WO2009027019A1 - Production of plastic molded parts by forming - Google Patents

Abstract

A method for producing molded parts (32), particularly micro-molded parts, is proposed. In the process, a press molding tool (22) having a die (24) and a counter-piece (26) corresponding to the die is used, wherein in an arrangement of the die in a predefined final position said die together with the counter-piece defines a cavity (28), the shape of which substantially corresponds to the shape of the molded part to be produced. The method uses a partially or fully fluorinated thermoplastic polymer material, which at room temperature is amorphous or semi-crystalline.

Description

 Production of plastic molded parts by forming

The present invention relates to a process for the production of plastic moldings from a room temperature amorphous or partially crystalline partially or fully fluorinated thermoplastic polymer material using a press mold with a punch and a counterpart corresponding to the stamp with a recess for receiving polymer material and the stamp, wherein the Stamp and the corresponding counterpart in an arrangement of the punch in a predetermined end position define a cavity whose shape corresponds substantially to the shape of the molded part to be produced. The invention further relates to a molded part produced or producible according to such a method.

For the production of molded parts from plastics, a whole series of processes are known from the prior art, in particular primary molding processes such as injection molding or reaction injection molding (RIM) and forming processes, in particular thermoforming processes.

In injection molding, a polymer material is plasticized and injected into an injection mold. The shape and surface structure of the molded part to be produced are determined by the cavity of the injection mold into which the plasticized material is injected. Even small parts, also called microform parts, with a weight of well below 1 g can be easily produced by injection molding. A disadvantage, however, the possible formation of weld lines and the mandatory sprue, which produces a percentage of waste, especially in the production of small moldings percentage. In addition, in particular problems occur in the processing of polymers with high viscosity, especially at high flow path wall thickness ratio. Above a certain molecular weight, many polymers are no longer processable by injection molding. Many of these disadvantages also occur in reaction injection molding. In this case, at least two components are mixed together and immediately injected as a reaction mass into a molding tool. Compared with thermoplastic melts, such reaction masses generally have a more favorable flow behavior, which is why larger flow paths can be achieved with the same wall thickness. For this, the mold life may be slightly higher than in the competitive injection molding.

In the meantime, microformed parts have gained considerable importance, in particular as components of so-called microelectromechanical systems (MEMS) and microsystem technology (MST).

Known thermoforming processes are, in particular, thermoforming and vacuum deep drawing processes. In these processes, films or thin plates are usually processed. Other semi-finished products are usually not usable as starting materials. As a result, usually only molded parts with almost homogeneous wall thickness can be produced.

The object of the present invention is to provide a new process for the production of molded plastic parts, which does not have the disadvantages of the known from the prior art method.

This object is achieved by the method having the features of claim 1.

Preferred embodiments of the method according to the invention are defined in the dependent claims 2 to 17.

Also, a plastic molding according to claim 18 is the subject of the present invention. Preferred embodiments of the plastic molding according to the invention can be found in the dependent claims 19 to 23. The wording of all claims is hereby incorporated by reference into the content of this specification.

An inventive method is particularly suitable for the production of moldings, in particular micro-components, with sub-areas with significantly different wall thicknesses, including very thin-walled areas which have a thickness of about 500 microns or less at least in a partial area. In particular, the inventive method is suitable for the production of molded parts with complex geometry.

In particular, the method according to the invention allows the production of essentially distortion-free molded parts, since at most slight pressure differences prevail within the cavity. This advantage is above all compared with the molded parts produced by extrusion molding.

The method according to the invention further provides molded parts with a substantially homogeneous morphology over the molded part cross-section. This results in homogeneous usage properties.

Furthermore, the process of the invention presents itself as a largely waste-free production process. This is of particular importance in the case of high-priced polymer materials, since waste recycling does not always succeed without sacrificing quality.

Special importance is given to the method according to the invention also because of a small residence time problem. This also thermally less stable polymer materials, especially those with thermally sensitive fillers and the like, can be processed without much effort.

The thermo-oxidative stress of the polymer materials used can be further reduced by an inert gas purging of the press-forming tool. The processing temperatures for the polymer material used can be set lower in comparison with the methods described above. Furthermore, the method according to the invention has virtually no venting problem.

Moreover, the method according to the invention can be designed relatively independently of the wall thickness / flow path ratio.

Furthermore, the process according to the invention can be used to process thermoplastic polymer materials which have high molar masses and are unsatisfactory or can not be processed at all using conventional processes.

The polymer materials may well have molecular weights that reach up to about 10 ⁸ g / mol.

In a first step of a method according to the invention, solid polymer material is introduced into the recess. The solid polymer material is introduced into the recess in an amount corresponding to the weight of the molded part to be produced.

In a further step, the polymer material is heated until it reaches a thermoelastic state.

In the processing of semi-crystalline polymer material, this is heated to a temperature above its glass transition temperature. The glass transition temperature is the temperature at which amorphous or partially crystalline polymers transition from the hard-elastic or glassy state into the liquid or rubber-elastic region.

At the top, this temperature is usually limited by the decomposition temperature of the polymer material used in each case. Furthermore, it is preferred that the polymer material is not heated to the melt.

Therefore, with substantially completely amorphous polymeric materials, the polymeric material is heated to below about half of its glass transition temperature (at ⁰ C) below the glass transition temperature.

The polymer material is added by the heating in a pressurizable flowable thermoelastic state, which differs from the molten state.

The punch is pressed into the recess until it reaches the predetermined end position, in which it encloses a cavity with the counterpart, which corresponds in shape and thus also in volume to the molded part to be produced or whose dimensions fall just short of its dimensions. On the initially not yet adapted to the dimensions and shape of the cavity polymer material, the punch exerts a usually very high pressure from.

Under the pressure of the stamp, a flow is initiated and the polymer material is distributed in the sequence substantially uniformly in the cavity. So there is a transformation under the influence of temperature and pressure. Accordingly, the method according to the invention is a special type of thermoforming process.

Particularly preferably, the solid polymer material is introduced into the recess in the form of particles and / or in the form of a preformed blank. Particularly preferred is the latter variant. As a preformed blank, in particular a semifinished product can be used which already partially corresponds in its dimensions to the molded part to be produced.

For example, blanks can be punched out of sheets or films. Other blank types include bodies derived from rod, tube or tubular semi-finished products. To capture the geometric change of a molded part in a forming process, for example, the forming factor can be specified. Particularly preferred methods have a forming factor of 20% of the molded part volume or more. The deformation factor is preferably not more than 70%, in particular not more than 50%.

In the method according to the invention, the polymer material is preferably selected from PTFE, modified PTFE, PFA, MFA, FEP, ETFE, ECTFE, PVDF, PCTFE, THF and mixtures of two or more of these polymers.

The less common abbreviations of the polymer materials are briefly explained below:

PFA:

Perfluoroalkyl vinyl ether modified PTFE polymer, wherein the co-monomer

PPVE (perfluoropropyl vinyl ether).

MFA:

Perfluoroalkyl vinyl ether modified PTFE polymer, wherein the co-monomer

Perfluoromethyl vinyl ether.

FEP:

Fully fluorinated ethylene-propylene copolymer.

ETFE: ethylene-tetrafluoroethylene copolymer.

ECTFE: ethylene-chlorotrifluoroethylene copolymer.

PVDF: polyvinylidene fluoride. Poly-chlorotrifluoroethylene.

THV: tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer.

The process according to the invention particularly preferably uses polymer material which comprises a substantially fully fluorinated polymer.

Such substantially fully fluorinated polymers are preferably a TFE copolymer whose co-monomer content is about 3.5 mol% or less, preferably 3 mol% or less, in particular about 1 mol% or less.

Such materials have properties that are very similar to conventional standard PTFE, but such materials are melt-processable and can be used to great advantage in the present inventive process.

Preferred co-monomers for the aforementioned TFE copolymers are selected from hexafluoropropylene, perfluoroalkyl vinyl ether, perfluoro (2,2-dimethyl-1,3-dioxole) and chlorotrifluoroethylene.

In the process according to the invention, it is also possible to use polymer materials which comprise a polymer compound with a filler material whose proportion is about 60% by weight or less, based on the mass of the polymer compound.

The filler material used in the polymer compounds preferably has a filler in fiber form and / or in granular form.

Preferably, the filler material comprises one or more components selected from glass fibers, glass spheres, hard and soft carbon. leparticles 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, in particular BaSO ₄ and organic polymer materials. The last-mentioned filling materials, namely the organic polymer materials in turn, are preferably selected from polyamide, polyamide, PPS, PEEK, PPSO ₂ , aromatic polyesters and aramids and mixtures of two or more of these materials.

Preferably, the proportion of the organic polymer material is limited to about 25 wt.% Or less, based on the mass of the polymer compound.

More preferably, this proportion is limited to about 20 wt.% Or less.

Particularly preferred polymeric materials include a blend of a thermoplastic PTFE and another thermoplastic polymer.

As already mentioned above, in the case of partially crystalline materials for forming, the polymer material must, according to the invention, be heated to a temperature above the glass transition temperature of the respective material. Particularly preferred is a temperature of about 140 ⁰ C or more, more preferably from about 160 ⁰ C to about 400 ⁰ C in fully fluorinated polymeric materials selected. In partially fluorinated, a temperature range of about 100 ⁰ C to about 350 ⁰ C is preferred.

For substantially amorphous polymer materials, for example THV, the temperature will be lower, preferably in the range of half the glass transition temperature (in ⁰ C) to below the glass transition temperature, that is for the example of the polymer material THV about 55 ⁰ C bis about 140 ⁰ C, wherein the choice of the glass transition temperature of the type of polymer used in each case depends.

The heating of the polymer material is particularly preferably carried out by means of an induction or microwave heating. In particular, by means of the first A polymer material can be brought to very high temperatures within a few seconds. The use of an induction heater thus enables a high throughput. The heating can be direct or indirect, depending on the electrical conductivity of the polymer material used.

More preferably, the polymer material used comprises as one component at least one polymer selected from the group consisting of polyethylene (PE), ultra-high molecular weight polyethylene (UHMWPE), polypropylene (PP), polyoxymethylene (POM), polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), and polyetheretherketone (PEEK).

Surprisingly, it has been found that, in particular, polymer materials which can no longer be processed by conventional processes due to their high viscosity or their infusibility can also be processed by a process according to the invention. Especially such materials are often very interesting as materials, for example because of their high resistance to chemicals. In preferred embodiments, polymer materials with average molecular weights of up to 10 ⁸ g / mol are processed according to the invention.

According to the method of the invention, both pure polymer materials can be processed and polymer materials which have one or more fillers. As fillers, a polymer which can be used in a process according to the invention can comprise organic and / or inorganic, in particular also metallic, fillers.

These and other aspects and advantages of the invention are explained in more detail below with reference to the drawing. They show in detail:

Fig. 1 is a schematic representation for explaining the

Umformfaktors;

Fig. 2 to 4 in a schematic representation of the sequence of individual steps of the method according to the invention.

1 shows a cuboid 10, which is intended to represent the geometry of a blank which is to be processed by the method according to the invention.

Furthermore, FIG. 1 shows a cuboid 12 which is intended to represent the shaped part as a result of the method according to the invention schematically.

The two cuboids 10 and 12 are identical in volume. The dimensions in height and width differ. The difference volumes .DELTA.V illustrated on the one hand in the cuboid 10, on the other hand in the cuboid 12, are identical in each case and correspond to the volume which was displaced spatially during the forming step according to the inventive method under pressure in a flow movement.

The deformation factor is defined by the ratio of ΔV to the volume of the cuboid 10 or of the identical volume of the cuboid 12.

FIGS. 2 to 4 show in a schematic way the sequence of the method according to the invention with reference to a substantially disk-shaped component to be produced. First, a blank 20 is produced in a conventional manner in the form of a precisely annular disk-shaped component. The production of such blanks, whether by extrusion, sintering or another method, is widely known in the art, so that will not be discussed in detail. In the case of this example, the blank can be punched out of a plate-shaped semi-finished product. This blank 20 is then reshaped by means of a die 22 comprising a punch 24 and a corresponding counterpart 26.

The counterpart 26 has a receptacle 28 for the polymer material, in the present example in the form of the blank 20, as well as the punch 24. The receptacle 28 has centrally a pin-shaped projection 29 which serves to center the blank 20 in the receptacle 28. At the same time the pin 29 is the shaping. At the beginning of the method according to the invention, the punch 24 is in an initial position in which this engagement with the counterpart 26 is positioned. Such a situation is shown in FIG. The blank 20 is positioned in the receptacle 28. The polymer material of the blank 20 is heated via the press-forming tool 22 to the temperature dependent on the polymer material itself (cf the above discussion), in which the polymer material is in the thermoelastic state. The heating is preferably done by means of an inductive heating device (not shown).

The tool 22 is closed, so that the punch 24 engages in the recess 28. The punch 24 is further acted upon by a force F (compare situation shown in Fig. 3), due to which the now heated to the process temperature polymer material of the blank 20 begins to flow and in the radial direction to the side walls of the recess 28 expands. Furthermore, the polymer material of the blank 20 is able to flow into a part of a recess 30 in the punch 24, forming an upwardly projecting annular volume fraction.

The forming process is completed by, as shown in Fig. 4, the punch 24 of the die is transferred to its final position in which the die 24 defines together with the counterpart 26, a cavity corresponding in shape and volume of the molded part 32 to be produced. The molding 32 shown schematically here has an annular disc-shaped base body 34 and an integrally formed thereon, upstanding Covenant 36 on. The resulting workpiece has no voids, weld lines or other undesirable features and can be fed substantially readily to its destination.

Of course, the inventive method can be combined with other molding processes, such as deep drawing, or even processes in which the polymer material is in a molten state. The method according to the invention is then preferably used for the final shaping.

Claims

claims Anspruch [en] A method for producing a plastic molding from a partially or fully fluorinated thermoplastic polymer material which is amorphous or partially crystalline at room temperature using a press mold with a punch and a counterpart corresponding to the punch with a recess for receiving polymer material and the punch, wherein the punch and the Corresponding counterpart in an arrangement of the stamp in a predetermined end position define a cavity whose shape substantially corresponds to the shape of the molded part to be produced, comprising the steps Providing the press-forming tool with the stamp transferred to a starting position in which it is positioned out of engagement with the recess of the counterpart, Introducing a quantity of the polymer material corresponding to the weight of the molded part in the solid state into the recess of the counterpart, Heating the polymer material to a temperature above its glass transition temperature, Pressurizing the heated polymer material by transferring the stamp to the final position, the polymer material being shaped into the shaped article, Cooling the polymer material to a temperature below the glass transition temperature, - Removing the stamp from the final position and removal of the molded part produced from the press mold. 2. The method according to claim 1, characterized in that the polymer material in the form of a preformed blank (semi-finished product) is introduced into the recess. 3. The method according to claim 1 or 2, characterized in that the deformation of the blank to the molding takes place with a deformation factor of the material volume involved in the process of about 20% or more. 4. The method according to claim 1 or 2, characterized in that the polymer material is introduced in the form of particles in the recess. 5. The method according to claim 4, characterized in that the polymer material is selected from PTFE, modified PTFE, PFA, MFA FEP, ETFE, ECTFE, PVDF, PCTFE, THF and mixtures of two or more of these polymers. 6. The method according to claim 5, characterized in that the polymer material comprises at least one substantially fully fluorinated polymer. 7. The method according to claim 6, characterized in that the substantially fully fluorinated polymer is a TFE copolymer whose co-monomer content is about 3.5 mol% or less, preferably about 3 mol% or less, in particular about 1 mole% or less. 8. The method according to claim 7, characterized in that the co-monomer is selected from hexafluoropropylene, perfluoroalkyl vinyl ether, perfluoro (2,2-dimethyl-l, 3-dioxole) and chlorotrifluoroethylene. 9. The method according to any one of claims 1 to 8, characterized in that the polymer material comprises a polymer compound with a filler material, the proportion of about 60 wt.% Or less, based on the mass of the polymer compound. 10. The method according to claim 9, characterized in that the filler material comprises a filler in fiber form and / or in granular form. 11. The method according to claim 10, characterized in that the filler material comprises one or more components selected from glass fibers, glass beads, hard and soft carbon particles and fibers, graphite, conductivity soot, 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. 12. The method according to claim 11, characterized in that the organic polymer materials of the filler material are selected from polyamide, polyamide-imide, PPS, PEEK, PPSO ₂ , aromatic polyesters and aramids and mixtures of two or more of these materials. 13. The method according to claim 12, characterized in that the proportion of the organic polymer material is about 25 wt.% Or less, based on the mass of the polymer compound. 14. The method according to claim 13, characterized in that the proportion is about 10 wt.% Or less. 15. The method according to any one of claims 1 to 14, characterized in that the polymer material comprises a mixture of a thermoplastic PTFE and another thermoplastic polymer. 16. The method according to any one of the preceding claims, characterized in that partially crystalline polymer material in the case of fully fluorinated materials to a temperature of about 140 ⁰ C or more, in particular from about 160 ⁰ C to about 400 ⁰ C, and in the case of partially fluorinated materials to a temperature in the range of about 100 ⁰ C to about 350 ⁰ C is heated. 17. The method according to any one of claims 1 to 15, characterized in that amorphous polymer material to a temperature in the range of Half the glass transition temperature (in ⁰ C) is heated to below the glass transition temperature. 18. The method according to any one of the preceding claims, characterized in that the polymer material is heated with an induction heater. 19. Plastic molded part, produced or producible by a method according to one of the preceding claims. 20. Plastic molding according to claim 19, characterized in that the plastic molding has a thickness of about 500 microns or less at least in a partial area. 21. Plastic molded part according to claim 19 or 20, characterized in that it is essentially rotationally symmetrical, in particular ring-shaped or disk-shaped. 22. Plastic molding according to one of claims 19 to 21, characterized by a varying thickness along a cross section. 23. Plastic molding according to one of claims 20 to 22, characterized in that the ratio between its maximum spatial extent and the thickness in the subregion about 10 or more, preferably about 50 to about 200, is. 24. Plastic molding according to one of claims 19 to 23, characterized in that it is free of a sprue and / or weave seams.