The invention provides a preparation method of high-
viscosity water-soluble
melamine formaldehyde resin, which comprises the following steps: adding a first part of
formaldehyde solution and water into a reaction kettle, fully and uniformly stirring, adjusting the pH value of the
system in the reaction kettle, and controlling the
reaction temperature in the reaction kettle at 25-30 DEG C; adding
polyvinyl alcohol into the reaction kettle, raising the temperature in the reaction kettle to 48-52 DEG C, and keeping the temperature for 10-30 minutes; slowly raising the temperature in the reaction kettle to 90 DEG C, adding
melamine and an environment-friendly
accelerant into the reaction kettle, stirring and preserving heat for 8-12 minutes, and adding a
melamine prepolymer modifier into the reaction kettle; adding a first part of
formaldehyde solution into the reaction kettle, controlling the
reaction temperature in the reaction kettle to be 92-95 DEG C, adding a second part of
formaldehyde solution into the reaction kettle after reacting for 10 minutes, continuously stirring, and controlling the
reaction temperature in the reaction kettle to be quickly reduced to 58-62 DEG C; and adding
urea into the reaction kettle, naturally cooling to
room temperature, and discharging glue. The melamino-formaldehyde resin prepared by the invention has the advantages of high
viscosity, good water
solubility, low free formaldehyde and longer storage life.