Field ofthe Invention

This invention relates to a method of manufacturing footwear, more particularly such a method which includes the step of reinforcing a footwear upper material by the application of a resin thereto.

Background of the Invention

It is customary for shoe manufacturers to reinforce the toe end of the upper to obtain improved wear and retention of shape. It is accepted practice throughout the shoe industry to obtain such reinforcement by the application of a thermoplastic stiffening resin, sometimes referred to as a box-toe resin, to the toe portion of the upper. The thermoplastic resin is applied as a melt and upon cooling forms a stiff resilient reinforcing coating on the upper.

For a thermoplastic resin to be an acceptable stiffener in this application the resin must satisfy the following requirements: first of all, the resin should have some adhesive character; it should have a low melt viscosity, preferably less than 150 poise at 190°C; the resin should set rapidly to prevent

"welding" of stacked assemblages of the manufactured articles; and the resin

must be stiff to impart and retain the desired shape but it must also have sufficient flexibility, even at low temperatures, to resist cracking upon impact and to "snap back" to its original shape. This latter property or more correctly, balance of properties is sometimes referred to as "rigid flexibility"and is perhaps the most troublesome and difficult property to develop in a thermoplastic resin, particularly in polyamide resins.

Polyamide resins derived from polymeric fatty acids and conventional diamines are unacceptable since they become brittle upon aging and have a tendency to crack when flexed, especially at low temperatures. The use of mixed diamines, e.g. mixtures of ethylene diamine and hexamethylene diamine, with polymeric fatty acids improves the flexibility at low temperatures, however, the resins lack resiliency and memory and are unable to "snap-back" to their original configuration. The incorporation of a short-chain dibasic acid with the polymeric fatty acid improves the stiffness but reduces the impact resistance of the resin to a point where it is unacceptable.

U.S. Patent No. 3,499,853 discloses thermoplastic adhesives derived from relatively low molecular weight ether diamines, by themselves or in combination with ethylene diamine, and polymeric fatty acids. The resulting thermoplastic copolyamides have high resistance to peel and excellent adhesive properties. When mixtures of ethylene diamine and ether diamines are employed the equivalent ratio of ethylene diamine to ether diamine can range as high as about 0.9:0.1 but, more preferably, will be between about 0.7:0.3 and about 0.6:0.4. Even though the copolyamides of U.S. Patent No. 3,499,853 have excellent impact resistance they are not suitable box-toe resins since they have unacceptable resilience and are too soft. British Patent No. 1 ,319,807 also discloses the use of copolyamide resins derived from polymeric fatty acids and low molecular weight aliphatic ether diamines.

U.S. Patent No.4, 122,229 (Mitchell) discloses copolyamides derived from mixed acids (a polymeric fatty acid and short-chain dibasic acid) and mixed amines (a polyoxyalkylene diamine and a short-chain diamine) as thermoplastic resin compositions and states that these compositions are

excellent reinforcing adhesives for flexible substrates and are particularly useful as box-toe construction resins.

U.S. Patent No. 4,151 ,155 (Chaplick) discloses a method for stiffening a flexible workpiece such as the toe portion of a shoe in which a layer of fast crystallizing linear synthetic polymer resin is deposited in molten condition on a transfer surface member which is at a temperature and has a heat take up capability to bring the resin at its surface to a temperature for rapid crystallization ofthe resin, the resin layer is pressed between the transfer surface member and the surface of the workpiece within a time after deposition of the resin on the transfer surface member during which at least the exposed surface of the resin layer remains molten for wetting adhesive engagement with the surface of the workpiece and the transfer surface member is separated from the resin layer at a time when at least a surface film of crystallized resin has formed adjacent said transfer surface member. This patent claims a method of joining a stiffening material consisting essentially of a thermoplastic synthetic resin stiffening agent containing homogeneously dispersed therein 3 to 50 parts per 100 parts of the synthetic resin of carbon black or graphite as an active substance to a shoe upper material of leather or synthetic resin which is devoid of such active substance without significantly heating the shoe upper material comprising heating the stiffening material to the temperature at which it becomes soft and adhesive by subjecting the stiffening material and adjacent shoe upper material to ultra high frequency radiation for about 2 to 15 seconds.

U.S. Patent No. 3,778,251 (Trask) discloses shoe stiffener materials such as box toe blanks and counter blanks that are formed of a base layer of an impregnated fabric carrying a polystyrene-type impregnant in incompletely coalesced particle form. At least one and preferably both sides of the base layer carries a polycaprolactone thermoplastic layer. The shoe stiffener material is solid and non-tacky at standard room temperature and has sufficient softness and flexibility to permit ease of use in conventional box toe and shoe back part forming apparatus. Heat is used to form a continuous thermoplastic film of the polymers in the shoe stiffener when formed into three-dimensional

box toes and counters. The heat also acts to adhesively unite the stiffener with surrounding layers such as shoe uppers and shoe linings.

U.S. Patent No. 3,961 ,124 (Matton) discloses a shoe-stiffening material useful as a stock material to stiffen selected parts of a shoe, which material comprises: a flexible fabric material saturated with a latex composition comprising a natural or synthetic elastomeric polymer, such as styrene-butadiene rubber, and a cross-linking system comprising a peroxide agent, a vinyl polymeric activator and a metal oxide catalyst, which system is adapted to effect cross-linking of the polymer at a temperature and in a time period employed in the shoe-manufacturing process, the sheet material optionally coated on one or both sides with an adhesive thermoplastic polymer, whereby the flexible sheet material may be employed between an outer leather and an inner shoe liner, and forms a bonded, stiff stock material as a box toe stiffener or shoe counter. U.S. Patent No. 4,247,427 (Edinger) discloses thermoplastic segmented copolyester elastomers consisting essentially of a multiplicity of recurring short chain ester units and long chain ester units joined through ester linkages, said short chain ester units amounting to 15 to 75 percent by weight of said copolyester and being derived from dicarboxylic acid such as an aromatic acid, e.g., terephthalic acid or a mixture of terephthalic acid and isophthalic acid, and an organic diol such as butanediol, and said long chain ester units amounting to 25 to 85 percent by weight of said copolyester and being derived from dicarboxylic acid such as an aromatic acid, e.g., terephthalic acid, or a mixture of terephthalic and isophthalic acids, and a long chain glycol such as polytetramethylene ether glycol, said copolyester having a melt index of less than 150 and a melting point of at least 90°C, modified with 0.75 to 20 parts by weight, per 100 parts by weight of elastomer, of a multi-functional carboxylic compound taken from the group consisting of aromatic and aliphatic anhydrides having at least two anhydride groups. The modified elastomer possesses improved adhesion particularly at high temperatures and under high applied stress. The adhesive composition can contain stabilizers as well as other

ingredients. It is disclosed that the adhesive is applied by hot melt techniques for surface lamination, for example, in furniture manufacture, vinyl lamination, sole attachment and box-toe construction in shoe assembly.

5 Summary of the Invention

This invention relates to a method of manufacturing a shoe, said method comprising coating at least a portion of a footwear upper with an ultra¬ violet curable resin composition having sufficient polymerizable functionality to cure to a thermoset state, but having insufficient polymerizable functionality to o embrittle the resin when cured, and exposing said coating to ultra-violet radiation sufficient to cure said coating. The coating and curing are typically integrated into the manufacture of the shoe and thus, the coating and curing are typically accomplished within the cycle time of said manufacturing. By "footwear upper" is meant that portion of the footwear above the sole. While this method is 5 particularly useful in reinforcing that the toe portion of the footwear upper, it will be useful in reinforcing other portions of the footwear upper, e.g. the heel portion, if desired. By "ultra-violet radiation" is meant radiant energy from that portion of the electromagnetic spectrum having a wavelength between about 0.01 micrometers and about 0.4 micrometers. By "embrittle" the resin is meant o that a cured film of the resin will have sufficient flexibility to resist fracture upon the incidence of impact forces normally encountered by dress or casual footwear.

Detailed Description of the Invention 5 It has been found that ultra-violet curable resins can be used in box-toe construction to obtain a coating with sufficient stiffness to reinforce a footwear upper material, but also sufficient flexibility to resist cracking during the footwear production process and in use in casual or dress footwear.

The resin can be of any chemical composition which yields a 0 polymerizable composition and a cured film with the desired characteristics.

Typically, however, the resin will be a polyester oligomer having acrylate

functionality. Such polyester oligomers are typically derived from hydroxy¬ functional polyesters by the reaction thereof with acrylic acid or a reactive derivative thereof, e.g. an anhydride, acid halide or transesterifiable ester thereof. The resin should have sufficient functionality polymerizable by exposure to UV radiation so that the resin will cure to a thermoset state. However, the functionality should not be so great that the resin has insufficient flexibility to withstand impact forces that can fracture a cured film of the resin. Typically, the resin will have a functionality of less than about 4, more typically less than about 3, and even more typically less than about 2, e.g. typically from about 1.1 to about 1.9. The resin may have a functionality of one or less when an additional monomer effective as a crosslinker, e.g. tripropylene glycol diacrylate, is employed. If the resin has too great a functionality, it will be too brittle to withstand the forces encountered in further manufacturing of the shoe from the coated upper and/or in use as footwear. A useful measure of embrittlement is whether a cured film at a thickness of 50 micrometers shows visible fractures when bent 180 degrees.

The reinforcing ultra-violet curable resins, after cure thereof, typically have a glass transition temperature (e.g. as measured by differential scanning calorimetry or by dynamic mechanical analysis of the torsional modulus) of less than about 20°, e.g. typically from about -10°C to about 10°C. Cured films of the reinforcing ultra-violet curable resins typically exhibit a tensile strength of from about 10 N/mm ² to about 100 N/mm ² . Cured films also typically exhibit a compression strength greater than 85 grams with a brittleness temperature less than -10°C. Uncured resin typically has a softening point in the range 70°C to 150°C and a viscosity (at 190°C.) of less than 150 poise.

The resin can be applied to a variety of footwear upper materials, including leather and synthetic materials, woven and nonwoven fabrics, and a wide variety of polymeric materials and will readily adhere thereto. A 1-50 mil film of the copolymer on the substrate provides a tough resilient reinforcing coating on the substrate so that it can be shaped and otherwise molded to the

desired configuration and will retain this shape during use. These resins are excellent reinforcing adhesives for box-toe construction since the products exhibit a high degree of stiffness or modulus while maintaining excellent impact resistance and low brittleness temperature. The resins can be employed to reinforce a variety of natural and synthetic, flexible substrates. They are particularly useful with leather, suede and synthetic materials; open- and closed-cell materials derived from polyurethane, vinyl, natural rubber, neoprene, styrene-butadiene copolymer, polybutadiene or the like; woven and nonwoven fabrics obtained from natural fibers such as cotton, wool, silk, sisal, hemp, jute, kenaf, sunn and ramie; woven and nonwoven fabrics derived from rayon (viscose), cellulose esters such as cellulose acetate and cellulose triacetate, proteinaceous fibers, such as those derived from casein, and synthetic fibers or filaments including polyamides such as those obtained by the condensation of adipic acid and hexamethylenediamine or the like, polyesters such as polyethylene terephthalate, acrylic fibers containing a minimum of about 85 percent acrylonitrile with vinyl chloride, vinyl acetate, methacrylonitrile or the like and the modacrylic fibers which contain lesser amounts of acrylonitrile, copolymers of vinyl chloride with vinyl acetate or vinylidene chloride, the formal derivatives of polyvinyl alcohol and olefin polymers such as polyethylene and polypropylene; paper; cork; elastomeric materials; and the like.

The resins are applied to the substrate as a neat liquid, with added diluents, or in solution and upon curing provide greater stiffness while maintaining flexibility of the substrate. The resin can be applied using conventional coating procedures, such as spraying, printing, dipping, spreading, rolling, drip coating, curtain coating, etc. and the film thickness can range from about 25 micrometers up to about 1 ,250 micrometers. While for most constructions the resin is applied to only one side of the substrate, it may be applied to both sides and a fabric or the like applied to either side, or both, to form a sandwich-type construction. In a typical box-toe construction, the resin is printed onto one side ofthe substrate to a thickness of 50 micrometers to 250

micrometers. A fabric liner that is sufficiently permeable by UV radiation (nylon, polyester, cotton, etc.) may be applied to the interior of the box-toe before the resin has been cured.

The resin is typically cured in the presence of a photoinitiator susceptible to ultra-violet radiation. Examples of such photoinitiators include oxygenated hydrocarbon compounds containing an aryl group, e.g. benzoin, benzoin ethers, alpha.alpha-dimethoxy-aipha-phenylacetophenone, diethoxyacetophenone, alpha-hydroxy-alpha.alpha-dimethylacetophenone, and 1-benzoylcyclohexanol. The photoinitiator is typically present at from about 0.01 to about 20%, more typically at from about 0.5 to about 5%, by weight of the radiation curable components. To ensure that the composition does not prematurely polymerize, a free radical inhibitor may be added to the resin. Examples of suitable inhibitors include hydroquinone and the methyl ether thereof or butylated hydroxy toluene at a level of from about 5 ppm to about 2000 ppm by weight of the polymerizable components.

The resin can be mixed with other coating components prior to application to the footwear material. The compositions may optionally include other substances such as fillers, resins, monomers and additives such as anti¬ oxidants and rheological modifiers. An example of a useful filler is a pigment such as titanium dioxide. For example, flow and levelling agents, e.g. BYK-307 and/or BYK 310, available form BYK-Chemie USA, Wallingford, Connecticut, can be used to modify the coating characteristics of the polymerizable composition. Methods of coating and materials used in coatings are described in Encyclopedia of Polymer Science and Engineering, vol. 3, pp. 552 - 671 and supp. vol., pp. 53, 109 and 110 (John Wiley & Sons, Inc., N.Y., N.Y., 1985), the disclosure of which is incorporated by reference.

Other coating components useful in this invention include materials which are capable of addition copolymerization with the resin to form a useful polymer composition. The copolymerizable components include mono-ethylenically unsaturated monomers capable of homopolymerization, or copolymerization with other ethylenically unsaturated monomers, as well as

copolymerization with the compound. Examples of such copolymerizable components are addition-polymerizable monomers and oligomers and polymers thereof. Addition-polymerizable monomers are compounds having one or more carbon-carbon unsaturated bonds. Examples of the compounds are acrylic acid and salts thereof, acrylates (e.g. Iower alkyl acrylates), acrylamides (e.g. Iower

N-alkyl acrylamides), methacrylic acid and salts thereof, methacrylates, methacrylamides, maleic anhydride, maieates, itaconates, styrenes, vinyl ethers, vinyl esters, N-vinyl-heterocyclic compounds, allyl ethers, and allyl esters and derivatives thereof. In addition, a crosslinking compound having an activity of increasing the degree of hardening of the formed polymeric compounds, by crosslinking the polymeric coating can be employed. Such crosslinking compounds are so-called poly-functional monomers having a plurality of ethylenic or vinyl groups or vinylidene groups in the molecule. This addition will be especially useful if the resin chosen has, on average, only one ethylenic unsaturation per molecule, e.g. a polyester monoacrylate.

Examples of a number of the various polymerizable compounds which may be included in the polymerizable compositions of the present invention include ethylene glycol diacrylate, propylene glycol dimethacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, bis(4- acryloxypolyethoxyphenyl)propane, 1,5-pentanediol diacrylate, neopentyl glycol diacrylate, 1 ,6-hexanediol diacrylate, polypropylene glycol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, N-methylol-acrylamide, diacetone-acrylamide, triethylene glycol dimethacrylate, pentaerythritol tetra-allyl ether.

Examples of useful reactive oligomers include low molecular weight polymers (e.g., about 1 ,000 to 25,000 g/mole) having polymerizable ethylenic unsaturation. Specific examples include maleic-fumaric unsaturated polyesters, acrylate-terminated polyesters (e.g. those described in U.S. Patent No. Re 29,131 to Smith et al.), acrylic copolymers having pendant vinyl unsaturation (e.g. allyl acrylate/acrylic copolymers), epoxy acrylates, and

polyurethane acrylates.

The polymerizable composition may also contain material which cure upon the exposure to heat and/or oxidants, e.g. drying oils. Drying oils are natural, modified or synthetic materials which cure upon exposure to air. Natural drying oils are triesters of glycerol with mixtures of fatty acids, some of the fatty acids having two or more double bonds that are conjugated or are separated by a single methylene group. Synthetic drying oils are typically natural or synthetic fatty acids esterified with a glycol or polyol other than glycerol, e.g. pentaerythritol. Drying oils are discussed in Z. Wicks, "Drying Oils", Encyclopedia of Polymer Science and Engineering, vol. 5, pp. 203-214 (John

Wiley & Sons, Inc. N.Y., N.Y., 1986), the disclosure of which is incorporated herein by reference.

The resin and copolymerizable component can be mixed in any convenient manner which will place the component and compound in a sufficiently reactive association to form a polymer on subsequent curing thereof.

Generally, simple mixing of the polymerizable component and the resin will suffice. Other useful techniques include conventional wet chemistry techniques, e.g., dissolution in a common solvent system.

The amount of other polymerizable component will be chosen in relation to the effect desired therefrom. The effect on the properties of the polymer and/or degree of crosslinking of the cured polymeric composition can be determined by conventional techniques, e.g., adhesion to substrates, resistance to solvents (e.g., swelling, extractibles, and/or spot-testing).

The coated surface is then exposed to sufficient energy, e.g. heat or electromagnetic radiation to cure the composition. Suitable sources of electromagnetic radiation that may be desirable in addition to the ultraviolet light include electron beam or radioactive sources such as are described in U.S. Pat. No. 3,935,330 issued Jan. 27, 1976 to Smith et al. To enhance the rate of curing of various components free radical initiators may be included in the composition such as benzoin, benzoin ethers, Michler's Ketone and chlorinated polyaromatic hydrocarbons. Other free radical initiators are ordinarily organic

peroxides, hydroperoxides, peroxy acids, peroxy esters, azo compounds, ditertiary butyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, tertiary butyl hydroperoxide, 1,5-dimethyl-2, 5-bis (hydroperoxy)-hexane, peroxyacetic acid, peroxybenzoic acid, tertiary butyl peroxypivalate, tertiary butyl peroxyacetic 5 acid and azobisisobutyronitrile. The free radical initiator is typically present at from about 0.01 to about 20% by weight of the radiation curable components. To ensure that the composition does not prematurely polymerize, a free radical inhibitor may be added to the polymerizable composition. Examples of suitable inhibitors include hydroquinone and the methyl ether thereof or butylated l o hydroxy toluene at a level of from about 5 ppm to about 2000 ppm by weight of the polymerizable components.

Particularly preferred sources of curing radiation emit electromagnetic radiation predominantly in the ultra-violet band. The amount of radiation necessary to cure the composition will of course depend on the angle

15 of exposure to the radiation, the thickness of the coating to be applied, and the amount of polymerizable groups in the coating composition, as well as the presence or absence of a free radical initiating catalyst. For any given composition, experimentation to determine the amount of radiation sensitive pi bonds not cured following exposure to the radiation source is the best method

20 of determining the amount and duration of the radiation required. Typically, an ultra-violet source with a wavelength between 200 and 300 nm (e.g. a filtered mercury arc lamp) is directed at coated surfaces carried on a conveyor system which provides a rate of passage past the ultra-violet source appropriate for the radiation absoφtion profile of the composition (which profile is influenced by the

25 degree of cure desired, the thickness of the coating to be cured, and the rate of polymerization of the composition).

The following examples illustrate the invention more fully, however, they are not intended to limit the scope ofthe invention and numerous variations will be evident to those skilled in the art. In these examples all parts,

30 percentages, and ratios are on a weight basis, unless otherwise indicated.

EXAMPLES

Example 1

A sample of an acrylated polyester (available from Huls, AG, Marl, Germany, as DYNACOLL A 6089) is heated to about 100°C and mixed with a photoinitiator susceptible to ultra-violet radiation. The mixture is then applied to a leather upper at a thickness of about 50 micrometers. The coating is then cured by passing at a line speed of 40 ft./minute under a UV lamp with an output of 400 watts/in.

Example 2

A sample of an acrylated polyester (available from Huls, AG, Marl, Germany, as DYNACOLL A 6183) is heated to about 100°C and mixed with a photoinitiator susceptible to ultra-violet radiation. The mixture is then applied to a leather upper at a thickness of about 50 micrometers. The coating is then cured by passing at a line speed of 40 ft/minute under a UV lamp with an output of 400 watts/in.