Preparation method of ENF-grade modified urea-formaldehyde resin for artificial board

Abstract

The invention discloses a preparation method of ENF-grade modified urea resin for an artificial board, and relates to the technical field of artificial boards. The urea formaldehyde resin is prepared from the following raw materials in parts by weight: 7500-12000 parts of formaldehyde, 2400-4000 parts of first urea and 2400-4000 parts of second urea, the invention relates to a urea-based composite material which comprises the following components in parts by weight: 450-900 parts of secondary urea, 1800-3800 parts of tertiary urea, 500-1200 parts of fourth urea, 180-420 parts of a first auxiliary agent A, 420-850 parts of a second auxiliary agent A, 320-700 parts of a first auxiliary agent B, 300-650 parts of a second auxiliary agent B, 150-400 parts of a first auxiliary agent C, 80-200 parts of a second auxiliary agent C, 100-500 parts of a modifier, an acid solution and an alkali solution. By strictly controlling reaction conditions, urea and formaldehyde are fully reacted, the bonding strength is improved, the formaldehyde release amount is reduced, the prepared urea-formaldehyde resin is low in free formaldehyde, suitable for production of ENF-grade artificial boards, low in cost, free of addition of auxiliaries during glue mixing, capable of reducing errors of workers, good in stability and suitable for industrial production. The problems mentioned in the background technology are solved.

Description

Technical Field

[0001] The invention relates to the technical field of artificial boards, and in particular to a method for preparing an ENF-grade modified urea-formaldehyde resin for artificial boards. Background Art

[0002] In today's construction and home decoration fields, wood-based panels are widely used as basic materials. Their environmental performance, especially formaldehyde emission, has become the focus of attention of consumers and the industry. With the official release of the GB / T39600-2021 "Grading of Formaldehyde Emissions of Wood-Based Panels and Their Products" standard, the market has put forward more stringent requirements on the formaldehyde emission of wood-based panels. Among them, ENF grade is the highest standard, which stipulates that the formaldehyde emission must be less than 0.025mg / m 3 This undoubtedly brings huge challenges to wood-based panel manufacturers.

[0003] At present, there is a relative shortage of products that can stably meet the ENF grade standard in the market. Some companies try to add formaldehyde removers to E0 glue to meet this standard requirement. However, this method has many disadvantages. First, in the actual production process, the precise control of the amount of additives added becomes a major problem. Due to the complexity of the production process and the inherent limitations of manual operation, it is difficult for workers to accurately control the amount of additives added, which directly leads to uneven product quality and the pass rate is difficult to be effectively guaranteed, greatly increasing the company's production costs and quality control risks. Secondly, from the perspective of product performance, the addition of additives often has a negative impact on the bonding strength of artificial boards. As one of the key indicators for measuring the quality of artificial boards, the reduction of bonding strength may cause quality problems such as debonding and deformation of artificial boards during use, seriously affecting the service life and safety of the product, thereby weakening the product's competitiveness in the market, and failing to fundamentally meet consumers' urgent needs for high-quality, environmentally friendly artificial boards.

[0004] To this end, we provide a method for preparing ENF-grade modified urea-formaldehyde resin for artificial panels to solve the above-mentioned problems. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing an ENF-grade modified urea-formaldehyde resin for artificial panels. By combining a specific raw material formula with a finely regulated preparation process, the problem that the formaldehyde emission of products in the prior art is difficult to reach the ENF-grade standard and the addition of additives affects the bonding strength is solved.

[0006] In order to solve the above technical problems, the present invention is achieved through the following technical solutions:

[0007] The invention discloses a method for preparing an ENF-grade modified urea-formaldehyde resin for artificial boards. The raw materials include, by weight, 7500-12000 parts of formaldehyde, 2400-4000 parts of the first urea, 450-900 parts of the second urea, 1800-3800 parts of the third urea, 500-1200 parts of the fourth urea, 180-420 parts of the first auxiliary agent A, 420-850 parts of the second auxiliary agent A, 320-700 parts of the first auxiliary agent B, 300-650 parts of the second auxiliary agent B, 150-400 parts of the first auxiliary agent C, 80-200 parts of the second auxiliary agent C, 100-500 parts of a modifier, acid solution and alkali solution. The preparation steps are as follows: step a: firstly, formaldehyde, the first auxiliary agent B and polyvinyl alcohol are added into a stirring device, a thermometer and a cooling device; In the reaction vessel of the condensation reflux device, stirring is turned on, and the temperature is raised to 60°C at a heating rate of 5-10°C / min, and the temperature is kept for 10 minutes to make the raw materials preliminarily mixed and uniform and undergo a preliminary reaction, and then the first portion of liquid alkali is slowly added to adjust the pH value of the reaction system to 8.5, and the dripping speed is controlled at 1-2mL / min to prevent the local pH from being too high and causing side reactions. Then, the first portion of auxiliary agent C, the first portion of urea and the first portion of auxiliary agent A are added, and the temperature is continued to be raised to 90-95°C at a heating rate of 3-5°C / min, and the temperature is kept for 30-40 minutes. At this stage, the reaction system undergoes a hydroxymethylation reaction to generate a certain amount of hydroxymethyl urea, which provides active groups for the subsequent polycondensation reaction; step b: Subsequently, the second portion of auxiliary agent B and acid solution are added to the reaction system, the pH value is adjusted to 5.4, and the acid solution dripping speed is controlled at 0.5-1mL / min, avoid sudden drop in pH value causing violent polymerization, continue the reaction until large pieces of water drawing appear at 35℃, which indicates that the hydroxymethyl urea in the reaction system begins to undergo polycondensation to form polymer chains of a certain molecular weight. At this time, add the second portion of liquid alkali, the second portion of urea and the second portion of auxiliary agent A, and react at 85-90℃ until a specific second phenomenon appears, such as a significant increase in the viscosity of the reaction system, a darkening of the solution color, and large flake precipitation in 40-45℃ water (this phenomenon can be used as an important basis for judging the reaction process and product structure). When this phenomenon occurs, add the third portion of liquid alkali and the third portion of urea, and keep warm at 80-85℃ for 30 minutes to further promote the polycondensation reaction. The molecular weight and cross-linking degree of the lipid are improved, thereby enhancing its bonding performance and stability; Step c: Afterwards, the reaction system is cooled, and the cooling rate is controlled at 2-3℃ / min. When the temperature drops to an appropriate range (such as 50-55℃), the fourth portion of urea is added, and the second portion of auxiliary agent C is added at 60-65℃. Finally, the temperature is continued to be cooled to 40℃ at a cooling rate of 1-2℃ / min to obtain ENF-grade modified urea-formaldehyde resin for artificial boards. During the entire reaction process, the molecular structure and performance of the resin are precisely controlled by reasonably controlling the addition order of each raw material, reaction temperature, pH value, and insulation time, thereby preparing a modified urea-formaldehyde resin with low formaldehyde release and excellent bonding performance. .

[0008] The present invention is further configured that the acid solution and the alkali solution are added as required to adjust the reaction pH, the first auxiliary agent A and the second auxiliary agent A are triazine-type nitrogen-containing heterocyclic organic compounds, and the triazine-type nitrogen-containing heterocyclic organic compounds include at least one of melamine, trimethyl cyanurate, and trichloromelamine; the first auxiliary agent B and the second auxiliary agent B are hydroxides; the first auxiliary agent C and the second auxiliary agent C are ammonia substances.

[0009] The present invention is further configured such that in the preparation step, the reaction container is made of stainless steel with a volume of 100-500L, and the stirring blade of the stirring device is an anchor blade with a stirring speed of 200-500rpm to ensure that the raw materials are fully mixed during the reaction process, thereby improving the reaction efficiency and product quality stability.

[0010] The present invention is further configured that in the preparation step, when the temperature reaches 40-50°C during the process of heating to 60°C, the reaction system is vacuumed, and the vacuum degree is maintained at -0.05-0.08MPa for 5-10 minutes to remove part of the moisture and low-boiling impurities in the reaction system, which is beneficial to the subsequent reaction and improves the purity of the resin.

[0011] The present invention is further configured such that the first and second auxiliary agents C in the preparation step are respectively diluted before being added to the reaction system to a concentration of 18-25% to prevent excessive concentration and high loss at high temperature, thereby improving the effect of the auxiliary agents.

[0012] The present invention is further configured such that, in the preparation step, after adding the third portion of urea, nitrogen is introduced into the reaction system for protection, with a nitrogen flow rate of 10-20 L / min, until the reaction is completed, so as to prevent the active groups in the reaction system from being oxidized and ensure the performance stability and bonding performance of the resin.

[0013] The present invention is further configured that in the preparation step, before cooling to 40°C for discharging, an antioxidant is added to the reaction system, the amount of the antioxidant added is 0.1-0.5% of the total amount of the resin, and the antioxidant is one or more of hindered phenol antioxidants or phosphite antioxidants to improve the antioxidant properties of the modified urea-formaldehyde resin during storage and use and extend its service life.

[0014] The present invention is further configured such that, in the preparation step, formaldehyde is first pretreated before being added to the reaction container, and the formaldehyde solution is passed through an adsorption column filled with a cation exchange resin to remove metal ion impurities that may be contained therein, and the removal rate of the metal ion impurities reaches more than 90%, thereby avoiding the adverse effects of metal ions on the reaction process and resin performance.

[0015] The present invention is further configured that, in the preparation step, the polyvinyl alcohol is first dissolved in water at 80-90°C for 30-60 minutes before being added to form a polyvinyl alcohol solution with a mass fraction of 10-20%, and then added to the reaction system. This allows it to be better dispersed in the reaction system, exert its modification effect, and improve the flexibility and water resistance of the resin.

[0016] The present invention is further configured that after the reaction in the preparation step is completed, the resin is filtered before discharging, and the filter medium is a filter paper or filter screen with a pore size of 5-10 microns to remove insoluble impurities generated during the reaction, thereby improving the purity and quality of the resin and ensuring its use effect in the production of artificial boards.

[0017] The present invention has the following beneficial effects:

[0018] 1. The present invention strictly controls the reaction conditions to make urea and formaldehyde react fully, improve the bonding strength and reduce the formaldehyde release, so that the prepared urea-formaldehyde resin has low free formaldehyde, is suitable for the production of ENF-grade artificial boards, and has low cost. No additives are needed when adjusting the glue, which reduces the mistakes of workers and has good stability.

[0019] 2. The present invention can make the formaldehyde emission reach the ENF level standard, ensure the indoor air quality, and have good bonding performance. By accurately controlling the addition of raw materials and reaction conditions, the bonding strength is not affected, the quality of the board is guaranteed, the process is controllable, and the parameters of each link are accurately set to ensure stable product quality and repeatable production. The raw materials are used efficiently, waste and residue are reduced, resource allocation is optimized, and both economic and environmental benefits are achieved. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention are described below. The described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0021] Example 1

[0022] A method for preparing an ENF-grade modified urea-formaldehyde resin for artificial boards, wherein the raw materials include, by weight: 7500-12000 parts of formaldehyde, 2400-4000 parts of the first urea, 450-900 parts of the second urea, 1800-3800 parts of the third urea, 500-1200 parts of the fourth urea, 180-420 parts of the first auxiliary agent A, 420-850 parts of the second auxiliary agent A, 320-700 parts of the first auxiliary agent B, 300-650 parts of the second auxiliary agent B, 150-400 parts of the first auxiliary agent C, 80-200 parts of the second auxiliary agent C, 100-500 parts of a modifier, acid solution and alkali solution; preparation steps: step a: firstly, add formaldehyde, the first auxiliary agent B and polyvinyl alcohol into a stirring device, a thermometer and a condensation return; In the reaction vessel of the flow device, stirring is turned on, and the temperature is raised to 60°C at a heating rate of 5-10°C / min, and the temperature is kept for 10 minutes to make the raw materials preliminarily mixed and uniform and undergo a preliminary reaction, and then the first portion of liquid alkali is slowly added to adjust the pH value of the reaction system to 8.5, and the dripping speed is controlled at 1-2mL / min to prevent the local pH from being too high and causing side reactions. Then, the first portion of auxiliary agent C, the first portion of urea and the first portion of auxiliary agent A are added, and the temperature is continued to be raised to 90-95°C at a heating rate of 3-5°C / min, and the temperature is kept for 30-40 minutes. At this stage, the reaction system undergoes a hydroxymethylation reaction to generate a certain amount of hydroxymethyl urea, which provides active groups for the subsequent polycondensation reaction; step b: Subsequently, the second portion of auxiliary agent B and acid solution are added to the reaction system, the pH value is adjusted to 5.4, and the acid solution dripping speed is controlled at 0.5-1mL / min, avoid sudden polymerization caused by pH drop, continue the reaction until large pieces of water drawing appear at 35℃, which indicates that the hydroxymethyl urea in the reaction system begins to undergo condensation reaction to form polymer chains of a certain molecular weight. At this time, add the second portion of liquid alkali, the second portion of urea and the second portion of auxiliary agent A, and react at 85-90℃ until a specific second phenomenon appears, such as a significant increase in the viscosity of the reaction system, a darkening of the solution color, and large flake precipitation in 40-45℃ water (this phenomenon can be used as an important basis for judging the reaction process and product structure). When this phenomenon occurs, add the third portion of liquid alkali and the third portion of urea, and keep warm at 80-85℃ for 30 minutes to further promote the condensation reaction, so that the molecular weight and cross-linking degree of the resin are improved, thereby enhancing its bonding performance and stability; Step c: Afterwards, cool the reaction system, and the cooling rate is controlled at 2-3℃ / min. When the temperature drops When the temperature reaches a suitable range (such as 50-55°C), the fourth portion of urea is added, and the second portion of auxiliary agent C is added at 60-65°C. Finally, the temperature is continued to be lowered to 40°C at a cooling rate of 1-2°C / min to obtain ENF-grade modified urea-formaldehyde resin for artificial boards. During the entire reaction process, the molecular structure and performance of the resin are precisely controlled by reasonably controlling the addition sequence of each raw material, the reaction temperature, the pH value, the insulation time and other parameters, thereby preparing a modified urea-formaldehyde resin with low formaldehyde release and excellent bonding performance. Acid and alkali are added as required to adjust the reaction pH. The first auxiliary agent A and the second auxiliary agent A are triazine-type nitrogen-containing heterocyclic organic compounds, and the triazine-type nitrogen-containing heterocyclic organic compounds include at least one of melamine, tripropylene cyanurate, and trichloromelamine; the first auxiliary agent B and the second auxiliary agent B are hydroxides; the first auxiliary agent C and the second auxiliary agent C are ammonia substances. .

[0023] The reaction vessel is made of stainless steel with a volume of 100-500L, and the stirring blade of the stirring device is an anchor blade with a stirring speed of 200-500rpm to ensure that the raw materials are fully mixed during the reaction process, improve the reaction efficiency and product quality stability. In the process of heating to 60°C, when the temperature reaches 40-50°C, the reaction system is vacuumed and the vacuum degree is maintained at -0.05--0.08MPa for 5-10 minutes to remove part of the water and low-boiling impurities in the reaction system, which is beneficial to the subsequent reaction and improves the resin. Purity, the first part of the auxiliary agent A, the second part of the auxiliary agent A, the first part of the auxiliary agent B, the second part of the auxiliary agent B, the first part of the auxiliary agent C and the second part of the auxiliary agent C shall be ground before being added to the reaction system to make the particle size reach 50-100 mesh, so as to increase the contact area between the auxiliary agent and other raw materials, promote the full progress of the reaction and improve the effect of the auxiliary agent. After adding the third part of urea, nitrogen is introduced into the reaction system for protection, and the nitrogen flow rate is 10-20L / min until the reaction is completed to prevent the active groups in the reaction system from being oxidized, so as to ensure the performance stability and bonding performance of the resin. After cooling to 4 Before discharging at 0℃, an antioxidant is added to the reaction system. The amount of the antioxidant added is 0.1-0.5% of the total amount of the resin. The antioxidant is one or more of a hindered phenol antioxidant or a phosphite antioxidant to improve the antioxidant performance of the modified urea-formaldehyde resin during storage and use and extend its service life. Before adding formaldehyde to the reaction vessel, the formaldehyde solution is pretreated by passing it through an adsorption column equipped with a cation exchange resin to remove metal ion impurities that may be contained therein. The removal rate of metal ion impurities reaches more than 90%, avoiding the adverse effects of metal ions on the reaction process and resin performance. Before adding polyvinyl alcohol, it is first dissolved in water at 80-90°C for 30-60 minutes to form a polyvinyl alcohol solution with a mass fraction of 10-20%, and then added to the reaction system. This allows it to be better dispersed in the reaction system, play its modifying role, and improve the flexibility and water resistance of the resin. After the reaction is completed, the resin is filtered before discharging. The filter medium is a filter paper or filter screen with a pore size of 5-10 microns to remove insoluble impurities generated during the reaction, improve the purity and quality of the resin, and ensure its use effect in the production of artificial boards.

[0024] Performance display:

[0025] The various quality indicators tested according to GB / T 14732-2017 "Urea-formaldehyde, phenol-formaldehyde and melamine-formaldehyde resins for adhesives in the wood industry" and GB / T14074-2017 "Test methods for adhesives and resins for the wood industry" are shown in Table 1.

[0026] Test items Small test Pilot Normal production Solid content (%) 53.4 52.9 53.1 Curing time(s) ＞600 ＞600 ＞600 Viscosity(cps) 110 120 110 pH 8.0 8.5 8.6 Free formaldehyde (%) 0.09 0.08 0.09

[0027] Table 1

[0028] According to the bonding strength and formaldehyde emission determination in GB / T 17657-2013 "Test methods for physical and chemical properties of wood-based panels and veneer wood-based panels" - climate chamber method, small-scale, pilot and normal production samples were tested. 40×40×1.7mm eucalyptus veneer, five layers, double-sided glue 360~400g / m2, 28% flour was added during glue adjustment, 200 mesh, and hot pressing was performed at 120~130℃ for 12 minutes. The results are shown in Table 2.

[0029] Test items Small test Pilot Normal production <![CDATA[Formaldehyde emission (mg / m 3 )]]> 0.009 0.013 0.011 Type II bonding strength (MPa) 0.85 0.90 0.87 Type II immersion stripping (≥5) 6 6 6

[0030] Table 2

[0031] Example 2

[0032] Raw material preparation: formaldehyde: 8000 parts, first urea: 3000 parts, second urea: 600 parts, third urea: 2500 parts, fourth urea: 800 parts, first auxiliary agent A: 250 parts, second auxiliary agent A: 600 parts, first auxiliary agent B: 400 parts, second auxiliary agent B: 400 parts, first auxiliary agent C: 200 parts, second auxiliary agent C: 100 parts, modifier (polyvinyl alcohol): 200 parts, acid solution (20% formic acid): appropriate amount and alkali solution (30% sodium hydroxide): appropriate amount.

[0033] Preparation process:

[0034] A stainless steel reaction vessel with a volume of 300L was selected, and the stirring blade of the stirring device was an anchor blade, and the stirring speed was set to 300rpm. Formaldehyde, the first auxiliary agent B and polyvinyl alcohol were added to the reaction vessel, stirring was turned on, and the temperature was raised to 60°C at a heating rate of 8°C / min, and kept warm for 10 minutes. Then the first portion of liquid alkali was slowly added to adjust the pH value of the reaction system to 8.5, and the drop rate was controlled at 1.5mL / min. Then the first portion of auxiliary agent C, the first portion of urea and the first portion of auxiliary agent A were added, and the temperature was continued to be raised to 92°C at a heating rate of 4°C / min, and kept warm for 35 minutes.

[0035] When the temperature reaches 45°C, the reaction system is evacuated, and the vacuum is maintained at -0.06MPa for 8 minutes. Then, the second portion of auxiliary agent B and acid solution are added to the reaction system, the pH value is adjusted to 5.4, the acid solution drop rate is controlled at 0.8mL / min, and the reaction is continued until large pieces of 35°C water drawing appear. At this time, the second portion of liquid alkali, the second portion of urea and the second portion of auxiliary agent A are added, and reacted at 88°C until the solution viscosity increases significantly, the color becomes darker, and large flakes of precipitation appear in 42°C water, and the third portion of liquid alkali and the third portion of urea are added, and kept warm at 82°C for 30 minutes.

[0036] After adding the third portion of urea, nitrogen is introduced into the reaction system for protection, and the nitrogen flow rate is 15L / min until the reaction is completed. Then the reaction system is cooled, and the cooling rate is controlled at 2.5°C / min. When the temperature drops to 52°C, the fourth portion of urea is added, and the second portion of auxiliary agent C is added at 62°C. Finally, the temperature is continued to be cooled to 40°C at a cooling rate of 1.5°C / min. Before cooling to 40°C and discharging, 0.3% (based on the total amount of resin) of hindered phenol antioxidant is added to the reaction system, and then the resin is filtered, and the filter medium is a filter paper with a pore size of 8 microns, and the ENF grade modified urea-formaldehyde resin for artificial board is obtained.

[0037] Example 3

[0038] Raw material preparation: formaldehyde: 10,000 parts, first urea: 3,500 parts, second urea: 700 parts, third urea: 3,000 parts, fourth urea: 1,000 parts, first auxiliary agent A: 300 parts, second auxiliary agent A: 700 parts, first auxiliary agent B: 500 parts, second auxiliary agent B: 500 parts, first auxiliary agent C: 250 parts, second auxiliary agent C: 150 parts, modifier (polyvinyl alcohol): 300 parts, acid solution (20% formic acid): appropriate amount and alkali solution (30% sodium hydroxide): appropriate amount.

[0039] Preparation process:

[0040] A stainless steel reactor with a volume of 400L was used, the stirring blade was anchor type, and the stirring speed was 400rpm. Formaldehyde was first pretreated and passed through an adsorption column equipped with a cation exchange resin to achieve a removal rate of 92% for metal ion impurities. Then formaldehyde, the first auxiliary agent B and polyvinyl alcohol were added to the reactor. Polyvinyl alcohol was dissolved in 85°C water for 45 minutes. After forming a solution with a mass fraction of 15%, it was added and heated to 60°C at a heating rate of 7°C / min and kept warm for 10 minutes. The first portion of liquid alkali was slowly added to adjust the pH value to 8.5, with a drop rate of 1.8mL / min, followed by the first portion of auxiliary agent C, the first portion of urea and the first portion of auxiliary agent A. The temperature was raised to 93°C at a heating rate of 4.5°C / min and kept warm for 38 minutes.

[0041] During the heating process to 60°C, when the temperature reaches 48°C, the reaction system is evacuated to a vacuum degree of -0.07MPa for 6 minutes. Then, the second portion of auxiliary agent B and acid solution are added to adjust the pH to 5.4, and the acid solution is added at a rate of 0.7mL / min. The reaction is continued until large pieces of water-drawn silk form at 35°C. The second portion of liquid alkali, the second portion of urea, and the second portion of auxiliary agent A are added. The reaction is continued at 87°C until a specific phenomenon (a sharp increase in viscosity, a significant darkening of the color, and large pieces of precipitation in 43°C water) occurs. The third portion of liquid alkali and the third portion of urea are added, and the temperature is kept at 83°C for 30 minutes.

[0042] After adding the third portion of urea, nitrogen protection was passed through at a flow rate of 18 L / min until the reaction was completed. The cooling rate was 2.8°C / min, the fourth portion of urea was added at 53°C, the second portion of auxiliary agent C was added at 63°C, and then the temperature was cooled to 40°C at 1.8°C / min. Before discharging, 0.4% (total amount of resin) of phosphite antioxidant was added, and filtered with a filter screen with a pore size of 7 microns to obtain a modified urea-formaldehyde resin product.

[0043] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that technicians in the relevant technical field can better understand and utilize the present invention.

Claims

1. A method for preparing an ENF-grade modified urea-formaldehyde resin for artificial panels, characterized in that: The raw materials prepared by weight include: formaldehyde: 7500-12000 parts, the first urea is 2400-4000 parts, the second urea is 450-900 parts, the third urea is 1800-3800 parts, the fourth urea is 500-1200 parts, the first auxiliary agent A is 180-420 parts, the second auxiliary agent A is 420-850 parts, the first auxiliary agent B is 320-700 parts, the second auxiliary agent B is 300-650 parts, the first auxiliary agent C is 150-400 parts, the second auxiliary agent C is 80-200 parts, the modifier is 100-500 parts, acid solution and alkali solution; Preparation steps: Step a: first, formaldehyde, the first auxiliary agent B and polyvinyl alcohol are added to a reaction vessel equipped with a stirring device, a thermometer and a condensation reflux device, stirring is started, and the temperature is raised to 60°C at a heating rate of 5-10°C / min, and the temperature is kept for 10 minutes to make the raw materials preliminarily mixed and react preliminarily, and then the first liquid alkali is slowly added to adjust the pH value of the reaction system to 8.5, and the dropwise addition speed is controlled at 1-2mL / min to prevent the local pH from being too high and causing side reactions, and then the first auxiliary agent C, the first urea and the first auxiliary agent A are added, and the temperature is continued to be raised to 90-95°C at a heating rate of 3-5°C / min, and the temperature is kept for 30-40 minutes. At this stage, the reaction system undergoes a hydroxymethylation reaction to generate a certain amount of hydroxymethyl urea, which provides active groups for the subsequent polycondensation reaction; Step b: Subsequently, the second portion of the auxiliary agent B and the acid solution are added to the reaction system, the pH value is adjusted to 5.4, the acid solution dripping speed is controlled at 0.5-1 mL / min, and the pH drop is avoided to cause violent polymerization, and the reaction is continued until the phenomenon of large pieces of water drawing at 35°C appears, which indicates that the hydroxymethyl urea in the reaction system begins to undergo a polycondensation reaction to form a polymer chain of a certain molecular weight. At this time, the second portion of liquid alkali, the second portion of urea, and the second portion of auxiliary agent A are added, and the reaction is carried out at 85-90°C until a specific second phenomenon occurs, such as a significant increase in the viscosity of the reaction system, a darkening of the solution color, and a large flake precipitation in 40-45°C water. When this phenomenon occurs, the third portion of liquid alkali and the third portion of urea are added, and the temperature is kept at 80-85°C for 30 minutes to further promote the polycondensation reaction, thereby improving the molecular weight and cross-linking degree of the resin, thereby enhancing its bonding performance and stability; Step c: Afterwards, the reaction system is cooled, and the cooling rate is controlled at 2-3°C / min. When the temperature drops to an appropriate range, the fourth portion of urea is added, and the second portion of auxiliary agent C is added at 60-65°C. Finally, the temperature is continued to be cooled to 40°C at a cooling rate of 1-2°C / min to obtain ENF-grade modified urea-formaldehyde resin for artificial panels. During the entire reaction process, the molecular structure and properties of the resin are precisely controlled by reasonably controlling parameters such as the addition order of each raw material, the reaction temperature, the pH value, and the insulation time, thereby preparing a modified urea-formaldehyde resin with low formaldehyde release and excellent bonding properties.

2. The method for preparing an ENF-grade modified urea-formaldehyde resin for artificial panels according to claim 1, characterized in that: The acid solution and the alkali solution are added as required to adjust the reaction pH. The first auxiliary agent A and the second auxiliary agent A are triazine-type nitrogen-containing heterocyclic organic compounds, and the triazine-type nitrogen-containing heterocyclic organic compounds include at least one of melamine, tripropylene cyanurate, and trichloromelamine; the first auxiliary agent B and the second auxiliary agent B are hydroxides; the first auxiliary agent C and the second auxiliary agent C are ammonia substances.

3. The method for preparing an ENF-grade modified urea-formaldehyde resin for artificial panels according to claim 1, characterized in that: In the preparation step, the reaction container is made of stainless steel with a volume of 100-500L, and the stirring blade of the stirring device is an anchor blade with a stirring speed of 200-500rpm to ensure that the raw materials are fully mixed during the reaction process, thereby improving the reaction efficiency and product quality stability.

4. The method for preparing an ENF-grade modified urea-formaldehyde resin for artificial panels according to claim 1, characterized in that: In the preparation step, when the temperature reaches 40-50°C during the process of heating to 60°C, the reaction system is evacuated and the vacuum degree is maintained at -0.05-0.08MPa for 5-10 minutes to remove part of the water and low-boiling impurities in the reaction system, which is beneficial to the subsequent reaction and improves the purity of the resin.

5. The method for preparing an ENF-grade modified urea-formaldehyde resin for artificial panels according to claim 1, characterized in that: In the preparation step, the first and second auxiliary agents C need to be diluted before being added to the reaction system to make their concentrations reach 18-25% to prevent excessive concentrations and high losses at high temperatures, thereby improving the effects of the auxiliary agents.

6. The method for preparing an ENF-grade modified urea-formaldehyde resin for artificial panels according to claim 1, characterized in that: In the preparation step, after adding the third portion of urea, nitrogen is introduced into the reaction system for protection, with a nitrogen flow rate of 10-20 L / min, until the reaction is completed to prevent the active groups in the reaction system from being oxidized, thereby ensuring the performance stability and bonding performance of the resin.

7. The method for preparing an ENF-grade modified urea-formaldehyde resin for artificial panels according to claim 1, characterized in that: In the preparation step, before the temperature is lowered to 40° C. for discharging, an antioxidant is added to the reaction system, the amount of the antioxidant added is 0.1-0.5% of the total amount of the resin, and the antioxidant is one or more of a hindered phenol antioxidant or a phosphite antioxidant, so as to improve the antioxidant performance of the modified urea-formaldehyde resin during storage and use and extend its service life.

8. The method for preparing an ENF-grade modified urea-formaldehyde resin for artificial panels according to claim 1, characterized in that: In the preparation step, formaldehyde is pretreated before being added to the reaction container. The formaldehyde solution is passed through an adsorption column filled with a cation exchange resin to remove metal ion impurities that may be contained therein. The removal rate of metal ion impurities reaches more than 90%, thereby avoiding the adverse effects of metal ions on the reaction process and resin performance.

9. The method for preparing an ENF-grade modified urea-formaldehyde resin for artificial panels according to claim 1, characterized in that: In the preparation step, before adding the polyvinyl alcohol, it is first dissolved in water at 80-90°C for 30-60 minutes to form a polyvinyl alcohol solution with a mass fraction of 10-20%, which is then added to the reaction system. This allows it to be better dispersed in the reaction system, exert its modification effect, and improve the flexibility and water resistance of the resin.

10. The method for preparing an ENF-grade modified urea-formaldehyde resin for artificial panels according to claim 1, characterized in that: After the reaction in the preparation step is completed, the resin is filtered before discharging, and the filter medium is a filter paper or filter screen with a pore size of 5-10 microns to remove insoluble impurities generated during the reaction, improve the purity and quality of the resin, and ensure its use effect in the production of artificial boards.