以下，對本發明之實施形態進行說明，但本發明並不限定於該等實施形態。 A.偏光板之整體構成 圖1係本發明之1個實施形態之偏光板之剖視圖。偏光板10具有偏光元件1、及配置於偏光元件1之一側之保護膜2。保護膜2包含丙烯酸系樹脂、及分散於丙烯酸系樹脂之核殼型粒子。保護膜2之表面之算術平均粗糙度Ra為6.0 μm以上。較佳為於保護膜2之與偏光元件1相反側之表面形成有由核殼型粒子所引起之凹凸。較佳為保護膜2相對於丙烯酸系樹脂100重量份，含有3重量份～50重量份之核殼型粒子。核殼型粒子代表性地具有包含橡膠狀聚合物之內核、及包含玻璃狀聚合物且被覆內核之被覆層。較佳為保護膜2為雙軸延伸膜。於1個實施形態中，偏光板10於保護膜2之表面不具有擴散層。關於本發明之偏光板，例如即便於合併至圖像顯示裝置中與擴散片等其他光學構件接觸之情形時，亦能夠抑制由與上述其他光學構件之摩擦所引起之損傷之產生。 圖2係本發明之另一實施形態之偏光板之剖視圖。偏光板11具有偏光元件1、配置於偏光元件1之一側之保護膜2(第1保護膜)、及配置於偏光元件1之另一側之第2保護膜3。第2保護膜3可為由與第1保護膜2相同之材料所形成之膜，亦可為由另外之材料所形成之膜。偏光板11可具有依據目的及用途之任意適當之光學功能膜代替第2保護膜3。 偏光板10及偏光板11可為單片狀，亦可為長條狀。又，偏光板10可於偏光元件1之表面具有黏著劑層(未圖示)，偏光板11亦可於第2保護膜3之表面不具有黏著劑層(未圖示)。 B.偏光元件 作為偏光元件，可採用任意適當之偏光元件。例如，形成偏光元件之樹脂膜可為單層之樹脂膜，亦可為兩層以上之積層體。 作為由單層之樹脂膜所構成之偏光元件之具體例，可列舉：於聚乙烯醇(PVA)系膜、部分縮甲醛化PVA系膜、乙烯-乙酸乙烯酯共聚物系部分皂化膜等親水高分子膜上，實施有利用碘或二色性染料等二色性物質所進行之染色處理及延伸處理者；PVA之脫水處理物或聚氯乙烯之脫氯化氫處理物等多烯系配向膜等。自光學特性優異之方面而言，較佳為使用藉由碘對PVA系膜進行染色且單軸延伸而得之偏光元件。 關於上述利用碘所進行之染色，例如，係藉由將PVA系膜浸漬於碘水溶液中而進行。上述單軸延伸之延伸倍率較佳為3～7倍。延伸可於染色處理後進行，亦可一邊染色一邊進行。又，亦可於延伸之後進行染色。根據需要，於PVA系膜上，實施有膨潤處理、交聯處理、洗淨處理、乾燥處理等。例如，藉由於染色之前將PVA系膜浸漬於水中進行水洗，不僅能夠洗淨PVA系膜表面之污垢或抗黏連劑，且能夠使PVA系膜膨潤而防止染色不均等。 作為使用積層體而獲得之偏光元件之具體例，可列舉使用樹脂基材與積層於該樹脂基材上之PVA系樹脂層(PVA系樹脂膜)之積層體，或者樹脂基材與塗佈形成於該樹脂基材上之PVA系樹脂層之積層體而獲得之偏光元件。關於使用樹脂基材與塗佈形成於該樹脂基材上之PVA系樹脂層之積層體而獲得之偏光元件，可藉由以下方式製作：例如，將PVA系樹脂溶液塗佈於樹脂基材，使其乾燥後於樹脂基材上形成PVA系樹脂層，獲得樹脂基材與PVA系樹脂層之積層體；對該積層體進行延伸及染色而將PVA系樹脂層製成偏光元件。於本實施形態中，延伸代表性地包括將積層體浸漬於硼酸水溶液中進行延伸。進而，根據需要，延伸進而可包括在於硼酸水溶液中之延伸之前以高溫(例如，95℃以上)對積層體進行空中延伸。所得之樹脂基材/偏光元件之積層體可直接使用(即，樹脂基材可作為偏光元件之保護層)，亦可自樹脂基材/偏光元件之積層體剝離樹脂基材，於該剝離面積層根據目的之任意適當之保護層並使用。此種偏光元件之製造方法之詳細內容記載於例如日本專利特開2012-73580號公報中。該公報之全部記載作為參考被引用於本說明書。 偏光元件之厚度例如為1 μm～80 μm。於1個實施形態中，偏光元件之厚度較佳為1 μm～15 μm，進而較佳為3 μm～10 μm，特佳為3 μm～8 μm。 C.保護膜 C-1.保護膜之特性 保護膜如上所述，包含丙烯酸系樹脂、及分散於丙烯酸系樹脂中之核殼型粒子，保護膜之表面之算術平均粗糙度Ra為6.0 μm以上。上述算術平均粗糙度Ra較佳為6 μm～50 μm，更佳為6 μm～40 μm。藉由將算術平均粗糙度Ra設為上述範圍內之值，抑制保護膜表面之滑動性變得過高，其結果為，能夠抑制於將保護膜(及偏光板)長條化之情形時之捲繞偏移。上述算術平均粗糙度Ra可根據保護膜中之核殼型粒子之含量、後述保護膜之製造方法中之延伸條件等而於所需之範圍內進行調整。保護膜之厚度較佳為5 μm～150 μm，更佳為10 μm～100 μm。 較佳為保護膜實質上具有光學等向性。於本說明書中，所謂「實質上具有光學等向性」，指面內相位差Re(550)為0 nm～10 nm，厚度方向之相位差Rth(550)為-10 nm～+10 nm。面內相位差Re(550)更佳為0 nm～5 nm，進而較佳為0 nm～3 nm，特佳為0 nm～2 nm。厚度方向之相位差Rth(550)更佳為-5 nm～+5 nm，進而較佳為-3 nm～+3 nm，特佳為-2 nm～+2 nm。若保護膜之Re(550)及Rth(550)為此種範圍，則能夠防止於將偏光板應用於圖像顯示裝置之情形時對顯示特性之不良影響。再者，Re(550)係以23℃中之波長550 nm之光進行測定之膜之面內相位差。Re(550)藉由公式：Re(550)＝(nx－ny)×d而求出。Rth(550)係以23℃中之波長550 nm之光進行測定之膜之厚度方向之相位差。Rth(550)藉由公式：Rth(550)＝(nx－nz)×d而求出。其中，nx係面內之折射率達到最大之方向(即，遲相軸方向)之折射率，ny係於面內與遲相軸正交之方向(即，進相軸方向)之折射率，nz係厚度方向之折射率，d係膜之厚度(nm)。 保護膜之厚度80 μm中之於380 nm之透光率越高越佳。具體而言，透光率較佳為85%以上，更佳為88%以上，進而較佳為90%以上。若透光率為此種範圍，則能夠確保所需之透明性。關於透光率，例如，可藉由依據ASTM-D-1003之方法進行。 保護膜之霧度越低越佳。具體而言，霧度較佳為5%以下，更佳為3%以下，進而較佳為1.5%以下，特佳為1%以下。若霧度為5%以下，則能夠賦予膜良好之透明感。進而，即便於使用於圖像顯示裝置之視認側偏光板之情形時，顯示內容亦能夠良好地辨識。 保護膜之厚度80 μm中之YⅠ較佳為1.27以下，更佳為1.25以下，進而較佳為1.23以下，特佳為1.20以下。若YⅠ超過1.3，則存在光學透明性變得不充分之情況。再者，關於YⅠ，例如，可根據藉由使用高速積分球式分光透過率測定機(商品名DOT-3C：村上色彩技術研究所製造)之測定而得之顏色之三刺激值(X、Y、Z)，利用下式而求出。 YⅠ＝[(1.28X－1.06Z)/Y]×100 保護膜之厚度80 μm中之b值(依據漢特(Hunter)之表色系統之色相之尺度)較佳為未達1.5，更佳為1.0以下。於b值為1.5以上之情形時，存在產生不希望之色調之情況。再者，關於b值，例如，可藉由將保護膜樣品剪裁為邊長3 cm之方形，使用高速積分球式分光透過率測定機(商品名DOT-3C：村上色彩技術研究所製造)對色相進行測定，依據漢特之表色系對該色相進行評價而獲得。 保護膜之透濕度較佳為300 g/m2
・24hr以下，更佳為250 g/m2
・24hr以下，進而較佳為200 g/m2
・24hr以下，特佳為150 g/m2
・24hr以下，最佳為100 g/m2
・24hr以下。若保護膜之透濕度為此種範圍，則可獲得耐久性及耐濕性優異之偏光板。 保護膜之拉伸強度較佳為10 MPa以上且未達100 MPa，更佳為30 MPa以上且未達100 MPa。於未達10 MPa之情形時，存在無法表現充分之機械強度之情況。若超過100 MPa，則有加工性變得不充分之虞。拉伸強度例如可依據ASTM-D-882-61T進行測定。 保護膜之拉伸伸長率較佳為1.0%以上，更佳為3.0%以上，進而較佳為5.0%以上。拉伸伸長率之上限例如為100%。於拉伸伸長率未達1%之情形時，存在韌性變得不充分之情況。拉伸伸長率例如可依據ASTM-D-882-61T進行測定。 保護膜之拉伸彈性模數較佳為0.5 GPa以上，更佳為1 GPa以上，進而較佳為2 GPa以上。拉伸彈性模數之上限例如為20 GPa。於拉伸彈性模數未達0.5 GPa之情形時，存在無法表現充分之機械強度之情況。拉伸彈性模數例如可依據ASTM-D-882-61T進行測定。 保護膜可根據目的包含任意適當之添加劑。作為添加劑之具體例，可列舉：紫外線吸收劑；受阻酚系、磷系、硫系等抗氧化劑；耐光穩定劑、耐候穩定劑、熱穩定劑等穩定劑；玻璃纖維、碳纖維等補強材料；近紅外線吸收劑；三(二溴丙基)磷酸酯、磷酸三烯丙酯、氧化銻等阻燃劑；陰離子系、陽離子系、非離子系之界面活性劑等抗靜電劑；無機顏料、有機顏料、染料等著色劑；有機填料或無機填料；樹脂改質劑；有機填充劑或無機填充劑；塑化劑；潤滑劑；等。添加劑可於丙烯酸系樹脂之聚合時添加，亦可於膜形成時添加。添加劑之種類、數量、組合、添加量等可根據目的進行適當設定。 於1個實施形態中，第2保護膜可由與第1保護膜相同之材料形成。於另外之實施形態中，第2保護膜可由與第1保護膜不同之材料形成。於第2保護膜由與第1保護膜不同之材料形成之情形時，作為第2保護膜之形成材料，例如可列舉：不含有核殼型粒子之丙烯酸系樹脂、二乙醯纖維素、三乙醯纖維素等纖維素系樹脂；環烯烴系樹脂、聚丙烯等烯烴系樹脂；聚對苯二甲酸乙二酯系樹脂等酯系樹脂；聚醯胺系樹脂、聚碳酸酯系樹脂、該等之共聚物樹脂等。第2保護膜之厚度較佳為10 μm～100 μm。 C-2.丙烯酸系樹脂 C-2-1.丙烯酸系樹脂之構成 作為丙烯酸系樹脂，可採用任意適當之丙烯酸系樹脂。丙烯酸系樹脂代表性地含有作為單體單元之(甲基)丙烯酸烷基酯作為主成分。於本說明書中，所謂「(甲基)丙烯酸」，表示丙烯酸及/或甲基丙烯酸。作為構成丙烯酸系樹脂之主骨架之(甲基)丙烯酸烷基酯，可例示直鏈狀或支鏈狀之烷基之碳數1～18者。該等可單獨或者組合使用。進而，丙烯酸系樹脂中，可藉由共聚合導入任意適當之共聚合單體。此種共聚合單體之種類、數量、共聚合比等可根據目的進行適當設定。關於丙烯酸系樹脂之主骨架之構成成分(單體單元)，參照通式(2)並於後文進行敍述。 丙烯酸系樹脂較佳為具有選自戊二醯亞胺單元、內酯環單元、順丁烯二酸酐單元、順丁烯二醯亞胺單元及戊二酸酐單元中之至少1種。具有內酯環單元之丙烯酸系樹脂例如記載於日本專利特開2008-181078號公報中，該公報之記載作為參考被引用於本說明書。戊二醯亞胺單元較佳為由下述通式(1)表示： [化1]於通式(1)中，R1
及R2
分別獨立，表示氫原子或碳數1～8之烷基，R3
表示氫原子、碳數1～18之烷基、碳數3～12之環烷基、或碳數6～10之芳基。於通式(1)中，較佳為R1
及R2
分別獨立且為氫原子或甲基，R3
為氫原子、甲基、丁基或環己基。更佳為R1
為甲基，R2
為氫原子，R3
為甲基。 上述(甲基)丙烯酸烷基酯代表性地由下述通式(2)表示： [化2]於通式(2)中，R4
表示氫原子或甲基，R5
表示氫原子或者可經取代之碳數1～6之脂肪族或脂環式烴基。作為取代基，例如可列舉：鹵素、羥基。作為(甲基)丙烯酸烷基酯之具體例，可列舉：(甲基)丙烯酸甲酯、(甲基)丙烯酸乙酯、(甲基)丙烯酸正丙酯、(甲基)丙烯酸正丁酯、(甲基)丙烯酸第三丁酯、(甲基)丙烯酸正己酯、(甲基)丙烯酸環己酯、(甲基)丙烯酸氯甲酯、(甲基)丙烯酸2-氯乙酯、(甲基)丙烯酸2-羥基乙酯、(甲基)丙烯酸3-羥丙酯、(甲基)丙烯酸2,3,4,5,6-五羥基己酯及(甲基)丙烯酸2,3,4,5-四羥基戊酯。於通式(2)中，R5
較佳為氫原子或甲基。因此，特佳之(甲基)丙烯酸烷基酯為丙烯酸甲酯或甲基丙烯酸甲酯。 上述丙烯酸系樹脂可僅包含單一之戊二醯亞胺單元，亦可包含上述通式(1)中之R1
、R2
及R3
不同之複數個戊二醯亞胺單元。 上述丙烯酸系樹脂中之戊二醯亞胺單元之含有比率較佳為2莫耳%～50莫耳%，更佳為2莫耳%～45莫耳%，進而較佳為2莫耳%～40莫耳%，特佳為2莫耳%～35莫耳%，最佳為3莫耳%～30莫耳%。若含有比率少於2莫耳%，則有源自戊二醯亞胺單元而表現之效果(例如，高光學特性、高機械強度、與偏光元件優異之接著性、薄型化)不會充分發揮之虞。若含有比率超過50莫耳%，則例如有耐熱性、透明性變得不充分之虞。 上述丙烯酸系樹脂可僅包含單一之(甲基)丙烯酸烷基酯單元，亦可包含上述通式(2)中之R4
及R5
不同之複數個(甲基)丙烯酸烷基酯單元。 上述丙烯酸系樹脂中之(甲基)丙烯酸烷基酯單元之含有比率較佳為50莫耳%～98莫耳%，更佳為55莫耳%～98莫耳%，進而較佳為60莫耳%～98莫耳%，特佳為65莫耳%～98莫耳%，最佳為70莫耳%～97莫耳%。若含有比率少於50莫耳%，則有源自(甲基)丙烯酸烷基酯單元而表現之效果(例如，高耐熱性、高透明性)不會充分發揮之虞。若上述含有比率多於98莫耳%，則有樹脂變得脆弱易於破裂，不能充分發揮較高機械強度，生產性差之虞。 上述丙烯酸系樹脂亦可包含除戊二醯亞胺單元及(甲基)丙烯酸烷基酯單元以外之單元。 於1個實施形態中，丙烯酸系樹脂可包含例如0～10重量%之不參與後述分子內醯亞胺化反應之不飽和羧酸單元。不飽和羧酸單元之含有比率較佳為0～5重量%，更佳為0～1重量%。若含量為此種範圍，則能夠維持透明性、滯留穩定性及耐濕性。 於1個實施形態中，丙烯酸系樹脂可含有上述以外之能夠共聚合之乙烯系單體單元(其他之乙烯系單體單元)。作為其他之乙烯系單體，例如可列舉：丙烯腈、甲基丙烯腈、乙基丙烯腈、烯丙基縮水甘油基醚、順丁烯二酸酐、衣康酸酐、N-甲基順丁烯二醯亞胺、N-乙基順丁烯二醯亞胺、N-環己基順丁烯二醯亞胺、丙烯酸胺基乙酯、丙烯酸丙基胺基乙酯、甲基丙烯酸二甲胺基乙酯、甲基丙烯酸乙基胺基丙酯、甲基丙烯酸環己基胺基乙酯、N-乙烯基二乙胺、N-乙醯基乙烯胺、烯丙基胺、甲基烯丙胺、N-甲基烯丙基胺、2-異丙烯基㗁唑啉、2-乙烯基-㗁唑啉、2-丙烯醯基-㗁唑啉、N-苯基順丁烯二醯亞胺、甲基丙烯酸苯基胺基乙酯、苯乙烯、α-甲基苯乙烯、對縮水甘油基苯乙烯、對胺基苯乙烯、2-苯乙烯基-㗁唑啉等。該等可單獨使用，亦可併用。較佳為苯乙烯、α-甲基苯乙烯等苯乙烯系單體。其他之乙烯系單體單元之含有比率較佳為0～1重量%，更佳為0～0.1重量%。若為此種範圍，則能夠抑制不希望之相位差之表現及透明性之降低。 上述丙烯酸系樹脂中之醯亞胺化率較佳為2.5%～20.0%。若醯亞胺化率為此種範圍，則能夠獲得耐熱性、透明性及成形加工性優異之樹脂，且能夠防止膜成形時之焦糊之產生或機械強度之降低。於上述丙烯酸系樹脂中，醯亞胺化率由戊二醯亞胺單元與(甲基)丙烯酸烷基酯單元之比表示。該比例如可自丙烯酸系樹脂之NMR光譜、IR光譜等獲得。於本實施形態中，醯亞胺化率能夠使用1
HNMR BRUKER Avance III(400 MHz)，藉由樹脂之1
H-NMR測定而求出。更加具體而言，將源自3.5至3.8 ppm附近之(甲基)丙烯酸烷基酯之O-CH3
質子之峰面積設為A，將源自3.0至3.3 ppm附近之戊二醯亞胺之N-CH3
質子之峰面積設為B，利用下式而求出。 醯亞胺化率Ⅰm(%)＝{B/(A＋B)}×100 上述丙烯酸系樹脂之酸值較佳為0.10 mmol/g～0.50 mmol/g。若酸值為此種範圍，則能夠獲得耐熱性、機械物性及成形加工性之平衡優異之樹脂。若酸值過小，則存在產生由用於調整至所需之酸值之改性劑之使用所導致之成本提高、由改性劑之殘存所導致之凝膠狀物之產生等問題之情況。若酸值過大，則有變得容易發生膜成形時(例如，熔融擠出時)之發泡，且成形品之生產性降低之傾向。於上述丙烯酸系樹脂中，酸值係該丙烯酸系樹脂中之羧酸單元及羧酸無水物單元之含量。於本實施形態中，酸值可藉由例如WO2005/054311或日本專利特開2005-23272號公報中所記載之滴定法算出。 上述丙烯酸系樹脂之重量平均分子量較佳為1000～2000000，更佳為5000～1000000，進而較佳為10000～500000，特佳為50000～500000，最佳為60000～150000。關於重量平均分子量，例如，可使用凝膠滲透層析儀(GPC系統，東曹製造)，利用聚苯乙烯換算而求出。再者，作為溶劑，可使用四氫呋喃。 上述丙烯酸系樹脂之Tg(玻璃轉移溫度)較佳為110℃以上，更佳為115℃以上，進而較佳為120℃以上，特佳為125℃以上，最佳為130℃以上。若Tg為110℃以上，則包含自此種樹脂所得之保護膜之偏光板易於成為耐久性優異者。Tg之上限值較佳為300℃以下，更佳為290℃以下，進而較佳為285℃以下，特佳為200℃以下，最佳為160℃以下。若Tg為此種範圍，則有可能成形性優異。 C-2-2.丙烯酸系樹脂之聚合 上述丙烯酸系樹脂例如可利用以下之方法進行製造。該方法包括：(I)使與由通式(2)表示之(甲基)丙烯酸烷基酯單元對應之(甲基)丙烯酸烷基酯單體、與不飽和羧酸單體及/或其前驅物單體共聚合而獲得共聚物(a)；及(II)藉由使用醯亞胺化劑對該共聚物(a)進行處理，進行該共聚物(a)中之(甲基)丙烯酸烷基酯單體單元與不飽和羧酸單體及/或其前驅物單體單元之分子內醯亞胺化反應，將由通式(1)表示之戊二醯亞胺單元導入共聚物中。 作為不飽和羧酸單體，例如可列舉：丙烯酸、甲基丙烯酸、丁烯酸、α-經取代丙烯酸、α-經取代甲基丙烯酸。作為其前驅物單體，例如可列舉：丙烯醯胺、甲基丙烯醯胺等。該等可單獨使用，亦可併用。較佳之不飽和羧酸單體為丙烯酸或甲基丙烯酸，較佳之前驅物單體為丙烯醯胺。 作為使用醯亞胺化劑對共聚物(a)進行處理之方法，可使用任意適當之方法。作為具體例，可列舉使用擠出機之方法、使用間歇式反應槽(壓力容器)之方法。使用擠出機之方法包括使用擠出機對共聚物(a)進行加熱熔融，使用醯亞胺化劑對其進行處理。於該情形時，作為擠出機，可使用任意適當之擠出機。作為具體例，可列舉單軸擠出機、二軸擠出機、多軸擠出機。於使用間歇式反應槽(壓力容器)之方法中，可使用任意適當之間歇式反應槽(壓力容器)。 作為醯亞胺化劑，只要能夠生成上述通式(1)所表示之戊二醯亞胺單元即可使用任意適當之化合物。作為醯亞胺化劑之具體例，可列舉：甲基胺、乙基胺、正丙基胺、異丙基胺、正丁胺、異丁胺、第三丁胺、正己基胺等含有脂肪族烴基之胺；苯胺、苄胺、甲苯胺、三氯苯胺等含有芳香族烴基之胺；環己胺等含有脂環式烴基之胺。進而，可使用例如藉由加熱產生此種胺之脲系化合物。作為脲化合物，例如可列舉：脲、1,3-二甲基脲、1,3-二乙基脲、1,3-二丙基脲。醯亞胺化劑較佳為甲基胺、氨、環己胺，更佳為甲基胺。 於醯亞胺化中，除上述醯亞胺化劑以外，根據需要，亦可添加閉環促進劑。 關於醯亞胺化中之醯亞胺化劑之使用量，相對於共聚物(a)100重量份，較佳為0.5重量份～10重量份，更佳為0.5重量份～6重量份。若醯亞胺化劑之使用量少於0.5重量份，則多數情況下不會達到所需之醯亞胺化率。其結果為，存在所得之樹脂之耐熱性變得非常不充分，誘發成形後之焦糊等外觀缺陷之情況。若醯亞胺化劑之使用量超過10重量份，則存在樹脂中殘存醯亞胺化劑，由於該醯亞胺化劑而誘發成形後之焦糊等外觀缺陷或發泡之情況。 本實施形態之製造方法根據需要，除上述醯亞胺化以外，可包括利用酯化劑所進行之處理。 作為酯化劑，例如可列舉：碳酸二甲酯、2,2-二甲氧基丙烷、二甲基亞碸、原甲酸三乙酯、原甲酸三乙酸酯、原甲酸三甲酯、碳酸二苯酯、二甲基硫酸鹽、甲苯磺酸甲酯、甲基三氟甲磺酸酯、甲基乙酸酯、甲醇、乙醇、甲基異氰酸酯、對氯苯基異氰酸酯、二甲基碳二醯亞胺、氯化二甲基-第三丁基矽烷、異丙烯基乙酸酯、二甲脲、氫氧化四甲基銨、二甲基二乙氧基矽烷、四-N-丁氧基矽烷、二甲基(三甲基矽烷)亞磷酸酯、亞磷酸三甲酯、磷酸三甲酯、磷酸三甲苯酯、重氮甲烷、環氧乙烷、環氧丙烷、環氧環己烷、2-乙基己基縮水甘油醚、苯基縮水甘油醚、苄基縮水甘油醚。該等之中，自成本及反應性等觀點而言，較佳為碳酸二甲酯。 酯化劑之添加量可以丙烯酸系樹脂之酸值達到所需之值之方式進行設定。 C-2-3.其他樹脂之併用 於本發明之實施形態中，亦可併用上述丙烯酸系樹脂與其他樹脂。即，可使構成丙烯酸系樹脂之單體成分與構成其他樹脂之單體成分共聚合，將該共聚物供於D項中敍述之膜形成；亦可將丙烯酸系樹脂與其他樹脂之摻合物供於膜形成。作為其他樹脂，例如可列舉：苯乙烯系樹脂、聚乙烯、聚丙烯、聚醯胺、聚苯硫醚、聚醚醚酮、聚酯、聚碸、聚苯醚、聚縮醛、聚醯亞胺、聚醚醯亞胺等其他熱塑性樹脂；酚系樹脂、三聚氰胺系樹脂、聚酯系樹脂、矽酮系樹脂、環氧系樹脂等熱硬化性樹脂。所併用之樹脂之種類及調配量可根據目的及所得之膜所需之特性等而進行適當設定。例如，苯乙烯系樹脂(較佳為丙烯腈-苯乙烯共聚物)可作為相位差控制劑併用。 於併用丙烯酸系樹脂與其他樹脂之情形時，丙烯酸系樹脂與其他樹脂之摻合物中之丙烯酸系樹脂之含量較佳為50重量%～100重量%，更佳為60重量%～100重量%，進而較佳為70重量%～100重量%，特佳為80重量%～100重量%。於含量未達50重量%之情形時，則有丙烯酸系樹脂原本所具有之高耐熱性、高透明性不能充分反映之虞。 C-3.核殼型粒子 於上述保護膜中，關於核殼型粒子，相對於丙烯酸系樹脂100重量份，較佳為調配3重量份～50重量份，更佳為調配3重量份～40重量份。藉此，可將保護膜之表面之算術平均粗糙度Ra調整至所需之範圍內。核殼型粒子可藉由一部分露出於保護膜之表面而於保護膜之表面形成凹凸，亦可在不露出於保護膜之表面之情況下(被丙烯酸系樹脂所覆蓋之狀態下)於保護膜之表面形成凹凸。 核殼型粒子代表性地具有包含橡膠狀聚合物之內核、及包含玻璃狀聚合物且被覆該內核之被覆層。核殼型粒子作為最內層或中間層，可具有一層以上之包含玻璃狀聚合物之層。 構成內核之橡膠狀聚合物之Tg較佳為20℃以下，更佳為-60℃～20℃，進而較佳為-60℃～10℃。若構成內核之橡膠狀聚合物之Tg超過20℃，則有丙烯酸系樹脂之機械強度之提高不充分之虞。構成被覆層之玻璃狀聚合物(硬質聚合物)之Tg較佳為50℃以上，更佳為50℃～140℃，進而較佳為60℃～130℃。若構成被覆層之玻璃狀聚合物之Tg低於50℃，則有丙烯酸系樹脂之耐熱性降低之虞。 核殼型粒子中之內核之含有比率較佳為30重量%～95重量%，更佳為50重量%～90重量%。關於內核中之玻璃狀聚合物層之比率，相對於內核之總量100重量%則為0～60重量%，較佳為0～45重量%，更佳為10重量%～40重量%。核殼型粒子中之被覆層之含有比率較佳為5重量%～70重量%，更佳為10重量%～50重量%。 於1個實施形態中，分散於丙烯酸系樹脂中之核殼型粒子可具有扁平形狀。核殼型粒子可藉由於C-4項中所敍述之延伸而扁平化。扁平化後之核殼型粒子之長度/厚度之比為7.0以下。長度/厚度之比較佳為6.5以下，更佳為6.3以下。另一方面，長度/厚度之比較佳為4.0以上，更佳為4.5以上，進而較佳為5.0以上。於本說明書中，所謂「長度/厚度之比」表示核殼型粒子之俯視形狀之代表長度與厚度之比。其中，所謂「代表長度」，於俯視形狀為圓形之情形時指直徑，於橢圓形之情形時指長徑，於矩形或多邊形之情形時指對角線之長度。該比例如可利用以下之順序求出。藉由利用穿透式電子顯微鏡(例如，加速電壓80 kV，RuO4
染色超薄切片法)拍攝所得之膜截面，自存在於所得之照片中之核殼型粒子之中從較長者(獲得接近代表長度之截面者)依次抽取30個，算出(長度之平均值)/(厚度之平均值)，可獲得該比。 關於構成核殼型粒子之內核之橡膠狀聚合物、構成被覆層之玻璃狀聚合物(硬質聚合物)、該等之聚合方法、及其他構成之詳細內容，例如記載於日本專利特開2016-33552號公報中。該公報之記載作為參考而引用於本說明書。 C-4.保護膜之形成 關於本發明之實施形態之保護膜，代表性地，可藉由包括膜形成包含上述丙烯酸系樹脂(於併用其他樹脂之情形時，為與該其他樹脂之摻合物)及核殼型粒子之組成物之方法而形成。進而，形成保護膜之方法可包括延伸上述膜。 用於膜形成之核殼型粒子之平均粒徑較佳為1 nm～500 nm。若為此種平均粒徑，則能夠將所得之保護膜之表面之算術平均粗糙度Ra調整至所需之範圍內。內核之平均粒徑較佳為50 nm～300 nm，更佳為70 nm～300 nm。 作為形成膜之方法，可採用任意適當之方法。作為具體例，可列舉：塗鑄法(例如，流鑄法)、擠出成形法、射出成形法、加壓成形法、轉移成形法、吹塑成形法、粉末成形法、FRP(Fiber Reinforced Plastics，纖維強化塑膠)成形法、壓延成形法、熱壓法。較佳為擠出成形法或塗鑄法。其原因在於能夠提高所得之膜之平滑性，獲得良好之光學均一性。特佳為擠出成形法。其原因在於不需要考慮由殘存溶劑所引起之問題。其中，使用T型模頭之擠出成形法自膜之生產性及以後之延伸處理之容易性之觀點而言較佳。成形條件可根據所使用之樹脂之組成或種類、所得之膜所需之特性等進行適當設定。 作為延伸方法，可採用任意適當之延伸方法、延伸條件(例如延伸溫度、延伸倍率、延伸速度、延伸方向)。作為延伸方法之具體例，可列舉：自由端延伸、固定端延伸、自由端收縮、固定端收縮。該等可單獨使用，亦可同時使用，亦可逐次使用。藉由以適當之延伸條件延伸相對於丙烯酸系樹脂之核殼型粒子之調配量經適當調整之膜，核殼型粒子移動至(滲出)膜之表面，其結果為，於膜之表面形成有凹凸，可將所得之保護膜之表面之算術平均粗糙度Ra調整至上述所需之範圍內。 延伸方向可根據目的而採用適當之方向。具體而言，可列舉：長度方向、寬度方向、厚度方向、斜方向。延伸方向可為一個方向(單軸延伸)，亦可為兩個方向(雙軸延伸)，亦可為三個方向以上。於本發明之實施形態中，代表性地，可採用長度方向之單軸延伸、長度方向及寬度方向之同時雙軸延伸、長度方向及寬度方向之逐次雙軸延伸。較佳為雙軸延伸(同時或逐次)。其原因在於面內相位差之控制較為容易，易於實現光學等向性。 延伸溫度可根據保護膜所需之光學特性、機械特性及厚度、所使用之樹脂之種類、所使用之膜之厚度、延伸方法(單軸延伸或雙軸延伸)、延伸倍率、延伸速度等進行變化。具體而言，延伸溫度較佳為Tg～Tg＋50℃，進而較佳為Tg＋15℃～Tg＋50℃，最佳為Tg＋35℃～Tg＋50℃。藉由以此種溫度進行延伸，可獲得具有適當特性之保護膜。具體之延伸溫度例如為110℃～200℃，較佳為120℃～190℃。若延伸溫度為此種範圍，則藉由適當調整延伸倍率及延伸速度，核殼型粒子滲出至膜之表面，可將所得之保護膜之表面之算術平均粗糙度Ra調整至上述所需之範圍內。 又，延伸倍率與延伸溫度同樣地，亦可根據保護膜所需之表面之算術平均粗糙度Ra、光學特性、機械特性及厚度、所使用之樹脂之種類、所使用之膜之厚度、延伸方法(單軸延伸或雙軸延伸)、延伸溫度、延伸速度等進行變化。於採用雙軸延伸之情形時，寬度方向(TD)之延伸倍率與長度方向(MD)之延伸倍率之比(TD/MD)較佳為1.0～1.5，更佳為1.0～1.4，進而較佳為1.0～1.3。又，採用雙軸延伸之情形時之面積倍率(長度方向之延伸倍率與寬度方向之延伸倍率之積)較佳為2.0～6.0，更佳為3.0～5.5，進而較佳為3.5～5.2。若延伸倍率為此種範圍，則藉由適當調整延伸溫度及延伸速度，核殼型粒子滲出至膜之表面，可將所得之保護膜之表面之算術平均粗糙度Ra調整至上述所需之範圍內。 又，延伸速度與延伸溫度同樣地，亦可根據保護膜所需之表面之算術平均粗糙度Ra、光學特性、機械特性及厚度、所使用之樹脂之種類、所使用之膜之厚度、延伸方法(單軸延伸或雙軸延伸)、延伸溫度、延伸倍率等進行變化。延伸速度較佳為3%/秒～20%/秒，更佳為3%/秒～15%/秒，進而較佳為3%/秒～10%/秒。於採用雙軸延伸之情形時，一個方向之延伸速度與另一方向之延伸速度可相同，亦可不同。若延伸速度為此種範圍，則藉由適當調整延伸溫度及延伸倍率，核殼型粒子滲出至膜之表面，可將所得之保護膜之表面之算術平均粗糙度Ra調整至上述所需之範圍內。 利用以上之方式進行，可形成保護膜。 D.圖像顯示裝置 上述A至C項中所記載之偏光板可應用於圖像顯示裝置。因此，本發明亦包含使用了此種偏光板之圖像顯示裝置。作為圖像顯示裝置之代表例，可列舉液晶顯示裝置、有機電致發光(EL)顯示裝置。圖像顯示裝置代表性地依次具備顯示單元、偏光板、擴散片、及光源(背光源)，偏光板之保護膜與擴散片對向配置。 實施例 以下藉由實施例對本發明進行具體說明，但本發明並不限定於該等實施例。各特性之測定方法如下所述。再者，只要無特別載明，實施例中之「份」及「%」皆為重量基準。 (1)厚度 使用數位式測微計(安利知公司製造，製品名「KC-351C」)進行測定。 (2)保護膜之表面之算術平均粗糙度Ra 算術平均粗糙度Ra使用光學式表面輪廓測量儀(Veeco Instruments公司製造，商品名「Optical Profilometer NT3300」)進行測定。 (3)損傷評價 藉由於玻璃板(MICRO SLIDE GLASS Pre-cleaned水綠磨t1.3(MATSUNAMI公司製造)，製品型號「S200423」，尺寸：65 mm×165 mm，厚度1.2～1.5 mm)上，介隔黏著劑層貼合剪裁成50 mm×1500 mm之尺寸之上述偏光板，而製作玻璃板與偏光板之積層體。上述積層體係疑似地再現液晶面板之構成者。 於托盤之中，配置擴散片(Sumitomo 3M股份有限公司製造，製品名「DBEF-D2-400」)，於上述擴散片之上，使偏光板側之面朝下而配置上述積層體。繼而，使上述托盤以200次/min×10 min之條件振盪。其後，取出積層體，目視確認偏光板之第1保護膜之摩耗損傷(擦傷塊)之有無。 ＜實施例1＞ (偏光板之製作) 1.保護膜之製作 對MS樹脂(MS-200；甲基丙烯酸甲酯/苯乙烯(莫耳比)＝80/20之共聚物，新日鐵化學(股)製造)以單甲基胺進行醯亞胺化(醯亞胺化率：5%)。所得之醯亞胺化MS樹脂具有通式(1)所表示之戊二醯亞胺單元(R1
及R3
為甲基，R2
為氫原子)、通式(2)所表示之(甲基)丙烯酸酯單元(R4
及R5
為甲基)、及苯乙烯單元。再者，上述醯亞胺化中使用口徑15 mm之嚙合型同方向旋轉式雙軸擠出機。將擠出機之各調溫區域之設定溫度設為230℃，設定螺桿轉速150 rpm，以2.0 kg/hr供給MS樹脂，單甲基胺之供給量相對於MS樹脂100重量份設為2重量份。自漏斗投入MS樹脂，藉由捏和段使樹脂熔融及充滿之後，自噴嘴注入單甲基胺。於反應區之末端放入密封圈使樹脂充滿。將排氣口之壓力減壓至-0.08 MPa而對反應後之副產物及過剩之甲基胺進行去揮發。自設置於擠出機出口之模嘴作為線料而排出之樹脂於水槽中冷卻之後，利用造粒機進行顆粒化。所得之醯亞胺化MS樹脂之醯亞胺化率為5.0%，酸值為0.5 mmol/g。 藉由將上述中所得之醯亞胺化MS樹脂100重量份及核殼型粒子10重量份投入單軸擠出機中進行熔融混合，通過T型模頭形成膜而獲得厚度40 μm之擠出膜。將所得之擠出膜以延伸溫度160℃於長度方向及寬度方向分別同時雙軸延伸至2倍。延伸速度於長度方向及寬度方向均為10%/秒。 以此方式而製作保護膜。所得之保護膜之厚度為10 μm，算術表面粗糙度Ra為22.18 μm，面內相位差Re(550)為2 nm，厚度方向相位差Rth(550)為2 nm。 2.偏光元件之製作 藉由將厚度30 μm之聚乙烯醇(PVA)系樹脂膜(可樂麗製造，製品名「PE3000」)之長條輥，利用輥延伸機以於長度方向達到5.9倍之方式於長度方向進行單軸延伸，並且同時實施膨潤、染色、交聯、洗淨處理，最後實施乾燥處理而製作厚度12 μm之偏光元件。 具體而言，膨潤處理係以20℃之純水進行處理並且延伸至2.2倍。繼而，染色處理係以所得之偏光元件之單體透過率達到45.0%之方式於碘濃度經過調整之碘與碘化鉀之重量比為1：7之30℃之水溶液中進行處理並且延伸至1.4倍。進而，交聯處理係採用2個階段之交聯處理，第1階段之交聯處理係於40℃之溶解硼酸與碘化鉀之水溶液中進行處理並且延伸至1.2倍。第1階段之交聯處理之水溶液之硼酸含量為5.0重量%，碘化鉀含量為3.0重量%。第2階段之交聯處理係於65℃之溶解硼酸與碘化鉀之水溶液中進行處理並且延伸至1.6倍。第2階段之交聯處理之水溶液之硼酸含量為4.3重量%，碘化鉀含量為5.0重量%。又，洗淨處理係以20℃之碘化鉀水溶液進行處理。洗淨處理之水溶液之碘化鉀含量為2.6重量%。最後，乾燥處理係於70℃下乾燥5分鐘而獲得偏光元件。 3.偏光板之製作 (第2保護膜) 於上述偏光元件之一面，介隔聚乙烯醇系接著劑，貼合上述所得之保護膜作為第1保護膜，於上述偏光元件之另一面，介隔聚乙烯醇系接著劑，貼合TAC(triacetyl cellulose，三乙醯纖維素)膜(大日本印刷公司製造，商品名「DSG-03」，厚度70 μm)作為第2保護膜。 (黏著劑層) 於具備冷卻管、氮氣導入管、溫度計及攪拌裝置之反應容器中，與乙酸乙酯一起加入丙烯酸丁酯94.9份、丙烯酸5份、丙烯酸2-羥基乙酯0.1份、及相對於上述單體合計(固形物成分)100份為0.3份之過氧化二苯甲醯，氮氣氣流下，於60℃下反應7小時後，於該反應液中加入乙酸乙酯，獲得含有重量平均分子量220萬、分散比3.9之丙烯酸系聚合物(B)之溶液(固形物成分濃度30%)。每100份上述含有丙烯酸系聚合物(B)之溶液之固形物成分，調配0.6份之三羥甲基丙烷甲苯二異氰酸酯(日本聚胺酯工業(股)製造：Coronate L)、及0.075份之γ-環氧丙氧基丙基甲氧基矽烷(信越化學工業(股)製造：KBM-403)，獲得黏著劑之溶液。對上述溶液，以固形物成分濃度達到15%之方式，利用乙酸乙酯進行稀釋而製備黏著劑塗佈液。於實施了矽酮處理之38 μm之聚對苯二甲酸乙二酯(PET)膜(三菱化學聚酯膜(股)製造，MRF38)之單面，以塗佈厚度達到134.0 μm之方式，使用噴注式模嘴塗佈機塗佈上述所製備之黏著劑塗佈液。繼而，於155℃下進行乾燥1分鐘，形成厚度20 μm之黏著劑層。將該黏著劑層轉印於上述TAC膜之表面，製作偏光板(附黏著劑層)。將所得之偏光板供於上述評價。將結果示於表1。 ＜實施例2＞ 除形成厚度80 μm之擠出膜，且使用該擠出膜以外，與實施例1同樣地製作保護膜。所得之保護膜之厚度為20 μm，算術平均粗糙度Ra為12.37 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 ＜實施例3＞ 除形成厚度160 μm之擠出膜，且使用該擠出膜以外，與實施例1同樣地製作保護膜。所得之保護膜之厚度為40 μm，算術平均粗糙度Ra為6.48 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 ＜實施例4＞ 除形成厚度120 μm之擠出膜，且使用該擠出膜以外，與實施例1同樣地製作保護膜。所得之保護膜之厚度為30 μm，算術平均粗糙度Ra為8.17 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 ＜實施例5＞ 除藉由將醯亞胺化MS樹脂100重量份及核殼型粒子3重量份投入單軸擠出機中進行熔融混合而形成擠出膜，且使用該擠出膜以外，與實施例4同樣地製作保護膜。所得之保護膜之厚度為30 μm，算術平均粗糙度Ra為6.11 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 ＜實施例6＞ 除藉由將醯亞胺化MS樹脂100重量份及核殼型粒子5重量份投入單軸擠出機中進行熔融混合而形成擠出膜，且使用該擠出膜以外，與實施例4同樣地製作保護膜。所得之保護膜之厚度為30 μm，算術平均粗糙度Ra為6.79 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 ＜實施例7＞ 除藉由將醯亞胺化MS樹脂100重量份及核殼型粒子20重量份投入單軸擠出機中進行熔融混合而形成擠出膜，且使用該擠出膜以外，與實施例4同樣地製作保護膜。所得之保護膜之厚度為30 μm，算術平均粗糙度Ra為23.45 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 ＜實施例8＞ 除藉由將醯亞胺化MS樹脂100重量份及核殼型粒子30重量份投入單軸擠出機中進行熔融混合而形成擠出膜，且使用該擠出膜以外，與實施例4同樣地製作保護膜。所得之保護膜之厚度為30 μm，算術平均粗糙度Ra為31.37 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 ＜實施例9＞ 除藉由將醯亞胺化MS樹脂100重量份及核殼型粒子40重量份投入單軸擠出機中進行熔融混合而形成擠出膜，且使用該擠出膜以外，與實施例4同樣地製作保護膜。所得之保護膜之厚度為30 μm，算術平均粗糙度Ra為32.79 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 ＜實施例10＞ 除將所得之擠出膜於延伸溫度140℃下進行延伸以外，與實施例4同樣地製作保護膜。所得之保護膜之厚度為30 μm，算術平均粗糙度Ra為8.06 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 ＜實施例11＞ 除將所得之擠出膜於延伸溫度130℃下進行延伸以外，與實施例4同樣地製作保護膜。所得之保護膜之厚度為30 μm，算術平均粗糙度Ra為6.72 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 ＜實施例12＞ 除將所得之擠出膜於延伸溫度170℃下進行延伸以外，與實施例4同樣地製作保護膜。所得之保護膜之厚度為30 μm，算術平均粗糙度Ra為15.76 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 ＜實施例13＞ 除將所得之擠出膜於延伸溫度180℃下進行延伸以外，與實施例4同樣地製作保護膜。所得之保護膜之厚度為30 μm，算術平均粗糙度Ra為17.29 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 ＜比較例1＞ 除藉由僅將醯亞胺化MS樹脂投入單軸擠出機中進行熔融混合而形成擠出膜，將所得之擠出膜於延伸溫度145℃下進行延伸以外，與實施例3同樣地製作保護膜。所得之保護膜之厚度為40 μm，算術平均粗糙度Ra為4.2 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 ＜比較例2＞ 除藉由將醯亞胺化MS樹脂100重量份及核殼型粒子1重量份投入單軸擠出機中進行熔融混合而形成擠出膜，且使用該擠出膜以外，與實施例3同樣地製作保護膜。所得之保護膜之厚度為40 μm，算術平均粗糙度Ra為4.93 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 ＜比較例3＞ 除藉由將醯亞胺化MS樹脂100重量份及核殼型粒子5重量份投入單軸擠出機中進行熔融混合而形成擠出膜，將所得之擠出膜於延伸溫度100℃下進行延伸以外，與實施例3同樣地製作保護膜。所得之保護膜之厚度為40 μm，算術平均粗糙度Ra為5.14 μm。除使用上述保護膜以外，與實施例1同樣地製作偏光板。將上述偏光板供於與實施例1相同之評價。將結果示於表1。 [表1]
自表1可知，比較例1～3之偏光板由於以與擴散片相接觸之狀態進行振盪而產生摩耗損傷，而實施例1～13之偏光板即便以與擴散片相接觸之狀態進行振盪亦未產生摩耗損傷。 [產業上之可利用性] 本發明之偏光板較好地用於圖像顯示裝置。本發明之圖像顯示裝置可用於攜帶型資訊終端(PDA)、智慧型手機、行動電話、鐘錶、數位相機、攜帶型遊戲機等行動裝置；電腦顯示器，筆記型電腦，影印機等辦公自動化設備；攝錄影機、電視、微波爐等家用電氣設備；後部監視器、汽車導航系統用監視器、汽車音響等車輛用設備；數位標牌、商業店鋪用資訊用監視器等展示設備；監視用監視器等警備設備；護理用監視器、醫療用監視器等護理、醫療設備；等各種用途。Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the embodiments. A. Overall Configuration of Polarizing Plate FIG. 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention. The polarizing plate 10 has a polarizing element 1 and a protective film 2 disposed on one side of the polarizing element 1. The protective film 2 contains an acrylic resin and core-shell particles dispersed in an acrylic resin. The arithmetic mean roughness Ra of the surface of the protective film 2 is 6.0 μm or more. It is preferable that the surface of the protective film 2 opposite to the polarizing element 1 is formed with irregularities caused by the core-shell type particles. It is preferable that the protective film 2 contains 3 parts by weight to 50 parts by weight of core-shell type particles with respect to 100 parts by weight of the acrylic resin. The core-shell type particle typically has an inner core comprising a rubbery polymer and a coating layer containing a glassy polymer and covering the inner core. Preferably, the protective film 2 is a biaxially stretched film. In one embodiment, the polarizing plate 10 does not have a diffusion layer on the surface of the protective film 2. In the case where the polarizing plate of the present invention is brought into contact with other optical members such as a diffusion sheet in the image display device, for example, it is possible to suppress the occurrence of damage caused by friction with the other optical members. Figure 2 is a cross-sectional view showing a polarizing plate according to another embodiment of the present invention. The polarizing plate 11 includes a polarizing element 1 , a protective film 2 (first protective film) disposed on one side of the polarizing element 1 , and a second protective film 3 disposed on the other side of the polarizing element 1 . The second protective film 3 may be a film formed of the same material as the first protective film 2, or may be a film formed of another material. The polarizing plate 11 may have any suitable optical functional film in place of the second protective film 3 depending on the purpose and use. The polarizing plate 10 and the polarizing plate 11 may be in the form of a single piece or may be elongated. Further, the polarizing plate 10 may have an adhesive layer (not shown) on the surface of the polarizing element 1, and the polarizing plate 11 may not have an adhesive layer (not shown) on the surface of the second protective film 3. B. Polarizing Element As the polarizing element, any suitable polarizing element can be employed. For example, the resin film forming the polarizing element may be a single layer of a resin film, or may be a laminate of two or more layers. Specific examples of the polarizing element composed of a single-layer resin film include hydrophilic groups such as a polyvinyl alcohol (PVA) film, a partially formalized PVA film, and an ethylene-vinyl acetate copolymer-based partial saponified film. On the polymer film, a dyeing treatment and elongation treatment using a dichroic substance such as iodine or a dichroic dye, a dehydration treatment of PVA, or a polyene alignment film such as a dehydrochlorination treatment of polyvinyl chloride is carried out. . From the viewpoint of excellent optical characteristics, a polarizing element obtained by dyeing a PVA film by iodine and uniaxially stretching is preferably used. The dyeing by the above iodine is carried out, for example, by immersing the PVA-based film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably from 3 to 7 times. The stretching can be carried out after the dyeing treatment, or can be carried out while dyeing. Further, it is also possible to perform dyeing after stretching. If necessary, a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, and the like are performed on the PVA film. For example, by immersing the PVA-based film in water and washing it with water before dyeing, not only the dirt or the anti-blocking agent on the surface of the PVA film can be washed, but also the PVA film can be swollen to prevent uneven dyeing. Specific examples of the polarizing element obtained by using the laminate include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a resin substrate and coating. A polarizing element obtained by laminating a PVA-based resin layer on the resin substrate. A polarizing element obtained by using a resin substrate and a laminate of a PVA-based resin layer formed on the resin substrate can be produced by, for example, applying a PVA-based resin solution to a resin substrate. After drying, a PVA-based resin layer is formed on a resin substrate to obtain a laminate of a resin substrate and a PVA-based resin layer, and the laminate is stretched and dyed to form a PVA-based resin layer as a polarizing element. In the present embodiment, the stretching typically includes immersing the layered body in an aqueous boric acid solution for stretching. Further, the stretching may further include, as needed, extending the laminate at a high temperature (for example, 95 ° C or higher) before extending in the aqueous boric acid solution. The laminated body of the obtained resin substrate/polarizing element can be used as it is (that is, the resin substrate can serve as a protective layer of the polarizing element), or the resin substrate can be peeled off from the laminated body of the resin substrate/polarizing element, and the peeling area can be peeled off. The layers are used according to any suitable protective layer for the purpose. The details of the method for producing such a polarizing element are described in, for example, Japanese Laid-Open Patent Publication No. 2012-73580. The entire disclosure of this publication is incorporated herein by reference. The thickness of the polarizing element is, for example, 1 μm to 80 μm. In one embodiment, the thickness of the polarizing element is preferably from 1 μm to 15 μm, more preferably from 3 μm to 10 μm, particularly preferably from 3 μm to 8 μm. C. Protective film C-1. Characteristics of protective film As described above, the protective film contains an acrylic resin and core-shell particles dispersed in an acrylic resin, and the arithmetic mean roughness Ra of the surface of the protective film is 6.0 μm or more. . The arithmetic mean roughness Ra is preferably 6 μm to 50 μm, more preferably 6 μm to 40 μm. By setting the arithmetic mean roughness Ra to a value within the above range, the slidability of the surface of the protective film is suppressed from being excessively high, and as a result, it is possible to suppress the case where the protective film (and the polarizing plate) is elongated. Winding offset. The arithmetic mean roughness Ra can be adjusted within a desired range in accordance with the content of the core-shell type particles in the protective film, the elongation conditions in the method for producing the protective film to be described later, and the like. The thickness of the protective film is preferably from 5 μm to 150 μm, more preferably from 10 μm to 100 μm. Preferably, the protective film has substantially optical isotropic properties. In the present specification, the term "substantially optically isotropic" means that the in-plane retardation Re (550) is 0 nm to 10 nm, and the phase difference Rth (550) in the thickness direction is -10 nm to +10 nm. The in-plane retardation Re (550) is more preferably 0 nm to 5 nm, further preferably 0 nm to 3 nm, and particularly preferably 0 nm to 2 nm. The phase difference Rth (550) in the thickness direction is more preferably -5 nm to +5 nm, further preferably -3 nm to +3 nm, and particularly preferably -2 nm to +2 nm. When Re (550) and Rth (550) of the protective film are in such a range, it is possible to prevent adverse effects on display characteristics when the polarizing plate is applied to an image display device. Further, Re (550) is an in-plane retardation of a film measured by light having a wavelength of 550 nm at 23 °C. Re(550) is obtained by the formula: Re(550)=(nx-ny)×d. Rth (550) is a phase difference in the thickness direction of the film measured by light having a wavelength of 550 nm at 23 °C. Rth (550) is obtained by the formula: Rth (550) = (nx - nz) × d. Wherein, the refractive index of the direction in which the refractive index in the nx plane reaches the maximum (ie, the direction of the slow axis), ny is the refractive index in the direction orthogonal to the axis of the late phase (ie, the direction of the phase axis), The refractive index of the nz-based thickness direction and the thickness (nm) of the d-type film. The higher the transmittance of the protective film at 80 nm in 380 nm, the better. Specifically, the light transmittance is preferably 85% or more, more preferably 88% or more, still more preferably 90% or more. When the light transmittance is in this range, the required transparency can be ensured. Regarding the light transmittance, for example, it can be carried out by a method in accordance with ASTM-D-1003. The lower the haze of the protective film, the better. Specifically, the haze is preferably 5% or less, more preferably 3% or less, further preferably 1.5% or less, and particularly preferably 1% or less. When the haze is 5% or less, it is possible to impart a good transparency to the film. Further, even when used in the case of the viewing side polarizing plate of the image display device, the display content can be well recognized. The YI of the thickness of the protective film of 80 μm is preferably 1.27 or less, more preferably 1.25 or less, further preferably 1.23 or less, and particularly preferably 1.20 or less. When the YI exceeds 1.3, the optical transparency may be insufficient. In addition, for the YI, for example, the tristimulus value of the color (X, Y) obtained by measurement using a high-speed integrating sphere type spectroscopic transmittance measuring machine (trade name: DOT-3C: Murakami Color Technology Research Institute) can be used. , Z), obtained by the following formula. YI=[(1.28X-1.06Z)/Y]×100 The thickness of the protective film is 80 μm (the scale of the hue according to Hunter's color system) is preferably less than 1.5, more preferably It is 1.0 or less. When the b value is 1.5 or more, there is a case where an undesired color tone is generated. Further, regarding the b value, for example, a protective film sample can be cut into a square having a side length of 3 cm, and a high-speed integrating sphere type spectroscopic transmittance measuring machine (trade name: DOT-3C: Murakami Color Technology Research Institute) can be used. The hue was measured and obtained by evaluating the hue according to the color spectrum of Hunter. The moisture permeability of the protective film is preferably 300 g/m. 2 ・24 hr or less, more preferably 250 g/m 2 ・24 hr or less, and further preferably 200 g/m 2 ・Under 24hr, especially 150g/m 2 ・Under 24hr, the best is 100 g/m 2 ・24hr or less. When the moisture permeability of the protective film is in this range, a polarizing plate excellent in durability and moisture resistance can be obtained. The tensile strength of the protective film is preferably 10 MPa or more and less than 100 MPa, more preferably 30 MPa or more and less than 100 MPa. In the case of less than 10 MPa, there is a case where sufficient mechanical strength cannot be expressed. If it exceeds 100 MPa, the workability may become insufficient. The tensile strength can be measured, for example, in accordance with ASTM-D-882-61T. The tensile elongation of the protective film is preferably 1.0% or more, more preferably 3.0% or more, still more preferably 5.0% or more. The upper limit of the tensile elongation is, for example, 100%. When the tensile elongation is less than 1%, the toughness may be insufficient. The tensile elongation can be measured, for example, in accordance with ASTM-D-882-61T. The tensile modulus of the protective film is preferably 0.5 GPa or more, more preferably 1 GPa or more, and still more preferably 2 GPa or more. The upper limit of the tensile modulus of elasticity is, for example, 20 GPa. When the tensile modulus of elasticity is less than 0.5 GPa, there is a case where sufficient mechanical strength cannot be expressed. The tensile modulus of elasticity can be measured, for example, in accordance with ASTM-D-882-61T. The protective film may contain any appropriate additives depending on the purpose. Specific examples of the additives include ultraviolet absorbers; hindered phenol-based, phosphorus-based, and sulfur-based antioxidants; stabilizers such as light stabilizers, weathering stabilizers, and heat stabilizers; and reinforcing materials such as glass fibers and carbon fibers; Infrared absorber; flame retardant such as tris(dibromopropyl)phosphate, triallyl phosphate, cerium oxide; antistatic agent such as anionic, cationic or nonionic surfactant; inorganic pigment, organic pigment Colorants such as dyes; organic fillers or inorganic fillers; resin modifiers; organic fillers or inorganic fillers; plasticizers; lubricants; The additive may be added during the polymerization of the acrylic resin or may be added at the time of film formation. The type, amount, combination, addition amount, and the like of the additive can be appropriately set depending on the purpose. In one embodiment, the second protective film may be formed of the same material as the first protective film. In another embodiment, the second protective film may be formed of a material different from the first protective film. In the case where the second protective film is formed of a material different from the first protective film, examples of the material for forming the second protective film include an acrylic resin that does not contain core-shell particles, diethyl cellulose, and three. a cellulose resin such as acetonitrile cellulose; an olefin resin such as a cycloolefin resin or a polypropylene; an ester resin such as a polyethylene terephthalate resin; a polyamide resin; a polycarbonate resin; Such as copolymer resin and the like. The thickness of the second protective film is preferably from 10 μm to 100 μm. C-2. Acrylic resin C-2-1. Configuration of acrylic resin Any suitable acrylic resin can be used as the acrylic resin. The acrylic resin typically contains, as a main component, an alkyl (meth)acrylate as a monomer unit. In the present specification, "(meth)acrylic acid" means acrylic acid and/or methacrylic acid. The alkyl (meth)acrylate constituting the main skeleton of the acrylic resin may, for example, be a linear or branched alkyl group having 1 to 18 carbon atoms. These may be used singly or in combination. Further, in the acrylic resin, any appropriate copolymerized monomer can be introduced by copolymerization. The kind, amount, copolymerization ratio, and the like of such a copolymerizable monomer can be appropriately set depending on the purpose. The constituent components (monomer units) of the main skeleton of the acrylic resin are referred to the following formula (2) and will be described later. The acrylic resin preferably has at least one selected from the group consisting of a pentaneimine unit, a lactone ring unit, a maleic anhydride unit, a maleimide unit, and a glutaric anhydride unit. The acrylic resin having a lactone ring unit is described, for example, in JP-A-2008-181078, the disclosure of which is incorporated herein by reference. The pentacene imine unit is preferably represented by the following formula (1): [Chemical Formula 1] In the general formula (1), R 1 And R 2 Individually independent, representing a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, R 3 It represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an aryl group having 6 to 10 carbon atoms. In the formula (1), preferably R 1 And R 2 Separately and independently hydrogen or methyl, R 3 It is a hydrogen atom, a methyl group, a butyl group or a cyclohexyl group. More preferably R 1 Is methyl, R 2 Is a hydrogen atom, R 3 Is a methyl group. The above alkyl (meth)acrylate is typically represented by the following formula (2): [Chemical 2] In the general formula (2), R 4 Represents a hydrogen atom or a methyl group, R 5 A hydrogen atom or an aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms which may be substituted. Examples of the substituent include a halogen and a hydroxyl group. Specific examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and n-butyl (meth)acrylate. Tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, chloromethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, (methyl) 2-hydroxyethyl acrylate, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate and 2,3,4, (meth)acrylic acid 5-tetrahydroxypentyl ester. In the general formula (2), R 5 It is preferably a hydrogen atom or a methyl group. Therefore, a particularly preferred alkyl (meth)acrylate is methyl acrylate or methyl methacrylate. The acrylic resin may contain only a single pentaneimine unit, and may also contain R in the above formula (1). 1 , R 2 And R 3 A plurality of different pentaneimine units. The content ratio of the pentamethylene imine unit in the acrylic resin is preferably from 2 mol% to 50 mol%, more preferably from 2 mol% to 45 mol%, still more preferably 2 mol%. 40% by mole, particularly preferably 2% by mole to 355% by mole, most preferably 3% by mole to 30% by mole. When the content ratio is less than 2 mol%, the effect derived from the pentacamine unit (for example, high optical properties, high mechanical strength, excellent adhesion to a polarizing element, and thinning) are not sufficiently exhibited. After that. When the content ratio exceeds 50 mol%, for example, heat resistance and transparency are insufficient. The acrylic resin may contain only a single alkyl (meth)acrylate unit, and may also contain R in the above formula (2). 4 And R 5 Different plural alkyl (meth) acrylate units. The content ratio of the alkyl (meth)acrylate unit in the acrylic resin is preferably from 50 mol% to 98 mol%, more preferably from 55 mol% to 98 mol%, still more preferably 60 mol%. Ear % to 98% by mole, particularly preferably 65 mole % to 98 mole %, most preferably 70 mole % to 97 mole %. When the content ratio is less than 50% by mole, the effect derived from the (meth)acrylic acid alkyl ester unit (for example, high heat resistance and high transparency) does not sufficiently exert. When the content ratio is more than 98% by mole, the resin becomes brittle and easily broken, and the high mechanical strength cannot be sufficiently exhibited, and the productivity is poor. The acrylic resin may further contain units other than the glutarylene imide unit and the (meth)acrylic acid alkyl ester unit. In one embodiment, the acrylic resin may contain, for example, 0 to 10% by weight of an unsaturated carboxylic acid unit which does not participate in the intramolecular oxime imidization reaction described later. The content ratio of the unsaturated carboxylic acid unit is preferably from 0 to 5% by weight, more preferably from 0 to 1% by weight. When the content is in this range, transparency, retention stability, and moisture resistance can be maintained. In one embodiment, the acrylic resin may contain a vinyl monomer unit (other vinyl monomer unit) which is copolymerizable other than the above. Examples of other vinyl monomers include acrylonitrile, methacrylonitrile, ethacrylonitrile, allyl glycidyl ether, maleic anhydride, itaconic anhydride, and N-methylbutylene. Diquinone imine, N-ethyl maleimide, N-cyclohexyl maleimide, aminoethyl acrylate, propylaminoethyl acrylate, dimethylamino methacrylate Ethyl ester, ethyl aminopropyl methacrylate, cyclohexylaminoethyl methacrylate, N-vinyldiethylamine, N-ethylidenevinylamine, allylamine, methylallylamine, N -methylallylamine, 2-isopropenyloxazoline, 2-vinyl-oxazoline, 2-propenyl-oxazoline, N-phenylbutyleneimine, methyl Phenylaminoethyl acrylate, styrene, α-methylstyrene, p-glycidylstyrene, p-aminostyrene, 2-styryl-oxazoline, and the like. These may be used alone or in combination. A styrene monomer such as styrene or α-methylstyrene is preferred. The content ratio of the other vinyl monomer unit is preferably from 0 to 1% by weight, more preferably from 0 to 0.1% by weight. If it is such a range, the expression of an undesired phase difference and the fall of transparency can be suppressed. The ruthenium iodide ratio in the acrylic resin is preferably 2.5% to 20.0%. When the imidization ratio is in such a range, a resin excellent in heat resistance, transparency, and moldability can be obtained, and generation of scorching or reduction in mechanical strength during film formation can be prevented. In the above acrylic resin, the ruthenium iodide ratio is represented by the ratio of the glutarylene imide unit to the alkyl (meth)acrylate unit. This ratio can be obtained, for example, from an NMR spectrum, an IR spectrum or the like of an acrylic resin. In the present embodiment, the sulfhydrylation rate can be used. 1 HNMR BRUKER Avance III (400 MHz), by resin 1 It was determined by H-NMR measurement. More specifically, O-CH derived from an alkyl (meth)acrylate in the vicinity of 3.5 to 3.8 ppm 3 The peak area of the proton is set to A, which will be derived from the N-CH of pentaneimine near 3.0 to 3.3 ppm. 3 The peak area of the proton is set to B and is obtained by the following formula. The hydrazine imidation ratio Im (%) = {B / (A + B)} × 100 The acid value of the above acrylic resin is preferably from 0.10 mmol / g to 0.50 mmol / g. When the acid value is in this range, a resin excellent in balance of heat resistance, mechanical properties, and moldability can be obtained. If the acid value is too small, there are problems in that the cost is increased by the use of the modifier for adjustment to the desired acid value, and the gelation of the modifier is caused. When the acid value is too large, foaming tends to occur at the time of film formation (for example, at the time of melt extrusion), and the productivity of the molded article tends to be lowered. In the above acrylic resin, the acid value is the content of the carboxylic acid unit and the carboxylic acid anhydride unit in the acrylic resin. In the present embodiment, the acid value can be calculated by, for example, the titration method described in WO2005/054311 or JP-A-2005-23272. The weight average molecular weight of the acrylic resin is preferably from 1,000 to 2,000,000, more preferably from 5,000 to 1,000,000, still more preferably from 10,000 to 500,000, particularly preferably from 50,000 to 500,000, most preferably from 60,000 to 150,000. The weight average molecular weight can be determined, for example, by using a gel permeation chromatography (GPC system, manufactured by Tosoh Corporation) in terms of polystyrene. Further, as the solvent, tetrahydrofuran can be used. The Tg (glass transition temperature) of the acrylic resin is preferably 110 ° C or higher, more preferably 115 ° C or higher, further preferably 120 ° C or higher, particularly preferably 125 ° C or higher, and most preferably 130 ° C or higher. When the Tg is 110 ° C or more, the polarizing plate containing the protective film obtained from such a resin tends to be excellent in durability. The upper limit of Tg is preferably 300 ° C or lower, more preferably 290 ° C or lower, further preferably 285 ° C or lower, particularly preferably 200 ° C or lower, and most preferably 160 ° C or lower. When Tg is in such a range, it may be excellent in moldability. C-2-2. Polymerization of Acrylic Resin The above acrylic resin can be produced, for example, by the following method. The method comprises: (I) an alkyl (meth) acrylate monomer corresponding to the alkyl (meth) acrylate unit represented by the general formula (2), and an unsaturated carboxylic acid monomer and/or Copolymerization of a precursor monomer to obtain a copolymer (a); and (II) treatment of the copolymer (a) by using a ruthenium iodide to carry out (meth)acrylic acid in the copolymer (a) The intramolecular oxime imidization reaction of the alkyl ester monomer unit with the unsaturated carboxylic acid monomer and/or its precursor monomer unit introduces the pentylene diimide unit represented by the general formula (1) into the copolymer. Examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, α-substituted acrylic acid, and α-substituted methacrylic acid. Examples of the precursor monomer include acrylamide, methacrylamide, and the like. These may be used alone or in combination. Preferably, the unsaturated carboxylic acid monomer is acrylic acid or methacrylic acid, and preferably the precursor monomer is acrylamide. As a method of treating the copolymer (a) using a ruthenium imidating agent, any appropriate method can be used. Specific examples thereof include a method using an extruder and a method using a batch reaction tank (pressure vessel). The method using an extruder includes heating and melting the copolymer (a) using an extruder, and treating it with a hydrazide. In this case, as the extruder, any appropriate extruder can be used. As a specific example, a single-axis extruder, a two-axis extruder, and a multi-axis extruder are mentioned. In the method of using a batch type reaction tank (pressure vessel), any appropriate batch type reaction tank (pressure vessel) can be used. As the quinone imidization agent, any appropriate compound can be used as long as it can form the pentamethylene imine unit represented by the above formula (1). Specific examples of the quinone imidization agent include fats such as methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, third butylamine, and n-hexylamine. An amine group-containing amine; an aromatic hydrocarbon group-containing amine such as aniline, benzylamine, toluidine or trichloroaniline; or an alicyclic hydrocarbon group-containing amine such as cyclohexylamine. Further, for example, a urea-based compound which produces such an amine by heating can be used. Examples of the urea compound include urea, 1,3-dimethylurea, 1,3-diethylurea, and 1,3-dipropylurea. The hydrazine imidating agent is preferably methylamine, ammonia or cyclohexylamine, more preferably methylamine. In the imidization of the oxime, a ring closure accelerator may be added as needed in addition to the above quinone imidization agent. The amount of the ruthenium imidating agent used in the ruthenium imidization is preferably from 0.5 part by weight to 10 parts by weight, more preferably from 0.5 part by weight to 6 parts by weight, per 100 parts by weight of the copolymer (a). If the amount of the ruthenium imidating agent used is less than 0.5 parts by weight, the desired ruthenium imidization ratio will not be achieved in most cases. As a result, the heat resistance of the obtained resin is extremely insufficient, and the appearance defects such as burnt after molding are induced. When the amount of the ruthenium imidating agent used exceeds 10 parts by weight, the quinone imidization agent remains in the resin, and the quinone imidization agent induces appearance defects or foaming of the burnt after molding. The production method of the present embodiment may include, in addition to the above-described quinone imidization, a treatment by an esterifying agent, as needed. Examples of the esterifying agent include dimethyl carbonate, 2,2-dimethoxypropane, dimethyl hydrazine, triethyl orthoformate, triacetate orthoformate, trimethyl orthoformate, and carbonic acid. Diphenyl ester, dimethyl sulfate, methyl toluenesulfonate, methyl triflate, methyl acetate, methanol, ethanol, methyl isocyanate, p-chlorophenyl isocyanate, dimethyl carbon two醯imine, dimethyl-tert-butyl decane chloride, isopropenyl acetate, dimethyl urea, tetramethylammonium hydroxide, dimethyldiethoxy decane, tetra-N-butoxy Decane, dimethyl (trimethyldecane) phosphite, trimethyl phosphite, trimethyl phosphate, tricresyl phosphate, diazomethane, ethylene oxide, propylene oxide, epoxycyclohexane, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, benzyl glycidyl ether. Among these, dimethyl carbonate is preferred from the viewpoints of cost and reactivity. The amount of the esterifying agent to be added can be set such that the acid value of the acrylic resin reaches a desired value. C-2-3. Other resins are used in the embodiment of the present invention, and the above acrylic resin and other resins may be used in combination. That is, the monomer component constituting the acrylic resin may be copolymerized with the monomer component constituting the other resin, and the copolymer may be formed in the film described in item D; or a blend of the acrylic resin and other resins may be used. For film formation. Examples of the other resin include styrene resin, polyethylene, polypropylene, polyamine, polyphenylene sulfide, polyether ether ketone, polyester, polyfluorene, polyphenylene ether, polyacetal, and polyacetal. Other thermoplastic resins such as amines and polyether phthalimides; thermosetting resins such as phenol resins, melamine resins, polyester resins, fluorenone resins, and epoxy resins. The type and amount of the resin to be used in combination can be appropriately set depending on the purpose and characteristics required for the obtained film. For example, a styrene resin (preferably an acrylonitrile-styrene copolymer) can be used as a phase difference controlling agent. When the acrylic resin and other resins are used in combination, the content of the acrylic resin in the blend of the acrylic resin and the other resin is preferably 50% by weight to 100% by weight, more preferably 60% by weight to 100% by weight. Further, it is preferably from 70% by weight to 100% by weight, particularly preferably from 80% by weight to 100% by weight. When the content is less than 50% by weight, the high heat resistance and high transparency which the acrylic resin originally has cannot be sufficiently reflected. C-3. The core-shell type particle is preferably 3 parts by weight to 50 parts by weight, more preferably 3 parts by weight to 40 parts by weight based on 100 parts by weight of the acrylic resin. Parts by weight. Thereby, the arithmetic mean roughness Ra of the surface of the protective film can be adjusted to a desired range. The core-shell type particle may be partially exposed on the surface of the protective film to form irregularities on the surface of the protective film, or may be exposed to the surface of the protective film (in a state covered with the acrylic resin) to the protective film. The surface is formed with irregularities. The core-shell type particle typically has an inner core comprising a rubbery polymer and a coating layer containing a glassy polymer and covering the inner core. The core-shell type particle may be one or more layers containing a glassy polymer as the innermost layer or the intermediate layer. The Tg of the rubbery polymer constituting the inner core is preferably 20 ° C or lower, more preferably -60 ° C to 20 ° C, still more preferably -60 ° C to 10 ° C. When the Tg of the rubber-like polymer constituting the inner core exceeds 20 ° C, the improvement in mechanical strength of the acrylic resin is insufficient. The Tg of the glassy polymer (hard polymer) constituting the coating layer is preferably 50 ° C or higher, more preferably 50 ° C to 140 ° C, still more preferably 60 ° C to 130 ° C. When the Tg of the glassy polymer constituting the coating layer is less than 50 ° C, the heat resistance of the acrylic resin is lowered. The content ratio of the core in the core-shell type particles is preferably from 30% by weight to 95% by weight, more preferably from 50% by weight to 90% by weight. The ratio of the glassy polymer layer in the core is from 0 to 60% by weight, preferably from 0 to 45% by weight, more preferably from 10% to 40% by weight, based on 100% by weight of the total of the core. The content ratio of the coating layer in the core-shell type particles is preferably from 5% by weight to 70% by weight, more preferably from 10% by weight to 50% by weight. In one embodiment, the core-shell type particles dispersed in the acrylic resin may have a flat shape. The core-shell particles can be flattened by extensions as described in Section C-4. The ratio of the length/thickness of the flattened core-shell type particles is 7.0 or less. The length/thickness ratio is preferably 6.5 or less, more preferably 6.3 or less. On the other hand, the length/thickness ratio is preferably 4.0 or more, more preferably 4.5 or more, still more preferably 5.0 or more. In the present specification, the "length/thickness ratio" means the ratio of the representative length to the thickness of the plan shape of the core-shell type particles. The term "representative length" refers to the diameter in the case where the shape is circular in plan view, the long diameter in the case of an ellipse, and the length of the diagonal in the case of a rectangle or a polygon. This ratio can be obtained, for example, by the following procedure. By using a transmission electron microscope (for example, an accelerating voltage of 80 kV, RuO 4 The film cross-section obtained by the dyeing ultra-thin section method is taken from the longer ones (the ones which are close to the representative length) from the core-shell type particles existing in the obtained photograph, and is calculated (average length) / (average of thickness), the ratio can be obtained. The details of the rubber-like polymer constituting the core of the core-shell type particle, the glassy polymer (hard polymer) constituting the coating layer, the polymerization method, and the like are described in, for example, Japanese Patent Laid-Open No. 2016- Bulletin No. 33552. The description of this publication is incorporated herein by reference. C-4. Formation of Protective Film According to the protective film of the embodiment of the present invention, the acrylic resin may be formed by including a film (in the case of using another resin in combination, it is blended with the other resin) And a method of forming a composition of core-shell particles. Further, the method of forming a protective film may include extending the above film. The average particle diameter of the core-shell type particles for film formation is preferably from 1 nm to 500 nm. If it is such an average particle diameter, the arithmetic mean roughness Ra of the surface of the obtained protective film can be adjusted to the required range. The average particle diameter of the core is preferably from 50 nm to 300 nm, more preferably from 70 nm to 300 nm. As a method of forming the film, any appropriate method can be employed. Specific examples include a coating method (for example, a casting method), an extrusion molding method, an injection molding method, a pressure molding method, a transfer molding method, a blow molding method, a powder molding method, and FRP (Fiber Reinforced Plastics). , fiber reinforced plastic) forming method, calendering method, hot pressing method. It is preferably an extrusion molding method or a coating method. The reason for this is that the smoothness of the obtained film can be improved, and good optical uniformity can be obtained. Particularly preferred is extrusion molding. The reason for this is that it is not necessary to consider the problem caused by the residual solvent. Among them, the extrusion molding method using the T-die is preferable from the viewpoint of the productivity of the film and the easiness of the subsequent elongation treatment. The molding conditions can be appropriately set depending on the composition or type of the resin to be used, the properties required for the obtained film, and the like. As the stretching method, any appropriate stretching method, stretching conditions (for example, elongation temperature, stretching ratio, stretching speed, and stretching direction) may be employed. Specific examples of the stretching method include a free end extension, a fixed end extension, a free end contraction, and a fixed end contraction. These can be used alone or in combination or sequentially. The core-shell type particle is moved to the surface of the film by a film which is appropriately adjusted by extending the amount of the core-shell type particle with respect to the acrylic resin under appropriate extension conditions, and as a result, a film is formed on the surface of the film. The unevenness can adjust the arithmetic mean roughness Ra of the surface of the obtained protective film to the above-mentioned desired range. The direction of extension can be in the appropriate direction depending on the purpose. Specifically, the longitudinal direction, the width direction, the thickness direction, and the oblique direction are mentioned. The extension direction can be one direction (uniaxial extension), two directions (biaxial extension), or more than three directions. In the embodiment of the present invention, the uniaxial stretching in the longitudinal direction, the simultaneous biaxial stretching in the longitudinal direction and the width direction, and the sequential biaxial stretching in the longitudinal direction and the width direction may be employed. It is preferably a biaxial extension (simultaneous or sequential). The reason for this is that the control of the in-plane phase difference is relatively easy, and optical isotropic is easily achieved. The extension temperature can be determined according to the optical characteristics, mechanical properties and thickness required for the protective film, the kind of the resin to be used, the thickness of the film to be used, the stretching method (uniaxial stretching or biaxial stretching), the stretching ratio, the stretching speed, and the like. Variety. Specifically, the stretching temperature is preferably from Tg to Tg + 50 ° C, more preferably from Tg + 15 ° C to Tg + 50 ° C, most preferably from Tg + 35 ° C to Tg + 50 ° C. By stretching at such a temperature, a protective film having appropriate characteristics can be obtained. The specific extension temperature is, for example, 110 ° C to 200 ° C, preferably 120 ° C to 190 ° C. If the extension temperature is in such a range, the core-shell type particles are oozing out to the surface of the film by appropriately adjusting the stretching ratio and the stretching speed, and the arithmetic mean roughness Ra of the surface of the obtained protective film can be adjusted to the above-mentioned desired range. Inside. Further, similarly to the stretching temperature, the stretching ratio may be an arithmetic mean roughness Ra of the surface required for the protective film, optical characteristics, mechanical properties and thickness, type of resin to be used, thickness of the film to be used, and elongation method. (uniaxial extension or biaxial extension), elongation temperature, elongation speed, etc. are changed. When the biaxial stretching is employed, the ratio of the stretching ratio in the width direction (TD) to the stretching ratio in the length direction (MD) (TD/MD) is preferably 1.0 to 1.5, more preferably 1.0 to 1.4, and further preferably It is 1.0 to 1.3. Further, the area magnification (the product of the stretching ratio in the longitudinal direction and the stretching ratio in the width direction) in the case of biaxial stretching is preferably 2.0 to 6.0, more preferably 3.0 to 5.5, still more preferably 3.5 to 5.2. If the stretching ratio is such a range, the core-shell type particles are oozing out to the surface of the film by appropriately adjusting the stretching temperature and the stretching speed, and the arithmetic mean roughness Ra of the surface of the obtained protective film can be adjusted to the above-mentioned desired range. Inside. Further, the stretching speed may be the same as the stretching temperature, or the arithmetic mean roughness Ra of the surface required for the protective film, the optical characteristics, the mechanical properties and the thickness, the kind of the resin to be used, the thickness of the film to be used, and the stretching method. (uniaxial extension or biaxial extension), elongation temperature, extension ratio, and the like are changed. The stretching speed is preferably from 3%/second to 20%/second, more preferably from 3%/second to 15%/second, still more preferably from 3%/second to 10%/second. In the case of biaxial stretching, the extension speed in one direction may be the same as or different from the extension speed in the other direction. If the stretching speed is in such a range, the core-shell type particles are exuded to the surface of the film by appropriately adjusting the stretching temperature and the stretching ratio, and the arithmetic mean roughness Ra of the surface of the obtained protective film can be adjusted to the above-mentioned desired range. Inside. By performing the above method, a protective film can be formed. D. Image Display Device The polarizing plate described in the above items A to C can be applied to an image display device. Accordingly, the present invention also encompasses an image display device using such a polarizing plate. Typical examples of the image display device include a liquid crystal display device and an organic electroluminescence (EL) display device. The image display device typically includes a display unit, a polarizing plate, a diffusion sheet, and a light source (backlight) in this order, and the protective film of the polarizing plate is disposed opposite to the diffusion sheet. EXAMPLES Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited to the examples. The measurement method of each characteristic is as follows. Further, the "parts" and "%" in the examples are based on weight unless otherwise specified. (1) The thickness was measured using a digital micrometer (manufactured by Amway Corporation, product name "KC-351C"). (2) Arithmetic average roughness Ra of the surface of the protective film The arithmetic mean roughness Ra was measured using an optical surface profilometer (manufactured by Veeco Instruments, trade name "Optical Profilometer NT3300"). (3) Damage evaluation by glass plate (MICRO SLIDE GLASS Pre-cleaned water green mill t1.3 (manufactured by MATSUNAMI), product type "S200423", size: 65 mm × 165 mm, thickness 1.2 to 1.5 mm), The polarizing plate cut into a size of 50 mm × 1500 mm was attached to the adhesive layer to form a laminate of the glass plate and the polarizing plate. The above laminated system suspiciously reproduces the constituents of the liquid crystal panel. A diffusion sheet (manufactured by Sumitomo 3M Co., Ltd., product name "DBEF-D2-400") was placed in the tray, and the laminate was placed on the diffusion sheet with the surface on the side of the polarizing plate facing downward. Then, the tray was oscillated under the conditions of 200 times/min × 10 minutes. Then, the laminate was taken out, and the presence or absence of abrasion damage (scratch block) of the first protective film of the polarizing plate was visually confirmed. <Example 1> (Production of polarizing plate) 1. Preparation of protective film for MS resin (MS-200; copolymer of methyl methacrylate/styrene (mole ratio) = 80/20, Nippon Steel Chemical Co., Ltd. (manufactured by the company)) oxime imidization with monomethylamine (醯 imidization ratio: 5%). The obtained quinone imidized MS resin has a pentane diimide unit represented by the formula (1) (R 1 And R 3 Is methyl, R 2 Is a hydrogen atom), a (meth) acrylate unit represented by the formula (2) (R) 4 And R 5 It is a methyl group, and a styrene unit. Further, in the above iridization, a mesh type co-rotating twin-screw extruder having a diameter of 15 mm was used. The set temperature of each temperature adjustment zone of the extruder was set to 230 ° C, the screw rotation speed was set to 150 rpm, and the MS resin was supplied at 2.0 kg/hr. The supply amount of monomethylamine was set to 2 weights with respect to 100 parts by weight of the MS resin. Share. The MS resin was introduced from the funnel, and after the resin was melted and filled by the kneading section, monomethylamine was injected from the nozzle. A sealing ring is placed at the end of the reaction zone to fill the resin. The pressure of the exhaust port was reduced to -0.08 MPa to devolatize the by-products after the reaction and the excess methylamine. The resin discharged from the nozzle which is provided at the outlet of the extruder as a strand is cooled in a water tank, and then pelletized by a granulator. The obtained hydrazine imidized MS resin had a hydrazine imidation ratio of 5.0% and an acid value of 0.5 mmol/g. 100 parts by weight of the ruthenium imidized MS resin obtained in the above and 10 parts by weight of the core-shell particles were melt-mixed in a single-axis extruder, and a film was formed by a T-die to obtain an extrusion having a thickness of 40 μm. membrane. The obtained extruded film was simultaneously biaxially stretched to 2 times in the longitudinal direction and the width direction at an extension temperature of 160 ° C. The extension speed is 10%/second in both the length direction and the width direction. A protective film was produced in this manner. The obtained protective film had a thickness of 10 μm, an arithmetic surface roughness Ra of 22.18 μm, an in-plane retardation Re (550) of 2 nm, and a thickness direction phase difference Rth (550) of 2 nm. 2. The polarizing element was produced by using a long-length roll of a polyvinyl alcohol (PVA) resin film (manufactured by Kuraray, product name "PE3000") having a thickness of 30 μm by a roll stretching machine to reach 5.9 times in the longitudinal direction. In the manner of uniaxial stretching in the longitudinal direction, swelling, dyeing, cross-linking, and washing treatment were simultaneously performed, and finally, drying treatment was performed to prepare a polarizing element having a thickness of 12 μm. Specifically, the swelling treatment was treated with pure water at 20 ° C and extended to 2.2 times. Then, the dyeing treatment was carried out in an aqueous solution having an adjusted iodine concentration of iodine and potassium iodide at a weight ratio of 1:7 to 30 ° C and extended to 1.4 times in such a manner that the monomer transmittance of the obtained polarizing element was 45.0%. Further, the crosslinking treatment was carried out by a two-stage crosslinking treatment, and the first-stage crosslinking treatment was carried out in an aqueous solution of dissolved boric acid and potassium iodide at 40 ° C and extended to 1.2 times. The aqueous solution of the crosslinking treatment in the first stage had a boric acid content of 5.0% by weight and a potassium iodide content of 3.0% by weight. The second stage crosslinking treatment was carried out in an aqueous solution of dissolved boric acid and potassium iodide at 65 ° C and extended to 1.6 times. The aqueous solution of the crosslinking treatment in the second stage had a boric acid content of 4.3% by weight and a potassium iodide content of 5.0% by weight. Further, the washing treatment was carried out with a potassium iodide aqueous solution at 20 °C. The potassium iodide content of the aqueous solution of the washing treatment was 2.6% by weight. Finally, the drying treatment was carried out by drying at 70 ° C for 5 minutes to obtain a polarizing element. 3. Production of a polarizing plate (second protective film) The protective film obtained as described above is bonded to one surface of the polarizing element via a polyvinyl alcohol-based adhesive as a first protective film, and the other surface of the polarizing element is interposed. A TAC (triacetyl cellulose) film (manufactured by Dainippon Printing Co., Ltd., trade name "DSG-03", thickness: 70 μm) was bonded as a second protective film. (Adhesive layer) In a reaction vessel equipped with a cooling tube, a nitrogen gas introduction tube, a thermometer, and a stirring device, 94.9 parts of butyl acrylate, 5 parts of acrylic acid, 0.1 part of 2-hydroxyethyl acrylate, and the like were added together with ethyl acetate. 100 parts of the total of the above monomers (solid content) was 0.3 parts by weight of benzamidine peroxide, and after reacting at 60 ° C for 7 hours under a nitrogen gas stream, ethyl acetate was added to the reaction mixture to obtain a weight average. A solution of a polymer (B) having a molecular weight of 2.2 million and a dispersion ratio of 3.9 (solid content concentration: 30%). 0.6 parts of trimethylolpropane toluene diisocyanate (manufactured by Nippon Polyurethane Co., Ltd.: Coronate L) and 0.075 parts of γ- per 100 parts of the above solid content of the solution containing the acrylic polymer (B). Glycidoxypropyl methoxy decane (manufactured by Shin-Etsu Chemical Co., Ltd.: KBM-403) to obtain a solution of an adhesive. The above solution was diluted with ethyl acetate so that the solid content concentration became 15% to prepare an adhesive coating liquid. The single side of a 38 μm polyethylene terephthalate (PET) film (Mitsubishi Chemical Polyester Film, MRF38) which was treated with an anthrone was applied in a thickness of 134.0 μm. The above-prepared adhesive coating liquid was applied by a spray nozzle coater. Then, drying was performed at 155 ° C for 1 minute to form an adhesive layer having a thickness of 20 μm. The adhesive layer was transferred onto the surface of the TAC film to prepare a polarizing plate (adhesive layer). The obtained polarizing plate was subjected to the above evaluation. The results are shown in Table 1. <Example 2> A protective film was produced in the same manner as in Example 1 except that an extruded film having a thickness of 80 μm was formed and the extruded film was used. The obtained protective film had a thickness of 20 μm and an arithmetic mean roughness Ra of 12.37 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. <Example 3> A protective film was produced in the same manner as in Example 1 except that an extruded film having a thickness of 160 μm was formed and the extruded film was used. The obtained protective film had a thickness of 40 μm and an arithmetic mean roughness Ra of 6.48 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. <Example 4> A protective film was produced in the same manner as in Example 1 except that an extruded film having a thickness of 120 μm was formed and the extruded film was used. The obtained protective film had a thickness of 30 μm and an arithmetic mean roughness Ra of 8.17 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. <Example 5> An extruded film was formed by injecting 100 parts by weight of a ruthenium imidized MS resin and 3 parts by weight of core-shell particles into a uniaxial extruder to form an extruded film, and using the extruded film, A protective film was produced in the same manner as in Example 4. The obtained protective film had a thickness of 30 μm and an arithmetic mean roughness Ra of 6.11 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. <Example 6> An extruded film was formed by injecting 100 parts by weight of a ruthenium iodide MS resin and 5 parts by weight of core-shell particles into a uniaxial extruder to form an extruded film, and using the extruded film, A protective film was produced in the same manner as in Example 4. The obtained protective film had a thickness of 30 μm and an arithmetic mean roughness Ra of 6.79 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. <Example 7> An extruded film was formed by injecting 100 parts by weight of a ruthenium iodide MS resin and 20 parts by weight of core-shell particles into a uniaxial extruder to form an extruded film, and using the extruded film, A protective film was produced in the same manner as in Example 4. The obtained protective film had a thickness of 30 μm and an arithmetic mean roughness Ra of 23.45 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. <Example 8> Except that 100 parts by weight of a ruthenium iodide MS resin and 30 parts by weight of core-shell type particles were put into a uniaxial extruder and melt-mixed to form an extruded film, and the extruded film was used, A protective film was produced in the same manner as in Example 4. The obtained protective film had a thickness of 30 μm and an arithmetic mean roughness Ra of 31.37 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. <Example 9> An extruded film was formed by injecting 100 parts by weight of a ruthenium iodide MS resin and 40 parts by weight of core-shell particles into a uniaxial extruder to form an extruded film, and using the extruded film, A protective film was produced in the same manner as in Example 4. The obtained protective film had a thickness of 30 μm and an arithmetic mean roughness Ra of 32.79 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. <Example 10> A protective film was produced in the same manner as in Example 4 except that the obtained extruded film was stretched at a stretching temperature of 140 °C. The obtained protective film had a thickness of 30 μm and an arithmetic mean roughness Ra of 8.06 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. <Example 11> A protective film was produced in the same manner as in Example 4 except that the obtained extruded film was stretched at an elongation temperature of 130 °C. The obtained protective film had a thickness of 30 μm and an arithmetic mean roughness Ra of 6.72 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. <Example 12> A protective film was produced in the same manner as in Example 4 except that the obtained extruded film was stretched at a stretching temperature of 170 °C. The obtained protective film had a thickness of 30 μm and an arithmetic mean roughness Ra of 15.76 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. <Example 13> A protective film was produced in the same manner as in Example 4 except that the obtained extruded film was stretched at an elongation temperature of 180 °C. The obtained protective film had a thickness of 30 μm and an arithmetic mean roughness Ra of 17.29 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. <Comparative Example 1> An extruded film was formed by merely melt-mixing a ruthenium imidized MS resin into a single-axis extruder, and the obtained extruded film was stretched at an extension temperature of 145 ° C, and was carried out. In Example 3, a protective film was produced in the same manner. The obtained protective film had a thickness of 40 μm and an arithmetic mean roughness Ra of 4.2 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. <Comparative Example 2> An extruded film was formed by injecting 100 parts by weight of a ruthenium iodide MS resin and 1 part by weight of core-shell particles into a single-axis extruder to form an extruded film, and using the extruded film, A protective film was produced in the same manner as in Example 3. The obtained protective film had a thickness of 40 μm and an arithmetic mean roughness Ra of 4.93 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. <Comparative Example 3> An extruded film was formed by injecting 100 parts by weight of a ruthenium imidized MS resin and 5 parts by weight of core-shell particles into a single-screw extruder to form an extruded film, and the obtained extruded film was stretched. A protective film was produced in the same manner as in Example 3 except that the temperature was extended at 100 °C. The obtained protective film had a thickness of 40 μm and an arithmetic mean roughness Ra of 5.14 μm. A polarizing plate was produced in the same manner as in Example 1 except that the above protective film was used. The above polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. [Table 1] As can be seen from Table 1, the polarizing plates of Comparative Examples 1 to 3 are oscillated in a state of being in contact with the diffusion sheet, and the wear of the polarizing plates of Examples 1 to 13 is oscillated even in a state of being in contact with the diffusion sheet. No wear and tear was caused. [Industrial Applicability] The polarizing plate of the present invention is preferably used for an image display device. The image display device of the invention can be used for mobile devices such as portable information terminals (PDAs), smart phones, mobile phones, clocks, digital cameras, portable game machines, office automation devices such as computer monitors, notebook computers, and photocopying machines. ; household electrical equipment such as video cameras, televisions, microwave ovens; rear monitors, monitors for car navigation systems, vehicle audio equipment, etc.; display equipment for digital signage, information monitors for commercial shops, etc.; monitors for surveillance; Such as security equipment; care monitors, medical monitors and other care, medical equipment; and other uses.