Preparation process of formaldehyde-free composite board and product

Abstract

The invention relates to the technical field of formaldehyde-free wood boards, in particular to a preparation process of a formaldehyde-free composite board and a product. The preparation process comprises the following steps: S1, in a dark environment, adding the waterborne polyurethane acrylate and the photoinitiator into the soybean protein glue, and uniformly mixing to obtain the soybean protein-based formaldehyde-free glue; s2, in a dark environment, coating one side of a wood board base material with the soybean protein-based formaldehyde-free glue, carrying out ultraviolet irradiation, carrying out pre-curing, then placing another wood board on the glue-coated surface, carrying out board combination, and carrying out light pressing to prevent slippage; s3, the laminated board serves as a wood board base material, the step S2 is repeated for multiple times, and an assembled board is obtained; and S4, the assembly plate is subjected to hot pressing, and the formaldehyde-free composite plate is obtained. The low-price soybean protein glue is used as the main raw material, only a small amount of PUA and photoinitiator are added, the cost is superior to that of an MDI glue composite board, the performance is also remarkably improved, the preparation process is simple, and the popularization prospect is achieved.

Description

Technical Field

[0001] This invention relates to the field of formaldehyde-free wood-based panels, specifically a preparation process and product for formaldehyde-free composite panels. Background Technology

[0002] Formaldehyde-free engineered wood products refer to boards produced using formaldehyde-free adhesives and additives, with formaldehyde emissions controlled to extremely low levels. As people's environmental awareness gradually increases, the demand for formaldehyde-free boards is growing, and quality requirements are also rising.

[0003] The main difference between formaldehyde-free boards and traditional boards lies in the formaldehyde-free adhesives used, such as MDI, EPI, or biomass adhesives. However, while MDI and EPI adhesives offer excellent performance, their manufacturing costs are prohibitively high, typically 4-5 times that of general composite boards. Therefore, formaldehyde-free composite boards made with these adhesives offer lower cost-effectiveness and are less appealing to consumers. Biomass adhesives, such as soybean protein adhesives, while relatively inexpensive, suffer from poor weather resistance. Furthermore, the use of formaldehyde-free adhesives can lead to a reduction in the mechanical properties and processing stability of the boards, resulting in lower bonding strength and durability compared to traditional urea-formaldehyde resin boards.

[0004] In summary, there is an urgent need for a formaldehyde-free composite board that is low in cost, has high bonding strength, and is highly weather-resistant. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a preparation process and product for formaldehyde-free composite boards, so as to achieve at least lower preparation cost, higher board bonding strength, and stronger weather resistance.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A process for preparing a formaldehyde-free composite board includes the following steps: S1: In a dark environment, add waterborne polyurethane acrylate (PUA) and photoinitiator to soybean protein glue and mix evenly to obtain soybean protein-based formaldehyde-free glue. S2: In a dark environment, apply the soybean protein-based formaldehyde-free adhesive to one side of the wood board substrate, irradiate with ultraviolet light for pre-curing, and then place another wood board with the wood grain direction perpendicular to the adhesive surface to put the boards together, and press lightly to prevent slippage. S3: Using the plywood as the substrate, repeat step S2 several times to obtain the assembled board; S4: The preformed board is hot-pressed to obtain the formaldehyde-free composite board.

[0008] Further, in step S1, the photoinitiator includes photoinitiator 2959, photoinitiator 819 and photoinitiator TPO, and the soybean protein gum is preferably an epoxy compound modified soybean protein gum.

[0009] Further, in step S1, the weight ratio of the waterborne polyurethane acrylate, photoinitiator, and soybean protein glue is 10~20:0.5~2:100.

[0010] Further, in step S2, the coating amount of the soybean protein-based formaldehyde-free adhesive is 180-250 g / m². 2 .

[0011] Furthermore, in step S2, the wavelength of the ultraviolet light is 365-405 nm.

[0012] Furthermore, in step S2, the pre-curing time is 5-15 seconds.

[0013] It is worth noting that the pre-curing light exposure time is extremely short. The purpose is to allow the double bonds of the PUA molecules in the adhesive layer to open rapidly, causing a chain polymerization reaction and forming a highly rigid three-dimensional network. Macroscopically, this forms a viscous but no longer flowing gel / semi-cured film, providing initial strength to the board, facilitating subsequent assembly, and preventing slippage during subsequent hot pressing.

[0014] Furthermore, in step S2, the plywood is assembled within 1 minute after the pre-curing.

[0015] Furthermore, in step S3, the number of repetitions is even, that is, the number of veneers is odd, and the wood grain direction of two adjacent veneers needs to be arranged in a cross-sectional and cross-sectional manner.

[0016] Furthermore, in step S4, the hot pressing temperature is 110~130℃, and the hot pressing pressure is 1.2-1.8 MPa.

[0017] Furthermore, in step S4, the hot pressing time is based on the thickness of the single board, with 0.8-1.5 min for every 1 mm of hot pressing.

[0018] In a further step S4, after the hot pressing is completed, the temperature is reduced to below 60°C while maintaining the hot pressing pressure before the pressure is released.

[0019] It is worth noting that the adhesive strength of a single biomass adhesive is limited. This invention addresses this by adding a photocurable material, PUA, to soybean protein adhesive. Upon irradiation with ultraviolet light, a rigid PUA photocrosslinking network is formed, significantly improving the cohesive strength and resistance to damage of the adhesive layer itself. During hot pressing, the soybean protein adhesive undergoes thermosetting, forming a flexible thermocrosslinking network that interweaves and wraps around this photocrosslinking network. The two network structures intertwine and fill each other, providing a large contact area and significantly enhancing the adhesive strength of the plywood.

[0020] The beneficial effects of this invention are: 1. This invention employs a photo-thermal dual crosslinking process, first photocuring and then thermal curing, to successfully construct an interpenetrating polymer network within the adhesive layer. The high-density network formed by UV pre-curing of PUA gives the adhesive layer excellent cohesive strength and tensile strength. The flexible network formed by hot-pressing curing of soybean protein fills and wraps between the rigid networks, effectively absorbing and dispersing stress. The dual network structure overcomes the defects of low crosslinking density and high brittleness of single biomass adhesives, significantly improving the bonding strength, static bending strength, and elastic modulus of the board.

[0021] 2. The PUA network formed by photocrosslinking has excellent hydrophobicity and chemical stability, which can block the erosion of soybean protein matrix in the adhesive layer by a certain extent, improve the weather resistance of the board, and enable the board to maintain high bonding strength in high temperature and high humidity environment. Its weather resistance and durability are significantly better than those of boards prepared by traditional single adhesive.

[0022] 3. This invention uses inexpensive soybean protein glue as the main raw material, with only a small amount of PUA and photoinitiator added. It is superior to MDI glue composite board in terms of cost, and also has significantly improved performance. Moreover, the preparation process is simple and has promising prospects for promotion. Detailed Implementation

[0023] The technical solution of the present invention will be described in further detail below, but the scope of protection of the present invention is not limited to the following description.

[0024] In the following examples and comparative examples, the soybean protein gum was prepared on-site, and the specific method is as follows: Add defatted soybean flour to water and stir at room temperature for 40 minutes. Control the temperature at 35°C, slowly add NaOH solution, adjust the pH to 10-11, and continue the reaction for 30 minutes. Then add 9%wt of THPTG crosslinking agent, stir well, raise the temperature to 70°C, and react for 50 minutes. Finally, lower the temperature to 35°C, add acid to adjust the pH to 5, and react for 30 minutes.

[0025] Example 1 This embodiment is used to prepare a formaldehyde-free composite board, and the specific method is as follows: S1: Mixing the adhesive: Add water-based PUA and photoinitiator 2959 to soybean protein gum (freshly prepared), and stir at 400 rpm for 20 minutes under light-protected conditions to ensure uniform mixing, thus obtaining soybean protein-based formaldehyde-free gum.

[0026] The ratio of soybean protein gum, water-based PUA, and photoinitiator is 100:20:1.

[0027] S2: Single-layer coating, pre-curing, and plywood: Using furniture-grade poplar plywood as the substrate (1220×2440 mm, veneer thickness 18.0 mm, sanded), under light-protected conditions, apply the aforementioned soybean protein-based formaldehyde-free adhesive to one side, with the coating amount controlled at 200±10 g / m². 2 This ensures that the adhesive layer is uniform and without any breaks.

[0028] The coating layer is irradiated with an LED surface light source (manufacturer: Shanghai Benyue Technology Co., Ltd., model: BYSF-81T, wavelength: 385nm) for 8 seconds to cure the adhesive layer surface into a gel state (it is sticky but not sticky to the touch). Then, the boards are immediately put together. Another piece of wood with a wood grain direction perpendicular to the adhesive layer is placed on top of the adhesive layer and gently pressed by hand to make the boards initially fit together to prevent slippage.

[0029] Repeat this step, applying a layer of adhesive to one side of the double-layered board obtained above, then curing it with light. Take another piece of wood with a grain direction perpendicular to the board and combine them to form a composite board composed of three veneers.

[0030] S3: Thermosetting / Hot-pressing: The preforms are fed into a hot press for hot pressing at 120℃, 1.6MPa, and for 20 minutes. After hot pressing, the preforms are cooled to below 60℃ under pressure before being released to prevent warping and deformation, ultimately yielding a formaldehyde-free composite board.

[0031] Example 2 This embodiment is used to prepare a formaldehyde-free composite board. The specific method is the same as in Example 1, except that the wood substrate used is different and the corresponding parameters are adjusted as follows: S1: Mixing the adhesive: Add water-based PUA and photoinitiator 2959 to soybean protein gum (freshly prepared), and stir at 400 rpm for 20 minutes under light-protected conditions to ensure uniform mixing, thus obtaining soybean protein-based formaldehyde-free gum.

[0032] The ratio of soybean protein gum, water-based PUA, and photoinitiator is 100:20:1.

[0033] S2: Single-layer coating, pre-curing, and plywood: Using furniture-grade degreased pine wood as the substrate (1220×2440 mm, veneer thickness 18.0 mm, sanded), under light-protected conditions, apply the aforementioned soybean protein-based formaldehyde-free adhesive to one side, with the coating amount controlled at 200±10 g / m². 2 This ensures that the adhesive layer is uniform and without any breaks.

[0034] The coating layer is irradiated with an LED surface light source (manufacturer: Shanghai Benyue Technology Co., Ltd., model: BYSF-81T, wavelength: 385nm) for 10 seconds to cure the adhesive layer surface into a gel state (it is sticky but not sticky to the touch). Then, the boards are immediately put together. Another piece of wood with a wood grain direction perpendicular to the adhesive layer is placed on top of it and the boards are gently pressed together to prevent slippage.

[0035] Repeat this step, applying a layer of adhesive to one side of the double-layered board obtained above, then curing it with light. Take another piece of wood with a grain direction perpendicular to the board and combine them to form a composite board composed of three veneers.

[0036] S3: Thermosetting / Hot-pressing: The preforms are fed into a hot press for hot pressing at a temperature of 110℃, a pressure of 1.4MPa, and a time of 25 minutes. After hot pressing, the preforms are cooled to below 60℃ under pressure before being released to prevent warping and deformation, ultimately yielding a formaldehyde-free composite board.

[0037] Comparative Example 1 This comparative example is used to prepare a formaldehyde-free composite board, using soybean protein adhesive as the binder. The specific method is as follows: 1) Using furniture-grade poplar plywood as the substrate, apply soybean protein adhesive to one side, with the coating amount controlled at 200±10g / m². 2 Ensure the adhesive layer is uniform and without gaps. Take another piece of wood with a grain direction perpendicular to the adhesive layer, align it, and place it on top of the adhesive layer. Gently press it down to initially adhere the boards and prevent slippage. Then repeat this step. Based on the double-layered board obtained above, apply a layer of adhesive to one side, and then take another piece of wood with a grain direction perpendicular to the adhesive layer to join the boards. Finally, you will get a board assembly consisting of three veneers.

[0038] 2) The preform is fed into a hot press for hot pressing at a temperature of 120℃, a pressure of 1.6MPa, and a time of 20 minutes. After hot pressing, the preform is cooled to below 60℃ under pressure before being released to prevent warping and deformation, thus obtaining a formaldehyde-free composite board.

[0039] Comparative Example 2 This comparative example is used to prepare a formaldehyde-free composite board, using a mixture of water-based PUA and a photoinitiator as an adhesive, and then photocuring it. The specific method is as follows: 1) Mix water-based PUA and photoinitiator at a ratio of 20:1, and stir at 400 rpm for 20 minutes under light-protected conditions to ensure uniform mixing and obtain adhesive.

[0040] 2) Using furniture-grade poplar wood as the substrate, apply the above-mentioned soybean protein-based formaldehyde-free adhesive to one side under light-protected conditions, with the coating amount controlled at 200±10g / m². 2 This ensures that the adhesive layer is uniform and without any breaks.

[0041] The coating layer is irradiated with an LED surface light source (manufacturer: Shanghai Benyue Technology Co., Ltd., model: BYSF-81T, wavelength: 385nm) for 8 seconds to cure the adhesive layer surface into a gel state (it is sticky but not sticky to the touch). Then, the boards are immediately put together. Another piece of wood with a wood grain direction perpendicular to the adhesive layer is placed on top of the adhesive layer and gently pressed by hand to make the boards initially fit together to prevent slippage.

[0042] Repeat this step, applying a layer of adhesive to one side of the double-layered board obtained above, and then curing it with light. Take another piece of wood with a wood grain direction perpendicular to the first one and put them together to obtain a composite board composed of three veneers.

[0043] Comparative Example 3 This comparative example was used to prepare a formaldehyde-free composite board, using a mixture of water-based PUA and a photoinitiator as an adhesive, and then subjecting it to photocuring and hot pressing. The specific methods are as follows: 1) Mix water-based PUA and photoinitiator at a ratio of 20:1, and stir at 400 rpm for 20 minutes under light-protected conditions to ensure uniform mixing and obtain adhesive.

[0044] 2) Using furniture-grade poplar wood as the substrate, apply the above-mentioned soybean protein-based formaldehyde-free adhesive to one side under light-protected conditions, with the coating amount controlled at 200±10g / m². 2 This ensures that the adhesive layer is uniform and without any breaks.

[0045] The coating layer is irradiated with an LED surface light source (manufacturer: Shanghai Benyue Technology Co., Ltd., model: BYSF-81T, wavelength: 385nm) for 8 seconds to cure the adhesive layer surface into a gel state (it is sticky but not sticky to the touch). Then, the boards are immediately put together. Another piece of wood with a wood grain direction perpendicular to the adhesive layer is placed on top of the adhesive layer and gently pressed by hand to make the boards initially fit together to prevent slippage.

[0046] Repeat this step, applying a layer of adhesive to one side of the double-layered board obtained above, then curing it with light. Take another piece of wood with a grain direction perpendicular to the board and combine them to form a composite board composed of three veneers.

[0047] 3) The preform is fed into a hot press for hot pressing at a temperature of 120℃, a pressure of 1.6MPa, and a time of 20 minutes. After hot pressing, the preform is cooled to below 60℃ under pressure before being released to prevent warping and deformation, thus obtaining a formaldehyde-free composite board.

[0048] Experimental Example 1 This experimental example is used to test the bonding strength of formaldehyde-free composite boards. The test method refers to GB / T 17657-2013, as follows: 1) Specimen preparation: The formaldehyde-free composite boards from Examples 1-2 and Comparative Examples 1-3 were cut into T-shaped standard specimens along each adhesive layer (same as Figure 23 in GB / T 17657-2013). Six specimens were prepared for each group, each specimen being 100 mm long, 25 mm wide, with a cut surface length of 25 mm and a width of 25 mm.

[0049] 2) The shear strength (N) of each specimen was tested using a universal mechanical testing machine, and the bonding strength (MPa) was calculated according to the following formula: X=P / (A×B), where P is the shear strength, A is the cross-sectional width of the specimen, and B is the cross-sectional length of the specimen.

[0050] The bonding strength test results (average values) for each group are shown in Table 1: Table 1

[0051] As can be seen, Examples 1 and 2 of this invention used soybean protein glue, PUA, and a photoinitiator as adhesives. After photocuring and hot pressing, the bonding strength was relatively high, reaching 9.05 MPa with poplar wood as the substrate and 8.22 MPa with pine wood as the substrate. However, if only soybean protein glue was used as the adhesive, the bonding strength was low, only 0.82 MPa. Comparative Example 2 used PUA + a photoinitiator as the adhesive and only underwent photocuring, resulting in relatively low bonding strength, possibly because the bonding force between PUA and wood is relatively weak. Comparative Example 3, based on Comparative Example 2, also underwent hot pressing, further improving the bonding strength to 8.72 MPa. However, compared to this invention which only added 20% PUA, it had a significant cost disadvantage, thus its application prospects were poor.

[0052] Experimental Example 2 This experimental example is used to test the weather resistance of formaldehyde-free composite boards. The specific method is as follows: 1) Specimen preparation: T-shaped specimens were prepared from the formaldehyde-free composite boards of Examples 1-2 and Comparative Examples 1-3, respectively, using the same method as in Experiment 1.

[0053] 2) Weather resistance model preparation: The specimens were placed under sunlight for 12 hours, then transferred to water for 12 hours, and then taken out for sunlight exposure. This cycle was repeated for 21 days.

[0054] 3) After 21 days, the shear strength (N) of each specimen was tested using a universal mechanical testing machine. The bonding strength (MPa) was calculated according to the following formula: X=P / (A×B), where P is the shear strength, A is the cross-sectional width of the specimen, and B is the cross-sectional length of the specimen.

[0055] The bonding strength test results (average values) for each group are shown in Table 2: Table 2

[0056] As can be seen, the formaldehyde-free composite board of the present invention has good weather resistance, with the bonding strength decreasing by about 30% after 21 days. In comparison, Comparative Example 1, which uses only soybean protein adhesive as a binder and undergoes hot pressing, experienced a 53.6% decrease in bonding strength; Comparative Example 2, which uses only PUA + photoinitiator as a binder and undergoes photocuring, experienced a 30% decrease in bonding strength; and Comparative Example 3, which uses PUA + photoinitiator as a binder and undergoes both photocuring and hot pressing, experienced the smallest decrease in bonding strength, at 24%, with a final bonding strength slightly higher than that of Example 1. However, the raw material cost of Example 1 of the present invention is equivalent to 1 / 5 of that of Comparative Example 3, while the final bonding strength is comparable. Overall, the solution of the present invention has more practical prospects. Furthermore, it can be shown that the combined use of soybean protein adhesive and PUA in the solution of the present invention enhances the bonding strength of the board, achieving a similar or even better bonding strength with 1 / 5 of the PUA addition, while the addition of PUA also enhances the weather resistance of the main component, soybean protein adhesive.

[0057] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A preparation process for formaldehyde-free composite panels, characterized in that, Includes the following steps: S1: In a dark environment, add waterborne polyurethane acrylate and photoinitiator to soybean protein glue and mix evenly to obtain soybean protein-based formaldehyde-free glue. S2: In a dark environment, apply the soybean protein-based formaldehyde-free adhesive to one side of the wood substrate, irradiate with ultraviolet light for pre-curing, and then place another wood board on the adhesive surface to join the boards, pressing lightly to prevent slippage. S3: Using the plywood as the substrate, repeat step S2 several times to obtain the assembled board; S4: The preformed board is hot-pressed to obtain the formaldehyde-free composite board.

2. The preparation process according to claim 1, characterized in that: In step S1, the photoinitiator includes photoinitiator 2959, photoinitiator 819, and photoinitiator TPO.

3. The preparation process according to claim 1, characterized in that: In step S1, the weight ratio of the waterborne polyurethane acrylate, photoinitiator, and soybean protein glue is 10~20:0.5~2:

100.

4. The preparation process according to claim 1, characterized in that: In step S2, the coating amount of the soybean protein-based formaldehyde-free adhesive is 180-250 g / m². 2 .

5. The preparation process according to claim 1, characterized in that: In step S2, the pre-curing time is 5-15 seconds.

6. The preparation process according to claim 1, characterized in that: In step S3, the number of repetitions is an even number.

7. The preparation process according to claim 1, characterized in that: In step S4, the hot pressing temperature is 110~130℃ and the hot pressing pressure is 1.2-1.8 MPa.

8. The preparation process according to claim 1, characterized in that: In step S4, the hot pressing time is based on the thickness of the single board, with 0.8-1.5 min for every 1 mm of hot pressing.

9. The preparation process according to claim 1, characterized in that: In step S4, after the hot pressing is completed, the temperature is reduced to below 60°C while maintaining the hot pressing pressure before the pressure is released.

10. Formaldehyde-free composite board prepared by the preparation method according to any one of claims 1-9.

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