Piston assembly and method for operating a piston assembly

Abstract

The invention relates to a piston assembly (10, 110) containing a body (30, 130) having a first cylindrical cavity (12) and a piston (16, 116) that can be displaceably guided in the first cylindrical cavity (12) and has a piston seal (20, 120) for sealing against the inner wall (22) of the first cylindrical cavity (12), wherein sealing forces can be absorbed on the inner wall (22) of the first cylindrical cavity (12), which forces can be generated by the piston seal (20, 120) in the radial direction, characterised in that a relief cavity (14, 114) is provided in which the piston seal (20, 120) located on the piston (16, 116) can be stored free of sealing forces until use.

Description

[0001] Patent application

[0002] Piston arrangement and method for operating a piston arrangement

[0003] Technical area

[0004] The invention relates to a piston assembly comprising a body with a first cylindrical cavity and a piston that can be displaceably guided in the first cylindrical cavity, with a piston seal for sealing against the inner wall of the first cylindrical cavity. Sealing forces generated by the piston seal in the radial direction can be absorbed on the inner wall of the first cylindrical cavity. The invention further relates to a method for operating such a piston assembly.

[0005] The invention also relates to a tribological system with two bodies rubbing against each other in a contact area, wherein at least one of the bodies consists of a thermoplastic elastomer at least in the contact area, and to a method for reducing friction in such a tribological system.

[0006] State of the art

[0007] Typical plungers in syringes or other plunger systems used in medical technology, for example, for administering medication or other pharmaceuticals, use a rubber plunger that is often silicone-coated to reduce the actuation forces of the devices. This poses the risk that undesirable components of the rubber or silicone, or of a lubricant used, may dissolve in the liquid containing the pharmaceutical. This is particularly detrimental in the field of ophthalmology because foreign substances are not broken down in the eye. With repeated application, such substances accumulate and can lead to health problems. Foreign substances, such as silicone residues, can impair the effectiveness of the pharmaceuticals.

[0008] The use of thermoplastic elastomer as a material for piston assemblies is known. EP 3222 311 B1 describes a syringe with an uncoated piston-cylinder system made of thermoplastic elastomer. The document discloses the use of paraffin as an internal lubricant.

[0009] The publication "Effect of Paraffin Migration on the Surface Free Energy of Natural Rubber" by A. Ansarifar and Yu Hail in GFKUED 2 63 (2) 69 - 128 (2010), Dr. Gupta Verlag ISSN 0176-1625, investigates the effect of paraffin wax migration on the surface free energy (surface tension) of natural rubber. Surface tension decreases undesirably with increasing storage time due to the migration of the wax to the surface.

[0010] The seals of conventional piston assemblies with a piston or piston seal made of thermoplastic elastomer become leaky over time. They are therefore unsuitable for long-term storage, for example, two years.

[0011] Disclosure of the invention

[0012] The object of the invention is to overcome the disadvantages of the prior art. According to the invention, this object is achieved by an arrangement of the type mentioned above, which is characterized in that the piston seal located on the piston can be stored free of sealing forces until use. For example, a relief cavity can be provided in which the piston seal located on the piston can be stored until use.

[0013] The invention is based on the discovery that the thermoplastic material of the seal in the piston is subjected to radial sealing forces, which cause compression deformation of the material and thus a reduction in the diameter of the seal. This compression set leads to leaks over time.

[0014] According to the invention, the piston seal on the piston is stored free from sealing forces until use. A relief cavity is provided for this purpose. The relief cavity ensures that the piston with the seal can be stored under sterile conditions outside the first cylindrical cavity for a long time without the effects of forces. No compression deformation occurs. The seal retains the same dimensions even after extended storage. The sealing force is not impaired by storage. In particular, regulations regarding a minimum shelf life of, for example, two or more

[0015] years will be reliably fulfilled.

[0016] According to the invention, an arrangement with a long minimum shelf life, good sealing, high consistent lubricity with a significantly reduced stick-slip effect is created, without the risk of the introduction of undesirable substances into the liquid to be administered.

[0017] Radial sealing forces are only exerted when the piston seal is inserted into the first cylindrical cavity. Since this occurs only shortly before use, for example, a few minutes before, the compression set occurring during this time is negligible. The invention allows the use of materials with high compression set, such as thermoplastic elastomers, thermoplastic urethane, and materials from the liquid silicone rubber (LSR) group.

[0018] The piston seal can be stored alone or with other piston seals in a separate relief cavity. The piston seal, with or without the piston attached, must then be removed from the relief cavity and transferred to the first cylindrical cavity. This poses a risk of contamination. It is therefore advantageously provided that the relief cavity is connected to the first cylindrical cavity, forms a second cylindrical cavity arranged coaxially to the first cylindrical cavity, and has a diameter that is larger than the diameter of the first cylindrical cavity. In this embodiment of the invention, a seal already located on the piston can be stored in the second cylindrical cavity. In this second cylindrical cavity, no radial sealing forces are exerted on the seal. The second cylindrical cavity can be sterile.The piston can be moved axially from the second cylindrical cavity directly into the first cylindrical cavity without contact with the environment. This eliminates any risk of contamination.

[0019] In an alternative embodiment of the invention, the piston is connectable to a profiled piston rod which extends coaxially through the first and second cylindrical cavities. The piston has a profiled cavity into whose profile the profiled piston rod engages when the connection is made and expands the piston such that radial sealing forces are generated. A piston rod is particularly useful for simple and inexpensive syringes. The piston is moved by pressure on the end of the piston rod facing away from the syringe outlet or by pulling in the opposite direction. In this embodiment, the piston rod is also used to expand the piston and create the sealing forces. In this case, no additional relief cavity is required. The cylinder can, in particular, have the same diameter over its entire length.

[0020] Preferably, a releasable locking mechanism is provided, allowing the piston seal to be locked in position within the relief cavity until use. This prevents the piston seal from accidentally entering the first cylindrical cavity, for example, during transport, and being exposed to radial sealing forces too early.

[0021] In one embodiment of the invention it is provided that

[0022] (a) the cylindrical cavity is enclosed by a housing;

[0023] (b) the locking device comprises a clamp with a resilient recess through which the piston rod is guided; and

[0024] (c) the locking device comprises a thickening on the piston rod which, when passing through the elastic recess, forms a resistance which can only be overcome by exerting an additional force when the piston seal is moved into the first cylindrical cavity.

[0025] The locking can be achieved by a wedge or a snap device.

[0026] In particular, the thickened portion on the piston rod can be provided in an area that never enters or comes into contact with the first cylindrical cavity in front of the piston. This prevents contamination and the introduction of particles into the first cylindrical cavity.

[0027] The locking mechanism influences the movement of the piston into the first cylindrical cavity. A further thickening can also be provided on the piston rod to limit the movement of the piston in the direction out of the first cylindrical cavity. This prevents the piston from being accidentally pulled out of the sensitive sealing chamber in the first cylindrical cavity or relief cavity. A limitation that prevents the piston seal from returning to the relief cavity is particularly preferred. In this way, for example, in a syringe or PRP kit, medication fluid is prevented from being drawn into the relief cavity and causing the device to leak.

[0028] A simple embodiment of the invention provides for the thickened portion to be formed by a ball held in the piston rod, the diameter of which is selected so that it protrudes through an opening beyond the edge of the piston rod. The ball can rotate along with the clamp's recess as it passes over it, so that little or no abrasion occurs. Alternatively, the thickened portion can be formed by molded-on projections.

[0029] In the arrangement according to the invention, the piston can comprise a head made of rubber, thermoplastic elastomer, or another suitable plastic, which is mounted on the piston rod and to which at least one coaxially circumferential ring is molded, forming the piston seal. The piston rod can be made of virtually any material, particularly a rigid one. It is important that, for medical use, the head and seal are made of a material that does not allow undesirable substances to enter the fluid contained in the cylindrical cavity.

[0030] The plunger assembly is suitable for a wide variety of applications. However, its use is particularly advantageous when the plunger assembly forms part of a syringe with an injection needle.

[0031] In an alternative embodiment of the invention, the piston or piston rod comprises a threaded spindle that interacts with a thread fixed to the housing, allowing the piston to move by rotation. Such a configuration is particularly useful when the volume of the cylindrical cavity defined by the piston is to be precisely adjusted. This is the case, for example, when a specific fraction of a liquid is to occupy a specific area of ​​a cavity. The piston can then be moved with high precision to the position where the level of this fraction is at a desired height.

[0032] In a further embodiment of the invention, a locking mechanism or other mechanism is provided which, upon insertion of the piston seal on the piston into the first cylindrical cavity, engages or otherwise prevents the piston seal from moving out of the cylindrical cavity. The locking mechanism prevents the piston from being moved out again and becoming contaminated outside the cylindrical cavity.

[0033] A method according to the invention for operating such a piston assembly is characterized in that the piston, with the piston seal, is stored outside the first cylindrical cavity, free from sealing forces until use. This eliminates any compressive deformation during storage. If the piston, with the piston seal, is stored in a relief cavity connected to the first cylindrical cavity, contamination by unwanted substances in the environment or incorrect operation is avoided.

[0034] According to the invention, the object is further achieved by a tribological system with two bodies rubbing against one another in a contact area, wherein at least one of the bodies consists of a thermoplastic elastomer, at least in the contact area, which is characterized in that the thermoplastic material has a paraffin content and was stored in air or an oxygen-containing gas prior to use in the tribological system, so that paraffin migrates to the surface. Unlike in the above-mentioned publication by Ansarifar et al., the effect of migrating paraffin is desirable in some tribological systems. In a first variant, the system is stored until sufficient paraffin has reached the surface. One such system is, for example, a system in which the body is a piston with a piston seal made of a thermoplastic elastomer and a paraffin content.The minimum storage time depends on the material selection, the paraffin content, and the desired lubricity of the tribological system. A high paraffin content and a long storage time result in good lubricity.

[0035] It has been found that good lubricity can be achieved even if the thermoplastic material has been stored for at least 8 days, preferably at least 10 days. In particular, one of the bodies can be a piston with a piston seal made of a thermoplastic elastomer and a paraffin component. The piston can be guided in a cylindrical cavity.

[0036] In a particularly advantageous method, it is provided that a body which consists at least in the contact area of ​​a thermoplastic elastomer or other thermoplastic material and has a paraffin content, is stored in air or in an oxygen-containing gas before use in the tribological system, so that paraffin migrates to the surface.

[0037] To reduce the actuation forces required for piston movement, the contact area of ​​the bodies can be pre-coated with paraffin. The coating of the contact area can be carried out using a second body, which also consists at least partially of a thermoplastic elastomer with a paraffin content. In this way, for example, in a piston assembly, a separately mounted sliding body can be used at the factory to coat the inner wall with paraffin.

[0038] The body can be a piston with a piston seal or another freely formed structure of low geometry made of a thermoplastic elastomer and a paraffin component. The body can be guided in a cylindrical cavity, the inner wall of which is coated with paraffin through its sliding movement before the final piston is inserted.

[0039] Embodiments of the invention are the subject of the dependent claims. Exemplary embodiments are explained in more detail below with reference to the accompanying drawings.

[0040] Definitions

[0041] In this description and the appended claims, all terms have a meaning familiar to the person skilled in the art, as set forth in the technical literature, standards, and relevant websites and publications, particularly lexical ones, such as www.Wikipedia.de, www.wissen.de, or those of competitors, research institutes, universities, and associations. In particular, the terms used do not have the opposite meaning to what the person skilled in the art would derive from the above publications. Brief description of the drawings

[0042] Fig.l is a schematic cross-section through a piston arrangement with a cylindrical cavity and relief cavity with a piston in a relief position.

[0043] Fig.2 shows the arrangement from Figure 1 with the piston in a sealing position.

[0044] Fig.3 is a longitudinal section through a piston rod with a locking device according to a first embodiment.

[0045] Fig.4 is a perspective view of the locking mechanism from Figure 3 in detail.

[0046] Fig.5a is a cross section through the piston rod along the axis shown in Figure 3

[0047] Cutting line.

[0048] Fig.5b is a top view of the piston rod from Figure 3.

[0049] Fig.5c is a separate illustration of a clamp for the locking device from Figure 3.

[0050] Fig.6 is a longitudinal section through the clamp from Figure 3.

[0051] Fig.7 is a longitudinal section through the piston rod of Figure 3 in a syringe barrel in which the piston seal is mounted in a relief cavity.

[0052] Fig.8 shows the piston seal from Figure 7 in detail.

[0053] Fig.9 shows the arrangement of Figure 7, in which the piston is in the cylindrical cavity of the

[0054] Syringe housing is sealed with the piston seal.

[0055] Fig. 10 shows the piston seal from Fig. 9 in detail. Fig. 11 is a longitudinal section through a piston assembly in the delivery state according to a second embodiment.

[0056] Fig.12 is a detail from Figure 11.

[0057] Fig.13 is a longitudinal section through the piston arrangement of Figure 11 in the unloaded state.

[0058] Fig.14 is a detail from Figure 13.

[0059] Fig.15 shows the arrangement from Figure 11, in which the piston is sealingly guided in the cylindrical cavity of the housing with the piston seal.

[0060] Fig.16 is a detail from Figure 15.

[0061] Fig.17 shows a piston with a separate piston rod according to a third embodiment.

[0062] Fig.18 shows the piston from Figure 17 with the piston rod connected.

[0063] Description of the embodiments

[0064] 1. Example: Syringe

[0065] Figure 1 and Figure 2 schematically show a piston arrangement, generally designated 10, with a housing 30. The housing 30 has a section 40 with a cylindrical cavity 12 and a section 32 with a coaxial, also cylindrical relief cavity 14.

[0066] Figure 1 shows a piston 16 located in the relief cavity 14, which is connected to a piston rod 18. The piston 16 is provided with a circumferential piston seal 20. In Figure 1, the piston 16 is in a position in which the piston seal 20 is arranged in the relief cavity. The cross-sectional diameter of the relief cavity 14 is selected such that no radial sealing forces are exerted on the piston seal 20 and the piston 16. This can be clearly seen in Figure 1. In this position, no compression deformation of the piston seal 20 occurs. The piston assembly 10 can be in the

[0067] Piston seal in the relief cavity 14 can be stored for a long time.

[0068] By applying pressure to the end 34 of the piston rod 18, the piston 16 can be moved downward in the illustration for deployment of the piston assembly. Figure 2 shows the piston 16 in a position in which the piston seal 20 is arranged in the cylindrical cavity 12. In this position, radial sealing forces are exerted on the piston seal 20 by the inner wall 22 of the cylindrical cavity 12. The area 24 in front of the piston 16 is sealed off from the remaining area within the housing 30.

[0069] The assembly 10 can, for example, be part of a syringe and be used to inject medication. In this case, it is important that the piston 16 and the sections of the piston rod 18 that enter the cylindrical cavities 12 and 14 are stored in a completely sterile manner until use. Particularly simple handling is achieved if the piston 16 is already inserted into the syringe housing 30 by the manufacturer and is transported and stored in this position. To use, only pressure must be exerted on the end 34 in the direction of the syringe opening. It is important that the piston 16 cannot slip out of the relief cavity 14 or be pulled out before use. To prevent the removal of the piston 16 from the housing 30, a locking mechanism 50 is provided, the structure and function of which are illustrated in Figures 3 to 6.

[0070] Figure 3 is a longitudinal section through the piston rod 18 and the locking device 50. In the present embodiment, the piston rod 18 has a triangular cross-section. This can be seen in Figure 5a. The locking device 50 comprises two balls 26 and 28, which are arranged inside the piston rod 18. This can be seen in Figure 3. The ball 28 facing away from the piston 16 is slightly larger than the other ball 26. Both balls 26 and 28 have a diameter that protrudes through openings beyond the flat sides of the piston rod 18. They thus form a thickened portion on the piston rod 18. It goes without saying that a molded-on thickened portion can also be used.

[0071] In the present exemplary embodiment, the locking device 50 further comprises a clamp 36, which is shown separately in Figure 5c and Figure 6. The clamp 36 comprises two flat, double-layered wings 38 and 42. The wings 38 and 42 extend horizontally in the illustration. The wings 38 and 42 are arranged opposite one another around a recess 44 that is open on the long side. Between the layers 48 and 52 of the wings 38 and 42, an intermediate space 46 is provided, which extends over the entire length of the wings 38 and 42 except for one edge. This can be seen in Figure 6. In the plane of the layer 52, which faces the end 34 - at the top in Figure 6 - the recess 44 is somewhat larger than in the plane of the lower layer 48 shown in Figure 6. This can also be clearly seen in Figures 5c and 3.

[0072] The recess 44 extends from an open side (bottom in Figure 5) to a bridge 54, which connects the wings 38 and 42. Two tongues 56 and 58 are formed on the bridge 54 in the plane of the layer 52 (top in Figures 3 and 6). These are clearly visible in Figure 5c. The tongues 56 and 58 are beveled on the mutually facing long sides until just before the free end, forming a triangular receptacle 60. The free ends project slightly inward in the plane and are rounded.

[0073] The clamp 50 can be clipped onto the piston rod 18 with the receptacle 60 through a slot in the syringe housing 30, which is horizontal in the illustration. This is clearly visible in Figure 5a. The plane of the layer 52 is located between the balls 26 and 28. The projecting free ends of the tongues 56 and 58 form a resistance and hold the clamp 50 in its lateral position. Neither displacement nor rotation of the clamp in the plane of the layer 52 is possible. The balls 26 and 28 form a resistance for the tongues 56 and 58 and secure the axial position of the clamp 50 on the piston rod 18.

[0074] In the area in front of the end of the syringe housing 30 facing away from the needle, two opposing wings 62 are molded onto the housing 30 in the usual manner. These are clearly visible in Figure 7. The wings 62 serve as abutments when pressure is exerted on the end 34 of the piston rod 18. In the present embodiment, the clamp 50 is dimensioned just so that it can be pushed onto the wings 62 of the syringe housing 30 with the gap 46 between the layers 48 and 52. The piston rod 18 and the piston 16 located thereon are thus secured against displacement in the axial direction.

[0075] The balls 26 and 28 have a position in the piston rod 18, at which the piston seal

[0076] 20 on the piston 16 is located in the relief cavity 14 when the piston rod 18 is locked with the lock 50 as described above. In this state, the syringe assembly 10 can be easily stored and transported. The piston is locked in such a storage position from the outside, thus avoiding contamination by abrasion or other unwanted particles. No pressure is exerted on the piston seal 20.

[0077] To use the syringe, the lock 50 must be released. To do this, pressure is exerted on the end 34 of the piston rod. The tongues 56 and 58 can also shear apart slightly in a lateral direction if sufficient pressure is applied. The piston rod 18, with its thickened portion in the form of the lower ball 26 in Figure 3, is pressed through the recess 60. The piston seal 20 is moved into the cylindrical cavity 12 with a smaller diameter. Medication can then be drawn from a vial and injected, or medication already in the syringe can be injected. The slightly larger ball 28 prevents the piston 16 from being pulled back into the storage and transport position and prevents too much liquid from being drawn up and entering the relief cavity.

[0078] In the present embodiment, an arrangement with a piston rod 18 and a separate piston 16 formed as a head with a molded-on piston seal 20 made of a thermoplastic elastomer is used. It is understood that the arrangement can also be formed as a single piece from a rigid material with a sealing groove for a separate seal.

[0079] Figures 7 to 10 show the arrangement in detail. Figure 7 shows the entire arrangement with the circumferentially running, annular piston seal 20 in the relief cavity 14. Figure 9 shows the arrangement from Figure 7 after activation of use with the piston seal 20 in the cylindrical cavity 12. When comparing the detailed representations in Figures 8 and 10, it can be seen that in this position there is pressure between the piston seal 20 and the inner wall 22, which leads to a slight deformation of the piston seal 20 in the area 64. The rounded shape of the piston seal shown in Figure 8 is pressed straight against the inner wall 22 in the position in Figure 10 and seals the area in front of the piston 16 well.

[0080] The elastic material of the piston 16 with the piston seal 20 forms a head that tapers conically on the side of the piston seal 20 facing away from the piston rod 18. This allows easy insertion into the narrower part 40 of the housing 30. The part 68 located on the other side of the piston seal 20 has a recess on its front side. Using this recess, the elastic material is placed onto the funnel-shaped end 66 of the piston rod. The recess is slightly smaller than the funnel-shaped end of the piston rod 18, so that the material is slightly expanded and tensioned. This prevents the attached piston 16 from becoming detached from the piston rod 18.

[0081] 2. Example: Separation of a liquid fraction

[0082] The second embodiment illustrated in Figures 11 to 16 relates to a piston assembly 110 with a piston 116 whose advance is achieved by rotation. The piston assembly 110 comprises a housing 130 and the piston 116. The housing 130 has an upper housing section 133, a lower housing section 140, and an intermediate middle housing section 135 formed by a taper with a small cross-sectional diameter. The middle housing section 135 is reinforced with four reinforcing ribs 137. The reinforcing ribs 137 extend vertically in the illustration in a star shape around the middle housing section 135 and are integrally formed on all housing sections. They stabilize the assembly.

[0083] A liquid, such as blood, introduced into the housing 130, which is closed with a lid, can be centrifuged or otherwise divided into fractions within the housing 130. The volumes in the housing sections are selected such that a selected fraction of the liquid is located in the central housing section 135. This fraction can then be easily removed, for example, with a pipette.

[0084] Depending on the composition of the fluid, the fluid levels of the fractions vary. For example, the level of the DNA and long-chain protein-containing fraction in blood depends on the physiology of the person from whom the blood was drawn. The piston 116 can be used to adjust the volume in the lower housing section 140 and thus the level of the fraction in the housing section 135.

[0085] Since the piston 116 serves to finely adjust the volume in the lower housing section 140, the adjustment in the present embodiment is not made by pressure on the piston. Rather, the piston 116 is connected to a threaded spindle 118. The threaded spindle 118 is screwed into a thread 122 fixed to the housing. The thread 122 can, for example, be part of a plug that is inserted from below into an opening in the housing 130. By turning the threaded spindle 118, for example with the aid of a rotary knob that can be inserted into the threaded insert with the thread 122, the piston 116 is moved in the axial direction. This changes the volume in the housing section 140, and the level of the fractions above it can be set to a desired level.

[0086] As in the first embodiment, the piston 116 is provided with a head made of a thermoplastic elastomer. A piston seal 120 is molded onto the head. Before the assembly is used, the head is located in a relief cavity 114 in a housing section 113 below the lower housing section 140. The relief cavity 114 has—as in the first embodiment—a larger diameter than the associated, coaxial cavity in the lower housing section 113.

[0087] Figure 12 shows the storage and transport state of the assembly 110 from Figure 11 in detail. It can be seen that the piston seal 120 is not subjected to any radial forces and, accordingly, no compressive deformation occurs. Figure 14 shows the assembly 110 from Figure 13 in detail. The piston seal 120 is located just above the annular shoulder formed between the lower housing section 140 and the housing section 113 with the relief cavity 114. In this state, sealing forces are exerted on the piston seal 120.

[0088] To prevent the piston 116 from being turned back and the piston seal 120, once it has reached the area of ​​the narrower housing section 140, from returning to the relief cavity 114, a locking mechanism is provided. The locking mechanism comprises two opposing locking elements 119 that are integrally formed on the threaded spindle 118. In the storage and transport state, which is shown in Figure 11 and Figure 12, the locking elements 119 lie closely together and are held in position by the threaded insert 122. When the piston 116 is moved upwards in the illustrations, the lower edge of the locking elements 119 is also moved out of the threaded insert 122. The locking elements 119 are subjected to tension. When the locking elements 119 are no longer held in position by the threaded insert (Figures 11 and 12), they snap outwards. This is illustrated in Figure 15 and Figure 16.They then form a resistance that can no longer be overcome without destruction, which prevents the piston 116 from being moved back downwards in the illustration. It goes without saying that any other locking device or other latching mechanism suitable for moving the piston 116 back can also be used. The piston can be made of a thermoplastic, for example TPE (SEBS base) thermoplastic elastomer with parafinole modification; TPO / TPE-0 thermoplastic polyolefin elastomers, TPU thermoplastic polyurethane with parafinole modification or PP / PE with parafinole modification (particularly soft versions) or of a thermoset, for example LSR liquid silicone rubber with parafinole modification. In the present embodiment, the piston is made of TPE.

[0089] For the cylinder, it is advisable to choose a thermoplastic, such as PETG (glycol-modified polyethylene terephthalate), PET (polyethylene terephthalate), PBT (polybutyl terephthalate), COC (cycloolefin copolymer), or PMMA (polymethyl methacrylate). A PETG cylinder was chosen for this example.

[0090] 3.Exemplary example (Fig.17-18): separate piston rod

[0091] The piston 210 is inserted into a cylinder 212 with a continuous inner diameter. During storage, the piston 210 is separated from the piston rod 214. There is no connection between the piston 210 and the piston rod 214 and their inner filling contour. The piston 210 in this arrangement is stored safely and largely free from radial forces and the associated compression set. This can be seen in Figure 17. The inner diameter of the cylinder 212 corresponds exactly to the diameter of the piston 210 or, in some cases, its subsequent slight oversize for the sealing function 210 at the point of the largest diameter 216. Furthermore, a gap 218 is formed between the inner wall of the cylinder 212 and the piston 210. The soft, elastic piston 210 can yield and deform without changing its dimensions.

[0092] Joining the piston rod 214 with the connection into the piston 210 only takes place immediately before use. The connection is created by an irreversible click by pushing the fixed piston rod 214 toward the elastomeric piston 210. This creates a positive connection, which enables movement in the longitudinal direction. This is illustrated in Figure 18. It can be seen that the piston 210 has an opening on the side facing the piston rod 214, which opens into a profiled cavity 220. The profile of the cavity 220 roughly corresponds to the outer profile 222 of the piston rod 214. In Figure 17, it can be seen that the elastic piston can yield to external pressure by deformation. Fig. 18 shows the assembled piston with piston rod 214. The profiled lower part 222 of the piston rod 214 sits firmly in the cavity 220. The piston 210 is pushed slightly outwards, similar to a dowel, and seals completely.

[0093] This design allows storage at different temperatures, for example sterilization with EO gas at over 50°C and over a period of, for example, 24 hours.

[0094] The exemplary embodiments explained above serve to illustrate the invention claimed in the claims. Features which are disclosed together with other features can generally also be used alone or in combination with other features which are explicitly or implicitly disclosed in the text or in the drawings in the exemplary embodiments. Dimensions and sizes are given only as examples. Suitable ranges will become apparent to those skilled in the art from their specialist knowledge and therefore need not be explained in more detail here. The disclosure of a specific embodiment of a feature does not mean that the invention is to be limited to this specific embodiment. Rather, such a feature can be implemented by a multitude of other embodiments familiar to those skilled in the art.The invention can therefore be implemented not only in the form of the embodiments explained, but also in all embodiments covered by the scope of the appended claims. In particular, the piston assembly can also be used outside the medical field. The piston assembly serves not only for administering medications and pharmaceuticals, but also for use as a cavity with an adjustable volume.

[0095] The terms "top," "bottom," "right," and "left" refer exclusively to the attached drawings. It is understood that claimed devices may also assume other orientations. The terms "containing" and "comprising" mean that additional, unmentioned components may be provided. The terms "essentially," "predominantly," and "predominantly" include all features that exhibit a property or content in the majority, i.e., more than all other mentioned components or properties of the feature—for example, more than 50% for two components.

Claims

Patent claims 1. Piston arrangement (10, 110) comprising a body (30, 130) with a first cylindrical cavity (12) and a piston (16, 116) which can be displaceably guided in the first cylindrical cavity (12) and which has a piston seal (20, 120) for sealing against the inner wall (22) of the first cylindrical cavity (12), wherein sealing forces which can be generated by the piston seal (20, 120) in the radial direction can be absorbed on the inner wall (22) of the first cylindrical cavity (12), characterized in that the piston seal (20, 120) located on the piston (16, 116) can be stored free of sealing forces until use.

2. Piston arrangement according to claim 1, characterized in that a relief cavity (14, 114) is provided in which the piston seal located on the piston can be stored free of sealing forces until use.

3. Piston arrangement (10, 110) according to claim 1 or 2, characterized in that the relief cavity (14, 114) is connected to the first cylindrical cavity (12), forms a second cylindrical cavity (14, 114) arranged coaxially to the first cylindrical cavity (12) and has a diameter which is larger than the diameter of the first cylindrical cavity (12).

4. Piston arrangement (10, 110) according to claim 3, characterized in that the piston is connectable to a profiled piston rod (18, 118) which extends coaxially through the first and the second cylindrical cavity, wherein the piston has a profiled cavity, in the profile of which the profiled piston rod engages when the connection is made and expands the piston in such a way that radial sealing forces are generated.

5. Piston arrangement (10, 110) according to claim 3 or 4, characterized in that a releasable locking device (50) is provided, with which the piston seal (20) can be locked in its position in the relief cavity (14) until use.

6. Piston arrangement according to claim 5, characterized in that (a) the cylindrical cavity (12) is enclosed by a housing (30); (b) the locking device (50) comprises a clamp with an elastic recess (60) through which the piston rod (18) is guided; and (c) the locking device (50) comprises a thickening (28) on the piston rod (18) which, when passing through the elastic recess (60), forms a resistance which can only be overcome by exerting an additional force when the piston seal (20) is moved into the first cylindrical cavity (12).

7. Piston arrangement (10, 110) according to claim 6, characterized in that a further thickening (26) is provided on the piston rod (18) for limiting the movement of the piston (16) in the direction out of the first cylindrical cavity (12).

8. Piston arrangement according to claim 7, characterized in that the thickening (28) is formed by a ball held in the piston rod (18), the diameter of which ball is selected such that it projects beyond the edge of the piston rod.

9. Piston arrangement according to claims 5 to 8, characterized in that the piston (16, 116) comprises a head made of rubber, thermoplastic elastomer or another suitable plastic, which is placed on the piston rod (18, 118), to which head at least one coaxially circumferential ring is formed, which forms the piston seal (20, 120).

10. Piston assembly (10, 110) according to one of the preceding claims, characterized in that the piston assembly forms part of a syringe or a PRP kit.

11. Piston arrangement according to one of claims 1 to 9, characterized in that the piston (116) or the piston rod (118) has a threaded spindle which cooperates with a thread (122) fixed to the housing, so that a piston movement can be effected by a rotary movement.

12. Piston arrangement (10, 110) according to one of the preceding claims, characterized in that a locking mechanism (119) or other mechanism is provided which engages upon insertion of the piston seal (120) on the piston (116) into the first cylindrical cavity (112) or otherwise prevents the piston seal (120) from moving out of the first cylindrical cavity (112).

13. A method for operating a piston arrangement (10, 110) comprising a body (30, 130) with a first cylindrical cavity (12) and a piston (16, 116) which can be displaceably guided in the first cylindrical cavity and has a piston seal (20, 120) for sealing against the inner wall (22) of the first cylindrical cavity, wherein sealing forces which can be generated by the piston seal in the radial direction can be absorbed on the inner wall of the first cylindrical cavity, characterized in that the piston with the piston seal is mounted outside or inside the first cylindrical cavity free from sealing forces until use.

14. The method according to claim 13, characterized in that the piston (16, 116) with the piston seal (20, 120) is mounted in a relief cavity (14, 114) which is connected to the first cylindrical cavity (12).

15. Tribological system with two bodies rubbing against each other in a contact area, wherein at least one of the bodies consists of a thermoplastic elastomer or other thermoplastic material at least in the contact area, characterized in that the thermoplastic material has a paraffin content and was stored in air or in an oxygen-containing gas before use in the tribological system, so that paraffin migrates to the surface.

16. Tribological system according to claim 15, characterized in that the thermoplastic material has been stored for at least 6 days, preferably at least 10 days.

17. Tribological system according to claim 16, characterized in that the body is a piston with a piston seal made of a thermoplastic elastomer and a paraffin component.

18. Method for reducing friction in a tribological system according to claim 15 or 16, characterized in that a body which is at least in the contact area consists of a thermoplastic elastomer or other thermoplastic material and contains a paraffin content, is stored in air or an oxygen-containing gas prior to use in the tribological system, so that paraffin migrates to the surface.

19. Method according to claim 18, characterized in that the body is a piston with a piston seal made of a thermoplastic elastomer and a paraffin content.

20. Method according to claim 19, characterized in that the piston is guided in a cylindrical cavity, the inner wall of which has been previously coated with paraffin, the coating of the inner wall being carried out with a second paraffin-containing sliding body of smaller or equal diameter, which also consists at least partially of a thermoplastic material with a paraffin content.

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