JPH0891882A - Pane for fire protection and crime prevention - Google Patents

Abstract

PURPOSE: To provide a pane having fire protection performance and crime prevention performance in combination by interposing a metallic sheet between two or more of glass sheets and adhering the glass sheet surface facing the front surface thereof by the frit, thereby forming an integral structure. CONSTITUTION: The metallic sheet 4 having through-parts 3 of a circular, elliptic or polygonal shape and having a thickness of 0.1 to 1.0mm is formed. The respective through-parts 3 have a diameter of 3 to 20mm when converted in area to a circle. The through-parts 3 have a linear expansion coefft. of 70 to 130×10<-7> / deg.C at 30 to 350 deg.C. The frit 5 which is an amorphous material having a sealing temp. of 400 to 750 deg.C or an amorphous material having a sealing temp. of <=750 deg.C and having a coefft. of linear expansion of 80 to 120×10<-7> / deg.C at 30 to 350 deg.C is mixed with a vehicle and is thinly applied on both surfaces of the metallic sheet formed in the manner described above. The coating is then dried. Next, the metallic sheet 4 is held between the glass sheet 1 having a soda lime silicate glass compsn. and the glass sheet 2 and the frit mixed with the vehicle is applied on the outer peripheries of the glass sheets 1 and 2 and the glass sheets are heat treated on a flat rack plate at 450 to 630 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fire / security glass which has a fire-proof property and is difficult to generate a through hole due to an impact or the like and has a high effect of suppressing the intrusion of a criminal.

[0002]

2. Description of the Related Art A glass plate with a metal mesh is most well known as a glass plate having a fireproof property capable of preventing the spread of fire in the event of a fire. In recent years, examples of using transparent crystallized glass having a small coefficient of thermal expansion and a high softening temperature or reinforced borosilicate glass have been seen in place of the glass plate with metal mesh. However, none of these have sufficient impact resistance and penetration resistance, and the effect of suppressing the intrusion of criminals is not sufficient.

On the other hand, laminated glass is known as a glass plate having impact resistance and penetration resistance and having crime prevention performance. A tempered laminated glass using a tempered glass for further improving the performance is also known. In addition, a laminated glass for crime prevention window, in which a metal plate material having a porosity is inserted between the intermediate films, has also been devised (Actual Kaihei 2-140938). Since all of these use an organic interlayer film for matching, there is a risk that harmful gas will be generated in a high temperature state at the time of a fire, and the shape cannot be maintained, so that the fire prevention performance is weak.

There is also a device in which a metal having a watermark is sandwiched in a space between two glass plates (Actual No. 56-14673).
4). Further, there is a light-transmitting surface material in which a thin metal plate having a punched hole is adhered to one glass plate (Shokai Sho 63-11632).
6). Neither of these two devices can be expected to have sufficient fire protection.

A laminated glass in which a PET film is sandwiched between heat-resistant low-expansion transparent crystallized glass and ordinary soda-lime glass or low-expansion borosilicate glass is disclosed as a fire and safety glass plate. (JP-A-6-48
786). This is also inadequate in terms of crime prevention because of its thin film thickness.

There is a device in which a thin metal plate having a watermark is sandwiched between two glass plates and the thin metal plate and the glass plate are fused by induction heating (Japanese Patent Laid-Open No. 6-56485). This method has a drawback in that the glass sheet is likely to be cracked because the thin metal plate is rapidly heated.

[0007] Further, there is a fire / security glass that has been devised such that an electrically conductive pattern is formed on the surface of the meshed glass and an alarm is issued by utilizing the fact that if the glass is broken, it will not conduct electricity. There are fears and it is impossible to prevent the intrusion of intentional criminals.

[0008]

Recently, there has been a demand for a translucent material having both fireproof property and crime prevention property for entrance doors of high-rise apartment houses. In the case of laminated glass, it is necessary to use an organic interlayer film, and since this interlayer film is generally flammable, it is difficult to expect its function as a Class A or Class B fire door. There are some organic thin films that are difficult to burn, but they are very expensive and have problems with adhesion. On the other hand, if fire protection is important,
As can be seen in the glass plate with metal mesh, it cannot be provided with impact resistance and penetration resistance enough to prevent the intentional intrusion of criminals.

An object of the present invention is to provide a translucent glass plate window having fireproof performance for blocking flames and the like, excellent shock resistance in normal times, and crime prevention performance in which a through hole is hardly formed.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above-mentioned object, and as a result, have achieved a light-transmitting property having both fire and crime prevention properties without using an organic material such as an interlayer film. I found the structure of the glass window. That is, according to the present invention, a metal thin plate having a watermark portion is interposed between at least two glass plates, and the surface of the metal thin plate and the glass plate surface opposite thereto are bonded by a frit to form an integrated structure. It is a characteristic fire and crime prevention window glass.

The window glass for fire / crime prevention according to the present invention is 2
It has an integrated structure in which at least one thin metal plate having a predetermined thickness is sandwiched and adhered between one or three or more glass plates. The metal sheet has a plurality of watermark portions separated from each other. This watermark makes the window glass transparent. The surface of the thin metal plate and the surface of the glass plate facing it are adhered by a frit. As the frit, it is possible to use one widely used in electronic parts and the like as an inorganic material for adhering and sealing glass to glass, metal to metal, or metal and glass. The frit is mixed with an organic solvent called a vehicle, applied on both sides of a thin metal plate, sandwiched between glass plates, and heated at the frit fusion temperature to create a fire and crime prevention glass in which the thin metal plate and the glass plate are integrated. can get.

In the present invention, by selecting the difference in the coefficient of thermal expansion of the glass plate, the frit and the metal thin plate within a predetermined range, the glass plate and the metal thin plate may come off during the cooling process of the heat treatment or during use. It is possible to prevent the glass plate from being cracked easily due to a large strain remaining after the bonding. Usually, the coefficient of thermal expansion of the glass of soda lime silicate composition used as a glass plate,
It is about 85 × 10 ⁻⁷ / ° C. at 30 to 350 ° C. It is preferable that the difference in the coefficient of thermal expansion between the thin metal plate and the glass plate is as small as possible because the risk of damage due to the generation of thermal stress is small. By selecting a frit having an appropriate coefficient of thermal expansion between the glass plate and the metal thin plate, the generated thermal stress is relieved. Therefore, the coefficient of thermal expansion of the metal thin plate is 70 to 1
The integrated structure can be maintained by using a material in the range of 30 × 10 ⁻⁷ / ° C. (30 to 350 ° C.). At this time, the coefficient of thermal expansion of the frit is 80 to 120 × 10 ⁻⁷ / ° C. (30 to
If the temperature is 350 ° C), the integrated structure can be maintained and
The glass will not break. As a material of the thin metal plate in such a thermal expansion coefficient range, for example, Sylvani
a # 4 (42Ni-6Cr-Fe), SUS410 (1
3Cr-Fe), SUS430 (18Cr-Fe), Ca
rpenter 52 (50Ni-Fe) and the like.

In the present invention, the temperature at which the heat treatment is performed by sandwiching the frit-coated thin metal plate between the glass plates is lower than the softening point (about 750 ° C.) of the glass plate, so that the smoothness of the glass plate surface is affected. The glass plate portion facing the watermark of the metal thin plate is not softened and deformed and the surface smoothness is not impaired. Therefore, since the light travels straight through the glass plate portion, not only the translucency but also the transparency can be maintained. As the frit, an amorphous frit having a sealing temperature of 400 to 750 ° C. or a crystalline frit having a sealing temperature of 750 ° C. or lower is preferable. If the amorphous frit is less than 400 ° C., the frit is softened when a fire occurs, the integrated structure cannot be maintained, and the fire prevention performance is deteriorated. When the temperature is higher than 750 ° C, the glass plate is softened as described above and the transparency is deteriorated.

There are two types of frit, an amorphous system which retains a glass state after heat treatment and adhesion and a crystalline system which crystallizes.
Although any of them can be used, a crystalline system that is difficult to soften is generally advantageous in view of a fire. Further, considering the environmental measures and the recyclability when discarded, a frit containing no harmful substances such as lead and cadmium is desirable. For example, a frit made of glass made of oxides of silicon, boron, alkali metal and alkaline earth metal and a filler containing no harmful substances such as cordierite and zircon is desirable. It is also possible to color the frit by including various inorganic colorants.

In the present invention, the frit is applied to the entire peripheral edge of the glass sheet which is retracted from the edge of the glass by about 2 to 10 mm from the edge of the glass and does not contact the metal sheet. If the metal thin plates are adhered to each other, the metal thin plates can be completely enclosed in the glass plate, so that the metal thin plates can be prevented from rusting due to intrusion of rainwater. The glass plate portion facing the watermark portion of the metal thin plate is not softened and deformed, and a space is created between the two glass plate portions on both sides of the watermark portion of the metal thin plate.

The thickness of the thin metal plate inserted between the glass plates is preferably 0.1 to 1.0 mm. If it is less than 0.1 mm, the effect of improving impact resistance and penetration resistance is small, and invasion of criminals cannot be suppressed. If it is 1.0 mm or more, the window glass having an integrated structure becomes too heavy. More preferably 0.3-
It is 1.0 mm. If it is 0.3 mm or more, a performance of 10 minutes or more can be obtained in a penetration resistance test described later, which is satisfactory as crime prevention performance.

The shape of the metal watermark is preferably circular, elliptical or polygonal, and the diameter when converted to a circle is preferably in the range of 3 to 20 mm. 3m
If it is less than m, the translucency is not sufficient, and if it exceeds 20 mm, there are problems in penetration resistance and fire resistance. A more preferable diameter range is 6 to 15 mm. Within this range, transparency is improved while ensuring penetration resistance. The aperture ratio of the metal watermark is preferably 20 to 70%. If it is less than 20%, the translucency is not sufficient, and if it exceeds 70%, the penetration resistance and fire resistance are deteriorated. Usually, a plurality of watermark portions having substantially the same size are regularly provided on a thin metal plate by punching or the like.

If a thin metal plate is adhered between adjacent glass plates of three or more glass plates together with a watermark portion, the fireproof performance and the impact resistance performance are dramatically improved while ensuring the light-transmitting property.

The glass plate to be used may be a glass plate which absorbs and reflects heat rays, ultraviolet rays or specific wavelengths in the visible range, in addition to transparent glass. Further, it may be a shaped glass plate, a metal wire or a metal mesh-containing glass plate.

The integrated structure (frit method) for adhering a thin metal plate and a glass plate with a frit has been described above. However, without using a frit, the thin metal plate is sandwiched between the glass plates to heat the glass plate to a softening point or higher. By doing so, an integrated structure can be obtained. (Hereinafter referred to simply as fusion method)

In the fusion method, a thin metal plate is sandwiched between glass plates and heated to a temperature at which the glass plate and the thin metal plates and the glass plates are fused to each other, and an inorganic sealing agent such as frit is used as well as an organic material. The glass plate and the thin metal plate are integrated without doing. In addition, the heating furnace uses fossil fuel such as natural gas or heavy oil, or by an electric resistor such as Nichrome wire,
The entire glass plate is heated so that the glass plate is not cracked by local heating. In the case of the fusion method, since the heat treatment is performed at a softening point or higher, the smoothness of the surface of the glass plate is deteriorated, and thus the transparency is not good, but the transparency is sufficient. The transparency is improved by polishing the surface of the glass plate after the integration process.

The size of the thin metal plate is made slightly smaller than that of the glass plate so that the end of the thin metal plate is 5 mm from the end of the glass plate.
It is preferable that the thin metal plate is completely retracted and the entire peripheral end portion of the glass plate protruding from the end portion of the thin metal plate is fused so that the thin metal plate is completely enclosed in the glass plate and the thin metal plate does not rust. However, if the end of the thin metal plate is retracted much more than the end of the glass plate, air tends to remain between the two glass plates in the open part of the thin metal plate. The temperature distribution of the glass plate such that the central part of the glass plate has a higher temperature than the peripheral part so that the fusion gradually progresses from the central part of the glass plate to the peripheral part to prevent air from remaining. And so on. Also in this respect, rapid heating by induction heating is not preferable. In the case of the fusion method, the range of the coefficient of thermal expansion of the metal sheet that can be used is 80 to 120 as described above.
× 10 ⁻⁷ / ° C. (30 to 350 ° C.). 80 x 10 ^-7
If the temperature is lower than / ° C or higher than 120 × 10 ^-7 / ° C, the glass plate may be cracked or the adhesion may be broken as described above. The thickness of the thin metal plate, the shape and size of the metal watermark portion, the aperture ratio of the metal watermark portion, and the like are the same as in the case of using the frit described above.

[0023]

According to the present invention, the window glass in which the glass plate and the metal thin plate having the watermark portion are integrally structured has a strong adhesion between the metal thin plate and the glass plate via the frit or directly when a fire occurs. Similar to the glass plate with metal mesh, passage of flames and smoke is blocked for a predetermined time without the glass pieces falling off and forming a through hole, and it is effective in preventing the spread of fire. Since a thin metal plate with good thermal conductivity is sandwiched, the temperature difference between the high temperature part in the center of the window glass and the low temperature part in the surroundings, which is heated by flames, is suppressed, and the development of cracks generated from the edge part is prevented by ordinary metal mesh. It is more effective than the fire protection glass that contains it.

Further, in a normal state, since the thin metal plate having a watermark is integrated with the glass plate, it is hard to be deformed and has excellent impact resistance and penetration resistance, and a criminal intentionally damages the window glass of the present invention. Then, even if an attempt is made to invade, it has excellent crime prevention performance because it is not easily intruded. Then, by adjusting the size and aperture ratio of the watermark portion, an appropriate translucency or transparency can be obtained.

[0025]

EXAMPLES Table 1 shows the configurations and performances of Examples (1 to 4 are frit methods in the present invention, 5 to 6 are fusion methods in the present invention) and Comparative Examples. A partial sectional view of Examples 1 to 4 in Table 1 is shown in FIG. A thin metal plate 4 having a watermark 3 between the glass plate 1 and the glass plate 2 is adhered via a frit 5 to form an integrated window glass. FIG. 2 is a partial plan view thereof. FIG. 3 is a partial cross-sectional view of Examples 5-6. The glass plate 1 and the glass plate 2 are fused with the metal thin plate 4 having the watermark portion 3 without the interposition of the frit to form a window glass having an integrated structure.

Each sample in the examples and comparative examples was prepared by the following method. First, the frit method will be described. Watermark portion having an opening diameter (converted diameter) of 6 to 15 mm, an opening ratio of 25 to 82%, and 95 to 180 × 10
Thickness having a coefficient of thermal expansion of ⁻⁷ / ° C. (30 to 350 ° C.).
A metal thin plate of 05 to 0.8 mm and 59 cm square is prepared.
Amorphous frit (composition system; Bi2O3-B2O3-Zn)
O, PbO-B2O3-SiO2, and SIO2-B2O3
-R2O) or crystalline frit (composition system; PbO)
-B2O3-ZnO) vehicle (nitrocellulose 2%
Mixed with a mixed isoamyl acetate), thinly coated on both surfaces of the above metal thin plate, and dried. Next, sandwich this thin metal plate between two glass plates having a thickness of 3 mm or 6.8 mm and a 60 cm square soda-lime silicate composition, with its end part retracted by 0.5 cm from the end part of the entire circumference of the glass plate. The frit mixed with the vehicle is also applied to the outer peripheral portion of the glass plate without the metal sheet before the metal sheet is sandwiched. Then, the sample is placed on a flat shelf and heat-treated in a resistance electric furnace at a temperature of 450 to 630 ° C. for about 30 minutes to obtain a window glass having an integrated structure.

Next, the fusion method will be described. 60 cm
A 59 cm square metal thin plate having a watermark between two square glass plates is sandwiched with its edge retracted 0.5 cm from the edge of the glass plate and placed on a flat shelf plate with a resistance electric furnace. Heat treatment is performed at a temperature of 730 to 770 ° C. for about 45 minutes to obtain a window glass having an integrated structure. The induction heating method in which the heating furnace is rapidly heated is not preferable in terms of crack generation, and a furnace using fossil fuel such as gas or heavy oil may be used instead of the resistance type electric furnace.

The evaluation of Examples and Comparative Examples was carried out as follows. As for the integrated structure, in each sample manufactured by the frit method or the fusion method, if the glass plate and the thin metal plate are not adhered or the glass plate is cracked, it is ×, and the glass plate is integrated without cracking. Those that were present were marked as ○.

The fireproof performance was determined by mounting the sample on one side of a box-type electric furnace, setting a thermometer near the glass surface inside the furnace, and heating it according to the temperature rising curve of the fire extinguisher door test, and then dropping the glass or the through hole. If there was a crack, the glass was cracked but not dropped.

As for the crime prevention performance, impact resistance and penetration resistance were evaluated as follows. Impact resistance is JIS R3205
(Laminated glass) was evaluated according to the shot bag test (Category 3), and the one that conformed was evaluated as ◯. Penetration resistance is similar to that of a burrow, and it took less than 3 minutes x 3 minutes or more to measure the time it took to open the sample in the sash with a flathead screwdriver to open the hole and unlock the crescent lock. The sample was rated as ◯ and the sample that took 10 minutes or more was rated as ◎.

In each of the samples of the frit method of Examples 1 to 4 and the fusion method of 5 to 6, the glass plate and the thin metal plate are integrated, and the predetermined fireproof performance and crime prevention performance are exhibited.

In Comparative Example 1, the coefficient of thermal expansion of the thin metal plate was too large to bond it to the glass plate, resulting in no integrated structure. In Comparative Example 2, the aperture ratio of the metal thin plate is too large, and in Comparative Example 3, the metal thin plate is too thin and the penetration resistance is insufficient, and the predetermined crime prevention performance is not satisfied. In Comparative Example 4, the fusion temperature is too low to be integrated. Comparative Example 5 is an example of a commercially available cloth-type metal mesh-containing glass plate, which has fireproof performance but not crime prevention performance.
Although the cracks of the glass plate with metal mesh have progressed from the peripheral portion to the central portion when the Class B fire door test is carried out, the examples according to the present invention show that the cracks in the peripheral portion are the central portion regardless of the frit method and the fusion method. It is thought that it will be possible to cope with severe fire conditions such as longer time or higher temperature without progressing to the above.
4A and 4B show cracked states of the samples after Example B fire door tests for Example 1 and Comparative Example 5, respectively. In Comparative Example 5, the crack reached the center of the window glass and the fireproof performance was insufficient. However, in Example 1, the crack remains in the peripheral portion of the window glass, and the fire prevention performance is excellent.

[0033]

[Table 1] Table 1 ===================================== Example 1 2 3 4 --- −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Glass plate Transparent 3 mm Transparent 5 mm Transparent 3 mm Transparent 3 mm 2 sheets 2 sheets Heat ray reflection 3 mm 2 Sheet metal sheet Material SUS430 Sylvania # 4 SUS430 SUS430 Thickness mm 0.4 0.2 0.2 0.6 0.8 Coefficient of thermal expansion 10 ⁻⁷ / ° C. 110 95 110 110 (30 to 350 ° C.) Opening diameter mm 6 6 15 3 ( Converted diameter) Aperture ratio% 40 51 68 25 Frit Amorphous system Crystal system Amorphous system Amorphous system PbO-B ₂ O ₃ -SiO ₂ PbO-B ₂ O ₃ -ZnO B ₂ O ₃ -SiO _2- ZnO B ₂ O ₃ -Bi ₂ O ₃ -ZnO -R ₂ O -R ₂ O Sealing temperature ℃ 500 450 630 550 Coefficient of thermal expansion 10 ^-7 / ℃ 110 92 95 85 (30-350 ℃) Fusion temperature ℃ − − − − Integrated structure ○ ○ ○ ○ Fireproof performance ○ ○ ○ ○ Crime prevention performance Impact resistance performance ○ ○ ○ ○ Penetration resistance performance ◎ ○ ◎ ◎ ================ ===================

Table 1 (continued) ===================================== Example Comparative Example 5 6 1 2 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Glass plate Transparent 3 mm Transparent 3 mm 1 sheet Transparent 3 mm Transparent 3 mm 2 sheets 6mm with metal wire 1 2 2 2 Metal thin plate Material Carpenter52 SUS430 SUS304 SUS430 Thickness mm 0.2 0.4 0.4 0.4 0.3 Coefficient of thermal expansion 10 ⁻⁷ / ° C. 95 110 180 110 (30 to 350 ° C.) Opening diameter mm 8 6 6 15 (converted diameter) Opening ratio% 34 61 53 53 82 Frit − − − − Sealing temperature ℃ − − − − Coefficient of thermal expansion 10 ⁻⁷ / ° C. − − − − (30 to 350 ° C.) Fusion temperature ℃ 760 770 770 760 Integrated structure ○ ○ × ○ Fire prevention performance ○ ○ Not evaluated ○ Prevention Performance Impact resistance performance ○ ○ Not evaluated ○ Penetration resistance ○ ◎ Not evaluated × ================================ ====

Table 1 (continued) ===================================== Comparative Example 3 4 5 −− −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Glass plate Transparent 3 mm Transparent 3 mm Cloth with mesh 6.8 mm 2 sheets 2 sheets 1 Sheet Metal thin plate-Material SUS430 SUS430 Plated mild steel wire Thickness mm 0.05 0.4 Thermal expansion coefficient 10 ^-7 / ° C 110 110 (30 to 350 ° C) Opening diameter mm 6 6 (converted diameter) Opening rate% 60 48 Frit crystal System − − Sealing temperature ℃ 500 − − Coefficient of thermal expansion 10 ⁻⁷ / ° C. 92 − − (30 to 350 ° C.) Fusing temperature ℃ − 730 − Integrated structure ○ × ○ Fire prevention performance ○ Not evaluated ○ Crime prevention performance Impact performance ○ Not evaluated ○ Penetration resistance × Not evaluated × ====================== ============

[0036]

INDUSTRIAL APPLICABILITY The fire / security window glass according to the present invention exhibits fire-preventing performance of preventing the spread of fire by blocking the flame for a predetermined time without the glass falling off in the event of a fire, and is normally damaged intentionally by a criminal. Even if an attempt is made, since it has penetration resistance, it does not easily permit its entry, and thus exhibits excellent crime prevention performance. In addition, appropriate translucency or transparency can be obtained.

[Brief description of drawings]

FIG. 1 is a partial sectional view of an embodiment of the present invention.

FIG. 2 is a partial plan view of the embodiment shown in FIG.

FIG. 3 is a partial cross-sectional view of another embodiment of the present invention.

FIG. 4 is a plan view showing a crack state after a fireproof test of an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1; Glass plate 2; Glass plate 3; Watermark part of metal thin plate 4; Metal thin plate 5; Frit 11; Glass plate 12; Glass plate 13; Watermark part of metal thin plate 14; Metal thin plate

Claims (6)

[Claims] 1. A metal thin plate having a watermark is interposed between at least two glass plates, and the surface of the metal thin plate and the glass plate surface opposite thereto are bonded by a frit to form an integrated structure. Fire and crime prevention window glass. 2. The glass plate has a soda lime silicate glass composition, and the thin metal plate is 0.1 to 1.0.
mm thickness, 70-130x at 30-350 ° C
The fire protection according to claim 1, which has a linear expansion coefficient of 10 ^-7 / ° C.
Security window glass. 3. The thin metal plate has a plurality of watermarks each having a circular, elliptical or polygonal shape, each watermark having a diameter of 3 to 20 mm when converted into a circle, and The fire / security window glass according to claim 1 or 2, wherein the thin metal plate has an aperture ratio of 20 to 70%. 4. The fire / security window glass according to claim 1, wherein the frit is an amorphous frit having a sealing temperature of 400 to 750 ° C. or a crystalline frit having a sealing temperature of 750 ° C. or lower. 5. The fire / security window glass according to claim 2, wherein the frit has a linear expansion coefficient of 80 to 120 × 10 ⁻⁷ / ° C. at 30 to 350 ° C. 6. A metal thin plate having a watermark portion is interposed between at least two glass plates having a soda lime silicate glass composition, and the metal thin plate and the glass plate are fused to form an integrated structure, The thin metal plate has a thickness of 0.1 to 1.0 mm, a linear expansion coefficient of 80 to 120 × 10 ⁻⁷ / ° C. at 30 to 350 ° C., and a plurality of watermark portions having a circular, elliptical or polygonal shape. Each of the watermark portions has a diameter of 3 to 20 mm when converted into a circle, and the thin metal plate has a diameter of 20 to 20 mm.
Fire and crime prevention window glass with an aperture ratio of 70%.