DE1404373A1 - Method and device for the production of elongated and transverse structures made of polytetrafluoroethylene - Google Patents

Description

B e s c h r e i b u n g Method and device for production of structures made of polytetrafluoroethylene stretched in longitudinal and transverse directions the Invention relates to the manufacture of poles, ribbons and the like shaped Buildings made from Bluohydrocarbons, in particular from polytetrafluoroethylene, which are highly stretched and have high strengths.

If you press molding powder made of polytetrafluoroethylene su a film with just enough mechanical pressure that the starting material for the context is brought and no more voids remain between the particles, so is the film is friable, breaks with almost no stretching and generally crumbles, when pressed between rollers.

The toughness of such a film can be considerably improved, when heated to 2000-3000. At these temperatures a pressed Film passed between rollers and stretched so far that it thins and becomes longer in the rolling direction. If the film is then cooled to room temperature, it has considerable toughness and elongation in the rolling direction, provided that the rolling operation at least half the thickness of the original film Has decreased in value and doubled its length. The maximum dilution that this takes can be achieved is about 0.1 of the original thickness.

In addition, the film becomes brittle and torn. Higher temperatures in the range of about 3000 increase the possibility of diluting the original Foil. However, this processing only improves the stretching of the non-sintered ones Film in the rolling direction, while the film in the transverse direction is still friable and can be easily split into long splinters. The known methods of stretching in two directions by means of tensile stress in frame-like devices are non-sintered Polytetrafluoroethylene films cannot be used because they are not stretched State are very frictional, even when heated to a high temperature.

The present invention solves the problem of foils, binders and the like made of polytetrafluoroethylene with high stretching and high strength in longitudinal and cross direction.

The invention relates to a method in which polytetrafluoroethylene first stretched in the longitudinal direction by the action of clay pressure and the resulting Structure is still stretched in the transverse direction by applying further pressure. To this one The purpose is for the polymer to first flow through a narrowed passage and the material emerging from this passage is then passed through a second narrowed passage pressed in which it is essentially in a to the first plied seal perpendicular direction is made to flow. This is how the plastic becomes first in one direction and then in a substantially perpendicular to it running other direction stretched. For example, the polymer mass is pressed first through a square or round opening and forms a rod, whose cross-section corresponds to that of the opening. This rod is then through a Schlitsdtise pressed out of it in this second stretching phase forms a thin band. In this way, films or tapes of great lengths are obtained. The order of the nozzles can be reversed to accommodate cylindrical objects, g, D, Rods or threads. Regardless of the forms generated in each case, wind always effective shear forces, which a certain percentage of the particles of the Pormpulver, from which one assumes fibrils to form.

The first stretching operation creates a number of fibrils, which run in the direction of stretching, and the individual fibers are then unchanged or apparently unchanged plastic particles. In the second stretching phase of the method of the invention, a certain percentage of this is unchanged Particles in turn converted into fibrils, but they are now in the second direction of stretching run and therefore essentially perpendicular to those in the first stretching formed fibrils lie. These fibrils are also more or less spherical Surrounded unchanged plastic particles. Also some of the ones in the first stretching phase The fibrils formed are transverse to the film axis during the second stretching phase oriented. In this way, a shaped structure is created as a product of the process with a strong internal solidification, which is caused by that lying lengthways and transversely. Fibrils are more or less entangled and hold on to each other. This requires high levels of pest and allows strong Elongation.

Another object of the invention is a device for exercising of the method described, shown in the accompanying figures in one embodiment is shown.

Figure 1 inclines a section of the device allowing stretching in two directions; Figure 2 shows ii section the end face of the device from Figure 1g Figure 3 is a section in the plane 3-3 ton Figure 1 and shows the Uiriss of the part for the first stretch; Figure 4 is a section in the plane 4-4 of Figure 2 and shows the outline of the intermediate or transitional stage; Figure 5 is a section on the plane 5-5 of Figure 1 and shows the outline of second stretching phase; Figure 6 is a microscopic view of the plastic conglomerate after the first stretching; Figure 7 is a microscopic view of the plastic conglomerate after the long stretching.

According to Figure 1, a piston 10 is located in a cylindrical part 11 arranged. In the cylindrical part 11, the polytetrafluoroethylene is used as a molding powder or as a lubricated mixture, s, B, according to US Pat. No. 2,586 357, introduced. The supplied plastic material or the entire device can be heated to, for example, 2000 to 3200. When working with with lubricants mixed mixtures, it is recommended that the plastic mass through at room temperature usual, not shown, to introduce feed lines into the device. By Lowering the piston 10 becomes the plastic mass through the cylindrical Section 12 pressed through and stretched in the longitudinal direction. After leaving ouch section 12 is di. Mass pressed through the mold 13, which laterally expanded in relation to the fed stretched material. When passing through This porm stretches the material in the transverse direction. The product the double stretching is a tape made of polytetrafluoroethylene, the cross-section of which corresponds to that of form 13 (FIG. 5).

Figure 3 shows the cross section of tube 11, Figure 3 and 4 seigen the Cross Section of Section 12. The thickness of the various elements and their miscellaneous Dimensions can be varied within wide limits, depending on the amount of plastic, to be processed. The dimensions of one part in relation to those the others are in certain relationships.

In order to produce products with significant strength and elongation in length and transverse direction, the stretching must be at least in both directions twice the original dimensions. This principle can be exact in the requirements for the construction of devices for practicing the method of the invention. In Figure 1, r means the radius of the arc A or, in other words, the greatest distance in a straight line over the Plastic material from the output end of the cylinder 11 to the output end of the Werkseugs 13 moves. If the widening angle of the tool 13 is denoted as X, the cross-sectional area of the cylinder 11 as B and the width of the exit end of the tool 13 as H, and the width of the part 12 as W, then apply to the Construction the conditions:> longitudinal stretching = R = 2 rOH> transverse stretching = r O = 2 W If the plastic material passes through the tool 13 both be stretched in length as well as in transverse direction, 80 one shapes the circumference of the tool 13 such that its Cross-sectional area equal to or less than at the entry point or as the cross-sectional area of the exit end of part 12 is. It is essential that the cross-sectional area of the tool 13 either from the Entry level to exit level remains the same or decreases. If one leaves the cross-sectional area of the tool 13 become larger than the exit surface of the part 12, so that can Tear off plastic material in the tool, so that it is in the band to be produced Form cracks.

To allow the pouring of the material in the device of the invention investigate, different colored strands of molding powder were processed. Included it was observed that the material adhered to the surfaces of the bounding walls and slides within the device so that the primary displacements within the Material already occur when the material is under the pressure Adjusts the topography of the boundary sands within the device. The inner surfaces of the device are well polished so that the Rebunga forces are smaller than those for Shearing and working through the compressed material required forces. As a result, the plastic material comes into contact with the burning walls the device only a very small internal displacement in the material. The railways or tapes that are manufactured according to the process have smooth surfaces and can optionally be cut into smaller or different shapes or be slotted.

It is also possible to further work on the products of the process, if they have only been sufficiently stretched in the transverse direction. For example the tape is subjected to a further stretching after the transverse stretching by passing it between rollers and in this way a walking one Longitudinal stretching causes. Such a treatment affects the transverse elongation in general not or only marginally, but of course reduces the elongation that is still possible longitudinal. In a preferred embodiment of the method of the invention the plastic is at room temperature in the form of a dried dispersion of powdery polytetrafluoroethylene mixed with about 18 percent naphtha gasoline extruded.

The extruded tape is then cylindrical through the gap between two Rollers guided to further reduce its thickness and produce exactly the desired format to reach. The naphtha gas olin is evaporated from the rolled strip, whereupon it is cut to the desired widths.

Draw the shaped structures obtained as products of the process is characterized by a very characteristic physical structure from which @show their unusual properties. Figure 6 shows the microscopic Image of a product stretched only in the longitudinal direction The round, elliptical or In any case, non-fibrous particles 14 are not essentially in the form which they already owned before they were applied to the apparatus of the invention. During the first stretching operation of the invention, the fibrils formed 15 from, which essentially in a single direction, namely that of the longitudinal extension, are oriented.

After the second stretching, a number of spherical or substantially spherical particles converted into fibrils 16, the across the formed structure and predominantly at right angles to the first Yeratreekung formed fibrils lie. But there remains quite a number of spherical particles still unchanged and the fibrils 15 and 16 are of these surrounded or embedded in them. So a conglomerate has formed within its intertwining fibrils into a mass of spherical or approximately spherical Parts are embedded. The formation and entanglement of these fibrils is for that Toughness and the high elongations of the process products are responsible. This inner Structure is completely different from the structure obtained when stretching homogeneous linear high polymers such as polyethylene, polyamides and sintered polytetrafluoroethylene by stretching in two directions. In all of these cases, form only homogeneous structures that are consistently similar under the microscope. in the The case of the unsintered polytetrafluoroethylene forms after the process According to the invention, however, a heterogeneous structure that is partly unchanged and non-tibrillated particles and elsewhere relatively long and intertwined braided Contains fibrils, some of which are transverse and some of which are longitudinal. The invention allows the uniform and advantageous production of tapes, foils, sheets and the like, which are ideal for wrapping electrical conductors and other objects suitable. The process is also suitable for the production of rods and strands and the same. Thanks to the high elongation of the shaped ones made by the process Structures fit easily and precisely to the outlines of those to be covered with them Objects. The unsintered coating is easy to flow together by turning it to form a dense, homogeneous and tough coating srhitst to about 3300 or little over it to get that within a few minutes Bringing polymers to sintering.

In principle, the method is characterized in that the plastic material initially pressed through a limited space and from this to a second limited space Space reaches the cross-sectional area of which is smaller than that of the first space and through which the plastic is also pressed.

The largest cross-sectional area of the first space tapers to the smaller entry level of the second or connecting space-is the cross-section of the The first space is cylindrical, it tapers in a conical shape to form the connecting space. If the first space has a right-angled cross-section, it generally tapers in pyramid shape. In any case, learns when passing through these two rooms the plastic has a stretch in one direction. One often works with a right-angled Cross-section of the connecting space and a cylindrical or conical cross-section of the first room. In general, the longitudinal stretching is done first. Afterward the material is forced to flow in one direction and in such a way that it is practically perpendicular to the longitudinal axis of the flow in the previous space must flow. This is achieved by passing the material through a third room presses through, the cross-sectional area of which is not larger than that of the second l-skin and which changes over the length of the third room in such a way that it becomes low and wide when the exit surface of the second room round or square, or that it becomes relatively high and narrow when the exit surface of the second room was low and wide.

The method and apparatus of the invention allow processing different plastics, but especially the fluorocarbons and especially polytetrafluoroethylene in question.

The following examples illustrate embodiments of the Invention, a subsequent counterexample the poor results of the state-of-the-art methods.

EXAMPLE 1 A device according to Figure 1 is used with the following dimensions cylinder 11 diameter = 25 mm height of part 12 = 3.75 mm width of the part 12 s 15.6 mm tool 13 length r = 112.5 mm tool 15 slot width d = 75 mm tool 13 height H = 0.6 mm tool 13 angle (radians) a = 14.5 mm Man presses a dry dispersion of powdery polytetrafluoroethylene with 20 percent Naphtha gasoline at room temperature through the extruder and receives a tape that is about 75mm wide and 0.75mm thick. After evaporation of the naphtha gasoline is the stretching to the formation of cavities between the fibrils about 200 percent, both in the longitudinal and in the transverse direction. The flnnd is then between rollers passed through and thinned to 0.125 mm, while the width remains unchanged at 75 mm amounts to. After this treatment, the elongation in the transverse direction is still about Percent, while the elongation in the longitudinal direction is reduced to about 70 percent.

Gleie @ e @@ gehnis @@ rden received when mon others acquaintance Dispersants used, for example, in US Pat. No. 2,586 357 are described. If the device parts 11 and 13 are exchanged, the result is the product is a cylindrical rod. cloth corresponding devices with others Shapes of the cross-sectional areas result in strong structures of high elongation.

EXAMPLE 2 The device according to Example 1 is heated up about 250 °, charged the cylinder with granular, heated to the same temperature Polytetrafluoroethylene powder and lets the plastic pass through the extruder. Man - a tape that has an elongation of 50 to 75 percent in the longitudinal direction, in the transverse direction is 50 to 9 percent. This product too is firm and can withstand multiple kinks and other handling well. Man wrapped with the tape electrical conductors of various types and shapes, then sintered the wrapping and insulation that is both mechanically and electrically excellent Have properties.

3 e i a p i e 1 3 A \ cube is made in a mold by pressing of 12.5 mm edge length from a dried dispersion of Polyw tetrafluoroethylene with 0.5 percent soot and 20 percent naphtha gasoline. This cube is turned into a Cavity inserted into a cylinder of 25 mm diameter from the same ¢ plastic, but with the omission of the black pigment, is incised. This Plastic cylinder with the inserted black plastic cube is then according to Example 1 pressed by the device of only 1. The 3and thus formed contains a black stripe that is about 25 mm wide, 0.375 mm thick and about 175 mm long is. The front band of the black stripe has the shape of a convex that. rear edge that of a concave arc. The black pigmented cube Runst-stoff with an edge length of 12.5 mm is included - it is 14 times more pure ursprür @@ fchen Stretched length.

The experiment is repeated, but the extrusion is interrupted while the black plastic material is still inside the device is located. The device is taken apart and the plastic wedge it contains lifted out. It contains an inner wedge made of black plastic compound, the in its narrow part (device part 12) has a width of about 5 mm and becomes 25 mm wide in the extruded tape. From this it can be seen that in the procedure According to the invention, the plastic material is stretched up to approximately five times is shifted sideways. The observed and the calculated deformation of the black Plastic cubes with an edge length of 12.5 n face each other as follows: observed calculates transverse direction S-fold 4.9-fold r9 4.5. 0.68 0.625 lengthways 14-fold 10.3-fold B 3,14.0.25 = r @ H 4.5.0.68.0.25 This shows that the processed material communicated deformations correspond to those necessary to adapt to the limiting Passages are required and that the stretching of a bulk cube are calculated according to the geometry of the passage through which the plastic material is performed according to the invention in the device.

This example also shows that within the scope of the invention Plastic masses can be processed with fillers, for example pigments, Titanium dioxide, asbestos, aluminum silicate, glass and the like in powder or fibrous form Shape. Such filled plastics are also made according to the method of the invention Obtain strong uniform products with high length.

G e n g e p i o r t Between two pressure plates, one Dispersion of dry polytetrafluoroethylene in 20 percent by weight of naphtha gasoline with a pressure of 225 kg on 6.25 qom a plate made of non-sintered polytetrafluoroethylene Made in a dimension of 50 x 50 mm and with a thickness of about 3 mm. The T "pt is pretty cheesy and won't fold or fold over more than a few Stretch percent without breaking.

A plate made in the same way is placed between two rollers Having passed through, their thickness was reduced from 3 to 1.5 mm, their length increased 100 mm enlarged. The film obtained in this way can be spread over its narrow width fold without breaking, but splinters if you fold them lengthways seeks.

As in the previous paragraph, a film 1.5 mm thick is made here, but then roll it out again between two rollers in the transverse direction, so that a film of 0.75 mm thickness in a format of 100 x 100 mm is created. These Foil can be folded in any direction without splintering and can be more than 50 percent stretched before it shows flaws that are noticeable to the eye.

A film is produced as in the preceding paragraph and then roll it out again in the direction of the first roll down to 0.125 mm. IEan receives a tape about 600 mm long and 100 mm wide, which extends lengthways and the transverse direction can be stretched over 50 percent without recognizing any visible defects permit.

You work as in the previous paragraphs, but with a grainy one Polytetrafluoroethylene powder, which at about 1350 kg pressure on 6.25 square cm to plates of 50 x 50 mm and 3 mm thick pressed vnirde. These plates are very brittle and will destroyed if you try to roll them at room temperature. If you heat them up about 250 ° and then guides them through rollers, which are also heated to this temperature, in this way, films with the same stretching behavior can be produced in the same way as before produce. But if you roll out the foil to a bead of 0.125 mm, then show sicl malfunctions.

Claims (12)

P a t e n t a n s p r ü c h e 1.) Process for manufacturing lengthways and transversely stretched molded structures made from unsintered polytetrafluoroethylene or other fluorocarbons, characterized in that the plastic one after the other through two narrowed passages and so first in one direction and then causes it to flow in a direction substantially perpendicular thereto, the plastic either in powder form or with lubricating or sliding making additives is applied. 2. The method according to claim 1, characterized in that the plastic is pressed successively through three chambers or spaces, of which the middle one has a smaller cross-sectional area than the exit cross-section of the first, while the area of the exit cross-section of the third space is not greater than that is the exit surface of the second space and its flow axis is practically right-angled to the flow axis of the second space, based on the freedom of expansion of the plastic, runs. 3. The method according to claim 1 or 2, characterized in that the Forms emerging from the last room are planar. 4. The method according to claim 1 to 3, characterized in that the The structures emerging from the last room are non-planar. 5. The method according to claim 1 to 4, characterized in that the Shaped structures made of non-sintered tlaorohydrocarbon emerging from the last room, in particular polyfluorotetraethylene, then by the action of heat for sintering is brought. 6. Device sur exercising the method according to claim 1 to 4, characterized by a first molding chamber with input and Outlet opening for the plastic, a second molding chamber adjoining this outlet opening, whose cross-sectional area is smaller than the largest cross-sectional area of the first chamber is and which also has an inlet and outlet opening for the plastic material possesses, and a third shaping chamber adjoining the last-mentioned outlet opening, whose cross-sectional area is not larger than the exit area of the second chamber and changes in the course of its length in such a way that it is typically different or opposite configuration than the exit surface of the second molding chamber accepts. 7. Apparatus according to claim 1, characterized in that the exit surface of the second forming chamber is round, square or similarly compact, while the The exit surface of the third molding chamber is flat and wide. 8. Apparatus according to claim 6, characterized in that the exit surface of the second Pormunga chamber is flat and wide, while the exit surface of the third molding chamber has a round, square or similar compact shape. 9. Apparatus according to claim 6 to 8, characterized in that the third molding chamber is designed as a tool whose cross-sectional shape changes gradually over its length and by that of the second shaping space supplied plastic molding has a flow resistance in a practically vertical direction to the longitudinal axis of the tool. 10. Apparatus according to claim 6 to 9, characterized in that the ratio of the surface area to the cross-section of the first shaping roughness see below of the third forming space and the ratio of the width of the outlet openings of the second and the third forming space is at least 2 t 1. 11. Apparatus according to claim 6 to 10, characterized in that the amount of longitudinal stretching from the inlet opening of the first shaping space corresponds to the formula B / r # H up to the outlet opening of the third molding space and has at least the value 2, while r # H is the transverse extension of the formula r # / W and has at least the value 2, where B is the largest cross-sectional area of the first shaping space, r is the longest straight-line distance from the outlet opening of the first shaping space to that of the third shaping space, ç the angle of inclination in the third molding space, B the width of the outlet opening of the third molding space and W denotes the width of the outlet opening of the second molding space. 12. Shaped structure with flat or non-flat shape and a main axis, the length of which is a high multiple of the other two axes, characterized in that it consists of unsintered polytetrafluoroethylene, which is partly in the form of spherical particles, partly in the form of fibers or fibrils, the fibrils lying transversely and longitudinally to the main axis and intertwined and are embedded between the spherical particles.