Apparatus for performing weather resistance test

An apparatus for performing a weather resistance test on a composite material having a metallic, inorganic, or organic base member, and an organic material covering the base member. The apparatus includes a sample holding device disposed in a sample chamber for holding a sample of the composite material. An artificial light source irradiates light substantially in the ultraviolet light area to one surface of the sample. A dipping mechanism dips the sample in a corrosive ionized water, and dew condensation is formed through a temperature control device disposed in the sample holding device, working with a moisture source, for causing dew condensation in the surface of the sample. A cleaning device is provided for cleaning the surface of the sample, and steaming of the sample is performed through the use of a heating element disposed in the sample chamber, and the moistening means, for steaming the sample in an atmosphere of high temperature and high humidity. A control system controls the execution of the operation of the light source, the dipping mechanism, the dew condensation devices, the cleaning device, and the steaming devices, in a sequential manner.

BACKGROUND OF THE INVENTION 
The present invention relates to a method of and an apparatus for 
performing a weather resistance test. More particularly, the invention is 
concerned with a method of and apparatus for performing a weather 
resistance test capable of producing, in a short time, test results having 
close correlation to actual degradation which is caused on a composite 
material having a base member of a metal, an inorganic material or an 
organic material and a coating layer of an organic material, e.g., a 
plastic when such a composite material is left in natural environment 
including corrosive substances. 
In general, weather resistance of plastics and materials coated with 
plastics is tested by a weather resistance testing apparatus as specified 
by JIS (Japanese Industrial Standards) B 7751-7754. Usually, this testing 
apparatus employs a light source such as a carbon arc lamp or a xenon lamp 
for generating light rays which are applied to the test samples to promote 
the degradation thereby enabling the test to be finished in a short time. 
In general, structures in seashore areas are exposed to air which is rich 
in salt, while offshore structures are held in corrosive condition due to 
contact with sea water. Thus, structures on seashores and offshore 
structures are exposed to much severe condition as compared with 
structures in environment which do not contain salty air. Furthermore, in 
industrial areas where there are many factories, structures are under 
severe conditions as they are often subjected to acidic rain. The ordinary 
weather test apparatus mentioned above, therefore, cannot perform promoted 
test results with good correlation to actual degradation, when the 
material to be tested is a composite material composed of a metallic 
substrate and a coating plastic, as in the cases of materials used in 
structures on seashore areas, offshore structures, ships and fishery 
equipments, as well as structures in industrial areas. 
A composite weather resistance testing apparatus has been known in which a 
brine spray process is combined with functions of ordinary weather meter 
such as light irradiation and dew condensation to enable evaluation of 
resistance to salty environment. A marine exposure promotion testing 
apparatus is also known in which, as disclosed in Japanese Utility Model 
Laid-Open No. 55-105153, the tested material is subjected to light 
irradiation, brine spray and strain. 
The known composite testing apparatus and marine exposure promotion testing 
apparatus, however, can provide only a small ultraviolet irradiation 
intensity, e.g., 6 mW/cm.sup.2, due to the use of a carbon arc amp or a 
xenon lamp as the light source. In addition, the speed of degradation of 
the tested material is too low and the test results do not show close 
correlation to actual degradation, due to the fact that the test operation 
includes only the testing processes such as light irradiation, brine 
spray, dew condensation and generation of strain. 
SUMMARY OF THE INVENTION 
In order to overcome the above-described problems encountered with known 
weather resistance testing method and apparatus incorporating brine 
condition, the present invention is aimed at providing a method of and an 
apparatus for performing a weather resistance test which can provide, in a 
short time, test results of good correlation to the actual natural 
degradation under corrosive environment rich in salt or acidic rain. 
To this end, according to one aspect of the present invention, there is 
provided a method of performing a weather resistance test on a composite 
material having a base member made of a metallic, inorganic or an organic 
material and a covering material of an organic material covering the base 
member, the method having the steps of preparing a sample of the composite 
material, irradiating step for irradiating the sample with light rays 
including ultraviolet rays from an artificial light source, dipping step 
for dipping the sample in a corrosive ionized water, and dew condensation 
step for causing dew condensation on the surface of the sample, the method 
being characterized by comprising: a cleaning step for cleaning the 
surface of the sample; and a steaming step for subjecting the sample to an 
atmosphere having high temperature and high humidity. 
The cleaning step removes, from the surface of the test piece, matters 
which have been formed in the step of irradiation with lights including 
ultraviolet rays, so as to facilitate execution of a subsequent step, 
e.g., to facilitate permeation of ionized water such as brine in the 
dipping step executed subsequently to the light irradiation step, thereby 
promoting the degradation. The steaming step for exposing the test piece 
to an atmosphere of high temperature and high humidity simulates a hot and 
humid weather condition, thus contributing to prompt development of 
results with close correlation to actual degradation. 
According to another aspect of the present invention, there is provided an 
apparatus for performing a weather resistance test on a composite material 
having a metallic, inorganic or an organic base member and an organic 
material covering the base member, comprising: sample holding means for 
holding a sample of the composite material; irradiating means including an 
artificial light source for irradiating one surface of the sample with 
light rays containing ultraviolet rays; dipping means for dipping the 
sample in a corrosive ionized water; dew condensation means including 
moistening means for causing dew condensation in the surface of the 
sample; cleaning means for cleaning the surface of the sample; steaming 
means including heating means and humidifying means for steaming the 
sample in an atmosphere of high temperature and high humidity; and control 
means for controlling execution of operations of the irradiating means, 
dipping means, dew condensation means, cleaning means and steaming means 
in a sequential manner. 
The use of the cleaning means for cleaning the test piece surface and the 
steaming means for exposing the test piece to an atmosphere of high 
temperature and high humidity makes it possible to provide a weather 
resistance testing apparatus which is capable of promptly developing test 
results with high degree of correlation to the actual degradation. 
These and other objects, features and advantages of the present invention 
will become clear from the following description of the preferred 
embodiments when the same is read in conjunction with the accompanying 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the present invention will be described 
hereinunder. 
Referring to FIG. 1 which is a schematic diagrammatic illustration of an 
embodiment of the weather resistance testing apparatus in accordance with 
the present invention, the apparatus has a light source 1 which includes a 
metal halide lamp capable of radiating considerably great energy in a 
predetermined wavelength region, e.g., 250 to 550 nm, a filter for 
substantially restricting the wavelength region to 300 to 450 nm, and a 
water-cooling jacket. The light source 1 is disposed in a reflector which 
is composed of a dome-shaped collimating main reflector plate 2 and 
collimating auxiliary reflector plates 3. Numeral 4 denotes a shield plate 
made of quartz and capable of transmitting ultraviolet rays while 
hermetically isolating the light source from a sample chamber 5 disposed 
beneath the light source unit. 
The sample chamber 5 is inclined at, for example, 15.degree. due to a 
specific arrangement of a later-mentioned sample holder. The light source 
unit, which is mounted on the sample chamber 5. is inclined 
correspondingly. The sample holder 7 in the form of a tray and capable of 
holding a sample 6 thereon is disposed in the sample chamber 5 for a 
pivotal movement about an axis near one end thereof. More specifically, 
the sample holder 7 is adapted to be moved by an actuator 8 so as to pivot 
between an inclined position where it is held at about 15.degree. 
inclination with respect to horizontal plane to enable a later-mentioned 
cleaning agent from a later-mentioned spray nozzle to smoothly flow down 
without stagnation and a horizontal position where it enables the test 
sample 6 held thereon to be dipped in an ionized water. Temperature 
control means 7a such as water-cooling means or electronic cooling means 
are associated with the sample holder 7. 
An air inlet port 5a and an air outlet port 5b are provided in one of the 
side walls of the sample chamber 5 so as to project therefrom,and dampers 
9,9 for selectively opening and closing these ports are provided in these 
ports 5a and 5b. A dampening water reservoir 5c is provided at a bottom 
corner of the sample chamber 5. A moistening heater 10 is provided so as 
to surround the water reservoir 5c and a heater 11 for heating the 
interior of the sample chamber 5 is provided on the bottom of the sample 
chamber 5. The aforementioned spray nozzle 12 for spraying a cleaning 
agent towards the sample holder 7 is disposed in the sample chamber 5 at a 
position above the sample holder 7 in the inclined state. A nozzle 13 for 
supplying ionized water is disposed at a position which is on an obliquely 
upper side of the sample holder 7 held in horizontal posture. The cleaning 
agent may be a water, a surface active agent, a water containing air, 
alcohol or the like. The ionized water may be an aqueous solution of NaCl, 
MgCl.sub.2, H.sub.2 SO.sub.4 and NaOH, a mixture of such aqueous solutions 
and natural sea water. 
A temperature controlling blower 14 is capable of supplying air into the 
sample chamber 5 through the air inlet port 5a so as to maintain a 
predetermined temperature of the sample 6 on the sample holder 7. The 
cleaning agent spray nozzle 12 is connected through a pipe having a 
solenoid valve 15 to a cleaning agent supply port 16, while the ionized 
water nozzle 13 is connected to the ionized water tank 18 via an ionized 
water pump 17. The ionized water tank 18 is provided with a heater 19 for 
maintaining the temperature of the ionized water at a predetermined level. 
The water reservoir 5c provided at the bottom corner of the sample chamber 
5 is connected to a draining port through a draining solenoid valve 20. 
The light source 1, temperature control blower 14, automatic damper 9, 
cleaning agent solenoid valve 15, ionized water pump 17, draining solenoid 
valve 20 and heaters 10, 11 and 19 are controlled by a controller 21. 
A description will be given of an example of the weather resistance testing 
method of the invention which is carried out by using the weather 
resistance testing apparatus having the described construction. The sample 
6 held on the sample holder 7 is subjected to ultraviolet irradiation of 
an intensity of 50 to 80 mW/cm.sup.2 caused by the activation of the light 
source 1 for a predetermined period, e.g., 6 to 18 hours, while being held 
in an atmosphere of a relative humidity of 20 to 80%, e.g., 30%, and while 
being maintained at a constant temperature, e.g., 40.degree. 
C..+-.1.0.degree. C. to 100.degree. C..+-.1.0.degree. C., by the air which 
blown by the blower 14. Then, the light source 1 is turned off to 
terminate the ultraviolet irradiation and the solenoid valve 15 is 
operated to supply an ion-exchange water of 20.degree. to 80.degree. C., 
e.g., 60.degree. C. so that the ion exchange water is sprayed from the 
spray nozzle 12 for 30 seconds, thereby removing matters depositing on the 
surface of the sample. This cleaning step facilitates permeation of an 
ionized water such as brine into the sample in the subsequent step. 
Then, the actuator 8 is operated to set the sample holder 7 horizontally 
and the ionized water pump 17 starts to operate so that an ionized water 
in the ionized water tank 18, e.g., a 5% NaCl aqueous solution (pH 6.5 to 
7.5) of 40.degree. C., is supplied to the tray-type sample holder 7 from 
the spray nozzle 13, whereby the sample 6 is dipped in the ionized water 
for 10 seconds. Subsequently, the actuator 8 operates again to incline the 
sample holder 7 so as to allow the ionized water to flow down from the 
sample holder 7 and then the draining solenoid valve 20 operates to 
discharge the water. Then, the blower 14 operates again to supply dried 
air so as to dry the sample at a drying rate of 1.degree. to 5.degree. 
C./min for 30 minutes. The humidifying heater 10 is then controlled to 
maintain a relative humidity of 95% within the sample chamber. Meanwhile, 
ion exchange water for cleaning purpose is supplied to the portion around 
the humidifying heater in the sample chamber. In addition, temperature 
control means 7a operates in accordance with a signal from a temperature 
sensor 22 on the sample holder 7, so as to lower the temperature of the 
sample holder 7 down to a predetermined temperature below the dew point, 
e.g., down below about 30.degree. C., so that dew condensation takes place 
on the surface of the sample 6 held by the sample holder 7, whereby a heat 
shock is applied to the sample 6. 
The sample 6 is held under this dewing condition for a predetermined time, 
e.g., 1 hour, and, thereafter, the sample holder 7 is set to a horizontal 
position. The ionized water pump 17 is then operated to supply ionized 
water again from the ionized water nozzle 13 so as to dip the sample 6 in 
the ion water for 10 seconds. The sample holder 7 is then inclined again. 
The application of heat shock and the subsequent dipping in the ion water 
greatly promote the corrosion. 
Then, after the sample 6 is dried, the humidifying heater 10 and the sample 
chamber heater 11 are controlled to create a highly humid and hot 
condition, e.g., 95% relative humidity and 50.degree. C., in the sample 
chamber 5, and the sample 6 is exposed to this humid and hot atmosphere 
for 12 hours. The sample 6 is heated and moistened as a result of 
execution of this steaming step. The ultraviolet irradiation is then 
conducted again following the execution of the steaming step. In this 
step, ultraviolet rays of high intensity is applied to the surface of the 
sample which is in a steamed state, so that a very severe condition is 
realized to further promote the degradation. These steps are then executed 
repeatedly and cyclically. 
The described method of executing weather resistance test imparts to the 
samples conditions which closely approximate natural conditions in the 
seashore areas or offshore areas and can provide, in a short time, weather 
resistance test results with close correlation to the natural degradation, 
by virtue of addition of the cleaning and steaming steps. 
In the described embodiment, the steaming step for exposing the sample to 
an atmosphere of high temperature and high humidity is executed between 
the ionized-water dipping step and ultraviolet irradiation step. This, 
however, is not exclusive and similar effects are obtainable also when the 
steaming step is executed, for example, after the cleaning step or before 
or after the forcible dew condensation step. 
In the described embodiment, only one spray nozzle for spraying the 
cleaning agent is provided above the sample. The number and positions of 
the spray nozzle or nozzles, however, may be freely determined in 
accordance with factors such as the shape and size of the sample holder. 
The ionized water dipping step in the described method is executed by 
dipping the sample in the ionized water filling the tray-type sample 
holder. This, however, is only illustrative and the dipping may be 
effected by spraying the ionized water onto the sample held on the sample 
holder in the inclined state as in the case of cleaning, or by immersing 
for a predetermined time the sample holder together with the sample in a 
bath of the ionized water contained in a separate ionized water tank and 
then lifting the sample holder. By using an acidic solution such as of 
H.sub.2 SO.sub.4 as the ionized water, it is possible to evaluate the 
resistance to acidic rain. 
Tests were conducted in accordance with the weather resistance testing 
method of the invention and also by conventional weather resistance 
testing methods and actual exposure, in order to confirm the effects 
brought about by the invention, the results being shown below. 
(1) Conditions of Testing Method According to Invention 
Light source: metal halide lamp 4 KW 
Irradiation light wavelength: 300 to 450 nm 
Black panel temperature (when irradiated with ultraviolet rays): 63.degree. 
C..+-.3.degree. C. 
Ultraviolet rays intensity on sample surface: 80.+-.5 mW/cm.sup.2 
Ultraviolet irradiation time: 6 hours 
Cleaning period: 30 seconds (after completion of ultraviolet ray 
irradiation) 
Cleaning agent: Ion exchange water 
Cleaning agent temperature: 60.degree. C. 
Rate of spray of cleaning agent: 9 cc per 1 cm.sup.2 of sample surface 
Pressure of spray of cleaning agent: 1.5 kg/cm.sup.2 
Ionized water: 5% Nacl solution 
Ionized-water dipping period: 10 seconds 
Ionized water temperature: 40.degree. C. 
Drying period: 30 minutes 
Drying rate: 1.degree. to 5.degree. C./min 
Sample chamber air humidity at dewing: 95% RH 
Sample temperature at dewing: 30.degree. C. 
Dewing period: 6 hours 
Sample chamber air temperature at steaming: 50.degree. C. 
Sample chamber air humidity at steaming: 95% RH 
Steaming period: 11.5 hours 
(2) Conditions of Actual Exposure Test 
Period: 3 years (as from Mar. 26, 1985) 
Place: A facility for general research of marine technology, Ministry of 
Construction (Suruga Bay, Japan) 
(3) Conditions of Conventional Testing Method 1 (With Sunshine weather 
meter) 
Light source: Sunshine carbon arc lamp 
Irradiation light wavelength: 280 to 1400 nm 
Black panel temperature: 63.degree. C..+-.3.degree. C. 
Ultraviolet rays intensity on sample surface: 5 mW/cm.sup.2 
Water spray: 18 minutes within 2 hours 
(4) Conditions of Conventional Testing Method 2 (brine spray test according 
to JIS-Z 2371) 
Nacl solution: 5.+-.1% 
Test room temperature: 35.degree..+-.1.degree. C. 
Brine tank temperature: 35.degree..+-.1.degree. C. 
Continuous spray 
The following six types of coated plates (a) to (f) were used as the test 
samples: 
(a) Vinyl chloride laminate galvanized steel sheet (laminate layer 
thickness: 200 .mu.m) 
(b) Galvanized steel sheet coated with vinyl chloride sol (coating layer 
thickness: 300 .mu.m) 
(c) 55% Al--Zn-plated steel sheet coated with vinyl chloride sol (coating 
layer thickness: 200 .mu.m) 
(d) Galvanized steel sheet coated with fluororesin (coating layer 
thickness: 30 .mu.m) 
(e) Fluororesin laminate galvanized steel sheet (laminate layer thickness: 
38 .mu.m) 
(f) Galvanized steel sheet coated with polyester (coating layer thickness: 
18 .mu.m) 
These samples were tested by the testing methods shown above, and the color 
difference .DELTA.E* in terms of a CIE1976L*, a*, b* space colorimetric 
system and gloss retention rate were measured on these tested samples, the 
results being shown in FIGS. 2 to 13. The color difference .DELTA.E* is 
the measured value of a change in hue of one side of each sample, while 
the gloss retention rate was obtained in accordance with the following 
formula, on the basis of the change in the 60.degree. mirror surface 
reflectivity as measured by a gloss meter on each sample: 
EQU Gloss retention rate={(gloss after test)/(initial gloss)}.times.100 (%) 
The same tests were also executed on the same samples with scratches formed 
on these samples so as to reach the underlying metallic layers, for the 
purpose of evaluation of corrosion and change in the coating layers on 
these samples, the results being shown in Tables 1 and 2. In case of the 
actual exposure test, however, no scratch was formed and results of 
observation of cut sections are shown in these tables. 
The curves a.sub.1, a.sub.2, a.sub.3 and a.sub.4 shown in FIG. 2 represent 
the changes in the color difference .DELTA.E* on the vinyl chloride 
laminate galvanized steel sheet tested by the actual exposure, testing 
method of the invention and conventional testing methods 1 and 2, 
respectively. In case of the actual exposure test, the .DELTA.E* value 
showed a rapid rise up to 5 or higher in 18 months after the commencement 
of the test, and is then substantially saturated as will be seen from the 
curve a.sub.1. The weather resistance testing method of the present 
invention showed a tendency substantially the same as that in the actual 
exposure test as shown by the curve a.sub.2. It was confirmed that the 
.DELTA.E* value equivalent to that obtained in 18 months in the actual 
exposure can be attained in quite a short time of 300 hours when the 
testing method of the invention is used. 
On the other hand, in the case of the conventional testing method 2, no 
substantial change was observed in the .DELTA.E* value. In the 
conventional testing method 1 also, the change in the .DELTA.E* value 
obtained in 1500 hours after the commencement of the test was as small as 
that obtained in 200 hours in the testing method of the invention. 
The curves b.sub.1, b.sub.2, b.sub.3 and b.sub.4 shown in FIG. 3 and the 
curves c.sub.1, c.sub.2, c.sub.3 and c.sub.4 shown in FIG. 4 represent the 
changes in the color difference .DELTA.E* on the samples of the galvanized 
steel sheet coated with vinyl chloride sol and Al--Zn-plated steel sheet 
coated with vinyl chloride sol, respectively, tested by the actual 
exposure, testing method of the invention and conventional testing methods 
1 and 2, respectively. In case of the actual exposure test, the .DELTA.E* 
value showed a rapid rise in 12 months after the commencement of the test, 
and is then substantially saturated in both types of samples, as will be 
seen from the curves b.sub.1 and c.sub.1. The weather resistance testing 
method of the present invention showed a tendencies substantially the same 
as that in the actual exposure test as shown by the curves b.sub.2 and 
c.sub.2. Namely, the .DELTA.E* value rapidly increased in 300 hours after 
the commencement of the test and then saturated. Furthermore, the 
.DELTA.E* values attained in 200 hours of the test by the testing method 
of the invention well coincided with those obtained in 12 months in the 
actual exposure test, thus proving specifically high degree of closeness 
of correlation therebetween. It will also be understood that the 
conventional testing methods 1 and 2 could not provide changes in the 
.DELTA.E* values equivalent to those of the actual exposure test and the 
testing method of the invention, despite prolonged testing periods. 
The curves d.sub.1, d.sub.2, d.sub.3 and d.sub.4 shown in FIG. 5, curves 
e.sub.1, e.sub.2, e.sub.3 and e.sub.4 shown in FIG. 6, and the curves 
f.sub.1, f.sub.2, f.sub.3 and f.sub.4 shown in FIG. 7 represent the 
changes in the color difference .DELTA.E* on the samples of the galvanized 
steel sheet coated with fluororesin, the fluororesin laminate galvanized 
steel sheet and galvanized steel sheet coated with polyester, 
respectively, as tested by the actual exposure, testing method of the 
invention and conventional testing methods 1 and 2, respectively. These 
samples showed smaller values of change in the color difference .DELTA.E* 
than the samples employed in the preceding tests. Nevertheless, the 
testing method of the invention provided results with close correlation to 
the results of the actual exposure test. 
In FIG. 8, the curves a.sub.1, a.sub.2, a.sub.3 and a.sub.4 show the 
results of measurement of changes in the gloss retention rate as obtained 
when samples of vinyl chloride laminate galvanized steel sheet were tested 
by the actual exposure, testing method of the invention, and the 
conventional testing methods 1 and 2. As will be seen from the curves 
a.sub.1 and a.sub.2, the samples tested by the actual exposure and the 
testing method of the invention showed substantially constant values of 
gloss retention rate, thus proving a high degree of closeness of 
correlation therebetween. On the other hand, the sample tested by the 
conventional testing method 1 showed a significant reduction in the gloss 
retention rate in relation to time, unlike the result of the actual 
exposure test, as will be seen from the curve a.sub.3. 
In FIG. 9, the curves b.sub.1, b.sub.2, b.sub.3 and b.sub.4 show the 
results of measurement of changes in the gloss retention rate as obtained 
when samples of galvanized steel sheet coated with vinyl chloride sol were 
tested by the actual exposure, testing method of the invention, and the 
conventional testing methods 1 and 2. The sample tested by the actual 
exposure showed a rapid decrease in the gloss retention rate in 12 months 
after the commencement of the test and, thereafter, a substantially 
constant value of the gloss retention rate, as will be seen from the curve 
b.sub.1. On the other hand, the sample tested by the testing method of the 
invention initially showed a gentle reduction in the gloss retention rate 
but the rate started to rapidly decrease about 200 hours after the start 
of the test and reached, in 400 hours after the start of the test, the 
value which is substantially the same as that reached in 24 months in the 
actual exposure test. In contrast, the test according to the conventional 
testing method 2 showed no significant change in the gloss retention rate, 
while the conventional method 1 caused an occasional rise in the gloss 
retention rate followed by a reduction. The change observed in the 
conventional method 1, however, much less significant than the result of 
the test according to the testing method of the present invention. 
FIGS. 10, 11 and 12 show the changes in the gloss retention rate as 
observed with samples of Al--Zn-plated steel sheet coated with vinyl 
chloride sol, galvanized steel sheet coated with fluororesin and the 
fluororesin laminate galvanized steel sheet, respectively, when these 
samples were tested by the actual exposure, testing method of the 
invention and the conventional testing methods 1 and 2, respectively. In 
the case of the actual exposure test, all the samples showed small values 
of changes in the gloss retention rate as shown by the curves c.sub.1, 
d.sub.1 and e.sub.1. The results of the test by the testing method of the 
invention also showed small changes in the gloss retention rate as shown 
by curves c.sub.2, d.sub.2 and e.sub.2, thus proving high degree of 
closeness of correlation to the actual exposure test. In contrast, the 
results of the test conducted in accordance with the conventional testing 
method 1 showed a large reduction in the gloss retention rate particularly 
in the case of the sample of the Al--Zn-plated steel sheet with vinyl 
chloride sol, as will be seen from the curve c.sub.3, thus exhibiting a 
significant difference from the results of the actual exposure test. 
FIG. 13 shows the changes in the gloss retention rates exhibited by the 
samples of the galvanized steel sheets coated with polyester as observed 
when these samples were tested by the actual exposure, the testing method 
of the invention and the conventional testing methods 1 and 2. As shown by 
the curve f.sub.1, the sample tested by the actual exposure showed a rapid 
reduction in the gloss retention rate in the period of 24 months after the 
commencement of the test and thereafter no significant change was 
observed. The sample tested by the testing method of the present invention 
showed a similar tendency: namely, a rapid reduction in the gloss 
retention rate was observed when 200 hours has elapsed after the start of 
the test, as shown by the curve f.sub.2. The conventional testing method 1 
also showed a drastic decrease in the gloss retention rate after elapse of 
200 hours from the start of the test, as shown by the curve f.sub.3. This, 
however, seems to be attributable to the presence of light rays of 
wavelengths of 300 nm or less in the lights from the light source. 
As stated before, each of the same samples (a) to (f) used in the tests 
described hereinbefore was tested by the same testing methods after 
forming scratches reaching the underlying metallic layer, and the state of 
corrosion in the scratched portion was observed to obtain the result as 
shown in Table 1. The sample used in the actual exposure test, however, 
had no scratch, and the state of corrosion was observed at a cut sectional 
surface of the sample and compared with the results of other testing 
methods on a assumption that the corrosion state at the cut cross-section 
is substantially the same as that shown by scratched portions of the 
samples. 
TABLE 1 
______________________________________ 
Method of Actual Conventional 
Conventional 
Samples 
Invention Exposure Method 1 Method 2 
______________________________________ 
a white rust 
white rust 
black rust 
heavy white 
red rust rust 
b white rust 
red rust slight white 
heavy white 
red rust rust rust 
c red rust white rust 
no rust slight black 
red rust rust 
d white rut white rust 
white rust 
slight white 
red rust rust 
e slight white 
white rust 
slight white 
slight white 
rust red rust rust rust 
f white rust 
white rust 
slight white 
white rust 
red rust red rust rust red rust 
______________________________________ 
The states of corrosion shown in Table 1 are those obtained 432 hours after 
the start of the test in case of the method of the invention, 30 months 
after the start of the test in case of the actual exposure test, 1500 
hours after the start of the test in case of the conventional method 1 and 
450 hours after the start of the test in case of the conventional method 
2, respectively. 
Table 2 shows the states of the coating layers around the scratched 
portions of the samples (cut surface in case of actual exposure test) as 
observed after expiration of the same testing periods as those explained 
in connection with the test results shown in Table 1. 
TABLE 2 
______________________________________ 
Method of Actual Conventional 
Conventional 
Samples 
Invention Exposure Method 1 Method 2 
______________________________________ 
a end swell no change slight end 
no change 
swell 
b end swell no change no change 
no change 
c no change no change end swell 
no change 
d end swell end swell slight end 
no change 
swell 
e end swell end swell no change 
no change 
f end swell end swell end swell 
no change 
______________________________________ 
As will be seen from Table 1, the weather resistance testing method of the 
present invention can realize, in quite a short time of about 400 hours, a 
state of corrosion equivalent to that obtained in 30 months of actual 
exposure. Thus, the method of the invention can promote the degradation 
also in the aspect of corrosion. 
Referring now to Table 2, the weather resistance testing method of the 
present invention can develop a degradation which is equivalent to or 
heavier than that obtained in 30 months of the actual exposure, thus 
proving the possibility of promoting the degradation also in the aspect of 
the state of the coating layer. 
As will be understood from the results of tests described hereinbefore, the 
weather resistance testing method of the present invention can realize, in 
quite a short time, a degradation of a degree which very closely 
approximates that of the degradation caused by a long period of actual 
exposure, thus proving high degree of correlation between the test results 
and the natural degradation. 
The embodiment described hereinbefore incorporated, as the light source 
unit, a combination of a metal halide lamp of wavelength ranging between 
250 and 550 nm and a filter for restricting the wavelength substantially 
to a range of 300 to 450 nm, the light source unit illuminating the sample 
surface at an ultraviolet intensity of 80.+-.5 mW/cm.sup.2. This, however, 
is only illustrative and the invention can be carried out with different 
types of light source unit such as an artificial light source including 
ultraviolet rays of an intensity not lower than several tens of 
mW/cm.sup.2 together with visible or infrared rays. The advantages of the 
invention described before can be obtained even when such an alternative 
light source is used.