A method for continuous flat pressing of rapid-curing polyurethane-based plywood

Abstract

This invention discloses a continuous flat-press manufacturing method for rapidly curing polyurethane-based blockboard, relating to the field of wood processing technology. The method involves using finger-jointing and cross-jointing methods to form core boards from strips. When the finger-jointed strips are cross-jointed, the finger joints are staggered and do not overlap. The core boards are then longitudinally joined using finger-jointing on the production line to form continuous core boards. Continuous wood veneers are obtained by splicing wood veneers. Solvent-free foaming polyurethane resin is used as an adhesive; after applying the adhesive to the continuous core board and continuous wood veneers, the continuous wood veneers are laid on the upper and lower surfaces of the continuous core board to obtain a continuous blockboard blank. After hot pressing, the blank is sawn to obtain blockboard of the desired specifications. This invention solves the technical problems of high formaldehyde release, low production efficiency, and limited product width in blockboard manufacturing. This invention can also be used to prepare blockboard products with oriented strand board (OSB) as the substrate.

Description

Technical Field

[0001] This invention relates to a continuous flat-press manufacturing method for rapidly curing polyurethane-based plywood, belonging to the field of wood processing technology. Background Technology

[0002] Blockboard is a special type of plywood made by splicing wood strips or using hollow core boards as the core, and covering both sides with two or more layers of plywood, then pressing them together with glue. The characteristics of blockboard are mainly determined by its core board structure. Blockboard has good screw-holding power, high strength, and is characterized by its sturdiness, sound absorption, and heat insulation. It is easy to process and is widely used in furniture manufacturing, interior decoration, automobile and shipbuilding production, and construction.

[0003] Currently, the main problems in the production of blockboard include: First, the extensive use of formaldehyde-based resin adhesives such as urea-formaldehyde resin in the production process leads to high formaldehyde release during both production and use; second, the use of intermittent or periodic production methods results in low production efficiency; and third, the limited range of blockboard sizes, with my country mainly producing 1220mm×2440mm and 915mm×1830mm, restricts its application. Summary of the Invention

[0004] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a method for continuous flat pressing manufacturing of rapid curing polyurethane-based blockboard. The method of the present invention, through the reasonable selection of adhesives, not only ensures that the formaldehyde emission of the prepared blockboard reaches the ENF level, but also helps to improve the performance of the prepared blockboard.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] 1. Preparation of solvent-free foaming polyurethane resin

[0007] (1) Under stirring, 10-50 parts by weight of sucrose polyether tetraol and 100 parts by weight of polypropylene glycol are mixed evenly to obtain a mixed polyether polyol with a hydroxyl value of 300-400 mg KOH / g.

[0008] (2) 300 parts by weight of polyglycerol were dehydrated at 110~130℃ for 120 minutes, cooled to 95℃ with stirring, polymethylene polyphenyl polyisocyanate was added, and the reaction was carried out at 85~95℃ for 120 minutes. After cooling, the prepolymer was obtained. The isocyanate group content in the prepolymer was 1~3%.

[0009] (3) Mix 100 parts by weight of mixed polyether polyol, 1.5 parts by weight of organosilicon foam stabilizer, 0.1 parts by weight of dibutyltin dilaurate, 10-50 parts by weight of prepolymer, 100 parts by weight of polymethylene polyphenyl polyisocyanate, and 10 parts by weight of cyclohexanone, and stir evenly to obtain solvent-free foaming polyurethane resin; the curing speed of polyurethane resin is 40-90s;

[0010] 2. The core board is made by finger-jointing and cross-jointing methods. When the finger-jointed strips are cross-jointed, the finger joints are staggered and do not overlap. The core board is formed into a continuous core board by finger-jointing and longitudinal joining on the production line. The moisture content is 8~20%.

[0011] 3. Continuous wood veneer is obtained by splicing wood veneers with a thickness of 1.5~5.0mm, with a moisture content of 8~20%;

[0012] 4. Using solvent-free foamed polyurethane resin as adhesive, after applying the adhesive to the continuous core board and continuous wood veneer, the continuous wood veneer is laid on both sides of the continuous core board to obtain a continuous blockboard blank. After hot pressing and shearing, the blockboard of the required specifications is obtained. The wood grain of the core board is parallel to the direction of production line travel, and the wood grain of the wood veneer is perpendicular to the direction of production line travel.

[0013] The adhesive is applied by single-sided spraying or double-sided roller coating. For the wood veneer, single-sided spraying is used, with the coated surface being the side in contact with the core board. For the core board, double-sided roller coating is used, with the coated surface being the side in contact with the wood veneer. The adhesive application rate is 250-300 g / m². 2 The hot pressing temperature is 50~190℃, the pressure is 1.0~1.5MPa, and the hot pressing factor is 10~50s / mm.

[0014] The advantages and technical effects of this invention are as follows:

[0015] 1. This invention reduces labor costs and improves production efficiency in the production of plywood. Traditionally, the assembly of plywood core boards and veneer panels relies heavily on manual labor. This invention automates and continuously assembles these components, saving labor costs and increasing production efficiency. When using a medium-temperature curing process, energy consumption during production can be reduced. Furthermore, this invention uses solvent-free foaming polyurethane resin instead of traditional formaldehyde-based resins. The cured polyurethane has a stable molecular structure and does not release formaldehyde.

[0016] 2. Expanded the dimensions of plywood. Because the products coming out of the hot press are continuous, they can be cut to any length, resulting in a wider variety of product specifications, especially in terms of length.

[0017] 3. Superior physical and mechanical properties of the plywood. By adjusting the polyurethane resin formula and the thickness of the wood veneer, the static bending strength and nail-holding force of the plywood can be adjusted, ensuring that the plywood of this invention has superior physical and mechanical properties. Since oriented strand board (OSB) and plywood core board have the same wood grain arrangement characteristics, the technology of this invention can be used for similar plywood products using OSB as the base material;

[0018] 4. This invention utilizes foamed adhesive technology, which reduces adhesive consumption during production. To improve the production efficiency of plywood, the curing speed of polyurethane is increased by using methods such as mixing polyether polyols and prepolymers, and the ratio is adjusted to meet different hot-pressing temperature requirements. The manufacturing process employs plywood core boards and wood veneers with higher moisture content, improving drying efficiency and reducing breakage during the drying process. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the plywood core board of the present invention, which features horizontal splicing of slats and staggered finger joints;

[0020] Figure 2 This is a schematic diagram of the continuous flat pressing process for single-sided glue spraying of plywood according to the present invention;

[0021] Figure 3 This is a schematic diagram of the continuous flat pressing process for double-sided roller gluing of plywood according to the present invention;

[0022] Figure 4 This is a schematic diagram of the continuous flat pressing preparation process for adhesive coating in Example 3. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] The rapid curing polyurethane-based blockboard continuous flat pressing manufacturing method of the present invention combines the performance advantages of polyurethane resin and the efficiency advantages of continuous flat pressing production method. The manufacturing process also fully incorporates the advantages of various existing blockboard production technologies, and is more efficient than existing intermittent production methods.

[0025] The plywood core board of this invention is a relatively independent manufacturing unit, produced on a conventional production line according to conventional technology, and used for subsequent manufacturing.

[0026] Example 1: Continuous flat-press manufacturing method for 915mm wide rapid-curing polyurethane-based plywood

[0027] 1. Preparation of plywood core board

[0028] (1) A strip with a thickness of 15 mm, a length of 610 mm, and a moisture content of 20% is finger-jointed to obtain a strip with a length of 1830 mm;

[0029] (2) 1830mm long strips according to Figure 1 The plywood core board is obtained by horizontally splicing the plywood.

[0030] 2. Wood Veneer Preparation

[0031] A 915mm long wood segment is rotary cut to obtain a horizontally grained wood veneer with a thickness of 1.5mm, a width of 915mm, and a moisture content of 20%.

[0032] 3. Preparation of solvent-free foaming polyurethane resin

[0033] (1) Under stirring, 50 parts of sucrose polyether tetraol and 100 parts of polypropylene glycol were mixed evenly to obtain a mixed polyether polyol with a hydroxyl value of 400 mg KOH / g.

[0034] (2) Add 300 parts of polyglycerol to the reactor, dehydrate at 120°C for 120 minutes, cool to 95°C with stirring, add an appropriate amount of polymethylene polyphenyl polyisocyanate, and keep the reaction at 90°C for 120 minutes. After cooling, the prepolymer is obtained. The isocyanate group content in the prepolymer is 3%.

[0035] (3) Mix 100 parts of mixed polyether polyol, 1.5 parts of organosilicon foam stabilizer, 0.1 parts of dibutyltin dilaurate, 50 parts of prepolymer, 100 parts of polymethylene polyphenyl polyisocyanate, and 10 parts of cyclohexanone evenly to obtain solvent-free foaming polyurethane resin; the curing speed of polyurethane resin is 40 seconds.

[0036] 4. Continuous splicing of fine wood core layer and wood veneer

[0037] The continuous splicing of plywood core board and wood veneer is achieved using conventional splicing technology, with the core board being spliced ​​longitudinally by finger joint on the production line;

[0038] 5. Apply glue

[0039] Using solvent-free foamed polyurethane resin as the adhesive, a single-sided coating method is applied to both the top and bottom surfaces of the wood veneer. The coated surface is the one in contact with the plywood core, and the coating amount is 250~300g / m². 2 ( Figure 2 );

[0040] 6. Embryo forming

[0041] A continuous blockboard blank is obtained by sequentially laying down the glued lower surface veneer, the blockboard core, and the glued upper surface veneer. The wood grain of the blockboard core is parallel to the direction of production line travel, while the wood grain of the upper and lower surface veneers is perpendicular to the direction of production line travel. The blockboard blank is continuously hot-pressed at a temperature of 50℃, a pressure of 1.0~1.5MPa, and a hot-pressing factor of 10s / mm. After cutting, blockboard products with specified specifications are obtained.

[0042] The performance of the finished plywood was tested, and the results are shown in Table 1.

[0043] Example 2: Continuous flat-press manufacturing method for 1220mm wide rapid-curing polyurethane-based plywood

[0044] 1. Preparation of plywood core board

[0045] (1) Finger-jointed strips with a thickness of 8mm, a length of 610mm and a moisture content of 8% are finger-jointed to obtain strips with a length of 2440mm;

[0046] (2) 2440mm long strip Figure 1 The plywood core board is obtained by horizontally splicing the plywood.

[0047] 2. Wood Veneer Preparation

[0048] A 1220mm long wood segment is rotary cut to obtain a horizontally grained wood veneer with a thickness of 5mm, a width of 1220mm, and a moisture content of 8%.

[0049] 3. Preparation of solvent-free foaming polyurethane resin

[0050] (1) Under stirring, 10 parts of sucrose polyether tetraol and 100 parts of polypropylene glycol were mixed evenly to obtain a mixed polyether polyol with a hydroxyl value of 300 mg KOH / g.

[0051] (2) Add 300 parts of polyglycerol to the reactor, dehydrate at 120°C for 120 minutes, cool to 95°C with stirring, add an appropriate amount of polymethylene polyphenyl polyisocyanate, and keep the reaction at 90°C for 120 minutes. After cooling, the prepolymer is obtained. The isocyanate group content in the prepolymer is 1%.

[0052] (3) 100 parts of mixed polyether polyol, 1.5 parts of organosilicon foam stabilizer, 0.1 parts of dibutyltin dilaurate, 10 parts of prepolymer, 100 parts of polymethylene polyphenyl polyisocyanate, and 10 parts of cyclohexanone are stirred and mixed evenly to obtain solvent-free foaming polyurethane resin; the curing speed of polyurethane resin is 90 seconds.

[0053] 4. Continuous splicing of plywood core board and wood veneer

[0054] The continuous splicing of plywood core board and wood veneer is achieved using conventional splicing technology, with the core board being spliced ​​longitudinally by finger joint on the production line;

[0055] 5. Apply glue

[0056] Solvent-free foamed polyurethane resin was used as the adhesive, and a double-sided roller coating method was used to apply the adhesive to both sides of the plywood core board. The adhesive side was the surface in contact with the wood veneer, and the amount of adhesive applied to each side was 250~300g / m². 2 ( Figure 3 );

[0057] 6. Embryo forming

[0058] The bottom veneer, the glued plywood core board, and the top veneer are laid in sequence to obtain a continuous plywood blank. The wood grain of the plywood core board is parallel to the direction of production line travel, while the wood grain of the top and bottom veneers is perpendicular to the direction of production line travel. The plywood blank is continuously hot-pressed at a temperature of 180℃, a pressure of 1.0~1.5MPa, and a hot-pressing factor of 50s / mm. After cutting, a plywood product with specified specifications is obtained.

[0059] The performance of the finished plywood was tested, and the results are shown in Table 1.

[0060] Example 3: Continuous flat-press manufacturing method of blockboard with 1220mm width rapid-curing polyurethane-based oriented strand board substrate

[0061] 1. Preparation of Oriented Strand Board

[0062] Using conventional oriented strand board (OSB) production technology, a conventional OSB with a thickness of 15mm is obtained.

[0063] 2. Wood Veneer Preparation

[0064] A 1220mm long wood segment is rotary cut to obtain a horizontally grained wood veneer with a thickness of 1.5mm, a width of 1220mm, and a moisture content of 8%.

[0065] 3. Preparation of solvent-free foaming polyurethane resin

[0066] (1) Under stirring, 25 parts of sucrose polyether tetraol and 100 parts of polypropylene glycol were mixed evenly to obtain a mixed polyether polyol with a hydroxyl value of 300 mg KOH / g.

[0067] (2) Add 300 parts of polyglycerol to the reactor, dehydrate at 120°C for 120 minutes, cool to 95°C with stirring, add an appropriate amount of polymethylene polyphenyl polyisocyanate, and keep the reaction at 90°C for 120 minutes. After cooling, the prepolymer is obtained. The isocyanate group content in the prepolymer is 2%.

[0068] (3) Mix 100 parts of mixed polyether polyol, 1.5 parts of organosilicon foam stabilizer, 0.1 parts of dibutyltin dilaurate, 25 parts of prepolymer, 100 parts of polymethylene polyphenyl polyisocyanate, and 10 parts of cyclohexanone evenly to obtain solvent-free foaming polyurethane resin; the curing speed of polyurethane resin is 65 seconds.

[0069] 4. Continuous splicing of oriented strand board core and wood veneer

[0070] The core board is oriented strand board produced by continuous flat pressing process. The adhesive used in the manufacturing process of oriented strand board is a non-formaldehyde adhesive. Conventional splicing technology is used to achieve continuous splicing of wood veneer for the upper and lower surface layers.

[0071] 5. Apply glue

[0072] Solvent-free foamed polyurethane resin is used as the adhesive. Both the wood veneer and oriented strand board (OSB) are coated with the adhesive simultaneously. The wood veneer is coated on one side only, the surface in contact with the OSB. The OSB core layer, after sanding, is coated with adhesive on both sides using rollers, the surface in contact with the wood veneer. The amount of adhesive applied on one side is 250~300 g / m². 2 ( Figure 4 );

[0073] 6. Embryo forming

[0074] The bottom surface wood veneer, the glued oriented strand board (OSB), and the top surface wood veneer are laid sequentially to obtain a continuous blockboard blank. The wood grain of the core board is parallel to the direction of production line travel, while the wood grain of the top and bottom surface veneers is perpendicular to the direction of production line travel. The blockboard blank is continuously hot-pressed at a temperature of 90℃, a pressure of 1.0~1.5MPa, and a hot-pressing factor of 30s / mm. After cutting, a blockboard product with an OSB substrate of specified specifications is obtained.

[0075] The performance of the finished plywood was tested, and the results are shown in Table 1.

[0076] Table 1

[0077]

[0078] Note: In this implementation, the formaldehyde release source is extracts from wood.

Claims

1. A method for manufacturing a rapidly cured polyurethane-based blockboard by continuous flat pressing, characterized by, The steps are as follows: (1) the board is made into a core plate by finger jointing and transverse splicing, wherein the finger jointed board is transversely spliced with the finger joint seams staggered and not coinciding, and the core plate is formed into a continuous core plate by longitudinal splicing on a production line; (2) a continuous wood veneer is obtained by splicing wood veneers with a thickness of 1.5-5.0 mm; (3) a continuous block of plywood is prepared by coating a solvent-free foaming polyurethane resin as an adhesive on the continuous core plate and the continuous wood veneer, laying the continuous wood veneer on the upper and lower surfaces of the continuous core plate, and hot pressing to obtain the required size of the plywood, wherein the wood grain of the core plate is parallel to the direction of the production line, and the wood grain of the wood veneer is perpendicular to the direction of the production line; The preparation method of the solvent-free foaming polyurethane resin is as follows: (1) 10-50 parts by weight of sucrose polyether tetraol is mixed with 100 parts by weight of polypropylene glycol under stirring to obtain a mixed polyether polyol, and the hydroxyl value of the mixed polyether polyol is 300-400 mgKOH / g; (2) 300 parts by weight of polyglycerol is dehydrated at 110-130°C for 120 minutes, cooled to 95°C under stirring, and then polymeric methylene polyphenyl polyisocyanate is added, and the pre-polymer is obtained after being kept at 85-95°C for 120 minutes, and the isocyanate group content in the pre-polymer is 1-3%; (3) 100 parts by weight of the mixed polyether polyol, 1.5 parts by weight of silicone foam stabilizer, 0.1 parts of dibutyltin dilaurate, 10-50 parts by weight of the pre-polymer, 100 parts by weight of polymeric methylene polyphenyl polyisocyanate, and 10 parts by weight of cyclohexanone are mixed and stirred uniformly to obtain the solvent-free foaming polyurethane resin; The hot pressing temperature is 50-190°C, the pressure is 1.0-1.5 MPa, and the hot pressing factor is 10-50 s / mm.

2. The rapid-curing polyurethane-based blockboard continuous flat-press manufacturing method according to claim 1, characterized by: The water content of the continuous core plate and the continuous wood veneer is 8-20%.

3. The rapid-curing polyurethane-based blockboard continuous flat-press manufacturing method according to claim 1, characterized in that: The adhesive coating method is single-sided spraying or double-sided roller coating, and the coating amount is 250-300 g / m 2 .

4. The process for the continuous flat pressing production of fast curing polyurethane-based blockboards according to claim 1, characterized in that: The oriented shaving board is used as the core plate.

5. The rapid-curing polyurethane-based blockboard continuous flat-press manufacturing method according to claim 1, characterized in that: The wood veneer is sprayed on one side for gluing, and the gluing surface is the surface in contact with the core plate; the core plate is coated with adhesive by double roller coating, and the gluing surface is the surface in contact with the wood veneer.

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