DE60101141T2 - Production process for a PCT polymer product - Google Patents

Abstract

The method is provided for forming a form product from a PTC-polymer material consisting of a conducting filler material and optionally further filler material in a matrix of polymer material. During the forming process the PTC-polymer material is deformed my means of a tool under heat and pressure. Hereby the PTC polymer material is heated to an absolute temperarture of at most 1,1 x TS, TS being the absolute melting temperature of said matrix polymer material. PTC-polymer products made according to this method comprise a very stable tripping behaviour. <IMAGE>

Description

Background of the invention

THE iNVENTION field

The The present invention relates to a production process for a product, that of a polymer with a specific electrical resistance made with a positive temperature coefficient (more specific PTC resistor; hereinafter: PTC polymer product), namely one Molding process, at the heat and pressure on a PTC polymer material to affect the material to deform and a desired one To obtain product form.

general State of the art

Various Techniques for Such shaping processes are known.

polymers have to Generally, to be ductile, they are heated to reduce their viscosity and around breaks and to avoid cracks. Especially for mass produced parts is the time for the forming process required is an essential parameter. In addition, when molding acting pressures not too high to be overly technical Device too avoid. Thus, in conventional polymer molding processes the polymer material temperature much higher than the so-called melting temperature of this Material.

The above concerns first pure polymer materials. In PTC polymer materials, on which According to the invention, there are solid filling materials which are in one Polymer matrix are included, for example, carbon powder or Metal powder. It goes without saying that the inclusion of considerable Quantities of filling materials the viscosity of the polymer material drastically increased so that the pressure or the temperature of the molding process must be increased even more.

Short illustration the invention

The The present invention is based technical problem in the provision of a production process for molding a PTC polymer product with improved and stabilized quality.

The The present invention accordingly relates to a method for Manufacture of a molded product of a PTC polymer material, which consists of a conductive filling material and optionally another filler material in a matrix of polymer material, the product being formed by a molding process is formed, which is the PTC polymer material with the help of heat and pressure deformed, characterized in that the PTC polymer material during the Forming process to an absolute temperature of at most the 1.1 times the absolute melting temperature of the matrix polymer material heated as well as a method for producing elements from PTC polymer material, wherein semi-finished products of the PTC polymer material with a method as defined above and dividing the semi-finished product is to make the elements.

The The idea underlying the invention is to deform of the PTC polymer material to use a relatively low temperature. It turned out that at higher Temperatures the quality of PTC products decreases, namely the stability their triggering behavior. As in the description of the embodiments in detail is shown, namely the resistance values in the cold, normally conductive state via a larger number repetitive trigger actions stabilized when reduced temperatures in molding according to the invention be used.

For the upper limits of the maximum temperatures of the molding process, a general formulation is used, which refers to the so-called melting temperature of the polymer of the matrix. According to the invention, this melting temperature should be exceeded by not more than 10% with respect to the absolute temperatures. It should be noted that this criterion uses the absolute temperature for the process temperature and the melting temperature, namely the Kelvin temperature scale. Further preferred upper limits are 7.5% above the melting temperature and most preferably 5% above the melting temperature (hereinafter the melting temperature is abbreviated as T _S ).

Of the Forming process used with the above-described temperature limit may include Pressing process, an injection molding process or a Be extrusion process. Among these types of processes However, extrusion and pressing are preferred. In particular, will preferably uses such a process, to produce semi-finished products, later subdivided into smaller elements should be. These elements can be used as PTC elements, for example, resistance elements for short-circuit interruption or for current limitation. When semi-finished products are manufactured and later divided into several PTC elements, this compensates for this greater temporal Effort in the molding process, which results from the relatively low temperature used, if excessive pressures, the also lead to material problems can be avoided. The Dividing the relatively large Semi-finished product can be a process step very fast expires without for the material quality a big Having relevance when using in particular subdivision techniques be that an excessive melting of the polymer. Preference is given to cutting techniques, wherein the term cutting sawing and besides, especially prefers cutting techniques such as high pressure water jet cutting or laser cutting.

A simple and preferred embodiment relates to a plate-like semi-finished product. Such plates can be extruded from PTC polymer material even at very low temperatures (but preferably above T _s ) without any problems. Injection molding or extrusion is also possible, but these techniques require higher pressures compared to pressing. Preferred pressures are not more than 300 bar, more preferably not higher than 200 bar and further preferably not higher than 120 bar.

The Invention can be practiced with a vast number of polymer and filler materials. Preferred polymer materials for the matrix include PE, PP, ETFE, polyimides such as Aurum, PPS or PEEK. The am Most preferred material is high density PE (HDPE).

PTC polymer materials generally include, as already mentioned above, a conductive filler material.

Preferred quantitative ranges for receiving the highly conductive first filling material which is to be obtained from PTC polymer materials are 20-60% by volume, more preferably 30-55% by volume and most preferably 35-50% by volume (based on the total volume of the PTC polymer material). A preferred choice for this (first) conductive filler is TiB ₂ .

The PTC polymer material may include a second filler material having varistor characteristics in addition to the first filler material. This second filler is preferably SiC. The preferred amount ranges are 10 to 30% by volume, preferably 12 to 28% by volume and more preferably 14 to 26% by volume of this second filler. However, the invention should also apply without second filler material (SiC), for example 50% HDPE and 50% TiB ₂ .

These filling materials are contained in the form of a powder dispersed in the polymer matrix. In addition, the average particle size of the second filler should to be taller than that of the first filling material, namely around a factor of 2 - 5. Preferred areas for the particle sizes are 10 um to 50 um for the first filling material and 20 to 250 um for the second filler.

The above-mentioned thermoplastic polymer matrix is preferably contained in an amount of 30-55% by volume, and more preferably 37-50% by volume. According to the present results, the above-specified PTC polymer material exhibits a remarkably high resistance zone ("hot zone") at a predetermined voltage. A typical example of a PTC polymer material according to the invention thus comprises 40% by volume HDPE, 40 Vol .-% TiB ₂ and 20 vol .-% SiC.

The above defined particle sizes, in addition to the materials themselves, in particular the polymer material, for the viscosities relevant to the overall mix. Such viscosities can be defined by a melt flow index which, according to the German Industry standard (DIN) with a standard opening at a standard temperature from 190 ° C and a standard load of 21.6 kg measured by the amount of material which runs through the opening in 10 minutes. Preferred values for this Invention are melt flow indices of at least 1 g / 10 min, preferably at least 1.5 g / 10 min and most preferably at least 2 g / 10 min.

With the method according to the invention can Semi-finished products, later should be divided, especially plates, easily manufactured be, namely by pressing. The occurring in them during the molding process according to the invention relatively large Time spent in this case may be due to simultaneous manufacture many PTC elements are compensated.

description preferred embodiments

following become preferred embodiments of the invention. The various disclosed features can also for the invention may be relevant alone or in combinations.

The embodiments are shown in the figures.

1 illustrates a typical construction of a PTC polymer element according to the invention;

2 and 3 FIGURES are diagrams illustrating the improvement in tripping characteristics achieved by the invention.

The production process begins with the mixing of the appropriate amounts of polymer powder or granules, in this case HDPE, and filler by standard mixing with a BUSS-MDK / E46-11D (screw mixer). About 100 kg of mixture must be prepared to obtain about 2 x 10 ⁴ samples, as in 1 mentioned.

The Mixing material is then placed in a standard pressing device (PINETTE EMIDECAU INDUSTRIE, maximum load of 15 tons) at a temperature of 140 - 145 ° C, that is 413 - 418 K, pressed, and The result is a rectangular plate with side lengths 16 cm, 4 cm and a thickness of, for example, 0.2 cm. For mass production can also much larger plates pressed become. The above size is one experimental size.

In the 1 The structure shown is contacted after cutting to produce PTC resistor elements. However, these steps are conventional and need not be described in detail here.

Table 1 lists several melting temperatures of typical polymers to be used and other typical molding temperatures according to the invention. Melting temperatures are abbreviated T _s and given in ° C, maximum molding temperatures are abbreviated T _P and also indicated in ° C. The last column indicates the temperature difference ΔT in between, divided by the melting temperature T _S (indicated in K), in%.

Table 1:

by the way Aurum is the name of a polyimide.

For comparison: Typical values for the melt injection of pure PE are between 200 and 280 ° C, ie at ΔT / T _S values of 16 - 36%. Even with other polymer materials, the usual molding temperatures are much higher than those given in Table 1. It should be noted, however, that the conventional temperatures refer to pure polymer without filler material. Since the viscosity increases drastically as a result of the considerable quantities of filling materials, one would usually choose much higher temperatures for filler-containing PTC polymer materials.

Yet the pressure used is not very high, for example 110 bar at HDPE containing 50% by volume of metal powder. Pressure values for further Materials are in the same range.

The plates thus formed can now for extended periods without any quality problems be stored. They can be used to cut special and very complicated component geometries. In this embodiment, high pressure water jet cutting is used. A typical geometry to cut is in 1 shown. The pressing direction during the pressing process is perpendicular to the plane of the figure. The panels are made by adding the thickness of the in 1 shown component pressed. Thus, only the in 1 to be recognized boundary lines to divide the pressed plate into individual components and to obtain the desired geometry. The current direction runs in the plane of the drawing and horizontally. How to get out 1 can recognize, the preferred geometry shows distinct ridges 1 in which the opening angle 2 of the material on each side of each ridge be 60 °. A typical bridge length can be about 2 cm. Several webs are, also in the electrical sense, parallel to each other.

The details of the geometry used herein are described in a prior application of the same Applicant, namely EP 00810069.5 with the application date of 25.01.00 and entitled "An electrical device comprising a PTC polymer element for overcurrent fault and short-circuit current fault protection" [an electrical device comprising a PTC polymer element for overcurrent and short circuit current fault protection] It is particularly preferred to use web lengths of at least 5 mm in the main flow direction, more preferably values of 7, 10, 15 or even 20 mm The web length should usually not be longer than 150 mm preferred values are 80, 40 and even 30 mm as upper limit The opening angle 2 of 60 ° in 1 that is, the opening angle of the restriction at the edge of the web in a longitudinal sectional plane containing the main flow direction should be at least 100 ° in the sum of both sides, preferably at least 110 ° (ie it is in 1 120 °). For further details and explanations, reference is made to the above mentioned earlier application.

The pressing process according to the invention has several advantages for the geometry outlined above, since it is quite difficult to do such produce long webs with injection molding. It is very important, especially within the footbridges, to have an optimal one material quality so that the Temperature reduction according to the invention to a greatly improved performance of the manufactured components leads.

The 2 and 3 show the improvement in the electrical characteristics achieved by the invention. In 2 a comparison between injection molded parts (triangular symbols) and parts according to the invention (square symbols) is shown. In a geometry according to 1 and a land length of 1.8 cm was the material composition 45 vol .-% HDPE / 35 Vol .-% _TiB2 / 20 vol .-% SiC.

Even though the resistance elements according to the invention a higher one Have cold resistance, i. a resistance at a normal conductive state, is the cold resistance compared to the injection molding example very stabilized. Dis meets the cold resistance after the first one Trigger and to each following cold resistance value after another Trigger up to the value after a tenth triggering too. Thus, this resistance element at least between the first and the ninth triggering very can be well described by a constant resistance value.

Farther are more trigger actions possible. The injection-molded resistor element was destroyed after the fourth trigger, in comparison to the ten trigger actions in the example according to the invention.

The Tests were short circuit tests at a system voltage of 690V (root mean square) and one expected short-circuit current of 12 kA (root mean square) at 50 Hz.

3 shows another example of the electrical characteristics of resistance elements according to the invention. The square symbols again refer to pressed and cut elements according to the invention, whereas the triangular and circular symbols refer to injection-molded and press-molded samples. Preßguß is a technique that is virtually between the injection molding and pressing. It is a quasi-static pressing of molten composite material into a mold to form a final product. The parameters are close to the limits defined by the melt flow of the material, for example the polymer material is at a lower temperature compared to injection molding. The press-molded elements are part of the invention, since the temperature limit is met. 3 shows, however, that the pressed and cut elements are even better. Table 2 shows the parameters used for the examples of 2 and 3 are relevant. It can be seen that during compression molding and pressing, the mold temperature and the material temperature are identical and both are less than 1.1 T _s . In the case of pressing, the temperature of 146 ° C is even below 1.03 T _s . The material temperature of the injection molding However, the element was 260 ° C, ie about 1.31 T _s . The pressure in the pressing process was only 110 bar, but was much higher in the other two cases.

The geometry was that of 1 with a bridge length of 2 cm. The material composition was 40 vol .-% HDPE / 40 Vol .-% _TiB2 / 20 vol .-% SiC. The electrical data of the tests in 3 were the same as stated above. In this case, the pressed and cut resistance element according to the invention exhibits a greater number of possible triggering actions and a more stable behavior between the first and the ninth triggering.

In any case can the differences between the cold resistance before the first triggering and the cold resistance after the first triggering optionally avoided by taking a triggering action in the manufacturing process.

Table 2

Claims (19)

A method of making a molded product from a PTC polymer material consisting of a conductive filler material and optionally further filler material in a matrix of polymeric material, wherein the product is formed by a molding process that deforms the PTC polymer material by means of heat and pressure characterized in that the PTC polymer material is heated during the molding process to an absolute temperature of at most 1.1 × T _s , where T _{S is} the absolute melting temperature of the matrix polymer material. The method of claim 1, wherein the molding process comprises pressing, an injection molding, an extrusion process or is an infiltration process. The method of claim 2, wherein the molding process is a pressing process or a Extrusion process is. Method according to one of the preceding claims, wherein the matrix polymer material PE, PP, ETFE, polyimide, PPS or PEEK includes. The method of claim 4, wherein the matrix polymer material mainly made of HDPE. Process according to claims 3 and 5, wherein the pressing process with a Pressure in the PTC polymer material of at most 300 bar, preferably 200 bar and more preferably 120 bar. A method according to any one of the preceding claims wherein the temperature is at most 1.075 x T _s and more preferably at most 1.05 x T _s . Method according to one of the preceding claims, wherein the PTC polymer material comprises a first conductive filler in an amount of 20 - 60 Vol .-%, preferably in an amount of 30 - 55 vol .-% and especially preferably in an amount of 35-50 vol.%. A method according to any one of the preceding claims, wherein the PTC polymer material comprises a first conductive filler, namely TiB ₂ . Method according to one of the preceding claims, wherein the PTC polymer material is a second filler having a varistor characteristic includes. The method of claim 10, wherein the second filler material doped SiC is. The method of claim 10 or 11, wherein the second filling material in an amount of 10 - 30 Vol .-%, preferably in an amount of 14 - 26 Vol .-% is contained. Method according to one of the preceding claims, wherein the matrix polymer material in an amount of 30-55 vol.%, preferably in an amount from 37 - 50 Vol .-% is included. Method for producing PTC elements from PTC polymer material, wherein semi-finished products with a method according to one of the preceding claims made of the PTC polymer material and wherein the semi-finished product is divided to create the PTC elements. The method of claim 14, wherein dividing by cutting (including saws) he follows. The method of claim 15, wherein said cutting by a high-pressure water jet or by means of a laser. A method according to any one of claims 14 to 16, wherein the semi-finished product is essentially a plate of PTC polymer material. A method according to any one of claims 14 to 17, wherein the PTC elements Resistor elements for the short-circuit interruption or the current limit can be established. The method of claim 18, wherein the resistive elements before commissioning a preliminary trip action be subjected.