Fabric coating containing energy absorbing phase change material and method of manufacturing same

[0002] This is a division of application Ser. No. 08/850,944 filed on May 5, 1997 now U.S. Pat. No. 6,207,738 which is a continuation application of prior application Ser. No. 08/259,964 filed on Jun. 14, 1994 abandoned.

[0003] This invention relates to substrate coatings containing energy absorbing, temperature stabilizing phase change materials and methods of manufacturing same. More particularly, this invention relates to fabric coatings containing microspheres of phase change material dispersed in a polymer binder and methods of manufacturing same.

[0004] Coatings are typically applied to fabrics to increase water resistance, water transport, insulative ability or heat storage properties of the fabrics. Recently, microencapsulated phase change materials have been described as a suitable component for fabric coatings when exceptional heat transfer and storage capabilities are desired. In particular, International Patent Application No. PCT/93/05119 for “Fabric with Reversible Enhanced Thermal Properties” to Colvin, et al., which is incorporated herein by reference, discloses that fabrics coated with a binder containing microcapsules filled with energy absorbing phase change material enables the fabric to exhibit extended or enhanced heat retention or storage properties.

[0005] Research has demonstrated that applying a binder containing microspheres of phase change materials with commercial coating equipment can be problematic. For example, use of solvent based gravure printing techniques in which a solvent system was employed to achieve uniform dispersion of the microspheres in a binder proved unsuccessful because the solvent systems damaged the microspheres.

[0006] Thermoplastic gravure printing techniques also proved unsatisfactory for use with microspheres of phase change material. When using higher temperature thermoplastic gravure printing techniques, sustained temperature of 325° F. caused severe damage to the microspheres. Although lower temperature thermoplastic gravure printing techniques avoided significant damage to the microspheres, the resulting coating was found lacking in washability and durability. Moreover, lower temperature thermoplastic gravure printing techniques precluded addition of the desired amounts of the microspheres, allowing addition of microspheres of up to only about 20% by dry weight of the microsphere/binder material. This low percentage of phase change material in the coating makes the coating susceptible to undesirable heat transfer across the coating, especially in locations where phase change material is sparsely applied.

[0007] Attempts to encapsulate microspheres of phase change materials in a thermoplastic spray have also proved unsatisfactory. In particular, scattering microspheres into a stream of sprayed, fibrous thermoplastic material resulted in a binder matrix that did not fully encase the microspheres. The resulting binder/microsphere material was susceptible to loss of microspheres, which worked loose and were continually shedded from the fabric. In addition, the coating lacked uniformity of thickness and microsphere distribution.

[0008] Attempts were also made to utilize thermoplastic extrusion techniques to create a film of continuous web in which microspheres of phase change material were uniformly distributed. However, thermal breakdown of the microspheres resulted from the higher temperatures utilized. The extrusion screw employed with these techniques also physically damaged the microspheres.

[0009] Phase change materials in microencapsulated form are commonly supplied as a dry powder. This powder is difficult to wet and uniformly disperse in aqueous systems. Moreover, some microencapsulated phase change materials have an internal layer of modified gelatin which is hydrophilic and capable of absorbing its own weight in water. Not only does the hydrophilic quality of such microcapsules make more standard component proportions inapplicable, microcapsules which have absorbed water tend to swell and associate, increasing the viscosity of the coating system above acceptable limits. Although the precise behavior of microcapsules in the coating system which have absorbed water is uncertain, it is believed that such microcapsules agglomerate, reducing their dispersion throughout the binder of the coating system, which de-stabilizes the binder. This de-stabilization can increase over time. When latex binders are used with microencapsulated phase change material, de-stabilization of the latex binder can continue until the latex binder coagulates.

[0010] U.S. Pat. Nos. 5,254,380, 5,211,949, 5,282,994 and 5,106,520 for “Dry Powder Mixes Comprising Phase Change Materials” describe free flowing, conformable powder-like mixes of silica particles and a phase change material which the silica particles of between 7×10⁻³to 7×10⁻²microns are mixed with phase change material in a ratio of up to 80% by weight of phase change material. While these patents describe a matrix in which microspheres of phase change materials need not be separately encapsulated, they do not describe the use of dry powder mixes containing phase change materials in binder matrices for coating fabrics.

[0011] It is against this background that the significant improvements and advancement of the present invention have taken place in the field of fabric coatings containing energy absorbing, temperature stabilizing phase change materials and methods of manufacturing same.

[0012] It is the principal object of the present invention to provide an improved fabric coating composition containing phase change material of a density sufficient to effect or control heat and energy transfer across the coating and/or store heat in the coating.

[0013] It is another object of the present invention to provide a coating composition of the foregoing character which will maintain substantially all of the breathability, flexibility or other principal qualities of the fabric to which it is applied.

[0014] It is a further object of the present invention to provide coated fabrics having the aforementioned properties which are resistant to heat, pressure and chemicals encountered during the coating process.

[0015] It is a still further object of the present invention to provide coated fabrics having the aforementioned qualities which are durable, resistant to heat, moisture, solvents, laundering, and/or drycleaning, without degradation to or loss of the phase change material.

[0016] It is still another object of the present invention to provide an improved method of applying coating compositions containing phase change materials and having the aforementioned qualities as coatings on fabrics by utilizing commercially available equipment.

[0017] It is yet another object of the present invention to provide an improved method of applying coatings containing phase change materials to fabrics without damage or degradation to the phase change materials.

[0018] It is still another object of the present invention to provide an improved method for evenly dispersing phase change material throughout a binder and maintaining an even distribution of the phase change material while coating a fabric with the binder and phase change material dispersion.

[0019] The present invention comprises coatings for fabrics and methods for manufacturing the same. A preferred coating includes wetted microspheres containing a phase change material dispersed throughout a polymer latex binder, and including a surfactant, a dispersant, an antifoam agent and a thickener. Preferred phase change materials include paraffinic hydrocarbons. To prepare a preferred coating composition of the present invention, microspheres containing phase change material are dispersed in an aqueous solution of a surfactant, a dispersant, and an antifoam agent mixture, followed by dispersion in a polymer mixture to form a coating composition. An alternative method of preparing the coating composition of the present invention includes dispersing microspheres containing phase change material in wet cake form in an aqueous solution of a surfactant, a dispersant, antifoam agent and polymer to form a coating composition. The coating composition of the present invention are then applied as a coating on a fabric.

[0020] In accordance with the present application, it has been discovered that wetting microspheres of phase change materials with water and maintaining a uniform dispersion of the microcapsules in a wet coating minimizes or eliminates the tendency of such microspheres to destabilize the binder polymer in which the microspheres are dispersed.

[0021] A coating composition which includes microspheres containing a phase change material is prepared by mixing dry microspheres with an excess of water to induce the microspheres to swell with water until swelling is complete. Preferably, a surfactant and a dispersant are added to the water prior to mixing with the microspheres. The surfactant decreases surface tension of the layers of the microspheres and thereby promotes wetting of the microspheres. An antifoam agent is added to and mixed slowly with the microsphere/water mixture to remove air trapped as dispersed bubbles in the mixture. A thickener is added to adjust the viscosity of the mixture to prevent the microspheres from floating or sinking in the mixture. A viscosity of at least 500 cps is preferred. Adjusting the pH of the mixture to 8.5 or greater promotes swelling of the microspheres. Swelling is typically complete in from 6 to 24 hours, at which time the microspheres will have reached an equilibrium with the aqueous phase in which they are dispersed. Thereafter, the microsphere dispersion is added to a mixture of a polymer dispersion, surfactant and dispersant having a pH approximately the same as the pH of the microsphere dispersion. The viscosity and rheology of the resulting coating compound is adjusted to meet the requirements of the coating method employed.

[0022] The polymeric binder may be in the form of a solution, dispersion or emulsion in water or in organic solvent. The polymeric binder may initially be polymeric, or in the form of monomers and/or oligomers, or low molecular weight polymers which upon drying and/or curing are converted to their final molecular weight and structure. These binders are preferably film-forming, elastomeric, and have a glass transition temperature in the range of about −45° C. to +45° C., depending upon the desired application. For most garment applications, an elastomeric polymer with a glass transition temperature of about −30° C. to about +12° C. is preferred.

[0023] The polymers may be linear or branched. Copolymers may be random, block or radial. The polymers may have pendant reactive groups, reactive ends or other crosslinking mechanisms, or be capable of entanglement and/or hydrogen bonding in order to increase the toughness of the finished coating and/or its resistance to heat, moisture, solvents, laundering, dry-cleaning or other chemicals.

[0024] Suitable monomers include, but are not limited to, acrylic eaters (preferably alkylacrylates and methacrylates containing 4 to 17 carbon atoms); styrene; isoprene; acrylonitrile; butadiene; vinyl acetate; vinyl chloride; vinyldiene chloride; ethylene; butylene; propylene; chloroprene; etc. Polymers and copolymers based upon the above mentioned monomers and/or upon silicone; epoxy; polyurethane; fluorocarbons; chlorosulfonated polyethylene; chlorinated polyethylene; and other halogenated polyolefins are also useful.

[0025] The surfactant described above has a preferred wetting time of not greater than 50 seconds at a concentration of 0.10 % by the Draves Wetting Test. Nonionic and anionic surfactants are acceptable. Dioctyl sodium sulfosuccinamate (sometimes referred to herein as “DOS”) is a preferred surfactant.

[0026] The dispersing agent employed as described above is preferably a nonionic or anionic dispersant, such as dispersants based upon phosphate esters. A 90% solution of the potassium salt of a phosphated coester of an alcohol and an aliphatic ethoxylate such as Strodex PK907 available from Dexter Chemical Company of New York City, N.Y. is a preferred dispersant.

[0027] From 0.1% to 0.8% by weight of dry DOS to dry microspheres and from 0.1% to 0.8% by weight of dry PK90™ to dry microspheres is effective. The total amount of DOS and PK90™ is preferably apportioned equally between the dry microsphere dispersion and the polymer dispersion to which the microspheres will be added after swelling is complete.

[0028] Suitable thickeners include polyacrylic acid, cellulose esters and their derivative, polyvinyl alcohols, and others known in the art. A preferred thickener is Acrysol ASE60™ available from Rohm and Haas Company of Philadelphia, Pa. ASE60™ is preferably obtained as a 28% solution of an alkali-swellable polyacrylic acid which increases in viscosity upon neutralization. As described above, thickener is added first to achieve the desired viscosity of the microsphere dispersion, which will vary depending on the particular phase change material selected, and then to adjust the wet coating to meat the requirements of the coating method employed.

[0029] Preferred antifoam agents include aqueous dispersions of silicone oil, such as polydimethylsiloxane, containing dispersed fine particle silica, and mixtures of mineral oil, surfactant and fine particle silica, such as AF 9020™ available from General Electric Company of Waterford, N.Y., and Advantage 831™ available from Hercules Chemical Company of Wilmington, Del.

[0030] A preferred polymer binder is made with a dispersed polymer latex is an anionic, heat reactive, acrylic latex containing 59% non-volatiles in water, such as the acrylic polymer latex marketed under the tradename Hycar XT9202™ and available from B. F. Goodrich Chemical Company of Cleveland, Ohio. The polymer latex has a glass transition temperature of −25° C. When properly dried and cured, fabric coatings made from polymer latex such as Hycar XT9202™ are washable and dry-cleanable.

[0031] The coating compositions of the present invention preferably include from 30 to 500 parts by dry weight of microspheres for each 100 parts by dry weight of acrylic polymer latex. The coating compositions preferably include from 0.005% to 6% dry weight each of surfactant and dispersant to dry weight of microspheres. Water is added to total 25% to 80% of the final wet coating composition. An antifoam agent of from 0% to 1% dry weight to total weight of the final wet coating composition is preferred. The most preferred ratios of components of the coating composition of the present invention are: 70 to 300 parts by dry weight of microspheres for each 100 parts by dry weight of acrylic polymer latex, 0.1% to 1% dry weight each of surfactant and dispersant to dry weight of microspheres, water totaling 40% to 60% of the final wet coating composition and antifoam agent of from 0.1% to 0.5% dry weight to total weight of the final wet coating composition.

[0032] An alternative method utilizes microspheres of phase change material which are not completely dried during the manufacturing process. Wet microspheres containing from about 25% to about 65% by weight water are preferred and can be readily handled. When using such microspheres, a surfactant and a dispersant are added to a polymer binder dispersion before the wetted microspheres are dispersed therein. DOS and Strodex PK90™ are preferably mixed with the polymer binder dispersion before the wet microspheres are mixed with and dispersed therein.

[0033] Generally speaking, phase change materials have the capability of absorbing or releasing thermal energy to reduce or eliminate heat transfer at the temperature stabilizing range of the particular temperature stabilizing material. The phase change material inhibits or stop the flow of thermal energy through the coating during the time the phase change material is absorbing or releasing heat, typically during the material's change of phase. This action is transient, i.e., it will be effective as a barrier to thermal energy until the total latent heat of the temperature stabilizing material is absorbed or released during the heating or cooling process. Thermal energy may be stored or removed from the phase change material, and can effectively be recharged by a source of heat or cold. By selecting an appropriate phase change material, a fabric can be coated for use in a particular application where the stabilization of temperatures is desired. Two or more different phase change materials can be used to address particular temperature ranges and such materials can be mixed.

[0034] Paraffinic hydrocarbon phase change materials suitable for incorporation into fabric coatings are shown below in Table I. The number of carbon atoms contained in such materials and is directly related to the melting point of such materials.

[0035] Phase change materials such as the listed paraffinic hydrocarbons are preferably formed into microspheres and encapsulated in a single or multi-layer shell of gelatin or other materials. Encapsulated microsphere diameters of from 1 to 100 microns are preferred, most preferably in the range 10 to 60 microns. Encapsulated microspheres containing phase change materials are sometimes referred to herein as “microPCMs.” Microspheres may also be bound in a silica matrix of sub-micron diameters. Microspheres containing n-octadecane or n-eicosane are suitable for fabric coatings for clothing. Such microspheres are available from MacGill Enterprises, Inc. of West Milton, Ohio and Microtek Laboratories, Inc. of Dayton, Ohio.

[0036] A preferred coating formulation where high phase change material content and limited extensibility is required, for example with non- or low-stretch fabrics such as non-woven or woven fabrics, is prepared as shown in Table II.

[0037] An alternative coating formulation where high phase change material content and limited extensibility is required, for example with non- or low-stretch fabrics such as non-woven or woven fabrics, is prepared as shown in Table III.

[0038] Addition of microspheres as described above in the preferred weight ratios eliminates tack and prevents blocking of the coated fabrics typically experienced with coatings having low glass transition temperature polymers such as those based on acrylic latex polymers. Tack, the tendency of material to stick to itself, can make rolls of coated fabric difficult to unroll. This can occur when rolls of coated fabric are stored in warm places or are stored under pressure of rolls stacked on top of one another. Antiblocking additives are typically added to coating formulations to prevent tack. The presence of microspheres in the coatings of the present invention eliminates the need for antiblocking additives.

[0039] Non-foam coating compositions like those described in Examples I and II above are suitable for application to substantially non-extensible fabrics of both woven and non-woven construction. A preferred coated fabric is produced using the non-foam coating like that of Example I and a 100% polyester, non-woven fabric having a weight of 0.8 oz/sq yd. A preferred fabric selected is HEF™ (a hydro-entangled fiber) obtained from Veretec™ of Bethune, S.C. Similar fabrics are available from du Pont de Nemours Company. Using a wet coating composition containing 50% by dry weight of microspheres, a knife-over-roll coating head configuration is employed. A desired weight of 2.5 oz dry weight of microspheres/sq yd is obtained with a knive-over roll gap of 0.022 inches off the fabric. The coating line speed is 8 linear yards per minute. The coating is cured at a temperature of approximately 260° F.

[0040] A preferred foam coating formulation of the present invention may be used with breathable fabric to maintain the heat and moisture dissipation capability of the fabric. In this example, the materials are subject to mechanical frothing. Foam stabilizers are added to maintain the foam after application to the fabric. Foam stabilizers may be inorganic salts of fatty acids or their sulfate partial esters, anionic surfactants, among other compounds. Preferred foam stabilizers for use with phase change material microspheres are sodium lauryl sulfate, ammonium stearate, di-sodium-n-octadecyl sulfosuccinamate and mixtures thereof. Ammonium stearate concentrations (dry as a percent of wet coating) of 0.5% to 6% plus 0.2% to 4% sulfosuccinamate are most preferred. The coatings are prepared as shown in Table IV.

[0041] Preferred foam coatings contain ammonium stearate in an amount by dry weight of from 0.25% to 10% of the total weight of the final wet coating composition foam is preferred and from 0.1 to 8% dry weight of sulfosuccinamate to total weight of the final wet coating composition foam. Most preferably, ammonium stearate by dry weight 1% to 3% of the total weight of the final wet coating composition foam and the sulfosuccinamate by dry weight comprises from 0.3 to 2% dry weight to total weight of the final wet coating composition foam.

[0042] The liquid coating is mechanically foamed by pumping through an Oakes mixer or similar mechanical foamer. The mixer injects air into the liquid and finely disperse the air. The foamed liquid is pumped to a coating head, usually a knife coater, where it is spread onto the fabric. The fabric/foam coating is then passed through a heated oven to dry and cure the foam.

[0043] Foam coating compositions like those described in Example III are also suitable for application to substantially non-extensible fabrics of both woven and non-woven construction when maintaining breathability of the fabric is desired. A preferred methodology includes applying the foam coating of Example III to HEF™ having a weight of 1¼ oz/sq yd. The wet coating composition of Example III is foamed to a preferred blow ratio of air to wet compound of 2:1, with acceptable blow ratios ranging from ½:1 to 10:1. A knife-over-roll coating head configuration is employed. The desired weight of 0.5 oz dry weight of microspheres/sq yd is obtained with a knive-over roll gap of 0.018 inches off the fabric. The fabric is drawn through the coating line at a rate of 10 linear yards per minute. The coating is cured at a temperature of approximately 260° F., with the fabric carried on a tenter frame to prevent shrinkage of the fabric.

[0044] Tests were conducted on acrylic fleeces in which the fibers containing microPCMs, and on non-woven materials (sometimes referred to herein as A“substrate”) having a coating containing microPcMs. Acrylic fleeces without microPCMs having approximately the same weight per unit area as the fleeces with microPCMs, and substrates without microPCMs having the same thickness as the non-woven substrates having a coating containing microPCMs, served as comparison materials. Specific data regarding the sample materials tested are included in Table V.

[0045] The content of microPCMs in the acrylic fleeces was approximately 10 per cent. About 7 g/m²microPCM was included in the coating of the non-woven substrate. This is equal to a content of microPCM of about 3%. The phase change temperature of the microPCM material ranged from about 22° C. to about 25° C.

[0046] Tests of water-vapor permeability and water-vapor absorption of the materials were based upon the test methods of the standards DIN 53 332 and DIN 53 333. The tests of the water-vapor permeability were carried out under constant climatic conditions of 23° C. temperature and 40% relative humidity. The water-vapor absorption of the materials was tested at a constant environmental temperature of 23° C. at varying relative humidities. The following thermophysical parameters of the materials were measured: thermal conductivity (A); thermal resistance (R); temperature conductivity (a); and specific thermal capacity (c).

[0047] Test results indicated that the water-vapor permeability is not influenced by the incorporation of microPCMs. The acrylic fleeces tested possess a water-vapor permeability of about 5 mg/cm²/h as a result of the material structure. The non-woven substrate to which the microPCM layer is applied is with about 0.75 mg/cm²/h, nearly impermeable for water-vapor.

[0048] The water-vapor absorption of the samples is primarily determined by the absorption ability of the basic material. The incorporated microPCM causes a slight increase of the water-vapor absorption under the same climatic conditions. The water-vapor absorption of the acrylic fleece without microPCM was about 1.5% at a temperature of 23° C. and a relative humidity of 80%. The acrylic fleece with microPCM absorbs about 0.3% more water-vapor under the same conditions.

[0049] Tests of heat insulation and the heat storage were carried out under varying temperature, humidity and static pressure. Test conditions with a material temperature in the phase change range of 24° C., a material humidity that results from 30% air humidity and a pressure of 1 kPa were selected as a starting point for the measurements. Table VI is a summary of the test results.

[0050] As shown above in Table VI, materials with incorporated microPCM possess an essentially higher heat storage than the comparison material. The heat insulation of the compact non-woven substrate is enhanced by the microPCM coating. The heat insulation of the acrylic fleece is mainly determined by the air enclosed in the material as a result of the dispersed structure of the fabric.

[0051] It has been determined that the heat insulation properties of the materials containing microPCM remain nearly constant in the temperature range of the specific phase change, in contrast to the behavior of materials which do not contain microPCM. The variation of the heat insulation of the materials with microPCM is essentially lower contrary to the comparison material in changes of material humidity. The materials with microPCM possess when raising the pressure on the textile a lower decrease in the heat insulation than the comparison material due to a lower compressibility of the materials with microPCM.

[0052] To determine the protection effect of the samples, the samples were brought in contract with a 70° C. tempered plate after cooling under the phase change temperature. The time required to reach a temperature equivalent to the pain threshold of the human skin on back of the sample was determined. The higher protection effect for the materials with microPCM was confirmed.

[0053] Presently preferred embodiments of the present invention and many of its improvements have been described with a degree of particularity. It should be understood that this description has been made by way of preferred examples, and that the invention is defined by the scope of the following claims.