WO2009026972A1 - Component - Google Patents

Abstract

The invention relates to a component comprising an insert and a polymer material that at least partially surrounds the insert. The polymer material comprises a thermoplastically processable, substantially fully fluorinated plastic material.

Description

 component

The invention relates to a component with an insert part and a polymer material at least partially surrounding the insert.

Components made of metallic materials or plastics are exposed to highly aggressive media in a number of applications, for example in coating technology or in chemical plants. Since these components often do not withstand a chemical attack, they must be protected by a correspondingly resistant coating or coating.

Even in contact with high-purity products or in the medical field, components are required in which the material of the components is not necessarily compatible with the environment in contact. Again, components are preferably provided with a cladding or coating which avoids such problems.

In friction-stressed components abrasion must be prevented or at least reduced and here too is used to coatings that cope with this task due to their low coefficient of friction.

In such applications, PTFE is commonly used as a polymeric material because of its chemical resistance, high temperature resistance, physiological safety, and lack of water absorption, to name only the most important benefits of PTFE. The PTFE materials are usually processed by means of isostatic pressing process to a coating or coating of the components. It is a complex multi-stage pressing / sintering process. In order to be able to meet the often demanded surface qualities as well as narrow tolerance fields, a step with subsequent machining (turning or milling process) is followed.

For a complete coating of inserts by means of PTFE materials and two or more Hüllteile can be made separately and then connected by welding or pressing with inserted to be sheathed component.

Since the insert must be embedded in the powdery PTFE raw material, due to the inhomogeneous bulk density accurate centering is not possible. Furthermore, only inserts that resist the mechanical and thermal stress of the PTFE press / sintering cycle can be enveloped.

The coefficients of thermal expansion of the inserts and of the PTFE material used for the covering differ regularly very strongly. In addition, the PTFE material undergoes a phase change twice during the sintering process, whereas this is normally not the case for the insert material. As a result, strong relative movements between PTFE and insert are generated. The creation of a good adhesive bond is made more difficult.

When using several individual parts for the production of an envelope additionally at least one joining step is required with the additional risk of incorrect positioning. The strength of the weld is also often a weak point. In addition, the joint has to be reworked. If several inserts are to be joined together to form a system, these problems increase, so that in particular mass production becomes uneconomical.

The object of the invention is to propose a component which meets the above-mentioned requirements and can be produced economically.

This object is achieved by a component according to claim 1.

The polymer material at least partially surrounding the insert preferably forms an envelope or coating.

Under thermoplastically processable plastic materials, such materials are meant, which have a melt flow index (MFI) which is different from zero (ASTM Test D1238-88 at 372 ⁰ C and a load of 5 kg at a maximum extrudate-collection time of 1 hour).

The thermoplastically processable, substantially fully fluorinated plastic material used in accordance with the invention can be processed into coatings of the inserts, in particular by injection molding or by transfer molding, so that the component according to the invention can be produced in a single-stage process.

The particular economy of the components according to the invention not only results from the simplified manufacturing process. Of considerable importance is also the lower thermal and mechanical loading of the inserts, so that a much wider circle of inserts with the coating can be provided according to the invention. In addition, it is possible to produce the components according to the invention with lower raw material waste. Furthermore, the components according to the invention allow a higher precision of the positioning of the inserts in the component. The component itself has a smoother surface, resulting not least in a lower material removal when using the components. Furthermore, lower dirt deposits can be achieved.

The components according to the invention open up novel design options, which for the most part feed from the simplified production method. This also makes better adhesion possible between insert and wrapping or coating, which in many cases even makes it possible to dispense with adhesion promoters.

The fully fluorinated plastic materials to be used according to the invention also show a lower cold flow than the conventionally used PTFE materials. Further, there is a higher dimensional stability, which is of particular importance in various applications, e.g. with valve balls.

Frequently even the replacement of PTFE compounds is successful, so that there are fewer restrictions in the application than is the case with PTFE compounds.

The fully fluorinated plastic materials used according to the invention show a reduced permeation to solvents, liquid acids or bases, resulting, for example, in a reduced leaching of ionic components. As a result, the layer thicknesses of the coating can be minimized in many cases. This is particularly advantageous if magnetic or magnetizable materials must be wrapped or coated as inserts or the inserts must be protected from corrosion.

Finally, the plastic materials used according to the invention enable so-called CIP (cleaning-in-place) and SIP (sterilization-in-place) -compatible complete solutions. Typical applications are mentioned below by way of example:

Encapsulated magnets for laboratory use and medical diagnostics (for example for the measurement of the gastrointestinal tract);

Connectors with molded contact pins;

Components of valves and fittings, for example coated metal balls for inlet and outlet valves, as well as closed shut-off elements of ball and plug valves;

Covered or coated metal rings for blow-out-proof seals.

On the one hand, the component according to the invention may contain the insert substantially surrounded on all sides by the polymer material. However, in some cases unobserved areas may remain uncovered, or specific functional parts of the insert may remain uncovered, such as e.g. the metallic plug contacts with connectors.

As a fully fluorinated thermoplastic material, preferably thermoplastically processable PTFE is used. A large number of such materials is described, for example, in WO 01/60911 and WO 03/078481.

In particular, TFE copolymers are suitable in which the co-monomer content is less than 3.5 mol%, since in this case the PTFE properties are largely retained and, nevertheless, thermoplastic processing is possible. More preferably, the comonomer content is limited to less than about 3 mole%, even more preferred are comonomer levels of less than about 1 mole%, for example, 0.5 mole% or less.

Preferred comonomers which on the one hand ensure good thermoplastic processability and on the other hand oppose the material properties PTFE are largely unchanged are hexafluoropropylene, perfluoroalkyl vinyl ether, PerfIuor- (2,2-dimethyl-l, 3-dioxole) and chlorotrifluoroethylene.

The fully fluorinated plastic materia I used according to the invention can also be used in the form of a polymer compound, the filler of the compound having a proportion of up to about 60% by weight.

As fillers can be selected depending on the specific purpose of the component a number of different materials.

Frequently, fillers in fiber form and / or in granular form are used.

Preferred fillers are selected from glass fibers, glass spheres, hard and soft carbon particles and fibers, graphite, conductivity carbon black, metal fibers, metal particles, in particular bronze particles and steel powder, quartz, Al ₂ O ₃ , CaF ₂ , mica, minerals, in particular BaSO ₄ and organic polymer materials in granular and fibrous form.

In addition, fillers made of organic polymer materials can be used. Preferred fillers of this type are preferably selected from polyimide, polyamide-imide, PPS, PEEK, PPSO ₂ , aromatic polyesters and aramid, or mixtures of two or more of these materials.

All of the aforementioned fillers can be used individually or in any desired mixture of two or more of the fillers.

In demanding applications, the proportions of the filler are preferably limited to about 25 wt% or less, more preferably 10 wt% or less.

In general, when using fibers as fillers, lower filler contents are preferred over the contents of granular fillers. For example, instead of about 25% by weight of granular coal, about 15% by weight of carbon fibers can be used.

Polymer blends of PTFE and one or more thermoplastically processable plastics are used in addition to the TFE copolymers as the fully fluorinated plastic material to be used according to the invention. These other plastics are selected in particular from the group of PTFE micropowders. These are PTFE types with low molecular weight and low melt viscosity compared to high molecular weight (standard) PTFE. They are typically prepared by either emulsion polymerization, by thermomechanical degradation of high molecular weight PTFE in the extruder, or by jet 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 (cf., S. Ebnesajjad, Fluoroplastics, Vol 1, Non-Melt Processible Fluoropolymers, Verlag William Andrew Publishing, 2000):

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

The insert is not necessarily integrally formed, although this is preferred, since it usually facilitates the handling of the insert in the manufacture of the component. The insert is preferably placed in an injection mold and then encapsulated with the fully fluorinated plastic material to be used according to the invention.

Metallic or ceramic inserts are particularly suitable for the components according to the invention.

The present invention further relates to a method for producing a component according to the invention as defined in more detail in claim 15.

The cavity of the mold is preferably formed so that it forms a receptacle for an insert, wherein the insert is introduced into the mold before the cavity of the mold is filled with the polymer material.

The filling of the cavity of the mold is preferably carried out by means of injection of the polymer material.

In order to ensure a defined position of the insert in the finished component according to the invention, the insert is preferably held in the mold by means of a holder at a distance from the surface of the mold.

Preferably used brackets comprise a plurality of retractable from the outside into the cavity of the mold retaining pins.

Preferably, the retaining pins hold the insert during filling in a predetermined position and are then removed from the cavity of the mold.

Particularly preferably, the retaining pins are removed during a so-called reprinting phase. At this time, the cavity of the mold is largely or substantially completely filled with the polymer material. terial filled and a change in the position of the insert in the subsequent steps of the manufacturing process is no longer to be feared. At this time, however, there is still over the reprinting polymer material that can be pressed into the cavity of the mold, on the one hand to compensate for the shrinkage occurring during the solidification of the polymer material and on the other hand to fill the resulting by the removal of the retaining pins free volumes , The time sequence of the steps is preferably selected so that the polymer material in the cavity of the mold when removing the retaining pins is still molten and so can fill the free volumes on the still filled by polymer material, thereby achieving a virtually seamless enclosure or coating of the insert is.

In addition to the retaining pins or alternatively, the cavity of the molding tool can be formed with one or more small-area supports for the insert.

Preferably, the insert is preheated prior to introduction thereof into the cavity of the mold to a predetermined temperature. With respect to the melting temperature of the polymer materials be filled a preheat temperature of preferably about 200 ⁰ C or more is selected.

The melt temperature of the polymer material fed into the cavity of the molding tool is preferably selected to be equal to or greater than the peak temperature in the DSC diagram, determined in the second reflow, preferably a temperature of about 330 ^° C. or higher.

In a preferred variant of the method according to the invention, it is provided that a predominant part of the polymer material is fed into the cavity at an injection pressure and that thereafter a further part of the polymer material is fed into the cavity at a pressure, wherein the injection pressure is selected higher than the reprint , In particular, a proportion of about 70 wt.% To about 90 wt.% Of the polymer material is filled with the injection pressure in the cavity of the mold.

More preferably, after filling the cavity with the polymer material, the mold is kept closed for a predetermined holding time.

This hold time is preferably in the range of about 5 seconds or more, more preferably about 10 seconds or more.

These and other advantages of the invention will be explained in more detail below with reference to the examples and drawings. They show in detail:

FIG. 1 shows a schematic representation of an extruder screw for use in the production of components according to the invention;

Figures 2a and 2b: an insert for an inventive component or a component with this insert; and

FIG. 2c shows an injection molding tool for producing the component of FIG. 2b.

Example 1:

Injection molding of thermoplastically processable PTFE

For the processing of the invention to be used fully fluorinated plastic materials by injection molding, the use of a special machine equipment is recommended.

As hydrofluoric acid can form during the processing of fluorothermoplasts, it is recommended that all parts in contact with the melt are designed to be corrosion resistant (eg from Hastelloy C4 or Inconel 625). In order to further ensure optimum processing of the fluorothermoplastics, it is recommended to use a screw 10 with a design of the screw geometry as shown, for example, in FIG. 1 and described below.

The screw 10 comprises 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 screw length approx. 20 D

Length of the intake zone approx. 10 to approx. 12 D

Length of the compression zone approx. 4 to approx. 5 D

Length of metering zone approx. 4 to approx. 5 D

Gradient a approx. 1 D

Bridge width b approx. 0.1 D

Channel depth of the feed zone c about 0.16 to about 0.18 D

Channel depth of metering zone d approx. 0.06 to approx. 0.07 D

Compression ratio about 2.5 to about 2.7

Example 2:

Production of a erfindungsqemäßen component with insert

In the following, the production of a component 20 according to the invention will be described with reference to FIGS. 2a and 2b. The component 20 has an insert 22 in the form of an insert, which is shown separately in FIG. 2a. The insert 22 is completely surrounded by an envelope or coating 24 which can be manufactured in a precisely predetermined wall thickness.

As insert 22, a magnetic pin is used in this example.

The magnetic pin 22 is positioned in an injection molding tool 30 (see Figure 2c). The fixation of the insert 22 in the cavity 32 of the Spritzgusswerk- 30 was carried out via two, arranged in the parting plane of the tool 30 retaining pins 34th

After closing the tool, this insert 22 is encapsulated with a fully fluorinated plastic material in a cavity 32 of the injection molding tool 30 and forms an essentially all-round covering or coating 24. The fully fluorinated plastic material used was a TFE copolymer with a comonomer content of 0.5 mol%. The comonomer was perfluoropropyl vinyl ether (PPVE).

The injection molding for the production of the components 20 was carried out on an Arburg Allrounder 420C-250 with the machine design described above in Example 1 (not shown).

When designing the tool 30, care was taken to ensure that the specified final dimensions were observed. The insert 22 should be pre-tempered (T about 200 ⁰ C or more), otherwise the melt of the polymer material on the surface of the insert 22 could solidify too quickly.

To close the injection molding tool 30, a small closing force is sufficient (about 0.4 t / cm ² or more), since on the one hand the thermoplastic polymer materials used according to the invention less due to their high viscosity tend to burr formation and on the other hand so additionally the parting plane of the tool 30th can act as a vent.

The mold temperature was about 230 ⁰ C or more.

Injection is with an injection pressure of about 1000 bar or less and a melt temperature of about 330 ⁰ C or higher. During the injection process, the thermoplastic polymer material flows around the insert 22 while it fills the cavity 32. At a level of about 80% was switched to a holding pressure of about 800 bar or less. After the cavity 32 was completely filled, the tool 30 remained for a time about 8 seconds or more in the closed state to give the polymer material 36 the possibility to cool to a dimensionally stable temperature level.

When opening the tool 30, the retaining pins 34 extend out of the cavity 32, then the component 20 is removed from the injection molding tool 30.

The cycle time for the complete process is about 35 seconds or more.

In a subsequent finishing step, the gate is removed. The recesses (not shown) of the retaining pins 34 may, depending on the application, remain without aftertreatment.

Alternatively, the retaining pins 34 can still be pulled out of the cavity 32 of the tool 30 in the holding pressure phase, so that the remaining free volumes still fill with polymer material.

From the above results as an advantage of the manufacturing method of the invention, the economy in the production of a solid composite by a single-stage Umspritzungsprozess an insert. An assembly of individual components is eliminated. The time required for the production is much lower compared to the previous production. The thermoplastically processable, fully fluorinated plastic material used for the examples furthermore has an even smaller flow of the refrigerant than modified PTFE.

Claims

claims 1. component with an insert and a part of the insert at least partially surrounding polymer material, wherein the polymer material comprises a thermoplastically processable substantially fully fluorinated plastic material. 2. Component according to claim 1, characterized in that the insert is surrounded substantially on all sides by the polymer material. 3. Component according to claim 1 or 2, characterized in that the thermoplastically processable plastic material is a thermoplastically processable PTFE material. 4. Component according to claim 3, characterized in that the thermoplastic PTFE material is a TFE copolymer, wherein the comonomer content is preferably 3.5 mol% or less, in particular less than 3 mol%, more preferably less than 1 mole%. 5. Component according to claim 4, characterized in that the comonomer is selected from hexafluoropropylene, perfluoroalkyl vinyl ether, perfluoro (2,2-dimethyl-l, 3-dioxole) and chlorotrifluoroethylene. 6. Component according to one of claims 1 to 5, characterized in that the polymer material is a polymer compound and comprises a filler in a proportion of up to about 60 wt.%. 7. Component according to claim 6, characterized in that the filler is in fiber form and / or granular form. 8. The component according to claim 7, characterized in that the filler comprises one or more components selected from glass fibers, glass beads, hard and soft carbon particles and fibers, graphite, Conductivity carbon black, metal fibers, metal particles, in particular bronze particles and steel powder, quartz, Al ₂ O ₃ , CaF ₂ , mica, minerals, in particular BaSO 4 and organic polymer materials in granular and fibrous form. 9. The component according to claim 8, characterized in that the organic polymer materials of the filler are selected from polyimide, polyamido, PPS, PEEK, PPSO ₂ , aromatic polyesters and aramid or mixtures of two or more of these materials. 10. Component according to one of claims 6 to 9, characterized in that the proportion of filler is about 25 wt.% Or less. 11. Component according to claim 10, characterized in that the proportion of filler is about 10 wt.% Or less. 12. Component according to one of claims 2 to 11, characterized in that the PTFE material is a polymer mixture comprising PTFE and a thermoplastically processable plastic. 13. Component according to one of claims 1 to 12, characterized in that the insert is a metallic or ceramic insert. 14. Component according to one of claims 1 to 13, characterized in that the insert part comprises a magnet or a magnetizable material. 15. A method for producing a component according to one of claims 1 to 14, comprising the steps Providing a mold with a cavity for at least partially receiving the insert; Inserting the insert into the mold; Heating the mold to a temperature of 230 ⁰ C or more; and Filling the mold with a polymer material, wherein the polymer material comprises a thermoplastically processable substantially fully fluorinated plastic material and surrounds the insert at least partially. 16. The method according to claim 15, characterized in that the insert is completely received in the cavity and that the polymer material surrounds the insert substantially completely after filling of the mold. 17. The method according to claim 15 or 16, characterized in that the filling takes place by means of injection of the polymer material into the cavity of the mold. 18. The method according to any one of claims 15 to 17, characterized in that the insert is held in the mold by means of a holder at a distance from the surface of the mold. 19. The method according to claim 18, characterized in that the holder comprises a plurality of insertable from the outside into the cavity of the mold retaining pins. 20. The method according to claim 19, characterized in that the retaining pins hold the insert during filling in a predetermined position and then removed from the cavity of the mold. 21. The method according to claim 20, characterized in that the retaining pins are removed during a Nachdruckphase from the cavity of the mold. 22. The method according to any one of claims 15 to 21, characterized in that the cavity of the mold is formed so that one or more small area supports are formed for the insert. 23. The method according to any one of claims 15 to 22, characterized in that the insert is preheated before the introduction of the same into the cavity of the mold to a predetermined temperature. 24. The method according to claim 23, characterized in that the pre-preheating temperature is about 200 ⁰ C or more. 25. The method according to any one of claims 15 to 24, characterized in that the polymer material is fed at a temperature of 330 ⁰ C or higher in the cavity of the mold. 26. The method according to any one of claims 15 to 25, characterized in that a predominant part of the polymer material is fed into the cavity at an injection pressure and that thereafter, a further portion of the polymer material is fed at a reprint in the cavity, wherein the injection pressure is selected higher is considered the reprint. 27. The method according to claim 26, characterized in that about 70 to about 90 wt.% Of the polymer material with the injection pressure in the cavity is fed. 28. The method according to any one of claims 15 to 27, characterized in that after filling the cavity with the polymer material, the mold is kept closed for a predetermined holding time. 29. The method according to claim 28, characterized in that the holding time is about 5 seconds or more, in particular about 10 seconds or more.