DE2654931A1 - Reduction of friction of rubbers and plastics - by addn. of polymer material which is depolymerised by irradiation - Google Patents

Abstract

Prodn. of rubbers or plastics with reduced coeffts. of friction involves addn. of an oligomer or polymer which is depolymerised by ionising radiation before or after incorporation. The additive is pref. a fluorine-contg. polymer esp. PTFE. Prods are used in sealing elements e.g. O-rings shaft seals hydraulic and pneumatic packings, pref. of nitrile silicone, acrylate, fluoro SBR chloroprene epichlorhydrin or chlorosulphonated polyethylene rubber polyethylene or PVC. Friction and heat generated in used are reduced, giving extended life. Other properties e.g. strength, hardness, elongation at break, swelling in aggressive media etc. are also improved by the irradiation.

Description

Process for the production of elastics or panels

with reduced coefficient of friction The invention relates to a Process for the production of elastics or panels with a reduced coefficient of friction, in particular of sealing elements, preferably of sealing elements made of nitrile rubber, Silicone rubber, acrylic rubber, fluororubber, styrene rubber and polychloroprene rubber, Epichlorohydrin rubber, chlorine-ulformed polyethylene as well as polyethylene and polyvinyl chloride with simultaneous wecentlocher improvement of other properties, such as tensile strength, Hardness, elongation, swelling behavior when exposed to aggressive media Us.

It is known through the properties of high polymer materials Influence of ionizing rays, e.g. B. electron or gamm @@ rays, in wide Modify boundaries. In the influence of high-energy rays on high-polymer substances excited molecules, molecular ions and free radicals are formed primarily in various secondary reactions, depending on the reaction conditions (e.g. absence certain gases, such as oxygen), to breakdown and / or crosslinking of the macromolecules, d. H. to a depolymerization and / or to the formation of spatial network structures being able to lead.

Decisive for the occurrence of degradation or crosslinking phenomena In the case of high-polymer materials, there is on the one hand the type of polymer itself, and on the other hand have the irradiation conditions (e.g. presence of oxygen during irradiation, Dose rate, d. H. Speed of energy supply during irradiation, etc.) significant influence on the irradiation result.

In the case of polymers that tend to crosslink, for example nitrile rubber, Silicone rubber, acrylic rubber, fluororubber, styrene rubber, polychloroprene rubber and polyethylene, are caused by the influence of ionizing rays through the formation of a molecular spatial network structure, in particular the Tensile strength, the tension value (module), the hardness, the elongation at break and the swelling behavior improved when exposed to aggressive media. For example, some silicone rubber sealing elements, especially in the form of round rings and lip seals, the oil resistance higher temperatures are significantly improved. When using silicone rubber rings in particular Excellent properties result from chemical chemical cross-linking.

For example, round rings made of silicone rubber had the task of the frontal passage of turbine oil, which with an overpressure vXn was 0.5 kp / cm on the outer diameter of the floating ring up to the round ring, against to seal a gas pressure of about 30 kp / cm2. As a result of the high thermal load of the swimming ring, temperatures of around 130 to 1500C were at the sealing point at. These harsh conditions resulted in conventionally vulcanized O-rings made of silicone rubber in a relatively short time (3000 to 4000 hours) became. Radiation-crosslinked silicone rubber round rings installed at the point described above were in use for over 19,000 hours without any complaints about the sealing function could.

The tendency to swell z. B. lip seals and O-rings Nitrile rubber base, which is particularly effective against gear oils and other high-swelling Media can be used, through a crosslinking with ionizing radiation can be significantly reduced.

In the above-described crosslinking reactions that lead to a considerable However, the coefficient of friction will lead to improvement in numerous polymer properties only slightly influenced by the simultaneous increase in hardness. For example, shows Nitrile rubber has an unfavorable friction behavior, leading to high energy losses leads. A reduction in friction can be achieved here, for example, when using molybdenum disulfide, by using special lubricants (chain) or by means of coatings with polytetrafluoroethylene, the latter procedure because of the occurring Abrasion does not bring lasting effects.

But especially where low pressures have to be controlled, in pneumatics and hydraulics, for example, are low coefficients of friction necessary. The same applies to shaft seals. With a reduction in the coefficient of friction the heating of the sealing lip is lower, which increases the praise for the sealing element is increased significantly.

It is the purpose of the invention to determine the coefficient of friction from El @ -sten and plastics, in particular from sealing elements, preferably from sealing elements Nitrile rubber, silicone rubber, acrylic rubber, fluororubber, styrene rubber and polychloroprene rubber as well as polyethylene and polyvinyl chloride and the favorable property improvements that can be achieved with radiation-chemical crosslinking reactions such as tensile strength, hardness, elongation at break, compression set and the swelling behavior when exposed to aggressive media at the same time as one substantial reduction of the coefficient of friction through "self-lubricating" properties of the polymer.

The invention is based on the object of the loads or plastics Adding substances that have a lubricant effect through radiation-chemical reactions is achieved.

The object is achieved according to the invention in that the to be crosslinked polymer matrix prior to exposure to ionizing radiation such oligomeric until polymeric substances are added, which under the influence of high-energy rays are depolymerized.

This increases the exposure to ionizing radiation crosslinking polymeric matrix and the added oligomeric to polymeric substance depolymerized. The depolymerized and partially covalent to the polymeric matrix Bound substance, which is present in the cross-linked polymer matrix, acts in the event of frictional loads as a lubricant.

Because of the low molecular weight of the depolymerized and not The substance covalently bound to the polymer matrix is capable of binding to the To migrate surface of the crosslinked polymer matrix, so that in addition a "dopot effect" is achieved.

It is advantageous as depolymerizable oligomeric to polymeric Substance polytetrafluoroethylene to use, which when exposed to ionizing Radiation is broken down into low-molecular fragments and has excellent lubricating properties having.

Thus, in the method according to the invention, the polymer matrix is used crosslinked with a certain radiation dose and an added oligomeric to polymeric Substance degraded, cross-linking and degradation reactions at the same time, however in two different components, used technically.

The method according to the invention also offers the possibility of Polytetrafluoroethylene waste, which in the case of polytetrafluoroethylene because of its specific properties necessary machining deformation occur, makes sense to utilize.

The polytetrafluoroethylene waste is disposed of in a suitable manner (e.g. using impact mills), whereby it is necessary to achieve a certain grain size or a certain degree of polymerization is appropriate, the polytetrafluoroethylene waste either before or after the grinding process, but before mixing in the one to be crosslinked polymer matrix to be subjected to the influence of ionizing radiation.

This procedure is advantageously used when the polymer matrix to be crosslinked is already crosslinked at such radiation doses, where not yet a sufficient one Degradation (depolymerization) of the added oligomeric to polymeric substance, in particular polytetrafluoroethylene, takes place.

The irradiation is preferably carried out with electron beams in the energy range from 0.3 to 10 MeV, but it can also be done with gamma rays, e.g. B. 60 Co- rays, take place. The temperature during the irradiation is generally around 20 ° C, However, to improve the desired effects it can also be dependent on the polymeric substances to be crosslinked can be increased to 100 ° C.

Air is generally used as the irradiation medium, however A stream of inert gas, for example nitrogen, can advantageously also be used come in order to exclude the influence of the oxygen on the irradiation result.

It is also advantageous to have multiple or partial irradiations Apply irradiation.

In the case of multiple irradiation, the entire polymeric material can initially be used be irradiated homogeneously. Subsequently, by variation z. B. the electron energy the transmitted radiation is a partial irradiation, e.g. B. certain parts of the polymeric material, whereby a structural (e.g.

Hardness) difference is achieved. With multiple irradiation you can different types of radiation for the individual irradiations (e.g. for the first exposure gamma rays, second exposure electron radiation) be applied. This also makes it possible to use radiation-chemical radiation to compact polymeric materials to modify because only with gamma rays because of their long range in fixed Substances a radiation-chemical modification of compact workpieces is possible.

Partial irradiation or partial radical formation can, for example by using cover plates or by targeted control of the electron beam on certain subregions of the polymeric material, e.g. B. on the floor or lip areas of sealing elements.

In the following, the invention will be based on a few exemplary embodiments are explained in more detail: Example 1 In one for the production of Sealing elements Usual nitrile rubber mixture with an acrylonitrile content of 18 8% by mass of polytetratluoroethylene are subsequently mixed in on a rolling mill. The rolling process for the purpose of homogenizing the mixture of substances is carried out according to FIG Minutes finished, the mixture removed from the rolling mill, the corresponding blanks manufactured and grooved rings pressed. The pressed U-rings are made by means of electron beams irradiated with a dose of 25 billion, which is achieved by crosslinking the nitrile coach a self-lubricating "sealing element thanks to the radiation-chemically degraded polytetrafluoroethylene receives.

At the same time, the following advantageous properties occur: essential higher tension value (module), increase in hardness, decrease in the tendency to swell, lower tendency to extrusion in the gap between piston and cylinder wall bs rod and skins.

Example 2 In a customary for the production of sealing elements Jitrile rubber mixture with an acrylonitrile content of 26% are processed on a rolling mill subsequently mixed in 10% by mass of polytetrafluoroethylene. The polytetrafluoroethylene was previously carried out by means of electron beams of an energy of 1 MoV with a dose of 5 billion irradiated. The rolling process for the purpose of homogenizing the material mixture is ended after 8 minutes, the mixture is removed from the rolling mill, the corresponding Blanks manufactured and grooved rings pressed The pressed grooved rings are made by means of Electron beams with a Doi of 20 billion irradiated, whereby one by crosslinking the nitrile rubber creates an "self-lubricating" sealing element through the radiation-chemical degraded polytetrafluoroethylene receives.

At the same time, the following advantageous properties occur: essential higher tension value (module), increase in hardness, decrease in the tendency to swell, less tendency to extrusion in the gap between piston and cylinder wall or rod and skins.

Example 3 In a standard for the production of shaft sealing rings Silicone rubber mixture with a methyl vinyl content of 0.2% are on a Rolling mill subsequently 12 mass% polytetrafluoroethylene, which was previously made with electron beams an energy of 1 MeV was irradiated with a dose of 8 Mrad. The rolling process for the purpose of homogenizing the mixture of substances is started after 15 minutes finished, the milk removed from the rolling mill and the corresponding blanks made. The blanks are then pressed into shaft sealing rings and these using Electron beams irradiated at a dose of 12 Mrad. This is followed by a repeated irradiation with a dose of 8 degrees, which is rich only on the lip areas limited. This procedure ensures that in the event of a terber erosion the lubricating effect at the same time the elasticity and the restoring force are essential improved, whereby a significant increase in the service life of the shaft seal a under extreme operating conditions, especially at high temperatures, and a Significant improvement in swelling resistance to oils at high temperatures results.

Claims (4)

Pstentancoriichc 1. Process for the production of elastics or plastics with a reduced coefficient of friction, especially of sealing elements, in which the elastics or plastics are irradiated with ionizing radiation, characterized in that that the elastics or plates to be crosslinked prior to irradiation with ionizing Rays under the influence of these rays depolymerizing oligomeric to polymeric Substances are added. 2. The method according to claim 1, characterized in that al oligomers until polymeric substance a fluorine-containing polymer is used. 3. The method according to claim 1 and 2, characterized in that al oligomeric to polymeric substance polytetrafluoroethylene is used. 4. The method according to claim 1 to 3, characterized in that des Polytetrafluoroethylene before mixing in the elastics or plastics to be crosslinked is irradiated with ionizing rays.