Method for connecting plastic tubes by plastically deforming and widening connecting stub

Abstract

A method for coaxially connecting a first plastic tube (10, 110) to a second plastic tube (20, 120), said plastic tubes (10, 20) in particular being provided as part of a medical catheter (102), the two plastic tubes (10, 20) being connected by way of a tubular connecting piece (50), characterized in that the first plastic tube (10) and/or the second plastic tube (20) are integrally molded from the outside onto the tubular connecting piece (50) using a forming process such that an adhesive and/or positive connection is produced.

Claims

1. A method for coaxially connecting a first plastic tube of a medical catheter to a second plastic tube of said medical catheter comprising the steps of: a) plastically deforming an end region of the first plastic tube into a connecting stub having a length, wherein the first plastic tube is plastically deformed such that an outside diameter of the connecting stub is substantially narrowed in comparison with an outside diameter of the first plastic tube while a thickness of the first plastic tube remains constant, said plastic deformation comprising the steps of inserting an end portion of a cylindrical piece of wire into the end region of the first plastic tube and integrally moulding said end region of said first plastic tube onto the end portion of the cylindrical piece of wire to produce the connecting stub; b) widening a free end of the connecting stub by pushing a thickened region of the cylindrical piece of wire that adjoins the end portion of the cylindrical piece of wire into the free end of the connecting stub in a direction toward the first plastic tube, wherein an outside diameter of the thickened region corresponds to an inside diameter of the first plastic tube; c) pushing the second plastic tube coaxially over the connecting stub, at least over the length of said connecting stub; and d) forming at least one of an adhesive and a positive connection in a forming process.

2. The method as claimed in claim 1, wherein during said step of inserting, an outside diameter of the end portion of the cylindrical piece of wire measures 60-80% of an inside diameter of the first plastic tube.

3. The method as claimed in claim 1, wherein, during the forming process, the second plastic tube is integrally molded onto the connecting stub, the connecting stub being widened at the end, thereby forming a positive connection.

4. The method as claimed in claim 1, wherein, during the forming process: a) the end portion of the cylindrical piece of wire remains in the connecting stub; and b) at least one of the widened transitional region and the thickened region of the cylindrical piece of wire remains in the widened free end of the connecting stub.

5. The method as claimed in claim 1, wherein at least one of the first and the second plastic tube are spirally wound up after the forming process and formed into a dimensionally stable spiral under the application of heat.

6. The method as claimed in claim 1, further comprising the steps of: a) softening the second plastic tube during the forming process by a heat treatment; b) integrally molding the second plastic tube onto the connecting stub by a pressing force acting in a radial direction.

7. The method as claimed in claim 1, wherein to widen the free end of the connecting stub, pushing a widened transitional region of the cylindrical piece of wire located between said end portion of the cylindrical piece of wire and said thickened region of said cylindrical piece of wire into the free end of the connecting stub in a direction toward the first plastic tube.

8. A method for coaxially connecting a first plastic tube of a medical catheter to a second plastic tube of said medical catheter comprising the steps of: a) plastically deforming an end region of the first plastic tube into a connecting stub having a length, wherein the first plastic tube is plastically deformed such that an outside diameter of the connecting stub is substantially narrowed in comparison with an outside diameter of the first plastic tube while a thickness of the first plastic tube remains constant, said plastic deformation comprising steps of inserting an end portion of a cylindrical piece of wire into the end region of the first plastic tube and integrally moulding said end region of said first plastic tube onto the end portion of the cylindrical piece of wire to produce the connecting stub; b) pushing the second plastic tube coaxially over the connecting stub, at least over the length of said connecting stub; c) widening a free end of the connecting stub by pushing a thickened region of the cylindrical piece of wire that adjoins the end portion of the cylindrical piece of wire into the free end of the connecting stub in a direction toward the first plastic tube, said thickened region having an outside diameter corresponding substantially to an inside diameter of the first plastic tube; and d) forming at least one of an adhesive and a positive connection in a forming process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings used to explain the exemplary embodiment:

(2) FIG. 1a shows a longitudinal section through a first plastic tube with an inner tube protruding from it, a tubular connecting piece having been pushed over the inner tube;

(3) FIG. 1b shows a longitudinal section through the tubular connecting piece that has been pushed into an end region of a first plastic tube and an end region of a second plastic tube;

(4) FIG. 1c shows a longitudinal section through the arrangement from FIG. 1b, the end region of the first plastic tube additionally having been pushed over the end region of the second plastic tube and surrounded by a shrink-fit tube;

(5) FIG. 1d shows a longitudinal section through the arrangement from FIG. 1c after the forming process and removal of the shrink-fit tube;

(6) FIG. 2a shows a longitudinal section through a cylindrical piece of wire protruding into the first plastic tube;

(7) FIG. 2b shows a longitudinal section through the arrangement from FIG. 2a after the end region of the first plastic tube has been formed into a narrowed connecting stub;

(8) FIG. 2c shows a longitudinal section through the arrangement from FIG. 2b, a second plastic tube additionally having being pushed over the cylindrical piece of wire and the connecting stub;

(9) FIG. 2d shows a longitudinal section through the arrangement from FIG. 2c once a free end of the connecting stub has been widened by a thickened region of the cylindrical piece of wire and a shrink-fit tube has been arranged around the connected joint;

(10) FIG. 2e shows a longitudinal section through the arrangement from FIG. 2d after the forming process and removal of the shrink-fit tube;

(11) FIG. 3 shows a longitudinal section through a variant of FIG. 1d, a helical spring being arranged as the tubular connecting piece;

(12) FIG. 4 shows a medical catheter formed into a dimensionally stable spiral and comprising the arrangement from FIG. 2e.

(13) In principle, the same parts are provided with the same designations in the figures.

(14) Ways of Implementing the Invention

(15) In FIGS. 1a-1c, various intermediate stages that are run through when a first method according to the invention is carried out are represented. FIG. 1d shows a first arrangement 1 that can be produced by the method according to the invention.

(16) On the left-hand side in FIG. 1a, an end region 11 of the first plastic tube 10 is depicted in longitudinal section. The first plastic tube 10 is cylindrical and has an inside diameter 13 of, for example, 0.7 mm with a wall thickness 14 of, for example, 0.1 mm and consists of polyethylene terephthalate (PET). Arranged inside the first plastic tube 10 is a coaxial and cylindrical inner tube 30, which protrudes from the end region 11 of the first plastic tube 10. The outside diameter 31 of the inner tube 30 in this case corresponds approximately to the inside diameter 13 of the first plastic tube 10.

(17) As a tubular connecting piece, a cylindrical polyimide tube 50 has been pushed coaxially over a region of the inner tube 30 protruding from the first polyimide tube 10. The inside diameter of the polyimide tube 50 corresponds approximately to the inside diameter 13 of the first plastic tube 10. In the region of the first end 51 of the polyimide tube 50 that is facing the first plastic tube 10, a first flange 51.1 protrudes from the outer lateral surface of the first plastic tube 10. The first flange 51.1 has a semicircular cross section and runs completely around the polyimide tube 50, which however cannot be seen in FIG. 1a. In the region of the second end 52 of the polyimide tube 50, a second flange 52.1 protrudes from the outer lateral surface of the polyimide tube 50. Like the first flange 51.1, the second flange 52.1 has a semicircular cross section and runs completely around the polyimide tube 50, which likewise cannot be seen in FIG. 1a.

(18) FIG. 1b shows the situation after the first end 51 of the polyimide tube 50 has been pushed into the first plastic tube 10 and a second plastic tube 20 has been pushed onto the second end 52 of the polyimide tube 50.

(19) In this case, the first end 51 of the polyimide tube 50 is in the end region 11 of the first plastic tube 10. The end region 11 of the first plastic tube 10 therefore completely surrounds the first end of the polyimide tube 50. In a longitudinal direction of the polyimide tube 50, the end region 11 of the first plastic tube 10 thereby protrudes beyond the first flange 51.1 of the polyimide tube 50. On account of the pushed-in polyimide tube 50, the end region 11 of the first plastic tube 10 is widened slightly in the radial direction.

(20) Furthermore, an end region 21 of a second plastic tube has been pushed over the second end 52 of the polyimide tube 50. The second plastic tube 20 thereby protrudes coaxially in the longitudinal direction beyond the second flange 52 of the polyimide tube 50. The second plastic tube 20 is likewise cylindrical, consists, for example, of nylon and has an inside diameter 23 of, for example, 0.7 mm with a wall thickness 24 of, for example, 0.1 mm. The end region 21 of the second plastic tube 20 is likewise slightly widened in the radial direction on account of the pushed-in polyimide tube 50. The first plastic tube 10 and the second plastic tube 20 accordingly have the same dimensions with respect to their diameters 13, 23 and wall thicknesses 14, 24 and lie with their end faces coaxially opposite.

(21) A modulus of elasticity of the polyimide tube 50 is in this case greater than a modulus of elasticity of the first plastic tube 10, while a modulus of elasticity of the second plastic tube 20 is less than the modulus of elasticity of the first plastic tube 10.

(22) FIG. 1c shows the situation after the end region 11 of the first plastic tube 10 has been pushed in the longitudinal direction over the end region 21 of the second plastic tube 20. The first plastic tube 10 in this case protrudes in the longitudinal direction beyond the second end 52 of the polyimide tube 50 and beyond the widened end region 21 of the second plastic tube 20. The end region 11 of the first plastic tube 10 therefore completely surrounds the end region 21 of the second plastic tube 20 and in the overlapping region is additionally partially widened in the radial direction. A rear region 12, adjoining the end region 11, of the first plastic tube 10 also surrounds the region of the polyimide tube 50 that is not surrounded by the second plastic tube 20.

(23) Loosely arranged around the end region 11 and around the rear region 12 of the first plastic tube 10 is a shrink-fit tube 40. The shrink-fit tube 40 completely surrounds the widened regions of the two plastic tubes 10, 20.

(24) The arrangement represented in FIG. 1c corresponds to the starting situation directly before the forming process.

(25) In FIG. 1d, a first arrangement 1 according to the invention, comprising the two plastic tubes 10, 20 and the polyimide tube 50, is represented after the forming process. The shrink-fit tube 40 represented in FIG. 1c has been removed again after the forming process.

(26) On account of the forming process, the end region 21 of the second plastic tube 20 has been integrally molded onto the region of the second end 52 of the polyimide tube 50 and adhesively connected to it. Since the end region 21 of the second plastic tube 20 has also been integrally molded onto the second flange 52.1, there is also a positive connection between the end region 21 of the second plastic tube 20 and the polyimide tube 50.

(27) The end region 11 of the first plastic tube 10 has been integrally molded from the outside onto the end region of the second plastic tube 20 and adhesively connected to it. The rear region 12 of the first plastic tube 10 has been integrally molded onto the first end 51 of the polyimide tube 50 and in this way also onto the first flange 51.1, whereby there is an adhesive and positive connection between the first plastic tube 10 and the polyimide tube 50.

(28) In FIGS. 2a-2d, various intermediate stages that are run through when a second method according to the invention is carried out are represented. In FIG. 2e, the second arrangement 2 that can be produced by the method according to the invention is depicted.

(29) In FIG. 2a, an end region 111 of a first cylindrical plastic tube 110 is depicted in longitudinal section on the left-hand side. The first plastic tube 110 has an inside diameter 113 of, for example, 0.7 mm with a wall thickness 114 of, for example, 0.1 mm and consists of polyethylene terephthalate (PET). An end portion 181 of a cylindrical piece of wire 180 protrudes coaxially into the interior of the end region 111. The outside diameter 181.1 of the end portion 181 of the cylindrical piece of wire 180 measures about 0.5 mm, which corresponds to about 71% of the inside diameter 113 of the first plastic tube 110. Outside the first plastic tube 110, the cylindrical piece of wire goes over into a conically widening transitional region 182, which in turn is adjoined by a thickened region 183 of the cylindrical piece of wire 180. The outside diameter 183.1 of the thickened region of the cylindrical piece of wire 180 measures about 0.7 mm and consequently corresponds substantially to the inside diameter 113 of the first plastic tube 110.

(30) FIG. 2b shows the situation after the end region 111 of the first plastic tube 110 has been integrally molded onto the end portion 181 of the cylindrical piece of wire 180 and thereby formed into a connecting stub 111.1. The inside diameter of the connecting stub 111.1 in this way corresponds to the outside diameter of the end portion 181 of the cylindrical piece of wire 180 and has a narrowed outside diameter and a narrowed inside diameter in comparison with the other regions of the first plastic tube 110.

(31) FIG. 2c shows the situation after a second plastic tube 120 has been pushed coaxially over the thickened region 183 of the cylindrical piece of wire 180 and the connecting stub 111.1 of the first plastic tube 110. The second plastic tube 120 is likewise cylindrical, consists, for example, of nylon and has an inside diameter 123 of, for example, 0.7 mm with a wall thickness 124 of, for example, 0.1 mm. An end region 121 of the second plastic tube thereby protrudes in the longitudinal direction beyond the connecting stub 111.1 of the first plastic tube 110 and lies behind the connecting stub 111.1 on a non-narrowed region of the first plastic tube 110. The end region 121 of the first plastic tube 120 is in this case widened slightly in the radial direction.

(32) A modulus of elasticity of the second plastic tube 120 is in this case less than a modulus of elasticity of the first plastic tube 110.

(33) FIG. 2d shows the situation after the cylindrical piece of wire 180 has been pushed in the longitudinal direction partially into the formed end region 111.1 of the first plastic tube 110. The conical transitional region 182 of the cylindrical piece of wire 180 is in this case in a region of a free end 111.2 of the connecting stub 111.1. As a result, the free end 111.2 of the connecting stub 111.1 is in a state in which it is substantially conically widened and pressed from the inside against the surrounding second plastic tube 120.

(34) In the region of the widened free end 111.2 of the first plastic tube 110 that is surrounded by the second plastic tube 120, the second plastic tube 120 has a bulged region 122, in which the widened end 111.2 of the first plastic tube 110 engages.

(35) Loosely arranged outside the two plastic tubes 110, 120 is a shrink-fit tube 140, which completely surrounds an overlapping region of the two plastic tubes.

(36) In FIG. 2e, a second arrangement 101 according to the invention, comprising the two plastic tubes 110, 120, is represented after the forming process. The shrink-fit tube 140 represented in FIG. 2c and the cylindrical piece of wire have been removed after the forming process. On account of the forming process, on the connecting stub 111.1 there is a free end 111.3 that has undergone forming and is dimensionally stable.

(37) The end region of the second plastic tube 120 now takes the form of an end region 121.1 that has undergone forming and has been integrally molded from the outside in a forward region onto the connecting stub 111.1 of the first plastic tube 110 and behind the connecting stub 111.1 onto the first plastic tube 110. Further toward the rear, the second plastic tube 120 has a region 122.1 that has undergone forming by bulging and has been integrally molded from the outside onto the widened and formed free end 111.3 of the first plastic tube 110.

(38) In this way, between the connecting stub 111.1 of the first plastic tube 110 and the second plastic tube there is an adhesive and at the same time positive connection that withstands high tensile loads.

(39) The second arrangement 102 is, for example, a component part of a medical catheter 102, which is represented in FIG. 4.

(40) FIG. 3 shows a third arrangement 201 according to the invention, which has been produced substantially like the first arrangement 1 and is, for example, a component part of a medical catheter. Instead of the polyimide tube 50 that is present in the first arrangement 1, however, a helical spring 250 has been used in the case of the third arrangement 201 as a tubular connecting piece for connecting a first plastic tube 210 and a second plastic tube 220.

(41) The helical spring 250 consists, for example, of stainless steel wire with a wire diameter 254 of, for example, 0.1 mm. The inside diameter of the helical spring is constant over the entire length and measures, for example, about 0.7 mm, while the individual turns of the helical spring 250 have a spacing 253 of, for example, 0.03 mm. Altogether, the helical spring 250 has ten turns.

(42) The first plastic tube 210 is cylindrical and has an inside diameter of, for example, 0.7 mm with a wall thickness of, for example, 0.1 mm and consists of polyethylene terephthalate (PET). The second plastic tube 20 is likewise cylindrical, consists, for example, of nylon and has an inside diameter 23 of, for example, 0.7 mm with a wall thickness 24 of, for example, 0.1 mm. A modulus of elasticity of the second plastic tube 220 is in this case less than a modulus of elasticity of the first plastic tube 210.

(43) A rear region 212 of the first plastic tube, lying behind an end region 211 of the first plastic tube 210, has in this case been integrally molded coaxially from the outside onto a region of the first end 251 of the helical spring 250 or onto six first turns of the helical spring 250. An end region 221 of the second plastic tube 220 has likewise been integrally molded coaxially from the outside onto a region of the second end 252 of the helical, spring 250 or onto the four remaining turns of the helical spring 250. On account of the integral molding, the helical spring 250 is partially embedded both in the first plastic tube 210 and the second plastic tube 220, the helical spring 250 being let into the two plastic tubes 210, 220 to about a depth of half the wire diameter 254 of the helical spring 250. In this way there is both an adhesive and a positive connection between the two plastic tubes 210, 220 and the helical spring 250.

(44) The end region 211 of the first plastic tube 210, which adjoins the rear region 212 of the first plastic tube in a step-like manner, has also been integrally molded from the outside onto the end region 221 of the second plastic tube 220 and adhesively connected to it.

(45) The helical spring 250 guarantees great bending flexibility, in particular with respect to a longitudinal direction of the third arrangement 201 according to the invention, but at the same time the third arrangement 201 has high tensile strength.

(46) The third arrangement 102 is therefore particularly suitable in the region of the forwardmost 30 cm of a catheter, since this region of the catheter must have great bending flexibility.

(47) FIG. 4 shows a medical catheter 102, which comprises the second arrangement 101 from FIG. 2e. On the right-hand side in FIG. 4 there is a connecting stub 190 of the medical catheter 102, which opens out into the first plastic tube 110. The two connected plastic tubes 110, 120, which form the second arrangement 102 shown in detail in FIG. 2e, in this case take the form of a spiral that has undergone forming and is dimensionally stable, formed by a prior heat treatment at 50 C. Also arranged on the second plastic tube 120 in a known way is a catheter tip 195.

(48) The intermediate stages represented in FIGS. 1c and 2d are subjected to a forming process. For this, shrink-fit tubes 40, 140 from FIGS. 1c and 2d are blown on, for example with hot air. It is important in this case that the plastic tubes that are to undergo forming have been heated up sufficiently, so that at least incipient melting of the plastic tubes occurs. The process parameters required for this, such as the temperature and duration of the blowing on, depend on the one hand on the material of the plastic tubes that are used and on the other hand on the hot air source that is used. Optimum process parameters can be simply determined, for example, in the course of tests.

(49) The previous embodiments should be understood merely as illustrative examples that can be modified as desired within the scope of the invention.

(50) For instance, instead of a polyimide tube 50 with flanges 51, 52, a polyimide tube that is unstructured on the outer side and without flanges can also be used.

(51) In this case, an adhesive connection is substantially formed between the plastic tube and the polyimide tube. It is also possible to use a polyimide tube that has an external thread and/or grooves or to use a tube made of another material that has high strength and dimensional stability even at relatively high temperatures.

(52) It is similarly possible, for example, to use instead of the polyimide tube a tube of a plastic that is reinforced with a wire coil and/or fibrous materials.

(53) It is also conceivable in principle to dispense with the provision of shrink-fit tubes 40, 140 and, for example, instead to carry out the forming process with a press.

(54) It is also conceivable for the tubular connecting piece or the polyimide tube 50 and/or the helical spring 250 to have regions with different inside and/or outside diameters.

(55) This may be expedient in particular whenever plastic tubes with different inside and/or outside diameters are to be connected to one another by the method according to the invention.

(56) The method illustrated in FIGS. 1a-1d may also be carried out moreover without an inner tube 30. The inside diameter of the polyimide tube 50 may in this case also be smaller or greater than the inside diameter of the plastic tubes. Similarly, the helical spring 250 from FIG. 3 may have a smaller or greater inside diameter than the plastic tubes.

(57) The cylindrical piece of wire 180 from FIG. 2a may, for example, also have instead of the conically widening transitional region 182 a differently formed transitional region, which, for example, is formed in a substantially step-like manner. Also conceivable is the use of a cylindrical piece of wire of which the end portion is of a completely conically form.

(58) In the case of the medical catheter 102 depicted in FIG. 4, it is also possible that there are more than two plastic tubes connected to one another. Instead of or in addition to the arrangement 101, the medical catheter 102 may, for example, also include further connections between plastic tubes. This can be produced, for example, by the methods illustrated in FIGS. 1a-1d and in FIGS. 2a-2e. In particular in the region of the tip, the connection of the plastic tubes by a helical spring, as represented for example in FIG. 3, is advantageous, since this type of connection is particularly distinguished by great bending flexibility.

(59) In principle, it is also possible with the method according to the invention to fasten balloons, which may, for example, take the form of tubular elements made of plastic, to a catheter shaft. In this way, the method according to the invention is also suitable in the case of the production of balloon catheters.

(60) To sum up, it can be stated that the invention provides a particularly flexible method that makes it possible to obtain a secure and high-quality connection between thin plastic tubes with extremely small dimensions of a wide variety of materials. At the same time it is possible in particular to dispense with adhesives and with the welding processes offering limited choice of materials. The arrangements or connections produced according the invention from the two plastic tubes have extremely high mechanical strength, so that in particular they even withstand high tensile loads. The method according to the invention can be used particularly advantageously in the production of catheters.