EP1329262B1 - Pipette and method of manufacturing a pipette - Google Patents

Description

The invention relates to a pipette with a pipette shaft made of preferably thermoplastic material for attaching a likewise made of plastic pipette tip with the features of the preamble of claim 1. The invention also provides a method for producing such a pipette having the features of the preamble of claim 11th

Both for single pipettes as well as for multichannel pipettes or larger pipetting devices, the problem arises that the pipette tip must be attached to the pipette shaft sealing, but at the same time by means of a mechanical Abwerfens again with the least possible effort repelled from the pipette shaft. High withdrawal forces of the pipette tip require a high amount of force when operating the ejector sleeve. Therefore, it has already become known here to provide translation devices between the Abwerferbetätigung and the ejector. As a result, but the actuation paths are increased.

The problem of pull-off forces is particularly great in pipettes known hitherto in practice when the pipette shaft is made of relatively hard, abrasion-resistant plastic and the tip is made of somewhat less hard, deformable plastic, in particular polypropylene. The pipette shaft may be easily damaged in the attachment section. The cone-shaped surfaces are then leaky. The user tries to compensate for this by particularly pushing the pipette tip onto the attachment section of the pipette shaft.

The prior art has already attempted to circumvent the recognized and previously described problem by providing an actively deformable seal between the slip-on section of the pipette tip and the attachment section ( WO 91/16975 ). For this one uses an O-ring or otherwise elastic, deformable material. Here, however, there is the problem of cleaning and a structurally comparatively large effort for the adjustment mechanism. In addition, the present Column problematic. Over-pipetted sample liquid can be carried off and contaminate a following sample.

Regardless of this, the previously described concept has been developed in a different way. The pipette known in this regard, which forms the starting point for the teaching of the present patent application (US Pat. DE 38 87 205 T2 / EP 0 293 075 B1 / US 4,863,695 A ) has a separate sealing cone of well-sealing, elastically yielding plastic material, which is attached to the lower end of the pipette shaft at a recess and ensures the sealing of the attachment portion to Aufsteckabschnitt. Axially above this formed in a separate molding sealing portion is located on the material of the pipette shaft itself shaped fixation portion with a conical contour, which corresponds to the conical contour of the plugged-up there on top of the pipette tip. On the pipette shaft a circumferential annular flange is provided as a stop for pushing the pipette tip.

The above-explained, known from the prior art pipette has the advantage that this construction of the pipette shaft allows the use of different pipette tips of different manufacturers. The pipette shaft is relatively insensitive to tolerances both in terms of the pipette tips used and in terms of the accuracy of the Aufsteckvorganges. However, the separate design of the Abdichtabschnittes in a plugged sealing element in terms of gap formation, cleaning options and risk of contamination in the same manner as in the previously described prior art is problematic.

It should be noted that the previously discussed pipette from which the invention is based is provided with an ejector sleeve and a pipette tip ejector. The problem explained at the beginning of the withdrawal forces when ejecting the pipette tip is therefore given there. Safe seat and good sealing of the pipette tip on the pipette shaft on the one hand and low withdrawal forces when ejecting the pipette tip on the other hand are mutually contradictory requirements that should be reconciled with each other in this prior art by using the separate sealing cone.

Another problem with the use of different generic pipette tips from different manufacturers in connection with the known Abwerferhülse is that the effective axial length of the Aufsteckabschnittes the pipette tip is different at the different pipette tips. The effective axial length thus designated is the length at which the attachment portion of the pipette tip is seated on the attachment portion of the pipette shaft. The effective axial length of the Aufsteckabschnittes is therefore decisive for which axial distance has the end of the pipette tip from the front edge of the ejector.

It has already been recognized in the prior art that there are cases in which the ejector sleeve of the pipette actuated by the ejection actuator only just touches the edge of the pipette tip, or in any case can no longer effectively eject the pipette tip. To solve this problem, the use of an annular adapter has been proposed ( US 4,965,050 A ). With such an adapter you can bridge the distance of the ejector sleeve and edge of the Aufsteckabschnittes the pipette tip accurately.

In a pipette of the type in question, in which the ejector sleeve is rotated by the Abwerferbetätigung relative to the pipette shaft about its longitudinal axis ( US-A-4,187,724 ), the sealing portion is located at the attachment portion of the pipette shaft with inserted pipette tip deep within the pipette tip. The sealing section is located in a circumferential recess extending from the end of the pipette shaft, in which this sealing section is formed in an immediately adhesive manner from an elastically yielding, well-sealing elastomeric material.

The teaching is based on the problem, a pipette of the type in question to design and further that a tolerance insensitive pipette shaft is realized, low withdrawal forces when discarding the pipette tip present and yet the previously described problems with cleaning options and contamination risk are eliminated.

The above-indicated problem is solved in the pipette having the features of the preamble of claim 1 by the features of the characterizing part of claim 1. According to the invention, the sealing portion is not executed separately, but formed directly adherent to the thermoplastic resin of the pipette shaft. This has the advantage that the sealing portion is held captive and not displaced when attaching the pipette tip. This avoids a spongy touch feeling for the user. Also, no gap is created by a displacement of the Abdichtabschnittes, so that contamination is avoided. It eliminates the second sealing between the recess of the pipette shaft and the Abdichtabschnitt. The boundary layer is sealed and neither dirt nor liquid can penetrate.

It is particularly advantageous if the pipette shaft with the sealing portion is designed cost-effectively without assembly activity as a two-component plastic injection-molded part. Further preferred variants are the subject of the further subclaims.

The invention also provides a process for producing a pipette having the features of the preamble of claim 11, which is described in more detail by the features of the characterizing part of claim 11. In that regard, advantageous embodiments are the subject of the subsequent dependent claims.

Fig. 1

in einer Gesamtdarstellung ein Ausführungsbeispiel einer erfindungsgemäßen Pipette,

Fig. 2

im Schnitt den Bereich des unteren Endes des Pipettenschaftes der Pipette aus Fig. 1,

Fig. 3

in einer Fig. 2 ähnlichen Darstellung einen Pipettenschaft mit einem zusätzlichen Distanzelement für eine bestimmte Pipettenspitze.

In the following the invention will be explained in more detail with reference to a drawing showing only one embodiment. In the drawing shows

Fig. 1

in an overall representation of an embodiment of a pipette according to the invention,

Fig. 2

on average, the area of the lower end of the pipette shaft of the pipette Fig. 1 .

Fig. 3

in a Fig. 2 similar representation a pipette shaft with an additional spacer for a particular pipette tip.

Fig. 1 shows a pipette 1 as a single-channel pipette. As already explained in the general part of the description, the teaching of the present invention is not limited to a single-channel pipette. It is equally usable for multichannel pipettes (cf. DE 100 13 511 A1 ) as well as for mechanical pipetting devices. The teaching of the invention involves the coupling of a pipette tip to the pipette shaft of a pipette.

The DE 100 13 511 A1 deals with constructive solutions of the interchangeability of the pipette shaft in a multi-channel pipetting device. These design solutions can also be used in a multi-channel pipette, which is designed according to the teaching of the present patent application.

Fig. 1 shows the pipette 1 with a handle 2, a manual control button as Pipettierbetätigung 3 and an adjustment 4 for adjusting the volume to be pipetted and / or for calibration of the pipette 1. At the bottom is indicated a pipette shaft 5, the in Fig. 1 is covered by an ejector 6. The Abwerferhülse 6 is a Abwerbetätigung 7, which is also designed as a push button, in Fig. 1 be pushed axially down to drop a bottom of the pipette shaft 5 plugged pipette tip 8 after performing the pipetting process or the multiple desired pipetting.

The teaching of the present invention is concerned with the sealingly secure attachment of the pipette tip 8 onto the pipette shaft 5 and with the smoothest possible ejection of the pipette tip 8 from the pipette shaft 5 by actuation of the ejection sleeve 6. All this should be feasible against the background that one not only uses matching OEM pipette tips (OEM = original equipment manufacturer) 8, but also can use generic pipette tips 8 on the pipette shaft 5. Also, it should be ensured that a pipette tip 8 on the pipette shaft 5 is easy and fast attachable, including a certain tolerance insensitivity at slightly oblique attachment of the pipette shaft. 5

Fig. 2 shows now in an enlarged and sectional view of the lower end of the pipette shaft 5 with an axially recognizable axial flow channel 9 for performing the pipetting process, and from below on the pipette shaft 5 plugged a pipette tip 8. The pipette shaft 5 is of the in Fig. 1 already identified ejector sleeve 6 surrounded.

The invention thus relates to a pipette 1 with a pipette shaft 5 made of preferably thermoplastic material for attaching a pipette tip 8, which is also preferably made of thermoplastic material, which has a plug-on section 10 which opens at least slightly conically, with a fastening section formed on the lower end of the pipette shaft 5 11, onto which the slip-on section 10 of the pipette tip 8 is slipped, wherein a sealing section 12 consisting of elastically yielding plastic material which already seals well with low withdrawal forces is provided on the fastening section 11. In the illustrated embodiment, it is additionally provided that at the attachment portion 11 axially offset to the sealing portion 12 a formed on the plastic material of the pipette shaft 5 fixing portion 13 is provided. The latter will be explained later in more detail.

It is essential that the sealing portion 12 of elastic-flexible plastic material on the plastic of the pipette shaft 5 is formed directly adherent. In the illustrated embodiment, this is realized so that the sealing portion 12 is integrally formed on the pipette shaft 5.

In principle, another possible attachment, which leads to an immediate firm adhesion to the pipette shaft 5, realized. For example, one can think of a spray-on process, which is then possibly combined with a subsequent shrinking process. Also by thermocompression or ultrasonic bonding to obtain an immediately adherent arrangement, as well as by using a reaction adhesive o. The like.

However, the illustrated and preferred embodiment is particularly characterized by the fact that the pipette shaft 5 is designed with the sealing portion 12 as a two-component plastic injection molded part, wherein the one component is the material of the pipette shaft 5 and the other component is the material of the Abdichtabschnittes 12. The elastic and flexible plastic material, on which or in which the sealing portion 12 is formed, can be implemented particularly expedient in two-component plastic injection molding. The compound of the materials is particularly intimate, it leaves create a perfect material connection of the plastic materials.

The illustrated and preferred embodiment provides in detail before that the plastic of the pipette shaft 5 is a polypropylene, which is preferably carried talumverstärkte. In particular, this material selection then fits that the plastic material of the Abdichtabschnittes 12 is a mixture polypropylene / ethylene-propylene-diene terpolymer (PP / EPDM blend). A likewise compatible with polypropylene material choice is, for example, a thermoplastic elastomer (TPE).

There are now various ways to equip the pipette shaft 5 of the pipette 1 with the sealing portion 12. First, it is possible to simply apply the sealing portion 12 to the plastic material of the pipette shaft 5 in an orderly manner. The forces directed in the axial direction when attaching and dropping the pipette tip 8 can lead to problems here. Accordingly, it is particularly expedient that in the illustrated embodiment, the pipette shaft 5 in the region of the Abdichtabschnittes 12 has a circumferential, ringnutartige recess 14 of a certain axial extent and that the sealing portion 12 is formed in the recess 14. One recognizes this recess 14 in the partial section of Fig. 2 Left. Therein is incorporated in the two-component plastic injection molding process, the sealing portion 12th

The sealing portion 12 may be extended in the upper region to below the ejector sleeve 6. Thus, the transition from the sealing portion 12 to the surface of the pipette shaft 5 is not critical and need not be made flush. For example, it could be provided there that the pipette shaft 5 protrudes a little further radially outwards, forms a ring-like shoulder and represents the guide for the ejector sleeve 6.

In any case, the illustrated embodiment of the pipette 1 according to the invention is optimally sealable, the junction sealing portion 12 / pipette shaft 5 is in the region of the recess 14 on all sides gap-free and completely sealed. The seal for Aufsteckabschnitt 10 of the pipette tip 8 is in elastic-compliant plastic material realized and optimally functional.

It has already been pointed out above that the requirement for secure seating and good sealing of the pipette tip 8 on the pipette shaft 5 contradicts the requirement for low withdrawal forces when the pipette tip 8 is ejected to a certain extent. Accordingly, the plastic material of the sealing portion 12 is set conflicting demands that must be reconciled with each other. It is necessary to choose the plastic material of the Abdichtabschnittes 12 so that deformability and wear resistance in a balanced relationship to each other. Abrasive surface wear, which becomes particularly strong when the plastic material of the Abdichtabschnittes 12, for example, the thermoplastic elastomer, is greatly compressed, can be counteracted by increasing the flexibility of the plastic material.

In addition, one can provide the plastic material of the sealing portion 12 in turn with a low-wear and / or low-friction protective layer or protective modification of the surface. For illustrative reasons, this additional protective layer is in Fig. 2 not shown in the drawing. In Fig. 3 However, this is indicated at 12 '. It can be provided that the plastic material of the Abdichtabschnittes 12 is provided at least in the main investment area with this protective layer, which in turn is directly adherent, in particular material-locking, formed on the plastic material of the Abdichtabschnittes 12. As a result, the elastomeric material core of the sealing section 12, which provides the necessary and desired deformability of the sealing section 12, is then coated with a thin, flexible, sleeve-like layer of preferably thermoplastic material, which gives the desired wear resistance.

An example is a coating of PTFE (polytetrafluoroethylene). For example, one can try to apply PTFE in powder form in a suspension with oil on the core of the Abdichtabschnittes 12. It is also possible to produce a fine PTFE protective layer by using very fine PTFE powder disperse and electrostatically distributed on the core of the Abdichtabschnittes 12 and this layer then thermally melts to a closed coating. Another interesting alternative to PTFE is FEP (a copolymer of hexafluoropropylene and tetrafluoroethylene). In itself and if this does not contradict the other conditions of use is also a silicone grease applied in the dispersion process as a variant of the protective layer in question.

The production of corresponding protective layers is known from the field of the production of coated O-rings (brochure Busak + Shamban "O-rings" 99D / 012/011/0401). In the O-rings known from the previously-mentioned, publicly available reference it is pointed out that for the purpose of reducing friction and smoothness, the surface can be improved by dipping, spraying or coating. As a processing method, the following methods are explained: RF coating, which is applied to the elastomer surface. Surface treatment in the DF method, in which the surface of the elastomer itself is modified by embedding molecules from a process gas, without a layer application in the strict sense. Plastic coating by means of a thin, wear-resistant plastic layer. PTFE powder coating, PTFE hard coating (sprayed on). Diffusion wax coating. Overall, the disclosure of the reference cited here is incorporated by reference into the disclosure of the present patent application.

In connection with the fact that one wants to realize the seal in an optimally functional manner, it may further be advisable to form at least one annular region 15 of larger diameter on the sealing section 12. This creates a defined annular seal at this point. Especially in this embodiment, a concentrated line-shaped contact area is created, in which the previously explained considerations for low-wear and / or low-friction protective layer gain special significance. Possibly you will actually have this protective layer only in this annular area 15 of larger diameter.

Of course, there are also special variants for the design of the annular region 15 of larger diameter. For example, it is also possible to use two successive rings or specially shaped rings as in the case of DE 38 87 205 T2 or lip-shaped ring-like shapes as in the DE 100 13 511 A1 realize in the region of the tip seal, if the application has been found to be appropriate.

Two axially successively formed on the pipette shaft 5 sections that serve to seal and fix, are appropriate. They make it possible to align the pipette tip 8 on the pipette shaft 5 and to fasten the pipette tip 8 stably on the pipette shaft 5 even with transverse forces, without this frictional connection loosening. The illustrated embodiment shows that at the attachment portion 11 axially offset from the sealing portion 12 a formed on the plastic material of the pipette shaft 5 fixing portion 13 is provided. It is expedient in this case that the fixing section 13 is formed at the lower end of the pipette shaft 5 and the sealing section 12 is arranged at an axial distance from the lower end of the pipette shaft 5. The fixing portion 13 serves as a stop in the dulling inner cone of the slip-on section 10 of the pipette tip 8.

This in Fig. 2 illustrated preferred embodiment further shows that the attachment portion 11 of the pipette shaft 5 has a broken here from the annular portion 15 of the Abdichtabschnittes 12 cylindrical outer contour or a less conical contour than the Aufsteckabschnitt 10 of the pipette tip 8, so that the lower edge of the pipette shaft 5, the fixing portion 13 forms.

Fig. 3 shows a further preferred embodiment of a pipette 1. Here it is first important that a circumferential annular flange 16 is provided at a distance from the end of the pipette shaft 5 on the pipette shaft 5, which optionally serves as a Aufsteckanschlag for the Aufsteckabschnitt 10 of the pipette tip 8. Such an annular flange 16 can be seen already at the lower end of the ejector 6 in Fig. 1 , The lower edge of the Abwerferhülse 6 forms this annular flange 16, which ultimately performs the ejector function.

Fig. 3 shows a modification that extends the scope of the claimed pipette 1 again significantly. It is namely provided that at the lower end of the ejector 6, a spacer element 17 of certain axial length is interchangeably arranged, which forms the annular flange 16 so that pipette tips 8 different effective axial length of the Aufsteckabschnittes 10 together with the pipette shaft 5 can be used. The illustrated embodiment shows that here the spacer 17 is designed as a kind of spacer sleeve made of plastic. This spacer 17 is not only simply plugged onto the pipette shaft 5, but it is attached to the ejector 6, namely attached to this. It therefore forms with the Abwerferhülse 6 a total by means of the Abwerferbetätigung 7 movable unit.

It is obvious that the present variant serves to realize different distances between the lower edge of the ejector 6 and the upper edge of the Aufsteckabschnittes 10 a plugged-pipette tip 8. So you can use different pipette tips 8. It is therefore expedient that a plurality of spacer elements 17 of different axial length can be arranged on the ejector sleeve 6, in particular attachable.

To replace or remove the spacer 17, in the latter case would then the lower edge of the ejector 6 itself to the annular flange 16, the illustrated embodiment also shows that the spacer 17 on the outside with a Manipulationsausformung 18, in particular in the form of an annular recess or Ring groove, provided. A manipulation tool, that is to say a pull-off and plug-on tool, can act on the manipulation formation 18 in order to remove or place the spacer 17.

For the special process steps of the manufacturing process may otherwise be pointed to the claims 11ff.

In the particularly useful manufacturing process of the two-component plastic injection molding proposed in claim 13, there are various possible procedures.

In the classical two-component plastic injection molding technique different, but chemically matched to each other and intimately associated with each other in the injection mold materials are injected into an injection mold. Characterized the areas of different hardness are formed simultaneously in the injection mold. This is the procedure which is also foreseen in the present case. The materials listed in the corresponding subclaims for the pipette shaft and the sealing portion on the pipette shaft can be used accordingly.

When using other materials, however, it is also possible to work in such a way that the areas of the pipette shaft are first formed and the molding volumes of the sealing section are closed and, after adequate cooling of the areas of the pipette shaft thus formed, the molding volumes of the other areas are opened the plastic material to be used there is injected and thus formed.

Another, also manufacturing technically expedient alternative is to work with two injection molds, ie first to form the pipette shaft in a first injection mold and then introduce after sufficient cooling the semi-finished molding "pipette shaft" in a second injection mold and to form the Abdichtabschnitt therein.

The two last-mentioned process techniques make it possible to work with different materials for the pipette shaft on the one hand and the sealing section on the other hand, which only have to fulfill a sufficient adhesion of the sealing section formed in the second step to the surface of the pipette shaft formed in the first step. However, such a far-reaching material connection as in a classic two-component injection molding process is so difficult to achieve. The use of one or the other method is so a corresponding analysis of the withdrawal forces and sealing forces occurring in practice on the finished part.

The applied two-component plastic injection molding process as a manufacturing method at the present location of a pipette unfolds various effects, which results in a particularly expedient and unpredictable synergetic result.

Above in connection with the explanation of the design of the seal for Aufsteckabschnitt 10 of the pipette tip 8, the formation of a protective layer on the plastic material of the Abdichtabschnittes 12 has been explained in detail. The production methods mentioned there for such a low-friction protective layer are applicable in the present case.

Claims (15)

1. Pipette with a pipette shaft (5) produced from plastic, an ejector sheath (6) surrounding the pipette shaft (5), and an ejector actuator (7), the pipette shaft (5) being designed for the attachment of a pipette tip (8) which is likewise composed of plastic and has an attachment section (10) which preferably opens out slightly in a conical fashion,
   with a fastening section (11), formed on the lower end of the pipette shaft (5), to which the attachment section (10) of the pipette tip (8) is attached,
   a sealing section (12), composed of an elastic-yielding plastic material which already has good sealing properties at low withdrawal forces, being provided on the fastening section (11) and the ejector sheath (6) being pushed axially downwards relative to the pipette shaft (5) by the ejector actuator (7) in order to eject a pipette tip (8), attached to the pipette shaft (5) from the bottom, after carrying out a pipetting process or a number of pipetting processes,
   characterized
   in that the sealing section (12) composed of the elastic-yielding plastic material with good sealing properties is formed such that it directly adheres to the plastic of the pipette shaft (5),
   in that, in the upper region, the sealing section (12) is extended as far as under the ejector sheath (6), and in that a spacer element (17) of a certain axial length is interchangeably arranged at the lower end of the ejector sheath (6) and forms an encircling annular flange (16) so that pipette tips (8) with different effective axial lengths of the attachment section (10) can be used together with the pipette shaft (5).
2. Pipette according to Claim 1, characterized in that the sealing section (12) has a material connection with the pipette shaft (5), the pipette shaft (5) with the sealing section (12) preferably being designed as a two component plastic injection moulding part, the one component being the pipette shaft (5) material and the other component being the sealing section (12) material.
3. Pipette according to Claim 1 or 2, characterized
   in that the pipette shaft (5) plastic is a preferably talc-strengthened polypropylene,
   and/or in that the sealing section (12) plastic is a polypropylene/ethylene-propylene-diene-terpolymer blend (PP/EPDM blend) or a thermoplastic elastomer (TPE),
4. Pipette according to one of Claims 1 to 3, characterized in that the pipette shaft (5) has an encircling annular groove-like recess (14) with a certain axial extent in the region of the sealing section (12), the sealing section (12) being arranged in the recess (14) and the sealing section (12) plastic material terminating in a gap-free manner at all edges of the recess (14) and/or terminating flush with at least the edges of the recess (14) assigned to the end of the pipette shaft (5) but preferably with all edges of the recess (14).
5. Pipette according to one of Claims 1 to 4, characterized in that the sealing section (12) plastic material is provided, at least in the main abutment region, with a low-wear and/or low-friction protective layer (12') or a protective modification of the surface which in turn is formed on the sealing section (12) plastic material in a directly adhering fashion, in particular by means of a material connection with the latter.
6. Pipette according to one of Claims 1 to 5, characterized in that at least one annular region (15) with a relatively large diameter is moulded on the sealing section (12).
7. Pipette according to one of Claims 1 to 6, in which a fixing section (13) formed on the pipette shaft (5) plastic material is provided, axially offset to the sealing section (12), on the fastening section (11), characterized in that the fixing section (13) is formed on the pipette shaft (5) at the lower end of the pipette shaft (5) and the sealing section (12) is arranged at an axial distance from the lower end of the pipette shaft (5),
   the fastening section (11) of the pipette shaft (5) preferably having a cylindrical outer contour, possibly interrupted by the annular region (15) of the attachment section (10), or a contour which is less conical than the attachment section (10) of the pipette tip (B), so that the lower edge of the pipette shaft (5) forms the fixing section (13).
8. Pipette according to one of Claims 1 to 7, characterized in that the spacer element (17) is attached to, in particular plugged onto, the ejector sheath (6),
   preferably a number of spacer elements (17) with different axial lengths being able to be arranged on, in particular be attached to, the ejector sheath (6).
9. Pipette according to one of Claims 1 to 8, characterized in that the lower end of the ejector sheath (6) itself, without a spacer element (17), likewise forms the annular flange (16) for a pipette tip (8) with a certain effective axial length of the attachment section (10).
10. Pipette according to one of Claims 1 to 9, characterized in that a manipulation mould (18), in particular in the form of an annular recess or an annular groove, is provided on the outer side of the spacer element (17).
11. Method for producing a pipette according to Claim 1, with a pipette shaft produced from plastic, an ejector sheath surrounding the pipette shaft, and an ejector actuator, a fastening section being formed at the lower end of the pipette shaft on which an attachment section of a pipette tip is attached,
    in which a sealing section, composed of an elastic-yielding plastic material which already has good sealing properties at low withdrawal forces, is affixed on the fastening section, which sealing section abuts against the inner side of the attachment section in a sealing fashion when a pipette tip is attached,
    characterized
    in that the sealing section composed of elastic-yielding plastic material is formed together with the pipette shaft in a two-component plastic injection moulding process,
    the sealing section plastic material being formed in an encircling, annular groove-like recess with a certain axial extent on the pipette shaft, with all edges of the recess being formed in a gap-free manner.
12. Method according to Claim 11, characterized in that a polypropylene is used as pipette shaft plastic, which polypropylene is preferably talc-strengthened, and/or
    in that a polypropylene/ethylene-propylene-diene-terpolymer blend (PP/EPDM blend) or a thermoplastic elastomer (TPE) is used as the sealing section plastic material.
13. Method according to Claim 11 or 12, characterized
    in that the sealing section plastic material is formed flush with at least the edges of the recess assigned to the end of the pipette shaft but preferably with all edges of the recess.
14. Method according to one of Claims 11 to 13, characterized in that at least one annular region with a relatively large diameter is moulded on the sealing section.
15. Method according to one of Claims 11 to 14, characterized in that, at least in the main abutment region, a low-wear and/or low-friction protective layer is applied to the sealing section plastic material in a directly adhering fashion, in particular by means of a material connection, or in that the surface of the plastic material is modified to have low wear and/or low friction,
    a PTFE coating in powdered form in a suspension with oil preferably being applied to the sealing section plastic material as a protective layer, or very fine PTFE powder being distributed in a dispersive fashion on the sealing section plastic material and subsequently being thermally melted on to form a cover.

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