Dry-coated oxygen-scavenging particles and methods of making them

1. A method of dry coating oxidizable particles with activating particles, comprising steps of:

(a) adding a relatively soft, dry powder of activating particles and a dry powder of oxidizable particles to a mixer, wherein the mixer applies a compressive force and a shear force on the activating particles and the oxidizing particles to coat a surface of the oxidizing particles with the activating particles to form composite particles; and

(b) collecting the activating, oxidizable, and the composite particles;

(c) returning the activating, oxidizable, and composite particles to be further compressed and sheared as in step (a); and

(d) repeating steps (b) and (c) to more evenly coat the surface of the oxidizable powder with the activating particles.

2. The method of claim 1 in which the steps of collecting and returning are repeated in succession through a plurality of cycles to produce round-shaped, coated particles.

3. The method of claim 2 in which each of the cycles provides for progressively accreting at least portions of the activating particles on different areas of the surfaces of the oxidizable particles.

4. The method of claim 3 in which the step of repeating steps (b) and (c) includes removing irregular accretions of the activating particles on the surfaces of the oxidizable particles.

5. The method of claim 1 in which step (a) further comprises adding optically masking particles together with the activating particles and the oxidizable particles.

6. The method of claim 5 in which the step of repeating steps (b) and (c) evenly distribute the optically masking particles over the surface of the oxidizable particles.

7. A method of forming an oxygen-scavenging masterbatch, comprising steps of:

(a) dry coating oxidizable particles with activating particles to form composite oxygen scavenging particles; wherein the dry coating comprises the steps of;

i. adding a dry powder of activating particles and a dry powder of oxidizable particles to a mixer, wherein the mixer applies a compressive force and a shear force on the activating particles and the oxidizing particles to coat a surface of the oxidizing particles with the activating particles to form composite particles,

ii. collecting the activating, oxidizable, and composite particles,

iii. returning the activating, oxidizable, and composite particles to be further compressed and sheared, and

iv. repeating steps (ii) and (iii) to more evenly coat the surface of the oxidizing particles with the activating particles to form a batch of composite particles with rounded shapes;

(b) embedding the batch of oxygen-scavenging particles within a matrix of a base polymer at a concentration above its intended use; and

(c) transforming the base polymer embedded with the oxygen-scavenging particles into a plurality of solid concentrates.

8. The method of claim 7 in which the step of embedding includes blending the batch of composite oxygen-scavenging particles in a liquid state of the base polymer.

9. The method of claim 7 in which the batch of composite oxygen-scavenging particles occupies at least five percent by weight of the solid concentrates.

10. The method of claim 9 in which the batch of composite oxygen-scavenging particles occupies between 5 percent and 25 percent by weight of the solid concentrates.

11. The method of claim 7 in which the oxidizable particles include an oxidizable metal or an alloy of such metals.

12. The method of claim 11 in which the activating component particles include at least one of electrolytic particles, acidifying particles, and protic solvent hydrolyzable particles.

13. A method of forming an active barrier to oxygen permeation, comprising steps of:

(a) embedding a batch of composite oxygen-scavenging particles within a matrix of a base polymer at a first concentration, wherein the batch of composite oxygen-scavenging particles is prepared by dry coating oxidizable particles, the dry coating comprising the steps of;

i. adding a dry powder of activating particles and a dry powder of oxidizable particles to a mixer, wherein the mixer applies a compressive force and a shear force on the activating particles and the oxidizing particles to coat a surface of the oxidizing particles with the activating particles to form composite particles,

ii. collecting the activating, oxidizable, and composite particles,

iii. returning the activating, oxidizable, and composite particles to be further compressed and sheared, and

iv. repeating steps (ii) and (iii) to more evenly coat the surface of the oxidizing particles with the activating particles, and form the batch of oxygen-scavenging particles with rounded shapes;

(b) transforming the base polymer embedded with the composite oxygen-scavenging particles into a plurality of solid concentrates;

(c) mixing the solid concentrates together with solid concentrates of the base polymer or a compatible polymer; and

(d) transforming the mixture of solid concentrates into a barrier layer in which the composite oxygen-scavenging particles are embedded within the barrier layer in a second lower concentration, wherein the oxygen-scavenging particles with rounded shapes result in lower haze in the barrier layer than irregularly-shaped particles with multiple facets.

14. The method of claim 13 in which the first concentration of the composite oxygen-scavenging particles is between 5 percent and 25 percent by weight.

15. The method of claim 14 in which the second concentration of the composite oxygen-scavenging particles is less than 2 percent by weight.

16. The method of claim 1 wherein the activating particles are selected from a group consisting of sulfate, bisulfate, hydrated metal sulfate and bisulfate complex.

17. The method of claim 16 wherein the activating particles includes NaCl.

18. The method of claim 7 wherein the activating particles are selected from a group consisting of sulfate, bisulfate, hydrated metal sulfate and bisulfate complex.

19. The method of claim 18 wherein the activating particles includes NaCl.

20. The method of claim 5 wherein the optically masking particles are particles of AlCl 3 .

21. The method of claim 13 in which step (a)(i) further comprises adding AlCl 3 together with the activating particles and the oxidizable particles.

22. A method of dry coating oxidizable particles with activating particles, comprising steps of:

(a) adding a dry powder of relatively soft, activating particles and a dry powder of oxidizable particles to a mixer flushed with an inert gas; and

(b) applying a compressive force and a shear force on the softer activating particles and the oxidizing particles to coat a surface of the oxidizing particles with the activating particles to form composite particles; and

(c) collecting the activating, oxidizable, and composite particles and repeating steps (b) and (c) to more evenly coat the surface of the oxidizing particles with the activating particles, and produce round-shaped, coated oxygen-scavenging particles.

23. The method of claim 22 wherein the activating particles are selected from a group consisting of sulfate, bisulfate, hydrated metal sulfate and bisulfate complex.

24. The method of claim 23 wherein the activating particles includes NaCl.

25. The method of claim 22 in which step (a) further comprises adding AlCl 3 together with the activating particles and the oxidizable particles.