WO1997002194A1

WO1997002194A1 - Protection of sealed packages from water condensation

Info

Publication number: WO1997002194A1
Application number: PCT/US1996/011197
Authority: WO
Inventors: Amy J. Lacher; Richard E. Cleary, Sr.; Raymond J. Sauro; James Neil Pryor
Original assignee: W.R. Grace & Co.-Conn.
Priority date: 1995-06-30
Filing date: 1996-06-26
Publication date: 1997-01-23
Also published as: AU6674896A

Abstract

Condensation in the packaging of moisture-containing foods and other substances can be prevented without the undesired effects associated with conventional desiccants. These benefits are achieved via the use of certain types of silica gel and/or other siliceous oxide adsorbents having substantial capacity to adsorb moisture at high relative humidity and/or at the onset of condensation. Preferred adsorbents are silica xerogels having less than 650 m2/g surface area. The condensation protecting adsorbents may also contain fungistats such as 2-nonanone.

Description

PROTECTION OF SEALED PACKAGES FROM WATER CONDENSATION

Background of the Invention In many sealed environments which contain moisture such as plastic packaging for foods like meats or produce, water condensation may occur resulting in undesired effects on the package and/or the contents thereof. For example, water condensation may lead to increased microbial activity in the package environment and a corresponding decrease in shelf life for the product contained therein. Also, water condensation may cause degradation of the aesthetic appearance of the product making the product unmarketable by virtue of its appearance.

The use of desiccants to adsorb water is certainly well known. However, most desiccation applications involve the maintenance of very low relative humidity. The desiccants typically used are active adsorbers of moisture at low to moderate relative humidity and will act to drive the relative humidity down to a low level. Further, typical desiccant applications involve the use of sufficient desiccant such that the humidity is maintained at a low to moderate level. Unfortunately, the use of typical desiccants in packaging environments is problematic where the packaged or contained substance (e.g., food) itself contains significant essential moisture. Namely, typical desiccants would cause the food or other contained substance to lose moisture, thereby degrading or ruining the contained substance. Further, typical desiccants are not responsive to the presence of condensation.

Accordingly, there is a need for improved means of addressing condensation problems in packaging applications.

Summary of the Invention The invention overcomes the problem of the condensation in the packaging of moisture-containing foods and other substances without the undesired effects associated with typical desiccants. These benefits are achieved via the use of certain types of silica gel and/or other siliceous oxide adsorbents having substantial capacity to adsorb moisture at high relative humidity and/or at the onset of condensation. In one aspect, the invention encompasses the use of siliceous oxides having a surface area of less than 650 m²/g in contact with a package environment which environment is adapted to contain a substance. The siliceous oxide is preferably selected from the group consisting of silica gel, precipitated silica, silica alumina, swellable clays, acid-treated clay materials and mixtures thereof. The siliceous oxide is preferably a silica xerogel which has a surface area of about 225-650 m²/g and a pore volume of about 0.7-1.4 ml/g.

In another aspect, the invention encompasses the use of siliceous oxide material having a water adsorption capacity between 60 and 90% relative humidity of at least 20 wt.% (based on the dry weight of the material) in contact with a package environment which environment is adapted to contain a substance. Preferably, the siliceous oxide material has a water adsorption capacity between 80 and 90% relative humidity of at least 15 wt.%. The invention further encompasses packaging means which incorporate the siliceous oxide adsorbents of the invention. The invention is especially useful in the packaging of moisture-containing substances such as foods.

Brief Description of the Drawings

Figure 1 is a plot of amount of adsorbed water (wt.% based on the weight of the adsorbent) as a function of relative humidity for xerogels of the invention in comparison to a typical desiccant. Detailed Description of the Invention

The invention is characterized by the use of certain types of siliceous oxide adsorbents in packaging systems or assemblages wherein the siliceous oxide provides adsorption of moisture at high relative humidity and/or at the onset of condensation whereby condensation is prevented or removed while avoiding substantial moisture extraction from the package contents by the adsorbent. The siliceous oxides preferably adsorb little moisture at low relative humidity.

The siliceous oxides useful in the invention are preferably selected from the group consisting of silica gel, precipitated silicas, silica aluminas, swellable clays, acid-treated clay materials, and mixtures thereof. The preferred siliceous oxides are silica gels, most preferably xerogels such as ID xerogel. The silica ID xerogels are especially advantageous since they do not provide significant adsorption at low relative humidity. The siliceous oxides of the invention are preferably such that a substantial amount of their total water adsorption capacity (based on the weight after removal of all free water, preferably by activation at 260-315°C for about two hours) is available only at relative humidity above 60%. More preferably, a substantial amount of the water adsorption capacity is available only at relative humidity above about 80%. The siliceous oxide material preferably has a water adsorption capacity between 60 and 90% relative humidity of at least 20 wt.%, more preferably at least 40 wt.%. The siliceous oxide material preferably has a water adsorption capacity between 80 and 90% relative humidity of at least 15 wt.%, more preferably at least 30 wt.%. The water adsorption performance is preferably measured by contacting a sample of the adsorbent (activated to remove free water) with a constant relative humidity air environment until an equilibrium amount of water has been adsorbed by the sample. The sample is then weighed and tested at a higher relative humidity in a similar manner to determine the adsorption over a range of relative humidity. Preferably, the air is passed through the sample to accelerate the achievement of equilibrium. The water adsoφtion is preferably tested at about 25°C, however for most of the siliceous oxides of interest, the adsorption performance is relatively stable as a function of temperature in the range of temperature seen by most packaging environments (i.e. 0-100°C).

The siliceous oxides preferably have a surface area of less than about 650 m²/g, more preferably about 200-650 m²/g, most preferably about 250- 450 m²/g. The siliceous oxides preferably have a pore volume of about 0.7- 1.4 ml/g. In general, the higher pore volume and lower surface area values within the above ranges will result in a siliceous oxide whose water adsorption capacity becomes available at a higher relative humidity. If desired, a siliceous oxide which serves to adsorb moisture at the onset of condensation (i.e. at relative humidity above 90%) may be used wherein the siliceous oxide has surface area below about 300 m²/g and pore volume greater than about 1.0 ml/g. The surface area and pore volume data given in this application were obtained using the standard nitrogen-BET technique in the absence of free water wherein the free water has been removed by any appropriate known technique which avoids or minimizes effects on the surface area and pore volume of the underlying siliceous oxide. The actual water content of the preferred siliceous oxides of the invention may be varied considerably without destroying their condensation protection capability. This is especially true where the oxide is a silica ID xerogel. Preferably, the initial water content of the siliceous oxide adsorbent is about 5-25 wt.%, more preferably about 10-20 wt.%. In some cases, it may be possible to use an adsorbent having the majority of its total water adsorption capacity available below 60% relative humidity. In such cases, it is preferable to pre-load the adsorbent with water (or other compatible solvent) whereby the majority of the adsorbent's remaining water adsorption capacity (after pre-loading) is available above 60% relative humidity. These adsorbents are generally not preferred since their adsorption capacity after pre-loading may be relatively limited, thus requiring a higher loading of adsorbent in the package to achieve the same condensation prevention capacity as with the preferred embodiment.

Figure 1 shows a comparison of three different silica xerogels of the invention with a conventional desiccant gel. The plot shows that the xerogels of the invention exhibit relatively low adsoφtion below 60% relative humidity whereas the conventional desiccant gel's capacity to adsorb is available below 60% relative humidity. The three xerogels of the invention shown in Figure 1 have the following surface area and pore volume characteristics:

Xeroαel Surface Area (m²/g) Pore Volume (ml/g) A 325 1.2

B 520 0.8

C 550 0.9

The silica xerogels used in the invention can be prepared by any conventional method. See for example, "The Chemistry of Silica" by R. K. Her, John Wiley & Sons (1979), "Sol-gel Science: The Physics and Chemistry of Sol-gel Processing" by Brinker et al., Academic Press, Inc. (1990), and "Applied Industrial Catalysis," Academic Press, Inc. Vol. 3, Chap. 3, (1984) by

M. E. Winyall. Other adsorbent siliceous oxides useful in the invention can be prepared according to known techniques. The adsorbents of the invention are preferably in the form of beads or granules. Where necessary, the adsorbent may be combined with other materials such as binders to facilitate or enhance their use. The use of binders to form adsorbent beads is well known. See, for example, the disclosures of US Patents 3,624,003 and 3,625,866 which are incorporated herein by reference.

The adsorbents of the invention may by used in manner known for exposure of desiccants/adsorbents to closed environments. For example, the xerogel may be placed in a breathable pouch or canister which is then incorporated into the package. See for example, US Patents 4,830,643; 3,990,872; 2,838,795; 2,635,742; 4,272,264 and 4,453,955. The disclosures of these patents are incorporated herein by reference. The package or container may be of any suitable construction, for example, plastic bags, rigid walled containers, etc.

It is also possible to incorporate agents onto the condensation protection adsorbent to perform other desired tasks within the package or container environment. For example, fungistats such as those disclosed in US Patent 5,334,619 (based on 2-nonanone) may be incorporated directly into the siliceous adsorbent by impregnation (with any necessary removal of solvent thereafter by activation at a suitable temperature). Other agents might include anti-bacterial agents, fragrances, flavors, etc. The disclosure of US Patent 5,334,619 is incorporated herein by reference. Where other auxiliary agents are employed, preferably they are added in an effective amount for their intended purpose.

Claims

ClaimsWhat is claimed is:

1. A package comprising an environment adapted to contain a substance wherein the improvement comprises providing a siliceous oxide having a water adsorption capacity between 60 and 90% relative humidity of at least 20 wt.% in contact with said package environment, said contact being such that said siliceous oxide is capable of adsorbing water from said environment.

2. The package of claim 1 wherein said environment is adapted to contain a moisture-containing substance.

3. The package of claim 1 wherein said environment is protected from direct contact with an external environment.

4. The package of claim 1 wherein said siliceous oxide is selected from the group consisting of silica gel, precipitated silica, silica alumina, swellable clays, acid-treated clay materials and mixtures thereof.

5. The package of claim 1 wherein said siliceous oxide is a silica xerogel.

6. The package of claim 1 wherein said siliceous oxide has a water adsorption capacity between 80 and 90% relative humidity of at least 15 wt.%.

7. The package of claim 1 wherein said siliceous oxide has a water adsorption capacity between 60 and 90% relative humidity of at least 40 wt.%

8. The package of claim 6 wherein said siliceous oxide has a water adsorption capacity between 80 and 90% relative humidity of at least 30 wt.%.

9. The package of claim 1 wherein said siliceous oxide has a surface area of less than 650 m²/g.

10. The package of claim 9 wherein said siliceous oxide has a surface area of about 200-650 m²/g.

11. The package of claim 1 wherein said siliceous oxide has a pore volume of about 0.7-1.4 ml/g.

12. The package of claim 5 wherein said xerogel has a surface area of less than 650 m²/g.

13. The package of claim 1 wherein said siliceous oxide contains an auxiliary agent selected from the group consisting of fungistats, anti-bacterial agents, fragrances, flavors, and combinations thereof.

14. The package of claim 13 wherein said auxiliary agent is a fungistat.

15. The package of claim 14 wherein said fungistat is 2-nonanone.

16. The package of claim 1 wherein said environment is bounded by a flexible plastic.

17. The package of claim 16 said environment is the interior of a plastic bag.

18. The package of claim 1 wherein said environment is bounded by one or more rigid walls.

19. The package of claim 1 wherein said siliceous oxide is contained in a breathable pouch.

20. The package of claim 1 wherein said siliceous oxide is in granular form.