1. What's Ultraviolet Rays (UV Rays)?
UV Rays are invisible to the naked eye even they are similar to Visible Ray in all physical aspects because their wavelength is 100~400nm which is shorter than that of Visible Ray. In case sunlight contains lots of UV Rays, it makes human's skin burnt or does sterilizing action, and it may cause a skin cancer if human skin is exposed to the sunlight excessively.
As UV Rays have strong chemical action, especially bleaching action, the colors of pigments and dyes are faded by sunlight.
 
2. What's Photo-Oxidation preventing Agent (POPA)?
Light Energy in the wavelength range (290~400nm) of UV Rays is 71~100Kcal/mol which is enough to dissociate the comnination among the elements consisting resin. This deterioration by UV Rays is an oxidation reaction occurred under the presence of Oxygen and is identical to the deterioration reaction except Free Radicals are generated by UV Photon at the beginning stage. ('Free Redical' is a kind of chemicals capable of existing independently with one or more noncovalent electrons).
By cutting the peneteration of UV Rays in sunlight, POPA does the role of prolonging the functions and the lifespan of plastic products by retarding the occurance of the oxidation in plastic products for a certain period of time due to the chemical action and/or the bleaching action.
The methods and the kinds of POPA used to prevent deterioration due to UV Rays are as below;
a) UV Absorber : absorbs UV Rays and converts them into Heat Energy
b) Quencher : absorbs Chromophore Energy and releases in Heat Energy
c) Hals : terminates Radical
d) Carbon Black : cuts UV Rays
2. 1. UV Absorber
UV Absorber converts the absorbed energy into Heat Energy which is released and no harmful to Polymer. Most of UV Absorbers are the compounds of Benzophenon, Benzotrizol and/or Salicylate, and the common feature of these molecular structure releases the Light Energy into Heat Energy stably by forming the Hydrogen Bond mutually because they have Phenol OH and atom of high electronegativity such as O, N in the vicinity.
2. 2. Quencher
If Polymer is exposed to UV Rays, it absorbs UV Rays Energy and then become an excitation state because Double Bond, Catalyst Residue(Metal), Keton and/or Peroxides in Polymer act as a Chromophore.
2. 3. Radical Terminating Agent (RTA) : Hals
RTA prevents the oxidation reaction by eliminating Free Radicals generated during Light Oxidation Reaction even it does not have the UV Rays Absorption action.
2. 4. UV Rays Cutting Agent : Carbon Black
Well dispersed Carbon Black does the role of Peroxides decomposition and RTA by cutting all lights actually. As carbon Black is stable chemically and no migration, it is the strongest Light Oxidation Reaction Preventing Agent. This is generally used in Polymers as masterbatches, which do not require transparency or white color.
3. Light Stability Test Result on Light Oxidation Prevention Agent
▶ This Test has been performed on 170um film for the purpose of Quality Control at Samjin Polytech.
3. 1. Test Sample Specification
|
Article |
Sample #1 |
Sample #2 |
Sample #3 |
Sample #4 |
Sample #5 |
Remark |
|
Sample Color |
Natural |
White |
Silver |
Silver |
Silver |
Film |
|
Kind of UV Agents |
None |
None |
None |
Hals |
Benzotriazol |
|
| Content of UV Agent |
- |
- |
- |
3000ppm |
3000ppm |
|
3. 2. Test Equipments
- Equipment Name : Ultra-Violet / Condensation Weathering Device
- Manufacturer : ATLAS Electronic Device Company
- UV Lamp : Phillips Cp. 40W * 8ea
3. 3. Test Conditions
<Test Temperature>
- Violet Cycle : 60℃
- Condensate Cycle : 50℃
<Cycle Program Conditions>
- Violet Cycle (4 Hours) ⇔ Condensate Cycle (4 Hours)
3. 4. Light Stability Test Result depending on UV Agents
|
Article |
Remaining Elongation (%) |
|
Sample #1 |
Sample #2 |
Sample #3 |
Sample #4 |
Sample #5 |
Remark |
| Elapsed Time (Hour) |
Natural |
White |
Silver |
Hals계 |
Benzotriazol |
|
0 |
100 |
100 |
100 |
100 |
100 |
|
|
56 |
94 |
82 |
60 |
99 |
86 |
|
|
80 |
75 |
47 |
30 |
98 |
79 |
|
|
92 |
8.6 |
3.9 |
1.9 |
99 |
57 |
|
|
104 |
6.5 |
2.5 |
0.5 |
83 |
54 |
|
|
116 |
2.3 |
1.5 |
0.5 |
82 |
11 |
|
|
140 |
0 |
0 |
0 |
83 |
3 |
|
|
164 |
- |
- |
- |
88 |
0.5 |
|
? Elapsed Time (Hour) : Detention Time of Specimen in UV Irradation Equipment
? Remaining Elongation (%) : (Elongation after UV Irradation / Elongation before UV Irradation) x 100
※ Light Stability Test Result depending on UV Agents
#5) : Benzotriazol
3. 5. Conclusion
- The decrease in UV stability according to the increase of additive content is identical to the result of the first test.
- As a result of Light Stability Evaluation on UV stabilizers, Masterbatch made of HALS UV Stabilizer (#4 HALS) shows the best function.
- Therefore, UV Stability shall be secured for minimum one year if film is produced based on HALS UV Stabilizer.
w/o UV Stabilizer vs. with UV Stabilizer
▶ The above test result has been obtained through the test performed at Daeduk Technology Research Center of SK Corporation on on the specimen presented by Samjin Polytech (Nov. 26, 1998).
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