JP3700166B2 - Binder for polyurethane-based printing ink and printing ink composition using the same - Google Patents

Description

【００２９】
【化２】

【００３０】
式１に該当する化合物としては、Ｎ−メチルジエタノールアミン、Ｎ−メチルジプロパノールアミン、Ｎ−エチルジエタノールアミン等のＮ−アルキルジアルカノールアミン類、Ｎ−フェニルジエタノールアミン、Ｎ−フェニルジプロパノールアミン等のＮ−アリールジアルカノールアミン類等が挙げられる。
【００３１】
式２に該当する化合物としては、ジメチルアミノメタノール、ジメチルアミノプロパノール等のジアルキルアミノアルコール等が挙げられる。
【００３２】
本発明で好ましい第三級アミノ基含有活性水素化合物（Ｃ）は、式１に該当するものであり、更にはＮ−メチルジエタノールアミン、Ｎ−メチルジプロパノールアミン、Ｎ−エチルジエタノールアミン等のＮ−アルキルジアルカノールアミン類が好ましい。これは、式２のタイプでは、ポリウレタン系樹脂の末端に第三級アミノ基が導入されることになるため、ポリウレタン系樹脂の分子量によって導入量が影響される。しかし、式１のタイプでは、ポリウレタン系樹脂の中に第三級アミノ基が導入されるため、導入量はポリウレタン系樹脂の分子量に影響されることがないからである。
【００３３】
本発明で用いられる有機ジイソシアネート（Ｄ）としては、２，４−トリレンジイソシアネート、２，６−トリレンジイソシアネート、４，４′−ジフェニルメタンジイソシアネート、２，４′−ジフェニルメタンジイソシアネート、２，２′−ジフェニルメタンジイソシアネート、１，５−ナフチレンジイソシアネート、１，４−ナフチレンジイソシアネート、ｐ−フェニレンジイソシアネート、ｍ−フェニレンジイソシアネート、ｏ−キシリレンジイソシアネート、ｍ−キシリレンジイソシアネート、ｐ−キシリレンジイソシアネート、テトラメチルキシリレンジイソシアネート、４，４′−ジフェニルエーテルジイソシアネート、２−ニトロジフェニル−４，４′−ジイソシアネート、２，２′−ジフェニルプロパン−４，４′−ジイソシアネート、３，３′−ジメチルジフェニルメタン−４，４′−ジイソシアネート、４，４′−ジフェニルプロパンジイソシアネート、３，３′−ジメトキシジフェニル−４，４′−ジイソシアネート等の芳香族ジイソシアネート、テトラメチレンジイソシアネート、ヘキサメチレンジイソシアネート、２−メチル−１，５−ペンタンジイソシアネート、３−メチル−１，５−ペンタンジイソシアネート、リジンジイソシアネート等の脂肪族ジイソシアネート、イソホロンジイソシアネート、水素添加トリレンジイソシアネート、水素添加ジフェニルメタンジイソシアネート、水素添加キシリレンジイソシアネート、水素添加テトラメチルキシリレンジイソシアネート、シクロヘキシルジイソシアネート等の脂環族ジイソシアネートや、これらの２種類以上の混合物、これらの有機ジイソシアネートのウレタント変性体、アロファネート変性体、ウレア変性体、ビウレット変性体、ウレトジオン変性体、ウレトイミン変性体、イソシアヌレート変性体、カルボジイミド変性体等、公知のあらゆる有機ジイソシアネートであってもよい。
【００３４】
本発明では、イソシアネート成分における脂肪族ジイソシアネート及び／又は脂環族ジイソシアネートが５０〜１００モル％含有するものが好ましく、特に８０〜１００モル％のものが好ましい。脂肪族ジイソシアネート及び／又は脂環族ジイソシアネートが下限未満の場合、インキが黄変しやすくなり、また、密着性も低下する。上記の有機ジイソシアネートの中では、イソホロンジイソシアネートが最も好ましい。
【００３５】
なお、必要に応じて反応停止剤を用いてもよい。反応停止剤としては、メタノール、エタノール等のようなモノアルコール、エチルアミン、プロピルアミン、ジブチルアミン等のようなモノアミン、モノエタノールアミン、ジエタノールアミン、Ｎ−メチルジエタノールアミン、Ｎ−フェニルジプロパノールアミン等のアミノアルコールがある。また、場合によっては、前述のポリエステルポリオールやポリエステル−アミドポリオールに用いられる低分子ポリオールや低分子ポリアミンも使用できる。
【００３６】
本発明におけるポリウレタン系印刷インキ用バインダーを合成する際の反応触媒としては、公知のいわゆるウレタン化触媒を用いることができる。具体的には、ジブチルチンジラウレート、ジオクチルチンジラウレート等の有機金属化合物や、トリエチレンジアミンやトリエチルアミン等の有機アミンやその塩等が挙げられる。
【００３７】
本発明のポリウレタン系印刷インキ用バインダーの合成方法は、公知の方法が用いられる。すなわち、（１）活性水素基成分と有機ジイソシアネートを、活性水素基過剰の条件で所定分子量に達するまで反応させる方法（ワンショット法）、（２）ポリオール成分と有機ジイソシアネートを、イソシアネート基過剰の条件で反応させ、イソシアネート基含有のプレポリマーを得て、次にこのプレポリマーを低分子グリコールや低分子ジアミンで鎖延長させて所定分子量に達するまで反応させる方法（プレポリマー法）等がある。
【００３８】
また、必要に応じて有機溶剤を用いることができる。この有機溶剤は、トルエン、キシレン等の芳香族炭化水素系溶剤、ペンタン、ヘキサン、オクタン等の脂肪族炭化水素系溶剤、シクロペンタン、シクロヘキサン、メチルシクロヘキサン等の脂環族炭化水素系溶剤、アセトン、メチルエチルケトン、メチルブチルケトン、メチルイソブチルケトン、ジイソブチルケトン、シクロヘキサノン、メチルシクロヘキサノン等のケトン系溶剤、ジエチルエーテル、１，４−ジオキサン、テトラヒドロフラン等のエーテル系溶剤、エチレングリコールジメチルエーテル、エチレングリコールモノメチルエーテルアセテート、プロピレングリコールジメチルエーテル、プロピレングリコールモノメチルエーテルアセテート等のセロソルブ系溶剤、酢酸エチル、酢酸ブチル等の一塩基酸エステル系溶剤、アジピン酸ジメチル、コハク酸ジメチル、フタル酸ジオクチル等の二塩基酸エステル類、ジメチルホルムアミド、ジメチルアセトアミド、Ｎ−メチルピロリドン等のイソシアネート基に不活性なものであれば特に制限はない。また、条件によっては、イソプロパノールのようなアルコール系溶剤も用いることができる。
【００３９】
本発明のポリウレタン系印刷インキ用バインダーの反応装置としては、上記の反応が達成できればいかなる装置でもよく、例えば、攪拌装置の付いた反応釜やニーダー、一軸又は多軸押出し反応装置等の混合混練装置が挙げられる。
本発明のポリウレタン系印刷インキ用バインダーの好ましい合成方法は、溶液中でのプレポリマー法である。
【００４０】
溶液中でのプレポリマー法について、更に詳しく述べる。
ポリウレタン系印刷インキ用バインダーを製造するに当たって、まず、活性水素基を有する原料を混合し、必要により活性水素基を持たないケトンやエステル、炭化水素系の溶剤等で適宜希釈する。
【００４１】
この活性水素基成分の混合物に有機ジイソシアネートを加え、必要に応じてウレタン化触媒を添加した後、反応温度を３０〜１００℃、好ましくは５０〜８０℃にて、数時間反応させ、イソシアネート基含有ウレタンプレポリマー溶液を合成する。このときのイソシアネート基／水酸基のモル比（Ｒ値）は１．１〜２．５が好ましく、特に１．１〜２が好ましい。
【００４２】
Ｒ値が１．１未満の場合は、最終的に得られるポリウレタン系印刷インキ用バインダーの耐久性や耐ブロッキング性が低下する。また、Ｒ値が２．５を越える場合は、最終的に得られるポリウレタン系印刷インキ用バインダーの溶剤への溶解性や密着性が低下する。
【００４３】
このようにして得られるイソシアネート基含有ウレタンプレポリマー溶液に、低分子グリコールや低分子ジアミンのような鎖延長剤及び必要に応じて反応停止剤を加えて、反応温度を３０〜８０℃、好ましくは３０〜５０℃にて、イソシアネート基が消失するまで鎖延長反応させることにより、目的とするポリウレタン系印刷インキ用バインダーが得られる。
【００４４】
本発明の印刷インキ組成物は、上述のポリウレタン系印刷インキ用バインダーに、顔料、染料、溶剤、揺変剤、酸化防止剤、紫外線吸収剤、消泡剤、増粘剤、分散剤、界面活性剤、防かび剤、抗菌剤、防腐剤、触媒、充填剤等のような添加剤や塩化ビニル−酢酸ビニル共重合体や硝化綿等の副バインダーを添加し、混練、分散して製造されたものにポリイソシアネート硬化剤を配合したものである。
【００４５】
インキ製造装置としては、公知の装置を用いることができ、例えば、サンドグラインドミル、ボールミル、三本ロール、ペイントシェイカー等が挙げられる。
【００４６】
ポリイソシアネート硬化剤の添加量は、印刷インキ用バイダー１００重量部に対して、１〜２０重量部である。（各固形分換算）ポリイソシアネート硬化剤としては、例えば、日本ポリウレタン工業（株）の商品で、ヘキサメチレンジイソシアネート変性タイプのコロネートＨＸ、コロネートＨＬ、トリレンジイソシアネート変性タイプのコロネートＬ、コロネート２０３０、コロネート２０３１等が挙げられ、これらは単独あるいは混合して用いてもよい。
【００４７】
【実施例】
以下に実施例により本発明を説明するが、本発明はこれら実施例に限定されるものではない。なお、例中における「部」とは重量部、「％」は重量％をそれぞれ示す。
【００４８】
実施例１
攪拌機、温度計、アリーン冷却管、窒素ガス導入管を組んだ反応装置に、ポリオールＡを１２５．８部、ポリオールＥを５３．９部、ＣＨＤＭを２５．９部、ＭＤＥＡを６．４部、ＭＥＫを３００部仕込み、均一に攪拌した。このポリオール溶液にＩＰＤＩを８１．８部仕込み、ＤＢＴＤＬを０．０６部仕込み、７０℃にて４時間反応させて、イソシアネート基含有ウレタンプレポリマー溶液を得た。このプレポリマー溶液に、ＭＥＫを３００部加え均一にした後、ＭＥＫ１００部とＩＰＤＡ２．３部とＭＥＡ３．８部を混合したアミン液を一気に加え、４０℃で、ＦＴ−ＩＲによるイソシアネート基のピークが消失するまで反応させ、ポリウレタン系印刷インキ用バインダーＰＵ−１を得た。ＰＵ−１の固形分は３０％、粘度は４００ｍＰａ・ｓ／２５℃、色数は３０ＡＰＨＡ、数平均分子量は２８，０００、ガラス転移温度は−９℃であった。また、ＰＵ−１を容器に充填して、窒素パージしてからこれを５０℃にて３０日保管したが、分子量低下はほとんど認められなかった。
【００４９】
実施例２〜５、比較例１〜４
実施例１と同様な装置と反応方法で、表１、２に記載した原料、量を使用してポリウレタン系印刷インキ用バインダーＰＵ−２〜５、７〜１０を得た。
【００５０】
実施例１〜５、比較例１〜４、及び表１、２における原料を以下に示す。
ポリオールＡ：テレフタル酸／アジピン酸＝１／１（モル比）と３−メチル−１，５−ペ ンタンジオールからなるポリエステルジオール
Ｍｎ＝２，０００
芳香環含有量＝１．９８ｍｍｏｌ／ｇ
ポリオールＢ：テレフタル酸／アジピン酸＝２／１（モル比）と３−メチル−１，５−ペ ンタンジオールからなるポリエステルジオール
Ｍｎ＝３，０００
芳香環含有量＝２．６５ｍｍｏｌ／ｇ
ポリオールＣ：テレフタル酸／アジピン酸＝１／２（モル比）と３−メチル−１，５−ペ ンタンジオールからなるポリエステルジオール
Ｍｎ＝１，０００
芳香環含有量＝１．２５ｍｍｏｌ／ｇ
ポリオールＤ：２，６−ナフタレンジカルボン酸／アジピン酸＝３／７（モル比）と３− メチル−１，５−ペンタンジオールからなるポリエステルジオール
Ｍｎ＝２，０００
芳香環含有量＝１．１３ｍｍｏｌ／ｇ
ポリオールＥ：１，３−ブタンジオールとアジピン酸からなるポリエステルジオール
Ｍｎ＝２，０００
ポリオールＦ：ネオペンチルグリコールとアジピン酸からなるポリエステルジオール
Ｍｎ＝１，０００
ポリオールＧ：３，３−ジメチロールヘプタンとアジピン酸からなるポリエステルジオー ル
Ｍｎ＝３，０００
ポリオールＨ：テレフタル酸／イソフタル酸＝１／１（モル比）とエチレングリコール／ ネオペンチルグリコール＝１／１（モル比）からなるポリエステルジオー ル
Ｍｎ＝２，０００
芳香環含有量＝４．５０ｍｍｏｌ／ｇ
ＣＨＤＭ ：シクロヘキサン−１，４−ジメタノール
ＭＤＥＡ ：Ｎ−メチルジエタノールアミン
ＩＰＤＩ ：イソホロンジイソシアネート
ＩＰＤＡ ：イソホロンジアミン
ＭＥＡ ：モノエタノールアミン
ＤＢＴＤＬ ：ジブチルチンジラウレート
ＭＥＫ ：メチルエチルケトン
数平均分子量測定方法
：ポリスチレン検量線によるゲルパーミエーションクロマトグラフィー（ＧＰＣ）法
ガラス転移温度測定法
：動的粘弾性におけるＥ″が極大となった時の温度
測定条件 周波数：３５Ｈｚ 昇温速度：２℃毎分
経時安定性測定法
：５０℃にて３０日保管し、数平均分子量を測定した。
評価 ○：分子量低下がほとんど認められない。
×：分子量低下が認められる。
芳香環含有量及び第三級アミノ基含有量は、仕込みから算出した。
【００５１】
【表１】

【００５２】
【表２】

【００５３】
〔印刷インキ評価〕
実施例７
ＰＵ−１を頑丈な容器に以下に示す割合で配合し、配合量と同量のガラスビーズ（直径１〜１．５ｍｍ）を仕込み、ペイントシェイカーにて１時間分散させてインキ化し、インキＡを得た。このインキの密着性、耐ブロッキング性、耐久性を評価した。
インキ配合処方 ＰＵ−１ ３３．３部
酸化チタン ３０．０部
ＭＥＫ ３６．７部
コロネートＨＸ １．０部
コロネートＨＸ：日本ポリウレタン工業（株）製品
ヘキサメチレンジイソシアネートのイソシアヌレート変性ポ リイソシアネート
【００５４】
（１）密着性
インキＡをグラビア印刷機にて、印刷速度２０ｍ／分、インキ厚１μになるように、厚さ１５μのコロナ放電処理延伸ポリプロピレン（以後ＯＰＰと略称する）フィルムの放電処理面、厚さ１５μのコロナ放電処理ポリエチレンテレフタレートフィルムの放電処理面、厚さ１５μのコロナ放電処理ナイロンフィルムの放電処理面に印刷し、１日放置後、印刷面にセロハンテープを貼り付け、これを急速に剥がした。
評価 ◎：印刷被膜が全く剥がれなかった。
○：印刷被膜が８０％〜１００％残存した。
△：印刷被膜が５０％〜８０％残存した。
×：印刷被膜が５０％以下しか残存しなかった。
【００５５】
（２）耐ブロッキング性
インキＡをＯＰＰフィルムの放電処理面に上記と同様な方法で印刷し、１日放置した後、面−裏に重ね、５０℃、８０ＲＨ％にて２４時間、ブロッキングテスターで５ｋｇｆ／ｃｍ^２の荷重をかけて、耐ブロッキング性を評価した。
評価 ○：剥がすときに全く抵抗なく剥がれ、印刷面の脱落がない。
△：剥がすときの抵抗がやや大きく、印刷面の脱落が多少見られる。
×：剥がすときの抵抗が大きく、印刷面の脱落が見られる。
【００５６】
（３）耐久性
インキＡをＯＰＰフィルムの放電処理面に上記と同様な方法で印刷し、その上にＰＵ−１をそのままプライマーにして塗布し、５０℃×１分にて溶剤を飛散させた。その後厚さ２０μの未処理の未延伸ポリプロピレン（以後、ＣＰＰと略称する）フィルムと重ねて、温度：１５０℃、圧：２ｋｇｆ／ｃｍ² にて貼り合わせた。その後、室温にて１日静置してから、Ｑ−ＰＡＮＥＬ社製のＱＵＶ試験機にセットして、以下のサイクルを１０回繰り返した後、剥離強度を測定し、ブランクの剥離強度との物性保持率で耐久性を評価した。ブランクは、貼り合わせ後１日静置したものとした。なお、物性保持率は、下記式により算出した。
物性保持率（％）＝暴露後の剥離強度／ブランクの剥離強度×１００
ＱＵＶ試験機による１サイクルの条件
：７０℃×８時間（Ｄｒｙ）＋５０℃×４時間（Ｗｅｔ）
プライマー塗布量
：ドライで３ｇ／ｍ²
評価 ○：８０＜保持率≦１００％
△：５０＜保持率≦８０％
×： 保持率≦５０％
【００５７】
実施例８〜１１、比較例５〜８
実施例７におけるＰＵ−１をＰＵ−２〜１０（ＰＵ−６は欠番）に置き換えること以外は、実施例７と同様の方法でインキを調製し、同様に評価した。なお、プライマーは、インキに用いた樹脂と同じものを用いた。
密着性、耐ブロッキング性、耐久性の評価結果を表３、４に示す。
【００５８】
【表３】

【００５９】
【表４】

【００６０】
表３、４において
ＯＰＰ：厚さ１５μのコロナ放電処理延伸ポリプロピレン
ＰＥＴ：厚さ１５μのコロナ放電処理ポリエチレンテレフタレート
ＮＹ ：厚さ１５μのコロナ放電処理ナイロン
【００６１】
【発明の効果】
以上説明してきた通り、本発明のポリウレタン系印刷インキ用バインダーは、経時安定性に優れ、これを用いた印刷インキは、特にポリオレフィンフィルムを含めたあらゆる種類のプラスチックフィルムに良好な密着性を示し、耐ブロッキング性、耐久性等に優れていることが判明した。本発明の印刷インキ用バインダーは、耐久性に優れることから、特に建装材用印刷インキに適している。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polyurethane-based printing ink binder and a printing ink composition that can be printed on films of various materials. More specifically, plastic substrates used for plastic containers and building materials due to environmental problems such as acid rain and global warming are in line with the current trend of conversion from polyvinyl chloride to polypropylene and polyethylene. The present invention relates to an environmentally friendly polyurethane-based printing ink binder and printing ink composition corresponding to PVC.
[0002]
[Prior art]
Conventionally, polyurethane-based binders have been used as printing ink binders, particularly for gravure printing ink binders for plastic films. For example, Japanese Patent Publication No. 1-37427 discloses a binder for printing ink using a polyurethane-based resin having a tertiary amino group. Japanese Examined Patent Publication No. 5-64192 discloses a hydrogenated polybutadiene having a molecular weight of 500 to 4,000 and having a hydroxyl group at the terminal, or other polymer diol, alicyclic diisocyanate, chain extender, and, if necessary, And a binder for polyurethane-based printing inks formed from a terminal blocker. Japanese Patent Publication No. 7-2932 discloses a chlorinated polyolefin having a chlorine content of 5 to 50% by weight, a chlorinated polydiene having a chlorine content of 5 to 50% by weight, and at least one double bond and hydroxyl group in one molecule. There is described a binder for printing inks obtained by reacting a polyurethane resin containing at least one free isocyanate group in one molecule with a resin obtained by reacting a compound having the same.
[0003]
However, the technique specifically disclosed in Japanese Patent Publication No. 1-37427 is a technique in which a polyurethane resin using an adipate-based or ether-based high molecular weight diol is applied to a printing ink binder. In general, adipate-based or ether-based polyurethane-based resins tend to have insufficient durability. Moreover, when it winds up after printing on a long original fabric, it becomes easy to generate | occur | produce blocking. The technique disclosed in Japanese Examined Patent Publication No. 5-64192 is a technique in which a polyurethane resin into which hydrogenated polybutadiene is introduced is applied to printing ink. Since this hydrogenated polybutadiene has a large average number of functional groups, it tends to gel when an attempt is made to forcibly increase the molecular weight in the production of a polyurethane-based resin, making it difficult to obtain the intended binder itself. For this reason, the molecular weight of the obtained binder for polyurethane-based printing ink has to be reduced, which is unsatisfactory in terms of durability. The technology disclosed in Japanese Examined Patent Publication No. 7-2932 is an application of a polyurethane resin into which a chlorinated polypropylene (hereinafter abbreviated as chlorinated PP) is introduced as a binder for printing ink. Printing inks using polyurethane resins into which chlorinated polyolefins such as chlorinated PP are introduced are sufficiently satisfactory in blocking resistance, laminating suitability, boil and retort suitability, and adhesion including polyolefin films. However, since the dehydrochlorination reaction occurs over time, the stability over time such as corrosion of the filled container and coloring of the resin is poor. In addition, since chlorine is contained during recycling and combustion, chlorine gas and hydrogen chloride gas are generated, and there is a risk of adverse effects on the environment such as acid rain. From the standpoint of environmental protection, chlorine is not contained. Development of environmentally friendly printing ink binders is desired.
[0004]
[Problems to be solved by the invention]
In consideration of recent environmental problems, the present invention does not use a halogen-based raw material, and adheres to any substrate including polyolefin-based substrates, suitability for processing after printing, stability over time, weather resistance, It aims at providing the binder for printing inks and printing ink composition excellent in various physical properties, such as blocking property.
[0005]
[Means for Solving the Problems]
In view of the above circumstances, the present inventors sufficiently satisfy the adhesiveness to all plastic films including general-purpose polyolefin films, and are suitable for processing after printing, stability over time, weather resistance, and blocking resistance. As a result of extensive studies on an environmentally friendly binder for polyurethane-based printing inks excellent in various physical properties such as properties, the concept of glass transition temperature was introduced to complete the present invention.
[0006]
That is, this invention is the following (1)-( 2 ).
(1) A part or all of a resin used as a binder for printing ink is obtained by reacting the following (A) to (D), and has a glass transition temperature of −35 to + 20 ° C., aromatic ring content Is a polyurethane resin having a tertiary amino group content of 0.1 to 0.5 mmol / g , and a polyurethane-based printing ink binder.
(A) A mixed polyester polyol having a number average molecular weight of 500 to 10,000 and having the following (A1) :( A2) = 50: 50 to 90:10.
(A1): Polyester polyol having an aromatic ring content of 0.5 to 5 mmol / g
(A2): Polyester diol obtained from a low molecular diol having a side chain having 10 or less carbon atoms and an aliphatic dicarboxylic acid (B) A chain extender comprising cyclohexane-1,4-dimethanol and isophoronediamine .
(C) Tertiary amino group-containing active hydrogen compound.
(D) Organic diisocyanate.
[0008]
(2) A printing ink composition comprising 100 parts by weight of the binder for polyurethane-based printing ink according to (1) and 1 to 20 parts by weight of a polyisocyanate curing agent.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The polyurethane resin used for the printing ink binder of the present invention is obtained by reacting the following (A) to (D), and has a glass transition temperature of −35 to + 20 ° C. (preferably −20 to 0). ° C), the aromatic ring content is 0.1 to 2 mmol / g, and the tertiary amino group content is 0.1 to 0.5 mmol / g .
(A) A mixed polyester polyol having a number average molecular weight of 500 to 10,000 and having the following (A1) :( A2) = 50: 50 to 90:10.
(A1): Polyester polyol having an aromatic ring content of 0.5 to 5 mmol / g
(A2): Polyester diol obtained from a low molecular diol having a side chain having 10 or less carbon atoms and an aliphatic dicarboxylic acid (B) A chain extender comprising cyclohexane-1,4-dimethanol and isophoronediamine .
(C) Tertiary amino group-containing active hydrogen compound.
(D) Organic diisocyanate.
When the glass transition temperature is less than the lower limit, the blocking resistance when used as a printing ink is insufficient. Moreover, when exceeding an upper limit, adhesiveness is insufficient. In the printing process, since there is a case where the film is wound after being printed on a long original fabric, blocking resistance is one of the important performances of the binder for printing ink.
[0010]
The aromatic ring content of the polyurethane resin used in the present invention is 0.1 to 2 mmol / g , and more preferably 0.15 to 1.8 mmol / g. When the aromatic ring content is less than the lower limit, blocking resistance, durability and the like are likely to be insufficient. Moreover, when exceeding an upper limit, adhesiveness tends to be insufficient. In addition, the aromatic ring in this invention shows a benzene ring, a naphthalene ring, an anthracene ring, etc. The aromatic ring contained in the polyurethane-based resin is derived from any one of a long-chain polyol, a chain extender, a tertiary amino group-containing active hydrogen compound, and an organic diisocyanate.
[0011]
Further, the content of the tertiary amino group in the polyurethane-based resin is 0.1 to 0.5 mmol / g , and more preferably 0.12 to 0.48 mmol / g. When the tertiary amino group content is less than the lower limit, adhesion and dispersibility are insufficient. On the other hand, if the upper limit is exceeded, the stability over time, durability, etc. of the resin tends to deteriorate.
[0012]
The glass transition temperature of the polyurethane-based resin in the printing ink binder of the present invention is the temperature at which E ″ (loss elastic modulus) in dynamic viscoelasticity is maximized, and the measurement condition is the frequency: 35 Hz, heating rate: 2 ° C./min.
[0013]
The number of colors of the polyurethane resin used in the binder for printing ink of the present invention is 150 APHA or less, preferably 100 APHA or less, in a methyl ethyl ketone solution having a solid content of 30%. When the number of colors exceeds the upper limit, it is particularly difficult to use as a medium ink.
[0014]
The viscosity of the polyurethane-based resin used for the printing ink binder of the present invention is 500 to 10,000 mPa · s / 25 ° C. in a methyl ethyl ketone solution having a solid content of 30%. When the viscosity exceeds the upper limit, workability is inferior.
[0015]
The number average molecular weight of the binder for polyurethane-based printing inks of the present invention is measured by a gel permeation chromatography (GPC) method using a polystyrene calibration curve, and is preferably 8,000 to 100,000, particularly 10,000. ~ 50,000 is preferred. When the number average molecular weight is less than 8,000, durability and blocking resistance are lowered. When the number average molecular weight exceeds 100,000, ink adhesion, fluidity, pigment dispersibility, and workability are poor.
[0016]
Subsequently, raw materials (A) to (D) of the polyurethane resin used for the binder for printing ink of the present invention will be described.
The long chain polyol (A) used in the present invention is a polyester polyol, polyamide ester polyol, polyether polyol, polyether ester polyol, polycarbonate having a number average molecular weight of 500 to 10,000, preferably 1,000 to 5,000. Examples include polyols, polyolefin polyols, and animal and plant polyols.
[0017]
As this polyester polyol, known phthalic acid, isophthalic acid, terephthalic acid, naphthalene dicarboxylic acid, succinic acid, tartaric acid, oxalic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, kurtaconic acid, azelaic acid, Sebacic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, 1,4-cyclohexyldicarboxylic acid, α-hydromuconic acid, β-hydromuconic acid, α-butyl-α-ethylglutaric acid, α, β-diethyl One or more of dicarboxylic acids or anhydrides such as succinic acid, maleic acid, fumaric acid and the like, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3- Butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexane All, 1,8-octanediol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, 3,3-dimethylolheptane, diethylene glycol, dipropylene glycol, neopentyl glycol, diethylene glycol, dipropylene glycol , Cyclohexane-1,4-diol, cyclohexane-1,4-dimethanol, dimer acid diol, ethylene oxide and propylene oxide adducts of bisphenol A, bis (β-hydroxyethyl) benzene, xylylene glycol, glycerin, trimethylol It can be obtained from a polycondensation reaction with one or more low molecular polyols such as propane and pentaerythritol. Furthermore, there are lactone-based polyester polyols obtained from ring-opening polymerization of cyclic ester (so-called lactone) monomers such as ε-caprolactone, alkyl-substituted ε-caprolactone, δ-valerolactone, and alkyl-substituted δ-valerolactone. Further, a low molecular polyol such as hexamethylene diamine, isophorone diamine, monoethanol amine or the like may be used as a part of the low molecular polyol. In this case, a polyester-amide polyol is obtained.
[0018]
Examples of the polyether polyol include epoxides such as ethylene oxide, propylene oxide, and tetrahydrofuran, and homopolymers and copolymers of cyclic ethers.
[0019]
The polycarbonate polyol is obtained from a dealcoholization reaction or a dephenol reaction between one or more low molecular diols or low molecular triols from the above-mentioned polyester polyol source and ethylene carbonate, diethyl carbonate, or diphenyl carbonate.
[0020]
Examples of polyether ester polyols include copolyols obtained from the aforementioned polyether polyols and the aforementioned dicarboxylic acids. Further, there are those obtained by reacting the aforementioned polyester or polycarbonate with epoxide or cyclic ether.
[0021]
Examples of the polyolefin polyol include polybutadiene having two or more hydroxyl groups, hydrogenated polybutadiene, polyisoprene, and hydrogenated polyisoprene.
[0022]
Examples of animal and plant-based polyols include castor oil-based polyols and silk fibroin.
[0023]
Moreover, if it has a number average molecular weight of 500 to 10,000 and an average of one or more active hydrogen groups in one molecule, in addition to dimer acid polyol, hydrogenated dimer acid polyol, epoxy resin, Active hydrogen group-containing resins such as polyamide resin, polyester resin, acrylic resin, rosin resin, urea resin, melamine resin, phenol resin, coumarone resin, and polyvinyl alcohol can also be used.
[0024]
Preferred long-chain polyols in the present invention are those in which (A1) shown below is contained in the long-chain polyol in an amount of 50 to 90% by weight, more preferably (A1) and (A2) shown below. Is a mixed polyester polyol having a weight ratio of A1: A2 = 50: 50 to 90:10. By introducing A1 (and A2) into the polyurethane-based resin in an appropriate balance, it is possible to satisfy both the stability with time and durability, and to achieve the contradictory performances of blocking resistance and adhesion.
A1: Polyester polyol having an aromatic ring content of 0.5 to 5 mmol / g A2: Polyester diol obtained from a low molecular diol having a side chain having 10 or less carbon atoms and an aliphatic dicarboxylic acid
Moreover, the preferable thing of A1 is the polyester diol shown below.
Acid component: A mixture of one or more isomers of phthalic acid and aliphatic dicarboxylic acid in a molar ratio of 1/4 to 4/1 Alcohol component: Aliphatic diol having a side chain of 10 or less carbon atoms [0026]
The chain extender (B) used in the present invention has 20 or less carbon atoms and has two or more active hydrogen groups in one molecule. Specific examples include low molecular polyols, low molecular polyamines, low molecular amino alcohols and the like used in the above-described polyester polyols. These can be used as one kind or a mixture of two or more kinds. Preferred chain extenders in the present invention are alicyclic diols and / or alicyclic diamines that have good solubility and can impart durability, and specifically include cyclohexane-1,4-diol and isophorone. Diamine.
[0027]
The tertiary amino group-containing active hydrogen compound (C) used in the present invention is represented by the following formula 1 or formula 2. These can be used as one kind or a mixture of two or more kinds.
[0028]
[Chemical 1]

[0029]
[Chemical formula 2]

[0030]
Examples of the compound corresponding to Formula 1 include N-alkyldialkanolamines such as N-methyldiethanolamine, N-methyldipropanolamine, N-ethyldiethanolamine, N-phenyldiethanolamine, N-phenyldipropanolamine and the like N- Examples include aryl dialkanolamines.
[0031]
Examples of the compound corresponding to Formula 2 include dialkylamino alcohols such as dimethylaminomethanol and dimethylaminopropanol.
[0032]
The tertiary amino group-containing active hydrogen compound (C) preferred in the present invention corresponds to the formula 1, and further N-alkyl such as N-methyldiethanolamine, N-methyldipropanolamine, N-ethyldiethanolamine and the like. Dialkanolamines are preferred. This is because, in the type of Formula 2, a tertiary amino group is introduced at the terminal of the polyurethane resin, and therefore the introduction amount is affected by the molecular weight of the polyurethane resin. However, in the type of Formula 1, a tertiary amino group is introduced into the polyurethane resin, so that the amount introduced is not affected by the molecular weight of the polyurethane resin.
[0033]
Examples of the organic diisocyanate (D) used in the present invention include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'- Diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, 1,4-naphthylene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, o-xylylene diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, tetramethylxylylene Range isocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-dii Aromatic diisocyanates such as cyanate, 3,3′-dimethyldiphenylmethane-4,4′-diisocyanate, 4,4′-diphenylpropane diisocyanate, 3,3′-dimethoxydiphenyl-4,4′-diisocyanate, tetramethylene diisocyanate, Hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, aliphatic diisocyanates such as lysine diisocyanate, isophorone diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated Alicyclic diisocyanates such as xylylene diisocyanate, hydrogenated tetramethyl xylylene diisocyanate, cyclohexyl diisocyanate, A mixture of two or more of these, urethanet-modified products, allophanate-modified products, urea-modified products, biuret-modified products, uretdione-modified products, uretoimine-modified products, isocyanurate-modified products, carbodiimide-modified products, etc. Organic diisocyanate may be used.
[0034]
In this invention, what contains 50-100 mol% of aliphatic diisocyanate and / or alicyclic diisocyanate in an isocyanate component is preferable, and the thing of 80-100 mol% is especially preferable. When the aliphatic diisocyanate and / or alicyclic diisocyanate is less than the lower limit, the ink is liable to yellow, and the adhesiveness also decreases. Of the above organic diisocyanates, isophorone diisocyanate is most preferred.
[0035]
A reaction terminator may be used as necessary. Reaction terminators include monoalcohols such as methanol and ethanol, monoamines such as ethylamine, propylamine and dibutylamine, aminoalcohols such as monoethanolamine, diethanolamine, N-methyldiethanolamine and N-phenyldipropanolamine. There is. Moreover, depending on the case, the low molecular polyol and low molecular polyamine which are used for the above-mentioned polyester polyol and polyester-amide polyol can also be used.
[0036]
As the reaction catalyst for synthesizing the polyurethane printing ink binder in the present invention, a known so-called urethanization catalyst can be used. Specific examples thereof include organic metal compounds such as dibutyltin dilaurate and dioctyltin dilaurate, organic amines such as triethylenediamine and triethylamine, and salts thereof.
[0037]
As a method for synthesizing the binder for polyurethane-based printing ink of the present invention, a known method is used. That is, (1) a method in which an active hydrogen group component and an organic diisocyanate are reacted until reaching a predetermined molecular weight under conditions of excess of active hydrogen groups (one-shot method), and (2) a condition of excess of isocyanate groups in the polyol component and organic diisocyanate. There is a method in which an isocyanate group-containing prepolymer is obtained, and then this prepolymer is chain-extended with a low molecular glycol or low molecular diamine and reacted until a predetermined molecular weight is reached (prepolymer method).
[0038]
Moreover, an organic solvent can be used as needed. This organic solvent includes aromatic hydrocarbon solvents such as toluene and xylene, aliphatic hydrocarbon solvents such as pentane, hexane and octane, alicyclic hydrocarbon solvents such as cyclopentane, cyclohexane and methylcyclohexane, acetone, Ketone solvents such as methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, methylcyclohexanone, ether solvents such as diethyl ether, 1,4-dioxane, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol monomethyl ether acetate, propylene Cellosolve solvents such as glycol dimethyl ether and propylene glycol monomethyl ether acetate; monobasic acid ester solvents such as ethyl acetate and butyl acetate; Phosphate, dimethyl succinate, dibasic esters such as dioctyl phthalate, dimethyl formamide, dimethyl acetamide, not particularly limited as long as it is inactive to the isocyanate group, such as N- methylpyrrolidone. Depending on the conditions, an alcohol solvent such as isopropanol may be used.
[0039]
The reaction apparatus for the binder for polyurethane-based printing ink of the present invention may be any apparatus as long as the above reaction can be achieved. For example, a mixing and kneading apparatus such as a reaction kettle or kneader equipped with a stirrer, a uniaxial or multiaxial extrusion reaction apparatus Is mentioned.
A preferred method for synthesizing the binder for polyurethane-based printing ink of the present invention is a prepolymer method in a solution.
[0040]
The prepolymer method in solution will be described in more detail.
In producing a polyurethane printing ink binder, first, a raw material having an active hydrogen group is mixed, and if necessary, appropriately diluted with a ketone or ester having no active hydrogen group, a hydrocarbon solvent, or the like.
[0041]
After adding an organic diisocyanate to the mixture of active hydrogen group components and adding a urethanization catalyst as necessary, the reaction temperature is 30 to 100 ° C., preferably 50 to 80 ° C., and reacted for several hours to contain isocyanate groups. A urethane prepolymer solution is synthesized. At this time, the isocyanate group / hydroxyl molar ratio (R value) is preferably 1.1 to 2.5, and more preferably 1.1 to 2.
[0042]
When the R value is less than 1.1, the durability and blocking resistance of the finally obtained polyurethane-based printing ink binder are lowered. Moreover, when R value exceeds 2.5, the solubility and adhesiveness to the solvent of the binder for polyurethane type printing inks finally obtained will fall.
[0043]
The isocyanate group-containing urethane prepolymer solution thus obtained is added with a chain extender such as a low molecular glycol or low molecular diamine and a reaction terminator if necessary, and the reaction temperature is 30 to 80 ° C., preferably By subjecting the chain extension reaction to disappearance of the isocyanate group at 30 to 50 ° C., a target polyurethane-based printing ink binder is obtained.
[0044]
The printing ink composition of the present invention includes the above-described binder for polyurethane-based printing inks, pigments, dyes, solvents, thixotropic agents, antioxidants, ultraviolet absorbers, antifoaming agents, thickeners, dispersants, and surfactants. Manufactured by adding, kneading, and dispersing additives such as additives, fungicides, antibacterial agents, antiseptics, catalysts, fillers, and other binders such as vinyl chloride-vinyl acetate copolymer and nitrified cotton. This is a mixture of a polyisocyanate curing agent.
[0045]
As the ink production apparatus, a known apparatus can be used, and examples thereof include a sand grind mill, a ball mill, a three roll, a paint shaker and the like.
[0046]
The addition amount of the polyisocyanate curing agent is 1 to 20 parts by weight with respect to 100 parts by weight of the printing ink binder. (Each solid content conversion) As a polyisocyanate curing agent, for example, a product of Nippon Polyurethane Industry Co., Ltd., hexamethylene diisocyanate-modified coronate HX, coronate HL, tolylene diisocyanate-modified coronate L, coronate 2030, coronate 2031 etc., and these may be used alone or in combination.
[0047]
【Example】
EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In the examples, “parts” means parts by weight, and “%” means% by weight.
[0048]
Example 1
In a reaction apparatus including a stirrer, a thermometer, an Allen cooling pipe, and a nitrogen gas introduction pipe, 125.8 parts of polyol A, 53.9 parts of polyol E, 25.9 parts of CHDM, 6.4 parts of MDEA, 300 parts of MEK was charged and stirred uniformly. This polyol solution was charged with 81.8 parts of IPDI and 0.06 part of DBTDL and reacted at 70 ° C. for 4 hours to obtain an isocyanate group-containing urethane prepolymer solution. After adding 300 parts of MEK to this prepolymer solution and homogenizing it, an amine solution in which 100 parts of MEK, 2.3 parts of IPDA and 3.8 parts of MEA were mixed was added all at once. At 40 ° C., the peak of the isocyanate group by FT-IR was observed. It was made to react until it lose | disappeared and binder PU-1 for polyurethane type printing ink was obtained. The solid content of PU-1 was 30%, the viscosity was 400 mPa · s / 25 ° C., the color number was 30 APHA, the number average molecular weight was 28,000, and the glass transition temperature was −9 ° C. Moreover, although PU-1 was filled in the container and purged with nitrogen, it was stored at 50 ° C. for 30 days, but almost no decrease in molecular weight was observed.
[0049]
Examples 2-5, Comparative Examples 1-4
With the same apparatus and reaction method as in Example 1, polyurethane-based printing ink binders PU-2 to 5 and 7 to 10 were obtained using the raw materials and amounts described in Tables 1 and 2.
[0050]
The raw materials in Examples 1 to 5 and Comparative Examples 1 to 4 and Tables 1 and 2 are shown below.
Polyol A: Polyester diol composed of terephthalic acid / adipic acid = 1/1 (molar ratio) and 3-methyl-1,5-pentanediol
Mn = 2,000
Aromatic ring content = 1.98 mmol / g
Polyol B: Polyester diol consisting of terephthalic acid / adipic acid = 2/1 (molar ratio) and 3-methyl-1,5-pentanediol
Mn = 3,000
Aromatic ring content = 2.65 mmol / g
Polyol C: Polyester diol composed of terephthalic acid / adipic acid = 1/2 (molar ratio) and 3-methyl-1,5-pentanediol
Mn = 1,000
Aromatic ring content = 1.25 mmol / g
Polyol D: Polyester diol comprising 2,6-naphthalenedicarboxylic acid / adipic acid = 3/7 (molar ratio) and 3-methyl-1,5-pentanediol
Mn = 2,000
Aromatic ring content = 1.13 mmol / g
Polyol E: Polyester diol composed of 1,3-butanediol and adipic acid
Mn = 2,000
Polyol F: Polyester diol composed of neopentyl glycol and adipic acid
Mn = 1,000
Polyol G: Polyesterdiol consisting of 3,3-dimethylolheptane and adipic acid
Mn = 3,000
Polyol H: Polyesterdiol consisting of terephthalic acid / isophthalic acid = 1/1 (molar ratio) and ethylene glycol / neopentyl glycol = 1/1 (molar ratio)
Mn = 2,000
Aromatic ring content = 4.50 mmol / g
CHDM: cyclohexane-1,4-dimethanol MDEA: N-methyldiethanolamine IPDI: isophorone diisocyanate IPDA: isophoronediamine MEA: monoethanolamine DBTDL: dibutyltin dilaurate MEK: methyl ethyl ketone number average molecular weight measurement method: gel permeation by polystyrene calibration curve Chromatographic (GPC) method Glass transition temperature measurement method: Temperature when E ″ in dynamic viscoelasticity becomes maximum Measurement conditions Frequency: 35 Hz Temperature increase rate: 2 ° C./minute stability measurement method: 50 ° C. Stored for 30 days, the number average molecular weight was measured.
Evaluation ○: Almost no decrease in molecular weight is observed.
X: A decrease in molecular weight is observed.
The aromatic ring content and the tertiary amino group content were calculated from the preparation.
[0051]
[Table 1]

[0052]
[Table 2]

[0053]
[Printing ink evaluation]
Example 7
Put PU-1 in a sturdy container in the proportions shown below, charge glass beads (diameter 1-1.5 mm) in the same amount as the blended amount, disperse it with a paint shaker for 1 hour, and turn it into ink. Obtained. The adhesion, blocking resistance, and durability of this ink were evaluated.
Ink blending formula PU-1 33.3 parts
Titanium oxide 30.0 parts
MEK 36.7 parts
Coronate HX 1.0 part Coronate HX: Nippon Polyurethane Industry Co., Ltd.
Isocyanurate-modified polyisocyanate of hexamethylene diisocyanate
(1) Adhesion The discharge-treated surface of a 15 μm thick corona discharge-treated stretched polypropylene (hereinafter abbreviated as OPP) film so that the ink A is printed on a gravure printing machine at a printing speed of 20 m / min and an ink thickness of 1 μm. Print on the discharge-treated surface of a 15 μm thick corona discharge-treated polyethylene terephthalate film and the discharge-treated surface of a 15 μm-thick corona discharge-treated nylon film. After leaving for 1 day, paste cellophane tape on the printed surface. I peeled it off.
Evaluation A: The printed film was not peeled off at all.
○: The printed film remained 80% to 100%.
Δ: 50% to 80% of the printed film remained.
X: Only 50% or less of the printed film remained.
[0055]
(2) Blocking resistance Ink A was printed on the discharge-treated surface of the OPP film in the same manner as described above, and left for 1 day, and then overlapped on the surface and back, using a blocking tester at 50 ° C. and 80 RH% for 24 hours. The blocking resistance was evaluated by applying a load of 5 kgf / cm ² .
Evaluation (circle): It peels without resistance at the time of peeling, and a printing surface does not fall off.
Δ: Slightly large resistance when peeled off, and some loss of printed surface is observed.
X: The resistance when peeling off is large, and the printed surface is dropped.
[0056]
(3) Durability Ink A was printed on the discharge-treated surface of the OPP film by the same method as above, and PU-1 was applied as a primer as it was, and the solvent was scattered at 50 ° C. for 1 minute. . Thereafter, it was superposed on an untreated unstretched polypropylene (hereinafter abbreviated as CPP) film having a thickness of 20 μm and bonded at a temperature of 150 ° C. and a pressure of 2 kgf / cm ² . Then, after leaving still at room temperature for 1 day, it set to the QUV test machine made from Q-PANEL, and after repeating the following cycles 10 times, peel strength was measured and physical properties with the peel strength of a blank. Durability was evaluated by the retention rate. The blank was left standing for 1 day after bonding. In addition, the physical property retention was calculated by the following formula.
Physical property retention ratio (%) = peel strength after exposure / peel strength of blank × 100
1 cycle condition with QUV tester: 70 ° C. × 8 hours (Dry) + 50 ° C. × 4 hours (Wet)
Primer coating amount: 3 g / m ² dry
Evaluation ○: 80 <retention rate ≦ 100%
Δ: 50 <retention rate ≦ 80%
×: Retention rate ≦ 50%
[0057]
Example 8-11, Comparative Examples 5-8
Inks were prepared in the same manner as in Example 7 except that PU-1 in Example 7 was replaced with PU-2 to 10 (PU-6 is a missing number) , and evaluated in the same manner. The same primer as the resin used for the ink was used.
Tables 3 and 4 show the evaluation results of adhesion, blocking resistance and durability.
[0058]
[Table 3]

[0059]
[Table 4]

[0060]
In Tables 3 and 4, OPP: 15 μm thick corona discharge treated stretched polypropylene PET: 15 μm thick corona discharge treated polyethylene terephthalate NY: 15 μm thick corona discharge treated nylon
【The invention's effect】
As described above, the binder for polyurethane-based printing ink of the present invention is excellent in stability over time, and the printing ink using the binder exhibits good adhesion to all kinds of plastic films including polyolefin film, It was proved that it was excellent in blocking resistance, durability and the like. Since the binder for printing inks of the present invention is excellent in durability, it is particularly suitable for printing inks for building materials.

Claims (2)

Part or all of the resin used as a binder for printing ink is obtained by reacting the following (A) to (D), and has a glass transition temperature of −35 to + 20 ° C. and an aromatic ring content of 0. A polyurethane-based printing ink binder characterized by being a polyurethane-based resin having a content of 1 to 2 mmol / g and a tertiary amino group content of 0.1 to 0.5 mmol / g .
(A) A mixed polyester polyol having a number average molecular weight of 500 to 10,000 and having the following (A1) :( A2) = 50: 50 to 90:10.
(A1): Polyester polyol having an aromatic ring content of 0.5 to 5 mmol / g
(A2): Polyester diol obtained from a low molecular diol having a side chain having 10 or less carbon atoms and an aliphatic dicarboxylic acid (B) A chain extender comprising cyclohexane-1,4-dimethanol and isophoronediamine .
(C) Tertiary amino group-containing active hydrogen compound.
(D) Organic diisocyanate. A printing ink composition comprising 100 parts by weight of the binder for polyurethane-based printing ink according to claim 1 and 1 to 20 parts by weight of a polyisocyanate curing agent.