DE1494293A1 - Manufacture of molded structures from polytetrafluoroethylene - Google Patents

Description

Manufacture of molded structures from Polyte trailuoräthylen Di. Invention bezicht on a process only production of structures from polytetrafluoroethylene.

The discovery only provides a novel process, the @an can be referred to as slip-forming.

This consists in the fact that in. At first an 'essentially hydrostatic versehaslabare (coalesoible) Tetrafluoräthylenhar @@@ sse manufactures from porous Aggregates of colloidal @ Tetrafluoräthylenhar @@@ particles in a liquid embedding (Matrix) with an initial liquid: resin volume ratio of at least 0.65, and then deform this mass into a film-like or skin-shaped structure. These takes place using compressive shear forces, in which the compressive components predominantly normal to the areal expansion of the structure and the gravitational forces are directed biaxially and predominantly parallel to these surfaces. With this deformation fluidity is expressed from the structure until the fluid: resin volume ratio in it less than ale 0.65, with nan the structure under an essentially Holds in hydrostatic condition.

The film-like structures obtained in this way shrink during drying and sintering by less than 39 vol% and contained the polytetrafluoroethylene substantially entirely in pora of discreet leaflets or lamellae of a thickness less than 10 microns, which is molecularly oriented parallel to the surface area of the structure are. The structures have exceptional cohesive strength, and was both on their own as well as when they form solid objects with one another are laminated, d. H. form a laminate. You can get rid of lubricant and are sintered, making objects of extraordinarily high cohesive strength develop.

In the preferred embodiment of the 3 bond, the initial one occurs Liquid: resin volume ratio at least 0.75, and the biaxially attacking Shear forces are during or after the decrease in the liquid: resin volume ratio to below 0.65, but during the forming object in substantially hydrostatic condition is maintained at a minimum: maximum ratio to each other normal vectors of at least 0.4 borrowed. The structures thus obtained have a minimum: Mzsimum ratio of the social orientation of at least 0.4 in the plane parallel to its areal extent, and less than 0.7 in the plane lying in its areal extent. The structures are particularly excellent in particular to their cohesive strength and also have excellent dimensional stability during sintering.

Fusible Tetrafluoräth lenharze are known. Masses of this The type and its production are described, for example, in US Patents 2,510 112, 2,586,357, 2,593,582, 2,670,417, 2,685,707 and in British Patent 829 503. Such masses contain tetrafluoroethylene urine from a crystal melting point (Transition point) above 320, preferably from 325 to 32700 in general terms spherical porous aggregates from 5 to 700 microns in diameter by im general spherical colloidal resin particles from 0.05 to 0.5 micron diameter resins of this type are commercially available as tetrafluoroethylene resin fine powder available. The meltable tetrafluoroethylene resin compounds also contain a liquid Lubricant which is able to wet the perfluorocarbon resin, wherein the tetrafluoroethylene resin expediently has a critical angle with a smooth plate less than 90, preferably less than 450 forms.

The lubricants preferably have a viscosity in the range of 0.4 to 1000 P at roughness temperature, although also liquids of higher or lower viscosity can be used. Relatively volatile hydrocarbon liquids, such as refined kerosene, are generally used for reasons of economy in those cases where it is desired, the lubricant is preferred over the Remove sintering by volatilization. You can also use less volatile lubricants use and, if necessary, extract with more volatile liquids or leave them in place if the mass will be used as fuel is intended or is intended for another purpose for which the removal the lubricant is not required.

Xan can also contain unsaturated monomers or monomers and polymers Syrups polymerize in situ after shaping, creating unsintered items of increased Rigidity or restoring force arise. The fusible ones Masses can also contain finely divided solid fillers for pigmentation, thickening, Stretching or increasing the flammability or conductivity of the finished object contain. The amount of such fillers is not critical as long as the hydrostatic fusible mass is preserved as such, and can bia su 95 vol% of the total amount of Pestetoffe present. For a nazimal regularity of the mass are the filler particles are preferably non-porous and smaller in diameter than 10 microns. Amounts in excess of 20 s result in maximum tensile strength in unsintered State0 The amount of liquid that is necessary in a hydrostatic fusible The mass obtained depends on the size and the porosity of the discrete solid particles away. Commercially available tetrafluoroethylene barz fine powders contain discrete porous aggregates of an average diameter of about 300 microns and require -like 3 to 6 Rouuterle liquid each, displacement space part resin, and a hydrostatic Forming mass without compaction of the aggregates. With increasing compaction of the Aggregates ni @@ t the required amount until it is at a liquid: resin volume ratio slightly less than 0.4 is difficult to maintain hydrostatic conditions.

If the compaction is not carried out hydrostatically, agglomerate the aggregates with progressive compression with formation becoming increasingly larger Particles, and the structures are compared to structures that are in the same Way, but under hydrostatic conditions, were compacted, becoming increasingly friable.

According to the preferred embodiment of the invention, it is necessary to achieve this a maximum cohesive strength, a non-compacted tetrafluoroethylene resin fine powder first hemmed in 20 to 40 rough parts of a resin-wetting liquid and the cutting action of a YlUgel clock rotating at high speed subjected to discrete in general at temperatures ranging from 0 to 600C Obtain spherical aggregates that have an average diameter of 10 microns or less.

Cutting temperatures below 1900 are preferred for plasticizing of the aggregates to a minimum. If finely divided fillers are to be used, expediently adds this to the slurry before this to the cutting effect is suspended in order to facilitate an even distribution. But you can even small aggregates are obtained by taking from an aqueous colloidal dispersion This is a water-immiscible liquid such as carbon tetrachloride mixed in, then one Add electrolytes such as hydrochloric acid, stir until the resin is transferred to the non-aqueous plus and the aqueous phase is through Separate decanting. In any case, excess lubricant is then removed, to leave a hydrostatic mass that has a liquid: resin volume ratio of slightly above 0.75 and is then subjected to further deformation, To calculate the liquid: resin volume ratio, use the volume of the tetrafluoroethylene resin taken as a weight divided by 2.3.

A more economical, if somewhat less effective, process the uncompacted fine powder is carefully mixed with the liquid at a liquid: resin (displacement) volume ratio blurred by 0.65 or more and this genic compacted, bit a hydrostatic one sae for further deformation is obtained. The advantages of the invention will be somewhat diminished if the powders are partially compacted before using the Lubricants can be mixed, or if not compacted powder with resin-wetting agents Liquid at liquid:: resin volume ratios below half 0.75 mixed and then compressed into the hydroatatic state for further deformation. However, powders that have been excessively compacted prior to mixing will form no hydrostatic, fusible leave.

See the hydrostatic fusible masses according to the invention gray and have a uniform structure.

When they are constricted, they transmit the pressure hydrostatically. Every beginning deviation from the hydrostatic state shows that the Surface that begins to whiten and tiny cracks form, or in a limited space it shows itself by falling off the Drgoke in places next to it a compression point. If there is an incipient deviation in the course of the deformation Noticed by hydrostatic state, this state of the mass can be renewed by Saturation of the same with further amounts of the hard-wetting liquid is restored will.

In the following deformation of the hydrostatic, fusible let squeezing out lubricant become the discrete, porous, spherical Aggregates of the colloidal resin particles converted into parallel lamellae, which in have substantially greater length and width than thickness and with their flat Expansion are arranged parallel through the thickness of the formed object. It should be noted that the application of a nornal sur surface of the structure directional compression force without accompanying shear stress or application a shear force parallel to the surface of the structure without accompanying compressive stress the formation of the waxed fine structure does not interfere. Therefore such a independent Loading through compression and shear stresses take place and: will also in some cases from the end of cooking of the expediency in the course the deformation preferred. Furthermore, there is only a relatively small deformation the resin aggregates takes place until the liquid: resin volume ratio in the structure reduced to a value below 0.75, the direction of the applied compression and shear forces at higher liquid: resin volume ratios not critical, unless maximum cohesive strength is desired. Same with liquid: Hzrz volume ratios below 0.75 there may be minor deviations from the prescribed orientation the compression and shear forces due to a further deformation at the prescribed Orientation.

In the course of the deformation, as described above, the porous spherical resin aggregates converted into lamellae.

As long as the serforming that takes place with the squeezing out of liquid when approaching a liquid: resin volume distribution of less than 0.65 progresses, only relatively minor ones occur outside the discrete aggregates Tensions on. However, if the fluid: Har ratio decreases below this value is, essentially all of the particles inside are subject to strong stresses with the result that they are essentially stay discreet, but practically entirely converted into thin, tightly packed lamellae, which parallel to their two-dimensional extension, a pronounced molecular orientation aufueisen. In addition, there is the agimuthal molecular orientation within the lamellae due to the biaxial orientation of the prescribed shear forces are unequal. In the preferred implementation of the invention, in which the shear forces at a minimum: maximum ratios of mutually normal vectors of at least 0.4, the structures obtained have a corresponding agimutal Minimum: maximum directional orientation and point in the particularly preferred embodiment if at all, only a low preferred agimuthal orientation.

The deformation itself can be carried out over a wide temperature range will. At temperatures below 1900, however, pressure fusibility tends to be the mass leads to a reduction, while at temperatures above 19,000 the tendency to agglomerate of the discrete resin aggregates, even if you have relatively non-volatile liquids used to avoid hydrostatic losses is increased, although the for Deformation of the mass required shear forces have become minimal. Accordingly it is generally preferred that the. Deformation at temperatures from 20 to .40 ° C to be carried out, if not during the deformation your high shear forces for the application @@@ to be brought.

As a further consequence of squeezing out the liquid until the liquid: resin volume ratio is lowered below 0.65, the discrete lamellae are packed so tightly that the Thickness of the thin liquid films that separate the lamellae, evenly the same order of magnitude as the distances are reduced: which is the final separate colloidal resin particles within the lamellae. When the final colloidal Harp particles have approached so closely and evenly, it will not be possible that To dry the structure and to sinter it to a flawless, non-porous structure, without the strength-giving molecular orientation of the individual lamellae to destroy. In the case of more extensive or less even distances, however, incline the deformed particles to regain their induced molecular orientation, before they grow together to form flawless non-porous structures, creating structures of normal cohesive strength. The sintered structures of high cohesive strength also differ significantly from structures that are after the .sintering treatment subjected to the action of orienting shear forces became. In the latter case, the oriented structure shows a massive elastic Memory in such a way that when heated to elevated temperatures it quickly turns into its non-oriented massive state is transformed back into oriented structures, ' which by drying and Sintering the new preforms according to Invention obtained are practically dimensionally stable at elevated temperatures and require a long time, on the order of 30 minutes or more at temperatures over 38,000 to experience a noticeable change in shape. To structures of masimaler Achieving strength in the sintered state becomes that required for sintering Heating is preferably carried out at temperatures above 3400C for the maximum period of time, which is necessary to obtain a satisfactory void-free structure, z. B. 10 to 30 minutes to 360 bia 3900C and even shorter bia down to 0.5 minutes at higher temperatures for very thin structures below the temperature of resin decomposition.

In the examples, all data refer to parts, amounts and Percentage of displacement, unless otherwise stated.

B e i 5 p i e 1 1 A commercially available tetrafluoroethylene resin fine powder, that consists of discrete spherical aggregates with an average diameter of about 300 microns is in refined kerosene of 20 times the displacement volume Slurried and a minute at room temperature, the effect of a rotating Subject to the cutting knife whose slinging with a peripheral speed of about 600 m / minute, and the average size of the discrete units reduce to about tO microns su. The slurry becomes after the cutting treatment placed on a suction filter, covered with a flexible rubber sheet and under Suction sur removal of the lubricant compacted, with a hydrostatic fusible Filter cake remains in which the liquid: resin volume ratio is about 0.8. The cake is used on a flat metal surface and is monoaxial rolled out into an elongated polie about 1.5 mm thick, with nan uses a cylindrical metal roller that is above and parallel to the flat surface on 2 sets of 12 stacked washers of a thickness of each 0.127 mm is supported. After this rolling process, one half of the elongated The foil is carefully picked up and placed congruently over the other half, un Two-layer structure, see below, in which the two halves of the original Cover the longitudinal axis of the film. This layer structure is then picked up, around 900 rotated in the horizontal plane, brought back onto the flat metal surface and again rolled out to a thickness of 1.5 mm in the same manner as before. The following The steps of doubling, turning and rolling are then repeated several times, where nan after each rolling process @g a washer of 0.127 mm of thickness from each roller base, until finally a film of one Thickness of about o, 635-mn has arisen. In the course of this sliding deformation Kerosene is squeezed out of the surface of the formed film until the liquid: Resin volume ratio within the film is about 0.64, although the structure is still hydrostatic, looks uniformly gray and has no visible cracks.

The measures and vest described below are on. hydrostatic Foils carried out, which would be produced in the following way: (a) The hydrostatic Foil is gently heated to remove keroain and heated for 20 minutes sintered to 380 ° C and cooled to room temperature in air. The population is shrinking un less than 35 vol%, the ratio of length to width being essentially remains constant and a practically void-free structure is retained. According to According to ASTM-D-1457-56T, the sintered film has a breaking strength of about 422 kg / cm2 both in the longitudinal and in the width direction, and an elongation at break of etvia 500% o In this test, the amount required to continue the stretch increases Loading progressively so that a defined yield point is not achieved If heated for a further 20 minutes at 380 ° C the film shows a very small change in shape and a small decrease in strength values.

(b) The hydrostatic sheet becomes un 500% in the length and width directions stretched without giving blemishes or cracks. It is also consecutive gradually in perpendicular directions to a defect-free sheet of a thickness stretched less than 0.025mm and stepped in perpendicular directions in a defect-free film of a thickness of less than 0.025 mm is rolled out while one maintains a liquid film on the surface, and the hydrostatic one State to be maintained0 In these stretching and rolling processes, the hydrostatic film has a low elasticity and gains about 5% of the induced Stretching back when the stretching tension ceases. It will give similar results as indicated in paragraph (a), if you use the slide as in paragraph (a) specified dries and sintered free (c) The hydrostatic film is over a vented hemispherical cavity and placed under the pressure of a flowing Medium, which is used through a rubber barrier layer, is adapted to the flohlraiim. The pressure is applied several times to allow elastic recovery practically to eliminate. The preform obtained in this way is dried and at 380 ° C. for 30 minutes Free-sintered to a flawless. hemisphere see below The sintered structure shows strength properties similar to those according to paragraph (a).

(d) The hydrostatic pole is placed over a 10 x 10, -cm copper screen (16 # 20 sticks) made of copper wire 0.635 mm in diameter is, and rolled into the mesh of this screen. After drying and, 30 minutes Sintering at 380 ° C gives a defect-free reinforced structure0 (3) At rapid drying of the hydrostatic film at 380 ° C, without. beforehand for removal of lubricant, to dry, separate eggob lamellae of one, thickness of 5 microns or less on the surface of the film.

In the case of an identical, but, with the stipulation manufactured film, That the solids contained 2 P carbon black is shown by microscopic examination of frozen ones Microtome cross-sections of the hydrostatic film at 400x magnification that the lamellae are discrete, about 1 to 5 microns thick, and the lateral dimensions are several times as large, and the lanelles in planes parallel arranged below the surfaces of the film and no spherical particles can be seen are. Examination of the same cross-section under the electron microscope at a magnification of 10,000 diameters shows that the final colloidal particles of uniformly packed an average diameter of 0.1 to 0.3 microns and almost touch each other. cherished from the hydrostatic foil Disc is examined radiographically. Rierbei becomes a by a circular. X-ray beam incident through the hole directed perpendicular to the flat film surface.

The continuous beam is recorded on a sheet of film, the is also arranged perpendicular to the flat film surface. The intensity of the Debye-Scherrer-Ring (100), which with a Bragg layer line spacing of about 4.9 Å (25 ° C) occurs, is a puncture of the location on the periphery of the Debye-Scherrer ring enjoyed. At the points of maximum and minimum intensity, it crosses the Debye-Scherrer ring a radial intensity measurement carried out, where nanohmiest a distance, of all angles within 50 of the Bragg angle defining the ring is equivalent to.

The areas of the crystalline (100) vertices above the diffuse background blackening at each point are compared, and a minimum: maximum ratio of approximately t to get what indicates that the molecular orientation is in all directions is practically uniform parallel to the flat surfaces of the disc.

A rectangular segment 0.635 mm wide will now be made from the disk cut out and examined by a similar technique, but using the X-ray Enters through a trimmed edge, penetrating the segment in its width and exits through the opposite cut edge. In this case become maximum intensities in directions normal to the uncut areas observed, and minimal intensities in directions parallel to the uncut Areas, at a minimum: maximum ratio of about 0.4, reflecting the molecular orientation indicates in the plane parallel to the planar surfaces of the structure.

B e i s p i e l 2 Commercially available tetrafluoroethylene resin powder of the type described in. Beiapiel 1 and refined kerosene are in a cylindrical The vessel collapsed to form an even mixture of 60 parts of tetrafluoroethylene resin and 40 parts of kerosene. The mixture is under a pressure of 14 kg / cm2 compressed to a hydrostatic, fusible mass in the form of a hollow cylinder 8.2 cm Diameter with a concentric bore of 19.6 mm to get. The hollow cylinder is attached to a cylindrical extruder cylinder from Abandoned 8.3 cm in diameter, of a concentric spike 18.4 'nn in diameter which extends through the cylinder to the hose nozzle and at an apex angle of 30 ° to a cylindrical opening of 22.43 mm in diameter and tapers 8 inches in length. The mast is raised at a speed of approx 30 cm / minute to form a tube with a wall thickness of about 2 mm and an outside diameter is about 22 mm.

During the extrusion, the liquid: resin volume ratio remains practically unchanged, In contrast to the results given below, shows a Sample of this extrudate when dried and sintered at 380 ° C for 30 minutes will have a tensile strength of about 316 kg / cm2 in the machine (extrude) direction and about 225 kg / cm2 in the transverse (circumferential) direction.

Another blessing of the hydrostatic hose is in a series of rolling operations that correspond to those of Example 1 with the exception, that in the present case a metal cylinder of 12.7mm diameter for rolling is used and all rolling operations take place in the transverse direction, except for one outer diameter rolled out from 10.5 cm. In the course of the rolling treatment, liquid becomes out of the hose squeezed out while maintaining hydrostatic conditions until the liquid: resin volume ratio is about 0.64. By drying and sintering the rolled-out Segrientes for 10 minutes at 3800C, an im is obtained essentially void-free product, which has a tensile strength of about 394 kg / cm2 has both longitudinal and transverse directions, and deseen other properties correspond roughly to the few, as they are in the numbered paragraphs of the example 1 are specified if this was determined on samples from the hose walls are cut out and carefully spread out. The slats of this example are less than about 10 microns thick and have a substantially larger average Diameter than the few of example 1. e i s p i e l 3 It is through a Extrusion process similar to that of Example 2 produced a hose, however, with the proviso that the mandrel, which penetrates the mold, starts here provided its circumference with 4 rounded projections of about 6.35 m in diameter which is arranged on the surface of the mandrel 900 in a spiral shape offset from one another are such that they start 10 on from the outlet end of the proseform and about 7 1/2 cm from it, and radially bia at a distance of 0.5 mm from the inner wall the The mold protrudes, the mandrel rotates during the ejection process at 60 revolutions / minute. Be in the course of the pass through the mold the walls of the hose while maintaining hydrostatic conditions up spread to a thickness of about 0.5 mm; the liquid: resin volume ratio inside the hose is made up by the action of the rotating projections about 0.63 reduced, with the squeezed out liquid through the annular space between the mandrel and the inner wall of the hose is exuded.

A segment of the extruded tube has a minimum to maximum directional orientation in the plane tangentially parallel to the hose surface of about 0.4, and a minimum to maximum molecular orientation in the plane normal to the tube surface is about 0.5, determined on a carefully spread wall segment. By Drying and sintering for 10 minutes at 38,000 gives an essentially void-free Hose that has a tensile strength of about 350 kg / cm2 in both extrusion and Has transverse direction, determined by the method of paragraph (a) of the example 1. The sintered tube also exhibits markedly improved resistance to Exudation when exposed to fluid pressures compared to in conventionally extruded tubing of similar wall thickness values and diameter. For this The reason is that produced according to the invention Hose is particularly suitable as a component of a braided hose.

Similar results are achieved if the one ejected from the mold hydrostatic hose before drying or sintering by the pressure of a flowing Medium is further expanded.

Example @ 4 According to the method of Example 1, a hydrostatiache Sealable mass produced with the proviso that the initial slurry from 40 parts of resin powder, 30 parts of aluminum powder and 30 parts of powdered potassium chloride consists of 2,000 parts of kerosene. The hydrostatic mass is according to the procedure from example 1 slide deformed into a 0.635 mm thick film. The film obtained is rolled up under slight tension to form a solid cylinder about 12 cm in diameter to build. The poles are heated to remove most of the liquid evaporate as the winding progresses. The resulting cylinder is very uniform and visually flawless. A massive object that emerged from it cut segment has a tensile strength of over 7 kg / cm2.

Similar masses of excellent burning properties are obtained, if, instead of aluminum powder and potassium chloride, components of the thermite process are used used as fillers.

EXAMPLE 5 The manufacture of the attachment and the sliding deformation are carried out under nitrogen. 1 part commercial polytetrafluoroethylene fine powder is slurried with 20 parts of liquid 1,1,7-trihydrododecafluoroheptyl methacrylate, containing 0.05 part of N, N'-dimethyl-p-toluidine and 0.5 part of benzoyl peroxide. Excess liquid is filtered off to obtain a hydrostatic mass, which contains about 1 part resin and 2.3 parts liquid.

This mast is made according to the procedure of Example 1 into a 0.635 mn thick film slip deformed. Overlying layers of the film are over laid a ventilated cone-shaped cavity with a rounded bottom, and, as in Example 1, deformed around the film by pressure of a flowing medium close to the wall de.

Create a cavity until a 6.3 mm thick jacket is obtained. The resulting laminate is hardened in the cavity for 24 hours to remove the remaining Polymerize liquid in situ. The resulting product is extremely tough and has excellent shock resistance and excellent electrical properties.

Claims (14)

p a t e n t a n s p r ü c h e 1. Process for the production of shaped Structure made of polytetrafluorethylene, characterized in that an essentially hydrostatic, fusible tetrafluoroethylene resin mass produced, which from porous aggregates of colloidal tetrafluoroethylene resin solids in an embedding liquid with an initial liquid: resin volume ratio of less than 0965, then this mass by the action of compressive shear forces, the compressive Components predominantly normal to the areal expansion of the structure and the shear forces are directed biaxially and predominantly parallel to the two-dimensional extent, in a Foil-like structure is deformed and liquid from the structure during this deformation squeezes out until the liquid: resin volume ratio in the structure is less is than 0.65 and maintains essentially hydrostatic conditions. 2. The method according to claim 1, characterized in that the initial Liquid: resin volume ratio is at least 0.75. 3. The method according to claim 1, characterized in that the shear forces biaxial at a minimum: maximum ratio of mutually normal vectors of at least 0.4 can be directed. 4. Verfahren @ inob claim 1, characterized in that the film-shaped structure su a laminated body 5. Verfahrea according to claim 4, characterized geke @@ seichnet that the hydrestatic negligible mass is an essential Contains non-porous, finely divided solid filler. 6. The method according to claim 1, characterized in that the film-like structure dry and at a temperature of 360 to 390 ° C 10 to Slat for 30 minutes. 7. The method according to claim 1, characterized in that the liquid A polymerisable ethylenically water-saturated compound is and this polymerisable Compound is polymerized after the Verferung in @ i @ n. 8. Film-shaped structure, containing 0 to 39 per 100 parts by volume Parts of liquid and 100 to 61 parts of solid material, you in turn from 5 to 100 vol% tetrafluoroethylene resin and 95 to 0 vol% faintailigem solid filler, the structure has a volume shrinkage of less than 39% on drying and Has sintering and is further characterized thereby. that au fluoroethylene hares is essentially ugly in the form of discrete la @ elles containing one dicks of less than 10 microns and parallel to the surfaces of the structure molecular are oriented. 9. Structure Moh claim S, characterized in that the molkulars Orientation of the lanelles a minimum: maximum ratio of the axial orientation of at least 0.4 in the Ebese parallel sa the surfaces of the structure and ves waniger than 0.7 in the Ebans normal se corresponds to this area. 10. The structure gesäes claim 9 in Schlemchform. 11. The structure according to claim @ in l @@ i @@ rer F @@@@. 12. The S @@@@@@@ according to claim 11, wherein the solid material @ 0 to @ 5 vol% de @ finely divided solid precipitates au @ night. 13. Essentially hollow-free, thermally dimensionally stable film-shaped Tetrafluoroethylene hares structure having a tensile strength of at least about 350 kg / om2 in at least 2 mutually perpendicular directions, measured according to ASTH-D-1 457-56T. 14. The structure of claim 13 in the form of a tube.