ENVIRONMENT, ENERGY & RESOURCES

Development of Window Films for Solar Shading andHeat Insulating Applications
Tetsuya TAKEUCHI*, Osamu GOTO, Masataka INUDUKA, Tetsuji NARASAKI,
Yoshihiro TOKUNAGA, Hisami BESSHO and Hitoshi TAKEDA*

Tokai Rubber Industries, Ltd. (TRI) has developed window films for solar shading and heat insulating applications by
combining its advanced technologies of optical multi-layered membrane design, precision coating, and elongatedsputtering, as well as material technology. The optical functional membrane is a multi-layered membrane that consistsof thin Ag alloy membranes and thin dielectric membranes with a high refractive index. TRI has significantly reduced thecost of manufacturing the dielectric membranes by using its original sol-gel wet film forming method, and has
accordingly succeeded in producing competitively-priced optical function membranes. The solar shading and heatinsulating effects of the films were proven in the verification tests by using the experimental equipment of Tokyo
University of Science. Furthermore, the energy-saving effects for annual air-conditioning-related power consumption
were estimated by using the thermal load calculation program “LESCOM-wind” in a model office.

In response to a growing awareness of energy-saving
and power-saving and the need for improving the living environment near windows, the applications of transparent
heat ray blocking films that can be affixed to window glass
have been proposed.
We have promoted the development of optical functional films by combining our technologies of optical multilayered membrane design, precision coating, and elongatedsputtering, as well as material technology. We report here
the development of transparent window films for solar
shading and heat insulating applications which meet themarket needs mentioned above very well.

250
200

Ultraviolet light
Visible light

150
50
0

Distribution of sunlight and indoor radiant energy
Infrared light (heat rays)

100

Transmittance, reflectance (%)

1. Introduction

Energy (mWcm-2 · μm-1)

Keywords: window film, solar shading, heat insulating, infrared light, sol-gel

Radiant energy from indoors

Sunlight energy
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

5.0

10

20

50

Wavelength (μm)
Ultraviolet light
Visible light

Reflectance

Optical characteristics sought for films

Infrared light (heat rays)

Transmittance
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

5.0

10

20

50

Wavelength (μm)

Fig. 1. Distribution of sunlight and indoor radiant heat energy,
and optical characteristics sought for window-affixed films

2. Outline of the Development
2-1 Functions of the solar shading and heat insulating
window films
As windows are required to ensure natural lighting andviews, solar-shading and heat-insulating window films need tosimultaneously pursue those goals while maintaining transparency. Figure 1 shows the distribution of sunlight energy according to light wavelength, the distribution of warming radiantheat energy from indoors, the transmission and reflection spectrum that is required for window-affixed films to produce transparency, heat shielding (solar shading), and heat insulating
functions. To enable windows to balance the maintenance oflighting and sunlight-energy-shielding, it is necessary to form
cut-off filters that transmit visible light (wavelength: 0.4 to
0.8µm) and reflect near-infrared light (wavelength: 0.8 to 2µm)
out of sunlight energy. Moreover, because the heat insulation
functions are produced by reducing thermal discharge throughthe reflection of far-infrared light (wavelength 5 to 20µm),
which is warming radiant heat energy from indoors, to the indoor side, the reflection of far-infrared light is also required.

Window film
Glass
SummerHeat shielding(solar shading)Indoors

Visible lighttransmission

Reflection ofsunlight heat(near-infrared light)

Window film
Glass

WinterHeat insulating

Indoors
Visible lighttransmission
Reflection ofwarming heat(far-infrared light)

Fig. 2. Functions of solar shading and heat insulating films

SEI TECHNICAL REVIEW · NUMBER 74 · APRIL 2012 · 95

thickness of hard coating membranes and protective membranes respectively to the appropriate range of not morethan 1 µm. Figure 4 shows the film compositions of the solar
shading and heat insulating type and the solar shading type.

Function

Solar shading typeSolar shading andheat insulating type

Film composition (cross section)
outdoors

Protective membrane

Solar
Heat
shading insulating

Hard coating

indoors

Reflectionof warming
Reflection
PET
heat
Glass
of sunlight
film(far-infrared)heat(near-infrared)
Adhesive Functional membranes
layer(heat ray reflective membrane)

outdoors

Protective membrane

Hard coating

indoors

×

Figure 2 shows the image of the functions of solar
shading and heat insulating films in the summer and thewinter.
2-2 Design and composition of functional membranes
When designing the functional membranes as opticalmulti-layered membrane filters, which can meet all demands for visible light transmission, near-infrared light reflection and far-infrared light reflection, we have selected
Ag alloy membranes that absorb little visible light andlargely reflect infrared light, as the layer possessing a low
refractive index. Additionally, we have secured naturallighting and views by making the reflectance low and thetransmittance high in the invisible light region throughmulti-layering of the alloy membranes and thin dielectricmembranes possessing a high refractive index. According
to the width of transparent wavelength in the required visible light region, starting inclination of the reflectance inthe near-infrared light region and reflectance in the far-infrared light region, the number of layers made by thin dielectric membranes with high refractive index and Ag
membranes, as well as the membrane thickness of eachlayer, are decided. Figure 3 shows the cross section photoof a seven-layered film.

No reflectionof warming
Reflection
PET
heatof sunlight
Glass
film
(far-infrared)heat(near-infrared) Adhesive
Functional membranes
layer(heat ray reflective membrane)

Fig. 4. Structure of the solar shading and heat insulating films

Metal (Ti/Ag/Ti)
sputtering membrane

Approx.
200nm

Functional
membranesHigh refractive index
dielectric substance(sol-gel)-coatedmembrane

PET film

Fig. 3. Sectional structure (TEM image) of the functional membrane

The actual films are composed of thin dielectric membranes with high refractive index and Ag alloy membranes,alternately laminated on the PET film; several nm-thick Ti
membranes are inserted into the interface between thethin dielectric membrane with high refractive index and
the Ag membrane to limit Ag migration and enhance ply
adhesion.
2-3 Technology of adding heat insulating functions
To add heat insulating functions, it is necessary to reflect warming heat (far-infrared light) generated from indoors to the indoor side without absorbing it. Conventional
solar shading films, however, have no heat insulating functions because the PET film and acrylic hard coating areplaced on the indoor side of functional membranes (heatray reflective coating), and the films in that combination
absorb warming heat (far-infrared light). Therefore, wehave simultaneously pursued heat insulating properties andabrasion resistance by changing the film composition fromthe glass side to the order of the adhesive layer, PET film,
heat ray reflection function membranes, acrylic protective
membranes and acrylic hard coating and by controlling the

2-4 Functional membranes manufacturing technology
We have significantly reduced the cost of manufacturing thin dielectric membranes with a high refractive index,
which are one component of functional membranes, byusing the wet coating method that ensures high linear
speed in the air, instead of high-cost reactive sputtering film
formation. Made by using organic titanate as the material,
the membranes are coated by the gravure roll method, and,after being dried, they are subjected to a low-temperature
sol-gel polymerization reaction by UV irradiation, whichmakes the formation of titanium dioxide (TiO2) on the PET
film possible. Considering stability in coating fluid, the easeof producing a high refractive index and the unlikelinessof generating cracks, we have used n-butoxytitanium (multimer) for organic titanate, which is chelated by acetylacetone to add UV absorbency. Figure 5 shows the mechanismof the UV assist sol-gel polymerization reaction.

3HC

OR
RO

Ti

O

OR

R

3HC
＋

n

Hydrolysis

Condensation

C

C

O

O

CH3

Ti

O

O
Ti

Ti

RO

O

O
O

Ti

C

CH

O

Acetylacetone

n-butoxytitanium (multimer)
Coating, drying, UV irradiation

CH2

Ti

O

C

CH3

O
Ti

O

OR OR n
UV absorbent
chelateOO

TiO2 thin film

TiO
R: Butyl group

Fig. 5. Mechanism of UV assist sol-gel polymerization reaction

96 · Development of Window Films for Solar Shading and Heat Insulating ApplicationsR3. Characteristics of the Solar Shading and Heat
Insulating Films

Transmittance, reflectance (%)

3-1 Optical characteristics
We have developed three types of window films forsolar shading and heating insulating applications: “Refleshine TX71” with solar shading functions, “Refle-shine
TW31” with heat insulating functions, and “Refle-shine
TU71” with solar shading and heat insulating functions.
Figures 6 to 8 show the transmission and reflection spectrum in the ultraviolet to the far-infrared light region. Eachfigure, respectively, shows that the solar shading film
“Refle-shine TX71” has visible light transmission and nearinfrared light reflection functions; that the heat insulating
film “Refle-shine TW31” has visible light transmission andfar-infrared light reflection functions; and that the solar
shading and heat insulating film “Refle-shine TU71” has100Transmission spectrum

80

Reflection spectrum

Solar shading
Solar shading
Heat
heat insu- Reference
type
insulating type andlating typeSolar shading

40

Heat
insulating

20
0.1

1

10

100

Wavelength (µm)

Fig. 6. Transmission and reflection spectrum of the solar shading film
“Refle-shine TX71”

Transmittance, reflectance (%)

Table 1. Characteristics of “Refle-shine TX71”, “Refle-shine TW31”
and “Refle-shine TU71”

Lighting

60

0visible light transmission and near-infrared light to far-infrared light reflection functions.
Table 1 shows the characteristics of “Refle-shine TX71”,“Refle-shine TW31” and “Refle-shine TU71”. The three typesof film ensure good lighting with more than 70% of visible
light transmittance. TX71 and TU71 ensure high solar shading with a shading coefficient of not higher than 0.6. Also,
TW31 and TU71 ensure good heat insulation with the overall heat transfer coefficient of not more than 4.5 W/m2K. In
particular, TU71 is the world's first film that ensures transparency, solar shading and heat insulating characteristics.

100

Transmission spectrum

Visible lighttransmittance

71.0%

81.6%

70.8%

90.4%

0.57

0.74

0.51

1.00

39.6%

61.0%

37.0%

87.4%

Overall heat
5.77W/m2K 4.49W/m2K 4.47W/m2K 5.92W/m2K
transfer coefficient

Safety of glass
against heat Solar absorptancecracking

32.4%

19.0%

34.1%

4.4%

Test method: Measured by affixing the films to 3mm-thick plate glass, based on
JISA5759 “Films for building window glass”

Reflection spectrum

Table 2. Weather resistant test conditions

Item

20
0.1

1

10

100

Fig. 7. Transmission and reflection spectrum of the heat insulating film
“Refle-shine TW31”

Light source

Power supply voltage

AC 200V±20V

Conditions for irradiation
Mean discharge voltage of power source

100
Transmission spectrum

Reflection spectrum

40
20
1

10

Wavelength (µm)

Fig. 8. Transmission and reflection spectrum of the solar shadingand heat insulating film “Refle-shine TU71”

50V±1V, 60A±1.2A

Temperature indicated by black panel thermometer 63˚C±3˚C

60

0.1

Condition
Sunshine carbon-arc lamp: 1 unit
Light filter
Spectral transmittanceNot more than 2% at 275nm
Not less than 90% at 400nm

Wavelength (µm)

Transmittance, reflectance (%)

Only
3mm-thickplate glass

Solar transmittance

40

0

Refleshine
TU71

Shading coefficient60

80

Refleshine
TW31

3-2 Weather resistanceBased on JISA5759 “Films for building window glass,”
films for building windows should be subjected to the weather

80

0

Refleshine
TX71

100

Relative humidity(50±5)%

Irradiance on the surface of specimen

255 (±10%) W/m2 (at 300nm to 700nm)

Water jetting

Normally, water is jetted for 18 minutes
during 120 minutes of irradiation.

Film-affixed glass

Spectral transmittanceNot more than 2% at 275nm
Not less than 90% at 400nm

Conditions of photoirradiation
to specimen

Affixed with the glass surface facing
the light source.

Method of water jetting

Water is jetted to the glass surface on
the photo-irradiation side.

SEI TECHNICAL REVIEW · NUMBER 74 · APRIL 2012 · 97

Table 3. Comparison of the characteristics of “Refle-shine TX71,”“Refle-shine TW31” and “Refle-shine TU71”
before and after the test

Type

Item
Visible light transmittance

Initial stage

After weather
resistant test

71.0%

71.8%

0.57

0.56

Solar Shading coefficient
shading
Solar transmittancetype
TX71 Overall heat transfer coefficient

39.6%

39.2%

5.77W/m2K

5.79W/m2K

Solar absorptance

32.4%

31.8%

Visible light transmittance

81.6%

79.4%

0.74

0.74

Shading coefficientHeat
insulating
Solar transmittancetype
TW31 Overall heat transfer coefficient

61.0%

60.0%

4.49W/m2K

4.63W/m2K

Solar absorptance

19.0%

20.4%

Solar Visible light transmittanceshading Shading coefficientandheat
Solar transmittanceinsulating
Overallheat transfer coefficient
type
TU71 Solar absorptance

70.8%

71.6%

0.51

0.54

37.0%

37.8%

4.47W/m2K

4.52W/m2K

34.1%

30.4%

used. The test box has an opening, 1 m wide and 2 m highon the southern side, to which single plate glass or multiple-layer glass is installed. Heat insulation is applied bypolystyrene foam, 100 mm thick, to all parts of the testboxes, except the glass surface. Among the four test boxes,
solar shading and heat insulating films were affixed to theinside of the glass for three units, while the remaining unit
was left with nothing affixed to the glass for comparison.
Using a PC and data logger, we performed the experiments
by measuring the air temperature in the test boxes, temperature inside the glass, and the amount of transmitted
solar radiation at intervals of one minute for 24 consecutive
hours. Figure 9 shows the installation of sensors in the testboxes. When measuring heat insulating effects, 400 W farinfrared ray heaters were installed, facing the polystyrene
foam side opposite the glass surface in each test box andthe on/off control of the heaters was simultaneously performed in the all test boxes, to maintain a temperature between 20˚C and 25˚C with the air temperature at a heightof 150 cm from the floor, within the glass-only test box as
the standard(1), (2).

Frontresistant test by using a weatherometer of the sunshine carbon-arc lamp type. Table 2 shows the test conditions.
Table 3 shows the test results of “Refle-shine TX71”,“Refle-shine TW31” and “Refle-shine TU71.” The results
confirmed that there were no changes in appearance andoptical characteristics of the three films after 1,000 hours
had passed since the start of the test.

Actinometer

Side cross section

Air temperature in the box

Long and shortwave radiometer

Heater

The heater isused only
when measuring
heat insulating
effects
Heat generation
side

Glass surface temperaturein the box

4. Experimental Verification of the Solar Shadingand Heat Insulating Effects
4-1 Experimental methodology
We have verified the thermal effects of the developed
solar shading and heat insulating films by using the experimental equipment of Tokyo University of Science. Photo 1
shows the experimental equipment.
There are six units of experimental equipment (hereinafter referred to as ”test box”), of which four units were

Fig. 9. Installation of sensors in the test box

Regarding solar shading and heat insulating effects,
using single plate glass or multiple-layer glass for the opening of the test box, the comparison was made respectively
between the situation of affixing solar shading and heat insulating films to the glass and a control setup using glass

Table 4. List of experiments performed

Used glass

Photo 1. Experimental equipment

SeasonTest date

Single plate Winter to interim period February 3 to 20, 2011
Verification
glassofSummerJune 28 to July 31, 2011
8mm thicksolar
Multiple-layer
Winter to interim period April 2 to 30, 2011
shadingglass
effects
SummerJune 1 to 26, 2011
8/A6/8mm
Single plate Winter to interim period March 14 to 15, 2011
Verification
glassofSummer—8mm thickheat
Multiple-layer
Wintertointerimperiod
April
7
to
8,
2011
insulating
glass
effects
Summer
—
8/A6/8mm

98 · Development of Window Films for Solar Shading and Heat Insulating Applications

(1) Experiments in the winter to the interim period

Air temperature in the box (℃)

80

2/5

70

2/6

2/7

Only single plate glass60

TW31 affixed50

TX71 affixed40

TU71 affixed

30
20
10
0
0:00

-10

12:00

0:00

12:00

0:00

12:00

0:00

Air temperature in the box (℃)

65
63
61

Partial enlargementof Feb.7

Only single plate glass

59
57

TW31 affixed

55
53
51
49

TX71 affixed
TU71 affixed

47
45
6:00

7:12

8:24

9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00(2) Experiments in the summer

Air temperature in the box (℃)

80
70

7/12

7/13

7/14

Only single plate glass60

TW31 affixed
TX71 affixed50

TU71 affixed

40
30
20
10
0
0:00

-10

12:00

0:00

12:00

0:00

12:00

0:00

54

Air temperature in the box (℃)

only. The experiments were performed from the winterthrough the interim period and in the summer. Table 4shows the list of experiments performed.
4-2 Experimental results(1) Verification of solar shading effects(a) When affixed to single plate glass
Figure 10 shows the temporal fluctuation of air temperature in the box when the films were affixed to the inside of the 8mm-thick single plate glass. They are theresults on February 5 to 7, 2011 in the winter and the interim period, and the results on July 12 to 14, 2011 in thesummer. When the experiments were performed, meteorological data were also simultaneously measured. As an example, Fig. 11 shows the data of outdoor air temperatureand vertical intensity of solar radiation in the winter andthe interim period and the summer experimental period.
In the measurements made in the winter and the interim period, February 5 and 6 were cloudy and on February 7 there was fine weather. In the measurements madein the summer, July 12 and 13 were cloudy and on July 14
there was fine weather. When there was sunlight, the airtemperature in the box fell by up to 12.9˚C for TU71,
11.9˚C for TX71 and 4.8˚C for TW31 in the winter and3.9˚C for TU71, 4.1˚C for TX71, and 0.6˚C for TW31 in thesummer, compared with the box with only glass installedwith no films. It is confirmed from the results that there
were temperature rise restraining effects when the films
were affixed to the glass and that the smaller the shading
coefficient was, the larger the temperature rise restraining
effects were.
In addition, the rising of air temperature in the box
was lower in the summer than in the winter. This is because
the vertical intensity of solar radiation on the southernside, where the opening was installed, is smaller in the summer, which decreases the amount of solar radiation flowing
into the box.
(b) When affixed to multiple-layer glass
Figure 12 shows the temporal fluctuation of air temperature in the box when TU71 was affixed to the insideof the multiple-layer glass [glass 8 mm / air 6 mm / glass 8mm]. The measurement in the case when the LowE multiple-layer glass of the same thickness (shading coefficient
0.69, overall heat transfer coefficient 2.5 W/m2K) was used
was simultaneously made for comparison. These are the results from April 14 to 16, 2011, in the winter and the interim period and the results from June 5 to 7, 2011, in thesummer. In the measurements made in the winter and theinterim period, on April 14 and 15 there was fine weather
and April 16 was cloudy. In the measurements made in thesummer, June 5 and 7 were cloudy and on June 6 there wasfine weather.
The air temperature in the box fell by up to 7.4˚C for
TU71 and 4.3˚C for the LowE multiple-layer glass in thewinter and the interim period and 2.9˚C for TU71 and1.2˚C for the LowE multiple-layer glass in the summer,
compared with the box where only multiple-layer glass was
installed with no films. From the above-mentioned results,
even in the case of multiple-layer glass, it is confirmed that
there were temperature rise restraining effects when thefilms were affixed to the glass and that, the smaller the
shading coefficient was, the larger the temperature rise re-Partial enlargementof July 14

53
52

Only single plate glass

51

TW31 affixed

50
49
48
47
46
6:00

TU71 affixed
TX71 affixed

7:12

8:24

9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00

Fig. 10. Temporal fluctuation of air temperature in the box in(1) the experiments in the winter to the interim period and(2) the experiments in the summer(in the case of single plate glass)

SEI TECHNICAL REVIEW · NUMBER 74 · APRIL 2012 · 99

(1) Experiments in the winter to the interim period

800

2/5

12:00

2/6

0:00

2/5

12:00

80

2/7

0:00

2/6

12:00

0:00

2/7

600
400
200
12:00

0:00

12:00

0:00

12:00

0:00

12:00

800

7/12

7/12

7/13

0:00

12:00

7/14

0:00

7/13

12:00

50
40

TU71 affixed

60

4/16

30
20
10
0
0:00

12:00

0:00

12:00

0:00

12:00

0:00

7/14

Partial enlargementof April 14

66
64
62

Only multiple-layer glass
LowE multiple-layer glass

60
58

TU71 affixed

56
54
6:00

0:00

7:12

8:24

9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00(2) Experiments in the summer

600

80

400
200
12:00

0:00

12:00

0:00

12:00

0:00

Fig. 11. Examples of the meteorological data during
the experimental periods

straining effects were.
(2) Verification of heat insulating effects(a) When affixed to the single plate glass
The experiments in the cases where the heat insulating type TW31 and the solar shading type TX71 were affixed to the inside of the 8mm-thick single plate glass, were
performed between March 14 and 15, 2011. The experiments were performed at night to avoid the effects of heatfrom sunlight. Figure 13 shows the temporal fluctuation of
the air temperature in the box. Moreover, Fig. 14 shows
the data of outdoor air temperature and the vertical intensity of solar radiation during the experimental period.
400 W far-infrared ray heaters were installed in eachtest box and the on/off control of the heaters was simultaneously performed in the all test boxes, to maintain a temperature between 20˚C and 25˚C with the air temperature
at a height of 150 cm from the floor within the glass-only
test box as the standard. The air temperature in the box repeats in a rising and falling waveform. When the heat insulating type TW31 was affixed to the glass, the temperature

Air temperature in the box (˚C)

Outdoor air temperature (˚C)

50
45
40
35
30
25
20
15
10
5
0
0:00

0
0:00

4/15
Only multiple-layer glass
LowE multiple-layer glass

68

Air temperature in the box (˚C)

0
0:00

4/14

70

-10

(2) Meteorological data of the experiments in the summer

Vertical intensity of solar radiation (Ｗ/m2)

Air temperature in the box (˚C)

40
35
30
25
20
15
10
5
0
-5 0:00
-10

6/5

70
60
50

6/6

LowE multiple-layer glass

6/7
Only multiple-layer glass
TU71 affixed

40
30
20
10
0
0:00

-10

12:00

0:00

12:00

0:00

12:00

0:00

50

Air temperature in the box (˚C)

Vertical intensity of solar radiation (Ｗ/m2) Outdoor air temperature (˚C)(1) Meteorological data of the experiments in the winter tothe interim period

49
48
47
46

Only multiple-layer glass

Partial enlargementof June 6

LowE multiple-layer glass

45

TU71 affixed

44
43
42
41
40
6:00

7:12

8:24

9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00

Fig. 12. (1) Temporal fluctuation of air temperature in the box in (1)the experiments in the winter to the interim period and(2) the experiments in the summer(in the case of multiple-layer glass)

100 · Development of Window Films for Solar Shading and Heat Insulating Applications

3/14

31

35

3/15

Air temperature in the box (˚C)

Air temperature in the box (˚C)

33

TX71 affixed TW31 affixed Only single plate glass

29
27
25
23
21
19
17
15
19:00

21:00

23:00

1:00

3:00

5:00

Air temperature in the box (˚C)

Air temperature in the box (˚C)

28

TX71 affixed27
26

Only single plate glass

25
24
23
22
21
20
1:05

1:10

1:15

1:20

1:25

1:30

Vertical intensity of solar radiation (Ｗ/m2)

Outdoor air temperature (˚C)

Fig. 13. Temporal fluctuation of air temperature in the box(in the case of single plate glass)

40
35
30
25
20
15
10
5
0
-5 19:00
-10
800

3/14

21:00

3/15

23:00

1:00

3/14

3:00

5:00

7:00

5:00

7:00

3/15

600
400
200
0
19:00

21:00

23:00

1:00

3:00

4/8

Only multiple-layer glass

31
29
27
25
23
21
19
17
21:00

23:00

1:00

3:00

5:00

7:00

32

Partial enlargementof March 15

TW31 affixed

4/7

TU71 affixed LowE multiple-layer glass

15
19:00

7:00

30
29

33

Partial enlargementof April 8

30

LowE multiple-layer glass
TU71 affixed28

Only multiple-layer
glass

26

24

22
1:45

1:50

1:55

2:00

2:05

2:10

2:15

2:20

Fig. 15. Temporal fluctuation of the air temperature in the box(in the case of multiple-layer glass)urement in the case where the LowE multiple-layer glass ofthe same thickness (shading coefficient 0.69, overall heattransfer coefficient 2.5 W/m2K) was used was simultaneously made for comparison. The tests were performed atnight to avoid the effects of heat from sunlight. Figure 15
shows the temporal fluctuation of the air temperature in
the boxes.
When the solar shading and heat insulating type TU71
was affixed to the glass, the temperature increased up to
1.0˚C, compared with the box with only multiple-layer glass
installed with no films and the heat insulating effects wereconfirmed. Moreover, when the LowE multiple-layer glass
was used, the temperature increased 1.5˚C.
(3) Summary of the results
The experimental results mentioned above are summarized in Table 5.

Fig. 14. Example of the meteorological data during
the experimental period

5. Simulation Verification of Solar Shading andHeat Insulating Effects
increased up to 2.7˚C compared with the box with only glass
installed with no films, and the heat insulating effects wereconfirmed. Moreover, when the solar shading type TX71
was affixed to the glass, the temperature increased 1.1˚C.
(b) When affixed to the multiple-layer glass
The experiments in the cases where the solar shadingand heat insulating type TU71 was affixed to the inside of
the multiple-layer glass [glass 8 mm/ air 6 mm/ glass 8mm] were performed from April 7 to 8, 2011. The meas-

5-1 Simulation method
We have verified the thermal effects of the solar shading and heat insulating films we have developed, this timeusing the non-stationary thermal-load calculation program“LESCOM-wind” based on the response factor method.
“LESCOM-wind” was developed for the parameters appropriate for the calculation of the effectiveness of window
films intended for solar shading and heating insulating ap-

SEI TECHNICAL REVIEW · NUMBER 74 · APRIL 2012 · 101

Table 5. Summary of the solar shading and heat insulation effects verification experiments

Effects of affixing the films (Comparison of the difference of air temperature in
the boxes compared with the box with only glass installed with no films)
Used glass

SeasonStandard

Winter to
Based on theSingle plate interim periodcase ofglass
only single plate
8mm thick
Summerglass
Verification ofsolar shading
Winter toeffects
Based on theMultiple- interim periodcase oflayer glass
only multiple8/A6/8mm
Summerlayer glass

Solar shading film
(TX71) affixed

Reference

Solar shading andHeat insulating film
LowE multipleheat insulating film
(TW31) affixedlayer glass(TU71) affixed

11.9˚C down

4.8˚C down

12.9˚C down

4.1˚C down

0.6˚C down

3.9˚C down－－

7.4˚C down

4.3˚C down－－

2.9˚C down

1.2˚C down

1.1˚C up

2.7˚C up－－－

1.0˚C up

Winter to
Based on theSingle plate interim periodcase ofglass
only single plate
8mm thick
Summerglass
Verification ofheat insulating
Winter toeffects
Based on theMultiple- interim periodcase oflayer glass
only multiple8/A6/8mm
Summerlayer glass

plications, based on the multi-room non-stationary thermalload calculation program “LESCOM,” developed by thetask force for “living function enhancement products” ofthe former Ministry of International Trade and Industry,
Consumer Goods Industries Bureau(3)-(6).
Figure 16 shows the conceptual diagram of heat balance of the opening, which is extremely complicated andwide-ranging. The non-stationary thermal load calculation
program “LESCOM-wind” reproduces the thermal environment by computer simulation, based on a thermal equilibrium formula in consideration of such heat balance.
5-2 Results of simulation verification(1) Verification of solar shading effects
We have verified the solar shading effects by performing the simulation calculation, namely; the thermal load
calculation based on the actual test box experiments, using
the thermal load calculation program “LESCOM-wind.”
The calculation was performed based on the solar shading
experiments using the 8 mm-thick single plate glass, whichwere performed from February 5 to 7, 2011, by using themeteorological data of the relevant days. Figure 17 shows
the simulation calculation results and the actual measurement data of the air temperatures in the box when TX71
was affixed to the glass. The simulation calculation results
using “LESCOM-wind” conformed to the actual measurement data very well and the solar shading effects of TX71
were also confirmed by the simulation calculation.
(2) Verification of heat insulating effects
As in the case of (1), using the thermal load calculation program “LESCOM-wind,” the simulation calculation
was performed based on the heat insulating experiments
conducted on March 14 and 15, 2011, using the 8 mmthick single plate glass and the meteorological data of therelevant days. Figure 18 shows the simulation calculation
results and the actual measurement data of the air temperatures in the box when TW31 was affixed to the glass. The

1.5˚C upsimulation calculation results using “LESCOM-wind” conformed to the actual measurement data very well, and theheat insulating effects of TW31 were also confirmed by thesimulation calculation.

6. Air-Conditioning Load Simulation
in a Model Office
6-1 Simulation method
As it was confirmed that the calculation results conformed well to the experimental results in the test boxes,
using the thermal load calculation program “LESCOMwind,” we have performed the simulation calculation of energy-saving effects for annual air-conditioning-related
power consumption in the case where solar shading andheat insulating films were used in a model office designated by the Architectural Institute of Japan. The calculations were performed in three locations— Sapporo, Tokyo,
and Naha. Table 6 shows the simulation calculation conditions, while Fig. 19 shows the plan view of a model officedesignated by the Architectural Institute of Japan(7).
6-2 Simulation results
Figure 20 shows the annual air-conditioning-related
power consumption when TU71, TW31, and TX71 wererespectively affixed to the 8 mm-thick single plate glass. Figure 21 shows the annual air-conditioning-related power
consumption when TU71 was affixed to the multiple-layer
glass [glass 8 mm / air 6 mm / glass 8 mm]. Table 7 shows
the annual air-conditioning-related thermal load in Tokyo
when the films were affixed to the single plate glass. Table
8 shows the annual air-conditioning-related thermal loadin Tokyo when the films were affixed to the multiple-layer
glass. Figure 21 and Table 8 show the calculation results
when the LowE multiple-layer glass of the same thickness

102 · Development of Window Films for Solar Shading and Heat Insulating Applications

Sash

Direct solar
radiation

Diffusesky radiation

Reflected
solar radiation

Exterior
wall

Floor

Indoors

TX71 affixed: Actual measurement data

TX71 affixed: Simulation calculation

40
30
20
10
0
2011/2/5 2011/2/5 2011/2/6 2011/2/6 2011/2/7 2011/2/7 2011/2/8-100:00
12:00
0:00
12:00
0:00
12:00
0:00

t 21

t 22

α 12c

α 21c

α 22c

ε 12

ε 21

ε 22

τ1

τ2

Solar reflectance of glass

ρ1

ρ2

Solar absorptance of glass

α1

α2Thermal resistance

R1

3/14
TW31 affixed:
Actual measurement data

31
29

3/15
TW31affixed:
TX71
affixed:Simulation calculation

27
25
23
21
19
17
15
19:00

t 12

Solar transmittance of glass

21:00

23:00

1:00

3:00

5:00

7:00

Fig. 18. Comparison of the simulation calculation results and the actual
measured values, when TW31 was affixed to the glass

Table 6. Simulation calculation conditions

item

Calculation conditions

Calculation program “LESCOM-wind”
Calculation point
[˚C]
[˚C]

t 21 : Indoor glass external surface temperature[˚C]

t 22 : Indoor glass inner surface temperature[˚C]t m : Mid-air layer temperature[˚C]

α 11c : Outdoor glass external surface convective heat transfer coefficient[W/m 2 • K]

α 11r : Outdoor glass external surface radiative heat transfer coefficient[W/m 2 • K]

α 12c : Outdoor glass inner surface convective heat transfer coefficient[W/m 2 • K]

α 21c : Indoor glass external surface convective heat transfer coefficient[W/m 2 • K]

α 22c : Indoor glass inner surface convective heat transfer coefficient[W/m 2 • K]

α 22r : Indoor glass inner surface radiative heat transfer coefficient[W/m 2 • K]

ε 11 : Outdoor glass external surface emissivity[—]

ε 12 : Outdoor glass inner surface emissivity[—]

ε 21 : Indoor glass external surface emissivity[—]

ε 22 : Indoor glass inner surface emissivity[—]

R 0 : Outdoor heat transfer resistance[m K/W]

R 1 : Outdoor glass thermal resistance (constant)[m 2 • K/W]

R m : Mid-air layer heat transfer resistance[m 2 • K/W]

R 2 : Indoor glass thermal resistance (constant)[m 2 • K/W]

R i : Indoor heat transfer resistance[m K/W]

R : Total thermal resistance of the glass part[m 2 • K/W]

2•

Meteorological data Using the typical annual data in the 1990s

Building model

One floor of an office model designated by theArchitectural Institute of Japan
Target floor area: 605m2 (office part)
Window area: 150m2

Glass type8mm-thick single plate glass or 8/A6/8mm multiplelayer glass with the solar shading and heat insulating
films affixed (to the room sides of all windows)

Air-conditioning
setting

Cooling preset temperature: 26.7°C,
Heating preset temperature: 21.9°C
Air conditioning operating time: 8:00 to 18:00⑤ NORTH（57.65m 2）④ WEST（115.29m 2）

Air
conditionerroom⑥ NORTH（57.65m 2）⑨ CORE（221.40m 2）⑧ INTERIOR⑦ INTERIOR（72.00m ）EV
hall

Office① EAST（115.29m 2）（72.00m 2）

2

Office6300

t 11 : Outdoor glass external surface temperature
t 12 : Outdoor glass inner surface temperature

Sapporo, Tokyo, Naha

6000

Ri

24600

R2

6000

Rm

Hot-water service room

③ SOUTH（57.65m 2）

Lavatory Lavatory② SOUTH（57.65m 2）

6300

R0

2/7

2/6

50

33

Mid-air layer

Emissivity ε 11

60

Room
temperature(2) Heat balance

Glass surface ttemperature 11
Convective heattransfer coefficient α 11c

2/5

70

Fig. 17. Comparison of the simulation calculation results and the actual
measured values when TX71 was affixed to the glass

Outdoor air
temperature

Outdoors

80

Air temperature in the box (˚C)

Effective
radiation

Air temperature in the box (˚C)(1) Handling of sunlight2•

Fig. 16. Conceptual diagram of heat balance of the opening(in the case of multiple-layer glass)

6300

6000

9000
33600

6000

6300

Fig. 19. Plan view of an office model designated by the Architectural
Institute of JapanSEI TECHNICAL REVIEW · NUMBER 74 · APRIL 2012 · 103

Annual air-conditioning-related
power consumption (kWh)30,000: TU71-affixed to single plate glass

26,000: TX71-affixed to single plate glass

24,00022,00020,00018,000100%: Only single plate glass

28,000: TW31-affixed to single plate glass

89%
86%

95%

100%

99%
93%
92%

100%

90% 95% 94%

16,00014,00012,00010,000

Sapporo

Tokyo

Naha

Fig. 20. Calculation results when the films were affixed
to the single plate glass(shading coefficient 0.69, overall heat transfer coefficient
2.5 W/m2K) was used, for comparison. The comparison of
the results for the single plate glass shows that, in all locations — Sapporo, Tokyo, and Naha — affixing the solar
shading and heat insulating films to the glass had the effects of reducing the annual air-conditioning-related power
consumption, compared with the conditions where nofilms were used. In particular, it is confirmed that TU71,
which has both solar shading and heat insulating functions,
had the largest reduction effects in all the locations. Moreover, it is confirmed from the simulation results that affixing TU71 to the multiple-layer glass had the reduction
results equivalent to those of the LowE multiple-layer glass(shading coefficient 0.69, overall heat transfer coefficient
2.5 W/m2K).

Table 7. Calculation results for the annual air-conditioning-related
thermal load in Tokyo when the films were affixed to thesingle plate glass

Annual cooling andheating load

Annual cooling load Annual heating load
kWh/ year Relative ratio
kWh/ year
kWh/ year

Only single plate glass

17,198100%

13,028

4,170

TU71-affixed to single plate glass

15,50290%

11,017

4,485

TX71-affixed to single plate glass

16,332

95%

11,266

5,067

TW31-affixed to single plate glass

16,13694%

12,3603,775Annual air-conditioning-related
power consumption (kWh)The relative ratio shows the rate when the air-conditioning-related thermal loadin using the single plate glass was regarded as 100.

30,000100%: Only multiple-layer glass

28,000: TU71-affixed multiple-layer glass

26,000: Reference: LowE multiple-layer glass

24,00092%

97%

22,00020,00018,00016,000100%
96% 94%14,000100%
94% 96%

12,00010,000

SapporoTokyo

7. Conclusion
We have developed window films for solar shading,heat insulating, and solar shading and heat insulating by
combining our technologies of optical multi-layered membrane design, precision coating, and elongated sputtering,as well as making advances in material technology. The optical functional membranes consist of membranes alternately laminated with the Ag alloy membrane and dielectricmembranes with a high refractive index. In particular, wehave significantly reduced the cost of forming dielectricmembranes with a high refractive index based on our original sol-gel wet film formation method. Through verification using the experimental equipment of Tokyo Universityof Science and the simulation verification using the thermalload calculation program “LESCOM-wind,” we have clarified the solar shading and heat insulating effects of ourfilms. Moreover, we have calculated the energy-saving effects for annual air-conditioning-related power consumption in a model office.
In the future, we aim to develop constituent materials
and make the design of functional membranes more widely
applicable and are planning to achieve even higher performance and greater cost reductions for the films.

NahaFig. 21. Calculation results when the films were affixed tothe multiple-layer glass

Table 8. Calculation results for the annual air-conditioning-related
thermal load in Tokyo when the films were affixed to themultiple-layer glass

Annual cooling andheating load
kWh/ year Relative ratio

Annual cooling load Annual heating load
kWh/ year
kWh/ year

Only multiple-layer glass

15,668100%

13,056

2,612

TU71-affixed multiple-layer glass

14,726

94%

11,8352,892

Reference: LowE multiple-layer glass

15,00496%

12,711

2,293

The relative ratio shows the rate when the air-conditioning-related thermal loadin using the multiple-layer glass was regarded as 100.

104 · Development of Window Films for Solar Shading and Heat Insulating Applications

Technical Term
1
Shadingcoefficient:
The numerical value that expresses*
the heat quantity of sunlight energy inflow, when theindoor inflow heat quantity by the transmission
through, and reradiation from, a 3 mm-thick transparent plate glass is 1.00
*2 Overall heat transfer coefficient: The numerical valuethat expresses the heat quantity passing the area of 1 m2
per hour when there is a temperature difference of 1˚C.
*3 Glass heat cracking: When a sheet of window glass receives direct sunlight, the parts exposed to sunlight
warm and expand, but the surrounding parts below
the sash and shaded parts warm only slightly and remain at a comparatively low temperature. This lowtemperature part restrains the expansion of warmed
parts and, as a result, tensile stress occurs in the surrounding glass edge. When the stress exceeds edge
strength of the glass, ”heat cracking of the glass” occurs.
*4 Cooling load: The amount of energy required for cooling a room to a certain temperature.
*5 Heating load: The amount of energy required forwarming a room to a certain temperature.

Contributors (The lead author is indicated by an asterisk (*).)

T. TAKEUCHI*• Project Deputy General Manager, New
Business R&D Laboratories, Tokai Rubber Industries, Ltd.
Engaged in the development of optical
functional films

O. GOTO• New Business R&D Laboratories, Tokai Rubber Industries, Ltd.

M. INUDUKA• New Business R&D Laboratories, Tokai Rubber Industries, Ltd.

T. NARASAKI• Project Manager, New Business R&D Laboratories,
Tokai Rubber Industries, Ltd.

Y. TOKUNAGA• Deputy Manager, Refle-shine Functional Film Business
Unit, Tokai Rubber Industries, Ltd.

(1)

(2)

(3)

(4)

(5)

(6)

(7)

References
Tetsuya Takeuchi, Hitoshi Takeda, Hiroki Inagaki, Hisami Bessho:
The study concerning solar shading and heat insulating effects of thesolar shading films, Part 1, Experimental verification of solar shading
effects, Digest of academic lectures of the Architectural Institute ofJapan, D-2, pp563-564, 2011
Hiroki Inagaki, Hitoshi Takeda, Tetsuya Takeuchi, Hisami Bessho:
The study concerning solar shading and heat insulating effects ofsolar shading films, Part 2, Experimental verification of the heat insulating effects of low radiation films, Digest of academic lectures of
the Architectural Institute of Japan, D-2, pp565-566, 2011
Yo Matsuo, Hitoshi Takeda: The thermal load calculation method
based on the response factor method and the sample calculation (1),
The journal of the Society of Heating, Air-Conditioning and SanitaryEngineers of Japan, Vol.44 No.4, pp1-14, 1970
Yo Matsuo, Hitoshi Takeda: The thermal load calculation method
based on the response factor method and the sample calculation (2),The journal of the Society of Heating, Air-Conditioning and SanitaryEngineers of Japan, Vol. 44 No.7, pp11-25, 1970
Hitoshi Takeda: Room temperature fluctuation analysis for non-airconditioned rooms, the collection of papers of the Society of Heating, Air-Conditioning and Sanitary Engineers of Japan, No. 7,
pp13-21, 1978
Hitoshi Takeda, Minoru Inanuma, Nozomu Yoshizawa, Kyoichiro
Isozaki: Standard meteorological data and thermal load calculation
program, LESCOM, Inoueshoin, 2005
Hiroshi Takizawa: Proposal of typical problems - Typical problems
for office, Architectural Institute of Japan, Research Committee on
Environmental Engineering, Documents of the 15th Heat Symposium, pp35-42, 1985

H. BESSHO• General Manager, New Business R&D Laboratories,
Tokai Rubber Industries, Ltd.

H. TAKEDA*• Doctor of Engineering
Professor Emeritus, Tokyo University of
Science, Specializes in environmental engineering of architecture* Refle-shine is a trademark or registered trademark of Tokai Rubber Industries, Ltd.

SEI TECHNICAL REVIEW · NUMBER 74 · APRIL 2012 · 105