NO20200854A1 - Sinkable ropes and nets - Google Patents

Description

BACKGROUND OF THE INVENTION

The invention is in the field of ropes and netting and the like. In particular the present invention is directed to ropes, nets and the like which have improved sinkable (i.e. negative buoyancy) properties.

A problem often encountered in marine environments is floating ropes. When floating, these ropes can be caught up by rotating propellers of motor boats or keels from sailboats. Apart from the immediate danger this presents, this may cause other problems, such as breaking of the rope, obstruction and damage to propellers and sealing systems used in those propellers, maneuvering difficulties for the boats and also damage to keels or rudders. Specifically in the salmon farming industry, floating ropes or twines can lead to loss of geometry of the bottom of the fish cages. This in turn leads to difficulties in the flow of dead fish to the center of the cages, where the dead fish are removed by a pumping system out of the dead fish chute.

In the art two types of sinking ropes exist. One type is based in fibers with a density higher than water. Examples of such fibers with a density higher than water are polyester anchor polyamides. These are almost exclusively produced as multifilaments which have a significant water uptake due to their high specific surface area and hydrophilicity, which makes it difficult to remove them from the water particularly in applications such as fish farming where tens of tons of netting need to be replaced at least once a year on each farm. The high surface area of multifilaments is also an excellent substrate for micro-organisms, thus increasing the fouling uptake in marine environments, which is very undesirable. The use of fibers with densities higher than that of water also may have a negative effect in the malleability of the ropes, due to the hydrophobicity, in particular when polyester and polyamide, the most popular synthetic (polymeric) fibers, are used.

The other type of sinking rope is based on fibers with a lower density than water, which are made heavier by combining them with a metal, such as lead or zinc. Such metals however may suffer from corrosion in the marine environment in which they are use. Also the release of the metal ions into the environment can be undesired, since it may result in concentrations that are too high for instance from the viewpoint of toxicity.

Lead is the most popular metal core used for the production of sinking ropes. Lead is a known poison which can lead to medical issues in both adult and children but that can also be absorbed by the flora and fauna in the marine environment.

DE20200500329 1 discloses a rope having anti-fouling properties. This prior art document does not address the problem of floating ropes and specific weights are not disclosed.

W02010106143 discloses yarns comprising a glass core around which a twisted polymeric fiber (such as UHMWPE) is present. The problem of floating or sinking is also not mentioned in this prior art document.

JP2003064541 describes composite fibers having a specific gravity of 1.5 or more.

US2949807 is directed to ropes comprising glass fibers as reinforcing filaments. The problem of floating or sinking is also not mentioned in this prior art document.

An object of the present invention is to produce sinking ropes or yarns and products made thereof, which do not require metal addition or fibers with densities heavier than water. A further object is to provide such sinking ropes that allow the use of polyolefin tapes, raffia or monofilaments to produce the sinking products, thus minimizing the water and fouling uptake.

The present inventors attempted numerous alternatives to obtain ropes having suficient negative buoyancy before arriving at the present invention.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a rope or yarn comprising a combination of polymeric fibers and inorganic fibers.

The present invention provides means to increase the density of products such as ropes or yarns for applications where it is required that floating of such products is avoided. In addition, the mechanical properties of the rope or yarn are not negatively affected. It was found that the inorganic fibers may in some cases even contribute to the mechanical properties.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic representation of a rope in accordance with the invention.

Figure 2 is a schematic top view of a rope according to the invention.

Figure 3 is a schematic representation of a single fringe that can be used to make ropes of the present invention.

Figure 4 is a schematic representation of a double fringe that can be used to make ropes of the present invention.

Figure 5 is a schematic representation of a fringe with loops that can be used to prepare fringes for use with the present invention.

Figure 6 is a detail of figure 5 showing schematically how fringes can be made.

Figure 7 is a schematic representation of a braided twine according to the present invention.

Figure 7A is a schematic representation of a rope of the invention comprising three strands.

Figure 7B schematically depicts a cross section of the rope of figure 7A.

Figure 8 is a schematic representation of a woven net according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention there is provided a rope or yarn comprising a combination of polymeric fibers and inorganic fibers. The rope or yarn has a density higher than water. The polymeric fibers may have a density that is lower or higher than water. For polymeric fibers having a density higher than water, the invention can be used to further increase the resulting product’s density in order to achieve an even faster sinking efect.

The mineral fibers are non-leaching and non-polluting. Another advantage of this sort of material, in particular of basalt, slate, or other oxide, nitride or carbide fibers, is that they show a textile-hke behavior, which allows them to be integrated with existing production processes without the need for modification of the machinery available to rope or yarn producers.

Surprisingly, according to the present invention, part of the load on the rope or yarn can be borne by the mineral fibers, reducing the needed amount of polymeric fibers in the final product. This was found to be not possible when metal fibers were used to increase the weight. When steel wire is used in conjunction with polymeric fibers, the mismatch in elastic modulus is too large to make them work together with the synthetic material so that all load is borne by the metal. Ropes with metal are also quite stiff to handle and corrode in the marine environment, whereas the mineral fibers proposed in accordance with the present invention are not normally affected by water. Lead is also poisonous and its use is seeing increased limitations. Such limitations are not experienced with mineral fibers, in particular when these fibers are basalt, slate, or other oxide, nitride or carbide fibers.

The present invention uses a combination of synthetic (in particular polymeric) and mineral fibers to achieve a high density product that has a density higher than water and will sink avoiding problems of the prior art, such as those described above.

The present inventors found that mineral fibers without the combination of polymeric fiber experienced low cycle fatigue. The combination of polymeric and mineral fibers also provides the advantage to increase the fatigue strength, in particular by encapsulating the mineral fibers with the polymeric fiber.

The polymeric fiber used in the present invention are for instance produced from polyolefins such as polypropylene homopolymer, high density polyethylene and mixtures thereof, particularly polypropylene-rich blends. The density of polypropylene is typically 905 kg/m<3 >whereas the density of the high density polyethylenes used in fibers are between 940 and 960 kg/m<3>. Other fibers that can be used are polyester terephthalate fibers with an approximate density of 1380 kg/m<3>, polyamides with an approximate density of 1140 kg/m<3>, UHMWPE fibers, with an approximate density of 970 kg/m<3>, as well as combinations thereof. More than one type of synthetic (in particular polymeric) fibers might be blended to achieve certain properties such as enhanced abrasion resistance or reduced fouling uptake. In addition to the polymeric fibers mentioned above other suitable polymeric fibers are rayon (viscose), acetate, polyester, aramid, aery he, polyamide, cellulose, polyurethane, polyolefins, polyolefin, and high performance fibres such as poly(p-phenylene-2,6-benzobisoxazole (PBO or Zylon) or carbon fibers, as well as combinations thereof.

The inorganic or mineral fiber can be produced from a number of materials. Very suitable are basalt fibers, slate fibers, glass fibers (e.g. S-Glass, E-Glass), silicon carbide fibers, silicon nitride fibers, boron nitride fibers, alumina, zirconia and combinations thereof. Other ceramic fibers than those mentioned can be used as well. Fibers to be used in accordance with the present invention may show densities higher than 2000 kg/m<3>, which allows the construction of ropes and yarns with varying densities by varying the type of fiber and amount to be used.

Basalt fiber is made from fine fibers of basalt. Basalt comprises the minerals plagioclase, pyroxene and ofivine. It is similar to carbon fiber and fiberglass, having better physico-mechanical properties than fiberglass, but being significantly cheaper than carbon fiber. Basalt fiber is typically made from a single material, crushed basalt. Typically, essentially no materials are added. The manufacture of basalt fiber requires the melting of the quarried basalt rock at about 1400 °C. The molten rock is then extruded through small nozzles to produce continuous filaments of basalt fiber. The fibers typically have a filament diameter of between 9 and 13 pm which is far enough above the respiratory limit of 5 pm to make basalt fiber a suitable replacement for asbestos. They also have a high elastic modulus, resulting in excellent specific strength, typically 80-100 GPa, e.g. about 90 GPa. Tensile strength is typically 4-5 GPa, e.g. about 4.8 GPa. Elongation at break is typically 3-4%, e.g. 3.15%. Density is typically 2.6-2. 8 g/cm<3>, e.g. 2.7 g/cm<3>.

Ropes in accordance with the present invention are particularly suitable as mussel ropes. Parameters that are improved by using the present invention as mussel ropes are the floatability, density, surface area, strength and/or the ease with which the mussels can be removed from ropes.

Also the ropes of the invention are metal free and therefore do not pose any threats for the ecosystem of the mussels.

In another embodiment, the ropes or yarns of the invention further comprise one or more tapes or fibrillated tapes, which allows the creation of a high surface area. These tapes can be present in the ropes or yarns in the form of a fringe, which is mechanically fixed to the strands making up the rope. In tins way the tapes can be, so that the release of the fibrillated tape during mussel removal is prevented. The tape or fibrillated tape is for instance produced from a blend of PP/PE, with higher content of PP giving the tape non-slippery properties.

The fringe can for instance be produced of a tape or fibrillated tape from polypropylene homopolymer, high density poly-ethylene and mixtures there-of, particularly polypropylene-rich blends. The tape or fibrillated tape is fixed to the fibers by sewing or crocheting. The fringe construction can e.g. be made by a continuous tape going through a central sewing mechanical fixing and provide strong fixation to the ends. These ends could be loops or loose ends. The fringe may have a natural spiral torsion that allows a perfect integration, for instance in a 3 strand rope of the present invention.

The strands comprise one or more mineral fibers, which may be twisted in conjunction with the polymeric fiber leading to a final product which can contain a varying density according to the blend of fibers and amount of mineral fiber used in its construction. The twisting may be carried out in order for the polymeric fiber to cover the mineral fibers, this does not include twisting by compounding the mineral and organic fibers. The mineral fibers become an integral part of the product, which has textilelike properties. Thus the mineral fibers contribute not only to the increase in density of the product but also to its mechanical strength and stiffness.

The fringe is added for instance during the twisting of strands projecting the fringe loose end or loops to the outside of the rope. This is illustrated in figures 1 and 2.

The mineral fibers contributing to an increased weight and density of the rope will assist in making the rope sinkable. Also the increased weight and density results in an increased submerged weight of the rope, resulting in a rope that is more still in the water. When used as a mussel rope, if a fringe present this will provide loose ends or lops, which create a high surface area for mussels to attach. The chemical nature of the tape used in the fringe creates a non-slippery surface, and the fringe construction prevents the detachment of the loose end or loops during mussel harvest.

In another embodiment, the ropes or yarns of the invention are used in structures such as nets, canopy ropes and mooring systems. These structures may be used e.g. for fish-farming. A neutral density net system allows for a reduction in buoyancy, which is particularly useful for the construction of fish farms. The buoyancy on these fish farms is normally supplied by floaters distributed along the perimeter of the fish farm and must guarantee the flotation of the farm. The weight of the farm is determined mainly by the weight of the nets used. In the art, these nets typically comprise polymers with a density higher than water (e.g. polyester anchor polyamides), or even copper or steel. In accordance with the invention netting based on fight-weight polymers such as HOPE netting can be used, which can be made heavier by combining it with inorganic fibers so that a netting is obtained that is just heavier than water, preferably having a specific weight of at least 1.025 g/cm<3>. As a result, the load on the buoys is reduced, thus allowing a reduction on the necessary investment in buoyancy for the farm.

Also, the bottom of fish cages can be made to have a neutral or sinking behavior, which improves the flow of dead fish to the dead fish chute, which typically comprises an inverted cone or pyramid shape built onto to base of the cage, from which center the dead fish accumulate by gravity.

The ropes or yarns of the present invention are sinkable in water, in particular in seawater. Preferably they have a density of at least 1.005 g/cm<3>, more preferably more than 1.025 g/cm<3>, even more preferably more than 1.035 g/cm<3>. Typically the density of the ropes of the present invention is less than 2.376 g/cm<3>, preferably less than 1.5 g/cm<3>, even more preferably less than 1.45 g/cm<3>, typically less than 1.4 g/cm<3>. When the density is 1.5 g/cm<3 >or more this causes significant stress in fish-farming installations, with raises additional requirements in flotation, structure strength and stiffness and mooring rope dimensions.

The diameter of the ropes or yarns may vary and are preferably from 1 to 40 mm, more preferably from 2 to 18 mm.

In figure 1 a schematic representation of a rope in accordance with the invention is given. It shows a rope that comprises strands, each strand comprising a core (1) of a twasted inorganic fiber, e.g. basalt. In each strand this core (1) is surrounded by twisted rope (2), for instance a 3-strand PP/PE rope. Three of such strands are twined as illustrated, while a fringe is present between each adjacent strand. Other numbers of strands can be used as well within the spirit of the present invention, such as tw^o, four or five strands.

In figure 2 a schematic top view of a rope thus obtained is given. In figure 3 a schematic representations of a single fringe and in figure 4 of a double fringe is given. Such fringes can be used in the rope of figure 1.

In figure 5 a fringe (3) with loops is schematically depicted. The fringes can be in the form of a continuous tape that runs through the central sewing where is fixed and positioned guarantying good fixation. Such a fringe is an alternative design when the loops are cut, as schematically shown in figure 6, the fringes with loose ends described above (e.g. as shown in figures 3 and 4) can be obtained. To cut the loops two sewing fines (indicated by (4) and (5) in figure 6) are first applied. Then the loops are cut between fine (4) and fine (5) (indicated by dashed fine (6)) after which fine (4) is removed, e.g. by a dye fine 5 can also be removed to obtain the loose ends without any damage and decrease of mechanical performance. Figure 7 shows schematically a braided twine in accordance with the invention wherein the low density fiber core, such as polymeric fibers (2) is parallel with a high density parallel strand of high density fiber, such as basalt (1). The blended core is overbraided with sheaths (11), which typically comprise polymer fibers or a blend of polymer and basalt.

In figures 7A and 7B the embodiment wherein the rope comprises three strands, wherein each strand comprises a sheath (11) which surrounds the inorganic and polymeric fibers. In the embodiment of figures 7A and 7B, the core may also comprise only inorganic fibers, as long as the sheath comprises polymeric material.

Figure 8 is a schematic representation of a woven net using said blended core, where the warp braided twine (8) and the weft braided twine (9) corresponds to that of figure 7. In the embodiment of figure 8, both warp and weft can carry cores comprising both synthetic (in particular polymeric) low density and high density fibers (10) to reach the target density.

In a preferred embodiment, the ropes of the present invention comprise a core, which core comprises both the polymeric and inorganic fibers. In this way the organic fibers will mainly bear the load of the core and the inorganic fibers will not break during the fabrication and final use of the ropes.

Around this core preferably a polymeric sheath (11) is present. The material of the sheath also preferably comprises a polymer produced from polyolefins such as polypropylene homopolymer, high density polyethylene and mixtures thereof, particularly polypropylene-rich blends.

The density of the polypropylene and the high density polyethylenes used in the sheath is as mentioned hereinabove.. Other materials that can be used for the sheath are polyester terephthalate (preferably with an approximate density of 1380 kg/m<3>), polyamides (preferably with an approximate density of 1140 kg/m<3>), UHMWPE fibers (preferably with an approximate density of 970 kg/m<3>), as well as combinations thereof. More than one type of synthetic (in particular polymeric) materials might be blended to achieve certain properties such as enhanced abrasion resistance or reduced fouling uptake. In addition to these polymeric materials mentioned other suitable polymeric materials for the sheath are rayon (viscose), acetate, polyester, aramid, aery he, polyamide, cellulose, polyurethane, polyolefins, polyolefin, and high performance fibres such as poly(p-phenylene-2,6-benzobisoxazole (PBO or Zylon) or carbon fibers, as well as combinations thereof.

In a preferred embodiment, a rope according to the invention comprises one or more strands, each strand comprising a sheath (11) and wherein polymeric and inorganic fibers are present within said sheath. It is preferred that the polymeric and inorganic fibers are laid in parallel, or twisted only shghtly, since this prevents friction, which could lead to abrasion and subsequent dust formation, which in turn may lead to health and safety hazards, resulting also in significant reduction of mechanical properties of the rope.

The ropes of the present invention can be applied in fish farming nettings (sinkable nettings) for example to be used on bottom cages to assure there is no “waving effect” on the netting. This waving efect would accumulate debris on them, and the debris would enter the center of the cage to be down collected, which would decrease the quality of the water/fish, which could increase diseases.

Also the ropes of the invention could be used to make nettings that could replace steel nettings.

Further applications are in seine nettings or purse seine nettings, which are in the prior art typically made very heavy at the bottom by adding several tons of lead or zinc weights to get the net to sink quickly when shot away. This prior art method requires many floats, often several thousands, which are fixed to the top of the net to keep it on the surface, and ensure that the netting hangs vertically in the water. This is avoided by the present invention.

The ropes of the present invention can also replace sinking ropes which rely on lead weights. Lead is being more and more prohibited due to its toxicity.

The ropes of the invention can also be used for mussel ropes, which are used for growing mussels.

The ropes of the invention can also be used for pot ropes (e.g. to secure crab pots or cages). The ropes of the present invention are then attached to the pots (cages) and sink readily to the bottom and will maintain good contact with the seabed to ensure that it is effective at herding the target fish into the pots and reducing the probability of entanglement of other species of marine animals.

EXAMPLES

Example 1. Lab scale twine tests 2.5 mm twines

In these tests, a small twine (diameter 2.5 mm, length 350 mm) according to the invention was produced by twisting basalt fiber (Yellow basalt) into a PE core using a Memmingen™ yarn twister. These twines were subjected to stretching tests using a MesdanLab™ dynamometer. As a reference, similar twines without basalt fiber were used. For each group (reference and inventive) ten samples were tested and from the results the statistics presented in Table 1 were obtained. The mean time for rupture was 29 seconds for the reference and 31 seconds for the inventive samples.

Table 1. Stretching test results 2.5 mm twines

As can be seen, mean, minimum and maximum breaking load are increased, while the elongation to break has decreased with the twined ropes of the invention.

Example 2. Lab scale twine tests 5 mm twines

In this example a twisted monofilament core was joined parallel to a basalt (made from the same material as in Example 1) untwisted core in a braider to produce a 5.0 mm braided twine. This alternative process allows for a greater flexibility in the production of braided twines by reducing the amount of intermediate products, wherein all twisted cores are common to both normal braided products and basalt-containing braided products. For each group (reference and inventive) ten samples were tested and from the results the statistics presented in Table 1 were obtained. The mean time for rupture was 59.1 seconds for the reference and 57 seconds for the inventive samples.

Table 2. Stretching test results 5 mm twines

Example 3. Sinking behavior

The braided twines were tested with regards to their sinking behavior. A piece of twine with a length of 8 cm was inserted in a bottle with water and the time required for it to sink to the bottom was measured. The time it took to sink varied between 30 seconds and 4 minutes but sooner or later the twine ended up sinking.

The product met the requirements of sinking behavior and no negative impact on the mechanical properties of the twine and net. It also showed acceptable behavior with regards to sinking.

Example 4. Toxicity Tests

Toxicity tests were carried out to determine the possible impact of the addition of basalt fibers to a 2.5 mm gold net in the toxicity of three well studied species in both chronic and acute exposure.

Tests were carried out are according to the EPA (US Environmental Protection Agency) guidelines. These tests involved testing with three species: algae, micro- algae and amphipods.

Ropes (2.5 mm diameter) were made with basalt (Yellow basalt) as described in Example 1 and a reference rope with no basalt for control purposes. The EPA guidelines were followed using three different microorganisms: amphipod {Monaco rophium insidiosum), algae (Macrocystis Pyrifera) and microalgae (Dunaliella tertiolecta). The following results were obtained.

Table 3. Results from toxicity tests

There was no negative impact in both chronic and acute toxicity tests in the development of the tested species according to the EPA guidelines. The material is deemed safe for use.

Claims (10)

Patent Claims

1. Rope or yarn having a specific weight of at least 1.005 g/cm<3 >and less than 1.5 g/cm<3>, comprising one or more strands which are a combination of polymeric fibers and mineral fibers, wherein at least one strand (7) comprises a core, which core comprises both mineral and polymeric fibers and which core is surrounded by a sheath (11).

2. Rope or yarn according to claim 1 wherein at least part of said mineral fibers (1) and said polymeric fibers (2) in said core are positioned parallel to the longitudinal axis of said strand (7).

3. Rope or yarn according to any of the previous claims comprising at least two, preferably at least three strands, which strands are twisted, laid parallel, twined, braided or combinations thereof.

4. Rope or yarn according to any of the previous claims wherein the mineral fibers are selected from basalt fibers, slate fibers, glass fibers, silicon carbide fibers, silicon nitride fibers, boron nitride fibers, and combinations thereof.

5. Rope or yarn according to any of the previous claims wherein the polymeric fibers are selected from polypropylene homopolymer, high density polyethylene, polyester terephthalate, polyamide, UHMWPE, rayon, acetate, polyester, aramid, acrylic, polyamide, cellulose, polyurethane, polyolefins, polyolefin as well as combinations thereof.

6. Rope or yarn according to any of the previous claims having a specific weight of less than 1.45 g/cm<3>.

7. Rope or yarn according to any of the previous claims having a specific weight of more than 1.025 g/cm<3>.

8. Rope according to any of the previous claims having a diameter of 1 to 40 mm, preferably from 2 to 18 mm.

9. Net comprising a rope according to any of the previous claims.

10. Mussel rope comprising a rope according to any of claims 1-8 and further comprising a fringe (3).