SHOE COMPRISING A SOLE OF A THERMOPLASTIC MATERIAL AND A METHOD FOR USE IN MANUFACTURING SUCH A SHOE

Abstract

The present invention pertains to a new shoe comprising a sole of a thermoplastic material adhered to an upper shoe with a hot melt adhesive that is applied between the sole and the upper shoe, wherein the hot melt adhesive is fused with the thermoplastic material. Advantageously, the fusion is brought about by heating the hot melt adhesive to a temperature THM such that it softens, heating the second body such that the thermoplastic material that has a melting temperature TM obtains a temperature T.sub.SUB below T.sub.M while making sure that (T.sub.HM+T.sub.SUB)/2 is equal to or higher than (T.sub.M−10° C.).

Claims

1. A shoe comprising a sole composed of a thermoplastic material adhered to an upper shoe with a hot melt adhesive that is applied between the sole and the upper shoe, wherein the hot melt adhesive is fused with the thermoplastic material.

2. A shoe according to claim 1, wherein the sole comprises a foamed composition comprising a thermoplastic copolyester elastomer in an amount of 70 to 99 wt % based on the total amount of the foamed composition.

3. A shoe according to claim 2, wherein the foamed composition comprises a thermoplastic copolyester elastomer in an amount of 70 to 99 wt % and a plasticizer in an amount of 1 to 30 wt % based on the total amount of the foamed composition.

4. A shoe according to claim 2, wherein the thermoplastic copolyester elastomer comprises hard segments built up from polyester repeating units derived from at least one aliphatic diol and at least one aromatic dicarboxylic acid or an ester thereof, and soft segments chosen from the group consisting of aliphatic polyether, aliphatic polyester, aliphatic polycarbonate, dimer fatty acids and dimer fatty diols and combinations thereof.

5. A shoe according to claim 4, wherein the hard segments are chosen from the group consisting of ethylene terephthalate (PET), propylene terephthalate (PPT), butylene terephthalate (PBT), polyethylene bibenzoate, polyethylene naphtalate (PEN), polybutylene bibenzoate, polybutylene naphtalate, polypropylene bibenzoate and polypropylene naphtalate and combinations thereof and the soft segments are chosen from the group consisting of aliphatic polyether, aliphatic polyester, aliphatic polycarbonate, dimer fatty acids and dimer fatty diols and combinations thereof.

6. A shoe according to claim 5, wherein the hard segment is chosen from PBT or PET and the soft segment is chosen from the group consisting of polybutylene adipate (PBA), polyethylene oxide (PEO), polypropylene oxide (PPO), polytetramethylene oxide (PTMO), PEO-PPO-PEO and combinations thereof.

7. A shoe according to claim 1, wherein the upper shoe comprises a layer of textile material that is contiguous with the sole.

8. A shoe according to claim 7, wherein textile material comprises polymeric yarns.

9. A shoe according to claim 8, wherein polymeric yarns comprise polyester polymer.

10. A shoe according to claim 1, wherein the hot melt adhesive comprises a polymer selected from the group consisting of (co)polyurethane(s), (co)polycarbonate(s), (co)polyester(s), (co)polyamide(s), (co)poly(ester-amide(s)), mixtures thereof and/or copolymers thereof.

11. A shoe according to claim 10, wherein the hot melt adhesive comprises a (co)polyester.

12. A shoe according to claim 1, wherein the hot melt adhesive is semi-crystalline, preferably having a melting enthalpy between 1 and 80 J/g.

13. A method of assembling a workpiece comprising a first body mechanically connected to a second body by adhering the first body to a surface of the second body, the second body being composed of a thermoplastic material that has a melting temperature T.sub.M, the method comprising: Heating a hot melt adhesive to a temperature T.sub.HM such that it softens; Heating the second body such that the thermoplastic material obtains a surface temperature T.sub.SUB below T.sub.M; Applying the heated hot melt adhesive to the surface of the heated second body; Applying the first body to the second body to form the workpiece; Cooling the workpiece such that the hot melt adhesive hardens; Wherein the temperatures are chosen such that (T.sub.HM+T.sub.SUB)/2 is equal to or higher than (T.sub.M−10° C.).

14. A method according to claim 13, wherein temperatures are chosen such that (T.sub.HM+T.sub.SUB)/2 differs from T.sub.M by a number of degrees chosen from the group consisting of −10, −9, −8, −7, −6, −5, −4, −3, −2, −1, 0, +1, +2, +3, +4, +5, +6, +7, +8, +9, +10, +11, +12, +13, +14, +15, +16, +17, +18, +19 or +20° C.

15. A method according to claim 13, wherein the second body is heated such that the thermoplastic material obtains a temperature T.sub.SUB that is at most X ° C. less than T.sub.M, X being chosen from the group that consists of 100, 90, 80, 70, 60, 55, 50, 45, 40, 35 and 30.

16. A method according to claim 13, wherein the second body is heated in its entirety.

17. A workpiece obtainable by a method according to claim 13.

Description

EXAMPLES

[0057] FIG. 1 schematically shows the interaction between hot melt adhesive and various substrates.

[0058] FIG. 2 schematically shows the constituting parts of a workpiece for use in the manufacture of a shoe.

[0059] FIG. 3 schematically shows a cross section of a material used for an upper shoe of an athletic shoe.

[0060] FIG. 4 schematically shows a test set-up for measuring the strength of a mechanical connection brought about by a hot melt adhesive.

[0061] FIG. 5 is the SEM picture from the connected thermoplastic bodies of example 1.

[0062] Example 1 describes the connection of two thermoplastic bodies using a hot melt adhesive.

[0063] FIG. 1

[0064] FIG. 1 schematically shows the interaction between hot melt adhesive 4 and various substrates (200, 200′ and 200″). In FIG. 1A, the interaction between a layer 4 of hot melt adhesive in its hardened form (thus after application in liquid form and subsequent cooling down to below its solidification temperature) and a non-smooth surface of a body 200 is depicted. The surface of the body has various protrusions (201) and indentations (202) which serve as anchoring point for the hardened hot melt adhesive. This brings about a good mechanical connection between the hot melt adhesive 4 and the body 200.

[0065] In FIG. 1B, a situation is depicted wherein the body 200′ has a smooth surface, leading to the absence of anchoring points for the hot melt adhesive 4. This means that the mechanical connection, if any, between the layer of hot melt adhesive 4 and the body 200′ is very weak. The layers can be easily separated by using a slight pulling force to either of the layers.

[0066] In FIG. 1C the situation is depicted where body 200″ is made of a thermoplastic material and the hot melt adhesive is heated sufficiently just before application thereof, to make sure that the upper region of the body 200″ is heated to above its melting temperature. This way, the molecules of the molten hot melt adhesive and the molten body 200″ may be able to mix and unite (to fuse) to form one new intermediate material 204, which material may ultimately (after solidification of all molten material) serve as a mechanical bridge between the layer of hot melt adhesive 4 and the body 200″. Although indicated in the schematic representation of FIG. 1C as individually identifiable layers, in practice the layers 4 and 200″ gradually change from one pure material to another with the mixed material of a gradually changing composition in between.

[0067] FIG. 2

[0068] FIG. 2 schematically shows in a cross section the constituting parts of a workpiece 1 for use in the manufacture of a shoe (which need not be more than the workpiece itself). In the figure, part 2 is the (mid-)sole of the shoe, in this case consisting of a foamed composition comprising a copolyether-ester elastomer (55 wt % PTMO and 45 wt % PBT with respect to the amount of copolyether-ester elastomer) in an amount of 85 wt %, and 15 wt % epoxidised soybean oil as a plasticizer with respect to the total amount of foamed composition, leading to a foam having a density of 0.24 g/cm.sup.3 and having T.sub.M of 160° C. The upper shoe 3 consists of a textile base layer and a top coat of polyurethane (see FIG. 3). Part 30 is a segment of the upper shoe 3 that is used for adhering the upper shoe 3 to the sole 2 using a hot melt adhesive (see Example 1). In dotted lines an outer sole 20 is depicted.

[0069] FIG. 3

[0070] FIG. 3 schematically shows a cross section of a material used for an upper shoe 3 of an athletic shoe. The upper shoe 3 consists of a textile base layer 31 and a top coat of polyurethane (32). The textile layer 31 is the layer that will be used to make the connection with the sole as indicated in FIG. 2.

[0071] FIG. 4

[0072] FIG. 4 schematically shows a test set-up for measuring the strength of a mechanical connection brought about by a hot melt adhesive (in line with standardised method ASTM D3936). In this set-up, two bodies 2 and 3 having a width L are mechanically connected with a layer of hot melt adhesive 4. These layers are separated at one of the ends, exerting a separating force F. To make adequate shoes, F/L should be larger than 30 Newton per inch (larger than 11.8 Newton per cm).

Example 1

[0073] Example 1 describes the connection of a thermoplastic body using a hot melt adhesive. In order to assess whether a hot melt adhesive could be used to adhere a first body to a thermoplastic body, two thermoplastic bodies were chosen, in this case foamed thermoplastic bodies as described in connection with FIG. 2. The melting temperature T.sub.M of these bodies is 160° C. (determined with ASTM D3418-03 as described in this patent application). In a first attempt, a polyester hot melt adhesive having a melting enthalpy of 27±3 J/g was used (the determination of which is based on ASTM standard D3418 using a Mettler STARe differential scanning calorimeter), showing a first order transition temperature (solid to liquid) around 110° C. The hot melt was heated to a temperature of 180° C., thus well above its melting temperature and at a level that is common for using this hot melt to obtain strong connections. The thermoplastic bodies were preheated to various temperatures, ranging from 80° C. to 100° C. before the hot melt adhesive was applied, meaning that (T.sub.HM+T.sub.SUB)/2 varied from 130 to 140° C., i.e. 30° to 20° below T.sub.M. Directly after application of the adhesive, both bodies were pressed together. In none of the cases a good mechanical connection could be obtained. F/L was less than 5 N/inch value for each workpiece. This confirmed the common knowledge that thermoplastic materials cannot be adequately connected using a hot melt adhesive.

[0074] In a second attempt, the hot melt adhesive was heated to 210° C. (i.e. still well below the temperature at which the polyester hot melt adhesive would (start to) degrade, i.e. around 250° C.) and the thermoplastic bodies to a temperature ranging from 120 to 130° C., meaning that (T.sub.HM+T.sub.SUB)/2 varied from 165 to 170° C., i.e. 5° to 10° over T.sub.M. Either one or both sides of the bodies were provided with the melted adhesive. In addition to the type of polyester adhesive used in the first experiment (“Type 1”), another type was used (“Type 2”). Keeping all other variables the same as in the first experiment, this way a very good mechanical connection between the two thermoplastic bodies could be obtained. The data are indicated in table 1 below. In FIG. 5 a Scanning Electronic Microscopy (SEM) picture is shown, which demonstrates that at an enlargement of 650 times no boundary between the thermoplastic bodies can be distinguished for the example with the Type 2 adhesive. In FIG. 5 the upper shoe 3 is connected to midsole 2 in the same way as is schematically depicted in FIG. 2.

[0075] This makes clear that the provision of a connection with a (very) high mechanical strength can be obtained for various hot melt adhesives, without relying on particular organic binding molecules, primers or complicated heat-cool cycles, simply by choosing the temperatures such that (T.sub.HM+T.sub.SUB)/2 is equal to or higher than (T.sub.M−10° C.).

TABLE-US-00001 TABLE 1 Strength of mechanical connection using various hot melt adhesives Load at failure Hot melt application Adhesive (N/inch) Comment One sided Type 1 49.1 — One sided Type 1 47.3 — Two sided Type 1 40.6 — Two sided Type 1 44.0 Two sided Type 1 n.a. Foam rupture* Two sided Type 2 98.2 — Two sided Type 2 n.a. Foam rupture* Two sided Type 2 n.a. Foam rupture* *Foam rupture means that the bond was stronger than the intrinsic tear strength of the thermoplastic foam.

[0076] Above experiments were also conducted using thermoplastic bodies consisting of a foamed composition comprising TPU. Similar results were obtained and connections with high mechanical strengths were provided accordingly.