DE19805650A1 - Joining method using a PTC polymer - Google Patents

Abstract

The invention concerns an improved joining method for joining two parts (1 and 2) by means of a joining material layer (3). By means of contacts (4 and 5), a voltage is applied to a PTC polymer material layer in the joining material (3) from an energy supply (6) via an external electric circuit. The PTC effect leads to automatic uniform distribution of the Joulean heat loss and to uniform two-dimensional melting when the joint is being produced.

Description

The present invention relates to a method in the field of connectors manure technology. In connection technology, two or more parts are mecha nisch firmly connected, so that the connection between them at least least is no longer easy and unintentional to solve.

Of course, the use of connecting elements with a is known certain physical form, e.g. B. screws, nails, rivets and Parentheses. Many processes in welding technology (e.g. lasers weld), where the connection without using an additional Connection material, i.e. from the material of the parts to be connected themselves will be produced. In the field of plastics technology, these are e.g. B. the Ultra sound and vibration welding.

However, this invention relates to a connection method in which a additional connecting material is used (which in its composition However, this does not necessarily depend on the materials of the parts to be connected must give way). In the field of metal processing, soldering techniques and the welding techniques using an additional welding wire ren. Furthermore, all adhesive techniques belong in this area.

In the field of plastics technology, plastic welding processes are also known, in which, by means of heating elements made of metal or carbon fibers embedded in the connection and ultimately remaining there, the parts to be connected are melted and melted together at least in the vicinity of a connection surface:
"A Review of Methods for Fusion Bonding Thermoplastic Composites",
"A. Benatar, TG Gutowski, SAMPE Journal, January / February 1987, pp. 33 ff;
"Thermoplastic Aromatic Polymer Composites", FN Cogswell, Butterworth-Heine mann Ltd. 1992, chap. 5.3.4;
"Resistance Welding of Graphite Polyetheretherketone Composites: An Experimental Investigation" EC Eveno, JW Gillespie, Jr., Journal of Thermoplastic Composite Materials, Vol. 1, 1988, pp. 322 ff;
"Joining Thermoplastic Composites", DM Maguire, SAMPE Journal, Vol. 25, No. 1, January / February 1989, pp. 11 ff.

Because with these techniques the embedded heating element makes the connection Delivering helps, but its durability is more restrictive than encouraging there is basically no question of additional connecting material. However are in the sources cited also additional films of insulating polymer material mentioned by thermal (A. Benatar, T. G. Gutowski) or electrical (F. N. Cogswell) Isolation to improve the distribution of heat from the heater in the connecting surface.

In the sources mentioned, the main difficulty is that shown there Welding techniques the uniformity of the temperature distribution along the Called connecting surface. In particular, the insulation layer mentioned Too much heat or electricity is injected from the heater into the prevent binding parts on the outer edge of the connecting surface. Nevertheless significant unevenness cannot be avoided.

The state of the art can also be said that current-limiting elements made of polymer materials are known which have a PTC effect (larger positive temperature coefficient of electrical resistance):
"Polymer Composite Thermistors for Temperature and Current Sensors", R. Strümpler, J. Appl. Phys. 80 (11), December 1996, p. 6091 ff;
"Polyethylene Current Limiters for Short-Circuit Protection", T. Hansson, ABB Review 4/92;
"PolySwitch PTC Devices - A New Low-Resistance Conductive Polymer-Based PTC-Device for Overcurrent Protection", FA Doljack, IEEE Transactions on Components, Hybrids and Manufacturing Technology, Volume CHMT-4, No. 4, December 1981, p. 372 ff;
U.S. Patent 5,313,184.

Elements with PTC polymers are also known as part of self-regulating heaters for two-wheel handles, car batteries, lines and tanks, antennas, electrical components, etc. A PTC polymer layer forms a heating element with metal electrodes for power supply:
U.S. P4,761,541.

The invention is directed to connection methods using a Connection material for establishing a firm connection between two Divide. It is based on a known method for connecting at least two parts by a connecting material, the connecting dimension material contains a polymer material and the connection by action Joule shear heat loss of electrical currents produced in the connecting material becomes.

The technical problem underlying the invention is a new and ver to provide a better connection method.

This problem is solved according to the invention in that the polymer material is a PTC polymer material and that the electric currents are the Joulesche Ver heat through the resistance created by the PTC effect in the Create PTC polymer material.  

The invention is based on the idea that in many connection technologies The connection is made by exposure to heat. In many cases and for various reasons, this heat is generated by electrical Currents in the connecting material are advantageous. Such reasons may be that in any case, the parts to be connected are not thermally stressed in their entirety The aim is that the connection should be made as quickly and specifically as possible is that the interface between the two parts to be connected for external heat input is difficult to access or others.

The Joule heat of the electrical currents can do various processes evoke or promote the connection. This can be an on melting a material according to a welding or soldering process, the strengthening of an interdiffusion, the activation of a chemical reaction, the improvement of an adhesive effect, etc. In any case it is important that the heat is distributed as evenly as possible.

Instead of the heat distribution through insulator layers, as in the prior art improve, the invention assumes that the heat generation itself possible Lich should be done evenly. For this purpose, the connecting material contains a PTC polymer whose PTC effect is used for the essential part of the Jouleschen waste heat responsible electrical resistance generated. Of the The term PTC polymer here denotes electrically conductive polymers which are used in the Environment of a transition temperature from a good conductive state in egg switch less conductive or insulating state. With semi-crystalline For polymers, this transition temperature is close to the melting temperature.

A distinction can be made by an increase in resistance in a tem temperature interval of 14 K by at least a factor of 2.5 or in a tempera interval of 30 K by a factor of 6 or in a temperature interval of 100 K by a factor of 10. (The fulfillment of a criterion defines the material  as a PTC polymer). A delimitation with an increase in the resistance is preferred in the temperature interval of 14 K by a factor of 5 or in the tem temperature interval of 30 K by a factor of 20 or in the temperature interval of 100 K by a factor of 100.

A delimitation with a factor of 7.5 in the interval of is particularly preferred 14 K, the factor 100 in the interval of 30 K or the factor 1000 in the Interval of 100 K.

Such PTC polymer materials can consist of a polymer matrix with one therein distributed filling material that promotes electrical conductivity, such as presented in more detail in the cited prior art. The filling material can be metal particles, carbides, borides, nitrides, short carbon fibers, conductive polymer particles or also be soot.

If the electrical currents through the PTC polymer material flows and the PTC effect with increasing warming for the essential part of the voltage drop and thus the essential part the Joule heat loss is responsible, there is automatically one even heat generation. (The essential part here means at least 50 preferably 80, 90 or 95 of the total voltage drop in the Connection material.) The strong increase in resistance in the temperature range of the PTC effect ensures that the electrical currents are distributed among the ge slightly colder parts of the PTC polymer material and their limitation in the area chen above a certain temperature.

This can cause overheating of the connection material or the connection the parts can be easily avoided. By suitable selection of the PTC tem temperature range can be one for the special application process sufficient temperature that is compatible with all materials involved is selected and be set.  

The strong increase in resistance in this temperature range ensures a suitable one external circuit for supplying the electrical currents for an automatic Setting the total power supply to this temperature range. Other On the one hand, PTC polymer materials can be made from a very large selection of poly mers for the polymer matrix are made, so that the connecting material not only with regard to the PTC temperature range but also under consideration consideration of other physical or chemical aspects on the type application can be optimized.

According to a preferred embodiment of the invention, the electrical Currents by applying a voltage to the connecting material by An connected to an external electrical circuit. So can in one streams of practically any size are generated. Ins In particular, the inductive conceivable in the context of the invention are omitted Coupling methods existing geometric restrictions.

To supply the current or to apply the voltage are advantageous Contact surfaces used, the comparatively thin PTC polymer ma include material areas between them, d. H. the current should go through relatively short stretches flow in the PTC polymer material. This is because with longer current paths through the PTC polymer material across the current device can form planes of higher temperature, in which the PTC effect the significant drop in resistance occurs. So there exist from embossed gradients of temperature and resistivity in the Current direction, the temperature and resistivity across Current direction are two-dimensionally relatively homogeneous. Depending on the sharpness of the PTC effect, i.e. H. the size of the derivative of the resistance according to the temperature, and the thermal conductivity of the material are formed accordingly Layer thicknesses of the "PTC level". These layer thicknesses are technically relevant  and should not be less than the thin ones mentioned above PTC polymer material areas between the contact surfaces.

Favorable contact surface geometries result e.g. B. from comb-like tooth th finger structures for the power supply lines in the connection level or by ver on and under a relatively thin layer of the connecting material running flat (not necessarily continuous) contact surfaces. In the latter ten case can e.g. B. net-shaped or finger-shaped power supply lines in the Contact areas. But it is also possible to connect the current through the the parts themselves if they have a certain electrical conductivity have speed so that the parts to be connected are not heated too much. Of course, this is particularly useful for metals; good conductive art however, fabrics are also conceivable.

In addition to metal structures, carbon fibers can also be used for the power supply lines be used. These are well tolerated and compatible with many polymer materials can therefore be particularly good in the connecting surface or in the connecting mat rial remain after establishing the connection. In addition to the function as a power supply cable - one-sided or two-sided - can also me mechanical reinforcement properties result. In contrast to the state of the However, these carbon fiber structures should not be used as heating elements ment serve by passing the current through essentially insulating polymers pass through. In particular, good results arise with carbon fiber structures Possibilities to shorten the length of the current paths in the connection material Zen. The currents can do very well due to the large number of carbon fibers be divided and distributed.

As already indicated above, it is also within the scope of the invention bar to generate the electrical currents inductively as eddy currents. To do this an electromagnetic wave is coupled into the connecting material, as is known from conventional induction welding of plastics.  

However, the essential effect of the Er already described also results here finding. If due to different levels of absorption or from other green the uneven heating of the connecting material takes place, so this is automatically compensated for in the temperature range of the PTC effect, in where larger eddy currents can flow in the somewhat colder areas.

Compared to the direct connection to a heating circuit, this has inductive Process the advantage that no power lines are necessary and ins special the problem in the interface or at least on its edge after the connection of remaining contact devices or Power supply lines do not provide. On the other hand, the coupling device for the electromagnetic wave, e.g. B. a coil, geometrically exactly to the forth The connection to be delivered must be adjusted so that there are no excessive losses in performance occur. This can also connect to geometric constraints lead the parts. On the apparatus side, the inductive process is basically more complex than that previously described.

In principle, the invention can be combined for a wide variety of materials Parts suitable. Often, however, it only becomes similar to an adhesion effect an adhesive connection, whether through the heated PTC poly mermaterial or by additional contained in the connecting material Adhesion layers conveyed. A preferred area of application is, however where at least one of the parts to be connected is also made of a poly material exists. Then, above all, it can become a lot to this part stronger connection similar to conventional plastic welding technology com men, which is particularly stable when at least one of the polymer materials the establishment of the connection melts. However, a certain softening and increased interdiffusion at the boundary layers very much stable connections are created. Experience has shown that they are thermal induced connections between polymer materials then particularly well, if the opposite materials correspond as much as possible  chen. To do this, the polymer material of the part or parts to be joined should also identical or to the material of the polymer matrix of the PTC polymer material be at least closely related.

In favor of compounds that are reliable even at somewhat higher temperatures, the invention is particularly aimed at high-temperature PTC polymer materials which have their PTC effect and melting point above 140 ° C., preferably above 200 ° C. In addition to the electrically conductive filler materials of the PTC polymer material, other constituent parts for mechanical stabilization can also be present in the connecting material. A preferred material is e.g. B. a composite material of carbon fibers and a PEEK (polyether ether ketone) as a polymer (melting point at 334 ° C), with fillers such. B. TiC, TiB ₂ or TiN can be used. Other preferred polymers are PPS (polyphenylene sulfide, melting point 288 ° C) and s-PS (syndiotactic polystyrene, melting point 263 ° C).

It has already been stated that because of the formation of "PTC effect level longer current paths through the PTC poly material can be disadvantageous. An alternative to training the be already mentioned extensive or interdigitated comb-like Power supply structures is that on an outside of the connec a conductive polymer contact layer with better electrical Conductivity than that of the PTC polymer material in the volume of the connection measure terials is provided. This contact layer can then only from the one Edge of the outside provided metallic or carbon current supply Distribute the current supplied so that the actual PTC poly material in turn result in short current paths. An example of a Ma Material combination is PEEK as a polymer matrix with carbon black as a conductive filler for the PTC polymer material and PEEK with a metal powder, e.g. B. Ni or Ag as a highly conductive filling material for the contact material. It is essential  that the metallic filling material has a significantly higher conductivity of the contact materials results as that of the soot-filled PEEK in the connection material volume.

The same applies with the same aim for the conductivity in the area the PTC effect. If a conductive polymer for the contact layer is used that either none, a comparatively weaker or in the temperature higher PTC effect compared to the PTC poly shows material in the volume of connecting material, the final result is same effect as the previous alternative if the resistance in the ver binding material volume increases due to the PTC effect. Conversely, that is allowed The ratio of the conductivities in the example above is of course not by one PTC effect can be reversed.

The invention is described below using two exemplary embodiments ben, which are shown in the figures. Individual features disclosed can also individually or in other combinations than those shown be substantial. In detail shows:

Figure 1 shows a first embodiment of the connection method according to the invention in a schematic view.

FIG. 2 shows a schematic cross-sectional view of a connecting material used in the method from FIG. 1;

., Figures 3 and 4 are schematic plan views of a connecting material having two power supply structures and a polymeric PTC material layer after egg nem second embodiment in a separated state;

. Figure 4 shows the elements of Figure 3 in the assembled state.

FIG. 5 shows an alternative power supply structure for the second game Ausführungsbei from Figures 3 and 4.

Fig. 6 is a perspective view of a bottom plate manufactured with the connec tion process according to the invention after the second embodiment; such as

Fig. 7 shows a detail from a cross section through the baseplate of Fig. 6.

Fig. 1 shows a simple schematic example of the inventive connecting method. As indicated by the arrows, two parts 1 and 2 made of PEEK are pressed onto an intermediate connecting material layer 3 and against one another. The connecting material intermediate layer 3 is further described with reference to FIG. 2. It is connected via two electrical contacts 4 and 5 in an external circuit and is energized by a power supply 6 .

The Joule heat loss heats the connecting material 3 up to the temperature range of its PTC effect and lets it melt there in the connecting surface (ie vertically and perpendicular to the plane of the drawing in the figure). This results in a welded connection with the likewise melting outer most outer layers of the parts 1 and 2 to be connected . The slight pressure on the parts is maintained during cooling down to a temperature which is so far below the melting point of PEEK that parts 1 and 2 are stably connected.

Fig. 2 shows schematically the structure of the compound material 3. It consists of two thin outer contact layers 7 and 8 made of Ag-filled PEEK and a PTC polymer material layer 9 between them made of soot-filled PEEK.

The contact layers 7 and 8 are in each case connected only at the edge to the current supply contacts 4 and 5 for the external circuit. Because of the Ag powder filling, however, they already have a significantly lower specific resistance than the PTC polymer material 9 at room temperature. Therefore, the electrical voltage provided by the external circuit is applied essentially planar to the large boundary surfaces of the PTC polymer material layer 9 and the current paths through the PTC polymer material layer 9 corresponding to the (horizontal in the figure) direct paths between these two large boundary surfaces .

In addition, Ag is a "soft" filler and therefore shows practically no appreciable PTC effect (see R. Strümpler, loc. Cit.). Accordingly, the difference between the specific resistances of layers 7 and 8, on the one hand, and 9, on the other hand, increases extremely if the PTC polymer material layer 9 reaches the region of the PTC effect with increasing heating. The contact layers 7 and 8 then act practically as a short circuit of the large surfaces.

Since they have a PEEK matrix, these contact layers 7 and 8 in no way interfere with the welding of the two PEEK parts 1 and 2 to be connected. This makes them compared to alternative contact options such. B. metal nets or foils, metal pastes or conductive foreign polymers of clear before part, as long as the filler does not interfere and the conductivity is sufficient in view of the dimensions of the connection surface.

Suitable PTC materials for the PTC polymer material layer 9 can be found in the variously cited publication by R. Strümpler (loc. Cit.), The disclosure of which is hereby incorporated by reference.

In contrast, in the second exemplary embodiment shown in FIGS. 3, 4, 6 and 7, network-shaped contact structures 10 and 11 are used, which are shown in FIG. 3 together with an intermediate PTC polymer material layer 12 . Fig. 3 shows the layers in the separated state in schematic plan view. The network-shaped contact structures 10 and 11 consist of carbon fibers and have a soldered-on metal contact 13 and 14 on one edge. These connections 13 and 14 are shown in Fig. 3 on the narrow sides of the rectangular connecting surface, but can be placed at any point on the edge of the rectangle after practical considerations.

The PTC polymer material layer 12 consists of PEEK with a soot filling. Soot is advantageous here as a filler because it has a sufficiently high resistance so that the greatest losses do not occur in the contacts.

FIG. 4 shows the structure from FIG. 3 in the compressed state. The carbon fiber contact structures 10 and 11 are simply pressed into the polymer layer 12 , taking care that no short circuits occur at the edge. The PTC polymer material layer 12 should therefore protrude somewhat. Overall, FIG. 4 shows a pre-bonding material layer 15.

FIG. 5 shows an alternative power supply structure compared to the structure shown in FIGS. 3 and 4. Here, two comb-like Lei terbahnen are arranged interlocked with each other, so that there are short distances between the conductor tracks over a larger rectangular area. This structure is mechanically less stable than that of FIGS. 3 and 4, but has the advantage that it only has to be applied to one side of a thin PTC polymer material layer. It could also be used in the second embodiment.

The connection material layer 15 from FIG. 4 is used for a connection problem shown in FIGS. 6 and 7. Fig. 6 shows a base plate made of fiber-reinforced plastic, which is shown in section AA in Fig. 7. It consists of a carbon fiber reinforced top plate 16 and a similar bottom plate 17 , which are connected by double T-beam-like intermediate profiles 18 .

Such floor slabs are used as prefabricated standard components in industrial construction, at airports and in other areas of the construction industry and have considerable length dimensions of several meters in length and width. In their manufacture, the double-T profiles 18 at the connec tion points 19 with the top of the upper T-cross leg and at the Ver connection points 20 with the underside of the lower T-cross leg are each connected to the top plate 16 and the bottom plate 17 . The large length of the connecting surfaces 19 and 20 in the direction of the double-T profiles 18 results in great difficulties with the conventional methods.

In particular, the base plates are so large that induction welding processes make very large induction coils and thus a considerable expense necessary. Conventional plastic welding processes with resistance heating could not produce uniformly satisfactory connections over the entire area of the connecting surfaces 19 and 20 . Other techniques, such as ultrasonic or vibration welding, are also ruled out because of the size of the structures.

According to the invention, the rectangular connection material layers 15 shown in FIG. 4 (comparatively somewhat shortened) are now interposed at the connection surfaces 19 and 20 and heated via the connections 13 and 14 , which in this example are advantageously arranged on the shorter sides of the connection surfaces 19 and 20 and are therefore easily accessible.

In the area of the PTC effect, ie at PEEK at 334 ° C., the PTC polymer material layer 12 melts in the connecting material layer 15 , the immediately adjacent area of the top plate 16 and the bottom plate 17 also being melted on. This results in an intimate welded connection between the double-T profiles 18 and the plates 16 and 17 , the carbon fiber contact networks 10 and 11 being virtually cast in. They practically do not disturb the quality of the connection. On the contrary, they offer additional reinforcement of the fiber reinforcement of the plates 16 and 17 in the area of the connecting surfaces 19 and 20 . In particular, despite the length of the connecting surfaces 19 and 20, they provide a low resistance.

Overall, there is a fast, simple and reliable Verbindungsver driving, which is suitable for very large geometric dimensions of the connecting surfaces Ver. Due to the improved strength and reliability of the connections at the connecting surfaces 19 and 20 , the stability of the entire base plate shown in FIG. 6 is significantly improved.

Claims (12)

1. Method for connecting at least two parts ( 1 , 2 , 16 , 17 ) using a connecting material ( 3 , 15 ),
wherein the connecting material ( 3 , 15 ) contains a polymer material ( 9 , 12 ) and
the connection is produced by the action of Joule heat loss from electrical currents in the connecting material ( 3 , 15 ), characterized in that the polymer material ( 9 , 12 ) is a PTC polymer material and
that the electrical currents generate the Joule heat loss through the resistance generated by the PTC effect in the PTC polymer material ( 9 , 12 ). 2. The method according to claim 1, wherein the electrical currents are generated by applying a voltage to the connecting material ( 3 , 15 ). 3. The method according to claim 2, wherein the PTC polymer material ( 9 , 12 ) forms a layer between two in comparison to the thickness of the PTC polymer material rialschicht ( 9 , 12 ) extensive contact surfaces ( 7 , 8 ). 4. The method according to claim 2 or 3, wherein the parts to be connected ( 1 , 2 , 16 , 17 ) are electrically conductive and are used to supply the electrical currents. 5. The method according to claim 2 or 3, wherein the connecting material ( 3 , 15 ) contains carbon fibers ( 10 , 11 ) which are used for supplying the electrical currents. 6. The method according to claim 1, wherein the electrical currents are generated by coupling an electromagnetic wave into the connecting material ( 3 , 15 ). 7. The method according to any one of the preceding claims, wherein at least one of the parts to be connected ( 1 , 2 , 16 , 17 ) consists of a polymer material. 8. The method according to claim 7, wherein at least the polymer material of this part ( 1 , 2 , 16 , 17 ) or the polymer material ( 9 , 12 ) in the connection material at least partially melts in the production of the connection. 9. The method according to claim 7 or 8, wherein the polymer material of this part ( 1 , 2 , 16 , 17 ) is substantially the same as the polymer material ( 9 , 12 ) in the connecting material ( 3 , 15 ). 10. The method according to any one of the preceding claims, wherein the PTC polymer material ( 9 , 12 ) is a high temperature polymer with a temperature of the PTC effect of more than 200 ° C. 11. The method according to any one of the preceding claims in connection with claim 2, in which the connecting material ( 3 ) on an outside of a contact layer ( 7 , 8 ) made of a conductive polymer with higher than the PTC polymer in the volume of the connecting material ( 3 ) has electrical conductivity. 12. The method according to any one of the preceding claims in conjunction with claim 2, in which the connecting material ( 3 ) on an outer side has a contact layer ( 7 , 8 ) made of a conductive polymer, which has no PTC effect or a weaker PTC in the connecting method -Effect compared to the volume of the connecting material ( 3 ) shows.