DE9421278U1 - Plastic parts with electrically conductive structures - Google Patents

Description

PolyID AG
Burggrabenweg 2
CH-8266 Steckborn
Switzerland

Representative:

Kohler Schmid + Partner
Patent attorneys
Ruppmannstrasse 27
D-70565 Stuttgart

Plastic parts with electrically conductive structures

The invention relates to a molded part made from a starting material with very low or negligible electrical conductivity, in particular plastic and/or polymer, which is initially present in a low-viscosity phase in which magnetic particles with significantly higher electrical conductivity are added to the starting material and dispersed therein, a magnetic field being applied to align the particles, and the starting material is then solidified.

Such a molded part is known, for example, from DE 36 41 828 Al.

Here, a prepreg is produced with aligned, metallized short fibers. The short fibers are aligned using a magnetic field according to the force line of the workpiece and then impregnated with a plastic. However, such a process only allows the fibers to be aligned in terms of their orientation to one another. The possibility of concentrating the fibers in certain areas of a part is not possible with this process.

Such a process is described in DE-OS 20 48 358. In this process, a concentration of metal fibers in the outer wall area is achieved by spinning for the production of metal fiber-reinforced ceramic tubes. A mixture of ceramic particles and metal fibers dispersed in water is introduced into the interior of a cylindrical spinning mold. During the spinning movement, the metal fibers are deposited on the outside of the wall of the spinning mold due to their higher density compared to the ceramic particles. A tube is created in whose outermost layer metal fibers are concentrated. However, this process does not allow any targeted influence on the fiber distribution. Furthermore, only rotationally symmetrical molded parts can be produced in this way. The application of this process to plastics is associated with a high level of effort, since the high viscosity and rapid solidification of the material means that the process has to take place in a very short time and at high rotation speeds.

A process that is better suited to the plastics sector is described in DE 32 3 8 090 A1. According to this process, molded parts whose outer skin is to be provided with a shield against electrical or magnetic fields are produced using two different layers. In the first step, the layer filled with electrically conductive material is injected into the mold. Immediately afterwards, further plastic is injected into the mold, whereby the electrically conductive plastic layer injected first comes to rest on the outer wall of the molded part. The various plastics can also be injected in the reverse order. However, this process also has the disadvantage that the distribution of the electrically conductive material in the molded body cannot be specifically influenced. In addition, two different materials have to be processed, which results in additional equipment expenditure, e.g. in the form of two plasticizing units. An additional disadvantage of this process lies in the mechanical properties of the part produced in this way. A weld line can form between the two plastic components, which can lead to a deterioration in the mechanical properties. In addition, the orientation of the electrically conductive filler is determined by the melt flow. It is impossible to influence the particle orientation independently of this.

The object of the invention is to present a molded part made of plastic or polymer material with conductive structures of predetermined anisotropy and defined spatial distribution of the type mentioned at the beginning, which can be manufactured in the simplest possible way, whereby compared to the known manufacturing processes in

With the same filling factor between the starting material and the conductive particles, a significantly increased local electrical conductivity of the conductive structures is achieved.

According to the invention, this object is achieved in a manner that is astonishingly simple as it is effective in that the applied magnetic field has a field distribution such that the particles are concentrated in one or more predetermined spatial regions within the part when they are aligned in the magnetic field.

The predeterminable, usually inhomogeneous field distribution of the applied magnetic field exerts predictable forces on the ferromagnetic or paramagnetic particles, so that they can be moved into precisely predeterminable, defined spatial areas in the starting material before it solidifies. Since practically any magnetic field distribution can be generated using known techniques, the spatial areas within which the particles are concentrated can also be specified in any way.

In a particularly simple embodiment of the molded part according to the invention, the field distribution of the applied magnetic field is selected so that the predetermined spatial areas are layered. There is a wide range of applications for plastic parts with conductive layers; for example, they can be used to produce electrically shielding housings that are required, for example, for the installation of electronic devices. The layered areas with the concentrated particles have a thermal expansion behavior that is significantly different from that of the surrounding material, which is specifically used to modify the properties of the part.

can be exploited. The same applies to the mechanical properties such as strength, hardness, stiffness etc. of the particles in relation to the surrounding material.

A particularly simple development of this embodiment is one in which the layered spatial areas are flat. An inhomogeneous magnetic field for producing flat particle layers can be generated without any major problems.

However, an alternative development of the above-mentioned embodiment is also advantageous, in which the layered spatial areas follow curved surfaces. This means that the electrically conductive layers can, for example, follow curved outer contours of the plastic part. In this embodiment, the layers with the concentrated particles can be adapted particularly well to the requirements of the plastic part to be produced, for example, certain shielding effects can be achieved.

In a special development of the above embodiment, at least one of the layered areas is tubular, in particular it lies on a cylinder shell. This means that, for example, conductor wires or cable ducts cast into the plastic part can be provided with a shield integrated into the plastic part. Incidentally, the conductor wire itself can also be replaced by creating a cylindrical area of concentrated particles with a relatively small cross-section and great length in the molded part according to the invention. By appropriately modifying the magnetic field, the "integrated conductor wire" made of concentrated particles can follow any predetermined path within the part.

Another preferred embodiment of the molded part according to the invention is one in which a layered spatial region with concentrated particles is produced on at least one outer surface of the part. This makes contacting the conductive structure, which is located on the surface when using this process variant, particularly easy. In addition, the mechanical properties (hardness, etc.) of the surface of the part to be produced are significantly improved.

An embodiment in which at least one layered spatial area with concentrated particles is produced, which essentially extends in sections of the part remote from the surface, is also advantageous. In this way, the electrically conductive layers produced within the part are electrically insulated from the outside and are also protected from corrosive attack. Since the particle layers are located inside the part, they do not interfere with the aesthetic design of the surface of the part.

In a further development of this embodiment, the layered spatial area meets a surface of the part at an angle, preferably at about 90. This creates simple contact options for the conductive structure.

In a particularly advantageous development of this embodiment, at least two layered spatial areas with concentrated particles are created, which meet at an obtuse angle, in particular at about 90. This would further simplify the possibilities of contacting the electrically conductive structures and result in variable adaptation options to the

Requirements, for example, for the electrical shielding of the part to be produced.

In an alternative embodiment of the molded part according to the invention, the field distribution of the applied inhomogeneous magnetic field is selected so that at least one spatial area with concentrated particles has a volumetric expansion. This enables a targeted adaptation of the electrical and mechanical properties of the conductive structures to the requirements of the part to be produced. Conductive volumes can thus be created in precisely defined spatial areas of the part, which can subsequently be specifically "tapped" e.g. by screwing in metal screws or the like.

In a particularly simple embodiment of the molded part according to the invention, a static magnetic field is applied.

In order to further exploit the movement of the electrically conductive particles caused by the inhomogeneous magnetic field, in a preferred embodiment an alternating magnetic field can either be applied on its own or superimposed on an already applied static magnetic field.

If the alternating magnetic field has a low frequency in the range of 1 Hz to 100 Hz, quasi-continuous concentration gradients of the electrically conductive particles can be created in the part to be produced due to their relatively slow movement within the starting material of the part to be produced, which solidifies from the outside to the inside, by the particles in the extreme areas of their movement paths with a lower probability.

probability of being frozen than on the inner track sections.

When a high-frequency alternating magnetic field in the frequency range of 100 Hz is applied, the particles are stimulated to relatively fast vibrational movements in the surrounding material, whereby the cooling rate of the starting material can be controlled in a defined manner, at least locally, due to targeted heating by the frictional heat resulting from the particle movement.

An embodiment of the molded part according to the invention is also particularly preferred in which fibrous ferromagnetic or paramagnetic particles are added to the starting material. This enables, on the one hand, an easier formation of increased local electrical conductivity, and, on the other hand, a mechanical reinforcement effect through the fibrous particles and an increased anisotropy of the conductive structures produced.

A particularly advantageous development of this embodiment is one in which the fibrous particles have thickened and/or rounded ends. When using particles with rounded ends, an increased mechanical strength of the part to be produced is achieved by reducing the notch effect of the fiber ends on the starting material. When using fibers with thickened ends, a positive connection is achieved between the particles and the starting material, which also increases the mechanical strength of the part to be produced.

Particularly preferably, metallized or metallic particles are added to the starting material. For example,

metallized glass beads, glass, carbon, aramid fibers or fibers made of other materials with specially selected mechanical properties can be used. This also makes it possible to influence the magnetic properties of the particles through the thickness of the metallization layer. In addition, the position or orientation of the particles can be easily controlled with particles that are metallized on one side. The use of purely metallic particles leads to particularly good electrical conductivity of the structures created by the concentration of the particles.

In a particularly advantageous embodiment of the molded part according to the invention, the starting material is a slow-curing material. This leaves enough time to form the areas with concentrated particles, even when relatively weak magnetic fields are used. In addition, the spatial areas with the concentrated particles are formed more evenly and in a more defined manner.

Further advantages of the invention emerge from the description and the drawing. Likewise, the features mentioned above and those listed below can be used individually or in combination in any desired way. The embodiments shown and described are not to be understood as an exhaustive list, but rather are exemplary in nature for the description of the invention.

Show it:

Fig. 1 shows a section through the wall of a part with isotropically distributed fibres;

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Fig. 2 shows a section through the wall of a part with fibres concentrated on one side of the wall;

Fig. 3 a test device for producing a plate with shaft-shaped concentrated particles in the initial state (fibers distributed isotropically);

Fig. 4 shows the experimental setup for producing a plate with particles concentrated in layers in a side view;

Fig. 5a shows the experimental setup for producing a panel with particles concentrated on the outside of the wall in plan view;

Fig. 5b shows the distribution of the magnetic field strength in the experimental arrangement according to Fig. 5a;

Fig. 6a shows the experimental setup for producing a plate with particles concentrated in the middle of the wall in plan view;

Fig. 6b shows the distribution of the magnetic field strength in the experimental arrangement according to Fig. 6a;

Fig. 7 a part with fibres concentrated in the centre and a "connector" leading out;

Fig. 8 a part with fibres concentrated on the outside and a "connector" led to the opposite wall side ;

Fig. 9 a part with a deliberately deformed flat layer; and

Fig. 10 a fibre with thickened ends.

The basic idea of the invention is based on the possibility of influencing the position of ferromagnetic or paramagnetic particles using a magnetic field.

Both the orientation of the particles and the position of the particles in a component can be specifically influenced.

Fig. 1 of the drawing shows a section through the wall of a part 1 filled with metal fibers, which was produced in a conventional manner, e.g. by injection molding. The fibers 2 are evenly distributed over the entire cross section in the matrix 3 and have no orientation whatsoever. As can easily be seen, the probability that the fibers touch each other and thus electrical conductivity is produced in the part 1 is very low. In practice, therefore, very high proportions of conductive materials must be used.

To avoid this, it is proposed to enable electrical conductivity even with very small amounts of electrically conductive particles 2 by concentrating the electrically conductive particles 2. Fig. 2 also shows a section through the wall of a metal fiber-filled part 1. Here, however, the metal fibers 4 are concentrated on one side in layers on the wall and are parallel in the longitudinal direction.

IeI oriented. On the opposite side of the wall, the matrix material 3 is free of metal fibers. The image clearly shows the denser packing of the fibers caused by the concentration of the fibers and the resulting easier formation of electrically conductive structures in the wall area.

The targeted local accumulation and orientation of particles in a material can be used in a variety of ways. In addition to the electrical properties, the magnetic, mechanical, optical and thermal properties can be specifically influenced via the position of the particles introduced.

Fig. 3 shows a top view of a simple device for producing plates with particles concentrated and aligned in layers. The matrix material 3 filled with magnetizable particles, here fibers 2, is introduced in a non-solidified state into a non-magnetic mold 5, which is shown as a simple plate tool. The magnetizable particles 2 are randomly distributed in the matrix 3 in the initial state. In order to enable the manufactured plate to be removed from the mold, one side of the mold 5 is designed as a removable plate. The matrix material 3 can be processed both as a hardening molding compound and as a melt. In both cases, the viscosity of the starting material is also crucial for the alignment process. The higher the viscosity of the matrix material 3, the higher the applied magnetic forces or moments and thus the magnetic field strength must be and the longer the alignment process takes. If the position of the magnetizable particles 2 in a matrix 3 of molten material is to be influenced, the shape 5

be designed to be heatable, or the matrix 3 filled with particles 2 must be introduced into the mold 5 in a molten state. The magnetizable particles 2 are then influenced in their position as desired by the applied magnetic field during the solidification process. In this case, relatively high magnetic field strengths must be used so that the alignment process takes place as quickly as possible before the matrix 3 solidifies.

Fig. 4 shows a side view of the experimental setup for producing a simple plate with particles 2 concentrated in layers. The mold 5 for producing a plate-shaped part is placed between the two poles 6 of an electromagnet and thus in a magnetic field. The magnetic field is shaped in the desired manner using attachments 7, 9 attached to the poles, thus creating a gradient in the magnetic field strength. It is this field gradient that makes a targeted concentration of the particles 2 in layers possible.

The test arrangement for producing a plate with particles 8 concentrated on one side of the outside of the wall is shown in Fig. 5a. The view shows a view from above of the test arrangement. Basically, the arrangement corresponds to the arrangement described in Fig. 4. Attachments 7 are attached to the two poles 6 of an electromagnet. The shape of the attachments must be selected so that the magnetic field strength increases across the cross-section of the component towards one side. The simple form 5 described in Fig. 3, filled with magnetizable particles dispersed in the matrix 3, here fibers 2, is introduced into the magnetic field thus formed. A magnetic field is then applied. The strength of the applied magnetic field depends mainly on

mainly depends on the viscosity of the matrix 3 and the distance between the magnetic poles. The magnetic field must apply such a high force or moment that the particles 8 can move to the desired location and align themselves along the magnetic field lines before the matrix 3 solidifies. After this process has been completed, the magnetizable particles 8 are concentrated on one side and at the same time aligned parallel to the magnetic field lines. Once this state has been reached, experience has shown that the magnetic field can be reduced to about half the field strength until the matrix 3 surrounding the particles 8 has finally solidified. However, care must be taken to prevent the particles 8 from sinking due to gravity.

Fig. 5b illustrates the qualitative course of the magnetic field strength H 11 during the production of a plate according to Fig. 4.

Fig. 6a shows an arrangement for producing a plate with particles 10 concentrated in layers in the middle of the wall cross-section. In principle, the production process is analogous to the plate described in Fig. 5a. However, differently shaped attachments 9 must be used to produce parts with particles 10 concentrated in the middle. For the particle distribution sought here, the maximum of the magnetic field strength must be in the middle area of the plate cross-section.

The qualitative curve 12 of the magnetic field strength H can be seen in Fig. 6b.

Of course, other arrangements can also be used to generate and shape the magnetic field.

In addition to electromagnets, permanent magnets that are mounted in or on the mold 5 can also be used. This considerably simplifies the effort required to produce a device for applying the method according to the invention. It is even possible to integrate the magnets directly into the mold 5, i.e. the magnet(s) form part of the mold 5 or the entire mold 5.

In order to ensure easy contact of the electrically conductive layers 10 to the outside, in one process variant, a "connecting piece" 13 is formed by appropriately shaping the magnetic field. Fig. 7 shows such a "connecting piece" 13 in a part 1, drawn to the surface through the matrix 3. The electrically conductive particles 10, which in this example were concentrated in layers in the middle of the part 1, are specifically drawn to the outside of the wall at a point where contact is to be made from the outside. In the area in which the particles 13 are present on the outside of the wall, the electrical contact can then be made either directly on the surface or, for example, by screwing in a screw or similar in this area.

An analogous procedure is obvious for parts 1 with particles 8 concentrated on the outside of the wall, as shown in Fig. 8. Here, a "connector" 14 is guided through the matrix 3 from one side of the wall to the opposite side. The contact is also made directly on the surface or by introducing corresponding elements.

As Fig. 9 shows, the method according to the invention allows not only the targeted arrangement of particles 2, but also the targeted deformation of particles introduced into the matrix material 3.

flat layers 15, such as mats, grids or fabrics made of magnetizable materials. Analogous to the procedure for forming "connecting pieces" 13, 14, a targeted deformation 16 is introduced into a flat layer 15. The deformation process must take place when the matrix 3 is either completely or partially not solidified.

It is also advantageous to superimpose an electric field over the magnetic field. The electric field then serves, for example, to heat the particles and thus indirectly to heat the matrix 3, while the magnetic field serves to align and/or concentrate. The electric field and the associated possibility of heating can, for example, considerably extend the time available for aligning the particles.

A significant increase in the mechanical properties of metal fiber-reinforced materials, especially plastics, can be expected through the use of reinforcing fibers with thickened ends 18. Such a fiber is shown in Fig. 10. In conventional, i.e. cylindrical reinforcing fibers 17, the load is transferred from the matrix material 3 surrounding the fiber to the fiber 17 through shear stresses in the fiber/matrix interface. Unlike with glass fibers, due to the chemical structure of metals, no interaction mechanisms can arise between the fiber 17 and a plastic matrix 3 in metal fibers. However, these interactions are an important prerequisite for optimal load transfer in fiber-reinforced plastics.

In order to guarantee sufficient load transfer between matrix 3 and fiber 17 even with metal fiber reinforced materials, different fiber shapes are more suitable here. As described, load transfer through shear stresses is ruled out. However, if a positive connection is made between matrix 3 and fiber 18, very high forces can be transmitted. This positive connection is achieved by a targeted thickening of the fiber end. The thickening prevents the fiber 18 from slipping out of the matrix 3. In order to produce fibers with thickened ends 18, the fibers are heated at their ends so that, controlled by the surface tension of the fiber material, a spherical thickening forms at the fiber end.

The mechanical properties can also be improved with metallized particles, preferably fibers. This makes use of the higher strength of glass, carbon or aramid fibers compared to most metals. Particles made of polymer materials can also be used here. After coating the fiber, e.g. by vaporizing a magnetic material, fibers made of a non-magnetic base material can also be aligned and/or concentrated using a magnetic field. The fact that the magnetic properties of the fiber can be easily influenced is an advantage here. The sensitivity to the magnetic field can be controlled by varying the thickness of the magnetic layer. In addition, partial coating of the fibers allows the fibers to be aligned in any orientation.

Another variant of the process consists in the fact that in addition to the magnetic particles, non-magnetic or less magnetic particles that have a reinforcing or filling effect are

function are introduced into the plastic mass. This makes it possible to use the process with filled materials, e.g. fiber-reinforced materials. The position of the magnetic particles in the component can thus be influenced independently of the filling or reinforcing material.

In addition to plastics, other non-magnetic materials, such as aluminum, are also suitable for the application of the method described above and its variants.

Claims (18)

Protection claims 1. Moulded part made from a starting material with very low or zero electrical conductivity, in particular plastic and/or polymer, which is initially present in a low-viscosity phase in which magnetic particles with significantly higher electrical conductivity are added to the starting material and dispersed therein, whereby a magnetic field is applied to align the particles, and whereby the starting material is subsequently solidified, characterized, that the applied magnetic field has a field distribution such that the particles (2, 4, 8, 10, 13, 14, 17, 18) are concentrated in one or more predetermined spatial regions within the part (1) when they are aligned in the magnetic field. 2. Moulded part according to claim 1, characterized in that the field distribution of the applied magnetic field is selected so that the predetermined spatial areas are shaft-shaped, 3. Molded part according to claim 2, characterized in that the field distribution of the applied magnetic field is selected so that the layered spatial regions are flat. 4. Molded part according to claim 2, characterized in that the field distribution of the applied magnetic field is selected so that the layered spatial regions follow curved surfaces. 5. Molded part according to claim 4, characterized in that the field distribution of the applied magnetic field is selected such that at least one of the layered regions is tubular, in particular lies on a cylinder jacket. 6. Molded part according to one of claims 2 to 5, characterized in that the field distribution of the applied magnetic field is selected such that a layered spatial region with concentrated particles (2, 4, 8, 10, 13, 14, 17, 18) is produced at least on an outer surface of the part. 7. Molded part according to one of claims 2 to 6, characterized in that the field distribution of the applied magnetic field is selected such that at least one layered spatial region with concentrated particles (2, 4, 8, 10, 13, 14, 17, 18) is produced, which extends essentially in sections of the part (1) remote from the surface. 8. Molded part according to claim 7, characterized in that the field distribution of the applied magnetic field is selected so that the layered spatial region strikes a surface of the part (1) at an angle, preferably at about 90. 9. Moulded part according to claim 8, characterized in that the field distribution of the applied magnetic field is selected so that at least two layered spatial regions with concentrated particles (2, 4, 8, 10, 13, 14, 17, 18) are produced, which meet at an obtuse angle, in particular at approximately 90. 10. Molded part according to one of the preceding claims, characterized in that the field distribution of the applied magnetic field is selected such that at least one spatial region with concentrated particles (2, 4, 8, 10, 13, 14, 17, 18) has a volumetric expansion. 11. Moulded part according to one of the preceding claims, characterized in that a static magnetic field is applied. 12. Moulded part according to one of the preceding claims, characterized in that an alternating magnetic field is applied. 13. Molded part according to claim 12, characterized in that the alternating magnetic field has a low frequency in the range of 1 Hz to 100 Hz. 14. Moulded part according to claim 12, characterised in that the alternating magnetic field has a frequency of 100 Hz. 15. Moulded part according to one of the preceding claims, characterized in that the starting material contains mechanical reinforcing agents, in particular fibrous particles (2, 4, 8, 10, 13, 14, 17, 18). 16. Moulded part according to claim 15, characterized in that the fibrous particles (18) have thickened and/or rounded ends. 17. Moulded part according to one of the preceding claims, characterized in that the starting material contains metallised or metallic particles (2, 4, 8, 10, 13, 14, 17, 18). 18. Moulded part according to one of the preceding claims, characterized in that the starting material is a slowly curing starting material.