GB2313383A

GB2313383A - Insole material

Info

Publication number: GB2313383A
Application number: GB9610904A
Authority: GB
Inventors: Robert Owen Symcox; Rodney Charles Fell; Clinton Bailey
Original assignee: British United Shoe Machinery Ltd
Current assignee: Noxet UK Ltd
Priority date: 1996-05-24
Filing date: 1996-05-24
Publication date: 1997-11-26
Anticipated expiration: 2016-05-24
Also published as: GB9610904D0; GB2313383B

Abstract

An insole material with good stitch-retention strength and suitable for force-lasted shoes comprises a blend of up to 75% polyester fibres and up to 45% bi-component polyester fibres which is carded and cross-lapped, needled, fusion-bonded with hot air and calendered to a gauge of up to 1 .8mm. The material may have a density in the range 0.275-0.395 g/cm3 and a tensile strength in two orthogonal directions of 200-300 and 225-360 N/cm respectively. The material may be impregnated with latex.

Description

INSOLE MATERIAL The present invention relates to an insole material having a high stitch retention strength to facilitate socalled force-lasted or slip-lasted shoe construction.

In force-lasted shoe construction, a sock lining, which takes the place of a normal insole, is sewn to the upper with an ordinary upper closing seam and the platform cover sewn in with a second seam running parallel with the first.

With this extra closing completed, the shoe last is forced into place to give the upper its shape, i.e. a shoe last is placed in the assembly of uppers and sock lining. An outer sole is then fitted and cemented in position with regard to this assembly of upper and sock lining. This outer sole may be achieved by directly injection moulding a polyurethane sole about the sock lining made from insole material.

It will be appreciated that, along with dimensional stability, two factors of paramount importance with regard to the sock lining in forced-lasted shoe construction are, firstly the sock lining or insole material must be capable of retaining a stitch under reasonably severe pressure produced by force inserting a shoe last into the assembly of uppers and sock lining and, secondly the sock lining/insole material must be resistant to strike-through of the polyurethane during an injection moulding stage.

Typically, insoles for shoes or other footwear are made from either cellulosic board or impregnated non-woven felt.

Cellulosic board is unsuitable for force-lasted shoes for the obvious reason that it is difficult for them to retain a stitch both on initial manufacture, and if during use the insole becomes wet the stitch will wear through the cellulosic insole board with the result that there could be a rupture between the upper components and the outsole allowing ingress of water. Similarly, impregnated non-woven materials are not ideal for force-lasted shoe construction due to potential stitch failure in use. These insole materials have the necessary flexibility and perspiration performance.

In recent times force-lasted footwear has become increasingly important as a manufacturing technique. For example, most sports footwear and casual footwear is manufactured by this technique due to the reduction in the necessity for skilled labour required to attach the upper component with the insole sock lining material; it is a simple stitching operation. Other constructions require a degree of skill in lasting the upper components to an insole board.

A solution to stitch retention in non-woven fabrics and felts is to include a woven reinforcement layer in the structure. Typically, this layer is a woven polypropylene scrim as part of the structure. While this scrim confers the required high tensile and low elongation properties, there is a limitation with regard to the temperatures the material can withstand on shoe making, e.g. upper conditioning. The maximum working temperature for polypropylene is 110-115"C before excessive shrinkage.

A number of approaches have been pursued to solve this problem such as incorporation of alternative woven scrims based on jute, polyester and polyamide. However, these also have their own drawbacks, in particular, delamination, i.e.

separation of the scrim and non-woven felt structure.

The present invention has the benefit in that it is not composite, thereby eliminating any problems of laminar failure.

It is an objective of the present invention to provide an insole material and a method of making such an insole material, which has a high stitch-retention strength suitable for force-lasted shoe construction as an insole sock.

In accordance with the present invention there is provided an insole material of high stitch-retention strength, the material comprising by weight, up to 75% polyester fibre and up to 45% bi-component polyester fibre mixed, consolidated by needle entanglement, fusion bonded and hot-air calendered to a weight in the range of 400-700 g/m2, a gauge up to 1.8 mm to give a density in the range 0.275-0.395 g/cm3 in order to have a tensile strength in a first, longitudinal, direction of between 200-300 N/cm and in a direction perpendicular to said first direction in a lateral direction in the order of 225-360 N/cm. Ideally, the gauge of the material will be between 1.5 and 1.8 mm.

Preferably, the polyester fibre has a 1.6 Dtex and 38 mm length and the bi-component polyester has a 3.0 Dtex, 50 mm staple configuration. An example of a bi-component fibre is Grinlene K170.

Preferably, the blend of polyester fibre to bicomponent polyester fibre is in the order of, by weight, 70% polyester fibre to 30% bi-component polyester fibre or 60% polyester fibre and 40% bi-component polyester fibre.

Alternatively, in accordance with the present invention there is provided a method of making an insole material of high stitch-retention strength comprising the steps of: (a) blending and mixing up to 75% polyester fibre with up to 35% bi-component polyester fibre to produce a material blend, (b) carding said material blend using a known carding technique and cross lapping said blend in order to provide a material web, (c) needle tacking said material web using a known needle-tacking technique in order to provide a non-woven felt having a weight in the range of 300-600 g/m2, a gauge between 1.5-2.5 mm and a density between 0.15-0.25 g/cm3, (d) fusion bonding said non-woven felt using a hot-air drier drum at a temperature to achieve shrinkage of said felt up to 35% of its area in order to provide a fused felt, (e) calendering said fused felt at a temperature in order to further consolidate said fused felt to a calibrated gauge up to 1.8 mm for use as an insole material.

Preferably, the non-woven felt is fusion bonded at a temperature of 1800C and calendered at a temperature of 175 C.

Preferably, in accordance with the method a blend of 75% by weight 1.5 Dtex polyester, 38 mm staple fibre is mixed in a blend with 30% by weight 3.0 Dtex bi-component polyester, 50 mm staple fibre in accordance with Step (a).

This blend is needle entangled to give a non-woven felt having a weight of approximately 510 g/m2 with a gauge of 2.2 mm and a density of approximately 0.23 g/cm3. In accordance with Step (b) this non-woven felt is fusion bonded and shrunk at an elevated temperature on a hot through-air drum drier and its thickness controlled by a hot calibration roller to give an insole material having a weight of approximately 680 g/m2 with a gauge of 1.8 mm and a density of 0.38 g/cm3, the area shrinkage due to throughair fusion bonding being in the order of 32%. Preferably, the elevated temperature is 1800C and the calibration roller is set at 175"C.

Alternatively, the material blend could be 60% by weight 1.5 Dtex polyester, 38 mm staple fibre mixed with 40% by weight 3.0 Dtex bi-component polyester, 50 mm staple fibre in accordance with Steps (a) and (b), said material web being needle tacked to provide a non-woven felt having a weight of approximately 340 g/m2 at a gauge of 1.75 mm to give a density in the order of 0.2 g/cm3 in accordance with Step (c) and said non-woven felt being fusion bonded and shrunk at an elevated temperature through a hot-air drum drier and calendered to a calibrated thickness in the order of 1.6 mm and a weight of approximately 450 g/m2 with a density of 0.28 g/cm3, said non-woven felt being shrunk by fusion bonding by approximately 30% of its area.

Preferably, the elevated temperature is 1800C.

An embodiment of the present invention will now be described by way of example only.

As indicated above, the usual manner for incorporating stitch-retention strength into a non-woven fabric is to add a cellular scrim usually made of polypropylene to the nonwoven felt. Unfortunately, such scrims reduce the laminar strength, adhesion and heat stability of the non-woven material. Furthermore, such scrims can damage strikethrough resistance to polyurethane (PU) moulded insoles by facilitating tension-induced pathways through the insole material.

In the present invention high stitch-retention strength is achieved by incorporating in the order of 30-408 by weight bi-component polyester fibre in a well-needled polyester non-woven felt. Bi-component polyester fibre includes a sheath of thermally-activated material which melts at an appropriate temperature in order that fibres become consolidated and adhered together. Thus, the bicomponent polyester fibre upon heating melts the sheath and the felt becomes fused and consolidated incorporating both the polyester fibre and the bi-component polyester fibre in one amorphous structure complementing the usual fibre entanglement of non-woven felts. Typically, this fusion bonding, i.e. activation of the bi-component polyester fibre, will be accompanied by a reduction in material area due to contraction upon activation of the bi-component polyester fibre. This area shrinkage is determined by fusion bonding conditions, in particular, temperature, and increases the density of the material. In the present invention area shrinkage is preferably in the order of 3035% and probably around 31% or 32% of the area of the non fusion-bonded non-woven felt.

It will be understood that bi-component polyester is quite expensive and thus the amount incorporated into the non-woven felt is a high determining factor with regard to material cost. Footwear materials should be as cheap as possible and thus the amount of bi-component fibre incorporated into the insole material should be limited.

Furthermore, too much bi-component polyester would result in too great an area shrinkage and density for the non-woven insole material in accordance with the present invention.

Bi-component polyester may also increase the stiffness of the insole material. Furthermore, due to crystallinity of bi-component polyester sheath, such insole material may be more brittle than conventional materials and so susceptible to failure in footwear as insole materials must flex many times in use.

It is a balance between provision of the polyester fibre to provide the bulk structural fibre matrix and the fused bi-component polyester acting as the fibre matrix structure fixing means. The adhesive effect of the bicomponent fibre sheath is to fix the entangled fibres in their respective locations and thus provide good stability against displacement of those fibres. Consequently, the fusion-bonded and shrunk non-woven felt has a high stitchretention strength and resistance to strike-through of a polyurethane outsole compound in an injection moulding stage of footwear manufacture, along with good dimensional stability.

Generally, the insole material of high stitch-retention strength in accordance with the present invention is manufactured using the following procedures: A fibre blend of polyester fibre and bi-component polyester fibre is mixed and blended, then carded, cross lapped and needle entangled in accordance with known procedure.

In a first example embodiment of the present insole material, a 70% by weight 1.5 Dtex polyester, 38 mm staple fibre is mixed with 30% by weight 3.0 Dtex bi-component polyester, 50 mm staple fibre and appropriately needle entangled to produce a non-woven felt having a weight of 512 g/m2 with a gauge of 2.2 mm and a density of 0.23 g/cm3.

This non-woven felt is then fusion bonded and shrunk at a temperature of 1800C using a hot through-air drum drier and its thickness controlled by hot-air calibration or calendering rolls set at 175"C to give the material the following properties: weight 678 g/m2; gauge 1.8 mm; density 0.377 g/cm3; tensile strength in the direction of felt manufacture of 301 N/cm and perpendicular to the direction of felt manufacture of 339 N/cm; the fusion-bonded felt has an extension in the direction of manufacture of 18% at breaking tension, and across the direction of manufacture of 30% at breaking tension; the extension at 35 N/cm in the direction of felt manufacture is 1.4% and perpendicular to that direction is 1.7%; a stitch-retention holding strength in the direction of manufacture is 137 N/cm and perpendicular to that direction is in excess of 200 N/cm.

This felt had an area shrinkage at 1800C, and after thickness control by the calibration rollers at 175it of 32%.

Alternatively, in a second example embodiment of the insole material the fibre blend could be 60% 1.5 Dtex polyester, 38 mm staple fibre mixed with 40% 3.0 Dtex bicomponent polyester, 50 mm staple fibre. This fibre blend is blended, carded, cross lapped and cross needle tacked to provide a felt having a weight of 342 g/m2, a gauge of 1.75 mm and density 0.2 g/cm3. This non-woven felt was fusion bonded and shrunk as previously at 1800C using a hot through-air drier and then thickness controlled using calibration rollers set at 175"C to give a material having the following properties: weight 448 g/m2; a gauge of 1.58 mm; a density of 0.284 g/cm3; a tensile strength in the direction of felt manufacture of 228 N/cm and perpendicular to that direction of manufacture of 253 N/cm; an extension at break strain of 18% in the direction of manufacture and 30% perpendicular to that direction of manufacture; an extension at 35 N/cm in the direction of manufacture of 1.9% and perpendicular to that direction of manufacture of 2.6%; and a stitch-retention strength of 127 N/cm in the direction of manufacture and perpendicular to that direction of manufacture of 133 N/cm.

Generally, non-woven felts, after fusion bonding and shrinking should have a dimension stability such that there is no shrinkage at a desired temperature, i.e. 1700C after two minutes' exposure. Thus, the fusion-bonded and shrunk non-woven felt in accordance with the present invention is suitable as an insole material, with high stitch-retention strength and resistant to temperatures of polyurethane injection moulding material.

The consolidation and shrinkage of the non-woven felt ensures that the eventual insole material produced has a density to resist polyurethane strike-through.

It will be appreciated that alternative fibre types and dimensions could be used. However, the fibres must be sufficiently fine to achieve the necessary close fibre matrix structure, which is fixed by the activation of the bi-component polyester. The bi-component fibre should have a sufficient Dtex to allow reasonable sheath melting to resiliently secure the polyester fibre matrix structure and contribute to that structure. It will be understood that normally non-woven felts depend upon fibre entanglement to ensure consolidation, but in the present invention the addition of a bi-component fibre upon fusion bonding ensures that this structure is further consolidated by shrinkage, and due to fibre amalgamation the structure is dimensionally stable and resistance to stitch abrasion.

The fusion-bonded and shrunk non-woven felt can be impregnated with a latex barrier to further reduce the possibility of polyurethane strike-through upon injection moulding a PU outer sole to an assembly of upper components and an insole sock lining using the fusion-bonded felt.

The principal feature of the material is that the high physical strength characteristics are achieved without scrim additions (generally polypropylene based) which may reduce laminar strength, adhesion and heat stability.

The high strengths are achieved by incorporating 30-40% bi-component polyester fibre in a well-needled polyester non-woven felt, then fusing and consolidating the melt part of the bi-component fibre to the remaining fibre matrix.

The fusion-bonded/shrunk felt can then be cut to provide insole sock material for force-lasted shoe constructions.

Claims

Claims:

1. A method of making an insole material of high stitch-retention strength comprising the steps of: (a) blending and mixing up to 75% polyester fibre with up to 45% bi-component polyester fibre to achieve a material blend, (b) carding said material blend using a known carding technique and cross lapping said blend in order to provide a material web, (c) needle tacking said material web using a known needle-tacking technique in order to provide a non-woven felt having a weight in the range of 300-600 g/m2, a gauge between 1.5 and 2.5 mm and a density between 0.15-0.25 g/m3, (d) fusion bonding said non-woven felt on a hot-air drier drum at a temperature to achieve shrinkage of said felt up to 35% of its area to a fused felt, (e) calendering said fused felt to ensure the fused felt provides an insole material having a gauge up to 1.8 mm.

2. A method as claimed in Claim 1 wherein the nonwoven felt is fusion bonded and shrunk at a temperature of 1800C and the fused felt is calendered to a calibrated gauge at a temperature of 175"C.

3. A method as claimed in Claim 1 or Claim 2 wherein the non-woven felt is fusion bonded and shrunk in order to provide an area shrinkage of 32%.

4. An insole material of high stitch-retention strength, the material comprising, by weight, up to 75% polyester fibre and up to 45% bi-component polyester fibre mixed, consolidated by needle entanglement and fusion bonded to a weight 400-700 g/m2 with a gauge up to 1.8 mm and a density in the range 0.275-0.395 g/cm3 to give a tensile strength in a first longitudinal direction of between 200300 N/cm and in a perpendicular lateral direction of 225-360 N/cm.

5. A material as claimed in Claim 4 wherein the polyester fibre is 1.5 Dtex 38 mm staple fibre and the bicomponent polyester fibre is 3.0 Dtex 50 mm staple fibre.

6. An insole material as claimed in Claim 4 or Claim 5 wherein the material includes 75% by weight polyester fibre and 30% by weight bi-component polyester fibre.

7. A material as claimed in Claim 4 or 5 wherein the material includes 60% by weight polyester fibre and 40% by weight bi-component polyester fibre.

8. A material as claimed in any of Claims 4 to 7 wherein the material is impregnated with a latex-based impregnant.