Preparation process and application of melamine formaldehyde resin with high viscosity and low free formaldehyde

Abstract

The invention belongs to the technical field of polymer adhesives, and relates to a preparation process of melamine formaldehyde resin with high viscosity and low free formaldehyde, which comprises the following steps: fully stirring formaldehyde and water, regulating the pH value to 9.0-9.5 by using a sodium hydroxide solution, and controlling the temperature to 25-30 DEG C; adding polyvinyl alcohol, heating to 50 DEG C, and preserving heat for 10-30 minutes; sequentially adding melamine and an environment-friendly accelerant, stirring, heating to 90 DEG C, keeping the temperature for 10 minutes, and adding residual formaldehyde; and keeping the temperature at 92-95 DEG C, reacting for 10 minutes, measuring a mist point, slightly cooling when the mist point reaches 20 DEG C, cooling when the water-soluble ratio is detected to be 1: 2.5, naturally cooling to 60 DEG C, adding urea, cooling to normal temperature, and discharging glue. The prepared melamino-formaldehyde resin is also applied to preparation of impregnated paper. The polyvinyl alcohol can improve the viscosity of the resin, reduce the brittleness of the cured glue and improve the yield of the impregnated paper; by adding the environment-friendly accelerant and urea, the plasticity of the resin is improved, the resin is fully reacted, and the content of free formaldehyde is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer adhesives and relates to melamine formaldehyde resin, in particular to a preparation process and application of a melamine formaldehyde resin with high viscosity and low free formaldehyde. Background Art

[0002] Melamine formaldehyde resin is a polymer with a linear network structure obtained by the reaction of melamine and formaldehyde, also known as melamine resin (abbreviated as MF in English). Usually, melamine and a 37% formaldehyde aqueous solution are heated under weak alkaline conditions according to a certain molar ratio to generate different numbers of N-hydroxymethyl melamine derivatives. As the temperature rises, a polycondensation reaction is further carried out to generate an insoluble and infusible melamine formaldehyde resin with a stable network structure. This resin can be used as an adhesive for fireproof boards, an impregnated glue for floor and furniture board decorative paper, and can also be used in coatings, plastic products, and hardeners.

[0003] At present, there are many studies on high-viscosity melamine formaldehyde resins, but most of them are used in other industries and cannot meet the production of impregnated paper. The present invention improves the melamine formaldehyde resin used for impregnated paper coating to meet the production process requirements of liquid / dry spray paper coating. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to disclose a preparation process of a melamine formaldehyde resin with high viscosity and low free formaldehyde.

[0005] Technical Solution

[0006] A preparation process of a high-viscosity, low-free-formaldehyde melamine-formaldehyde resin comprises the following steps:

[0007] A. Pump formaldehyde accounting for 39-42% of the total mass of the resin into the reactor, add water accounting for 10-13% of the total mass of the resin, stir thoroughly, adjust the pH to 9.0-9.5 with 30% by mass sodium hydroxide solution, and control the temperature of the reactor at 25-30°C;

[0008] B. Add 0.1-0.5% polyvinyl alcohol to the total mass of the resin, raise the temperature to 50°C and keep warm for 10-30 minutes until the polyvinyl alcohol is completely dissolved;

[0009] C. Add 38-40% of melamine and 3%-5% of environmental accelerator in total mass of resin, stir, heat to 90℃ and keep warm for 10min, and add the remaining 3-5% of formaldehyde;

[0010] D. Keep the temperature at 92-95℃ for 10 minutes and then start measuring the fog point. When the fog point reaches 20℃, cool it down slightly. When the water-soluble ratio reaches 1:2.5, start cooling. After it cools naturally to 60℃, add 1-3% urea to the total amount of resin, cool to room temperature, and then discharge the glue.

[0011] In the preferred disclosed example of the present invention, the concentration of formaldehyde in step A is 37%.

[0012] In the preferred disclosed example of the present invention, the formaldehyde added in step A accounts for 40% of the total amount of the resin.

[0013] In the preferred disclosed example of the present invention, in step A, water accounting for 11.7% of the total mass of the resin is added.

[0014] In the preferred disclosed example of the present invention, the water in step A is tap water, filtered water or deionized water.

[0015] In the preferred disclosed example of the present invention, in step B, 0.3% of polyvinyl alcohol is added to the total mass of the resin, and the model of the polyvinyl alcohol is 1799.

[0016] In the preferred disclosed example of the present invention, 39% of melamine is added in step C.

[0017] In the preferred disclosed example of the present invention, in step C, an environmental accelerator accounting for 3% of the total mass of the resin is added, and the environmental accelerator is purchased from Jiangsu Changzhou Zhuoxing Decoration Materials Co., Ltd., model number ST-A-01.

[0018] In the preferred disclosed example of the present invention, the water-soluble ratio is detected once every 10 minutes in step C.

[0019] In the preferred disclosed example of the present invention, 3% urea of ​​the total mass of the resin is added in step D.

[0020] The resin prepared by the process of the present invention has a solid content of 56-60%, a viscosity of 20-24s / 20°C, and a storage period of 10-30 days.

[0021] The second object of the present invention is to apply the prepared melamine formaldehyde resin to the preparation of impregnated paper.

[0022] Beneficial Effects

[0023] The present invention controls the viscosity of the resin by the amount of water and polyvinyl alcohol, prolongs the storage period of the resin, and improves the wide adaptability of the resin; when conditions permit, deionized water is used to prolong the storage period of the resin (the conventional process storage period is about 5 days); the addition of polyvinyl alcohol can increase the viscosity of the resin, reduce the brittleness of the glue after curing, and improve the yield of the impregnated paper; the addition of an environmental accelerator and a small amount of urea can increase the plasticity of the resin, make it fully react, and further reduce the free formaldehyde content. DETAILED DESCRIPTION

[0024] The present invention is described in detail below in conjunction with the embodiments so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following embodiments.

[0025] Example 1

[0026] A preparation process of a high-viscosity, low-free-formaldehyde melamine-formaldehyde resin for impregnated paper comprises the following steps:

[0027] A. Add 400g of weighed 37% formaldehyde and 117g of filtered water into a three-necked flask, turn on the magnetic stirrer, and adjust the pH to 9.0-9.5 with 30% sodium hydroxide; keep the temperature at 20-30°C, add polyvinyl alcohol and raise the temperature to 50 degrees, keep the temperature until the polyvinyl alcohol is completely dissolved, and add weighed 390g of melamine and 30g of environmental accelerator in turn;

[0028] B. After adding, slowly raise the temperature to 90℃ in 40-60 minutes; keep it at 90±2℃ for ten minutes, then add 37% formaldehyde②30g, keep the temperature at 92-95℃, and make sure the pH is not lower than 8.8;

[0029] C. Start to detect the fog point after 10 minutes (the glue solution is dropped into a beaker filled with zero-degree ice water, and the glue solution spreads in the form of white mist. As the reaction continues, the water temperature in the beaker is adjusted at any time to 0-20℃ to ensure that the dripped glue solution can spread in the form of mist); when the fog point is 20±1℃, slightly lower the temperature to 90-92℃,

[0030] After 10 minutes, test the water-soluble ratio (ratio of glue solution to clean water, keeping the mixed temperature of glue solution and clean water at 20°C during testing);

[0031] D. Test once every ten minutes. When the ratio of glue to water is 1:2.5, quickly open the cooling system to cool it down. When the temperature is 60-55 degrees, add 30g of urea. When the glue is tested to be qualified at room temperature, put it in a container for later use.

[0032] Example 2

[0033] The production process of high viscosity and low free formaldehyde melamine formaldehyde resin is as follows:

[0034] Raw material ratio: (%)

[0035]

[0036] 1. Preparation

[0037] Count the solid raw materials that have passed the test: the amount of melamine, urea, polyvinyl alcohol and the liquid raw materials formaldehyde (37%) and filtered water, environmental accelerators, check whether the cooling water, electricity, heating steam, etc. can meet the production requirements, check whether the reactor is clean and free of foreign matter, and whether the bottom valve of the reactor is closed;

[0038] 2. The primary formaldehyde required for production is pumped into the metering tank through a pipeline pump for metering, and then pumped into the inspected reactor after metering;

[0039] 3. Pump deionized water into the metering tank and then pump it into the reactor after metering;

[0040] 4. Start stirring the reactor, add 30% sodium hydroxide solution after stirring evenly to adjust the pH to 9.0-9.5;

[0041] 5. The temperature in the kettle is controlled at 25-30°C, polyvinyl alcohol is added into the reactor, and the temperature is raised to 45-50 degrees to completely dissolve it;

[0042] 6. A certain amount of melamine and a measured environmental accelerator are put into the reactor at one time;

[0043] 7. Start to slowly increase the temperature, control it to rise to 90°C in 40-60 minutes (the addition reaction between formaldehyde and melamine is more intense during the heating period, so control the steam pressure and temperature changes), and start to keep warm at 90°C;

[0044] 8. Pay attention to the temperature and pH changes in the kettle, and keep the temperature at 92-95°C during the insulation period;

[0045] 9. After keeping warm for ten minutes, add the secondary formaldehyde measured by the metering tank according to the process requirements and keep the temperature at 92-95℃;

[0046] 10. Start to detect the fog point of the solution in the kettle after ten minutes. When the fog point reaches 20℃, the temperature in the kettle will drop slightly to 90-92℃;

[0047] 12. Start testing the water-soluble ratio after ten minutes. When the water-soluble ratio reaches 1:2.5, immediately turn on the circulating water to cool down and terminate the reaction of the solution in the kettle;

[0048] 13. When the temperature drops to 60-55℃, add a certain amount of urea and continue cooling;

[0049] 14. After the temperature drops to room temperature, test various indicators. If there is no abnormality, the glue can be discharged into the glue tank for standby use. In this way, melamine formaldehyde resin with high viscosity and low free formaldehyde content is obtained.

[0050] The prepared high-viscosity, low-free-formaldehyde melamine formaldehyde resin is used to prepare impregnated paper according to conventional processes. The thickness, water absorption, wear resistance, scratch resistance, chemical corrosion resistance and environmental protection performance of the prepared impregnated paper all meet the requirements.

[0051] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the specification of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A process for preparing a high-viscosity, low-free-formaldehyde melamine-formaldehyde resin, characterized in that: The steps include: A. Pump 37% formaldehyde, which accounts for 39-42% of the total mass of the resin, into the reactor, add 10-13% water, which accounts for 10%-13% of the total mass of the resin, stir thoroughly, and adjust the pH to 9.0-9.5 with 30% sodium hydroxide solution by mass. The temperature of the reactor is controlled at 25-30℃. B. Add 0.1-0.5% polyvinyl alcohol to the total mass of the resin, raise the temperature to 50°C and keep it for 10-30 minutes until the polyvinyl alcohol is completely dissolved; C. Add 38-40% of melamine and 3%-5% of environmental accelerator in total resin mass, stir, heat to 90℃ and keep warm for 10 minutes, then add the remaining 3-5% of formaldehyde; D. Keep the temperature at 92-95℃ for 10 minutes and then start measuring the fog point. When the fog point reaches 20℃, cool it down slightly. When the water-soluble ratio reaches 1:2.5, start cooling. When it cools naturally to 60℃, add 1-3% urea to the total amount of resin. After cooling to room temperature, discharge the glue.

2. The process for preparing the high-viscosity and low-free-formaldehyde melamine-formaldehyde resin according to claim 1, characterized in that: The formaldehyde added in step A accounts for 40% of the total resin.

3. The process for preparing the high-viscosity and low-free-formaldehyde melamine-formaldehyde resin according to claim 1, characterized in that: As described in step A, water accounting for 11.7% of the total mass of the resin is added.

4. The process for preparing the high-viscosity and low-free-formaldehyde melamine-formaldehyde resin according to claim 1, characterized in that: The water in step A is tap water, filtered water or deionized water.

5. The process for preparing the high-viscosity and low-free-formaldehyde melamine-formaldehyde resin according to claim 1, characterized in that: In step B, 0.3% of polyvinyl alcohol is added to the total mass of the resin, and the model of the polyvinyl alcohol is 1799.

6. The process for preparing the high-viscosity and low-free-formaldehyde melamine-formaldehyde resin according to claim 1, characterized in that: In step C, 39% of the total mass of the resin is added with melamine.

7. The process for preparing the high-viscosity and low-free-formaldehyde melamine-formaldehyde resin according to claim 1, characterized in that: In step C, an environmental accelerator accounting for 3% of the total mass of the resin is added, and the environmental accelerator is purchased from Jiangsu Changzhou Zhuoxing Decoration Materials Co., Ltd., model number ST-A-01.

8. The process for preparing the high-viscosity and low-free-formaldehyde melamine-formaldehyde resin according to claim 1, characterized in that: When testing the water-soluble ratio in step C, test once every 10 minutes.

9. The process for preparing the high-viscosity and low-free-formaldehyde melamine-formaldehyde resin according to claim 1, characterized in that: In step D, 3% urea is added to the total mass of the resin.

10. An application of a high-viscosity, low-free-formaldehyde melamine formaldehyde resin prepared by the process according to any one of claims 1 to 9, wherein the resin has a solid content of 56-60% and a viscosity of 20-24s / 20°C, characterized in that: It is applied to the preparation of impregnated paper.

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