WO2000024648A1

WO2000024648A1 - Pouch assembly for moisture control

Info

Publication number: WO2000024648A1
Application number: PCT/US1999/024499
Authority: WO
Inventors: Daniel Adamek; David G. Ferris; Gregory L. Reichter; Kirk A. Schneider
Original assignee: Donaldson Company, Inc.
Priority date: 1998-10-28
Filing date: 1999-10-19
Publication date: 2000-05-04
Also published as: AU1125800A

Abstract

A pouch assembly contains a moisture absorbent material disposed in a porous pouch. The pouch assembly is, in some instances, formed from a hydrophobic material to contain the moisture absorbent material if the moisture absorbent material absorbs sufficient water to form a gel, liquid, or slurry within the pouch assembly. The pouch assembly may be configured and arranged to provide an internal volume that is greater than an initial volume of the moisture absorbent material. Typically, the pouch assembly includes first and second cover layers. At least one of the first and second cover layers includes a porous sheet material. In one example of a pouch assembly, the first and second cover layers are sealed at a peripheral region of the two layers and define a central region in which the moisture absorbent material is contained. The first and second layers also define at least one intermediate region between the central and peripheral regions. In the intermediate region, the first and second cover layers are initially disposed proximate to each other, but the first and second cover layers are configured and arranged to separate as the moisture absorbent material expands and provide an internal volume to the pouch assembly that is greater than a volume of the moisture absorbent material.

Description

POUCH ASSEMBLY FOR MOISTURE CONTROL

Field of the Invention

This invention relates to devices used for moisture control (e.g., control of relative humidity). In particular, the invention relates to a pouch assembly containing a moisture absorbent or hygroscopic material for controlling the level of moisture in a space.

Background of the Invention

Moisture control may be important for a number of purposes, including, for example, the storage and transport of moisture sensitive chemicals, desiccants, and absorbent or adsorbent devices, such as activated carbon filters. It may be necessary to store these items in an environment with a controlled moisture content so as not to use up the filter or desiccant capacity or degrade the chemicals. In addition, in some instances, it may be important to maintain an amount of moisture (e.g., relative humidity) to provide an environment that is not too wet and/or too dry. In other applications, the preservation of a particular level of moisture (e.g., relative humidity) in a confined space is also important. For example, electronic and other devices may be sensitive to the level of moisture (e.g., relative humidity) in the air surrounding the device. In some cases, the device is confined in a housing to prevent or reduce the fluctuations of moisture content in the air. This approach may not be sufficient if air moves in and out of the housing.

It is found that some hygroscopic chemical salts, combinations of these salts, polymer beads, and other moisture absorbent materials can maintain a constant relative humidity in a space by absorbing or adsorbing water when the moisture content is relatively high and releasing water when the moisture content of the air is relatively low. In some instances, the moisture absorbent materials may absorb sufficient water to form a liquid, gel, or slurry. The moisture absorbent materials typically need to be held in a container to prevent or reduce particulate and/or liquid contamination by the moisture absorbent material of the electronic equipment, other device, or moisture sensitive chemicals. Some conventional containers have been formed using non-porous molded plastic and glass with a porous material over an opening in the container. These containers are often rigid and may be relatively expensive and/or inconvenient for many applications. Moreover, these containers may provide only a small area for flow of water vapor into and out of the container. One additional difficulty with containing these moisture absorbent materials is that they often expand upon absorbing water. There is a need for improved assemblies or devices that contain moisture absorbent materials to maintain a moisture level.

Summary of the Invention

Generally, the present invention relates to assemblies for controlling the level of moisture in a confined space. One example is a pouch assembly containing a moisture absorbent material. The pouch assembly is, in some instances, formed from a porous hydrophobic material that permits the flow of water vapor through the material, but contains the moisture absorbent material if the moisture absorbent material absorbs sufficient water to form a gel, liquid, or slurry within the pouch assembly. The pouch assembly may be configured and arranged to provide an internal volume that is greater than an initial volume of the moisture absorbent material.

In one embodiment, the pouch assembly is configured and arranged to have a initial internal volume that is at least 10%, 25%, 50%, or 100% greater than the initial volume of the moisture absorbent material. Typically, the pouch assembly includes a first cover layer and a second cover layer. At least one, and in many instances, both, of the first and second cover layers includes a porous sheet material. The first and second cover layers may also contain, in some instances, a scrim or support layer. Another embodiment is a pouch assembly that includes a moisture absorbent material that expands beyond an initial volume as moisture is absorbed, a first cover layer and a second cover layer. The first and second cover layers are sealed at a peripheral region of the two layers and define a central region in which the moisture absorbent material is contained. The first and second cover layers also define at least one intermediate region between the central and peripheral regions. In the intermediate region, the first and second cover layers are initially disposed proximate to each other, but the first and second cover layers are configured and arranged to separate as the moisture absorbent material expands and provide an internal volume to the pouch assembly that is greater than a volume of the moisture absorbent material.

One method of making a pouch assembly includes receiving a central portion of a first cover layer in a central recess defined in a surface of a tool and an intermediate portion of the first cover layer in a perimeter recess defined around the central recess with the central recess being typically deeper than the perimeter recess. In addition, a peripheral portion of the first cover layer extends beyond the perimeter recess and over the surface of the tool. A moisture absorbent material is placed within the central recess. A second cover layer is positioned over the first cover layer so that the second cover layer is in contact with the peripheral portion of the first cover layer. At least one of the first and second cover layers includes a porous sheet material. A seal is then formed between the second cover layer and the peripheral portion of the first cover layer to form the pouch assembly.

Another embodiment includes a pouch assembly having a porous hydrophobic pouch and moisture absorbent material that is disposed in the pouch and is capable of absorbing water to form a gel, liquid, or slurry within the pouch. The hydrophobicity of the pouch helps to prevent or reduce leakage from the pouch. The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures and the detailed description which follow more particularly exemplify these embodiments.

Brief Description of the Drawings

The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

Figure 1 is a schematic cross-sectional view of one example of a pouch assembly according to the invention; Figure 2A is a perspective view of a first tool for use in one method of forming the pouch assembly of Figure 1 according to the invention;

Figure 2B is a cross-sectional view of the first tool of Figure 2 A; Figure 2C is a perspective view of a second tool for use in one method of forming the pouch assembly of Figure 1 according to the invention;

Figure 2D is a cross-sectional view of the second tool of Figure 2C; Figure 3 A is a schematic cross-sectional view of a second example of a pouch assembly according to the invention;

Figure 3B is a schematic cross-sectional view of the pouch assembly of Figure 3 A showing an expanded internal volume according to the invention;

Figure 4A is a perspective view of one tool for use in one method of forming the pouch assembly of Figure 3 A according to the invention;

Figure 4B is schematic side view of the tool of Figure 4A; Figure 5 is a schematic cross-sectional view of another tool for use in one method of forming the pouch assembly of Figure 3 A according to the invention; and Figure 6 is a schematic cross-sectional view of another pouch assembly, according to the invention.

While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Detailed Description of the Illustrated Embodiments The present invention is believed to be applicable to devices for the regulation of the level of moisture in the air. In particular, the present invention is directed to a pouch assembly containing a moisture absorbent material for controlling the level of moisture, especially within confined spaces. Although the terms "absorbent material", "absorb", "absorption", and the like are used, it will be understood that both absorbent and adsorbent processes and materials are included within the scope of these terms. While the present invention is not so limited, an appreciation of various aspects of the invention will be gained through a discussion of the examples provided below.

"Relative humidity" is defined as:

Relative humidity (%) = 100p/p₀

where p is the vapor pressure of water in the air and p₀ is the saturated vapor pressure of water in air at a temperature, T.

In general, a pouch assembly for the control of moisture content in a confined space includes a moisture absorbent material within a porous pouch. In at least some instances, the porous pouch is formed using a porous hydrophobic material to permit flow of water vapor through the material and to reduce or prevent the possibility of leakage from the pouch. For a number of moisture absorbent materials, including many hygroscopic salts, the material may absorb sufficient water to produce a gel, liquid, or slurry within the pouch and/or the material may be disposed within the pouch as a gel, liquid or slurry. Using a hydrophobic pouch material or a pouch having a larger internal volume or expandable internal volume may facilitate containing the moisture absorbent material.

In addition, because the moisture absorbent material may increase in volume with the absorption of moisture, the pouch may, at least in some instances, be prepared to provide additional internal volume to accommodate the increased volume of the moisture absorbent material. The pouch may, for example, include the additional internal volume when manufactured or the pouch may be expandable. If the pouch is expandable, the pouch is typically configured so that one or more opposing regions of the pouch can unfold or separate from each other to provide additional internal volume. This may reduce or prevent the stretching of the pouch material and/or reduce an internal pressure on the membrane caused by the moisture absorbent material which could result in tears in the pouch assembly.

One example of a pouch assembly 100 of the invention includes a first cover layer 102, a second cover layer 104, and a moisture absorbent material 106 between the first and second cover layers, as illustrated in Figure 1. The first and second cover layers 102, 104 are coupled together by a peripheral seal 110 to define an internal volume 108 within which the moisture absorbent material 106 is disposed.

The first and second cover layers 102, 104 are typically formed using a sheet material. At least one, and in many cases, both, of the first and second cover layers 102, 104 are formed using porous sheet material. Although the illustrated embodiment shows the second cover layer as a flat sheet, both the first and second cover layers may be formed in more complex shapes (see, e.g., first cover layer 102) that provide space for the moisture absorbent material. Examples of porous sheet materials include porous polymers, such as, for example, porous or microporous polyethylene, polypropylene, nylon, polycarbonate, polyester, polyvinyl chloride, polytetrafluoroethylene (PTFE), or expanded polytetrafluoroethylene. A variety of known polymer films can be used as non-porous sheet material if one of the first and second covers layers 102, 104 is non-porous. The first and second cover layers 102, 104 can be formed of the same or different materials. In some instances, the first and second cover layers 102, 104 are initially formed from the same sheet material which can be folded over to form the two layers.

The first and second cover layer 102, 104 may also include a scrim or support layer to provide support and/or protect the sheet material. The scrim or support layer may be a woven or non-woven film made from, for example, stretched or sintered plastics, such as polyesters, polycarbonate, polypropylene, polyethylene, and polyamides (e.g., nylon).

The thickness of the first and second cover layers 102, 104 can be the same or different and can be within the range of, for example, 25 to 1000 μm, although thinner or thicker layers 102, 104 may also be used. The thickness of the cover layers 102, 104 may depend on factors such as, for example, the porosity of the cover layers 102, 104, the strength of the material, the expected amount of expansion by the absorbent material, the amount of additional internal volume that can be or is provided in the pouch assembly 100, and the desired rate of diffusion through the pouch assembly 100. The peripheral seal 110 between the first and second porous layers 102, 104 can be formed by a variety of methods. For example, the peripheral seal 110 can be formed by heat sealing, ultrasonic welding, and/or adhering the two layers using an adhesive (e.g., a layer of adhesive or a double-sided adhesive tape).

The moisture absorbent material 106 can include, for example, a hygroscopic salt, a combination of such salts, or polymer beads. Examples of suitable hygroscopic salts include, for example, potassium carbonate, magnesium nitrate hexahydrate, magnesium sulfate heptahydrate, and the sodium salt of polyacrylic acid. Other examples are provided in the CRC Handbook of Chemistry and Physics, 59th Ed., Weast, Ed., E-46 (1978) and CRC Handbook of Chemistry and Physics, 77th Ed., Lide, Ed., 15-25 (1996), incorporated herein by reference. Typically, the choice of materials or combination of materials determines the level of moisture (e.g., relative humidity) within the confined space in which the pouch assembly is placed. The amount of material needed to maintain the level of moisture in the confined space depends on factors, such as, for example, the size of the space, the expected range of relative humidity, the temperature of the pouch assembly, and the presence of other moisture absorbent materials and desiccants.

The moisture absorbent material 106 may be formed as, for example, a tablet, wafer, disc, cube, or other shape, although, in some instances, granular, particulate, or powder materials may be used or the moisture absorbent material may be dispersed or dissolved in a liquid and optionally allowed to dry within the pouch assembly before or after sealing the pouch assembly. A binder may optionally be used to hold the moisture absorbent material in a shape. A shaped moisture absorbent material may be formed by a variety of methods, including for example, molding, compression molding, or extrusion. The moisture absorbent material, particularly, a moisture absorbent polymer, may, in some cases, be formed as small beads.

The first and second porous layers 102, 104 define an internal volume 108 bounded by the peripheral seal 110 and containing the moisture absorbent material. In the illustrated embodiment, the internal volume 108 is larger than an initial volume of the moisture absorbent material 106. The initial volume of the moisture absorbent material 106 is defined as the volume of the material 106 when placed within the pouch assembly. Typically, when the pouch assembly 100 is formed, the moisture absorbent material 106 is deposited in the pouch assembly 100 with less water absorbed within the moisture absorbent material than would be expected under normal operating conditions. The moisture absorbent material 106 typically increases in volume as moisture is absorbed. The internal volume 108 of the pouch assembly 100 is larger than the initial volume of the moisture absorbent material 106 to accommodate the increase in volume of the moisture absorbent material. The internal volume 108 of the pouch assembly may be at least 10%, 25%, 50%, 100%, greater than the initial volume of the moisture absorbent material. One advantage of providing this additional internal volume in the pouch assembly is that the moisture absorbent material may increase in volume with reduced stretching or, in some instances, little or no stretching of the cover layers 102, 104. This typically reduces the likelihood of tearing the cover layers 102, 104 which could result in particulate and/or liquid contamination or leakage by the moisture absorbent material resulting, for example, in a loss of performance of the pouch assembly and/or other materials or devices proximate to the pouch assembly.

The pouch assembly 100 can be formed by a variety of methods. For example, the pouch assembly can be prepared by providing first and second cover layers 102, 104 of appropriate sizes (e.g., the first cover layer being larger than the second cover layer), placing the moisture absorbent material 106 on the second cover layer 104, covering the moisture absorbent material with the first cover layer 102, and forming a peripheral seal 110 between the first and second cover layers 102, 104 with the internal volume of the pouch assembly being larger than the initial volume of the moisture absorbent material. Figures 2A through 2D illustrate two tools for use in another method of forming the pouch assembly 100. The first tool 150, illustrated in Figures 2A and 2B, has a recess 152 defined in a surface 154 of the tool 150 and an optional projection 156 around the perimeter of the recess 152 and extending from the surface 154. A second tool 160, illustrated in Figures 2C and 2D, has a projection 162 that is sized to fit within the recess 152 of the first tool 150. The first and second tools 150, 160 may be formed of plastic or metal. In particular, the first tool 150 may be formed of metal and used to support the pouch assembly during heat sealing or ultrasonic welding.

In operation, a first cover layer 102 is disposed on the first tool 150. In some instances, a portion of the first cover layer 102 may be placed within the recess 152 of the first tool 150. The second tool 160 is placed over the first cover layer 102 and the projection 162 is inserted into the recess 152 of the first tool to guide the first cover layer 102 into the shape of the recess 152. The second tool 160 is removed and the moisture absorbent material 106 (e.g., a tablet of the material) is deposited in the recess 152 on the first cover layer 102. Typically, the moisture absorbent material 106 is smaller in volume than the recess 152 and does not extend out of the recess 152. The second cover layer 104 is placed over the first cover layer 102 and moisture absorbent material 106. A peripheral seal 110 is then formed between the first and second cover layers 102, 104 by, for example, contacting the first and second cover layers with a heat sealing or ultrasonic welding device (not shown). Optionally, a cutting device may be used to size the pouch assembly 100 to the desired dimensions. The projection 156 may be useful to define a region of the first and second cover layers in which the perimeter seal can be formed by providing a surface against which a heat sealing or ultrasonic device can be rested.

Another example of a suitable pouch assembly 200 is illustrated in Figures 3 A and 3B. The pouch assembly 200 includes a first cover layer 202, a second cover layer 204, and moisture absorbent material 206. The first and second cover layers 202, 204 and the moisture absorbent material 206 can be formed using the same materials, shapes, and thicknesses as described with respect to pouch assembly 100. The pouch assembly 200 is initially formed with a central region 207 that contains the moisture absorbent material 206. Surrounding the central region 207 is an intermediate region 212 where the first and second cover layers 202, 204 are typically proximate to each other, but not completely sealed together. The pouch assembly 200 may have a single intermediate region 212 or the pouch assembly may have two or more intermediate region formed concentrically around the central region. In some instances, the intermediate region 212 may include a portion in which the first and second cover layers 202, 204 are separated, but not yet fully extended. In other instances, the first and second cover layers 202, 204 are proximate to each other but slightly separated in the intermediate region 212. In yet other instances, the first and second cover layers 202, 204 may be initially adhered together in the intermediate region 212 and then separate when the internal volume expands. Typically, the adherence of the first and second layers 202, 204 is significantly less in the intermediate region 212, than along the peripheral seal 210. For example, the first and second layer 202, 204 may be lightly welded, partially welded, or adhered using an adhesive in the intermediate region 212. A peripheral seal 210 between the first and second cover layers 202, 204 is formed around the periphery of the pouch assembly 200 to hold the moisture absorbent material 206 within the pouch assembly. The peripheral seal 210 can be made by a variety of methods including, for example, heat sealing, ultrasonic welding, or adhering the first and second cover layers 202, 204 together with an adhesive.

The pouch assembly 200 defines an initial pouch volume primarily in the central region 207 of the pouch assembly. This initial pouch volume is typically at least as large as the initial volume of the moisture absorbent material 206 and may be larger by 10%, 25%, 50%, 100%, or more than the initial volume of the moisture absorbent material 206.

As the moisture absorbent material 206 expands, the portions of the first and/or second cover layers 202, 204 in the intermediate region 212 separate to increase the internal volume 208 of the pouch assembly 200, as shown in Figure 3B. In some instances, prior to or in addition to the expansion of the moisture absorbent material 206, the first and/or second cover layers 202, 204 may be partially or fully separated by, for example, blowing gas into the internal volume 208. The separation of the first and/or second cover layers 202, 204 in the intermediate region 212 to increase the volume of the pouch assembly 200 permits the expansion of the moisture absorbent material 206, in at least some cases, with reduced stretching or little or no stretching of the first and/or second cover layers 202, 204. This prevents or reduces the likelihood of the pouch assembly 200 tearing. In addition, this may reduce particulate and/or liquid contamination or leakage by the moisture absorbent material resulting in a loss of performance of the pouch assembly and/or other materials or devices proximate to the pouch assembly. The expanded volume of the pouch assembly 200 is typically at least 10%, 25%, 50%, 100% larger than the initial volume of the moisture absorbent material 200.

The pouch assembly 200 can be made using the methods described above for making pouch assembly 100. Another method includes using a tool 250, one example of which is illustrated in Figures 4A and 4B, to make the pouch assembly 200. The tool 250 includes a tool body 252 having a surface 254 that defines a central recess 256 and two perimeter recesses 258, 260 concentrically formed around the central recess 256.

The tool body 252 is typically formed of metal. The central recess 256 is typically sized to contain the moisture absorbent material 206 and to form the central region 207 of the pouch assembly 200. The perimeter recesses 258, 260 are typically shallower than the central recess 256 and are provided to form the intermediate regions 212 in the pouch assembly 200. Typically, each perimeter recess is shallower than any other perimeter recess(es) nearer the central recess 256. The tool 250 optionally includes a port 262 in the central recess 256 and/or the perimeter recesses 258, 260 for applying a negative pressure differential to facilitate drawing the first cover layer 202 into one or more of the recesses 256, 258, 260. The pressure differential is typically provided via an access port 264 that is connected to the one or more ports 262 in the recesses 256, 258, 260 by a conduit 266. The negative pressure differential can be applied by a variety of methods including coupling a vacuum pump or other vacuum generator to the access port 264.

In operation, a first cover layer 202 is disposed over the tool 250 and directed into the central recess 256 and the perimeter recesses 258, 260 by, for example, applying a negative pressure differential through the ports 262 and/or pushing the layer 202 into the recesses 256, 258, 260 using, for example, the moisture absorbent material 206 or a tool similar to the second tool 160 (formed with an appropriate shape) illustrated in Figures 2C and 2D. The moisture absorbent material 206 is then placed onto the second cover layer 204 and aligned to go into the central recess 256. The perimeter seal 210 can then be formed using, for example, an ultrasonic welding or heat sealing technique.

An alternative tool 350 is illustrated in Figure 5. This tool 350 includes a tool body 352, a central recess 356 defined in a surface 354, one perimeter recess 358 around the central recess 356, and ports 362, an access port 364, and conduits 366 for applying a negative pressure differential to facilitate placement of the first cover layer within the recesses 356, 358. Other tools can be formed that, for example, include three or more perimeter recesses or that do not include ports, an access port, and conduits for applying a negative pressure differential.

Another example of a suitable pouch assembly 300 is illustrated in Figure 6. The pouch assembly 300 includes a first cover layer 302, a second cover layer 304, and a moisture absorbent material 306 that is capable of absorbing sufficient moisture to form a gel, liquid, or slurry. The first and second cover layers 302, 304 are coupled together by a peripheral seal 310 to define an internal volume 308 within which the moisture absorbent material 306 is disposed.

The first and second cover layers 302, 304 are typically formed using a hydrophobic sheet material. At least one, and in many cases, both, of the first and second cover layers 302, 304 are formed using porous hydrophobic sheet material. Examples of porous hydrophobic sheet materials include porous polymer films made from polymers, such as, for example, high-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, polyvinylidene fluoride, Nylon 6™, polyethersulfone, polytetrafluoroethylene or expanded polytetrafluoroethylene. [Others?] The first and second cover layers 302, 304 can be formed with the same or different materials. The first and second cover layers 302, 304 surround the moisture absorbent material 306 to form a hydrophobic polymer barrier. The thicknesses of the first and second cover layers 302, 304, as well as methods of forming the peripheral seal, are the same as those described for the pouch assembly 100. The moisture absorbent material 306 can include, for example, a hygroscopic salt, a combination of such salts, or polymer beads any of which are capable of absorbing sufficient moisture to form a gel, liquid, or slurry within the pouch assembly. The use of a hydrophobic polymer film for the pouch assembly 300 helps to prevent any leakage of the gel, liquid, or slurry into the environment. The moisture absorbent material 306 may be formed in any of the shapes and manners as described for the moisture absorbent material at 106 of pouch assembly 100. The internal volume 308 of the pouch assembly 300 is not necessarily larger than the initial volume of the moisture absorbent material 306, nor does the internal volume 308 necessarily expand, although, in some instances, larger volume or expandable pouch assemblies may be used. In some cases, the moisture absorbent material 306, although absorbing water, does not expand sufficiently beyond its initial volume to tear the pouch assembly 300. In these and other cases, it may be sufficient to provide a hydrophobic polymer material around the moisture absorbent material 306.

Examples

A first example of a pouch assembly is similar to the pouch assembly 100 illustrated in Figure 1. The pouch assembly can include first and second cover layers formed using 250 μm thick expanded polytetrafluoroethylene (Product No. 1109, Tetratec, Philadelphia, PA) with a 300 μm polypropylene scrim. The cover layers can form a pouch that is approximately 2.7 cm x 2.7 cm x 0.6 cm with a perimeter seal that extends inward about 0.02 cm from each side of the pouch. The perimeter seal is formed by ultrasonic welding and typically has a peel strength greater than the tensile strength of the first and second cover layers as determined by TAPPI #T-404-OM-87. The moisture absorbent material is a salt tablet containing ACS reagent grade magnesium nitrate hexahydrate. The moisture absorbent tablet can be approximately 1.5 cm x 1.5 cm x 0.5 cm. This pouch assembly is typically capable of maintaining a relative humidity of about 50 to 55 % in a 3.8 liter vapor barrier container at 24.5°C.

This first example of a pouch assembly can be formed using a first tool as illustrated in Figures 2 A and 2B and a second tool as illustrated in Figures 2C and 2D. The first tool can be formed of aluminum and is approximately 7.5 cm x 7.5 cm x 0.9 cm with a central recess that is about 2.3 cm x 2.3 cm x 0.6 cm and a perimeter projection that extends about 0.1 cm above the surface of the first tool. The second tool can be formed of polycarbonate and is approximately 7.5 cm x 7.5 cm x 0.5 cm with a central projection that is approximately 2.2 cm x 2.2 cm x 0.5 cm for fitting into the first tool. The first cover layer of the pouch assembly is placed in the first tool and the second tool is used to direct the first cover layer into the central recess of the first tool. The moisture absorbent tablet is placed into the central recess and the second cover layer is then placed over the tablet and first cover layer. The first and second layers are then ultrasonically welded to form the pouch assembly. A second example of a pouch assembly is similar to the pouch assembly 200 illustrated in Figures 3 A and 3B. The pouch assembly can include first and second cover layers formed using 250 μm thick expanded polytetrafluoroethylene (Product No. 1109, Tetratec, Philadelphia, PA) with a 300 μm polypropylene scrim. The cover layers can form a pouch that was approximately 2.7 cm x 2.7 cm x 0.7 cm with a perimeter seal extending inward about 0.02 cm from each side of the pouch. The perimeter seal is formed by ultrasonic welding and typically has a peel strength greater than the tensile strength of the first and second cover layers as determine by TAPPI #T-404-OM-87. The moisture absorbent material can be a salt tablet containing ACS reagent grade magnesium nitrate hexahydrate. The moisture absorbent tablet is approximately 1.5 cm x 1.5 cm x 0.5 cm. This pouch assembly is typically capable of maintaining a relative humidity of about 50-55% at 24.5° at 24.5°C.

This second example of a pouch assembly can be formed using a titanium tool that included a central recess having dimensions of about 1.9 cm x 1.9 cm x 0.7 cm with a first perimeter recess extending outward about 0.3 cm from the central recess with a depth of about 0.13 cm and second perimeter recess extending outward about 0.15 cm from the first perimeter recess with a depth of about 0.08 cm. The tool can include a port in the central recess and optional ports in the first perimeter recess. The first cover layer is placed on the tool and drawn into the central recess and the first and second recesses by application of a negative pressure differential at the ports in the central recess and optionally in the first perimeter recess. The moisture absorbent tablet is placed onto the second cover layer and aligned to go into the central recess. The first and second cover layers are then ultrasonically welded to form the perimeter seal.

The present invention should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as fairly set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable will be readily apparent to those of skill in the art to which the present invention is directed upon review of the instant specification.

Claims

WE CLAIM:

1. An assembly comprising: a porous pouch; and moisture absorbent material disposed in the porous pouch and having an initial volume, wherein the moisture absorbent material expands from the initial volume upon absorbing water and the pouch is configured and arranged to provide an internal volume that contains the moisture absorbent material after expanding upon absorbing water.

2. The assembly of claim 1, wherein the internal volume of the porous pouch is at least 10% greater than the initial volume of the moisture absorbent material.

3. The assembly of claim 1, wherein the internal volume of the porous pouch is at least 25% greater than the initial volume of the moisture absorbent material.

4. The assembly of claim 1 , wherein the porous pouch comprises an initial internal volume that is at least 10% greater than the initial volume of the moisture absorbent material.

5. The assembly of claim 1 , wherein the porous pouch comprises an initial internal volume that is at least 25% greater than the initial volume of the moisture absorbent material.

6. The assembly of claim 1, wherein the porous pouch is configured and arranged to expand and accommodate the moisture absorbent material as the moisture absorbent material expands.

7. The assembly of claim 1, wherein the porous pouch is formed from a porous pouch material and the pouch is configured and arranged to expand at least 10%) from an initial internal volume without substantial stretching of the porous pouch material.

8. The assembly of claim 1, wherein the porous pouch comprises a first cover layer and a second cover layer sealed to the first cover layer around a peripheral region of the first cover layer, wherein at least one of the first and second cover layers comprises a porous sheet material and the internal volume of the porous pouch is defined between the first cover layer and the second cover layer.

9. The assembly of claim 8, wherein both the first and second cover layers comprise a porous sheet material.

10. The assembly of claim 8, wherein the moisture absorbent material is disposed in a central region of the internal volume of the porous pouch and the first cover layer is at least partially disposed proximate to the second cover layer in an intermediate region between the central region and the peripheral region, wherein the first cover layer and second cover layer in the intermediate region are configured and arranged to separate when the moisture absorbent material expands.

11. The assembly of claim 10, wherein both the first and second cover layers comprise a porous sheet material.

12. The assembly of claim 1 , wherein the moisture absorbent material comprises at least one hygroscopic salt.

13. A pouch assembly comprising: a moisture absorbent material having an initial volume, wherein the moisture absorbent material expands beyond the initial volume as moisture is absorbed; a first porous cover layer; and a second porous cover layer sealed to the first porous cover layer at a peripheral region of the first and second porous cover layers, the first and second porous cover layers defining a central region between the first and second porous cover layers for containing the moisture absorbent material, the first and second porous cover layers also defining an intermediate region between the central region and the peripheral region, wherein the first and second porous cover layers are initially at least partially disposed proximate to each other and are configured and arranged to separate as the moisture absorbent material expands and provide an internal volume for the pouch assembly that is greater than a volume of the moisture absorbent material.

14. A method of making a pouch assembly containing a moisture absorbent material, comprising: receiving a central portion of a first cover layer in a central recess defined in a surface of a tool; receiving an intermediate portion of the first cover layer in a perimeter recess defined around the central recess, wherein the central recess is deeper than the perimeter recess and a peripheral portion of the first cover layer extends beyond the perimeter recess and over the surface of the tool; placing a moisture absorbent material within the central recess; positioning a second cover layer so that the second cover layer is in contact with the peripheral portion of the first cover layer and the moisture absorbent material is between the first and second cover layers, at least one of the first and second cover layers comprising a porous sheet material; and forming a seal between the second cover layer and the peripheral portion of the first cover layer.

15. The method of claim 14, wherein both the first and second cover layers comprise a porous sheet material.

16. The method of claim 14, wherein receiving a central portion of a first cover layer comprises applying a negative pressure differential to a port in the central recess to draw the central portion of the first cover layer into the central recess.

17. The method of claim 14, wherein receiving an intermediate portion of the first cover layer comprises receiving an intermediate portion of the first cover layer into at least two perimeter recesses formed concentrically around the central recess, wherein each perimeter recess is shallower than any other perimeter recess nearer the central recess.

18. An assembly comprising: a porous hydrophobic pouch; and moisture absorbent material sealed within the porous hydrophobic pouch, wherein the moisture absorbent material can absorb moisture to produce a gel, liquid, or slurry within the porous hydrophobic pouch.

19. The assembly of claim 18, wherein the porous hydrophobic pouch comprises polytetrafluoroethylene.

20. The assembly of claim 18, wherein the moisture absorbent material comprises a hygroscopic salt.

21. The assembly of claim 18, wherein the porous hydrophobic pouch comprises a first cover layer and a second cover layer that define an internal volume within which the moisture absorbent material is disposed, wherein the first and second cover layers comprise hydrophobic sheet material.

22. The assembly of claim 21, wherein the first and second cover layers comprise polytetrafluoroethylene.

23. The assembly of claim 21, wherein the internal volume of the porous hydrophobic pouch is greater than an initial volume of the moisture absorbent material.