GLASS FIBER AND METHOD FOR PRODUCING SAME

Abstract

Provided is a glass fiber having a low spinning temperature and a low liquidus temperature, and besides, having a large difference between the liquidus temperature and the spinning temperature, and a method of manufacturing the same. The glass fiber of the present invention includes as a glass composition, in terms of mass % on an oxide basis, 50% to 65% of SiO.sub.2, 0% to 3% of Al.sub.2O.sub.3, 0% to 1% of MgO, 0% to less than 0.7% of CaO, 0% to 1% of Li.sub.2O, 10% to 20% of Na.sub.2O, 0% to 2% of K.sub.2O, 6% to 10% of TiO.sub.2, and 15% to 20% of ZrO.sub.2, and has a value for (Na.sub.2O+K.sub.2O)/(MgO+CaO) of 6.0 or more.

Claims

1. A glass fiber, comprising as a glass composition, in terms of mass % on an oxide basis, 50% to 65% of SiO.sub.2, 0% to 3% of Al.sub.2O.sub.3, 0% to 1% of MgO, 0% to less than 0.7% of CaO, 0% to 1% of Li.sub.2O, 10% to 20% of Na.sub.2O, 0% to 2% of K.sub.2O, 6% to 10% of TiO.sub.2, and 15% to 20% of ZrO.sub.2, and having a value for (Na.sub.2O+K.sub.2O)/(MgO+CaO) of 6.0 or more.

2. The glass fiber according to claim 1, wherein the glass fiber comprises as a glass composition, in terms of mass % on an oxide basis, 0% to 0.1% of MgO and 0% to 0.6% of Li.sub.2O.

3. The glass fiber according to claim 1, wherein the glass fiber has a spinning temperature of 1,280° C. or less.

4. The glass fiber according to claim 1, wherein the glass fiber has a difference between a spinning temperature and a liquidus temperature of 120° C. or more.

5. The glass fiber according to claim 1, wherein the glass fiber has a liquidus temperature of 1,120° C. or less.

6. The glass fiber according to claim 1, wherein, when glass of a specific gravity fraction obtained by pulverizing and classifying the glass fiber into a particle size of from 300 μm to 500 μm is immersed in 100 ml of a 10 mass % NaOH aqueous solution under conditions of 80° C. and 90 hours, the glass has a mass reduction rate of 4% or less.

7. The glass fiber according to claim 1, wherein, when glass of a specific gravity fraction obtained by pulverizing and classifying the glass fiber into a particle size of from 300 μm to 500 μm is immersed in 100 ml of a 10 mass % HCl aqueous solution under conditions of 80° C. and 90 hours, the glass has a mass reduction rate of 4% or less.

8. The glass fiber according to claim 1, wherein the glass fiber has an alkali elution amount according to JIS R3502 (1995) of 0.35 mg or less.

9. A method of manufacturing a glass fiber, comprising: melting, in a glass melting furnace, a raw material batch blended so as to comprise as a glass composition, in terms of mass % on an oxide basis, 50% to 65% of SiO.sub.1, 0% to 3% of Al.sub.2O.sub.3, 0% to 1% of MgO, 0% to less than 0.7% of CaO, 0% to 1% of Li.sub.2O, 10% to 20% of Na.sub.2O, 0% to 2% of K.sub.2O, 6% to 10% of TiO.sub.2, and 15% to 20% of ZrO.sub.2, and have a value for (Na.sub.2O+K.sub.2O)/(MgO+CaO) of 6.0 or more; and continuously drawing the resultant molten glass from a bushing to form the molten glass into a fiber form.

10. The glass fiber according to claim 2, wherein the glass fiber has a spinning temperature of 1,280° C. or less.

11. The glass fiber according to claim 2, wherein the glass fiber has a difference between a spinning temperature and a liquidus temperature of 120° C. or more.

12. The glass fiber according to claim 3, wherein the glass fiber has a difference between a spinning temperature and a liquidus temperature of 120° C. or more.

13. The glass fiber according to claim 10, wherein the glass fiber has a difference between a spinning temperature and a liquidus temperature of 120° C. or more.

14. The glass fiber according to claim 2, wherein the glass fiber has a liquidus temperature of 1,120° C. or less.

15. The glass fiber according to claim 3, wherein the glass fiber has a liquidus temperature of 1,120° C. or less.

16. The glass fiber according to claim 4, wherein the glass fiber has a liquidus temperature of 1,120° C. or less.

17. The glass fiber according to claim 10, wherein the glass fiber has a liquidus temperature of 1,120° C. or less.

18. The glass fiber according to claim 11, wherein the glass fiber has a liquidus temperature of 1,120° C. or less.

19. The glass fiber according to claim 12, wherein the glass fiber has a liquidus temperature of 1,120° C. or less.

20. The glass fiber according to claim 13, wherein the glass fiber has a liquidus temperature of 1,120° C. or less.

Description

DESCRIPTION OF EMBODIMENTS

[0030] Now, a glass fiber of the present invention is described in detail.

[0031] First, the actions of constituent components of the glass fiber of the present invention and the reasons why the contents of the components are specified as described above are described. In the description of the ranges of the contents of the components, the expression “%” represents “mass %”. In addition, in the present invention, the “spinning temperature” means a temperature at which glass has a viscosity of 10.sup.3 dPa.Math.s, and the “liquidus temperature” means that a temperature at which an initial phase of a crystal serving as a factor for devitrification is deposited.

[0032] SiO.sub.2 is a main component that forms a glass skeleton structure. In addition, SiO.sub.2 is also a component that improves the acid resistance of glass. The content of SiO.sub.2 is from 50% to 65%, preferably from 55% to 60%, more preferably from 57% to 60%. When the content of SiO.sub.2 is too small, the mechanical strength of the glass is liable to be reduced. In addition, the acid resistance of the glass is reduced. Meanwhile, when the content of SiO.sub.2 is too large, the viscosity of the glass is increased, and thus energy required for melting the glass is increased. In addition, a bushing made of a noble metal is severely damaged, and exchange frequency thereof is increased, which results in an increase in production cost. In addition, the alkali resistance of the glass is reduced.

[0033] Al.sub.2O.sub.3 is a component that improves the chemical durability and the mechanical strength of the glass. Meanwhile, Al.sub.2O.sub.3 is also a component that increases the viscosity of the glass. The content of Al.sub.2O.sub.3 is from 0% to 3%, preferably from 0% to 2%, more preferably from 0% to 1%, from 0% to 0.8%, from 0% to 0.7%, or from 0% to 0.6%, most preferably from 0% to 0.5%. When the content of Al.sub.2O.sub.3 is too large, the viscosity of the glass is increased, and thus energy required for melting the glass is increased. In addition, the liquidus temperature of the glass is increased, and thus a difference between the spinning temperature and the liquidus temperature is reduced, which results in a reduction in productivity.

[0034] MgO is a component that reduces the viscosity of the glass and increases the elastic modulus of the glass. The content of MgO is from 0% to 1%, preferably from 0% to 0.5%, more preferably from 0% to 0.1%, still more preferably from 0% to 0.05%, most preferably from 0% to 0.03%.

[0035] However, as described above, in the glass fiber suitable for reinforcing GRC, an initial phase is formed of a crystal in which MgO, CaO, Na.sub.2O, K.sub.2O, and the like are solid solved in zircon (ZrSiO.sub.4). Moreover, of those solid solution components, a Mg ion, which has an ionic radius comparable to that of a Zr ion and is subjected to significantly high electric field strength, is more liable to be energetically stable as a solid solution crystal. As a result, zircon in which Mg is solid solved is liable to be deposited as the initial phase. Accordingly, when the content of MgO is too large, the liquidus temperature of the glass is increased, and thus a difference between the spinning temperature and the liquidus temperature is reduced, which results in a reduction in productivity. Therefore, the glass fiber of the present invention is preferably free of MgO on the design of a composition.

[0036] CaO is a component that reduces the viscosity of the glass and improves the water resistance of the glass. The content of CaO is from 0% to less than 0.7%, preferably from 0.1% to less than 0.7%, more preferably from 0.1% to 0.6% or from 0.2% to 0.6%, most preferably from 0.3% to 0.6%. When the content of CaO is too small, it becomes difficult to obtain the above-mentioned effect. Therefore, the glass fiber of the present invention preferably comprises CaO to the extent that the productivity is not reduced while the water resistance is ensured on the design of a composition. Meanwhile, a Ca ion is also subjected to high electric field strength as with the Mg ion, and hence when the content of CaO is too large, zircon in which Ca is solid solved is liable to be deposited as the initial phase. As a result, the liquidus temperature of the glass is increased, and thus a difference between the spinning temperature and the liquidus temperature is reduced, which results in a reduction in productivity.

[0037] Li.sub.2O is a component that reduces the viscosity of the glass to improve the meltability and the formability of the glass. However, Li.sub.2O has a high raw material cost, and hence the glass fiber of the present invention is preferably free of Li.sub.2O on the design of a composition. Therefore, the content of Li.sub.2O is from 0% to 1%, preferably from 0% to 0.8%, from 0% to 0.6%, or from 0% to 0.5%, more preferably from 0% to 0.4%, most preferably from 0% to 0.3%.

[0038] Na.sub.2O is a component that reduces the viscosity of the glass to improve the meltability and the formability of the glass. The content of Na.sub.2O is from 10% to 20%, preferably from 10% to 18%, more preferably from 12% to 18%, from 12% to 17%, from 13% to 17%, or from 13% to 16%, most preferably from 14% to 16%. When the content of Na.sub.2O is too small, the viscosity of the glass is increased, and thus energy required for melting the glass is increased. In addition, a bushing made of a noble metal is severely damaged, and exchange frequency thereof is increased, which results in an increase in production cost. Meanwhile, when the content of Na.sub.2O is too large, the initial phase in which MgO, CaO, Na.sub.2O, K.sub.2O, and the like are solid solved in zircon (ZrSiO.sub.4) is liable to be deposited. As a result, the liquidus temperature of the glass is increased, and thus a difference between the spinning temperature and the liquidus temperature is reduced, which results in a reduction in productivity. In addition, the water resistance of the glass is reduced.

[0039] K.sub.2O is a component that reduces the viscosity of the glass to improve the meltability and the formability of the glass. The content of K.sub.2O is from 0% to 2%, preferably from 0% to 1.5%, more preferably from 0% to 1%, still more preferably from 0% to 0.8%, most preferably from 0% to 0.5%. When the content of K.sub.2O is too small, the viscosity of the glass is increased, and thus energy required for melting the glass is increased. Meanwhile, when the content of K.sub.2O is too large, the water resistance of the glass is reduced. In addition, a raw material batch is liable to absorb a water content, and an agglomerate of raw material powder (a so-called “lump”) is liable to be formed. The case in which the agglomerate of raw material powder is formed is not preferred because the solubility of the raw material batch is reduced, and undissolved zirconia is liable to remain in a product glass.

[0040] MgO, CaO, Na.sub.2O, and K.sub.2O are each a component that reduces the viscosity of the glass to improve the meltability and the formability of the glass. In addition, those components each have a low raw material cost as compared to Li.sub.2O and are thus suitable for suppressing a manufacturing cost. Therefore, from the viewpoint of the manufacturing cost, MgO, CaO, Na.sub.2O, and K.sub.2O are each preferably incorporated in a larger amount than Li.sub.2O. Meanwhile, as described above, the initial phase of a devitrified crystal is formed of a crystal in which MgO, CaO, Na.sub.2O, K.sub.2O, and the like are solid solved in zircon (ZrSiO.sub.4). Therefore, when the total content of MgO+CaO+Na.sub.2O+K.sub.2O is too large, the initial phase is liable to be deposited, and there is a risk in that the liquidus temperature is increased. Therefore, the total content of MgO+CaO+Na.sub.2O+K.sub.2O is preferably from 10% to 23.5%, from 11% to 20%, from 12% to 18%, or from 13% to 17%.

[0041] The glass fiber of the present invention can maintain high productivity while reducing a raw material cost by strictly controlling a mass ratio of (Na.sub.2O+K.sub.2O)/(MgO+CaO) to 6.0 or more. When the ratio is too small, that is, when the content of Na.sub.2O+K.sub.2O is too small with respect to the content of MgO+CaO, the liquidus temperature of the glass is increased, and thus a difference between the spinning temperature and the liquidus temperature is reduced, which results in a reduction in productivity. Therefore, the mass ratio of (Na.sub.2O+K.sub.2O)/(MgO+CaO) is 6.0 or more, preferably 10 or more, 15 or more, 18 or more, 20 or more, 21 or more, 22 or more, 23 or more, 23.6 or more, 24 or more, or 25 or more, particularly preferably 26 or more. Meanwhile, when the mass ratio of (Na.sub.2O+K.sub.2O)/(MgO+CaO) is too large, there is a risk in that the water resistance of the glass is reduced. Therefore, the mass ratio of (Na.sub.2O+K.sub.2O)/(MgO+CaO) is preferably 3,000 or less, more preferably 2,000 or less, 1,500 or less, 1,000 or less, 500 or less, 300 or less, 100 or less, 80 or less, or 60 or less.

[0042] In addition, the contents of MgO, CaO, Na.sub.2O, and K.sub.2O are preferably such that the expression MgO<CaO<Na.sub.2O and/or the expression MgO<CaO<K.sub.2O is satisfied. With this, the liquidus temperature of the glass is reduced, and thus a difference between the spinning temperature and the liquidus temperature can be increased.

[0043] In addition, the content of MgO+CaO is preferably 1.5% or less, 1.2% or less, 1.0% or less, or 0.7% or less, more preferably 0.6% or less, still more preferably 0.5% or less. With this, the liquidus temperature of the glass is reduced, and thus a difference between the spinning temperature and the liquidus temperature can be increased.

[0044] TiO.sub.2 is a component that improves the water resistance and the alkali resistance of the glass. TiO.sub.2 is also a component that reduces the spinning temperature and significantly reduces the liquidus temperature. The content of TiO.sub.2 is from 6% to 10%, preferably from 6% to 9%, more preferably from 6% to 8.5%, most preferably from 6% to 8%. When the content of TiO.sub.2 is too small, the water resistance and the alkali resistance of the glass are reduced. In addition, the spinning temperature is increased, and thus the production cost is increased. Meanwhile, when the content of TiO.sub.2 is too large, a crystal comprising TiO.sub.2 is liable to be deposited in the glass, and the liquidus temperature is significantly increased. As a result, a difference between the spinning temperature and the liquidus temperature is reduced, which results in a reduction in productivity.

[0045] ZrO.sub.2 is a component that improves the alkali resistance, the acid resistance, and the water resistance of the glass. The content of ZrO.sub.2 is from 15% to 20%, preferably from 17% to 20%, from 17.2% to 19.5%, from 17.2% to 19.0%, from 17.2% to 18.5%, or from 17.5% to 18.5%, most preferably from 17.5% to 18.0%. When the content of ZrO.sub.2 is too small, the alkali resistance is reduced, and durability required for GRC cannot be achieved. Meanwhile, when the content of ZrO.sub.2 is too large, the liquidus temperature of the glass is increased, and thus a difference between the spinning temperature and the liquidus temperature is reduced, which results in a reduction in productivity.

[0046] In addition, the glass fiber of the present invention may comprise components other than the above-mentioned components (SiO.sub.2, Al.sub.2O.sub.3, MgO, CaO, Li.sub.2O, Na.sub.2O, K.sub.2O, TiO.sub.2, and ZrO.sub.2). However, it is desired that the composition be adjusted so that the contents of the above-mentioned components in terms of a total content are 98% or more, particularly 99% or more. The reason for this is as described below. When the total content of the above-mentioned components is less than 98%, there is liable to occur inconvenience such that the alkali resistance, the acid resistance, and the water resistance are reduced owing to unintended mixing of a foreign component, which results in reductions in characteristics as a product, or such that a difference between the spinning temperature and the liquidus temperature is reduced, which results in a reduction in productivity.

[0047] As the components other than the above-mentioned components, for example, trace components, such as H.sub.2, CO.sub.2, CO, H.sub.2O, He, Ne, Ar, and N.sub.2, may each be incorporated up to 0.1%. In addition, a noble metal element, such as Pt, Rh, or Au, may be added up to 500 ppm to the glass.

[0048] Further, in order to improve the alkali resistance, the acid resistance, the water resistance, and the liquidus temperature, B.sub.2O.sub.3, SrO, BaO, ZnO, Fe.sub.2O.sub.3, P.sub.2O.sub.5, Cr.sub.2O.sub.3, Sb.sub.2O.sub.3, SO.sub.3, MnO, SnO.sub.2, CeO.sub.2, Cl.sub.2, La.sub.2O.sub.3, WO.sub.3, Nb.sub.2O.sub.5, Y.sub.2O.sub.3, and the like may be incorporated up to 2% in terms of a total content. From the viewpoint of an environmental load, it is preferred that B.sub.2O.sub.3 be not incorporated in a large amount on the design of a composition. The content of B.sub.2O.sub.3 is preferably less than 1%, less than 0.5%, less than 0.3%, or less than 0.1%.

[0049] Next, the characteristics of the glass fiber of the present invention are described.

[0050] When glass of a specific gravity fraction obtained by pulverizing and classifying the glass fiber of the present invention into a particle size of from 300 μm to 500 μm is immersed in 100 ml of a 10 mass % NaOH aqueous solution under the conditions of 80° C. and 90 hours, the glass has a mass reduction rate of preferably 4% or less, more preferably 3.8% or less, 3.5% or less, 3.3% or less, or 3.1% or less, most preferably 3% or less. When the glass has a high mass reduction rate in this alkali resistance test, the alkali resistance of the glass is reduced, and thus reliability as a reinforcing material for a composite material, such as a calcium silicate board or GRC, is reduced.

[0051] When glass of a specific gravity fraction obtained by pulverizing and classifying the glass fiber of the present invention into a particle size of from 300 μm to 500 μm is immersed in 100 ml of a 10 mass % HCl aqueous solution under the conditions of 80° C. and 90 hours, the glass has a mass reduction rate of preferably 4% or less, more preferably 3.8% or less, 3.5% or less, 3.3% or less, 3.1% or less, 2.9% or less, 2.7% or less, or 2.5% or less, most preferably 2% or less. When the glass has a high mass reduction rate in this acid resistance test, the acid resistance of the glass is reduced, and thus reliability as a corrosion resistant material, such as a battery separator, is reduced.

[0052] The glass fiber of the present invention has an alkali elution amount measured by, as a water resistance test, a method in conformity with JIS R3502 (1995) of preferably 0.35 mg or less, more preferably 0.32 mg or less, most preferably 0.30 mg or less. When the glass fiber has a large alkali elution amount, an alkali component is eluted from the glass during autoclave treatment, and the glass is liable to deteriorate.

[0053] The glass fiber of the present invention has a spinning temperature of preferably 1,280° C. or less, more preferably 1,278° C. or less, 1,276° C. or less, 1,274° C. or less, 1,272° C. or less, or 1,270° C. or less, particularly preferably 1,270° C. or less. When the glass fiber has a high spinning temperature, a bushing made of a noble metal is severely damaged because spinning is required to be performed at high temperature, and exchange frequency thereof is increased, which results in an increase in production cost.

[0054] The glass fiber of the present invention has a difference between the spinning temperature and the liquidus temperature of preferably 120° C. or more, 125° C. or more, 128° C. or more, 130° C. or more, 132° C. or more, 134° C. or more, 136° C. or more, 138° C. or more, 140° C. or more, 141° C. or more, 142° C. or more, 143° C. or more, 144° C. or more, or 145° C. or more, most preferably 146° C. or more. When the glass fiber has a small difference between the spinning temperature and the liquidus temperature, the productivity is reduced.

[0055] The glass fiber of the present invention has a liquidus temperature of preferably 1,120° C. or less, 1,119° C. or less, 1,118° C. or less, 1,117° C. or less, 1,116° C. or less, 1,115° C. or less, 1,114° C. or less, 1,113° C. or less, 1,112° C. or less, 1,111° C. or less, or 1,110° C. or less, most preferably 1,109° C. or less. When the glass fiber has a high liquidus temperature, the productivity is reduced.

[0056] Next, a method of manufacturing a glass fiber of the present invention is described by taking a direct melt method (DM method) as an example. However, the present invention is not limited to the following method, and for example, a so-called indirect forming method (marble melt method: MM method), in which a glass material for fibers formed into a marble form is re-melted and spun with a bushing device, may also be adopted. This method is suitable for producing a wide variety of products in small quantities.

[0057] First, a raw material batch is blended so as to comprise as a glass composition, in terms of mass % on an oxide basis, 50% to 65% of SiO.sub.2, 0% to 3% of Al.sub.2O.sub.3, 0% to 1% of MgO, 0% to less than 0.7% of CaO, 0% to 1% of Li.sub.2O, 10% to 20% of Na.sub.2O, 0% to 2% of K.sub.2O, 6% to 10% of TiO.sub.2, and 15% to 20% of ZrO.sub.2, and have a value for (Na.sub.2O+K.sub.2O)/(MgO+CaO) of 6.0 or more. Glass cullet may be used as part or the whole of glass raw materials. The reasons why the contents of the components are specified as described above have already been described, and the description thereof is omitted.

[0058] Next, the blended raw material batch is loaded into a glass melting furnace to be vitrified, melted, and homogenized. A suitable melting temperature is from about 1,400° C. to about 1,600° C.

[0059] Subsequently, the resultant molten glass is formed into a glass fiber.

[0060] As part of an embodiment, the molten glass is supplied to a bushing, and the molten glass supplied to the bushing is continuously drawn in a filament form from a plurality of bushing nozzles arranged at a bottom of the bushing. A monofilament thus drawn has applied thereon various treatment agents, and a predetermined number of the monofilaments are bundled to obtain a glass strand. The glass fiber of the present invention encompasses not only the above-mentioned glass strand, but also a staple fiber, such as glass wool formed by a centrifugation method, and the monofilament before being bundled into the glass strand.

[0061] The glass fiber of the present invention thus formed is processed into, for example, a chopped strand, a yarn, or a roving, and is used for various applications. The “chopped strand” refers to a product obtained by cutting a glass fiber (strand) obtained by bundling glass monofilaments into a predetermined length. The “yarn” refers to a product obtained by twisting the strand. The “roving” refers to a product obtained by doubling a plurality of strands and winding the strands in a cylindrical shape.

EXAMPLES

Example 1

[0062] Now, the present invention is specifically described by way of Examples. Examples (Sample Nos. 1 to 8 and 17 to 22) of glass for forming the glass fibers of the present invention are shown in Table 1 and Table 3. Comparative Examples (Sample Nos. 9 to 16) are shown in Table 2.

TABLE-US-00001 TABLE 1 No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7 No. 8 SiO.sub.2 mass % 58.6 58.5 58.4 58.4 58.3 58.6 58.6 58.9 Al.sub.2O.sub.3 0.1 0.2 0.2 0.2 0.2 0.2 0.2 0.1 MgO 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 CaO 0.6 0.6 0.6 0.6 0.6 0.6 0.5 0.5 Li.sub.2O 0.3 0.3 0.2 0.2 0.2 0.1 0.1 — Na.sub.2O 14.6 14.8 14.9 14.9 15.1 15.0 15.0 15.2 K.sub.2O 1.2 1.0 0.8 0.7 0.6 0.4 0.4 — TiO.sub.2 7.0 7.1 7.3 7.4 7.5 7.6 7.6 7.8 ZrO.sub.2 17.6 17.5 17.6 17.6 17.5 17.5 17.6 17.5 (Na.sub.2O + K.sub.2O)/(MgO + CaO) — 26.3 25.9 25.7 25.6 25.7 25.2 30.2 29.8 Spinning temperature ° C. 1,254 1,253 1,255 1,258 1,258 1,261 1,262 1,271 Liquidus temperature 1,113 1,113 1,114 1,113 1,107 1,102 1,108 1,110 Spinning 141 141 142 145 151 159 154 161 temperature-liquidus temperature Acid resistance % — 0.7 — — — — — 0.7 Alkali resistance — 2.9 — — — — — 2.9 Water resistance mg — 0.28 — — — — — 0.26 (alkali elution amount)

TABLE-US-00002 TABLE 2 No. No. No. No. No. No. No. No. 9 10 11 12 13 14 15 16 SiO.sub.2 mass % 57.2 54.9 57.2 56.8 57.2 65.1 58.2 59.3 Al.sub.2O.sub.3 0.2 0.1 0.2 0.2 0.2 0.2 0.3 0.4 MgO 0.5 4.0 0.02 0.01 0.02 0.01 0.02 0.02 CaO 1.0 0.5 0.7 0.7 1.0 1.1 2.2 3.4 Li.sub.2O — — — 0.4 — — — — Na.sub.2O 15.5 15.1 15.5 15.5 15.5 15.5 15.2 14.8 K.sub.2O 0.3 — 1.4 1.1 0.8 0.6 0.7 0.5 TiO.sub.2 7.8 7.8 7.5 7.8 7.8 — 5.9 4.0 ZrO.sub.2 17.5 17.6 17.5 17.5 17.5 17.5 17.5 17.6 (Na.sub.2O + K.sub.2O)/(MgO + CaO) — 10.5 3.4 23.5 23.4 16 14.5 7.2 4.5 Spinning temperature ° C. 1,240 1,251 1,251 1,251 1,248 1,250 1,251 1,262 Liquidus temperature 1,184 1,304 1,140 1,140 1,135 1,132 1,166 1,174 Spinning 56 −53 111 111 113 118 85 88 temperature-liquidus temperature Acid resistance % — — 0.6 — — — — — Alkali resistance — — 2.9 — — — — — Water resistance mg — — 0.29 — — — — — (alkali elution amount)

TABLE-US-00003 TABLE 3 No. 17 No. 18 No. 19 No. 20 No. 21 No. 22 SiO.sub.2 mass % 58.8 58.5 57.1 58.5 57.6 55.8 Al.sub.2O.sub.3 — 0.2 0.2 0.2 0.2 0.1 MgO 0.01 — 0.01 0.01 0.01 0.01 CaO 0.6 0.6 — 0.6 0.4 0.3 Li.sub.2O 0.3 0.3 0.2 0.2 0.5 0.4 Na.sub.2O 14.3 14.8 14.9 15.1 14.0 14.3 K.sub.2O 1.2 1.0 0.8 0.6 0.8 1.5 TiO.sub.2 7.0 7.1 9.0 7.6 8.3 8.6 ZrO.sub.2 17.8 17.5 17.8 17.2 18.2 19.0 (Na.sub.2O + K.sub.2O)/(MgO + CaO) — 25.4 26.3 1,570 25.7 36.1 51 Spinning temperature ° C. 1,260 1,255 1,264 1,254 1,260 1,266 Liquidus temperature 1,119 1,110 1,113 1,108 1,119 1,120 Spinning 141 145 151 146 141 146 temperature-liquidus temperature Acid resistance % — 0.7 — — — — Alkali resistance — 2.9 — — — — Water resistance mg — 0.28 — — — — (alkali elution amount)

[0063] Each of the samples shown in the tables was prepared as described below.

[0064] First, various glass raw materials, such as a natural raw material and a chemical raw material, were weighed and mixed so as to give the glass composition shown in the table to produce a raw material batch. Next, the raw material batch was loaded into a crucible made of a platinum-rhodium alloy, and was then heated at 1,550° C. for 5 hours in an indirect heating electric furnace to obtain molten glass. In order to obtain homogeneous molten glass, the molten glass was stirred a plurality of times with a heat-resistant stirring rod. Subsequently, the obtained molten glass was poured out into a refractory mold to be formed into a sheet-shaped glass, and was then subjected to annealing treatment in an annealing furnace (the glass was heated at a temperature higher than the temperature at which the glass had a viscosity of 10.sup.13 dPa.Math.s by from 30° C. to 50° C. for 30 minutes, and was then reduced in temperature at a rate of 1° C./min in a temperature region of from an annealing point to a strain point). Each of the obtained samples was measured for alkali resistance, acid resistance, an alkali elution amount, a spinning temperature, and a liquidus temperature.

[0065] The spinning temperature was measured as described below. First, the above-mentioned sheet-shaped glass sample was crushed into appropriate dimensions, and was loaded into a crucible made of alumina so as to prevent inclusion of bubbles to the extent possible. Subsequently, the crucible made of alumina was heated to bring the glass sample into the state of a melt, and the viscosity of the glass was measured at a plurality of temperatures by a platinum sphere pull up method. After that, a viscosity curve was created based on the obtained plurality of measured values, and the temperature at which the glass had a viscosity of 10.sup.3 dPa.Math.s was calculated by interpolation.

[0066] The liquidus temperature was measured as described below. First, the above-mentioned sheet-shaped glass sample was pulverized and adjusted to a particle size falling within the range of from 300 μm to 500 μm, and was filled in a refractory container under the state of having an appropriate bulk density. Subsequently, the refractory container was loaded into a temperature gradient furnace of an indirect heating type set to a maximum temperature of 1,350° C. and left to stand still, and a heating operation was performed in the air atmosphere for 16 hours. After that, a test body was taken out of the temperature gradient furnace together with the refractory container and cooled to room temperature. After that, the liquidus temperature was specified with a polarizing microscope.

[0067] The difference between the spinning temperature and the liquidus temperature was calculated from both the values.

[0068] The acid resistance was measured as described below. First, the above-mentioned sheet-shaped glass sample was pulverized, and only glass of a specific gravity fraction having a particle size in terms of a diameter of from 300 μm to 500 μm was precisely weighed, and the glass was subsequently immersed in 100 ml of a 10 mass % HCl solution and shaken under the conditions of 80° C. and 90 hours. After that, the mass reduction rate of the glass sample was measured. A smaller value for the mass reduction rate indicates more excellent acid resistance.

[0069] The alkali resistance was measured as described below. First, the above-mentioned sheet-shaped glass sample was pulverized, and only glass of a specific gravity fraction having a particle size in terms of a diameter of from 300 μm to 500 μm was precisely weighed, and the glass was subsequently immersed in 100 ml of a 10 mass % NaOH solution and shaken under the conditions of 80° C. and 90 hours. After that, the mass reduction rate of the glass sample was measured. A smaller value for the mass reduction rate indicates more excellent alkali resistance.

[0070] The alkali elution amount indicating the water resistance was measured by a method in conformity with JIS R3502 (1995). A smaller value for the alkali elution amount indicates more excellent water resistance.

[0071] As apparent from Table 1 and Table 3, in each of Sample Nos. 1 to 8 and 17 to 22 serving as Examples, the spinning temperature and the liquidus temperature of the glass were 1,271° C. or less and 1,120° C. or less, respectively, and the difference between the spinning temperature and the liquidus temperature of the glass was 141° C. or more. Thus, each of Sample Nos. 1 to 8 and 17 to 22 was excellent in productivity. Further, the mass reduction rates serving as indicators of the acid resistance and the alkali resistance were each 4% or less, and the alkali elution amount serving as an indicator of the water resistance was 0.35 mg or less.

[0072] In contrast, in each of Sample Nos. 9 to 16 serving as Comparative Examples, the liquidus temperature was high, and the difference between the spinning temperature and the liquidus temperature was small. Specifically, the liquidus temperature was 1,132° C. or more, and the difference between the spinning temperature and the liquidus temperature of the glass was less than 120° C. Thus, stable continuous production becomes difficult.

Example 2

[0073] Next, raw material batches blended so as to give the glass compositions of Sample Nos. 1 to 8 and 17 to 22 shown in Table 1 and Table 3 were each loaded into a glass melting furnace, melted at a temperature of from 1,400° C. to 1,600° C., and homogenized. Subsequently, the obtained molten glass was supplied to a bushing, and was continuously drawn in a filament form from bushing nozzles arranged at a bottom of the bushing. A treatment agent was applied to a monofilament thus obtained, and 2,000 to 4,000 of the monofilaments were bundled to obtain a glass strand.

INDUSTRIAL APPLICABILITY

[0074] The glass fiber of the present invention is suitable as a reinforcing material for GRC, and as well, as a reinforcing material for a calcium silicate board and as a corrosion resistant material, such as a battery separator.