FR2749013A1 - MOLDED PART OF IODINE TREATED MATERIAL AND METHOD OF MANUFACTURING SUCH MATERIAL - Google Patents

Abstract

The invention relates to a molded part made of a material which consists, at least in the surface region, of acrylonitrilebutatiene rubber (NBR), the molded part being arranged between objects moving relative to each other, characterized by that 1 to 1000 mug of iodine, preferably 20 to 400 mug of iodine, are included in the surface area of the molded part per cm ** 2 of material surface area, a method of making this material by exposure to a fluid or a solid containing iodine to improve the sliding properties of the surface of the material without causing cracking on a microscopic scale, corresponding molded parts which can in particular be in the form of gaskets or blades of 'wiper.

Description

The present invention relates to a molded part made of a material

  which consists, at least in the surface area, of acrylonitrile-butadiene rubber (NBR) or which comprises in the surface area of

  related materials such as natural rubber (NR).

  Seals are known which consist of a material based on

  acrylonitrile-butadiene rubber (NBR).

  To modify or improve the surface properties of NBR seals, the surface of the seals is treated, for example, with talc, molykote (lubricant based on MoS2), by coating, with graphite, by application of a layer. polyurethane to reduce friction, fluorine or chlorine

(AF processing).

  In the known treatment (AF) with chlorine, the surface of the seal is hardened by crosslinking with chlorine. Due to this artificial aging, the seals thus treated can undergo greater abrasion. Furthermore, the crosslinking of the material with chlorine can cause tensions and cracks at the surface of the seals which, in the presence of gas, hamper the desired sealing function and therefore cause

larger fluids.

  Treatment with fluorine also causes crosslinking which can lead to cracks in the surface of the seals so that these seals cannot be used to provide gas tightness. Furthermore, at the reaction temperatures, the fluorine is in the gaseous state which requires very important safety measures. In addition, processes that involve the

fluorine are pollutants.

  US Pat. No. 4,292,150 discloses the treatment of printing plates with iodine (I2). In this process, the plates are placed in a liquid enriched with potassium iodine-iodide or exposed to iodine vapors to strongly lower the adhesive properties at the surface of the plates and to allow delaying or avoiding hardening from the surface of

plates after sunstroke.

  US Patent 4,300,970 describes a bonding technique which allows synthetic materials to be bonded together. According to this technique, a surface of synthetic material is treated for example with an iodine solution before the

  connecting plastic parts.

  On the contrary, the aim of the present invention is to develop a material of the type mentioned above so as to improve its properties, in particular its ability to slide, without its surface being appreciably deteriorated. According to the invention, this object is achieved by the inclusion of i to 1000 μg of iodine, preferably 20 to 400 μg of iodine, in the surface area of the part molded per cm 2 of surface of the material. Iodine is a relatively harmless, easy-to-handle element that is solid at room temperature. Compared to the two other halogens that are fluorine and chlorine, iodine is not very reactive, little polluting and does not require for its

  use no special security measures.

  Treatment of an NBR type material with iodinated compounds or

  with iodine constitutes a kind of post-vulcanization which is accompanied by a post-

  crosslinking of the surface. However, the crosslinking density of the surface by

  treatment with iodine is weaker than treatment with fluorine or chlorine.

  The advantages of the material according to the invention are explained below in the case of seals which consist of the material according to the invention. By seals is meant any type of seals, in particular O-rings, which can be used to seal fluids in static or dynamic applications or as sliding bearings. These advantages are as follows: absence of odor by comparison with NBR seals which are treated with chlorine or fluorine, - absence of degradation of the properties of the material by comparison with untreated NBR seals ; the properties of the NBR seals treated with iodine remain essentially identical to those of the initial material, - the treatment of the surface of the NBR seals inevitably leads to a treatment of the deeper layers which give rise to a determined depth effect, - clean handling is possible, which allows for wider areas of application, for example in medicine, - the use of molded parts treated according to the invention is also possible in the food sector because iodine included is present in concentrations which, according to current designs, do not have any harmful effect on health, - better mounting is possible because the NBR seals treated with iodine can be lengthened up to 60% without cracks appearing on the surface and without losing their elasticity; - seals treated with iodine have improved friction and slip (minimized friction) which remain constant throughout their useful life, and - the useful life is greater so that the effect on long term is improved so that iodine treated seals can be used for dynamic applications, for example by being

  arranged between moving objects relative to each other.

  In the embodiment of the material according to the invention in the form of a seal or a wiper blade, 1 to 1000 μg of iodine, preferably from 20 to 400 μg of iodine, are included by cm2 of material surface. On the one hand it is necessary to include enough iodine in the surface to obtain the effects mentioned above but on the other hand it is not necessary to include too much iodine in the surface because this could cause a embrittlement of NBRouNR type material. When the seals or wiper blades are treated with iodine according to the invention, these present in the area of the surface a low friction, a resistance to wear, a low noise and have a smooth surface. The seals thus treated are odorless. There is no waste left after treatment due to the fact that iodine is used which is completely included in the surface of the molded parts, and the treatment itself can be carried out without difficulty since iodine is an element not very reactive. The reaction, i.e. the course of treatment, is favored by heat and low pressure plasma

  with a pressure p less than 102 Pa (10 mbar).

  The present invention also relates to a method of manufacturing the material according to the invention in which an NBR type material is exposed to a fluid or a solid containing iodine. For example, an NBR gasket can be exposed to a gas or solid containing iodine or it can be immersed in a liquid containing iodine. We can easily determine experimentally the durations of action of the fluid or solid on the joint

NBR sealing.

  In one form of the process according to the invention which is particularly preferred, the NBR type material is exposed to a low pressure iodine plasma. This plasma treatment allows short treatment times and has the essential advantage over the other processes that the ionized iodine atoms formed (iodine plasma) react in part chemically with the material,

  i.e. are chemically included in acrylonitrilebutadiene rubber.

  A particularly advantageous development of this embodiment is characterized in that the plasma is produced in a rotary drum in which the NBR material to be treated is located and 1 to 1000 μg of iodine powder, preferably 20 to 400, pg of iodine powder, per cm2 of material surface. The plasma parameters (temperature, treatment time, acceleration voltage) are adjusted so that the iodine penetrates to the desired depth in the

NBR type material surface.

  In a particularly preferred manner, this plasma treatment is prolonged as long as iodine powder still remains in the rotary drum. In this case, a predetermined quantity of iodine powder is introduced into the rotary drum and the plasma treatment is carried out until there is no longer any iodine powder in the rotary drum, c i.e. until all of the iodine is included in the NBR material. The treatment time required can easily be determined experimentally by varying this treatment time. In the tests carried out so far, treatment times at

  plasma of about 5 minutes was sufficient to achieve the desired goal.

  In another embodiment of the method according to the invention, the NBR type material is introduced into a powder containing iodine, preferably an iodine powder. The diffusion parameters are chosen, for example the diffusion temperature and the diffusion duration, as a function of the depth of

  penetration of iodine into the desired NBR type material.

  In another embodiment, the iodine used for the treatment of the seals is brought to the gaseous state before being introduced into the rotary drum and is used in this form for the treatment which allows of

  make this treatment even more uniform.

  Other characteristics and advantages of the invention will appear better

  in the detailed description which follows and refers to the attached drawings, given

  by way of example only, and in which: FIG. 1 represents with a magnification of 2000 the surface of a seal made of NBR seal treated with iodine, FIG. 2 represents with a magnification of 2000 the surface of a seal in untreated NBR, Figure 3 shows at 2000 magnification the surface of a seal in NBR subjected to AF treatment, Figure 4 shows with 2000 magnification the surface of a seal of NBR treated with iodine and which is elongated by 25%, FIG. 5 shows with a magnification of 2000 the surface of a seal made of untreated NBR and which is elongated by 25%, and the figure 6 represents with a magnification of 2000 the surface of a

  NBR gasket subjected to AF treatment and which is elongated by 25%.

  In Figures 1 to 6 the scale is indicated at the top

(20 um).

  We will now describe the method of manufacturing seals according to the invention before describing the properties of seals

  in NBR treated by reaction with iodine.

  O-rings made of acrylonitrile-butadiene rubber (NBR) or natural rubber (NR), the surfaces of which have been cleaned beforehand, are exposed to a low-pressure iodine plasma. The plasma is produced in a rotary drum in which there are the NBR seals to be treated and an iodine powder. For 1000 O-rings with an internal diameter of 15 mm and a body thickness of 3 mm, 0.1 to 5 g of iodine are required. This corresponds to a

  iodine consumption from 20 to 400, ug of iodine per cm2 of joint surface.

  The plasma parameters (temperature, treatment time, acceleration voltage) and the quantity of iodine powder are adjusted so that the iodine penetrates the surface of the NBR type material to the desired depth. The plasma treatment is continued as long as iodine powder remains in the rotary drum. The iodine is then completely included in the NBR seals. The duration of plasma treatment necessary for this can be easily determined experimentally by varying the duration of

  plasma treatment while keeping the other plasma parameters constant.

  FIGS. 1 to 3 represent scanning electron microscope photographs of an O-ring made of NBR treated by reaction with iodine (FIG. 1), of an O-ring made of untreated NBR (FIG. 2) and of a seal toric in

  NBR subjected to AF treatment (Figure 3).

  By comparison with the surface of an untreated seal (FIG. 2), we observe on the surface treated by reaction with iodine (FIG. 1) structures comprising reliefs and hollows and it is found that the surface treated is smooth and has no cracks. On the contrary, the seal subjected to AF treatment (with chlorine) is structured to the depth. The individual troughs are partly interconnected, which already allows paths to be planned

gas leaks.

  Figures 4 to 6 show scanning electron micrographs of an NBR O-ring treated with iodine reaction (Figure 4), an untreated NBR O-ring (Figure 5) and a seal toric in NBR subjected to an AF treatment (FIG. 6), the internal diameter of which is increased in each case by 25%. We studied in particular the areas whose structure was apparent without magnification. Such enlargements of 25% or more occur for example when mounting the seals in the corresponding stripes. As indicated by subsequent surface examinations, there were impurities on the untreated surface of the seal (Figure 5). Despite the elongation, the surface is smooth and has no cracks. Even in the expanded or expanded state, the seal treated by reaction with iodine (fuguer 4)

  has a relief and hollow structure, as in the non-enlarged state (Figure 1).

  Despite the 25% enlargement or expansion, the surface is closed and has no cracks. On the other hand, the enlargement reveals the cracks that exist

  in the surface of the seal subjected to AF treatment.

  The friction behavior of the three types of seals (untreated, treated with iodine, subjected to AF treatment) was tested. The friction tests were carried out on a tensile testing machine. To do this, the seals were mounted in a groove and subjected to a traction on a glass plate with defined surface, in the non-lubricated state, after which the friction was

determined.

  The following O-rings were examined: 1. OR 012 N70B200V subjected to AF treatment (chlorine) 2. OR 012 N70B200V untreated 3. OR 012 N70B200V treated with iodine The friction behavior of the O-rings was determined at two speeds : a) V = 200mm / min b) V = 50Omm / min Three measurements were made on each type of O-ring and the following friction values were thus obtained: V = 200 mm / min V = 500 mm / min

1.1.0 N 0.75 N

2. 1.5 - 2.5 N 1.75 - 2.0 N

3. 1.35 N 1.0 N

  In the case of the untreated O-ring (2.) it was possible to highlight a peak at the start of the friction curve, that is to say that, for this O-ring,

  friction by adhesion had to be overcome initially.

  On the contrary, it was not possible to demonstrate such friction by initial adhesion ("take-off force") in the case of the O-ring.

treated with iodine (3.).

  The O-ring subjected to AF treatment (1.) had values of

  slightly lower friction than the iodine-treated O-ring (3.).

  The iodine treatment of an NBR O-ring caused a reduction in friction compared to an untreated seal, i.e. the iodine treatment caused an increase in slip, which

  which significantly reduced the grip strength.

Claims (6)

Claims   1. Molded part made of a material which consists, at least in the surface area, of acrylonitrile-butadiene rubber (NBR) or which comprises in the surface area of related materials such as natural rubber (NR), the molded part being arranged between moving objects in relation to each other, characterized in that 1 to 1000 ug of iodine, preferably 20 to 400 ug of iodine, are included in the surface area of the workpiece   molded per cm2 of material surface.   2. Molded part according to claim 1 characterized in that it is   a seal or a wiper blade.   3. Method for manufacturing a material for a molded part according to one   any one of the preceding claims, characterized in that a material of   NBR or NR type is exposed to a fluid or solid containing iodine.   4. Method according to claim 3 characterized in that the material of   NBR or NR type is exposed to an iodine plasma.   5. Method according to claim 4 characterized in that the plasma is produced in a rotary drum in which there is the material of the NBR or NR type to be treated and 1 to 1000 μg of iodine powder, preferably 20 to 400 # g of powder   iodine, per cm2 of material surface.   6. Method according to claim 5 characterized in that the plasma treatment is maintained as long as iodine powder is still in the rotating drum.