A wood colorant based on metal-ligand coordination and its application

Abstract

The present invention discloses a wood colorant based on metal-ligand coordination and its application. The wood colorant comprises a transition metal salt and an organic polyacid containing two or more carboxyl characteristic functional groups. Among them, the transition metal salt and the organic polyacid are formulated according to a molar ratio of 1:4 - 4:1 to obtain a wood colorant with metal-ligand coordination. By changing the types and dosages of the transition metal salt and the organic polyacid in the wood colorant, the color can be regulated. The present invention also provides a preparation method of a colored formaldehyde-free wood-based panel. In this preparation method, based on the metal-ligand coordination strategy, a wood colorant is added to wood particles, and the coloring process is combined with the forming process to achieve the coloring of wood particles and the through-coloring of the wood-based panel. The prepared colored formaldehyde-free wood-based panel can present a variety of adjustable colors, has excellent color abrasion resistance and mechanical strength, and is suitable for the preparation of large-size novel colored formaldehyde-free wood-based panels.

Description

Technical Field

[0001] The present invention relates to the technical field of wood coloring. More specifically, it relates to a wood coloring agent based on metal-ligand coordination and its application. Background Art

[0002] For many years, wood has been widely used in various fields such as construction, household items, and tools due to its sustainability, high mechanical strength, and aesthetic properties. In the past few decades, plastics and alloys have gradually become the main materials for furniture, door and window frames, and household tools. However, wooden materials still occupy an important position due to their environmentally friendly raw materials and renewability, especially artificial boards made from waste wood particles. However, the coloring process of various wooden boards overly relies on synthetic resin adhesives in paints. These adhesives will release a large amount of formaldehyde gas under ultraviolet irradiation, bringing environmental pollution and health risks. In recent years, researchers have been committed to developing new coloring methods for wood materials. Among them, the organic dye penetration method realizes coloring by impregnating wood in organic dyes. However, due to the easy degradation of organic dyes, their colors will gradually fade during long-term use. The structural coloring method realizes the coloring of wood by constructing gold, silver coatings or photonic crystal coatings on the wood surface. However, due to the small size of the wood that can be colored and the poor durability of the coatings, the coatings are damaged after wear and the natural color of the wood is exposed, which has certain limitations.

[0003] In addition to organic dyes, inorganic pigments such as cinnabar, malachite, and lapis lazuli, etc., are often used to color daily necessities and artworks due to their abundance and durability. For example, they have been used in fields such as ancient ceramic glazes, traditional murals, and glass colorants. In recent years, researchers have constructed color erasable papers, colored hydrogels, etc. by using metal-ligand coordination. Their colors come from the electronic transitions of metal ions and ligands in them. However, these studies basically stay at using metal-ligand coordination as ink color development or using a single coordination system for coloring in a single material field. There has not been any relevant research on the environmentally friendly coloring of wood with inorganic pigments reported yet. Summary of the Invention

[0004] To solve the problems existing in the prior art, the first object of the present invention is to provide a wood coloring agent based on metal-ligand coordination. The wood coloring agent provided by the present invention can realize the coloring of wood particles by using metal-ligand coordination, and can realize the color regulation by changing the types and dosages of transition metal salts and organic polyacids in the wood coloring agent.

[0005] The second object of the present invention is to provide an application of the above-mentioned wood coloring agent in the preparation of colored building materials.

[0006] The third object of the present invention is to provide a preparation method of a colored formaldehyde-free wood-based panel. This preparation method can achieve through-color coloring of the wood-based panel. Compared with traditional coating or spraying for coloring, there is no release of harmful gases (such as formaldehyde), nor the problem of fading of organic dyes. Through-color coloring effectively solves the problem of wear and fading faced by methods such as structural color coatings.

[0007] The fourth object of the present invention is to provide a colored formaldehyde-free wood-based panel. The colored formaldehyde-free wood-based panel prepared by the present invention can present a variety of adjustable colors, there is no problem of harmful gas release and wear and fading, and at the same time, the obtained wood-based panel also has excellent mechanical strength.

[0008] To achieve the above first object, the present invention adopts the following technical solutions:

[0009] The present invention provides a wood colorant based on metal-ligand coordination. The wood colorant includes a transition metal salt and an organic polyacid containing two or more carboxyl characteristic functional groups. Among them, the transition metal salt and the organic polyacid are prepared according to a molar ratio of 1:4 - 4:1 to obtain a wood colorant with metal-ligand coordination. As an example, the molar ratio of the transition metal salt to the organic polyacid can be 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, etc.

[0010] Furthermore, the transition metal salt includes but is not limited to one of iron salts, copper salts, cobalt salts, nickel salts, zinc salts; as an example, the iron salts include but are not limited to ionic salts containing trivalent iron ions such as ferric chloride hexahydrate, ferric nitrate nonahydrate, ferric sulfate nonahydrate, iron acetate, etc., and can also be ionic salts containing divalent iron ions such as ferrous chloride tetrahydrate, ferrous nitrate hexahydrate, ferrous sulfate heptahydrate, etc., the copper salts include but are not limited to ionic salts containing divalent copper ions such as copper sulfate pentahydrate, copper chloride dihydrate, copper nitrate trihydrate, etc., the cobalt salts include but are not limited to ionic salts containing divalent cobalt ions such as cobalt sulfate heptahydrate, cobalt chloride hexahydrate, cobalt nitrate hexahydrate, cobalt acetate tetrahydrate, etc., the nickel salts include but are not limited to ionic salts containing divalent nickel ions such as nickel sulfate hexahydrate, nickel chloride hexahydrate, nickel nitrate hexahydrate, nickel acetate tetrahydrate, etc., the zinc salts include but are not limited to ionic salts containing divalent zinc ions such as zinc sulfate, zinc chloride monohydrate, zinc nitrate hexahydrate, zinc acetate dihydrate, etc.;

[0011] On the one hand, the organic polyacid coordinates with the transition metal salt, playing the role of metal-ligand coordination. By changing the types and dosages of the transition metal salt and the organic polyacid, the coordination environment is adjusted, thereby achieving the regulation of color. On the other hand, to a certain extent, it acts like a binder, bonding the wood particles together, so that no other binder components need to be added, meeting the environmental protection requirements. As an example, in the embodiments of the present invention, the organic polyacid includes, but is not limited to, organic polyacids containing two or more carboxyl characteristic functional groups such as malic acid, succinic acid, malonic acid, oxalic acid, citric acid, tartaric acid, etc.

[0012] To achieve the above second object, the present invention adopts the following technical solution:

[0013] The present invention provides an application of the wood colorant as described above in the preparation of colored building materials.

[0014] To achieve the above third object, the present invention adopts the following technical solution:

[0015] The present invention provides a method for preparing a colored formaldehyde-free wood-based panel, comprising the following steps:

[0016] Dissolve the wood colorant as described above with water to obtain a coloring solution;

[0017] Mix the pretreated wood particles with the coloring solution in proportion, and heat and dry them with or without stirring to complete the coloring;

[0018] Fill the colored wood particles into a mold, hot press, and demold to obtain the colored formaldehyde-free wood-based panel.

[0019] In the above preparation method, those skilled in the art can add some functional components (excluding binders with bonding functions) according to application needs to enhance the performance of the wood-based panel, but it will not affect the coloring performance of the wood colorant.

[0020] Furthermore, the pH value of the coloring solution generally affects the mechanical properties of the material. It is found that it is advisable to control the pH value within the range of 0 - 3 (excluding 0) or 11 - 13. Generally, the pH value of the prepared coloring solution is between 0.5 - 3, and at this time, no pH adjustment is required, that is, the pH value of the system after mixing the transition metal salt, organic polyacid, and water is already within the above-defined range. If the required coloring solution is not strongly acidic, that is, the pH value is between 3 - 11 (excluding the end values), acid solution or alkali solution can be additionally added for adjustment, such as hydrochloric acid, sulfuric acid, sodium hydroxide solution, etc.

[0021] Furthermore, the heating temperature is 40 - 85 °C, and the heating time is 24 - 48 h.

[0022] Further, in the coloring solution, the concentration of the transition metal salt is 0.13 - 3.84 mol·L -1 ; Exemplarily, the concentration of the transition metal salt can be 0.13 mol·L -1 , 0.2 mol·L -1 , 0.4 mol·L -1 , 0.6 mol·L -1 , 0.8 mol·L -1 , 1 mol·L -1 , 1.2 mol·L -1 , 1.4 mol·L -1 , 1.6 mol·L -1 , 1.8 mol·L -1 , 2 mol·L -1 , 2.2 mol·L -1 , 2.4 mol·L -1 , 2.6 mol·L -1 , 2.8 mol·L -1 , 3 mol·L -1 , 3.2 mol·L -1 , 3.4 mol·L -1 , 3.6 mol·L -1 , 3.8 mol·L -1 etc.;

[0023] The mass ratio of the wood particles to the coloring solution is 1:1 - 1:5; Exemplarily, the mass ratio of the wood particles to the coloring solution can be 1:1, 1:2, 1:3, 1:4, 1:5, etc.

[0024] Further, the wood particles are generally selected from wood chips, sawdust, wood shavings or various wood fibers such as bagasse, etc. with a size of 3 - 30 mm.

[0025] It should be noted that during the coloring process of the wood particles (i.e., the heating and drying process), stirring needs to be introduced. Generally, due to the evaporation of water during the heating and drying process, the coloring area will show uneven shades. If stirring is introduced, usually the materials during heating and drying will be more evenly dispersed, and the coloring will also be more uniform, so that the color presented by the final obtained artificial board is more uniform. On the contrary, if no stirring is introduced or the stirring times are too few, the artificial board may have a stronger sense of particle and a stronger contrast between different regions. Therefore, the stirring times or time intervals can be adjusted according to actual needs, but it will not affect the obvious change of color. As an example, the materials can be stirred every 1 - 4 h during the heating and drying process.

[0026] The hot pressing process is the most crucial factor affecting the mechanical strength of wood-based panels. When the hot pressing temperature is appropriate, the greater the pressure applied during hot pressing, the greater the static bending strength of the wood-based panel. Since the wood-based panel developed in this invention features rich colors, its mechanical strength only needs to meet the application requirements. As an example, the hot pressing temperature is 60 - 210 °C, the hot pressing time is 1 - 120 min, and the pressure is 3 - 100 MPa.

[0027] The material of the mold used in this invention can be any metal or non-metal material with sufficient mechanical strength, sprayed with an anti-sticking coating on the surface or covered with a thin film of materials such as polyimide. After the material preparation is completed, the mold needs to meet the requirement of being detachable so that the material can be taken out intact.

[0028] Furthermore, the wood particles are pretreated according to the following steps:

[0029] Wash the wood particles and then place them in an oven for heating and drying. After all or part of the dried wood particles are decolorized, wash them clean with a mixed solution of ethanol / water, and then heat and dry them in the oven. As an example, the heating temperature is 40 - 85 °C, and the heating time is 24 - 48 h.

[0030] To achieve the fourth above-mentioned purpose, this invention adopts the following technical solution:

[0031] This invention provides a colored formaldehyde-free wood-based panel prepared by using the preparation method as described above.

[0032] The beneficial effects of this invention are as follows:

[0033] This invention discloses a wood colorant based on metal-ligand coordination, and the wood colorant includes transition metal salts and organic polyacids. This wood colorant is suitable for coloring wood particles, thereby preparing a colored formaldehyde-free wood-based panel.

[0034] This invention also discloses a method for preparing a colored formaldehyde-free wood-based panel by using the above wood colorant. This method is essentially a new formaldehyde-free coloring method for wood-based panels. By adding the above wood colorant to the wood particles, while the wood-based panel is being pressed and formed, formaldehyde-free through-color coloring is achieved. By changing the types and dosages of the transition metal salts and organic polyacids in the wood colorant, color regulation is realized, and the wood-based panels prepared by this coloring method present a variety of adjustable colors. Moreover, compared with the existing wood-based panel coloring methods, no additional coating or spraying is required for coloring, there is no release of harmful gases such as formaldehyde during long-term use, there is no problem of fading of organic dyes, and the through-color coloring effectively solves the problem of wear and fading faced by methods such as structural color coatings.

[0035] The colored formaldehyde-free wood-based panel prepared by the present invention not only has rich colors, but also has excellent mechanical strength. Exemplarily, the flexural strength of the colored formaldehyde-free wood-based panel prepared by the present invention can reach up to 55.3 ± 3.1 MPa at most, and the modulus of elasticity reaches 9.3 ± 1.9 GP, which is much higher than the strength requirement of 10 MPa for cement wood-based panels in GB / T 24312-2009, and is almost equivalent to the flexural strength of natural Pinus sylvestris var. mongolica wood. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The following further elaborates on the specific embodiments of the present invention in conjunction with the drawings.

[0037] Figure 1 The schematic flow diagram showing the coloring and forming of the colored formaldehyde-free wood-based panel in the present invention.

[0038] Figure 2 The physical diagram of the colored formaldehyde-free wood-based panel prepared in Example 1 of the present invention and the visible light region reflection spectrum scanned by its ultraviolet spectrophotometer.

[0039] Figure 3 The physical diagram of the colored formaldehyde-free wood-based panel prepared in Example 2 of the present invention and the visible light region reflection spectrum scanned by its ultraviolet spectrophotometer.

[0040] Figure 4 The physical diagram of the colored formaldehyde-free wood-based panel prepared in Example 3 of the present invention and the visible light region reflection spectrum scanned by its ultraviolet spectrophotometer.

[0041] Figure 5 The physical diagram of the large-sized colored formaldehyde-free wood-based panel prepared in Example 4.

[0042] Figure 6 The physical diagram of the colored formaldehyde-free wood-based panel prepared in Example 5 of the present invention and the visible light region reflection spectrum scanned by its ultraviolet spectrophotometer.

[0043] Figure 7 The physical diagrams of the colored formaldehyde-free wood-based panels obtained under different preparation conditions in the present invention.

[0044] Figure 8 The comparison diagram of the color abrasion durability test between the colored formaldehyde-free wood-based panel prepared in Example 5 and the commercial colored wood-based panel.

[0045] Figure 9 The test diagram of the aging durability test of the wood coloring agent prepared in Example 5. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] To illustrate the present invention more clearly, the present invention will be further described below in conjunction with preferred embodiments and the accompanying drawings. Similar components in the drawings are denoted by the same reference numerals. Those skilled in the art should understand that the specific content described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0047] Example 1

[0048] This example is based on Figure 1 the process schematic diagram to exemplarily provide a preparation process of a colored formaldehyde-free wood-based panel:

[0049] (1) For commercially available sawdust particles, clean them with ethanol and deionized water, and heat and dry them in an oven at 60 °C for 24 h;

[0050] (2) Place the sawdust particles washed in step (1) in a sodium hypochlorite solution with a concentration of 6%-14%, react under an ice-water bath for 2 h, wash them with a mixed solution of water and ethanol with a volume ratio of 1:1, and heat and dry them in an oven at 60 °C for 48 h.

[0051] (3) Dissolve 1.46 g of cobalt sulfate heptahydrate (CoSO 4 ·7H 2 O) and 1 g of anhydrous citric acid in 10 g of deionized water, where the molar ratio of cobalt ions (Co 2+ ) to citric acid is 1:1.

[0052] (4) Add 1 M NaOH solution to the solution obtained in step (3), and use a pH meter to adjust the pH value to 3.0 to obtain a coloring solution;

[0053] (5) Mix the sawdust particles obtained in step (2) and the coloring solution obtained in step (4) evenly, where the mass ratio of the sawdust particles to the coloring solution is 1:3, and then heat and dry them in an oven at 60 °C for 48 h. Stir every 3 h during the drying process to keep the color uniform, and complete the coloring of the sawdust particles.

[0054] (6) Fill the colored sawdust particles obtained in step (5) into a metal detachable mold covered with a polyimide film for hot pressing, where the hot pressing temperature is 120 °C, the hot pressing time is 5 min, and the pressure is 20 MPa.

[0055] (7) After the hot pressing is completed, disassemble the mold and demold to obtain it.

[0056] Figure 2 shows the visible light region reflection spectrum (wavelength 390 - 780 nm) obtained by scanning the colored formaldehyde-free wood-based panel under an ultraviolet spectrophotometer, Figure 2 and the upper left corner in is a physical picture taken by a digital camera.

[0057] Its modulus of rupture was measured to be 39.33 MPa according to ASTM D1037-12 of the American Society for Testing and Materials.

[0058] Example 2

[0059] This example is based on Figure 1 the process schematic diagram of

[0060] (1) For commercially available sawdust particles, they were cleaned with ethanol and deionized water and heated and dried in an oven at 60 °C for 30 h.

[0061] (2) The sawdust particles washed in step (1) were placed in a sodium hypochlorite solution with a concentration of 6%-14% and reacted in an ice-water bath for 4 h, washed with a mixed solution of water and ethanol with a volume ratio of 1:1, and heated and dried in an oven at 60 °C for 48 h.

[0062] (3) 2.70 g of cobalt sulfate heptahydrate (CoSO 4 ·7H 2 O) and 1 g of malonic acid were dissolved in 10 g of deionized water, and the molar ratio of cobalt ions (Co 2+ ) to malonic acid was 1:1. After mixing, no additional pH adjustment was required to obtain a coloring solution.

[0063] (4) The sawdust particles obtained in step (2) and the coloring solution obtained in step (3) were mixed evenly, and the mass ratio of the sawdust particles to the coloring solution was 1:4. Then, they were heated and dried in an oven at 60 °C for 36 h, and stirred every 2 h during the drying process to keep the color uniform, completing the coloring of the sawdust particles.

[0064] (5) The colored sawdust particles obtained in step (4) were filled in a metal detachable mold covered with a polyimide film for hot pressing, where the hot pressing temperature was 130 °C, the hot pressing time was 4 min, and the pressure was 15 MPa.

[0065] (6) After the hot pressing was completed, the mold was disassembled and demolded to obtain the product.

[0066] Figure 3 The visible light region reflection spectrum (wavelength 390 - 780 nm) obtained by scanning the colored formaldehyde-free wood-based panel with an ultraviolet spectrophotometer is shown, Figure 3 and the physical picture taken by a digital camera is shown in the upper left corner.

[0067] Its modulus of rupture was measured to be 30.43 MPa according to ASTM D1037-12 of the American Society for Testing and Materials.

[0068] Example 3

[0069] This example is based on Figure 1 the process schematic diagram to exemplarily provide a preparation process of a colored formaldehyde-free wood-based panel:

[0070] (1) For commercially available sawdust particles, clean them with ethanol and deionized water, and heat and dry them in an oven at 65 °C for 40 h;

[0071] (2) Place the sawdust particles washed in step (1) in a sodium hypochlorite solution with a concentration of 6%-14%, react under an ice-water bath for 3 h, wash them with a mixed solution of water and ethanol with a volume ratio of 1:1, and heat and dry them in an oven at 65 °C for 40 h.

[0072] (3) Dissolve 1.14 g of ferric chloride hexahydrate (FeCl 3 ·6H 2 O) and 1 g of succinic acid in 10 g of deionized water, where the molar ratio of ferric ions (Fe 3+ ) to succinic acid is 1:2. After mixing, no additional pH adjustment is required to obtain a coloring solution.

[0073] (4) Mix the sawdust particles obtained in step (2) and the coloring solution obtained in step (3) evenly, where the mass ratio of the sawdust particles to the coloring solution is 1:2, and then heat and dry them in an oven at 60 °C for 36 h, stirring once every 1 h during the process to keep the color uniform.

[0074] (5) Fill the colored sawdust particles obtained in step (4) into a removable mold covered with a polyimide film metal, and perform hot pressing, where the hot pressing temperature is 110 °C, the hot pressing time is 3 min, and the pressure is 25 MPa.

[0075] (6) After the hot pressing is completed, disassemble the mold and demold to obtain the product.

[0076] Figure 4 shows the visible light region reflection spectrum (wavelength 390 - 780 nm) obtained by scanning the colored formaldehyde-free wood-based panel under an ultraviolet spectrophotometer, Figure 4 and the upper left corner in

[0077] is a physical picture taken by a digital camera.

[0078] Example 4

[0079] This example is based on Figure 1 the process schematic diagram to exemplarily provide a preparation process of a colored formaldehyde-free wood-based panel:

[0080] (1) For commercially available sawdust particles, clean them with ethanol and deionized water, and heat and dry them in an oven at 65 °C for 30 h;

[0081] (2) Place the sawdust particles washed in step (1) in a sodium hypochlorite solution with a concentration of 6%-14%, react under an ice-water bath for 2 h, wash them with a mixed solution of water and ethanol with a volume ratio of 1:1, and heat and dry them in an oven at 65 °C for 30 h.

[0082] (3) Dissolve 54.75 g of cobalt sulfate heptahydrate (CoSO 4 ·7H 2 O) and 37.5 g of citric acid in 375 g of deionized water, where the molar ratio of cobalt ions (Co 2+ ) to citric acid is 1:1. After mixing, no additional pH adjustment is required to obtain a coloring solution.

[0083] (4) Mix the sawdust particles obtained in step (2) and the coloring solution obtained in step (3) evenly, where the mass ratio of the sawdust particles to the coloring solution is 1:3. Then heat and dry them in an oven at 60 °C for 24 h, and stir them once every 2 h during the process to keep the color uniform.

[0084] (5) Fill the colored sawdust particles obtained in step (4) into a metal detachable mold covered with a polyimide film, and perform hot pressing, where the hot pressing temperature is 120 °C, the hot pressing time is 10 min, and the pressure is 20 MPa.

[0085] (6) After the hot pressing is completed, disassemble the mold and demold to obtain the product.

[0086] Figure 5 It is a physical picture taken by a digital camera.

[0087] Measure its modulus of rupture according to the American Society for Testing and Materials standard ASTM D1037-12, which is 28.19 MPa.

[0088] Example 5

[0089] This example is based on Figure 1 of the process schematic diagram, and exemplarily provides a preparation process of a colored formaldehyde-free wood-based panel:

[0090] (1) For commercially available sawdust particles, clean them with ethanol and deionized water, and heat and dry them in an oven at 60 °C for 24 h;

[0091] (2) Place the sawdust particles washed in step (1) in a sodium hypochlorite solution with a concentration of 6%-14%, react under an ice-water bath for 2 h, wash them with a mixed solution of water and ethanol with a volume ratio of 1:1, and heat and dry them in an oven at 60 °C for 24 h.

[0092] (3) Dissolve 1.46 g of cobalt sulfate hexahydrate (CoSO 4 ·6H 2 O) and 1 g of citric acid in 10 g of deionized water, where the molar ratio of cobalt ions (Co 2+ ) to citric acid is 1:1. After mixing, no additional pH adjustment is required to obtain a coloring solution.

[0093] (4) Mix the sawdust particles obtained in step (2) and the coloring solution obtained in step (3) evenly, where the mass ratio of sawdust particles to the coloring solution is 1:3. Then heat and dry them in an oven at 60 °C for 36 h, and stir once every 1 h during the process to keep the color uniform.

[0094] (5) Fill the colored sawdust particles obtained in step (4) into a metal detachable mold covered with a polyimide film and perform hot pressing, where the hot pressing temperature is 120 °C, the hot pressing time is 5 min, and the pressure is 20 MPa.

[0095] (6) After the hot pressing is completed, disassemble the mold to demold, and it is obtained.

[0096] Figure 6 The visible light region reflection spectrum (wavelength 390 - 780 nm) obtained by scanning the colored formaldehyde-free wood-based panel under an ultraviolet spectrophotometer is shown, Figure 6 and the physical picture taken by a digital camera is shown in the upper left corner.

[0097] Measure its modulus of rupture according to the American Society for Testing and Materials standard ASTM D1037 - 12 to be 33.18 MPa.

[0098] To demonstrate that the present invention can prepare wood-based panels with a variety of adjustable colors, the preparation of the following samples is completed.

[0099] (1) For commercially available sawdust particles, clean them with ethanol and deionized water, and heat and dry them in an oven at 60 °C for 30 h;

[0100] (2) Place the sawdust particles washed in step (1) in a sodium hypochlorite solution with a concentration of 6% - 14%, react under an ice-water bath for 2 h, wash them with a mixed solution of water and ethanol with a volume ratio of 1:1, and heat and dry them in an oven at 65 °C for 30 h.

[0101] (3) Dissolve a certain amount of metal ion salt and 1 g of organic polyacid in 10 g of deionized water, where the molar ratio of metal ions to organic polyacid ranges from 1:4 to 2:1. After mixing, no additional pH adjustment is required or adjust it to the specified pH value using 1M NaOH solution to obtain a coloring solution.

[0102] (4) Mix the sawdust particles obtained in step (2) and the coloring solution obtained in step (3) evenly, where the mass ratio of the sawdust particles to the coloring solution is 1:3, and then heat and dry them in an oven at 60 °C for 24 h, stirring once every 1 h during the process to keep the color uniform.

[0103] (5) Fill the colored sawdust particles obtained in step (4) into a metal detachable mold covered with a polyimide film and perform hot pressing, where the hot pressing temperature is 120 °C, the hot pressing time is 5 min, and the pressure is 20 MPa.

[0104] (6) After the hot pressing is completed, disassemble the mold and demold to obtain the product.

[0105] Among them, the coloring solution is prepared according to Table 1. For the physical pictures of the colored formaldehyde-free wood-based panels obtained under different preparation conditions, see Figure 7 .

[0106] Table 1

[0107]

[0108] Note: In Table 1, the molar ratio refers to the molar ratio of the transition metal salt to the organic polyacid; the pH in Table 1 refers to the pH value of the coloring solution; the transition metal salt concentration in Table 1 refers to the concentration of the transition metal salt in the coloring solution; the labels in Table 1 are consistent with those in Figure 7 the labels in

[0109] Research shows that by adjusting the types and dosages of the transition metal salt and the organic polyacid in the wood coloring agent, as well as the pH value and the transition metal salt concentration of the coloring solution, wood-based panels with rich colors as shown in Figure 7 can be obtained. Among them, when the types and dosages of the transition metal salt and the organic polyacid are fixed, adjusting the pH value and the transition metal salt concentration of the coloring solution will only affect the depth change of the color of the wood-based panel, and there will not be a large color span such as changing from red to blue or from green to red. Of course, Figure 7 only exemplary wood-based panel samples are provided. Under this wood coloring agent system, actually hundreds of color changes can be presented, and they will not be listed one by one here.

[0110] Example 6

[0111] This example is based on the Figure 1 process schematic diagram and exemplarily provides a preparation process of a colored formaldehyde-free wood-based panel:

[0112] (1) For commercially available sawdust particles, clean them with ethanol and deionized water and heat and dry them in an oven at 60 °C for 30 h;

[0113] (2) Place the sawdust particles washed in step (1) into a sodium hypochlorite solution with a concentration of 6% - 14%, react for 2 h under an ice - water bath, wash with a mixed solution of water and ethanol with a volume ratio of 1:1, and heat - dry in an oven at 60 °C for 30 h.

[0114] (3) Dissolve 2.92 g of cobalt sulfate hexahydrate (CoSO 4 ·6H 2 O) and 2 g of citric acid in 20 g of deionized water. The molar ratio of cobalt ions (Co 2+ ) to citric acid is 1:1. After mixing, no additional pH adjustment is required to obtain a coloring solution.

[0115] (4) Mix the sawdust particles obtained in step (2) and the coloring solution obtained in step (3) evenly. The mass ratio of the sawdust particles to the coloring solution is 1:3. Then heat - dry in an oven at 60 °C for 30 h, and stir once every 1 h during the process to keep the color uniform.

[0116] (5) Fill the colored sawdust particles obtained in step (4) into a metal - removable mold covered with a polyimide film, and perform hot - pressing. The hot - pressing temperature is 150 °C, the hot - pressing time is 5 min, and the pressure is 50 MPa.

[0117] (6) After the hot - pressing is completed, disassemble the mold to demold, and it is obtained.

[0118] Measure its modulus of rupture according to the American Society for Testing and Materials standard ASTM D1037 - 12, and it is 49.49 MPa.

[0119] Color abrasion durability test

[0120] Adopt a wear - resistant color - rubbing test method that simulates the actual use environment, and conduct strict tests on the sample prepared in Example 5 and the commercially available colored particleboard. The results are shown in Figure 8 . By comparing the worn areas, it is found that after being rubbed by a 100 - mesh grinding wheel for 60 seconds, the commercially available particleboards with surface dye coatings or colored PVC coatings all show obvious wear and fading phenomena, and even the wood background color has been exposed, with poor durability. While the colored samples treated by the metal - ligand coordination in the present invention show excellent color stability, which can be attributed to the fact that the present invention conducts overall coloring on the wood - based panel, so there will be no such wear and fading phenomena. Through comparative analysis with existing products, the coloring technology of the present invention effectively improves the color stability and durability of surface coloring.

[0121] Colorant aging durability test

[0122] Considering that the pre-treated wood particles themselves will also age, an aging test method simulating the actual use environment was adopted to strictly detect the coloring solution prepared in Example 5 after drying the moisture (i.e., the wood colorant), and study the aging resistance of the wood colorant. The results are shown in Figure 9 . By comparing the reflection spectra in the visible light region, it was found that after being irradiated with 340 nm ultraviolet light of 0.89 W m −2 for 0 h, 200 h, 400 h, 600 h, 800 h, 1000 h (equivalent to 0 - 1 year of natural sunshine in Florida) at 60 °C, there was no obvious mutation in the ultraviolet spectrum of the wood colorant, and there were only minor changes in depth that were invisible to the naked eye.

[0123] Based on the above comparative analysis with existing products, the colorant of the present invention effectively improves the durability of color wear and long-term durability.

[0124] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for preparing a colored formaldehyde-free artificial board, characterized in that: The steps include: (1) Place the cleaned sawdust particles in a 6%-14% sodium hypochlorite solution, react in an ice-water bath for 2 h, wash with a 1:1 volume ratio of water and ethanol solution, and heat and dry in an oven at 60 °C for 48 h; (2) Dissolve 1.46 g of cobalt sulfate heptahydrate and 1 g of anhydrous citric acid in 10 g of deionized water, wherein the molar ratio of cobalt ion to citric acid is 1:1; (3) Add 1 M NaOH solution to the solution obtained in step (2), and adjust the pH value to 3.0 using a pH meter to obtain a colored solution; (4) mixing the sawdust particles obtained in step (1) and the coloring solution obtained in step (3) uniformly, wherein the mass ratio of the sawdust particles to the coloring solution is 1:3, and then heating and drying in an oven at 60° C. for 48 h, stirring every 3 h during the drying process to keep the color uniform, thereby completing the coloring of the sawdust particles; (5) filling the colored sawdust particles obtained in step (4) into a metal detachable mold covered with a polyimide film and hot pressing the mold, wherein the hot pressing temperature is 120°C, the hot pressing time is 5 min, and the pressure is 20 MPa; (6) After the hot pressing is completed, the mold is disassembled and demolded.

2. A method for preparing a colored formaldehyde-free artificial board, characterized in that: The steps include: (1) Place the cleaned sawdust particles in a 6%-14% sodium hypochlorite solution, react in an ice-water bath for 4 h, wash with a 1:1 volume ratio of water and ethanol solution, and heat and dry in an oven at 60 °C for 48 h; (2) dissolving 2.70 g of cobalt sulfate heptahydrate and 1 g of malonic acid in 10 g of deionized water, wherein the molar ratio of cobalt ion to malonic acid is 1:1, and after mixing, no additional pH adjustment is required to obtain a coloring solution; (3) mixing the sawdust particles obtained in step (1) and the coloring solution obtained in step (2) uniformly, wherein the mass ratio of the sawdust particles to the coloring solution is 1:4, and then heating and drying in an oven at 60° C. for 36 h, stirring every 2 h during the drying process to keep the color uniform, thereby completing the coloring of the sawdust particles; (4) filling the colored sawdust particles obtained in step (3) into a metal detachable mold covered with a polyimide film and hot pressing the mold, wherein the hot pressing temperature is 130° C., the hot pressing time is 4 min, and the pressure is 15 MPa; (5) After the hot pressing is completed, the mold is disassembled and demolded.

3. A method for preparing a colored formaldehyde-free artificial board, characterized in that: The steps include: (1) Place the cleaned sawdust particles in a 6%-14% sodium hypochlorite solution, react in an ice-water bath for 2 h, wash with a 1:1 volume ratio of water and ethanol solution, and heat and dry in an oven at 65 °C for 30 h; (2) dissolving 54.75 g of cobalt sulfate heptahydrate and 37.5 g of citric acid in 375 g of deionized water, wherein the molar ratio of cobalt ion to citric acid is 1:1, and no additional pH adjustment is required after mixing to obtain a coloring solution; (3) mixing the sawdust particles obtained in step (1) and the coloring solution obtained in step (2) uniformly, wherein the mass ratio of the sawdust particles to the coloring solution is 1:3, and then heating and drying in an oven at 60° C. for 24 h, stirring once every 2 h during the process to keep the color uniform; (4) filling the colored sawdust particles obtained in step (3) into a metal detachable mold covered with a polyimide film and hot pressing the mold, wherein the hot pressing temperature is 120° C., the hot pressing time is 10 min, and the pressure is 20 MPa; (5) After the hot pressing is completed, the mold is disassembled and demolded.

4. A method for preparing a colored formaldehyde-free artificial board, characterized in that: The steps include: (1) Place the cleaned sawdust particles in a 6%-14% sodium hypochlorite solution, react in an ice-water bath for 2 h, wash with a 1:1 volume ratio of water and ethanol mixed solution, and heat and dry in an oven at 60 °C for 24 h; (2) dissolving 1.46 g of cobalt sulfate hexahydrate and 1 g of citric acid in 10 g of deionized water, wherein the molar ratio of cobalt ion to citric acid is 1:1, and no additional pH adjustment is required after mixing to obtain a coloring solution; (3) mixing the sawdust particles obtained in step (1) and the coloring solution obtained in step (2) uniformly, wherein the mass ratio of the sawdust particles to the coloring solution is 1:3, and then heating and drying in an oven at 60° C. for 36 h, stirring once every 1 h during the process to keep the color uniform; (4) filling the colored sawdust particles obtained in step (3) into a metal detachable mold covered with a polyimide film and hot pressing the mold, wherein the hot pressing temperature is 120°C, the hot pressing time is 5 min, and the pressure is 20 MPa; (5) After the hot pressing is completed, the mold is disassembled and demolded.

5. A method for preparing a colored formaldehyde-free artificial board, characterized in that: The steps include: (1) Place the cleaned sawdust particles in a 6%-14% sodium hypochlorite solution, react in an ice-water bath for 2 h, wash with a 1:1 volume ratio of water and ethanol solution, and heat and dry in an oven at 60 °C for 30 h; (2) dissolving 2.92 g of cobalt sulfate hexahydrate and 2 g of citric acid in 20 g of deionized water, wherein the molar ratio of cobalt ion to citric acid is 1:1, and after mixing, no additional pH adjustment is required to obtain a coloring solution; (3) mixing the sawdust particles obtained in step (1) and the coloring solution obtained in step (2) uniformly, wherein the mass ratio of the sawdust particles to the coloring solution is 1:3, and then heating and drying in an oven at 60° C. for 30 h, stirring once every 1 h during the process to keep the color uniform; (4) filling the colored sawdust particles obtained in step (3) into a metal detachable mold covered with a polyimide film and hot pressing the mold, wherein the hot pressing temperature is 150°C, the hot pressing time is 5 min, and the pressure is 50 MPa; (5) After the hot pressing is completed, the mold is disassembled and demolded.

6. Colored formaldehyde-free artificial board, characterized in that: The preparation is obtained by the preparation method according to any one of claims 1 to 5.

Images