Cartridge with reduced friction

Abstract

A cartridge fillable or filled with a dispensable medium for dispensing the medium by movement of a piston receivable or received in the cartridge has a sliding surface for the piston to slide along during the movement of the piston. The sliding surface has a microstructure for reducing the friction between the piston and the sliding surface.

Claims

1. A cartridge fillable or filled with a dispensable medium for dispensing the medium by movement of a piston receivable or received in the cartridge, the cartridge comprising: a sliding surface for the piston to slide along during the movement of the piston, the sliding surface having a microstructure configured to reduce friction between the piston and the sliding surface, the microstructure formed by a plurality of protrusions, a height of a respective protrusion being defined in a direction perpendicular to the sliding surface and a width of a respective protrusion being defined in a direction perpendicular to the height of the protrusion and to a sliding direction of the piston.

2. The cartridge in accordance with claim 1, wherein the cartridge comprises one of polypropylene, polyamide and poly-butylene terephthalate, and the piston comprises one of polypropylene, polyamide and low-density polyethylene.

3. The cartridge in accordance with claim 1, wherein the height of the protrusions is less than the width of the protrusions.

4. The cartridge in accordance claim 1, wherein the protrusions have a height of between around 0.2 m and around 5 m or a width of between around 1 m and around 50 m.

5. The in accordance with claim 1, wherein the protrusions are regularly arranged over at least part of the sliding surface.

6. The cartridge in accordance with claim 1, wherein the protrusions have an at least essentially circular base.

7. The cartridge in accordance with claim 6, wherein the protrusions are arranged pursuant to a uniform circle packing.

8. The cartridge in accordance with claim 6, wherein the sliding surface comprises polypropylene and the protrusions have a height of between around 0.5 m and around 2.5 m and a width of between around 4 m and around 12 m.

9. The cartridge in accordance with claim 6, wherein the sliding surface comprises polyamide and the protrusions have a height of between around 0.5 m and around 1.5 m and a width of between around 1 m and around 8 m.

10. The cartridge in accordance with claim 6, wherein the sliding surface comprises polybutylene terephthalate and the protrusions have a height of between around 0.5 m and around 2.5 m and a width of between around 1 m and around 10 m.

11. The cartridge in accordance with claim 6, wherein the sliding surface comprises polybutylene terephthalate and the protrusions have a height of around 3 m and a width of around 10 m, and the piston comprises polyamide.

12. The cartridge in accordance with claim 1, wherein the protrusions have an at least essentially elongated form extending along the sliding direction.

13. The cartridge in accordance with claim 12, wherein the sliding surface comprises polyamide and the protrusions have a height of around 1 m and a width of around 12 m, and the piston comprises low-density polyethylene.

14. The cartridge in accordance with claim 1, wherein the cartridge has an elongated form extending along a cartridge axis from a first end to a second end, with the piston being receivable or received through the first end for dispensing the dispensable medium through the second end by applying a driving force to the piston towards the second end, and the microstructure is formed only within a longitudinal region of the sliding surface with respect to the cartridge axis, the longitudinal region being spaced from the first end of the cartridge by at least the longitudinal extension of the piston along the cartridge axis.

15. A method for producing a cartridge in accordance with claim 1 comprising forming the cartridge by injection molding using a mold core having a micro-structure complementary to the microstructure of the sliding surface of the cartridge, the microstructure of the mold core being formed by laser ablation.

16. The cartridge in accordance claim 1, wherein the protrusions have a height of between around 0.5 m and around 1.5 m or a width of between around 6 m and around 12 m.

17. The in accordance with claim 1, wherein the protrusions are arranged on a two-dimensional Bravais lattice.

18. The cartridge in accordance with claim 1, wherein the protrusions are at least essentially formed as spherical domes.

19. The cartridge in accordance with claim 6, wherein the protrusions are arranged pursuant to a hexagonal circle packing.

20. The cartridge in accordance with claim 1, wherein the protrusions are at least essentially formed as cylinder segments with the cylinder axes of the cylinder segments being parallel to the sliding direction.

Description

DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in more detail hereinafter with reference to the drawings.

(2) FIG. 1 shows a schematic illustration of an embodiment of the cartridge.

(3) FIG. 2A and FIG. 2B show schematic illustrations of details of respective micro structures of the sliding surfaces of different embodiments of the cartridge.

(4) FIG. 3 shows a schematic illustration of details of the microstructure of the sliding surface of a further embodiment of the cartridge.

(5) FIG. 4 shows a schematic illustration of the cartridge according to FIG. 1 filled with a dispensable medium.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) In FIG. 1, an embodiment of a cartridge 11 is shown in a schematic illustration. The cartridge 11 is formed by injection molding and has an essentially cylindrical form, in particular with a slight conicity of for example about 0.02, to facilitate separation of the cartridge 11 from a mold core (not shown) during production. The cartridge 11 extends along a cartridge axis A from a first end 13 (at the right of FIG. 1) to a second end 15 (at the left of FIG. 1).

(7) The cartridge 11 is hollow so that a chamber 17 is formed inside the cartridge 11 which is pre-filled or fillable with a dispensable medium (not shown). At the first end 13 the cartridge 11 has a reception opening 19 through which the dispensable medium can be filled into the cartridge 11 and through which a piston 21 can be received. The piston 21, which also has an essentially cylindrical form, has an outer diameter corresponding to an inner diameter of the cartridge 11. At its outer circumference the piston 21 has a sealing lip (not shown) which is flexible to such an extent that the outer diameter of the piston 21 adapts to the slightly varying inner diameter of the cartridge 11 for a continuously tight fit sealing the chamber 17 towards the first end 13 of the cartridge 11.

(8) The piston 21 is shown in an initial state, in which it is received in the cartridge 11 to seal the chamber 17 at a maximum volume. Starting from this initial state, the piston 21 can be moved in a sliding direction, which corresponds to movement along the cartridge axis A towards the second end 15, to reduce the volume of the chamber 17 and thus to press the medium contained in the chamber 17 through a discharge opening 23 at the second end of the cartridge 11 out of the cartridge 11.

(9) During such a movement of the piston 21, the piston 21, especially the sealing lip of the piston 21, slides along a sliding surface 25 of the cartridge 11 which is an inner circumferential surface of the cartridge 11. In a longitudinal region 27 (with respect to the cartridge axis A) of the sliding surface 25, a microstructure 29 is formed in the sliding surface 25 so as to reduce the contact area between the piston 21 and the sliding surface 25 in the longitudinal region 27. As a result of this microstructuring, the frictionat least one of the sliding friction and the static friction, preferentially bothbetween the piston 21 and the sliding surface 25 is reduced. Adjacent to one or both ends of the longitudinal region 27 the sliding surface may or may not include a microstructure. For front-filling it may be advantageous to have at least the region of the sliding surface 25 which is adjacent to the discharge opening 23 without microstructure. This region defines the position of the piston 21 in the empty cartridge 11 (before filling) and since the piston may remain at this position for a long time before the cartridge 11 is filled it may be advantageous to have this region unstructured. The region of the sliding surface adjacent to the first end 13 of the cartridge 11 may be advantageously unstructured for both, front-filling and back-filling. The piston 21 remains in this region during storage of the cartridge 11 it may be advantageous to have this region unstructured.

(10) FIGS. 2A and 2B as well as FIG. 3 show details of microstructures 29 of different embodiments of the cartridge 11.

(11) The microstructures 29 of FIGS. 2A and 2B are illustrative for a first type of microstructure 29 comprising regularly arranged protrusions 31 with an at least essentially circular base. The protrusions 31 of the shown microstructures 29 are formed as spherical domes protruding from a plane 33 of the sliding surface 25. The height T of the protrusions 31 is smaller than their width, which corresponds to the diameter D of the circular base of the protrusions 31 and is about 10 m.

(12) The microstructures 29 of FIGS. 2A and 2B differ in particular in their respective arrangement pattern. In the microstructure 29 shown in FIG. 2A, the protrusions 31 are densely arranged according to a hexagonal circle packing, whereas in the microstructure 29 shown in FIG. 2B, the arrangement is less dense as the protrusions 31 are spaced from each other, though also being arranged in a hexagonal or in an at least centered rectangular lattice, where the pitch Vx between the protrusions 31 of adjacent lines of the pattern is just half the pitch Ax of the protrusions 31 of the same line. If the lattice is hexagonal, the line pitch Ay is furthermore equal to the pitch Ax of the protrusions 31 within a respective line.

(13) The hexagonal pattern has a high degree of symmetry and hence a rather high degree of isotropy at least on the macroscopic scale. Notwithstanding this, a microstructure 29 of the type shown in FIGS. 2A and 2B is preferably oriented such that lines of the respective pattern are parallel to the sliding direction or to the cartridge axis A, respectively. This is the case in FIGS. 2A and 2B as the sliding direction and the direction of the cartridge axis A are both parallel to the x-axis indicated in Figures.

(14) The microstructure 29 shown in FIG. 3 is less isotropic than the microstructures 29 of FIGS. 2A and 2B, since the protrusions 31 of this type of microstructure 29 have an at least essentially elongated form and hence are rotationally asymmetric. Due to this asymmetry the orientation of the microstructure 29 may have an influence on the friction between the piston 21 and the sliding surface 25 of the cartridge 11. Preferably, the protrusions 31 of the microstructure 29 shown in FIG. 3 extend along the sliding direction parallel to the cartridge axis A (this corresponds to the x-axis indicated in FIG. 3) with a regular spacing Ay in a direction perpendicular to the sliding direction.

(15) The protrusions 31 are formed as cylinder segments lying with their flat side in the plane 33 of the sliding surface 25 and having cylinder axes parallel to the sliding direction (and hence to the cartridge axis A). The height T of the protrusions 31 is slightly smaller than half of their width W, which is about 12 m. The length Lx of the protrusions 31 in a direction parallel to the sliding direction is about ten times the width W, but may be much larger, especially in the same order of magnitude as the longitudinal extension of the entire microstructure 29 with respect to the cartridge axis A, which may amount to several centimeters.

(16) Providing a microstructure 29 at the sliding surface 25, in particular providing one of the two types of microstructure 29 exemplarily shown and described above, is a simple and effective manner of reducing the friction between the piston 21 and the sliding surface 25 of the cartridge 11 to facilitate discharge of a medium out of the cartridge 11 without unduly impairing the tight sealing of the chamber 17 by the piston 21.

(17) FIG. 4 shows the cartridge 11 of FIG. 1 filled with a dispensable medium 35. In such a pre-filled cartridge 11 the microstructure 29 reduces the friction between the piston 21 and the sliding surface 25 for facilitating dispensing the medium 35 through the discharge opening 23, without at the same time disengaging the piston 21 and the cartridge 11 from each other to such an extent that they no longer are in sealingly tight contact to each other. The cartridge 11 therefore is particularly suited not only for dispensing, but also for storing the medium 35 until dispensing the medium 35 (partly or fully) is actually desired. An undesired leakage of the medium 35, drying out or chemical reaction of the medium 35 with environmental oxygen or moisture is nevertheless prevented.