[發明所欲解決之問題]然而，添加氧化劑時，其本身可能會對分光特性產生不良影響。鑒於上述情況，本發明之目的在於提供一種能夠容易地製造分光特性優異之近紅外線吸收玻璃的方法及裝置。[解決問題之技術手段]本發明之近紅外線吸收玻璃之製造方法之特徵在於：其係包含P及Cu之近紅外線吸收玻璃之製造方法，並且將原料於熔融溫度T1
下進行加熱熔解而製成熔融玻璃後，於低於熔融溫度T1
之保持溫度T2
下保持熔融玻璃。若如此，則於熔融玻璃中，即使銅離子被還原為Cu+
之情形時，藉由在低於熔融溫度之保持溫度下保持熔融玻璃，Cu+
變得容易被氧化為Cu2+
。因此，由於可提高所獲得之近紅外線吸收玻璃所含之銅離子中之Cu2+
之比率，故而變得能夠獲得優異之分光特性。於本發明之近紅外線吸收玻璃之製造方法中，較佳為T1
－T2
為100～600℃。於本發明之近紅外線吸收玻璃之製造方法中，較佳為T1
為900～1400℃。於本發明之近紅外線吸收玻璃之製造方法中，較佳為T2
為800～1100℃。於本發明之近紅外線吸收玻璃之製造方法中，較佳為近紅外線吸收玻璃以質量%計含有P2
O5
20～80%、Al2
O3
2～20%、CuO 0.1～20%、R2
O 0～50%(其中，R為選自Li、Na及K中之至少1種)、R'O 0～50%(其中，R'為選自Mg、Ca、Sr及Ba中之至少1種)。於本發明之近紅外線吸收玻璃之製造方法中，較佳為將於保持溫度T2
下保持熔融玻璃時之熔融玻璃之液面之面積設為S(mm2
)，且將熔融玻璃之深度設為D(mm)之情形時，滿足S/D≧100(mm)之關係。若如此，則空氣中之氧氣變得容易進入熔融玻璃中，熔融玻璃變得容易被氧化。其結果為，對紫外線區域顯示出吸收之Cu+
離子之量因氧化而減少，紫外線～可見光區域之透光率上升，因此變得容易獲得可見光區域之透光率優異之玻璃。於本發明之近紅外線吸收玻璃之製造方法中，較佳為於保持溫度T2
下保持熔融玻璃時，對熔融玻璃中通入氧氣。若如此，則氧氣會進入熔融玻璃中，熔融玻璃變得容易被氧化。其結果為，對紫外線區域顯示出吸收之Cu+
離子之量因氧化而減少，紫外線～可見光區域之透光率上升，因此變得容易獲得可見光區域之透光率優異之玻璃。近紅外線吸收玻璃之製造裝置之特徵在於具有：用以將原料於熔融溫度T1
下進行加熱熔解而獲得熔融玻璃之熔融槽、與用以於低於熔融溫度T1
之保持溫度T2
下保持熔融玻璃之保持槽。藉由使用如此設置有熔融槽與保持槽之製造裝置，可連續地進行原料之加熱熔解、與熔融玻璃之低溫保持，因此可提高生產效率。[發明之效果]根據本發明之製造方法及製造裝置，變得能夠容易地製造分光特性優異之近紅外線吸收玻璃。[Problems to be Solved by the Invention] However, when an oxidizing agent is added, it may adversely affect the spectral characteristics. In view of the foregoing, an object of the present invention is to provide a method and an apparatus capable of easily manufacturing a near-infrared absorbing glass having excellent spectral characteristics. [Technical means to solve the problem] The method for manufacturing a near-infrared absorbing glass of the present invention is characterized in that it is a method for manufacturing a near-infrared absorbing glass containing P and Cu, and the raw material is prepared by heating and melting at a melting temperature T 1 After the molten glass is formed, the molten glass is held at a holding temperature T 2 which is lower than the melting temperature T 1 . In this case, even when copper ions are reduced to Cu + in the molten glass, Cu + is easily oxidized to Cu 2+ by maintaining the molten glass at a holding temperature lower than the melting temperature. Therefore, since the ratio of Cu 2+ in the copper ions contained in the obtained near-infrared absorbing glass can be increased, it becomes possible to obtain excellent spectroscopic characteristics. In the method for manufacturing a near-infrared absorbing glass of the present invention, T 1 to T 2 are preferably 100 to 600 ° C. In the method for manufacturing a near-infrared absorbing glass of the present invention, T 1 is preferably 900 to 1400 ° C. In the method for manufacturing a near-infrared absorbing glass of the present invention, T 2 is preferably 800 to 1100 ° C. In the method for producing a near-infrared absorbing glass according to the present invention, it is preferable that the near-infrared absorbing glass contains P 2 O 5 20 to 80%, Al 2 O 3 2 to 20%, CuO 0.1 to 20%, and R 2 O 0-50% (where R is at least one selected from Li, Na, and K), R'O 0-50% (where R 'is at least one selected from Mg, Ca, Sr, and Ba 1). In the method for manufacturing a near-infrared absorbing glass of the present invention, it is preferable that the area of the liquid surface of the molten glass when the molten glass is held at the holding temperature T 2 is set to S (mm 2 ), and the depth of the molten glass is set to In the case of D (mm), the relationship of S / D ≧ 100 (mm) is satisfied. In this case, oxygen in the air easily enters the molten glass, and the molten glass becomes easily oxidized. As a result, the amount of Cu + ions exhibiting absorption in the ultraviolet region decreases due to oxidation, and the light transmittance in the ultraviolet to visible light region increases. Therefore, it is easy to obtain a glass having excellent light transmittance in the visible light region. In the method for manufacturing a near-infrared absorbing glass of the present invention, it is preferable that oxygen is introduced into the molten glass while the molten glass is maintained at a holding temperature T 2 . If so, oxygen will enter the molten glass, and the molten glass will be easily oxidized. As a result, the amount of Cu + ions exhibiting absorption in the ultraviolet region decreases due to oxidation, and the light transmittance in the ultraviolet to visible light region increases. Therefore, it is easy to obtain a glass having excellent light transmittance in the visible light region. The manufacturing device for near-infrared-absorbing glass is characterized by having a melting tank for heating and melting raw materials at a melting temperature T 1 to obtain a molten glass, and holding at a holding temperature T 2 lower than the melting temperature T 1 . Holding tank for molten glass. By using the manufacturing device provided with the melting tank and the holding tank in this way, the raw material can be continuously heated and melted, and the molten glass can be kept at a low temperature, thereby improving the production efficiency. [Effects of the Invention] According to the manufacturing method and manufacturing apparatus of the present invention, it becomes possible to easily manufacture a near-infrared absorbing glass having excellent spectral characteristics.
本發明之近紅外線吸收玻璃之製造方法之特徵在於：其係包含P及Cu之近紅外線吸收玻璃之製造方法，並且將原料於熔融溫度T1
下進行加熱熔解而製成熔融玻璃後，於低於熔融溫度T1
之保持溫度T2
下保持熔融玻璃。熔融溫度T1
較佳為900～1400℃、1000～1300℃、尤其是1100～1250℃。若熔融溫度T1
過低，則變得難以獲得均質之玻璃。另一方面，若熔融溫度T1
過高，則Cu離子被還原而變得容易從Cu2+
轉化為Cu+
，因此變得難以獲得所需之光學特性。保持溫度T2
較佳為800～1100℃、尤其是850～1000℃。若保持溫度T2
過低，則於保持熔融玻璃之過程中或者成形時變得容易發生失透。另一方面，若保持溫度T2
過高，則Cu+
不被充分地氧化為Cu2+
，而變得難以獲得所需之光學特性。再者，熔融玻璃於保持溫度T2
下之保持時間較佳為1～20小時、尤其是3～18小時。若保持時間過短，則Cu+
不被充分地氧化為Cu2+
，而變得難以獲得所需之光學特性。另一方面，若保持時間過長，則玻璃成分會揮發，而變得難以獲得所需之組成。其結果為，有對耐候性、耐失透性、光學特性等各特性產生不良影響之虞。再者，熔融溫度T1
與保持溫度T2
之差T1
－T2
較佳為100～600℃、150～500℃、尤其是200～400℃。若T1
－T2
過小，則Cu+
不被充分地氧化為Cu2+
，而變得難以獲得所需之光學特性。另一方面，若T1
－T2
過大，則於保持熔融玻璃之過程中或者成形時變得容易發生失透。再者，較佳為將於保持溫度T2
下保持熔融玻璃時之熔融玻璃之液面之面積設為S(mm2
)，且將熔融玻璃之深度設為D(mm)之情形時，滿足S/D≧100(mm)之關係。若如此，則如上所述變得容易獲得可見光區域之透光率優異之玻璃。S/D較佳為200(mm)以上、500(mm)以上、尤其是800(mm)以上。S/D之上限並無特別限定，考慮到製造設備之限制及生產性等，較佳為10000000(mm)以下、500000(mm)以下、尤其是100000(mm)以下。又，較佳為於保持溫度T2
下保持熔融玻璃時，對熔融玻璃中通入氧氣。若如此，則如上所述變得容易獲得可見光區域之透光率優異之玻璃。於藉由本發明之方法而製造近紅外線吸收玻璃之情形時，雖然可使用1個熔融槽使熔融玻璃之溫度如上所述進行變化，但較佳為使用具有用以將原料於熔融溫度T1
下進行加熱熔解而獲得熔融玻璃之熔融槽、與用以於低於熔融溫度T1
之保持溫度T2
下保持熔融玻璃之保持槽的製造裝置。若使用該製造裝置，則將熔融槽與保持槽在各自設定為特定溫度之狀態下適當進行向熔融槽之原料之導入、與熔融玻璃從熔融槽向保持槽之移動，藉此可連續地進行玻璃之生產，因此可提高生產效率。於保持槽中保持一定時間之熔融玻璃於其後被成形為所需形狀。作為成形裝置，使用下拉裝置或輥成形裝置等。成形後之玻璃視需要經過切斷或研磨等後加工而獲得近紅外線吸收玻璃。本發明之近紅外線吸收玻璃之組成只要為包含P及Cu者，則無特別限定，例如可列舉以質量%計含有P2
O5
20～80%、Al2
O3
2～20%、CuO 0.1～20%、R2
O 0～50%(其中，R為選自Li、Na及K中之至少1種)、R'O 0～50%(其中，R'為選自Mg、Ca、Sr及Ba中之至少1種)之磷酸鹽系玻璃。以下，對如此規定玻璃組成之原因進行說明。P2
O5
係為了形成玻璃骨架而不可或缺之成分。P2
O5
之含量較佳為20～80%、35～75%、尤其是50～70%。若P2
O5
之含量過少，則變得難以進行玻璃化，而變得難以獲得所需之光學特性。具體而言，近紅外線吸收特性變得容易降低。另一方面，若P2
O5
之含量過多，則耐候性變得容易降低。Al2
O3
係使耐候性大幅度提昇之成分。Al2
O3
之含量較佳為2～20%、5～17%、尤其是8～14%。若Al2
O3
之含量過少，則變得難以獲得上述效果。另一方面，若Al2
O3
之含量過多，則有熔融性降低而熔融溫度上升之傾向。CuO係用以吸收近紅外線之必須成分。CuO之含量較佳為0.1～20%、0.3～15%、尤其是0.4～13%。若CuO之含量過少，則變得難以獲得所需之近紅外線吸收特性。另一方面，若CuO之含量過多，則紫外線～可見光區域之透光率變得容易降低。又，變得難以進行玻璃化。再者，為了獲得所需之光學特性，CuO之含量較佳為根據板厚而適當進行調整。具體而言，較佳為板厚越小，越增大CuO含量(板厚越大，越減小CuO含量)。R2
O(其中，R為選自Li、Na及K中之至少1種)係使熔融溫度降低之成分。R2
O之含量較佳為0～50%、3～30%、尤其是5～20%。若R2
O之含量過多，則變得難以進行玻璃化。再者，R2
O之各成分之較佳之範圍如下。Na2
O之含量較佳為0～50%、3～30%、尤其是5～20%。Li2
O之含量較佳為0～50%、3～30%、尤其是5～20%。K2
O之含量較佳為0～50%、3～30%、尤其是5～20%。R'O(其中，R'為選自Mg、Ca、Sr及Ba中之至少1種)係改善耐候性並且使熔融性提昇之成分。R'O之含量較佳為0～50%、3～30%、尤其是5～20%。若R'O之含量過多，則於成形時源於R'O成分之結晶變得容易析出。再者，R'O之各成分之含量之較佳之範圍如下。MgO係改善耐候性之成分。MgO之含量較佳為0～15%、尤其是0.4～7%。若MgO之含量過多，則變得難以進行玻璃化。CaO係與MgO同樣地改善耐候性之成分。CaO之含量較佳為0～15%、尤其是0.4～7%。若CaO之含量過多，則變得難以進行玻璃化。SrO亦係與MgO同樣地改善耐候性之成分。SrO之含量較佳為0～12%、尤其是0.3～5%。若SrO之含量過多，則變得難以進行玻璃化。BaO係提高玻璃化之穩定性並且使耐候性提昇之成分。尤其於P2
O5
較少之情形時，容易享受到因BaO產生之玻璃化穩定性之效果。BaO之含量較佳為0～30%、5～30%、7～25%、尤其是7.2～23%。若BaO之含量過多，則於成形過程中源於BaO之結晶變得容易析出。近紅外線吸收玻璃中除了上述成分以外亦可含有下述成分。ZnO係改善玻璃化之穩定性及耐候性之成分。ZnO之含量較佳為0～13%、0.1～12%、尤其是1～10%。若ZnO之含量過多，則熔融性降低，熔融溫度變高，結果變得難以獲得所需之光學特性。又，源於ZnO成分之結晶變得容易析出。再者，尤其於P2
O5
較少之情形時，容易享受到因ZnO產生之玻璃化穩定性之效果。Nb2
O5
及Ta2
O5
係提高耐候性之成分。Nb2
O5
及Ta2
O5
之各成分之含量較佳為0～20%、0.1～20%、1～18%、尤其是2～15%。若該等成分之含量過多，則熔融溫度變高，而變得難以獲得所需之光學特性。再者，Nb2
O5
及Ta2
O5
之合量較佳為0～20%、0.1～20%、1～18%、尤其是2～15%。GeO2
係提高耐候性之成分。GeO2
之含量較佳為0～20%、0.1～20%、0.3～17%、尤其是0.4～15%。若GeO2
之含量過少，則變得難以獲得上述效果。另一方面，若GeO2
之含量過多，則熔融溫度變高，而變得難以獲得所需之光學特性。SiO2
係強化玻璃骨架之成分。又，有使耐候性提昇之效果。SiO2
之含量較佳為0～10%、0.1～8%、尤其是1～6%。若SiO2
之含量過多，則耐候性反而變得容易降低。又，有玻璃化變得不穩定之傾向。又，除了上述成分以外，亦可於無損本發明之效果之範圍內含有B2
O3
、Y2
O3
、La2
O3
、CeO2
、Sb2
O3
等。具體而言，該等成分之含量分別較佳為0～3%、尤其是分別為0～2%。再者，藉由含有氟，能夠使化學耐久性提昇，但氟係環境負荷物質，因此較佳為不含有。近紅外線吸收玻璃之液相溫度較佳為770℃以下、尤其是750℃以下。若液相溫度過高，則於製造步驟(尤其是成形時)變得容易失透。藉由上述方法所獲得之近紅外線吸收玻璃變得能夠達成可見光區域之較高之透光率及近紅外區域之優異之光吸收特性兩者。具體而言，波長550 nm下之透光率較佳為79%以上、尤其是80%以上。另一方面，波長700 nm下之透光率較佳為13%以下、尤其是11%以下，波長1200 nm下之透光率較佳為25%以下、尤其是20%以下。近紅外線吸收玻璃通常使用板狀。厚度較佳為0.01～1.2 mm、尤其是0.05～1.2 mm。若厚度過小，則有機械強度變差之傾向。另一方面，若厚度過大，則有光學裝置之薄型化變得困難之傾向。[實施例]以下，基於實施例，對本發明之近紅外線吸收玻璃之製造方法進行詳細說明，但本發明並不限定於本實施例。(實驗1)將以質量%計成為P2
O5
46.3%、Al2
O3
6.6%、MgO 2.6%、CaO 4.2%、BaO 21.4%、K2
O 16.1%、CuO 2.8%之組成之方式調製之原料粉末投入圓筒狀之鉑坩堝中，於1200℃下進行加熱熔解，藉此製成均質之熔融玻璃。將熔融玻璃冷卻至900℃，於該狀態下保持5小時。其次，將熔融玻璃流出至碳板上，進行冷卻固化後，進行退火。針對所獲得之板狀玻璃，藉由以厚度成為0.5 mm之方式對兩面進行鏡面研磨，而獲得試樣a(近紅外線吸收玻璃)。針對所獲得之試樣，使用分光光度計(島津製作所製造之UV-3100PC)，於波長300～1300 nm之範圍內測定透光率。將結果示於圖1。再者，熔融玻璃之液面之面積設為4416 mm2
，深度設為4.5 mm。另一方面，作為比較例，不經過將熔融玻璃於900℃下進行保持之步驟，除此以外，藉由與上述相同之方式製作試樣甲。針對所獲得之試樣，藉由與上述相同之方式測定透光率。將結果示於圖1。由圖1明確得知，實施例之試樣a與比較例之試樣甲相比，可見光區域之透光率更高，又，將近紅外光進行銳截止。(實驗2)將熔融玻璃之液面之面積與深度變為表1所示，除此以外，藉由與實驗1相同之方式製作試樣b～m，並測定波長500 nm下之透光率。將結果示於表1及圖2。圖2中一併表示資料圖與線性化曲線。再者，熔融玻璃之液面之面積係藉由適當變更所使用之鉑坩堝之尺寸(直徑)而進行調整。[表1]
由表1及圖2明確，於熔融玻璃之液面之面積S與深度D之比S/D為100(mm)以上之情形時，於波長500 nm下顯示出約84%以上之優異之透光率。再者，隨著S/D之值增大，波長500 nm下之透光率亦顯示出提昇之傾向。(實驗3)將熔融玻璃之液面之面積設為4416 mm2
，將深度設為17 mm，及於將熔融玻璃於900℃下進行保持時，對熔融玻璃中通入氧氣，除此以外，藉由與實驗1相同之方式製作試樣n。為了進行比較，亦製作未通入氧氣之試樣乙。針對該等試樣，於波長300～1300 nm之範圍內測定透光率。將結果示於圖3。由圖3明確，若通入氧氣，則可見光區域之透光率變高。The method for manufacturing a near-infrared absorbing glass according to the present invention is characterized in that it is a method for manufacturing a near-infrared absorbing glass containing P and Cu, and the raw materials are heated and melted at a melting temperature T 1 to make molten glass, The molten glass is held at a holding temperature T 2 of the melting temperature T 1 . The melting temperature T 1 is preferably 900 to 1400 ° C, 1000 to 1300 ° C, and particularly 1100 to 1250 ° C. If the melting temperature T 1 is too low, it becomes difficult to obtain a homogeneous glass. On the other hand, if the melting temperature T 1 is too high, Cu ions are reduced, and it becomes easy to convert from Cu 2+ to Cu + . Therefore, it becomes difficult to obtain desired optical characteristics. The holding temperature T 2 is preferably 800 to 1100 ° C, particularly 850 to 1000 ° C. If the holding temperature T 2 is too low, devitrification tends to occur during holding of molten glass or during forming. On the other hand, if the holding temperature T 2 is too high, Cu + is not sufficiently oxidized to Cu 2+ and it becomes difficult to obtain desired optical characteristics. The holding time of the molten glass at the holding temperature T 2 is preferably 1 to 20 hours, particularly 3 to 18 hours. If the holding time is too short, Cu + is not sufficiently oxidized to Cu 2+ and it becomes difficult to obtain desired optical characteristics. On the other hand, if the holding time is too long, the glass component is volatilized and it becomes difficult to obtain a desired composition. As a result, there is a possibility of adversely affecting various characteristics such as weather resistance, devitrification resistance, and optical characteristics. The difference T 1 -T 2 between the melting temperature T 1 and the holding temperature T 2 is preferably 100 to 600 ° C, 150 to 500 ° C, and particularly 200 to 400 ° C. When T 1 -T 2 is too small, Cu + is not sufficiently oxidized to Cu 2+ and it becomes difficult to obtain desired optical characteristics. On the other hand, if T 1 -T 2 is too large, devitrification tends to occur during holding of molten glass or during forming. In addition, it is preferable that when the area of the liquid surface of the molten glass when the molten glass is held at the holding temperature T 2 is set to S (mm 2 ), and the depth of the molten glass is set to D (mm), The relationship between S / D ≧ 100 (mm). As described above, as described above, it becomes easy to obtain a glass having excellent light transmittance in the visible light region. The S / D is preferably 200 (mm) or more, 500 (mm) or more, and particularly 800 (mm) or more. The upper limit of S / D is not particularly limited. In consideration of restrictions on manufacturing equipment, productivity, etc., it is preferably 10,000,000 (mm) or less, 500,000 (mm) or less, and especially 100,000 (mm) or less. In addition, when the molten glass is held at the holding temperature T 2 , it is preferable to pass oxygen into the molten glass. As described above, as described above, it becomes easy to obtain a glass having excellent light transmittance in the visible light region. When the near-infrared absorbing glass is produced by the method of the present invention, although the temperature of the molten glass can be changed as described above using one melting tank, it is preferable to use a material having a temperature for melting the raw material at the melting temperature T 1 . A melting tank for heating and melting to obtain a molten glass, and a manufacturing device for holding the molten glass at a holding temperature T 2 lower than the melting temperature T 1 . When this manufacturing apparatus is used, the melting tank and the holding tank are each set to a specific temperature, and the raw materials are appropriately introduced into the melting tank, and the molten glass is moved from the melting tank to the holding tank. The production of glass can therefore increase production efficiency. The molten glass held in the holding tank for a certain time is then formed into a desired shape. As the forming device, a down-drawing device or a roll forming device is used. The formed glass is subjected to post-processing such as cutting or grinding as necessary to obtain a near-infrared absorbing glass. The composition of the near-infrared absorbing glass of the present invention is not particularly limited as long as it contains P and Cu. Examples include P 2 O 5 20 to 80%, Al 2 O 3 2 to 20%, and CuO 0.1 in terms of mass%. -20%, R 2 O 0-50% (where R is at least one selected from Li, Na, and K), R'O 0-50% (where R 'is selected from Mg, Ca, and Sr And at least one of Ba) phosphate-based glass. The reason why the glass composition is specified in this way will be described below. P 2 O 5 is an indispensable component for forming a glass skeleton. The content of P 2 O 5 is preferably 20 to 80%, 35 to 75%, and especially 50 to 70%. When the content of P 2 O 5 is too small, vitrification becomes difficult, and it becomes difficult to obtain desired optical characteristics. Specifically, the near-infrared absorption characteristics tend to decrease. On the other hand, if the content of P 2 O 5 is too large, the weather resistance tends to decrease. Al 2 O 3 is a component that significantly improves weather resistance. The content of Al 2 O 3 is preferably 2 to 20%, 5 to 17%, and particularly 8 to 14%. When the content of Al 2 O 3 is too small, it becomes difficult to obtain the above effects. On the other hand, when the content of Al 2 O 3 is too large, the meltability tends to decrease and the melting temperature tends to increase. CuO is an essential component for absorbing near-infrared rays. The content of CuO is preferably 0.1 to 20%, 0.3 to 15%, and particularly 0.4 to 13%. When the content of CuO is too small, it becomes difficult to obtain desired near-infrared absorption characteristics. On the other hand, when the content of CuO is too large, the transmittance in the ultraviolet to visible light region tends to decrease. Moreover, it becomes difficult to perform vitrification. In addition, in order to obtain desired optical characteristics, the content of CuO is preferably adjusted appropriately according to the thickness of the plate. Specifically, it is preferable that the smaller the plate thickness, the larger the CuO content (the larger the plate thickness, the smaller the CuO content). R 2 O (wherein R is at least one selected from Li, Na, and K) is a component that lowers the melting temperature. The content of R 2 O is preferably 0 to 50%, 3 to 30%, and especially 5 to 20%. When the content of R 2 O is too large, it becomes difficult to perform vitrification. Furthermore, R is preferably the range of each component 2 O as follows. The content of Na 2 O is preferably 0 to 50%, 3 to 30%, and especially 5 to 20%. The content of Li 2 O is preferably 0 to 50%, 3 to 30%, and especially 5 to 20%. The content of K 2 O is preferably 0 to 50%, 3 to 30%, and especially 5 to 20%. R'O (wherein R 'is at least one selected from the group consisting of Mg, Ca, Sr, and Ba) is a component that improves weather resistance and improves meltability. The content of R'O is preferably 0 to 50%, 3 to 30%, and especially 5 to 20%. When the content of R'O is too large, crystals derived from the R'O component during the forming process tend to precipitate. In addition, the preferable range of content of each component of R'O is as follows. MgO is a component that improves weather resistance. The content of MgO is preferably 0 to 15%, especially 0.4 to 7%. If the content of MgO is too large, vitrification becomes difficult. CaO is a component that improves weather resistance similarly to MgO. The content of CaO is preferably 0 to 15%, especially 0.4 to 7%. If the content of CaO is too large, it becomes difficult to perform vitrification. SrO is also a component that improves weather resistance similarly to MgO. The content of SrO is preferably 0 to 12%, especially 0.3 to 5%. When the content of SrO is too large, it becomes difficult to perform vitrification. BaO is a component that improves the stability of vitrification and improves the weather resistance. Especially when there is little P 2 O 5 , it is easy to enjoy the effect of glass transition stability due to BaO. The content of BaO is preferably 0 to 30%, 5 to 30%, 7 to 25%, and especially 7.2 to 23%. If the content of BaO is too large, crystals derived from BaO will easily precipitate during the forming process. The near-infrared absorbing glass may contain the following components in addition to the above-mentioned components. ZnO is a component that improves the stability and weatherability of vitrification. The content of ZnO is preferably 0 to 13%, 0.1 to 12%, and especially 1 to 10%. When the content of ZnO is too large, the meltability is lowered, and the melting temperature becomes higher. As a result, it becomes difficult to obtain desired optical characteristics. In addition, crystals derived from the ZnO component are easily precipitated. Moreover, especially when there is little P 2 O 5 , it is easy to enjoy the effect of glass transition stability due to ZnO. Nb 2 O 5 and Ta 2 O 5 are components that improve weather resistance. The content of each component of Nb 2 O 5 and Ta 2 O 5 is preferably 0 to 20%, 0.1 to 20%, 1 to 18%, and especially 2 to 15%. When the content of these components is too large, the melting temperature becomes high, and it becomes difficult to obtain desired optical characteristics. The total amount of Nb 2 O 5 and Ta 2 O 5 is preferably 0 to 20%, 0.1 to 20%, 1 to 18%, and especially 2 to 15%. GeO 2 is a component that improves weather resistance. The content of GeO 2 is preferably 0 to 20%, 0.1 to 20%, 0.3 to 17%, and particularly 0.4 to 15%. When the content of GeO 2 is too small, it becomes difficult to obtain the above effects. On the other hand, when the content of GeO 2 is too large, the melting temperature becomes high, and it becomes difficult to obtain desired optical characteristics. SiO 2 is a component that strengthens the glass skeleton. It also has the effect of improving weather resistance. The content of SiO 2 is preferably 0 to 10%, 0.1 to 8%, and especially 1 to 6%. If the content of SiO 2 is too large, the weather resistance tends to decrease. In addition, the glass transition tends to become unstable. In addition to the above components, B 2 O 3 , Y 2 O 3 , La 2 O 3 , CeO 2 , Sb 2 O 3 and the like may be contained within a range that does not impair the effect of the present invention. Specifically, the contents of these components are preferably 0 to 3%, especially 0 to 2%, respectively. In addition, chemical durability can be improved by containing fluorine, but it is preferably not contained because it is a fluorine-based environmentally hazardous substance. The liquidus temperature of the near-infrared absorbing glass is preferably 770 ° C or lower, especially 750 ° C or lower. When the liquidus temperature is too high, devitrification tends to occur during the manufacturing steps (especially during molding). The near-infrared absorbing glass obtained by the above method becomes capable of achieving both a high light transmittance in the visible light region and an excellent light absorption characteristic in the near-infrared region. Specifically, the light transmittance at a wavelength of 550 nm is preferably 79% or more, especially 80% or more. On the other hand, the light transmittance at a wavelength of 700 nm is preferably 13% or less, especially 11% or less, and the light transmittance at a wavelength of 1200 nm is preferably 25% or less, especially 20% or less. The near-infrared absorbing glass is generally plate-shaped. The thickness is preferably 0.01 to 1.2 mm, especially 0.05 to 1.2 mm. If the thickness is too small, the mechanical strength tends to deteriorate. On the other hand, if the thickness is too large, it may be difficult to reduce the thickness of the optical device. [Examples] Hereinafter, a method for manufacturing a near-infrared absorbing glass according to the present invention will be described in detail based on the examples, but the present invention is not limited to the examples. (Experiment 1) Modulated by mass% to P 2 O 5 46.3%, Al 2 O 3 6.6%, MgO 2.6%, CaO 4.2%, BaO 21.4%, K 2 O 16.1%, and CuO 2.8% The raw material powder is put into a cylindrical platinum crucible, and it is heated and melted at 1200 ° C to prepare a homogeneous molten glass. The molten glass was cooled to 900 ° C and kept in this state for 5 hours. Next, the molten glass was poured onto a carbon plate, cooled and solidified, and then annealed. The obtained plate-shaped glass was mirror-polished on both sides so that the thickness became 0.5 mm to obtain a sample a (near-infrared-absorbing glass). With respect to the obtained sample, the light transmittance was measured in the range of 300 to 1300 nm using a spectrophotometer (UV-3100PC manufactured by Shimadzu Corporation). The results are shown in FIG. 1. The area of the liquid surface of the molten glass was set to 4,416 mm 2 and the depth was set to 4.5 mm. On the other hand, as a comparative example, a sample A was produced in the same manner as described above, except that the step of holding the molten glass at 900 ° C was not performed. With respect to the obtained sample, the light transmittance was measured in the same manner as described above. The results are shown in FIG. 1. It is clear from FIG. 1 that the sample a of the example has a higher light transmittance in the visible region than the sample a of the comparative example, and sharply cuts off near-infrared light. (Experiment 2) Except that the area and depth of the liquid surface of the molten glass were as shown in Table 1, samples b to m were prepared in the same manner as in Experiment 1, and the light transmittance at a wavelength of 500 nm was measured. . The results are shown in Table 1 and FIG. 2. The data graph and the linearization curve are shown together in FIG. 2. The area of the liquid surface of the molten glass is adjusted by appropriately changing the size (diameter) of the platinum crucible used. [Table 1] It is clear from Table 1 and FIG. 2 that when the ratio S / D of the area S and the depth D of the liquid surface of the molten glass is 100 (mm) or more, it exhibits an excellent transparency of about 84% or more at a wavelength of 500 nm Photometric. Furthermore, as the value of S / D increases, the transmittance at a wavelength of 500 nm also shows a tendency to increase. (Experiment 3) In addition to setting the area of the liquid surface of the molten glass to 4416 mm 2 and the depth to 17 mm, and maintaining the molten glass at 900 ° C., oxygen was passed through the molten glass. Sample n was produced in the same manner as in Experiment 1. For comparison, Sample B was also made without oxygen. For these samples, the light transmittance was measured in a wavelength range of 300 to 1300 nm. The results are shown in FIG. 3. It is clear from FIG. 3 that when oxygen is introduced, the transmittance in the visible light region becomes high.