CN116003719A - Preparation method of E0-level melamine modified urea formaldehyde resin - Google Patents
Preparation method of E0-level melamine modified urea formaldehyde resin Download PDFInfo
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- CN116003719A CN116003719A CN202211230345.7A CN202211230345A CN116003719A CN 116003719 A CN116003719 A CN 116003719A CN 202211230345 A CN202211230345 A CN 202211230345A CN 116003719 A CN116003719 A CN 116003719A
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Abstract
The invention discloses a preparation method of E0-level melamine modified urea formaldehyde resin, and relates to the technical field of urea formaldehyde resin production. The main raw materials comprise formaldehyde, urea, melamine, starch slurry and active carbon. Urea was added in two batches, neutral and acidic respectively, with the molar ratio of urea to formaldehyde of the first batch ranging from 0.5 to 0.6:1, the molar ratio of urea to formaldehyde in the second batch is 0.4-0.5:1, melamine is added in the initial stage and the addition stage of the reaction respectively, the dosage is 3% and 7% of the dosage of urea respectively, starch slurry is added before the reaction, active carbon is added in the later stage of the reaction, and the E0-level melamine modified urea formaldehyde resin is finally prepared through three mediums of neutrality, acidity and alkalinity. According to the preparation method of the E0-grade melamine modified urea-formaldehyde resin, the prepared melamine modified urea-formaldehyde resin has the advantages of E0-grade environmental protection standard, high storage stability, high adhesive strength, low shrinkage, low cost and the like.
Description
Technical Field
The invention belongs to the technical field of urea-formaldehyde resin production, and particularly relates to a preparation method of E0-level melamine modified urea-formaldehyde resin.
Background
Urea-formaldehyde resin (UF), also known as urea-formaldehyde resin, is prepared by polycondensing urea and formaldehyde into initial urea-formaldehyde resin under the action of catalyst (alkaline or acid catalyst), and then forming insoluble and infusible final thermosetting resin under the action of curing agent or auxiliary agent, the color of the solidified urea-formaldehyde resin is shallower than that of phenolic resin, and the resin is semitransparent, weak acid and weak base resistant, good in insulating property, excellent in wear resistance and low in price, and is the kind of adhesive with the largest dosage, especially in the manufacture of various artificial boards in wood processing industry, the urea-formaldehyde resin and its modified products account for about 90% of the total dosage of the adhesive. However, urea-formaldehyde resin is easy to decompose when meeting strong acid and strong alkali, has poor weather resistance, poor initial adhesion, large shrinkage, large brittleness, no water resistance and easy aging, and the artificial board produced by the urea-formaldehyde resin has the problem of formaldehyde release in the manufacturing and using processes, so the artificial board must be modified, the existing urea-formaldehyde resin is often modified by melamine, the water resistance of the urea-formaldehyde resin can be effectively improved, but the existing urea-formaldehyde resin still has the following defects in actual use:
after the existing melamine modified urea formaldehyde resin is modified, the bonding strength and storage stability of the melamine modified urea formaldehyde resin are reduced, the curing shrinkage rate is high, the content of free formaldehyde is high, the human health is seriously damaged, the immune dysfunction, liver injury and lung injury are caused, and the nervous system is also influenced.
Therefore, the existing melamine modified urea formaldehyde resin cannot meet the requirements in practical use, so that an improved technology is urgently needed in the market to solve the problems.
Disclosure of Invention
The invention aims to provide a preparation method of E0-level melamine modified urea-formaldehyde resin, which solves the problems of reduced bonding strength and storage stability, large curing shrinkage and high free formaldehyde content of the existing melamine modified urea-formaldehyde resin through a neutral-acid-alkaline glue preparation process.
In order to solve the technical problems, the invention is realized by the following technical scheme:
the invention relates to a preparation method of E0-level melamine modified urea formaldehyde resin, which comprises the following steps:
(1) Firstly, adding formaldehyde aqueous solution with the mass concentration of 35% -40% into a reaction kettle, continuously heating the formaldehyde aqueous solution to 30-45 ℃, preserving heat, and then adding a small amount of starch slurry to obtain a first reaction solution;
(2) Then adding a first batch of urea into the first reaction liquid, adding a small amount of melamine, heating to 70-90 ℃, keeping the temperature at a certain time, and reacting for 5-10 minutes to obtain a second reaction liquid;
(3) Adjusting the pH value of the second reaction liquid, adding acid into the second reaction liquid, adjusting the pH value to 3.0-3.5, keeping the temperature at 70-90 ℃, adding a second batch of urea, and reacting for 35-50 minutes at a constant temperature;
(4) Adding alkali after the polymerization reaches the end point, adjusting the pH value to 7.5-8.2, adding a small amount of melamine again, carrying out heat-preserving polycondensation, and carrying out viscosity detection every 5 minutes until the reaction end point is reached;
(5) At the end of the reaction, the temperature of the reaction is reduced to 30-45 ℃, and a proper amount of alkaline activated carbon is mixed, and the pH value is regulated to 8.5-8.8, thus obtaining the E0-grade melamine modified urea-formaldehyde resin.
Further, in step (2), the molar ratio of urea to formaldehyde of the first batch is: and the melamine dosage is 3 percent of the urea dosage in a ratio of 0.5-0.6:1.
Further, in step (3), the molar ratio of the second batch of urea to the formaldehyde is from 0.4 to 0.5:1.
Further, the final molar ratio of urea to formaldehyde is controlled below 1.0.
Further, in the step (4), the melamine is used in an amount of 7% of the urea.
Further, the melamine addition should not exceed 10% of the urea addition.
Further, the starch slurry is an industrial water mixture of flour, bean flour and the like, and the addition amount of the starch slurry is 10% of the formaldehyde water solution.
Further, in the step (4), the pH adjuster for the alkali is a sodium hydroxide solution with a mass concentration of 30%.
Further, in the step (3), the pH regulator for acid is a formic acid solution with a mass concentration of 20%.
The invention has the following beneficial effects:
1. according to the method, the starch slurry is added in the early stage of urea-formaldehyde resin synthesis, hydrolysis occurs in the synthesis process, various pasty substances are formed, the viscosity of the urea-formaldehyde resin after synthesis is greatly improved, hydroxyl groups, hydroxymethyl groups, aldehyde groups generated by hydrolysis and the like on the molecular chain of starch participate in the synthesis reaction of some urea-formaldehyde resins, and after modification, the initial viscosity of the modified melamine urea-formaldehyde resin can be improved, and the adhesive strength and storage stability of the melamine modified urea-formaldehyde resin can be improved.
2. According to the method, the shrinkage rate of the melamine modified urea-formaldehyde resin during solidification is reduced through the filling capacity of the starch substance and the activated carbon, the adhesive strength of the adhesive layer is ensured, the problems of cracking and viscosity reduction after use are avoided, and the production cost is greatly reduced.
3. The method of the invention adopts a neutral-acid-alkaline preparation process and accurate control of the dosage of formaldehyde, urea and melamine, so that the temperature, the molar ratio and the pH value of the formaldehyde, urea and melamine reach the optimal reaction state during the reaction, the reaction of formaldehyde, urea and melamine can be greatly promoted, the free formaldehyde content in the melamine modified urea formaldehyde resin can be greatly reduced, and the adsorption of free formaldehyde can be carried out by mixing active carbon, so that the content of free formaldehyde can be further reduced, and the E0 level can be reached.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to comparative examples.
Example 1:
the invention relates to a preparation method of E0-level melamine modified urea formaldehyde resin, which comprises the following steps:
(1) Firstly, adding formaldehyde aqueous solution with the mass concentration of 35% -40% into a reaction kettle, continuously heating the formaldehyde aqueous solution to 30-45 ℃, preserving heat, and then adding a small amount of starch slurry to obtain a first reaction solution;
(2) Then adding a first batch of urea into the first reaction liquid, adding a small amount of melamine, heating to 70-90 ℃, keeping the temperature at a certain time, and reacting for 5-10 minutes to obtain a second reaction liquid;
(3) Adjusting the pH value of the second reaction liquid, adding acid into the second reaction liquid, adjusting the pH value to 3.0-3.5, keeping the temperature at 70-90 ℃, adding a second batch of urea, and reacting for 35-50 minutes at a constant temperature;
(4) Adding alkali after the polymerization reaches the end point, adjusting the pH value to 7.5-8.2, adding a small amount of melamine again, carrying out heat-preserving polycondensation, and carrying out viscosity detection every 5 minutes until the reaction end point is reached;
(5) At the end of the reaction, the temperature of the reaction is reduced to 30-45 ℃, and a proper amount of alkaline activated carbon is mixed, and the pH value is regulated to 8.5-8.8, thus obtaining the E0-grade melamine modified urea-formaldehyde resin.
In the step (2), the molar ratio of the urea to formaldehyde in the first batch is: and the melamine accounts for 3 percent of the urea consumption in a ratio of 0.5 to 0.6:1.
In step (3), the molar ratio of urea to formaldehyde in the second batch is 0.4-0.5:1.
The final molar ratio of urea to formaldehyde is controlled below 1.0.
In the step (4), the melamine accounts for 7 percent of the urea.
The melamine addition should not exceed 10% of the urea.
The starch slurry is a mixture of industrial flour, bean flour and the like and water, and the addition amount of the starch slurry is 10 percent of the formaldehyde aqueous solution.
In the step (4), the pH regulator for alkali is sodium hydroxide solution with the mass concentration of 30 percent.
In the step (3), the pH regulator used for regulating the acid is formic acid solution with the mass concentration of 20 percent.
Embodiment 2:
the method comprises the following steps:
(1) Firstly, adding a formaldehyde aqueous solution with the mass concentration of 35% -40% into a reaction kettle, continuously heating the formaldehyde aqueous solution to 30-45 ℃, and preserving heat to obtain a first reaction solution;
(2) Then adding a first batch of urea into the first reaction liquid, adding a small amount of melamine, heating to 70-90 ℃, keeping the temperature at a certain time, and reacting for 5-10 minutes to obtain a second reaction liquid;
(3) Adjusting the pH value of the second reaction liquid, adding acid into the second reaction liquid, adjusting the pH value to 3.0-3.5, keeping the temperature at 70-90 ℃, adding a second batch of urea, and reacting for 35-50 minutes at a constant temperature;
(4) Adding alkali after the polymerization reaches the end point, adjusting the pH value to 7.5-8.2, adding a small amount of melamine again, carrying out heat-preserving polycondensation, and carrying out viscosity detection every 5 minutes until the reaction end point is reached;
(5) At the end of the reaction, the temperature of the reaction is reduced to 30-45 ℃, and a proper amount of alkaline activated carbon is mixed, and the pH value is regulated to 8.5-8.8, thus obtaining the melamine modified urea-formaldehyde resin.
In the step (2), the molar ratio of the urea to formaldehyde in the first batch is: and the melamine accounts for 3 percent of the urea consumption in a ratio of 0.5 to 0.6:1.
In step (3), the molar ratio of urea to formaldehyde in the second batch is 0.4-0.5:1.
The final molar ratio of urea to formaldehyde is controlled below 1.0.
In the step (4), the melamine accounts for 7 percent of the urea.
The melamine addition should not exceed 10% of the urea.
In the step (4), the pH regulator for alkali is sodium hydroxide solution with the mass concentration of 30 percent.
In the step (3), the pH regulator used for regulating the acid is formic acid solution with the mass concentration of 20 percent.
Embodiment 3:
the method comprises the following steps:
(1) Firstly, adding formaldehyde aqueous solution with the mass concentration of 35% -40% into a reaction kettle, continuously heating the formaldehyde aqueous solution to 30-45 ℃, preserving heat, and then adding a small amount of starch slurry to obtain a first reaction solution;
(2) Then adding a first batch of urea into the first reaction liquid, adding a small amount of melamine, heating to 70-90 ℃, keeping the temperature at a certain time, and reacting for 5-10 minutes to obtain a second reaction liquid;
(3) Adjusting the pH value of the second reaction liquid, adding acid into the second reaction liquid, adjusting the pH value to 3.0-3.5, keeping the temperature at 70-90 ℃, adding a second batch of urea, and reacting for 35-50 minutes at a constant temperature;
(4) Adding alkali after the polymerization reaches the end point, adjusting the pH value to 7.5-8.2, adding a small amount of melamine again, carrying out heat-preserving polycondensation, and carrying out viscosity detection every 5 minutes until the reaction end point is reached;
(5) At the end of the reaction, the temperature of the reaction is reduced to 30-45 ℃, alkali is added, and the pH value is regulated to 8.5-8.8, thus obtaining the melamine modified urea formaldehyde resin.
In the step (2), the molar ratio of the urea to formaldehyde in the first batch is: and the melamine accounts for 3 percent of the urea consumption in a ratio of 0.5 to 0.6:1.
In step (3), the molar ratio of urea to formaldehyde in the second batch is 0.4-0.5:1.
The final molar ratio of urea to formaldehyde is controlled below 1.0.
In the step (4), the melamine accounts for 7 percent of the urea.
The melamine addition should not exceed 10% of the urea.
The starch slurry is a mixture of industrial flour, bean flour and the like and water, and the addition amount of the starch slurry is 10 percent of the formaldehyde aqueous solution.
In the step (4), the pH regulator for alkali is sodium hydroxide solution with the mass concentration of 30 percent.
In the step (3), the pH regulator used for regulating the acid is formic acid solution with the mass concentration of 20 percent.
Embodiment 4:
the method comprises the following steps:
(1) Firstly, adding a formaldehyde aqueous solution with the mass concentration of 35% -40% into a reaction kettle, continuously heating the formaldehyde aqueous solution to 30-45 ℃, and preserving heat to obtain a first reaction solution;
(2) Then adding a first batch of urea into the first reaction liquid, adding a small amount of melamine, heating to 70-90 ℃, keeping the temperature at a certain time, and reacting for 5-10 minutes to obtain a second reaction liquid;
(3) Adjusting the pH value of the second reaction liquid, adding acid into the second reaction liquid, adjusting the pH value to 3.0-3.5, keeping the temperature at 70-90 ℃, adding a second batch of urea, and reacting for 35-50 minutes at a constant temperature;
(4) Adding alkali after the polymerization reaches the end point, adjusting the pH value to 7.5-8.2, adding a small amount of melamine again, carrying out heat-preserving polycondensation, and carrying out viscosity detection every 5 minutes until the reaction end point is reached;
(5) At the end of the reaction, the temperature of the reaction is reduced to 30-45 ℃, alkali is added, and the pH value is regulated to 8.5-8.8, thus obtaining the melamine modified urea formaldehyde resin.
In the step (2), the molar ratio of the urea to formaldehyde in the first batch is: and the melamine accounts for 3 percent of the urea consumption in a ratio of 0.5 to 0.6:1.
In step (3), the molar ratio of urea to formaldehyde in the second batch is 0.4-0.5:1.
The final molar ratio of urea to formaldehyde is controlled below 1.0.
In the step (4), the melamine accounts for 7 percent of the urea.
The melamine addition should not exceed 10% of the urea.
In the step (4), the pH regulator for alkali is sodium hydroxide solution with the mass concentration of 30 percent.
In the step (3), the pH regulator used for regulating the acid is formic acid solution with the mass concentration of 20 percent.
Comparative example 1:
in the prior published invention document, the main raw materials of the preparation method (application number 201510881270.2) of the E0-grade melamine modified urea formaldehyde resin are formaldehyde, urea, polyvinyl alcohol and melamine.
1. Raw material formula of melamine modified urea formaldehyde resin:
| raw material composition | Parts by weight (kg) of each component |
| Formaldehyde | 542.13 |
| First batch of urea | 182.96 |
| Second batch of urea | 83.24 |
| Third batch of urea | 166.48 |
| Melamine | 19.81 |
| Polyvinyl alcohol | 5.37 |
| Sodium hydroxide | Proper amount of |
| Formic acid | Proper amount of |
2. The specific reaction steps are as follows:
1000 Kg of E0-grade melamine modified urea formaldehyde resin is produced, 542.13Kg of formaldehyde solution with the weight percentage of 37% and 5.37Kg of polyvinyl alcohol are added into a reaction kettle, the reaction kettle is heated by steam, the temperature of the reaction kettle is regulated, and when the temperature of the reaction liquid reaches 60 ℃, the reaction is carried out for 10 minutes, so as to obtain a first reaction liquid.
Adjusting the pH=8.0 of the first reaction liquid by using 30% sodium hydroxide aqueous solution by weight fraction, adding 182.96Kg of first urea with 46% nitrogen content, heating the reaction kettle by using steam, adding 19.81Kg of melamine with 99.8% purity when the temperature of the reaction liquid reaches 70 ℃, continuously heating the reaction kettle, and reacting for 30 minutes when the temperature of the reaction liquid reaches 90 ℃ to obtain a second reaction liquid.
Naturally cooling the second reaction liquid to 87 ℃, and adjusting the pH value of the second reaction liquid to be=5.1 by using a formic acid aqueous solution with the weight fraction of 20%, wherein the time for adding the formic acid is controlled to be 10-15 minutes. Directly taking the reaction liquid in the reaction kettle, detecting the viscosity of the reaction liquid by using a-4 cup viscosity ring, detecting the viscosity of the reaction liquid once every 5-10 minutes, immediately adding 30% sodium hydroxide aqueous solution in weight percent to adjust the pH value of the reaction mixed liquid to be 6.2 when the viscosity of the reaction liquid is 200-300 mPa.S (30 ℃), adding second urea with 46% nitrogen content, keeping the temperature of the reaction liquid at 89-90 ℃, reacting for 40-60 minutes, detecting the viscosity of the reaction liquid, and immediately adding 30% sodium hydroxide aqueous solution in weight percent to adjust the pH value of the reaction liquid to be 8.0 when the viscosity of the reaction liquid is 200-300 mPa.S (30 ℃), thus obtaining a third reaction liquid.
Naturally cooling the temperature of the third reaction liquid to 85 ℃, adding a third batch of urea with 46% of nitrogen content, reacting for 20 minutes, then cooling the temperature of the reaction liquid to 45 ℃ by using cooling water, adjusting the pH value of the reaction liquid to 8.0 by using 30% sodium hydroxide aqueous solution with the weight percentage, and discharging to obtain the urea-formaldehyde resin with milky appearance.
Comparative example 2:
the prior published invention document discloses a preparation method of E0-grade melamine modified urea formaldehyde resin (application number 201710098638.7).
The specific reaction steps are as follows:
adding hexamethylenetetramine, polyvinyl alcohol and water into formaldehyde solution with pH of 8.0-8.5, and controlling the temperature to be 45-47 ℃;
adding a first batch of melamine, controlling the temperature to be 52-54 ℃, controlling the pH to be more than or equal to 6.5, adding a first batch of urea, heating to 90-94 ℃, and controlling the pH to be 7.5-7.8;
controlling the temperature to be 90-94 ℃, controlling the pH to be more than or equal to 7.0 and the viscosity to be 90-130 mPa.s, cooling, rapidly adding alkali, adjusting the pH to be 8.5-9.0, adding a second batch of melamine, controlling the temperature to be 85-87 ℃, reacting until the reaction liquid in the kettle is turned clear, and checking the pH to be 8.0-8.5;
adding a third batch of melamine, continuously reacting at 82-85 ℃ until the viscosity is 150-180 mPa.s, cooling, rapidly adding alkali, adjusting the pH to 8.5-9.0, and detecting the pH=7.5-8.0 every 5 minutes in the cooling process;
cooling to 74-76 ℃, and adding a second batch of urea and corn starch slurry;
cooling to 58-62 ℃, adding a third batch of urea, fully stirring for 40 minutes, cooling to 40-44 ℃, and regulating the pH value to 8.5-9.0 to obtain the E0-level melamine modified urea-formaldehyde resin.
In the embodiment, the mass concentration of formaldehyde is 37%, the purity of urea is 98%, the nitrogen content is 46%, the purity of melamine is 99.5%, the pH regulator is a sodium hydroxide solution with the mass concentration of 30% and a formic acid solution with the mass concentration of 20%, the polyvinyl alcohol model is 2099 polyvinyl alcohol, and the corn starch slurry is mixed slurry prepared by mixing corn starch and water according to the ratio of 1:1. The molar ratio of formaldehyde to the total urea, F/u=1.39, the molar ratio of formaldehyde to the total melamine, F/m=3.65, the mass ratio of the first, second and third urea batches, U1: u2: u3=62: 23.7:14.3, the mass ratio of the first batch of melamine, the second batch of melamine and the third batch of melamine is M1: m2: m3=21.8: 43.8:34.4, the molar ratio of the polyvinyl alcohol to the total amount of urea is 0.014, the molar ratio of the hexamethylenetetramine to the urea is 0.015, the mass of the added corn starch slurry is 1.05% of the total mass of all materials, and the mass of the added water is 6.3% of the total mass of all materials.
The E0-grade melamine modified urea formaldehyde resin prepared in the embodiment is prepared into an adhesive, and comprises the following raw materials in parts by weight: 100 parts of E0-grade melamine modified urea formaldehyde resin, 0.4 part of ammonium chloride, 0.6 part of composite liquid curing agent, 8.5 parts of formaldehyde eliminating agent, 3.0 parts of reinforcing agent and 21 parts of industrial flour.
Wherein the composite liquid curing agent is formed by mixing phosphoric acid, formic acid and water, and the mass concentration is 65%; the aldehyde eliminating agent comprises the following raw materials in parts by weight: 22 parts of urea, 11 parts of thiourea, 6 parts of ammonium sulfate, 1 part of sodium pyrophosphate, 5 parts of phosphoric acid and 4 parts of diethylenetriamine; the preparation method of the aldehyde eliminating agent comprises the following steps: adding urea, thiourea, sodium pyrophosphate, ammonium sulfate and phosphoric acid into water, heating to 30 ℃, stirring until the materials are completely dissolved, adding diethylenetriamine, and stirring until the solution is converted to clear, thus obtaining the aldehyde eliminating agent.
The preparation method of the E0-level melamine modified urea-formaldehyde resin adhesive comprises the following steps: adding ammonium chloride, an acidic composite liquid curing agent, an aldehyde eliminating agent, an enhancer and industrial flour into the E0-level melamine modified urea-formaldehyde resin, and stirring until all the components are uniformly mixed to obtain the E0-level melamine modified urea-formaldehyde resin adhesive.
The E0-grade melamine modified urea-formaldehyde resin obtained by the method of the invention example 1 and the method of the comparative examples 1-2 is measured according to the standard detection method of GB/T14732-2006 and GB/T17657-2013 artificial board and decorative artificial board physicochemical property test method, and the solid content, pH value, viscosity, curing time, free formaldehyde content and other property indexes of the modified urea-formaldehyde resin are measured, and the results are shown in the following table:
TABLE 1
TABLE 2
Compared with the comparative examples 1, 2 and the examples 2, 3 and 4, the comparative example is added with the modifier with higher price such as polyvinyl alcohol, hexamethylenetetramine and the like, and the performance of the melamine modified urea-formaldehyde resin is improved, but the cost is greatly improved.
The foregoing is only a preferred embodiment of the present invention, and the present invention is not limited thereto, and any modification, equivalent replacement, and improvement of some of the technical features described in the foregoing embodiments are all within the scope of the present invention.
Claims (9)
1. A preparation method of E0-grade melamine modified urea formaldehyde resin is characterized by comprising the following steps: the method comprises the following steps:
(1) Firstly, adding formaldehyde aqueous solution with the mass concentration of 35% -40% into a reaction kettle, continuously heating the formaldehyde aqueous solution to 30-45 ℃, preserving heat, and then adding a small amount of starch slurry to obtain a first reaction solution;
(2) Then adding a first batch of urea into the first reaction liquid, adding a small amount of melamine, heating to 70-90 ℃, keeping the temperature at a certain time, and reacting for 5-10 minutes to obtain a second reaction liquid;
(3) Adjusting the pH value of the second reaction liquid, adding acid into the second reaction liquid, adjusting the pH value to 3.0-3.5, keeping the temperature at 70-90 ℃, adding a second batch of urea, and reacting for 35-50 minutes at a constant temperature;
(4) Adding alkali after the polymerization reaches the end point, adjusting the pH value to 7.5-8.2, adding a small amount of melamine again, carrying out heat-preserving polycondensation, and carrying out viscosity detection every 5 minutes until the reaction end point is reached;
(5) At the end of the reaction, the temperature of the reaction is reduced to 30-45 ℃, and a proper amount of alkaline activated carbon is mixed, and the pH value is regulated to 8.5-8.8, thus obtaining the E0-grade melamine modified urea-formaldehyde resin.
2. The method for preparing the E0-grade melamine modified urea formaldehyde resin according to claim 1, which is characterized in that: in the step (2), the molar ratio of the urea to formaldehyde in the first batch is: and the melamine dosage is 3 percent of the urea dosage in a ratio of 0.5-0.6:1.
3. The method for preparing the E0-grade melamine modified urea formaldehyde resin according to claim 1, which is characterized in that: in step (3), the molar ratio of the second batch of urea to the formaldehyde is 0.4-0.5:1.
4. The method for preparing the E0-grade melamine modified urea formaldehyde resin according to claim 1, which is characterized in that: the final molar ratio of urea to formaldehyde is controlled below 1.0.
5. The method for preparing the E0-grade melamine modified urea formaldehyde resin according to claim 1, which is characterized in that: in the step (4), the melamine is used in an amount of 7% of the urea.
6. The method for preparing the E0-grade melamine modified urea formaldehyde resin according to claim 1, which is characterized in that: the melamine addition should not exceed 10% of the urea.
7. The method for preparing the E0-grade melamine modified urea formaldehyde resin according to claim 1, which is characterized in that: the starch slurry is an industrial water mixture of flour, bean flour and the like, and the addition amount of the starch slurry is 10% of the formaldehyde aqueous solution.
8. The method for preparing the E0-grade melamine modified urea formaldehyde resin according to claim 1, which is characterized in that: in the step (4), the pH regulator for alkali is sodium hydroxide solution with the mass concentration of 30 percent.
9. The method for preparing the E0-grade melamine modified urea formaldehyde resin according to claim 1, which is characterized in that: in the step (3), the pH regulator for the acid is formic acid solution with the mass concentration of 20 percent.
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