CH714251B1 - Rolling unit for use in a thread cutting device and method for removing gas pockets from thread material. - Google Patents

Abstract

The rolling unit (2) according to the invention and its method serve to stiffen surgical thread material (12) and are used in devices for cutting such thread material to length. The rolling elements are equipped with a heating cartridge and a temperature sensor. The rolling elements are moved orthogonally to each other with the thread material (12) positioned orthogonal to the rolling elements. The distance between the rolling elements is specified by a cam track.

Description

The present invention relates to a rolling unit, suitable for use in a thread cutting device, for homogenizing a thermoplastic thread material, such as is used for surgical threads, in particular for removing gas inclusions in the thread material, and a thread material processed with such a rolling 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 9.

The suture material used in surgery is either monofilament or multifilament suture. Monofilament thread consists of a single filament that makes up the thread. The multifilament thread consists of a number of very thin individual threads that are twisted, twisted or braided together. Surgical thread material is available in various lengths and with one or two needles, either reinforced or not. Threads that are not reinforced are generally used in surgery with eye needles, as shown, for example, in WO 2017/170670 A1.

With drilled needles, the suture material is inserted 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.

[0004] The production of surgical thread material reinforced with needles is simplified if the thread ends of the monofilament and multifilament threads are stiffened. In the case of multifilament threads, you also want to prevent them from fraying at their ends. With monofilament threads, the main aim is to make them rounder and more compact so that they hold better in the armed needle.

EP-0'806'177 discloses a device for producing surgical thread material with stiffened, non-fraying thread ends without the thread or the thread ends having to be dipped in a binding resin agent. The device disclosed here consists essentially of dilatation 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 cutting off cut-to-length thread material.

However, the heating tool disclosed in this EP-0'806'177 has disadvantages for the processing of thread materials with significant gas pockets.

Gas inclusions can be recognized in an otherwise translucent thermoplastic by the fact that the material has a milky appearance. The multiple reflection and refraction of the light at the gas inclusions causes the light to be reflected back. A typical example is a thermoplastic made from polytetrafluoroethylene, which appears white in the untreated state. A characteristic of these thermoplastics is that they “flow” under pressure. The thermoplastic gives way over time as the gas pockets escape.

The flow of the thermoplastic is not desirable with a reinforced needle-thread combination, since 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 suturing falls out of the armor hole.

It is therefore an object of the present invention to provide a device which allows existing gas pockets 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 formerly white thread becomes translucent at the degassed point during degassing.

A further object of the present invention is to make the resulting translucent piece of thread as round as possible. This ensures that a large-area, long-term and resilient positive and non-positive connection with the thread material can be achieved during reinforcement.

This object is achieved according to the invention with a device according to claim 1 and a method according to claim 9, in particular by a rolling unit for homogenizing a thermoplastic thread material, such as is used for surgical threads, respectively. for removing gas inclusions from such a thread material, this rolling unit being suitable for use in a thread cutting device. This thread cutting device comprises at least two rolling elements, the spacing 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.

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 rolling area, resp. 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 9 and uses a rolling unit according to claim 1, the cross section in the rolling region of the hot thread material being reduced with a rolling movement and becoming translucent.

Further preferred embodiments of the method have the features of the dependent claims 10-12, in particular the rolling movement is carried out several times and an axial pull of at most 0.1N is exerted on the thread material during the rolling movement. In a preferred embodiment of the method, after the translucency has been reached and the rolling movement has ended, the thread material is cooled under an axial tensile force.

The processing of a thermoplastic thread made of polytetrafluoroethylene is to be considered in more detail below as an 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 special attention should therefore be paid to this material. In addition, among the thermoplastics, polytetrafluoroethylene has special properties. In particular, polytetrafluoroethylene has the highest melting point of all thermoplastics. It is therefore also the object of the present invention to also process thermoplastic threads which have a high melting point.

[0016] The melting point of polytetrafluoroethylene is 327° C., which must be reached at least so that gas inclusions can be permanently removed. This value can also be reduced by a few degrees by applying external pressure. At 327 °C, however, polytetrafluoroethylene does not yet become liquid but softens like a gel.

[0017] Polytetrafluoroethylene does not have a slightly viscous liquid phase, like other thermoplastics, since the material begins to decompose at temperatures above 400.degree. Fluorophosgene (COF2) is released in the process. This is a highly toxic pyrolysis product that can lead to illnesses such as Teflon or polymer fever. Therefore, in terms of occupational safety, precise temperature control must be ensured and exceeding 400 °C should be avoided.

All thread materials, regardless of the thermoplastic, are extruded products which are stretched immediately after extrusion, i.e. during cooling. When heated again towards the melting point, they contract. However, this contraction can be prevented if axial tension is applied to the thread and prevents contraction. Polytetrafluoroethylene shows this typical thermoplastic behavior more clearly than other thermoplastics.

The required high temperatures force those skilled in the construction to resort to solutions which are stable at high temperatures. This excludes components in the vicinity of the rolling unit, which age extremely quickly due to the effects of temperature. According to the data sheet, high-precision electronic linear axes (e.g. SMC LESH8-RJ-50) can only be operated up to 60 °C. Therefore, due to the spread of heat from the rolling unit, electronic linear actuators driving the rolling unit would soon fail. In the case of 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 compressive force of the pneumatic drive.

[0020] Particular 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 behind on the thread, which is also not permissible 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 chromium steel 1.4301 arranged around the rolling elements for thermal insulation. The rolling element is only mechanically connected to the cage at a few points. The heat exchange is thus greatly reduced since the rolling elements are thus wrapped in an air cushion. Type 1.4301 chrome steel is also one of the worst metallic heat conductors (approx. 30W/mK), which further reduces heat conduction to the drive. Heat conduction is further reduced by an air cushion (approx. 1mm thick) 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 at 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 moving along the cam track are arranged orthogonally, i.e. at a 90° angle to one another. The orthogonality is within the normal manufacturing tolerances, which is +/- 20 degree minutes for angles (Swiss standard SN258440-m). With 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 to the top right and 45° vertically to the top left.

For a better understanding of the present invention, the orthogonal axes for the definition of the axis directions are referred to as distance axis and roll axis, which does justice to the orthogonal arrangement of the drives. The terms distance drive for the first linear movement element and rolling drive for the movement element orthogonal thereto 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 a high degree of hardness and is also low in distortion. In addition, it conducts heat better than the steel of the cage and is rust-free under the given conditions.

The rolling element is heated to the required operating temperature by the heating cartridge. In order to generate a heat field that is as homogeneous as possible 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 are to be explained below with reference to the figures by way of example.

1 shows a representation of a reinforced needle FIG. 2 mechanical structure of the roller station, roller drive retracted, distance drive extended FIG. 3 mechanical structure of the roller station, roller drive extended, distance drive extended FIG. 4 shape of the cam plate FIG. 5 structure of the roller surface with stop elements Fig. 6a coiling of the thread at the beginning Fig. 6b coiling of the thread Fig. 6c sliding of the thread Fig. 7 thread material with gas inclusions

shows a reinforced needle (11), wherein the thread (12) is inserted axially into the drilled needle opening (13) and pressed.

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) is already in contact with the thread material (12), as a result of which it is heated and begins to shrink if there is no tension on the thread. The structuring of the rolling surface (41) is not shown. The structuring forms an adhesion resistance, which helps to roll the thread. Only two end stops (44, 45) are shown, the stops (42, 43) are not shown for the sake of clarity.

Fig. 3 shows the roller unit (2) in the end position, consisting of a vertically moving distance heating 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), which is advantageously designed as a metal ball bearing without lubricant, is fastened to the heat-insulating cage (210). The cage (210) is only connected to the spacer drive (250) via a few connecting elements (not shown). Most of the interface formed is an air cushion (251) about 1mm thick.

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

Figure 3 also shows the bores in the rolling elements (213, 223). The holes (221, 211) near the rolling surface (41, not shown here) are for inserting the temperature sensor (preferably a PT100 control sensor) and the other holes (212, 222) are each intended for the heating cartridge with a maximum output of approx. 250W. Using a programmable logic controller, the value of the temperature sensor is read and the temperature of the rolling surface (41) is constantly controlled using a software PID or a fuzzy logic control circuit (not shown) and controlled switching on 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 the two heating plates can have different setpoint 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).

shows a possible form of the contour of the cam plate (240). The curved track (31) is rolled over the roller (241). The starting point (33) defines the initial distance between the two rolling surfaces (41 and 41b). The starting point (33) is designed in such a way that the thread is not yet touched by the two rolling surfaces. With a 0.3 mm thick thread material, the cam disk at the starting point (33) is approx. 0.4 mm. The rolling process runs over the curve (31) to the end point (34). The height (32) of the curve is such that the thread is tapered during rolling. A 0.3 mm thick thread material is thus reduced to 0.2 mm in the rolling area, for example, while the length of the curve corresponds to the distance between the start and end point (x) of the rolling drive (260) (30 mm in the example shown). 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 corrugations (50).

The start stops (42, 43) just before the start position of the rolling surface and the end stops (44,45) are not needed for slip-free rolling. It turns out, however, that from time to time the thread does not roll but sticks to one rolling surface and slides on the other rolling surface. When gliding/sticking, however, the thread travels a greater distance than when rolling (see Fig. 5). Since the transition from rolling to sliding cannot be predicted, it is possible for the thread to slip out of the area of the rolling surface (41) if the thread is rolled several times. Therefore, start and end stops (42-45) are needed to prevent this. However, the stops must be at least 5 mm away from the heating element so that they are not heated up too much 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). Again, (x) shows the distance from the start to the end point of the roll drive. Figure 6b shows the displacement of the thread material as it rolls, namely half the distance (x/2) of movement of the rolling surface (41b). It is different when the thread slides all the way (x) as shown in Figure 6c. If the rolling movement is repeated several times, with the sliding/rolling being unpredictable, it can happen that the thread falls out on the inner side (61) or the outer side (62) (FIG. 6a).

7 shows thread material with gas inclusions (71). The thread can be tapered in the rolling area if, after the rolling phase, the thread is subjected to controlled tension (e.g. with a tensile force of 2.4 N for a polytetrafluoroethylene thread with a diameter of 0.3 mm). 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 reduce 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).

[0040] During the rolling, it is preferred to roll with as little tension as possible. A maximum tensile stress of up to 0.1 Newton in the axial direction of the thread can, with certain thread materials, prevent the thread from flattening out when sliding/rolling and accordingly produce a rounder end product.

It goes without saying that the inventive reel station can be used not only for monofilament threads, but also for multifilament threads. In the case of multifilament threads, gas inclusions are less pressed out, but it has been shown that multifilament threads are also homogenized under the influence of heat and rolling pressure and become stiff and tapered.

Claims (13)

1. Rolling 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 rolling unit ( 2) comprises two rolling elements (213, 223), the spacing of which can be determined by a control device, which control device controls two drives (250, 260) arranged orthogonally to the thread material, such that during operation at least one of the rolling elements follows a curved path (31), to move the thread material (12) orthogonally to the drives (250, 260) in such a way as to reduce the cross-sectional area of the thread material in the rolling region and preferably bring it into a circular shape. 2. Rolling unit (2) according to claim 1, characterized in that at least one rollclement (213, 223) can be heated with the aid of a control loop. 3. Rolling unit (2) according to claim 1 or 2, characterized in that at least one rolling surface (41, 41b) of the rolling elements (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 gap. 5. Rolling unit according to claim 4, characterized in that there is an air cushion (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) in order to prevent the thread material (12) from slipping out of the region of the rolling surface (41). 7. Rolling unit according to claim 1, characterized in that the control device has at least one cam plate (240) with a roller (241) in order to guide the rolling element along the cam track (31). 8. Rolling unit according to claim 7, characterized in that the at least one cam plate (240) reduces the distance between the rolling surfaces (41, 41b) in a monotonically decreasing manner, the distance always being greater than zero. 9. Method for removing gas inclusions from thread material (12), characterized in that a rolling unit (2) according to claim 1 is used for this purpose, 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 rolling area. 10. The method according to claim 9, characterized in that the rolling movement (B)(C) is carried out several times. 11. The method according to claim 9, characterized in that an axial tensile force of at most 0.1 N is exerted on the thread material (12) during the rolling movement (B)(C). 12. The method according to claim 9, characterized in that after the translucency has been reached and the rolling movement (B)(C) has ended, the thread material (12) is cooled under an axial tension. 13. Thread material (12) produced by the method according to any one of claims 9 to 12, characterized in that the thread material is translucent and homogeneous in the rolling area.