WO2005117578A1

WO2005117578A1 - Floating element and a method for production of such

Info

Publication number: WO2005117578A1
Application number: PCT/NO2005/000184
Authority: WO
Inventors: Finn Ivar Simonsen; Kenneth Hansen; Bjørn HÅGAN; Arild Mathisen; Johannes Strand
Original assignee: Primo Norge As; Mørenot As
Priority date: 2004-06-02
Filing date: 2005-06-02
Publication date: 2005-12-15
Also published as: NO20042281D0; NO20042281L

Abstract

The invention is directed to a floating element to maintain fishing nets and fishing gears floating. Furthermore a process for production of such floating elements is described. The floating elements are produced by an endothermic process using special mixture ratios between different plastic materials as for instance polypropylene, together with a blowing means. The floating elements have a particular density good upward pull, but are also resilient against bursting and collapsing at use on huge ocean depths.

Description

Floating element and a method for production of such

The present invention concerns a floating element to be used for keeping fishing net and fishing gear floating. It is also described a method for producing such floating elements.

There exist a number of floating elements with different shapes, area of application and properties within the fishing industry.

Modern fishery often takes place in ocean depths, where usual depths can be 600 - 900 meters. Experiments conducted with the floating elements according to the invention, have revealed that they withstand pressures on depths down to 1000 meters without collapsing or that the structures of the cells are damaged in other ways.

One of the problems of the methods for production of floating elements of the prior art, is that the processes utilize exothermal foaming. These processes have a tendency not to give an adequate strong and durable foaming process. A consequence of this is that the walls of the cells burst, and the product gets "large cavities". This further results in that the buoyancy properties of the floating elements are weakening due to the absorption of water being considerably higher.

The present invention utilizes special mixing ratios of the different raw materials of polypropylene (PP), polyetylene (PE), polystyrene (PS), polyvinyl chloride (PVC), acrylonitrile butadiene styrene (ABS).

It is only used one type of the raw material in each process batch, and the preferred plastic material is polypropylene (PP).

The blowing agent producing the structure of the cells is based on an endothermic process.

The mixing ratios between the raw material and the blowing agent are from 95 - 99.5 % of the raw material to 5 - 0.5 % of the blowing agent.

The invention will be further described with reference to drawings, wherein Fig. 1 shows a schematic outline of the process and the apparatus, Fig. 2 shows a cross-section of an extruded floating element.

The invention will be further explained by means of fig. 1 showing a schematic outline of the process and the apparatus. The process is starting with plastic raw material and the blowing agent being mixed in suitable mixing ratio, for about 15 minutes in a separate mixing unit. The purpose is to obtain a correct dispersion of the two materials. After the mixing they are emptied into a container where the mixture is sucked continuous into the extruder 1. When the mixture enters the extruder 1, the preparing of the raw material is initiated. The material is screwed through different zones (1 - 12) in the extruder where the material gradually becomes molten. By increasing the temperature and pressure, the chemical foaming process starts. The cavities filled with air (the cell structure) in the floating element are created when the molten material leave the nozzle, as the blowing agent expands. The extruder may consist of a number of zones. In the present case there are nine zones in the extruder, and four zones in the nozzle 2. The temperature will here depend on the raw material and the desired properties. For the present process, the temperature preferably varies from 120 °C to 250 °C.

The floating element is formed with a smooth surface film having a thickness from 0 to 0.5 mm. The thickness of the surface film is regulated in the process of cooling/calibration after the product emerges from the nozzle 2. The surface films produce a protection against external influences and damages, and provide that the floating elements are robust and resist larger load as exposed to during fishing in deep seas.

After the products have been pressed through the extruder 2, they are forwarded into a calibrating and cooling unit 3, and a subsequent cooling vessel 4. Thereafter the products are guided to an evacuation system 5, and continue to a shearing device 6. The shearing device 6, preferably a guillotine, is cutting the extruded material directly on the line into the desired length. A common length of the cylindrical floating elements is from 10 - 100 mm. The floating elements are produced simultaneously with a plurality of cavities (several strings simultaneously) and cut direct on the lines into desired length.

After the cutting the extruded floating elements are enveloped in suitable packaging, for instance big-bags 7.

The preferred blowing agent used in the process is HYDROCEROL (trademark) produced by Clariant Germany. This is a chemical blowing agent in master batch form, based on an endothermic blowing process. This is the preferred blowing agent, but the process for the production is not limited to this. Any blowing agent with the suitable chemical properties can be used to obtain the requested results.

The chemical reaction of the master batch initiates at ca. 160 °C. The optimum generation of gas occurs between 160 and 220 °C. There are two main points to utilize this process. Firstly, the wish to reduce the weight as much as possible in such a way that they obtain better buoyancy for the floating elements in the sea. Additionally, there is a wish to get a structure of the cells which does not "absorb water". This will be obtained with the process of the invention, by the fact that the structure of the cells is closed, i.e. there are cavities with entrapped air in the plastic material, and every single cavity/entrapped air "is on its own", as schematically depicted in the schematic sketch of Fig. 2. Figure 2 is a schematic cross-section of a floating element and shows that cells of relative equal size, pores or cavities 10, dispersed relatively uniform over the length and the cross-section of the entire floating element. The surface film 11 constitutes a protective layer providing that the floating element with the cavities will not be inflicted by damage, in such a way they resist the pressures the elements are exposed to during fishing in deep seas.

It is requested that the density in the completed finished elements is between 0.3 and 0.8 kg/dm³, preferably between 0.4 and 0.65 kg/dm³. It is in principle requested that the density is as low as possible, but if the density is too low, i.e. there are too many cavities in the structure, this can result in cracking the floating element, making it collapse and by taking in water. The floating element will be especially exposed for this on large depths under high pressure. If the density is low, i.e. few cavities in the structure, this will produce poor buoyancy properties. In the floating elements according to the invention a balance between the buoyancy properties and the regard towards collapse and cracking of the elements has been found.

The floating elements produced by the process are very robust as they withstand large pressures on ocean depths. The structure of the cells provide satisfactory buoyancy as floating elements to be used with net and other fishing gear.

Claims

C l a i m s

1.

Floating element to be used for buoyancy of fishing net, trawl bags and other catching equipment during fishing especially on large sea depths, c h a r a c t e r i s e d b y that it comprises

95 -99.5 % raw material, and

5 - 0.5 % blowing agent.

2.

Floating element according to claim 1, c h a r a c t e r i s e d b y that the raw material to be used is a plastic like polypropylen (PP), polyethylene (PE), polyvinyl chloride (PVC) or acrylonitrile butadiene styrene (ABS).

3.

Floating element according to claims 1-2, c h a r a c t e r i s e d b y that the raw material preferably to be used is polypropylene (PP).

4.

Floating element according to claims 1-2, c h a r a c t e r i s e d b y that the blowing agent that is used in the method provides gas formation in temperatures between 160 and 220 °C.

5.

Floating element according to claims 1-2, c h a r a c t e r i s e d b y that the blowing agent that is used, preferably is Hydrocerol. Method for producing a floating element according to any of the previous claims, c h a r a c t e r i s e d b y that a premixed plastic raw material and a blowing agent are introduced into an extruder (1) and further into a nozzle (2).

7.

Method for producing a floating element according to claim 6, c h a r a c t e r i s e d b y that the extruder (1) and the nozzle (2) contain a number of zones of temperature.

8.

Method for producing a floating element according to claims 6-7, c h a r a c t e r i s e d b y temperatures in the zones of temperature are from 120 °C to 250 °C.

9.

Method for producing a floating element according to claims 6-8, c h a r a c t e r i s e d b y that the extruder (1) may contain 5-10 zones of temperature, and the nozzle may contain 2-6 zones of temperature.