A cold pressing process for plywood

Abstract

The present application relates to a kind of plywood cold pressing process, comprising the following steps: S1.Preparation and drying of veneer;S2.Veneer gluing;S3.Pressurizing;S4.Core board sanding;S5.Paste anti-cracking surface plate;S6.Anti-cracking surface plate sanding;S7.Paste decorative panel;S8.Curing room curing;S9.Decorative panel sanding.Through the roller sanding treatment of veneer, the setting of plywood core board, anti-cracking surface plate and decorative panel, the configuration of adhesive, the control and selection of glueing mode, cold pressing process and other multiple factors, the production of plywood greatly reduces the production energy consumption, improves the wood utilization rate, reduces the compression rate, and has good deformation resistance.In addition, the plywood prepared from thick veneer can obtain better wood experience from cross section and as a whole.

Description

TECHNICAL FIELD

[0001] The present application relates to a cold pressing process of plywood, belonging to the technical field of plywood production process. BACKGROUND

[0002] The existing plywood processing process mostly adopts hot pressing process, usually adopts three categories of urea-formaldehyde glue, phenol-formaldehyde glue, and melamine-polyformaldehyde glue as the main adhesive, and water-based formaldehyde-free glue such as starch and soybean protein. The production equipment of plywood is a multi-layer hot press, which consumes a large amount of heat energy, and there is a large space for energy saving, but the largest reduction is to change the hot pressing process to cold pressing process. As long as there is a kind of glue that can form a bonding strength at room temperature in a short time, and the cost of adhesive is relatively low, it is completely possible to replace the traditional hot pressing process with cold pressing process, which is revolutionary for the plywood industry.

[0003] Because the hot pressing process is a device corresponding to one plate for one hot pressing plate, the hot pressing plate is repeatedly closed and loosened during the production process, and the heat loss of the pressing plate itself is not small, and a large amount of heat is wasted by the pressed plywood, so the unit energy consumption is very high. After high temperature, the compression rate of the plate is large, which reduces the utilization rate of wood.

[0004] In addition, the existing plate decoration, usually the surface of the plywood will not be decorated in order to obtain the texture of the solid wood itself, or use valuable wood veneer or decorative paper to obtain better sensory experience, but usually the thickness difference between the veneer and the plywood is small, and the single board of different materials will crack due to the difference in dry shrinkage and wet expansion.

[0005] Due to the limitations of the existing hot pressing process of plywood, thick veneer will affect the hot pressing efficiency, and the decoration of the plate usually contributes little to the cracking of the plate surface, so there is almost no thick plywood. In addition, the initial moisture content of the veneer is usually high, at least more than 8%, which is usually a conventional choice for the need of heat conduction during hot pressing, and the moisture content has a great influence on the curing of the adhesive in the cold pressing process. SUMMARY

[0006] In order to solve the technical problems of large energy consumption, low wood utilization rate, high compression rate, poor deformation resistance, lack of wood texture, and long cold pressing time of the existing plywood hot pressing process, the technical scheme of the present application is proposed.

[0007] A cold pressing process of plywood, comprising the following steps:

[0008] S1. Preparation and drying of veneer;

[0009] S2. Veneer gluing;

[0010] S3. Pressing;

[0011] S4. Sanding of core board;

[0012] S5. Attaching crack-resistant top board;

[0013] S6. Sanding of crack-resistant top board;

[0014] S7. Attaching decorative panel;

[0015] S8. Curing in curing room;

[0016] S9. Sanding of decorative panel.

[0017] The specific steps are as follows:

[0018] S1. Preparation and drying of veneer: control the quality of rotary cutting, planing or sawing of veneer to make the thickness uniform; control the drying process of veneer to keep the overall deformation as small as possible, local deformation and avoid cracking; planing or sawing should be spliced or finger jointed into a whole veneer; the thickness difference of the whole veneer is controlled within 0.2mm; control the final moisture content of the veneer, according to the thickness of the veneer, the final moisture content is within the range of 0%-10%, and the moisture content deviation of the veneer of the same specification is not more than ±1%(such as: the veneer controlled at 5% moisture content, the moisture content control range is 4%-6%); the dry thickness of the veneer is 2-10mm;

[0019] Further, as a preferred technical solution, the dry thickness of the veneer is 5.5-10mm to obtain better wood feel.

[0020] For the thickness of the plywood, especially for the thickness of the plywood below 18mm, 2-5.5mm thick veneer is selected for processing; for the thickness of the plywood more than 18mm, the thickness of the veneer is selected as 5.5-10mm. For the plywood with a thickness less than 18mm, 2-5.5mm thick veneer is selected according to actual needs, the maximum thickness of the veneer within the allowable range of thickness is selected to achieve the wood texture as much as possible; for the plywood with a thickness greater than 18mm, by selecting the dry thickness of the veneer as 5.5-10mm, one is to facilitate rotary cutting processing, the thickness below 5.5mm lacks the texture of wood, and the thickness greater than 10mm is difficult to obtain a whole veneer in the rotary cutting process, and the surface of the board cracks seriously, which needs to be repaired in a large area later. Controlling the final moisture content of the veneer within the range of 0%-10% is beneficial to the rapid absorption of water in the adhesive by the veneer and then to the rapid curing, and the moisture content of the plywood after uniform distribution can be controlled within the range required by the standard.

[0021] S2. Single board gluing: the single board is glued on the roller gluing machine; the three-layer board is only double-sidedly glued with the middle core board, the five-layer board is only double-sidedly glued with the second and fourth core boards, the seven-layer board is only double-sidedly glued with the second, fourth and sixth core boards, and so on, and then the core board assembly is put into the press; the core board assembly is assembled with the textures of adjacent single boards being staggered and perpendicular, and the grain direction of the outermost single board is consistent with the length direction of the assembly;

[0022] The above gluing method can greatly shorten the gluing process and thus the assembly process, and greatly improve the production efficiency. The adhesive is a water-based adhesive, and one of plant glue, animal glue, protein glue, white latex glue, water-based epoxy resin glue, water-based polyurethane glue, polyvinyl alcohol glue and modified adhesive of the above adhesive or other cold-pressing curing water-based adhesive is selected.

[0023] S3. Press pressure maintaining: at room temperature, the pressure maintaining time is maintained between 20-720 minutes and the board surface pressure is maintained between 0.6-1.2 MPa according to different adhesives;

[0024] S4. Core board sanding: after the pressure is released, the surface of the core board is inspected and simply repaired, and then the thickness is fixed by roller sanding with a pressure of 0.8-1.2 kN;

[0025] S5. Anti-cracking surface plate pasting: after the core board with fixed thickness is double-sidedly glued by the roller gluing machine, a whole piece of cross-grain surface plate with a thickness of 0.5-1.2 mm is covered on both sides and pressed into the press with a pressure of 0.6-0.8 MPa, and after pressure maintaining for 20-30 minutes, the pressure is released; the texture direction of the surface plate is perpendicular to that of the adjacent core board;

[0026] S6. Anti-cracking surface plate sanding: after the pressure is released, the board edge is repaired and defects are repaired, and then the thickness is fixed by precision sanding of the sanding machine, and the sanding amount of the upper and lower surfaces is 0.2-0.4 mm;

[0027] S7. Decorative panel pasting: after the core board with fixed thickness and anti-cracking surface plate is double-sidedly glued by the roller gluing machine, a whole piece of grain thin single board with a thickness of 0.5-1.2 mm is covered on both sides, and then it is pressed into the press with a pressure of 0.6-0.8 MPa, and after pressure maintaining for 20-30 minutes, the pressure is released; the texture direction of the decorative panel is perpendicular to that of the anti-cracking surface plate.

[0028] S8. Curing room curing: the board after pasting the decorative panel is put into the curing room in a whole pile shape for 5-10 days for curing, uniformizing water content and releasing internal stress, so as to ensure that the surface layer expansion and contraction process is completed before entering the decorative panel sanding process; for those with high water content, a link for dispersing water is added.

[0029] S9. Sanding of the decorative panel: the moisture content of the board after curing meets the standard requirements, and the sanding machine is used to sand the board to a certain thickness, and the sanding amount of the upper and lower surfaces is 0.1-0.2mm; then the four sides are sawn to a certain size, and the boards are packed in a pile, waiting for subsequent processes.

[0030] The subsequent processes include surface coating, mainly involving coloring, painting, and coating of protective layers.

[0031] Further, in step S1, if the prepared plywood thickness is less than 18mm, the veneer thickness is selected to be 2-5.5mm, if the prepared plywood thickness is less than 22mm, the veneer thickness is selected to be 5.5-7mm, and if the prepared plywood thickness is greater than 22mm, the veneer thickness is selected to be 5.5-10mm.

[0032] Further, when the veneer used in step S1 is a whole rotary-cut veneer, measures should be taken to control the drying rate and constrain out-of-plane deformation during the drying process.

[0033] Further, when the veneer used in step S1 is a finger jointed or other jointed veneer, the jointing is performed in the same grain direction.

[0034] The adhesive used in steps S2, S5, and S7 is a water-based adhesive, which is selected from one of plant glue, animal glue, protein glue, white latex, water-based epoxy resin glue, water-based polyurethane glue, polyvinyl alcohol glue, and modified adhesive of the above-mentioned adhesives, or other cold-pressing curing water-based adhesive.

[0035] Further, the adhesive used in steps S2, S5, and S7 is composed of the following components by mass percentage: EVA emulsion 85%, water-based polyurethane emulsion 10%, defoaming agent 2.5%, and preservative 2.5%. The adhesive does not need to add a curing agent, and the curing time can be shortened to 10-15 minutes. The solid content of the EVA emulsion is 60%, the solid content of the water-based polyurethane emulsion is 60%, the defoaming agent is a polysiloxane defoaming agent, and the preservative is an ammonia-soluble alkyl amine copper.

[0036] Further, the press used in step S3 is a vertical energy-saving circulating cold press (CN116423591A), which comprises a pressure maintaining channel, a bottom pressurizing system, a top pressurizing system, a recycling channel, a top indexing mechanism and a bottom transfer system; the pressure maintaining channel is a shaft space along the vertical direction for the upward movement and pressure maintaining of the carrier plate and the pressed package combined with the glued board blank; the bottom pressurizing system is arranged at the bottom of the pressure maintaining channel and is used to transfer the carrier plate and the pressed package from the bottom transfer system into the pressure maintaining channel and provide bottom pressure support during pressure maintaining; the top pressurizing system is arranged at the top of the pressure maintaining channel and is used to provide top pressure support during pressure maintaining of the pressure maintaining channel; the recycling channel is a shaft space for the downward movement of the carrier plate and the pressed package to the ground along the vertical direction; the top indexing mechanism is a conveying device for horizontally transferring a group of the carrier plate and the pressed package at the top of the pressure maintaining channel to the top opening of the recycling channel; and the bottom transfer system is located at the bottom of the pressure maintaining channel and the recycling channel and supports the carrier plate and the pressed package and is used to realize the reciprocating circulation of the carrier plate and the pressed package between the pressure maintaining channel, the recycling channel and the board blank table.

[0037] Further, the initial moisture content of the veneer is designed according to the solid content of the water-based adhesive, the veneer glue application amount, the veneer thickness, the veneer density and other factors, so that the moisture content of the veneer after completely absorbing the water in the water-based adhesive can meet the standard requirements.

[0038] Further, in step S8, for the plywood pressed from thinner veneers, when the equilibrium moisture content is higher than the standard requirement, an additional moisture dispersion link is added.

[0039] Further, in the control process of the veneer thickness difference of no more than 0.2 mm in step S1, the whole rotary-cut veneer with a thickness greater than 5 mm is sanded by a roller sander, and the pressure of the pressure roller is 0.8-1.5 kN.

[0040] Further, in the control process of the veneer thickness difference of no more than 0.2 mm in step S1, the veneer cut by planing or sawing is sanded by a sander after being spliced into a whole piece by finger jointing or other methods.

[0041] Further, the material of the 0.5-1.2 mm thick anti-cracking surface plate in step S5 is the same as or similar to the material of the veneer in step S1.

[0042] Further, the material of the 0.5-1.2 mm thick decorative panel in step S7 is the same as or similar to the material of the anti-cracking surface plate in step S5.

[0043] By selecting the same material for the surface plate and the panel, the overall dry shrinkage and wet expansion of the plywood is consistent, and deformation is unlikely. In addition, by controlling the thickness of the plywood core layer, the panel and surface plate, and selecting the cold pressing process, the plywood is not deformed and does not crack, and the compression rate of the board is reduced.

[0044] In addition, as a further technical solution, according to the quality of the veneer, the "veneer gluing" in step S2 can be adjusted as follows: one layer for three-layer board, one, three, and five layers for five-layer board, one, three, five, and seven layers for seven-layer board, and so on. In the case of good surface quality of the veneer, step S5 "attaching anti-cracking surface plate" can be combined with step S2 to complete a process, and then step S3 "pressing and pressure maintaining" is performed, thereby saving step S4 "core plate sanding".

[0045] The specific steps are as follows:

[0046] S1. Veneer preparation and drying: control the rotary cutting, planing or sawing quality of the veneer to make the thickness uniform; control the drying process of the veneer to keep the overall deformation as small as possible, local deformation, and avoid cracking; the planing or sawing should be spliced or finger jointed into a whole veneer; the thickness difference of the whole veneer is controlled within 0.2mm; control the final moisture content of the veneer, according to the thickness of the veneer, so that the final moisture content is within the range of 0%-10%, and the moisture content deviation of the same specification veneer is not more than ±1%; the dry thickness of the veneer is 5.5-10mm;

[0047] S2. Veneer gluing: glue the veneer on the roller type glue machine; only the first, third and double sides of the three-layer board are glued, only the first, third and double sides of the five-layer board are glued, and the first, third, fifth and double sides of the seven-layer board are glued, and so on, and then the anti-cracking surface plate is simultaneously assembled into the press; the assembly adopts adjacent veneer texture staggered vertical assembly, and the grain direction of the veneer is consistent with the length direction of the assembly;

[0048] S3. Pressing and pressure maintaining: according to the ambient temperature, the pressure maintaining time is maintained between 20-720 minutes, and the board surface pressure is maintained between 0.6-1.2MPa;

[0049] S4. Anti-cracking surface plate sanding: after unloading, the board edge is repaired and the defects are repaired, and then the thickness is precisely sanded in the sander to control the thickness, and the sanding amount of the upper and lower surfaces is 0.2-0.4mm;

[0050] S5. Attaching decorative panel: after the veneer with anti-cracking surface plate is sanded to the desired thickness and double-glued by the roller type glue machine, a whole veneer with a thickness of 0.5-1.2mm is covered on both sides, and then it is pressed into the press with a pressure of 0.6-0.8MPa and pressure maintained for 20-30 minutes before unloading; the grain direction of the decorative panel is perpendicular to the grain direction of the anti-cracking surface plate;

[0051] S6. The health room is healthy: after the decorative panel is attached, the board is in the form of a whole pile and is put into the health room for 5-10 days, the moisture is homogenized, and the internal stress is released, so that the surface layer expansion and contraction process is completed before entering the decorative panel sanding process; for those with high moisture content, the link of dispersing moisture is increased;

[0052] S7. Decorative panel sanding: the moisture content of the board after health care meets the standard requirements, and the thickness is accurately sanded by the sanding machine, and the sanding amount of the upper and lower surfaces is 0-0.2mm; then the four sides are sawn to the specified size, the pile is packed, and the subsequent process is waited.

[0053] The beneficial effects of the present application are:

[0054] 1. Reduce energy consumption: the unit energy consumption can be reduced by at least 80% by using cold pressing process;

[0055] 2. Reduce the compression rate of the board: the pressure used in the cold pressing process can be maintained in the elastic pressure range where the wood does not produce plastic deformation, so the board almost does not produce compression deformation, and the wood utilization rate can be increased by at least 5% compared with the hot pressing process;

[0056] 3. Good deformation resistance: under the premise of controlling the moisture content of the veneer, through the roller pressing treatment of the veneer and the control of the material quality and thickness matching of the core veneer and the surface, the internal stress of the cold pressing process board is extremely small, and there is basically no whole board deformation and deformation after sawing;

[0057] 4. There is more space for improving production efficiency than the hot pressing process. Through a series of equipment innovations suitable for cold pressing process (referring to the company's disclosed "tandem cold pressing machine" and "circulating cold pressing machine" patents), the production capacity per unit time in a unit factory area is higher than that of traditional hot pressing equipment and hot pressing process. The parameters such as stiffness, board flatness, bending degree and torsion angle of the plywood prepared by the process are greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 The cold pressing process flow chart of the plywood of the present application;

[0059] Figure 2 The cold pressing process flow chart of another plywood of the present application. DETAILED DESCRIPTION

[0060] In order to better understand the technical solutions of the present application, the exemplary embodiments of the present application will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a clearer, more thorough understanding of the present application and to fully convey the scope of the present application to those skilled in the art.

[0061] Example 1: 15mm thick three-layer board

[0062] S1. Preparation and drying of single board: control the quality of the rotary cutting of poplar single board to make the thickness uniform; control the drying process of the single board to keep the overall deformation as small as possible, local deformation, and avoid cracking; the thickness difference of the whole single board is controlled within 0.2mm; the final moisture content of the single board is controlled at 0%, and the dry thickness of the single board is 4.5mm;

[0063] S2. Gluing of single board: the middle layer single board of the three-layer board is glued on the roller gluing machine; then the assembly is put into the press; the core board assembly is assembled with the adjacent single board texture staggered vertically, and the grain direction of the outermost single board is consistent with the length direction of the assembly;

[0064] S3. Pressing: according to the ambient temperature of 25℃, the pressure maintaining time is maintained at 120 minutes, and the board surface pressure is maintained between 0.6MPa;

[0065] S4. Sanding of core board: after unloading, the surface of the core board is checked and simply repaired, and the thickness is sanded by the sander roller, the pressure of the sander roller is 0.8kN, and the sanding amount of both sides is 0.2mm;

[0066] S5. Paste anti-cracking surface plate: after the sanded and thicknessed core board is glued on both sides by the roller gluing machine, it is covered with 0.5mm thick whole cross-grain poplar surface plate and put into the press at a pressure of 0.6MPa, and after 60 minutes of pressure maintaining, the pressure is unloaded; the texture direction of the surface plate is perpendicular to the adjacent core board;

[0067] S6. Anti-cracking surface plate sanding: after unloading, the board edge is repaired and the defects are repaired, and then the sander is used for fine sanding and thicknessing, and the sanding amount of both upper and lower surfaces is 0.15mm;

[0068] S7. Paste decorative panel: after the sanded and thicknessed core board with anti-cracking surface plate is glued on both sides by the roller gluing machine, it is covered with 0.7mm thick whole-grain birch thin single board on both sides, and put into the press at a pressure of 0.6MPa, and after 60 minutes of pressure maintaining, the pressure is unloaded; the texture direction of the decorative panel is perpendicular to the anti-cracking surface plate.

[0069] S8. Curing room curing: after the decorative panel is pasted, the board is put into the curing room in the form of a whole pile for 5 days, the moisture is homogenized, and the internal stress is released, so as to ensure that the surface layer expansion and contraction process is completed before entering the decorative panel sanding process; for those with higher moisture content, increase the link of water dispersion.

[0070] S9. Decorative panel sanding: after curing, the moisture content of the board meets the standard requirements, and the fine sanding and thicknessing is carried out by the sander, and the sanding amount of both upper and lower surfaces is 0.1mm; then the four sides are sawn to the specified size, the pile is packed, and the subsequent process is waited.

[0071] Further, when the veneer used in step S1 is a whole rotary-cut veneer, measures should be taken in the drying process to control the drying rate and restrain the out-of-plane deformation.

[0072] Further, the adhesive used in steps S2, S5 and S7 is a water-based adhesive, white latex is selected, the solid content of the adhesive is 50%, the veneer coating amount is 220 g / m2, and the coating amounts of the anti-cracking veneer and the decorative veneer are both 180 g / m2.

[0073] Further, the initial moisture content of the veneer is absolutely dry (0%).

[0074] In step S3, the water in the adhesive is completely distributed in the veneer, and in steps S5, S6 and S7, it is considered that 50% of the water in the surface layer is naturally lost,

[0075] Further, in the curing process of step S8, the final equilibrium moisture content of the board is 10%.

[0076] Example Two: 25mm thick three-layer board

[0077] S1. Veneer preparation and drying: control the rotary-cut quality of the radiata pine veneer to make the thickness uniform; control the drying process of the veneer to keep the overall deformation and local deformation as small as possible and avoid cracking; the thickness difference of the whole veneer is controlled within 0.2mm; the final moisture content of the veneer is controlled to be 5%, and the dry thickness of the veneer is 7.5mm;

[0078] S2. Veneer gluing: the middle layer veneer of the three-layer board is glued on a roller gluing machine; then the assembly is put into the press; the core board assembly is assembled with the adjacent veneer textures staggered vertically, and the grain direction of the outermost veneer is consistent with the length direction of the assembly;

[0079] S3. Press pressure maintaining: according to the ambient temperature of 25 degrees, the pressure maintaining time is maintained for 25 minutes, and the veneer surface pressure is maintained between 0.6MPa;

[0080] S4. Core board sanding: after unloading, the core board surface is checked and simply repaired, and then the thickness is fixed by roller sanding, the pressure roller pressure is 0.8kN, and the sanding amount of both sides is 0.2mm;

[0081] S5. Anti-cracking veneer: after the core board with fixed thickness is glued on both sides by a roller gluing machine, it is covered with a whole cross-grain peach core veneer with a thickness of 0.5mm and put into the press with a pressure of 0.6MPa, and after 20 minutes of pressure maintaining, the pressure is unloaded; the texture direction of the veneer and the adjacent core board is perpendicular;

[0082] S6. Anti-cracking veneer sanding: after unloading, the board edge is repaired to repair defects, and then the thickness is fixed by sanding machine, and the sanding amount of both upper and lower surfaces is 0.15mm;

[0083] S7. Attaching decorative panel: after the sanding and thicknessing of the core plate with anti-cracking veneer is double-sidedly glued by a roller-type glue press, the whole piece of thin and smooth-grained birch veneer with a thickness of 0.7 mm is covered on both sides, and then the press is pressed at a pressure of 0.6 MPa, and the pressure is kept for 20 minutes before being released; the decorative panel is perpendicular to the grain direction of the anti-cracking veneer.

[0084] S8. Health room health care: after the decorative panel is attached, the whole stack of plates is put into the health room for 5 days of health care, to evenly distribute the moisture and release the internal stress, so as to ensure that the surface expansion and contraction process is completed before the decorative panel sanding process.

[0085] S9. Decorative panel sanding: after the moisture content of the health care plate meets the standard requirements, the plate is precisely sanded and thicknessed by a sander, and the sanding amount of the upper and lower surfaces is 0.1 mm; then the four sides are sawn to the specified size, and the stack is packed for subsequent processes.

[0086] Further, when the veneer used in step S1 is a whole piece of rotary-cut veneer, measures should be taken to control the drying rate and constrain the out-of-plane deformation.

[0087] Further, the polyvinyl alcohol-based water-based adhesive used in steps S2, S5 and S7 has a solid content of 60%, and the veneer coating amount is 220 g / m2, and the coating amount of the anti-cracking veneer layer and the decorative layer is 180 g / m2.

[0088] Further, the initial moisture content of the veneer is 5%.

[0089] In step S3, the moisture in the adhesive is completely distributed in the plate, and in steps S5, S6 and S7, the surface moisture is considered to be lost naturally by 50%.

[0090] Further, in the health care process of step S8, the final equilibrium moisture content of the plate is 10%.

[0091] Example Three 35mm Thick Five-layer Board

[0092] S1. Veneer preparation and drying: control the rotary cutting, planing or sawing quality of the veneer to make the thickness uniform; control the drying process of the veneer to keep the overall deformation and local deformation as small as possible, and avoid cracking; the planing or sawing should be spliced or finger jointed into a whole piece of veneer; the thickness difference of the whole piece of veneer is controlled to be within 0.2 mm; control the final moisture content of the veneer, according to the thickness of the veneer, so that the final moisture content is 6%, and the moisture content deviation of the same specification of veneer is not more than ±1%; the dry thickness of the veneer is 6.5 mm;

[0093] S2. Single board overgluing: the first, third, fifth layer of single board is overglued on the roller overgluing machine; at the same time, the anti-cracking surface plate is assembled into the press; the core plate assembly adopts adjacent single board texture staggered vertical assembly, and the grain direction of the outermost single board is consistent with the length direction of the assembly;

[0094] S3. Press holding: according to the ambient temperature, the holding time is maintained between 40 minutes, and the board surface pressure is maintained between 0.9 MPa;

[0095] S4. Anti-cracking surface plate sanding: after unloading, the plate edge is repaired and the thickness is determined by sanding machine, and the sanding amount of the upper and lower surfaces is 0.3 mm;

[0096] S5. Decorative panel: the single board with anti-cracking surface plate is overglued on the roller overgluing machine, and the thickness of the whole sheet is 0.8 mm, and then the pressure is added to 0.7 MPa, and the pressure is maintained for 25 minutes after unloading; the texture direction of the decorative panel and the anti-cracking surface plate is perpendicular.

[0097] S6. Curing room curing: the board after pasting the decorative panel is put into the curing room for 7 days, the moisture is evenly distributed, and the internal stress is released, so as to ensure that the surface layer expansion and contraction process is completed before entering the decorative panel sanding process; S7. Decorative panel sanding: the moisture content of the cured board meets the standard requirements, and the thickness is determined by sanding machine, and the sanding amount of the upper and lower surfaces is 0.2 mm; then four sides are sawn to size, and the pile is packed for subsequent process.

[0098] Further, when the single board used in step S1 is a whole rotary cut single board, measures should be taken to control the drying rate and constrain the out-of-plane deformation.

[0099] Further, when the single board used in step S1 is a finger joint or other form of spliced single board, the finger joint or other form of splicing is performed according to the same texture direction.

[0100] Further, the initial moisture content of the single board is 6%.

[0101] In S3, the water in the adhesive is completely distributed in the board, and in S5, S6 and S7, the surface water is considered to be lost naturally by 50%.

[0102] Further, the adhesive used in steps S2 and S5 is water-based polyurethane adhesive, the solid content of the adhesive is 50%, and the single board coating amount is 220 g / m2, and the decorative surface layer coating amount is 180 g / m2.

[0103] Further, the initial moisture content of the veneer is selected as 6% according to the solid content of the water-based adhesive, the veneer glue amount, the veneer thickness and the veneer density, so that the veneer can fully absorb the water in the water-based adhesive and meet the standard requirements.

[0104] Further, in the S2 step, the total water content in the double-sided adhesive of the third layer of veneer and the total water content in the inner adhesive of the first and fifth layers of veneer are all distributed in the board, and the water content in the outer adhesive of the first and fifth layers of veneer is considered to be naturally lost by 50% in the S4 process.

[0105] Further, in the S5 and S7 steps, the water content in the adhesive of the decorative panel is naturally lost by 50%.

[0106] Further, the equilibrium moisture content after the step S8 is 11%.

[0107] Through the control and selection of the veneer roller sanding treatment, the setting of the plywood core board, the crack-resistant surface plate and the decorative panel, the configuration of the adhesive, the glue application method, the cold pressing process and the like, the plywood production greatly reduces the production energy consumption, improves the wood utilization rate, reduces the compression rate and the cold pressing time, and has good anti-deformation ability. In addition, the prepared plywood can obtain a good wood experience from the cross section and the whole.

[0108] The following will be analyzed and explained by combining relevant experimental data to analyze the performance of the board brought by the process of the application:

[0109] Scheme one: 7 layers of 2.7mm thick veneer, the outermost veneer is cross grain, hot pressing, the compression rate is 8%, and the rough board thickness is 17.5mm;

[0110] Scheme two: 7 layers of 2.5mm thick veneer, the outermost veneer is parallel grain, cold pressing, the compression rate is 0, and the rough board thickness is 17.5mm;

[0111] Scheme three: 3 layers of 5.9mm thick veneer, the outermost veneer is parallel grain, cold pressing, the compression rate is 1%, and the rough board thickness is 17.5mm.

[0112] Due to the fissure of rotary-cut veneer, the fibers in the cross-grain veneer are not continuous in the length direction of the board, and the length direction stiffness of the board is mainly provided by the parallel-grain veneer. For convenience of calculation, the contribution of the cross-grain veneer to the moment of inertia is ignored, and it is set to 0. The unit (all taking 1 mm as the unit width) moment of inertia of scheme one is 150, the unit moment of inertia of scheme two is 320, and the unit moment of inertia of scheme three is 430. It can be seen that the stiffness of scheme two is 2.1 times that of scheme one, and the stiffness of scheme three is 2.9 times that of scheme one. The thicker the plywood, the more obvious the stiffness increasing effect of scheme two and scheme three.

[0113] Research shows that when the thickness of the veneer exceeds 5.5 mm, the stiffness of the board is significantly enhanced, and when the thickness of the veneer exceeds 10 mm, the stiffness of the board of the same thickness shows a slow downward trend, mainly due to defects in the processing of thick veneer.

[0114] Further, regarding the flatness of the plywood, according to the relevant standards for plywood, for boards with a width of 1220 mm*1830 mm and above, the flatness deviation should not be greater than 30 mm.

[0115] In order to verify the technical advantages of cold-pressed plywood, three pieces of hot-pressed plywood and cold-pressed plywood with a width of 1220 mm*1830 mm and a thickness of 22 mm were measured, and the results showed that the surface flatness of the hot-pressed plywood was 5 mm, 7 mm and 4 mm, with an average of 5.3 mm; the surface flatness of the cold-pressed plywood was 1 mm, 2 mm and 2 mm, with an average of 1.7 mm. It can be seen that the surface flatness of the cold-pressed plywood is significantly improved. Tests on other thicknesses of plywood show that the surface flatness of the cold-pressed plywood is all below 3 mm.

[0116] Compared with hot-pressed plywood, in addition to the great improvement in surface flatness, there is basically no warping and distortion phenomenon when the wide plywood is sawn into strips. Taking 18 mm thick wide plywood as an example, after sawing, 10 mm*2000 mm boards are obtained for three groups of measurement. The hot-pressed plywood has a bending degree of 6 mm, 4 mm and 7 mm, with an average of 5.7 mm, and a torsion angle of 11°, 7° and 14°, with an average of 11°. Looking at the test values of the cold-pressed plywood, the bending degree is 2 mm, 2 mm and 3 mm, with an average of 2.3 mm, and the torsion angle is 1.1°, 0.7° and 1.2°, with an average of 1.0°. It can be seen that the cold-pressed plywood is significantly better than the hot-pressed plywood in many indicators. Tests on other thicknesses of plywood show that the bending degree of the cold-pressed plywood is all below 3 mm, and the torsion angle is all below 2°.

[0117] The above merely describes the preferred embodiments of the present application, and the protection scope of the present application is not limited to the above-described embodiments. Any technical solution falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that, for ordinary skilled persons in the art, some improvements and refinements without departing from the principles of the present application shall also be considered as falling within the protection scope of the present application.

Claims

1. A plywood cold pressing process, comprising the following steps: S1. Veneer preparation and drying: control the rotary cutting, slicing or sawing quality of the veneer to make it uniform in thickness; control the drying process of the veneer to keep the overall deformation as small as possible, avoid local deformation and cracking; the sliced or sawed veneer should be spliced or finger jointed into a whole veneer; the thickness difference of the whole veneer is controlled within 0.2 mm; control the final moisture content of the veneer, according to the thickness of the veneer, the final moisture content is within the range of 0-10%, and the moisture content deviation of the veneer with the same specification is not more than ±1%; the dry thickness of the veneer is 2-10 mm; S2. Veneer gluing: the veneer is glued on the roller gluing machine; only the middle core board of three-layer board is double-sided glued, only the second and fourth core boards of five-layer board are double-sided glued, only the second, fourth and sixth core boards of seven-layer board are double-sided glued, and so on, and then the assembly is put into the press; the adjacent veneer textures of the core board assembly are staggered and perpendicular to each other, and the grain direction of the outermost veneer is consistent with the length direction of the assembly; S3. Pressing and pressure maintaining: according to the ambient temperature, the pressure maintaining time is maintained between 20-720 minutes, and the board surface pressure is maintained between 0.6-1.2 MPa; S4. Core board sanding: after unloading, the surface of the core board is checked and simply repaired, and then the thickness is fixed by roller sanding machine, and the pressure of the pressure roller is 0.8-1.2 kN; S5. Anti-cracking surface plate sticking: after the core board with fixed thickness is double-sided glued by the roller gluing machine, the double-sided whole veneer cross-grain surface plate with a thickness of 0.5-1.2 mm is covered, and then it is put into the press with a pressure of 0.6-0.8 MPa, and after pressure maintaining for 20-30 minutes, the pressure is unloaded; the texture direction of the surface plate is perpendicular to that of the adjacent core board; S6. Anti-cracking surface plate sanding: after unloading, the board edge is repaired to repair defects, and then it is precisely sanded to fix the thickness, and the sanding amount of the upper and lower surfaces is 0.2-0.4 mm; S7. Decorative panel sticking: after the core board with fixed thickness and anti-cracking surface plate is double-sided glued by the roller gluing machine, the double-sided whole veneer parallel-grain thin veneer with a thickness of 0.5-1.2 mm is covered, and then it is put into the press with a pressure of 0.6-0.8 MPa, and after pressure maintaining for 20-30 minutes, the pressure is unloaded; the texture direction of the decorative panel is perpendicular to that of the anti-cracking surface plate; S8. Curing room curing: the whole stack of the board after sticking the decorative panel is put into the curing room for 5-10 days for curing, uniformizing moisture and releasing internal stress, so as to ensure that the surface layer expansion and contraction process is completed before the decorative panel sanding process; S9. Decorative panel sanding: the moisture content of the board after curing meets the standard requirements, and the thickness is precisely sanded by the sanding machine, and the sanding amount of the upper and lower surfaces is 0.1-0.2 mm; then the four sides are sawn to the specified size, and the stack is packed, waiting for the subsequent process.

2. A cold pressing process for plywood as claimed in claim 1, wherein: In the step S1, when the veneer used is whole rotary cutting veneer, measures should be taken to control the drying rate and constrain the out-of-plane deformation.

3. A cold pressing process for plywood as claimed in any one of claims 1 or 2, wherein: In the step S1, when the veneer used is finger jointed or other form of spliced veneer, the same texture direction is followed during finger jointing or other form of splicing.

4. A cold pressing process for plywood as claimed in claim 3, wherein: The adhesive used in the steps S2, S5 and S7 is a water-based adhesive, which is selected from one of plant glue, animal glue, protein glue, white latex, water-based epoxy resin glue, water-based polyurethane glue, polyvinyl alcohol-based glue and modified adhesive of the above-mentioned adhesive, or other cold-pressing and curing water-based adhesive.

5. A cold press process for plywood as claimed in claim 1, wherein: The initial moisture content of the veneer is designed according to the solid content of the water-based adhesive, the veneer glueing amount, the veneer thickness, and the veneer density factors, so that the veneer can fully absorb the water in the water-based adhesive and meet the standard requirements.

6. A cold press process for plywood as claimed in claim 1, wherein: In the control process of the veneer thickness difference of not more than 0.2 mm in the step S1, the rotary-cut whole veneer with a thickness greater than 5 mm is sanded by using a roller sander, and the pressure of the pressing roller is 0.8-1.5 kN.

7. A cold press process for plywood as claimed in claim 1, wherein: In the control of the veneer thickness difference of not more than 0.2 mm in the step S1, the veneer cut by planing or sawing is sanded after being jointed or spliced into a whole.

8. A cold press process for plywood as claimed in claim 1, wherein: The material of the 0.5-1.2 mm thick crack-resistant surface plate in the step S5 is the same as or similar to the material of the veneer in the step S1.

9. A cold press process for plywood as claimed in claim 1, wherein: The material of the 0.5-1.2 mm thick decorative panel in the step S7 is the same as or similar to the material of the crack-resistant surface plate in the step S5.

10. A cold-pressing process of plywood, comprising the following steps: S1. Veneer preparation and drying: control the rotary-cut, planed or sawn quality of the veneer to make the thickness uniform; control the drying process of the veneer to keep the overall deformation as small as possible, avoid local deformation and cracking; the planed or sawn veneer should be jointed or finger-jointed into a whole; the thickness difference of the whole veneer is controlled within 0.2 mm; control the final moisture content of the veneer, according to the thickness of the veneer, so that the final moisture content is within the range of 0%-10%, and the moisture content deviation of the veneer of the same specification is not more than ±1%; the dry thickness of the veneer is 5.5-10 mm; S2. Veneer gluing: the veneer is glued on a roller gluing machine; only the first, third layers and both sides are glued for three-layer boards, only the first, third, fifth layers and both sides are glued for five-layer boards, the first, third, fifth, seventh layers and both sides are glued for seven-layer boards, and so on, and then the veneer is put into the press together with the crack-resistant surface plate; the adjacent veneers are staggered and perpendicular to each other in the assembly, and the grain direction of the veneer is consistent with the length direction of the assembly; S3. Pressing and pressure maintaining: according to the ambient temperature, the pressure maintaining time is maintained between 20-720 minutes, and the board surface pressure is maintained between 0.6-1.2 MPa; S4. Sanding of crack-resistant surface plate: after pressure relief, the board edges are repaired and defects are filled, and then the board is sanded to a certain thickness in a sander, and the sanding amount of the upper and lower surfaces is 0.2-0.4 mm; S5. Decorative panel attachment: the core board with crack-resistant surface plate after sanding to a certain thickness is double-glued by a roller gluing machine, and then a whole thin veneer with a thickness of 0.5-1.2 mm is attached to both sides, and then the board is put into the press with a pressure of 0.6-0.8 MPa, and after pressure maintaining for 20-30 minutes, the pressure is released; the grain direction of the decorative panel is perpendicular to that of the crack-resistant surface plate; S6. Health room health: after the decorative panel is installed, the board is in the form of a whole pile and is placed in the health room for 5-10 days for health care, moisture is homogenized, and internal stress is released to ensure that the surface layer expansion and contraction process is completed before entering the decorative panel sanding process; S7. Sanding of decorative panel: the moisture content of the board after health care meets the standard requirements, and the thickness is precisely sanded by a sander, and the sanding amount of the upper and lower surfaces is 0.1-0.2 mm; then the four sides are sawn to the specified size, and the pile is packed, waiting for the subsequent process.

11. A cold pressing process for plywood as claimed in claim 10, wherein: When the veneer used in step S1 is a whole rotary-cut veneer, measures should be taken to control the drying rate and constrain out-of-plane deformation during the drying process.

12. A cold pressing process for plywood as claimed in claim 10, wherein: When the veneer used in step S1 is a finger joint or other form of spliced veneer, the finger joint or other form of splicing is performed according to the same grain direction.

13. A cold press process for plywood as claimed in claim 10, wherein: The adhesive used in steps S2 and S5 is a water-based adhesive, which is selected from one of plant glue, animal glue, protein glue, white latex, water-based epoxy resin glue, water-based polyurethane glue, polyvinyl alcohol glue, and modified adhesive of the above adhesives, or other cold-pressing curing water-based adhesive.

14. A cold press process for plywood as claimed in claim 10, wherein: The initial moisture content of the veneer is designed according to the solid content of the water-based adhesive and the veneer glueing amount, so that the veneer can fully absorb the water in the water-based adhesive and meet the standard requirements.

15. A cold press process for plywood as claimed in claim 10, wherein: In the control process of the veneer thickness difference not greater than 0.2 mm in step S1, the rotary-cut whole veneer with a thickness greater than 5 mm is sanded using a roller sander, and the roller pressure is 0.8-1.5 kN.

16. A cold press process for plywood as claimed in claim 10, wherein: In the control of the veneer thickness difference not greater than 0.2 mm in step S1, the veneer is sanded by a sander after being spliced into a whole piece by finger joint or splicing.

17. A cold press process for plywood as claimed in claim 10, wherein: The material of the 0.5-1.2 mm thick anti-cracking surface plate in step S2 is the same as or similar to the material of the veneer in step S1.

18. A cold press process for plywood as claimed in claim 10, wherein: The material of the 0.5-1.2 mm thick decorative panel in step S5 is the same as or similar to the material of the anti-cracking surface plate in step S5.

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