Three-dimensional printing

A three-dimensional printing kit, comprising:

• a particulate build material including from about 80 wt % to 100 wt % metal particles based on a total weight of the particulate build material, the metal particles having a D50 particle size ranging from about 1 μm to about 150 μm;
• and
• a separate binder fluid including:
• water;
• and
• a curable polyurethane adhesion promoter in an amount ranging from about 0.5 wt % to about 15 wt % based on a total weight of the binder fluid, the curable polyurethane adhesion promoter being a reaction product of:
• (a) a polyisocyanate;
• (b) an acrylate or methacrylate, the acrylate or methacrylate having at least one hydroxyl functional group and having an acrylate functional group or a methacrylate functional group;
• (c) a carboxylic acid including one or two hydroxyl functional groups, an amount of the carboxylic acid ranging from 0 wt % to about 10 wt %;
• and
• (d) a sulfonate or sulfonic acid having one or two hydroxyl functional groups or one or two amino functional groups, an amount of the sulfonate or sulfonic acid ranging from about 2 wt % to about 20 wt %.