JPS6025375B2 - Cover glass for mobile watches - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has sufficient strength and hardness required as a cover glass for a wristwatch (hereinafter referred to as a cover glass for a portable watch), and has enough strength and hardness to display a wristwatch. The present invention relates to a watch cover glass that is inexpensive and increases processing efficiency, absorbing ultraviolet rays that are harmful to other parts of the body.

BACKGROUND ART Hitherto, as a cover glass for a wristwatch, a shelf silicate glass that is generally used as an optical cover glass, for example, a glass commonly called old K-7, has been used.

However, in the case of BK-7, the absorption edge in the ultraviolet region is approximately 25 m, so it is
) will transmit most of the light rays. As a result, the surface finish on the display portion of the wristwatch, such as the dial and hands, has become brown or discolored. For this reason, there is a drawback that the surface finish is limited, requiring the use of a paint or the like having excellent weather resistance. Furthermore, digital watches, which have recently replaced conventional analog display watches as multi-functional watches and occupy a large proportion of the product lineup of wristwatches, have had the disadvantage that the liquid crystal display is degraded by ultraviolet rays. Furthermore, in the case of BK-7, the material cost is high, and since the material cannot be made thin, several steps are required to process it to the thickness required for a wristwatch cover glass, resulting in high costs.

The present invention has been made to eliminate the above drawbacks.

That is, Si02 65-73%, Na20 in weight%
10-20%, Ca0 5-15%, Fe203 0.
05~0.2%, Mg○-2~5%, Aso2030-1
~0.5%, S〇30.1~0.5%, and is a strengthened cover glass for wristwatches that has a compressive stress layer formed on the glass surface by contacting with potassium molten salt. The present invention aims to improve processability and ion exchange strengthening effect by increasing Na20 in conventionally used shelf silicate glass such as BK-7, and in the case of optical glass, contamination is particularly avoided. This is a cover glass for wristwatches that is a new attempt to protect the wristwatch display by actively attaching Fe203 to it and taking advantage of the ultraviolet absorption properties of Fe203. Next, the effect of adding each component and the reason for limiting the composition range will be described.

Si02 is a basic substance forming glass and is necessary as a network structure forming material. In ion exchange strengthening, which is carried out to provide sufficient strength as a watch cover glass, the network structure of the glass must be strong so that the strain generated during ion exchange is retained as compressive stress without relaxing. is necessary. When Si02 is less than 65%, the network structure becomes weak, compressive stress generated by ion exchange strengthening is relaxed, and sufficient strength cannot be obtained. When Si02 exceeds 73%, the amount of alkali, which is responsible for strengthening ion exchange, becomes relatively small, resulting in a small amount of ion exchange. It may also become difficult to dissolve. Na
20 has an important influence on the ion exchange effect, and
It is a component that greatly improves the formability in raw material processing.

The higher the amount of Na20, the higher the efficiency of ion exchange reinforcement.
If it exceeds 20%, the amount of non-crosslinked oxygen ions in the glass structure increases, leading to a decrease in glass hardness and chemical durability, and also weakens the glass structure, making it impossible to obtain a glass with high strength. Since Na20 significantly lowers the softening point and improves formability, it becomes easier to process raw materials into plate materials suitable for processing parts such as cover glasses for wristwatches. In order to fully exhibit workability into plate material and ion exchange effect, the amount of Na20 is required to be 10% or more. Ca0 has the effect of improving the solubility of glass and increasing the chemical durability, and the effect becomes more apparent at 5%. However, since Ca0 also has the effect of stopping the movement of alkali ions, the upper limit of Ca0 is 15% in order to enhance the effect of strengthening ion exchange. M
g0 improves the processability of glass, reduces the tendency to devitrify,
Although it increases water resistance, it needs to be 2% or more in order to exhibit these effects, and on the other hand, like Ca○, it needs to be 5% or less because it prevents the movement of alkali ions.

Fe2Q is a component that is effective in absorbing ultraviolet rays, which is the object of the present invention.

Fe203 exhibits absorption in ultraviolet light as a colored ion of Fe30. This effect is desired from 0.05%, and the effect increases as Fe203 increases, but the coloring of the glass becomes obvious, so the upper limit is 0.42% from the viewpoint of appearance.

Conventionally, since optical glass does not want to be colored, it is necessary to strictly suppress the amount of Fe203 in the raw material, and great efforts have been made to obtain high-purity raw materials and melt them in platinum crucibles, making it an expensive raw material for watch cover glass. It had become something. If the composition of Fe203 is within the range of the present invention, an inexpensive material can be used as a raw material, and a reduction in raw material cost can also be realized. Regarding A-203 and S03, 0.1% is unavoidably mixed in when glass is melted industrially and processed into inexpensive plate material used as raw material for watch cover glass, but 0.1% of each is unavoidably mixed. If it is 5% or less, it will not affect the properties of the glass of the present invention. Rather, the addition of 0.1% or more of Aso203 has the effect of reducing the coefficient of thermal expansion, increasing tensile strength, and improving gloss.
It may be actively added within this limited range. Next, as a strengthening treatment liquid, the ions that can freely move in the material of the present invention are N, and the ions that can exchange with Na+ to form an effective compressive stress layer are K0, so potassium melt Salts are most suitable, especially potassium nitrate.

The stress value and depth of the compressive stress layer are optimally 50 to 65k9' side 2 in terms of stress value and 10 to 20A in depth. Deeper burrs are desirable in consideration of handling scratches, etc., but if the processing time is increased to obtain only the depth, the compressive stress value decreases due to the stress relaxation phenomenon, which is not preferable. Therefore, the above stress value depth is the optimum condition. Next, examples and characteristics of the present invention are shown in Table 1 and FIG.

The glass shown in the example has a diameter of 3 mm and a thickness of 1 mm. After finishing by grinding and polishing, ion exchange strengthening was performed in KN03 molten salt at 380-400°C for 1-5 hours. In order to investigate the degree of ion exchange strengthening, the surface compressive stress value and stress layer depth were measured non-destructively using a Toshiba Glass surface stress meter FSM-1000. Regarding the bending stress value, which is an important characteristic value for strength calculation, the fracture load of the above sample after ion-exchange strengthening was measured by simple support on the outer periphery and a circular ring loading method with a diameter IQ snout, and then the fracture was measured according to the formula of mechanics of materials. This is the calculated bending stress. The transmittance curve shown in Figure 1 was measured with a spectrophotometer at 20 m.
This figure shows the vicinity of the absorption edge of each glass in the near-ultraviolet region of the continuous measurements taken from 200 m to 70 m. Table 1 As mentioned above, the glass according to the present invention has relatively good ultraviolet absorption performance and sufficient strength as a cover glass for wristwatches, and its good workability makes it suitable for raw material shape for cover glass processing. It can be processed into a plate material, and is extremely useful for providing cover glasses for wristwatches that are inexpensive and have excellent performance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows transmittance curves of glasses 1 and 2 shown in the conventional BK-7 and in the embodiment according to the present invention. A: Transmittance curve of BK-7 glass, B: Invention Example 1
C: Transmittance curve of glass of Example No. 2 of the present invention. Talented 1!

Claims (1)

[Claims] 1% by weight SiO_265-73%, Na_2O10
~20%, CaO5~15%, Fe_2O_30.05
~0.2%, Mg0.2~5%, Al_2O_30.1
~0.5%, SO_30.1~0.5%, and by contacting with potassium molten salt,
A cover glass for a mobile watch characterized by having a compressive stress layer formed on the glass surface to strengthen it.