GB1601372A

GB1601372A - Lasting shoes with hot melt adhesives

Info

Publication number: GB1601372A
Application number: GB11911/78A
Authority: GB
Original assignee: Bostik Ltd
Current assignee: Bostik Ltd
Priority date: 1978-03-28
Filing date: 1978-03-28
Publication date: 1981-10-28
Also published as: FR2420936A1; AU4543079A; DE2912092A1; SE7902688L; IT7921312A0; IT1110655B; CA1126891A

Description

(54) IMPROVEMENTS IN OR RELATING TO LASTING SHOES WITH HOT MELT ADHESIVES (71) We, BOSTIK LIMITED, a British company of Ulverscroft Works, Ulverscroft Road in the City of Leicester, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is concerned with improvements in or relating to lasting shoes with hot melt adhesives.

The word "shoe" where used herein is used generically to include outer footwear generally and includes the article in the course of manufacture.

Various proposals have been made for adhesives for use in the lasting of shoe uppers.

During the shoe lasting operation a shoe upper is drawn to the shape of a supporting last.

Marginal portions of the upper are pulled across the shoe bottom and secured to the sole member. Usually the lasting operation is performed using machines designed to operate on toe, side, or heel portions of the shoe, or combinations thereof. It is required to secure these marginal portions to the shoe bottom in such a way that when the wiping instrumentalities are removed, the marginal portions of the upper remain in their wiped positions.

Modern lasting machines intended for use in lasting toe end, side, or heel portions of shoes are designed to operate quickly and require that adhesives used are applied readily and set sufficiently to hold the marginal portions of the upper adequately even though the wiping instrumentalities may dwell in their in-wiped position for only about two seconds, or not at all. Also, some manufacturing operations carried out subsequent to lasting are carried out at high temperatures, and it is therefore a requirement that the adhesives used for lasting should withstand temperatures in excess of 100"C so that the shoe can remain in its lasted condition. For example, toe lasting cements may be required to have softening points of more than 1200C, more often in the range 1500C to 2000C, and often in the region of about 1900C. These and other requirements impose restrictions on the time in which the adhesive must achieve a bond and on the flexibility and heat resistance required. Also, the adhesion characteristics must be such that at least the more commonly used shoe-making materials, e.g. leather and PVC (polyvinyl chloride) based upper materials and insole board materials, e.g. "Texon", are adequately bonded.

Modern lasting machines adapted for use with hot melt adhesives are equipped with facilities for accepting and melting the hot melts in various forms for example hot melts supplied in flexible rod form or as granules. In the case of rod form hot melt adhesives, further requirements are imposed on the adhesive in order that it may be supplied as a flexible, coilable rod which can be unwound from a coil and fed into the lasting machine by a rod feed device of the machine.

Butane diol terephthalate copolyesters are known to provide commercially acceptable hot melt toe lasting cements. However, these materials tend to be rather expensive to manufacture, and also, it is necessary, in order that the adhesive have good cohesive strength, to employ comparatively high viscosity materials. Unfortunately, higher viscosities tend to result in stringiness in the melted cement. Also, these materials tend to set quickly from mobile liquids to hard materials over a comparatively small temperature range, without demonstrating a tacky cohesive condition to any significant extent at or near their melting points. Consequently, although such materials can be formulated to be acceptable for toe and heel lasting, they tend to be less acceptable for lasting operations in which wiping instrumentalities do not dwell for any significant period of time to hold the marginal portions of the upper against the insole whilst the adhesive sets between them, and for lasting operations where flexibility together with toughness of the adhesive bond and a stable rod form of the adhesive are desirable.

It is one object of the present invention to provide an improved method of lasting using a hot melt adhesive.

We have found that certain copolyether esters can be formulated to provide hot melt adhesives highly satisfactory for use in a method of lasting shoes.

We have observed that these selected materials demonstrate less tendency to form "strings" when manufactured to the same viscosity as known butane diol terephthalate hot melt toe lasting adhesives, and are susceptible of manufacture to higher viscosities of the order of 1000 poise at 2400C without demonstrating stringing to an objectionable extent. A consequence of this possibility to provide polyester adhesives having viscosities within a wider range is the enhanced ability to select materials with viscosities appropriate for the particular blend of properties required of the adhesive including not only low stringing of the adhesive at higher viscosities but also the ability to bond shoe making materials, degree of crystallinity, speed of setting, and their tack and cohesive properties at or near the melting point, i.e. a less sharp setting, hereinafter referred to as their jammy nature.

Additionally, the molecular structure of the selected polyesters is such that bonds of good strength may be achieved with comparatively low viscosity polymers, and such that adhesives can be formulated having tack and cohesive properties at or near their melting point, and flexibility of the bonds formed which are more acceptable for side lasting operations than previously used hot melt polyester adhesives. Additionally, production of materials with comparatively higher viscosities facilitates extrusion of the resins into rod form of reproducibly uniform rod size.

The present invention provides, in one of its various aspects, in a method of lasting a shoe in which marginal portions of a shoe upper are secured to the shoe bottom by an adhesive, the use of a hot melt adhesive having a softening point (Ball & Ring) above 1200C, and a set-up time (as defined) of not more than 20 seconds, and comprising a copolyester and a stabilizer, the copolyester having a molecular chain made up of units corresponding to diol units and acid units derived from (a) one or more aliphatic diols having from 2 to 10 carbon atoms in its molecular chain; (b) an at least substantially difunctional poly(propylene oxide) diol having a molecular weight in excess of 500, to an extent of from 5 to 50 weight percent by weight of the diol units; and (c) terephthalic acid to an extent of from 60 to 100 mols per 100 mols of the acid units, and one or more other dicarboxylic acids to an extent of from 0 to 40 mols per 100 mols of the acid units.

By "set-up time" where used herein we mean the time for which the melted adhesive remains mobile after forming a bond under light pressure, as determined by dipping a strip of insole material into the molten cement, removing it and pressing it against a strip of shoe upper leather at room temperature under hand pressure, gently moving the insole and upper leather strips relative to each other about the bond, in the plane of the bond, and observing when the adhesive has set solid so that relative movement is no longer possible.

We prefer to use adhesives having a set-up time in the region of 2 to 10 seconds.

In an adhesive for use in a method according to the invention, the poly(propylene oxide) diol used is preferably a substantially difunctional poly(1,2-propylene oxide) diol of molecular weight from 1,000 to 2,500 more preferably about 2,000. Larger amounts of the poly(propylene oxide) diol confer increased flexibility to the adhesive coupled with increased flexibility of coilable rods of the adhesive, and also contribute to the jammy nature, low stringing ability, and setting characteristics of the polyester. However, larger amounts of the poly(propylene oxide) diol also render reaction times longer and conditions of production of the copolyester more time consuming, adversely affect adhesion characteristics and set-up time, and tend to lead to copolyesters of greater instability. For toe and heel lasting purposes, we have found that copolyesters having 5 to 35 %, more preferably 20 to 25 %, poly(propylene oxide) diol derived units by weight of the diol units are satisfactory, whereas for side lasting we may use copolyesters having up to 50% poly(propylene oxide) diol derived units by weight of the diol units.

Copolyesters for adhesives for use in a method according to the invention may have melting points (Ball & Ring) within a wide range of temperatures dependent on intended conditions of application and the materials to be lasted. Whilst materials with melting points as low as about 1200C may be acceptable in some instances, for toe and heel lasting, materials having melting points in the range 1500C to 2150C are more usually required. For side lasting, materials having melting points in the range 1500C to 1700C are more usually required. However, for use with automatic side lasting machines or seat lasting machines higher melting point materials may be used. Similarly, the copolyesters may have a viscosity within a wide range, and we prefer to use material which when manufactured has a viscosity in the range of about 100 to 1,000 poise at 2400C; materials with viscosities lower than 100 poise tend to have inadequate holding power to secure some stiffer shoe making materials whereas materials with viscosities greater than 1,000 poise tend to be rather difficult to use easily when forming adhesive bonds. In order to achieve melting points and crystallinity as required we prefer to employ polyesters having substantial quantities of terephthalate units and substantlal quantities of butane diol derived units in the molecular chain. Incorporation of units derived from the other acids and/or diols in the molecular chain affects various properties of the polyester, including not only the melting point but also for example adhesion, crystallinity, speed of setting, and flexibility of the polyester. Aliphatic diols for use in preparation of the polyester include saturated aliphatic diols especially 1.4 butane diol, and mixtures of 1.4 butane diol with 1.6 hexane diol. If desired, the aliphatic diol may include one or more diols having methyl or ethyl substituents on the molecular chain. Other short chain aliphatic diols and mixtures thereof may also be used, but in general we prefer to employ 1.4 butane diol to provide at least 50 mole % of the component (a) in order to achieve desirable adhesion and crystallinity. Where a mixture of aliphatic diols is employed to provide the component (a), it is convenient to employ terephthalic acid to provide all the dicarboxylic acid units, i.e. 100% of the acid units, although mixtures of acids may be used.

In other cases we prefer to employ in the acid units 60 to 90 mol %, more preferably, for toe lasting adhesives, 70 to 80 mol %, terephthalic acid derived units, and correspondingly 40 to 10 mol % or more preferably 30 to 20 mol % for toe lasting adhesives of one or more other dicarboxylic acids. Suitable dicarboxylic acids for use in admixture with terephthalic acid include cycloaliphatic, aromatic and aliphatic dicarboxylic acids and mixtures of two or more thereof. Suitable aliphatic dicarboxylic acids include those having from 6 to 12 carbon atoms as exemplified by suberic acid, adipic acid, dodecanoic acid, azelaic acid, sebacic acid, succinic acid, glutaric acid and mixtures of these. Terephthalic acid residues (because of the molecular structure of terephthalic acid which has carboxyl groups arranged at opposite positions on a benzene ring) when present in the polyester molecule tend to increase the crystallizability of the polyester. Isophthalic acid residues (because of the out-of-line relation of the carboxyl groups on the benzene ring of isophthalic acid molecules) tend to decrease the crystallizability of the polyester. Sebacic, azelaic and comparable aliphatic dibasic acids when present in the molecule with the phthalic acids introduce spacing between the benzene rings in the polymer chain and impart a flexibility to the polymer chain. Dimerized linoleic acid may also be included as a part of the acid component where it is desirable; the relatively long aliphatic chain of the dimerized acid does not align in orderly fashion and provides an internal plasticizing action and imparts a more resilient character to the polyester. For example, we may use isophthalic acid units to an extent of 5 to 30 mol % of the acid units, or 5 to 25 mole % aliphatic acid units, for example adipic acid; mixtures of terephthalic acid units, isophthalic acid units, and adipic acid units are preferred in which the units are present in the ratio of 76 to 78 mol % terephthalic acid units, 7 to 24 mol % isophthalic acid units, and 6 to 16 mol % adipic acid units. As will be understood by those skilled in the art, the acid units of the polyester may be derived directly from the acids themselves or their lower esters (e.g. methyl or ethyl esters), and the polyesters may be produced from esters of the required acids instead of the acids themselves where it is necessary or convenient to do so.

In order to control loss of viscosity and hydrolytic and oxidative behaviour of the copolyesters when molten, it is necessary to include a minor amount of stabilizer, and this is preferably introduced to the polyester charge during manufacture, prior to esterification.

Any suitable stabilizer system may be used and we prefer to employ triphenyl phosphite with any of the well-known high temperature resistant phenolic antioxidants, for example tris 2-methyl-4-hydroxy-5-t-butylphenyl butane, or pentaerythritol tetrakis 3.5-Di-t-butyl-4hydroxyhydrocinnamate. If desired, somewhat higher concentrations of phenolic resins may be used, an example being a terpene phenolic resin with a softening point of 1200C.

Whilst we prefer to formulate the copolyester to have the necessary properties, these may be enhanced by inclusion in the adhesive of minor amounts of fillers, colourants and resins if desired.

In order that the invention may become more clear there now follows a description of seven example polyester adhesives and their use in lasting machines. It will be understood that these examples have been selected for description to illustrate the invention by way of example and not by way of limitation thereof.

The example adhesives comprised copolyesters resulting from controlled reaction of charges of materials listed in Table I. After completion of the reaction, as indicated by viscosity determinations, the copolyesters were extruded into rod form for use as hot melt adhesives. It is calculated that the copolyesters comprised acid units in a molar ratio as set out in Table II and diol units in a weight ratio as shown in Table III. Physical properties of the copolyesters are shown in Table IV.

The various example polyesters were employed for toe and side lasting. To examine their abilities as toe lasting adhesives a BUSMC 4A Pulling and Lasting Machine was used to process shoe uppers of leather, "Porvair" (Registered Trade Mark) PVC, and Texon insoles. All the example polyesters were found to perform satisfactorily, example polyesters 3 and 4 being particularly satisfactory. Example polyesters 3 and 4 were compared at a 3-second dwell time with two control samples, namely a commercial terephthalic-adipic acid-butane diol type polyester with a viscosity of 200 poise at 2400C, and with a polyester of the same type having a viscosity of 400 poise at 2400C. Whilst example polyesters 3 and 4 showed little stringing, the conventional 400 poise ester showed excessive stringing and the commercial 200 poise material was only just satisfactory. When example polyesters 3 and 4 were produced as 4mm rod and wound on reels they showed considerably less tendency to crack in cold weather, to unwind and jump off the reels, than the control samples. Further, the lasted margins of shoes produced with example polyesters 3 and 4 were flatter and less wrinkled than those produced with the control samples.

Example polyester 7 was compared to the above control samples using a BUSMC Automatic Side Lasting Machine to process Porvair or leather uppers to Texon insoles.

Whereas the control samples were incapable of holding down the Porvair and only partially successful in holding down the leather, the material reasserting itself, example polyester 7 bonded both the leather and Porvair uppers to Texon insole material.

A polyester adhesive similar to example polyester 5 but having a viscosity of about 350 poise at 2400C was successfully employed as a heel lasting adhesive using a BUSMC seat lasting machine (BUSL Series 3) to process leather uppers to Texon insoles. In the resulting shoe, the lasting margin was securely held to the insole by the adhesive.

TABLE I Polyester charge (kilograms) Component Polyester: 1 2 3 4 5 6 7 Acid component Terephthalic acid 252.3 309.6 309.6 309.6 309.6 309.5 398.5 Isophthalic acid 79.7 27.88 27.9 46.5 69.2 44.5 Adipic acid - - 53.6 39.1 24.5 39.1 Mixed aliphatic acids 59.12 - - - - - Diol component 1.4 butane diol 225.0 259.0 269.0 269.0 269.0 269.0 207.4 1.6 hexane diol - - - - - - 68.0 Poly(propylene- 80.0 48.0 60.0 60.0 60.0 60.0 60.0 oxide) diol (mol.wt. 2000) Stabilizer 2.5 2.0 2.25 2.25 2.25 2.25 2.25 Catalyst 0.6 0.5 0.7 0.7 0.7 0.7 0.7

TABLE II Polyester - molar percentage of acid units Polyester: 1 2 3 4 5 6 7 Acid Units from Terephthalic acid 76.0 77.6 77.7 77.3 76.1 77.7 100.0 Isophthalic acid 24.0 7.0 7.0 11.6 17.0 11.2 Adipic acid 15.3 11.1 6.9 11.1 Mixed aliphatic acids 15.4 Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 TABLE III Polyester - weight percentage of diol units Polyester: 1 2 3 4 5 6 7 Diol Units from 1.4 Butane diol 68.75 83.4 78.0 78.0 78.0 78.0 60.0 1.6 hexane diol - - - - - - 18.0 Poly(propylene- 31.25 16.6 22.0 22.0 22.0 22.0 22.0 oxide) diol (mol.wt.2000) Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 TABLE IV Polyester properties Polyester: 1 2 3 4 5 6 7 Softening Point 186.0 195.0 192.0 192.0 192.0 192.0 190.0 (Ball & Ring) "C Viscosity at 2400C 100.0 350.0 520.0 340.0 590.0 320.0 600.0 (poise) Set-up time (seconds) 8.0 4.0 4.0 5.0 4.0 4.0 3.0 WHAT WE CLAIM IS : 1. In a method of lasting a shoe in which marginal portions of a shoe upper are secured to the shoe bottom by an adhesive, the use of a hot melt adhesive having a softening point (Ball & Ring) above 1200C, and a set-up time (as defined) of not more than 20 seconds, and comprising a copolyester and a stabilizer, the copolyester having a molecular chain made up of units corresponding to diol units and acid units derived from a) one or more aliphatic diols having from 2 to 10 carbon atoms in its molecular chain; (b) an at least substantially difunctional poly(propylene oxide) diol having a molecular weight in excess of 500, to an extent of from 5 to 50 percent by weight of the diol units; and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. TABLE II Polyester - molar percentage of acid units Polyester: 1 2 3 4 5 6 7 Acid Units from Terephthalic acid 76.0 77.6 77.7 77.3 76.1 77.7 100.0 Isophthalic acid 24.0 7.0 7.0 11.6 17.0 11.2 Adipic acid 15.3 11.1 6.9 11.1 Mixed aliphatic acids 15.4 Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 TABLE III Polyester - weight percentage of diol units Polyester: 1 2 3 4 5 6 7 Diol Units from 1.4 Butane diol 68.75 83.4 78.0 78.0 78.0 78.0 60.0 1.6 hexane diol - - - - - - 18.0 Poly(propylene- 31.25 16.6 22.0 22.0 22.0 22.0 22.0 oxide) diol (mol.wt.2000) Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 TABLE IV Polyester properties Polyester:

1 2 3 4 5 6 7 Softening Point 186.0 195.0 192.0 192.0 192.0 192.0 190.0 (Ball & Ring) "C Viscosity at 2400C 100.0 350.0 520.0 340.0 590.0 320.0 600.0 (poise) Set-up time (seconds) 8.0 4.0 4.0 5.0 4.0 4.0 3.0 WHAT WE CLAIM IS : 1. In a method of lasting a shoe in which marginal portions of a shoe upper are secured to the shoe bottom by an adhesive, the use of a hot melt adhesive having a softening point (Ball & Ring) above 1200C, and a set-up time (as defined) of not more than 20 seconds, and comprising a copolyester and a stabilizer, the copolyester having a molecular chain made up of units corresponding to diol units and acid units derived from a) one or more aliphatic diols having from 2 to 10 carbon atoms in its molecular chain; (b) an at least substantially difunctional poly(propylene oxide) diol having a molecular weight in excess of 500, to an extent of from 5 to 50 percent by weight of the diol units; and (c) terephthalic acid to an extent of from 60 to 100 mols per 100 mols of the acid units, and one or more other dicarboxylic acids to an extent of from 0 to 40 mols per 100 mols of the acid units.

2. A method according to claim 1 wherein, in the copolyester, the poly(propylene oxide) diol has a molecular weight in the range of 1000 to 2500.

3. A method according to claim 1 wherein, in the copolyester, thepoly(ropylene oxide) diol units are present to an extent of 5 to 35 percent by weight of the diol units.

4. 4. A method according to claim 3 wherein, in the copolyester, the poly(propylene oxide) diol units are present to an extent of 20 to 25 percent by weight of the diol units.

5. A method according to claim 1 wherein, in the copolyester, said one or more aliphatic diols comprises 1.4 butane diol to an extent of not less than 50 mol % of the aliphatic diol.

6. A method according to claim 1 wherein, in the copolyester, said one or more aliphatic diols consists of a mixture of 1.4 butane diol and 1.6 hexane diol.

7. A method according to claim 1 wherein, in the copolyester, the dicarboxylic acid units comprise units derived from terephthalic acid to an extent of 70 to 80 mol percent of the acid units.

8. A method according to claim 7 wherein, in the copolyester, the acid units comprise isophthalic acid units to an extent of 5 to 30 mole percent of the acid units.

9. A method according to claim 7 wherein, in the copolyester, the acid units comprise adipic acid units to an extent of 5 to 25 mole percent of the acid units.

10. A method according to claim 7 wherein, in the copolyester, the acid units comprise a mixture of aliphatic dicarboxylic acids to an extent of 5 to 25 mole percent of the acid units.

11. A method according to claim 1 wherein the polyester has a melting point (Ball & Ring) in the range 1500C to 215"C.

12. A method according to claim 1 wherein the stabilizer comprises triphenyl phosphite and one or more of tris-(2-methyl-4-hydroxy-5-t-butylphenyl)butane, pentaerythritol tetrakis-3 :5-di-t-butyl-4-hydroxyhydrocinnamate and a phenolic resin.

13. A method according to claim 12 wherein the phenolic resin is a terpene phenolic resin of softening point 1200C.