Method of regulating the viscosity of a mixture comprising at least two components having different viscosities

A method of regulating the viscosity of a mixture comprising at least two components having different viscosities, the method comprising:

• (a) determining the viscosity of the mixture via ultrasound measurements;
• (b) standardizing the viscosity determined to standard conditions;
• (c) comparing the standardized viscosity with a prescribed intended value;
• and
• (d) adjusting the viscosity of the mixture by increasing or decreasing a proportion of at least one component of the mixture,
• wherein the ultrasound measurements in the determining (a) are carried out at or in a line conveying the mixture or in a vessel,
• wherein
• the mixture comprising at least two components having different viscosities comprises monomeric diphenylmethane diisocyanates and oligomeric diphenylmethane diisocyanates,
• the mixture comprising a plurality of components is obtained from a crude mixture by distillation or crystallization, with a component being at least partly separated off,
• and wherein the crude mixture is obtained from a production process in which the crude mixture is obtained from a crude diaminodiphenylmethane mixture by a process comprising reacting the crude diaminodiphenylmethane with phosgene and changing the composition of the crude diaminodiphenylmethane mixture by changing the process parameters of the production process in order to adjust the viscosity in the adjusting (d).