DE102007040096B4 - Component and method of manufacture - Google Patents

Abstract

Component comprising an insert and a polymer material surrounding the insert partially or on all sides, the polymer material comprising a fully fluorinated TFE copolymer having a non-zero melt flow index according to ASTM Test D1238-88, whose co-monomer content is less than 1 mol%, and wherein the co-monomer is selected from hexafluoropropylene, perfluoroalkyl vinyl ether and perfluoro (2,2-dimethyl-1,3-dioxole).

Description

The invention relates to a component having an insert part and a polymer material at least partially surrounding the insert, and a method for its production.

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 required 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 part has to be embedded in the powdery PTFE raw material, exact centering is not possible due to the inhomogeneous bulk density. 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 DE 32 36 793 A1 describes a method for producing a metal screw at least partially coated with plastic on the shaft, wherein a fluoropolymer can be used as plastic.

The US 3,243,321 describes a method for coating metal surfaces with PTFE, wherein the PTFE is applied as an aqueous dispersion, dried and then sintered.

The US 3,511,690 also describes coatings for metallic substrates based on PTFE.

The DE 25 14 000 A1 describes a method for producing a fluorothermoplastic body bonded to a surface of a PTFE layer.

The EP 1 555 110 A1 describes a method for enhancing the adhesion of a thermoplastic fluoroelastomer to a substrate.

The WO 03/078481 A1 describes melt processable PTFE polymers.

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 surrounding the insert partially or on all sides preferably forms an envelope or coating.

Thermoplastic processable plastic materials are understood as meaning materials having a non-zero melt flow index (MFI) (ASTM Test D1238-88 at 372 ° C and a load of 5 kg with a maximum extrudate collection time of 1 hour).

The thermoplastically processable, 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 between the insert and wrapping or coating possible, which in many cases even waives adhesion promoter.

The fully fluorinated plastic materials to be used according to the invention also show a lower cold flow than the conventionally used PTFE materials. Furthermore, a higher dimensional stability, which is of particular importance in various applications, such as. B. in 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. In some cases, however, areas not included in tasks may remain uncovered or specific functional parts of the insert may remain uncovered, such as, for example, As the metallic plug contacts with connectors.

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

According to the invention, the TFE copolymers have a comonomer content of less than 1 mol%, since in this case the PTFE properties are largely retained and still a thermoplastic processing is possible. Even more preferred are comonomer levels of 0.5 mole% or less.

Comonomers used according to the invention, on the one hand ensure good thermoplastic processability and on the other hand, the material properties are largely unchanged from PTFE are hexafluoropropylene, perfluoroalkyl vinyl ether and perfluoro (2,2-dimethyl-1,3-dioxole).

The fully fluorinated plastic material used according to the invention can also be used in the form of a polymer compound, wherein the filler of the compound has a proportion of up to about 60 wt .-%.

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 beads, hard and soft carbon particles and fibers, graphite, conductivity carbon black, metal fibers, metal particles, especially bronze particles and steel powder, quartz, Al ₂ O ₃ , CaF ₂ , mica, minerals, especially 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% by weight or less, more preferably 10% by weight 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 wt .-% granular coal about 15 wt .-% carbon fibers are used.

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 11.

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, 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 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 regard to the melting temperature of the polymer materials to be filled, a preheating temperature of preferably about 200 ° C. or more is selected.

The melt temperature of the polymer material fed into the cavity of the molding tool is preferably chosen 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:

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

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

2c : an injection mold for the production of the component of 2 B ,

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 can arise in the processing of fluorinated thermoplastics hydrogen fluoride, it is recommended that all with the melt parts in contact corrosion resistant interpreted (for. Example, from Hastelloy ^® C4 or Inconel ^® 625).

In order to further ensure optimal processing of the fluorothermoplastics, the use of a screw is recommended 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

Example 2:

Production of a component according to the invention with insert

The following is based on the 2a and 2 B the production of a component according to the invention 20 described. The component 20 has an insert 22 in the form of an insert on the separately in 2a is shown. The insert 22 is completely from a cladding or coating 24 surrounded, which can be manufactured in a precisely predetermined wall thickness.

As an insert 22 In this example, a magnetic pen is used.

The magnetic pin 22 is in an injection mold 30 (see. 2c ). The fixation of the insert 22 in the cavity 32 of the injection mold 30 took place over two, in the parting plane of the tool 30 arranged holding pins 34 ,

After closing the tool, this insert becomes 22 with a fully fluorinated plastic material in a cavity 32 of the injection mold 30 overmolded and forms a substantially all-round wrapping or coating 24 out. The fully fluorinated plastic material used was a TFE copolymer having a comonomer content of 0.5 mol%. The comonomer was perfluoropropyl vinyl ether (PPVE).

Injection molding for the production of components 20 took place 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 ° C or more), otherwise the melt of the polymer material on the surface of the insert 22 could freeze too fast.

To close the injection mold 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 are less prone to burr formation due to their high viscosity and on the other hand so additionally the parting plane of the tool 30 can act as a vent.

The mold temperature was about 230 ° C or more.

Injection is carried out with an injection pressure of about 1000 bar or less and a melt temperature of about 330 ° C or higher. During the injection process, the thermoplastic polymer material flows around the insert 22 while it's the cavity 32 fills. 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 remained 30 a certain time about 8 sec or more in the closed state around the polymer material 36 to give the possibility to cool to a dimensionally stable temperature level.

When opening the tool 30 drive the retaining pins 34 from the cavity 32 out, then the component 20 the injection mold 30 taken.

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 can remain without aftertreatment, depending on the application.

Alternatively, the retaining pins 34 still in the pressure phase from the cavity 32 of the tool 30 be pulled out 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 lower cold flow than modified PTFE.

Claims (25)

Component comprising an insert and a polymer material surrounding the insert partially or on all sides, the polymer material comprising a fully fluorinated TFE copolymer having a non-zero melt flow index according to ASTM Test D1238-88, whose co-monomer content is less than 1 mol%, and wherein the co-monomer is selected from hexafluoropropylene, perfluoroalkyl vinyl ether and perfluoro (2,2-dimethyl-1,3-dioxole). Component according to claim 1, characterized in that the insert is surrounded on all sides by the polymer material. Component according to claim 1 or 2, characterized in that the polymer material is a polymer compound and comprises a filler in a proportion of up to 60 wt .-%. Component according to claim 3, characterized in that the filler is in fiber form and / or granular form. Component according to Claim 4, characterized in that the filler comprises one or more components selected from glass fibers, glass beads, hard and soft carbon particles and fibers, graphite, conductive carbon black, metal fibers, metal particles, in particular bronze particles and steel powder, quartz, Al ₂ O ₃ , CaF ₂ , mica, minerals, especially BaSO4 and organic polymeric materials in granular and fibrous form. Component according to claim 5, characterized in that the organic polymer materials of the filler are selected from polyimide, polyamide-imide, PPS, PEEK, PPSO ₂ , aromatic polyesters and aramid or mixtures of two or more of these materials. Component according to one of claims 3 to 6, characterized in that the proportion of filler is 25 wt .-% or less. Component according to claim 7, characterized in that the proportion of filler is 10 wt .-% or less. Component according to one of claims 1 to 8, characterized in that the insert is a metallic or ceramic insert. Component according to one of claims 1 to 9, characterized in that the insert part comprises a magnet or a magnetizable material. A method of manufacturing a component according to any one of claims 1 to 10, 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 ° C or more; and Filling the mold with a polymeric material, the polymeric material comprising a fully fluorinated TFE copolymer having a non-zero melt flow index according to ASTM Test D1238-88, the co-monomer content of which is less than 1 mole%, wherein the co-monomer is selected from Hexafluoropropylene, perfluoroalkyl vinyl ether and perfluoro (2,2-dimethyl-1,3-dioxole), and wherein the polymer material surrounds the insert partially or all sides. A method according to claim 11, characterized in that the insert is completely received in the cavity and that the polymer material completely surrounds the insert after filling of the mold. A method according to claim 11 or 12, characterized in that the filling takes place by means of injection of the polymer material into the cavity of the mold. Method according to one of claims 11 to 13, characterized in that the insert is held in the mold by means of a holder at a distance from the surface of the mold. A method according to claim 14, characterized in that the holder comprises a plurality of externally insertable into the cavity of the mold retaining pins. A method according to claim 15, characterized in that the holding pins hold the insert during filling in a predetermined position and are then removed from the cavity of the mold. A method according to claim 16, characterized in that the retaining pins are removed during a Nachdruckphase from the cavity of the mold. Method according to one of claims 11 to 17, characterized in that the cavity of the mold is formed so that one or more small area supports are formed for the insert. Method according to one of claims 11 to 18, characterized in that the insert is preheated before introducing it into the cavity of the mold to a predetermined temperature. A method according to claim 19, characterized in that the predetermined preheating temperature is 200 ° C or more. Method according to one of claims 11 to 20, characterized in that the polymer material is fed at a temperature of 330 ° C or higher in the cavity of the mold. Method according to one of claims 11 to 21, characterized in 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 with a reprint in the cavity, wherein the injection pressure is selected to be higher than the reprint. A method according to claim 22, characterized in that 70 to 90 wt .-% of the polymer material is fed with the injection pressure in the cavity. Method according to one of claims 11 to 23, characterized in that after filling the cavity with the polymer material, the mold is kept closed for a predetermined holding time. A method according to claim 24, characterized in that the holding time is 5 seconds or more, in particular 10 seconds or more.

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