CN-122011985-A - Method for preparing urea-formaldehyde resin adhesive powder by drying method

Abstract

The invention discloses a method for preparing urea-formaldehyde resin adhesive powder by a drying method, belongs to the technical field of urea-formaldehyde resin preparation, and is used for solving the problem of resin activity damage caused by a drying process when preparing urea-formaldehyde resin adhesive powder by a spray drying method. Firstly reacting formaldehyde with a first batch of urea under alkaline condition, regulating acidity to perform polycondensation after the reaction is finished, then regulating neutrality, adding a second batch of urea and melamine to perform reaction, regulating alkalinity again, respectively adding a third batch of urea and the rest urea to react, dehydrating, cooling, discharging, mixing mineral powder filler after discharging, drying and crushing, thus preparing the urea-formaldehyde resin adhesive powder. The glue powder prepared by the method has strong activity after being reduced into glue, greatly improves the bonding strength, heat resistance and cold resistance, and simultaneously has the free formaldehyde content of less than 0.2 percent.

Inventors

• LU WEIGUO
• Lu Xiayuan

Assignees

• 陆伟国
• 陆夏源

Dates

Publication Date

20260512

Application Date

20260310

Claims (8)

1. 1. The method for preparing urea-formaldehyde resin adhesive powder by using the drying method is characterized by comprising the following steps of: (1) Regulating the pH value of formaldehyde to 7.5-8.0, adding a first batch of urea, slowly heating to 90-95 ℃ for heat preservation reaction, wherein the mass ratio of the first batch of urea to the total formaldehyde is 1:1.43-1.63, and the mass ratio of the first batch of urea to the total urea is 50-55 percent; (2) Adjusting the pH value to be acidic, carrying out polycondensation reaction, and when the reaction liquid is in a dense cloud form, adjusting the pH value to be neutral or weak alkaline to terminate polycondensation; (3) Adding a second batch of urea and melamine for continuous reaction; (4) Adding a third batch of urea for continuous reaction, cooling, and adding the rest urea for continuous reaction in the cooling process; (5) Vacuum dewatering to form viscous colloid, cooling to 50 ℃ and discharging to obtain liquid urea-formaldehyde resin, and adding mineral powder into the liquid urea-formaldehyde resin and uniformly stirring; (6) Drying to solid state, and pulverizing to obtain urea-formaldehyde resin adhesive powder.
2. 2. The method for preparing urea-formaldehyde resin adhesive powder according to claim 1, wherein the second batch of urea is 7% -12% of the total urea mass.
3. 3. The method for preparing urea-formaldehyde resin adhesive powder according to claim 1, wherein the melamine is added in an amount of 8.0% of the sum of the total urea and formaldehyde.
4. 4. The method for preparing urea-formaldehyde resin powder according to claim 1, wherein the step (2) of adjusting the pH to an acidic condition is specifically adjusting the pH to 4.6-5.5.
5. 5. The method for preparing urea-formaldehyde resin adhesive powder by using the drying method according to claim 1, wherein the addition amount of the mineral powder is 5% -7% of the mass of the liquid urea-formaldehyde resin.
6. 6. The method for preparing urea-formaldehyde resin powder according to claim 1, wherein the mineral powder is kaolin or attapulgite powder.
7. 7. The method for preparing urea-formaldehyde resin adhesive powder according to claim 1, wherein the step (4) is specifically performed by adding a third batch of urea, continuing the reaction for 30-40 minutes, and then adding the rest urea.
8. 8. The method for preparing urea-formaldehyde resin adhesive powder according to claim 1, wherein the third batch of urea is 15% -20% of the total urea mass.

Description

Method for preparing urea-formaldehyde resin adhesive powder by drying method Technical Field The invention relates to the technical field of urea-formaldehyde resin preparation, in particular to a method for preparing urea-formaldehyde resin adhesive powder by a drying method. Background Urea-formaldehyde resin (UF) has the advantages of easily available raw materials, low cost, high curing speed and bonding strength which are suitable for the requirements of indoor artificial boards, and is dominant in the adhesive market for wood processing for a long time, and is widely applied to the production of various artificial boards such as plywood, shaving board, medium density fiberboard and the like. The traditional urea-formaldehyde resin is in the form of liquid latex, but the preparation process is mature, but has the obvious defects that the water content of the urea-formaldehyde resin in the liquid latex reaches about 50 percent, and the transportation cost is greatly increased, so that the sales range of the urea-formaldehyde resin product produced by a glue preparation plant is generally within 200-300 km, the sales area is limited, and the storage time is shorter. The urea-formaldehyde resin liquid latex is difficult to dry by adopting a traditional method, and in order to solve the problem of storage and transportation pain points of the liquid urea-formaldehyde resin, a spray drying method is generally adopted in the industry to prepare a liquid urea-formaldehyde resin prepolymer into a powdery product. The process disperses urea-formaldehyde resin prepolymer into micron-sized fog drops through high-pressure atomization, and the moisture in the fog drops is quickly evaporated by using a heat medium, so that dry urea-formaldehyde resin powder is obtained. However, after the urea-formaldehyde resin adhesive powder prepared by the existing spray drying process is reduced by adding water to prepare an adhesive solution, a core technology pain point with obviously reduced activity exists, and the popularization and practical application of the urea-formaldehyde resin adhesive powder in the artificial board manufacturing industry are severely restricted, and the specific expression is as follows: 1. The activity is reduced due to local excessive polycondensation in the drying process, namely the urea resin prepolymer is a thermosensitive system, and the high temperature (the air inlet temperature is usually 180-200 ℃) adopted in the spray drying process easily causes local unexpected subsequent polycondensation reaction of the prepolymer, so that the molecular chain of the resin is abnormally increased, the branching degree is increased, the water solubility and redispersibility are reduced, the reactivity of the reduced glue solution is reduced, and the curing reaction rate is slowed down. 2. The powder structure characteristics prevent reduction swelling, namely in the spray drying process, moisture on the surface of fog drops is quickly evaporated, partial particles are easy to form a denser surface layer structure, meanwhile, the internal moisture is easy to cause the particles to be cohesive to form a micropore structure when migrating to the surface, and the partial particles are also likely to be adhered and agglomerated. When the structural characteristic is adopted for reducing by adding water, water molecules are difficult to quickly and uniformly permeate into the particles, so that the prepolymer cannot be fully swelled and dispersed to form a glue solution system with uneven dispersion, and the film forming property of the glue solution and the binding force with a substrate interface are directly affected. 3. The service performance of the reduced urea-formaldehyde resin powder is greatly attenuated, and the curing activity of the glue solution is far lower than that of the original liquid urea-formaldehyde resin powder of the same type due to the influence of the structural change and activity reduction. In practical application, the curing induction period of the reduction glue solution is obviously prolonged, the crosslinking curing degree is insufficient, the gluing performance is obviously attenuated, the service performance of the reduction glue solution is difficult to reach the level of the same type of liquid urea resin, and the production requirement of part of artificial boards with higher requirements on the gluing strength is difficult to meet. Even if the proportion of the curing agent is optimized, the activity and the gluing performance of the reduced glue solution are difficult to recover to the level of the liquid resin on the premise of not increasing the formaldehyde release amount. Disclosure of Invention Aiming at the problems existing in the existing urea-formaldehyde resin powder preparation process, the invention provides a method for preparing urea-formaldehyde resin powder by a drying method, which is different from the existing spray drying method, and the prepare