referring to the drawings more particularly by reference number , reference numeral 10 refers to an infant heel heat pack in accordance with the present invention . an ideal but non - limiting size for heat pack 10 fitted to a baby &# 39 ; s foot is 3½ by 5 inches . heat pack 10 is formed as a flexible pouch 14 with a front panel 16 and a rear panel 18 , the construction of which is discussed below . pouch 14 provides a container for a supercooled aqueous salt solution which , when activated releases heat . suitable solutions include supercooled sodium acetate , lead acetate , calcium nitrate tetrahydrate , sodium pyrophosphate and sodium thiosulfate solutions . sodium acetate may be preferred because it is generally harmless to humans . the salt solution is made by dissolving the salt in a desired amount of water . the amount of salt to be utilized should permit the salt solution to be supercooled to at least the ambient temperature at which the heat pack is intended to be utilized . the supercooled aqueous salt solution may include a small amount of a viscosity increasing agent . a variety of gelling or thickening agents are commercially available , have been proposed for use in heat packs before and may be used . as seen in fig1 - 2 and 4 , a trigger 20 to initiate crystallization is included in pouch 14 . many triggers have been used in prior art heat packs and may be used in the present heat pack . for example , trigger 20 may be a metal disc or disc formed of flint , garnet , aluminum oxide , silicon carbide , alumina - zirconia , chromium oxide , ceramic aluminum oxide and so forth . what is important is that when trigger 20 is manually manipulated as shown in fig4 by pressing the disc between thumb and index finger of one or both hands , the disc initiates crystallization . front panel 16 of pouch 14 can be made from a flexible plastic material . suitable flexible materials include plastics used in the food industry such as polyolefins , copolymers of ethylene , substituted olefins , polyesters , polycarbonates , polyamides , acrylonitriles and so forth . a plastic laminate such as nylon polylaminate may also be used for front panel 16 ; suitable materials for such purpose having a thickness in the range of about 1 mil to 10 mils . rear panel 18 is formed as a laminate , an essential feature of which is that an outer layer 22 be formed of a nonwoven material . an illustrative cross - section of a rear panel 18 is shown in fig3 . non - limiting examples of nonwoven materials suitable for outer layer 22 include nylon , rayon , cellulose ester , polyvinyl derivatives , polyolefins , polyamides , polyesters , natural materials such as wool , silk , jute , hemp , cotton , linen , sisal , ramie and combination thereof . the nonwoven material may be formed by a suitable process such as , for example melt blowing , spunbonding , card webbing , etc . for example , 42 gsm white sms polypropylene untreated , product code b0116 , sold by pgi of mooresville , n . c . has been used . the polypropylene is spunbond and combined with meltblown polypropylene to form a layered sms ( spun - melt - spun ) product . the polypropylene sms is water - repellent but capable of adsorbing water on the surface and applying a film of water to an infant &# 39 ; s heel . other of the nonwoven materials mentioned above may also be wetted prior to application of the heat pack to an infant &# 39 ; s heel . an adhesive 24 attaches nonwoven outer layer 22 to an inner layer 26 which may be bonded to front panel 16 . inner layer 26 may also be a composite as shown in fig3 wherein a first layer 28 is formed of a biaxial oriented polymer film . biaxially oriented polyamides , polyethylene terephthalate or the like are generally much stronger in terms of tear strength and thus may be used to reinforce the nonwoven outer layer 22 . a second layer 30 is formed of a flexible plastic material that can be bonded to or fused with the plastic material making up front panel 16 . front panel 16 and second layer 30 may be formed of the same material or not . a specific example of rear panel 18 comprises nonwoven outer layer 22 , adhesive 24 , 60 gauge biaxially oriented nylon ( bon ) as first layer 28 , adhesive 24 and 3 mil clear low linear density polyethylene ( lldpe ) as second layer 30 . the 60 gauge bon is manufactured by american biaxis , inc . laminating adhesive 24 is sold under the trade name tycel and is manufactured by henkel adhesive . the lldpe is manufactured by appleton performance packaging - films . a band 32 is attached to heat pack 10 for the purpose of attaching the heat pack to a heel 34 of an infant as shown in fig5 . for this purpose a patch 36 of adhesive is provided on opposite ends of band 32 for connecting to front panel 16 . before heat pack 10 is applied to heel 34 and after crystallization has been initiated , a peel - off strip 38 over patch 36 as shown in fig2 may be removed exposing patch 36 for attachment of the free end of band 32 to front panel 16 . band 32 may have a non - slip coating to keep heat pack 10 in place on an infant &# 39 ; s heel . a message 40 such as “ safe ” as shown in fig1 , “ safe to use ” or the like may be printed on band 32 in a thermochromic ink or dye to let the operator know that heat pack 10 is at a proper temperature to be placed on infant &# 39 ; s heel 34 . for example , message 40 could appear when the temperature is somewhere between 98 ° and 105 ° fahrenheit . suitable thermochromic substances include liquid crystals and leucodyes . the indicator used for message 40 may include two or more different thermochromic materials that change color at different temperatures . for example , the indicator may include a first thermochromic material that is blue when heat pack 10 is below 98 °, a second thermochromic material that turns green when heat pack 10 is within the desired temperature range , and a third thermochromic materials that turns orange when heat pack 10 is above 105 °. thermochromic materials can also be combined with non - thermochromic dyes and / or pigments to form message 40 . for example , message 40 formed with non - thermochromic indicia may be obscured by a thermochromic coating that becomes translucent at a predetermined temperature , e . g ., when a temperature above 105 ° has been reached . in use , trigger 20 in heat pack 10 is flexed as shown in fig4 initiating crystallization . when heat pack 10 has reached the suitable operating temperature , message 40 on band 32 may appear signaling that heat pack 10 is safe to apply to heel 34 of the infant and nonwoven outer layer 22 is preferably wetted . strip 38 is peeled off patch 36 and heat pack 10 is attached to heel 34 with band 32 as shown in fig5 with nonwoven outer layer 22 in contact with the baby &# 39 ; s skin . as crystallization proceeds nonwoven layer outer layer 22 causes heat pack 10 to nest about the infant &# 39 ; s heel thereby keeping it in place . nonwoven outer layer 22 also insulates the infant &# 39 ; s skin from burning and cuts back on potential irritation . the heat of the heat pack 10 drives water which has been applied to nonwoven outer layer 22 into the infant &# 39 ; s skin where it is then trapped under the heat pack . the water moisturizes and softens the skin on the infant &# 39 ; s heel thereby facilitating entry of a needle . in view of the above , it will be seen that the several objects of the invention are achieved and other advantageous results attained . as various changes could be made in the above constructions without departing from the scope of the invention , it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense .
a heat pack for warming the heel of an infant with a front panel and a rear panel wherein the rear panel is adapted for placement on the infant &# 39 ; s heel and has an outer layer formed of a nonwoven material which may be wetted . a band is provided for attaching the heat pack to the infant &# 39 ; s heel . heat from the heat pack effectively drives water applied to the nonwoven material into the infant &# 39 ; s heel where it is then trapped in the skin under the heat pack . by thus moisturizing and softening the skin , a puncture necessary for taking a blood sample is eased .