels, heating flooring, and solid wood furniture.

[0054] Example 1: 1. Poplar boards with a thickness of 12mm were subjected to constant humidity treatment. The wood was placed in a constant temperature treatment chamber to adjust the moisture content of the wood to 23%. After constant humidity treatment, the wood was subjected to microwave radiation treatment. Under the condition that the mechanical properties of the wood were not affected, argon gas was introduced into the microwave reactor (flow rate 130 sccm), and microwaves with a frequency of 2450MHz and a power density of 4.0 kW / kg were used for intermittent irradiation treatment (30 seconds per cycle, 3 cycles).

[0055] 2. A low-melting-point metal with a melting point of 92.2°C was obtained by mixing and compounding 52 parts by mass of Bi, 26 parts by mass of Pb, 30 parts by mass of Sn, and 50 parts by mass of In (Formula 4).

[0056] 3. Spherical copper nanoparticles with an average particle size of 40 nm were selected and dispersed in anhydrous ethanol containing stearic acid (2% by mass). The dispersion was ultrasonically carried out for 45 min, and then centrifuged and dried (60℃, 6 h) to obtain surface-modified copper nanoparticles. The ratio of copper nanoparticles to anhydrous ethanol was 1:60 g / mL.

[0057] 4. Add the surface-modified nano-copper at a ratio of 2% of the total mass of the composite metal core to the molten (temperature 115℃) low-melting-point metal. Mechanically stir (600rpm, 30min) under nitrogen protection and supplement with ultrasonic dispersion (power 200W, frequency 30 kHz, 8min) to form a light gold low-melting-point metal / nano-copper composite metal.

[0058] 5. The prepared composite metal was added to an aqueous phase containing Tween 80 and sodium chloride (the mass ratio of composite metal to aqueous phase was 1:7, the amount of Tween 80 accounted for 3% of the mass of the aqueous phase, and the amount of nucleating agent accounted for 1% of the mass of the aqueous phase), and emulsified by high-speed shearing (12000 rpm, 10 min) to obtain an emulsion with a composite droplet size of 6 μm. Urea and formaldehyde (molar ratio 1:1.8, total mass of urea and formaldehyde to composite metal in emulsion mass ratio 1:2.5) were added to the emulsion, along with melamine, accounting for 12% of the urea mass. The pH was slowly adjusted to 4.8 using a 15% acetic acid aqueous solution, and the temperature was raised to 75℃. The reaction was allowed to proceed for 3 hours, resulting in in-situ condensation polymerization on the surface of the composite droplets to form urea-formaldehyde resin microcapsule wall material. The mixture was then allowed to cool naturally to room temperature and slowly neutralized to pH 7.5 using a 15% sodium hydroxide aqueous solution. The reaction solution was centrifuged at 12000 rpm for 15 minutes, the supernatant was discarded, and the precipitate was collected. Deionized water or ethanol aqueous solution was added to the precipitate, and the mixture was redispersed and centrifuged again. After washing 2-3 times, the mixture was dried (60℃, 6 hours) to obtain a microencapsulated low-melting-point metal / nano-copper composite with an average particle size of 9 μm, a capsule wall thickness of 180 nm, and a core material content of 72.2%.

[0059] 6. Prepare a 3% aqueous impregnation solution for KH550, using a mixture of deionized water and anhydrous ethanol (water:ethanol (volume ratio) = 2:8). Slowly add a 10% aqueous acetic acid solution to the solution, resulting in a pH of 4.5. Then add the metal microcapsules to the KH550 aqueous impregnation solution, ultrasonically disperse for 4 minutes, and mechanically stir for 50 minutes to form a metal microcapsule impregnation solution with a solid content of 10%.

[0060] 7. The wood with micro-cracks after microwave pretreatment is placed in the metal microcapsule impregnation solution and vacuumed for 20 min under a vacuum of -0.1 MPa. Then, the pressure is increased to 0.8 MPa and maintained for 45 min. The impregnated wood is then removed and dried at 70°C for 6 h to obtain decorative metal wood.

[0061] 8. The impregnated wood is placed in a microwave treatment device and subjected to microwave irradiation treatment for 6 minutes at a power density of 3 kW / kg and 2450 MHz, finally obtaining decorative metal-wood such as Figures 1-3 As shown.

[0062] Performance testing: Wood density range 1.1 g / cm³ 3 The impregnation weight gain is 120%, the thermal conductivity is 1.65 W / (m·K), and the flexural strength is 186.1 MPa. Example

[0063] 1. Pine wood boards with a thickness of 2mm were subjected to constant humidity treatment. The wood was placed in a constant temperature treatment chamber to adjust the moisture content of the wood to 15%. After constant humidity treatment, the wood was subjected to microwave radiation treatment. Under the condition that the mechanical properties of the wood were not affected, argon gas was introduced into the microwave reactor (flow rate 120 sccm), and microwaves with a frequency of 2450MHz and a power density of 3.0kW / kg were used for intermittent irradiation treatment (30 seconds per cycle, 2 cycles).

[0064] 2. A low-melting-point metal with a melting point of 61.8℃ was obtained by mixing and compounding 50 parts by mass of Bi, 24 parts by mass of Pb, 48 parts by mass of Sn, and 52 parts by mass of In (Formula 1).

[0065] 3. Select spherical copper nanoparticles with an average particle size of 20 nm, disperse them in anhydrous ethanol containing stearic acid (1% by mass), ultrasonically disperse for 30 min, and centrifuge and dry (50℃, 6 h) to obtain surface-modified copper nanoparticles, wherein the ratio of copper nanoparticles to anhydrous ethanol is 1:20 g / mL.

[0066] 4. Add the surface-modified nano-copper at a ratio of 15% of the total mass of the composite metal core to the molten (90℃) low-melting-point metal. Mechanically stir (500rpm, 30min) under nitrogen protection and supplement with ultrasonic dispersion (100W power, 20kHz frequency, 5min) to form a copper-colored low-melting-point metal / nano-copper composite metal.

[0067] 5. The prepared composite metal was added to an aqueous phase containing Tween 80 and sodium chloride (the mass ratio of composite metal to aqueous phase was 1:10, the amount of Tween 80 accounted for 0.5% of the mass of the aqueous phase, and the amount of nucleating agent accounted for 0.1% of the mass of the aqueous phase), and emulsified by high-speed shearing (8000 rpm, 5 min) to obtain an emulsion with a composite droplet size of 2 μm. Urea and formaldehyde (molar ratio 1:1.5, total mass of urea and formaldehyde to the mass ratio of composite metal in the emulsion 1:1.5) were added to the emulsion, along with melamine, accounting for 5% of the mass of urea. The pH was slowly adjusted to 5.5 using a 15% acetic acid aqueous solution, and the temperature was raised to 60℃. The reaction was allowed to proceed for 2 hours, during which urea-formaldehyde resin microcapsule wall material was formed by in-situ condensation on the surface of the composite droplets. The mixture was then allowed to cool naturally to room temperature and slowly neutralized to pH 7 using a 15% sodium hydroxide aqueous solution. The reaction solution was centrifuged at 8000 rpm for 5 minutes, the supernatant was discarded, and the precipitate was collected. Deionized water or ethanol aqueous solution was added to the precipitate, and the mixture was redispersed and centrifuged again. After washing 2-3 times, the mixture was dried (50℃, 6 hours) to obtain a microencapsulated low-melting-point metal / nano-copper composite with an average particle size of 3 μm, a capsule wall thickness of 50 nm, and a core material content of 60.1%.

[0068] 6. Prepare a 3% aqueous impregnation solution for KH550, using a mixture of deionized water and anhydrous ethanol (water:ethanol (volume ratio) = 2:10). Slowly add a 10% aqueous acetic acid solution to the solution until the pH reaches 5. Then add the metal microcapsules to the KH550 aqueous impregnation solution, ultrasonically disperse for 3 minutes, and mechanically stir for 30 minutes to form a metal microcapsule impregnation solution with a solid content of 2%.

[0069] 7. The wood with micro-cracks after microwave pretreatment is placed in the metal microcapsule impregnation solution and vacuumed for 10 min under a vacuum of -0.05 MPa. Then, the pressure is increased to 0.2 MPa and maintained for 30 min. The impregnated wood is then removed and dried at 50°C for 6 h to obtain decorative metal wood.

[0070] 8. The impregnated wood is placed in a microwave treatment device and subjected to microwave irradiation treatment for 2 minutes at a power density of 2kW / kg and 2450 MHz to finally obtain decorative metal wood.

[0071] Performance testing: Wood density range 0.9 g / cm³ 3 The impregnation weight gain is 85%, the thermal conductivity is 0.42 W / (m·K), and the flexural strength is 152.5 MPa. Example

[0072] 1. Eucalyptus boards with a thickness of 20mm were subjected to constant humidity treatment. The wood was placed in a constant temperature treatment chamber to adjust the moisture content of the wood to 30%. After constant humidity treatment, the wood was subjected to microwave radiation treatment. Under the condition that the mechanical properties of the wood were not affected, argon gas was introduced into the microwave reactor (flow rate 150 sccm), and microwaves with a frequency of 2450MHz and a power density of 5.0kW / kg were used for intermittent irradiation treatment (50 seconds per cycle, 4 cycles).

[0073] 2. A low-melting-point metal with a melting point of 118.3°C was obtained by mixing and compounding 56 parts by mass of Bi, 25 parts by mass of Pb, 48 parts by mass of Sn, and 50 parts by mass of In (Formula 7).

[0074] 3. Select spherical copper nanoparticles with an average particle size of 60 nm, disperse them in anhydrous ethanol containing stearic acid (3% by mass), ultrasonically disperse for 60 min, and centrifuge and dry (65℃, 6 h) to obtain surface-modified copper nanoparticles, wherein the ratio of copper nanoparticles to anhydrous ethanol is 1:100 g / mL.

[0075] 4. Add the surface-modified nano-copper at a ratio of 5% of the total mass of the composite metal core to the molten (temperature 140℃) low-melting-point metal. Mechanically stir (800rpm, 45min) under nitrogen protection and supplement with ultrasonic dispersion (power 300W, frequency 40kHz, 10min) to form a red copper-colored low-melting-point metal / nano-copper composite metal.

[0076] 5. The prepared composite metal was added to an aqueous phase containing Tween 80 and sodium chloride (the mass ratio of composite metal to aqueous phase was 1:2, the amount of Tween 80 accounted for 5% of the mass of the aqueous phase, and the amount of nucleating agent accounted for 2% of the mass of the aqueous phase), and emulsified by high-speed shearing (15000 rpm, 20 min) to obtain an emulsion with a composite droplet size of 10 μm. Urea and formaldehyde (molar ratio 1:2.0, total mass of urea and formaldehyde to composite metal in emulsion mass ratio 1:5.7) were added to the emulsion, along with melamine, accounting for 20% of the urea mass. The pH was slowly adjusted to 4.0 using a 15% acetic acid aqueous solution, and the temperature was raised to 90℃. The reaction was carried out for 4 hours, and urea-formaldehyde resin microcapsule wall material was formed by in-situ condensation on the surface of the composite droplets. The mixture was naturally cooled to room temperature and slowly neutralized to pH 8 using a 15% sodium hydroxide aqueous solution. The reaction solution was centrifuged at 15000 rpm for 20 minutes, the supernatant was discarded, and the precipitate was collected. Deionized water or ethanol aqueous solution was added to the precipitate, and the mixture was redispersed and centrifuged again. After washing 2-3 times, the mixture was dried (70℃, 6 hours) to obtain a microencapsulated low-melting-point metal / nano-copper composite with an average particle size of 15 μm, a capsule wall thickness of 300 nm, and a low-melting-point metal / nano-copper composite core material content of 85%.

[0077] 6. Prepare a 3% aqueous impregnation solution for KH550, using a mixture of deionized water and anhydrous ethanol (water:ethanol (volume ratio) = 2:8). Slowly add a 10% aqueous acetic acid solution to the solution to a pH of 4. Then add the metal microcapsules to the KH550 aqueous impregnation solution, ultrasonically disperse for 5 minutes, and mechanically stir for 60 minutes to form a metal microcapsule impregnation solution with a solid content of 15%.

[0078] 7. The wood with micro-cracks after microwave pretreatment is placed in the metal microcapsule impregnation solution and vacuumed for 30 min under a vacuum of -0.1 MPa. Then, the pressure is increased to 1.2 MPa and maintained for 60 min. The impregnated wood is then removed and dried at 80℃ for 6 h to obtain decorative metal wood.

[0079] 8. The impregnated wood is placed in a microwave treatment device and subjected to microwave irradiation treatment for 10 minutes at a power density of 5kW / kg and 2450 MHz to finally obtain decorative metal wood.

[0080] Performance testing: Wood density range 2.5 g / cm³ 3 The impregnation weight gain is 480%, the thermal conductivity is 2.5 W / (m·K), and the flexural strength is 203.6 MPa.

[0081] The metal composite decorative woods prepared in Examples 1-3 above have densities of 1.1, 0.90, and 2.5 g / cm³, respectively; impregnation weight gain rates of 120%, 85%, and 480%, respectively; thermal conductivity of 1.65, 0.42, and 2.5 W / (m·K), respectively; and bending strength of 186.1, 152.5, and 203.6 MPa, respectively. These values ​​cover the performance range achievable by this invention (density 0.80–2.6 g / cm³, weight gain rate 80–500%, thermal conductivity 0.31–2.6 W / (m·K), bending strength 150.3–205.4 MPa). This demonstrates that by adjusting process parameters, this invention can control product performance within a wide range, meeting the needs of different application scenarios such as decorative walls, heated floors, and solid wood furniture.

[0082] Below, based on Example 1, comparative experiments are conducted by changing some parts of the process, while other processes are the same as in Example 1.

[0083] Comparative Example 1: In step 1, the moisture content is adjusted to 60%.

[0084] The wood has a density of approximately 0.82 g / cm³, a weight gain of 52% after impregnation, a thermal conductivity of 0.31 W / (m·K), and a bending strength of 135 MPa.

[0085] The metal distribution on the surface of the finished product is uneven, and the color varies in shade.

[0086] Comparative Example 2: In step 1, the irradiation power is 2.5 kW / kg, and the duration is 20 seconds per session.

[0087] The wood has a density of approximately 0.88 g / cm³, an impregnation weight gain of 85%, a thermal conductivity of 0.35 W / (m·K), and a bending strength of 145 MPa.

[0088] The finished product has a light and uneven color.

[0089] Comparative Example 3: In step 1, the irradiation power is 5.5 kW / kg, and the duration is 60 seconds per session.

[0090] The wood has a density of approximately 1.05 g / cm³, a weight gain of 100% after impregnation, a thermal conductivity of 0.60 W / (m·K), and a bending strength of 130 MPa.

[0091] The distribution of metals is discontinuous.

[0092] Comparative Example 4: Nano-copper is mixed directly with low-melting-point metals without surface modification.

[0093] The wood has a density of approximately 1.08 g / cm³, a weight gain of 115% after impregnation, a thermal conductivity of 1.20 W / (m·K), and a bending strength of 165 MPa.

[0094] The finished product has a dull and uneven color, obvious black spots, and poor metallic luster.

[0095] Comparative Example 5: In step 3, ultrasonic dispersion is performed for 20 minutes.

[0096] The wood has a density of approximately 1.09 g / cm³, a weight gain of 118% after impregnation, a thermal conductivity of 1.45 W / (m·K), and a bending strength of 175 MPa.

[0097] The finished product has slightly uneven color and some dark spots.

[0098] Comparative Example 6: The temperature of the molten state in step 4 is 145℃.

[0099] The wood has a density of approximately 1.12 g / cm³, a weight gain of 125% after impregnation, a thermal conductivity of 1.55 W / (m·K), and a bending strength of 180 MPa.

[0100] The finished product is dark in color, and the gold tone is weakened.

[0101] Comparative Example 7: By controlling the mass ratio of urea and formaldehyde to composite metals, the capsule wall thickness can be increased to 400 nm.

[0102] The wood has a density of approximately 1.07 g / cm³, a weight gain of 115% after impregnation, a thermal conductivity of 0.80 W / (m·K), and a bending strength of 158 MPa.

[0103] The finished product is light in color.

[0104] Comparative Example 8: After adding urea, formaldehyde, and melamine to the emulsion, the pH was adjusted to 3.5, the temperature was raised to 50°C, and the reaction was carried out for 1 hour.

[0105] The wood has a density of approximately 1.02 g / cm³, a weight gain of 98% after impregnation, a thermal conductivity of 0.65 W / (m·K), and a bending strength of 150 MPa.

[0106] The metal distribution is uneven.

[0107] Comparative Example 9: After adding urea, formaldehyde, and melamine to the emulsion, the pH was adjusted to 6.5, the temperature was raised to 100℃, and the reaction was carried out for 6 hours.

[0108] The wood has a density of approximately 1.05 g / cm³, a weight gain of 112% after impregnation, a thermal conductivity of 0.55 W / (m·K), and a bending strength of 148 MPa.

[0109] The finished product has no metallic luster.

[0110] Comparative Example 10: In step 6, adjust the pH value to 3.5.

[0111] The wood has a density of approximately 1.05 g / cm³, a weight gain rate of 110% after impregnation, a thermal conductivity of 1.20 W / (m·K), and a bending strength of 160 MPa.

[0112] Comparative Example 11: In step 6, adjust the pH value to 5.5.

[0113] The wood has a density of approximately 1.08 g / cm³, a weight gain of 115% after impregnation, a thermal conductivity of 1.35 W / (m·K), and a bending strength of 168 MPa.

[0114] Comparative Example 12: In step 8, the microwave power density is 1 kW / kg.

[0115] The wood has a density of approximately 1.08 g / cm³, a weight gain of 117% after impregnation, a thermal conductivity of 0.65 W / (m·K), and a bending strength of 158 MPa.

[0116] The finished product is light in color.

[0117] Comparative Example 13: In step 8, the microwave irradiation time is 1 minute.

[0118] The wood has a density of approximately 1.09 g / cm³, a weight gain of 118% after impregnation, a thermal conductivity of 0.55 W / (m·K), and a bending strength of 156 MPa.

[0119] Uneven color distribution.

[0120] Comparative Example 14: In step 8, the microwave power density is 6 kW / kg, and the irradiation time is 12 min.

[0121] The wood has a density of approximately 1.06 g / cm³, a weight gain of 115% after impregnation, a thermal conductivity of 1.20 W / (m·K), and a bending strength of 142 MPa.

[0122] Localized carbonization of the wood.

[0123] Comparative Example 15: Step 8 is omitted, and secondary microwave irradiation is not performed.

[0124] The wood has a density of approximately 1.08 g / cm³, a weight gain rate of 116% after impregnation, a thermal conductivity of 0.32 W / (m·K), and a bending strength of 152 MPa.

[0125] The finished product has no metallic luster.

[0126] The comparison between Comparative Examples 1-15 and Example 1 above shows that the following conditions are crucial for achieving uniform metal distribution, strong interfacial bonding, controllable color, and good thermal conductivity: Step 1: a moisture content of 15-30%, microwave power density of 3.0-5.0 kW / kg, and 2-4 cycles of 30-50 seconds per cycle; Step 3: stearic acid modification and ultrasonic dispersion for more than 30 minutes; Step 4: dispersion temperature 20-30°C above the alloy melting point; Step 5: microencapsulation at pH 4.0-5.5, temperature 60-90°C, time 2-4 hours, and wall thickness 50-300 nm; Step 6: KH550 impregnation solution at pH 4-5; and Step 8: microwave power density of 2.0-5.0 kW / kg and irradiation time 2-10 minutes. Any deviation from these conditions will lead to decreased product performance or process failure.

[0127] It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Various modifications can be made to the invention within the scope defined by the claims. Different implementation methods or embodiments, as well as new modifications obtained through combinations of common technical means, should also be considered to be included within the scope of this invention.

Claims

1. A method for preparing decorative metal-wood using microwave synergistic processing. Its features are, include: Step 1: The wood with a thickness of 2-20mm is subjected to constant humidity treatment. After adjusting the moisture content of the wood to 15-30%, it is subjected to intermittent irradiation treatment using microwaves with a frequency of 2450MHz and a power density of 3.0-5.0kW / kg under the condition of argon gas introduction. Step 2: Mix bismuth, lead, tin and indium in parts by mass of 50-58, 24-27, 25-48 and 50-52, respectively, to form low-melting-point metals with melting points of 62-118°C. Step 3: Disperse copper nanoparticles with an average particle size of 20-60 nm in a mixture of stearic acid and anhydrous ethanol at a mass ratio of (1-3):

100. After ultrasonic dispersion for 30-60 min, perform solid-liquid separation, collect the precipitate and dry it to obtain surface-modified copper nanoparticles. Step 4: Add the surface-modified nano-copper to molten low-melting-point metal at a temperature 20–30°C higher than the alloy's melting point. Stir at 500–800 rpm for 15–45 minutes under nitrogen protection, then perform ultrasonic dispersion to obtain the low-melting-point metal / nano-copper composite metal. Surface-modified nano-copper accounts for 2–15% of the total mass of the composite metal. The ultrasonic dispersion process involves a power of 100–300W, a frequency of 20–40kHz, and a time of 5–10min. Step 5: The composite metal is added to an aqueous phase containing emulsifiers and nucleating agents and subjected to high-speed shear emulsification to obtain a composite emulsion containing metal composite droplets with a particle size of 2–10 μm. The high-speed shearing process involves a rotation speed of 8000–15000 rpm and a time of 5–20 minutes. Urea and formaldehyde in a molar ratio of 1:1.5 to 1:2.0 were added to a composite emulsion, along with melamine, where the melamine accounted for 5% to 20% of the urea mass. The pH was adjusted to 4.0 to 5.5, the temperature was raised to 60 to 90°C, and the reaction was carried out for 2 to 4 hours. This allowed the composite droplets to undergo in-situ condensation polymerization to form urea-formaldehyde resin microcapsule wall material. The mixture was then cooled and neutralized to pH 7 to 8. After centrifugation, washing, and drying, metal microcapsules of a microencapsulated low-melting-point metal / nano-copper composite with an average particle size of 3 to 15 μm and a wall thickness of 50 to 300 nm were obtained. Step 6: Prepare a 3-5% (w / w) KH550 aqueous impregnation solution. The solvent is a mixture of deionized water and anhydrous ethanol in a volume ratio of 2:(8-10), and adjust the pH to 4-5. Add the metal microcapsules to the KH550 aqueous impregnation solution, ultrasonically disperse for 3-5 minutes, and continue stirring for 30-60 minutes to obtain a metal microcapsule impregnation solution, wherein the solid content of the metal microcapsules is 2-15%. Step 7: Place the wood treated in Step 1 into the metal microcapsule impregnation solution, vacuum-treat it under a vacuum of -0.1 to -0.05 MPa for 10 to 30 minutes, then pressurize it to 0.2 to 1.2 MPa and maintain it for 30 to 60 minutes, remove the wood and dry it; Step 8: The impregnated wood is subjected to microwave irradiation treatment at a power density of 2.0-5.0 kW / kg and a frequency of 2450 MHz for 2-10 minutes to obtain microwave-co-treated decorative metal wood.

2. The preparation method according to claim 1, wherein, Adjusting the mass ratio of surface-modified nano-copper in the composite metal from 2% to 15% controls the variation of decorative colors from light gold, rose gold, red copper to purple copper.

3. The preparation method according to claim 1, wherein, Surface-modified nano-copper accounts for 2-5% of the total mass of the composite metal.

4. The preparation method according to claim 1, wherein, Surface-modified nano-copper accounts for 5-15% of the total mass of the composite metal.

5. The preparation method according to claim 1, wherein, The proportion of surface-modified nano-copper in the total mass of the composite metal is selected from any one of 2-3%, 3-5%, 5-8%, 8-12%, and 12-15%.

6. The preparation method according to claim 1, wherein, The intermittent irradiation treatment in step 1 is 30-50 seconds per session, repeated 2-4 times.

7. Microwave-treated decorative metal-wood prepared by the preparation method according to any one of claims 1 to 6.

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