GB2154899A

GB2154899A - Stiffening materials, a process for their production and the use thereof

Info

Publication number: GB2154899A
Application number: GB08503222A
Authority: GB
Inventors: Dr Elmar Hauschild; Dr Hans-Jurgen Puff
Original assignee: Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 1984-02-10
Filing date: 1985-02-08
Publication date: 1985-09-18
Also published as: DE3404701A1; FR2559503B1; GB2154899B; FR2559503A1; DE3404701C2; GB8503222D0; IT8567130A0; IT1182425B; IT8567130A1

Abstract

This invention relates to stiffening materials, particularly for leather, consisting of a woven textile fabric, worded fabric or non-woven fabric, paper, plastics film or metal film and a thermoplastic plastics layer sintered thereon, or of such a plastics layer alone, characterised in that the plastics layers consists, apart from optional fillers, of two polymer constituents which melt in different temperature ranges, the polymer constituent which melts in the higher temperature range being present in an amount of 5 to 40% by volume based on the unsintered mixture of the polymer constituents.

Description

SPECIFICATION Stiffening material, a process for their production and the use thereof This invention relates to stiffening material particularly for leather, which consist of support materials and a thermoplastic plastics layer sintered thereon or which consist of such a layer alone, as well as to a process for their production and the use thereof.

It is known to use thermoplastic plastics for stiffening and shaping materials of low stiffness, for example textile woven webs.

Possible methods for the preparation of such stiffened materials include the application of the desired coating materials as a dispersion, a solution or a melt on to the woven or worked fabrics.

DE-PS 847 968 describes the production of coatings and films from polyethylene, by distributing powdered polyethylene on a substrate and then heating to a temperature above the softening point.

According to DE-PS 2621 195, coated stiffening materials can be produced by fusing on powder mixtures of plastics material and fillers, for example sawdust, in which the two components have about the same particle size distribution.

The object of the invention is to provide stiffening materials with improved properties in terms both of its processing and the end product.

The present invention provides stiffening materials consisting of a woven textile fabric, worked fabric or nonwoven fabric, paper, plastics film or metal film and a thermoplastic plastics layer sintered thereon, or such a plastics layer alone, characterised in that the plastics layer consists, apart from optional fillers, of two polymer constituents which melt in different temperature ranges, the polymer constituent which melts in the higher temperature range being present in an amount of 5 to 40% by volume, preferably 10 to 25% by volume, based on the unsintered mixture of the polymer constituents.

According to one embodiment of the invention the two polymer constituents have the same summation formula but have different physical properties caused for example by the conditions during production for example high pressure and low pressure polyethylene.

Polymer constituents of different chemical types are preferable used.

Particularly suitable as the polymers which melt in the lower temperature range, are polyethylene or ethylene copolymers (with vinyl acetate or methyl methacrylate) or polycaprolactone individually or in a mixture, these polymers softening and melting from about 80"C upwards, used incombination with polymers which melt at a high temperature such as polymethyl methacrylate (PMMA).

The ethylene copolymers known as ionomer resins (Surlyn(RB, by Du Pont), are also suitable for use as the thermoplastic low-melting polymers.

The above-mentioned temperature ranges within which the polymers used according to the invention melt, are effectively selected, such that under the technical production conditions, the low-melting component(s) melt(s) completely, while the higher-melting polymer component(s) only soften(s) or begin(s) to melt.

The textile base materials, woven fabrics, worked fabrics, fleeces or non-woven fabrics can be produced from natural and/or synthetic fibres, for example cotton, synthetic fibres based on polyesters or polyacrylonitrile, staple fibre and other known raw materials for textile fibres.

Fillers which can optionally be included in the plastics layer in a quantity of from 1 to 11% by volume, based on the unsintered plastics material powder, may be of natural origin, for example chalk, kaolin, talcsilica sawdust, cork dust, or synthetic such as precipitated silica and carbon black,as well as optionally other pigments.

The invention also provides a process for the production of stiffening materials, particularly for leather, in which a cohesive layer is formed by applying a powder mixture of thermoplastic plastics and optionally fillers to woven textile fabrics, worked fabrics, webs or non-woven fabrics, paper, plastics films or metal film, followed by sintering.

The mixture applied to the support material, consists, apart from optional fillers, of two polymer constituents which melt in different temperature ranges, in which the polymer constituent which melts in the higher temperature range forms 5 to 40% by volume, preferably 10 to 25% by volume of the mixture.

Stiffening materials, which consist of the plastics layer alone, may be obtained by using a known release paper as the paper on to which the plastics layer is sintered. This release paper is removed after the sintering process and after the plastics layer has cooled.

The particle size distribution of the plastics powder is generally from 100 to 500 ,um.

If the higher-melting polymer constituent has a fraction of particle size from 10 to 50 'lem, it is advantageous, to limit this fraction to at most 30% by volume of this polymer constituent.

The shape of the individual polymer particles is of no importance. They can be beadshaped or have an irregular shape.

The homogeneous mixture of the thermoplastic powder and the optional filler, which is produced by intensive mixing in a powder mixer, is distributed on the support material by means of a known powder distribution machine and then heated for example, by means of infra-red radiation or by circulating hot air, preferably to a temperature at which the lower-melting polymer constituent is completely melted, whereas the higher-melting constituent is only softened or fused but on no account melts completely. Provided it is theorectically possible at the selected sintering temperature, a sintering time is set, which is sufficiently short that the higher-melting polymer constituent cannot be completely melted.

The viscosity of the resulting fused mass is thereby increased so that the support material is not penetrated. A powder mixutre of polyethylene and PMMA is advantageously used and sintering is carried out at a temperature of from 120 to 200"C, preferably from 1 50 to 1 80 C.

Inavariant of the process according to the invention, the support material with the powder mixture applied thereto is passed through aheated pressurezoneduringsintering.

Before cooling, the coated support material may optionally be smoothed.

The new stiffening materials according to the invention are particularly useful in the shoe industry and have clear advantages in relation to the present state of the art.

Whereas known stiffening materials, in which the required degree of stiffnes is produced by the addition of substantial amounts of fillers up to 100% by volume, easily break after repeated bending stress, this does not occur with the new stiffening materials, since the higher-melting polymer particles begin to melt during sintering at least in the marginal zones, and form an intimate bond with the melt of the other polymer constituent which surrounds them, unlike the fillers according to the prior.

The permanent shape and the shape-retaining properties of the stiffening material in the shoe are also improved by the admixture of the higher melting constituent, and in addition the shape of the last is reproduced more faithfully during the production of the shoe than in known processes.

A further part of the production process, the "sharpening" of the cap punched from the stiffening material is made easier, since the heat of friction arising during the sharpening process no longer causes the material to soften and therefore the sharpening tools no longer become soiled.

The stiffening materials according to the invention also have the advantage that their stiffness can be controlled not only via the quantity of the PMMA powder added, for example, but also by means of the sintering temperature.

With a constant PMMA content the stiffness increases as the sintering temperature increases.

This presents the opportunity, after incorporating the cap in a shoe, of increasing the stiffening effect thereof by subjecting it to a heat treatment at a temperature higher than the preceding sintering temperature.

This is of particular interest in ihe case of shoes, which are in any case subjected to a temperature of about 1 40 C over a period of from 8 to 10 min to pre-cure the soles onto the shoe upper.

According to a preferred embodiment, thermoplastic adhesive strips which may be activated by heat or by solvents are applied to one or optionally both extensive surfaces. The bonding properties of the material according to the invention are substantially improved as compared to pure polyethylene layers.

Example A powder of copolymers of ethylene vinyl acetate, having a particle size of up to 600 ym is mixed with 20% of PMMA powder with a particle size of from 500 to 600 cm and containing about 10% of a fraction with a particle size of from 10 to 50 ,um.

The melt index of the copolymer is 70.

This powder mixture is applied to a woven fabric with a fibre count of from 27/24 to 60/70 and a weight of about 90 g/m2 in a defined layer thickness of 3 mm.

By the action of warm air at 1 60 C over a period of 10 min, the powder is melted to form a bond with the support material, whereby the PMMA powder is not completely melted.

The surface is smoothed whilst still warm by a calender, and a know specific EVA powder, which produces an adhesive film activated by heat, may be optionally applied.

This sheet material is characterised inter alia in that its elasticity is maintained even under frequent bending stress, and no cracks caused by the bending, which could finally result in material fatigue, appear in the sheet.

Claims

1. Stiffening materials, particularly for leather, consisting of a woven textile fabric, worked fabric or non-woven fabric, paper, plastics film or metal film and a thermoplastic plastics layer sintered thereon, or of such a plastics layer alone, characterised in that the plastics layer consists, apart from optional fillers, of two polymer constituents which melt in different temperature ranges, the polymer constituent which melts in the higher temperature range being present in an amount of 5 to 40% by volume based on the unsintered mixture of the polymer constituents.

2. A stiffening material as claimed in claim 1, characterised in that the polymer constituent which melts in the higher temperature range is present in an amount of 10 to 25% by volume.

3. A stiffening material as claimed in claim 1 or 2, characterised in that the polymer constituents have the same chemical summation formula.

4. A stiffening material as claimed in claim 1 or 2, characterised in that the polymer constituents have different chemical summation formulae.

5. A stiffening material as claimed in claim 2 or 3, characterised in that the polymer constituent which melts in the lower temperature range consists of polyethylene and/or of copolymers of ethylene with vinyl acetate or methyl methacrylate, and the polymer constituents which melts in the higher temperature range consists of polymethyl methacrylate (PMMA).

6. A stiffening material as claimed in any of claims 1 to 5 characterised in that the plastics material layer contains from 1 to 1 1% by volume of fillers, based on the unsintered plastics powder.

7. A process for the production of a stiffening material as claimed in any of claims 1 to 6 by applying a powder mixture of thermoplastic plastics material and optional fillers to woven textile fabrics, worked fabrics, webs or non-woven fabrics, paper, plastics film or metal film followed by sintering to form a coherent layer, characterised in that the mixture applied to the support material, in addition to optional fillers, consists of two polymer constituents which melt in different temperature ranges, the polymer constituent which melts in the higher temperature range being present in an amount of 5 to 40% by volume, and in that during sintering only the polymer constituent which melts in the lower temperature range is completely melted.

8. A process as claimed in claim 7, characterised in that after sinterering, the coated support material is smoothed before cooling.

9. A process as claimed in claim 7, characterised in that the support material with the powder mixture applied thereto is passed through a heated pressure zone during sintering.

10. A process as claimes in any of claims 7 to 9, characterised in that an adhesive strip is applied to one or both of the extensive surfaces.

11. A stiffening material substantially as hereinbefore described with reference to the Example.

1 2. The use of stiffening material as claimed in any of claims 1 to 6 or 11 in shoes or shoe parts.