DE102007040099A1 - sealing ring - Google Patents

Abstract

It is proposed a sealing ring made of a polymeric material, in particular for use in optical arrangements, wherein the polymer material comprises a thermoplastically processable fluorinated plastic material.

Description

The The invention relates to a sealing ring, in particular for the use in optical arrangements made of a polymeric material.

optical Arrangements often require sealing rings with production technically more complex cross sections, such. B. angle rings. At the same time, optical arrangements make high Requirements for surface quality, dimensional stability and dimensional accuracy, which in the production of a lot of effort desire.

When Polymer materials have hitherto been PTFE or with low comonomer proportions (Perfluoropropyl vinyl ether) modified PTFE used which does not differ from PTFE in terms of processing technology. For these materials only comes from the machining and shaping of rod-shaped or tubular semi-finished products Blanks into consideration.

As PTFE is also used as polymer material in many other applications due to its chemical resistance, high temperature resistance, physiological safety and lack of water intake to mention only the most important benefits of PTFE.

Further common materials for the aforementioned Sealing rings are fluorosilicone (FVMQ), ethylene-propylene-diene terpolymers (EPDM) or fluoroelastomers (FKM, FEPM, FFKM) used with for Elastomeric typical processes, in particular injection molding followed by vulcanization or thermoplastic Variants of these polymer materials of injection molding and the Extrusion, to be processed.

The Sealing rings produced by machining of blanks often have a high surface roughness due to processing on. Similarly, wide tolerance fields due to internal tensions be accepted in the used semi-finished products. Due processing Here is the production burdened with a high rate of waste. The Sealing rings show in use an undesirably high particle abrasion (particle shedding).

The made of elastomers sealing rings are disadvantageous as their dimensional stability below that to be carried out by injection molding Vulkanisationsschritt suffers. At the same time one finds with these Polymeric materials due to manufacturing a high proportion of extractable Components, such. B. residual monomers, crosslinking agents and processing aids.

Depending on the material the sealing rings made of elastomeric materials have a low pressure stability and a low resistance to chemicals and solvents (swelling behavior). Partly problematic is also their limited temperature elasticity or their tendency to embrittle at low temperatures, especially when operating temperatures of up to -40 ° C are required. In addition, the limited weather resistance and taking into account the tendency to aging and embrittlement.

Also the reproducibility of component quality is often not sufficient and especially problematic in mass production.

Height Friction coefficients complicate the joining during assembly.

task The invention is to propose a sealing ring, the avoids the above-mentioned disadvantages and in particular economically can be produced.

These Task is achieved by a sealing ring according to claim 1 solved.

Under thermoplastically processable plastic materials are those Understand materials that have a melt flow index (MFI), which is different from zero (ASTM Test D1238-88 at 372 ° C and a load of 5 kg at a maximum extrudate collection time of 1 hour).

The used according to the invention, thermoplastically processable, Fluorinated plastic material can be used in particular Process injection molding, so that the inventive Sealing ring can be produced in a one-step process.

Fluorinated thermoplastically processable plastic materials in the context of the present invention are in particular ETFE, FEP, MFA, PFA and thermoplastically processable PTFE, in particular the latter being particularly preferred. Likewise, mixtures of two or more of these materials may be used.

A variety of such PTFE materials, for example, in WO 01/60911 and the WO 03/078481 described.

in this connection In particular TFE copolymers are to be considered in which the comonomer content is less than 3.5 mol%, since here The PTFE properties are largely retained and still a thermoplastic processing is possible. Further preferred the comonomer content is limited to less than approx. 3 mole%, even more preferred are comonomer levels of less as about 1 mol%, for example, 0.5 mol% or less.

preferred Comonomers, on the one hand a good thermoplastic processability ensure and on the other hand, the material properties to PTFE are largely unchanged Hexafluoropropylene, perfluoroalkyl vinyl ether, perfluoro (2,2-dimethyl-1,3-dioxole) and chlorotrifluoroethylene.

When Fully fluorinated according to the invention Plastic material comes in addition to the TFE copolymers and polymer blends of PTFE and one or more thermoplastically processable plastics for use.

These other plastics are selected in particular the group of PTFE micropowders. These are PTFE types with low molecular weight compared to high molecular weight (standard) PTFE and low melt viscosity. They are typically prepared either by emulsion polymerization, by thermomechanical Degradation of high molecular weight PTFE in the extruder or by radiation degradation of high molecular weight PTFE, followed by a milling process.

The differences in the properties of high-molecular-weight (standard) PTFE and low-molecular-weight PTFE micropowders can be represented, for example, as follows ( see. S. Ebnesajjad, Fluoroplastics, Vol. 1, Non-Melt Processible Fluoroplastics, published by William Andrew Publishing, 2000 ): product molecular weight Melt viscosity at 380 ° C in Pa · s Standard PTFE about 10 ⁶ -ca. 10 ⁸ about 10 ¹⁰ -ca. 10 ¹³ micropowder about 10 ⁴ -ca. 10 ⁶ about 10 ² -ca. 10 ⁵

Examples of such polymer blends can be found in the published patent applications WO 01/60911 and WO 03/078481 ,

Of the on the one hand completely from the invention to be made using fully fluorinated plastic material. On the other hand, the sealing ring according to the invention but also include an insert, for example in the form of a Inserts, wherein then preferably the insert of from the polymer material formed surface areas substantially on all sides is surrounded.

The Insertion of sealing rings according to the invention is preferably selected from metallic material, from organic polymers, aramid fiber, carbon fiber and / or glass fiber reinforced Materials as well as ceramic materials.

The Insert is not necessarily integrally formed, although this is preferred as it is usually handling the insert facilitates in the manufacture of the sealing ring.

The Insert is preferably placed in an injection mold and then with the invention to be used fully encapsulated fluorinated plastic material.

The Insert can be coated with fully fluorinated plastic before coating preformed around the sealing ring to an application specific Geometry or specific sealing tasks.

Of Furthermore, the sealing ring can be connected to a component, wherein the composite in particular cohesively or positively can be produced.

to Production of the associated with a component sealing ring can this molded onto the component or after its separate production be connected in a forming process with the component.

According to one Another alternative is the component with the sealing ring also weld in a downstream step.

One designed for optical applications sealing ring has a cylindrical wall, at the lower edge preferably a circumferential, radially inwardly projecting collar is formed. Prefers the wall thickness of the cylindrical wall is less than the thickness of the collar (measured in the axial direction).

Further Preferably, the lower edge of the cylindrical wall is at its outer periphery rounded.

The The present invention further relates to a method of preparation a sealing ring according to the invention as it is defined in more detail in claim 8.

Prefers the filling of the mold takes place by means of injection of the polymeric material in its cavity.

For the case that the sealing ring according to the invention an insert is to contain the cavity of the mold Preferably designed so that it has a receptacle for a Insert part forms, wherein the insert is introduced into the mold before the cavity of the mold with the polymer material is filled.

The Filling the cavity of the mold is preferably by injection of the polymer material, independently of whether the sealing ring to be produced have an insert should or not.

Around a defined position of the insert in the finished invention To ensure sealing ring, is preferably the insert in the mold by means of a holder at a distance from the surface held the mold.

Prefers used mounts include several, from the outside in the Cavity of the mold retractable retaining pins.

Prefers the retaining pins hold the insert during filling in a predetermined position and then out of the cavity removed from the mold.

Especially the retaining pins are preferred during a so-called Pressing phase removed. At this time, the cavity of the Mold largely or substantially completely filled with the polymer material and a change the position of the insert in the subsequent steps of the manufacturing process is no longer to be feared. At this time stands but still on the emphasis polymer material that in the cavity of the mold can be pressed, on the one hand during the the shrinkage of the polymer material entering the same and on the other hand by removing the retaining pins to fill resulting free volumes. The temporal Sequence of the steps is preferably chosen so that the Polymer material in the cavity of the mold when removing the retaining pins is still molten and so on the means Repressing still filled polymer material, the free volumes can be filled, and then a practical seamless wrapping of the insert is achievable.

additional to the retaining pins or alternatively, the cavity of the mold with one or more small-area supports for the insert are formed.

Prefers is the insert before introducing it into the cavity of the mold preheated to a predetermined temperature. With regard to the melting temperature of the einzuzulenden Polymeric materials are preferred for a preheat temperature about 200 ° C or more.

The above considerations for the introduction of an insert in the sealing ring apply ent speaking, when the sealing ring is to be sprayed on a component. The only difference is essentially that the component is not enveloped by the polymer material after the injection molding process, but only so far in contact with the polymer material as for injection molding, ie the positive or cohesive bond of sealing ring and component necessary or is advantageous.

The Melting temperature of the injected into the cavity of the mold Polymer material is preferably equal to or greater the peak temperature in the DSC diagram, determined in the second melting, chosen, preferably a temperature of about 330 ° C. or higher.

at a preferred variant of the invention Procedure is envisaged that a predominant part of the polymer material is injected into the cavity at an injection pressure and that thereafter added another portion of the polymeric material a pressure in the cavity is fed, the injection pressure is chosen higher than the reprint.

Especially is a proportion of about 70 wt .-% to about 90 wt .-% of the polymer material filled with the injection pressure in the cavity of the mold.

Further is preferred after filling the cavity with the Polymer material still the mold for a given Holding time kept closed.

These Holding time is preferably in the range of about 3 seconds or more, in particular about 5 seconds or more.

Prefers In the method described above, a molding tool that is is designed as a multiple tool used. This shows that Multiple mold especially 2, 4, 6, 8 or more cavities on, in which in a process step the invention Components can be formed in a corresponding variety.

Prefers so-called balanced distribution systems are used, where the cavities are all equidistant from a common one Feeding channel for the polymer material arranged away are. This guarantees a special good dimensional accuracy of the produced sealing rings, since all cavities (or cavities) of the multiple tool be filled with the same pressure and at the same time. As a result, the constancy of part quality is improved.

Especially for sealing rings with small dimensions is the volume of polymer material in the feed channels of the distributor system higher than that of the sealing rings themselves. This results in not inconsiderably increased waste costs.

Forming the feed channels as a hot runner system often results in a cost advantage in manufacturing because the polymer materials remaining in the channel system need not be discarded, but can be used for the next fill cycle to fill the cavity or cavities. It is important, however, that the supply channels in respect to the polymer material corrosion-resistant materials (eg. As Inconel ^® 625) are made. The hot runners should be aerodynamically designed with large radii on all curves.

alternative for the injection of the sealing ring to the component is conceivable to manufacture the sealing ring independently and a connection between the sealing ring and the component in a subsequent To make a step.

Of the Sealing ring can have its final shape in one Forming step obtained. In particular, the connection between the sealing ring and the component during the forming step be achieved.

The Component may in particular a housing or housing part be.

The present invention achieves a number of significant advantages over the use of conventional PTFE or modified PTFE in the sealing ring of the present invention through the use of the thermoplastically processable, fully fluorinated plastic materials. On the one hand, a reduced cold flow is observed. Furthermore, one achieves a reduced permeation, ie an increased density. Furthermore, the sealing ring is leich ter and easier to connect by welding with other components of a complex arrangement. This advantage results in particular against Elastomerma terialien.

Across from The materials FVMQ, EPDM, FKM and the like. Get one higher temperature resistance and higher Chemical and oil resistance. Further finds no embrittlement at low temperatures. aging effects are negligible as well as the so-called compression set.

improvements you also achieve in the manufacturing process. Opposite the processing of conventional PTFE and modified PTFE can in cases the use of inserts through the possibility of Umspritzens realized a significantly simpler manufacturing process become. For the entire production can be through connecting the sealing ring with other components the number reduce the components of the overall arrangement and thus simplify the construction.

simultaneously one obtains a reduction of the waste rate, since cutting Post-processing completely or at least largely omitted can. Increased the use of multiple cavities in injection molding the profitability in production continues.

Across from the processing of elastomers gives an improved Process safety, since the raw material in the form of granules, d. H. a single component can, while elastomers a multi-component system necessary, comprising the base polymer, the crosslinker, the accelerator, the acid scavenger, other processing aids as well as mold release agent, which is high the requirement of the Homogeneity of the mixture provides.

improvements are eventually achieved within the overall apparatus, because the sealing rings according to the invention a smaller Roughness on the surface show as conventional parts made of PTFE and modified PTFE. This facilitates the assembly increases the achievable tightness at comparable Contact surface pressure and at the same time provides the prerequisite for a smaller particle abrasion.

While one with PTFE surfaces due to machining Roughness Ra observed from about 0.6 to about 0.9 microns, receives one has surfaces with roughnesses Ra at the invention, Injection molded sealing rings, the smaller than about 0.25 microns fail.

Across from open the sealing rings made of elastomers There are more possibilities with the sealing rings in To select contact liquids and with the use of surfactants Substances is unproblematic. Furthermore, the purity remains get the fluids for a long time.

The last-mentioned advantages find particular attention in one of the application examples of the sealing rings according to the invention, namely liquid lens systems with variable focus, as z. B. in the EP 1 662 276 A1 are described.

These and further advantages of the invention are described below with reference to the Drawing explained in more detail. They show in detail:

1 a schematic representation of an extruder screw for use in the production of sealing rings according to the invention;

2 an inventive sealing ring; and

3 : a balanced multiple tool in a schematic representation.

Production of a sealing ring made of thermoplastic processable PTFE:

For the processing of the invention to be used fully fluorinated plastic materials by injection molding We recommend the use of special machine equipment.

There Hydrofluoric acid is formed in the processing of fluorothermoplastics It is recommended that all of them are in contact with the melt be designed corrosion-resistant parts (eg Hastelloy C4 or Inconel 625).

In order to further ensure optimum processing of the fluorothermoplastics is recommended the use of a snail 10 with a design of the screw geometry such as in 1 is shown and described below.

The snail 10 includes a feed zone 12 , a compression zone 14 and a metering zone 16 ,

The associated exemplary screw parameters are the following, where D denotes the nominal diameter of the screw: Effective snail length about 20 D Length of the feed zone about 10 to about 12 D Length of the compression zone about 4 to about 5 D Length of metering zone about 4 to about 5 D Gradient a about 1 D Bridge width b about 0.1 D Channel depth of the intake zone c about 0.16 to about 0.18 D Channel depth of the metering zone d about 0.06 to about 0.07 D compression ratio about 2.5 to about 2.7

2 shows a sealing ring according to the invention 20 with a cylindrical wall part 22 and one at the bottom 24 of the wall part 22 ange formed radially inwardly projecting collar 26 , Such a sealing ring 20 can be used in lens systems like in the EP 1 662 276 A1 described use.

When Fully fluorinated plastic material, a TFE copolymer was used with a comonomer content of 0.5 mol%. The comonomer was perfluoropropyl vinyl ether (PPVE).

Injection molding for the production of sealing rings 20 took place on a Elektra 50 with the machine design described above (not shown). The thickness of the portions of such seal rings is often in the range of about 0.1 mm to about 0.25 mm. Their outer diameter can be for example about 5 mm or 10 mm.

In the design of the tool (not shown) was taken to ensure that the specified final dimensions are met. For closing the injection molding tool, a small closing force is sufficient (about 0.05 t / cm ² or more), because on the one hand the thermoplastic polymer materials used according to the invention are less prone to burr formation due to their high viscosity and on the other hand so the separation plane of the tool as a vent can act.

The Tool temperature was about 230 ° C or more.

A sprue system was designed as a 4-way sprue in such a way that the melt entry into the cavity of the injection molding tool is exactly in the middle of the sealing ring to be produced 20 located. This guarantees a uniform distribution of the melt during injection in the present small, thin-walled parts.

injected is with an injection pressure of about 2300 bar or less and one Melt temperature of about 330 ° C or higher.

After the cavity was completely filled, the tool remained about 6 seconds or more in the closed state around the polymer material for some time 36 to give the possibility to cool to a dimensionally stable temperature level.

The Cycle time for the complete process is about 10 sec or a bit more.

In a subsequent finishing step removes the sprue, to produce the final inside diameter.

The Roughness Ra measured on the sealing ring was approx. 0.19 μm.

3 shows a balanced multiple tool 30 with 4 cavities or cavities 32 that have a balanced distribution or feed channel system 34 with a centrally arranged feed channel 36 (also on called casting rod) are connected. The feed channel system is designed so that the flow paths for the polymer material from the central feed channel 36 to all cavities 32 are the same length. The individual channels of the feed channel system 34 lead into the middle of each cavity and end each with a 4-way sprue.

The feed channel system 34 can also be trained as a hot runner system.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 01/60911 [0016, 0022]
• WO 03/078481 [0016, 0022]
• - EP 1662276 A1 [0064, 0074]

Cited non-patent literature

• - see. S. Ebnesajjad, Fluoroplastics, Vol. 1, Non-Melt Processible Fluoroplastics, published by William Andrew Publishing, 2000 [0021]

Claims (23)

Sealing ring, especially for the Use in optical arrangements made of a polymeric material, a thermoplastically processable fluorinated plastic material includes. Sealing ring according to claim 1, characterized that the thermoplastically processable plastic material selected is made of ETFE, FEP, MFA, PFA and thermoplastically processable PTFE material or mixtures thereof. Sealing ring according to claim 2, characterized in that that the thermoplastic PTFE material is a TFE copolymer, wherein the co-monomer proportion is preferably 3.5 mol% or less, in particular less than 3 mol%, more preferably less than 1 Mol%, more preferably 0.5 mol% or less. Sealing ring according to claim 3, characterized the co-monomer is selected from hexafluoropropylene, Perfluoroalkyl vinyl ether, perfluoro (2,2-dimethyl-1,3-dioxole) and Chlorotrifluoroethylene. Sealing ring according to one of claims 1 to 4, characterized in that the PTFE material is a polymer mixture is, comprising PTFE and a thermoplastically processable plastic. Sealing ring according to one of claims 1 to 5, characterized in that the sealing ring is a substantially cylindrical wall comprises. Sealing ring according to claim 6, characterized that at the cylindrical wall at one end a radially inward protruding collar is formed. Process for producing a sealing ring according to one of claims 1 to 7, comprising the steps Provide a mold having a cavity for forming the seal ring; Warm up the mold to a temperature of 230 ° C or more; and Filling the mold with a polymer material, wherein the polymer material is a thermoplastically processable in Substantially fully fluorinated plastic material. Method according to claim 8, characterized in that that filling by injecting the polymer material takes place in the cavity of the mold. Method according to claim 8 or 9, characterized arranged a component before filling in the mold is, to which the sealing ring is formed. Method according to one of claims 8 to 10, characterized in that the mold as a multiple tool is formed with a plurality of cavities. Method according to claim 11, characterized in that that the multiple tool a balanced distribution system for having the filling of the cavities. Method according to one of claims 8 to 12, characterized in that the mold with a hot runner system equipped. Method according to one of claims 10 to 13, characterized in that the component prior to introduction the same in the cavity of the mold to a predetermined Temperature is preheated. Method according to claim 14, characterized in that that the given preheating temperature is approx. 200 ° C or more. Method according to one of claims 8 to 15, characterized in that the polymer material with a temperature of 330 ° C or higher in the cavity of the mold is fed. Method according to one of claims 8 to 16, characterized in that the mold to a temperature preheated by about 230 ° C or more. Method according to one of claims 8 to 17, characterized in that a predominant part the polymer material is fed into the cavity at an injection pressure and that thereafter a further portion of the polymer material is fed into the cavity at a pressure, wherein the injection pressure is chosen to be higher than the reprinting. Method according to claim 18, characterized that about 70 to about 90 wt .-% of the polymer material with the injection pressure is fed into the cavity. Method according to one of claims 8 to 19, characterized in that after filling the cavity with the polymer material, the mold still for a predetermined holding time is kept closed. Method according to claim 20, characterized in that that the holding time about 3 sec or more, especially about 5 sec or is more. Method for producing a sealing ring according to of claims 1 to 7, characterized in that a Plastic part made from a precursor by forming and then connected to a component. Method for producing a sealing ring according to of claims 1 to 7, characterized in that a Plastic part made from a precursor by forming and it is connected to a component.