Urea formaldehyde resin, and preparation method

Abstract

This invention discloses a method for preparing urea-formaldehyde resin, which is prepared from: formaldehyde 200 parts, urea 100-250 parts, poly (vinyl alcohol) 0.5-6 parts, accelerator 0.05-0.5 part, and additive 0.5-5 parts. The concentration of formaldehyde is higher than 42%. During the reaction process, urea is added in batches, so the raw materials react in strongly acidic, neutral to week alkaline, weak acidic and neutral media in sequence. The prepared urea-formaldehyde resin has a free formaldehyde content of only 0.05-0.20%. The production of artificial board, such as flake board and low / high density fiberboard, from the urea-formaldehyde resin has such advantages as no need for vacuum dehydration treatment, no wastewater discharge, short production period, and low fuel and energy consumption. The artificial board, when compared with that produced from low-concentration formaldehyde (37%), has such advantages as obviously improved physical and mechanical properties, and low free formaldehyde content.

Description

technical field [0001] The invention relates to a urea-formaldehyde resin and a preparation method thereof, in particular to a urea-formaldehyde resin for producing wood-based panels and a preparation method thereof. Background technique [0002] Over the past 30 years of reform and opening up, my country's wood industry has achieved extraordinary rapid development. In 2004, the total output of wood-based panels (fiberboard, particleboard and plywood) in my country was 54.465 million cubic meters. In 2005, it reached 63.93 million cubic meters, an increase of 17.4%, which was 3.19 times that of 2000. It has become the world's largest wood-based panel production country. Among them, the amount of wood-based panel adhesives (100% solid content) exceeded 3.5 million tons in 2005, and urea-formaldehyde resin adhesives accounted for more than 90% of the amount of wood-based panel glue used, which is the largest variety in adhesives. The reason why urea-formaldehyde resin adhesive...

AI Technical Summary

Problems solved by technology

Due to the low concentration of formaldehyde, vacuum dehydration is often required in the manufacturing process of urea-formaldehyde resin, which not only increases the difficulty of the subsequent process, prolongs the production cycle, increases fuel and power consumption, but also discharges waste water containing free formaldehyde and other pollution. The reactivity of low-concentration formaldehyde is relatively small. When synthesizing urea-formaldehyde resin, if the molar ratio of formaldehyde and urea is too low, although the amount of free formaldehyde in the synthesized urea-formaldehyde resin can be reduced, the urea-formaldehyde resin produced The water solubility decreases, the storage period shortens, the curing time prolongs, and the curing performance deteriorates. When used in the production of wood-based panels, the physical and mechanical properties, durability and water resistance of the wood-based panels will all decrease; if the molar ratio of formaldehyde and urea High, although the physical and mechanical properties of the wood-based panels are guaranteed, it also leads to a significant increase in the amount of free formaldehyde in the manufactured wood-based panels