DE102007040893A1 - Production of plastic molded parts by forming - Google Patents

Abstract

A method is proposed for producing molded parts, in particular microformed parts. In this case, use is made of a counterpart piece that molds the die, wherein, when the punch is arranged in a predetermined end position, it defines with the counterpart a cavity whose shape essentially corresponds to the shape of the molded part to be produced. The method employs a room temperature amorphous or partially crystalline, partially or fully fluorinated thermoplastic polymer material and comprises the steps of: providing the die with the die transferred to a home position disengaged from the recess of the counterpart inserting the die Weight of the molded part corresponding amount of the polymer material in the solid state in the recess of the counterpart, - heating the polymer material to a temperature above its glass transition temperature, - applying pressure to the heated polymer material by transferring the stamp in the final position, wherein the polymer material is formed into the molded part cooling the polymer material to a temperature below the glass transition temperature, removing the stamp from the end position and removing the molded part from the press mold.

Description

The The present invention relates to a process for the preparation of Plastic moldings from a room temperature amorphous or partially crystalline partially or fully fluorinated thermoplastic polymer material using a die with a punch and a corresponding to the stamp counterpart with a recess for Receiving polymer material and the stamp, wherein the stamp and the corresponding counterpart in an arrangement of the punch define in a predetermined end position a cavity whose shape in Substantially corresponds to the shape of the molded part to be produced. The invention further relates to a manufactured according to such a method or manufacturable molding.

to Production of plastic moldings is quite a series of methods known from the prior art, in particular original molding method like injection molding or Reaction Injection Molding (RIM) and forming processes, in particular thermoforming process.

At the injection molding a polymer material is plasticized and placed in an injection mold injected. Shape and surface structure of the molded part to be produced by the cavity of the injection mold determines, in which the plasticized material is injected. Also small parts, also called microformed parts, with a weight of well below 1 g are easily produced by injection molding. However, the disadvantages are the possible ones Training of welds and the mandatory sprue, in particular in the Production of small molded parts a high percentage of waste generated. In addition, there are particular problems with processing high viscosity poly mers especially at high flow path wall thickness ratio. Above a certain molecular weight, many polymers are not at all by injection molding more workable.

Lots These disadvantages also occur in reaction injection molding. At least two components are mixed together and immediately subsequently injected as reaction mass in a shaping tool. Opposite thermoplastic Melting such reaction masses usually have a more favorable flow behavior on why can be achieved with the same wall thickness larger flow paths. For that, the Mold life may be slightly higher than the competing Injection molding.

Micro moldings have meanwhile, especially as components of so-called Microelectromechanical systems (MEMS) and microsystems technology (MST) gained considerable importance.

Known Thermoforming processes are in particular thermoforming and vacuum deep drawing processes. In these procedures are usually foils or thin plates processed. Other semi-finished products are used as starting materials in the Normally not applicable. As a result, usually only molded parts producible with almost homogeneous wall thickness.

The Object of the present invention is to provide a new process for the production of plastic moldings, this is the disadvantage of the methods known from the prior art does not have.

These Task is solved by the method having the features of claim 1.

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

Also a plastic molding according to claim 18 is the subject of the present invention. Preferred embodiments the plastic molding according to the invention can be found in the dependent claims 19 to 23.

Of the Wording of all claims is hereby incorporated by reference into the content of this specification.

One inventive method is particularly suitable for the production of moldings, in particular Microcomponents, with sections with significantly different wall thicknesses including very thin Areas which at least in a partial area has a thickness of approx. 500 μm or have less. In particular, the method according to the invention is suitable for the production of molded parts with complex geometry.

The inventive method allows in particular the production of substantially distortion-free Shaped parts, since within the cavity at best slight pressure differences to rule. This advantage is mainly compared to the molded parts produced by injection molding.

The inventive method further provides moldings having a substantially homogeneous morphology over the Molding cross section ready. This results in homogeneous usage properties.

Further the method according to the invention arises as a largely waste-free production process. This is special Importance of high-priced polymer materials, as a recycling of waste not always succeed without quality losses.

Special Significance comes to the method of the invention also because of a low residence time problem. This can also be thermally less stable polymeric materials, especially those with thermal sensitive fillers and the like, without much effort to process.

The thermo-oxidative stress of the polymer materials used can be Continue with an inert gas flush reduce the pressure forming tool.

The Processing temperatures for the polymer material used can lower in comparison with the methods described above chosen become. Furthermore, the method according to the invention has practically no knowledge Ventilation problems.

The inventive method goes beyond that relatively independent framing wall thickness flow path ratio.

Further can be thermoplastic with the inventive method Process polymer materials which have high molecular weights and with conventional Procedures are only unsatisfactory or not processable.

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 is fixed Polymer material introduced into the recess. The solid polymer material is introduced in an amount in the recess, the Weight of the molded part corresponds.

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

at the processing of semi-crystalline polymer material becomes this heated to a temperature above its glass transition temperature. The glass transition temperature is the temperature at which amorphous or semi-crystalline polymers from the hard-elastic or glassy state to the liquid or rubber-elastic one Pass over the area.

To Above this temperature is usually due to the decomposition temperature limited the polymer material used.

Farther it is preferred that the polymeric material is not melted heated becomes.

Therefore becomes substantially completely amorphous present polymer materials, the polymer material only to about the half its glass transition temperature (in ° C) to below the glass transition temperature heated.

The Polymer material is heated by being pressurized flowable thermoelastic Condition different, which differs from the molten state.

Of the Stamp is pressed into the recess until it reaches the specified End position reached in which he includes a cavity with the counterpart, the in shape and thus in volume corresponds to the molded part to be produced or just below its dimensions. At first The polymer is not adapted to the dimensions and shape of the cavity and is adapted to the shape of the cavity doing a usually very high pressure from.

Under The pressure of the punch is initiated a flow and the Polymer material is distributed substantially uniformly in the sequence Cavity. So there is a transformation under the influence of temperature and pressure. In the method according to the invention it is accordingly a special type of thermoforming process.

Especially preferred is the solid polymer material in the form of particles and / or introduced into the recess in the form of a preformed blank. Particularly preferred is the latter variant. As a preformed Blank can be used in particular a semi-finished, the in its dimensions the molded part already partially equivalent.

For example can Blanks are punched out of sheets or foils. Other blank types include rod-shaped, tubular or tubular semi-finished products Body.

Around the geometric change a molded part to detect in a forming process, for example the forming factor can be specified. Particularly preferred method 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%.

Prefers is in the inventive method the polymer material selected made of 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 Polymeric materials are briefly explained below:

PFA:

• Perfluoroalkyl vinyl ether modified PTFE polymer, wherein the co-monomer is PPVE (perfluoropropyl vinyl ether).

MFA:

• Perfluoroalkyl vinyl ether modified PTFE polymer, wherein the co-monomer is perfluoromethyl vinyl ether.

FEP:

• Fully fluorinated ethylene-propylene copolymer.

ETFE:

• ETFE copolymer.

ECTFE:

• Ethylene-chlorotrifluoroethylene copolymer.

PVDF

• Polyvinylidene fluoride.

PCTFE

• Poly-chlorotrifluoroethylene.

THV

• Tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer.

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

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

Such Materials have properties that are very similar to the conventional ones Standard PTFE are, however, such materials are melt processable and leave with great Use advantage in the present inventive method.

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 method according to the invention can Polymer materials are also used which are a polymer compound with a filler material comprise, the proportion of about 60 wt.% or less, based on the mass of polymer compounds.

The used filler material 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 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. The last-mentioned filling materials, namely the organic polymer materials in turn, are preferably selected from polyamide, polyamide-imide, PPS, PEEK, PPSO ₂ , aromatic polyesters and aramides and mixtures of two or more of these materials.

Prefers the proportion of the organic polymer material is limited to approx. 25% by weight or less, based on the mass of the polymer compound.

Further Preferably, this proportion is limited to about 20 wt.% or less.

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

As already mentioned above, In the case of semi-crystalline materials, the polymer material must be used for Forming according to the invention to a Temperature above the glass transition temperature heated the respective material become. Particularly preferred is a temperature of about 140 ° C or more, more preferably from about 160 ° C up to 400 ° C in the case of fully fluorinated polymer materials. When partially fluorinated becomes a temperature range of approx. 100 ° C up to 350 ° C prefers.

For essentially amorphous polymer materials, for example THV, becomes the Temperature are lower, preferably in the range of half the glass transition temperature (in ° C) below the glass transition temperature, this means for the Example of the polymer material THV about 55 ° C to about 140 ° C, wherein the choice of the glass transition temperature depends on the type of polymer used.

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 former, 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.

Especially Preferably, the polymer material used comprises as one component at least one polymer from the group with 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 because of 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 inventive method are both pure polymer materials processable and polymer materials, the one or more fillers exhibit. As fillers may be one in a method according to the invention usable polymer organic and / or inorganic, in particular also metallic, fillers exhibit.

These and other aspects and advantages of the invention will become apparent below closer to the drawing explained.

It show in detail:

1 a schematic representation for explaining the deformation factor;

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, the shows 1 a cuboid 12 which is intended to represent the molded 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, the cuboid 12 are identical in each case and correspond to the volume which was spatially displaced under pressure in a flow movement during the forming step according to the method according to the invention.

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

The 2 to 4 show in a schematic way the sequence of the method according to the invention with reference to a substantially disc-shaped component to be produced. First, a blank 20 manufactured 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 using a press tool 22 which is a stamp 24 and a corresponding counterpart 26 includes, reshaped.

The counterpart 26 has a recording 28 for the polymer material, in the present example in the form of the blank 20 , as well as the stamp 24 on. The recording 28 has a central peg-shaped projection 29 on top of the centering of the blank 20 in the recording 28 serves. At the same time the pin serves 29 the shaping. At the beginning of the process according to the invention is the stamp 24 in a starting position in which this engagement with the counterpart 26 is positioned. Such a situation is in 2 shown. The blank 20 will be in the recording 28 positioned. About the press mold 22 becomes the polymer material of the blank 20 heated to the polymer material itself dependent temperature (see discussion above), 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, leaving the stamp 24 into the recess 28 engages. The Stamp 24 is further acted upon by a force F (see situation illustrated in 3 ), due to which the now heated to the process temperature polymer material of the blank 20 begins to flow and extends in the radial direction up to the side walls of the recess 28 expands. Furthermore, the polymer material of the blank can 20 in a part of a recess 30 in the stamp 24 to flow Shen, forming an upstanding annular volume fraction.

The forming process is completed by, as in 4 shown, the stamp 24 of the press mold is transferred to its end position in which the punch 24 together with the counterpart 26 defines a cavity in shape and volume of the molded part to be produced 32 equivalent. The molded part shown schematically here 32 has an annular disk-shaped base body 34 as well as an integrally formed, upstanding collar 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 you can the inventive method combine with other forming processes, such as thermoforming, or also processes in which the polymer material is in a molten state is present. The inventive method is then preferred for the final one Forming used.

Claims (24)

Process for producing a plastic molding from an amorphous or partially crystalline room temperature at room temperature or fully fluorinated thermoplastic polymer material using a Press mold with a punch and a corresponding to the stamp counterpart with a recess for receiving polymer material and the stamp, wherein the punch and the corresponding counterpart in an arrangement define a cavity in a predetermined end position of the punch, whose shape is essentially the shape of the molded part to be produced corresponds, comprising the steps - Providing the press mold with the transferred to a starting position stamp in which this except Is engaged with the recess of the counterpart, - bring in a quantity corresponding to the weight of the molded part to be produced the polymer material in the solid state in the recess of the counterpart, - heating the Polymer material to a temperature above its glass transition temperature, - Apply of the heated Polymer material with pressure by transferring the stamp to the final position, wherein the polymer material is formed into the molded part, - cooling the Polymer material to a temperature below the glass transition temperature, - Remove of the stamp from the final position and removal of the produced Molded part from the press mold. Method according to claim 1, characterized in that the polymer material is in the form of a preformed blank (semifinished product) is introduced into the recess. Method according to claim 1 or 2, characterized that the deformation of the blank to the molding with a deformation factor of the material volume involved in the process of about 20% or more he follows. Method according to claim 1 or 2, characterized that the polymer material in the form of particles in the recess is introduced. Method according to claim 4, characterized in that that the polymer material is selected is made of PTFE, modified PTFE, PFA, MFA FEP, ETFE, ECTFE, PVDF, PCTFE, THF and mixtures of two or more of these polymers. Method according to claim 5, characterized in that in that the polymeric material is at least one substantially fully fluorinated one Polymer includes. Method according to Claim 6, characterized that the substantially fully fluorinated polymer is a TFE copolymer is, its co-monomer content about 3.5 mol% or less, preferably about 3 mol% or less, in particular about 1 mol% or less. Method according to claim 7, characterized in that that the co-monomer is selected is hexafluoropropylene, perfluoroalkyl vinyl ether, perfluoro (2,2-dimethyl-1,3-dioxole) and chlorotrifluoroethylene. Method according to one of claims 1 to 8, characterized in that the polymer material comprises a polymer compound with a filler material, its proportion is about 60% by weight or less, based on the mass of the Polymer compounds. Method according to claim 9, characterized that the filler material a filler in fibrous form and / or in granular form. A 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 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. A method according to claim 11, characterized in that the organic Polymermateria The materials of the filler material selected from polyamide, polyamide-imide, PPS, PEEK, PPSO ₂ , aromatic polyesters and aramids and mixtures of two or more of these materials. Method according to claim 12, characterized in that that the proportion of the organic polymer material about 25 wt.% Or less, based on the mass of the polymer compound. Method according to claim 13, characterized in that that the proportion is about 10% by weight or less. Method according to one of claims 1 to 14, characterized that the polymer material is a mixture of a thermoplastic PTFE and another thermoplastic polymer. Method according to one of the preceding claims, characterized characterized in that partially crystalline polymer material in the case of fully fluorinated materials to a temperature of about 140 ° C or more, in particular of about 160 ° C up to 400 ° C, and in the case of partially fluorinated materials to a temperature in the range of approx. 100 ° C up to 350 ° C heated becomes. Method according to one of claims 1 to 15, characterized that amorphous polymer material to a temperature in the range of half the glass transition temperature (in ° C) to below the glass transition temperature heated becomes. Method according to one of the preceding claims, characterized characterized in that the polymer material with an induction heating is heated. Plastic molding, manufactured or manufactured according to a method according to any one of the preceding claims. Plastic molding according to claim 19, characterized that the plastic molding at least in a partial area a Thickness of approx. 500 μm or less. Plastic molding according to claim 19 or 20, characterized characterized in that it is substantially rotationally symmetrical, in particular ring-shaped or disk-shaped, is trained. Plastic molding according to one of claims 19 to 21, characterized by a varying thickness along a cross section. Plastic molding according to one of claims 20 to 22, characterized in that the ratio between its maximum spatial Expansion and the thickness in the partial area about 10 or more, preferably about 50 to about 200, is. Plastic molding according to one of claims 19 to 23, characterized in that it is free of a sprue and / or weld lines is.