以下，一面參照圖式，一面對本發明之實施形態進行說明。於各圖式中，有時導入XYZ軸座標。 圖1(a)係表示本實施形態之研磨墊100之模式性立體圖。 研磨墊100具備研磨層101、接著層102及緩衝層103。 研磨層101係抵接於被研磨物而進行研磨之層。以下，將研磨層101之表面設為研磨面101a。亦可於研磨面101a形成用以使漿液之流動較佳之溝槽及孔(未圖示)。 接著層102係將研磨層101與緩衝層103接著之層，例如為黏著帶。 緩衝層103係使研磨層101更均勻地抵接於被研磨物之層。緩衝層103可由不織布或合成樹脂等具有可撓性之材料構成。 研磨墊100藉由配設於緩衝層103之黏著帶等而貼附於研磨裝置。研磨墊100之大小(直徑)可根據研磨裝置之尺寸等決定，例如，可設為直徑10 cm～1 m左右。再者，研磨墊100之形狀並不限於圓板狀，亦可為帶狀等。 研磨墊100以由研磨裝置按壓至被研磨物之狀態被旋轉驅動，而研磨被研磨物。此時，對研磨墊100與被研磨物之間供給漿液。漿液經由溝槽或孔而被供給至研磨面101a，並被排出。 [研磨層之構成] 圖1(b)係本實施形態之研磨墊100之模式性剖視圖。 於研磨墊100中，研磨層101包含聚合物110及中空微粒子(微小中空球體)111。 聚合物110係研磨材料之主要之構成材料。聚合物110可為藉由預聚物與硬化劑之聚合反應而生成之聚合物。作為此種聚合物，可列舉聚胺基甲酸酯。聚胺基甲酸酯之獲取性及加工性較佳，且具有較佳之研磨特性，因此，適合作為聚合物110。 預聚物可設為具有異氰酸基末端之化合物(以下，異氰酸酯化合物)，係藉由使聚異氰酸酯化合物與多元醇化合物於通常使用之條件下反應而獲得之化合物，且係分子內包含聚胺基甲酸酯鍵及異氰酸基者。又，亦可於不損害本發明之效果之範圍內，在含有聚胺基甲酸酯鍵之異氰酸酯化合物中包含其他成分。 聚異氰酸酯化合物意指分子內具有2個以上之異氰酸基之化合物，例如可使用二苯基甲烷二異氰酸酯。 除此以外，作為聚異氰酸酯化合物，可列舉間苯二異氰酸酯、對苯二異氰酸酯、2,6-甲苯二異氰酸酯(2,6-TDI)、2,4-甲苯二異氰酸酯(2,4-TDI)、萘-1,4-二異氰酸酯、二苯基甲烷-4,4'-二異氰酸酯、3,3'-二甲氧基-4,4'-聯苯二異氰酸酯、3,3'-二甲基二苯基甲烷-4,4'-二異氰酸酯、苯二甲基-1,4-二異氰酸酯、4,4'-二苯基丙烷二異氰酸酯、三亞甲基二異氰酸酯、六亞甲基二異氰酸酯(HDI)、異佛爾酮二異氰酸酯、伸丙基-1,2-二異氰酸酯、伸丁基-1,2-二異氰酸酯、伸環己基-1,2-二異氰酸酯、伸環己基-1,4-二異氰酸酯、二環己基甲烷-4,4'-二異氰酸酯(氫化MDI)、對苯二異硫氰酸酯、苯二甲基-1,4-二異硫氰酸酯及次乙基二異硫氰酸酯。可使用其等之1種或2種以上。 又，所謂多元醇化合物意指分子內具有2個以上之醇性羥基(OH)之化合物，例如，可使用聚(氧四亞甲基)二醇(或聚四亞甲基醚二醇)(PTMG)或二乙二醇(DEG)。 除此以外，作為多元醇化合物，可列舉乙二醇、丁二醇等二醇化合物、三醇化合物等；PTMG等聚醚多元醇化合物；乙二醇與己二酸之反應物或丁二醇與己二酸之反應物等聚酯多元醇化合物；聚碳酸酯多元醇化合物、聚己內酯多元醇化合物等。可使用其等之1種或2種以上。 硬化劑可利用聚胺系硬化劑。聚胺系硬化劑係具有2個以上之胺基之物質，可使用MOCA(3,3-二氯-4,4-二胺基二苯基甲烷)。又，作為聚胺系硬化劑，亦可利用包含3分子之氯苯胺經由亞甲基鍵結而成之三聚體之多聚體MOCA。又，亦可利用MOCA以外之聚胺系硬化劑。 又，硬化劑亦可利用多元醇系硬化劑。多元醇系硬化劑係具有2個以上之羥基之物質，例如，可設為乙二醇或聚醚多元醇。 除此以外，作為多元醇系硬化劑，可列舉丁二醇及己二醇等低分子量之多元醇化合物、以及聚乙二醇、聚丙二醇、聚四亞甲基醚二醇(PTMG)、雙酚A與環氧丙烷之反應物等聚醚多元醇化合物、乙二醇與己二酸之反應物、丁二醇與己二酸之反應物等聚酯多元醇化合物、聚碳酸酯多元醇化合物及聚己內酯多元醇化合物等高分子量之多元醇化合物。 硬化劑可利用聚胺系硬化劑與多元醇系硬化劑中之1種或複數種。 此處，以存在於硬化劑之胺基或羥基活性氫基相對於存在於預聚物之末端之異氰酸基之當量比即R值成為0.70～1.20之方式將各成分混合。R值較佳為0.70～1.20，更佳為0.80～1.00，進而較佳為0.85～0.95。藉由將R值設為1以下，而將成為過剩之異氰酸基用於下述交聯反應。 中空微粒子111分散至聚合物110。中空微粒子111係中空之球體狀之物體。於研磨面101a中露出之半球狀之中空微粒子111係於形成研磨層101之後，藉由切斷加工而露出者。 圖1(c)係本實施形態之中空微粒子111之模式性剖視圖。 中空微粒子111具有由熱塑性樹脂構成之球殼狀之外殼111a、及被外殼111a包圍之內部空間111b。中空微粒子111可設為藉由利用熱塑性樹脂殼將液狀之低沸點烴包圍並進行加熱而形成者。作為中空微粒子111，可使用已經被加熱而膨脹之已膨脹型者，亦可使用藉由伴隨著上述聚胺基甲酸酯之生成反應之生成熱而膨脹之未膨脹型者。 藉由加熱而使熱塑性樹脂軟化並且使低沸點烴變化為氣體，熱塑性樹脂因氣體之壓力而膨脹，藉此形成中空微粒子111。低沸點烴例如使用異丁烷或戊烷等，熱塑性樹脂例如使用偏二氯乙烯或丙烯腈。 中空微粒子111亦可利用市售品。例如，可將Matsumoto Microsphere Series(松本油脂製藥股份有限公司製造)或Expancel Series(AkzoNobel公司製造)用作中空微粒子111。 中空微粒子111之大小並無特別限定，可設為直徑數20 μm～200 μm左右，又，亦可使用2種以上直徑不同之中空微粒子。研磨材料中之中空微粒子111之含有比率較佳為相對於研磨材料為10～60體積%，更佳為15～45體積%。若研磨層101因研磨而磨耗，則中空微粒子111於研磨面101a露出，而對研磨面101a之研磨特性造成影響。可藉由使此種樹脂製之中空微粒子111分散至研磨層101，而使研磨層101中之空隙之大小均勻。進而，可藉由中空微粒子111之投入量而調整研磨墊100之研磨特性。 [研磨墊之製造裝置1] 於說明研磨墊100之製造方法之前，對製造研磨墊100之製造裝置進行說明。 圖2係用於本實施形態之研磨墊100之製造之製造裝置200之模式圖。 製造裝置200具備第1儲槽201(第1槽)、第2儲槽202(第2槽)、攪拌槽203(混合容器)、模具204、容器212、濾器400、泵401(第1泵)、泵401(第2泵)、切換閥410、切換閥420、流路501a、流路501b、流路501c、流路502a、流路502b、流路502c及流路503。 第1儲槽201可收容包含中空微粒子111及預聚物之內容物(液體)。中空微粒子111預先收容於設置於第1儲槽201之上之容器212。中空微粒子111經由流路503而自容器212投入至第1儲槽201。藉由經由此種流路503將中空微粒子111自容器212投入至第1儲槽201，而抑制中空微粒子111向第1儲槽201外之飛散。第2儲槽202可收容使預聚物硬化之硬化劑。攪拌槽203將包含中空微粒子111及預聚物之液體與硬化劑混合而形成研磨材料301。 可藉由使此種樹脂製之中空微粒子111分散至研磨層101，而使研磨層101中之空隙之大小均勻。進而，可藉由中空微粒子111之投入量而調整研磨墊100之研磨特性。 泵401可將包含中空微粒子111及預聚物之液體自第1儲槽201供給至攪拌槽203。泵401設置於流路501a之中途。若藉由切換閥410將流路501a與流路501b連通，使泵401作動，則經由流路501a、501b而將包含中空微粒子111及預聚物之液體自第1儲槽201供給至攪拌槽203。 泵402可將硬化劑自第2儲槽202供給至攪拌槽203。泵402設置於流路502a之中途。若藉由切換閥420將流路502a與流路502b連通，使泵402作動，則經由流路502a、502b而將硬化劑自第2儲槽202供給至攪拌槽203。 又，於製造裝置200中，若藉由切換閥410將流路501a與流路501c連通，且使泵401作動，則包含中空微粒子111及預聚物之液體經由流路501a、501c而於第1儲槽201與泵401之間循環。又，若藉由切換閥420將流路502a與流路502c連通，且使泵402作動，則硬化劑經由流路502a、502c而於第2儲槽202與泵402之間循環。模具204自攪拌槽203接受研磨材料301，且由研磨材料301形成研磨層101。 濾器400可於將包含中空微粒子111及預聚物之液體供給至攪拌槽203之前，將包含於該液體之異物去除。例如，濾器400設置於流路501a之中途，且設置於泵401之上游。異物例如較中空微粒子111之直徑(例如，最大粒徑)大。中空微粒子111之直徑例如係由雷射繞射式粒度分佈測定裝置、電子顯微鏡像等算出。 於濾器400內設置有過濾網(filter)400f。過濾網400f例如具有複數個貫通孔。過濾網400f例如由篩網構件、多孔狀之板材等構成。過濾網400f亦可於濾器400內配置複數個。中空微粒子111及預聚物通過該貫通孔，大於中空微粒子111之直徑之異物無法通過過濾網400f。即，異物係藉由濾器400而被去除。 於本實施形態中，所謂異物例如係異氰酸酯化合物與附著於中空微粒子111之微量之水進行反應而生成之粒子。該粒子例如係預聚物硬化而形成之粒子。或者，所謂異物係複數個中空微粒子111凝集而成之粒子。若此種粒子混入至研磨層101，則研磨層101之研磨特性會顯著地降低。例如，研磨層101內之中空微粒子111之分散會變得不均勻，或混入至研磨層101內之異物會對被研磨物造成損傷。 此處，對於附著於中空微粒子111之水，亦有於將中空微粒子111投入至第1儲槽201之前，充分地進行脫水而去除之方法。作為脫水方法，例如有加熱乾燥。然而，若進行加熱乾燥，則有因熱而導致中空構造之中空微粒子111變形或中空微粒子111破裂之情形。又，亦有利用有機溶劑將中空微粒子111事先洗淨之方法。但是，由於中空微粒子111係利用熱塑性樹脂構成，故而若中空微粒子111與有機溶劑接觸，則中空微粒子111會變形或溶解。 又，亦有為了避免附著於中空微粒子111之水與異氰酸酯化合物之反應，而將中空微粒子111投入至第2儲槽202之方法。然而，收容於第1儲槽201之液體之容量較收容於第2儲槽202之液體之容量大數倍(例如3倍左右)。因此，為了使中空微粒子111更均勻地分散至研磨材料301，較理想為將中空微粒子111投入至容量更大之第1儲槽201。 因此，於投入有中空微粒子111之第1儲槽201內，必然會產生異物。較理想為此種異物於與硬化劑混合存在之前藉由濾器400被除掉。 進而，亦存在如下情形，即，於中空微粒子111附著有在中空微粒子之形成時使用之觸媒之金屬成分。存在此種金屬成分亦成為異物而混合存在於第1儲槽201內之液體之情形。進而，於容器212之內壁之至少一部分或流路503之內壁之至少一部分由金屬構成之情形時，亦有金屬成分自該內壁混入至第1儲槽201內之情形。 為了將此種金屬成分去除，濾器400亦可具有可去除金屬成分之機構。例如，亦可將多孔狀或纖維狀之金屬吸附體設置於濾器400內。金屬吸附體可設置於過濾網400f之上游，亦可設置於過濾網400f之下游。 或者，金屬吸附體亦可設置於濾器400外之流路501a中而非濾器400內。亦即，過濾網400f及金屬吸附體亦可於流路501a之中途多段地設置。或者，亦可為過濾網400f本身係吸附金屬成分之吸附體。進而，流路501a之內壁亦可由金屬吸附體構成。又，濾器400亦可設置於泵401之下游，但藉由將濾器400設置於泵401之上游，而抑制異物向泵401內之流入，從而不易對泵401造成損傷。 [研磨墊之製造方法1] 其次，對研磨墊100之製造方法進行說明。 例如，將預聚物及中空微粒子111投入至第1儲槽201。預聚物可設為異氰酸酯化合物。將硬化劑投入至第2儲槽202。硬化劑係多元醇系硬化劑及聚胺系硬化劑之兩者或者一者。為了使各原料之流動性穩定，第1儲槽201及第2儲槽202被加熱至特定溫度。 其次，將第1儲槽201內之內容物(以下，第1溶液)自第1儲槽201通過濾器400而送出至攪拌槽203。藉此，於將第1溶液送出至攪拌槽203之前，自第1溶液將異物去除。將第2儲槽202之內容物(以下，第2溶液)自第2儲槽202送出至攪拌槽203。藉此，於攪拌槽203形成第1溶液及第2溶液混合而成之流體狀之研磨材料301。 其次，使研磨材料301流入至模具204而進行澆鑄成型。於研磨材料301中，預聚物與硬化劑進行聚合反應。此時，亦可對模具204進行加熱。與聚合反應之進行一併使混合物硬化，從而形成包含聚合物之塊狀物。 對所獲得之塊狀物進行加熱，而進行聚合物之交聯反應。進而，藉由將塊狀物切割，而獲得研磨層101。於研磨層101積層接著層102及緩衝層103並裁斷為所需之形狀，而形成研磨墊100。亦可視需要於研磨層101形成溝槽等。 如此，根據本實施形態，藉由濾器400將上述異物去除，而抑制異物混入至研磨墊100之研磨層101中。藉此，形成具有所需特性之研磨墊。 再者，中空微粒子111係細小之微粒子，若將中空微粒子111自第1儲槽201之上方投入至第1儲槽201，則會於第1儲槽201內飛舞，而中空微粒子111可能會附著於第1儲槽201之內壁。其結果，可能無法使中空微粒子111高效率地分散至預聚物中。因此，亦可將中空微粒子111自第1儲槽201之下側經由流路而投入。藉此，中空微粒子111於投入至第1儲槽201之後直接混入至積存於第1儲槽201之底部之預聚物。 又，於上述說明中，中空微粒子111被投入至第1儲槽201，但亦可將中空微粒子111投入至第2儲槽202。於此情形時，亦可與投入至第1儲槽201之方法同樣地，自第2儲槽202之下側利用流路而將中空微粒子111投入至第2儲槽202。 進而，於上述說明中，對將中空微粒子111投入至預聚物112之方法進行了說明，但除中空微粒子以外，亦可利用上述方法投入比重較小而可能會飛散之微粒子、例如氧化鈰等研磨粒或填料等。 [研磨墊之製造裝置2] 研磨墊100亦可利用以下之製造裝置及製造方法製造。 圖3係用於本實施形態之研磨墊100之製造之製造裝置1200之模式圖。 製造裝置1200具備第1儲槽1201(第1槽)、第2儲槽1202(第2槽)、攪拌槽1203(混合容器)、模具1204、泵1401(第1泵)、泵1402(第2泵)及控制裝置1601。進而，製造裝置1200具備切換閥1410、切換閥1420、流路1501a、流路1501b、流路1502a、流路1502b、容器1212、流路1503、容器1213及流路1504。製造裝置1200利用控制裝置1601對上述各零件統一進行自動控制。或者，於製造裝置1200中，亦可解除控制裝置1601對各零件之控制，而手動地使各零件動作。 第1儲槽1201可收容預聚物。於第1儲槽1201中，可於預聚物中混合中空微粒子111。例如，中空微粒子111預先收容於容器1212。容器1212經由流路1503而連接於第1儲槽1201。中空微粒子111經由流路1503而自容器1212投入至第1儲槽1201。 中空微粒子111係細小之微粒子，若將中空微粒子111自第1儲槽1201之上方投入至第1儲槽1201，則可能會在第1儲槽1201內飛舞，而中空微粒子111可能會附著於第1儲槽1201之內壁。其結果，可能無法使中空微粒子111高效率地分散至預聚物中。因此，中空微粒子111自第1儲槽1201之下側經由流路1503而投入。藉此，中空微粒子111被投入至第1儲槽1201之後直接混入至積存於第1儲槽1201之底部之預聚物。 第2儲槽1202可收容硬化劑。於製造裝置1200中，亦可於第2儲槽1202中，使中空微粒子111混合於硬化劑中。例如，中空微粒子111預先收容於容器213。容器213經由流路1504而連接於第2儲槽1202。中空微粒子111經由流路1504而自容器1213被投入至第2儲槽1202。 中空微粒子111可混合存在於第1儲槽1201或第2儲槽1202之任一者，亦可混合存在於第1儲槽1201及第2儲槽1202之兩者。又，中空微粒子111之比重較預聚物及硬化劑之比重更輕。因此，藉由將中空微粒子111自第1儲槽1201及第2儲槽1202之下方投入至第1儲槽1201及第2儲槽1202，中空微粒子111於第1儲槽1201及第2儲槽1202之各者中高效率地分散。 泵1401可將收容於第1儲槽1201內之內容物(以下，第1液體)自第1儲槽1201供給至攪拌槽1203。泵1401設置於流路1501a之中途。設置於流路1501a之中途之泵1401之數量並不限於1個。例如，亦可為複數個泵1401並列設置於流路1501a之中途。又，於流路1501a，經由切換閥1410而連接有流路1501b及流路1501c。切換閥1410係所謂三向閥。 例如，於將收容於第1儲槽1201內之第1液體自第1儲槽1201供給至攪拌槽1203時，藉由切換閥1410而使流路1501a與流路1501b連通。然後，藉由泵1401之作動，將第1液體自第1儲槽1201通過流路1501a、流路1501b而供給至攪拌槽1203。此處，於將第1液體自第1儲槽1201供給至攪拌槽1203時，流入至泵1401內之第1液體之流量被控制為特定之流量(第1流量)。 又，於製造裝置1200中，亦可停止向攪拌槽1203供給第1液體。此時，於製造裝置1200中，可使第1液體於泵1401與第1儲槽1201之間循環。例如，藉由切換閥1410而使流路1501a與流路1501c連通。然後，藉由泵1401之作動，將第1液體自第1儲槽1201通過流路1501a、流路1501c而回送至第1儲槽1201。重複進行該液體之回送動作。 此處，於第1液體在泵1401與第1儲槽1201之間循環時，流入至泵1401內之第1液體之流量被控制為小於第1流量。將該較第1流量小之流量設為第2流量。第2流量例如調整為第1流量之50%以下。例如，藉由調整泵1401之轉數，而將第1液體之流量調整為第1流量或第2流量。又，於停止向攪拌槽1203供給第1液體時，亦可使泵1401本身停止。又，亦可交替地重複泵1401之作動與停止。 泵1402可將收容於第2儲槽1202內之內容物(以下，第2液體)自第2儲槽1202供給至攪拌槽1203。泵1402設置於流路1502a之中途。設置於流路1502a之中途之泵1402之數量並不限於1個。例如，亦可為複數個泵1402並列設置於流路1502a之中途。又，於流路1502a，經由切換閥1420而連接有流路1502b及流路1502c。切換閥1420係所謂三向閥。 例如，於將收容於第2儲槽1202內之第2液體自第2儲槽1202供給至攪拌槽1203時，藉由切換閥1420而使流路1502a與流路1502b連通。然後，藉由泵1402之作動，而將第2液體自第2儲槽1202通過流路1502a、流路1502b而供給至攪拌槽1203。此處，於將第2液體自第2儲槽1202供給至攪拌槽1203時，流入至泵1402內之第2液體之流量被控制為特定之流量(第3流量)。 又，於製造裝置1200中，亦可停止向攪拌槽1203供給第2液體。此時，於製造裝置1200中，可使第2液體於泵1402與第2儲槽1202之間循環。例如，藉由切換閥1420而使流路1502a與流路1502c連通。然後，藉由泵1402之作動，將第2液體自第2儲槽1202通過流路1502a、流路1502c而回送至第2儲槽1202。重複進行該液體之回送動作。 此處，於第2液體在泵1402與第2儲槽1202之間循環時，流入至泵1402內之第2液體之流量被控制為較第3流量小。將該較第3流量小之流量設為第4流量。第4流量例如調整為第3流量之50%以下。例如，藉由調整泵1402之轉數而將第2液體之流量調整為第3流量或第4流量。又，於停止向攪拌槽1203供給第2液體時，亦可使泵1402本身停止。又，亦可交替地重複泵1402之作動與停止。 於製造裝置1200中，上述切換閥1410之切換、及泵1401、1402之作動係藉由控制裝置1601而進行控制。作為泵1401、1402，較佳地使用定量型之螺旋式泵(例如，單螺桿泵)或定量型之容積式泵(例如正弦泵)，其中尤其使用往復泵或旋轉泵。該等泵於移送包含中空微粒子111之黏性流體(第1及第2液體)方面較優異。控制裝置1601於要降低液體之流量時，進行降低該等泵之轉數之控制，於要提高液體之流量時，進行提高該等泵之轉數之控制。 攪拌槽1203接收預聚物、硬化劑、及中空微粒子111，將該等預聚物、硬化劑、及中空微粒子111混合而形成研磨材料301。模具1204自攪拌槽1203接受研磨材料301並使研磨材料301硬化而形成研磨層101。 [研磨墊之製造方法2] 一面參照圖3，一面對研磨墊100之製造方法進行說明。研磨層101之製造係藉由控制裝置1601而進行控制。首先，對中空微粒子111僅混合存在於第1儲槽1201時之研磨墊之製造方法進行說明。 例如，將預聚物及中空微粒子111投入至第1儲槽1201。預聚物可設為異氰酸酯化合物。將硬化劑投入至第2儲槽1202。硬化劑係多元醇系硬化劑及聚胺系硬化劑之兩者或一者。為了使各原料之流動性穩定，將第1儲槽1201及第2儲槽1202加熱至特定溫度。 其次，將收容於第1儲槽1201之包含預聚物及中空微粒子111之液體(第1液體)以第1流量自第1儲槽1201供給至攪拌槽1203。例如，藉由利用控制裝置1601使泵1401作動，而將第1液體通過流路1501a、切換閥1410及流路1501b自第1儲槽1201供給至攪拌槽1203。此時，自泵1401噴出之第1液體之流量被控制為第1流量。 例如，於泵1401為單螺桿泵之情形時，第1流量被控制為30 rpm以上且150 rpm以下之任一流量。又，噴出量被控制為12000 g/min以上且30000 g/min以下之任一噴出量。噴出壓力被控制為0.5 MPa以上且1.0 MPa以下之任一噴出壓力。 進而，與第1液體之供給一併，將收容於第2儲槽1202之硬化劑通過泵1402而自第2儲槽1202供給至攪拌槽1203。例如，藉由利用控制裝置1601使泵1402作動，而將硬化劑通過流路1502a、切換閥1420及流路1502b自第2儲槽1202供給至攪拌槽1203。 例如，於泵1402為單螺桿泵之情形時，硬化劑之流量被控制為30 rpm以上且150 rpm以下之任一流量。又，噴出量被控制為4000 g/min以上且10000 g/min以下之任一之噴出量。噴出壓力被控制為0.1 MPa以上且0.4 MPa以下之任一之噴出壓力。 其次，於攪拌槽1203中形成第1液體與硬化劑混合而成之流動體狀之研磨材料301。其次，將研磨材料301自攪拌槽1203供給至模具1204。於研磨材料301中，預聚物與硬化劑進行聚合反應。此時，亦可對模具1204進行加熱。與聚合反應之進行一併使混合物硬化，而形成包含聚合物之塊狀物。然後，於模具1204中，使研磨材料301硬化而形成研磨層101。 例如，對所獲得之塊狀物進行加熱，而使聚合物之交聯反應進行。進而，藉由對塊狀物進行切割(切斷加工)，而獲得研磨層101。於研磨層101積層接著層102及緩衝層103，並裁斷為所需之形狀，而形成研磨墊100。亦可視需要於研磨層101形成溝槽等。 此處，於研磨層101之製造中，亦有必要暫時停止向攪拌槽1203供給第1液體及硬化劑。於本實施形態中，於該停止中之期間，使第1液體於泵1401與第1儲槽1201之間循環。例如，藉由對切換閥1410進行切換，使流路1501a與流路1501c連通，而以第1儲槽1201、流路1501a、切換閥1410、流路1501c、第1儲槽1201之順序使第1液體循環。 藉由該循環，而於第1儲槽1201內、流路1501a內及流路1501c內將比重彼此不同之預聚物與中空微粒子111高效率地混合。又，藉由繼續此種循環，於再開始向攪拌槽1203供給第1液體時，立即自流路1501b取出將中空微粒子111高效率地分散至預聚物而成之第1液體。若停止第1液體之循環，則殘存於第1儲槽1201或流路1501a之微量之空氣與預聚物反應，而容易於第1儲槽1201內或流路1501a內產生複數個預聚物固化而成之異物。 但是，若使第1液體長時間循環，則中空微粒子111每次通過泵1401時都會自泵1401持續受到負荷。例如，於泵1401為單螺桿泵之情形時，第1液體藉由泵1401內之轉子之旋轉而被擠出，並噴出至泵1401外。此處，第1液體包含預聚物，且具有特定之黏度。藉此，第1液體具有黏性阻力或慣性阻力。因此，每當第1液體通過泵1401時，都會對中空微粒子111施加應力。若此種負荷長時間持續，則有中空微粒子111變形或破損之情形。 若受到損傷之中空微粒子111混入至研磨層101，則研磨墊100有可能不會顯示所需之特性。例如，若破損之中空微粒子111或中空混入有預聚物之中空微粒子111進入至研磨層101內，則研磨層101之硬度會局部地變高，或研磨層101整體變硬而對被研磨物造成損傷。 因此，於本實施形態中，於使第1液體於泵1401與第1儲槽1201之間循環時，使第1液體於泵1401與第1儲槽1201之間以較第1流量小之第2流量循環。藉此，中空微粒子111於通過泵1401時不易自泵1401受到負荷，而抑制中空微粒子111之變形、破損。藉此，包含中空微粒子111之研磨墊100顯示所需之特性。 例如，於泵1401為單螺桿泵之情形時，第2流量被控制為15 rpm以上且75 rpm以下之任一之流量。又，噴出量被控制為6000 g/min以上且15000 g/min以下之任一之噴出量。噴出壓力被控制為0.25 MPa以上且0.5 MPa以下之任一之噴出壓力。 又，於複數個泵1401配置於流路1501a時，即便複數個泵1401之各者之噴出量被控制為第2流量，流經流路1501a、1501c之第1液體之流量亦為自各個泵1401噴出之流量之合計。藉此，於循環中，亦可一面抑制泵1401對中空微粒子111之負荷，一面使流經流路1501a、1501c之第1液體之流量與第1流量相同。又，於停止向攪拌槽1203供給第1液體及硬化劑時，為了進而降低泵1401對中空微粒子111之負荷，亦可使泵1401本身停止。 其後，再次將第1液體及硬化劑供給至攪拌槽1203，而再次形成研磨層101。即，於循環結束後，第1液體藉由泵1401而以第1流量自第1儲槽1201被供給至攪拌槽1203，並且硬化劑自第2儲槽1202被供給至攪拌槽1203。 其次，對中空微粒子111僅混合存在於第2儲槽1202時之研磨墊之製造方法進行說明。例如，將硬化劑及中空微粒子111投入至第2儲槽1202。將第2儲槽1202內之內容物設為第2液體。 其次，將收容於第1儲槽1201之預聚物自第1儲槽1201供給至攪拌槽1203。例如，藉由利用控制裝置1601使泵1401作動，而將預聚物通過流路1501a、切換閥1410及流路1501b自第1儲槽1201供給至攪拌槽1203。 例如，於泵1401為單螺桿泵之情形時，預聚物之流量被控制為30 rpm以上且150 rpm以下之任一之流量。又，噴出量被控制為12000 g/min以上且30000 g/min以下之任一之噴出量。噴出壓力被控制為0.5 MPa以上且1.0 MPa以下之任一之噴出壓力。 進而，與預聚物之供給一併，將收容於第2儲槽1202之第2液體通過泵1402自第2儲槽1202供給至攪拌槽1203。例如，藉由利用控制裝置1601使泵1402作動，而將第2液體通過流路1502a、切換閥1420及流路1502b自第2儲槽1202供給至攪拌槽1203。此時，自泵1401噴出之第2液體之流量被控制為第3流量。 例如，於泵1402為單螺桿泵之情形時，第2液體之流量被控制為30 rpm以上且150 rpm以下之任一之流量。又，噴出量被控制為4000 g/min以上且10000 g/min以下之任一之噴出量。噴出壓力被控制為0.1 MPa以上且0.4 MPa以下之任一之噴出壓力。 其次，於攪拌槽1203中形成預聚物與第2液體混合而成之流動體狀之研磨材料301。其次，將研磨材料301自攪拌槽1203供給至模具1204。然後，於模具1204中，使研磨材料301硬化，而形成研磨層101。 此處，於暫時停止向攪拌槽1203供給預聚物及第2液體時，使第2液體於泵1402與第2儲槽1202之間循環。例如，藉由對切換閥1420進行切換，使流路1502a與流路1502c連通，而以第2儲槽1202、流路1502a、切換閥1420、流路1502c、第2儲槽1202之順序使第2液體循環。 於使第2液體於泵1402與第2儲槽1202之間循環時，使第2液體於泵1402與第2儲槽1202之間以較第3流量小之第4流量循環。藉此，中空微粒子111於通過泵1402時，不易自泵1402受到負荷，而抑制中空微粒子111之變形、破損。藉此，包含中空微粒子111之研磨墊100顯示所需之特性。 例如，於泵1402為單螺桿泵之情形時，第4流量被控制為15 rpm以上且75 rpm以下之任一之流量。又，噴出量被控制為2000 g/min以上且5000 g/min以下之任一之噴出量。噴出壓力被控制為0.05 MPa以上且0.2 MPa以下之任一之噴出壓力。 又，於複數個泵1402配置於流路1502a時，即便將複數個泵1402之各者之噴出量控制為第4流量，流經流路1502a、1502c之第2液體之流量亦成為自各個泵1402噴出之流量之合計。藉此，於循環中，亦可一面抑制泵1402對中空微粒子111之負荷，一面使流經流路1502a、1502c之第2液體之流量與第3流量相同。又，於停止向攪拌槽1203供給預聚物及第2液體時，為了進一步減少泵1402對中空微粒子111之負荷，亦可使泵1402本身停止。 此後，再次將預聚物及第2液體供給至攪拌槽1203，而再次形成研磨層101。 進而，於本實施形態中，亦可使中空微粒子111混合存在於第1儲槽1201及第2儲槽1202之兩者，而自第1儲槽1201及第2儲槽1202之兩者將中空微粒子111供給至攪拌槽1203。 [研磨層之評價] 圖4(a)係表示第1儲槽1201中之第1液體之黏度與循環時間之關係之曲線圖。實線係使用單螺桿泵作為泵1401之情形之結果。虛線係使用正弦泵作為泵1401之情形之結果。 如圖4(a)所示，於單螺桿泵之情形時，當第1液體之循環時間為5小時以內時，第1液體之黏度維持6000(cp)以上。然而，若循環時間超過5小時，則第1液體之黏度減少至4500(cp)以下。進而，若循環時間超過20小時，則第1液體之黏度較4000(cp)更低。 於正弦泵之情形時，當第1液體之循環時間為5小時以內時，第1液體之黏度維持12000(cp)以上。然而，若循環時間超過5小時，則第1液體之黏度減少至8500(cp)以下。進而，若循環時間超過20小時，則第1液體之黏度較7000(cp)更低。 如此，若第1液體之循環時間超過5小時，則第1液體之黏度顯著地減少。亦即，認為持續受到來自泵之負荷之結果為中空微粒子111之損傷會不斷進展。因此，第1液體之循環時間較佳為5小時以內。 圖4(b)係表示研磨層101之密度與循環時間之關係之圖表。灰色之柱形圖係使用單螺桿泵之情形之結果。白色之柱形圖係使用正弦泵之情形之結果。 如圖4(b)所示，於第1液體之循環時間為5小時以內時，於單螺桿泵及正弦泵之任一情形時，研磨層101之密度均維持0.85(g/cm3
)以下。然而，若第1液體之循環時間超過5小時，則密度於單螺桿泵及正弦泵之任一情形時均上升至0.9(g/cm3
)左右。進而，若第1液體之循環時間達到48小時，則於單螺桿泵及正弦泵之任一情形時，密度均上升至1.0(g/cm3
)左右。 如此，若第1液體之循環時間超過5小時，則包含中空微粒子111之研磨層101之密度顯著地上升。因此，第1液體之循環時間較佳為5小時以內。 又，於本評估中，於任一情形時，均係於第1儲槽1201中準備第1液體100 kg，且將第1液體之流量設為18 kg/min而進行，因此，理論上每5.6分鐘第1液體通過泵1401一次。每當通過泵1401時，中空微粒子111可能會因泵1401而變形、破損，但如上所述，若為5小時以內、即理論上之第1液體之泵通過次數為54次以內，則可將中空微粒子111之變形、破損抑制於特定範圍內。因此，較佳為將理論上之第1液體之泵通過次數設為54次以內。另一方面，若理論上之第1液體之泵通過次數超過上述次數，則中空微粒子111之變形、破損會增加，而研磨層101之密度會顯著地上升。 圖4(c)係表示研磨層101之蕭氏D硬度與循環時間之關係之圖表。灰色之柱形圖係使用單螺桿泵之情形之結果。白色之柱形圖係使用正弦泵之情形之結果。 如圖4(c)所示，於第1液體之循環時間為5小時以內(或理論上之第1液體之泵通過次數為54次以內)時，於單螺桿泵及正弦泵之任一情形時，研磨層101之蕭氏D硬度均維持48以下。然而，若第1液體之循環時間超過5小時(或理論上之第1液體之泵通過次數超過54次)，則蕭氏D硬度於單螺桿泵及正弦泵之任一情形時均上升至50左右。進而，若第1液體之循環時間達到48小時，則硬度於單螺桿泵及正弦泵之任一情形時均上升至52(°)左右。 如此，若第1液體之循環時間超過5小時(或理論上之第1液體之泵通過次數超過54次)，則包含中空微粒子111之研磨層101之硬度會顯著地上升。因此，第1液體之循環時間較佳為5小時以內(或理論上之第1液體之泵通過次數為54次以內)。 如以上所說明般，若第1液體之循環時間為5小時以內(或理論上之第1液體之泵通過次數為54次以內)，則抑制對中空微粒子111施加之應力，而抑制中空微粒子111之變形、破損。藉此，包含中空微粒子111之研磨墊100顯示所需之特性。 圖5係表示研磨層101之剖面圖像與循環時間之關係之圖。剖面圖像係藉由電子顯微鏡而取得。 如圖5所示，於第1液體之循環時間為5小時以內(或理論上之第1液體之泵通過次數為54次以內)時，於單螺桿泵及正弦泵之任一情形時，均使中空微粒子111均勻地分散至研磨層101。然而，若第1液體之循環時間超過5小時而達到24小時，則有中空微粒子111在研磨層101中之分散較5小時以內稀疏之傾向。若第1液體之循環時間達到48小時，則該傾向變得更顯著。即，使第1液體循環之時間較佳為5小時以內(或理論上之第1液體之泵通過次數為54次以內)。 以上，對本發明之實施形態進行了說明，當然本發明並不僅限定於上述實施形態，可施加各種變更。Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, XYZ axis coordinates may be introduced. FIG.1(a) is a schematic perspective view which shows the polishing pad 100 of this embodiment. The polishing pad 100 includes a polishing layer 101 , an adhesive layer 102 and a buffer layer 103 . The polishing layer 101 is a layer for polishing in contact with the object to be polished. Hereinafter, the surface of the polishing layer 101 is referred to as the polishing surface 101a. Grooves and holes (not shown) for better flow of the slurry can also be formed on the polishing surface 101a. The next layer 102 is a layer connecting the polishing layer 101 and the buffer layer 103, such as an adhesive tape. The buffer layer 103 is a layer that makes the polishing layer 101 abut the object to be polished more uniformly. The buffer layer 103 can be made of a flexible material such as non-woven fabric or synthetic resin. The polishing pad 100 is attached to the polishing apparatus by an adhesive tape or the like arranged on the buffer layer 103 . The size (diameter) of the polishing pad 100 can be determined according to the size of the polishing apparatus and the like, for example, it can be set to about 10 cm to 1 m in diameter. In addition, the shape of the polishing pad 100 is not limited to a disk shape, and may be a belt shape or the like. The polishing pad 100 is driven to rotate while being pressed against the object to be polished by the polishing device, thereby polishing the object to be polished. At this time, the slurry is supplied between the polishing pad 100 and the object to be polished. The slurry is supplied to the polishing surface 101a through the grooves or holes, and is discharged. [Configuration of Polishing Layer] FIG. 1( b ) is a schematic cross-sectional view of the polishing pad 100 of the present embodiment. In the polishing pad 100 , the polishing layer 101 includes a polymer 110 and hollow fine particles (micro hollow spheres) 111 . The polymer 110 is the main constituent material of the abrasive material. The polymer 110 may be a polymer formed by the polymerization of a prepolymer and a hardener. As such a polymer, polyurethane is mentioned. Polyurethane has better availability and processability, and has better grinding properties, so it is suitable as the polymer 110 . The prepolymer can be a compound having an isocyanate group terminal (hereinafter, an isocyanate compound), which is a compound obtained by reacting a polyisocyanate compound and a polyol compound under commonly used conditions, and which contains a polymer in the molecule. urethane bonds and isocyanate groups. Moreover, in the range which does not impair the effect of this invention, other components may be contained in the isocyanate compound containing a polyurethane bond. The polyisocyanate compound means a compound having two or more isocyanate groups in the molecule, and for example, diphenylmethane diisocyanate can be used. In addition, as the polyisocyanate compound, isophenylene diisocyanate, p-phenylene diisocyanate, 2,6-toluene diisocyanate (2,6-TDI), and 2,4-toluene diisocyanate (2,4-TDI) can be mentioned. , naphthalene-1,4-diisocyanate, diphenylmethane-4,4'-diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl diisocyanate, 3,3'-dimethylene diphenylmethane-4,4'-diisocyanate, xylylene-1,4-diisocyanate, 4,4'-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate (HDI), isophorone diisocyanate, propylidene-1,2-diisocyanate, butylene-1,2-diisocyanate, cyclohexylene-1,2-diisocyanate, cyclohexylene-1, 4-Diisocyanate, dicyclohexylmethane-4,4'-diisocyanate (hydrogenated MDI), p-phenylenediisothiocyanate, xylylene-1,4-diisothiocyanate and ethylene glycol Diisothiocyanate. One or more of these can be used. In addition, the polyol compound means a compound having two or more alcoholic hydroxyl groups (OH) in the molecule, for example, poly(oxytetramethylene) glycol (or polytetramethylene ether glycol) ( PTMG) or diethylene glycol (DEG). In addition, examples of the polyol compound include diol compounds such as ethylene glycol and butanediol, triol compounds, etc.; polyether polyol compounds such as PTMG; reaction products of ethylene glycol and adipic acid, or butanediol. Polyester polyol compounds such as reactants with adipic acid; polycarbonate polyol compounds, polycaprolactone polyol compounds, etc. One or more of these can be used. As the curing agent, a polyamine-based curing agent can be used. The polyamine-based curing agent is a substance having two or more amine groups, and MOCA (3,3-dichloro-4,4-diaminodiphenylmethane) can be used. Moreover, as a polyamine type hardening|curing agent, the multimer MOCA containing the trimer which 3 molecules of chloroaniline is bonded to via a methylene group can also be used. Moreover, a polyamine type hardening|curing agent other than MOCA can also be used. Moreover, a polyhydric alcohol type hardening agent can also be used for a hardening|curing agent. The polyol-based curing agent is a substance having two or more hydroxyl groups, and can be, for example, ethylene glycol or polyether polyol. In addition, the polyol-based curing agent includes low-molecular-weight polyol compounds such as butanediol and hexanediol, and polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol (PTMG), bismuth Polyether polyol compounds such as a reaction product of phenol A and propylene oxide, polyester polyol compounds such as a reaction product of ethylene glycol and adipic acid, and a reaction product of butanediol and adipic acid, and polycarbonate polyol compounds And high molecular weight polyol compounds such as polycaprolactone polyol compounds. As the curing agent, one or more of polyamine-based curing agents and polyol-based curing agents can be used. Here, the R value, which is the equivalent ratio of the amine group or hydroxyl active hydrogen group present in the hardener to the isocyanate group present at the end of the prepolymer, is 0.0. 70～1. 20 ways to mix the ingredients. The R value is preferably 0. 70～1. 20, preferably 0. 80～1. 00, and more preferably 0. 85～0. 95. By setting the R value to be 1 or less, the excess isocyanate group is used for the following crosslinking reaction. The hollow fine particles 111 are dispersed in the polymer 110 . The hollow fine particles 111 are hollow spherical objects. The hemispherical hollow fine particles 111 exposed on the polishing surface 101a are exposed by cutting after the polishing layer 101 is formed. Fig. 1(c) is a schematic cross-sectional view of the hollow fine particles 111 in the present embodiment. The hollow fine particles 111 have a spherical outer shell 111a made of thermoplastic resin, and an inner space 111b surrounded by the outer shell 111a. The hollow fine particles 111 can be formed by surrounding and heating liquid low-boiling hydrocarbons with a thermoplastic resin shell. As the hollow fine particles 111 , an expanded type which has been heated and expanded, or an unexpanded type which expands by the heat of formation accompanying the above-mentioned formation reaction of the polyurethane may be used. The thermoplastic resin is softened by heating and the low-boiling hydrocarbon is changed into a gas, and the thermoplastic resin is expanded by the pressure of the gas, whereby the hollow fine particles 111 are formed. Examples of low-boiling hydrocarbons include isobutane, pentane, and the like, and examples of thermoplastic resins include vinylidene chloride or acrylonitrile. A commercially available product can also be used for the hollow fine particles 111 . For example, Matsumoto Microsphere Series (manufactured by Matsumoto Oil & Gas Co., Ltd.) or Expancel Series (manufactured by AkzoNobel Corporation) can be used as the hollow fine particles 111 . The size of the hollow fine particles 111 is not particularly limited, and may be about 20 μm to 200 μm in diameter, and two or more kinds of hollow fine particles with different diameters may be used. The content ratio of the hollow fine particles 111 in the abrasive is preferably 10 to 60% by volume, more preferably 15 to 45% by volume, relative to the abrasive. When the polishing layer 101 is abraded by polishing, the hollow fine particles 111 are exposed on the polishing surface 101a, thereby affecting the polishing characteristics of the polishing surface 101a. The size of the voids in the polishing layer 101 can be made uniform by dispersing the hollow fine particles 111 made of the resin in the polishing layer 101 . Furthermore, the polishing characteristics of the polishing pad 100 can be adjusted by the amount of the hollow fine particles 111 charged. THE MANUFACTURING APPARATUS 1 OF THE POLISHING PAD Before explaining the manufacturing method of the polishing pad 100, the manufacturing apparatus which manufactures the polishing pad 100 is demonstrated. FIG. 2 is a schematic view of a manufacturing apparatus 200 used for manufacturing the polishing pad 100 of the present embodiment. The manufacturing apparatus 200 includes a first storage tank 201 (first tank), a second storage tank 202 (second tank), a stirring tank 203 (mixing container), a mold 204, a container 212, a filter 400, and a pump 401 (first pump) , pump 401 (second pump), switching valve 410, switching valve 420, channel 501a, channel 501b, channel 501c, channel 502a, channel 502b, channel 502c, channel 503. The first storage tank 201 can accommodate the content (liquid) containing the hollow fine particles 111 and the prepolymer. The hollow fine particles 111 are preliminarily accommodated in a container 212 provided on the first storage tank 201 . The hollow fine particles 111 are introduced into the first storage tank 201 from the container 212 via the flow path 503 . By injecting the hollow fine particles 111 from the container 212 into the first storage tank 201 through the flow path 503, scattering of the hollow fine particles 111 to the outside of the first storage tank 201 is suppressed. The second storage tank 202 can accommodate a curing agent for curing the prepolymer. The stirring tank 203 mixes the liquid containing the hollow fine particles 111 and the prepolymer with the hardener to form the abrasive material 301 . The size of the voids in the polishing layer 101 can be made uniform by dispersing the hollow fine particles 111 made of the resin in the polishing layer 101 . Furthermore, the polishing characteristics of the polishing pad 100 can be adjusted by the amount of the hollow fine particles 111 charged. The pump 401 can supply the liquid containing the hollow fine particles 111 and the prepolymer from the first storage tank 201 to the stirring tank 203 . The pump 401 is installed in the middle of the flow path 501a. When the flow path 501a and the flow path 501b are communicated by the switching valve 410 and the pump 401 is activated, the liquid containing the hollow fine particles 111 and the prepolymer is supplied from the first storage tank 201 to the stirring tank via the flow paths 501a and 501b 203. The pump 402 can supply the curing agent from the second storage tank 202 to the stirring tank 203 . The pump 402 is provided in the middle of the flow path 502a. When the flow path 502a and the flow path 502b are communicated with the switching valve 420 and the pump 402 is actuated, the curing agent is supplied from the second storage tank 202 to the stirring tank 203 through the flow paths 502a and 502b. In the production apparatus 200, when the flow path 501a and the flow path 501c are communicated with the switching valve 410 and the pump 401 is actuated, the liquid containing the hollow fine particles 111 and the prepolymer is passed through the flow paths 501a and 501c in the first 1 circulation between the storage tank 201 and the pump 401. Moreover, when the flow path 502a and the flow path 502c are communicated by the switching valve 420 and the pump 402 is actuated, the curing agent circulates between the second storage tank 202 and the pump 402 through the flow paths 502a and 502c. The mold 204 receives the abrasive material 301 from the stirring tank 203 , and the abrasive layer 101 is formed from the abrasive material 301 . The filter 400 can remove foreign matter contained in the liquid before supplying the liquid containing the hollow fine particles 111 and the prepolymer to the stirring tank 203 . For example, the filter 400 is provided in the middle of the flow path 501 a and upstream of the pump 401 . The foreign matter is, for example, larger than the diameter (eg, maximum particle diameter) of the hollow fine particles 111 . The diameter of the hollow fine particles 111 is calculated by, for example, a laser diffraction particle size distribution analyzer, an electron microscope image, or the like. Inside the filter 400, a filter 400f is provided. The filter net 400f has, for example, a plurality of through holes. The filter screen 400f is constituted by, for example, a screen member, a porous plate, or the like. A plurality of filter nets 400f may be arranged in the filter 400 . The hollow fine particles 111 and the prepolymer pass through the through holes, and foreign matter larger than the diameter of the hollow fine particles 111 cannot pass through the filter screen 400f. That is, foreign matter is removed by the filter 400 . In the present embodiment, the foreign matter is, for example, a particle produced by reacting an isocyanate compound with a trace amount of water adhering to the hollow fine particles 111 . The particles are, for example, particles formed by hardening a prepolymer. Alternatively, the so-called foreign matter is a particle in which a plurality of hollow fine particles 111 are aggregated. If such particles are mixed into the polishing layer 101, the polishing properties of the polishing layer 101 will be significantly reduced. For example, the dispersion of the hollow fine particles 111 in the polishing layer 101 may become uneven, or foreign matter mixed into the polishing layer 101 may damage the object to be polished. Here, there is also a method of sufficiently dehydrating and removing the water adhering to the hollow fine particles 111 before throwing the hollow fine particles 111 into the first storage tank 201 . As a dehydration method, there is heating drying, for example. However, when heat-drying is performed, the hollow fine particles 111 in the hollow structure may be deformed by heat or the hollow fine particles 111 may be broken. In addition, there is also a method of washing the hollow fine particles 111 in advance with an organic solvent. However, since the hollow fine particles 111 are made of thermoplastic resin, when the hollow fine particles 111 come into contact with an organic solvent, the hollow fine particles 111 are deformed or dissolved. Moreover, in order to avoid the reaction of the water adhering to the hollow fine particle 111, and an isocyanate compound, the method of injecting the hollow fine particle 111 into the 2nd storage tank 202 is also available. However, the volume of the liquid contained in the first storage tank 201 is several times larger (for example, about three times) than the volume of the liquid contained in the second storage tank 202 . Therefore, in order to disperse the hollow fine particles 111 in the abrasive 301 more uniformly, it is preferable to put the hollow fine particles 111 into the first storage tank 201 having a larger capacity. Therefore, foreign matter is inevitably generated in the first storage tank 201 into which the hollow fine particles 111 are put. Preferably, such foreign matter is removed by the filter 400 before being mixed with the hardener. Furthermore, there are cases in which the metal component of the catalyst used in the formation of the hollow fine particles is adhered to the hollow fine particles 111 . There is a case where such a metal component also becomes a foreign substance and is mixed with the liquid existing in the first storage tank 201 . Furthermore, when at least a part of the inner wall of the container 212 or at least a part of the inner wall of the flow path 503 is made of metal, the metal component may be mixed into the first storage tank 201 from the inner wall. In order to remove such metal components, the filter 400 may also have a mechanism capable of removing metal components. For example, a porous or fibrous metal adsorbent may also be provided in the filter 400 . The metal adsorbent may be disposed upstream of the filter screen 400f, or may be disposed downstream of the filter screen 400f. Alternatively, the metal adsorbent may be disposed in the flow path 501 a outside the filter 400 instead of in the filter 400 . That is, the filter screen 400f and the metal adsorbent may be provided in a plurality of stages in the middle of the flow path 501a. Alternatively, the filter mesh 400f itself may be an adsorbent for adsorbing metal components. Furthermore, the inner wall of the flow path 501a may be formed of a metal adsorbent. In addition, the filter 400 may also be installed downstream of the pump 401 , but by arranging the filter 400 upstream of the pump 401 , the inflow of foreign matter into the pump 401 is suppressed, so that the pump 401 is not easily damaged. THE MANUFACTURING METHOD 1 OF THE POLISHING PAD Next, the manufacturing method of the polishing pad 100 is demonstrated. For example, the prepolymer and the hollow fine particles 111 are put into the first storage tank 201 . The prepolymer may be an isocyanate compound. The curing agent is put into the second storage tank 202 . The hardener is both or one of the polyol-based hardener and the polyamine-based hardener. In order to stabilize the fluidity of each raw material, the first storage tank 201 and the second storage tank 202 are heated to a specific temperature. Next, the content (hereinafter, the first solution) in the first storage tank 201 is sent out to the stirring tank 203 through the filter 400 from the first storage tank 201 . Thereby, before sending out the 1st solution to the stirring tank 203, a foreign material is removed from a 1st solution. The content of the second storage tank 202 (hereinafter, the second solution) is sent from the second storage tank 202 to the stirring tank 203 . Thereby, the fluid-like abrasive 301 in which the first solution and the second solution are mixed is formed in the stirring tank 203 . Next, the abrasive 301 is poured into the mold 204 to perform casting. In the abrasive material 301, the prepolymer and the hardener undergo a polymerization reaction. At this time, the mold 204 may also be heated. In conjunction with the polymerization reaction, the mixture is allowed to harden to form a mass comprising the polymer. The obtained block is heated to carry out the crosslinking reaction of the polymer. Furthermore, the polishing layer 101 is obtained by cutting the block. The adhesive layer 102 and the buffer layer 103 are laminated on the polishing layer 101 and cut into a desired shape to form the polishing pad 100 . Trenches and the like may also be formed in the polishing layer 101 as required. In this way, according to the present embodiment, the foreign matter is removed by the filter 400 , and the mixing of the foreign matter into the polishing layer 101 of the polishing pad 100 is suppressed. Thereby, a polishing pad having desired characteristics is formed. In addition, the hollow fine particles 111 are fine fine particles, and if the hollow fine particles 111 are put into the first storage tank 201 from above the first storage tank 201, they will fly in the first storage tank 201, and the hollow fine particles 111 may adhere. on the inner wall of the first storage tank 201 . As a result, the hollow fine particles 111 may not be efficiently dispersed in the prepolymer. Therefore, the hollow fine particles 111 can also be injected through the flow path from the lower side of the first storage tank 201 . Thereby, the hollow fine particles 111 are directly mixed into the prepolymer stored in the bottom of the first storage tank 201 after being put into the first storage tank 201 . In addition, in the above description, the hollow fine particles 111 are put into the first storage tank 201 , but the hollow fine particles 111 may be put into the second storage tank 202 . In this case, the hollow fine particles 111 may be introduced into the second storage tank 202 using the flow path from the lower side of the second storage tank 202 in the same manner as in the method of putting into the first storage tank 201 . Furthermore, in the above description, the method of introducing the hollow fine particles 111 into the prepolymer 112 has been described. However, in addition to the hollow fine particles, fine particles whose specific gravity is small and may be scattered, such as cerium oxide, may also be introduced by the above method. Abrasive particles or fillers, etc. [Manufacturing Apparatus 2 of Polishing Pad] The polishing pad 100 can also be manufactured by the following manufacturing apparatus and manufacturing method. FIG. 3 is a schematic view of a manufacturing apparatus 1200 used for manufacturing the polishing pad 100 of the present embodiment. The manufacturing apparatus 1200 includes a first storage tank 1201 (first tank), a second storage tank 1202 (second tank), a stirring tank 1203 (mixing vessel), a mold 1204, a pump 1401 (first pump), and a pump 1402 (second pump) and control device 1601. Further, the manufacturing apparatus 1200 includes a switching valve 1410 , a switching valve 1420 , a flow path 1501 a , a flow path 1501 b , a flow path 1502 a , a flow path 1502 b , a container 1212 , a flow path 1503 , a container 1213 , and a flow path 1504 . The manufacturing apparatus 1200 uses the control apparatus 1601 to collectively and automatically control the above-mentioned components. Alternatively, in the manufacturing apparatus 1200, the control of each component by the control device 1601 may be released, and each component may be manually operated. The first storage tank 1201 can store the prepolymer. In the first storage tank 1201, the hollow fine particles 111 may be mixed with the prepolymer. For example, the hollow fine particles 111 are stored in the container 1212 in advance. The container 1212 is connected to the first storage tank 1201 via the flow path 1503 . The hollow fine particles 111 are introduced into the first storage tank 1201 from the container 1212 via the flow path 1503 . The hollow fine particles 111 are fine particles. If the hollow fine particles 111 are put into the first storage tank 1201 from above the first storage tank 1201, they may fly in the first storage tank 1201, and the hollow fine particles 111 may adhere to the first storage tank 1201. 1 The inner wall of the storage tank 1201. As a result, the hollow fine particles 111 may not be efficiently dispersed in the prepolymer. Therefore, the hollow fine particles 111 are injected through the flow path 1503 from the lower side of the first storage tank 1201 . Thereby, the hollow fine particles 111 are directly mixed into the prepolymer stored in the bottom of the first storage tank 1201 after being put into the first storage tank 1201 . The second storage tank 1202 can accommodate the curing agent. In the manufacturing apparatus 1200, in the second storage tank 1202, the hollow fine particles 111 may be mixed with the curing agent. For example, the hollow fine particles 111 are accommodated in the container 213 in advance. The container 213 is connected to the second storage tank 1202 via the flow path 1504 . The hollow fine particles 111 are introduced into the second storage tank 1202 from the container 1213 via the flow path 1504 . The hollow fine particles 111 may be mixed in either the first storage tank 1201 or the second storage tank 1202, or may be mixed in both the first storage tank 1201 and the second storage tank 1202. In addition, the specific gravity of the hollow fine particles 111 is lighter than that of the prepolymer and the curing agent. Therefore, by injecting the hollow fine particles 111 into the first storage tank 1201 and the second storage tank 1202 from below the first storage tank 1201 and the second storage tank 1202, the hollow fine particles 111 are stored in the first storage tank 1201 and the second storage tank 1202. Each of 1202 is dispersed efficiently. The pump 1401 can supply the content (hereinafter, the first liquid) accommodated in the first storage tank 1201 from the first storage tank 1201 to the stirring tank 1203 . The pump 1401 is provided in the middle of the flow path 1501a. The number of the pumps 1401 provided in the middle of the flow path 1501a is not limited to one. For example, a plurality of pumps 1401 may be provided in parallel in the middle of the flow path 1501a. Moreover, the flow path 1501b and the flow path 1501c are connected to the flow path 1501a via the switching valve 1410 . The switching valve 1410 is a so-called three-way valve. For example, when the first liquid contained in the first storage tank 1201 is supplied from the first storage tank 1201 to the stirring tank 1203, the flow path 1501a and the flow path 1501b are communicated by the switching valve 1410. Then, by the operation of the pump 1401, the first liquid is supplied from the first storage tank 1201 to the stirring tank 1203 through the flow path 1501a and the flow path 1501b. Here, when the first liquid is supplied from the first storage tank 1201 to the stirring tank 1203, the flow rate of the first liquid flowing into the pump 1401 is controlled to a predetermined flow rate (first flow rate). Moreover, in the manufacturing apparatus 1200, the supply of the 1st liquid to the stirring tank 1203 may be stopped. At this time, in the manufacturing apparatus 1200, the 1st liquid can be circulated between the pump 1401 and the 1st storage tank 1201. For example, the flow path 1501a and the flow path 1501c are communicated with each other by the switching valve 1410 . Then, by the operation of the pump 1401, the first liquid is returned from the first storage tank 1201 to the first storage tank 1201 through the flow path 1501a and the flow path 1501c. The returning action of the liquid is repeated. Here, when the first liquid circulates between the pump 1401 and the first storage tank 1201, the flow rate of the first liquid flowing into the pump 1401 is controlled to be smaller than the first flow rate. The flow rate smaller than the first flow rate is referred to as the second flow rate. The second flow rate is adjusted to, for example, 50% or less of the first flow rate. For example, by adjusting the rotational speed of the pump 1401, the flow rate of the first liquid is adjusted to the first flow rate or the second flow rate. In addition, when the supply of the first liquid to the stirring tank 1203 is stopped, the pump 1401 itself may be stopped. In addition, the operation and stop of the pump 1401 may be alternately repeated. The pump 1402 can supply the content (hereinafter, the second liquid) accommodated in the second storage tank 1202 to the stirring tank 1203 from the second storage tank 1202 . The pump 1402 is provided in the middle of the flow path 1502a. The number of pumps 1402 provided in the middle of the flow path 1502a is not limited to one. For example, a plurality of pumps 1402 may be provided in parallel in the middle of the flow path 1502a. Moreover, the flow path 1502b and the flow path 1502c are connected to the flow path 1502a via the switching valve 1420 . The switching valve 1420 is a so-called three-way valve. For example, when the second liquid contained in the second storage tank 1202 is supplied from the second storage tank 1202 to the stirring tank 1203, the flow path 1502a and the flow path 1502b are communicated by the switching valve 1420. Then, by the operation of the pump 1402, the second liquid is supplied from the second storage tank 1202 to the stirring tank 1203 through the flow path 1502a and the flow path 1502b. Here, when the second liquid is supplied from the second storage tank 1202 to the stirring tank 1203, the flow rate of the second liquid flowing into the pump 1402 is controlled to a predetermined flow rate (third flow rate). Moreover, in the manufacturing apparatus 1200, the supply of the 2nd liquid to the stirring tank 1203 may be stopped. At this time, in the manufacturing apparatus 1200, the second liquid can be circulated between the pump 1402 and the second storage tank 1202. For example, the flow path 1502a and the flow path 1502c are communicated with each other by switching the valve 1420 . Then, by the operation of the pump 1402, the second liquid is returned from the second storage tank 1202 to the second storage tank 1202 through the flow paths 1502a and 1502c. The returning action of the liquid is repeated. Here, when the second liquid circulates between the pump 1402 and the second storage tank 1202, the flow rate of the second liquid flowing into the pump 1402 is controlled to be smaller than the third flow rate. Let the flow rate smaller than the third flow rate be the fourth flow rate. The fourth flow rate is adjusted to, for example, 50% or less of the third flow rate. For example, by adjusting the rotational speed of the pump 1402, the flow rate of the second liquid is adjusted to the third flow rate or the fourth flow rate. In addition, when the supply of the second liquid to the stirring tank 1203 is stopped, the pump 1402 itself may be stopped. In addition, the operation and stop of the pump 1402 may be repeated alternately. In the manufacturing apparatus 1200 , the switching of the switching valve 1410 and the operation of the pumps 1401 and 1402 are controlled by the control device 1601 . As the pumps 1401 and 1402, a fixed-volume screw pump (eg, a single screw pump) or a fixed-volume positive displacement pump (eg, a sine pump) is preferably used, and a reciprocating pump or a rotary pump is particularly used. These pumps are excellent in transferring viscous fluids (first and second liquids) containing hollow fine particles 111 . The control device 1601 performs control to reduce the rotational speed of the pumps when the flow rate of the liquid is to be decreased, and performs control to increase the rotational speed of the pumps when the flow rate of the liquid is to be increased. The stirring tank 1203 receives the prepolymer, the curing agent, and the hollow fine particles 111 , and mixes the prepolymer, the curing agent, and the hollow fine particles 111 to form the abrasive 301 . The mold 1204 receives the abrasive 301 from the stirring tank 1203 and hardens the abrasive 301 to form the abrasive layer 101 . [Manufacturing method 2 of polishing pad] The manufacturing method of the polishing pad 100 will be described with reference to FIG. 3 . The manufacture of the polishing layer 101 is controlled by the control device 1601 . First, the manufacturing method of the polishing pad when only the hollow fine particles 111 are mixed in the first storage tank 1201 will be described. For example, the prepolymer and the hollow fine particles 111 are put into the first storage tank 1201 . The prepolymer may be an isocyanate compound. The curing agent is put into the second storage tank 1202 . The hardener is both or one of a polyol-based hardener and a polyamine-based hardener. In order to stabilize the fluidity of each raw material, the first storage tank 1201 and the second storage tank 1202 are heated to a specific temperature. Next, the liquid (first liquid) containing the prepolymer and the hollow fine particles 111 accommodated in the first storage tank 1201 is supplied from the first storage tank 1201 to the stirring tank 1203 at the first flow rate. For example, by operating the pump 1401 by the control device 1601, the first liquid is supplied from the first storage tank 1201 to the stirring tank 1203 through the flow path 1501a, the switching valve 1410, and the flow path 1501b. At this time, the flow rate of the first liquid ejected from the pump 1401 is controlled to be the first flow rate. For example, when the pump 1401 is a single screw pump, the first flow rate is controlled to be any flow rate of 30 rpm or more and 150 rpm or less. In addition, the discharge amount is controlled to be any one of 12,000 g/min or more and 30,000 g/min or less. The ejection pressure is controlled to 0. 5 MPa or more and 1. Any discharge pressure below 0 MPa. Furthermore, together with the supply of the first liquid, the curing agent accommodated in the second storage tank 1202 is supplied from the second storage tank 1202 to the stirring tank 1203 by the pump 1402 . For example, by operating the pump 1402 by the control device 1601, the curing agent is supplied from the second storage tank 1202 to the stirring tank 1203 through the flow path 1502a, the switching valve 1420, and the flow path 1502b. For example, when the pump 1402 is a single screw pump, the flow rate of the hardener is controlled to be any flow rate of 30 rpm or more and 150 rpm or less. In addition, the discharge amount is controlled to be any one of 4,000 g/min or more and 10,000 g/min or less. The ejection pressure is controlled to 0. 1 MPa or more and 0. Any one of the ejection pressure below 4 MPa. Next, in the stirring tank 1203, a fluid-like abrasive 301 in which the first liquid and the curing agent are mixed is formed. Next, the abrasive 301 is supplied to the mold 1204 from the stirring tank 1203 . In the abrasive material 301, the prepolymer and the hardener undergo a polymerization reaction. At this time, the mold 1204 may also be heated. In conjunction with the polymerization reaction, the mixture is hardened to form a mass containing the polymer. Then, in the mold 1204 , the polishing material 301 is hardened to form the polishing layer 101 . For example, the cross-linking reaction of the polymer is carried out by heating the obtained block. Furthermore, the polishing layer 101 is obtained by dicing (cutting) the lump. The adhesive layer 102 and the buffer layer 103 are stacked on the polishing layer 101 and cut into a desired shape to form the polishing pad 100 . Trenches and the like may also be formed in the polishing layer 101 as required. Here, in the manufacture of the polishing layer 101, it is necessary to temporarily stop the supply of the first liquid and the curing agent to the stirring tank 1203. In the present embodiment, the first liquid is circulated between the pump 1401 and the first storage tank 1201 during the period of stopping. For example, by switching the switching valve 1410 so that the flow path 1501a and the flow path 1501c communicate with each other, the first storage tank 1201, the flow path 1501a, the switching valve 1410, the flow path 1501c, and the first storage tank 1201 are connected in this order. 1 Liquid circulation. By this circulation, the prepolymers having different specific gravities and the hollow fine particles 111 are efficiently mixed in the first storage tank 1201, in the flow path 1501a, and in the flow path 1501c. Further, by continuing such a cycle, when the supply of the first liquid to the stirring tank 1203 is resumed, the first liquid obtained by efficiently dispersing the hollow fine particles 111 in the prepolymer is taken out from the flow path 1501b immediately. If the circulation of the first liquid is stopped, a small amount of air remaining in the first storage tank 1201 or the flow path 1501a reacts with the prepolymer, and a plurality of prepolymers are likely to be generated in the first storage tank 1201 or the flow path 1501a A solidified foreign body. However, when the first liquid is circulated for a long time, the hollow fine particles 111 will continue to receive a load from the pump 1401 every time the hollow fine particles 111 pass through the pump 1401 . For example, when the pump 1401 is a single-screw pump, the first liquid is squeezed out by the rotation of the rotor in the pump 1401 and is ejected out of the pump 1401 . Here, the first liquid contains a prepolymer and has a specific viscosity. Thereby, the first liquid has viscous resistance or inertial resistance. Therefore, every time the first liquid passes through the pump 1401 , stress is applied to the hollow fine particles 111 . If such a load continues for a long time, the hollow fine particles 111 may be deformed or damaged. If the damaged hollow fine particles 111 are mixed into the polishing layer 101 , the polishing pad 100 may not exhibit desired properties. For example, if the hollow fine particles 111 are damaged or the hollow fine particles 111 with prepolymer mixed in the hollow enter into the polishing layer 101, the hardness of the polishing layer 101 will be locally increased, or the polishing layer 101 will be hardened as a whole, and the abrasives will be hardened. cause damage. Therefore, in this embodiment, when the first liquid is circulated between the pump 1401 and the first storage tank 1201, the first liquid is caused to flow between the pump 1401 and the first storage tank 1201 at a flow rate smaller than the first flow rate. 2 flow cycles. As a result, the hollow fine particles 111 are less likely to receive a load from the pump 1401 when passing through the pump 1401, and deformation and breakage of the hollow fine particles 111 are suppressed. Thereby, the polishing pad 100 including the hollow fine particles 111 exhibits desired characteristics. For example, when the pump 1401 is a single screw pump, the second flow rate is controlled to be any flow rate of 15 rpm or more and 75 rpm or less. In addition, the discharge amount is controlled to be any one of 6000 g/min or more and 15000 g/min or less. The ejection pressure is controlled to 0. Above 25 MPa and 0. Any one of the ejection pressure below 5 MPa. In addition, when the plurality of pumps 1401 are arranged in the flow path 1501a, even if the discharge amount of each of the plurality of pumps 1401 is controlled to be the second flow rate, the flow rate of the first liquid flowing through the flow paths 1501a and 1501c is the same as that from each pump. 1401 The sum of the flow rate ejected. Thereby, the flow rate of the first liquid flowing through the channels 1501a and 1501c can be made the same as the first flow rate while suppressing the load of the pump 1401 on the hollow fine particles 111 during the circulation. In addition, when the supply of the first liquid and the curing agent to the stirring tank 1203 is stopped, in order to further reduce the load of the pump 1401 on the hollow fine particles 111, the pump 1401 itself may be stopped. Then, the 1st liquid and hardening agent are supplied to the stirring tank 1203 again, and the grinding|polishing layer 101 is formed again. That is, after the circulation is completed, the first liquid is supplied to the stirring tank 1203 from the first storage tank 1201 at the first flow rate by the pump 1401, and the curing agent is supplied to the stirring tank 1203 from the second storage tank 1202. Next, the manufacturing method of the polishing pad when only the hollow fine particles 111 are mixed in the second storage tank 1202 will be described. For example, the curing agent and the hollow fine particles 111 are put into the second storage tank 1202 . The content in the second storage tank 1202 is set as the second liquid. Next, the prepolymer accommodated in the first storage tank 1201 is supplied from the first storage tank 1201 to the stirring tank 1203 . For example, by operating the pump 1401 by the control device 1601, the prepolymer is supplied from the first storage tank 1201 to the stirring tank 1203 through the flow path 1501a, the switching valve 1410, and the flow path 1501b. For example, when the pump 1401 is a single screw pump, the flow rate of the prepolymer is controlled to be any flow rate of 30 rpm or more and 150 rpm or less. In addition, the discharge amount is controlled to be any one of 12,000 g/min or more and 30,000 g/min or less. The ejection pressure is controlled to 0. 5 MPa or more and 1. Any one of the ejection pressure below 0 MPa. Furthermore, together with the supply of the prepolymer, the second liquid accommodated in the second storage tank 1202 is supplied from the second storage tank 1202 to the stirring tank 1203 by the pump 1402 . For example, by operating the pump 1402 by the control device 1601, the second liquid is supplied from the second storage tank 1202 to the stirring tank 1203 through the flow path 1502a, the switching valve 1420, and the flow path 1502b. At this time, the flow rate of the second liquid ejected from the pump 1401 is controlled to be the third flow rate. For example, when the pump 1402 is a single screw pump, the flow rate of the second liquid is controlled to be any flow rate of 30 rpm or more and 150 rpm or less. In addition, the discharge amount is controlled to be any one of 4,000 g/min or more and 10,000 g/min or less. The ejection pressure is controlled to 0. 1 MPa or more and 0. Any one of the ejection pressure below 4 MPa. Next, in the stirring tank 1203, a fluid-like abrasive 301 in which the prepolymer and the second liquid are mixed is formed. Next, the abrasive 301 is supplied to the mold 1204 from the stirring tank 1203 . Then, the polishing material 301 is hardened in the mold 1204 to form the polishing layer 101 . Here, when supply of the prepolymer and the second liquid to the stirring tank 1203 is temporarily stopped, the second liquid is circulated between the pump 1402 and the second storage tank 1202 . For example, by switching the switching valve 1420 so that the flow path 1502a and the flow path 1502c communicate with each other, the second storage tank 1202, the flow path 1502a, the switching valve 1420, the flow path 1502c, and the second storage tank 1202 are connected in this order. 2 Liquid circulation. When the second liquid is circulated between the pump 1402 and the second storage tank 1202, the second liquid is circulated between the pump 1402 and the second storage tank 1202 at a fourth flow rate smaller than the third flow rate. Thereby, when the hollow fine particles 111 pass through the pump 1402, it is less likely to receive a load from the pump 1402, and the deformation and breakage of the hollow fine particles 111 are suppressed. Thereby, the polishing pad 100 including the hollow fine particles 111 exhibits desired characteristics. For example, when the pump 1402 is a single screw pump, the fourth flow rate is controlled to be any flow rate of 15 rpm or more and 75 rpm or less. In addition, the discharge amount is controlled to be any one of 2000 g/min or more and 5000 g/min or less. The ejection pressure is controlled to 0. 05 MPa or more and 0. Any one of the discharge pressure below 2 MPa. In addition, when the plurality of pumps 1402 are arranged in the flow path 1502a, even if the discharge amount of each of the plurality of pumps 1402 is controlled to the fourth flow rate, the flow rate of the second liquid flowing through the flow paths 1502a and 1502c becomes the flow rate from each pump 1402 The total amount of flow rate ejected. Thereby, the flow rate of the second liquid flowing through the channels 1502a and 1502c can be made the same as the third flow rate while suppressing the load of the pump 1402 on the hollow fine particles 111 during the circulation. When the supply of the prepolymer and the second liquid to the stirring tank 1203 is stopped, in order to further reduce the load of the pump 1402 on the hollow fine particles 111, the pump 1402 itself may be stopped. After that, the prepolymer and the second liquid are supplied to the stirring tank 1203 again, and the polishing layer 101 is formed again. Furthermore, in this embodiment, the hollow fine particles 111 may be mixed in both the first storage tank 1201 and the second storage tank 1202, and the hollow fine particles 111 may be formed from both the first storage tank 1201 and the second storage tank 1202. The fine particles 111 are supplied to the stirring tank 1203 . [Evaluation of Abrasive Layer] FIG. 4( a ) is a graph showing the relationship between the viscosity of the first liquid in the first storage tank 1201 and the cycle time. The solid line is the result of the case of using a single screw pump as pump 1401 . The dashed line is the result of the case where a sinusoidal pump is used as pump 1401 . As shown in Figure 4(a), in the case of a single screw pump, when the circulation time of the first liquid is within 5 hours, the viscosity of the first liquid is maintained above 6000 (cp). However, when the cycle time exceeds 5 hours, the viscosity of the first liquid decreases to 4500 (cp) or less. Furthermore, when the cycle time exceeds 20 hours, the viscosity of the first liquid is lower than 4000 (cp). In the case of a sinusoidal pump, when the circulation time of the first liquid is within 5 hours, the viscosity of the first liquid is maintained above 12000 (cp). However, when the cycle time exceeds 5 hours, the viscosity of the first liquid decreases to 8500 (cp) or less. Furthermore, when the cycle time exceeds 20 hours, the viscosity of the first liquid is lower than 7000 (cp). In this way, if the circulation time of the first liquid exceeds 5 hours, the viscosity of the first liquid is significantly reduced. That is, it is considered that the damage to the hollow fine particles 111 progresses as a result of the continuous load from the pump. Therefore, the circulation time of the first liquid is preferably within 5 hours. FIG. 4( b ) is a graph showing the relationship between the density of the polishing layer 101 and the cycle time. The grey bars are the results for the case of using a single screw pump. The white bar graph is the result for the case of using a sine pump. As shown in Fig. 4(b), when the circulation time of the first liquid is within 5 hours, in either case of the single screw pump and the sinusoidal pump, the density of the abrasive layer 101 is maintained at 0.0. 85(g/cm 3 )the following. However, if the circulation time of the first liquid exceeds 5 hours, the density increases to 0.9 (g/cm) in either the single-screw pump or the sinusoidal pump 3 )about. Furthermore, if the circulation time of the first liquid reaches 48 hours, the density increases to 1.0 (g/cm) in either the single-screw pump or the sinusoidal pump 3 )about. In this way, when the circulation time of the first liquid exceeds 5 hours, the density of the polishing layer 101 including the hollow fine particles 111 increases significantly. Therefore, the circulation time of the first liquid is preferably within 5 hours. In addition, in this evaluation, in any case, 100 kg of the first liquid is prepared in the first storage tank 1201, and the flow rate of the first liquid is set to 18 kg/min. Therefore, theoretically, every The first liquid passes through the pump 1401 once in 5.6 minutes. The hollow fine particles 111 may be deformed or damaged by the pump 1401 each time they pass through the pump 1401. However, as described above, if the number of pump passes of the first liquid is within 5 hours, that is, within 54 times in theory, the Deformation and breakage of the hollow fine particles 111 are suppressed within a specific range. Therefore, it is preferable to set the number of pump passes of the first liquid theoretically within 54 times. On the other hand, if the theoretical pumping times of the first liquid exceed the above-mentioned times, the deformation and breakage of the hollow fine particles 111 will increase, and the density of the polishing layer 101 will be significantly increased. FIG. 4( c ) is a graph showing the relationship between the Shore D hardness of the polishing layer 101 and the cycle time. The grey bars are the results for the case of using a single screw pump. The white bar graph is the result for the case of using a sine pump. As shown in Figure 4(c), when the circulation time of the first liquid is within 5 hours (or the theoretical number of pump passes of the first liquid is within 54 times), in either case of a single screw pump or a sinusoidal pump , the Shore D hardness of the polishing layer 101 is maintained below 48. However, if the circulation time of the first liquid exceeds 5 hours (or the theoretical number of pump passes of the first liquid exceeds 54 times), the Shore D hardness increases to 50 in either the single-screw pump or the sinusoidal pump. about. Furthermore, when the circulation time of the first liquid reaches 48 hours, the hardness increases to about 52(°) in both the single screw pump and the sinusoidal pump. Thus, if the circulation time of the first liquid exceeds 5 hours (or the theoretical number of pump passes of the first liquid exceeds 54 times), the hardness of the abrasive layer 101 including the hollow fine particles 111 will increase significantly. Therefore, the circulation time of the first liquid is preferably within 5 hours (or theoretically, the number of pump passes of the first liquid is within 54 times). As described above, if the circulation time of the first liquid is within 5 hours (or the theoretical number of pump passes of the first liquid is within 54 times), the stress applied to the hollow fine particles 111 is suppressed, and the hollow fine particles 111 are suppressed. deformation and damage. Thereby, the polishing pad 100 including the hollow fine particles 111 exhibits desired characteristics. FIG. 5 is a graph showing the relationship between the cross-sectional image of the polishing layer 101 and the cycle time. Cross-sectional images were acquired by electron microscopy. As shown in Figure 5, when the circulation time of the first liquid is within 5 hours (or the theoretical number of pump passes of the first liquid is within 54 times), in either case of a single screw pump or a sinusoidal pump, the The hollow fine particles 111 are uniformly dispersed in the polishing layer 101 . However, if the circulation time of the first liquid exceeds 5 hours and reaches 24 hours, the dispersion of the hollow fine particles 111 in the polishing layer 101 tends to be sparser than within 5 hours. This tendency becomes more remarkable when the circulation time of the 1st liquid reaches 48 hours. That is, the time for circulating the first liquid is preferably within 5 hours (or theoretically, the number of pump passes of the first liquid is within 54 times). As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention is not limited only to the said embodiment, Various changes can be added.
