以下，對本發明詳細地進行說明，但本發明並不限定於以下之實施形態，可於不脫離本發明之主旨之範圍內任意地變化而實施。又，於本說明書中，表示數值範圍之「～」係以包含其前後所記載之數值作為下限值及上限值之含義使用。 ＜化學強化玻璃之製造方法＞ 本發明之化學強化玻璃之製造方法之特徵在於包含如下步驟： (a)準備包含鹼離子之玻璃板； (b)準備包含離子半徑大於上述鹼離子之其他鹼離子之無機鹽； (c)於露點溫度為20℃以上之環境中，進行上述玻璃板之上述鹼離子與上述無機鹽之上述其他鹼離子之離子交換；以及 (d)去除經上述離子交換之上述玻璃板之表面之一部分。 (玻璃組成) 本發明所使用之玻璃可包含鹼離子，只要為具有能夠成形並藉由化學強化處理而強化之組成者即可，可使用各種組成者。其中，較佳為包含鈉，具體而言，例如可列舉：鋁矽酸鹽玻璃、鈉鈣玻璃、硼矽酸鹽玻璃、鉛玻璃、鹼性鋇玻璃、鋁硼矽酸鹽玻璃等。 玻璃之製造方法並無特別限定，可藉由將所需之玻璃原料投入至連續熔融爐中，以較佳為1500～1600℃加熱熔融玻璃原料並澄清後供給至成形裝置，其後將熔融玻璃成形為板狀並進行緩冷而製造。 再者，玻璃之成形可採用各種方法。例如，可採用下拉法(例如，溢流下拉法、流孔下引法及再曳引法等)、浮式法、滾壓法及加壓法等各種成形方法。其中，就容易於玻璃面之至少一部分產生龜裂，本發明之效果更顯著可見之方面而言，較佳為浮式法。 玻璃之厚度並無特別限制，為了有效地進行化學強化處理，通常較佳為5 mm以下，更佳為3 mm以下，進而較佳為1 mm以下，尤佳為0.7 mm以下。 又，本發明所使用之玻璃之形狀並無特別限定。例如，可採用具有均勻之板厚之平板形狀、於正面與背面中之至少一者具有曲面之形狀及具有彎曲部等之立體形狀等各種形狀的玻璃。 關於本發明之化學強化玻璃之組成，並無特別限定，例如可列舉以下之玻璃組成： (1)以氧化物基準之莫耳%所表示之組成包含50～80%之SiO2
、2～25%之Al2
O3
、0～10%之Li2
O、0～18%之Na2
O、0～10%之K2
O、0～15%之MgO、0～5%之CaO及0～5%之ZrO2
的玻璃 (2)以氧化物基準之莫耳%所表示之組成含有50～74%之SiO2
、1～10%之Al2
O3
、6～14%之Na2
O、3～11%之K2
O、2～15%之MgO、0～6%之CaO及0～5%之ZrO2
，SiO2
及Al2
O3
之含量之合計為75%以下，Na2
O及K2
O之含量之合計為12～25%，且MgO及CaO之含量之合計為7～15%的玻璃 (3)以氧化物基準之莫耳%所表示之組成含有68～80%之SiO2
、4～10%之Al2
O3
、5～15%之Na2
O、0～1%之K2
O、4～15%之MgO及0～1%之ZrO2
的玻璃 (4)以氧化物基準之莫耳%所表示之組成含有67～75%之SiO2
、0～4%之Al2
O3
、7～15%之Na2
O、1～9%之K2
O、6～14%之MgO及0～1.5%之ZrO2
，SiO2
及Al2
O3
之含量之合計為71～75%，Na2
O及K2
O之含量之合計為12～20%，且於含有CaO之情形時，其含量未達1%的玻璃 (5)以氧化物基準之質量%所表示之組成含有65～75%之SiO2
、0.1～5%之Al2
O3
、1～6%之MgO、1～15%之CaO，且Na2
O＋K2
O為10～18%的玻璃 (6)以氧化物基準之質量%所表示之組成含有60～72%之SiO2
、1～10%之Al2
O3
、5～12%之MgO、0.1～5%之CaO、13～19%之Na2
O、0～5%之K2
O，且RO/(RO＋R2
O)為0.20以上且0.42以下(式中，RO表示鹼土類金屬氧化物，R2
O表示鹼金屬氧化物)的玻璃 (7)以氧化物基準之莫耳%所表示之組成含有55.5～80%之SiO2
、12～20%之Al2
O3
、8～25%之Na2
O、2.5%以上之P2
O5
、1%以上之鹼土類金屬RO(RO為MgO＋CaO＋SrO＋BaO)的玻璃 (8)以氧化物基準之莫耳%所表示之組成含有57～76.5%之SiO2
、12～18%之Al2
O3
、8～25%之Na2
O、2.5～10%之P2
O5
、1%以上之鹼土類金屬RO的玻璃 (9)以氧化物基準之莫耳%所表示之組成含有56～72%之SiO2
、8～20%之Al2
O3
、3～20%之B2
O3
、8～25%之Na2
O、0～5%之K2
O、0～15%之MgO、0～15%之CaO、0～15%之SrO2
、0～15%之BaO及0～8%之ZrO2
的玻璃 本發明之化學強化玻璃於玻璃表面具有經離子交換之壓縮應力層。於離子交換法中，對玻璃之表面進行離子交換，形成殘留壓縮應力之表面層。具體而言，於玻璃轉移點以下之溫度下，藉由離子交換將玻璃板表面之離子半徑較小之鹼金屬離子(Li離子及/或Na離子)置換為離子半徑更大之其他鹼離子(Na離子及/或K離子)。藉此，壓縮應力殘留於玻璃之表面，玻璃之強度提高。 於本發明之製造方法中，化學強化處理係藉由將包含離子半徑大於玻璃所包含之鹼離子之其他鹼離子的無機鹽與上述包含鹼離子之玻璃接觸，並進行離子交換而實施。即，玻璃所包含之鹼離子與無機鹽所包含之其他鹼離子進行離子交換。 於玻璃所包含之鹼離子為Na離子之情形時，無機鹽為含有硝酸鉀(KNO3
)之無機鹽，進而，更佳為含有選自由K2
CO3
、Na2
CO3
、KHCO3
、NaHCO3
、Li2
CO3
、Rb2
CO3
、Cs2
CO3
、MgCO3
、CaCO3
、及BaCO3
所組成之群中之至少一種鹽。 例如，於無機鹽中包含硝酸鉀之情形時，硝酸鉀之熔點為330℃，於進行化學強化之玻璃之應變點(通常為500～600℃)以下具有熔點。又，上述鹽之中，除硝酸鉀以外之鹽(以下，亦有稱為「熔劑」之情形)具有將以Si-O-Si鍵為代表之玻璃之網絡切斷的性質。由於進行化學強化處理之溫度較高為數百℃，故而於該溫度下，玻璃之Si-O間之共價鍵被適度切斷，變得易於進行下述之低密度化處理。 再者，將共價鍵切斷之程度亦根據玻璃組成或所使用之鹽(熔劑)之種類、進行化學強化處理之溫度、時間等化學強化處理條件而不同，但認為較佳為選擇自Si伸出之4根共價鍵中之1～2根鍵被切斷之程度之條件。 藉由玻璃表面之Na離子(或Li離子)與無機鹽中之K離子(或Na離子)進行離子交換，而形成高密度之壓縮應力層。作為使玻璃與無機鹽接觸之方法，可為塗佈糊狀之無機鹽之方法、將無機鹽之水溶液噴射於玻璃之方法、將玻璃浸漬於加熱至熔點以上之熔鹽之鹽浴中之方法等，該等中，較理想為浸漬於熔鹽之方法。 熔劑之添加量較佳為0.1 mol%以上，更佳為0.5 mol%以上，進而較佳為1 mol%以上，尤佳為2 mol%以上。又，自生產性之觀點而言，較佳為各鹽之飽和溶解度以下。若過量地添加，則有導致玻璃之腐蝕之虞。例如，於將K2
CO3
用作熔劑之情形時，較佳為24 mol%以下，更佳為12 mol%以下，尤佳為8 mol%以下。 無機鹽除硝酸鉀及熔劑以外，亦可於不損害本發明之效果之範圍內包含其他之化學種類，例如可列舉氯化鈉、氯化鉀、硼酸鈉、硼酸鉀等鹼金屬氯化鹽或鹼金屬硼酸鹽等。該等可單獨添加，亦可組合複數種添加。 (熔鹽之製造) 熔鹽可藉由公知之步驟而製造。例如，於無機鹽為包含硝酸鉀及熔劑之熔鹽之情形時，可藉由製備硝酸鉀熔鹽，接著將熔劑添加至該硝酸鉀熔鹽而獲得。又，作為另一方法，可藉由將硝酸鉀與熔劑混合，接著使該硝酸鉀與熔劑之混合鹽熔融而獲得。 本案發明之製造方法中所使用之熔鹽之Na濃度較佳為500重量ppm以上，更佳為1000重量ppm以上。藉由使熔鹽中之Na濃度為2000重量ppm以上，利用下述之酸處理步驟，低密度層變得易於深化，因此進而較佳。作為Na濃度之上限，並無特別限制，可容許為能夠獲得所需之表面壓縮應力(CS)之範圍內。 再者，於進行過1次以上之化學強化處理之熔鹽中包含自玻璃溶出之鈉。因此，若Na濃度已為上述範圍內，則可將來源於玻璃之鈉直接用作Na源，於Na濃度不足之情形時，或於使用化學強化中未使用之熔鹽之情形時，可藉由添加硝酸鈉等無機鈉鹽而進行調整。 (進行離子交換之步驟) 其次，使用所製備之熔鹽進行化學強化處理。化學強化處理係藉由將玻璃浸漬於熔鹽中，使玻璃中之鹼離子(Li離子或Na離子)與熔鹽中之離子半徑較大之其他鹼離子(Na離子或K離子)進行離子交換(置換)而實施。藉由該離子交換，可使玻璃表面之組成發生變化，形成玻璃表面高密度化之壓縮應力層20[圖2(a)～(b)]。藉由該玻璃表面之高密度化而產生壓縮應力，因此可使玻璃強化。 再者，實際上，由於化學強化玻璃之密度自存在於玻璃之中心之中間層30(主體)之外緣朝向壓縮應力層表面逐漸高密度化，因此，於中間層30與壓縮應力層20之間不存在密度急遽變化之明確之邊界。此處，所謂中間層係指存在於玻璃中心部，被壓縮應力層夾持之層。該中間層與壓縮應力層不同，係未進行離子交換之層。 本發明中之化學強化處理(進行離子交換之步驟)具體而言可按照以下之程序進行。 首先，預熱玻璃，將上述之熔鹽調整為進行化學強化之溫度。其次，將經預熱之玻璃浸漬於熔鹽槽27之熔鹽中特定之時間後，將玻璃自熔鹽中撈出並放置冷卻。再者，較佳為於化學強化處理之前，對玻璃進行根據用途之形狀加工，例如，切斷、端面加工及開孔加工等機械加工。 玻璃之預熱溫度取決於浸漬於熔鹽之溫度，通常較佳為100℃以上。 化學強化溫度較佳為被強化玻璃之應變點(通常為500～600℃)以下，為了獲得更高之壓縮應力層深度，尤其較佳為350℃以上，為了縮短處理時間及促進低密度層形成，更佳為400℃以上，進而較佳為430℃以上。 玻璃之浸漬於熔鹽之時間較佳為1分鐘～10小時，更佳為5分鐘～8小時，進而較佳為10分鐘～4小時。於上述範圍內，可獲得強度與壓縮應力層之深度之平衡優異之化學強化玻璃而較佳。 本發明之製造方法中，藉由增加浸漬玻璃時之熔鹽中之水蒸氣量，可增厚於下述之與酸接觸之步驟中所形成之低密度層。於與鹼接觸之步驟中，能夠去除上述低密度層，因此，可藉由將該低密度層之厚度設為存在於玻璃表面之龜裂或潛在損傷之平均深度以上，而去除低密度層，並去除該龜裂或潛在損傷。因此，可達成化學強化玻璃之優異之面強度。 進行離子交換之步驟係於露點溫度為20℃以上之環境中進行。該露點較佳為30℃以上，更佳為40℃以上，進而較佳為50℃以上，進而更佳為60℃以上。又，上限較佳為設為進行離子交換之無機鹽(熔鹽)之溫度以下。 關於露點溫度(以下，存在簡稱為「露點」之情形)，只要熔鹽之至少界面附近之露點溫度為上述範圍內即可，所謂界面附近意指距熔鹽之界面200 mm以下之區域之環境。可藉由Vaisala DRYCAP(註冊商標)DMT346露點轉換器測定露點。再者，本說明書中之所謂露點，係指認為於熔鹽與熔鹽界面附近之環境之間達成平衡時的值。 藉由於進行離子交換之步驟之前及/或與進行離子交換之步驟同時，將水蒸氣導入至熔鹽及/或熔鹽之界面附近之環境中，可達成上述露點。例如，藉由將水蒸氣供給部附加於熔鹽槽，可將水蒸氣導入至熔鹽及/或熔鹽之界面附近之環境中。 即，可於熔鹽中直接通入藉由水蒸氣供給部供給之水蒸氣本身、或包含水蒸氣之氣體、及水(液體)，亦可將水蒸氣或包含水蒸氣之氣體導入至熔鹽上部之空間。又，亦可於不發生水蒸氣爆炸之範圍內，將水(液體)本身滴加至熔鹽上而導入。 於將水蒸氣或包含水蒸氣之氣體、水(液體)(之後，存在簡稱為「水蒸氣等」之情形)導入時，攪拌或不攪拌熔鹽均可，但於縮短達到平衡為止之時間之方面而言，較佳為進行攪拌。 由於自導入水蒸氣等至達到平衡為止之時間視所導入之氣體或液體之量或水蒸氣濃度、導入方法等而不同，故而無法一概而論，若上述環境之露點穩定，成為固定，則可判斷達到平衡。 包含水蒸氣之氣體可使用不影響化學強化處理之氣體，例如可藉由如圖3所示般，將空氣、氮氣、二氧化碳氣體等乾燥之氣體A導入至經加熱之水24中，而製成包含水蒸氣之濕度較高之氣體(包含水蒸氣之氣體)B。 用作水蒸氣供給源之水24於抑制配管等之水垢沈積之方面而言，較佳為使用離子交換水等純水。又，水24例如係藉由使用水槽25進行水浴等而加熱。又，亦可藉由例如利用鍋爐等加熱水24本身而產生水蒸氣。 作為水蒸氣等之導入方法，更具體而言，可列舉(1)自水蒸氣供給部將包含水蒸氣之氣體B導入至無機鹽(熔鹽26)之上部之空間，(2)自通氣部將包含水蒸氣之氣體B導入至無機鹽(熔鹽26)之中，或(3)將水(液體)直接導入至無機鹽(熔鹽26)等。其中，較佳為藉由上述(1)或(2)形成該環境。 作為將包含水蒸氣之氣體B導入至無機鹽(熔鹽26)之上部之空間之一形態，例如有將自水蒸氣供給部所供給之水蒸氣等藉由噴霧器而噴霧至無機鹽之上部或無機鹽之界面附近的方法。藉由利用噴霧器導入水蒸氣等，而變得易於將無機鹽上部之空間之水蒸氣濃度控制為大致均勻，故而較佳。 再者，水蒸氣供給部、通氣部、導入水(液體)之導入部或噴霧器配合裝置適當地設置即可，並無特別限制。具體而言，噴霧器可為單個，亦可為複數個。尤其是於熔鹽槽為大型之情形，利用複數個噴霧器噴霧水蒸氣等易於將無機鹽上部之空間之水蒸氣濃度控制為大致均勻。 於將包含水蒸氣之氣體導入至熔鹽之上部之空間之情形時，導入至每1 cm3
之氣體中之水蒸氣供給量較佳為0.01 mg/分鐘以上，更佳為0.02 mg/分鐘以上。於將水(液體)直接導入至熔鹽之情形時，導入至每1 cm3
之水之流量較佳為0.01 mg/分鐘以上，更佳為0.02 mg/分鐘以上。 於將包含水蒸氣之氣體直接通入至無機鹽中(熔鹽中)之情形時，導入至每1 cm3
之氣體中之水蒸氣供給量較佳為0.01 mg/分鐘以上，更佳為0.02 mg/分鐘以上。 藉由實施於水蒸氣量(水分量)較多之熔鹽中進行離子交換之步驟，所獲得之化學強化玻璃之面強度變得更高之原因考慮如下。 若形成熔鹽之碳酸根離子與水發生反應，則如下述式所示般，生成碳酸氫根離子與氫氧化物離子。 [化1]此處，若熔鹽中之水分量較多，則上述式中之平衡向右傾斜，較多地生成碳酸氫根離子與氫氧化物離子。由於氫氧化物離子係促進玻璃網絡之切斷之離子，故而認為藉由生成更多之氫氧根離子而促進玻璃表面之低密度層之形成。 無機鹽中之藉由下式所得之碳酸根陰離子濃度與碳酸氫根陰離子濃度之和較佳為4 mol%以上，更佳為6 mol%以上。藉由使該濃度為4 mol%以上，可促進玻璃表面之低密度層形成反應，因此較佳。 ｛(碳酸根陰離子濃度)＋(碳酸氫根陰離子濃度)｝(mol%)＝｛(無機鹽中之碳酸根陰離子量)＋(無機鹽中之碳酸氫根陰離子量)｝(mol)/(無機鹽中之總陰離子量)(mol)×100 再者，由於無法直接測定熔鹽中之碳酸根陰離子濃度及碳酸氫根陰離子濃度，故而將熔鹽取出一部分，使用二氧化碳計TiN-9004，以純水稀釋市售標準溶液(NaHCO3
)並製作校準曲線後，測定以純水稀釋為130倍之試樣溶液。此時，由於碳酸氫根陰離子全部轉換為碳酸根陰離子，故而由測定所檢測出之碳酸根陰離子濃度之值相當於碳酸根陰離子濃度與碳酸氫根陰離子濃度之和。 又，碳酸根陰離子濃度與碳酸氫根陰離子濃度之和為飽和碳酸根陰離子濃度及飽和碳酸氫根陰離子濃度之和以下。 該低密度層係藉由下述之去除玻璃板之表面之一部分之步驟中之與酸接觸之步驟而形成，其厚度於不導入水蒸氣之先前之進行離子交換之步驟中為100～200 nm左右，與此相對，可藉由於導入水蒸氣且露點溫度為20℃以上之環境中進行離子交換，而使該厚度為300 nm以上。 由於在玻璃製造步驟或包含化學強化處理步驟之玻璃加工步驟中所產生之玻璃表面之龜裂或潛在損傷之平均深度為約500 nm，故而低密度層之厚度更佳為500 nm以上，進而較佳為600 nm以上。 所形成之低密度層可藉由去除玻璃板之表面之一部分之步驟中之下述與鹼接觸之步驟而去除。因此，若玻璃表面之上述龜裂或潛在損傷之深度均較低密度層之厚度淺，則可藉由與鹼接觸之步驟而將該等龜裂及潛在損傷全部去除。 藉由去除成為化學強化玻璃之強度下降之原因的玻璃面之龜裂或潛在損傷，可使化學強化玻璃之面強度更高。 (進行洗淨之步驟) 本發明之製造方法中，較佳為於進行離子交換之步驟與去除玻璃板之表面之一部分之步驟之間進而包含洗淨玻璃板之步驟。於進行洗淨之步驟中，使用工業用水、離子交換水等進行玻璃之洗淨。工業用水係視需要使用經處理者。尤其是較佳為離子交換水。 洗淨之條件根據所使用之洗淨液而不同，於使用離子交換水之情形時，於0～100℃下進行洗淨就可將所附著之鹽完全去除之方面而言較佳。 於進行洗淨之步驟中，可使用將化學強化玻璃浸漬於放入有離子交換水等之水槽中之方法、或將玻璃表面暴露於流水下之方法、藉由噴水器將洗淨液朝向玻璃表面噴射之方法等各種方法。 (去除玻璃板之表面之一部分之步驟) 將經離子交換之玻璃板供至將該玻璃板之表面之一部分去除之步驟。將玻璃板之表面之一部分去除之步驟較佳為包含使玻璃板與酸接觸之步驟，更佳為於上述與酸接觸之步驟之後，進而包含使玻璃板與鹼接觸之步驟。 (與酸接觸之步驟) 於本發明之製造方法中，作為於上述進行離子交換之步驟或上述進行洗淨之步驟之後去除玻璃板之表面之一部分的步驟，較佳為進行使玻璃與酸接觸之步驟(酸處理步驟)。 所謂玻璃之酸處理，係藉由將化學強化玻璃浸漬於酸性之溶液中而進行，藉此，可將化學強化玻璃表面之Na及/或K置換為H。即，於玻璃表面進而具有壓縮應力層之表層發生變質、具體而言低密度化而成之低密度層。 溶液只要為酸性，則並無特別限制，pH值未達7即可，所使用之酸可為弱酸亦可為強酸。具體而言，較佳為鹽酸、硝酸、硫酸、磷酸、乙酸、草酸、碳酸及檸檬酸等酸。該等酸可單獨使用，亦可將複數種組合使用。 進行酸處理之溫度亦根據所使用之酸之種類或濃度、時間而不同，較佳為於100℃以下進行。 進行酸處理之時間根據所使用之酸之種類或濃度、溫度而不同，自生產性之方面而言，較佳為10秒～5小時，更佳為1分鐘～2小時。 進行酸處理之溶液之濃度根據所使用之酸之種類或時間、溫度而不同，較佳為容器腐蝕之擔憂較少之濃度，具體而言較佳為0.1重量%～20重量%。 由於低密度層係藉由下述之鹼處理而去除，故而低密度層越厚，則玻璃表面越易被去除。低密度層之厚度如上所述，自玻璃表面去除量之觀點而言，較佳為300 nm以上，更佳為500 nm以上，進而較佳為600 nm以上。 低密度層之密度自玻璃表面去除性之觀點而言，較佳為低於較經離子交換之壓縮應力層深之區域(主體)之密度。低密度層之厚度可根據利用X射線反射率法(X-ray-Reflectometry：XRR)所測得之週期(Δθ)而求得。低密度層之密度可藉由利用XRR所測得之臨界角(θc)而求得。 再者，簡單而言，亦可藉由利用掃描式電子顯微鏡(SEM，Scanning Electron Microscope)觀察玻璃之剖面而確認低密度層之形成與層之厚度。 (與鹼接觸之步驟) 於本發明之製造方法中，較佳為於經過與酸接觸之步驟後，進而進行與鹼接觸之步驟(鹼處理步驟)。更佳為在與酸接觸之步驟之後且與鹼接觸之步驟之前，經過與上述之進行洗淨之步驟相同之洗淨玻璃板之步驟。 所謂鹼處理，係藉由將化學強化玻璃浸漬於鹼性之溶液中而進行，藉此，可去除上述與酸接觸之步驟中所形成之低密度層之一部分或全部。 溶液只要為鹼性，則並無特別限制，pH值超過7即可，可使用弱鹼亦可使用強鹼。具體而言，較佳為氫氧化鈉、氫氧化鉀、碳酸鉀、碳酸鈉等鹼。該等鹼可單獨使用，亦可將複數種組合使用。 進行鹼處理之溫度亦根據所使用之鹼之種類或濃度、時間而不同，較佳為0～100℃，更佳為10～80℃，尤佳為20～60℃。若為上述溫度範圍，則無玻璃被腐蝕之虞而較佳。 進行鹼處理之時間亦根據所使用之鹼之種類或濃度、溫度而不同，自生產性之方面而言較佳為10秒～5小時，更佳為1分鐘～2小時。 進行鹼處理之溶液之濃度根據所使用之鹼之種類或時間、溫度而不同，自玻璃表面去除性之觀點而言，較佳為0.1重量%～20重量%。 藉由上述鹼處理，H所侵入之低密度層之一部分或全部被去除，藉此，可獲得面強度提高之化學強化玻璃。尤其是於本發明中，可使低密度層之厚度深於存在於玻璃表面之龜裂或潛在損傷之深度。因此認為可將存在於玻璃表面之龜裂或潛在損傷與低密度層一同去除，更有助於玻璃之面強度提高。再者，較佳為於鹼處理之後，亦經過利用與前文相同之方法進行洗淨之步驟。 ＜化學強化玻璃＞ 根據本發明之化學強化玻璃之製造方法，與先前之化學強化處理相比，可更深地形成低密度層，因此於去除該低密度層後所獲得之化學強化玻璃之表層，龜裂或潛在損傷更少。因此，藉由本發明所獲得之化學強化玻璃具有非常高之面強度。 (玻璃面強度) 化學強化玻璃之面強度可藉由球環試驗進行評價。 (球環試驗) 化學強化玻璃係藉由利用球環(Ball on Ring；BoR)試驗而測得之BoR面強度F(N)進行評價，上述球環試驗係將玻璃板配置於直徑為30 mm、接觸部具有曲率半徑為2.5 mm之弧度之包含不鏽鋼的環上，以使直徑為10 mm之包含鋼之球體與該玻璃板接觸之狀態而使該球體於靜態負載條件下對該環之中心施加負載。 化學強化玻璃較佳為第1主面及第2主面之強度均滿足F≧1500×t2
，更佳為F≧1800×t2
，進而較佳為F≧2000×t2
[式中，F為藉由球環試驗所測得之BoR面強度(N)，t為玻璃基板之板厚(mm)]。藉由使BoR面強度F(N)為上述範圍，而即便於薄板化之情形時，亦表現出優異之面強度。再者，BoR試驗可藉由下述之實施例所記載之方法而進行。 (壓縮應力層) 化學強化玻璃之壓縮應力層之壓縮應力值及壓縮應力層之深度可使用EPMA(electron probe micro analyzer，電子探針微量分析儀)或表面應力計(例如，折原製作所製造之FSM-6000)等進行測定。 (玻璃表面(低密度層)之去除量) 鹼處理後之玻璃表面(低密度層)之去除量(厚度)可藉由利用分析用電子天平測定藥液處理前後之重量並使用下式進行厚度換算而求得。 (每單面之去除量厚度)＝[(處理前重量)－(處理後重量)]/(玻璃比重)/處理面積/2 此時，將玻璃比重設為2.48(g/cm3
)進行計算。 實施例 以下，列舉實施例對本發明具體地進行說明，但本發明並不限定於該等。 ＜評價方法＞ 本實施例中之各種評價係利用以下所示之分析方法而進行。 (玻璃之評價：面強度) 玻璃面強度係藉由球環(Ball on Ring；BoR)試驗而測定。於圖1中，表示用以說明本發明所使用之球環試驗之概略圖。於將玻璃板1水平載置之狀態下，使用SUS(Steel Use Stainless)304製之加壓治具2(淬火鋼，直徑10 mm，鏡面拋光)對玻璃板進行加壓，測定玻璃板之面強度。 於圖1中，於SUS304製之承受治具3(直徑30 mm，接觸部之曲率為R2.5 mm，接觸部為淬火鋼，鏡面拋光)之上，水平設置有成為試樣之玻璃板。於玻璃板之上方，設置有用以對玻璃板進行加壓之加壓治具。 於本實施之形態中，自所獲得之玻璃板之上方對玻璃板之中央區域加壓。再者，試驗條件如下。 加壓治具之下降速度：1.0(mm/分鐘) 此時，將玻璃被破壞時之破壞負載(單位N)設為BoR面強度，將20次測定之平均值設為BoR平均面強度。但於玻璃板之破壞起點距球壓抵位置2 mm以上之情形時，自用於算出平均值之資料中排除。 (玻璃之評價：表面應力) 玻璃之表面壓縮應力值(CS，單位為MPa)及壓縮應力層之深度(DOL，單位為μm)係使用折原製作所公司製造之表面應力計(FSM-6000)而測定。 (玻璃之評價：去除量) 玻璃之去除量厚度係藉由利用分析用電子天平(HR-202i，AND製造)測定藥液處理前後之重量並使用下式進行厚度換算而求得。 (每單面之去除量厚度)＝[(處理前重量)－(處理後重量)]/(玻璃比重)/處理面積/2 此時，將玻璃比重設為2.48(g/cm3
)進行計算。 (玻璃之評價：龜裂或潛在損傷) 玻璃表面上之龜裂或潛在損傷之有無係於照度1500 Lux之光源下進行目視檢查，若無可視認之缺陷，則判斷不存在龜裂或潛在損傷。 ＜實施例1＞ (進行離子交換之步驟) 向不鏽鋼(SUS)製之坩堝中加入硝酸鉀8454 g、碳酸鉀1324 g、硝酸鈉222 g，利用加熱套加熱至490℃，製備碳酸鉀10 mol%、鈉6000重量ppm之熔鹽。藉由向熔鹽之界面附近之環境中通入曾導入至加熱至55℃之水中之空氣，而使熔鹽中包含水蒸氣。 將實驗體系示於圖3中，使用空氣作為乾燥之氣體A，藉由將該空氣通入至利用水槽25加熱至55℃之水24中而進行加濕，製為經加濕之包含水蒸氣之氣體(空氣)B。 藉由將該包含水蒸氣之氣體B經由利用電熱帶而經加熱之路徑導入至進行化學強化處理之槽之無機鹽(熔鹽)26之上部空間，從而控制進行離子交換之步驟中之露點。此時之每1 cm3
之水蒸氣供給量為0.02 mg/分鐘，熔鹽之界面附近之露點為38℃。 準備50 mm×50 mm×0.7 mm之玻璃板A，預熱至350～400℃後，浸漬於490℃之熔鹽中1小時，進行離子交換處理後，冷卻至室溫附近，藉此進行化學強化處理。對所獲得之化學強化玻璃進行水洗，並供於下一步驟。 玻璃板A之玻璃組成(氧化物基準之莫耳%表示)：SiO2
為64.2%、Al2
O3
為8.0%、Na2
O為12.5%、K2
O為4.0%、MgO為10.5%、CaO為0.1%、SrO為0.1%、BaO為0.1%、ZrO2
為0.5% (去除表面之一部分之步驟1：與酸接觸之步驟) 於燒杯中準備6.0重量%之硝酸(藉由離子交換水稀釋硝酸1.38(關東化學公司製造))，使用水浴將溫度調整為40℃。將藉由上述化學強化步驟所獲得之玻璃浸漬於所製備之硝酸中120秒，進行酸處理。之後，對該玻璃進行水洗，並供於下一步驟。 (去除表面之一部分之步驟2：與鹼接觸之步驟) 於燒杯中準備4.0重量%之氫氧化鈉水溶液(藉由離子交換水稀釋48%氫氧化鈉溶液(關東化學公司製造))，使用水浴將溫度調整為40℃。將於與酸接觸之步驟之後經洗淨之玻璃浸漬於所製備之氫氧化鈉水溶液中120秒而進行鹼處理。之後，對該玻璃進行水洗而洗淨玻璃表面之鹼。之後，藉由鼓風進行乾燥。 藉由以上，獲得實施例1之化學強化玻璃。 未確認到於所獲得之化學強化玻璃存在龜裂及潛在損傷。 ＜實施例2＞ 將進行離子交換之步驟中之熔鹽之碳酸鉀濃度設為8 mol%，將熔鹽之界面附近之露點設為71℃，將化學強化處理條件設為於450℃下進行2小時，除此以外，與實施例1同樣地製造化學強化玻璃。再者，為了控制露點而導入包含水蒸氣之氣體時每1 cm3
之水蒸氣供給量為0.08 mg/分鐘。未確認到於所獲得之化學強化玻璃存在龜裂及潛在損傷。 ＜比較例1＞ 除了將進行離子交換之步驟中之熔鹽之界面附近之露點設為9℃以外，與實施例2同樣地製造化學強化玻璃。再者，未為了控制露點而導入包含水蒸氣之氣體。 未確認到於所獲得之化學強化玻璃存在龜裂及潛在損傷。 ＜比較例2＞ 不向進行離子交換之步驟中之熔鹽加入碳酸鉀，將鈉設為2000重量ppm，不進行酸處理及鹼處理，除此以外與比較例1同樣地製造化學強化玻璃。未確認到於所獲得之玻璃存在龜裂及潛在損傷。 ＜實施例3＞ 除了使用玻璃板B以外，於與實施例1同樣之條件下製造化學強化玻璃。未確認到於所獲得之化學強化玻璃存在龜裂及潛在損傷。 玻璃板B之玻璃組成(氧化物基準之莫耳%顯示)：SiO2
為68.0%、Al2
O3
為12.0%、Na2
O為18.6%、MgO為8.0% ＜實施例4＞ 除了使用與實施例3同樣之玻璃以外，於與實施例2同樣之條件下製造化學強化玻璃。未確認到於所獲得之化學強化玻璃存在龜裂及潛在損傷。 ＜比較例3＞ 除了使用與實施例3同樣之玻璃以外，於與比較例1同樣之條件下製造化學強化玻璃。未確認到於所獲得之化學強化玻璃存在龜裂及潛在損傷。 ＜比較例4＞ 除了使用與實施例3同樣之玻璃以外，於與比較例2同樣之條件下製造化學強化玻璃。未確認到於所獲得之玻璃存在龜裂及潛在損傷。 ＜實施例5＞ (進行離子交換之步驟) 除了使用厚度0.55 mmt之玻璃板C，將熔鹽之界面附近之露點設為66℃以外，於與實施例2同樣之條件下製造化學強化玻璃。未確認到於所獲得之化學強化玻璃存在龜裂及潛在損傷。 玻璃板C之玻璃組成(氧化物基準之莫耳%表示)：SiO2
為67%、B2
O3
為4%、Al2
O3
為13%、Na2
O為14%、K2
O＜1%、MgO為2%、CaO＜1% ＜比較例5＞ 除了使用與實施例5同樣之玻璃以外，於與比較例2同樣之條件下製造化學強化玻璃。未確認到於所獲得之化學強化玻璃存在龜裂及潛在損傷。 對於上述所得之化學強化玻璃進行各種評價。將玻璃之處理條件及評價結果顯示於表1中。再者，顯示BoR平均面強度作為BoR面強度。 [表1]
如上所述，實施例1～5及比較例1～5於照度1500 Lux之光源下進行目視檢查時，均未確認到存在龜裂及潛在損傷。然而，如表1所示般，實施例1～5相較於比較例1～5，顯示較高之BoR面強度F(N)。 關於實施例1～5相較於比較例1～5顯示較高之BoR面強度F(N)之原因，可想到如下原因。於本發明之製造方法中，藉由於露點溫度為20℃以上之環境中進行上述玻璃板之上述鹼離子與上述無機鹽之上述其他鹼離子之離子交換之步驟，可增加使玻璃化學強化時之熔鹽中之水蒸氣量，形成具備存在於玻璃表面之龜裂或潛在損傷之平均深度以上之深度的低密度層。藉由去除經上述離子交換之上述玻璃板之表面之一部分的步驟，可去除上述低密度層，並且充分去除上述龜裂或潛在損傷，或充分減少其數量，可實現較高之BoR面強度F(N)。 參照特定之態樣對本發明詳細地進行說明，但業者知曉，可不脫離本發明之精神及範圍而進行各種變更及修正。再者，本申請係基於2015年12月28日提出申請之日本專利申請(特願2015-256894)，藉由引用而援用其整體。又，此處所引用之所有參照係作為整體併入至本文中。 [產業上之可利用性] 根據本發明之化學強化玻璃之製造方法，可於化學強化後，不進行研磨或不進行使用氫氟酸等之蝕刻處理而獲得面強度非常高之化學強化玻璃。即，可獲得一種化學強化玻璃，其不存在由伴隨利用氫氟酸等進行之蝕刻處理產生之潛在損傷之擴大而導致之外觀不良、或伴隨研磨產生之研磨損傷，並且面強度優異。 因此，不論化學強化處理前之玻璃之表面損傷、潛在損傷之有無或程度，可應用於所有之玻璃，通用性較高。並且，由於可藉由浸漬於溶液而進行處理，故而於易於應對各種玻璃形狀或大面積之玻璃等方面而言有效率。進而，相較於使用氫氟酸等之蝕刻處理，安全性較高，成本較低。Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following embodiments, and can be implemented with arbitrarily changed without departing from the gist of the present invention. In addition, in this specification, "~" indicating a numerical range is used to include the numerical value described before and after it as the lower limit and the upper limit. <The manufacturing method of chemically strengthened glass> The manufacturing method of chemically strengthened glass of the present invention is characterized by including the following steps: (a) preparing a glass plate containing alkali ions; (b) preparing other alkali ions with an ion radius larger than the above alkali ions (C) Perform ion exchange between the alkali ion of the glass plate and the other alkali ion of the inorganic salt in an environment with a dew point temperature of 20°C or higher; and (d) remove the ion exchanged A part of the surface of the glass plate. (Glass composition) The glass used in the present invention may contain alkali ions, as long as it has a composition that can be shaped and strengthened by a chemical strengthening treatment, and various compositions can be used. Among them, sodium is preferably contained. Specifically, for example, aluminosilicate glass, soda lime glass, borosilicate glass, lead glass, alkaline barium glass, aluminoborosilicate glass, etc. can be cited. The method of manufacturing glass is not particularly limited, and the required glass material can be fed into a continuous melting furnace, and the glass material can be heated and clarified at a temperature of preferably 1500 to 1600°C and then supplied to the forming device, and then the molten glass It is manufactured by forming into a plate shape and slowly cooling. Furthermore, various methods can be used to form the glass. For example, various forming methods such as down-drawing method (for example, overflow down-drawing method, orifice down-drawing method, redrawing method, etc.), float method, rolling method, and pressurizing method can be used. Among them, in terms of easily generating cracks on at least a part of the glass surface and the effect of the present invention is more obvious, the float method is preferred. The thickness of the glass is not particularly limited. For effective chemical strengthening treatment, it is usually preferably 5 mm or less, more preferably 3 mm or less, further preferably 1 mm or less, and particularly preferably 0.7 mm or less. In addition, the shape of the glass used in the present invention is not particularly limited. For example, various shapes of glass, such as a flat plate shape having a uniform thickness, a shape having a curved surface on at least one of the front and back surfaces, and a three-dimensional shape having a curved portion, etc. can be used. The composition of the chemically strengthened glass of the present invention is not particularly limited. For example, the following glass compositions can be cited: (1) The composition represented by mole% based on oxide includes 50 to 80% of SiO 2 and 2 to 25 % Al 2 O 3 , 0～10% Li 2 O, 0～18% Na 2 O, 0～10% K 2 O, 0～15% MgO, 0～5% CaO and 0～ 5% ZrO 2 glass (2) The composition expressed by mole% based on oxide contains 50-74% SiO 2 , 1-10% Al 2 O 3 , 6-14% Na 2 O, 3～11% K 2 O, 2～15% MgO, 0～6% CaO and 0～5% ZrO 2 , the total content of SiO 2 and Al 2 O 3 is 75% or less, Na 2 O The total content of K 2 O and K 2 O is 12 to 25%, and the total content of MgO and CaO is 7 to 15%. (3) The composition represented by mole% on the basis of oxide contains 68 to 80% SiO 2 , 4～10% Al 2 O 3 , 5～15% Na 2 O, 0～1% K 2 O, 4～15% MgO and 0～1% ZrO 2 glass (4) The composition expressed in mole% based on oxides contains 67-75% SiO 2 , 0-4% Al 2 O 3 , 7-15% Na 2 O, 1-9% K 2 O, 6 ～14% of MgO and 0～1.5% of ZrO 2 , the total content of SiO 2 and Al 2 O 3 is 71 to 75%, the total content of Na 2 O and K 2 O is 12 to 20%, and When CaO is contained, the glass whose content is less than 1% (5) The composition expressed by mass% based on oxide contains 65-75% SiO 2 , 0.1-5% Al 2 O 3 , 1-6 % Of MgO, 1-15% of CaO, and 10-18% of Na 2 O + K 2 O (6) The composition represented by mass% on the basis of oxide contains 60-72% of SiO 2 , 1-10 % Al 2 O 3 , 5～12% MgO, 0.1～5% CaO, 13～19% Na 2 O, 0～5% K 2 O, and RO/(RO＋R 2 O) is 0.20 or more And 0.42 or less (in the formula, RO represents alkaline earth metal oxides, R 2 O represents alkali metal oxides) glass (7) The composition represented by mole% on the basis of oxides contains 55.5 to 80% of SiO 2 , 12-20% Al 2 O 3 , 8-25% Na 2 O, 2.5% or more P 2 O 5 , 1% or more alkaline earth metal RO (RO is MgO＋CaO＋SrO＋BaO) glass (8) based on oxide Mole% The composition contains 57～76.5% of SiO 2 , 12～18% of Al 2 O 3 , 8～25% of Na 2 O, 2.5～10% of P 2 O 5 , and more than 1% of alkaline earth metal RO. (9) The composition expressed in mole% based on oxides contains 56 to 72% of SiO 2 , 8 to 20% of Al 2 O 3 , 3 to 20% of B 2 O 3 , and 8 to 25% of Na 2 O, 0～5% K 2 O, 0～15% MgO, 0～15% CaO, 0～15% SrO 2 , 0～15% BaO and 0～8% ZrO 2 The chemically strengthened glass of the present invention has an ion-exchanged compressive stress layer on the glass surface. In the ion exchange method, ion exchange is performed on the surface of the glass to form a surface layer with residual compressive stress. Specifically, at a temperature below the glass transition point, the alkali metal ions (Li ions and/or Na ions) with a smaller ion radius on the surface of the glass plate are replaced by other alkali ions ( Na ion and/or K ion). Thereby, compressive stress remains on the surface of the glass, and the strength of the glass is improved. In the manufacturing method of the present invention, the chemical strengthening treatment is performed by contacting an inorganic salt containing other alkali ions having an ion radius larger than the alkali ions contained in the glass with the glass containing alkali ions, and performing ion exchange. That is, the alkali ions contained in the glass are ion-exchanged with other alkali ions contained in the inorganic salt. When the alkali ion contained in the glass is Na ion, the inorganic salt is an inorganic salt containing potassium nitrate (KNO 3 ), and more preferably contains K 2 CO 3 , Na 2 CO 3 , KHCO 3 , NaHCO 3. At least one salt from the group consisting of Li 2 CO 3 , Rb 2 CO 3 , Cs 2 CO 3 , MgCO 3 , CaCO 3 , and BaCO 3 . For example, when potassium nitrate is contained in the inorganic salt, the melting point of potassium nitrate is 330°C, which has a melting point below the strain point (usually 500-600°C) of the chemically strengthened glass. In addition, among the above-mentioned salts, salts other than potassium nitrate (hereinafter also referred to as "fluxes") have the property of cutting the glass network represented by the Si-O-Si bond. Since the temperature for chemical strengthening is as high as several hundred degrees Celsius, the covalent bond between Si-O of the glass is appropriately cut at this temperature, making it easier to perform the following low-density treatment. Furthermore, the degree to which the covalent bond is cut also differs according to the glass composition or the type of salt (flux) used, the temperature and time of the chemical strengthening treatment, and other chemical strengthening treatment conditions, but it is considered that it is better to select from Si The condition of the degree to which 1 to 2 of the 4 extended covalent bonds are severed. The high-density compressive stress layer is formed by ion exchange between Na ions (or Li ions) on the glass surface and K ions (or Na ions) in the inorganic salt. As a method of contacting glass with inorganic salt, there can be a method of applying a paste of inorganic salt, a method of spraying an aqueous solution of inorganic salt on the glass, and a method of immersing the glass in a salt bath of molten salt heated above the melting point Among them, the method of immersing in molten salt is more desirable. The addition amount of the flux is preferably 0.1 mol% or more, more preferably 0.5 mol% or more, still more preferably 1 mol% or more, and particularly preferably 2 mol% or more. In addition, from the viewpoint of productivity, the saturated solubility of each salt is preferably or less. If it is added excessively, it may cause corrosion of the glass. For example, when K 2 CO 3 is used as a flux, it is preferably 24 mol% or less, more preferably 12 mol% or less, and particularly preferably 8 mol% or less. In addition to potassium nitrate and flux, the inorganic salt may also include other chemical species within the range that does not impair the effects of the present invention. For example, alkali metal chlorides such as sodium chloride, potassium chloride, sodium borate, potassium borate, etc. Alkali metal borates, etc. These can be added individually or in combination of plural kinds. (Production of Molten Salt) Molten salt can be produced by a well-known procedure. For example, when the inorganic salt is a molten salt containing potassium nitrate and a flux, it can be obtained by preparing a potassium nitrate molten salt, and then adding a flux to the potassium nitrate molten salt. Furthermore, as another method, it can be obtained by mixing potassium nitrate and a flux, and then melting the mixed salt of potassium nitrate and the flux. The Na concentration of the molten salt used in the manufacturing method of the present invention is preferably 500 ppm by weight or more, more preferably 1,000 ppm by weight or more. By making the Na concentration in the molten salt 2000 ppm by weight or more, the low-density layer becomes easy to deepen by the following acid treatment step, which is further preferred. As the upper limit of the Na concentration, there is no particular limitation, and it can be allowed to be within a range that can obtain the desired surface compressive stress (CS). Furthermore, the molten salt that has undergone chemical strengthening treatment more than once contains sodium eluted from the glass. Therefore, if the Na concentration is within the above range, the sodium derived from glass can be directly used as the Na source. When the Na concentration is insufficient, or when using molten salt that is not used in chemical strengthening, it can be used It is adjusted by adding inorganic sodium salt such as sodium nitrate. (Step of performing ion exchange) Next, use the prepared molten salt for chemical strengthening treatment. The chemical strengthening treatment is to immerse the glass in molten salt to exchange the alkali ions (Li ion or Na ion) in the glass with other alkali ions (Na ion or K ion) in the molten salt with a larger ion radius (Replacement) and implement. By this ion exchange, the composition of the glass surface can be changed to form a compressive stress layer 20 with a higher density on the glass surface [FIG. 2(a)-(b)]. The high density of the glass surface generates compressive stress, so the glass can be strengthened. Furthermore, in fact, the density of chemically strengthened glass gradually increases from the outer edge of the intermediate layer 30 (main body) existing in the center of the glass toward the surface of the compressive stress layer. Therefore, between the intermediate layer 30 and the compressive stress layer 20 There is no clear boundary between rapid changes in density. Here, the so-called intermediate layer refers to a layer that exists in the center of the glass and is sandwiched by the compressive stress layer. The intermediate layer is different from the compressive stress layer in that it is not ion-exchanged. The chemical strengthening treatment (the step of performing ion exchange) in the present invention can be specifically performed according to the following procedure. First, preheat the glass and adjust the above molten salt to the temperature for chemical strengthening. Secondly, after the preheated glass is immersed in the molten salt in the molten salt tank 27 for a specified period of time, the glass is removed from the molten salt and left to cool. Furthermore, it is preferable to perform mechanical processing such as cutting, end surface processing, and drilling processing on the glass before the chemical strengthening treatment. The preheating temperature of the glass depends on the temperature of immersion in the molten salt, and it is usually preferably above 100°C. The chemical strengthening temperature is preferably below the strain point of the glass to be strengthened (usually 500-600°C). In order to obtain a higher compressive stress layer depth, it is particularly preferably above 350°C, in order to shorten the processing time and promote the formation of low-density layers , More preferably 400°C or higher, still more preferably 430°C or higher. The immersion time of the glass in the molten salt is preferably 1 minute to 10 hours, more preferably 5 minutes to 8 hours, and still more preferably 10 minutes to 4 hours. Within the above range, it is preferable to obtain a chemically strengthened glass having an excellent balance of strength and depth of the compressive stress layer. In the manufacturing method of the present invention, by increasing the amount of water vapor in the molten salt when immersing the glass, the low-density layer formed in the following step of contacting with acid can be thickened. In the step of contact with alkali, the above-mentioned low-density layer can be removed. Therefore, the low-density layer can be removed by setting the thickness of the low-density layer to above the average depth of cracks or potential damage existing on the glass surface. And remove the crack or potential damage. Therefore, the excellent surface strength of chemically strengthened glass can be achieved. The step of ion exchange is carried out in an environment where the dew point temperature is above 20°C. The dew point is preferably 30°C or higher, more preferably 40°C or higher, still more preferably 50°C or higher, and still more preferably 60°C or higher. In addition, the upper limit is preferably set to be equal to or lower than the temperature of the inorganic salt (molten salt) for ion exchange. Regarding the dew point temperature (hereinafter referred to as "dew point" for short), as long as at least the dew point temperature near the interface of the molten salt is within the above range, the so-called near the interface means the environment in the area less than 200 mm from the interface of the molten salt . The dew point can be measured by Vaisala DRYCAP (registered trademark) DMT346 dew point converter. Furthermore, the so-called dew point in this specification refers to a value that is considered to be a balance between the environment near the interface of molten salt and molten salt. The aforementioned dew point can be achieved by introducing water vapor into the environment near the interface of molten salt and/or molten salt before and/or simultaneously with the step of performing ion exchange. For example, by adding a water vapor supply part to a molten salt tank, water vapor can be introduced into the molten salt and/or the environment near the interface of the molten salt. That is, the water vapor itself, or gas containing water vapor, and water (liquid) supplied by the water vapor supply part can be directly passed into the molten salt, or water vapor or gas containing water vapor can be introduced into the molten salt. The upper space. In addition, water (liquid) itself may be dropped onto the molten salt and introduced within the range where no steam explosion occurs. When introducing water vapor, a gas containing water vapor, or water (liquid) (hereinafter referred to as "steam, etc."), the molten salt can be stirred or not stirred, but it can shorten the time to equilibrium From the aspect, stirring is preferable. Since the time from the introduction of water vapor to the equilibrium is different depending on the amount of gas or liquid introduced, the concentration of water vapor, the method of introduction, etc., it cannot be generalized. If the dew point of the above environment is stable and becomes fixed, it can be judged to reach balance. The gas containing water vapor can be used without affecting the chemical strengthening process. For example, it can be made by introducing dry gas A such as air, nitrogen, carbon dioxide gas, etc. into the heated water 24 as shown in FIG. 3 Gas containing water vapor with higher humidity (gas containing water vapor) B. The water 24 used as a water vapor supply source is preferably pure water such as ion exchange water in terms of suppressing scale deposition in piping and the like. Moreover, the water 24 is heated by performing a water bath etc. using the water tank 25, for example. In addition, water vapor may be generated by heating the water 24 itself with a boiler or the like, for example. As a method of introducing water vapor, more specifically, (1) introducing gas B containing water vapor from the water vapor supply part into the space above the inorganic salt (molten salt 26), and (2) from the vent The gas B containing water vapor is introduced into the inorganic salt (molten salt 26), or (3) water (liquid) is directly introduced into the inorganic salt (molten salt 26) or the like. Among them, it is preferable to form the environment by the above (1) or (2). As a form of introducing the gas B containing water vapor into the space above the inorganic salt (molten salt 26), for example, there is a sprayer spraying the water vapor supplied from the water vapor supply part to the upper part of the inorganic salt or The method near the interface of inorganic salt. By using a sprayer to introduce water vapor, etc., it becomes easy to control the water vapor concentration in the space above the inorganic salt to be substantially uniform, which is preferable. In addition, the water vapor supply part, the ventilation part, the water (liquid) introduction part, or the sprayer fitting device may be appropriately provided, and there is no particular limitation. Specifically, the atomizer may be single or plural. Especially when the molten salt tank is large, it is easy to control the water vapor concentration in the space above the inorganic salt to be approximately uniform by spraying water vapor with multiple sprayers. When the gas containing water vapor is introduced into the space above the molten salt, the supply amount of water vapor per 1 cm 3 of the gas is preferably 0.01 mg/min or more, more preferably 0.02 mg/min or more . When water (liquid) is directly introduced into the molten salt, the flow rate of the water introduced per 1 cm 3 is preferably 0.01 mg/min or more, more preferably 0.02 mg/min or more. When the gas containing water vapor is directly introduced into the inorganic salt (molten salt), the supply amount of water vapor per 1 cm 3 of the gas is preferably 0.01 mg/min or more, more preferably 0.02 Above mg/min. The reason why the surface strength of the obtained chemically strengthened glass becomes higher by performing the step of performing ion exchange in molten salt with a large amount of water vapor (water content) is considered as follows. When the carbonate ion forming the molten salt reacts with water, as shown in the following formula, bicarbonate ion and hydroxide ion are generated. [化1] Here, if the amount of water in the molten salt is large, the balance in the above formula tilts to the right, and more bicarbonate ions and hydroxide ions are generated. Since hydroxide ions are ions that promote the cutting of the glass network, it is believed that by generating more hydroxide ions, the formation of a low-density layer on the glass surface is promoted. The sum of the carbonate anion concentration and the bicarbonate anion concentration obtained by the following formula in the inorganic salt is preferably 4 mol% or more, more preferably 6 mol% or more. By setting the concentration to 4 mol% or more, the formation reaction of the low-density layer on the glass surface can be promoted, which is preferable. {(Carbonate anion concentration) + (bicarbonate anion concentration)} (mol%) = {(amount of carbonate anion in inorganic salt) + (amount of bicarbonate anion in inorganic salt)}(mol)/( Total anion in inorganic salt) (mol)×100 Furthermore, since it is impossible to directly measure the concentration of carbonate anion and bicarbonate anion in the molten salt, a part of the molten salt is taken out and the carbon dioxide is used as TiN-9004. After diluting a commercially available standard solution (NaHCO 3 ) with pure water and creating a calibration curve, measure the sample solution diluted 130 times with pure water. At this time, since the bicarbonate anions are all converted into carbonate anions, the value of the carbonate anion concentration detected by the measurement is equivalent to the sum of the carbonate anion concentration and the bicarbonate anion concentration. In addition, the sum of the carbonate anion concentration and the bicarbonate anion concentration is equal to or less than the sum of the saturated carbonate anion concentration and the saturated bicarbonate anion concentration. The low-density layer is formed by the step of contacting with an acid among the steps of removing a part of the surface of the glass plate as described below, and its thickness is 100-200 nm in the previous step of ion exchange without introducing water vapor In contrast, the thickness can be 300 nm or more by ion exchange in an environment where water vapor is introduced and the dew point temperature is 20°C or more. Since the average depth of cracks or potential damage on the glass surface generated during the glass manufacturing step or the glass processing step including the chemical strengthening treatment step is about 500 nm, the thickness of the low-density layer is more preferably 500 nm or more, which is more Preferably, it is 600 nm or more. The formed low-density layer can be removed by the following step of contacting with alkali among the steps of removing a part of the surface of the glass plate. Therefore, if the depths of the above-mentioned cracks or potential damages on the glass surface are all low-density layer thicknesses, all these cracks and potential damages can be removed by the step of contact with alkali. The surface strength of chemically strengthened glass can be made higher by removing cracks or potential damages on the glass surface that cause the decrease in the strength of chemically strengthened glass. (Step of washing) In the manufacturing method of the present invention, it is preferable to further include a step of washing the glass plate between the step of performing ion exchange and the step of removing a part of the surface of the glass plate. In the cleaning step, industrial water, ion exchange water, etc. are used to clean the glass. For industrial water, use treated ones as needed. In particular, ion exchange water is preferred. The conditions for washing differ depending on the washing liquid used. In the case of using ion-exchange water, washing at 0-100°C is preferable in terms of completely removing the attached salt. In the cleaning step, the method of immersing the chemically strengthened glass in a water tank filled with ion-exchange water, or the method of exposing the glass surface to running water, using a water jet to direct the cleaning liquid toward the glass Various methods such as surface spraying. (Step of removing part of the surface of the glass plate) The ion-exchanged glass plate is supplied to the step of removing a part of the surface of the glass plate. The step of removing a part of the surface of the glass plate preferably includes a step of contacting the glass plate with an acid, and more preferably after the step of contacting with the acid described above, further includes a step of contacting the glass plate with an alkali. (Step of contacting with acid) In the manufacturing method of the present invention, as the step of removing a part of the surface of the glass plate after the step of performing ion exchange or the step of performing cleaning, it is preferable to perform contacting glass with acid的 step (acid treatment step). The so-called acid treatment of glass is performed by immersing the chemically strengthened glass in an acidic solution, whereby Na and/or K on the surface of the chemically strengthened glass can be replaced with H. That is, the surface layer further having a compressive stress layer on the glass surface is modified, specifically, a low-density layer formed by lowering the density. The solution is not particularly limited as long as it is acidic, and the pH value is less than 7, and the acid used may be a weak acid or a strong acid. Specifically, acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, oxalic acid, carbonic acid, and citric acid are preferred. These acids can be used alone or in combination of plural kinds. The temperature at which the acid treatment is carried out also varies according to the type or concentration of the acid used, and the time, and it is preferably carried out below 100°C. The time for the acid treatment varies depending on the type or concentration of the acid used, and the temperature. From the viewpoint of productivity, it is preferably 10 seconds to 5 hours, and more preferably 1 minute to 2 hours. The concentration of the acid-treated solution varies according to the type of acid used, time, and temperature. It is preferably a concentration with less fear of container corrosion, and specifically, it is preferably 0.1% by weight to 20% by weight. Since the low-density layer is removed by the alkali treatment described below, the thicker the low-density layer, the easier the glass surface is removed. The thickness of the low-density layer is as described above, and from the viewpoint of the amount of removal from the glass surface, it is preferably 300 nm or more, more preferably 500 nm or more, and still more preferably 600 nm or more. From the viewpoint of the removability of the glass surface, the density of the low-density layer is preferably lower than the density of the region (body) deeper than the ion-exchanged compressive stress layer. The thickness of the low-density layer can be obtained from the period (Δθ) measured by the X-ray-Reflectometry (XRR) method. The density of the low-density layer can be obtained by using the critical angle (θc) measured by XRR. Furthermore, in simple terms, the formation of the low-density layer and the thickness of the layer can also be confirmed by observing the cross-section of the glass with a scanning electron microscope (SEM, Scanning Electron Microscope). (Step of contact with alkali) In the production method of the present invention, it is preferable to perform the step of contact with alkali (alkali treatment step) after the step of contact with acid. More preferably, after the step of contacting with acid and before the step of contacting with alkali, a step of washing the glass plate is the same as the step of washing described above. The so-called alkali treatment is performed by immersing the chemically strengthened glass in an alkaline solution, whereby part or all of the low-density layer formed in the step of contacting with the acid can be removed. The solution is not particularly limited as long as it is alkaline, as long as the pH value exceeds 7, and either a weak base or a strong base can be used. Specifically, alkalis such as sodium hydroxide, potassium hydroxide, potassium carbonate, and sodium carbonate are preferred. These bases can be used alone or in combination of plural kinds. The temperature for alkali treatment also varies according to the type or concentration of alkali used, and time, and is preferably 0-100°C, more preferably 10-80°C, and particularly preferably 20-60°C. If it is in the above-mentioned temperature range, it is preferable that there is no risk of glass being corroded. The time for the alkali treatment also varies depending on the type or concentration of the alkali used, and the temperature. From the viewpoint of productivity, it is preferably 10 seconds to 5 hours, and more preferably 1 minute to 2 hours. The concentration of the alkali-treated solution varies depending on the type of alkali used, time, and temperature. From the viewpoint of the removability from the glass surface, it is preferably 0.1% by weight to 20% by weight. By the above-mentioned alkali treatment, part or all of the low-density layer invaded by H is removed, thereby obtaining a chemically strengthened glass with improved surface strength. Especially in the present invention, the thickness of the low density layer can be made deeper than the depth of the cracks or potential damage existing on the glass surface. Therefore, it is believed that the cracks or potential damages existing on the glass surface can be removed together with the low-density layer, which is more helpful to improve the surface strength of the glass. Furthermore, it is preferable that after the alkali treatment, a step of washing using the same method as above is also carried out. <Chemically strengthened glass> According to the method for manufacturing chemically strengthened glass of the present invention, the low-density layer can be formed deeper than the previous chemical strengthening treatment. Therefore, the surface layer of the chemically strengthened glass obtained after the low-density layer is removed, Less cracking or potential damage. Therefore, the chemically strengthened glass obtained by the present invention has very high surface strength. (Glass surface strength) The surface strength of chemically strengthened glass can be evaluated by the ball ring test. (Ball on Ring Test) The chemically strengthened glass is evaluated by the BoR surface strength F(N) measured by the Ball on Ring (BoR) test. The above-mentioned ball ring test is to arrange the glass plate with a diameter of 30 mm 、The contact part has a radius of curvature of 2.5 mm on a ring containing stainless steel, so that a sphere containing steel with a diameter of 10 mm is in contact with the glass plate so that the sphere is placed on the center of the ring under static load conditions Apply load. For chemically strengthened glass, it is preferable that the strengths of the first main surface and the second main surface satisfy F≧1500×t 2 , more preferably F≧1800×t 2 , and more preferably F≧2000×t 2 [where, F is the BoR surface strength (N) measured by the ball ring test, t is the thickness of the glass substrate (mm)]. By setting the BoR surface strength F(N) to the above range, even in the case of thinning, it exhibits excellent surface strength. Furthermore, the BoR test can be performed by the method described in the following examples. (Compressive stress layer) The compressive stress value and depth of the compressive stress layer of chemically strengthened glass can use EPMA (electron probe micro analyzer, electron probe micro analyzer) or surface stress meter (for example, FSM manufactured by Orihara Manufacturing Co., Ltd.) -6000) and so on. (Removal amount of glass surface (low-density layer)) The removal amount (thickness) of the glass surface (low-density layer) after alkali treatment can be measured by measuring the weight before and after the chemical solution treatment by using an analytical electronic balance and use the following formula to determine the thickness Obtained by conversion. (Removal thickness per single side)=[(weight before treatment)-(weight after treatment)]/(glass specific gravity)/treatment area/2 At this time, set the glass specific gravity to 2.48 (g/cm 3 ) for calculation . EXAMPLES Hereinafter, the present invention will be specifically described with examples, but the present invention is not limited to these. <Evaluation method> Various evaluations in this example were performed using the analysis methods shown below. (Evaluation of Glass: Surface Strength) The surface strength of the glass was measured by the Ball on Ring (BoR) test. In Fig. 1, there is shown a schematic diagram for explaining the ball ring test used in the present invention. In the state where the glass plate 1 is placed horizontally, press the glass plate 2 (hardened steel, diameter 10 mm, mirror polished) made of SUS (Steel Use Stainless) 304 to measure the surface of the glass plate strength. In Figure 1, on the SUS304 bearing jig 3 (diameter 30 mm, the contact part has a curvature of R2.5 mm, the contact part is hardened steel, mirror polished), a glass plate used as a sample is horizontally arranged. Above the glass plate, a pressure jig for pressing the glass plate is provided. In the form of this embodiment, the central area of the glass plate is pressurized from above the obtained glass plate. Furthermore, the test conditions are as follows. Lowering speed of the pressurized jig: 1.0 (mm/min) At this time, the breaking load (unit N) when the glass is broken is set as the BoR surface strength, and the average value of 20 measurements is set as the BoR average surface strength. However, when the breaking point of the glass plate is more than 2 mm from the ball pressing position, it is excluded from the data used to calculate the average value. (Evaluation of glass: surface stress) The surface compressive stress value (CS, unit of MPa) of glass and the depth of compressive stress layer (DOL, unit of μm) are measured by the surface stress meter (FSM-6000) manufactured by Orihara Manufacturing Co., Ltd. Determination. (Evaluation of Glass: Removal Amount) The removal thickness of the glass is obtained by measuring the weight before and after the chemical solution treatment with an analytical electronic balance (HR-202i, manufactured by AND) and converting the thickness using the following formula. (Removal thickness per single side)=[(weight before treatment)-(weight after treatment)]/(glass specific gravity)/treatment area/2 At this time, set the glass specific gravity to 2.48 (g/cm 3 ) for calculation . (Glass evaluation: cracks or potential damages) Whether there are cracks or potential damages on the glass surface is visually inspected under a light source with an illuminance of 1500 Lux. If there is no visible defect, it is judged that there is no crack or potential damage . <Example 1> (Step of performing ion exchange) Put 8454 g of potassium nitrate, 1324 g of potassium carbonate, and 222 g of sodium nitrate into a crucible made of stainless steel (SUS), and heat to 490°C with a heating mantle to prepare 10 mol of potassium carbonate %, 6000 wtppm of sodium molten salt. The molten salt contains water vapor by introducing air that has been introduced into the water heated to 55°C into the environment near the interface of the molten salt. The experimental system is shown in Figure 3. Air is used as the dry gas A, and humidified by passing the air into water 24 heated to 55°C in a water tank 25, the humidified water vapor is prepared. The gas (air) B. The gas B containing water vapor is introduced to the upper space of the inorganic salt (molten salt) 26 of the tank for chemical strengthening through a heated path by using an electric heating tape, thereby controlling the dew point in the step of ion exchange. At this time, the water vapor supply rate per 1 cm 3 is 0.02 mg/min, and the dew point near the interface of the molten salt is 38°C. Prepare a glass plate A of 50 mm×50 mm×0.7 mm, preheat it to 350～400℃, immerse it in molten salt at 490℃ for 1 hour, perform ion exchange treatment, and cool it to around room temperature for chemical Strengthen processing. The obtained chemically strengthened glass is washed with water and used for the next step. The glass composition of glass plate A (indicated by mole% on the basis of oxide): SiO 2 is 64.2%, Al 2 O 3 is 8.0%, Na 2 O is 12.5%, K 2 O is 4.0%, and MgO is 10.5%, CaO is 0.1%, SrO is 0.1%, BaO is 0.1%, ZrO 2 is 0.5% (step 1: step of removing a part of the surface: step of contacting with acid) Prepare 6.0% by weight of nitric acid in a beaker (by ion exchange water Dilute 1.38 nitric acid (manufactured by Kanto Chemical Co., Ltd.), and adjust the temperature to 40°C using a water bath. The glass obtained by the above chemical strengthening step is immersed in the prepared nitric acid for 120 seconds, and acid treatment is performed. After that, the glass was washed with water and used for the next step. (Step 2 of removing part of the surface: Step of contact with alkali) Prepare a 4.0% by weight sodium hydroxide aqueous solution (diluted with ion-exchange water 48% sodium hydroxide solution (manufactured by Kanto Chemical Co.)) in a beaker, and use a water bath Adjust the temperature to 40°C. After the step of contacting with acid, the cleaned glass is immersed in the prepared sodium hydroxide aqueous solution for 120 seconds for alkali treatment. After that, the glass is washed with water to clean the alkali on the glass surface. After that, it is dried by blowing air. Through the above, the chemically strengthened glass of Example 1 was obtained. No cracks and potential damage were confirmed in the obtained chemically strengthened glass. <Example 2> The potassium carbonate concentration of the molten salt in the ion exchange step was set to 8 mol%, the dew point near the interface of the molten salt was set to 71°C, and the chemical strengthening treatment conditions were set to be performed at 450°C Except for 2 hours, a chemically strengthened glass was produced in the same manner as in Example 1. In addition, the supply amount of water vapor per 1 cm 3 when a gas containing water vapor is introduced to control the dew point is 0.08 mg/min. No cracks and potential damage were confirmed in the obtained chemically strengthened glass. <Comparative Example 1> A chemically strengthened glass was produced in the same manner as in Example 2, except that the dew point near the interface of the molten salt in the step of performing ion exchange was 9°C. Furthermore, no gas containing water vapor was introduced in order to control the dew point. No cracks and potential damage were confirmed in the obtained chemically strengthened glass. <Comparative Example 2> A chemically strengthened glass was produced in the same manner as in Comparative Example 1 except that potassium carbonate was not added to the molten salt in the step of performing ion exchange, sodium was set to 2000 ppm by weight, and acid treatment and alkali treatment were not performed. No cracks and potential damage were confirmed in the obtained glass. <Example 3> Except for using the glass plate B, a chemically strengthened glass was produced under the same conditions as in Example 1. No cracks and potential damage were confirmed in the obtained chemically strengthened glass. The glass composition of glass plate B (indicated by mole% on the basis of oxide): SiO 2 is 68.0%, Al 2 O 3 is 12.0%, Na 2 O is 18.6%, and MgO is 8.0%. <Example 4> Except for the use of Except for the same glass in Example 3, a chemically strengthened glass was produced under the same conditions as in Example 2. No cracks and potential damage were confirmed in the obtained chemically strengthened glass. <Comparative Example 3> A chemically strengthened glass was manufactured under the same conditions as in Comparative Example 1, except that the same glass as in Example 3 was used. No cracks and potential damage were confirmed in the obtained chemically strengthened glass. <Comparative Example 4> A chemically strengthened glass was manufactured under the same conditions as in Comparative Example 2 except that the same glass as in Example 3 was used. No cracks and potential damage were confirmed in the obtained glass. <Example 5> (Step of performing ion exchange) A chemically strengthened glass was manufactured under the same conditions as Example 2, except that a glass plate C with a thickness of 0.55 mmt was used and the dew point near the interface of the molten salt was set to 66°C. No cracks and potential damage were confirmed in the obtained chemically strengthened glass. Glass composition of glass plate C (indicated by mole% on the basis of oxide): SiO 2 is 67%, B 2 O 3 is 4%, Al 2 O 3 is 13%, Na 2 O is 14%, K 2 O< 1%, MgO 2%, CaO<1% <Comparative Example 5> A chemically strengthened glass was produced under the same conditions as in Comparative Example 2 except that the same glass as in Example 5 was used. No cracks and potential damage were confirmed in the obtained chemically strengthened glass. Various evaluations were performed on the chemically strengthened glass obtained above. Table 1 shows the processing conditions and evaluation results of the glass. Furthermore, the BoR average surface strength is displayed as the BoR surface strength. [Table 1] As described above, when Examples 1 to 5 and Comparative Examples 1 to 5 were visually inspected under a light source with an illuminance of 1500 Lux, no cracks and potential damage were confirmed. However, as shown in Table 1, Examples 1 to 5 show higher BoR surface strength F(N) than Comparative Examples 1 to 5. The reason why Examples 1 to 5 show higher BoR surface strength F(N) than Comparative Examples 1 to 5 can be thought of as follows. In the manufacturing method of the present invention, the step of ion exchange between the alkali ions of the glass plate and the other alkali ions of the inorganic salt in an environment with a dew point temperature of 20°C or higher can increase the chemical strengthening of the glass. The amount of water vapor in the molten salt forms a low-density layer with a depth above the average depth of cracks or potential damage on the glass surface. By removing a part of the surface of the glass plate that has undergone the ion exchange, the low-density layer can be removed, and the cracks or potential damage can be fully removed, or the number can be fully reduced to achieve a higher BoR surface strength F (N). The present invention will be described in detail with reference to specific aspects, but the industry knows that various changes and modifications can be made without departing from the spirit and scope of the present invention. In addition, this application is based on the Japanese patent application (Japanese Patent Application 2015-256894) filed on December 28, 2015, and the entirety is used by reference. Also, all reference systems cited here are incorporated into this text as a whole. [Industrial Applicability] According to the method for manufacturing chemically strengthened glass of the present invention, after chemical strengthening, it is possible to obtain chemically strengthened glass with very high surface strength without polishing or etching using hydrofluoric acid. That is, it is possible to obtain a chemically strengthened glass that does not have poor appearance caused by the expansion of potential damage caused by etching treatment with hydrofluoric acid or the like, or polishing damage caused by polishing, and has excellent surface strength. Therefore, regardless of the presence or extent of the surface damage and potential damage of the glass before the chemical strengthening treatment, it can be applied to all glass and has high versatility. In addition, since it can be processed by immersing in a solution, it is efficient in terms of easy handling of various glass shapes or large-area glass. Furthermore, compared to etching treatment using hydrofluoric acid or the like, it has higher safety and lower cost.
