Title of the Invention

Bendable multi-layer tube

Technical Field

The present invention relates to a bendable multi-layer tube, in particular a plastic tube.

Background Art

Multi-layer plastic tubes can be widely used for the delivery of a variety of liquids and gases. A multi-layer tube currently on the market that is manufactured by extrusion mainly consists of three parts: an inner tube, reinforcing layers and an outer layer. The reinforcing layers are generally formed by weaving or winding various metallic or non-metallic fibers. An intermediate joining layer or isolating layer is generally also provided between the reinforcing layers, to connect the reinforcing layers or prevent friction therebetween.

The use of an adhesive such as glue as an isolating layer, and its addition between the reinforcing layers by a coating process, are known in the prior art. However, such a process has the following shortcomings: the production process is quite complex; the amount of glue is difficult to control; the volatilization of some of the solvent during production is not environmentally friendly; and generally, the chief component of such an adhesive is a thermosetting resin which, when used in a plastic tube, makes recycling of the final product difficult.

The application of an intermediate layer between the reinforcing layers by an extrusion process is also known in the prior art. However, such a process has the following shortcomings: co-extrusion equipment is needed, which requires a large investment and involves a complex process; and when this process is used, the processing process parameters of the intermediate layer material need to be close to those of the inner tube material to enable extrusion in the co-extrusion equipment, and consequently the choice of materials is limited.

For these reasons, the present invention needs to propose a new technical solution to solve at least one of the many technical problems mentioned above.

Summary of the Invention

Based on the prior art described above, an objective of the present invention is to provide a bendable multi-layer tube which can be obtained by a simple and environmentally friendly process, and effectively prevents sliding and friction between reinforcing layers.

To achieve the abovementioned technical objective, the present invention proposes a bendable multi-layer tube, comprising an inner tube, an outer layer, and at least two reinforcing layers located between the inner tube and the outer layer, with an isolating layer provided between each adjacent reinforcing layers, wherein the isolating layer is formed by winding a thin film, the thin film being of hardness 45 A - 85 A and thickness 0.1 mm - 2.0 mm.

According to the present invention, by using a thin film instead of an adhesive (e.g. glue) and a thin film winding process instead of an adhesive coating process, the shortcomings of the adhesive coating process can be avoided. Firstly, by winding the thin film directly onto the reinforcing layer of the plastic tube, the isolating layer can be formed by a simple process; little investment is needed for equipment, and there is flexibility in the choice of materials. Furthermore, no solvent is produced or volatilized during production, so the production workshop environment can be favorably improved. The isolating layer thus formed can effectively prevent friction between the reinforcing layers, for example when the multi-layer tube is bent; over a long period of time, friction would damage the reinforcing layers and thus have an adverse effect on their reinforcing effect.

According to the present invention, in order to reliably wind the thin film to form the isolating layer, a thin film with suitable characteristics must be chosen. The thickness and hardness of the thin film are key indices. The thin film has a hardness of 45 A - 85 A. This hardness is measured in accordance with standard ASTM D2240, under the condition of 15 s. When the hardness is less than 45 A, the thin film is too soft, easily slipping and falling off during winding, so production is not possible; when the hardness is greater than 85 A, the thin film is too hard and cannot wrap the reinforcing layer effectively, so production is not possible in this case either. At the same time, the thin film has a thickness of 0.1 mm - 2.0 mm. When the thickness of the thin film is less than 0.1 mm, the winding step cannot be performed; when the thickness exceeds 2.0 mm, the superposition of multiple layers in the tube will affect the outer diameter of the final finished tube.

In addition, in order to ensure the physical properties of the multi-layer tube, preferably, the thin film has density of 0.7 - 1 .3 g/cm ³ determined in accordance with ASTM D792, and/or a tensile strength of 5.0 - 15.0 MPa determined in accordance with ASTM D412, and/or an elongation at break > 80% determined in accordance with ASTM D412. Furthermore, the thin film is preferably insulating.

The winding of the thin film according the present invention may be achieved in different ways.

Preferably, the isolating layer is formed by winding the thin film longitudinally in the length direction of the multi-layer tube. For this purpose, the thin film is provided in the form of strip material for example; when the thin film is applied, the longitudinal direction i.e. the length direction of the strip material is kept in line with the length direction of the multi-layer tube, and the thin film is wound widthwise around the entirety of the periphery of the tube to be wound, thereby surrounding the periphery of the tube. When wound on the reinforcing layer, the thin film surrounds the periphery of the reinforcing layer. A sleeve-shaped isolating layer is thus formed. This winding method does not require additional winding equipment, and can achieve relatively uniform wrapping with the thin film.

When the isolating layer is formed by winding the thin film longitudinally in the length direction of the multi-layer tube, preferably, the width of the thin film corresponds to the outer circumference of the tube wound by the thin film. Thus, when the thin film is wound widthwise around the entirety of the periphery of the tube to be wound, it precisely surrounds the periphery of the tube. Also preferably, the isolating layer is formed in a helical shape by winding the thin film longitudinally in a diameter direction of the multi-layer tube. For this purpose, the thin film is also provided in the form of strip material for example; when the thin film is applied, the longitudinal direction i.e. the length direction of the strip material forms a certain angle with the circumferential direction of the multi-layer tube, and the strip material is wound helically, ring by ring, thereby surrounding the periphery of the tube. When wound on the reinforcing layer, the strip material surrounds the periphery of the reinforcing layer. A helical isolating layer is thus formed. With this winding method, the helical winding needs to be performed with the aid of winding equipment.

When the isolating layer is formed in a helical shape by winding the thin film longitudinally in a diameter direction of the multi-layer tube, the width of the thin film and the helical winding angle may both be adjusted as required.

The two thin film winding methods described above may be flexibly used for the isolating layers in a single multi-layer tube. The isolating layers in a single multi-layer tube may employ the same thin film winding method or different thin film winding methods.

Moreover, the winding of the thin film according to the present invention does not require additional joining; firstly, the thin film itself has a certain degree of adhesiveness; secondly, the reinforcing layer outside the isolating layer has the effect of fixing the isolating layer thin film; and furthermore, when the outer layer is formed by extrusion at the outermost part, applied heat causes further fusion of the thin film.

Preferably, a material of the inner tube is a thermosoft plastic or a thermoplastic elastomer, and/or a material of the outer layer is a thermosoft plastic or a thermoplastic elastomer. As the thermosoft plastic or thermoplastic elastomer, the following may for example be used: polypropylene (PP), polyethylene (PE), polymethylpentene (PMP), thermoplastic elastomers (TPE), polyamide (e.g. PA6, PA66, PA11 , PA12, PA46, PA610, PA9T, PA6T), polyvinyl chloride (PVC), polystyrene (PS), fluoropolymers, silicone polymers, polyether ether ketone (PEEK), polyketone (POK), etc. When the inner tube and outer layer are formed of a thermosoft plastic or thermoplastic elastomer, they are easy to form and process, and can be recycled repeatedly.

Preferably, the thin film is formed of a thermoplastic elastomer. The thermoplastic elastomer has good compatibility with the thermoplastic material used in the inner tube and outer layer, and is easy to recycle. As the thermoplastic elastomer (TPE) forming the thin film, the following may preferably be used: thermoplastic vulcanizate (TPV), styrene thermoplastic elastomer (TPS), polyurethane thermoplastic elastomer (TPU) or polyolefin thermoplastic elastomer (TPO). However, the choice of materials is not limited to this, and it is also possible to use a thermoplastic elastomer such as polyamide thermoplastic elastomer (TPAE), polyester thermoplastic elastomer (TPEE) or polyvinyl chloride thermoplastic elastomer (PVC-TPE) to form the thin film, and thereby form the isolating layer of the present invention.

Preferably, the thin film wraps the entire length of the multi-layer tube, thereby effectively preventing slippage and friction between the reinforcing layers.

The reinforcing layer may use fibers, yam or cord as a reinforcing element, applied by weaving or helical winding. Examples of materials suitable for use as reinforcing elements are: metal wire, aromatic polyamide (also called aramid, e.g. para-aramid or meta-aramid), polyamide, polyester (e.g. polyethylene terephthalate (PET)), polyvinyl alcohol (PVOH), or a combination of the abovementioned materials in the form of a mixed system. Preferably, the reinforcing layer is formed by weaving or winding steel wire, or polyester or aramid fibers.

The number of reinforcing layers between the inner tube and outer layer may vary according to the application conditions. For example, for high- pressure tube (10 - 100 MPa) applications, 3 - 4 reinforcing layers are generally applied. For low-pressure tube (0.1 - 1 .6 MPa) applications, 1 - 2 reinforcing layers are generally applied.

Also preferably, the isolating layer is provided between the inner tube and the innermost reinforcing layer, thereby preventing relative slippage between the reinforcing layer and the inner tube.

Preferably, the multi-layer tube is a high-pressure delivery tube. The multi-layer tube according to the present invention may be used as a hose or a hard tube, both of which can bend.

Correspondingly, the present invention also proposes a method for manufacturing a multi-layer tube, comprising the following steps:

- forming an inner tube, for example by extrusion;

- optionally, applying an inner isolating layer on the inner tube;

- applying a reinforcing layer on the inner tube or inner isolating layer by weaving or winding;

- applying an outer layer on the outermost reinforcing layer, for example by extrusion, wherein at least two reinforcing layers are provided between the inner tube and outer layer, with an isolating layer applied between each adjacent reinforcing layers; for this purpose, the isolating layer is formed of a thin film by a winding process.

In the case where the inner tube and/or outer layer is/are formed of a thermoplastic elastomer, the elastomer is finally vulcanized to obtain the finished tube.

The abovementioned features applying to the multi-layer tube of the present invention likewise apply to the manufacturing method of the present invention, so to avoid redundancy are not repeated here.

The present invention has the following advantages: the isolating layer can be formed on the reinforcing layer by a simple process, thus effectively avoiding friction between reinforcing layers; little investment is needed for equipment to accomplish this, and there is flexibility in the choice of materials for the isolating layer; furthermore, no solvent is produced or volatilized during production, which is environmentally friendly.

Brief Description of the Drawings

The present invention is explained further below with reference to the drawings. All of the drawings use a simplified schematic form and imprecise proportions.

Fig. 1 shows an embodiment of a multi-layer tube according to the present invention in a 3D drawing. Fig. 2 shows a thin film winding method for forming an isolating layer according to the present invention.

Fig. 3 shows another thin film winding method for forming an isolating layer according to the present invention.

Detailed Description of the Invention

To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is described clearly and completely below in conjunction with embodiments and comparative examples. Obviously, the embodiments described are some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

Fig. 1 shows an embodiment of a multi-layer tube according to the present invention. Radially innermost and outermost parts of the multi-layer tube are an inner tube 1.1 and an outer layer 1.3 respectively. Four reinforcing layers 1 .2 are provided between the inner tube 1.1 and the outer layer 1 .3. Isolating layers 1.4 are provided between the reinforcing layers 1.2. In addition, as shown in the figure, an isolating layer 1.4 may also be provided between the inner tube 1.1 and the innermost reinforcing layer 1.2, but this is not necessary.

The multi-layer tube can be prepared by the following process.

Firstly, a thermosoft plastic is applied to a core rod by extrusion to form the inner tube 1 .1 ; a thermoplastic elastomer thin film is then optionally wound on the inner tube 1 .1 to form an inner isolating layer; steel wire is woven or wound on the inner tube 1 .1 or optional inner isolating layer to form an innermost first reinforcing layer 1 .2; a thermoplastic elastomer thin film is then wound on the innermost reinforcing layer to form a first isolating layer 1 .4; a second reinforcing layer, a second isolating layer, a third reinforcing layer, a third isolating layer and an outermost fourth reinforcing layer are then sequentially applied to the first isolating layer; and a thermosoft plastic is then applied by extrusion to the outermost fourth reinforcing layer to form the outer layer 1 .3. All of the isolating layers wrap the entire length of the tube. Finally, the multi-layer plastic tube is taken off the core rod.

In some embodiments, a thermoplastic elastomer may also be used as the material of the inner tube 1.1 and/or the outer layer 1 .3. In this case, the multi-layer tube is taken off the core rod after vulcanizing the elastomer.

In some embodiments, the reinforcing layers 1.2 may be formed by weaving or winding non-metallic polyester or aramid fibers.

The multi-layer tube shown in Fig. 1 is suitable for use as a high- pressure delivery tube. In some embodiments, a smaller number of reinforcing layers may be provided between the inner tube and the outer layer. For example, precisely 2 reinforcing layers may be provided between the inner tube and the outer layer, and the multi-layer tube thus obtained is suitable for use as a low-pressure delivery tube.

To form the isolating layer 1 .4, see the two methods of winding the thermoplastic elastomer thin film shown in Figs. 2 and 3.

According to the thin film winding method shown in Fig. 2, when the thin film is applied, the longitudinal direction i.e. the length direction of the thin film strip is laid on the tube in the length direction of the tube. The width of the thin film strip corresponds to the outer circumference of the tube to be wound. The thin film is wound widthwise around the entirety of the periphery of the tube to be wound, such that the thin film precisely surrounds the periphery of the tube, thereby forming a sleeve-shaped isolating layer.

According to the thin film winding method shown in Fig. 3, when the thin film is applied, the longitudinal direction i.e. the length direction of the thin film strip forms a certain angle with the circumferential direction of the tube, and winding is performed helically, ring by ring, with the aid of winding equipment, thereby surrounding the periphery of the tube to be wound and thus forming a helical isolating layer.

In accordance with the two thin film winding methods described above, Examples 1 - 4 and Comparative examples 1 - 4 below are specifically implemented.

Example 1 :

A thin film formed of thermoplastic vulcanizate (TPV) is used; the hardness of the thin film is 45 A (ASTM D2240, 15 s), the thickness of the thin film is 0.1 mm, the density of the thin film (ASTM D792) is 0.7 g/cm ³ , the tensile strength (ASTM D412) is 5.0 Mpa, and the elongation at break (ASTM D412) is 85%. The thin film is wound longitudinally in the length direction of the tube.

Example 2:

A thin film formed of a styrenic thermoplastic elastomer (TPS) is used; the hardness of the thin film is 60 A (ASTM D2240, 15 s), the thickness of the thin film is 0.8 mm, the density of the thin film (ASTM D792) is 0.9 g/cm ³ , the tensile strength (ASTM D412) is 15.0 Mpa, and the elongation at break (ASTM D412) is 85%. The thin film is wound longitudinally in the length direction of the tube.

Example 3:

A thin film formed of polyurethane thermoplastic elastomer (TPU) is used; the hardness of the thin film is 70 A (ASTM D2240, 15 s), the thickness of the thin film is 1 .5 mm, the density of the thin film (ASTM D792) is 1 .1 g/cm ³ , the tensile strength (ASTM D412) is 20.0 Mpa, and the elongation at break (ASTM D412) is 90%. The thin film is wound longitudinally in a helical shape in a diameter direction of the tube.

Example 4:

A thin film formed of a polyolefin thermoplastic elastomer (TPO) is used; the hardness of the thin film is 85 A (ASTM D2240, 15 s), the thickness of the thin film is 2.0 mm, the density of the thin film (ASTM D792) is 1 .3 g/cm ³ , the tensile strength (ASTM D412) is 25.0 Mpa, and the elongation at break (ASTM D412) is 90%. The thin film is wound longitudinally in a helical shape in a diameter direction of the tube.

Examples 1 - 4 above all successfully form the isolating layer by winding, and preserve the physical properties of the multi-layer plastic tube.

Comparative example 1 :

A thin film formed of thermoplastic vulcanizate (TPV) is used; the hardness of the thin film is 40 A (ASTM D2240, 15 s), the thickness of the thin film is 0.1 mm, the density of the thin film (ASTM D792) is 0.7 g/cm ³ , the tensile strength (ASTM D412) is 5.0 Mpa, and the elongation at break (ASTM D412) is 85%. The thin film is wound longitudinally in the length direction of the tube.

Comparative example 2:

A thin film formed of thermoplastic vulcanizate (TPV) is used; the hardness of the thin film is 90 A (ASTM D2240, 15 s), the thickness of the thin film is 0.1 mm, the density of the thin film (ASTM D792) is 0.7 g/cm ³ , the tensile strength (ASTM D412) is 5.0 Mpa, and the elongation at break (ASTM D412) is 85%. The thin film is wound longitudinally in the length direction of the tube.

Comparative example 3:

A thin film formed of polyurethane thermoplastic elastomer (TPU) is used; the hardness of the thin film is 70 A (ASTM D2240, 15 s), the thickness of the thin film is 0.05 mm, the density of the thin film (ASTM D792) is 1 .1 g/cm ³ , the tensile strength (ASTM D412) is 20.0 Mpa, and the elongation at break (ASTM D412) is 90%. The thin film is wound longitudinally in a helical shape in a diameter direction of the tube.

Comparative example 4:

A thin film formed of polyurethane thermoplastic elastomer (TPU) is used; the hardness of the thin film is 70 A (ASTM D2240, 15 s), the thickness of the thin film is 2.5 mm, the density of the thin film (ASTM D792) is 1 .1 g/cm ³ , the tensile strength (ASTM D412) is 20.0 Mpa, and the elongation at break (ASTM D412) is 90%. The thin film is wound longitudinally in a helical shape in a diameter direction of the tube.

The hardness of the thin film in Comparative example 1 is too low, so the thin film is too soft, sliding and falling off in the winding process, and thus unable to form the isolating layer. The hardness of the thin film in Comparative example 2 is too high, so the thin film is too hard and cannot effectively wrap the tube, so is unable to form the isolating layer. The thickness of the thin film in Comparative example 3 is too small, so the thin film cannot be effectively wound and is unable to form the isolating layer. The thickness of the thin film in Comparative example 4 is too large, so after applying multiple isolating layers and reinforcing layers according to Fig. 1 , the outer diameter of the final finished tube is too large. It will be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, and the present invention is not limited thereto. Various modifications and improvements can be made by a person skilled in the art without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered as falling within the protection scope of the present invention.