Preparation method of urea glue reinforcing agent and application of urea glue reinforcing agent in plywood

Abstract

The invention relates to the technical field of urea-formaldehyde resin adhesives, and discloses a preparation method of a urea glue reinforcing agent and application of the urea glue reinforcing agent in plywood, and the preparation method comprises the following steps: (1) adding 5-15 parts by weight of polyvinyl alcohol into 100 parts by weight of water, dissolving, adding 30-60 parts by weight of swelling clay and 1-5 parts by weight of a curing agent, and mixing to obtain a polyvinyl alcohol coated clay material; (2) mixing 3-6 parts of polyacrylamide, 1-3 parts of cellulose, 5-10 parts of nano filler and 100 parts of water, adding the polyvinyl alcohol coated clay material, and mixing to obtain a dual-network coated material; and (3) adding 50-150 parts of flour into the double-network coating material, mixing, and granulating to obtain the urea glue reinforcing agent. According to the urea glue reinforcing agent, polyvinyl alcohol-polyacrylamide is adopted as a main body, inorganic filler is adopted as an auxiliary material, the stability of a urea-formaldehyde resin adhesive is guaranteed, the cost is reduced, meanwhile, the bonding strength of plywood is improved, and the formaldehyde release amount is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of urea-formaldehyde resin adhesives, and in particular to a preparation method of a urea glue enhancer and its application in plywood. Background Art

[0002] Urea-formaldehyde resin adhesive (urea glue) is one of the most widely used adhesives in plywood production. In order to meet the sizing process of roll coating, flour is usually added to increase its solid content and viscosity. However, the addition of flour not only increases the use cost of urea glue, but also has an adverse effect on the bonding strength of urea glue due to the water absorption and retrogradation characteristics of flour. Therefore, developing a filler for urea glue to reduce the use cost of urea glue and improve the water absorption and retrogradation characteristics of flour is of great significance for improving the quality of plywood products.

[0003] The invention patent with publication number CN 111560225 B discloses a filler for urea-formaldehyde resin for multi-layer plywood and its preparation method. The filler is prepared from the following raw materials in parts by weight: 30-40 parts by weight of coal gangue powder, 30-50 parts by weight of cottonseed meal powder, 5-10 parts by weight of zeolite powder, 10-15 parts of nano-zeolite and lignin composite particles, 1-3 parts by weight of enhancer, 4-8 parts by weight of thickener, and 8-12 parts by weight of acidulant. Using inorganic fillers and cottonseed meal as the main raw materials and cooperating with a small amount of auxiliaries to prepare the urea-formaldehyde resin filler, and further effectively utilizing lignin, can effectively use industrial by-products instead of flour, enhance the strength of urea glue resin adhesive, reduce the formaldehyde release amount, and increase the pre-pressing performance.

[0004] The invention patent with publication number CN 104762026 B discloses a filler for urea-formaldehyde resin for multi-layer plywood and its preparation method, which is prepared from 40-60 parts by weight of coal gangue powder, 40-60 parts by weight of cottonseed meal powder, 1-3 parts by weight of enhancer, 4-8 parts by weight of thickener, and 8-12 parts by weight of acidulant. Add 30 parts by weight of cottonseed meal powder and 70 parts by weight of water to the reaction kettle, then add 3 parts by weight of sodium hydroxide and 6 parts by weight of urea, stir for 20 minutes, heat up to 80 degrees Celsius and continue to stir for 1 hour, cool down and dry, and grind into 300-mesh powder after drying; mix and stir evenly with coal gangue powder, enhancer, acidulant, and thickener to obtain the product. This invention uses industrial by-products instead of flour filler, saves resources, has low cost, simple process, low equipment requirements, convenient operation, and good product performance.

[0005] However, using industrial and agricultural residues such as coal gangue and cottonseed meal powder instead of flour can effectively reduce the production cost of urea glue filler. However, the components of these industrial and agricultural residues are complex, lacking clear product component indicators, and at the same time, the influence of impurities on the curing of glue is not clear, which easily leads to instability of plywood products and large fluctuations in product performance. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a preparation method of a urea resin adhesive enhancer and its application in plywood. The urea resin adhesive enhancer uses polyvinyl alcohol - polyacrylamide as the main body and is assisted by inorganic fillers to ensure the stability of the urea - formaldehyde resin adhesive, and to improve the bonding strength of plywood and reduce the formaldehyde emission while reducing the filler dosage and cost.

[0007] The object of the present invention is achieved through the following technical solutions: In the first aspect, the present invention provides a preparation method of a urea resin adhesive enhancer, which includes the following steps by weight: (1) Dissolve 5 - 15 parts of polyvinyl alcohol in 100 parts of water, then add 30 - 60 parts of swelling clay and 1 - 5 parts of curing agent and mix to obtain a polyvinyl alcohol - coated clay material; (2) Mix 3 - 6 parts of polyacrylamide, 1 - 3 parts of cellulose, 5 - 10 parts of nano - filler and 100 parts of water, then add the polyvinyl alcohol - coated clay material and mix to obtain a double - network - coated material; (3) Add 50 - 150 parts of flour to the double - network - coated material, and after granulation, obtain the urea resin adhesive enhancer.

[0008] The urea resin adhesive enhancer in the present invention uses polyvinyl alcohol - polyacrylamide as the main body to construct a micro - shielding double - network system, improve the compatibility between the filler layer and the urea resin system, and reinforce the urea resin system. The introduction of clay minerals plays a role in moisture absorption and swelling to ensure the coating thickness of the glue layer, and forms a micro - shielding system by coating the clay minerals with a polyvinyl alcohol - polyacrylamide network to reduce the adverse effects of impurities in the clay. The introduction of nano - fillers improves the stability and consistency of the glue. The introduction of flour increases the solid content of the material and facilitates subsequent granulation. Therefore, the urea resin adhesive enhancer prepared by the present invention can cooperate with a more stable micro - shielding double - network system through the limitation of each component and its proportioning, has obvious thickening and viscosity - increasing effects, and has a certain reinforcing effect on the urea resin system.

[0009] Preferably, the degree of alcoholysis of the polyvinyl alcohol is 85 - 99%, and the degree of polymerization is 1700 - 2500.

[0010] Preferably, the water absorption of the swelling clay is 10 - 15 times its own volume, and the particle size is 300 - 1600 mesh.

[0011] Preferably, the swelling clay includes one or a combination of bentonite, montmorillonite and kaolin.

[0012] Preferably, the swelling-type clay is subjected to pickling treatment; the pickling treatment is to soak it in a hydrochloric acid or sulfuric acid solution with a concentration of 0.05 - 0.2 mol / L for 8 - 12 h, then wash it until neutral, and then dry and crush it.

[0013] The swelling-type clay is subjected to pickling treatment to remove some impurities.

[0014] Preferably, the curing agent includes ammonium chloride and / or ammonium sulfate.

[0015] Preferably, the polyacrylamide is cationic polyacrylamide with an average molecular weight of 8 - 12 million.

[0016] Preferably, the cellulose includes one or a combination of several of nanocellulose, carboxymethyl cellulose, and hydroxypropyl cellulose.

[0017] Preferably, the nano filler includes nano silica and / or nano alumina.

[0018] Preferably, before granulation, its moisture content is adjusted to 10 - 30%; the particle size of granulation is 2 - 10 mm.

[0019] Preferably, after granulation, it is dried, ground, and sieved to obtain the urea-formaldehyde resin strengthening agent.

[0020] Preferably, the drying temperature is 50 - 80 °C; the mesh number of sieving is 50 - 80 meshes.

[0021] In the second aspect, the present invention also provides an application of the urea-formaldehyde resin strengthening agent in plywood, including the following steps: After mixing the urea-formaldehyde resin strengthening agent and flour according to a mass ratio of 3 - 5:1, the mixed raw materials are mixed with urea-formaldehyde resin clear glue according to a mass ratio of 20 - 30:100, coated on the surface of the veneer, and then after assembling the billets, aging, cold pressing, and hot pressing, plywood is obtained.

[0022] After the urea-formaldehyde resin strengthening agent and flour are first mixed and then mixed with the urea-formaldehyde resin clear glue, the compatibility between the filler system and the urea-formaldehyde resin system can be further improved. Flour can also adjust the consistency and viscosity of the urea-formaldehyde resin and offset the viscosity fluctuation of the urea-formaldehyde resin clear glue with seasons. Among them, the urea-formaldehyde resin clear glue is a urea-formaldehyde resin solution with a solid content of 40 - 60% and no flour is added.

[0023] Preferably, the coating amount is 1.1 - 1.3 kg per layer.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) Coating the swelling clay with polyvinyl alcohol to form the first - layer micro - shielding structure. The hydrophilic structure of polyvinyl alcohol allows water to migrate freely, ensuring that the clay can play the role of water absorption and swelling in urea formaldehyde resin. At the same time, it increases the migration resistance of free particles in the swelling clay to the glue, thereby weakening the adverse effects caused by the component differences of the swelling clay.

[0025] (2) Coating the polyvinyl alcohol - swelling clay with a polyacrylamide - cellulose network secondly. On the one hand, polyacrylamide has excellent water absorption, which can improve the water absorption and viscosity - increasing effect of the urea formaldehyde resin enhancer. At the same time, the amide groups on it can undergo physical and chemical reactions with the free residues in polyvinyl alcohol and urea formaldehyde resin, improving the compatibility between the urea formaldehyde resin enhancer and urea formaldehyde resin. On the other hand, the cellulose - reinforced polyacrylamide network can further hinder the migration of free particles in the swelling clay, playing the role of adsorbing and complexing some particles.

[0026] (3) The swelling clay is an intercalated porous structure, having a good adsorption effect and a good loading effect on the curing agent. The loaded curing agent can catalyze the chemical reaction between free aldehyde and the active groups or urea formaldehyde resin residues on the viscosity - increasing group of urea formaldehyde resin during the hot - pressing process, playing the role of reducing the formaldehyde release amount of urea formaldehyde resin.

[0027] (4) The addition of nanoparticles, on the one hand, has a rolling lubrication effect, which is beneficial to improving the granulation success rate of the urea formaldehyde resin enhancer. On the other hand, it can absorb water and thicken, forming a - Si - O - H structure or an Al(OH)₂ gel, enhancing the water absorption and thickening effect of the urea formaldehyde resin enhancer.

[0028] (5) The appropriate granulation and drying temperature is the key to the forming of the urea formaldehyde resin enhancer. If the temperature is too high, the water in the urea formaldehyde resin enhancer system will lose, and it is easy to appear the phenomenon of delamination between the swelling clay and the polymer. If the temperature is too low, the moisture content of the urea formaldehyde resin enhancer system is high, affecting its passing rate of grinding and sieving and the water absorption after subsequent addition to urea formaldehyde resin. Specific embodiments

[0029] The following specific examples are used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto.

[0030] 1. Urea formaldehyde resin enhancer Calculated by weight parts, the preparation of the urea formaldehyde resin enhancer includes the following steps: (1) Dissolve 5 - 15 parts of polyvinyl alcohol in 100 parts of water, then add 30 - 60 parts of swelling clay and 1 - 5 parts of curing agent and mix to obtain the polyvinyl alcohol - coated clay material; (2) Mix 3 - 6 parts of polyacrylamide, 1 - 3 parts of cellulose, 5 - 10 parts of nano - filler and 100 parts of water, then add the polyvinyl alcohol - coated clay material and mix to obtain the double - network - coated material; (3) Add 50 - 150 parts of flour to the double - network coating material, adjust its moisture content to 10 - 30%, granulate it, with the particle size being 2 - 10 mm, then dry it at 50 - 80 °C, grind it, and sieve it to 50 - 80 mesh to obtain the urea - formaldehyde glue enhancer.

[0031] In a specific embodiment of the present invention, the degree of alcoholysis of polyvinyl alcohol is 85 - 99%, and the degree of polymerization is 1700 - 2500.

[0032] In a specific embodiment of the present invention, the water absorption of the swelling clay is 10 - 15 times its own volume, and the particle size is 300 - 1600 mesh. The swelling clay includes one or a combination of bentonite, montmorillonite, and kaolin.

[0033] In a specific embodiment of the present invention, the swelling clay is subjected to pickling treatment; the pickling treatment is to soak it in a hydrochloric acid or sulfuric acid solution with a concentration of 0.05 - 0.2 mol / L for 8 - 12 h, then wash it to neutral, and then dry and crush it.

[0034] In a specific embodiment of the present invention, the curing agent includes ammonium chloride and / or ammonium sulfate.

[0035] In a specific embodiment of the present invention, the polyacrylamide is cationic polyacrylamide, and the average molecular weight is 8 million - 12 million.

[0036] In a specific embodiment of the present invention, the cellulose includes one or a combination of nanocellulose, carboxymethyl cellulose, and hydroxypropyl cellulose.

[0037] In a specific embodiment of the present invention, the nano - filler includes nano - silica and / or nano - alumina.

[0038] 2. Plywood The preparation of plywood includes the following steps: Mix the urea - formaldehyde glue enhancer and flour in a mass ratio of 3 - 5:1, then mix the mixed raw materials and urea - formaldehyde glue sizing in a mass ratio of 20 - 30:100, stir evenly, roll - coat it on the surface of the veneer, with the roll - coating amount being 1.1 - 1.3 kg / layer, and obtain the plywood product after assembling the billets, conditioning, cold pressing, core - cutting and repairing, hot pressing, puttying, sanding, and veneering.

[0039] In a specific embodiment of the present invention, the urea - formaldehyde glue sizing is a urea - formaldehyde resin solution, and the solid content is 52%.

[0040] In a specific embodiment of the present invention, assembling the billets, conditioning, cold pressing, core - cutting and repairing, hot pressing, puttying, sanding, and veneering are all conventional technological steps.

[0041] Example 1 (1) Weigh 5 kg of polyvinyl alcohol (commercially available, model 2488, degree of alcoholysis 86.5 - 88.5%, degree of polymerization 2488), 100 kg of water, heat to 90 °C and stir until completely dissolved. Add 30 kg of bentonite (the selected bentonite has a water absorption capacity 15 times its own volume, soaked in 0.05 mol / L hydrochloric acid for 12 h, then washed to neutral, dried, and crushed to 300 mesh), 1 kg of ammonium chloride. After mixing evenly, a polyvinyl alcohol-coated clay material is obtained.

[0042] (2) Weigh 3 kg of cationic polyacrylamide (average molecular weight 12 million), 1 kg of carboxymethyl cellulose, 100 kg of water, 10 kg of nano-silica. After mixing and fully dispersing them, add the polyvinyl alcohol-coated clay material obtained in step (1), and stir until a homogeneous phase is obtained to get a double-network coated material.

[0043] (3) Add 150 kg of flour to the double-network coated material, stir evenly, adjust its moisture content to 10 - 30%, granulate by mechanical stirring, with a particle size of 2 - 6 mm, then dry at 50 °C, grind, and sieve to 50 mesh to obtain a urea-formaldehyde adhesive enhancer.

[0044] Mix the urea-formaldehyde adhesive enhancer and flour in a mass ratio of 5:1. Then mix the mixed raw materials with urea-formaldehyde clear glue in a mass ratio of 30:100 and stir evenly. The obtained adhesive is roll-coated on the surface of the veneer, with a roll-coating amount of 1.3 kg / layer. After sequential operations of assembling the billets, cold pressing, conditioning, core cutting and repair, hot pressing, puttying, sanding, and veneering, a plywood product is obtained.

[0045] Example 2 (1) Weigh 15 kg of polyvinyl alcohol (commercially available, model 1788, degree of alcoholysis 86.5 - 88.5%, degree of polymerization 1788), 100 kg of water, heat to 80 °C and stir until completely dissolved. Add 60 kg of montmorillonite (the selected montmorillonite has a water absorption capacity 10 times its own volume, soaked in 0.2 mol / L hydrochloric acid for 8 h, then washed to neutral, dried, and crushed to 1600 mesh), 5 kg of ammonium sulfate. After mixing evenly, a polyvinyl alcohol-coated clay material is obtained.

[0046] (2) Weigh 6 kg of cationic polyacrylamide (average molecular weight 8 million), 3 kg of carboxypropyl cellulose, 100 kg of water, 5 kg of nano-aluminum oxide. After mixing and fully dispersing them, add the polyvinyl alcohol-coated clay material obtained in step (1), and stir until a homogeneous phase is obtained to get a double-network coated material.

[0047] (3) Add 50 kg of flour to the double-network coating material. After stirring evenly, adjust its moisture content to 10 - 30%. After mechanical stirring and granulation, the particle size is 2 - 10 mm. Then, dry at 80 °C, grind, and sieve to 80 mesh to obtain the urea-formaldehyde resin enhancer.

[0048] After mixing the urea-formaldehyde resin enhancer and flour in a mass ratio of 3:1, the mixed raw materials are further mixed and stirred evenly with urea-formaldehyde clear glue in a mass ratio of 20:100. The obtained adhesive is roller-coated on the surface of the veneer, and the roller-coating amount is 1.1 kg / layer. After sequential operations of assembling the billets, cold pressing, conditioning, core cutting and repairing, hot pressing, puttying, sanding, and veneering, a plywood product is obtained.

[0049] Example 3 (1) Weigh 10 kg of polyvinyl alcohol (commercially available, model 2099, alcoholysis degree 85 - 89%, polymerization degree 2099), 100 kg of water, heat to 85 °C and stir until completely dissolved. Add 45 kg of kaolin (the selected kaolin has a water absorption capacity 12 times its own volume, soaked in 0.1 mol / L hydrochloric acid for 10 h, then washed to neutral, dried, and crushed to 1000 mesh), 3 kg of ammonium chloride, and mix evenly to obtain the polyvinyl alcohol-coated clay material.

[0050] (2) Weigh 5 kg of cationic polyacrylamide (average molecular weight 10 million), 2 kg of nanofibrillated cellulose, 100 kg of water, 8 kg of nano-silica. After mixing and fully dispersing them, add the polyvinyl alcohol-coated clay material obtained in step (1), and stir until a homogeneous phase is obtained to get the double-network coating material.

[0051] (3) Add 100 kg of flour to the double-network coating material. After stirring evenly, adjust its moisture content to 10 - 30%. After mechanical stirring and granulation, the particle size is 5 - 10 mm. Then, dry at 60 °C, grind, and sieve to 60 mesh to obtain the urea-formaldehyde resin enhancer.

[0052] After mixing the urea-formaldehyde resin enhancer and flour in a mass ratio of 4:1, the mixed raw materials are further mixed and stirred evenly with urea-formaldehyde clear glue in a mass ratio of 25:100. The obtained adhesive is roller-coated on the surface of the veneer, and the roller-coating amount is 1.2 kg / layer. After sequential operations of assembling the billets, cold pressing, conditioning, core cutting and repairing, hot pressing, puttying, sanding, and veneering, a plywood product is obtained.

[0053] Comparative Example 1 (the difference from Example 3 is that polyvinyl alcohol is not added) (1) Weigh 100 kg of water, add 45 kg of kaolin (the selected kaolin has a water absorption capacity 12 times its own volume, soaked in 0.1 mol / L hydrochloric acid for 10 h, then washed to neutral, dried, and crushed to 1000 mesh), 3 kg of ammonium chloride, and mix evenly to obtain the polyvinyl alcohol-coated clay material.

[0054] (2) Weigh 5 kg of cationic polyacrylamide (average molecular weight 10 million), 2 kg of nanocellulose, 100 kg of water, and 8 kg of nanosilica, mix and fully disperse them, add the polyvinyl alcohol-coated clay material obtained in step (1), and stir until a uniform phase is obtained to obtain a double network coating material.

[0055] (3) Add 100 kg of flour to the double network coating material, stir evenly, adjust the moisture content to 10-30%, granulate by mechanical stirring, the particle size is 5-10 mm, dry at 60° C., grind, and sieve to 60 mesh to obtain a urea glue reinforcing agent.

[0056] The urea glue enhancer and flour are mixed in a mass ratio of 4:1, and the mixed raw materials are then mixed with the urea glue clear glue in a mass ratio of 25:100 and stirred evenly. The obtained adhesive is roller-coated on the surface of the veneer with a roller coating amount of 1.2 kg / layer. After assembly, cold pressing, aging, core cutting and repairing, hot pressing, puttying, sanding, and veneering, a plywood product is obtained.

[0057] Comparative Example 2 (the difference from Example 3 is that no swelling clay is added) (1) Weigh 10 kg of polyvinyl alcohol (commercially available, model 2099, alcoholysis degree of 85-89%, polymerization degree of 2099) and 100 kg of water, heat to 85° C. and stir to completely dissolve, add 3 kg of ammonium chloride, mix well, and obtain a polyvinyl alcohol-coated clay material.

[0058] (2) Weigh 5 kg of cationic polyacrylamide (average molecular weight 10 million), 2 kg of nanocellulose, 100 kg of water, and 8 kg of nanosilica, mix and fully disperse them, add the polyvinyl alcohol-coated clay material obtained in step (1), and stir until a uniform phase is obtained to obtain a double network coating material.

[0059] (3) Add 100 kg of flour to the double network coating material, stir evenly, adjust the moisture content to 10-30%, and granulate by mechanical stirring to a particle size of 5-10 mm. Then, dry at 60° C., grind, and sieve to a mesh size of 60 to obtain a urea-gel reinforcing agent (the granulation is relatively soft, and after drying, it is very brittle and in powder form).

[0060] The urea glue enhancer and flour are mixed in a mass ratio of 4:1, and the mixed raw materials are then mixed with the urea glue clear glue in a mass ratio of 25:100 and stirred evenly. The obtained adhesive is roller-coated on the surface of the veneer with a roller coating amount of 1.2 kg / layer. After assembly, cold pressing, aging, core cutting and repairing, hot pressing, puttying, sanding, and veneering, a plywood product is obtained.

[0061] Comparative Example 3 (the difference from Example 3 is that no polyacrylamide is added) (1) Weigh 10 kg of polyvinyl alcohol (commercially available, model 2099, alcoholysis degree of 85-89%, degree of polymerization of 2099) and 100 kg of water, heat to 85°C and stir to completely dissolve, add 45 kg of kaolin (the selected kaolin has a water absorption capacity of 12 times its own volume, and is washed to neutrality after being soaked in 0.1 mol / L hydrochloric acid for 10 h, dried, and crushed to 1000 mesh), and 3 kg of ammonium chloride, mix well, and obtain a polyvinyl alcohol-coated clay material.

[0062] (2) Weigh 2 kg of nanocellulose, 100 kg of water, and 8 kg of nanosilica, mix and fully disperse them, add the polyvinyl alcohol-coated clay material obtained in step (1), and stir until a uniform phase is obtained to obtain a double network coating material.

[0063] (3) Add 100 kg of flour to the double network coating material, stir evenly, adjust the moisture content to 10-30%, granulate by mechanical stirring, the particle size is 5-10 mm, dry at 60° C., grind, and sieve to 60 mesh to obtain a urea glue reinforcing agent.

[0064] The urea glue enhancer and flour are mixed in a mass ratio of 4:1, and the mixed raw materials are then mixed with the urea glue clear glue in a mass ratio of 25:100 and stirred evenly. The obtained adhesive is roller-coated on the surface of the veneer with a roller coating amount of 1.2 kg / layer. After assembly, cold pressing, aging, core cutting and repairing, hot pressing, puttying, sanding, and veneering, a plywood product is obtained.

[0065] Comparative Example 4 (the difference from Example 3 is that no nanofiller is added) (1) Weigh 10 kg of polyvinyl alcohol (commercially available, model 2099, alcoholysis degree of 85-89%, degree of polymerization of 2099) and 100 kg of water, heat to 85°C and stir to completely dissolve, add 45 kg of kaolin (the selected kaolin has a water absorption capacity of 12 times its own volume, and is washed to neutrality after being soaked in 0.1 mol / L hydrochloric acid for 10 h, dried, and crushed to 1000 mesh), and 3 kg of ammonium chloride, mix well, and obtain a polyvinyl alcohol-coated clay material.

[0066] (2) Weigh 5 kg of cationic polyacrylamide (average molecular weight 10 million), 2 kg of nanocellulose, and 100 kg of water, mix and fully disperse them, add the polyvinyl alcohol-coated clay material obtained in step (1), and stir until a uniform phase is obtained to obtain a double network coating material.

[0067] (3) Add 100 kg of flour to the double-network coated material. After stirring evenly, adjust its moisture content to 10 - 30%. After granulating by mechanical stirring, the particle size is 5 - 10 mm. Then, dry at 60 °C, grind, and sieve to 60 mesh to obtain the urea-formaldehyde glue enhancer.

[0068] Mix the urea-formaldehyde glue enhancer and flour in a mass ratio of 4:1. Then, mix the mixed raw materials with urea-formaldehyde clear glue in a mass ratio of 25:100 and stir evenly. The obtained adhesive is roll-coated on the surface of the veneer with a coating amount of 1.2 kg / layer. After successive operations of assembling the billets, cold pressing, conditioning, core cutting and repair, hot pressing, puttying, sanding, and veneering, a plywood product is obtained.

[0069] Comparative Example 5 (the difference from Example 3 is that the drying temperature after granulation is too high) (1) Weigh 10 kg of polyvinyl alcohol (commercially available, model 2099, degree of alcoholysis 85 - 89%, degree of polymerization 2099), 100 kg of water, heat to 85 °C and stir until completely dissolved. Add 45 kg of kaolin (the selected kaolin has a water absorption capacity 12 times its own volume, soaked in 0.1 mol / L hydrochloric acid for 10 h, then washed to neutral, dried, and crushed to 1000 mesh), 3 kg of ammonium chloride, and mix evenly to obtain the polyvinyl alcohol-coated clay material.

[0070] (2) Weigh 5 kg of cationic polyacrylamide (average molecular weight 10 million), 2 kg of nanofibrillated cellulose, 100 kg of water, 8 kg of nano-silica. Mix them and disperse fully, then add the polyvinyl alcohol-coated clay material obtained in step (1), and stir until a homogeneous phase is obtained to get the double-network coated material.

[0071] (3) Add 100 kg of flour to the double-network coated material. After stirring evenly, adjust its moisture content to 10 - 30%. After granulating by mechanical stirring, the particle size is 5 - 10 mm. Then, dry at 95 °C, grind, and sieve to 60 mesh to obtain the urea-formaldehyde glue enhancer.

[0072] Mix the urea-formaldehyde glue enhancer and flour in a mass ratio of 4:1. Then, mix the mixed raw materials with urea-formaldehyde clear glue in a mass ratio of 25:100 and stir evenly. The obtained adhesive is roll-coated on the surface of the veneer with a coating amount of 1.2 kg / layer. After successive operations of assembling the billets, cold pressing, conditioning, core cutting and repair, hot pressing, puttying, sanding, and veneering, a plywood product is obtained.

[0073] Comparative Example 6 (blank sample) Mix flour and urea-formaldehyde clear glue in a mass ratio of 35:100 and stir evenly. The obtained adhesive is roll-coated on the surface of the veneer with a coating amount of 1.2 kg / layer. After successive operations of assembling the billets, cold pressing, conditioning, core cutting and repair, hot pressing, puttying, sanding, and veneering, a plywood product is obtained.

[0074] The bonding strength of the plywood prepared in the above Examples 1-3 and Comparative Examples 1-6 was tested according to the provisions in GB / T 9846 "General Plywood", and the formaldehyde release was determined by the desiccator method in GB / T 17657 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels".

[0075] Table 1 Test of Bonding Strength, Formaldehyde Release and Flame Retardant Performance Project Gluing strength / MPa Formaldehyde emission / (mg / L) Example 1 0.87 0.21 Example 2 1.01 0.16 Example 3 0.95 0.19 Comparative Example 1 0.61 0.42 Comparative Example 2 0.72 0.37 Comparative Example 3 0.67 0.40 Comparative Example 4 0.74 0.30 Comparative Example 5 0.59 0.43 Comparative Example 6 0.73 0.35 As shown in Table 1, it can be seen from Examples 1-3 and Comparative Example 6 that, according to the appropriate raw material ratio and production process, the urea resin enhancer manufactured has a significant enhancing effect on urea resin, the bonding strength is increased by about 20-40%, the formaldehyde release is decreased by about 40-50%, and at the same time, the total amount of fillers used is decreased compared with the case of only using flour as the filler, achieving the purpose of cost reduction and efficiency improvement.

[0076] It can be seen from Example 3 and Comparative Example 1 that without adding polyvinyl alcohol, the coating effect of a single polyacrylamide network on swelling clay is limited, resulting in the clay being easily separated from the coating during the granulation and grinding process, thus unable to play the role of micro-shielding and having an adverse effect on the bonding strength of the formed board.

[0077] It can be seen from Example 3 and Comparative Example 2 that without adding swelling clay, there is a lack of hard support material inside the urea resin filler. During the granulation process, polyvinyl alcohol and polyacrylamide are brittle, the particles are significantly pulverized, and the prepared glue is also thinner and easily penetrates into the veneer, resulting in a decrease in the bonding strength of the board and an increase in the amount of glue required to achieve the same bonding strength.

[0078] It can be seen from Example 3 and Comparative Example 3 that without adding polyacrylamide, the adhesion between the single polyvinyl alcohol coating of swelling clay and flour is poor, resulting in a layering phenomenon between the two during the granulation process. After being formulated into an adhesive, the consistency of the adhesive decreases, and a longer stirring time is required (the solubility of polyvinyl alcohol is relatively low), and it is not easy to stir evenly, thus affecting the bonding strength of the formed board.

[0079] It can be seen from Example 3 and Comparative Example 4 that without adding nanoparticles, the particle size of granulation is uneven, affecting the drying efficiency, resulting in particle pulverization during the granulation process (partially dried, partially undried, and partially over-dried).

[0080] It can be seen from Example 3 and Comparative Example 5 that the drying temperature after granulation is too high, resulting in the dissolution and adhesion of some polyvinyl alcohol under high humidity conditions, resulting in irregular granulation shapes, and at the same time, some of the coated swelling clay is exposed, affecting its coating effect, and then there is a small amount of layering phenomenon when added to the glue, affecting the bonding strength of the formed board.

[0081] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the specification of the present invention, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present invention.

Claims

1. A method for preparing a urea-gel reinforcing agent, characterized in that: By weight, the method comprises the following steps: (1) adding 5-15 parts of polyvinyl alcohol to 100 parts of water to dissolve, and then adding 30-60 parts of swelling clay and 1-5 parts of curing agent to mix, to obtain a polyvinyl alcohol-coated clay material; (2) After mixing 3-6 parts of polyacrylamide, 1-3 parts of cellulose, 5-10 parts of nanofiller and 100 parts of water, polyvinyl alcohol coated clay material is added and mixed to obtain a double network coated material; (3) Add 50-150 parts of flour to the double network coating material and mix, and after granulation, obtain the urea glue reinforcing agent.

2. The method for preparing the urea-gel reinforcing agent according to claim 1, characterized in that: The alcoholysis degree of the polyvinyl alcohol is 85-99%, and the polymerization degree is 1700-2500.

3. The method for preparing the urea-gel reinforcing agent according to claim 1, characterized in that: The water absorption capacity of the swelling clay is 10-15 times of its own volume, and the particle size is 300-1600 meshes.

4. The method for preparing the urea-gel strengthening agent according to any one of claims 1 to 3, characterized in that: The swelling clay includes one or a combination of bentonite, montmorillonite and kaolin.

5. The method for preparing the urea-gel reinforcing agent according to claim 1, characterized in that: The polyacrylamide is cationic polyacrylamide with an average molecular weight of 8-12 million.

6. The method for preparing the urea-gel reinforcing agent according to claim 1, characterized in that: The nano filler includes nano silicon dioxide and / or nano aluminum oxide.

7. The method for preparing the urea-gel reinforcing agent according to claim 1, 5 or 6, characterized in that: The cellulose includes one or a combination of nanocellulose, carboxymethyl cellulose and hydroxypropyl cellulose.

8. The method for preparing the urea-gel reinforcing agent according to claim 1, 5 or 6, characterized in that: The curing agent includes ammonium chloride and / or ammonium sulfate.

9. The method for preparing the urea-gel strengthening agent according to claim 1, characterized in that: The moisture content is adjusted to 10-30% before granulation; and the particle size of the granulation is 2-10 mm.

10. Use of the urea adhesive reinforcing agent prepared by the preparation method according to any one of claims 1 to 9 in plywood, characterized in that: The method comprises the following steps: mixing a urea-glue enhancer and flour in a mass ratio of 3-5:1, mixing the mixed raw materials with a urea-glue clear glue in a mass ratio of 20-30:100, coating the mixed raw materials on the surface of a veneer, and then assembling, aging, cold pressing and hot pressing to obtain a plywood.