US20120190259A1

US20120190259A1 - Evaporative cooling material

Info

Publication number: US20120190259A1
Application number: US12/931,115
Authority: US
Inventors: Douglas R. Frost
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-01-24
Filing date: 2011-01-24
Publication date: 2012-07-26

Abstract

Three-layer quilted textile material is suitable for evaporative cooling garments and articles. Superabsorbent layer is a non-woven felt; a blend of cellulose and polyacrylate fibers bonded together to form a non-linting fibrous core. Absorbent layer has inner and outer facings of nylon fabrics for controlled transpiration of water vapor without surface dampness. Cooling material requires immersion in water for one to two minutes and useful cooling time is five to ten hours.

Description

FIELD OF THE INVENTION

This invention relates generally to a sheet material for absorbing, holding, and releasing water and more specifically to sheet material optimized for the manufacture of evaporative cooling garments.

BACKGROUND OF THE INVENTION

The discovery that wearing water-soaked clothing cooled the wearer probably occurred shortly after clothing became standard for humans. While this can be a pleasing effect, for example when backpacking in hot dry weather, it has many drawbacks for every day use.
When outdoors in the sun or a dry breeze; even fully saturated clothing dries quickly. Pouring water over oneself every few minutes is not practical, except perhaps when walking along a clean brook. Saturated, clinging clothing may look all right during leisure activity, but is not appropriate for a nursery salesperson or policeman.
Much of the water in saturated clothing drips off, both wasting its cooling potential and inconveniencing the wearer by making it risky to handle papers or go indoors onto a nice floor. Soaking one's clothes repeatedly can also lead to skin irritation or infection, or foot blisters due to shoes made wet by dripping.
Thus, pouring a hatful of water over one's head remained an occasional childlike treat until the 1980s or 1990s, when certain classes of materials became available that showed potential for creating more civilized cooling garments. In the main, these were “superabsorbent” polymer particles (developed for agricultural use); re-useable, encased solid/liquid phase-change materials; and advanced synthetic fibers, such as highly branched polyester filaments and “microfibers”.
All three classes of material have been employed in the construction of cooling clothing, as well as more complex schemes with self-contained water supply, pumps, fans, or even Peltier thermoelectric devices.
Polymer particles have been the most popular evaporative cooling material, due to the relative simplicity and cheapness of manufacturing items that contain them. They are typically used to fill internal pockets or channels provided in garments, especially caps and neckerchiefs. The cap or neckerchief is soaked for up to an hour until the particles absorb many times their weight in water, allowed to drain a bit, then worn to provide a modest degree of cooling for an hour or two opinions differ on the length and quality of cooling these provide. Probably some of the disappointment people sometimes experience with these products is due to high ambient humidity slowing the evaporation such that the cooling is imperceptible, as well as the limited exposure to key thermal zones on the body.
Several attempts were made to fill larger garments such as vests or pants with superabsorbent polymer particles to provide a more effective cooling. There were several drawbacks with such garments. Most obviously, the particles swell greatly upon saturation with water. The pockets or channels into which the particles are inserted must be large enough to accommodate the swollen “gel” or they may rupture when the garment is soaked. Thus the garment is heavy and lumpy when moist; baggy and wrinkled when dry.
The dried particles of polymer are free-flowing and settle in the bottom of the generous pockets provided for them. Users are typically warned to monitor the garment while it is soaking and spread out the particles periodically so that they do not just fill and tear the bottom part of the pocket and so that the lumps in the garment are no more unsightly than necessary. While it may be easy enough to soak a bandanna in a bowl of water overnight, spending an hour leaning over the bathtub to help a work jacket puff up properly is not how many people want to start their day.
Another drawback of polymer particles is that they have little mechanical strength when hydrated. For this reason, users of clothing containing them are told to never wring or squeeze the soaked garment. If the wearer wishes to avoid having his shoes and pants soaked by dripping water, a vest or jacket must be left lying while excess water drains away. Once the garment is donned, though, mechanical damage is unavoidable as the wearer fastens a seatbelt and leans back in a vehicle seat, or carries a heavy object against his chest. The ruptured bits of gel dry to ever-smaller solid particles, which eventually filter through the fabric as dust.
A last drawback of using superabsorbent particles to make cooling garments or blankets is the diffusion rate. The dry particles are typically one to three millimeters across for ease of handling and to allow for the inevitable breakage. The surface area of particle is small compared to its volume, in both its dry and hydrated states. This is what makes it necessary to soak even a narrow neckerchief for an hour to fully hydrate the polymer particles. Conversely, the water is even slower to diffuse back out from the hydrated particle as cooling vapor. This is why some people find that their neck warms the neckerchief faster than evaporation cools it, especially in humid, still air.
After all, the main motivation for developing superabsorbent polymers was to retain and immobilize liquids, whether in agricultural soil, in a disposable diaper, or in a wound dressing. Constant, free evaporation from the particle surface was not an intended goal, even if it were achievable. A problem this leads to when polymer particles are included in a garment or other non-disposable article is that the article often does not dry out fully during one day's use. Not only does this represent lost opportunity for cooling, it leads to mildewing or other degradation of the article.
There is great need and demand for cooling garments, for comfort and health as well as for improved productivity and performance. One factor driving the search for improved evaporative cooling materials is the continuing presence of American and European soldiers in regions with weather that is far hotter than the soldiers are adapted for. Practical and effective cooling garments, blankets, and other articles could be vitally useful to these soldiers, as well as to others who often must work in hot conditions, such as firemen, police, utility linemen, and roofers.
Garments that are filled with loose particles of superabsorbent polymer clearly are not a sufficient solution to this need, due to the several disadvantages discussed above. Materials have been developed that attempt to mitigate some of the disadvantages by combining superabsorbent particles with fibrous materials, such as polyester fiber. The fibrous matrix is intended to hold the particles in place, either by actual attachment or simple entanglement. The absorbent particles used are typically granules of absorbent polymer as described above.
An example of this approach is the published application US2001/0027071 A1, now abandoned, of Bumbarger et al. The exemplary insulating and cooling material disclosed is composed of grains of polyacrylamide (one to two cubic millimeters in volume) embedded in fiberfill (i.e., non-woven polyester fiber) batting. Bumbarger et al. also suggest that polyester fibers may be mixed with “hydrophilic” fibers (composition not disclosed). The invention appears to have undergone a good deal of thought and testing to function as a material for high-end evaporative cooling garments intended for “firemen, law enforcement officers, military personnel . . . ” and others working in high heat, but drawbacks are still evident.
Because the “very tiny” grains of superabsorbent polymer are stabilized and protected by the fiberfill, the particle size is toward the smaller end of the typical distribution of particles conventionally used for filling small garments such as neckerchiefs. Bumbarger et al. do not need to start with large granules to allow for breakage, as discussed above. Also, because the grains are pre-distributed in the fiber matrix, it is not important to Bumbarger that large granules are easier to insert in chambers in the garment as it is sewn. Yet even using this smaller particle size, Bumbarger et al. note that care must be taken to allow sufficient expansion room within the garment to avoid rupture. Thus the garments illustrated in FIGS. 10 and 11 have a markedly bulbous appearance unless covered by a bullet- or fire-resistant shell.
A more serious drawback is that a Bumbarger garment must be soaked 15 to 25 minutes to achieve at least 50 per cent of total hydration of the grains. The Bumbarger reference does not treat this as a great problem; in fact, it is suggested that full hydration is not desirable in most cases, so as to leave capacity for absorption of perspiration.
Bumbarger et al. suggest that if the cooling garment may be needed in an emergency, it may be stored in pre-hydrated condition or else garments could be quick-soaked in heated water inside pressurized vessels. This attention to detail is laudable, but it is hard to imagine a long-distance cyclist prudently soaking a cooling jacket overnight in a plastic bag on the floor of her tent, or police officers lining up to use the pressure hydrator before going on patrol. Also, if the garment is worn or even potentially needed every day, it could never be allowed to dry out fully, thus would perhaps have to be stored in a refrigerator or saturated with antifungal solution instead of pure water so as not to become a health hazard due to mold.
It is also desirable that the stock material for evaporative cooling uses such as garments be easy and inexpensive to manufacture and easy to cut and sew. The manner in which Bumbarger et al. introduce the grains of polymer into the fiberfill batting is not taught, so it is impossible to evaluate if the manufacturing process is robust or cost-effective. It also seems likely that grains of polymer would spill out when the material is cut and handled, being a nuisance and possibly harming sewing machines or other delicate equipment.
Additionally, Bumbarger et al. suggest that the inner layer of textile that is disposed closest to the wearer's body be treated with a moisture barrier coating, such as BREATHE-TEX®. The importance of this coating to the invention may be deduced from the fact that claim 1 includes the limitation of “a coating impervious to liquids while allowing free passage of gasses therethrough”. Such coatings tend to be expensive and relatively fragile, subject to mechanical damage and environmental degradation. As reported by the International Association of Fire Fighters on Dec. 15, 1999, several manufacturers of fire fighting apparel with BREATHE-TEX® moisture barrier coating recalled garments due to degradation of the coating. Their Joint Statement on the issue quoted from a letter from the CEO of the company described as “the producer of the majority of the moisture barriers being used today” in which the CEO said: “investigations suggest that the garments may have been subject to attack resulting from storage conditions, length of service, care and/or maintenance. [The writer] also indicates there are a number of factors that may cause this degradation to occur over time.” One hopes that moisture barrier coatings have improved since then, but such a finicky coating, prone to damage from many poorly-understood sources, probably does not belong on a garment that is critical to the health of soldiers, police officers, and others unless there is no alternative at all.
Bumbarger et al. have addressed some of the problems associated with use of polymer particles in evaporative cooling material. The fibrous matrix supporting the particles reduces mechanical damage to the absorbent polymer, helps maintain the particles in place so that they don't have to be manually arranged as they swell, and allows use of smaller particles so that hydration time is possibly as short as 15 minutes (at ordinary room temperature and pressure). Using a smaller size distribution of particles probably also implies that evaporation of water from the particles is correspondingly faster than for conventional cooling neckerchiefs as have been used since the 1990s. Distributing the particles evenly throughout the fibrous matrix, instead of loading them into individual channels, probably makes the cooling effect more pleasant and “convincing” to the body, although the coverage is still somewhat spotty.
Cooling garments for extreme conditions have also been made using packets of solid/liquid phase change material, thermoelectric cooling, fans and air channels to speed evaporation of sweat, and cooling liquid replenished periodically or supplied continuously through a hose. All these approaches may have applications in which they are practical and make sense. However, the simplicity and reliability of garments cooled by evaporation of a modest amount of water, potable or not, with no requirement for electricity or other support, is desirable for use in emergencies and in remote or primitive conditions, such as desert camp.
Problems that still remain to be solved to achieve an optimal evaporative cooling material for producing fully practical and desirable cooling garments include: very short hydration time for convenience and response to emergencies, thinner and flatter material for better and less intrusive appearance and freedom of movement, and faster evaporation rate for consistent and effective cooling even in humid atmosphere. With specific regard to the Bumbarger et al. reference, such a material must be manufactured by a robust process and be reliable and durable even under hard use or severe conditions.

SUMMARY OF THE INVENTION

The present invention is a three-layer textile material that absorbs liquid water then releases water vapor freely to create evaporative cooling of 15 to 20 degrees F. below ambient. The material is thin, flat, and is easily cut and sewn, so it may be used for the entire construction of comfortable garments such as jackets or hats. The material is also useful for cooling blankets for people, food, or equipment; for miscellaneous articles such as beverage container holders; and for blankets, rest pads, and vests for animals such as dogs and horses.
The sheet material is composed of three layers that are attached together by patterned stitching. The central layer is a non-woven fibrous felt, or batting, that absorbs water readily and releases it as vapor over a useful period of time. The absorbent felt is typically a blend of three types of fiber: cellulose, a cross-linked polyacrylate co-polymer, and a polyolefin bonding fiber. The fiber blend is largely biodegradable.
The central fibrous layer is sandwiched between two sheets of conventional fabric, selected for suitable surface texture, tightness of weave, and durability. The fabrics are typically two different grades of woven nylon.
The cooling sheet material is thin and flat enough to be rolled into bolts for shipping and storage. Garments made from the sheet material are trim and smooth and are not much different in appearance from garments made from conventional fabrics. The sheet material is cut and sewn using industry-standard methods and equipment. No special surface finish or coating of the material is needed. Cutting the absorbent material does not release loose fibers, particles, or dust.
The cooling material, or an article made from it, is “activated” by immersing it in room temperature or cold water for one or two minutes to hydrate the middle absorbent fiber mat. The item can be squeezed to remove excess water and the surfaces can be wiped dry if desired. Evaporative cooling lasts for five to ten hours but varies depending on humidity, airflow and ambient temperature.
The problems associated with conventional cooling garments or accessories containing granulated superabsorbent resins, such as dripping, clamminess, powdery deposits on the skin or clothing, lumps and bulges, spotty cooling, and the long process of immersion and spreading of granules by hand are not experienced when using the novel laminated absorbent material. Except for two minutes of soaking, the cooling garments are nearly as convenient to wear and care for as traditional non-cooling garments.
The absorbent material is especially useful for creating cooling garments for active sports and work outdoors in hot weather. Garments made from the material are lightweight even when hydrated, soft and non-chafing, and are re-useable through an indefinite number of hydration cycles without loss of cooling power.
The invention will now be described in more particular detail with respect to the accompanying drawings in which like reference numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view, partly cut away, of the evaporative cooling sheet material of the present invention.

FIG. 2 is a cross-sectional view of the material of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a perspective view, partly cut away, of the evaporative cooling sheet material 10 of the present invention. FIG. 2 is a cross-sectional view of material 10 of FIG. 1. Sheet material 10 generally comprises three layers of different composition and function attached together to form a single sheet 10, as will be described fully below.
An inner barrier layer 12 is for contact with an item to be cooled, such as a person. It is typically a sheet of Taslan™ nylon 13, a smooth, shiny fabric that is inherently resistant to wind and water. Inner layer 12 protects the skin or clothing from dampness and provides a soft, draping surface for good thermal transfer between sheet material 10 and the person.
An outer transmission layer 14 is for being exposed to the atmosphere and allowing transmission of water vapor to pass. It is typically made from oxford nylon 15, a durable fabric with a coarser weave than Taslan™, often used for the outer shell of jackets. Oxford nylon 15 inherently allows free passage of water vapor and limited passage of liquid water, due to the size of the openings between threads.
Neither Taslan 13 nor oxford nylon 15 are treated with a surface finish, such as a moisture barrier coating. The ease with which liquid and gas passes through Taslan 13 and oxford nylon 15 is preferably controlled only by selection of fabrics of suitable thickness and thread count to provide the desired properties.
Absorbent middle layer 20 comprises a non-woven fibrous mat 22 that both wicks liquid water quickly and absorbs and retains water. It has been found that a blend of hydrophilic fibers, such as cellulose fibers 24, such as fibers derived from cotton or wood, with superabsorbent fibers such as a polyacrylate 25, provides a desirable balance of properties. Cellulose 24 provides rapid uptake of water into fibrous mat 22 then releases the water quickly, giving an immediate cooling effect. Cellulose 24 is very effective at transporting water by capillary action (as evidenced by tall trees) and spreads water throughout fibrous mat 22 without any need for manipulating sheet material 10 by swishing, squeezing, or massaging.
Polyacrylate 25 is not as efficient at wicking as cellulose 24, but it absorbs a far greater quantity of water and retains the water well. By holding water fairly tightly with hydrogen bonds, polyacrylate 25 prevents water from being drained out of fibrous mat 22 by gravity and releases water vapor at a steady rate over a period of hours. The polyacrylate 25 composition most preferred is a cross-linked co-polymer of acrylic acid, methylacrylate, and an acrylate/methylacrylate monomer wherein sodium acrylate is substituted for a portion of the acrylic acid. A suitable polyacrylate fiber 25 is produced by Technical Absorbents Limited of the United Kingdom under the name OASIS SAF®.
Water vapor transmission to the atmosphere and hence amount of cooling produced by sheet material 10 is fairly constant over time until the water is exhausted, although both amount and duration of cooling are influenced by the humidity, air temperature, and movement of air. The expected duration of cooling is five to ten hours.
Because absorbent fibers 23 are thin and elongate and have a high surface to volume ratio, the rate of diffusion into and out of fibers 23 is very rapid compared to the rate of diffusion for the one to three millimeter wide chunks of polyacrylamide or similar granular absorbent used in conventional 20th-century cooling neckerchiefs. Rapid diffusion results in activation time of two minutes instead of the conventional 30 minutes to an hour, as well as a stronger and longer-lasting cooling effect.
Non-woven mat 22 preferably also includes stabilizing means for holding the fibers together, such as a bonding fiber 26, such as a thermoplastic polyolefin fiber that is softened by heat to create an adhesive for binding the other fibers 23 into a felt-like mat 22.
The nominal preferred composition of fibers 23,26 to create non-woven mat 22 is 40 % polyacrylate 25, 30 % cellulose 24, and 30% bonding fiber. The fibers are bonded together to create a mat 22 that typically has a density of 120 grams per square meter.
Non-woven mat 22 is sandwiched between inner layer 12 and outer layer 14 and attached to them by suitable means as are well known, such as point bonding or stitching. Alternatively, bonding fiber 26 can be adapted to attach non-woven mat to layers 12, 14 or other adhesive means as known in the textile field may be used.
Garments made from sheet material 10 are very effective for cooling a person or animal under most conditions. If additional cooling power is needed, a garment made from sheet material 10 may also include auxiliary cooling devices, as have been noted above.
Although particular embodiments of the invention have been illustrated and described, various changes may be made in the form, composition, construction, and arrangement of the parts herein without sacrificing any of its advantages. Therefore, it is to be understood that all matter herein is to be interpreted as illustrative and not in any limiting sense, and it is intended to cover in the appended claims such modifications as come within the true spirit and scope of the invention.

Claims

1. Evaporative cooling material, including:

an outer water-vapor transmission layer for providing mechanical protection of said material without substantially hindering the evaporation of water or passage of water vapor;

an inner moisture barrier layer for providing a smooth inner surface and for blocking transmission of liquid water or vapor; and

a middle fibrous absorbent layer disposed between said outer and said inner layers, for absorbing applied water and releasing the water as vapor over a useful time period, thereby causing said inner barrier layer to be maintained at a temperature substantially cooler than ambient temperature; said fibrous absorbent layer created from a blend of suitable fibers bonded together by suitable bonding means such that said cooling material can be cut without shedding fibers or particles; said outer, inner, and absorbent layers being connected together by suitable connection means to provide stability of said material.

2. The evaporative cooling material of claim 1, said fibrous absorbent layer comprising:

a non-woven mat of cellulose and sodium acrylate co-polymer fibers blended in the ratio of approximately three parts cellulose to four parts acrylate.

3. The evaporative cooling material of claim 1, said fibrous absorbent layer further including:

a suitable bonding fiber for bonding together all fibers comprising said fibrous layer.

4. The evaporative cooling material of claim 1 wherein: said inner barrier layer blocks water and said outer transmission layer allows passage of liquid and vapor due to intrinsic properties of the materials selected, including suitable weave density and type, and suitable fiber composition

5. The evaporative cooling material of claim 4, said inner barrier layer being composed of Taslan™ nylon fabric and said outer transmission layer being composed of oxford nylon fabric.

6. The evaporative cooling material of claim 1, wherein the component goods are selected such that the evaporative cooling material has properties suitable for cutting, shaping, and sewing said material to create evaporative cooling garments