阅读说明：本技术 等离子体涂层的密封元件 (plasma coated sealing element ) 是由 F·冯·弗拉格斯特因 M·艾德勒 S·鲁兹 T·世内兹 K·哈尔斯特因 K·菲勒 B·特 于 2018-04-18 设计创作，主要内容包括：本发明的主题是密封元件用于在存在润滑剂的情况下将密封体动态密封的用途,其中所述密封元件具有弹性体基体和等离子体涂层,其中所述涂层含有元素碳、氧、硅、氢和任选的氟,其中所述涂层至少在表面上具有如下特性：C:Si的摩尔比(at％/at％)>5,O:Si的摩尔比(at％/at％)>3,并且表面能<50mN/m。本发明还涉及密封系统、密封方法、密封元件及其制造方法。(The invention relates to the use of a sealing element for dynamically sealing a sealing body in the presence of a lubricant, wherein the sealing element has an elastomer base and a plasma coating, wherein the coating contains the elements carbon, oxygen, silicon, hydrogen and optionally fluorine, wherein the coating has the following properties at least at the surface: a molar ratio of C to Si (at%/at%) >5, a molar ratio of O to Si (at%/at%) >3, and a surface energy of <50 mN/m. The invention also relates to a sealing system, a sealing method, a sealing element and a method for manufacturing the same.)

1. use of a sealing element for dynamically sealing a sealing body in the presence of a lubricant, wherein the sealing element comprises an elastomer matrix and a plasma coating,

Wherein the coating contains the elements carbon, oxygen, silicon, hydrogen and optionally fluorine,

Wherein the coating has the following properties at least on the surface:

The molar ratio of C to Si (at%/at%) >5,

si in a molar ratio (at%/at%) >3, and

Surface energy <50 mN/m.

2. Use according to at least one of the preceding claims, wherein the molar ratio of Si at least at the surface of the coating is from 0.5 at% to 5 at%, and/or

Wherein the molar ratio of C at least at the surface of the coating is >60 at%.

3. Use according to at least one of the preceding claims, wherein the molar ratio of C: O at least at the surface of the coating is >3 (at%/at%).

4. Use according to at least one of the preceding claims, wherein the molar ratio of C: Si is from 10 to 80 (at%/at%), the molar ratio of O: Si is from 4 to 15 (at%/at%), and the molar ratio of C: O is from 3 to 12 (at%/at%), at least at the surface of the coating.

5. Use according to at least one of the preceding claims, wherein the coating is obtainable in a plasma coating process using a gaseous silicon precursor compound.

6. Use according to at least one of the preceding claims, wherein the coating has, at least at the surface, the following molar ratios (in at%):

carbon: 50% to 95%, preferably 60% to 90% Oxygen: 5% to 25%, preferably 9% to 18% silicon: 0.5 to 5%, preferably 1 to 4% Fluorine: 0% to 35%, preferably 0% to 25%.

7. Use according to at least one of the preceding claims, wherein the elastomer matrix is a fluoroelastomer.

8. Use according to at least one of the preceding claims, wherein the contact angle of the coating layer with respect to the lubricating material is from 10 ° to 50 °, preferably from 15 to 30 °.

9. Use according to at least one of the preceding claims, wherein the lubricant contains, measured at 40 ℃, a lubricant>200mm²Kinematic viscosity in/s, and/or

Wherein the lubricant is a polyether, especially a polyalkylene glycol; or a polyester; or mixtures of the foregoing.

10. Use according to at least one of the preceding claims, wherein the use is effected at an oil sump temperature <80 ℃.

11. Use according to at least one of the preceding claims, wherein the sealing element and/or the base body is a sealing ring.

12. A sealing system comprising a sealing element according to at least one of the preceding claims, a sealing body, a dynamic sealing gap between the sealing element and the sealing body, and optionally a lubricant.

13. An apparatus comprising a dynamic sealing system according to claim 12, in particular of the form: a transmission, a pump, a motor or a motor vehicle.

14. a sealing element for dynamically sealing a sealing body in the presence of a lubricant, wherein the sealing element has an elastomer matrix composed of a fluoroelastomer and a plasma coating,

wherein the coating contains the elements carbon, oxygen, silicon, hydrogen, and optionally fluorine,

Wherein the coating has the following properties at least on the surface:

the molar ratio of C to Si (at%/at%) >5,

Si in a molar ratio (at%/at%) >3, and

Surface energy <50 mN/m.

15. A method of manufacturing a sealing element according to claim 14 by plasma assisted vapour deposition, the method comprising the steps of:

(a) Introducing the elastomer matrix into a plasma apparatus,

(b) Introducing at least one gaseous silicon precursor compound into the apparatus, and

(c) Coating the substrate in the apparatus.

Technical Field

The invention relates to the use of a sealing element for dynamically sealing a sealing body in the presence of a lubricant, wherein the sealing element comprises an elastomer matrix and a plasma coating. The invention also relates to a sealing system, a sealing method, a sealing element and a method for manufacturing the same.

Background

In the field of sealing technology, moving machine parts in assemblies are sealed by means of suitable sealing elements (sealing articles). In the case of dynamic sealing, a movement of the sealing body to be sealed relative to the sealing element takes place. Exemplary dynamic seals are sliding ring seals, radial shaft seal rings, labyrinth shaft seals, rod seals, O-rings, or piston rings. In dynamic sealing, the moving interface is referred to as the seal gap. The sealing element abuts against a machine part, such as a shaft, piston or rod. The dynamic seal may contain a lubricant. The lubricant is used in an assembly (e.g., a transmission) to lubricate moving machine components. Wherein lubricant can enter the seal gap. The sealing element is typically constructed from a polymeric material, such as a thermoplastic or elastomer. Due to the flexibility of such an elastomer, the sealing element can be adapted to the sealing body during installation and during operation.

in a movable sealing system, significant forces act on the sealing element, which, due to the relatively low hardness of the elastomer, causes the sealing element to wear out due to abrasion. Therefore, the sealing elements often have a limited service life and must be replaced regularly. In order to improve the stability, elastomers are used in the prior art which are as hard as possible, said elastomers being usually reinforced with fillers. But this has the disadvantages that: although the wear of the sealing element can be reduced, at the same time the sealing body is worn away by abrasion. If the mating object of the sealing element is a shaft, this effect which occurs in practice in sealing bodies made of steel is referred to as shaft penetration.

In the case of dynamic sealing, the lubricant of the assembly to be sealed can enter the sealing gap. The lubricant can thus improve tribological properties and thereby reduce wear. In the case of dynamic sealing with lubricants, the person skilled in the art is faced with the particular challenge of coordinating the sealing elements, the sealing body and the lubricant with one another so as to obtain simultaneously good sealing, good tribological properties and low wear. In practice, it is extremely difficult or even infeasible to: in particular sealing systems exposed to high loads, it is very difficult or even impossible to completely prevent wear of the sealing element and the sealing body or at least to keep them small. Sealing systems in which lubricants are used behave differently than dry systems.

to solve the problem of abrasion, EP 2291439B 1 proposes: the elastomer sealing element is provided with a plasma coating which consists essentially of carbon, oxygen, silicon, hydrogen and optionally fluorine. The ratio of silicon to oxygen is high. Thus, the coating is glassy and has a relatively high hardness. The coated sealing element will thus have a high wear resistance on the surface, while the material flexibility desired for sealing purposes will remain inside. Disadvantageously, however, such hard coatings often cause high wear (shaft penetration) of the sealing body. Shaft cut-in is generally more problematic in practical applications than wear of the sealing elements, since machine parts are generally more expensive to manufacture and replace in comparison. Compatibility with different lubricants cannot always be provided. Therefore, especially under high load conditions, the stability of such sealing systems is in great need of improvement and they are not suitable for many applications. In the case of very hard coatings, there is also a risk that the sealing element loses its sealing action.

plasma-assisted chemical or physical vapor deposition (CVD or PVD) processes are also known in the art to provide elastomeric substrates with hard plasma coatings that are almost entirely composed of carbon. Such coatings are known as "diamond-like carbon" (DLC) because of their hardness and structure. An overview of such processes and products is provided in Martinez-Martinez, De Hosson, 2014, surface and Coating Technology 258, 677-. However, such coated articles are not suitable or only limitedly suitable for dynamic sealing applications, since in practice, due to the high hardness, relatively strong abrasion and wear (shaft penetration) of the sealing body is caused. This abrasion of the sealing body is problematic, since in practice the sealing body is usually a machine part. The function of the machine is impaired by abrasion. Replacement of machine parts (e.g. shafts) is generally significantly more costly and expensive than replacement of sealing elements (e.g. sealing rings). The wettability of such products with respect to lubricants is often also insufficient. This leads to a need to improve its tribological properties, wear and abrasion. Furthermore, there is no indication in said document that these layer systems are also suitable for use on sealing bodies, since there is no discussion of maintaining the sealing action.

the tribological properties of DLC-coated elastomers in dry sealing systems are described, for example, in third, 2016, Surface and Coating Technology 302, 244-. Among these, significant wear of various coated substrates was observed due to friction. Dynamic seals using lubricants are not investigated here.

DE 102012010603B 4 relates to sealing elements with a plasma coating for dynamic sealing in the presence of a lubricant. In the case of application in lubricated sealing systems, undesirable shaft cut-in is obtained at the sealing body, even if said shaft cut-in is significantly reduced compared to uncoated sealing elements. There is also a need to improve tribological properties. The surface energy of the coating is more than 50 mN/m. Since surface energy is a measure of wettability, there is also a need to improve compatibility with many lubricants.

The Michael Lubwama paper "Tribological properties of DLC and Si-DLC filmed on nitride rubbers for hand pump piston seals", 2013, university of town, relating to DLC coatings on elastomeric sealing elements consisting of nitrile rubber containing only a low proportion of silicon. The sealing element acts as a dry seal to seal the wellbore against water flow. The use of synthetic lubricants is not described.

In general, the sealing elements and sealing systems known in the prior art therefore still need to be improved. Accordingly, there is a general need for a sealing system that overcomes the above-mentioned disadvantages.

Object of the invention

the invention aims to: a sealing system for dynamic sealing is provided which overcomes the above-mentioned disadvantages. The object of the invention is, inter alia: a sealing system is provided which has advantageous properties, in particular a high stability, in the presence of synthetic lubricants. Here, the sealing system should exhibit good tribological properties, in particular good tribological properties, in dynamic sealing applications.

Another object of the invention is: a sealing system is provided which in the presence of a lubricant exhibits in any case a small, but preferably no, abrasion of the sealing body (shaft cut-in). In particular, a stable and effective sealing system should be provided over a long period of time.

The object of the invention is, inter alia: an effective and stable sealing system is provided for use with polar lubricants such as polyethers (e.g. polyalkylene glycols), polyesters or water-based lubricants, particularly at relatively low temperatures such as equipment with sump temperatures below 80 ℃.

Disclosure of Invention

Surprisingly, the main object of the invention is achieved by the use, the sealing system, the sealing element and the method according to the claims. Other advantageous embodiments are disclosed in the description.

The invention relates to the use of a sealing element for dynamically sealing a sealing body in the presence of a lubricant, wherein the sealing element comprises an elastomer matrix and a plasma coating,

Wherein the coating contains the elements carbon, oxygen, silicon, hydrogen and optionally fluorine,

Wherein the coating has the following properties at least on the surface:

The molar ratio of C to Si (at%/at%) >5,

si in a molar ratio (at%/at%) >3, and

Surface energy <50 mN/m.

The invention relates to a sealing system (seal) having a sealing element, which has at least one sealing body. The sealing system is, for example, an assembly, such as a transmission. The seal body is typically a machine component. The sealing element and the sealing body form an interface, which is referred to in the sealing art as a sealing gap. The sealing system is a dynamic seal in which the sealing element and the sealing body move relative to each other in the intended use. Here, a lubricant is preferably used. The lubricant is able to enter the seal gap in use, thereby improving tribological properties. The term "tribology" (reibangsleehre tribology) denotes the theory of friction, in particular the theory of calculating and measuring the coefficient of friction, wear and lubrication between a body and a surface in interacting motion.

In the case of dynamic sealing, such sealing systems are mainly used to ensure the cooperation of the different machine parts. Such a sealing system should have good tribological properties and have low wear. Lubricants, such as oils and greases, are commonly used to improve the properties. Lubricants can also be used to seal the sealing system from the fluid.

the sealing element has an elastomer base as a substrate and a plasma coating applied thereto. Preferably, the coating is applied directly to the substrate. However, additional intermediate layers may also be present, for example in order to improve adhesion. The elastomer matrix preferably contains or consists of an elastomeric polymer. The substrate can be completely or partially coated. The plasma coating is present at least on a portion of the substrate, said portion constituting a sealing gap in the sealing system.

The substrate is provided with a plasma coating. The plasma coating is preferably produced by means of a plasma-assisted chemical vapor deposition (PE-CVD) method. The substrate is introduced into a PE-CVD device (plasma device) and volatile (i.e. gaseous or vaporous) precursor compounds (precursors, monomers) for the coating are introduced into the PE-CVD device. In the plasma, the precursor compounds undergo chemical and physical changes and form reactive intermediates and polymers that are deposited on the substrate surface. Plasma coatings generally constitute a three-dimensional crosslinked structure. Thus, the plasma coating is generally referred to as a plasma polymer coating. It is also possible to: the coating is produced by plasma assisted Physical Vapor Deposition (PVD).

The coating comprises the elements carbon, oxygen, silicon, hydrogen and optionally fluorine. This means that the polymer molecules are composed of at least said elements. Preferably, the coating consists here of carbon, oxygen, silicon, hydrogen and optionally fluorine. In a preferred embodiment, fluorine is included. In another embodiment nitrogen is contained, for example in a proportion of at most 10 at% or at most 5 at%. Small amounts of unavoidable other elemental impurities may typically be present, for example in an amount of <5 at%, <2 at%, or <1 at%. In addition, such impurities are formed when the constituents of the substrate are transferred to the plasma phase in the reactive plasma and build up or become incorporated into the coating. Typical impurities are, for example, metals such as sodium or zinc.

According to the invention, the coating is further characterized in that: the coating contains relatively much carbon and only a small amount of silicon. The coating has a molar ratio of C: Si (at%/at%) of >5 and a molar ratio of O: Si (at%/at%) of >3 at least at the surface.

In the context of the present application, unless expressly stated otherwise, the amounts of substance and the molar ratios of the coatings are expressed in atomic percent (at%). The amount of substance at the surface of the coating can be determined by means of X-ray photoelectron spectroscopy (ESCA, electron spectroscopy for chemical analysis, also known as XPS, X-ray photoelectron spectroscopy). The molar composition at the surface up to a depth of a few nanometers is determined by means of this method customary in the art. Preferably, the composition is measured at the upper 1 to 20nm, especially at the upper 2 to 10nm, or approximately at the upper 4 or 5nm surface. The method allows the detection of all chemical elements except hydrogen.

In a preferred embodiment, the coating as a whole contains a molar ratio of C: Si (at%/at%) of >5 and a molar ratio of O: Si (at%/at%) of > 3. This means that: the coating contains on average the molar ratio. The coating preferably contains this molar ratio everywhere or at least in regions which constitute >80, >90 or > 95% of the coating or in its cross section. In a preferred embodiment, the composition of the coating is substantially uniform. By keeping the type and concentration of the gaseous precursor compounds constant during the coating process, a uniform coating can be produced. This does not exclude: for example, a short-term pretreatment with another process gas at the start of the process, for example in order to clean and/or activate the surface of the substrate and/or in order to improve the adhesion of the substrate at the boundary surface. As is known to the person skilled in the art, the composition of the surface can vary in particular at the boundary surface of the substrate, since reactions with the substrate and its activated components also occur at the start of the production process of the plasma coating.

According to the invention, it is also possible: the coating has different sublayers with different molar compositions and/or the coating has a gradient structure. Such a coating with a non-uniform composition can be produced by: i.e. the kind and/or concentration of the precursor compounds is changed during plasma coating.

The preferred molar compositions disclosed below can each be set only at the surface of the coating or throughout the coating. Essential according to the invention is here: an advantageous composition is set at the surface of the coating where the coating is in contact with the lubricant and forms the sealing gap.

In a preferred embodiment, the molar ratio of C: Si (at%/at%) is >10 or >20, preferably <80 or < 70. Preferably, the molar ratio of C: Si (at%/at%) is in the range of 5 to 80, preferably 10 to 70 or 25 to 70.

Preferably, the molar ratio of O to Si (at%/at%) >4 or more and 5 or less. Preferably, it is <20 or < 15. In particular, it is in the range of 3 to 20, preferably 4 to 15.

Preferably, the molar ratio of C: O (at%/at%) >3, more preferably > 4. It is preferably <12, in particular < 10. In particular, the ratio is from 3 to 12, especially from 4 to 10.

In a preferred embodiment, the molar ratio of C: Si (at%/at%) is from 10 to 80, the ratio of O: Si is from 4 to 15, and the ratio of C: O is from 3 to 12.

In a preferred embodiment, the molar ratio of Si is from 0.5 at% to 5 at%, preferably from 1 at% to 5 at% or from 1 at% to 4 at%. It was surprisingly found that: even with such small proportions deliberately incorporated in the polymer coating, significant improvements in properties can be achieved.

The coating consists essentially of carbon, preferably in a molar ratio of at least 50 at%, preferably more than 60 at%, preferably in a molar ratio of from 50 at% to 95 at%, in particular between more than 60 at% and 90 at%. The proportion of oxygen is preferably from 5 at% to 25 at%, in particular from 9 at% to 18 at%. The proportion of fluorine may be up to 35 at%, in particular up to 25 at%. If fluorine is present, the molar ratio is preferably between 5 at% and 35 at%, in particular between 7 at% and 25 at%.

In a preferred embodiment, the coating has the following molar ratios (at%):

Carbon:	50% to 95%, preferably>60 to 90 percent
		Oxygen:	5% to 25%, preferably 9% to 18%
Silicon:	0.5 to 5%, preferably 1 to 4%
		Fluorine:	0% to 35%, preferably 0% to 25%

the coating is characterized as a whole: which contains only a relatively small proportion of silicon and oxygen. The coating is thus different from conventional coatings which contain mainly carbon and no silicon ("DLC coating") or conventional coatings which contain a relatively high proportion of silicon and oxygen of 20 to 25 at%, and is thus glassy ("SiOx coating"). DLC-like coatings are characterized by high hardness. The coating can be produced, for example, from acetylene or methane as precursor compounds. An overview on the manufacture and properties of DLC coatings on elastomers is presented in Martinez-Martinez (see above).

It has been found that: in sealing applications, the properties of the coating according to the invention differ significantly from those of a carbon rich coating without silicon. Thus, the coatings according to the invention, for example, exhibit different wettabilities and surface energies, which is important in the presence of lubricants. Although the coating according to the invention contains a relatively high proportion of carbon, it is believed that silicon incorporated with oxygen added to the precursor compound in small quantitative ratios produces a structure that is significantly different from known carbon-rich coatings.

Furthermore, due to the relatively low proportion of silicon, the coating is also significantly different from known coatings containing a high proportion of silicon and oxygen. Such coatings are glassy and have a relatively high hardness. The coating is described in EP 2291439B 1.

according to the invention, the coating can be obtained in a PECVD process, wherein a volatile (i.e. gaseous or vaporous) silicon-precursor compound is used. In the PECVD process, the composition of the coating is adjusted by the choice and amount of gaseous precursor compounds. Here, at least one silicon-containing precursor compound is used. It is particularly preferred to use compounds consisting of silicon, carbon and hydrogen. The compounds are in particular alkylsilanes, preferably tetraalkylsilanes, particularly preferably Tetramethylsilane (TMS).

In general, it is preferred to use precursor compounds that contain at least silicon, carbon and/or oxygen. In order to achieve a low silicon proportion, it is preferred according to the invention to use a further precursor compound which does not contain silicon, and which is in particular a carbon-precursor compound. In particular, at least one compound composed of carbon and hydrogen is used here, particularly preferably methane, ethylene or acetylene (Ethin acetylene, C)₂H₂). Especially mixtures of acetylene and TMS are used. To obtain the desired low silicon ratio, a significant excess (e.g., at least a 10:1 weight ratio) of non-silicon containing compounds is typically used. The exact concentrations and conditions are set in consideration of the specific compound, the plasma equipment and the desired layer composition.

It is known in the art that the components of the matrix may also be activated in a reactive plasma. The constituents can be released into the gas phase as reactive compounds and converted into a coating. This phenomenon occurs mainly at the beginning of the process when the substrate surface is not yet coated and is thus not protected. Thus, in practice it is often observed that: the plasma coating has a slightly different composition just at the boundary with the substrate. However, according to the invention, this is not important, since it is important that the coating has the desired advantageous composition on the surface.

The coating is applied to an elastomeric substrate. The main constituent of the matrix is at least one organic polymer, which may also be a silicon-organic polymer or a fluoropolymer. The polymer may be an elastomer that forms a three-dimensional cross-linked matrix. The elastomer gives the matrix elasticity and flexibility which is advantageous when mounting and normal use of the sealing element.

preferred elastomers are selected from: fluoroelastomers (FKM, FFKM), EPDM (ethylene-propylene-diene elastomer), nitrile-butadiene elastomers (NBR), hydrogenated nitrile-butadiene elastomers (HNBR), silicones, NR (natural rubber), polyacrylate elastomers (ACM), CR (chloroprene elastomer), IIR (isobutylene-isoprene elastomer), AU (polyester-polyurethane), EU (polyether-polyurethane), MQ (methylene-silicone-elastomer), VMQ (vinyl-methyl-silicone-elastomer), PMQ (phenyl-methyl-silicone-elastomer), FMQ (fluoro-methyl-silicone-elastomer), FEPM (tetrafluoroethylene-propylene-elastomer), or mixtures of these elastomers. In a preferred embodiment of the invention, the elastomer matrix comprises at least one polymer selected from the group consisting of fluoroelastomers (FKM, FFKM), EPDM (ethylene-propylene-diene elastomer), nitrile-butadiene elastomers (NBR) and hydrogenated nitrile-butadiene elastomers (HNBR).

The matrix preferably comprises at least 40 wt.%, at least 50 wt.% or at least 60 wt.% of at least one such polymer. The matrix can contain conventional additives, such as fillers, dyes, stabilizers or plasticizers, which can be organic or inorganic. Elastomers used for sealing applications typically contain fillers to improve hardness and stability.

in a preferred embodiment, the elastomer matrix is a fluoroelastomer. This generally means a fluorine-containing organic polymer. Preferably, the fluoroelastomer is a Fluoroelastomer (FKM) or a perfluororubber (FFKM). Fluororubbers (FKM) are produced by polymerization using vinylidene fluoride (VDF), wherein other monomers, such as Hexafluoropropylene (HFP) or Tetrafluoroethylene (TFE), may additionally be used. Suitable FKM's are, for example, copolymers of vinylidene fluoride (VDF) and Hexafluoropropylene (HFP), and terpolymers of VDF, HFP and Tetrafluoroethylene (TFE). FKM is particularly preferred according to the definition of DIN ISO 1629 or ASTM D1418. Other suitable fluorinated elastomers are tetrafluoroethylene/propylene rubber (FEPM) and fluorinated silicone rubber. In a preferred embodiment, the fluoroelastomer is crosslinked. Such crosslinked fluoroelastomers and their preparation are described, for example, in EP 1953190B 1.

In a preferred embodiment, the fluoroelastomer consists essentially of carbon and fluorine. It is possible here to: for example, other elements also constitute minor proportions due to the use of additives (e.g., crosslinking agents) other than fluorine and carbon in the polymerization reaction. Thus, in a preferred embodiment, greater than 90 wt%, greater than 95 wt%, or greater than 98 wt% of the fluoroelastomer is comprised of carbon and fluorine.

Preferably, the base body and/or the sealing element is a sealing ring, a rotary seal or a cartridge seal. The sealing ring is in particular a shaft sealing ring. Preferred sealing elements for dynamic sealing are, for example, sliding ring seals, radial shaft seal rings, labyrinth shaft seals, rod seals, O-rings or piston rings. These sealing elements seal the machine housing from the environment at the projecting elements (such as shafts or push rods). In a particularly preferred embodiment, the sealing element is a radial shaft sealing ring (RWDR). Radial shaft seal rings are in particular those defined in DIN 3760. In a preferred embodiment, the sealing ring is an axial shaft sealing ring. In dynamic sealing applications, such sealing rings are subjected to strong forces to a large extent, which, in combination with lubricants, lead to high wear of the sealing elements and to high shaft penetration.

The elastomer substrate is at least partially provided with a coating. In one embodiment of the invention, the elastomer matrix is provided with a coating throughout. In a preferred embodiment, only a plurality of partial regions of the substrate are coated. The partial regions of the coating can, for example, form 5 to 90%, in particular 10 to 60%, of the surface of the substrate. What is important here is that: the sealing gap, the contact surface with the sealing body and/or preferably also the adjoining region of the sealing body are coated.

The coating preferably has a layer thickness in the nanometer range. For example, the layer thickness is between 5 and 3000nm, in particular between 100 and 1500 nm.

The coating has a relatively low surface energy of <50mN/m, preferably <45mN/m or <40 mN/m. The surface energy here is preferably >20mN/m, in particular >25mN/m or >30 mN/m. It is preferable that: the surface energy is in the range from 20 to 50mN/m, in particular in the range from 25 to 45mN/m or from 30 to 40 mN/m.

Surface energy (surface tension) is the total potential energy of a molecule at or near the surface of a solid. In a solid, attractive forces between molecules act, which immobilize the molecules. The attractive force does not act on the molecules at the surface from all directions, but only from the inside. This results in a pulling force which acts inwardly on the molecules at the surface. Therefore, work is required to bring the molecules from the interior to the surface, and the molecules at the surface have a corresponding potential energy. Surface energy is a characteristic value of the interaction of the surface of a solidified phase (solid or liquid) with its environment. The surface energy is expressed in mN/m. Surface energy is a measure of the wettability of a material. The surface energy can be increased by various plasma methods. The surface energy of the solid is from less than 20mN/m (e.g. PTFE) to several thousand mN/m (metal, diamond).

In the case of the production of plasma, the surface energy of the coating can be influenced in a targeted manner by various measures. Thus, the surface energy is influenced by varying the proportion of oxygen-containing gas, the total amount of gas selected, the power or the reactivation of the surface, for example by varying the composition in the plasma. A suitable measure for increasing the surface energy is to use process gases containing polar atoms, such as nitrogen or oxygen. According to the invention, a relatively low surface energy of <50mN/m can be obtained, for example, if the coating contains a relatively small proportion of silicon, a relatively high proportion of carbon and a relatively low proportion of oxygen.

The measurement of the surface energy is indirectly carried out via the contact angle, which is constituted at the phase boundary between a solid and a liquid with a known surface tension. The young's equation describes the relationship between the contact angle, the surface tension of a liquid, the interfacial tension between two phases, and the surface energy of a solid. According to the present invention, the surface energy is measured according to a static contact angle measurement method using water and diiodomethane as polar or nonpolar liquids. Evaluation of contact angle measurements was performed according to the equations of Owens and Wendt. In particular, DIN 55660-2 is suitable for the determination (12 months 2011, wettability of coating materials-part 2: determination of the free surface energy of solid surfaces by measuring the contact angle).

The sealing element abuts the sealing body. The sealing body is in particular a machine component common for sealing applications, such as a shaft. Such sealing bodies are usually made of metal, for example steel. Known in the field of sealing technology are: shaft cut-in, i.e. erosion of the seal, is a serious practical problem, which can lead to leakage of the entire system or to destruction of the seal. Abrasion is caused by: the sealing element usually also has a relatively high hardness so as not to be strongly abraded or destroyed itself. In the prior art, the hardness of the elastomer sealing element is generally increased by the addition of fillers. Leakage refers in particular to an undesired outflow of lubricant from the sealing system.

The application according to the invention is carried out in the presence of a lubricant. Lubricants are materials that reduce friction or wear in a sealed system. In this case, the sealing element is wetted by the lubricant in the region of the sealing gap, wherein the wetting is carried out in particular on the so-called oil side. Lubricants are used primarily to reduce friction and wear, thereby extending the useful life of the sealing system.

Under operating conditions, the lubricant is liquid or lubricable. Which is typically an organic substance or mixture of substances. Common lubricants are, for example, fats or oils. The lubricant is preferably selected from: organic lubricating oils, especially synthetic lubricating oils. Due to the low surface energy, the sealing element according to the invention is also suitable for sealing in the presence of polar and lipophilic lubricants. In general, lubricants may be polar or oleophilic (miscible with oil). Suitable lubricants include or are as follows: such as polyethers, polyesters, water-based lubricants, silicone oils or polyalphaolefins. The water-based lubricant preferably contains water and an organic compound such as polyether, polyester and/or surfactant in an amount of 5% by weight or more. They are described, for example, in EP 2473587B 1.

Polar lubricating oils are particularly preferably used. Preferably, the polarity is higher than that of the mineral oil. In particular, the lubricant is preferably hydrophilic, i.e. miscible with water or partially miscible. Polar lubricating oils contain polar groups, particularly oxygen-containing groups, such as hydroxyl groups, ether groups, or ester groups. Preferably, the lubricant is a polyether polyester or a mixture thereof.

The lubricant is particularly preferably a polyalkylene glycol, which is made by polymerization of alkylene oxide units, usually ethylene oxide or propylene oxide units or combinations thereof, where the proportion of ethylene oxide determines its solubility in water, polypropylene glycol is particularly preferably used various polyalkylene glycols are commercially available under the trade name "polyethylene glycol" polyalkylene glycols show high potential for friction minimization in gears and high temperature resistance suitable polyalkylene glycol oils are available from UH ü ber Lubrication germany, for example under the trade name Kl ü bersynth GH 6 or Kl ü bersynth 16-460 polar lubricating oils, especially polyalkylene glycols have been found to be particularly compatible with the sealing system according to the invention.

In a preferred embodiment, the contact angle of the coating with respect to the lubricant is less than 50 °, less than 40 ° or less than 30 °, preferably from 10 ° to less than 50 °, still more preferably between 15 ° and 30 °. With such a relatively low contact angle, the coating can be wetted well by the lubricant. It has been found that: polar lubricating oils, in particular polyalkylene glycols, have such contact angles with the sealing element according to the invention, which results in an effective, low-abrasion sealing system. The contact angle is preferably determined at room temperature in the state of equilibrium in accordance with DIN 55660-2 (12 months 2011).

the surface tension of the lubricant is 10 to 70mN/m, preferably 15 to 60mN/m or 20 to 40 mN/m. The surface tension was determined by the hanging drop method according to DIN55660-3 (12 months 2011).

The system according to the invention is particularly suitable in the case of use with lubricants containing a relatively high viscosity. Thus, in a preferred embodiment, the kinematic viscosity of the lubricant>150mm²S, preferably>250mm²S or>400mm²And s. The kinematic viscosity is preferably measured at 40 ℃ according to ISO 3104/ASTM D445.

The application is preferably effected at an oil sump temperature of <80 ℃, in particular <60 ℃ or <40 ℃. The oil sump temperature was as follows: at this temperature, the oil in the entire apparatus is merged and stored at the lowest point (oil sump). In the dynamic sealing system itself, there may be locally significantly higher temperatures caused by frictional heating of the components.

It is particularly advantageous to utilize such high viscosity lubricants and/or to apply them at relatively low temperatures <80 ℃. According to the invention, the following discovery is made: it is under such conditions that particularly stable, extremely low-wear sealing systems are obtained, in particular when synthetic hydrophilic oils (e.g. polyalkylene glycols) are used. This is particularly used in connection with fluoroelastomer-based sealing elements. In such sealing systems it has been found that: not only can shaft cut-in be reduced, but shaft cut-in can even be completely prevented. This is particularly advantageous since in the prior art, under similar conditions, a relatively strong wear of the sealing element and/or a relatively strong axial cut-in of the sealing body is usually observed.

According to the present invention, it was surprisingly found that: the sealing element in a dynamic sealing system has a particularly advantageous combination of properties. It is generally known in the art that: seal elements used in dynamic sealing applications must be relatively stiff to prevent damage to the seal element due to abrasion. Thus, it is proposed according to EP 2291439B 1: the sealing element is provided with a glassy coating containing a high proportion of silicon and oxygen. In addition, hard coatings (DLC) containing a high proportion of carbon have been proposed in the prior art. However, the disadvantages in such coatings are: in practice, although the abrasion of the sealing element can be reduced, the sealing body itself is damaged by abrasion. As a result, undesirable shaft cuts are observed at the seal body in shaft applications.

The sealing system according to the invention has excellent tribological properties. At the same time, the abrasion of the sealing body can be greatly reduced and can often even be completely avoided. The sealing system is particularly suitable for dynamic sealing applications in the presence of synthetic lubricants. Thus, shaft cut-in can be largely or even completely avoided in the case of a dynamic shaft seal.

The subject matter of the invention also relates to a sealing system (seal) comprising a sealing element, a sealing body, a dynamic sealing gap between the sealing element and the sealing body, and optionally a lubricant. The sealing system is preferably a dynamic seal.

Fig. 1 shows schematically and exemplarily a sealing system 1a, 1b of a sealing element 2 and a sealing body 3 and a lubricant 5, wherein the sealing element 2 and the sealing body 3 form a sealing gap 4. On the left, the conventional system 1a shows a system in which the lubricant 5 does not completely fill the sealing gap 4 because of insufficient wettability. By means of the coating according to the invention, a sealing system 1b can be obtained, as shown on the right, in which the sealing gap 4 is completely filled with the lubricant 5, that is to say in which the sealing element 2 and the sealing body 3 are completely wetted in the sealing gap 4.

the subject of the invention is also an apparatus comprising the device to be sealed, said apparatus comprising a dynamic sealing system (seal). In a preferred embodiment, the device is a transmission, a pump, a motor or a motor vehicle.

The invention also relates to a method for dynamically sealing a sealing body with a dynamic sealing system according to the invention, wherein the sealing body and the sealing element are moved dynamically relative to one another.

In the method according to the invention, a sealing system consisting of a sealing body, a sealing element and a lubricant is provided. The sealing body and the sealing element move relative to each other. Here, it is observed that: the sealing system is stable during a longer period of time. Slight abrasion of the sealing element during the initial phase is not disadvantageous. A system is obtained which can operate stably over a long period of time. Thus, for example, it has been found that: slight abrasion of the sealing element can occur in less than 96 hours, while in a longer period of up to 1000 hours thereafter no further significant abrasion occurs. In addition, it was observed that: during 1000 hours of operation, no wear was observed on the shaft as a seal body, and no shaft cut was observed. The effect is particularly obvious in the case of high viscosity lubricants and relatively low temperatures. In general, a system is provided that is stabilized with increasing duration of operation and has consistently good tribological properties.

The subject of the invention is also a sealing element for the dynamic sealing of a sealing body in the presence of a lubricant, wherein the sealing element comprises an elastomer matrix made of a fluoroelastomer and a plasma coating,

Wherein the coating contains the elements carbon, oxygen, silicon, hydrogen and optionally fluorine,

Wherein the coating has the following properties at least on the surface:

The molar ratio of C to Si (at%/at%) >5,

Si in a molar ratio (at%/at%) >3, and

Surface energy <50 mN/m.

The sealing element can also be designed as described above in general terms. The sealing element with a base body composed of a fluoroelastomer exhibits particularly advantageous properties in the system according to the invention, in particular in combination with a polar lubricant, such as a polyalkylene glycol.

the subject of the invention is also a method for producing a sealing element according to the invention by means of plasma-assisted, preferably chemical vapor deposition, comprising the following steps:

(a) The elastomer matrix is introduced into a plasma apparatus,

(b) Introducing at least one gaseous silicon precursor compound into the apparatus, and

(c) coating the substrate in the apparatus.

plasma-assisted chemical vapor deposition is generally the following method: wherein a plasma excited gaseous precursor compound (also referred to as a precursor or monomer) is deposited as a crosslinked layer on a substrate. The monomers in the gas phase are excited or fragmented by bombardment with electrons and/or energetic ions, for example. This forms molecular fragments of radicals or ions which react with each other in the gas phase and deposit on the substrate surface. The discharge of the plasma and its intensive ion and electron bombardment continue to act on the thus deposited layer, triggering further reactions and effecting cross-linking of the deposited molecules. The plasma is preferably a low pressure plasma, but an atmospheric pressure plasma may also be used. Elastomer coatings in plasma are known from the prior art and are disclosed, for example, in DE 102005025253 a 1. The methods disclosed therein are incorporated herein by reference.

According to the invention, the matrix can be introduced first in step (a) and then the precursor compound(s) added in step (b), or vice versa. In the plasma, the silicon precursor compound and optionally other precursor compounds are activated. The actual polymerization reaction can take place in the gas phase and/or in the coating. In step (c), the intermediate is deposited on a substrate. Methods for producing carbon-containing coatings by means of plasma-assisted chemical or physical vapor deposition on elastomeric substrates are generally known in the prior art and are described, for example, in EP 2291439B 1, Lubwama, 2003 or Martinez-Martinez and De Hosson, 2014 (see above, respectively).

The primary object of the invention is achieved according to the use, sealing element, sealing system, device and method of the invention. A combined dynamic sealing system with advantageous properties is provided. The sealing element and the sealing system exhibit excellent tribological properties and here in particular very good tribological properties. They also have high stability. In particular, the seal is at most slightly abrasive, but generally not. In this way, for example, in practice, shaft cuts at the sealing body can be completely prevented. According to the invention, a stable system is provided, which is stable during a long period of time, optionally after initial self-stabilization due to slight abrasion of the sealing element. This is very advantageous for a number of practical applications, such as motors, transmissions or pumps, where the service life is generally dependent on wear of parts.

Drawings

Fig. 1 shows schematically and exemplarily a sealing system consisting of a sealing element, a sealing body and a lubricant.

Fig. 2 shows the results of contact angle measurements of polyethylene glycol lubricants on FKM with a coating (dashed line) and without a coating (solid line) as described in example 11.

Fig. 3 shows the stribeck curves for coated FKM (circles) and uncoated FKM (squares) as described in example 12.

Detailed Description

Examples 1 to 9: production and characterization of coatings

In the plasma assisted chemical vapor deposition process, various elastomers (see table 1) were coated. For this purpose, low-pressure plasma facilities are used for asymmetrical, capacitively coupled radio-frequency discharges. The elastomer matrix (substrate) is positioned in contact with the electrodes. In the process, acetylene and optionally an oxygen-free alkylsilane compound are used as a carbon source and a primary layered precursor compound. The addition of other reactive gases, such as oxygen, argon, nitrogen, is likewise conceivable. The gas is placed in a plasma state at a process pressure of several pascals by excitation with electromagnetic radiation, for example in radio frequency. In the case of alkylsilanes containing a low proportion of silicon, the molecules split and condense into a carbon-rich layer on the substrate surface. To better bond the layers, the elastomer is first activated in a plasma (e.g., a plasma composed of argon and/or oxygen) that does not form a layer. Here, fragments of the substrate are transferred from the surface into the plasma phase and incorporated into the coating. The main coating steps are listed in table 2 by way of example. Layer 4 formation is an exception to what was previously set forth. In contrast thereto, the layer is deposited in a manner not in contact with the electrodes and serves as a contrast to patent EP 2291439B 1.

Name (R)	Polymer and method of making same	Mechanism of crosslinking	Main packing
				FKM I	fluororubber	Bisphenol	Mineral filler
EPDM I	ethylene propylene diene rubber	Peroxides and their use in the preparation of pharmaceutical preparations	Soot
				NBR I	Nitrile butyl rubber	Sulfur	Mineral filler

TABLE 1 sealing materials used

TABLE 2 Process parameters of the coating Process

The chemical composition (in the boundary surface with air) of the coating thus deposited is characterized by X-ray photoelectron spectroscopy. Here, the method of course determines only the uppermost nano-layer chemistry, not the composition of the entire coating at all. All samples were washed with ethanol prior to measurement. The measured spectrum was calibrated to the C1s peak at 285.0 eV.

TABLE 3 chemical composition of different surfaces

The results are summarized in table 3. Examples 2, 3, 6 and 8 are according to the invention. Examples 1, 5 and 7 (no coating), 1a (no Si precursor compound), 4 (containing a Si-O rich coating) and 9 (on steel) denoted by (V) are comparative examples. Here, example 4 containing layer 4 corresponds to the layer described in EP 2291439B 1, since the binding energy of the Si 2p signal measured by XPS is shifted by about 1eV towards higher binding energy compared to the trimethyloxy-terminated PDMS. The low Si content in the uncoated comparative examples 1, 5 and 7 can be explained as: the elastomer contains additives such as silicone or silica fillers. Comparison of the properties shows that: the structure of the surface of the coating according to the invention is very different and the advantageous effects with respect to tribological properties and shaft penetration are only obtained in the case of the plasma coating according to the invention (see the examples below).

example 10: determination of surface energy and contact Angle

To determine the surface energy, contact angle measurements were made at the placed drops. The treatment was carried out in a manner similar to DIN 55660-2 standard on month 12, 2011, except for the test climate. The measurements were carried out at a temperature of 23-26 ℃. Water and diiodomethane were used as the measurement liquid. The surface energy was calculated based on the contact angle derived from the measurements according to the Owens-Wendt method. The total surface can in this case consist of polar and dispersed fractions.

contact angle measurements were taken 1 day, 7 days, and 30 days after the coating process. All surfaces were cleaned with ethanol prior to measurement. Since the matrix material is a multi-component system, the individual components thereof tend to migrate in part, and the contact angle measurements fluctuate around at most 10 ° depending on the material. The results are summarized in table 4. Overall, measurements show that the surface energy is relatively low, so that the coating wets relatively well.

TABLE 4 surface energy (in mN/m) of carbon-rich coatings on different elastomers.

Contact angles with commercially available polyalkylene glycol oils of ISO viscosity grade 460 (trade Mark Kl ü bersynth UH 16-460; Kl ü ber Lubrication, Germany) were measured on FKM I coated and uncoated with layer 2 FIG. 2 shows the contact angle measurements on FKM with (dashed line) and without coating (solid line) the coating improves wetting significantly and reduces the contact angle in equilibrium by about two thirds, i.e. from about 68 to about 22%.

Example 11: friction performance without lubricant

To characterize the friction reduction of the coating, the coated and uncoated test specimens were moved (Ra ═ 1.062 μm) over a stainless steel plate and subjected to the necessary force. For this purpose, three samples are placed in a special receptacle which makes it possible to achieve, for each sample, approximately 6.5mm with the mating object²The contact surface of (a). The receiving part is placed with the sample down onto the mating object and weighed out with a mass of 1 kg. Then, the mating object was moved at a speed of 150mm/min, and the force required to hold the receiving member in place was measured. The measurements were performed three times in sequence and the average values are summarized in table 5. The results show that the coating significantly improved the tribological properties of the elastomer.

From the examples	Substrate	force [ N ]]
			1(V)	FKM I	12.4
2	FKM I with layer 2	2.3
			5(V)	EPDM I	10.9
6	EPDM with layer 2	2.4
			7(V)	NBR I	11.1
8	NBR I comprising layer 2	2.5

TABLE 5 Friction force of different surfaces

The friction measurements were performed similarly to the previous description. However, the polished stainless steel surface was used as a mating object.

From the examples	Substrate	Force [ N ]]
			1(V)	FKM I	16.1
1a(V)	FKM I with layer 1	4.0
			2	FKM I with layer 2	2.2
3	ComprisesFKM I of layer 3	2.3
			4(V)	FKM I with layer 4	9.5

TABLE 6 Friction force of different coatings

The results are shown in table 6. The result shows that: the tribological properties of the elastomers coated according to the invention (examples 2, 3) are clearly superior to those of the elastomers with a coating which does not contain silicon (example 1a) or with a high Si-O content (example 4).

Example 12: friction performance containing lubricant

To characterize the lubricated sealing system, comparative experiments were carried out on a disk test bench (for this reason see also m.sommer, w.haas: "a new approach on grease Tribology in sealing technology: Influence of thickener particles", Tribology International, volume 103, 2016, p. 574 583.) for this purpose, a test specimen consisting of FKM I was used and a comparative test was carried out with a layer 2 coating (according to examples 1 and 2), polyalkylene glycol oil (Kl ü bersynth UH 16-460) of ISO viscosity grade 460 was used as a lubricant, the tempering device was set to 60 ℃ fig. 3 shows that the results of the uncoated m (round) and uncoated m (square) coatings also in the optical friction system showed a marked reduction in the friction-induced wear zone, particularly after the optical inspection of the tribological wear zone of the lubricant.

Example 13: determining erosion Using seal rings and Lubricant in short term component testing

As described in example 2, a radial shaft seal ring (RWDR) consisting of a metal insert coated with a fluoroelastomer FKM i was investigated in typical short-term tests for the application properties of the component, as a comparison, an uncoated component was also tested, in which short-term test a steel shaft (90MnCrV8, hardness 55 to 60HRC, Rz ═ 1 to 5 μm, no distortion) was rotated in the seal ring (p ═ 0.3bar) for 96 hours at 3000 revolutions per minute, at an oil bath temperature of 45 ℃, a polyalkylene glycol oil of ISO viscosity grade 460 (Kl ü bersynth UH 16-460) was used as a lubricant.

In another series of tests, a radial shaft seal (RWDR constructed of rubber FKM I) was provided with layers 1 through 4 and characterized in the 96 hour test described. This time a polyalkylene glycol oil of ISO viscosity grade 460 was used as a lubricant at an oil sump temperature of 80 ℃. The results are summarized in table 7.

coating layer	Surface energy [ mN/m]	Width of running trace [ mm ]]	Axial incision [ mu ] m]
				Layer 1	44.0	0.39-0.43	4.25
Layer 2	33.6	0.22-0.28	0
				Layer 3	38.5	0.19-0.28	0
Layer 4	49.2	0.39-0.49	5.89

TABLE 7 RWDR surface energies and abrasions of different coatings after 96 hours of part testing

The results show that: in the sealing system according to the invention, it is not only possible to reduce the shaft cut-in of the sealing body, but it is even possible to completely prevent the shaft cut-in. In contrast, comparative tests with silicon-free carbon-rich layer 1 and layer 4 (rich in Si — O) showed significant shaft cut, i.e. wear of the seal body composed of steel. No leaks were found in any of the sealed systems.

example 14: determination of abrasion Using seal rings and Lubricant in the Siemens-Frand test

As described in example 2, an RWDR consisting of FKM I (75FKM 585) was provided with layer 2. comparative testing of coated and uncoated components was carried out according to the protocol of the dynamic Siemens-Frandd test [ FB 7311008 (30 days 7.2015: static and dynamic oil compatibility tests using the Freudenberg West molar ring, approved for use in Frandd transmissions, Table T7300 https:// cache. industry. siemens. com/dl/files/658/44231658/att-861254/v 1/DE-5-2 RWDR _ and-O-Ringtest-Rev 06___2015-07-30. pdf.) A polyalkylene glycol oil of ISO viscosity grade 460 (Kl ü 16-synththuh460) was used as lubricant at 110 ℃.

After the series of tests has ended, the wear of the sealing edge is in the order of 0.2 to 0.4mm for uncoated rings and 0.1 to 0.3mm for coated rings. The shaft cut in the tribological system with uncoated FKM rings is 30-40 μ. In tribological systems with coated rings, shaft cut-in cannot be determined. Likewise, no leakage of the sealing system was found.

example 15: determination of abrasion with greased sealing rings in Long-term tests

as described in example 2, the RWDR made of FKM I is provided with layer 2. Prior to the test, the coating surfaces of the test series were additionally provided with grease. Now, both greased and ungreased components (shaft: C45R, Rz. RTM. 1 to 5 μm, no distortion; test parameters: T. 240h, T-_{Lubricant agent}70 ℃ and p 0.25 bar). In this test, the steel shaft was rotated in the seal ring for a total of 240 hours, alternating between 20 hours at 2000 rpm and 4 hours at rest. Polyethylene glycol oil of ISO viscosity grade 220 was used as a lubricant at 70 ℃.

The running trace width of the greased and unprimed seals after the end of the test series was 0.1 to 0.2 mm. No shaft cut was detected in all tribological systems (rings with or without greasing). This means that: the good tribological properties of the sealing ring of the coating according to the invention are maintained even in the case of the additional use of grease. When uncoated, but greased RWDR was used, significant shaft cutting occurred. No leaks were found in any of the sealed systems.