2 - 2. Cleaning

When polymer is scarce in quantity and distributed in the form of thin film, oxidizing reactions of UV/Ozone proceed to inside and polymers ultimately decompose to molecules of CO2, H2O, O2, N2 and so on.
They are evaporated and scattered, disappearing from the surface.
This reaction causes the cleaning effects.
Therefore, the UV/Ozone method can get rid of the organic compound, namely oily pollution, but is not effective to inorganic dust or the like.
This cleaning effect is characteristic in its extremely high cleanliness far above the wet cleaning methods as shown in Table 3.

Table 3.Comparison of the cleaning powers among the various cleaning methods

Cleaning conditions Contact angle (degree)
Non-treated glass plate 26
Synthetic detergent(US) Water(US) Hydrocarbon solvent(US)(Vap) 39
Synthetic detergent(US) Water(US) Pure water(US) Dry(70ºC) 17
Synthetic detergent(US) Water(US) IPA(Vap) 13
Ozone solution <10
Synthetic detergent(US) Water(US) Plasma 5
Synthetic detergent(US) Water(US) UV/O3 4

Note 1, Plasma: 200W, 1torr, 5sec, 13.56MHz
Note 2, UV/O3:Low pressure mercury lamp , Atmosphere, 60sec
Note 3, (US): Ultra sonic (Vap): Steam washing(70°C): Air dry

It is as capable as the plasma method.
By just that much it is weak against any massive pollution. In order to make the best of the cleaning effect of the UV/Ozone method, it is essential for you to remove large amount of stains first beforehand by some other cleaning method.
Hydrocarbon solvents have a strong cleaning power, but Table 3 shows a large contact angle on the contrary.
This means that the solvents remain on the surface.
In precision cleaning it is important to rinse with pure water at the last stage of cleaning.
The UV/Ozone process is free from any such residual problems.

2 - 3. Light Source

In order to break optically the molecular bonds of organic compounds, it is an essential precondition that light is absorbed by the compounds and its energy is larger than the molecular bond energy.

table4.bond energy of molecules(unit :kj/mol)

Bondage Molecule(AB) Molecule(A;B) Bond energy
H-H H2 2H 432.07
H-C C6H6
CH4
CH3
CH		 H, CHO
H, CH3
H, CH2
H, C		 464
431.8
457
334.7
O-C CO2
CH3OH		 CO, O
CH3, OH		 526.1
378.1
N-N N2
N2O4		 2N
2NO2		 941.6
53
O-O O2
O2+
O3
H2O2		 2O
O, O+
O, O2
2OH		 493.6
642.8
102
206.8
C-F CH3F
C6H5F		 CH3, F
C6H5, F		 472
524
Cl-Cl Cl2 2Cl 239.2
H-O H2O
H2O
OH		 2H, O
H, OH
O, H		 [458.9]
493.4
424.4

Table 4 shows the bond energy of plastics, while Table 5 shows the spectroscopic energy of low-pressure mercury lamp, xe-excimer lamp and high-pressure mercury lamp.

Table 5.Wavelength of lamps and its energy

Low pressure
mercury lamp		 Xe excimer lamp High pressure
mercury lamp
Wavelength (nm) 185 254 172 365
Energy (kJ/mol) 647 472 696 328
(eV) 6.7 4.9 7.2 3.4

Table 6 shows the relation among the UV wavelength range, wavelength and energy.
With regard to the electromagnetic wave of light and so on, the shorter wavelength, the higher energy.

Table 6.Wavelength range and division of UV

Xray UV(Ultraviolet dadiation) Visiblelight Infra-
redradiation
UV-C B UV-A
ƒÉ(nm)                 100                             280 315           400                                                                   780
energy  
(kJ/mol)                1196                            427 380            299                                                                  153
(eV)                12.4                             2.9 3.3             3.1                                                                    1.6

The energy of low-pressure mercury lamp (185nm and 254nm) and xenon excimer lamp (172nm) is as high as or higher than the bond energy of organic compounds shown in Table 4.
This is the first reason that these lamps are suitable for surface modification.
The second reason is that they are well structured to facilitate formation of a surface light source.
As for the typical wavelength of high-pressure mercury lamp (365nm), its energy is as low as 328kJ/mol, not suitable for surface treatment. Infra-red radiation cannot be used for surface modification either.

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