HK1128159B - Humidity control device - Google Patents

Description

Humidity control device

Technical Field

The present invention relates to humidity control devices, and more particularly to humidity control devices that may be used to confine an environment to maintain a desired level of humidity.

Background

Typically, deliquescent compounds, usually salts, have in the past often reduced relative humidity in closed environments. It is well known that different compounds have varying affinity for moisture. For example, each deliquescent compound, when hydrated, has a characteristic moisture sorption capacity and a characteristic Equilibrium Relative Humidity (ERH).

Desiccants may be considered humidifiers, where they are commonly used to completely (or nearly completely) remove all moisture from the air coming from a closed system. In a package, a sufficient amount of an effective desiccant will adsorb moisture from the air, lowering the Equilibrium Relative Humidity (ERH) to the point where condensation no longer occurs, or to the point where the threshold ERH within a sealed package or system never exceeds the conditions to which the package or system is exposed. In closed systems well below the dew point, large amounts of active desiccant will reduce moisture to the following levels: wherein the relative humidity of the system matches the ERH of the desiccant at the current hydration level.

However, there are applications (food, pharmaceutical, analytical, medical diagnostics, to name a few) where desiccants are not the best choice. In this case, the ERH of the product must be maintained at some specific intermediate level, rather than near zero. A common and economical method of controlling humidity in a humid environment is the use of humectant (humectant) compounds. Inorganic salts are the most effective and most commonly used, although many deliquescent or hydratable compounds may be used in the appropriate system. These compounds have an affinity for water, which regulates the water vapor pressure in the atmosphere within the closed container or chamber. In essence, these compounds will absorb moisture until they are completely in solution. When this occurs, a mixture of solid salt and salt solution will be present simultaneously. The solution will be saturated and will have the ERH characteristics of the particular salt or compound used.

In this case, the particular humectant is selected based on the desired Equilibrium Relative Humidity (ERH). The salt may be substantially single, such as lithium chloride. Mixtures of the two salts may also be used. For example, potassium carbonate solution has a relative humidity of about 43%. Thus, a solution of potassium carbonate containing an excess of insoluble potassium carbonate crystals will maintain a constant relative humidity of about 43%. If the relative humidity begins to increase above 43%, the salt solution will pick up moisture from the environment, thereby lowering the relative humidity to approximately 43%. Conversely, if the relative humidity begins to fall below 43%, the solution will release moisture until the humidity of the surrounding environment reaches about 43%. The ERH values of different saturated aqueous salt solutions may vary from 11% to 98%.

Other inventions for humidity control devices describe the inclusion of viscous solutions in fabric nonwoven polymer pouches. In this case, the viscous solution contains bound water, salt, and may contain a thickening agent (e.g., alginate or xanthan gum). In practice, these salt solutions are difficult to handle because they are liquids that can spill or permeate through the packaging or container in which they are contained. Since the stabilized saline solution may drip or wick from the package, it must necessarily be water vapor vented in order to function. The tendency for more dripping complicates the problem as the moisturizer absorbs moisture from its environment and becomes more fluid. If the moisture permeation rate of the film or pouch is too great, or if the surface energy or "wettability" is too great, for a fluid, even a thickened fluid, seepage can occur through the package. Obviously, this would have an adverse effect on the intended goal of protecting the product.

Summary of The Invention

The invention comprises a device for controlling the relative humidity in a closed or defined environment. The present invention includes a solidified humectant composition including a humectant salt, water, and a carrier. A preferred embodiment contains the composition in the form of a tablet, which may include the use of a binder different from the carrier. Preferred tablet form embodiments contain a durable coated tablet. Suitable coatings will include polyethylene or other thermoplastic resins, polytetrafluoroethylene, polyvinylpyrrolidone and cellulose ethers.

The present invention also provides a device for controlling the relative humidity in an enclosed environment or product packaging comprising a moisture vapor permeable container having a stabilized or solidified humectant composition stored therein. The solidified humectant composition comprises a humectant salt, water, and a carrier. Preferred container materials include thermoformed felt (felt) materials, sachets, moisture permeable canisters or plastics which may be sealed except for the "breather" hole or sealed with a breathable film or membrane. In a preferred embodiment, the small drug isThe bladder comprises a micro-perforated polyester/paper/polyethylene substance. Preferred humectant salts include CaCl₂、LiCl₂、K₂CO₃、NaCl、K₂SO₄And combinations thereof. A preferred embodiment of the invention comprises the use of an antimicrobial agent in the container.

The preferred embodiments described above will also include specific additional ingredients of the composition that can make the device multifunctional. Examples herein would include activated carbon and/or oxygen absorbers to control volatility.

Detailed Description

The present invention provides a generally solid moisturizer that eliminates the possibility of leakage, spillage or seepage of the moisturizer and the resulting damage to the product or substance that the moisturizer is designed to protect. The present invention provides a substance in solid form that is stable in a container that is independent or permeable to non-water vapor for controlling the relative humidity in a closed system, such that the product or substance retained within the package is protected and does not degrade, denature or spoil in any way.

This can be achieved by stabilizing or solidifying the humectant to provide a packaged humidity control device that is impermeable to water, solutions, or the humectant itself. The use of a solid humectant compound controls the enclosed environment at a desired humidity and below the dew point, and also prevents the possibility of condensation.

Another aspect of the present invention is to provide additional functionality to the solid state, humidity conditioning system. For example, a basic salt may function as a humectant, as well as neutralizing a volatile acid, which may be present in the package, or generated from the product in the package. It is understood that the salt may function to regulate humidity and buffer systems within the system, or to provide a reducing environment in which oxygen is scavenged from the closed system.

In an exemplary embodiment of the invention, the solidified form containing the humectant salt may also include an antimicrobial preservative which controls the growth of microorganisms within the humectant package. Further, by selecting an antimicrobial agent that is somewhat volatile and suitable for the container, compartment or package and its components, the entire closed system can be protected from microbial degradation.

Preferably, the humectant compound or salt solution according to the present invention is prepared as follows: at a predetermined dissolution temperature, the salt is slowly introduced into the particular salt by adding distilled water, with constant stirring. The appearance of the solution appeared to be "mud-like", reflecting the presence of undissolved excess salt crystals. Careful preparation of the salt solution is necessary because it requires precise attainment of the desired and intended humidity level.

Alternatively, a true solution can be prepared and solidified or infiltrated into the solid carrier phase and then partially dried to the point of supersaturation at which point the excess salt can be expected to precipitate out leaving a saturated solution containing the excess salt. The proportion of excess salt in the saturated solution will determine the moisture content which can be absorbed or released in a given system within the range of humidity in which it is effective. When the service environment is expected to have a higher humidity than the ERH of the moisturizer, it is expected that it may completely dry the saturated or solidified moisturizer to the maximum adsorption capacity.

Preferred embodiments of the present invention include an antimicrobial agent contained within the container. Preferably, the antimicrobial agent is added to the humectant salt solution. This is a preferred embodiment because microbial growth, most commonly mold, can be a factor in the degradation of many moist packaged products.

As mentioned above, the humectant salts of the present invention may be present in the form of a saturated solution. The solution is then coagulated (stabilized) by adding it to the support medium. The carrier may be cellulose, silica gel, clay, carbon, sugar or protein gelling agents, hydrophilic colloids such as carrageenan or alginate, gelatinous konjac (konjac), hydrophilic polymers such as acrylates or polyvinyl alcohol, or any other substance capable of stabilizing, coagulating, encapsulating or adsorbing a solid humectant. The humectant in solid form is then sealed in a suitable container according to the present invention and used in packaging that is not hazardous to the packaged components.

In a preferred embodiment of the invention, the packaged, hydrocolloid-solidified humectant is contained within a felt-like envelope, and the combination is placed in an enclosed environment that stores a moisture sensitive analytical reagent. The preferred monosalt is potassium sulfate, e.g., a potassium sulfate solution provides about 98% ERH (at a temperature of 20 ℃). In this case, the humectant acts as a moisture source while keeping the atmosphere within the sealed chamber from condensing. Similarly, packaging water/acrylate in a felt may provide a constant source of moisture. In the latter case, however, no salt is present to keep the relative humidity below the dew point inside the storage of the package, and therefore condensation may occur as the temperature changes.

As noted above, the solidified humectant may be contained within a water vapor permeable container to suit the sealed system package for which humidity control is desired. The container interface must have sufficient moisture permeability between the solidified humectant and the product and its environment within the package, and safely contain the solidified humectant. Typical containers may take the form of thermoformed felts, cans or perforated rigid or semi-rigid containers, or sachets made of micro-perforated polyester/paper/polyethylene structures or woven or non-woven materials.

In another preferred embodiment of the invention, the cured insulating agent may be formulated into a tablet comprising a suitable binder in the composition. In addition to the carrier described above, the adhesive may be a separate element. For example, the carrier may be a silicone gel and the binder may be any of a number of known binders, such as polyvinyl pyrrolidone, cellulose ether resins, thermoplastic polymers, or waxes. In addition, the binder may also function as a carrier if present in sufficient quantity to stabilize and solidify the humectant salt.

The tablet humectant can be used without further packaging, or it can be included. As mentioned above, it may be included or coated with a water vapor permeable coating for added durability (as compared to using only the tablet humectant). In the case where a coating is desired, the tablet may be coated with a suitable water vapour permeable coating. Suitably, these coatings will comprise a powdered polymer, such as polyethylene or polytetrafluoroethylene, which is dried or held in suspension and then heat cured. Alternatively, the tableted humectant may be resin coated, for example with polyvinyl pyrrolidone or a cellulose ether, and then subjected to a drying and curing step again.

The purpose of the tablet humectant may be to control humidity only, or it may be multifunctional, such as for the volatile acid absorbing tablet of example 6 below, which contains activated carbon and silica gel in addition to the warming salt. For example, if the salt is present with the silica gel and activated carbon, all of the binder, the humectant salt can neutralize harmful acids present in the environment, which are then adsorbed by the activated carbon.

Another example is shown in example 7, in which the following embodiment is illustrated: it contains carbon alone for adsorption of hydrocarbons or other Volatile Organic Compounds (VOCs), and humectant salts for humidity control.

This versatility may further be obtained by incorporating an oxygen absorber into the cured composition. In this case, the humectant/water/carrier/binder combination may include iron or ascorbic acid or other reducing compound. The selection of these ingredients can be made by one of ordinary skill in the art, without undue experimentation, in light of the teachings of this disclosure.

Examples

Example 1

The solidified humectant composition was prepared by adding 100 grams of distilled water to 20 grams of potassium sulfate with constant stirring. The mixture may be mixed with 15 grams of carrageenan. The mixture was found to have an ERH of 98%.

Example 2

The solidified humectant composition was prepared by adding 0.1 grams of ProClin 300 bactericide to 100 grams of distilled water (ProClin is a registered trademark of the preservative used by Rohm and Haas corporation in the preparation of biological, chemical, diagnostic and laboratory reagents). The solution was then introduced into 20 g of potassium sulfate, with constant stirring. This mixture was mixed with 15 grams of carrageenan. Finally, the mixture was found to have an ERH of 98%. The mixture may cause the gel encapsulated and sealed in the polyester felt to harden. The resulting structure can be deformed by hand pressure but cannot be made to leak with a large amount of manual work.

Example 3

The solidified humectant container was prepared by the following method: first 0.4 g of sodium propionate was added to 50 g of distilled water, and then the solution was introduced into 58 g of potassium carbonate with continuous stirring. The mixture was then mixed with macroporous silica gel in a ratio of 75: 25 (gel weight percent: solution weight percent). The resulting granulated solid humectant was encapsulated in a non-woven HDPE sachet. Finally, the mixture was found to have an ERH of about 44%.

In a wet environment, the humectant container will absorb 25% of its weight in water, and in a dry environment, will provide 10% of its weight in water. Within these limits, the relative humidity within the enclosed environment remains close to 44%.

Example 4

The solidified humectant container is prepared by respectively adding 1 part of 50% (w/w) CaCl₂Solution and 1 part of 50% (w/w) K₂CO₃The solution was prepared by adding two parts by weight of silica gel (u.s.p. grade). The solution was completely adsorbed within 24 hours and then dried to about 2% humidity. The entire dry granulated moisturizer was packaged in a tightly bound (welded) nonwoven sachet.

The humectant container was found to have an ERH of 18.1%, a moisture sorption capacity of 5.5% at 29% r.h., and an acid absorption capacity of at least 0.5 meq/g.

The product is effective in protecting and maintaining active chemiluminescent medical diagnostic devices during extended storage periods of 12 months.

Example 5

Saturated NaCl solution was infiltrated into an equal amount of macroporous silica gel. Solid ascorbic acid and sodium ascorbate were added as humectants each solidified at 1/3 weight. Iron powder, in an amount equal to the total amount of humectant and solid acid and salt, is then added and the combined granular and powdered mixture is packaged in a micro-perforated sachet.

The ERH of the solidified humectant was 56%. This relative humidity is maintained while oxygen is removed from the pharmaceutical package. The resulting atmosphere provides extended stability to the active pharmaceutical tablet.

Example 6

The potassium carbonate solution was added to the mixture of granular activated carbon and granular silica gel so that 2.5% potassium carbonate on a dry basis was present. A polyvinylpyrrolidone binder resin was added and after the mixture was partially dried to an optimum level of about 16% humidity, the mixture was compressed into tablet form. Heat curing the tablets rehydrated to about 25% ERH. Uncoated, tablets not contained within a closed chamber have the ability to adsorb moisture while maintaining the ERH below 44% in the chamber. The tablet also absorbs and neutralizes volatile acids, thereby protecting delicate electronic components that are also contained within the chamber. In this example, no coating was applied to the tablets.

Example 7

To increase the moisture adsorption and low humidity performance, tablets made of carbon can be impregnated with LiCl₂In solution and then dried. The tablets must be hard and therefore a PE binder is used which gives good strength.

The preparation method of the tablet comprises the following steps:

1. mixing of 142.6gms LiCl₂And 440gmsH₂O, mixing for 1 hour.

2. 1960gms of dry low activated carbon and 490gms of high activated carbon were added to the "V" blender.

3. The carbon was impregnated with the salt solution in a "V" blender for 4.0 minutes.

4. The carbon was dried in an oven at 110 ℃ for 16 hours.

5. The carbon was placed in a "V" blender and 457.5gms PE was added and mixed for 4 minutes.

6. Tabletting was carried out with a tablet press and cured at 110 ℃ for 1 hour.

7. The tablet formula comprises:

low active carbon 64.2%

16.1 percent of high-activity carbon

LiCl₂Salt 4.7% (5.5% on carbon)

PE binder 15.0%

As a result:

tablets were tested in a humidity chamber at 90% RH and 29 ℃ until full load (to capacity). The tablets contained 40% by weight of total tablet of H₂O, showing an uptake of 47% by mass of carbon.

Although the invention has been illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the spirit of the invention. It is therefore intended that the appended claims cover all such modifications as fall within the true spirit and scope of this present invention.

Claims (6)

1. An apparatus for controlling relative humidity in a closed system environment, comprising:

a water vapor permeable container; and

a solidified humectant composition within the container, the solidified humectant composition comprising:

a humectant salt, water, and a carrier, wherein the container is in the form of a sachet, wherein the sachet is comprised of a micro-perforated polyester/paper/polyethylene structure, and further comprising an antimicrobial agent in the container.

2. The device of claim 1, wherein the humectant salt is selected from CaCl₂、K₂CO₃、NaCl、K₂SO₄And combinations thereof.

3. The device of claim 1 wherein the carrier is selected from the group consisting of silica gel, clay, carbohydrate or protein gelling agents, aqueous colloidal gums, and hydrophilic polymers.

4. The device of claim 1, wherein the solidified humectant composition further comprises activated carbon.

5. The device of claim 1, wherein the solidified humectant composition further comprises an oxygen absorber.

6. The device of claim 1, wherein the carrier is cellulose.