**6. Reduction of adhesion of CIIR rubber to steel plate with plasma irradiation**

**Silicone oil**

Fused silica glass PFPE

**Figure 17.** Schematic of photochemical treating process with UV and PFPE.in vacuum

**In vacuum ( In vacuum (**䍦**0.1 Pa) 0.1 Pa)**

Specimen

**Figure 16.** Schematic view of plastic syringe

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0.0

**Figure 18.** Relation between irradiation time to TPE and friction coefficient.

1.0

2.0

3.0

Friction coefficient

4.0

5.0

6.0

**Barrel** (PP etc.) **Plunger** (PP etc.)

Micro-Nano Mechatronics — New Trends in Material, Measurement, Control, Manufacturing and Their Applications in

PP: Polypropylene TPE: Thermoplastic elastomer

Rotary pump

**Gasket** (TPE etc.)

**UV 172 nm**

0 20 40 60 80 100

Normal load W: 1 N , Sliding speed V: 2 mm/s

in air (30-50 %RH) TPE vs. Non-treated PP

Wavelength of UV: 172 nm Dropped PFPE & Cleaned by HFE

Irradiation time to TPE *t* , min

Adhesion, or the sticking of different materials at their interface, is of general interest in many branches of technology, including micro‐electronic devices, medical products and manufac‐ turing. Adhesion between rubbers and metals is often the main source of trouble in a machine. Thus, if molded rubber products easily stick to molds, rollers, and pick‐up hands made of metals, the productivity of their manufacturing line becomes low. Therefore, efficient utiliza‐ tion ofrubber sheets demands modifications on some desirable properties ofthe rubber surface without affecting the bulk characteristics. Plasma treatment is one of the most employed methods to attain this goal. One of the most significant benefits of the plasma process is it offers and additional advantage that the surface modification does not affect the desirable bulk properties of the rubber.

In a previous study, we have demonstrated that the surface wave‐excited plasma treatment reduced the adhesion force between a medical rubber, chloride‐isobutene‐isoprene rubber (CIIR) and stainless‐steel ball (SUS440C) by using oxygen and argon gases.

We have also shown a decrease in the real contact area with increasing time and micro wave power, and a similar trend in the residual rates of the adhesion force and the real contact area of CIIR rubber. Therefore, it is assumed that the adhesion force is strongly subjected to the real contact area [14]. However, the main reason for the reductions in the real contact area remains unknown.Recent works have shown that plasma treatmentincreases the roughening ofrubber surfaces [15]. The surface roughness may affect the adhesion force, which is largely dependent on the contact geometry and surface topography [16].

The objective of this research, we report on our attempts to clarify the factor to reduce the adhesion force during the surface wave excited plasma treatment process. It is also attempted to figure out the Young's modulus behavior in micro scale to measure without bulk property by using micro slicer and surface roughness changes are measured by 3D laser scanning microscope.

Results of adhesion forces between CIIR rubber and stainless‐steel ball as a function of plasma treatmenttime at 200Ware shown in Figure 19.Itis apparentfrom the figures thatthe adhesion force dramatically decreased with oxygen plasma treatment according to treatment time. Similar decreasing trend was also observed with argon plasma treatment. However, at 1 min treatment time, the adhesion force was higher with argon treatment than oxygen plasma treatment of CIIR rubber. After 1 min, argon plasma treatment was more effective than oxygen plasma treatment in decreasing the adhesion force. The adhesion force couldn't be measured after 10 min because it was lowerthan the measurable value of 0.001 N.In summary,the figures showed that plasma treatmenttime is a very importantfactorthat decreases the adhesion force.

Load‐penetration depth curves by using the nano‐indenter with 50 μN maximum loads were obtained. The thickness of the prepared CIIR rubber was about 3 mm for the general thickness and about 50 μm for the cutting thickness by using the microwave slicer. Despite the same conditions, the penetration depth obtained from the 3mm thickness CIIR rubber was clearly

different from that obtained from the 50 μm thickness. In particular, the unloading curve coincided with the loading curve at a penetration depth of more than 290 nm due to the thickness difference. This indicates that not only the bulk property has greatly affected the Young's modulus, but also it is affected its accurate measurement. In other words, a surface wave‐excited plasma treatment increased the Young's modulus in μm thickness scale. As a result, we determined that it is possible to develop a clear difference between 3 mm and 50 μm Young's modulus of the CIIR rubber without any influence from the bulk property by using the microwave slicer.

Figure 20 shows the Young's modulus profile of 50 μm thickness CIIR rubber measured by nano‐indenter after oxygen and argon plasma treatment with increasing time. The results treatment time (206.1 MPa), and followed by a steady state. A higher Young's modulus (236.4 MPa) was obtained with argon plasma treatment, but only after 15 min treatment with argon gas. As a result, this improved Young's modulus by the oxygen and argon are depicted with squares (oxygen plasma treatment) and circles (argon). For the oxygen plasma treatment, Young's modulus was slightly higher (39.8 MPa) than the untreated CIIR rubber (38.0 MPa). However, it increased significantly between 5 min (53.8 MPa) and 10 min surface wave‐excited

Tribology for Biological and Medical Applications 237

**Figure 21.** Surface roughness changes of CIIR sheet as a function of plasma treatment time. The measurements were done for oxygen (dotted line) and argon (solid line) plasma-treated CIIR sheets. The surface roughness parameters, Rz

Figure 21 shows surface roughness as a function of plasma treatment time. The surface roughness deviations of CIIR rubber by oxygen and argon plasma treatment has changed. The

Especially,theRz of argon plasma treated CIIRrubber(25.78 μm)is rougherthan that of oxygen plasma treated rubber (12.88 μm).And these results imply that change in morphology due to

Figure 22 shows 3D laser scanning microscope photographs of argon plasma treated to CIIR rubber. In the absence of argon plasma treatment at 1 min, the subsurface of the CIIR rubber looks less granular and generally has a smoother shape. However, with 5 min argon plasma treatment at 200W, changes in the surface were visible. Nevertheless,the surface of CIIRrubber pattern was changed compared to the untreated CIIRrubber. The subsurface ofthe CIIRrubber was growing rougher with increasing treatment time (Figure 4c). In this study, the 200 W, 15 treatment conditions resulted in the roughest surface. As a result, this surface roughness

(maximum peak height roughness), Rq (Root mean square roughness) are defined by JIS B 0601 2001.

entire surface roughness factors increased with increasing treatment time.

surface roughness reduced the real contact area against the SUS440C ball.

plasma treatment is an important factor that reduces the adhesion force.

**Figure 19.** Adhesion force between CIIR sheet and stainless-steel ball after oxygen and argon plasma treatments at a microwave power of 200 W and a gas pressure of 30 Pa, for 0, 1, 5, 10, and 15 minutes.

**Figure 20.** Effect of plasma treatment time on the elastic modulus of CIIR rubber 50 μm in thickness which was cut from the top surface of treated CIIR sheet. The elastic modulus was measured by nano-indenter for oxygen (black) and argon (red) plasma treated CIIR sheets.

Figure 20 shows the Young's modulus profile of 50 μm thickness CIIR rubber measured by nano‐indenter after oxygen and argon plasma treatment with increasing time. The results treatment time (206.1 MPa), and followed by a steady state. A higher Young's modulus (236.4 MPa) was obtained with argon plasma treatment, but only after 15 min treatment with argon gas. As a result, this improved Young's modulus by the oxygen and argon are depicted with squares (oxygen plasma treatment) and circles (argon). For the oxygen plasma treatment, Young's modulus was slightly higher (39.8 MPa) than the untreated CIIR rubber (38.0 MPa). However, it increased significantly between 5 min (53.8 MPa) and 10 min surface wave‐excited plasma treatment is an important factor that reduces the adhesion force.

different from that obtained from the 50 μm thickness. In particular, the unloading curve coincided with the loading curve at a penetration depth of more than 290 nm due to the thickness difference. This indicates that not only the bulk property has greatly affected the Young's modulus, but also it is affected its accurate measurement. In other words, a surface wave‐excited plasma treatment increased the Young's modulus in μm thickness scale. As a result, we determined that it is possible to develop a clear difference between 3 mm and 50 μm Young's modulus of the CIIR rubber without any influence from the bulk property by

Micro-Nano Mechatronics — New Trends in Material, Measurement, Control, Manufacturing and Their Applications in

**Figure 19.** Adhesion force between CIIR sheet and stainless-steel ball after oxygen and argon plasma treatments at a

**Figure 20.** Effect of plasma treatment time on the elastic modulus of CIIR rubber 50 μm in thickness which was cut from the top surface of treated CIIR sheet. The elastic modulus was measured by nano-indenter for oxygen (black) and

microwave power of 200 W and a gas pressure of 30 Pa, for 0, 1, 5, 10, and 15 minutes.

using the microwave slicer.

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argon (red) plasma treated CIIR sheets.

**Figure 21.** Surface roughness changes of CIIR sheet as a function of plasma treatment time. The measurements were done for oxygen (dotted line) and argon (solid line) plasma-treated CIIR sheets. The surface roughness parameters, Rz (maximum peak height roughness), Rq (Root mean square roughness) are defined by JIS B 0601 2001.

Figure 21 shows surface roughness as a function of plasma treatment time. The surface roughness deviations of CIIR rubber by oxygen and argon plasma treatment has changed. The entire surface roughness factors increased with increasing treatment time.

Especially,theRz of argon plasma treated CIIRrubber(25.78 μm)is rougherthan that of oxygen plasma treated rubber (12.88 μm).And these results imply that change in morphology due to surface roughness reduced the real contact area against the SUS440C ball.

Figure 22 shows 3D laser scanning microscope photographs of argon plasma treated to CIIR rubber. In the absence of argon plasma treatment at 1 min, the subsurface of the CIIR rubber looks less granular and generally has a smoother shape. However, with 5 min argon plasma treatment at 200W, changes in the surface were visible. Nevertheless,the surface of CIIRrubber pattern was changed compared to the untreated CIIRrubber. The subsurface ofthe CIIRrubber was growing rougher with increasing treatment time (Figure 4c). In this study, the 200 W, 15 treatment conditions resulted in the roughest surface. As a result, this surface roughness

change by etching effect might have affected the adhesion force, which is largely dependent on the contact geometry and surface topography [16].

**Author details**

**References**

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JSME C 2010;76(767) 1833‐1837.

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Noritsugu Umehara, Takayuki Tokoroyama and Hiroyuki Kousaka

Department of Mechanical Science and Engineering, Nagoya University, Japan

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Tribology for Biological and Medical Applications 239

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**Figure 22.** laser scanning microscope images of CIIR sheets after argon plasma treatment with 200 W at a gas pres‐ sure of 30 Pa for treatment times of (a) 1, (b) 5, (c) 10, and (d)15 min.

In this work, we tried to clarify the change in surface mechanical properties of CIIR sheet after the plasma treatments. In order to evaluate the change in Youngʹs modulus of CIIR sheet surface, the top 50 μm thickness of a plasma‐treated CIIR sheet was cut away to avoid the bulk property. The Youngʹs modulus measurements with nano‐indenter showed the clear differ‐ ence between the surface and bulk elastic modulus of CIIR rubber after plasma treatment, indicating the success of surface modification without changing bulk property. In addition, it was shown that the plasma treatment with Ar gas increased theYoung's modulus of CIIRsheet surface from 38 MPa to 236.4 MPa. And also, surface roughness of CIIR rubber has changed to rougher with both oxygen and argon gas plasma treatments. These changes in Young's modulus and roughness at the surface of CIIR sheet are considered to be the main reasons for the plasma‐assisted reduction of adhesion force between stainless‐steel ball (SUS 440C, JIS) and CIIR sheet.
