PURPOSE: To obtain a polymer containing no free formaldehyde, usable for improving the opacity of paper, by adding urea to a urea-formaldehyde polymer dispersion under acidic conditions, and by neutralizing the mixture after a specific time to suppress the particle coarsening.
CONSTITUTION: Urea in an amount equimolar or more with formaldehyde is added to a dispersion of a crosslinked urea-formaldehyde, wherein free formaldehyde is dissolved, at a pH≤4, and the reaction mixture is neutralized 3minW1hr after the urea ddition to give a polymer having a particle size of 0.1W1.0μ containing no free formaldehyde.
PURPOSE: To obtain a polymer containing no free formaldehyde, usable for improving the opacity of paper, by adding urea to a urea-formaldehyde polymer dispersion under acidic conditions, and by neutralizing the mixture after a specific time to suppress the particle coarsening.CONSTITUTION: Urea in an amount equimolar or more with formaldehyde is added to a dispersion of a crosslinked urea-formaldehyde, wherein free formaldehyde is dissolved, at a pH≤4, and the reaction mixture is neutralized 3minW1hr after the urea ddition to give a polymer having a particle size of 0.1W1.0μ containing no free formaldehyde.
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