CA1077352A

CA1077352A - Coating and bonding method particularly for sole attaching

Info

Publication number: CA1077352A
Application number: CA244,952A
Authority: CA
Inventors: Conrad Rossitto
Original assignee: USM Corp
Current assignee: USM Corp
Priority date: 1975-03-06
Filing date: 1976-02-03
Publication date: 1980-05-13
Also published as: DE2609266C2; FR2303058A1; DE2609266A1; FR2303058B1; GB1540634A; JPS51112882A; JPH0262314B2; JPS6361352B2; JPS6485175A

Abstract

Abstract This is a method for coating or adhesively bonding surface, particularly for bonding tread members to shoe uppers, in which urethane polymeric material containing reactive -NCO groups and having crystalline segments in the polymer molecule is applied in fluid condition for wetting engagement with a surface and is converted through reaction to tough solid but still heat softenable condition.
The coated surface in heat softened condition may be pressed against a surface to which it is to be bonded to form an adhesive joint, and the joint cooled to give a strong adhesive union between the surfaces.

Description

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This invention relates to a rnethod for coating sur~aces and particularly to a method for adhesively bonding surfaces such as tread members to shoe uppers .
An important requirement in the attachment of tread members such as outsoles to shoe uppers is that the adhesive mus-t be applied in a fluid condition to enable it to wet and effect limited penetration of the surfaces to be joined.
It is also important that the adhesive become tough and strong thereafter.
The initial fluidity has been secured by the use of volatile organic solvent 10 solutions of adhesives where the development of strength and toughness after application was achieved by evaporation of the solvent. However, solvent type adhesives require a time delay for drying of the adhesive and present fire and health hazards from the solvent vapors.
~ ot melt adhesives have been used with some success; but the need for relatively high temperature to bring the adhesive viscosity to a low enough value for wetting adhesive engagement with the surfaces has created problems both with degradation of the adhesive and in some instances harm to the surfaces to be bonded. Additionally, the relatively short open time has imposed undesirably rigid time requirements in the assembly of surfaces with the adhesive still in fluid condition.
It is an object of the present invention to provide a method for coating or bonding surfaces using a coating material which is initially fluid at relatively low temperatures to enable it more readily to enter into wetting adhesive engagement with a surface and which is convertible by relatively mild treatment to a tough, solid but heat softenable condition capable of establishing substantially immediate strong adhesive union with a compatible adhesive or resin surface.

To this end and in accordance with a feature of the present invention, a polymeric urethane containing reactive -NCO groups and crystalline segments in the polymer molecule and having a relatively low crystalline melting point .

is coated on ~ surface at a relatively low temperature at which it is freely fluid for entering wetting adheqive engagement with that surface. The coating of the urethane material is converted to tough solid condition by reaction with a chain extender containing a compound having active hydrogens reactive with the-NC0 groups of the urethane. The chain extended coating may be assembled in heat softened condition against a compatible surface to be joined to the first mentioned surface to establish adhesive engagement and thereafter cooled to tough strong condition.
The invention relates to the method comprising the steps of bringing a normally solid polymeric urethane to fluid form, applying said urethane as a coating to a surface of an article, said urethane containing reactive ~NC0 groups and comprising segments having a crystalline melting point of from about 40C to about 90C, the reactive -NC0 groups in said urethane being in proportions to form after chain extension polymeric polyurethane which is viscoelastic when heated above said crystalline melting point, solidifying and crystallizing the urethane of said coating, thereafter bringing a compound providing active hydrogens into contact with said urethane coating at temperatures at which the solidified urethane coating is not distorted and reacting said compound with said -NC0 groups to chain extend said polymeric urethane, heating said chain extended polyurethane to a temperature above its crystalli-ne melting point to bring it to heat softened viscoelastic condition, pressing said heat softened viscoelastic chain-extended polyurethane against a coating of heat activatable adhesive compatible with said chain-extended polyurethane on the attaching surface of a second article said heat activatable adhesive comprising a polyurethane having reactive -NC0 groups ~)773S;~

and thereafter cooling said chaln-extended polyur~thane to tough strong condition bon~ing said second article to said ~irs-t mentioned article.

Reference is made to the attached drawings forming part of the disclosure of the present case in which:
FIG. 1 is a diagrammatic angular view with parts broken away of an outsole cementer disposing a band of adhesive on the attaching margin of an outsole.
FIG. 2 is a diagrammatic elevational view showing acti-vation of the adhesive on an outsole and show upper by radiantheating, and FIG. 3 is ~ diagrammatic elevational view showing the bonding of an outsole to a show upper in a sole attaching press.
The method of the present invention is primarily useful in adhesive bonding, particularly in bonding tread members to shoe uppers, and will be described with particular relation to this use. However, in some of its aspects the method is also useful in coating and bonding other surfaces such as wood, resinous or rubber materials, metal and fabrics and in reinforc-ing and stiffening sheet materials, for example, in stiffeningthe toes or counters of shoes.
As shown in FIG. 1, use of the adhesive in the process of cement outsole attaching may include the application of a band 10 of the urethane adhesive in fluid condition on the attaching margin of an outsole 12, preferably by an outsole cementer 14. The outsole cementer 14 comprises a nozzle 16 for applying ,~
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and spreading the adhesive, a drive wheel 18 for moving the outsole 12 at a desired rate passed the nozzle 16 and a guide 20 for maintaining the margin of the outsole 12 in desired relation to the no~le 16. As shown in FIG. 1, the cementer applies a band 10 extending around at least the forward portion of the outsole 12, but the band 10 may extend around the entire margin of the outsole depending on the shoe construction involved.
The same or other compatible adhesive may also be applied to the attaching surface of the bottom of a shoe upper.
The deposited urethane adhesive is then subjected to moisture, suitably in a steam cabinet or other device for providing moisture, and preferably, limited heating to the deposited adhesive to effect chain extension of the adhesive.
After chain extension of the adhesive, completion of the sole attaching process involves (see FIG. 2) disposing the outsole 12 and a shoe upper 22 having adhesive on the attaching surface 24 on the bottom of the shoe upper on a rack 26 spaced from a radiant heating unit 28 to warm the adhesive to a temperature above its crystalline melting point and bring it to viscoelastic condition. After heating of the adhesive on the bottom of the shoe upper 22 20 and on the outsole 12, the outsole 12 is positioned on the bottom of the shoe upper 22 and the assembled outsole 12 and shoe upper 22 are placed in a sole attaching press 30, (see FIG. 3) and subjected to sole attaching pressure.
The present method gives novel advantage~s through the ordered sequence of the development of physical properties resulting from temperature and chemical actions on the adhesive coordinated with the crystalline properties of segments of the resin and the relatively low molecular weight of the adhesive. The adhesive may be brought to liquid form for application either by heating it to molten ' condition or by addition of a solvent.

Where the adhesive is applied in molten form, it requires only a temperature above the crystalline melting point of the resin segments to give it the Eluidity :~07735'~
needed for wetting aclhesive engagement with a surEace to be bonded. The term "crystalline melting point" is the temperature at which crystalline segments of the polymer melt and is determined as the temperature of the major endotherm peak in a differential thermal analysis. When the polymer is brought above this temperature in activation, the crystalline segments melt and cause softening of the polymer coating or film. After application, the adhesive is brought below that crystalline melting point and is al:Lowed to crystallize to develop a resistance to flow and distortion at temperatures used in the succeeding step.
The adhesive may also be brought to liquid form by dissolving it in an inert volatile solvent for application at room temperature or at slightly elevated temperatures. Solvents which may be used are volatile organic liquids which do not contain active hydrogen. Among those which have been employed are xylol, toluene~ dimethyl formamide, acetone, methyl ethyl ketone, ethyl acetate, cellulose acetate, methylene chloride and mixtures of these. Particularly useful solvents have been mixtures of toluene with up to about 85% by weight based on the weight of the solvent mixture of methylene chloride or methyl ethyl ketone. Because OI the nature of the urethanes employed in the present method, relatively high solids content solutions, for example, 60% by weight and higher have viscosities low enough for application in wetting engagement with surfaces.
Also, smaller percentages of solvents may be useful where it is desired to apply the urethane material at moderately elevated temperatures below temperatures needed to melt the urethane in the absence of solvents. If the adhesive applied is a solution, the solvent is evaporated off before subsequent treatment.
That step following the formation of a coating of the adhesive is the reaction o~active isocyanate-groups of the adhesive at warm or moderately elevated temperatures with a chain extending agent providing at least two active hydrogens such as water vapor or steam or similar chain extending agents to bring the adhesive to a tough flow resistant, but heat softenable condition. In chain , , ~07~35'~

extended state, the crystalline melting point i8 substantially unchanged from that of the original urethane adhesive so that when heated above the crystalline melting point the chain extended adhesive becomes viscoelastic, namely, somewhat rubbery, but deformable and tlowable under pressure and is tacky and capable of adhesive union with a compatible surface such as a wood, metal, or Eabric surface coated with the same or a compatible adhesive or with a resin e . g .
vinyl resin, surface. By reason of the viscoelastic condition and the somewhat rubbery physical state of the chain extended adhesive at temperatures above 10 its crystalline melting point, bonds established by contact of the adhesive surface with another surface have very high initial bond strength so that, for example, in assembly of a shoe sole and a shoe upper, tendency of the sole to separate from the upper because of the springiness of the sole is prevented.
The adhesive which develops the successive advantageous physical states under the successive physical and chemical treatments is based on a polyurethane having reactive -NCO groups, suitably an -NCO terminated prepolymer from reaction of a relatively low molecular weight polyol having a crystalline melting point in the range of from about 40C . to about 90C., preferably from about 40C. to 65C. with an excess of diisocyanate.
Suitable polyol materials include the hydroxyl terminated polycaprolactones and polyesters of 6 to 12 carbon atom aliphatic dicarboxylic acids such as sebacic, adipic, azelaic, suberic and dodecanedioic acids with, preferably even numbered, glycols having from 2 to 6 carbon atom chains such as 1,4-butanediol . The ~ acid component of the polyester polyol may include from about 5% to about - 25% on a molar basis of cycloaliphatic acid such as 1,4-cyclohexane dicarboxylic acid or 1, 2-cyclohexane dicarboxylic acid to promote adhesion particularly to resin-rubber surfaces and from about 5% to about ~5% on a molar basis of aromatic dicarboxylic acid such as terephthalic acid or isophthalic acid to improve resistance to plastici~ers. The glycol component may include from . . .
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about 5O to about 15% on a molar basis o~ diethylene glycol or cycloaliphatic glycols such as 1,4-cyclohexane dimethanol to improve tack and wetting proper-ties and give better reactivity with water vapor. These polyols should have a molecular ~,veight in the range from about 1, 000 to about 10, 000 and preferably from about 2,000 to about 4,000.
The polyurethane material for application to the surface to be bonded is made by reaction of one or more of -the above polyols with a diisocyanate in proportions to give an -NCO to -OH ratio in a range from about~5 to about 10 3Ø Any of the available diisocyanates may be used including tolylene diisocyanate, diphenylmethane diisocyanate, dicyclohexyl methane diisocyanate. The polyurethane material is preferably made without the use of a catalyst and it is desirable to include a stabilizer such as an acid chloride, for example, benzoyl chloride, acetyl chloride or sebacoyl chloride in amount of from about 0 . 05% to about 0. 2% by weight of the polyurethane material .
It has been ~ound that polyurethanes formed using diphenylmethane diisocyanate, react with water much more rapidly than do polyurethane materials from reaction using tolylene diisocyanate; but that the latter polyurethane materials are more stable on storage. Improved storage stability coupled with rapid reaction rate may be obtained by a combination of both diisocyanates.
Because of the differences in rate of reaction, it is preferred to add the tolylene diisocyanate first and allow it to react for a limited time which enables the -NCO group in the para position to react with the polyol, after which diphenylmethane diisocyanate may be added. Useful ratios of these diisocyanates may be from equal parts on a molar basis to 80 moles of diphenylmethane diisocyanate with 20 moles of tolylene diisocyanate.

The speed of the chain extension reaction of the urethane layers may be increased by the use of catalysts. Where chain extension is effected by moisture, tertiary amines such as N-methyl morpholine, triethylene diamine ,: :

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and other known catalysts such as dibutyl tin dilaurate and stannous swlfate may be incorporated in the urethane material. In general, amounts of catalyst from about 0 . 05% to about P6 by weight, basecl on the weight Oe the urethane may be used.
While the urethane forms an excellent adhesive or coating by itself, it may be desirable to include other materials æuch as plastici~ers, fillers and tackifiers. Plasticizers, particularly normally solid plasticizers, are of value both to reduce the viscosity of the urethane when in hot molten condition and 10 to modify the properties of the final film. Among plasticizers useful with the urethane are dicyclohexyl phthalate, triphenyl phosphate, diphenyl phthalate and cycloaliphatic epoxies such as monomers of the Bisphenol-A type.
Tackifiers effective to improve the establishment of adhesive relation include tackifiers of the hydrocarbon type such as the terpenes e . g. alpha-and beta-pinene polymers, low molecular weight styrenes such as polyalphamethyl styrene, and rosin esters.
Also inert fillers in general such as clays, carbonates, titanium dioxide and others may be included in the urethane compositions.
Reaction of the diisocyanate with the polyol has been found to raise the crystalline melting point only a few degrees above the crystalline melting point of the polyol itself. For example, a butanediol sebacate polyol may have a crystalline melting point of 49C., and the polyurethane from reaction of this polyol with diphenylmethane diisocyanate in a ratio of 1. 5 -NCO to 1 -OH will have a crystalline melting point OI only 54C.
The polyurethane material may be applied in fluid condition to a surface such as the sole attaching surface on the bottom of a shoe upper or the attaching surface of an outsole by conventional applicator means or even by hand. Relatively low application temperatures, for example, temperatures of 80C. to 100C., have been found usefi,ll with solvent-free polyurethane materials having crystalline . . .

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melting points as high as about 70C. Solvent containing polyurethane compositions may be applied at room temperature or at slightly elevated temperatures.
It is desirable that the thickness of coatings of the urethane material be uniform in order that the action of the chaln extending agent over the whole extent of it and throughout, thickness of the urethane coating or filler be uniform.
It is preferred that the coating be from about l to about 5 mils in thickness for most satisfactory and uniform chain extensions throughout the thickness of the coating. Relatively thin coatings which may be as thin as 0. 001" are 10 effective on relatively regular surfaces such as the attaching surface of an outsole, and coatings as thin as 0 . 003" may be applied to more irregular surfaces such as the sole attaching surface on the bottom of a shoe upper.
After deposition of the polyurethane, the material of the coating is preferably allowed to crystallize before being subjected to chain extension. That is, the development of crystallinity serves to resis-t distortion through flow of the deposited material under the higher temperatures to which the coating is subjected in the chain extension step.
To bring the deposited polyurethane to the desired state for bond formation, it is subjected to a chain extension treatment involving exposing the surface of the coating to a compound having two active hydrogens for reaction with the -NCO groups of the polyurethane. A preferred chain extension agent is water, preferably in the form of vapor or steam, for example, in a high humidity room or in proximity to a steam or vapor source. Other chain extending agents such as diamines or glycols may also be used. It is preferred to use temperatures somewhat above room temperature for the chain extension step and temperatures from about 90F. up to about 190F. at a relative humidity of from about 50%

to about 95% have been found effective to insure chain extension at reasonable speed, e . g. from about 10 to about 30 minutes, without distortion of the urethane coating. The chain extension reaction should be carried to on extent at which . . .
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the film becomes elastoplastic on heat activation, but not markedly cross-linked, i . e . the film is still soluble or attacked by active polyurethane solventa such as dimethyl formamide or tetrahydrofurane.
After chain extension, and elimination of free water or other chain extending agents from the surface of the urethane coating, the coating may be heated to bring it to actively adhesive condition. Radiant heating is preIerred but other forms of heating such as convective heating may be used. The heating should be such as to bring at least the surface of the urethane coating rapidly, 10 preferably within about 15 to 30 seconds, to a temperature above the crystalline melting point, preferably to a temperature in the range of from about 120F.
to about 180F. so that at least the surface is in a viscoelastic condition capable of adhesive union with a compatible surface such as a vinyl resin or adhesive layer on the article to be bonded to the coated surface. Using urethanes with crystalline melting points up to about 158F., excellent bonds have been obtained with attaching temperatures as little as 9F. above the crystalline melting point.
Completion of the adhesive bond involves bringing together the surfaces with heat activated urethane between them and subjecting the assembly to pressure to insure good overall engagement. It has been found that limited relative movement of the surfaces to be joined may be secured after the initial assembly and before pressure because of the viscoelastic condition of the adhesive;
but that after the assembly is subjected to pressure, an initial high strength bond is secured. The ultimate bond on cooling of the urethane adhesive has excellent toughness and flexibility in order that the adhesive may successfully withstand the stresses encountered in the use of a shoe having the sole attached by means of this urethane adhesive.

While the coating or bonding method of the invention has been described in terms of applying the adhesive in fluid molten or solution form, the method may also be practiced by providing the chain extended adhesive as a supported _g_ ~7~;~5~
or unsupported ~lm and bonding it in heat activated form to a compatible surface as a coating or between compatible surfaces as an adhesive bonding the surfaces together .
The following examples are given to ald in understanding the invention.
It is to be understood that the invention is not restricted to the particular materials, proportions or procedural details set forth in the examples.
Example 1 An -NCO terminated prepolymer is prepared by reacting a hydroxyl 10 terminated butanediol adipate polyester having a molecular weight of 2600 and a crystalline melting point of about 49C . with diphenylmethane diisocyanate in proportions providing an -NCO to -OH ratio of 1. 5 . The resulting prepolymer has a melting point of about 54C. and is fluid with a viscosity of about ô,000 cps. at 100C.
The above and other melting points given in this and subsequent examples are crystalline melt points determined as endotherm peaks by differential thermal analysis .

The prepolymer is melted and brought to a temperature of 100C. and applied as a coating 0 . 003!' thick to the previously roughened sole attaching surface of a leather shoe upper and to the attaching surface of an outsole compounded -~
of a vulcanized butadiene styrene copolymer synthetic rubber.
The applied coatings are exposed to a high humidity atmosphere on a steam table at 70C . for 15 minutes for reaction of the moisture with -NCO groups of the prepolymer to effect chain extension. After this treatment, the material of the coatings is tough, strongly adherent to the attaching surface and capable of being softened to tacky condition adhesive to like adhesive surfaces at temperatures about 65C. The coatings on the attaching surfaces are subjected to infrared heat activation in a radiant heat activator for 30 seconds with the heat unit set at 60% input. The sole is assembled against the attaching surfaces of the -~07~35'~:
bottom of the shoe upper and the spotting tack is excellent. The assembly is pressed in a sole attaching press to complete the bond. A strong initial bond is formed with no separation or "grinning" and the bond strength is considered satisfactory for use of -the shoe.
Example 2 Test strips 1" by 7" of the materials listed in the following Table I are coated with molten prepolymer of Example l at 80C . to 90C . to provide a , coating thickness of 0 . 003" . After 15 minutes from the time of application of 10 the coatings, the strips are placed in a high humidity atmosphere on a steam table at 70C. or in a room at about 36C. and 68% relative humidity for times as noted in the table to react the -NCO groups in the material of the coating with water to effect chain extension. The strips are then activated by infrared heat in a conventional radiant heat activator (RHA) for 30 seconds with the heat unit of the activator set at 60% input. Activation raises the temperature of the coatings on the strips to about 68C. to 75C. The activated strips are then assembled in pairs as noted in the table, and pressed to complete bonds after which the assembled strips are cooled to room temperature and the bonds subject to testing. The results of the tests are reported in the table.

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An -NCO terminated prepolymer is prepared by reacting a hydroxyl terminated butanediol adipate polyester having a molecular weight of 3,000 and a melting point of about 50C with mixed diisocyanate in the molar ratio of two parts of diphenyl-methane diisocyanate and one part of tolylene diisocyanate in proportions providing an -MCO to -OH ratio of 2Ø The resulting prepolymer had a melting point of about 54C and is fluid with a viscosity of about 11,000 cps at 100C.
Test s-trips 1" by 7" were cut from an outsole sheet material purchased as surface-chlorinated Krato ~ , which is a styrene butadiene block copolymer of which the surface has been chlorinated, a polyvinyl chloride outsole sheet material, and a styrene butadiene copolymer outsole stock. Similar strips were also cut of shoe upper material including the backed polyvinyl chloride material known as Pattina~ and leather.
The strips of outsole material were coated with the molten prepolymer at 80C to 90C to provide a coating thickness of 0.003", and after application and cooling of the coatings, the strips were placed in a high RH 90% humidity atmosphere on a steam table at 70C for about one-quarter hour.
The strips of upper material were coated respectively with a solvent-type polyurethane (Estane)6~ adhesive on the backed polyvinyl chloride upper material and with a solvent-type phenolic resin-polychloroprene sole àttaching cement on the leather upper material. In each case the deposited adhesive coating was allowed to dry for elimination of the solvent.
The adhesive coated surfaces of the outsole material and upper material test strips were put in a radiant heat activator for 10 seconds with the radiant heat unit set at 55%
input. The surface temperature of the adhesive on the surfaces of the strips was about 80~C

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Strips of the adhesive coatecl backed polyvinyl chloride upper material were assembled with strips of the adhesive coated block copolymer outsole material and with the styrene butadiene copolymer outsole stock, and strips of the adhesive coated leather were assembled with the polyvinyl chloride outsole material and the assemblies were pressed together to comple-te the bonds.
When tested after seven days, the peel bond strengths were 31 lbs. per linear inch between the polyvinyl chloride material and the block copolymer, 27 lbs.
per linear inch between the leather and the polyvinyl chloride outsole material 10 and 39 lbs. per linear inch between the polyvinyl chloride material and styrene butadiene copolymer outsole stock.

Example 4 An -NCO terminated prepolymer was prepared by reaction of diphenyl methane diisocyanate and a polycaprolactone having a molecular weight of about 2B60 and a melting point of about 5~C., the prepolymer having a free -NCO content of 2.18%.
The prepolymer was melted and brought to a temperature of 100C. and 20 applied as a coating 0 . 003" thick to a previously roughened surface of outsole material formed of styrene-isoprene-styrene block copolymer. The applied coating was exposed to a 95% REl humidity atmosphere on a steam table at 70C.
for 30 minutes for reaction of the mixture with -NCO groups of the prepolymer to effect chain extension.
A viscous adhesive was prepared by dissolving a thermoplastic linear poly~ster urethane elastomer in a solvent mixture of approximately equal parts of tetrahydrofurane and methyl ethyl ketone, the solids content of this solution being about 20%. The urethane elastomer was a commercial product ("Estane"), 30 substantially free from cross links, obtained by reaction of one mol of an -OH terminated polyesterJ an aliphatic glycol and a diphenyl diisocyanate in :

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proportions leaving essentially no unreacted isocyanate or hydroxyl groups.
The resulting solution had a viscosity at room temperature of from about 2,000 to 3, 000 Cp9 . as determined by the Brookfield viscometer .
The above solution type adhesive was brushed on the previously roughened surface of a fabric backed polyvinyl chloride shoe upper material.
Twenty-four hours after application of the adhesive to the backed polyvinyl chloride material, the coating was subjected to infrared heat activation in a radiant heat activator for 30 seconds with the heat unit set at 60% input. The 10 heat activated backed polyvinyl chloride material was assembled with its adhesive coated surface against the similarly heat activated adhesive coating on the block copolymer sole material. Spotting tack was good. The assembly was pressed together to complete the bond. The initial bond as determined by a peel pull test was from 15 to 20 lbs. per linear inch. When the bond was tested after 7 days, the peel bond strength was 45 lbs. per linear inch, and failure occurred in the block copolymer.

Example 5 The procedure oP Example 4 was repeated except that a styrene butadiene copolymer rubber outsole material was used in place of the block copolymer material. The assembly showed good initial tack, very good initial bond strength and a peel bond strength after 7 days of 39 lbs. per linear inch.
In this case failure occurred in the backed polyvinyl chloride shoe upper material .

~xample 6 The following -NCO terminated prepolymers are prepared by reacting polyols with diphenylmethane diisocyanate in the -NCO to -OH ratio shown in the following Table II. The polyol for prepolymer 2 is a polycaprolactone 1~7735'~

having a molecular weight of 2890 and a melting point of about 56C. and the prepolymer is prepared by reaction of the polyol with diphenylmethane diisocyanate in proportions providing an -NCO/-OH ratio of 1. 75 . The polyol for prepolymer 3 is an -OH terminated butanediol sebacate polyester having a molecular weight of about 2000 and a m~elting point of about BD~C., and the prepolymer is prepared by reaction of the polyol with diphenylmethane diisocyanate in proportions providing an -NCO/-OH ratio of 1.75.

Test strips 1" by 7" of the materials listed in the following Table II
10 are coated with molten prepolymer at 80C. to 90C. to provide a coating thickness of 0.003". After 15 minutes from the time of application of the coatings, the strips are placed in a high humidity atmosphere on a steam table at 70C. for 15 minutes to react the -NCO groups in the material of the coating with water to effect chain extension. The strips are then activated by infrared heat in a conventional radiant heat activator (~HA) for 30 seconds with the heat unit of the activator set at 60% input.
Activation raises the temperature of the coatings on the strips to about 68C. to 75C. The activated strips are then assembled in pairs as noted in the table, and pressed to complete bonds after which the assembled strips are cooled to room temperature and the bonds subject to testing. The results of the tests are reported in the table.

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Example 7 An -NCO terminated prepolymer is prepared by reacting a hydroxyl terminated butanediol adipate polyester having a molecular weight of 2600 and a crystalline melting point of about 4~lC. with diphenylmethane diisocyanate in proportions providing an -NCO to -OF~ ratio of 1. 5 . The resulting prepolymer has a melting point ~ ut 54C. and is fluid with a viscosity of about 8000 cps. at 100C~

The prepolymer was dissolv~ m a 60% by weight solids solution 10 in a solvent mixture of 4 parts ~ne chloride and 1 part of toluene.

The solution had a viscosity of about 1500 cps.
The solution is applied as coatings 0.005" thick to the previously roughened surface of leather shoe upper material and to the surface of an outsole material compounded of a vulcanized butadiene styrene copolymer - synthetic rubber and the coatings were dried.
The coatings are exposed to a high humidity atmosphere on a steam ta~le at 70C. for 15 minutes for reaction of the moisture with -NCO groups of the prepolymer to effect chain extension. After this treatment, the material of the coatings is tough, strongly adherent to the surfaces and capable of being softened to tacky condition adhesive to like adhesive surfaces at temperatures of about 65C. The coatings are subjected to infrared heat activation in a radiant heat activator for 20 seconds with the heat unit set at 55% output.
The surfaces are assembled together and pressed to complete the bond.
When tested after 7 days, the peel bond strength is 40 lbs. per linear inch.

Example 8 A prepolymer solution was prepared as in Example 7 but containing 0,25% of dimethyl pipera~ine based on the weight of the prepolymer.

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The solution was coated onto leather and to vulcani~ed butadiene styrene copolymer synthetic rubber and the coatings dried as in Example 7.
Chain extension was effected by exposing the coatings for 15 minutes at 85C. to an atmosphere having only 18% to 20% relative humidity to bring the coatings to tough, strongly adherent condition.
Thereafter the coatings wexe heat activated and the leather and synthetic rubber assembled and pressed as in Example 7. Peel bond strength after seven days was 40 lbs. per linear inch.

Example 9 An -NCO terminated prepolymer is prepared by reacting a polycaprolactone having a molecular weight of 2860 and a crystalline melting point of about 54C. with diphenylmethane diusocyanate in proportions providing a free -NCO content of 2.18%.
The prepolymer is dissolved to form a 60% by weight solids solution in toluene. The solution has a viscosity of about 1600 cps.
The solution is applied as coatings 0.005" thick to the previously 20 roughened surface of backed polyvinyl chloride shoe upper material and to the surface of an outsole material compounded of a sytrene butandiene styrene block copolymer.
The applied coatings are exposed to a 90Q6 relative humidity atmosphere on a steam table at 70C. for 30 minutes for reaction of the moisture with -NCO groups of the prepolymer to effect chain extension. After this treatment, the mater;al of the coatings is tough, strongly adherent to the surfaces and capable of being softened to tacky condition adhesive to like adhesive surfaces at temperatures of about 65C. The coatings are subjected 30 to infrared heat activation in a radiant heat activator for 20 seconds with the heat unit set at 55% output. The surfaces are assembled together and .
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pressed to complete the bond. When tested after 7 days, the peel bond strength is 42 lbs. per linear inch.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The method comprising the steps of bringing a normally solid polymeric urethane to fluid form, applying said urethane as a coating to a surface of an article, said urethane containing reactive -NCO groups and comprising segments having a crystalline melting point of from about 40°C to about 90°C, the reactive -NCO groups in said urethane being in proportions to form after chain extension polymeric polyurethane which is viscoelastic when heated above said crystalline melting point, solidifying and crystallizing the urethane of said coating, thereafter bringing a compound providing active hydrogens into contact with said urethane coating at temperatures at which the solidified urethane coating is not distorted and reacting said compound with said -NCO groups to chain extend said polymeric urethane, heating said chain extended polyurethane to a tempera-ture above its crystalline melting point to bring it to heat softened viscoelastic condition, pressing said heat softened viscoelastic chain-extended polyurethane against a coating of heat activatable adhesive compatible with said chain-extended polyurethane on the attaching surface of a second article, said heat activatable adhesive comprising a polyurethane having reactive -NCO groups and thereafter cooling said chain-extended polyurethane to tough strong condition bonding said second article to said first mentioned article.

2. The method as defined in claim 1 in which said polymeric urethane is an -NCO terminated prepolymer from reaction of a diisocyanate and a polymeric polyol in proportions to give a ratio of -NCO to -OH in the range of from about 1.25:1 to about 3.0:1, said prepolymer having a molecular weight in the range of from about 1,000 to about 10,000 and said chain-extension is effected at temperatures of from about 90°F to about 190°F.

3. The method as defined in claim 2 in which said polyurethane is brought to fluid form for application as a coating by heating to a temperature above its crystalline melting point.

4. The method as defined in claim 2 in which said prepolymer is brought to fluid state for application as a coat-ing by dissolving it in a volatile organic solvent.

5. The method as defined in claim 2 in which polymeric polyol is a hydroxyl terminated polyester from the group consisting of polycaprolactones and aliphatic polyester of dicarboxylic acids having from 6 to 12 carbon atoms and glycols having from 2 to 6 carbon atoms, said polyol having a molecular weight of from about 2,000 to about 4,000 and a crystalline melting point of from about 40°C to about 60°C
and in which the diisocyanate and the polyol are reacted in proportions to give a ratio of -NCO to -OH in the range of from about 1.5:1 to about 2.5:1.

6. The method as defined in claim 1 in which said compound containing active hydrogen is water and is in the form of vapor or steam when brought in contact with said polymeric urethane to effect chain extension.

7. The method as defined in claim 6 in which said polymeric urethane is an -NCO terminated prepolymer from reaction of a diisocyanate and a polymeric polyol in proportions to give a ratio of -NCO to -OH in the range of from about 1.25:1 to about 3.0:1, said prepolymer having a molecular weight in the range of from 1,000 to about 10,000.