WO1997020671A1

WO1997020671A1 - Latex dipping method for manufacturing waterproof knee boots

Info

Publication number: WO1997020671A1
Application number: PCT/IB1996/001444
Authority: WO
Inventors: Hugh David Niblock
Original assignee: Gates U.K. Limited
Priority date: 1995-12-05
Filing date: 1996-12-05
Publication date: 1997-06-12
Also published as: GB2307873A; GB2307873B; AU7706896A; GB9524882D0

Abstract

A heat-sensitive latex dipping method for manufacturing fabric-reinforced waterproof knee boots such as agricultural boots, firefighters' boots and hunting boots, wherein a fabric sock is mounted on a last, the last is heated to a temperature of from about 100 °C to about 110 °C, the sock is briefly dipped or immersed into a heat-sensitive latex to form a boot having an acceptable rubber wall gauge with only one dip into the latex, the boot is removed from the latex and dried, external elements such as foxing, heels, insulation and toe caps are added in conventional manner, and finally the entire assembly is sprayed with a polymeric lacquer, vulcanized, trimmed, and removed from the last.

Description

LATEX DIPPING METHOD FOR MANUFACTURING WATERPROOF KNEE BOOTS

The present invention is directed to a method for manufacturing fabric-reinforced waterproof knee boots such as agricultural boots, firefighters' boots and hunting boots, and more particularly to a highly efficient and time saving heat-sensitive latex dipping method for the manufacture of such boots.

Traditional methods of manufacturing fabric-reinforced waterproof knee boots such as agricultural boots, hunting boots and firefighters' boots are characterized by the predominantly manual steps of calendering and stitching rubberized fabric panels to one another in a conventional arrangement followed by vulcanization of the boot. This process is characterized by the use of heavy equipment for mixing and processing the dry rubber compounds. These procedures may result in product variation, unavoidable material waste, and are marked by high time and labor costs.

It is also known to form such boots using coagulant/latex dipping technology, wherein an elastic fabric sock is mounted upon a shaped last; the sock is coated with a coagulant capable of destabilizing the latex and depositing it on the surface of the fabric sock; the coated sock is dipped or immersed into a liquid rubber latex bath a sufficient number of times to effect the desired rubber wall gauge; heel, foxing and other usual external elements are added after drying, and the boot is vulcanized, trimmed, and removed from the last. While potentially significant savings in time and labor may be effected by this method, the process still requires the use of an additional component, i.e., a coagulant, which serves as the destabilizer and barrier to strike-through between the latex and the fabric sock. In addition, the coagulant/latex dipping process requires multiple dipping steps to effect the final gauge required in a given boot. Accordingly, an improved method for the manufacture of fabric-reinforced waterproof knee boots that would decrease time and labor costs associated with prior art methods, and that would achieve the desired rubber wall gauge without the necessity of multiple immersions of the fabric sock into a latex bath or the use of a coagulant is highly desirable.

It is therefore an object of the present invention to provide a novel latex dipping method for the manufacture of fabric reinforced waterproof knee boots, including agricultural boots, hunting boots, wading boots, firefighters' boots and the like, wherein adhesion of the rubber latex to the fabric sock, prevention of rubber strike-through, and acceptable rubber wall gauge with only one immersion of the fabric sock into a latex bath are effected.

Accordingly, the present invention provides a method for the manufacture of waterproof knee boots wherein a fabric sock is mounted on a last, the last is heated, the sock is dipped or immersed into a heat-sensitive latex for at least about 10 seconds to form a boot having an acceptable rubber wall gauge preferably with only one dip into the latex, the boot is removed from the latex and dried, external elements such as foxing, heels, insulation and toe caps are added in conventional manner, and finally the entire assembly is sprayed with a polymeric lacquer, preferably vulcanized, trimmed, and removed from the last.

The method of the present invention can also make use of pre-vulcanized latexes, in which cases the step of vulcanizing may not be necessary. The method of the present invention makes it possible for virtually all of the essential boot manufacture steps to be performed upon a last, which may be constructed so as to move from one process step or station to the next by means of a completely automated system, thus eliminating the need for manual transfer of the last from step to step, such as for example, from the heat-sensitive latex dip to a drying chamber.

The sock construction useful in the present invention preferably has a specific density, elasticity and thickness, which promote adhesion of the latex to the sock while allowing the sock

to conform to the last without the formation of gaps or bridges, and permitting sufficient heat transfer from the last to the latex to result in proper gel formation.

The heat-sensitive latex is formulated and processed to form a dry rubber wall gauge in a fabric-reinforced waterproof knee boot which is acceptable with a single dip of the fabric sock into the latex bath. In one embodiment, the heat-sensitive latex is formulated and processed to result in gel formation at temperatures above approximately 28 C, with the rate of formation increasing with temperature, penetration of the sock with the latex ceasing at approximately 75 C, and rapid latex build-up without strike- through occurring in the range of from 75 C to 120 C.

It has been surprisingly found that by varying the temperature of the heat-sensitive latex and the dwell time of the sock in the latex, various rubber wall gauges may readily be effected with a single dip of the last into the latex. In one embodiment of the present invention for example, dry rubber wall gauge of from 1.90 to 2.05 mm may be achieved with a single dip of the last-mounted sock into the heat-sensitive latex for a dwell time of from 10 to 20 seconds.

The process of the present invention, through its use of rubber latex as the primary material of the boot body, results in an exceptionally leak-proof and crack-proof boot having superior finish and comfort. In one embodiment the process of the present invention provides the additional advantage of facilitating a variation in rubber wall gauge in the same boot by differential control of dwell time, temperature gradients or both, with a single dip of the sock into the heat-sensitive latex.

Specific embodiments of the present invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic illustration of the steps of the present invention. FIG. 2 is a cross-sectional side view of a finished boot made in accordance with the present invention.

Referring to FIG. 1, the steps of one embodiment of the present invention are illustrated, wherein the various steps required to build a fabric-reinforced waterproof knee boot are shown. As one skilled in the art would readily appreciate, these steps could easily be automated, such that any number of lasts may be moved through the process steps or stations by means of an automatic conveyor system. Such automatic conveyor systems and their constructions are well known to the art.

In the embodiment shown at FIG. 1, at station 20 a fabric sock is pulled onto a rigid last having an outer surface shaped to coincide with the inner surface of the finished boot. The last may be formed from any suitable rigid material, such as aluminium, stainless steel, nylon, polyester or polysulfone, and is preferably made of aluminium. At this station, an insole may be placed between the fabric sock and the last. The last may be one of several such lasts arranged on a conveyor system such that several fabric socks may be automatically moved through the various process steps or stations of the boot building process in sequential order.

The last having the sock mounted upon it is heated at station 22 to a temperature sufficient to destabilize the heat-sensitive latex quickly enough to prevent strike-through. In a preferred embodiment, the last having the sock mounted upon it is heated to a temperature greater than about 100 C, preferably between 100 and 110 C, and more preferably to a temperature of 105 C. While the time required for the last to reach this temperature will vary with the type of last material and its dimensions as well as the type of heating apparatus used, where an aluminium last having a standard height of 47 cm is utilized, such increase in temperature usually requires approximately from 20 to 30 minutes, using a mixture of hot air impingement and infra red radiation. Other heating methods, including induction coil heating, may equally well be used for this purpose. The last-mounted sock is next moved to station 24, where it is dipped into a bath of heat-sensitive latex to a point extending slightly below the top of the fabric sock, for a dwell time of from about 10 to about 20 seconds, and then is removed from the bath to form a rubber latex boot having a dry rubber wall gauge in excess of lmrn, and usually of the order of from about 1.90 to about 2.05mm. Typically, this wall gauge may be achieved in a dwell time of from about 15 to about 18 seconds. While a single immersion of a last- mounted sock into a heat-sensitive latex has been found to be sufficient to result in the wall gauges described, it is anticipated that two or more immersions of a last-mounted sock into a heat-sensitive latex may be desirable under certain circumstances. Such multiple immersions and the knee boots resulting from same are considered to be within the scope of the present invention. The vessel for holding the heat-sensitive latex may be suitably constructed by one skilled in the art to allow for a constant latex level throughout an automated conveyor process. As an optional step, the last may next be moved to station 26, where water soluble matter is leached from the boot using a cool water wash. This step is entirely optional however, as applicant has found that knee boots having excellent performance, aesthetic and aging characteristics may successfully be formed in the absence of this leaching step, provided the surface of the boot is subsequently sealed with a suitable polymeric lacquer.

The last is next moved to station 38, where the boot is dried in a suitable drying oven, drying chamber or equivalent apparatus. The boot is dried, typically by hot air circulation until a sufficient amount of water is removed from the latex to permit acceptable vulcanization. Typically, less than about 5% water retained in the latex is appropriate. Using a conventional drying oven the boot may be held at 55 "C for approximately 4 hours to dry the latex sufficiently.

The last is next moved to station 39, where the external elements of the boot are added. The term, "external elements" is used in this context to include foxing, outsoles, eyelets, heels and so forth. These elements may be added in any conventional manner known to the art. For this step, the last may remain on the conveyor if a conveyor is used, or it may be removed from the conveyor for manual application of the external elements.

The last is next moved to station 32, where the surface of the boot is sprayed with a polymeric lacquer or varnish to impart an aesthetically pleasing appearance. One such polymeric lacquer is a chlorosulfonated polyethylene available under the registered trade mark, Hypalon. This surface finishing step may likewise be accomplished through halogenation of the surface such as by dipping the boot into chlorinated water. Finally, the last is moved to station 34, where the boot is vulcanized. Vulcanization may be accomplished by any suitable method, such as by hot air vulcanization at 135 C for approximately one hour and twenty minutes. Excess rubber portions if present are then trimmed, and the boot is removed from the last for pairing and packing.

FIG. 2 illustrates a cross-sectional side view of a finished boot made in accordance with one embodiment of the process of the present invention. A variation in rubber wall gauge in the same boot may be achieved by differential control of dwell time, temperature gradients or both, with a single dip of the sock into the heat-sensitive latex. FIG. 2 illustrates one embodiment of this phenomenon, wherein a fabric sock 40 forms the innermost layer of a fiber-reinforced waterproof knee boot. An insole (not shown) may be placed in the bottom of the foot area of the sock 40. A rubber latex wall 42 is bonded to the outer surface of the fabric sock 40. The rubber latex wall possesses an increased gauge compared to the balance of the boot at the reinforced portion 44. In this embodiment, the reinforced portion 44 encompasses the toe portion of the boot, and extends slightly above the foxing 48 at the heel of the boot, but boots may be reinforced according to the present invention in any other suitable area. In the embodiment shown in FIG. 2, the reinforced portion terminates in an obvious ridge around the boot, which is suggested by the hashed rib 45 across the boot body. A polymeric lacquer or varnish spray coating 46 covers the rubber latex wall 42 and the reinforced portion 44 of the boot. Other common external elements are shown, including foxing 48, an outsole 50, and a heel 52 mounted to the outsole 50. Heat-sensitive latex dipping processes in accordance with the present invention differ from existing methods of manufacture of fabric reinforced waterproof rubber knee boots by latex dipping techniques utilizing a coagulant such as calcium nitrate to destabilize the latex. In these methods, an article is first coated with the coagulant, then dipped into the rubber latex. The coagulant, once in physical contact with the latex, causes the liquid latex to gel or solidify. Typically, a 1 mm latex rubber wall gauge can be established after 5 minutes of coagulant/latex contact according to this process, but multiple immersions are necessary for a higher gauge.

Heat-sensitive latex dipping conversely uses heat to destabilize the liquid rubber latex. The latex, having been made heat-sensitive through the addition of a heat-sensitizing agent such as polyvinyl methyl ether (PVME) , once exposed to sufficiently high temperature begins to form small micelles at the heat interface. These micelles unite to form larger conglomerates, until the latex entirely gels. This process is fragile compared to coagulant/latex dipping techniques; the amount of PVME utilized, temperature, and pH of the latex at dip combine to provide a specific gel formation profile. The process is further sensitive to raw material variation common in natural rubber latex systems. In fabric-reinforced latex rubber articles, strike-through prevention and adhesion of the latex to a fabric reinforcement are further concerns which must be addressed.

It has been surprisingly found in the practice of the present invention, that only one dip or immersion of a last-mounted fabric sock into the heat-sensitive latex for a dwell time of from 10 to 20 seconds, and preferably of from 15 to 18 seconds, yields a rubber coating having a dry rubber wall gauge in excess of 1 mm, and usually of from 1.90 to about 2.05 mm. Careful control of process conditions substantially prevents strike-through or complete penetration of the rubber latex completely through the interstices of the fabric sock, and results in a boot having excellent adhesion of the rubber latex component to the fabric sock without the need for additional components such as a coagulant.

A further advantage is realized through practice of the present invention. Namely, with a single immersion of the fabric sock into the heat-sensitive latex useful in the present invention, the rubber wall gauge of a boot may be varied to reinforce certain areas, e.g., the heel or foot area. This is accomplished by altering dwell time, temperature gradient or both as they apply to the area sought to be reinforced. For example, by holding the foot area in the heat-sensitive latex for 10 seconds longer than the leg portion, the dry wall gauge of the foot area will be made significantly greater than that of the leg portion, e.g., by 1.50 to 2.00 mm. A ridge or step in the rubber latex wall between the reinforced and un-reinforced portions may be made obvious for aesthetic purposes by dipping the entire sock into the latex for 10 to 20 seconds, removing the boot to a point of immersion equal to that sought to be reinforced, holding the boot at that point for an additional five seconds, removing the boot from that point slightly for 1 to 2 seconds, then re-immersing the boot to that point for yet another five seconds. Alternatively, less obvious build-up in gauge can be achieved by maintaining a gradation in the heat energy available to the latex on the sock. That is, the metal last can be preheated to a uniform temperature and the thickness of the metal varied such that the heat energy source changes; or the last can be heated on a temperature gradient prior to immersion in the latex.

A further advantage is recognized by the present invention. Namely, different color or stiffness characteristics may be imparted to sections of the boot by subsequent dips of those sections in suitable latex compounds which have been modified as well known in the art to provide a different color or stiffness latex to the dipped section of the boot. Thus for example a yellow knee boot may be constructed having a black foot portion, or having a stiffer latex in the toe portion. As is known in the art of heat- sensitive latex dipping, subsequent dips into latex baths must be performed before the rubber insolubles of the latex inhibit gel cohesion between subsequent layers.

The sock construction useful in the present invention preferably has density, elasticity and thickness, which promote adhesion of the latex to the sock while allowing the sock to conform to the last without the formation of gaps or bridges, and permitting sufficient heat transfer from the last to the latex to result in proper gel formation. The materials suitable for use in the construction of the fabric sock of the present invention include natural and synthetic materials such as cotton, nylon and polyester. Where woolly fibres such as cotton are used for the sock, the outer surface of the finished boot may have a somewhat crinkled or pleated finish. The preferred material for the fabric sock is nylon 6,6. The fabric sock may be of a suitable weft knit, such as circular knitted or flat-bed knitted. The latter knit may be used where a stitched or welded seam in the sock is acceptable. In the preferred embodiment of the present invention, the knitted fabric is nylon 6,6, and comprises at least one continuous weft yarn and at least one warp yarn. When used with the particular heat-sensitive latex formulation preferred in the present invention, the weft yarn preferably comprises two strands, each consisting of 34 filaments, and possesses a linear density of 110 decitex. The warp yarn preferably comprises four strands, each consisting of 20 filaments, and possesses a linear density of 78 decitex. While sock dimensions will vary with the particular waterproof knee boot application, a preferred sock is a tube measuring from about 10 to about 20 and preferably from about 12 to about 16 cm in width, and from about 50 to about 70, and preferably from about 55 to about 65 cm in length. The fabric is sufficiently elastic to conform to the contours of the rigid last without the formation of bridges or gaps, and in a preferred embodiment, should stretch to greater than 150% of its width. A sock having the same dimensions is characterized by a density of from about 225 to about 255 g/cm², and preferably from about 235 to about 245 g/cm². When used with the particular heat-sensitive latex formulation preferred in the present invention the thickness of the fabric sock may be from about 0.65mm to about 0.95-πn and is preferably from about 0.75mm to about 0.85πι-n.

The heat-sensitive latex useful in the present invention, when used with the fabric sock construction preferred in the present invention, is specifically formulated and processed to yield gel formation at temperatures above approximately 28 C, with the rate of gel formation increasing with temperature, penetration of the sock with the latex ceasing at approximately 75 C, and rapid latex build-up occurring without strike-through in the range of from about 75 C to about 120 C. In order to achieve optimum adhesion of the latex to the fabric sock, proper balance of latex penetration into the sock without strike-through, and proper latex build-up are needed. Careful control of processing conditions including temperature, dwell time, and pH are required accordingly. Optimum adhesion, latex penetration and latex build-up are all related to the density, elasticity and thickness of the fabric sock, as well as the particular formulation and processing conditions of the heat-sensitive latex.

The heat-sensitive latex preferably comprises a base rubber latex, a thickener, a pH adjusting agent, an activator and a heat- sensitizing agent. Suitable rubber latexes for this purpose include natural rubber latex, nitrile rubber latex and polychloroprene rubber latex. The preferred latex is natural rubber latex. The most preferred rubber latex is low ammonia natural rubber latex, having a pH in the range of from 9.00 to 10.00, solids in the range of from about 55% to about 62% and preferably in the range of from about 57.5% to about 59.5%, and a total alkalinity of from 0.07% to about 0.13% expressed as ammonia. One such natural rubber latex is available from Vita Liquid Polymers of Manchester, England under the trade name, Diptex 5779. To form the heat-sensitive latex of the present invention, the base liquid rubber latex is stirred in a suitably sized vat to gently disperse it.

Next, a thickener is preferably added to the latex to increase viscosity and thereby reduce the flow rate of the latex. Reducing the flow rate of the latex decreases the speed with which the latex would otherwise penetrate the fabric sock. The time required for the latex to penetrate through the entire fabric sock must exceed the time required to destabilize the latex. In other words, the gel reaction must take place and be substantially complete prior to full penetration of the latex into the sock. As the thickener, an acrylate-based thickener available from Vita Liquid Polymers under the trade name, Dispersion 3613T is preferred. It is believed that methyl cellulose thickeners may also be used for this purpose. The thickener is first mixed with water in a ratio of thickener to water of 1:6.5. Air is allowed to liberate from the thickener mixture, and the thickener mixture is added to the liquid rubber latex to form a latex mixture.

A pH adjusting agent is preferably added to the system to adjust the pH of the latex mixture to the proper range. Improper pH jeopardizes the gel formation process. In the preferred embodiment of the present invention, the liquid rubber latex is a low ammonia natural rubber latex. In this embodiment, the pH adjusting agent is added in an amount sufficient to bring the latex mixture pH to from 8.0 to 8.3. Suitable pH adjusting agents for this purpose include formaldehyde. Calcium chloride may also be used for this purpose. Where formaldehyde is used as the pH adjusting agent, a 10% solution in water is preferred. The pH adjusting agent is slowly added to the latex mixture, which is then stirred quickly for two minutes, and then stirred slowly for approximately an hour. An activator is preferably added to the latex mixture to serve as a vulcanizing agent. As the activator, an aqueous dispersion of rubber vulcanizing agents containing zinc oxide, and having a solids content of from about 50 to about 53% and a pH of from about 8.00 to about 9.50 is preferred. One such dispersion which operates successfully within the preferred natural rubber latex system of the present invention is available from Vita

Polymer Liquids under the registered trade mark, Activator 3405B.

As the heat-sensitizing agent, poly vinyl methyl ether (PVME) is preferred. A preferred form is a 50% dispersion of PVME in water. One such dispersion is available from BASF under the registered trade mark Lutanol M40. Prior to addition to the latex mixture, the dispersion is mixed with water in a ratio of dispersion to water of 1:4. The heat-sensitizing agent is slowly added to the latex mixture, and the thus completed heat-sensitive latex is allowed to stand for several hours or overnight prior to beginning the dipping process outlined in the description for FIG.

1, in order for the heat-sensitive latex to reach the proper maturation point, and to allow the latex mixture to liberate air introduced during the mixing process.

Table 1 shows a preferred formula for the heat-sensitive latex useful in the present invention. In Table 1:

Natural Rubber Latex = Diptex 5779 by Vita Liquid Polymers of Manchester, England water/thickener = Dispersion 3613T by Vita Liquid Polymers, first mixed with water in a ratio of Dispersion 3613T to water of 1:6.5. activator = Activator 3405B by Vita Liquid Polymers, heat sensitizing agent = Lutanol M40, by BASF, first mixed with water in a ratio of Lutanol to water of 1:4.

TABLE 1

Description Amount (grams)

Natural Rubber Latex 170.00 water/thickener 15.00 formaldehyde solution (10%) 4.50 activator 3.50 heat-sensitizing agent 9.00

The process of the present invention, through the use of rubber latex as the primary material of the boot body, results in an exceptionally leak-proof and crack-proof boot having superior finish and comfort. The heat-sensitive latex dipping process of the present invention provides a method for the .manufacture of fabric- reinforced waterproof knee boots which is faster and more efficient than prior art methods. In addition, in one embodiment, the process of the present invention allows for a variation in rubber wall gauge in the same boot, accomplished by only a single dip of a last-mounted fabric sock into a heat-sensitive latex, by differential control of dwell time, temperature gradients or both. The above embodiments have been described by way of example only. Many other embodiments falling within the scope of the accompanying claims will be apparent to the skilled reader.

Claims

CLAIMS :

1. A method of making waterproof knee boots comprising the steps of: a) mounting a fabric sock on a rigid last; b) heating the last; c) dipping the fabric sock mounted on the last into a heat- sensitive latex; d) holding the fabric sock mounted on the last in the heat- sensitive latex for a dwell time of at least 10 seconds; e) removing the last from the latex to form a boot having a dry wall gauge in excess of 1mm; f) drying the boot; g) mounting external elements onto the boot; and h) removing the boot from the last.

2. The method of Claim 1, further comprising the step of vulcanizing the boot.

3. The method of Claim 1 or 2 wherein the last is mounted on a conveyor, the conveyor arranged to deliver the last to each said step a-h.

4. The method of Claim 1, 2 or 3, wherein the steps are performed in the substantial absence of a coagulant.

5. The method of any preceding Claim further comprising the step of varnishing the boot.

6. The method of any preceding Claim further comprising the step of trimming excess portions from the boot.

7. The method of any preceding Claim wherein the fabric sock comprises a tube made of a weft knit fabric having at least one weft yarn and at least one warp yarn.

8. The method of Claim 7, wherein the weft knit fabric is one selected from the group consisting of nylon, polyester or cotton.

9. The method of Claim 7 or 8 wherein the weft knit fabric is nylon 6,6.

10. The method of Claim 7, 8 or 9 wherein the weft yarn comprises two strands, each consisting of 34 filaments, and possesses a linear density of 110 decitex, and the warp yarn comprises four strands, each consisting of 20 filaments, and possesses a linear density of 78 decitex.

11. The method of any preceding Claim wherein the fabric sock measures from about 10 to about 20cm in width, and from about 50 to about 70cm in length, the fabric sock is sufficiently elastic to conform to the contours of the rigid last without the formation of bridges or gaps, the fabric sock is characterized by a density of from about 225 to about 255 g/cm², and the fabric sock has a thickness of from about 0.65mm to about 0.95mm.

12. The method of any preceding Claim wherein the heat-sensitive latex comprises a base rubber latex, a thickener, a pH adjusting agent, an activator and a heat-sensitizing agent.

13. The method of Claim 12 wherein the heat-sensitizing agent is polyvinyl methyl ether.

14. The method of Claim 12 or 13 wherein the base rubber latex is one selected from the group consisting of natural rubber latex, nitrile rubber latex and polychloroprene latex.

15. The method of Claim 12 or 13 wherein the base rubber latex is low ammonia natural rubber latex.

16. The method of Claim 15 wherein the heat-sensitive latex has a pH in the range of from 8.0 to 8.3.

17. The method of any preceding Claim wherein the fabric sock is heated to a temperature of from about 100 C to about 110 C.

18. The method of any preceding Claim wherein the fabric sock is dipped in the heat-sensitive latex for from 15 to 18 seconds

19. A method for making waterproof knee boots comprising the steps of: a) mounting a fabric sock on a rigid last, said fabric sock comprising a tube made of a nylon 6,6 weft knit fabric having at least one weft yarn and at least one warp yarn; b) heating the last to a temperature between 100 and 110 C; c) making a single dip of the fabric sock mounted on the last into a heat-sensitive latex having a pH in the range of from 8.0 to 8.3, said latex comprising a low ammonia natural rubber latex, a thickener, a pH adjusting agent, an activator and a heat- sensitizing agent; d) holding the fabric sock mounted on the last in the heat- sensitive latex for a period of from 10 to 20 seconds; e) removing the last from the latex to form a boot having a dry wall gauge in excess of 1 mm; f) drying the boot; g) mounting external elements onto the boot; and h) vulcanizing the boot and removing the boot frn the last.

20. The method of any preceding Claim further comprising the step of selectively altering dwell time and temperature gradient to form a boot having a variation in dry rubber wall thickness.

21. The method of any preceding Claim further comprising the step of dipping a portion of the boot into a second heat-sensitive latex, said second heat-sensitive latex having a color distinct from the color of the first heat-sensitive latex, to form a boot having a variation in wall color.

22. A fabric-reinforced waterproof knee boot made according to the method of any preceding Claim, said waterproof knee boot comprising a foot portion and a leg portion, a fabric sock defining the inner layer of the foot portion and leg portion, a rubber latex wall bonded to the outer surface of the fabric sock, foxing mounted around the foot portion of the boot, an outsole mounted to the bottom of the foot portion, a heel mounted to the outsole, and a lacquer spray coating covering the rubber latex wall.

23. A fabric-reinforced waterproof knee boot made according to the method of any of Claims 1 to 22 , said waterproof knee boot having a reinforced portion, an un-reinforced portion, a foot portion and a leg portion, a fabric sock defining the inner layer of the foot portion and leg portion, a rubber latex wall bonded to the outer surface of the fabric sock, foxing mounted around the foot portion of the boot, an outsole mounted to the bottom of the foot portion, a heel mounted to the outsole, and a lacquer spray coating covering the rubber latex wall, said reinforced portion having an increased wall thickness compared to said un-reinforced portion.