WO2024105527A1

WO2024105527A1 - A woven fabric having improved tear strength

Info

Publication number: WO2024105527A1
Application number: PCT/IB2023/061407
Authority: WO
Inventors: Claus Sonderborg; Colin Appleyard
Original assignee: Nautosphere Technology Limited
Priority date: 2022-11-14
Filing date: 2023-11-11
Publication date: 2024-05-23

Abstract

The present invention relates to a woven fabric having improved tear strength and, in some embodiments, also bi-modulus properties. The fabric of the invention is suitable for boat sails, parachutes, kites, tents, balloons and other products. The fabric of the invention comprises a first type of yarn woven into a first direction and at least a second type of yarn woven into said first direction, where the first type of yarn has a higher tear strength than the second type of yarn, and where at least a portion of the first type of yarn is wrapped around core yarns. A method for weaving a fabric having improved tear strength is also disclosed.

Description

Title

A WOVEN FABRIC HAVING IMPROVED TEAR STRENGTH

Field of the invention

The present invention relates to a woven fabric having improved tear strength and, in some cases, also bi-modulus properties. The fabric is suitable for products such as boat sails or parachutes.

Background of the invention

In some woven fabrics, such as those used for parachutes, kites, boat sails, hot air balloons and the like, it is often desirable to incorporate a ripstop to improve its tear strength. Such a ripstop can be woven from the ground yams of the fabric, by altering the weave pattern at regular intervals. A problem with this type of ripstop is that the improvement in tear strength, over a plain weave, is relatively small and the fabrics are often prone to tearing regardless.

US5304414 discloses a woven fabric, having yarns of high tensile modulus incorporated between yarns of lower tensile modulus, at regular intervals. Although the focus is on increasing the overall elastic modulus of the fabric, it is well known to those skilled in the art, that the preferred yams, LIHMWPE and aromatic polyamide multi-filament yams, have higher tear strength than the yams they are blended with, such as poly(ethylene terephthalate) (PET) multi-filament yams. The solution disclosed in US5304414 will therefore increase the tear strength while also increasing the elastic modulus of the fabric. It is, however, also well known that reinforced fabrics of this type can be difficult to manufacture, particularly if the fabric must be heated during the manufacturing process, for example during washing, drying, heat-setting or coating, as the two different yams typically have different thermal shrinking characteristics, potentially leading to differential shrinkage between the two yams and, in turn, both visual and structural defects. Conventionally, fabrics containing yams with different shrinking characteristics blended into the same direction are finished at a low temperature, carefully selected so that the two yams having different shrinking characteristics will shrink by the same amount, or not at all, to avoid creating the aforementioned defects. However, a relatively low temperature is often not ideal for achieving the desired properties of the fabric. In particular, it’s often desirable to shrink a woven fabric to reduce its porosity, or to create dimensional stability by increasing the friction between warp and fill yams. However, a temperature high enough to shrink the overall fabric by any significant amount is also likely to create differential shrinkage between the different types of yarns. Consequently, some properties of the fabrics of US5304414 will likely be inferior to those of fabrics that do not incorporate high- modulus yarns. Furthermore, some applications, such as spinnakers or parachutes, require fabrics with some elasticity, to give them shock absorbing properties. The higher elastic modulus of the fabrics of US5304414 is therefore not desirable for these applications.

EP2446076 discloses a method for shrinking a fabric by exposing it to a chemical shrinking agent that shrinks the fabric in only one direction, thereby allowing two yams having different shrinking characteristics to be mixed in the direction that doesn’t shrink. While this method creates dimensional stability and reduced porosity, said fabrics do not have improved tear strength in the direction of the shrinking.

EP3464693 discloses a similar fabric to that of US5304414, consisting of first yam and a second yam having a higher tear resistance than the first yam, woven into and forming a regular network within the woven fabric, where at least one of two yams is individually coated to assist the yam with higher tear resistance being pulled out of the fabric, as the ground yams of the fabric tears. The claimed benefit is that the higher modulus yam will bridge the gap of the tear, thereby providing emergency running properties. While the disclosed fabric may also have an overall improved tear strength, over the fabrics of US US5304414, coating yams individually is cumbersome and expensive, particularly if the yam with higher tear resistance is UHMWPE which, according to the disclosed invention, then requires that the other yam, often used in much higher proportion, is individually coated. Also, the restrictions on the temperature range available for finishing, the limitations on the level of shrinkage that can be achieved during finishing, as well as the sometimes undesirable increase of tensile modulus, as describes above, all applies to the fabrics of EP3464693.

A purpose of the present invention is to provide a woven fabric, suitable, for example, for sails, parachutes, hot air balloons and the likes, that has high resistance to tearing, that has a wide temperature range available for finishing, that can be shrunk without creating defects and that offers shock absorbing properties. Another purpose is to provide a woven fabric having high peak tear strength.

Summary of the Invention

The present invention discloses a woven fabric comprising a first type of yam woven into a first direction and at least a second type of yam woven into said first direction, where the first type of yam has a higher tear strength than the second type of yam.

In some embodiments, the fabric comprises groups of at least 3 yams of the first type.

In some embodiments, each group comprises at least 8 yams of the first type. In some embodiments, each group comprises 16 or more yams of the first type. The gap between groups is generally at least 30% larger than any gap within a group. In some embodiments, the gap between groups can be as wide as the group itself, or wider still. For any given number of yams having higher tear strength that are woven into a particular direction of a fabric, placing these yams in groups rather than spacing them evenly will result in a higher peak tear strength of said direction, without reducing the total energy required to tear across said direction.

In some embodiments, at least a portion of the first type of yam (6) is wrapped around core yams (5). Another portion of the first type of yam can optionally be woven into one or both directions of the fabric without core yams. In some embodiments, all yams of the first type are wrapped around core yams. Wrapping the first type of yam around a core yam increases the tear strength of the fabric it is woven into, compared to fabrics of prior art, by allowing the yam of the first type to change orientation towards the direction of the force being applied when tearing across said yams. In one embodiment, the present invention discloses a fabric which, in addition to high tear strength, has bi-modulus properties, wherein the number of turns of one or more yams of the first type, along the length of the core yarn, is lower than 300 Turns Per Metre. A bi-modulus fabric is suitable for applications that, in addition to improved tear strength, can benefit from improved shape holding, resistance to overstretching and to bursting.

The present invention also discloses a method of weaving a fabric, the method comprising the steps of: wrapping a first type of yarn around core yarns; weaving said first type of yam and at least a second type of yam into a first direction, where the first type of yam has a higher tear strength than the second type of yam. In some embodiments this method comprises the subsequent step of shrinking the fabric in at least said first direction. In some embodiments, the step of shrinking is performed until the differential shrinkage between yams of the first type and the yams of the second type is at least 3%, in at least one direction of the fabric. In some embodiments, where the fabric is shrunk, the shrinking is performed by exposing the fabric to a chemical shrinking agent.

In some embodiments, it can be advantageous to wrap additional yams around the core yam, for example an additional yam of the first type. The fabrics according to the present invention can also comprise additional yams of yet different types. It is also perfectly possible that the yams of the first type and/or the second type differ between the two directions of the fabric.

The Invention also discloses different products made, at least partially, from the fabrics of the present invention, such as a sail, including a spinnaker, a kite, a parachute, a tent, a balloon and an automotive airbag.

Brief description of the drawings

In the following, the invention will be described in greater detail with reference to embodiments shown by the enclosed figures. It should be emphasized that the embodiments shown are used for example purposes only and should not be used to limit the scope of the invention.

Figure 1 shows a woven fabric comprising yams of a second type in the warp direction (1 ), yarns of said second type in the fill direction (2) and yams of a first type, wrapped around core yams, in both the warp direction (3) and fill direction (4) of the fabric.

Figure 2 shows a yam of a first type (6) wrapped around a core yam (5) so that the covering of the core yam is less than 50%.

Figure 3 shows a woven fabric comprising yams of a second type in the warp direction (7), yams of a second type in the fill direction (8) and yams of a first type (9) placed in groups of 8 in the warp direction.

Detailed description of the embodiments

In tear testing, a woven fabric is tom, often tearing individual yams one yam at a time, while measuring the force required to tear. The tear strength of an individual yam depends in part on the density of the woven fabric it is in, among other factors. It is well known in the art that the higher the density of a fabric, the lower a force will be required to tear the yams of that fabric. For the purpose of the present invention, a first yam having higher tear strength than a second yam means that if both yams are woven into a fabric, placed in the same direction of the fabric, said fabric woven as a plain weave and having a uniform density, and if said fabric is subjected to tear testing, the force required to tear the first yam, per unit of mass of said first yam, is higher than the force required to tear the second yam, per unit of mass of said second yam. It should also be noted that the tear strength of a particular yam is measured by tearing the fabric perpendicular to the direction of said yam.

It should furthermore be noted that, with carbon fibre being an exception, the tear strength of a yam is correlated with the breaking tenacity of said yam. It can generally be assumed that if a first multi-filament yam has a breaking tenacity that is at least 50% higher than the breaking tenacity of a second multi-filament yarn, then said first yam will also have a tear strength that is higher than that of said second yarn.

In the present description, the phrases tear resistance, tear strength, and resistance to tearing are used interchangeably and should be interpreted to all have the same meaning.

For the purpose of the present invention, a type of yam means a plurality of yams that are identical in terms of at least chemical composition, and whenever a first type and a second type of yam are mentioned, is should be understood that they differ in terms of at least chemical composition.

In some embodiments, the fabric comprises groups of at least 3 yams of the first type. A group of yams of a first type is defined by all yams in said group comprising at least one yam of the first type, by all yams in said group being placed in the same direction of the fabric, and by the presence of at least one gap, between adjacent groups of yams of the first type, which is larger than any gap between yams of the first type within said group. Within each group, yams of the first type can be spaced out evenly or they can be placed in sub-groups.

In some embodiments, each group comprises at least 8 yams of the first type. In some embodiments, each group comprises 16 or more yams of the first type. The gap between groups is generally at least 30% larger than any gap within a group. In some embodiments, the gap between groups can be as wide as the group itself, or wider still. It is also possible to weave a fabric having groups of varying number of yams and varying gaps between groups. The benefits of placing yams with higher tear strength in groups, rather than spacing them evenly in the fabric, is that a concentration of these yarns create a higher peak tear strength. As the fabric tears through a group of yarns with higher tear strength, spaced apart by yams having lower tear strength, the yams with higher tear strength tend to hold for longer, while yams having lower tear strength continue to tear, even on the other side of the yam that still holds. If spaced evenly across the fabric, it is likely that only one yam with higher tear strength will hold at any point in time. By placing these yams in group, closer together, it is likely that more than one yam of the first type will hold at the same time. For any given number of yams having higher tear strength that are woven into a particular direction of a fabric, placing these yams in groups rather than spacing them evenly will result in a higher peak tear strength of said direction, without reducing the total energy required to tear across said direction. A high peak tear strength is desirable as it can potentially stop certain types of tearing, particularly if the tear is caused by a sequence of events. For example, if a sequence of energy is applied to a sailcloth, as the sail is flogging in the wind, a high peak tear strength can be too high for some or all of these events to overcome, thereby stopping or at least slowing the tearing, compared to fabrics of prior art. If, on the other hand, a larger amount of energy is applied to the sailcloth in a single event, the overall resistance to tearing will be largely unaffected by the higher peaks since the total number of yams, and their individual resistance to tearing, will be the same as in a fabric made according to prior art.

In some embodiments, at least a portion of the first type of yam (6) is wrapped around core yams (5). Another portion can optionally be woven into one or both directions of the fabric without core yams. In some embodiments, all yams of the first type, woven into a first direction, are wrapped around core yams. In preferred embodiments, the core yam is of the second type of yam, although the core yam could also be of any other type. In preferred embodiments, the core yam has a lower tear strength than the first type of yam.

It should be noted that if a yam of a first type is wrapped around a core yam, and if said yam of the first type is woven into a first direction of a fabric, the core yam will necessarily also be woven into said first direction of the fabric. It should further be noted that a yam of the first type, that is wrapped around a core yam, will necessarily be longer than said core yarn. To distinct from other yarn assembly techniques, such as for example twisting, a yam of a first type that is wrapped around a core yarn should be at least 1 % longer than said core yam. In most embodiments, said yam of a first type should be at least 2% longer than the core yam and in some embodiments said yam should be at least 5% longer. In some embodiments, said yam should be at least 10% longer than the core yam and in some embodiments at least 20% longer.

Wrapping the first type of yam around a core yam increases the tear strength of the fabric it is woven into, compared to fabrics of prior art. The reason is that the yam of the first type will be longer than the core yam it is wrapped around and, after weaving, also longer than the yams of the second type. As the fabric tears, the core yam, being shorter, will tear before the yam of the first type wrapped around it. Consequently, the yam of the first type, still attached to both sides of the fabric, will be pulled off the now tom core yam, allowing the yam of the first type to change orientation so that its longitudinal direction will start to carry a load. Due to its molecular orientation, a continuous filament yam can resist much higher loads if applied to its longitudinal direction than if applied perpendicular to this direction. By allowing the yam of the first type to change orientation towards the direction of the force being applied, said yam will eventually break rather than tear, which will happen at a higher load. Consequently, the overall tear strength of the fabrics is therefore improved, compared to fabrics of prior art.

Wrapping the first type of yam around a core yam also solves the problem with reduced elasticity of the fabrics of prior art. The yam of the first type, being longer than both the core yam and the yam of the second type, will not be immediately loaded when the fabric is stretched, and will therefore not reduce the initial elasticity of the fabrics. This is particularly desirable for applications where a high tear strength is desirable but where the fabrics must be able to withstand shock loading, such as parachutes, boat sails including spinnakers, or automotive airbags.

Wrapping the yam of the first type around a core yam can entirely prevent the yam of the first type ever becoming taut, thereby preserving the full elasticity of the fabric, to the point of rupture. It is, however, possible to create a fabric which, in addition to high tear strength, has bi-modulus properties. In one embodiment, the invention discloses a fabric wherein the number of turns of one or more yarns of the first type, along the length of the core yarn, is lower than 300 Turns Per Metre (hereafter TPM) of the core yarn. In some preferred embodiments the TPM is less than 200 and in other preferred embodiments the TPM is even less than 100. When such low TPM is used, it is often desirable to apply this low TPM to at least a plurality and often to all yarns of the first type, in at least one direction of the fabric. Although depending on the size of the yarn of the first type, the aforementioned TPM most often corresponds to the surface area of the core yams being less than 50% covered by yams of the first type, and in most cases also less than 40% covered or even less than 30% covered by yams of the first type. So few turns per metre results in the yam of the first type being only slightly longer than the core yam, therefore allowing it to eventually become taut, as the fabric is stretched. Once the load on the fabric is released, the fabric will recover, contracting and returning to it’s original shape and size, either partially or entirely. The yams of the first type will move with the core yams, due to the friction between these two yams. As the core yam contracts, the yam of the first type, haivng elongated less, will instead increase its TPM.

By adjusting the TPM, the manufacturer of this fabric can adjust the degree of stretching required for the yam of the first type to start bearing a load, marking the beginning of the secondary elastic modulus of the fabric. In most cases, the secondary elastic modulus of these fabrics should begin after at least 1 % of stretching and before the breaking point of the fabric. In many cases, the secondary modulus should begin after at least 2% of stretching. Very often it is desirable that the secondary modulus begins after at least 3% stretching, thereby preserving most or all of the initial elasticity and shock absorbing properties of the fabric. It is possible to further adjust the bi-modulus properties of this fabric during weaving, for example by allowing some yams, often the core yams and yams of the first type, to float over more yams than the yams of the second type. Particularly floats in the warp direction can be desirable, as a way to reduce the crimp in these yams. It is also possible to adjust the secondary modulus of the fabric by selecting yams of the first type that have a desirable elastic modulus. In most cases, when bi-modulus properties are desired, the yam of the first type should have a modulus of elasticity that is higher, often twice as high, than that of the second type of yarn. A preferred yam of the first type for bi-modulus applications is LIHMWPE multi-filament yam. A bi-modulus fabric according to the embodiment is suitable for applications that, in addition to improved tear strength, can benefit from improved shape holding, resistance to overstretching and to bursting, for example parachutes, boat sails including spinnakers, and automotive airbags.

Wrapping the first type of yam around a core yam also solves the problem of having only a narrow and low temperature range available for finishing. Those fabrics of the present invention that comprise yams of a first type wrapped around core yams, can indeed be shrunk, generally to the full potential of the yam having the highest inherent shrinkage, without creating defects, even if the differential shrinkage between the yams of the first and second type is significant. Often, the yam of the first type will shrink less than the yams of the second type, if the fabric is exposed to either heat or to a chemical shrinking agent. Even so, due to the friction between the core yam and the yam of the first type wrapped around it, the core yam can shrink while the yam of the first type, while shrinking less or not at all, instead increases its TPM, similar to a spring being compressed, thereby allowing the fabric to shrink without defects. In some embodiments, the differential shrinkage, between yams of the first type and yams of the second type, in at least one direction of the fabric, is at least 3%, often at least 5% and sometimes at least 8%. For the purpose of the present specification, whenever differential shrinkage between two yams is expressed as a percentage, said percentage should be understood as being percentage points, even if this is not explicitly stated. For example, if a yam of the first type shrinks by 3% and a yam of the second type shrinks by 8%, the differential shrinkage will be stated as being 5% which should be understood as being 5 percentage points.

In many embodiments, to avoid visible defects, the core yam should shrink by approximately the same amount as the yam of the second type. This can easily be achieved by using a core yarn of the second type. In some preferred embodiments, the core yams are yarns of the second type.

The invention also discloses a method of weaving a fabric, the method comprising the steps of: wrapping a first type of yarn around core yarns; weaving said first type of yam and at least a second type of yam into a first direction, where the first type of yam has a higher tear strength than the second type of yam. In many embodiments, the yam of the first type also has a higher breaking tenacity than the yam of the second type. In some embodiments this method comprises the subsequent step of shrinking the fabric in at least said first direction. In some embodiments, the step of shrinking is performed until the differential shrinkage between yams of the first type and the yams of the second type is at least 3%, often at least 5% and in many cases even at least 8%, in at least one direction of the fabric.

In all of the aforementioned embodiments, the yam of the first type should have a tear strength that is significantly higher than that of the second type of yam. In most cases it is desirable that the tear strength is at least 20% higher, often it is desirable that the tear strength is at least 50% higher and in some preferred embodiments it’s desirable that the tear strength is at least twice as high as that of the yams of the second type. An LIHMWPE continuous multi-filament yam is particularly suitable as the first type of yam, as its tear strength is at least twice, and sometimes three or more times as high as some preferred yams of the second type, namely poly(ethylene terephthalate) multi-filament yams and polyamide multi-filament yams. In many embodiments that comprise a core yam and a yam of the first type wrapped around it, the breaking tenacity of the first type of yam becomes just as important as its tear strength, due to the reorientation of said first yam during tearing. In these embodiments, the breaking tenacity of the first type of yam should be higher than the breaking tenacity of the second type of yam. In preferred embodiments, the first type of yam has a breaking tenacity that is at least 20% higher and ideally at least 50% higher than that of the second type of yam. In many embodiments, the breaking tenacity of the first type of yam should be at least twice as high as that of the yam of the second type. Yams that are particularly suitable as the first type of yarn are LIHMWPE or aromatic polyamide (para-aramid) continuous multi-filament yams, both of which have breaking tenacities that are at least twice as high as the aforementioned preferred yams of the second type. For some applications, poly(ethylene terephthalate) continuous multi-filament yams are used as the yam of the first type, particularly when the yam of the second type is polyamide, even though the difference in breaking tenacity can be as low as 20% and sometimes as low as 10%.

In some embodiments, at least the yam of the second type, and in some embodiments also the core yam, if used, should be relatively non-elastic, having an elastic modulus of at least 40 cN/Decitex, ideally above 60 cN/Decitex and often over 80 cN/Decitex. In many embodiments, the yam of the second type should have a breaking tenacity that is at least 4cN/Decitex, and ideally above 6 cN/Decitex. Some preferred yams of the second type, such as PET, can have a breaking tenacity of at least 7 cN/Decitex. In those embodiments that comprise a core yam, said core yam can often be of he same type as the second type of yam, sometimes having a different linear density (size) or a different level of twist.

However, in some embodiments, for example those where yams of the first type, wrapped around core yams, are woven so that they have less woven crimp than adjacent yams of this second type, the core yams can become the shortest of all yams in a particular direction and therefore the first yam to carry a load when the fabric is stretched. This can cause the core yams to break, thereby rendering the fabric unable to recover from stretching and return to its original shape and size. In some embodiments, to avoid the core yams breaking, a core yam having higher elongation to break than the yams of the second type is desirable. In some embodiments, the core yam can be an elastomer having an elongation to break of at least 50 % and sometime 100% of more.

In some embodiments, It can be advantageous to wrap additional yams around the core yam, for example an additional yam of the first type. This results in a fabric where one or more of the core yams each have two or more yams of the first type wrapped around them. In those embodiments where the fabric is shrunk, the core yarn should ideally shrink by the same amount as the yams of the second type, or close to that amount, when exposed to the selected shrinking method. When an elastomer is used as a core yam, its ability to shrink is less relevant, as it will often contract while the surrounding yams of the second type shrinks. In many embodiments, where the fabric is shrunk, the shrinking is performed by exposing the fabric to a chemical shrinking agent. This is often preferable to thermal shrinking, partly because it can be done at a lower temperature than thermal shrinking, thereby avoiding doing damage to low melting point yams such as LIHMWPE, and partly because it is possible to shrink only the core yams and the yams of the second type to their full potential, without shrinking the yam of the first type at all, thereby preserving, or even increasing, the additional length of the yams of the first type, compared to the length of the yams of the second type.

The fabrics according to the present invention can comprise additional yams of yet different types. It is also perfectly possible that the yams of the first type and/or the second type differ between the two directions of the fabric. It should be noted that whenever the properties of two or more types of yam are being compared, the yams being compared are those used, or intended to be used, in the same direction of the fabric.

For all of the above embodiments, the first type of yam should preferably be a continuous multi-filament yams since these yams generally have higher tear strength and higher breaking tenacity than staple yams or spun yams, if made from the same polymer. For example, meta-aramid yams are often used in fabrics, due to their fire resistance, but these yams are manufactured as staple yams and therefore less suitable for fabrics of the present invention. For many preferred embodiments, the second type of yam, as well as the core yams, are also continuous multi-filament yams.

The fabrics of the present invention will sometimes be coated or impregnated with a resin, as required for the specific application of the fabric. The invention also discloses different products made, at least partially, from the fabrics of the present invention, such as, but not limited to, a sail, including a spinnaker, a kite, a parachute, a tent, a balloon and an automotive airbag.

The below examples are incorporated for purpose of clarification and illustration of some embodiments only and they should therefore not be used to limit the scope of the present invention.

Example 1

A sailcloth for upwind sails is woven. 420 Dtex PET multi-filament yarn is used as the second type of yarn in the warp direction and 830 Dtex PET multi-filament yarn is used as the second type of yarn in the fill direction. 280 Dtex LIHMWPE multifilament yam is used as the first type of yam in the warp as well as in the fill direction. Said yam of the first type is wrapped around a core yam to 500 TPM, said core yam being a 420 Dtex PET multi-filament yam, prior to weaving. The yams of the first type, wrapped around core yams, are optionally placed in groups of 12 yams in the warp direction and optionally placed in groups of 4 yams in the fill direction. After weaving, the sailcloth is exposed to a temperature of 135 degrees Celcius, causing the core yams and the yams of the second type to shrink around 5% and the yams of the first type to shrink around 1 percent. The fabric is without aesthetic or structural defects even though the differential shrinkage, between yams of the first type and yams of the second type, is 4%.

Example 2

As example 1 , where the woven fabric is exposed to a chemical shrinking agent rather than heating, causing the core yams and yams of the second type to shrink 12% in the warp direction and 7% in the fill direction, while not causing the yam of the first type to shrink at all. The fabric is without aesthetic or structural defects even though the differential shrinkage, between yams of the first type and yams of the second type is 7% in the fill direction and 12% in the warp direction.

Example 3 As example 1 , where the yarns of the first type, in the fill direction of the fabric, is replaced with 1500 Dtex LIHMWPE multi-filament yam and where the yarns of the second type in the fill direction is replaced with polyethylene naphthalate) multifilament yarns (PEN). A core yam is not used in the fill direction. The fabric is exposed to a chemical shrinking agent capable of shrinking PET but not capable of shrinking PEN or LIHMWPE yams. Said chemical shrinking agent shrinks both the core yams and the yams of the second type in the warp direction by 12%, and does not shrink any yam in the fill direction. The fabric is without structural or visual defects.

Example 4

A fabric for spinnakers or parachutes is woven. 33 Decitex polyamide multi-filament yams are used as the second type of yam and 55 Decitex poly(ethylene terephthalate) multi-filament yams are used as the first type of yams in both directions of the fabric. The yams of the first type are wrapped around core yams of the second type to a TPM of 300, prior to weaving. The yams of the first type are placed in groups of 8 yams, with a maximum distance of 4mm between each yam within a group and 30mm distance between each group. To facilitate weaving, the 8 yams of the first type are not spaced evenly within each group but rather placed in subgroups of two yams. The fabric is woven as a plain weave, then washed and coated with a resin.

Example 5

As example 4, where the yam of the first type is replaced with 55 dtex LIHMWPE multi-filament yam, then wrapped around core yams of the second type to a TPM of 100, equivalent to a covering of the core yams of less than 40%. The warp yarns of the first type are woven so that they float over 5 fill yams, to reduce the amount of crimp in those warp yams, whereas the yams of the second type are woven as a plain weave. This unusually low number of TPM, combined with long floats, allows the yam of the first type to become taut when the fabric stretches under load, thereby effectively creating a fabric which, in addition to improved resistance to tearing, has a secondary, higher modulus of elasticity that kicks in after some initial stretching but well before the fabric ruptures. Example 6

As example 5, where the core yarns in the warp direction have been replaced with yams having lower elastic modulus than the yams for the second type and having an elongation to break of at least 30%. The core yams will not break, despite the longer floats, even if the fabric is stretched to the point of rupture.

Example 7

A fabric for spinnakers or parachutes is woven. 33 Decitex polyamide multi-filament yams are used as the second type of yam and 55 Decitex IIHMWPE multi-filament yams are used as the first type of yams in both directions of the fabric. A core yam is not used in any direction. The yams of the first type are placed in groups of 16 yams, with a maximum of 4mm distance between each yam within a group and 20 mm distance between each group. The 16 yams of the first type are placed in subgroups of two yams. The fabric is woven as a plain weave, then washed and coated with a resin. The resulting fabric will have high peak tear strength.

It should be emphasized that the term "comprises/comprising/comprised of" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims

\Ne Claim:

1 . A woven fabric comprising a first type of yam woven into a first direction and at least a second type of yam woven into said first direction, where the first type of yam has a higher tear strength than the second type of yam, and where at least a portion of the first type of yam is wrapped around core yams.

2. The fabric of claim 1 , wherein the breaking tenacity of the first type of yam is higher than the breaking tenacity of the second type of yam

3. The fabric of any previous claim comprising groups of at least 3 yams of the first type.

4. The fabric of any previous claim, wherein the number of turns of one or more yams of the first type, along the length of the core yam, is lower than 300 per metre of the core yam.

5. The fabric of any previous claim, wherein the surface area of one or more core yams is less than 50% covered by yams of the first type.

6. The fabric of any previous claim, wherein one or more of the core yams are yams of the second type.

7. The fabric of any previous claim, wherein one or more of the core yams each have two or more yams of the first type wrapped around them.

8. A method of weaving a fabric, the method comprising the steps of: wrapping a first type of yam around core yams; weaving said first type of yam and at least a second type of yam into a first direction, where the first type of yam has a higher tear strength than the second type of yam.

9. The method of claim 8, comprising the subsequent step of shrinking the fabric in at least said first direction.

10. The method of claim 9, where the step of shrinking is performed until the differential shrinkage, between the yams of the first type and the yarns of the second type, is at least 3% in at least one direction of the fabric.

11. The method of any of claim 9 to 10, where the step of shrinking is performed by exposing the woven fabric to a chemical shrinking agent.

12. The method of any of claim 8 to 11 , where the yarns of the first type are placed in groups of at least 3

13. A sail, a kite, a parachute, a balloon, a tent, an automotive airbag or another product made, at least partially, of a fabric of any one of claims 1 to 7 or of a fabric made according to the method of any one of claims 8 to 12.