WO2021004762A1

WO2021004762A1 - Ballistic laminate comprising unidirectional layers joined together by stitching with the yarns of one of the layers stably locked in place

Info

Publication number: WO2021004762A1
Application number: PCT/EP2020/067199
Authority: WO
Inventors: Giorgio Celeste Citterio; Filippo Citterio
Original assignee: Societa' Per Azioni Fratelli Citterio
Priority date: 2019-07-09
Filing date: 2020-06-19
Publication date: 2021-01-14
Also published as: IT201900011265A1

Abstract

The present invention relates to a structure for producing ballistic protection which combines high levels of performance in terms of stopping bullets and reducing trauma with great flexibility during processing. In particular, a ballistic laminate is produced comprising joined-together unidirectional layers which enables the production, using the laminate, of curved ballistic protection which is readily adapted even to a small radius of curvature. The ballistic laminate provided by the present invention is preferably produced by superposing at least two layers of ballistic yarns 101 and 103, arranged unidirectionally in directions inclined relative to one another by approximately 90° (+/-10°). Each layer comprises a plurality of yarns arranged unidirectionally according to a substantially mutually parallel direction (+/- 10°). A layer of polymer, preferably in film form, is applied to the outside of one of the two textile layers, in such a manner as to prevent the yarns of said layer from slipping.

Description

BALLISTIC LAMINATE COMPRISING UNIDIRECTIONAL LAYERS JOINED TOGETHER BY STITCHING WITH THE YARNS OF ONE OF THE LAYERS

STABLY LOCKED IN PLACE

FIELD OF THE INVENTION

The present invention relates to a structure for producing ballistic protection which combines high levels of performance in terms of stopping bullets and reducing trauma with great flexibility during processing.

BACKGROUND OF THE INVENTION

Rigid ballistic elements are normally produced using various layers of impregnated or laminated woven fabrics which are then subjected to the action of pressure and heat to obtain a monolithic structure. Such layers take the form of textile structures which are familiar to relevant skilled persons.

In these structures of the semi-unidirectional or unidirectional warp and weft type or multiaxial structures, better ballistic qualities are obtained by using laminated woven fabrics in which the threads are arranged unidirectionally without being interwoven. These types are, however, much less deformable and thus more difficult to use than warp and weft woven fabrics for the production of rigid ballistic elements with a small radius of curvature, such as helmets, for example.

OBJECT OF THE INVENTION

The primary object of the present invention is to provide a ballistic laminate which reduces the disadvantages of the prior art. BRIEF DESCRIPTION OF THE INVENTION

Said object has been achieved in accordance with the present invention by the production of a ballistic laminate for ballistic protection, the laminate comprising at least one first unidirectional textile element and at least one second unidirectional textile element, the first textile element comprising a first plurality of ballistic yarns arranged substantially in a first direction, the second textile element comprising a second plurality of ballistic yarns arranged substantially in a second direction, the first and the second directions forming a relative angle of 90° +/- 10°, the laminate being covered by a polymeric layer external to the first unidirectional textile element such that the ballistic yarns of the first textile element are at least partially impregnated by the polymeric external layer, while the ballistic yarns of the second textile element are not impregnated by the polymeric external layer. The at least first and the at least second textile elements are stitched together in such a manner that the ballistic yarns of the second textile element are withdrawable, without breaking, when subjected to a tensile force greater than a predetermined threshold value, while the ballistic yarns of the at least first textile element are kept in place by the polymeric external layer. According to a preferred embodiment, the ballistic yarns are made from aramid, polyaramid, ultra-high molecular weight polyethylene (UHMWPE), copolyaramid, polybenzoxazole, polybenzothiazole or liquid crystal polymers, glass or carbon, also in blends with one another.

The at least first and the at least second unidirectional textile elements and the layer external to the first unidirectional textile element are preferably joined together by pressing. In a preferred embodiment of the present invention, the polymeric layer is in film form and comprises one or more of the following materials: polyurethane, polyester, polyamide, polyethylene, polypropylene, phenolic or PVB-modified phenolic film. The weight of each textile element is preferably between 10 g/m² and 500 g/m² A second aspect of the present invention provides a process for producing a ballistic laminate as described above.

A further aspect of the present invention provides ballistic protection comprising at least one layer of the above-described ballistic laminate.

BRIEF DESCRIPTION OF THE FIGURES

These and further advantages, objects and features of the present invention will become more apparent to a skilled person from the following description and appended drawings, which relate to embodiments of an exemplary nature which should not be understood to be limiting, in which:

-Figure 1 shows a perspective view of a structure for producing ballistic protection according to one possible embodiment of the present invention;

-Figure 2 shows a side view of the structure of Figure 1 illustrating one of the stitching threads.

DETAILED DESCRIPTION

The ballistic laminate provided by the present invention is preferably produced by superposing at least two layers of ballistic yarns 101 and 103, arranged unidirectionally in directions inclined relative to one another by approximately 90° (+/- 10°). Each layer (in the example of Figure 1 , layers 101 and 103) comprises a plurality of yarns 1 arranged unidirectionally in a substantially mutually parallel direction (+/- 10°).

As an alternative to yarns, which are generally composed of numerous filaments, it is possible to use tapes or monofilaments comprising ballistic fibres. The linear densities of such yarns (tapes, monofilaments) are advantageously between 20 and 6500 dtex, tenacity values are greater than 10 g per dtex, modulus values are greater than 400 GPa and tensile elongation values are between 1 % and 10%; these classes include, for example, aramid yarns produced by Teijin^®, DuPont^®, Kolon or Hyundai^® respectively having the trade names Twaron^®, Kevlar^®, Heracron^® or Alkex^®.

In addition to aramid yarns, it is also possible to use ultra-high molecular weight polyethylene yarns produced by Honeywell^® or DSM^®, having the respective trade names Spectra^® and Dyneema^®, or also in the form of known tapes having the trade names Tensylon^® or Endumax^®. Copolyaramid yarns under the name Ruslan^®, Rusar^®, Autx^® manufactured by Kamenksvolokno^® have recently been introduced. These yarns are characterised by dynamic tensile strength which is at least twice the static strength and so enable elevated ballistic performance. Such dynamic strength values are measured using a procedure developed by Purdue University in the USA, as described, for example, in the document:

- MECHANICAL PROPERTIES OF A265 SINGLE FIBER - Jaeyoung Lima and Weinong W Chena - School of Aeronautics and Astronautics, Purdue University, West Lafayette, IN 47907-2045 -

For the purposes of the present invention, as shown in Figure 1 , the unidirectional structures are produced by superposing two or more layers of ballistic yarns 101 and 103.

The at least two textile layers (101 and 103 in the figure) are joined together by stitching, which creates a connection between the yarns of one layer and those of the other.

Such stitching is preferably of the "chain stitching" type. The stitching thread is selected on the basis of the structure and the weight of the laminate which is to be produced. The linear density of the stitching thread is between 20 dtex and 300 dtex. Yarns based on organic polymers such as, for example, polyester, polyamides, polyethylene, polypropylene, or inorganic yarns such as, for example, basalt, carbon or glass are used.

An element 105 which impregnates, at least in part, the ballistic yarns of the layer 101 is applied to the external face of the at least two layers of ballistic yarns 101 and 103 (in the present example, layer 101 ). The yarns of the layer 103, in contrast, are not impregnated by the element 105 and are only held in position by the connection created by the above-mentioned stitching. Such stitching must exert a locking force such that the yarns of layer 103 are "withdrawable" when subjected to tension greater than a threshold force, which is dependent on the stitching. This feature of "withdrawability" imparts greater flexibility to the structure during processing in comparison with conventional unidirectional structures, and is of great utility when it is desired to produce ballistic protection with a small angle of curvature, which thus has to conform to curved shapes, such as protective helmets, for example.

Layer 105 may, for example, also be composed of discontinuous films, felts, meshes and woven/non-woven fabrics. The composition of layer 105 should enable permanent adhesion to the ballistic yarns of layer 101 . This explains the preferred use of elements based on thermoplastic, elastomeric or thermosetting polymers also in blends with one another. Films of polyethylene, polyurethane, polycarbonate, polyamide, polypropylene, polyester, also in the form of copolymers, are particularly useful. The weights of such additional elements are advantageously between 10 and 100 g/m² and preferably between 25 and 50 g/m²

The resultant structure is subjected to the action of pressure and temperature. Pressures are advantageously between 2 and 100 bar and more advantageously between 5 and 40 bar. The pressing temperature and the duration of application of said temperature must be appropriate and suitably adjusted such that layer 105 is joined to the yarns of layer 101 , but without binding the yarns of layer 103. In other words, thanks to the applied temperature and pressure, layer 105 (for example in the form of a polymer film) is intended to melt and impregnate, at least in part, the yarns of layer 101 ; on completion of the pressure/heating procedure, the yarns of layer 101 are locked in place by the impregnation of layer 105 (in our example, the polymer film), while the yarns of layer 103 will not be impregnated and may be withdrawn by overcoming the connection force of the stitching which joins textile layers 101 and 103 together. A preferred embodiment involves applying a temperature of between 50° and 140°C for a duration of between 1 and 5 seconds, preferably of 1 10°C for 2 seconds.

A stabilisation operation (e.g. by pressing) is optionally also carried out prior to deposition of the film 105.

Figure 2 is a schematic, sectional view of the structure of Figure 1 showing, from top to bottom, the polymeric layer 105 (e.g. adhesive film), the unidirectional ballistic textile layer 101 and the unidirectional ballistic textile layer 103 with yarns arranged in a direction substantially perpendicular to that of the yarns of layer 101 . One of the threads (201 ) which provides the stitching which joins textile layers 101 and 103 together is also shown.

A biaxial structure (with unidirectional layers) has thus been produced in which the yarns of one of the at least two textile layers are locked in place by impregnation by the external polymeric layer while the yarns of the at least one other textile layer are even manually withdrawable from the structure on application of a tensile force which overcomes a threshold value corresponding to the locking force of the stitching which joins the at least two textile layers together. This threshold value for the force required to withdraw yarns from the "free" layer may be adjusted by controlling the connection force of the stitching threads by means of predeterm inable tension values of the connecting thread. The feature of withdrawability of the yarns from at least one of the textile layers is very useful if there is a need to produce ballistic protection including bending of the structure to adapt it to curved profiles, for example in the production of protective ballistic helmets. When the structure is bent in the direction corresponding to the "withdrawable" yarns, such bending will exert tension on said yarns which will be withdrawn from the stitching, so enabling the structure to adapt better to the curvature required by the shape to be produced.

Devices and machines, optionally modified, which are familiar to a person skilled in the art, such as biaxial and multiaxial looms for example, may be used for producing the structure according to the present invention, and more particularly for laying down the textile layers and stitching them together.

The structure of the laminate is made up of at least 2 layers of yarns superposed on one another, with the direction of the unidirectional yarns of each layer being inclined relative to one another by 90° +/- 10°. One of the layers (layer 101 in the example shown in the attached figures) will have the yarns "locked in place", while the yarns of the at least one other textile layer will, as explained above, be able to slip if subjected to a tensile force.

Ballistic protection produced with the laminate of the present invention may comprise a variable number of above-described laminated structures, preferably between a minimum of 1 and a maximum of 50, assembled with one another using methods known to a person skilled in the art.

Claims

1 . Ballistic laminate for ballistic protection, the laminate comprising at least one first unidirectional textile element and at least one second unidirectional textile element, the first textile element comprising a first plurality of ballistic yarns arranged substantially according to a first direction, the second textile element comprising a second plurality of ballistic yarns arranged substantially according to a second direction, the first and the second directions forming a relative angle of 90° +/- 10°, the laminate being covered by a polymeric layer external to the first unidirectional textile element such that the ballistic yarns of the first textile element are at least partially impregnated by the polymeric external layer, while the ballistic yarns of the second textile element are not impregnated by the polymeric external layer, the at least first and the at least second textile elements being stitched together in such a manner that the ballistic yarns of the at least second textile element are withdrawable, without breaking, when subjected to a tensile force greater than a predetermined threshold value, while the ballistic yarns of the at least first textile element are blocked by the polymeric external layer.

2. Ballistic laminate according to claim 1 in which the ballistic yarns comprise one or more of the following materials: aramid, polyaramid, ultra-high molecular weight polyethylene (UHMWPE), copolyaramid, polybenzoxazole, polybenzothiazole, liquid crystal, glass or carbon, also in blends with one another.

3. Ballistic laminate according to one of the preceding claims in which the external layer and the at least first and the at least second unidirectional textile elements are subjected to a pressing action.

4. Ballistic laminate according to one of the preceding claims, in which the external layer comprises one or more of the following materials: phenolic (also modified), polyurethane, polyester, polyamide, polyethylene, polypropylene, in the form of a film or other structure, such as meshes, felts or woven/non-woven fabric.

5. Ballistic laminate according to one of the preceding claims, in which the weight of each textile element is between 10 g/m² and 500 g/m²

6. Process for constructing the ballistic laminate of one of the preceding claims, comprising the steps of:

arranging at least one first unidirectional textile element and at least one second unidirectional textile element in contact with each other, the first textile element comprising a first plurality of ballistic yarns arranged substantially according to a first direction, the second textile element comprising a second plurality of ballistic yarns arranged substantially according to a second direction and the first and the second directions forming a relative angle of 90° +/- 10°;

joining the at least first textile element and the at least second textile element together by stitching;

arranging a polymeric layer externally to the first unidirectional textile element; joining the at least first and the at least second textile elements and the polymeric layer together with a pressure of between 2 and 100 bar, applied for a period of between 1 and 5 seconds at a temperature between 50° and 140°.

7. Construction process according to claim 6 in which the pressure applied for joining the at least first and the at least second textile element with the polymeric layer together is between 4 and 40 bar, the temperature is approx. 110° and the pressure and temperature application time is approx. 2 seconds.

8. Ballistic protection comprising a plurality of ballistic laminate layers of one of claims 1 -5.

9. Curved ballistic protection comprising a plurality of ballistic laminate layers of one of claims 1 -5.

10. Protective helmet made with the ballistic protection of claim 9.