Formaldehyde-free fiber surface shaving board and production process thereof

Abstract

The invention relates to a formaldehyde-free fiber surface shaving board and a production process thereof, the surface layer of the shaving board is made of wood fibers, the core layer is made of large-size wood shavings, and the formaldehyde-free fiber surface shaving board is prepared from a polyurethane adhesive without aldehyde auxiliaries, a waterproof agent and process water. The production process of the formaldehyde-free fiber surface shaving board comprises the steps of raw material preparation, raw material drying, additive adding, raw material sizing, paving and hot press molding. The formaldehyde-free fiber surface shaving board has the characteristics of low density and high strength, integrates the advantages and disadvantages of a fiber board and a shaving board, effectively improves the problems that the super-strong veneer shaving board is easy to break edges and the veneer is easy to crack during processing, effectively improves the static bending intensity and routing effect of the board, and expands the application range of the veneer shaving board.

Description

Technical Field

[0001] The invention relates to a formaldehyde-free fiber surface particleboard and a production process thereof, belonging to the field of formaldehyde-free artificial boards. Background Art

[0002] Wood-based panels can be divided into three categories according to the form of raw materials: particleboard, fiberboard and plywood, as well as other boards such as blockboard and integrated materials. Among them, particleboard can be divided into ordinary particleboard and super particleboard according to the difference in the form of the core layer particles.

[0003] In recent years, due to the rise of the concept of formaldehyde-free home furnishing, the demand for formaldehyde-free panels has increased year by year. Due to the relatively low cost, lower density and excellent processing performance of formaldehyde-free super-strong particleboard, its market share in the formaldehyde-free panel market is much higher than that of fiberboard, making it the largest formaldehyde-free panel in China, with an annual output of more than 7 million cubic meters.

[0004] In China, the mainstream adhesive for formaldehyde-free wood-based panels is isocyanate. In addition to being formaldehyde-free, isocyanate has many advantages, such as high bonding strength, fast curing speed, no strict requirements on the moisture content of wood straw materials, and excellent physical properties of the panels. However, the formaldehyde-free super-strong particleboard produced by this adhesive still has some disadvantages when used, the most obvious of which is the phenomenon of edge collapse during sawing and poor surface milling effect.

[0005] At the same time, the static bending strength requirement of super-strong particleboard is higher than that of ordinary particleboard. In order to improve the static bending strength, it is usually achieved by increasing the density and the amount of glue applied. This solution will lead to a decrease in hot pressing efficiency, increase fixed production costs, and ultimately lead to an increase in production costs.

[0006] Patent application CN 115160973A proposes a curing agent, which is added to the surface material of the particle board to slow down the edge collapse and cracking, but it cannot effectively improve the milling effect and has no obvious effect on improving the static bending strength.

[0007] Therefore, it is necessary to develop a particle board that is not easy to break and has good milling effect, and has high static bending strength. Summary of the invention

[0008] In view of the above-mentioned shortcomings in the prior art, the present invention provides a formaldehyde-free fiber surface particleboard, which is not easy to break and has good milling effect and high static bending strength.

[0009] Another object of the present invention is to provide a production process of formaldehyde-free fiber surface particleboard, by selecting and optimizing the proportion and morphology of wood raw materials, using polyurethane adhesive in combination with a specific production process, so as to produce formaldehyde-free fiber surface particleboard with high static bending strength, not easy to collapse edges and good engraving effect.

[0010] In order to achieve the above technical objectives, the scheme of the present invention is as follows:

[0011] The first aspect of the present invention provides a formaldehyde-free fiber facing particleboard, wherein the number of layers of the board is 3, including an upper surface layer, a lower surface layer and a core layer located in the center of the board in the thickness direction of the board, wherein the raw material form of the upper surface layer and the lower surface layer is in the form of wood fiber, also known as the wood fiber surface layer, and the raw material state of the middle layer is in the form of wood shavings, known as the wood shavings core layer; the raw materials for preparing the formaldehyde-free fiber facing particleboard include: wood fiber, wood shavings, polyurethane adhesive, waterproofing agent, process water;

[0012] Among them, the quality of absolute dry wood fiber or absolute dry wood shavings is used as the basis, and the materials of other raw materials are:

[0013] In the surface layer, the amount of polyurethane adhesive is 4-5% of the mass of wood fiber, such as 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5%, etc.; the amount of waterproofing agent is 0.5-1% of the mass of wood fiber, such as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.;

[0014] In the core layer, the amount of polyurethane adhesive is 2-4% of the mass of wood shavings, for example, 2%, 2.5%, 3%, 3.5%, 4% and the like; the amount of waterproofing agent is 0.5-1% of the mass of wood shavings, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% and the like; the amount of process water in the core layer is 0.5-2.5% of the mass of wood shavings, for example, 1%, 1.5%, 2%, 2.5% and the like.

[0015] In the formaldehyde-free fiber surface particleboard of the present invention, the weight proportion of the absolute dry wood fiber after applying the polyurethane adhesive and the waterproofing agent is 30-60%, for example, 40%, 45%, 50%, 55%, etc., and the weight proportion of the absolute dry wood shavings after applying the polyurethane adhesive, the waterproofing agent and process water is 40-70%, for example, 45%, 50%, 55%, 60%, 65%, 70%, etc., based on the total absolute dry mass of the formaldehyde-free fiber surface particleboard.

[0016] The board density of the formaldehyde-free fiber surface particleboard of the present invention is 0.58-0.65g / cm 3 , for example 0.59 g / cm 3 , 0.6g / cm 3 , 0.61g / cm 3 , 0.62g / cm 3 、0.63g / cm 3 , 0.64g / cm 3 , 0.65g / cm3 Etc., with the characteristics of low density and high strength.

[0017] In the formaldehyde-free fiber surface particleboard of the present invention, the raw materials of the wood fiber and / or wood shavings are one or more of poplar, pine, eucalyptus, fir, birch, hardwood, etc. The raw material ratio is required to be stable when preparing the wood fiber and wood shavings, wherein the air-dry density is higher than 0.5g / cm 3 The amount of wood used is not less than 60%. Before preparing wood fiber and / or wood shavings, the raw wood is preferably debarked and the debarked wood is used as the processing raw material.

[0018] In the present invention, the adhesive is a prepolymer of an aromatic isocyanate and a polyol composition. The aromatic isocyanate is a mixture of one or more of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate or toluene diisocyanate. The polyol composition is a mixture of a difunctional polyether polyol and a trifunctional polyether polyol, the molecular weights of the difunctional polyether polyol and the trifunctional polyether polyol are not less than 1000, such as 1500, 2000 or more, and the mass ratio of the difunctional polyether polyol to the trifunctional polyether polyol is 1:(0.4-2.5), such as 1:0.5, 1:1, 1:1.5, 1:2, etc. The ratio of the isocyanate to the polyol composition is to ensure that the isocyanate index is 30<R<200, such as 40, 50, 60, 75, 80, 90, 100, 120, 150, 160, 170, 185, 190, 200, etc. The present invention uses the isocyanate and the polyol composition as an adhesive, and the cured product thereof is a polyurethane. The hardness and toughness of the polyurethane can be adjusted by adjusting the ratio and amount of different components to match the post-processing requirements of the plate, thereby avoiding the problem that when isocyanate is used alone as an adhesive, the cured product is a polyurea with high hardness and poor toughness, which cannot meet the requirements of routing and milling.

[0019] The formaldehyde-free fiber surface particleboard of the present invention, the waterproofing agent is molten paraffin and / or emulsified paraffin.

[0020] In a preferred embodiment, the formaldehyde-free fiber surface particleboard of the present invention is made of wood fiber, wood shavings, polyurethane adhesive, waterproofing agent, and process water, and includes a wood fiber surface layer and a wood shavings core layer;

[0021] In the surface layer, based on the mass of the absolute dry wood fiber, the amount of polyurethane adhesive is 4-5% of the mass of the absolute dry wood fiber; the amount of waterproofing agent is 0.5-1% of the mass of the absolute dry wood fiber;

[0022] In the core layer, based on the mass of the absolute dry wood shavings, the amount of polyurethane adhesive is 2-4% of the mass of the absolute dry wood shavings; the amount of waterproofing agent is 0.5-1wt% of the mass of the absolute dry wood shavings; the amount of process water is 0.5-2.5% of the mass of the absolute dry wood shavings;

[0023] The polyurethane adhesive is a prepolymer of an aromatic isocyanate and a polyol composition; the aromatic isocyanate is selected from one or more of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and toluene diisocyanate; the polyol composition is a composition of a difunctional polyether polyol and a trifunctional polyether polyol; the molecular weights of the difunctional polyether polyol and the trifunctional polyether polyol are not less than 1000, and the mass ratio of the difunctional polyether polyol to the trifunctional polyether polyol is 1:(0.4-2.5); the ratio of the aromatic isocyanate to the polyol composition satisfies the isocyanate index 30<R<200.

[0024] The second aspect of the present invention provides a method for preparing a formaldehyde-free fiber surface particleboard, including: fiber preparation, particle preparation, fiber sizing, fiber drying, particle drying, particle sizing, paving and hot pressing forming and other process flows.

[0025] In a specific embodiment, the specific production process of the formaldehyde-free fiber surface particleboard includes:

[0026] (1) Fiber preparation. The specific process requirements are as follows:

[0027] The fiber preparation can refer to conventional technical means in the art. For example, the fiber preparation equipment includes a peeling machine, a chipper, a flaker, a pre-cooking equipment, and a hot grinder. The operating parameters of each equipment are adjusted according to the fiber quality requirements.

[0028] Specifically, for example, the bark content of the prepared fiber is less than 5%, such as less than 4%, 3%, 2%, 1%, etc., the hot grinding energy consumption is 80-150 degrees / ton, such as 90 degrees / ton, 100 degrees / ton, 110 degrees / ton, 120 degrees / ton, 130 degrees / ton, 140 degrees / ton, etc., preferably 100-130 degrees / ton; the fiber water filtration rate is 20-30s, such as 21s, 22s, 23s, 24s, 25s, 26s, 27s, 28s, 29s, etc., preferably 25-28s. The fiber diameter does not exceed 0.5mm, and the length does not exceed 4mm.

[0029] (2) Shavings preparation. The specific process requirements are as follows:

[0030] The shavings can be prepared by referring to conventional technical means in the art, for example, the equipment includes a peeling machine, a chipper, a flaker, and a super screen. The operating parameters of each equipment are adjusted according to the shavings quality requirements.

[0031] Specifically, for example, the prepared wood chips have a thickness of 0.3-0.6 mm, such as 0.4 mm, 0.5 mm, 0.55 mm, etc.; a width of 5-10 mm, such as 6 mm, 7 mm, 8 mm, 9 mm, etc.; and a length of 30-60 mm, such as 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, etc.

[0032] (3) Fiber sizing. The specific process requirements are as follows:

[0033] The waterproofing agent is added according to the set ratio at the hot mill; the polyurethane adhesive is added according to the set ratio at a distance of 4-8m from the outlet of the spray pipe. The adhesive and water are quickly mixed by high-pressure compressed air of at least 25 bar and then sprayed into the spray pipe through the glue nozzle. Through the improvement of the aforementioned glue application process, the glue is atomized by the nozzle and contacts the fibers in the spray pipe. After high-speed transmission, the turbulent layer is formed and the fibers contact and collide with each other to ensure the uniformity of glue application.

[0034] (4) Fiber drying. The specific process requirements are as follows:

[0035] The fiber is dried in a drying pipeline, with an inlet temperature of 110-150°C, such as 120°C, 130°C, 140°C, etc., and an outlet moisture content (mass fraction) controlled at 7-12%, such as 8%, 9%, 10%, 11%, etc.

[0036] (5) Wood shavings drying. The specific process requirements are as follows:

[0037] The shavings are dried using a single-channel dryer at a drying temperature of 100-160° C., such as 110° C., 120° C., 130° C., 140° C., 150° C., etc. The moisture content after drying is controlled between 1.5-2.5%, such as 2%.

[0038] (6) Shavings gluing. The specific process requirements are as follows:

[0039] The adhesive is added in proportion, and process water is added when necessary. After gluing, the absolute dry moisture content of the wood chips is controlled at 3-5%, for example, 4%. The process equipment for gluing wood chips can refer to the existing technology, for example, a drum glue mixer or a ring glue mixer is used for gluing wood chips.

[0040] (7) Paving. Specific process requirements are as follows:

[0041] The paving process equipment mainly includes paving machines and pre-pressing machines.

[0042] The fibers and shavings are laid by a laying head. The fibers and shavings are laid in proportion. After laying the lower surface fiber, the fiber slab needs to be pre-pressed, and then the slab is laid by a shavings laying machine. After the shavings are laid, the slab is pre-pressed again by a pre-pressing machine, and finally, it passes through the fiber laying machine again to lay the top layer of fiber. After the overall paving is completed, it needs to be pre-pressed again by a heavy-duty pre-pressing machine. The overall board thickness is controlled to be 1.5-3 times the final board thickness, for example 2 times, 2.5 times, etc.

[0043] (8) Hot pressing. The specific process requirements are as follows:

[0044] A continuous flat press is used for hot pressing. A special mold release agent must be sprayed before hot pressing. The unit pressure during hot pressing is 0.5-4MPa, for example: the high pressure in the high pressure section is 2.5-3.5MPa, the pressure in the pressure holding section is 0.8-2.5MPa, the pressure in the thickness setting section is 0.5-2MPa, the hot pressing temperature is 170-240℃, for example, the temperature distribution is 230-240℃, 220-230℃, 200-210℃, 190-200℃, 170-180℃, and the hot pressing factor is 5-10s / mm, for example, 6s / mm, 7s / mm, 8s / mm, 9s / mm, etc. Among them, the unit pressure refers to the pressure per unit area acting on the plate.

[0045] Compared with the existing board types and production processes, the present invention has the following beneficial effects:

[0046] The present invention designs a new type of board with a surface layer of wood fiber and a core layer of wood shavings, and develops a polyurethane adhesive composed of specific materials, which not only solves the problems of easy edge collapse, low static bending strength, and difficulty in engraving and milling of particleboard, but also solves the problem of high production cost of fiberboard.

[0047] Traditional wood shavings are large in size and have a high surface roughness after milling, so using wood shavings alone cannot meet the requirements for producing milled boards. Wood fiber has a small physical size. When it is produced using urea-formaldehyde glue with balanced hardness and toughness, it is smooth and neat after milling, which can meet the production requirements. When it is produced using isocyanate adhesives with high hardness and poor toughness, it becomes fuzzy and has a high roughness after milling. By adding a polyol composition to form a polyurethane adhesive and increasing the toughness of the adhesive, a board with a good milling effect can be produced. However, if the toughness of the adhesive is too strong, it may cause insufficient static bending strength of the board. The present invention achieves a balance between hardness and toughness by adjusting the type and composition of the polyol and the isocyanate index R (R refers to the molar ratio of NCO groups to OH groups in the formula) to meet the milling requirements. In addition, since the production energy consumption and cost of wood fiber are much higher than wood shavings, if all wood fiber raw materials are used, the overall production cost is too high. The present invention forms a fiber surface particleboard by designing the surface wood fiber and the core wood shavings, which can control the cost increase within an acceptable range. DETAILED DESCRIPTION

[0048] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0049] Polymethylene polyphenyl polyisocyanate (CW20): functionality about 2.7, viscosity 180-250 cP at 25°C, -NCO content 30.5-32%, Wanhua Chemical Group Co., Ltd.;

[0050] Polymethylene polyphenyl polyisocyanate (9132FC): functionality about 2.4, viscosity 320-550 cP at 25°C, -NCO content 27.5-30%, Wanhua Chemical Group Co., Ltd.

[0051] Difunctional polyether polyol (C2010D), molecular weight about 1000, hydroxyl value 112±3.5mg KOH / g, Wanhua Chemical Group Co., Ltd.;

[0052] Difunctional polyether polyol (C2020), molecular weight about 2000, hydroxyl value 56±1.5mg KOH / g, Wanhua Chemical Group Co., Ltd.;

[0053] Trifunctional polyether polyol (F3150), molecular weight about 5000, hydroxyl value 33-37 mg KOH / g, Wanhua Chemical Group Co., Ltd.;

[0054] Tetrafunctional polyether polyol (R8241), molecular weight about 550, hydroxyl value 410±20mg KOH / g, Wanhua Chemical Group Co., Ltd.;

[0055] Trifunctional polyether polyol (R2305), molecular weight about 500, hydroxyl value 335±10mg KOH / g, Wanhua Chemical Group Co., Ltd.;

[0056] Waterproofing agent, Yangzi Petrochemical No. 58 molten paraffin.

[0057] Example 1

[0058] The process scheme is as follows:

[0059] Design thickness: 18.5mm,

[0060] Design density: 0.61g / cm 3 ,

[0061] Surface core layer ratio: 15:70:15,

[0062] The ratio of wood materials is: eucalyptus: pine: miscellaneous wood = 60:20:20,

[0063] The adhesive solution for the surface fiber is based on the mass of the absolute dry wood fiber, the amount of CW20 is 3wt% of the fiber mass, the polyol composition is a mixture of C2010D and F3150, the amount of the polyol composition is 1.5wt% of the fiber mass, the mass ratio of the two polyether polyols is 1:1.5, and the R value is about 40.

[0064] The adhesive for the core layer wood particles is 9132FC, based on the mass of the absolutely dry wood particles, the adhesive is 3wt%,

[0065] The waterproofing agent is Yangzi Petrochemical No. 58 molten paraffin. The surface layer is based on the mass of absolute dry wood fiber, with a waterproofing agent of 0.5wt%. The core layer is based on the mass of absolute dry wood shavings, with a waterproofing agent of 0.5wt%.

[0066] The process water is tap water or well water, which is adjusted according to the moisture content requirements of the pavement.

[0067] The preparation process includes:

[0068] (1) Fiber preparation:

[0069] Fiber preparation equipment includes peeling machines, chippers, flakers, pre-cooking equipment, and hot grinders. The operating parameters of each equipment are adjusted according to the fiber quality requirements.

[0070] The bark content of the prepared fiber is 4%, the hot grinding energy consumption is 130 degrees / ton, and the fiber water filtration rate is 28s.

[0071] (2) Wood shavings preparation:

[0072] Shavings preparation equipment includes debarkers, chippers, flakers, and super screens. The operating parameters of each device are adjusted according to the shavings quality requirements.

[0073] The prepared wood chips have a thickness of 0.3-0.6 mm, a width of 5-10 mm, and a length of 30-60 mm.

[0074] (3) Fiber sizing:

[0075] The waterproofing agent is added at the hot mill; the adhesive is added according to the set ratio, and the glue application position is 6m away from the outlet of the spray pipe. The adhesive and water are quickly mixed in a ratio of 1:2 through 25bar high-pressure compressed air and then sprayed into the spray pipe through the glue application nozzle.

[0076] (4) Fiber drying:

[0077] The fiber is dried in a drying pipeline, with an inlet temperature of 125°C and an outlet moisture content controlled at 12%;

[0078] (5) Wood shavings drying:

[0079] The wood chips are dried using a single-channel dryer, and the moisture content after drying is controlled at 2%.

[0080] (6) Wood shavings gluing:

[0081] The particleboard is glued with a ring glue mixer, and process water is added as needed. After gluing, the moisture content of the particles is controlled at 4.5%.

[0082] (7) Paving: specific process requirements are as follows:

[0083] The paving process equipment mainly includes paving machines and pre-pressing machines.

[0084] The fibers and shavings are laid by a laying head in proportion. After laying the lower surface fiber, the fiber slab needs to be pre-pressed, and then the slab is laid by a shavings laying machine. After the shavings are laid, the slab is pre-pressed again by a pre-pressing machine, and finally, it passes through the fiber laying machine again to lay the top layer of fiber. After the overall paving is completed, it needs to be pre-pressed again by a heavy-duty pre-pressing machine. The overall board thickness is controlled to be twice the thickness of the final board.

[0085] (8) Hot pressing molding, the specific process requirements are as follows:

[0086] A continuous flat press is used for hot pressing. A special release agent must be sprayed before hot pressing. The unit pressure during hot pressing is: 2.5-3.5MPa in the high pressure section, 0.8-2.5MPa in the pressure holding section, 0.5-2MPa in the thickness setting section, and the temperature distribution is 235℃, 225℃, 210℃, 200℃, and 180℃.

[0087] A summary of the relevant process parameters is shown in Table 1.

[0088] Table 1

[0089] Design density <![CDATA[0.61g / cm 3 ]]> Design thickness 18.5mm Wood raw material ratio Eucalyptus: pine: miscellaneous wood = 60:20:20 Surface core ratio 30:70 Fiber filterability 28s Shavings shape Thickness: 0.3-0.6mm; Width: 5-10mm; Length: 30-60mm Surface adhesive addition amount 3%CW20+0.6%C2010D+0.9%F3150 Surface waterproofing agent addition amount 0.5% No. 58 molten paraffin Core layer adhesive addition amount 3%9132FC Core layer waterproofing agent addition amount 0.5% No. 58 molten paraffin Moisture content of surface paving fibers 12％ Moisture content of wood chips for core layer paving 4.5％ Thickness of slab after pre-pressing 37mm Hot pressing pressure High pressure section 2.5-3.5MPa, pressure holding section 0.8-2.5MPa, thickness setting section 0.5-2MPa Hot pressing temperature 235℃、225℃、210℃、200℃、180℃

[0090] Example 2

[0091] The difference between Example 2 and Example 1 is that the amount of surface adhesive added is 2.5% CW20+0.71% C2020+1.79% F3150 (the mass ratio of the two polyether polyols is 1:2.5, and the R value is about 32.), and the other processes adopt the same preparation process as Example 1.

[0092] Example 3

[0093] The difference between Example 2 and Example 1 is that the amount of surface adhesive added is 3.5% CW20+0.36% C2020+0.14% F3150 (the mass ratio of the two polyether polyols is 1:0.4, and the R value is about 184.), and the other processes adopt the same preparation process as Example 1.

[0094] Comparative Example 1

[0095] The difference between Comparative Example 1 and Example 1 is that the amount of surface adhesive added is 5% CW20, and the other processes adopt the same preparation process as Example 1.

[0096] Comparative Example 2

[0097] The difference between Comparative Example 2 and Example 1 is that the surface adhesive is urea-formaldehyde adhesive, the adhesive solid content is 50%, and the surface adhesive solid addition amount is 8%.

[0098] When applying glue to the fiber, the glue application position is the urea-formaldehyde glue application port, which is delivered and atomized by a delivery pump.

[0099] The other processes adopt the same preparation process as Example 1.

[0100] Comparative Example 3

[0101] The difference between Comparative Example 3 and Example 1 is that the amount of surface adhesive added is 3% CW20+0.6% C2010D+1.8% F3150 (the mass ratio of the two polyether polyols is 1:3, and the R value is about 30), and the other processes adopt the same preparation process as Example 1.

[0102] Comparative Example 4

[0103] The difference between Comparative Example 4 and Example 1 is that the amount of surface adhesive added is 3% CW20+1.5% C2010D+0.5% F3150 (the mass ratio of the two polyether polyols is 1:0.33, and the R value is about 21.25), and the other processes adopt the same preparation process as Example 1.

[0104] Comparative Example 5

[0105] The difference between Comparative Example 5 and Example 1 is that the amount of surface adhesive added is 3% CW20+1.6% C2010D (R value = about 21.96), and the other processes adopt the same preparation process as Example 1.

[0106] Comparative Example 6

[0107] The difference between Comparative Example 6 and Example 1 is that the amount of surface adhesive added is 3% CW20+1.6% F3150 (R value = about 71.53), and the other processes adopt the same preparation process as Example 1.

[0108] Comparative Example 7

[0109] The difference between Comparative Example 7 and Example 1 is that the amount of surface adhesive added is 3% CW20+0.6% C2010D+0.9% R8241 (the mass ratio of the two polyether polyols is 1:1.5, and the R value is about 30), and the other processes adopt the same preparation process as Example 1.

[0110] Comparative Example 8

[0111] The difference between Comparative Example 8 and Example 1 is that the amount of surface adhesive added is 3% CW20+0.6% C2010D+0.9% R2305 (the mass ratio of the two polyether polyols is 1:1.5, and R value is about 10.7), and the other processes adopt the same preparation process as Example 1.

[0112] Performance Testing

[0113] The artificial boards described in Application Examples 1-3 and Comparative Examples 1-8 were tested in accordance with GB / T17657-2022. At the same time, the produced plain boards were veneered and their edge collapse, cracking and milling effects were measured. The test results are summarized in Table 2.

[0114] Table 2

[0115]

[0116] The results of Examples 1-3 show that a polyurethane adhesive composed of an aromatic isocyanate and a polyol composition is applied to the surface wood fiber, and a specific adhesive dosage (the adhesive dosage is 4-5wt% of the mass of the wood fiber) and an adhesive composition (the ratio of the isocyanate to the polyol composition is to ensure that the isocyanate index is 30<R<200, the polyol composition is a mixture of a difunctional polyether polyol and a trifunctional polyether polyol, and the molecular weights of the difunctional polyether polyol and the trifunctional polyether polyol shall not be less than 1000, and the mass ratio of the difunctional polyether polyol to the trifunctional polyether polyol is 1:(0.4-2.5) is obtained, and a fiber surface particleboard with high static bending strength, elastic modulus, and surface bonding strength is obtained. Not only is the mechanical property of the board excellent, but the processing performance is also significantly improved. It is not easy to collapse the edge during sawing, and the proportion of cracks after veneer is significantly reduced. Moreover, it is smooth and burr-free after milling, and has excellent processing performance, which can better meet the needs of customers and the market.

[0117] The results of Example 1 and Comparative Example 1 show that the polyol component must be added according to specific requirements to effectively improve the mechanical properties and processing properties of the board. The results of Example 1 and Comparative Example 2 show that the polyol component must be added according to specific requirements to effectively improve the mechanical properties of the board, and the processing properties of the board can be improved to be equivalent to the processing properties of the urea-formaldehyde board. The results of Example 1 and Comparative Examples 3 and 4 show that the mass ratio of difunctional polyether polyol to trifunctional polyether polyol in the polyol must be 1: (0.4-2.5). If the amount of difunctional polyol is more than the above ratio, the board is soft and the elastic modulus is low; if the amount of trifunctional polyol is more than the above ratio, the board is hard and the static bending strength is low. The results of Example 1 and Comparative Examples 5 and 6 show that a combination of difunctional polyether polyol and trifunctional polyether polyol must be used, and the use of one polyol alone will cause some performance to be low. The results of Example 1 and Comparative Example 7 show that materials with too high functionality (greater than 3) cannot be used in the polyol composition. The results of Example 1 and Comparative Example 8 show that the molecular weight of the polyol should not be lower than 1000, otherwise the crosslinking density will increase and the proportion of the soft segment will be low at the same R value, which will lead to processing performance not meeting the requirements.

[0118] The production process of the present invention can be used to prepare a fiber surface particleboard with excellent performance. The board has excellent physical and mechanical properties and processing properties, can effectively solve the application problems of existing formaldehyde-free particleboards, and effectively improve the performance of the board.

[0119] Finally, it should be noted that the above embodiments are only used to describe the preferred implementation methods of the present invention, rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that various modifications and improvements made by modifying or equivalently replacing the technical solution of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims

1. A formaldehyde-free fiber surface particleboard, It is characterized in that The board comprises a wood fiber surface layer located on the surface and the lower surface in the thickness direction of the board, and a wood shavings core layer located in the center of the board. The raw materials for preparing the formaldehyde-free fiber surface particleboard include: wood fiber, wood shavings, polyurethane adhesive, waterproofing agent, and process water; The quality of the absolute dry wood fiber or absolute dry wood shavings is used as the benchmark. In the surface layer, the amount of polyurethane adhesive is 4-5% of the weight of wood fiber; the amount of waterproofing agent is 0.5-1% of the weight of wood fiber; In the core layer, the amount of polyurethane adhesive is 2-4% of the mass of wood shavings; the amount of waterproofing agent is 0.5-1wt% of the mass of wood shavings; and the amount of process water is 0.5-2.5% of the mass of wood shavings.

2. The formaldehyde-free fiber surface particleboard according to claim 1, It is characterized in that The weight ratio of the absolutely dry wood fiber after applying the polyurethane adhesive and the waterproofing agent is 30-60%, and the weight ratio of the absolutely dry wood shavings after applying the adhesive, the waterproofing agent and the process water is 40-70%; Preferably, the density of the formaldehyde-free fiber surface particleboard is 0.58-0.65 g / cm 3 .

3. The formaldehyde-free fiber surface particleboard according to claim 1 or 2, It is characterized in that The raw materials of the wood fiber and wood shavings are selected from one or more of poplar, pine, eucalyptus, fir, birch, and hard miscellaneous wood; and / or The polyurethane adhesive is a prepolymer of an aromatic isocyanate and a polyol composition; and / or The waterproofing agent is molten paraffin and / or emulsified paraffin.

4. The formaldehyde-free fiber surface particleboard according to any one of claims 1 to 3, It is characterized in that The aromatic isocyanate is selected from one or more of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and toluene diisocyanate; and / or The polyol composition is a composition of a difunctional polyether polyol and a trifunctional polyether polyol. Preferably, the molecular weights of the difunctional polyether polyol and the trifunctional polyether polyol are not less than 1000, and the mass ratio of the difunctional polyether polyol to the trifunctional polyether polyol is 1:(0.4-2.5); Preferably, the ratio of the aromatic isocyanate to the polyol composition satisfies an isocyanate index of 30<R<200.

5. A process for producing the formaldehyde-free fiber surface particleboard according to any one of claims 1 to 4, It is characterized in that The process includes fiber preparation, wood shavings preparation, fiber gluing, fiber drying, wood shavings drying, wood shavings gluing, paving and hot pressing steps.

6. The production process according to claim 5, It is characterized in that The fiber preparation and wood shavings preparation also include the step of peeling the raw materials; Preferably, the fiber is prepared to have a water filterability of 20-30s, preferably 25-28s; and / or The shavings are prepared such that the thickness of the shavings is 0.3-0.6 mm, the width is 5-10 mm, and the length is 30-60 mm.

7. The production process according to claim 5, It is characterized in that The fiber sizing is to quickly mix the three materials of isocyanate, polyol composition and water by high-pressure compressed air of at least 25 bar and then spray them into the spray pipe through a sizing nozzle; and / or The fiber is dried in a drying pipeline, with an inlet temperature of 110-150° C. and an outlet moisture content controlled at 7-12 wt %.

8. The production process according to claim 5, It is characterized in that The wood chips are dried using a single-channel dryer, and the moisture content after drying is controlled between 1.5-2.5wt%; and / or In the shavings gluing, process water is added to control the moisture content of the shavings after gluing to be 3-5%.

9. The production process according to claim 5, It is characterized in that The paving includes paving and three pre-pressing processes, which are pre-pressing once after the lower surface fiber is paved, pre-pressing once after the shaving core layer is paved, and pre-pressing once after the upper surface fiber is paved.

10. The production process according to claim 5, It is characterized in that The hot pressing molding is performed by using any one of a continuous flat press, a multi-layer press, and a single-layer press, and a special release agent is sprayed before hot pressing; Preferably, during the hot pressing process, the unit pressure is 0.5-4 MPa, the temperature is 170-240° C., and the hot pressing factor is 5 s / mm-10 s / mm.

Images