JPH0436181B2 - - Google Patents

Description

Claim 1: Randomly dispersed in a solid polymeric matrix, about
A solid polymer having reinforcing fibers of length greater than 1270 microns (0.05 inch) and less than such that entanglement occurs during wet mixing with said polymer and having an aspect ratio within the range of 100:1 to 300:1. A reinforcing material comprising a matrix, wherein the polymer is selected from polyethylene and polytetrafluoroethylene and has a molecular weight greater than 1 million, and the fibers are each independent within the polymer matrix. The fibers are dispersed and arranged irregularly with respect to each other primarily in a planar manner, and are held firmly in place by the polymer matrix to form a network of fibers that extends throughout the polymer matrix, thereby making the reinforcing material more susceptible to creep and abrasion. A reinforcing material characterized by stabilizing against. 2. The reinforcing material according to claim 1, wherein the fibers are made of an organic polymer. 3. The reinforcing material according to claim 2, wherein the fibers are made of aromatic polyamide. 4. The reinforcing material according to claim 1, wherein the fibers are selected from the group consisting of boron, glass, graphite, quartz and metal. 5. The reinforcing material according to claim 1, having a mixing ratio of 5 to 60% by weight of fibers and 40 to 95% by weight of polymer. 6. The reinforcing material according to claim 5, having a mixing ratio of 5 to 15% by weight of fibers and 85 to 95% by weight of polymer. 7 a The polymer has a molecular weight of 2×10 ⁶ to 6×
10 ⁶ , a polyethylene with a particle size of 300 μm, and b the fibers have a length of 3175 μm and an aspect ratio of 250:
1. The reinforcing material according to claim 1, which is an aromatic polyamide. 8 Randomly dispersed in a solid polymer matrix, approximately
A solid polymer having reinforcing fibers of length greater than 1270 microns (0.05 inch) and less than such that entanglement occurs during wet mixing with said polymer and having an aspect ratio within the range of 100:1 to 300:1. A reinforcing material comprising a matrix, wherein the polymer is selected from polyethylene and polytetrafluoroethylene and has a molecular weight greater than 1 million, and the fibers are each independent within the polymer matrix. dispersed, irregularly arranged with respect to each other primarily in a planar manner, and mechanically anchored to form a network of fibers extending throughout the polymer matrix, thereby stabilizing the reinforcing material against creep and abrasion. A piston ring seal formed from a reinforced material characterized by: 9 a) providing a macromolecular weight polymer of a predetermined particle size selected from polyethylene and polytetrafluoroethylene and having a molecular weight greater than 1 million; b) during wet mixing with said polymer for a length greater than about 1270 microns (0.05 inch); The length is shorter than that at which tangling occurs, and is 100:1 to 300:1.
providing an inert liquid carrier capable of uniformly dispersing fibers and polymer particles having aspect ratios within the range of c. mixing the fibers and polymer particles in the inert carrier such that a uniform dispersion is obtained; d This mixed solution is passed through a filter to obtain an intermediate on the filter consisting of a fiber network randomly oriented in a quasi-isotropic arrangement and polymer particles dispersed in the gaps, and e this The intermediate is dried to remove excess liquid carrier, f a positive pressure is applied to this intermediate to remove any air entrapped within it and densify it, and g the polymer dissolves but the fibers do not. The dense intermediate is compressed in a mold at high temperatures such as How to manufacture. 10. The method of claim 9, wherein the proportion of the mixture of fibers and polymer does not exceed 3% by weight of the total mixture of liquid carrier, fibers and polymer. 11 a The polymer has a molecular weight of 2 million to 300
10,000, the fiber is made of polyethylene with a particle size of 300 μm, and b the fiber has a length of 3175 μm and an aspect ratio of 250:
1 aromatic polyamide, c the positive pressure for densification is approximately 5000 lbs/in 2 (34 x ¹⁰ Pascals), and d the compression is up to 5000 lbs/in 2 (34
10. The method of claim ⁹ , wherein said elevated temperature is approximately 204°C (400°F). FIELD OF THE INVENTION The present invention relates to reinforcing materials of solid-solid composition consisting of polymers and fibers. More specifically, the present invention relates to a reinforcement material made of a macromolecular weight polymer reinforced with relatively long fibers greater than 0.05 inches (1270 μm) in length, which is itself a lubricant, and which is resistant to friction and its manufacture. Regarding the method. BACKGROUND OF THE INVENTION Macromolecular weight polymers typically have a molecular weight in excess of one million. Polyethylene and polytetrafluoroethylene are typical macromolecular weight compounds. These substances inherently have lubricant properties. However, due to their large molecular weights, these materials have poor fluidity and are difficult to mix with reinforcing fibers. Furthermore, even if this large molecular weight polymer were mixed with fibers, it would not be possible to mold them using conventional techniques other than dipping or compression molding, as the molecular chains would be cut and the molecular weight would decrease. . Therefore, in recent years, when extruding these materials, the raw materials are reinforced using very short fibers or powders such as glass with a diameter of about 10 μm and an aspect ratio (ratio of length to diameter) of about 1 to 10. is customary. Although the raw materials described above have many uses, they have been unsuitable for applications such as aircraft, where extreme conditions of use require more specialized materials. An example of such a requirement for special materials is piston ring seals for cryogenic equipment used at high altitudes.
These piston rings usually have lubricant properties themselves and wear to a low degree over a long period of time, so that their sealing function is not impaired. However, the previously used materials containing the aforementioned glass fibers cause debris to protrude and act as an abrasive, causing premature wear of the seal, which is undesirable. It is an object of the present invention to provide a fiber-reinforced polymer for use in piston ring seals that withstands extreme high-altitude service conditions, exhibits low wear, and has no abrasive properties. The present invention also includes a method for producing this polymer. SUMMARY OF THE INVENTION The reinforcing material of the present invention is made of a macromolecular weight polymer reinforced with fibers having a length of at least about 0.05 inches (1270 μm). The fibers have an aspect ratio of about 100:1 to about 300:1. The present invention also provides a method of manufacturing this reinforcing material as shown in the following steps. a. Prepare a granular macromolecular weight polymer of a predetermined size. b. Provide an inert liquid carrier capable of uniformly dispersing the fibers and particulate polymer. c. Mix the fibers and particulate polymer in an inert liquid carrier to form a homogeneous dispersion. d. The above dispersion is passed through a filter to obtain an intermediate consisting of a quasi-isotropic and irregularly arranged fiber network and polymer particles dispersed in the spaces between them. e Dry the intermediate to remove excess liquid carrier. f Positive pressure is applied to this intermediate to remove any air trapped therein and densify it. g The dense intermediate is molded and compressed at high temperatures that dissolve the polymer but not the fibers, and is then cooled to form giant, irregularly dispersed reinforcing fibers longer than 0.05 inch (1270 μm). A reinforced material consisting of a solid polymer matrix of molecular weight is produced.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an intermediate prior to forming the dense solid reinforcement material of the present invention. FIG. 2 is an enlarged view of a part of the formation shown in FIG. FIG. 3 is a sectional view of an apparatus used in one step of the manufacturing method of the present invention. FIG. 4 is an enlarged view of a continuum matrix made of densified fibers in the portion shown in FIG. 2. FIG. 5 is a perspective view of the final disc-shaped formation of the invention after compression. FIG. 6 is a perspective view of an annular component made of the reinforcing material of the present invention.

[Detailed description of the invention]

The polymers that make up the reinforcing material of the invention have a molecular weight greater than 1 million, preferably polyethylene, polytetrafluoroethylene or other large molecular weight or low flow materials. An example of a low flow polymer is polytetrafluoroethylene. It has a viscosity of about 10 ¹¹ poise at a melting point of 700°C (371°C). Such materials act as lubricants themselves and are usually not abrasive. However, other lubricants or pigments may be added to these polymers. For example molybdenum, disuride or powdered graphite are suitable lubricants for these and have many uses. It is desirable that the polymer used be in the form of particles of an appropriate size so as not to clog or pass through the paper during the process described herein. The fibers used in the reinforcing material of the present invention must not lose their properties even at the melting point of the above-mentioned macromolecular weight matrix polymer. When used as a lubricant itself, the fibers are preferably made of non-abrasive organic polymers. Examples of such are the polyamides Kevlar and Nomex manufactured by DuPont.
In cases where non-abrasiveness is not required,
Other fibers such as boron, glass, graphite, quartz or metal may be used in place of or in conjunction with the polymer fibers. The length of the fiber used in the present invention is subject to the following limitations. (a) It must be of a length that will not tangle and form a lump when mixed in a wet state. (b) They are short and granular and cannot be mixed well with large molecular weight polymers using conventional methods such as pole milling. Regarding the former limitation, the length at which such entanglement occurs depends on the fiber diameter and the fiber concentration in the dispersion. Preferred length is 0.05 inch (1270μm)
approximately 1/8 inch (3175μm)
are particularly effective. The preferred method of mixing fibers and polymers is
For example, a wear ring mixer with flat disc blades may be used to disperse them in an inert liquid carrier by the shear force. The blend ratio of fibers and polymer is typically 5-60% by weight fibers and 40-95% by weight polymer, preferably 5-15% by weight fibers and 85-95% by weight polymer. The proportion of the fiber and polymer mixture in the total mixture with the liquid carrier is approximately 3.
%. The inert liquid carrier lubricates the polymer and fibers to provide a good dispersion, but must be easily removable by drying. One suitable liquid carrier for polyethylene is a mixture of isopropyl alcohol and water in a 2:1 volume ratio. Other known carriers may also be used depending on the type of polymer and fiber. The combination of polymer particle size, fiber size and liquid carrier is selected appropriately to produce a good dispersion in the carrier. Among the material properties that affect the dispersion are viscosity, surface tension, density, length, aspect ratio, and particle size. If the solid material is not well dispersed in the carrier, the polymer and fibers will form several layers over time. When a dispersion of polymer particles and fibers is passed through the method of the present invention, the fibers are randomly oriented on the filter, but are generally intermixed in a quasi-isotropic or nearly three-dimensional network structure. . The polymer particles are dispersed and mechanically retained in the free space of the fiber network. The network of fibers and polymer is then dried in vacuum (preferably about 20 mmHg), typically at 150°C (66°C) for just over 2 hours.
Positive pressure is then applied at room temperature to form a dense preform. This densification is performed to bring the polymers into close contact with each other on a macroscopic level and to remove trapped air to form a continuous polymer matrix on a macroscopic level. This dense preform is further compressed into a mold. Once the polymer melts, it binds the fibers to the polymer matrix when cooled. The final product has the shape of the mold used. In the final step when the polymer dissolves, the molecular chains of the polymer particles penetrate at the microscopic level to form a continuous polymer matrix at the microscopic level. Previous methods, even when powders or short fibers were dispersed in polymers, did not provide materials with the desired wear resistance. This can be seen by the fact that the filler is forced out of the surface where the material has been worn away, leaving small holes behind. However, in the present invention, since the long fibers are randomly oriented, the filler is not extruded in this way. Fibers, especially polymer fibers, gradually wear out.
It is not extruded from the material. Since the fibers used in the present invention have a high aspect ratio, they increase the surface tension of the polymer matrix and strengthen the adhesion between the fibers.
However, the energy required to extrude such long fibers is significantly greater than that required to extrude the conventionally used chopped fibers. Therefore, the high aspect ratio and mechanical adhesion of the fibers used in the present invention, despite the weak bond strength between the fibers and the macromolecular weight polymer as mentioned above, Prevents fibers from popping out of the polymer matrix. Therefore, although the reinforced material using long fibers of the present invention has low wear resistance,
No abrasive fragments are produced. Additionally, the use of non-abrasive polymer fibers in the present invention further enhances the low abrasiveness of the reinforcing materials of the present invention. As is clear from the above description, the advantage of the reinforced material of the present invention is that it functions as a lubricant, and although it has low wear resistance, it is not abrasive. Most importantly, this material can be formed into structures of various shapes, such as annular parts for use as piston ring seals and other aircraft parts. Further advantages of the invention will now be explained with reference to the drawings. In the present invention, a mass of discontinuous fibers such as Kevlar is used as one of the starting materials. These fibers are chopped, have an aspect ratio of about 250:1, and are typically about 1/8 inch (3175 μm) long and about 12 μm in diameter. These fibers cannot be mixed well with large molecular weight polymers in some extruders. However, the inventors believe that the
We have discovered that these fibers can be mixed with a macromolecular weight granular polyethylene polymer branded as 1900UHMW Polymer. The particulate polymer typically has a molecular weight of about 2 million to about 6 million and a particle size of about 300 μm. The fibers and 1900 UHMW polymer in a mixture of isopropyl alcohol and water are mixed and a shearing means such as a wear ring mixer with disk blades is used to disperse the fibers and polymer. Passing the fibers and polymer dispersed in this liquid carrier yields an intermediate consisting of a mixture of fiber network and polymer, as shown in FIG. Figure 2 shows the first
It is a partially enlarged view of the intermediate body 10 shown in the figure. This intermediate is made up of fibers 11 that are quasi-isotropically oriented and have an almost three-dimensional network structure, and polymer particles 12 that are mechanically held in a space surrounded by the fiber network. Become. However, FIG. 2 is a schematic representation and only shows the general orientation of the fibers and polymer particles. Furthermore, this figure is not to scale and does not represent the aspect ratio of the fibers or the relative sizes of the polymer particles of the present invention. The dimensions of the polymer will be readily determined from the disclosure herein. In carrying out the manufacturing method of the present invention, an apparatus as shown in FIG. 3 is used at the laboratory level. A dispersion or mixture 13 of polymer particles and fibers is placed in a beaker 14 as shown here;
Buchner funnel 1 with 40/60 filter 18
Aspirate through 6. The cylindrical adapter 20 is used to draw the dispersion from the beaker 14 into the funnel 16 using a vacuum device. The conduit 21 passes through the stopper 23 and connects the outlet of the funnel 16 and the Erlenmeyer flask 2.
2 are connected. Spout 24 of flask 22 is connected to a vacuum generator (not shown), such as a modest laboratory pump. This vacuum device sucks up the dispersion 13 in the beaker 14 to the filter 18. The liquid carrier is then introduced into flask 22 through line 21. The fibers sucked up into the funnel 16 have a quasi-isotropic orientation as shown in FIG. 2, and together with the polymer particles 12 incorporated into the fiber network 11, the intermediate shown in FIG. form 10. This filtered mixture is shaped by the surface of the filter and the surrounding device. This intermediate 10 is removed from the filter and dried at high temperature in vacuo to remove moisture and excess liquid carrier (e.g. 1900UHMW polymer and isopropel alcohol/water liquid carrier at 150ⓓ (66°C)). (performed under a pressure of 20 mmHg for an hour). The dry mixture is further densified at room temperature under a pressure of 5000 pounds per square inch (34×10 ⁶ Pascals). FIG. 4 is a partially enlarged view of this compressed mixture. This consists of substantially planarly oriented, intertwined fibers 11 and a continuous polymer matrix (not shown) dispersed in the spaces created in the fiber network.
It consists of As already mentioned, a continuous polymer matrix is formed by the polymer particles coming into close contact with each other on a macroscopic level during densification. As mentioned in Figure 2, Figure 4 is shown schematically and the scale is not accurate. The final dense mixture is compressed in the desired mold at 5000 pounds per square inch and heated to a temperature at which the polymer used melts (e.g., 400° for a 1900 UHMW polymer). When it is then cooled, the polymer particles become entangled with each other, binding even the unmelted fibers to the polymer. The time, temperature and pressure in each step depend on the polymer used for the base material. The final product takes the form of a disk 28, as shown in FIG. Consists of a continuous polymer matrix reinforced with Such a structure has a unique property of being oriented in multiple directions because the fibers are highly entangled. The fiber network thus restricts the movement of the polymer matrix at the surface of the fibers and matrix. The present invention
In response to the demand for strong fiber-to-matrix bonds, new combinations of fibers and polymers are used to create new reinforcing materials and structures. The present invention makes it possible to use polymers with low fluidity in the production of the matrix, which was not possible using conventional methods. Furthermore, the material made of the polymer and fibers of the present invention has increased friction resistance thanks to the fiber network, and the polymer itself has the property of being a lubricant and causing less friction. When the center of the disc 28 in FIG. 5 is hollowed out, an annular part 30 as shown in FIG. 6 is obtained. The corners of this part 30 may be made smooth by placing it in a suitable mold and compressing it at a high temperature of, for example, 350°C (177°C).
Structures with other different geometries can be made using a variety of molds. Furthermore, by using filters of various shapes during the drying process, dry mixtures other than the disk shape shown here can be created. Example 1 Alcohol/
A reinforced material was formed using a large molecular weight polyethylene (1900UHMW polymer) and Kevlar fibers in a water carrier. 6.8 g of 1900 UHMW polymer with molecular weight 2 million to 6 million, particle size 300 μm and 1/8 inch (3175 μm) length, aspect ratio approximately 250:1, in 300 ml of a mixture of isopropyl alcohol and water (2:1 by volume);
1.2g of Kevlar fiber cut into pieces with a diameter of approximately 12μm
A mixture was formed. The mixture was mixed for 2 minutes in a wear ring mixer equipped with flat disk blades. Using the apparatus shown in Figure 3, the fibers and polymer dispersed in the liquid carrier are prepared in beaker 1.
I put it in 3. Approximately 20mmHg (3.4×10 ³
The entire dispersion was withdrawn from the beaker 13 by applying a vacuum of 100 mPascals. After the filtration is completed, the mixture collected on the wire mesh is heated to 20 mmHg (3.4
^150〓 (66
℃). This dry mixture was heated at room temperature for 5 minutes.
It was densified at 500 pounds per square inch (34×10 ⁶ Pascals) to form a dense preform. Next, put this preform into a mold and heat it at 400㎓ (204℃).
heated to. Further pressure was applied to the preform and the mold was then cooled to room temperature at a cooling rate of 10㎓ per minute (6°C). Pressure was applied gradually to the mold and preform. The material is cooled down to 200〓(93
℃), the pressure is at its maximum, 500 lbs.
20 minutes after ^cooling began. The molded product was then removed from the mold. The final product was disc-shaped as shown in FIG. The disc-shaped final product was subjected to the following abrasion resistance test. This is approximately 190 pounds per square inch (1.3 x ¹⁰ Pascals) of the product and stainless steel.
When rubbed at a speed of 17 feet (5.2 m) per minute under pressures of We also investigated the creep properties of this product.
This test was carried out at 150°C (66°C) for 24 hours on this structure.
3000 pounds per square inch (21× ¹⁰⁶ pascals)
I went there under pressure. The resulting 0.5 inch (1.27 cm) cube of ordered polyethylene is 0.16
inch deformation, whereas those made from the reinforced material of the present invention deformed only 0.011 inch (0.027 cm). Furthermore, the products of the present invention are made of polymer fibers and are softer than conventional glass reinforcement materials, making them more non-abrasive. Example 2 Using polytetrafluoroethylene (PTFE) as the macromolecular weight polymer in Example 1,
A reinforcing material according to the invention was formed in a similar manner.
Because PTFE is more dense than macromolecular weight polyethylene, the combination of polymer particle size, fiber size, and liquid carrier were tailored to give just the right dispersion. Although what has been described thus far indicates the best way to carry out the invention, modifications may be made to the drawings and the embodiments described above.