CH714251A2 - Roller unit for use in a thread cutting device and method for removing gas inclusions from thread material. - Google Patents

Abstract

The roller unit (2) according to the invention and its method serve to stiffen surgical thread material (12) and find application in devices for cutting such thread material. The rolling elements are equipped with a heating cartridge and a temperature sensor. The rolling elements are moved orthogonal to each other with the thread material (12) positioned orthogonal to the rolling elements. The distance between the rolling elements is determined by a curved path.

Description

Description: The present invention relates to a roll unit, suitable for use in a thread cutting device, for homogenizing a thermoplastic thread material as used for surgical threads, in particular for removing gas inclusions present in the thread material, and to a thread material processed with such a roll unit . The present invention also relates to a method for homogenizing a thermoplastic thread material, in particular for removing gas inclusions present in the thread material, according to the preamble of claim 10.

The thread material used in surgery is either a monofilament or a multifilament thread. The monofilament thread consists of a single filament that forms the thread. The multifilament thread consists of a plurality of very thin individual threads that are twisted, twisted or intertwined. Surgical thread material is available in different lengths and armored with one or two needles or also non-armored. Non-armored threads are usually sewn with eye needles, e.g. shown in WO 2017/170 670 A1, used in surgery.

In the case of drilled needles, the thread material is introduced axially into the drilled needle and held in place by deforming the needle steel. This process is called reinforcement and results in the reinforcement. The ready-to-use end product, a reinforced needle with thread material, is offered on the market as shown in Fig. 1.

The production of needle thread-reinforced surgical thread material is simplified if the thread ends of the mono, as well as the multifilament threads are stiffened. With multifilament threads, you also want to prevent them from fraying at their ends. The main aim of monofilament threads is to make them rounder and more compact so that they hold better in the reinforced needle.

[0005] EP-0 806 177 discloses an apparatus for producing surgical thread material with stiffened, non-fraying thread ends without the thread or the thread ends having to be immersed in a binder resin. The device disclosed here essentially consists of dilating means for tensioning the thread material, a two-part heating tool for producing a local fusion connection, the heating tool coming into contact with the thread to be processed, and a cutting device for severing cut thread material.

The heating tool disclosed in this EP-0 806 177, however, has disadvantages for the processing of thread materials with significant gas inclusions.

Gas inclusions in an otherwise translucent thermoplastic can be recognized by the fact that the material has a milky appearance. The multiple reflection and refraction of the light at the gas inclusions creates a reflection of the light. A typical example is a thermoplastic made of polytetrafluoroethylene, which appears white when untreated. A characteristic of these thermoplastics is «flowing» under pressure. As the gas inclusions escape, the thermoplastic gives way over time.

The flow of the thermoplastic is not desirable in a reinforced needle-thread combination, because after a certain time (depending on the composition of the thermoplastic it can take days to months), the thread material in the reinforcement dissolves and at the latest during surgical sewing falls out of the reinforcement hole.

It is therefore an object of the present invention to provide a device which allows existing gas inclusions to be removed from the end piece of the thread material which is subsequently used for the reinforcement on the needle. As previously mentioned, a previously white thread becomes translucent at the degassed point during degassing.

Another object of the present invention is to make the resulting translucent thread piece as round as possible. This can ensure that a large-area, long-term and resilient positive and non-positive connection with the thread material can be achieved when reinforcing.

This object is achieved according to the invention with a device according to claim 1 and a method according to claim 10, in particular by a roller unit for homogenizing a thermoplastic thread material, as is used for surgical threads, respectively. for removing gas inclusions from such a thread material, this roller unit being suitable for use in a thread cutting device. This thread cutting device comprises at least two rolling elements, the distance of which is determined by a control device and which is controlled by two orthogonally arranged drives, in such a way that at least one of the rolling elements follows a curved path, as a result of which the thread material is moved orthogonally to the drives in such a way that the cross-sectional area of the Thread material is reduced and is preferably brought into a circular shape.

[0012] Preferred embodiments of the device according to the invention have the features of the dependent claims 2-8. The thread material thus generated is homogeneous in the roll area, respectively. translucent and has a reduced cross-sectional area.

A method suitable for producing such a thread material according to the invention has the features of claim 10 and in particular uses a rolling station according to claim 1, the cross section in the rolling area of the hot thread material being reduced with a rolling movement and being translucent.

CH 714 251 A2 [0014] Further preferred embodiments of the method have the features of the dependent claims 11-13, in particular the rolling movement is carried out several times and an axial pull of a maximum of 0.1 N is exerted on the thread material during the rolling movement. In a preferred embodiment of the method, after the translucency has been reached and after the rolling movement has ended, the thread material is cooled under an axial tensile force.

In the following, the processing of a thermoplastic thread made of polytetrafluoroethylene will be considered in more detail by way of example and for a detailed description of the invention. This is because its gas content is normally much higher than that of other thermoplastics and this material should therefore be given special attention. In addition, among the thermoplastics, the polytetrafluoroethylene has special properties. In particular, polytetrafluoroethylene has the highest melting point of all thermoplastics. It is therefore also an object of the present invention to process thermoplastic threads which have a high melting point.

The melting point of polytetrafluoroethylene is 327 ° C, which must at least be reached so that a permanent removal of gas inclusions is possible at all. By applying external pressure, this value can also be reduced by a few degrees. At 327 ° C, however, polytetrafluoroethylene does not become liquid, but softens like a gel.

Polytetrafluoroethylene does not have a slightly viscous liquid phase, like other thermoplastics, since the material begins to decompose at temperatures above 400 ° C. Fluorophosgene (COF2) is released. This is a highly toxic pyrolysis product that can lead to diseases such as Teflon or polymer fever. For this reason, precise temperature control must be observed in the interests of occupational safety and should be prevented from exceeding 400 ° C.

All thread materials, no matter what thermoplastic, are extruded products, which immediately after extrusion, i.e. when cooling, be stretched. When they are heated again in the direction of the melting point, they contract. However, this contraction can be prevented if an axial tension is applied to the thread and prevents the contraction. Polytetrafluoroethylene shows this typical thermoplastic behavior more clearly than other thermoplastics.

The high temperatures required force the person skilled in the construction to fall back on solutions which are stable at high temperatures. This excludes components in the vicinity of the roller unit, which change extremely quickly due to the effects of temperature. For example, high-precision electronic linear axes (e.g. SMC LESH8-RJ-50) can only be operated up to 60 ° C according to the data sheet. Because of the heat spreading from the roller unit, electronic linear axes as drives for the roller unit would shortly be defective. In the present invention, therefore, cam plates with rollers and temperature-resistant pneumatic drives with linear guides are used, which function precisely and with a long service life even at high temperatures. The roller is pressed against the cam plate with the pressure of the pneumatic drive.

Special attention is paid to the fact that the device according to the invention is suitable for the production of medical products. The components touching the thread must not leave any abrasion on the thread, which is also not permitted for medical reasons. Likewise, no fibrous thermal insulation mats are allowed because their fibers could settle on the surface of the surgical thread.

The present invention uses a cage made of chrome steel 1.4301 arranged around the rolling elements for thermal insulation. The rolling element is mechanically connected to the cage at only a few points. The heat exchange is thus greatly reduced, since the rolling elements are packed in an air cushion. Chrome steel grade 1.4301 is also one of the worst metallic heat conductors (approx. 30 W / mK), which further reduces the heat conduction to the drive. The heat conduction is further reduced by an air cushion (approx. 1 mm thick) provided between the cage and the drive elements. The cage with a base area of 900 mm ² is only in direct contact with the drive on 28 mm ² . This means that the air cushion covers 97% of the base area, while the metallic contact area is only 3%.

The drives for traversing the cam track are arranged orthogonally, i.e. at a 90 ° angle to each other. The orthogonality lies within the normal manufacturing tolerances, which for angles are +/- 20 degrees minutes (Swiss standard SN258 440-m). In the orthogonal arrangement of the drives, as shown in the present figures, they are horizontal and vertical. However, all other orthogonal arrangements are also conceivable, such as 45 ° vertically upward to the right and 45 ° vertically upward to the left.

For a better understanding of the present invention, the orthogonal axes for the definition of the axial directions with distance axis and roll axis are referred to below, which does justice to the orthogonal arrangement of the drives. The terms distance drive for the first linear movement element and roller drive for the movement element orthogonal to it are also used.

The rolling element is preferably made of steel. Steel is dimensionally stable even at a temperature of 400 ° C. In a preferred embodiment, the tool steel 1.2083 is used because it has good machinability and high hardness acceptance and is also low in warpage. It also conducts heat better than the steel of the cage and is rust-free under the given conditions.

CH 714 251 A2 [0025] The rolling element is heated to the required operating temperature via the heating cartridge. In order to generate the most homogeneous possible heat field on the contact surface, the temperature sensor is preferably parallel to the heating cartridge and as close as possible to the rolling surface.

The present invention, its advantages and properties will be explained in the following by way of example with reference to the figures.

[0027] Thereby shows:

Fig. 1 shows an armored needle

Fig. 2 mechanical structure of the roll station retracted drive, distance drive extended

Fig. 3 mechanical structure of the roller station roll drive extended, distance drive extended

Fig. 4 shape of the cam plate

Fig. 5 structure of the rolling surface with stop elements

Fig. 6a roll of thread at the beginning

Fig. 6b rolls of thread

Fig. 6c sliding the thread

Fig. 7 thread material with gas inclusions. Fig. 1 shows a reinforced needle (11), the thread (12) being inserted axially into the drilled needle opening (13) and compressed.

2 shows a rolling unit (2) according to the invention in the starting position for rolling. The distance drive is already retracted. The rolling surface (41) already touches the thread material (12), whereby it is heated and begins to shrink, provided there is no tension on the thread. The structure of the rolling surface (41) is not shown. The structuring forms a holding resistance, which helps the thread to roll. Only two end stops (44, 45) are shown; the stops (42, 43) are not shown for the sake of a better overview.

Fig. 3 shows the roller unit (2) in the end position, consisting of a vertically moving spacer element (21), a heat-insulating cage (210), which consists of a 1.5 mm thick stainless steel sheet 1.4301. This includes the rolling element (213). A roller (241) is attached to the heat-insulating cage (210) and is advantageously designed as a metal ball bearing without lubricant. The cage (210) is connected to the distance drive (250) only via a few connecting elements (not shown). The majority of the interface formed is an air poster (251) of approximately 1 mm in thickness.

Fig. 3 further shows the other rolling element (22) which is driven by the second rolling drive (260). Otherwise it contains the same elements as for the first rolling element (21), i.e. Cage (220), rolling element (223), air gap (261).

Fig. 3 also shows the holes in the rolling elements (213, 223). The holes (221 and 221) near the rolling surface (41, not shown here) are intended for inserting the temperature sensor (preferably a PT100 control sensor) and another hole (212 or 222) for the heating cartridge with a maximum output of approx. 250W. With the aid of a programmable logic controller, the value of the temperature sensor is read out and the temperature of the rolling surface (41) is constantly controlled by means of software PID or a Fussy-Logic control circuit (not shown) and by regulated activation of the heating cartridge. It has been shown that with this embodiment the temperature on the rolling surface (41, 41b) fluctuates less than +/- 1 ° C. at 390 ° C.

Since both heating plates can have different target temperatures, a separate heating control circuit can be provided for both heating plates.

In contrast to the rolling element (21) with the spacer axis (25), a cam plate (240) is provided for the rolling element (22) with the rolling axis (26) on the cage. The cam plate (240) defines the distance between the two rolling surfaces (41 and 41b).

Fig. 4 shows a possible shape of the contour of the cam plate (240). The cam track (31) is rolled over the roller (241). The starting point (33) defines the initial distance between the two rolling surfaces (41 and 41 b). The starting point (33) is designed so that the thread is not yet touched by both rolling surfaces. Accordingly, with a thread material 0.3 mm thick, the cam disc at the rigid point (33) is approximately 0.4 mm. The rolling process runs over the curve (31) to the end point (34). The height (32) of the curve is dimensioned such that the thread is tapered during the rolling. A 0.3 mm thick thread material is thus in the roll area e.g. tapered to 0.2 mm while the curve length of the distance

CH 714 251 A2 between the start and end point (x) of the roller drive (260) corresponds (in the example shown 30 mm). The drives generate the movement (A) - (B) - (C) - (D), which can be repeated several times.

Fig. 5 shows a plan view of the lower rolling surface (41) and the inserted thread material (12). A structure on the rolling surface (41) makes sense so that the thread rolls cleanly on the rolling surface (41). A parallel corrugation in the direction of the thread is shown. This corrugation can be applied mechanically or electrochemically. However, other corrugations can also be applied, such as cross corrugation (50).

The start stops (42, 43) shortly before the start position of the rolling surface and the end stops (44, 45) are not needed for non-slip rollers. It turns out, however, that from time to time it happens that the thread does not roll but sticks on one roll surface and slides on the other roll surface. When sliding / gluing, the thread makes a larger path than when rolling (see Fig. 5). Since the transition from rolling to sliding cannot be predicted, the thread can slip out of the rolling surface (41) if it rolls several times. Therefore start and end stops (42-45) are required to prevent this. However, the stops must be at least 5 mm away from the heating element so that they are not overheated by infrared radiation from the hot heating plate and the thread then sticks to them when touched.

Fig. 6a shows schematically the starting position of the rolling of the thread (12) with the two rolling surfaces (41 and 41b). Here too (x) shows the distance from the start to the end point of the roller drive. Fig. 6b shows the displacement of the thread material when it rolls, namely half the distance (x / 2) of the movement of the rolling surface (41 b). Otherwise, if the thread slides all the way (x), as shown in Fig. 6c. If the rolling movement is repeated several times, whereby the sliding / rolling cannot be foreseen, it may happen that the thread on the inner side (61) or the outer side (62) falls out (FIG. 6a).

Fig. 7 shows thread material with gas inclusions (71). The thread can be tapered in the roll area if the thread is placed under tension after the rolling phase (e.g. with tensile force = 2.4 N for a polytetrafluoroethylene thread of 0.3 mm diameter). The tapering (72) in the rolling area is stopped by the cooling and the accompanying hardening of the thread material (12). It has been shown that it is possible to taper the thread material (12) from 0.3 mm to 0.2 mm, which corresponds to a diameter reduction of 33%. The cut (73) is made at one point of the taper (72) and thus allows the taper (72) to be connected to the needle (11) in a reinforcement (13).

During rolling, rolling is preferably carried out with as little tension as possible. A minimum tension of up to 0.1 Newton in the axial thread direction can protect the thread from flattening when sliding / rolling with certain thread materials and accordingly produce a rounder end product.

It goes without saying that the roll station according to the invention can be used not only for monofilament threads, but also for multifilament threads. With multi-filament threads there is less pressing of gas inclusions, but it has been shown that multifilament threads are also homogenized under the influence of heat and rolling pressure and stiffen and rejuvenate.

Claims (13)

Claims 1. roller unit (2), suitable for use in a thread cutting device, for homogenizing a thermoplastic thread material (12) as used for surgical threads, in particular for removing gas inclusions in the thread material (12), characterized in that this roller unit ( 2) comprises two rolling elements (213 & 223), the distance between which is determined by a control device which controls two orthogonally arranged drives (250 & 260) in such a way that at least one of the rolling elements follows a curved path (31), as a result of which the thread material (12 ) is moved orthogonally to the drives (250 & 260) in such a way that the cross-sectional area of the thread material is reduced in the roll area and is preferably brought into a circular shape. 2. Rolling unit (2) according to claim 1, characterized in that at least one rolling element (213 & 223) can be heated with the aid of a control loop. 3. Rolling unit (2) according to one of the preceding claims 1, 2, characterized in that at least one rolling surface (41, 41b) of the rolling element (213 & 223) is structured. 4. Rolling unit according to claim 1, characterized in that each rolling element (213, 223) is integrated in a cage (210, 220) with an air cushion. 5. Rolling unit according to claim 1, characterized in that there is an air poster (251 & 261) between the cage (210 & 220) and the drive (250, 260). 6. Rolling unit according to claim 1, characterized in that it is provided with at least one stop element (42-45). 7. Roller unit according to claim 1, characterized in that the control device has at least one cam plate (240) with a roller (241) to guide the rolling element along the cam track (31). 8. Rolling unit according to claim 1, characterized in that the at least one cam plate (240) reduces the distance between the rolling surfaces (41, 41 b) in a monotonically decreasing manner, the distance always being greater than zero. CH 714 251 A2 9. Thread material (12) processed with a roller unit (2) according to claim 1, characterized in that the thread material in the roll area is translucent and homogeneous. 10. A method for removing gas inclusions from thread material (12), characterized in that a rolling station (2) according to claim 1 is used, the cross section of the hot thread material (12) being reduced with a rolling movement (B) (C), to make the thread material translucent and homogeneous in the roll area. 11. The method according to claim 10, characterized in that the rolling movement (B) (C) is carried out several times. 12. The method according to claim 10, characterized in that during the rolling movement (B) (C) on the thread material (12) an axial pull of 0.1 N is exerted. 13. The method according to claim 10, characterized in that after reaching the translucency and completion of the rolling movement (B) (C), the thread material (12) is cooled under an axial pull.