サイズ剤は，紙•板紙への液体浸透性をコントロールしインクの滲み防止や耐水性付与のために広く使用されている製紙用薬品である.製紙工程での使用場所により，内添サイズ剤と表面サイズ剤に分類される.表面サイズ剤はサイズプレスなどの塗工機で紙に塗布される表面処理剤であり，内添サイズ剤とは異なり紙への歩留りがほぼ100%である.また，紙表面に直接作用するため効率的なサイジングが可能で，サィズ性のみならず紙-板紙にさまざまな機能(ペン書き適性，各種印刷適性，摩擦係数のコントロール，撥水加工適性)を効率的に付与することができるという特徴がある.さらに，内添サイズ剤使用時の操業性の問題(抄紙機の汚れ，発泡,高温抄造でのサイズ低下)を回避できることから，近年では表面サイズ剤重視の処方(内添サイズ剤の添加量を減らし，表面サイズ剤の塗工量を増やす処方変更)が提案されてきた.%In recent years, we are faced with new challenges, including:1)a decrease in sizing efficiency of the internal sizing agents due to the increase of the paper pH associated with an increasing trend of printing on acid-free paper and the reduction of the use of aluminum sulfate; 2) destabilization of a surface sizing agent, and its decrease in sizing efficiency due to an increased number of calcium ions in coating liquid. This increase was caused by calcium carbonate falling from paper surfaces into coating liquid which was associated with an increase of the amount of calcium carbonate in paper, etc. In China, the world's largest containerboard producer, satisfactory effect of internal sizing agents and internal paper strengthening agents could not be obtained due to the natural hardness of fresh water and the processing water for papermaking is highly recycled due to water intake and waste water regulations. When manufacturing the corrugating medium, more importance is attached to surface coating chemicals than dosing chemicals. This is done in order to maintain the strength of the corrugated fiberboard in the high humidity climate, and much starch has been used for coating as a paper strengthening agent together with the surface sizing agents. As a result, the coating liquid contains much anionic trash such as fine fibers which fell off the low-strength paper. Thus, a high performance surface sizing agent, which can efficiently impart stable sizing performance to the paper and has superior performance related to operability such as mechanical stability, etc. even under these conditions. We have developed a new surface sizing agent which is different from the traditional surface sizing agents and adapts to this environment by reviewing the chemical composition and manufacturing method to solve the problems such as the improvement of the sizing effect of surface sizing agents; the reduction or influence by contaminants including calcium carbonate, calcium ion derived from the calcium carbonate, and anionic trash; and the improvement of mechanical stability.
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