Chemistry Reference
In-Depth Information
O
O
.
O
2
+
~ CH
2
C
CH
2
~
C
CH
2
~
~ CH
2
CH
3
CH
3
FIGURE 8.29
Peroxy radical formation on the PP surface in a reaction of the alkyl radical
with O
2
.
O
.
~CH
2
C
CH
3
CH
2
~
+
O
2
(g)
O
3
+
~CH
2
C
CH
3
CH
2
~
FIGURE 8.30
Alkoxy radical formation by ozone.
H
H
OH
.
OH
(g)
+
~CH
2
C
C
O
~CH
2
C
C
O
CH
3
CH
3
FIGURE 8.31
Termination reaction.
Reaction with ozone results in alkoxy radical formation (see Figure 8.30).
A termination reaction is, e.g., shown in Figure 8.31.
These reactions illustrate some possibilities of radical processes initiated by
plasma interaction with a polypropylene surface.
An important application of polyimide caused by its outstanding properties as
high tensile strength (70-150 MPa), high upper working temperature (250
◦
C-320
◦
C),
and dielectric strength (
22 kV/mm) is the use as material for flexible chip carriers.
For this purpose, a metallization with copper is necessary but is difficult because of
the low adhesion between copper and polyimide. A treatment of polyimide by an
atmospheric pressure DBD in N-containing gas enhances the free surface energy and
leads to successful metallization. Amino-, nitrile, and imine-groups were detected
on the surface [150]. Oxygen-containing polar groups were observed at a polyimide
surface after air plasma treatment [160,161].
The treatment of a, e.g., low-density polyethylene (LD-PE) foil in atmospheric
pressure air DBD leads to an increase of oxygen content on the surface up to 40%.
Water contact angle decreases from untreated material of 102.2
◦
down to 54.3
◦
after plasma treatment. Similar behavior was observed for other polymers (ultrahigh
density polyethylene, high-density polyethylene, polysterene, polymethylpentene)
also. Essentially smaller effects show polytetrafluorethylene [162].
>
8.2.3.1.5 Surface Treatment by Low-Pressure Plasmas
The application of low-pressure plasmas for surface treatment includes the action of
energetic ions, reactive neutrals, and plasma radiation. Treatment of polyamide in
an inductive coupled RF oxygen plasma during 15 min change the surface energy
of 40 up to 67 mJ/m
2
. Storage in air for week nearly destroys this high value by
aging. The application of additional high-voltage pulses (10 kV, duty cycle 0.5%;
