PUNCTURE-RESISTANT COMPOSITE FABRICS

Description

Field of the invention The present invention relates to the field of safety fabric items, and specifically to puncture-resistant composite fabrics. Prior art

The clothing of personnel working in occupations exposed to the risk of accidents (e.g. constructions, metallurgy, work sites in general, etc.) must be able to protect without hindering the wearer's movements.

In addition to ensuring the required protection, these items must also be as comfortable as possible, especially with regards to weight and flexibility thereof and must ensure good transpiration properties even when waterproof properties are required. Various types of multi-layer composite materials suitable for making protective clothing are known and described, specifically puncture-resistant soles containing metal reinforcing plates, aramid-fiber fabric layers and polymer resins. Patent application EP 04 727 364 describes a puncture-resistant fabric structure including one or more aramid-fiber layers and one or more layers of high-strength non-aramid fiber layers, reciprocally joined by means of a thermoplastic film, wherein each layer is treated with a polyurethane and/or acrylic resin filled with powders of hard, abrasive material.

It is worth noting that the essential presence of the aramid fibers in the textile according to the aforesaid application involves high production costs of the finished product and machining difficulties of the fabrics themselves, precisely due to the particular strength of this type of fibers.

It is thus apparent that, despite the several studies and suggestions, a need exists for safety fabrics which are able to combine a great puncture resistance with a flexibility such that the maximum comfort of the items made of these fabrics is ensured to the user, and specifically of puncture-resistant shoe soles. Brief description of the drawing Figure 1 shows a specific weave of a fabric according to the invention (Diagram

(A)).

Summary of the invention

A fabric for composite material is described, which may be either sewn to the vamp by means of Strobel technology, or inserted in the footwear sole during the injection process or during the subsequent steps of machining, in which the filaments which form the threads composing the fabric are able to reciprocally move. Furthermore, two-layer composite materials obtained by coupling two layers made of such fabrics are described. Detailed description of the invention The present invention allows to overcome the aforesaid drawbacks in virtue of a composite material consisting of two layers of fabric which may be either sewn to the vamp by means of Strobel technology, or inserted in the footwear sole during the injection process, or during subsequent steps of machining. In opposition to the expectations, it has been surprisingly found that a very high density of threads per square decimeter, although necessary, is not the only essential condition for obtaining the desired results, but the filaments which form the thread must be able to reciprocally move.

Indeed, if the fabric is excessively rigid, a nail will find an inelastic structure which is not able to comply and oppose the advancement of the tip in the desired manner, thus allowing a possible penetration of the tip between the weft and the warp.

Instead, by satisfying the aforesaid condition, there is obtained a fabric which, although is not formed by aramid fibers, not only meets the puncture-resistance parameters required by the standards in force (specifically the EN 12568 standard, which provides for a strength of at least 1100 N to the penetration of a nail at a speed of 10 mm/min. +/- 3 mm/min, the ISO EN 20344 and ANSI Z41 standards, and the CSA guidelines), but has also a very high lightness, flexibility and permeability to transpiration. Furthermore, the fabric thus obtained is much more flexible than the fabrics currently present on the market obtained by using aramid fibers or several layers of material, with evident advantages in terms of comfort and wearability for the soles made by using such a support.

The material is also more competitive because it achieves the requirements of the

Standard by means of only two layers of high-strength material without requiring to avail of expensive aramid fibers or yarns.

The cost saving is also apparent in relation to the less need for polyurethane and/or acrylic resins filled with particles of hard, abrasive materials, as declared by the current manufactures of similar material formed by three, four or five layers.

The fabric according to the invention normally consists of continuous, preferably parallel, high-strength polyester threads, so that the filaments composing the thread may reciprocally slip; obviously, in addition to the aforesaid continuous, high-strength polyester threads, other similar threads may be used, such as for example Nylon, acrylic, polypropylene, polyethylene fiber such as Dyneema ^® , or other high-strength fibers except for aramid or para-aramid fibers, such as Kevlar ^® or Nomex ^® .

According to the invention, the warp thread count is in the range of 110 - 3,300 Dtex, with a number of filaments in the range of 19 - 384, said filaments having dimensions in the range of 3 - 20 Dtex.

According to a preferred embodiment, the warp thread has a 550 Dtex count and consists of 96 filaments of 5.7 Dtex each.

Similarly, according to the invention, the weft thread count is included between 550 Dtex and 4,400 Dtex, with a number of filaments included between 96 and

576, said filaments having the aforesaid dimensions.

A thread having a 2,200 Dtex count, consisting of 384 filaments of 5.7 Dtex each, is preferably used for the weft.

The warp thread density should be in the range of 300 - 900 threads/dm, preferably 570 threads/dm equal to 54,720 filaments/dm.

Similarly, the weft density will be in the range of 200 - 800 threads/dm, preferably

440 threads/dm, equal to 168,960 filaments/dm.

Therefore, the fabric according to the preferred embodiment of the invention as described above has a number of threads equal to 1 ,010/dm ² and thus to 223,680 filaments/dm ² .

The wefts and the warp may be bound to one another, using the looms normally employed to form this type of textiles, with various types of traditional weaves,

such as for example plain weave - twill cloth; however, according to a preferred embodiment of the invention, the weft and the warp are bound to each other with a very special weave which may be defined as "quadruple", according to the diagram A shown in Fig. 1. Looms with 4, 6, 8, 10, 12, 14, 16 or 18 heddles may be used to form the weave according to the invention.

Specifically, for example, in an eight-heddle loom, the heddles move following a specific quadruple armature pattern, binding each weft to the warp with eight different evolutions. The weft ratio is equal to 32 i.e. 32 different evolutions are performed by each weft before repeating again the same one, thus 26,700 different bindings are made between the warp and the wefts in one dm ² .

This special weave allows the wefts to bind with the warp not only in the horizontal direction but also in the vertical one, thus forming a fabric which has 4 layers of threads indissolubly bound to one another. This allows the wefts to relax, take-up and place themselves so as to close and fill all spaces to the maximum, thus obtaining the maximum density of threads or filaments per dm ² . An example of fabric thus obtained has a warp density of 5,700 threads per meter (and 547,200 filaments per m ² ) and a weft density of 4,400 threads per meter (and 1 ,689,600 filaments per m ² ), whereby in one m ² there are 10,100 threads (and 2,236,800 filaments) which reciprocally bind 267,000 times. If required, the fabric density may be increased, and concurrently the weave overlapping of the single threads which form the fabric weft may be modified by means of a specific heat-setting, calendering and possibly printing process. Preferably, the material is heat-set by means of calendering onto a temperature- controlled cylinder at 140 - 240 ⁰ C, for example at 203 ⁰ C, which allows a weft take- up of approximately 11 % and a warp take-up of approximately 9%. A heat-setting process at higher temperatures would ensure even higher thread density levels, but this would not result in significant advantages in terms of puncture load values because the progressive softening and the consequent loss of the initial mechanical features of the polyester fibers would thwart the benefit obtained by the higher density.

Printing may be carried out by using a sublimation paper transfer process, a photogravure process or by means of colored thermoplastic resin transfer on polyester film.

In all cases, the only function of the printing is to valorize the product and to certify the origin, quality and trademark thereof.

If desired, the obtained fabric may be made antistatic and/or antibacterial by means of impregnation and treatment in appropriate chemical solutions or by means of a mesh, which is obtained by interposing continuous threads or short fibers which prevent bacteria from proliferating and/or conductive fibers made of carbon, silver, copper, steel or any other yarn or fiber which may dissipate electric discharges, between the warp and the weft threads.

In order to adjust the antibacterial activity, silver fiber in a variable percentage between 2 and 8% by weight as compared to the total weight of the fabric will preferably be used. Preferably, the fabric will have both features and thus will include carbon filaments in the warp to make it antistatic and silver filaments in the wefts to make it antibacterial.

In addition to have antibacterial features, silver is also an excellent conductor and braiding it with carbon improves its static charge dissipation. According to a further specific embodiment of the invention, the fabric obtained as described above may be treated by means of dispersions of thermoplastic, thermosetting or adhesive resins, thus obtaining an impregnation of the filaments which constitute the threads, so as to increase their friction to the internal sliding and therefore increase the puncturing load of the nail. Preferably, the polymers which in the common conditions of use of the textile are in the vitreous transition range, are used for the aforesaid treatment and thus do not behave either as rubber or as glass but are characterized by an intermediate

Young modulus, of viscoelastic type, which may thus dissipate a great amount of deformation energy. Furthermore, said polymers will have a viscosity which allows them to deeply penetrate into the filaments at the melting temperature and, at the normal operating temperature, allows to oppose the puncturing load by means of the

friction generated by the internal sliding of the filaments.

Preferably, the polymers used when machining are punctiform copolyester-, polyurethane-, copolyamide or polyolefin-based thermoplastic resins of grain size from 100 to 500 mμ. If desired, said resins may be mixed with mineral beads having a differentiated grain size from 10 to 500 mμ.

The preferable mixture consists of 1 -1 -1 parts of thermoplastic copolyester polymers of grain size 100 - 500 mμ, corundum particles of grain size 10 - 100 mμ and tempered soda-lime glass of grain size 100 - 200 mμ. This combination is particularly preferred because it allows optimal efficiency because the small grain size of the corundum allows the particles to insinuate into the cavities between the fabric wefts, the larger grain size of the glass beads allows these particles to remain on the surface hollows blocking the corundum particles underneath, while the large grain size and the lighter specific weight of the thermoplastic material allows the latter to remain firstly on the surface, thus ensuring the adhesion on the upper layer of the concerned composite. The thermoplastic polymers may be also used without mixing with beads, while other mixtures filled with particles of garnet, ceramics, steel grit, quartzite, vegetable grit or silicon carbide, etc, may be used alternatively to the mineral particles listed above.

The above-described resin layer is thus trapped by hot-coupling between two layers of fabric in order to form the two-layer composite material ready for the final use.

The antistatic features of the laminated is ensured by filling the resin with conductive particles if the fabric is made of conductive fibers.

If customers manufacturing footwear complying with ESD safety standards will require conductivity values such that the filling of the impregnating resin is insufficient, single, equispaced, conductive threads or fibers of carbon, silver, copper, steel or any other yarn or fiber which may help in dissipating the electric discharge may be arranged between the two layers of fabric which compose the composite by means of an appropriate creel. If the waterproof, transpiring version of the support is implemented, either a

transpiring waterproof resin may be coated on the surface of one of the supports which form the composite, or a transpiring waterproof membrane made of PTFE or a polyurethane membrane having a microporous structure may be either inserted between the two fabrics or coupled onto the external surface of one of the two fabrics by means of thermoplastic resins applied in a punctiform manner.