Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
2001-12-05
2003-12-02
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S192000, C428S210000, C428S213000, C428S218000, C296S146100, C065S114000, C065S115000
Reexamination Certificate
active
06656597
ABSTRACT:
DISCUSSION OF BACKGROUND
The present invention relates to a laminated glass and a glass plate used for producing the laminated glass.
Heretofore, tempered glass has mainly been used, in a form of single plate, for a shielding window of automobiles. In recent years, however, laminated glass has been used because of its having good security performance and sound insulating properties. The laminated glass is prepared by interposing an interlayer made of polyvinylbutyral or the like between two glass plates and bonding them. Accordingly, even if crushing to the laminated glass is attempted by knocking it with a blunt instrument, the laminated glass can not easily be penetrated because the interlayer has stretching properties. A criminal actor or actors of car such as robbery or burglar often break a window glass, unlock the door and invade into the cabin. If the invasion is not successful in a short time, he or they may give up the criminal act. Accordingly, it will be effective to use the laminated glass, which is difficult to break, as a window glass from the viewpoint of security for automobile.
There are the following publications in which a laminated glass is used for a window glass.
(1) JP-A-4-231361 (hereinafter “JP '361 publication”)
The JP '361 publication discloses a glass plate in which the residual stress in a peripheral region (region A
1
) of the glass plate and the residual stress in a central region (region C
1
) of the glass plate are described.
(2) JP-A-6-503063 (hereinafter “JP '063 publication”)
The JP '063 publication discloses a glass plate in which the residual stress in a peripheral region (region A
2
), the residual stress in a central region (region C
2
) and an intermediate region (region B
2
) between the region A
2
and the region C
2
are described.
(3) JP-A-6-87328 (hereinafter “JP '338 publication”)
The JP '328 publication discloses a glass plate in which the residual stress in an edge region (region B
3
) adjacent to a peripheral region (region A
3
) and the residual stress in a central region (region C
3
) are described.
In each of the publications, the distribution of stress values of a glass plate is described specifically using concrete numerical values which are shown in Tables 1 to 3. In the tables, each tensile stress in a core portion (or an inner portion) indicates the principal stress difference at an intermediate point in a thickness direction of the glass plate, which is known in principle ½ of the compression stress in the surface portion. Accordingly, in Tables 1 and 2 described below, the compression stress in the surface portion which can be estimated from the tensile stress in the core portion is also described. Further, the stress in the edge portion is the principal stress difference in a peripheral portion of the glass plate. In this case, a positive value indicates a compression stress and a negative value indicates a tensile stress.
For example, when two principal stresses perpendicularly crossing to each other are both compression stresses, the principal stress difference has compressive properties, and when two principal stresses perpendicularly crossing to each other are both tensile stresses, the principal stress difference has tensile properties. When either of two principal stresses is a compression stress and the other is a tensile stress, the principal stress difference has compressive properties when the principal stress of compression is stronger, and has tensile properties when the principal stress of tensile is stronger.
TABLE 1
Tensile
Region C
1
Thickness
stress of
Tensile stress
Compression
of plate
core portion
of core portion
stress of
(mm)
of region A
1
(MPa)
surface (MPa)
2.0
54-64
38-60
76-120
3.0
46.7-55
33-55
66-110
TABLE 2
Tensile stress
Compression
Stress of edge
of core
stress of
Thickness
portion of
portion of
surface of
of plate
region A
2
region B
2
region C
2
(mm)
(MPa)
(MPa)
(MPa)
1.5-4
50-100
10 or less
40-100
TABLE 3
Tensile
Region C
3
Thickness
stress of
Tensile stress
Compression
of plate
core portion
of core portion
stress of
(mm)
of region B
3
(MPa)
surface (MPa)
1.5
27-57
25-42
50-84
3.0
20-47
17.5-33
35-66
Here, the generally used method for producing tempered glass and the mechanism of generating the residual stress will be described. The tempered glass is produced by forming a residual compression stress layer in the surface of a glass plate and at the same time, forming a residual tensile stress layer in the core portion. Specifically, the residual stress layers are formed by causing a temperature difference between the surface and the core portion of the glass plate by blowing cooling air to the surface of the glass plate heated to nearly the softening point. If the glass plate has a certain thickness and infinite surface dimensions and if both surfaces are cooled uniformly, the distribution of the stress along its thickness direction exhibits a distribution of substantially parabolic shape. Further, the compression stress in the surface becomes twice as large as the tensile stress in the center in a thickness direction of the glass plate, and the integrated value of stress along the thickness direction becomes “0”.
However, glass plates have actually finite dimensions, and end surfaces exist in the peripheral portion. Accordingly, the glass plate is cooled from not only the surface but also the end surfaces, whereby a region (peripheral region) having a width two or three times as much as the thickness of the glass plate in the peripheral portion in which the principal stress difference averaged in the thickness direction has compressive properties, is produced. Further, at an inner peripheral side of the peripheral region, there is formed a region (intermediate region) in which the principal stress difference averaged in the thickness direction has tensile properties, so as to balance with the compression stress in the peripheral region.
Next, description will be made as to the principal stress difference. When a plane perpendicular to a main surface of the glass plate (a plane cross-sectioned perpendicularly to a main surface of the glass plate) is selected, such plane can take any angle with respect to a linear line extending parallel to the main surface of the glass plate. When a single point is selected in such plane, the stress value acting on this point and having a direction perpendicular to the selected plane can take different values depending on an angle of the selected plane. In various angles, there are an angle at which the stress value is maximal and an angle at which the stress value is minimal. The principal stress direction includes a direction of stress indicating the maximum value and a direction of stress indicating the minimum value, which is perpendicular to the direction indicating the maximum value. In this specification, the direction of stress indicating the maximum value is called as the principal stress direction.
However, the principal stress itself can not directly be measured. Therefore, the principal stress is evaluated indirectly by using the principal stress difference obtained by a photoelasticity method. The principal stress difference obtained by the photoelasticity method corresponds to a value obtained by dividing the sum of the values which are obtained by subtracting the minimum value of stress from the maximum value of stress at each point in all points arranged in a thickness direction of the plate, by the thickness of the plate. Namely, the principal stress difference corresponds to an averaged value obtained by dividing an integrated value of the maximum value of stress minus the minimum value of stress by the thickness of the plate at each point. Accordingly, when a certain point on a main surface of the glass plate is chosen, an average of the integrated value obtained by subtracting the minimum value of stress from the maximum value of stress at each point in the thickness direction of the plate from the selected point is the principal stress difference at the selected po
Asahi Glass Company Limited
Blackwell-Rudasill G. A.
Jones Deborah
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