Method for producing a toothbrush having an inner cavity

1. A method for extrusion blow molding a toothbrush comprising:

a) providing an extrusion blow mold having a longitudinal axis and a cavity, the cavity having a handle portion, a neck portion, a head portion, and a surface that defines a cross-sectional area; wherein the cavity has at least one of a maximum cross-sectional area, bordered by two smaller cross-sectional areas along the longitudinal axis of the blow mold or a minimum cross sectional area bordered by two greater cross-sectional areas along the longitudinal axis of the blow mold;

b) providing a subassembly positioned in the head portion of the cavity;

c) extruding a parison comprising a thermoplastic material, the parison includes an interior cavity and an outer surface, wherein the outer surface defines a cross-sectional area of the parison;

d) expanding the parison using a fluid to contact the cavity surface and subassembly to produce a toothbrush handle having an inner cavity.

2. The method of claim 1 , wherein the subassembly comprises a front surface and a parison contacting surface.

3. The method of claim 2 , wherein the parison contacting surface of the subassembly has a convex shape.

4. The method of claim 1 , wherein the subassembly comprises at least one cleaning element extending from the front surface.

5. The method of claim 4 , wherein the at least one cleaning element extends into a recess positioned in the head portion of the cavity.

6. The method of claim 1 , wherein the parison and subassembly comprise the same thermoplastic material.

7. The method of claim 1 , wherein the subassembly comprises a mechanical feature.

8. The method of claim 1 , wherein the minimum cross-sectional area of the extrusion blow mold cavity is less than the cross-sectional area of the parison.

9. The method of claim 1 , wherein the maximum cross-sectional area of the extrusion blow mold cavity is greater than the cross-sectional area of the parison.

10. The method of claim 1 , wherein the extrusion blow mold includes a label prior to extrusion of the parison.

11. A toothbrush produced by the method of claim 1 comprising:

a) a head, neck, handle, handle end, head end, outer surface, inner cavity, and longitudinal axis;

b) the inner cavity having a surface defining a cross-sectional area; wherein the inner cavity has at least one of a greater cross-sectional area, bordered by two lesser cross-sectional areas along the longitudinal axis of the toothbrush or a lesser cross sectional area bordered by two greater cross-sectional areas along the longitudinal axis of the toothbrush;

c) the outer surface defining an outer surface cross-sectional area;

d) a wall formed from the outer cavity surface and inner cavity surface;

e) a subassembly positioned in the head;

wherein the toothbrush comprising a single unitary component.

12. The toothbrush of claim 11 , wherein the square root of the outer surface cross-sectional area varies proportionally to the square root of the inner cavity cross-sectional area along the longitudinal axis of the toothbrush.

13. The toothbrush of claim 12 , wherein the square root of the inner cavity surface cross-sectional area varies proportionally less than 5% to the variations in the square root of the outer surface cross-sectional area along the longitudinal axis of the toothbrush handle.

14. The toothbrush of claim 11 , wherein the in the thickness of the toothbrush handle wall varies in inverse proportion to the square root of the outer surface cross-sectional area.

15. The toothbrush of claim 11 having a specific gravity below about 0.60 g/cm 3 and wherein the toothbrush handle deforms less than about 20 mm under a 5.0N force applied as determined by ASTM D 790.

16. A method for extrusion blow molding a toothbrush comprising:

a) providing an extrusion blow mold having a longitudinal axis and a cavity, the cavity having a handle portion, a neck portion, a head portion, and a surface that defines a cross-sectional area; wherein the cavity has at least one of a maximum cross-sectional area, bordered by two smaller cross-sectional areas along the longitudinal axis of the blow mold or a minimum cross sectional area bordered by two greater cross-sectional areas along the longitudinal axis of the blow mold;

b) providing a subassembly positioned in the head portion of the cavity;

c) extruding a parison comprising a first thermoplastic material and a second thermoplastic material, the parison includes an interior cavity and an outer surface, wherein the outer surface defines a cross-sectional area of the parison;

d) expanding the parison using a fluid to contact the cavity surface and subassembly to produce a toothbrush handle having an inner cavity.

17. The method of claim 16 , wherein the first material forms an inner layer and the second thermoplastic material forms an outer layer.

18. The method of claim 16 , wherein the first thermoplastic material and the second thermoplastic material form a single layer.

19. A toothbrush produced by the method of claim 16 comprising:

a) a head, neck, handle, handle end, head end, outer surface, inner cavity, and longitudinal axis;

b) the inner cavity having a surface defining a cross-sectional area; wherein the inner cavity has at least one of a greater cross-sectional area, bordered by two lesser cross-sectional areas along the longitudinal axis of the toothbrush or a lesser cross sectional area bordered by two greater cross-sectional areas along the longitudinal axis of the toothbrush;

c) the outer surface defining an outer surface cross-sectional area;

d) a wall formed from the outer cavity surface and inner cavity surface;

e) a subassembly positioned in the head;

wherein the toothbrush comprising a single unitary component.

20. The toothbrush of claim 19 , wherein the square root of the outer surface cross-sectional area varies proportionally to the square root of the inner cavity cross-sectional area along the longitudinal axis of the toothbrush.