JPH09124338A - Tempered glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tempered glass having extremely high abrasion resistance. SOLUTION: This tempered glass is obtained by subjecting a glass board substantially composed of SiO2 : 74-83, B2 O3 : 0-5, SiO2 +B2 O3 : 74-83, MgO: 0-10, CaO: 0-10, ZnO: 0-10, Na2 O+K2 O+Li2 O: 12-23 and Al2 O3 : 0-5 by wt.% and having a density of <=2.45g/cc and a thermal expansion coefficient of >=80×10<-7> / deg.C to a thermally tempering treatment consisting of heating and subsequent quenching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tempered glass which is manufactured using a glass which has a low density and is excellent in scratch resistance and which can be easily tempered like conventional soda lime glass.

[0002]

2. Description of the Related Art Conventionally, tempered glass has been used for vehicles, constructions, etc., and has been used as a glass that has the drawback of being easily broken. The tempered glass for vehicles and buildings is produced by a heat strengthening method in which a glass plate manufactured by the float method is heated to near the softening point temperature and then air is blown onto the surface to rapidly cool it.

This method utilizes the heat shrinkage during cooling,
Since the surface is first cooled and shrunk and then the inner part is shrunk, compressive stress remains on the glass surface and the strength of the glass is improved. Also, from the viewpoint of scratch resistance, the tempered glass has a compressive stress remaining on the surface thereof, and thus has an effect of suppressing the progress of scratches and has an effect of improving scratch resistance.

As the tempered glass, soda lime silica glass produced by the float method is usually used, and generally has the following composition and a density of about 2.5 g at room temperature.
It is about / cc. SiO ₂ 66 to 75 (wt%), MgO 0 to 5 (wt%), CaO 7 to 12 (wt%), Na ₂ O 12 to 20 (wt%), K ₂ O 0 to 3 (wt%), al ₂ O ₃ 0~ 4 (wt%).

[0005]

Since tempered glass for vehicles and buildings is used outdoors, it is used in an environment where dust from wind and rain is constantly applied. For this reason, even if it is reinforced, the surface is likely to be scratched, which may cause deterioration of the visibility and damage due to the scratch for a long period of time. Further, if the reinforcement is excessively strong, the scratch resistance is improved, but the stress inside the glass becomes too large, and there is a drawback that the glass is easily broken by a slight impact. That is, the improvement in scratch resistance that relies only on heat strengthening has reached the limit.

When glass is used in high-rise buildings and vehicles, it has been a problem that the weight of the glass itself is considerably heavy. There is no essential improvement measure for reducing the weight of the glass, and the weight of the glass has been reduced by reducing the thickness of the glass. Therefore, the weight-reduced glass has a problem that the strength is reduced. Further, since tempered glass is tempered by utilizing the temperature difference between the surface and the inside when the glass is cooled, it is difficult to essentially strengthen tempered glass with a glass of 2.8 mm or less, and weight reduction by thinning tempered glass is limited. Had reached.

It is known from the compositional knowledge that the hardness of soda lime silica glass increases as the content of silica increases, but simply increasing the content of silica decreases the coefficient of thermal expansion, resulting in tempered glass. Was unsuitable as Borosilicate glass containing 10% or more of B ₂ O ₃ is used in physics and chemistry equipment and the like, and it is known as a glass having a low density and being hard to break, but these glasses also have a small thermal expansion coefficient and are tempered glass. Could not be used as

That is, it was generally recognized that the improvement of scratch resistance and the ease of strengthening are contradictory properties, and it is difficult to strengthen glass having high scratch resistance.

It is an object of the present invention to provide a tempered glass having a coefficient of thermal expansion similar to that of ordinary soda lime silica glass, capable of sufficient heat strengthening, and having high scratch resistance and low density. .

[0010]

Means for Solving the Problems That is, the present invention essentially has the following composition, a coefficient of thermal expansion at 50 to 300 ° C. of 80 × 10 ⁻⁷ / ° C. or more, and a density at room temperature: 2.4
It is a tempered glass toughened by heating and quenching a glass plate having a weight of 5 g / cc or less. SiO ₂ 74-83 (wt%), B ₂ O ₃ 0-5 (wt%), SiO ₂ + B ₂ O ₃ 74-83 (wt%), MgO 0-10 (wt%), CaO 0-10 ( % By weight), ZnO 0-10 (% by weight), Na ₂ O + K ₂ O + Li ₂ O 12-23 (% by weight), Al ₂ O ₃ 0-5 (% by weight).

In a preferred embodiment of the present invention, the glass contains 0.5% by weight or more of B ₂ O ₃ . In another preferred embodiment, the glass is B ₂ O ₃
Of 0 to less than 0.5 (% by weight), and the density at room temperature is 2.43 g / cc or less.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The tempered glass referred to in the present invention is a tempered glass that utilizes heat shrinkage of glass called heat tempering or physical tempering, and is used for passenger cars, trucks, buses, railways, ships, aircrafts, etc. Tempered glass used for vehicle windows, headlights, taillights, windows of buildings and houses,
Tempered glass used for building doors, show windows, etc., tempered glass used for furniture such as partitions, desktops, bookshelves, and showcases, office supplies, etc., and tempered glass used for household appliances such as cookware.

According to the present invention, the inventors have found that, in a composition range close to that of conventional soda lime silica glass, the density of glass governs how cracks spread when glass breaks. based on. That is, in a specific composition range, glass having a density of 2.45 g / cc or less is less likely to be broken due to crack extension, and as a result, the strength of the glass itself is high, and the same strengthening as soda lime silica glass is obtained. It is possible to use it as a tempered glass, and it is possible to reduce the number of cracks that extend the surface layer due to friction or impact, and to dramatically improve the scratch resistance.

In the present invention, the brittleness index value B proposed by Lawn et al. Is used as an index of the ease of glass crack extension (BR Lawn and DBMarsh).
all, J. Am. Ceram. Soc., 62 [7-8] 347-350 (1979)). Here, the brittleness index value B (unit: m ^−1/2 ) is defined by the equation (1) from the Vickers hardness H _v of the material and the fracture toughness value K _c .

[0015]

(Equation 1)

A major problem in applying this brittleness index to glass is that the fracture toughness value K _c is difficult to evaluate accurately. Therefore, the present inventor, as a result of studying several methods, regarding the mother glass for tempered glass, when the Vickers indenter is pushed in, the size of the trace of the indenter remaining on the glass surface and the length of cracks generated from the four corners of the trace and It was found that the brittleness can be quantitatively evaluated from the relationship. The relationship is defined by equation (2).

[0017]

(Equation 2)

Here, P is the pushing load of the Vickers indenter (unit: N), and a and c are the diagonal lengths of the Vickers indentations and the crack lengths generated from the four corners (see FIG. 2), respectively. It is the total length of two symmetrical cracks including indenter traces.

By using the dimensions of the Vickers indentation formed on the surface of each glass and the equation (2), the ease of spreading the cracks in the glass can be easily evaluated. A small brittleness index value means that cracks are unlikely to progress,
It serves as an evaluation standard for glass having excellent scratch resistance and strength.

The brittleness index value of the conventional soda lime silica glass is 6800 to 7400 m ^-1/2 , and the brittleness index value is 5000 to 6000 m by thermally strengthening this.
^-1/2 tempered glass is obtained. However, in the measurement in which the Vickers indenter is pushed into the tempered glass, the progress of the scratch is not constant due to the stress on the glass surface, and it is difficult to measure accurately. Therefore, in the following, the brittleness index value of the mother glass before tempering will be used.

In the tempered glass of the present invention, the preferable index of brittleness of the mother glass before tempering is 6000 m ^-1/2 or less,
It is more preferably 5500 m ^-1/2 or less. Since the brittleness index value decreases as the density decreases, the density is set to 2.45 g / cc or less. Since the brittleness index value changes more rapidly especially when the density is around 2.41 to 2.43 g / cc, the density is preferably 2.43 g / cc or less.

In order to maintain an appropriate density, as a constituent component of the tempered glass of the present invention, SiO ₂ is 74 to 83% by weight.
And B ₂ O ₃ is not essential, but is 0 to 5% by weight. Further, the total amount of SiO ₂ and B ₂ O ₃ is 74 to 83% by weight.

In the present invention, the content of B ₂ O ₃ is
It is up to 5% by weight. If it exceeds 5% by weight, it becomes difficult to maintain a large coefficient of thermal expansion. Further, the life of the kiln may be shortened due to the scattering of boric acid during melting. Furthermore, since mechanical properties such as thermal expansion are different from those of soda lime silica glass, it is difficult to simply apply the same device as that of soda lime silica glass to production.

Those containing B ₂ O _{3 in the} glass maintain low brittleness index values up to higher densities. From this viewpoint, the content of B ₂ O ₃ is 0.5 (% by weight) or more, or
₂ O ₃ containing less than 0-0.5 (wt%),
The density is 2.43 g / cc or less, more preferably 2.41.
It is preferable to use a glass having g / cc or less as a mother glass of tempered glass. In the latter case, the inclusion of B ₂ O ₃ is not essential.

Each of MgO, CaO and ZnO is not essential, but may be contained in an amount of 10% by weight or less in order to enhance chemical durability. Al ₂ O ₃ is not essential, but may be contained in an amount of 5% by weight or less in order to enhance chemical durability.

Further, in order to carry out effective heat strengthening,
A glass having a coefficient of thermal expansion α at 300 ° C. of 80 × 10 ⁻⁷ / ° C. or more is thermally strengthened. From the viewpoint of making the thermal expansion coefficient α relatively large, the composition of the glass is Na ₂ O, K ₂ O, L
The total amount of i ₂ O is set to 12 to 23 (% by weight). It is preferably 14 to 23 (% by weight).

In the present invention, "essentially" means that other components can be added as long as the effects of the present invention can be exhibited, that is, as long as the easy strengthening property and the scratch resistance are compatible. There is. Other components include additives for homogenizing glass, coloring agents for controlling transmittance of ultraviolet light, visible light, infrared light, and fining agents.
e ₂ O ₃ , CoO, NiO, CeO ₂ , TiO ₂ , V ₂
O ₅ , Cr ₂ O ₃ , SnO ₂ , Se, SO ₃ , NO ₃ ,
As ₂ O ₃ , Sb ₂ O ₃ , F, Cl and the like are exemplified.

The present invention is basically based on the inventors' finding that the density of glass governs the scratch resistance of glass. Therefore, the tempered glass of the present invention,
Not only is it more resistant to scratches and impacts, but its low density is also effective in reducing the weight of glass.

When a glass containing B ₂ O _{3 in an amount} of 0 to less than 0.5 (% by weight) is used as the tempered glass of the present invention, the brittleness index value B is set to be sufficiently low, and 50 to 300 ° C.
In order to set the coefficient of thermal expansion α at 80 × 10 ⁻⁷ / ° C. or more, it is preferable that the glass has essentially the following components in the above range.

SiO ₂ 75.5-83 (wt%), RO 1-8 (wt%), R ′ ₂ O 14-23 (wt%), RO + R ′ ₂ O 15-24 (wt%), Al ₂ O _{30 to} 5 (wt%), RO / R ′ ₂ O (weight ratio) 0.5 or less. However, R is at least one selected from Mg, Ca, and Zn,
R'is at least one selected from Li, Na, and K.

Here, RO is contained in an amount of 1% by weight or more in order to ensure durability such as water resistance.
The reason why the R ′ ₂ O (weight ratio) is 0.5 or less is to make the brittleness index value sufficiently low.

In particular, the following glasses are preferable in the above range. SiO ₂ 75.5-83 (wt%), MgO 0-8 (wt%), CaO 0-8 (wt%), ZnO 0-8 (wt%), RO 1-8 (wt%), Na ₂ O 0-23 (wt%), K ₂ O 0-10 (wt%), Li ₂ O 0-10 (wt%), R ′ ₂ O 14-23 (wt%), Al ₂ O ₃ 0.5 ~ 5 (wt%).

Here, the reason why Al ₂ O ₃ is contained in an amount of 0.5% by weight or more is to improve durability such as water resistance.

When a glass containing B ₂ O _{3 in an amount} of 0.5 to 5 (% by weight) is used as the tempered glass of the present invention, the brittleness index value is made sufficiently low and at 50 to 300 ° C.
In order to set the coefficient of thermal expansion α at 80 × 10 ⁻⁷ / ° C. or more, it is preferable that the glass has essentially the following components in the above range.

SiO ₂ 74 to 83 (wt%), B ₂ O ₃ 0.5 to 5 (wt%), SiO ₂ + B ₂ O ₃ 75.5 to 83 (wt%), RO 1 to 9 (wt%) ), R ′ ₂ O 14 to 23 (wt%), RO + R ′ ₂ O 15 to 24 (wt%), Al ₂ O _{30 to} 5 (wt%), RO / R ′ ₂ O (weight ratio) 0. 6 or less. However, R is at least one selected from Mg, Ca, and Zn,
R'is at least one selected from Li, Na, and K.

Here, the RO content of 1% by weight or more is to ensure durability such as water resistance.
The reason why R ′ ₂ O (weight ratio) is set to 0.6 or less is to make the brittleness index value sufficiently low.

In particular, the following glasses are preferable in the above range. SiO ₂ seventy-four to eighty-three _{(wt%), B 2 O 3 0.5~} 5 ( _{wt%), SiO 2 + B 2} O 3 75.5~83 ( wt%), MgO 0~ 9 (wt%), CaO 0-9 (wt%), ZnO 0-9 (wt%), RO 1-9 (wt%), Na ₂ O 0-22 (wt%), K ₂ O 0-10 (wt%), Li ₂ O 0-10 (wt%), R ′ ₂ O 14-23 (wt%), RO + R ′ ₂ O 15-24 (wt%), Al ₂ O ₃ 0.5-5 (wt%).

Here, the reason why Al ₂ O ₃ is contained in an amount of 0.5% by weight or more is to improve durability such as water resistance.

[0039]

EXAMPLE In order to investigate the performance of the glass of the present invention, a small sample piece was prepared and evaluated. That is, after charging 200 g of raw material powder of each composition into a platinum crucible, 1450
˜1650 ° C. It was heated and dissolved in the air while stirring for 4 hours. The uniformly melted glass of each composition was poured into a carbon mold to form a plate having a side of about 10 cm and a thickness of 5 mm and cooled. The obtained glass is annealed at 490 to 570 ° C. to remove strain, and then cut and polished to a thickness of 4 m.
m sample.

In order to remove the surface stress due to polishing, the sample polished to a mirror surface was heated to a temperature slightly higher than the strain temperature of glass at 100 ° C./hour, and then held for 3 hours at 60 ° C./hour. It was gradually cooled and used as a sample for evaluation as a glass before tempering. For the evaluation of the tempered glass, a sample was used which was blown with air and rapidly cooled at about 500 ° C./min.

In this way, the brittleness index value B was evaluated for the sample piece from which the surface stress due to polishing was removed. In addition, the scratch resistance of the sample piece from which the surface stress due to polishing was removed and the sample piece after strengthening were evaluated by the amount of abrasion due to sandblasting. That is, a circular area having a diameter of 2 cm was sandblasted at a pressure of 1 kgf / cm ² for 2 minutes, and the amount of wear was converted from the weight reduction of the material. Note that D1
Is the amount of wear of the glass before tempering, and D2 is the amount of wear of the glass after tempering. For D2, only some samples were measured.

The density ρ at room temperature was calculated from the dry weight of the sample and the weight in water by the Archimedes method.

As Examples and Comparative Examples of the present invention, in Tables 1 and 2, the composition of the glass used (% by weight), the density at room temperature ρ (g / cc), and the brittleness index value B (m ^{-1) / 2} ) and wear amount D1 (μm), D2 (μ
m), coefficient of thermal expansion at 50 to 300 ° C α (× 10 ^-7 /
° C). Examples 1 to 18 are examples of the present invention, and Examples 19 to 37 are comparative examples. Molding by melting was possible except for Example 37. Si + B is SiO ₂ and B ₂ O ₃
And the total amount is shown. Blank columns are not measured.

As shown in the results of the sandblast test in the table, in the glasses obtained in Examples 1 to 18, the abrasion amount D1 of the glass before tempering was 24 μm or less, and the scratch resistance was good. The abrasion amount D2 when a part of the glass is quenched and strengthened by blowing air is, for example, 17 μm.
It is below, and it is recognized that the scratch resistance is further improved. The tempered glass of the present invention is JIS R3206, JIS
It is presumed to satisfy the standards of R3211 and JIS R3212.

In Examples 19 to 26, the coefficient of thermal expansion α was 80 ×.
Heat strengthening is difficult at 10 ^-7 / ° C or less, and no improvement in scratch resistance is observed even when a rapid cooling operation by blowing air is performed. In addition, in Examples 27 to 36, the wear amount D2 even after strengthening
Was 20 μm or more, and the scratch resistance was lower than that of the glass of the present invention.

FIG. 1 shows the relationship between the cooling rate and the brittleness index value of the conventional soda lime silica glass (Example 27) and the glass of Example 1 of the present invention. In the figure, black circles indicate conventional soda lime glass, and white circles indicate the glass of the present invention. From the figure,
The higher the cooling rate, the stronger the strengthening. Ordinary tempered glass is 4
Although it is cooled at a very high cooling rate of about 000 ° C./min, here, cooling was performed at 1 to 50 ° C./min which can be controlled by the electric furnace. The glass according to the present invention exhibits scratch resistance equal to or higher than that of conventional tempered glass even in a state where it is hardly tempered, and the scratch resistance is further improved by strengthening.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

According to the tempered glass of the present invention, the scratch resistance of the tempered glass can be remarkably enhanced, and the damage to the glass due to the flaw can be suppressed. Further, the weight of the glass can be reduced at the same time. The present invention can be variously applied within a range that does not impair the effects of the present invention.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the cooling rate and the brittleness index value of the glass of the present invention and the conventional glass.

FIG. 2 is an explanatory diagram illustrating measurement of a brittleness index value.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Takada 1150 Hazawa-machi, Kanagawa-ku, Yokohama, Kanagawa Prefecture Asahi Glass Co., Ltd. Central Research Laboratory (72) Inventor Koichi Nagata 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Asahi Glass Within the corporation

Claims (3)

[Claims] 1. An essentially 50-300 having the following composition:
A tempered glass which is reinforced by heating and quenching a glass plate having a coefficient of thermal expansion of 80 × 10 ⁻⁷ / ° C. or more and a density at room temperature of 2.45 g / cc or less. SiO ₂ 74-83 (wt%), B ₂ O ₃ 0-5 (wt%), SiO ₂ + B ₂ O ₃ 74-83 (wt%), MgO 0-10 (wt%), CaO 0-10 ( % By weight), ZnO 0-10 (% by weight), Na ₂ O + K ₂ O + Li ₂ O 12-23 (% by weight), Al ₂ O ₃ 0-5 (% by weight). 2. The tempered glass according to claim 1, wherein the glass contains B ₂ O _{3 in an amount} of 0.5 (% by weight) or more. 3. The glass contains 0 to 0.5 (% by weight) of B ₂ O _3.
Less than, and has a density at room temperature of 2.43 g / c
The tempered glass according to claim 1, which is c or less.