A polyurethane adhesive, a hollow flakeboard comprising the same, and a method for manufacturing a hollow flakeboard

Abstract

The application provides a polyurethane adhesive, a hollow flakeboard containing the same and a preparation method of the hollow flakeboard, raw materials for preparing the polyurethane adhesive include polyols and polyisocyanate; in the raw materials, the isocyanate index is 50-150; the polyols include a combination of low-functionality polyols and high-functionality polyols; the low-functionality polyols have a functionality of 2; the high-functionality polyols have a functionality of >2; the mass ratio of the low-functionality polyols to the high-functionality polyols is 1:0.2-0.4; in the application, the polyurethane adhesive is used for preparing the hollow flakeboard, no formaldehyde is added, the formaldehyde release of the hollow flakeboard is not increased, the environmental protection level is high; and the static bending strength of the hollow flakeboard can be improved, and the size change rate and thickness deviation of the hollow flakeboard are reduced.

Description

Technical Field

[0001] This invention belongs to the field of engineered wood products technology, specifically relating to a polyurethane adhesive, a hollow particleboard containing the same, and a method for preparing the hollow particleboard. Background Technology

[0002] Hollow core particleboard, also known as bridge-hole board, is a hollow board made from wood and non-wood plant shavings. After drying and gluing, the shavings are continuously extruded in an extruder equipped with metal pipes under heat. It features good thermal insulation, sound insulation, and light weight. Hollow core particleboard is mainly used as a filling material for wooden doors, and is currently primarily produced using urea-formaldehyde resin, mostly at grade E1.

[0003] However, urea-formaldehyde resin contains free formaldehyde, and the cured product is unstable, gradually releasing formaldehyde, which is a Group 1 carcinogen. Therefore, with increasing environmental awareness and higher demands for home safety, hollow particleboard produced using urea-formaldehyde resin will gradually be phased out, necessitating the development of formaldehyde-free hollow particleboard.

[0004] For example, CN105946087A reports a flame-retardant particleboard and its preparation method, which uses a modified urea-formaldehyde resin adhesive. Although the urea-formaldehyde resin is modified, it still leads to the addition of aldehydes, increasing the formaldehyde release of the hollow particleboard and resulting in a low environmental protection level for the product.

[0005] For example, CN1115401762A reports a manufacturing process for ENF-grade flame-retardant hollow particleboard, which uses lignin-based adhesives. However, all lignin-based adhesives currently on the market contain free formaldehyde, although the free formaldehyde content is lower than that of traditional urea-formaldehyde adhesives. Essentially, they cannot be called formaldehyde-free adhesives. Furthermore, boards produced with lignin-based adhesives will have a noticeable odor after being soaked in water. Although water damage to doors is not common in daily life, in the hot and humid environment of southern China during the summer, boards produced with lignin-based adhesives may emit an unpleasant odor, failing to meet people's requirements for comfortable home environments.

[0006] Therefore, developing a formaldehyde-free adhesive that can improve the static bending strength of hollow particleboard and reduce its dimensional change rate is an urgent problem to be solved in this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a polyurethane adhesive, a hollow particleboard containing the same, and a method for preparing the hollow particleboard. The polyurethane adhesive used to prepare the hollow particleboard is formaldehyde-free, does not increase the formaldehyde release of the hollow particleboard, and has a high environmental protection level. Furthermore, it can improve the static bending strength of the hollow particleboard and reduce the dimensional change rate and thickness deviation of the hollow particleboard.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a polyurethane adhesive, wherein the raw materials for preparing the polyurethane adhesive include a polyol and a polyisocyanate; wherein the isocyanate index (R) of the raw materials is 50 to 150; the polyol includes a combination of a low-functionality polyol and a high-functionality polyol; the functionality of the low-functionality polyol is 2; the functionality of the high-functionality polyol is >2; and the mass ratio of the low-functionality polyol to the high-functionality polyol is 1:0.2 to 0.4.

[0010] Isocyanates can be directly used as adhesives for hollow particleboard, and their bonding principle mainly relies on the reaction of isocyanates with water in the raw materials to form polyurea. However, polyurea is hard and brittle, easily leading to problems such as board deformation. Therefore, this invention uses polymeric polyols to modify isocyanates to form polyurethane adhesives, and controls the modification ratio within a specific range, i.e., controlling R between 50 and 150. Simultaneously, specific compositions and ratios of polyols are selected as adhesives for hollow particleboard, which can improve the static bending strength of hollow particleboard and reduce its dimensional change rate and thickness deviation. Furthermore, the adhesive is a formaldehyde-free additive adhesive, which will not increase the formaldehyde release of hollow particleboard, thereby improving its environmental protection level.

[0011] In this invention, the isocyanate index is 50 to 150, for example, it can be 50, 52, 55, 58, 60, 62, 65, 68, 70, 72, 75, 78, 80, 82, 85, 88, 90, 92, 95, 98, 100, 102, 105, 108, 110, 112, 115, 118, 120, 122, 125, 128, 130, 132, 135, 138, 140, 142, 145, 148, 150, etc.

[0012] In this invention, a low isocyanate index results in a high dimensional change rate during hollow particleboard extrusion; a high isocyanate index results in a high dimensional change rate and low static bending strength during hollow particleboard extrusion.

[0013] Preferably, the mass ratio of the low-functionality polyol to the high-functionality polyol is 1:0.2 to 0.4, wherein the specific values ​​of 0.2 to 0.4 can be, for example, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, etc.

[0014] In this invention, a low-functionality polyol and a high-functionality polyol are blended, and the mass ratio of the low-functionality polyol and the high-functionality polyol is controlled within the above-defined range. The resulting hollow particleboard has higher static bending strength and lower dimensional change rate.

[0015] In this invention, the high-functionality polyol has a functionality greater than 2, for example, it can be 3, 4, 5, 6, etc.

[0016] Preferably, the polyol comprises polyether polyol and / or polyester polyol.

[0017] Preferably, the number average molecular weight of the polyol is 500-4000, for example, 500, 600, 800, 1000, 1200, 1400, 1600, 1800, 2000, 2200, 2400, 2600, 2800, 3000, 3200, 3400, 3600, 3800, 4000, etc.; the hydroxyl value is 35-450 mg KOH / g, for example, 35 mg KOH / g, 40 mg KOH / g, 45 mg KOH / g, 50 mg KOH / g, 60 mg KOH / g, 80 mg KOH / g, 100 mg KOH / g, 120 mg KOH / g, 140 mg KOH / g, 160 mg KOH / g, 180 mg KOH / g, 200 mg KOH / g, 220 mg KOH / g, 240 mg KOH / g, etc. KOH / g, 260mg KOH / g, 280mg KOH / g, 300mg KOH / g, 320mg KOH / g, 340mg KOH / g, 360mg KOH / g, 380mg KOH / g, 400mg KOH / g, 420mg KOH / g, 440mg KOH / g, 450mg KOH / g, etc.

[0018] Preferably, the polyol comprises at least one of a combination of low-functionality polyether polyol and high-functionality polyether polyol, or a combination of low-functionality polyester polyol and high-functionality polyether polyol.

[0019] Preferably, when the polyol is selected from a combination of low-functionality polyether polyols and high-functionality polyether polyols, the low-functionality polyol includes polyether polyol A and / or polyether polyol B; the number-average molecular weight of polyether polyol A is less than that of polyether polyol B, and the hydroxyl value of polyether polyol A is greater than that of polyether polyol B.

[0020] Preferably, the number average molecular weight of the polyether polyol A is 500-1500, for example, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, etc.; the hydroxyl value is 75-225 mg KOH / g, for example, 75 mg KOH / g, 80 mg KOH / g, 90 mg KOH / g, 100 mg KOH / g, 110 mg KOH / g, 120 mg KOH / g, 130 mg KOH / g, 140 mg KOH / g, 150 mg KOH / g, 160 mg KOH / g, 170 mg KOH / g, 180 mg KOH / g, 190 mg KOH / g, 200 mg KOH / g, 205 mg KOH / g, 210 mg KOH / g, 215 mg KOH / g, 220 mg KOH / g, etc. The KOH / g value is 225 mg KOH / g, etc.; the number average molecular weight of the polyether polyol B is 1500-2500, for example, it can be 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, etc.; the hydroxyl value is 45-75 mg KOH / g, for example, it can be 45 mg KOH / g, 50 mg KOH / g, 55 mg KOH / g, 60 mg KOH / g, 65 mg KOH / g, 70 mg KOH / g, 75 mg KOH / g, etc.

[0021] Preferably, when the polyol is selected from a combination of low-functionality polyether polyols and high-functionality polyether polyols, the high-functionality polyether polyol includes polyether polyol C and / or polyether polyol D; the number-average molecular weight of polyether polyol C is less than that of polyether polyol D, and the hydroxyl value of polyether polyol C is greater than that of polyether polyol D.

[0022] Preferably, the number average molecular weight of the polyether polyol C is 500–2500, for example, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1800, 2000, 2200, 2400, 2500, etc.; the hydroxyl value is 65–450 mg KOH / g, for example, 65 mg KOH / g, 70 mg KOH / g, 80 mg KOH / g, 90 mg KOH / g, 100 mg KOH / g, 120 mg KOH / g, 140 mg KOH / g, 160 mg KOH / g, 180 mg KOH / g, 200 mg KOH / g, 220 mg KOH / g, 240 mg KOH / g, 260 mg KOH / g, 280 mg KOH / g, etc. The KOH / g values ​​are 300mg KOH / g, 320mg KOH / g, 340mg KOH / g, 360mg KOH / g, 380mg KOH / g, 400mg KOH / g, 420mg KOH / g, 440mg KOH / g, 450mg KOH / g, etc.; the number average molecular weight of the polyether polyol D is 2500-4000, for example, 2500, 2600, 2800, 3000, 3200, 3400, 3600, 3800, 4000, etc.; the hydroxyl value is 39-90mg KOH / g, for example, 40mg KOH / g, 50mg KOH / g, 60mg KOH / g, 70mg KOH / g, 80mg KOH / g, 90mg KOH / g, etc.

[0023] Preferably, when the polyol is selected from a combination of low-functionality polyether polyols and high-functionality polyether polyols, the polyol includes a combination of polyether polyol A and polyether polyol C, and / or a combination of polyether polyol B and polyether polyol D.

[0024] Preferably, when the polyol is selected from a combination of low-functionality polyester polyol and high-functionality polyether polyol, the low-functionality polyester polyol has a number-average molecular weight of 1500-2500 and a hydroxyl value of 45-75 mg KOH / g; the high-functionality polyether polyol has a number-average molecular weight of 500-2500 and a hydroxyl value of 65-450 mg KOH / g.

[0025] Preferably, the high-functionality polyol includes trifunctional polyols and / or tetrafunctional polyols.

[0026] Preferably, the polyisocyanate includes aromatic polyisocyanates and / or aliphatic polyisocyanates.

[0027] Preferably, the polyisocyanate includes at least one of isophorone diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, or polymethylene polyphenyl polyisocyanate, and more preferably at least one of toluene diisocyanate, diphenylmethane diisocyanate, or polymethylene polyphenyl polyisocyanate.

[0028] In a second aspect, the present invention provides a method for preparing the polyurethane adhesive according to the first aspect, the method comprising:

[0029] The polyol and polyisocyanate are reacted to obtain the polyurethane adhesive.

[0030] Preferably, the reaction temperature is 60-95℃, for example, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, etc.; the time is 2-6h, for example, 2h, 3h, 4h, 5h, 6h, etc.

[0031] Thirdly, the present invention provides a hollow particleboard, the material of which includes wood chips and an adhesive; the adhesive includes the polyurethane adhesive according to the first aspect.

[0032] In this invention, the wood shavings are made of wood and / or non-wood materials; exemplary, the wood shavings can be made of poplar, pine, eucalyptus, fir, birch, hardwood, wheat straw, rice straw, cotton and hemp stalks, corn stalks, sorghum stalks, reeds, bamboo, etc.; the thickness of the wood shavings is 0.15-5mm, the width is 0.4-15mm, and the length is 0.5-50mm; before use, the wood shavings are dried to ensure uniform moisture content; the moisture content of the wood shavings is 5-15%.

[0033] Preferably, the adhesive is 1.5% to 4% of the wood shavings by mass, for example, it can be 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 4%, etc.

[0034] Preferably, the material of the hollow particleboard also includes a waterproofing agent.

[0035] In this invention, the waterproofing agent includes paraffin wax and / or emulsified paraffin wax.

[0036] Preferably, the water-repellent agent accounts for 0.2% to 0.4% of the wood shavings by mass, for example, 0.2%, 0.22%, 0.24%, 0.26%, 0.28%, 0.3%, 0.32%, 0.34%, 0.36%, 0.38%, 0.4%, etc.

[0037] Fourthly, the present invention provides a method for preparing hollow particleboard according to the third aspect, the method comprising:

[0038] The hollow particleboard is prepared by applying an adhesive to the surface of the wood chips and using a pulse extrusion method.

[0039] Because polyurethane adhesives have good bonding properties to materials such as wood and metal, the production of hollow particleboard using polyurethane adhesives is prone to board sticking problems, which in turn affect equipment operating efficiency and board surface quality. In this invention, a pulse extrusion method is used to produce hollow particleboard, eliminating the need for a release agent and ensuring that board sticking does not occur during production, thus improving production efficiency and product quality. By using a specific polyurethane adhesive in combination with the pulse extrusion process, the resulting hollow particleboard has high static bending strength, low dimensional change rate and thickness deviation, and does not experience board sticking problems during production, does not increase the formaldehyde content of the particleboard, and has a high environmental protection level.

[0040] Preferably, the temperature of the pressure plate of the pulse extrusion is 120-220°C, for example, it can be 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, etc.

[0041] Preferably, the gap between the pressure plates of the pulse extrusion is 15 to 60 mm, for example, it can be 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, etc.

[0042] Preferably, the frequency of the pulse compression is 2 to 120 times / min, for example, it can be 2 times / min, 4 times / min, 6 times / min, 8 times / min, 10 times / min, 15 times / min, 20 times / min, 25 times / min, 30 times / min, 35 times / min, 40 times / min, 45 times / min, 50 times / min, 55 times / min, 60 times / min, 65 times / min, 70 times / min, 75 times / min, 80 times / min, 85 times / min, 90 times / min, 95 times / min, 100 times / min, 105 times / min, 110 times / min, 115 times / min, 120 times / min, etc.; a single... The extrusion stroke ranges from 2 to 200 mm, for example, it can be 2 mm, 4 mm, 6 mm, 8 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, 70 mm, 75 mm, 80 mm, 85 mm, 90 mm, 95 mm, 100 mm, 105 mm, 110 mm, 115 mm, 120 mm, 125 mm, 130 mm, 135 mm, 140 mm, 145 mm, 150 mm, 155 mm, 160 mm, 165 mm, 170 mm, 175 mm, 180 mm, 185 mm, 190 mm, 195 mm, 200 mm, etc.

[0043] In this invention, by controlling the extrusion frequency and extrusion stroke, effective heat transfer is ensured, and the board is prevented from sticking, thus maintaining a high surface quality of the board. At the same time, it can also improve the static bending strength of hollow particleboard and reduce the dimensional change rate and thickness deviation of hollow particleboard.

[0044] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] The polyurethane adhesive provided by this invention modifies isocyanate with polymeric polyols to form a polyurethane adhesive, and controls the isocyanate index within a specific range. Simultaneously, it selects polyols with specific compositions and ratios as adhesives for hollow particleboard, which can improve the static bending strength of hollow particleboard and reduce its dimensional change rate and thickness deviation. Furthermore, the adhesive is a formaldehyde-free type, which does not increase the formaldehyde release of the hollow particleboard, thereby improving its environmental protection level. The hollow particleboard has a static bending strength ≥2.2 MPa, an extrusion dimensional change rate ≤5.9%, and is formaldehyde-free. Detailed Implementation

[0047] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0048] Unless otherwise specified, the materials used in this invention are as follows:

[0049] Polyisocyanates

[0050] Polymethylene polyphenyl polyisocyanate (PMDI): CW20, -NCO content 30-32wt%, Wanhua Chemical Group Co., Ltd.

[0051] Low-functionality ether polyols

[0052] Difunctional polyether polyol C2010D, number average molecular weight 1000, hydroxyl value 112±3.5mg KOH / g, Wanhua Chemical Group Co., Ltd.

[0053] Difunctional polyether polyol C2020, number average molecular weight 2000, hydroxyl value 56±1.5mg KOH / g, Wanhua Chemical Group Co., Ltd.

[0054] Low-functionality polyester polyols

[0055] Difunctional polyester polyol FA2817P, number average molecular weight 2000, hydroxyl value 53-59 mg KOH / g, BGI Chemical Group.

[0056] High-functionality polyether polyols

[0057] Trifunctional polyether polyol R2305, number average molecular weight 500, hydroxyl value 335±10mg KOH / g, Wanhua Chemical Group Co., Ltd.

[0058] Tetrafunctional polyether polyol R8241, number average molecular weight 550, hydroxyl value 410±20mg KOH / g, Wanhua Chemical Group Co., Ltd.

[0059] Trifunctional polyether polyol F3140, number average molecular weight around 4000, hydroxyl value 39.5-43.5 mg KOH / g, Wanhua Chemical Group Co., Ltd.

[0060] Waterproofing agent: No. 58 refined paraffin wax, Yangzi Petrochemical.

[0061] Eucalyptus wood shavings: moisture content 10%, thickness 1-2mm, width 3-5mm, length 3-15mm, Wanhua Ecological Board Industry.

[0062] In this invention, the isocyanate index (R) is the molar ratio of isocyanate groups to hydroxyl groups in the raw materials.

[0063] Example 1

[0064] This embodiment provides a polyurethane adhesive, the raw materials of which include 5.2 kg of polyol and 100 kg of PMDI; the polyol includes difunctional polyether polyol C2010D and trifunctional polyether polyol R2305 in a mass ratio of 1:0.3; the isocyanate index R is 50; the preparation method of the polyurethane adhesive includes: reacting the polyol and PMDI at 75°C for 4 h to obtain the polyurethane adhesive.

[0065] Example 2

[0066] This embodiment provides a polyurethane adhesive, the raw materials of which include 5.6 kg of polyol and 100 kg of PMDI; the polyol includes difunctional polyether polyol C2020 and trifunctional polyether polyol F3140 in a mass ratio of 1:0.4; the isocyanate index R is 147; the preparation method of the polyurethane adhesive includes: reacting the polyol and PMDI at 65°C for 5 h to obtain the polyurethane adhesive.

[0067] Example 3

[0068] This embodiment provides a polyurethane adhesive, the raw materials of which include 4.8 kg of polyol and 100 kg of PMDI; the polyol includes difunctional polyether polyol C2010D and tetrafunctional polyether polyol R8241 in a mass ratio of 1:0.2; the isocyanate index R is 55; the preparation method of the polyurethane adhesive includes: reacting the polyol and PMDI at 65°C for 5 h to obtain the polyurethane adhesive.

[0069] Example 4

[0070] This embodiment provides a polyurethane adhesive, the raw materials of which include 5.6 kg of polyol and 100 kg of PMDI; the polyol includes a difunctional polyester polyol FA2817P and a trifunctional polyether polyol R2305 in a mass ratio of 1:0.4; the isocyanate index R is 56; the preparation method of the polyurethane adhesive includes: reacting the polyol and PMDI at 60°C for 6 h to obtain the polyurethane adhesive.

[0071] Example 5

[0072] This embodiment provides a polyurethane adhesive, which differs from Example 1 only in that the trifunctional polyether polyol R2305 is replaced with an equal mass of trifunctional polyether polyol F3140, and the PMDI content is adjusted so that the R value remains unchanged. Other raw materials, dosages, and preparation methods are the same as in Example 1.

[0073] Example 6

[0074] This embodiment provides a polyurethane adhesive, which differs from Example 4 only in that the trifunctional polyether polyol R2305 is replaced with an equal mass of trifunctional polyether polyol F3140, and the PMDI content is adjusted so that the R value remains unchanged. Other raw materials, dosages, and preparation methods are the same as in Example 4.

[0075] Comparative Example 1

[0076] This comparative example provides a polyurethane adhesive, which differs from Example 1 only in that the total molar amount of hydroxyl groups in the polyol remains unchanged, and the trifunctional polyether polyol R2305 is not present. All other raw materials, dosages, and preparation methods are the same as in Example 1.

[0077] Comparative Example 2

[0078] This comparative example provides a polyurethane adhesive, which differs from Example 1 only in that the total molar amount of hydroxyl groups in the polyol remains unchanged, and there is no difunctional polyether polyol C2010D. The other raw materials, dosages, and preparation methods are the same as in Example 1.

[0079] Comparative Example 3

[0080] This comparative example provides a polyurethane adhesive, which differs from Example 1 only in that the total molar amount of hydroxyl groups in the polyol remains unchanged, the mass ratio of difunctional polyether polyol C2010D to trifunctional polyether polyol R2305 is 1:0.1, and other raw materials, dosages and preparation methods are the same as in Example 1.

[0081] Comparative Example 4

[0082] This comparative example provides a polyurethane adhesive, which differs from Example 1 only in that the total molar amount of hydroxyl groups in the polyol remains unchanged, the mass ratio of difunctional polyether polyol C2010D to trifunctional polyether polyol R2305 is 1:0.5, and other raw materials, dosages and preparation methods are the same as in Example 1.

[0083] Comparative Example 5

[0084] This comparative example provides a polyurethane adhesive, which differs from Example 1 only in that the amount of PMDI is adjusted so that R is 38, while the other raw materials, amounts, and preparation methods are the same as in Example 1.

[0085] Comparative Example 6

[0086] This comparative example provides a polyurethane adhesive, which differs from Example 1 only in that the amount of PMDI is adjusted so that R is 160, while the other raw materials, amounts, and preparation methods are the same as in Example 1.

[0087] Comparative Example 7

[0088] This comparative example provides an adhesive, which is a melamine-modified urea-formaldehyde resin purchased from Shengwanjia.

[0089] Application Example 1

[0090] This application example provides a hollow particleboard and its preparation method, wherein the preparation method of the hollow particleboard includes:

[0091] 3 kg of polyurethane adhesive (Example 1) and 0.2 kg of waterproofing agent were evenly applied to the surface of 100 kg of wood shavings. The wood shavings after adhesive application were extruded into shape using a pulse extrusion method. The platen temperature was controlled at 180°C, the platen gap was 35 mm, the pulse extrusion frequency was 60 times / minute, and the single extrusion stroke was 8 mm, thus obtaining the hollow wood shavings board.

[0092] Application Example 2

[0093] This application example provides a hollow particleboard and its preparation method, wherein the preparation method of the hollow particleboard includes:

[0094] 3.5 kg of polyurethane adhesive (Example 2) and 0.3 kg of waterproofing agent were evenly applied to the surface of 100 kg of wood shavings. The wood shavings after adhesive application were extruded into shape using a pulse extrusion method. The platen temperature was controlled at 120°C, the platen gap was 35 mm, the pulse extrusion frequency was 120 times / minute, and the single extrusion stroke was 2 mm, thus obtaining the hollow wood shavings board.

[0095] Application Example 3

[0096] This application example provides a hollow particleboard and its preparation method, wherein the preparation method of the hollow particleboard includes:

[0097] 2 kg of polyurethane adhesive (Example 3) and 0.3 kg of waterproofing agent were evenly applied to the surface of 100 kg of wood shavings. The wood shavings after adhesive application were extruded into shape using a pulse extrusion method. The platen temperature was controlled at 120°C, the platen gap was 35 mm, the pulse extrusion frequency was 2 times / minute, and the single extrusion stroke was 200 mm, thus obtaining the hollow wood shavings board.

[0098] Application Example 4

[0099] This application example provides a hollow particleboard and its preparation method, wherein the preparation method of the hollow particleboard includes:

[0100] 1.5 kg of polyurethane adhesive (Example 4) and 0.4 kg of waterproofing agent were evenly applied to the surface of 100 kg of wood shavings. The wood shavings after adhesive application were extruded into shape using a pulse extrusion method. The platen temperature was controlled at 160°C, the platen gap was 35 mm, the pulse extrusion frequency was 30 times / minute, and the single extrusion stroke was 20 mm, thus obtaining the hollow wood shavings board.

[0101] Application Examples 5-6, Comparison with Application Examples 1-7

[0102] Application Examples 5-6 and Comparative Application Examples 1-7 each provide a hollow particleboard and its preparation method. The only difference between them and Application Example 1 is that the polyurethane adhesive used is the adhesive provided in Examples 5, 6, and Comparative Examples 1-7, respectively. Other components, dosages, and preparation processes are the same as in Application Example 1.

[0103] Comparative Application Example 8

[0104] This comparative application example provides a hollow particleboard and its preparation method. The only difference between this example and application example 1 is that in the preparation method, the pulse extrusion frequency is 1 time / minute and the single extrusion stroke is 480 mm. Other components, dosages, and preparation processes are the same as in application example 1.

[0105] Performance testing

[0106] The performance, formaldehyde emission, and adhesion of the obtained hollow particleboard were tested, and the sticking of the boards during hot pressing were observed. Specifically, the performance of the obtained particleboard was determined according to GB / T 34717-2017 Extruded Particleboard; the formaldehyde emission of the obtained particleboard was tested using the climate chamber method according to GB / T 17657-2022 Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels. The specific test data and results are shown in Table 1; among them, the formaldehyde emission of the tested particleboard raw material (i.e., eucalyptus shavings) was 0.01 mg / m³. 3 .

[0107] Table 1

[0108]

[0109]

[0110] As shown in Table 1, the hollow particleboard prepared using the polyurethane adhesive of this invention has a static bending strength of 2.2 to 2.6 MPa, a dimensional change rate in the extrusion direction of 5.5 to 5.9%, a small thickness deviation, and the same formaldehyde release as the original particleboard material. It can achieve formaldehyde-free production and does not stick to the board during hot pressing.

[0111] As can be seen from the comparison between Application Example 1 and Comparative Application Examples 1 to 4, it is necessary to use difunctional and higher functional polyols to modify isocyanates together, and the ratio of difunctional and higher functional polyols must be within a specific range in order to obtain a sheet with high static bending strength and low extrusion dimensional change rate.

[0112] As can be seen from the comparison between Application Example 1 and Comparative Application Examples 5 and 6, when the R value is less than 50 or greater than 150, the dimensional stability or mechanical properties of the sheet material decrease significantly.

[0113] As can be seen from the comparison between Application Example 1 and Comparative Application Example 8, the pulse extrusion frequency should not be less than 2 times / minute, otherwise the plate will easily stick, resulting in a large deviation in plate thickness and a significant decrease in static bending strength.

[0114] A comparison of Application Example 1 and Comparative Application Example 7 shows that hollow particleboard prepared with polyurethane adhesive has significant advantages over urea-formaldehyde resin in terms of mechanical properties and dimensional stability.

[0115] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A core flakeboard characterised in that, The hollow particleboard is made of particleboard and polyurethane adhesive. The raw materials for preparing the polyurethane adhesive include polyols and polyisocyanates; The isocyanate index of the raw materials used in the preparation is 50-150. The polyols include combinations of low-functionality polyols and high-functionality polyols; The low-functionality polyol has a functionality of 2; the high-functionality polyol has a functionality > 2. The mass ratio of the low-functionality polyol to the high-functionality polyol is 1:0.2~0.4; The polyol includes at least one of a combination of low-functionality polyether polyol and high-functionality polyether polyol, or a combination of low-functionality polyester polyol and high-functionality polyether polyol. When the polyol is selected from a combination of low-functionality polyether polyols and high-functionality polyether polyols, the low-functionality polyether polyol includes polyether polyol A or polyether polyol B. The number-average molecular weight of polyether polyol A is less than that of polyether polyol B, and the hydroxyl value of polyether polyol A is greater than that of polyether polyol B. The polyether polyol A has a number average molecular weight of 500-1500 and a hydroxyl value of 80-225 mg KOH / g; the polyether polyol B has a number average molecular weight of 1500-2500 and a hydroxyl value of 45-75 mg KOH / g. When the polyol is selected from a combination of low-functionality polyether polyols and high-functionality polyether polyols, the high-functionality polyether polyol includes polyether polyol C or polyether polyol D. The number-average molecular weight of the polyether polyol C is less than that of the polyether polyol D, and the hydroxyl value of the polyether polyol C is greater than that of the polyether polyol D. The polyether polyol C has a number-average molecular weight of 500-2500 and a hydroxyl value of 300-450 mg KOH / g; the polyether polyol D has a number-average molecular weight of 2500-4000 and a hydroxyl value of 39-90 mg KOH / g. When the polyol is selected from a combination of low-functionality polyester polyol and high-functionality polyether polyol, the low-functionality polyester polyol has a number-average molecular weight of 1500-2500 and a hydroxyl value of 45-75 mg KOH / g; the high-functionality polyether polyol has a number-average molecular weight of 500-2500 and a hydroxyl value of 65-450 mg KOH / g. The polyisocyanate includes at least one of isophorone diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, or polymethylene polyphenyl polyisocyanate. The hollow particleboard is prepared by the following method, the preparation method including: The hollow particleboard is prepared by applying polyurethane adhesive to the surface of the wood chips and using a pulse extrusion method. The pressure plate temperature of the pulse extrusion is 120~220℃; The gap between the pressure plates in the pulse extrusion is 15~60 mm; The frequency of the pulse extrusion is 2~120 times / min, and the stroke of a single extrusion is 2~200 mm.

2. The hollow core panel according to claim 1, characterized in that The polyol is selected from a combination of low-functionality polyether polyols and high-functionality polyether polyols, including a combination of polyether polyol A and polyether polyol C, and / or a combination of polyether polyol B and polyether polyol D.

3. The hollow core panel according to claim 1, characterized in that The high-functionality polyols include trifunctional polyols and / or tetrafunctional polyols.

4. The hollow core panel according to claim 1, characterized in that The polyisocyanate is at least one of toluene diisocyanate, diphenylmethane diisocyanate, or polymethylene polyphenyl polyisocyanate.

5. The hollow particleboard according to claim 1, characterized in that, The preparation method of the polyurethane adhesive includes: The polyol and polyisocyanate are reacted to obtain the polyurethane adhesive.

6. The hollow particleboard according to claim 5, characterized in that, The reaction is carried out at a temperature of 60-95°C for 2-6 hours.

7. The hollow particleboard according to claim 1, characterized in that, The mass of the polyurethane adhesive is 1.5 to 4% of the mass of the wood shavings.

8. The hollow particleboard according to claim 1, characterized in that, The hollow particleboard also includes a waterproofing agent.

9. The hollow particleboard according to claim 8, characterized in that, The water-repellent agent is used at a concentration of 0.2-0.4% of the wood shavings.

10. A method for preparing hollow particleboard according to any one of claims 1-9, characterized in that, The preparation method includes: The hollow particleboard is prepared by applying polyurethane adhesive to the surface of the wood chips and using a pulse extrusion method. The pressure plate temperature of the pulse extrusion is 120~220℃; The gap between the pressure plates in the pulse extrusion is 15~60 mm; The frequency of the pulse extrusion is 2~120 times / min, and the stroke of a single extrusion is 2~200 mm.

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