The invention is directed to a rope and a method of producing the rope. In particular, the invention is directed to a sealed rope and the use thereof in fishing.

Ropes used in fishing are susceptible to penetration of sand and/or other small particles that enter the voids in between the yarns or filaments of which the ropes are made of. Upon penetration of the particles, the rope's weight may increase and the rope may be damaged internally by abrasion. Penetration of sand particles into ropes may in particular be the case with trawling or fly-shoot fishing where nets made of the ropes frequently touch the bottom of the ocean, sea or lake. In these fields, penetration of sand in the rope is especially considered problematic because it also results in a decrease of the mesh size of the fishing nets.

In trawling, fishing nets are e.g. funnel- or trouser- shaped, wherein the narrow end of the funnel or trouser is closed by a cod-end (see figure 1 for a funnel-shaped net). The cod-end comprises small braided ropes that are connected by knots to form a square mesh of a particular size. The cod-end should allow small fish to escape the fishing net. When sand penetrates the rope, the rope's diameter increases and consequently its length decreases by decreasing the length of the rope, the mesh size also decreases.

Mesh size of fishing nets are determined by measuring the longest length between two knots when the mesh of the net is stretched (see figure 2). Known methods to determine mesh size are e.g. described in "Mesh Shrinkage in Fishing nets", E. S. Strange, Marine laboratory, Aberdeen (1984), which is incorporated herein in its entirety.

As is for instance known from "The effect of smaller mesh sizes on catching larger fish with trawls" by Mous et al., Fisheries Research

54(2002)171-179, small fish are not able to escape the net when the mesh size becomes too small. As such, the mesh size is regulated by national authorities who regularly control the mesh size of fishermen's nets.

Consequently, fishermen have to discard the fishing nets of which mesh sizes have become too small but may otherwise still be in good conditions.

Some known solutions rely on coating the rope at the outside with a coating that is impenetrable for sand and other small particles, thus producing ropes that are sealed. The drawback of this method, however is that the coating is exposed to the surroundings and will start to wear down to a point when holes develop through which the sand can penetrate. This coating is therefore only a temporary solution and has not proven very effective in extending the lifetime of e.g. fishing nets.

US4378725, which is incorporated herein in its entirety, addresses this problem and describes a method wherein a sealed rope is produced by melting a thermoplastic core that is surrounded by heat- shrinkable filaments under tension. The thermoplastic core is dispersed into the voids of the heat- shrinkable filaments and forms a internal sealed layer that prevents the sand from being able to penetrate the rope. It is described that the core comprises a supporting fiber of polyamide or polyester coated by a thermoplastic material such as polyethylene.

However, the rope resulting from the method according to

US4378725 has several drawbacks. For instance, the method results in a hollow rope that may fill with sand or small particles when the sealing layer is damaged. Moreover, the described thermoplastic material does not bind with the heat- shrinkable filaments and leaks out the rope in time. As such the thermoplastic material is only advantageous for a limited time.

Furthermore, the fact that the core comprises at least two materials, viz. the supporting fiber and the coating, results in a cumbersome manufacturing procedure of the rope.

The present invention aims to provide a solution to at least part of these problems. It was found that this objective can be met by a sealed rope comprising an elongated thermoplastic core and yarns arranged around the core in the elongated direction, wherein at least part of the thermoplastic core has at least partly penetrated the voids between the yarns.

Figure 1 is a schematic representation of a fishing net in accordance with the present invention.

Figure 2 is a schematic representation of a single mesh in accordance with the present invention.

Figure 3 is a schematic representation of a particular embodiment of a sealed rope in accordance with the present invention.

The yarns may be arranged around the core by braiding, twisting, twining and the like. Such arrangements typically result in voids or openings between the yarns through which and in which the sand may penetrate.

The yarns may be of different sizes and shapes. The yarns in accordance with the present invention may be flat yarns, round yarns, tapes, bundles of fibers such as threads, wires and the like.

Typical materials for the yarns are polymeric materials such as polyamides, preferably polyamide-6, polyesters, polylactic acid, polyolefins, polypropylene, polyaramid, high-molecular weight polyolefins, such as high- molecular weight polyethylene. The material may however not be limited to polymeric materials. For instance, other materials that may be suitable for the yarns are metals, such as stainless steel. Hence, it will be appreciated that the present invention may also apply to wire ropes, e.g. cables.

The inventors have surprisingly found that in particular a thermoplastic core comprising thermoplastic polyurethane (TPU) is suitable for the present invention.

Thermoplastic polyurethanes are typically multiphase block copolymers that are based on polyol, diisocyanate, and chain-extender blocks. Depending on the blocks the TPU is based on, TPUs are divided into certain classes such as polyester TPU, polyether TPU or polycaprolactone TPU.

Typical TPU classes that may be used for the thermoplastic core are polyester TPU or polyether TPU. When the yarns comprise nylon, a polyether TPU is preferred.

The diisocyanate block of the TPU can be based on either aliphatic or aromatic. The specific TPU class is typically carefully selected to chemically match the yarns arranged around the core in order to have a good adhesion between the yarns and the core after thermo stabilization.

TPU commonly comprises soft (typically the polyol block) and hard (typically the extended diisocyanate) blocks. The ratio between the amount of soft-blocks and hard-blocks is typically one of the TPU properties that is important to find said chemical match. Other properties of the TPU that are important in this aspect are the melting temperature and polarity of the TPU.

Hence, in a preferred embodiment, the thermoplastic core and the yarns may comprise materials that have a certain affinity for each other due to e.g. supramolecular interaction. Such materials may thus have a certain affinity for each other at a molecular level, thereby bonding at a molecular level. Without wishing to be bound by theory, such bonding may result from non-covalent interaction such as dipole-dipole interaction, hydrogen bridges, electrostatic interactions between (partially) charged groups, ionic

interaction, pi-pi-stacking, Van der Waals interaction, and the like. When the materials of the thermoplastic core and the yarns are bonded at a molecular level, the thermoplastic core is less likely to leak out of the rope thereby i.a. prolonging the lifetime of the rope. Hence, in a preferred embodiment of the present invention, the thermoplastic core and the yarns are at least partially bonded at a molecular level. It will be appreciated that in the context of the present invention the term bonded at a molecular level means any type of interaction between the thermoplastic core and the yarns that limits leaking of the core out of the rope.

Other materials than TPU that may be suitable for the core are polyamides such as nylon, ethyl vinyl acetate (EVA), thermoplastic elastomers (TPE) and linear low-density polyethylene LLDPE.

Preferably, the thermoplastic core is an extruded monofilament. Such a core greatly facilitates the production process of the rope.

It was surprisingly found that in particular TPU is suitable for the present invention because this material may easily be extruded to a monofilament. Moreover, a thermoplastic core comprising TPU is both elastic and strong.

In another particular embodiment of the present invention, the thermoplastic core is an extruded monofilament or multifilament of another material than TPU, but is covered with TPU.

The maximum breaking force of the thermoplastic core depends on the diameter for the thermoplastic core. With diameter is meant the diameter of the core in case the cross-section of the thermoplastic core is circular or an equivalent diameter in case the cross-section of the core is not circular. The equivalent diameter is the diameter of a circle having the same surface area as the non-circular cross-section in question. For instance, when the diameter of the thermoplastic core is 1.6 mm, the thermoplastic core preferably has a breaking force of 6 to 8 kgf.

In a preferred embodiment of the present invention, the thermoplastic core has a diameter of more than 1.4 mm and a breaking force of more than 2 kgf as determined by the standardized method DIN EN 527. Typically, the diameter of the thermoplastic core may be up to 3 mm. For instance the diameter may be up to 1.8 mm whereby the core may have a breaking force of 15 kgf or less. Preferably, the thermoplastic core has a diameter of 1.5 to 1.7 mm and a breaking force of 4 to 9 kgf. The preferred mechanical properties, as determined by the standardized method DIN EN 527, may also be expressed by the tensile strength. Typically, the tensile strength of the thermoplastic core is more than 12 MPa and preferably less than 58 MPa. More preferably the tensile strength is 22-45 MPa, most preferably 29-39 MPa.

The elongation to break of the thermoplastic core is typically 100% to 300%, preferably 120-200%, more preferable 130-150%. Such properties are particular advantageous when the rope is used in fishing nets.

The sealed rope according to the present invention may typically be used in fishery, in particular fishing nets, preferably the cod-end of the fishing net may comprise the sealed rope to prevent reduction of the mesh size due to sand penetration in the rope. Hence, a particular embodiment of the present invention, is a fishing net comprising the sealed rope in accordance with the present invention.

Furthermore, it may be appreciated the sealed rope may also be advantageously used in other fields than fishery. For instance sealed ropes in accordance with the present invention which are limited susceptible for penetration of sand and other small particle and wear may be used in docking boats and ships, platforms, sailing boats, but also in rock-climbing and in for instance construction works and mining applications. In principle, any field wherein ropes are exposed to sand and small particles may benefit from the present invention.

The rope construction may vary depending on its intended application.

It may be appreciated that the sealed rope in accordance with the present invention may serve as a yarn or strand in the construction of thicker ropes. For instance, braided or twisted thicker ropes can be constructed containing more than one rope, e.g. 8, 12, 16, 32 and 48 ropes wherein at least one of the 8, 12, 16, 32 or 48 ropes is a sealed rope in accordance with the present invention. Said more than one ropes of this particular embodiment, can surround a further thermoplastic core.

Production process

A method for producing a sealed rope in accordance with the present invention, comprises the steps of:

a) providing a elongated thermoplastic core;

b) arranging, typically braiding, twisting and/or twining yarns around said core, resulting in a non-sealed rope;

c) stabilizing the non-sealed rope at elevated pressure and temperature at about the melting point of the thermoplastic core, whereby the thermoplastic core at least partially melts and at least partially penetrates the voids between the yarns;

d) solidifying the at least partially melted core to obtain a sealed rope.

The thermoplastic core may be provided by melting a

thermoplastic resin (e.g. a resin comprising TPU) in an extruder and extruding from the melt a monofilament, a tape, yarn or a bundle of multifilaments. Preferably, for the purpose of this invention, a

monofilament will be produced. Thermoplastic materials that can be used are typically thermoplastic elastomers, preferably thermoplastic

polyurethanes (TPU). Other materials that can be used are e.g. polyolefin or nylon.

The rope with the thermoplastic core can be produced by using a standard 8, 12,16, 32 or 48 strands braider that has the capability to receive the core material from an extra position to feed it to the core of the rope during the braiding process.

Because of the possible elasticity of the core an adjusted unwinding bobbin holder, that runs on ball bearings, may be required to avoid tension buildup during the unwinding process. The thermoplastic core material is located in the center and the other strands are braided around it. The braiding speed and the speed of feeding of the core may be carefully synchronized, without over- stretching the core. The synchronization prevents tension build up in the final braid.

As an alternative to braided ropes also twisted ropes can be produced by twisting the strands around the thermoplastic core.

The above described process may result in a braided rope as shown in figure 3. Rope (1) of figure 3 comprises an outer braid (2) that can be produced from 8, 12, 16, 32 or 48 strands of yarn, and a thermoplastic core (3) that is preferably a monofilament, more preferably a monofilament of TPU. At this stage in the process, the thermoplastic core (3) is still able to freely inside the outer braid.

The braided rope is cut into several smaller ropes and each rope end is winded on small bobbins to be used in a creel and the bobbins of a loom. The desired configuration of the net may be defined on the netting loom by varying the number of meshes in the length direction, the number of meshes in the width direction, the mesh size, single or double braid/twine and/or single or double knot

The inventors found that a too rigid thermoplastic core may lead to difficulties in the looming process and an unstable production process resulting in a large variation of mesh sizes. It was found that a lower diameter of the thermoplastic core reduces the rigidity of the core and improved production stability. Preferred diameters of the thermoplastic core is in the range of 0.1 to 5 mm, preferably 0.5 to 3 mm, more preferably 1 to 2 mm.

The net resulting from the looming that was produced may be submitted to a heat stabilization process in an autoclave under controlled pressure, temperature and water vapor concentration in order to fix the mesh size, by fixation of the knots. This process can be performed with or without tensioning the net in the lengthwise direction. During this autoclave process the thermoplastic core of the ropes inside the netting is at least partially melted in a controlled way. Thereby the melted thermoplastic core material partially fills the voids in the hollow braided rope and binds to the inner circle of the hollow braid surrounding the core. This may result in the sealing of the rope inside the netted construction.

An alternative technique to produce the net is braiding instead of knotting the netted construction. Knotless nets are being produced by braiding the meshes from the braided, twisted or twined ropes in a circular net braiding machine. Mesh Size stability Evaluation

The mesh size is the longest distance between two knots when the net is stretched (figure 2).

To measure the mesh size an objective mesh gauge is being used as described in ISO 16663-1. The measuring jaws of the mesh gauge are being placed between the opposite knots and they create a predetermined force, while measuring the distance between these knots. The recommended forces for measurement of the mesh size are 10 N for general netting for all mesh sizes; and more specifically for cod-ends: 20 N for mesh sizes < 35 mm; 50 N for mesh sizes > 35 mm and < 55 mm; 125 N for mesh sizes > 55 mm.

For a single measurement, always a series of 20 meshes, parallel in the towing direction are being measured. When measuring cod-ends or extensions of the net, care must be taken with measurements too close to stitched joints, mending lines and other inconsistencies of the net.

The mesh stability is the change in mesh size in time during the use of the net. First, the mesh size is determined before use of the net according to the procedure described above. Subsequently, the mesh size measurement has to be repeated at a specified time interval during the period that the net is in use. The process is repeated as long as the mesh size is still inside the allowed specifications. A soon as the mesh size is lower than allowed, the net is discarded. The invention is illustrated by the following example. Example

A TPU comprising monofilament was produced by extruding the polyether TPU through a circular shaped nozzle and stretched 4 times in a two-step process. For this process a characteristic set of properties is typically of importance (Tm = 160°C, good hydrolysis resistance, good microbial resistance, hardness shore 81 A).

The TPU monofilament that was hereby produced had a diameter of 1.6 mm and a weight of 2.2 g/m.

Mechanical properties were measured by a tensile test as described in DIN EN 527:

• MBL (maximum breaking load, breaking force): 7.4 kgf; and

• elongation at break: 147%

An 8 strand nylon braid with a TPU monofilament core was produced following the method as described above.

A net was produced with the following specifications:

• Bale weight 99kg;

· 424 meshes long; and

• 49.5 meshes deep.

The net was depth- wise thermostabilized. Adhesion of the TPU monofilament to the outer nylon strands after thermostabilization was good.

The mesh sizes of the first prototype were measured using the

Omega method in accordance with ISO 16663-1.

• Mesh size at the beginning of the net: 79.6 mm ifm (inside full mesh)

• Full mesh average was 90.35 mm

· Mesh size at the middle of the net: 78.3 mm ifm • Full mesh average 88.05 mm

• Mesh size at the end of the net: 77.4mm ifm

• Full mesh average 86.2 mm The type of netting that was produced was evaluated by a field test. It was used in the cod-end of netting gear that is normally used in bottom fishing (mainly place and sole), the so called beamers (both conventional as electrical). 3 cod ends could be cut out from the piece of net that was produced, and 2 ships were able to test the prototype. At certain time intervals the mesh size was measured. After 2-3 months field trials the test was finished. Good results were obtained in terms of mesh- stability.