Dispensing system for mixture of two components and static mixing nozzle therefor

1. A dispensing system for dispensing a mixture of a first component and a second component, the dispensing system comprising:

a dispensing gun comprising an inlet body with a first passage for feeding in the first component under pressure and a second passage for feeding in the second component under pressure, the first and second passages respectively comprising a closable first outlet and a closable second outlet;

a static mixing nozzle, detachably connectable to the outlets of the body and provided for mixing and dispensing the components, the static mixing nozzle comprising a first section containing a first chamber and a second chamber for conducting the first and second component respectively and a second section, subsequent to the first section, containing a mixing chamber with static mixing elements which promote mixing the first and second components and conducting the mixture to a nozzle tip serving as an outlet for the mixture;

wherein at least one of the first and second chambers of the static mixing nozzle contains a series of static backflow prevention elements, arranged for hindering backflow of the respective component within the respective chamber,

wherein the flow path for the respective component is formed by a series of orifices through the static backflow prevention elements.

2. The dispensing system according to claim 1 , wherein the series of static backflow prevention elements is formed by a plurality of walls, dividing the respective chamber up into at least two compartments.

3. The dispensing system according to claim 2 , wherein the compartments have a volume of 50 to 400 mm 3 .

4. The dispensing system according to claim 2 , wherein the plurality of walls comprise two alternating sets of walls which protrude into the chamber from two opposing side walls of the chamber.

5. The dispensing system according to claim 2 , wherein the walls are arranged in a slanting direction with respect to the forwards flow direction of the respective component through the respective chamber.

6. The dispensing system according to claim 1 , wherein the orifices are arranged in a zig-zag configuration.

7. The dispensing system according to claim 1 , wherein the static mixing elements comprise a further series of walls forming a meandering or spiraling flow path through the mixing chamber.

8. The dispensing system according to claim 1 , wherein the static mixing nozzle is an assembly of a sleeve and an insert, the insert fitting into a cavity of the sleeve.

9. The dispensing system according to claim 8 , wherein the static mixing elements and the static backflow prevention elements are provided on the insert.

10. The dispensing system according to claim 7 , wherein the sleeve is made of a transparent material, allowing visual inspection of the first, second and mixing chambers.

11. The dispensing system according to claim 1 , wherein the lengths of the first and second chambers of the mixing nozzle are a minimum length of 10 mm.

12. A static mixing nozzle for mixing a first component and a second component and dispensing the mixture, the static mixing nozzle comprising

an inlet part, detachably connectable to outlets of a dispensing gun via which said components are supplied to the inlet part;

a first section containing a first chamber and a second chamber for conducting the first and second component respectively; and

a second section containing a mixing chamber with static mixing elements which promote mixing the first and second components and conducting the mixture to a nozzle tip serving as an outlet for the mixture;

wherein at least one of the first and second chambers of the static mixing nozzle contains a series of static backflow prevention elements, arranged for hindering backflow of the respective component within the respective chamber,

wherein the flow path for the respective component is formed by a series of orifices through the static backflow prevention elements.

13. The static mixing nozzle according to claim 12 , wherein the series of static backflow prevention elements is formed by a plurality of walls, dividing the respective chamber up into at least two compartments.

14. A process of forming a polyurethane foam comprising: (i) providing an isocyanate component comprising a diisocyanate or a polyisocyanate and optionally a blowing agent and/or further additives; (ii) providing a polyol component comprising a blowing agent, a catalyst, a polyol and optionally further additives; and (iii) mixing said isocyanate component and said polyol component to form the polyurethane foam, wherein the mixing step is performed in a static mixing nozzle according to claim 12 .

15. The static mixing nozzle of claim 13 , wherein the plurality of walls comprise two alternating sets of walls which protrude into the chamber from two opposing side walls of the chamber and/or wherein the walls are arranged in a slanting direction with respect to the forwards flow direction of the respective component through the respective chamber.

16. The static mixing nozzle of claim 12 , wherein the orifices are arranged in a zig-zag configuration.

17. The static mixing nozzle of claim 12 , wherein the static mixing elements comprise a further series of walls forming a meandering or spiraling flow path through the mixing chamber.

18. The static mixing nozzle of claim 12 , wherein the static mixing nozzle is an assembly of a sleeve and an insert, the insert fitting into a cavity of the sleeve.

19. The static mixing nozzle of claim 18 , wherein the sleeve is made of a transparent material.