Piston and handheld dispenser including a piston

A piston for use in expelling a material from a chamber, comprising:

• (a) a piston body having a side wall;
• and
• (b) a front seal for sealing a gap between the side wall of the piston body and a wall of the chamber, wherein the front seal comprises an annular ridge having a generally “V” shaped profile tapering off to the outer periphery of the seal, and has a leading edge included angle, and a trailing edge included angle that is smaller than the leading edge included angle, the leading and trailing edge included angles being measured relative to the side wall of the piston, wherein the leading edge corresponds to the flank of the “V” shaped part of the front seal profile that is adapted to face the material in the chamber, and the trailing edge is the edge opposite to the leading edge adapted to face away from the material in the chamber, and the leading edge included angle is approximately 60 degrees, and the trailing edge included angle is approximately 55 degrees.

The piston of any of the preceding claims, wherein the piston is made of low-density polyethylene (LDPE), and has a Shore D hardness of between 85 and 95.

The piston of any of the preceding claims, wherein the front seal projects from the side wall of the piston body by between 0.8 mm and 1.4 mm.

The piston of any of the preceding claims, wherein the piston comprises a coaxial pin protruding from the piston front.

The piston of any of the preceding claims, in combination with a dispenser cartridge that includes the chamber.