基于红外激光敏感聚合物微球的热敏成像材料的研究

Lithographic printing presses use a printing plate as a so-called printing master. It carries a lithographic image on its surface and a print is obtained by applying ink to said image and then transferring the ink from the master onto a receiver material, which is typically paper. The printing plates are generally obtained by computer to plate (CTP) technology. In this technology, an image created in application is output directly to a printing plate by using a laser selective-exposure and development. The types of thermal sensitive printing plates which form latent images by 830 nm infrared laser are main products at resent. Thermal sensitive printing plate usually employ infrared radiation dye and organic soluble resin. However, traditional development processes will generate a large number of pollution by using chemical reagents, therefore, chemical-free plates are extremely desirable for environment reasons. In this research, polymer particles containing 830 nm IR-sensitive dye will be prepared through mini-emulsion polymerization. The polymer particles absorbe laser scanning and produce high temperature instantaneously by means of infrared exposure，leading to great changes of structure and properties. Meanwhile, water solutions thermal sensitive polymer resin will be synthesized, and incorporated the above prepared polymer particles to get the thermal sensitive coating. Upon computer-controlled laser beam exposure of the coating, the polymer particles of the exposed areas should be fused due to high temperature, and the borders of the particles will vanish. As a result, the exposed areas lose water solubility or dispersity; whereas the particles in the non-exposed areas remain intact, and still exhibit water solubility or dispersity. When developing with water, negative graphics will be obtained. In this way, the information recording process is realized. A water-developing thermo-sensitive laser imaging material can be built according to this principle.

平版印刷中，印版的作用是将油墨转移至纸张上形成图文的载体。制备印版主要采用计算机直接制版技术（CTP），通过激光选择性曝光，经显影得到图文和空白部分。利用波长830nm红外激光曝光的热敏CTP版材为主流产品。该版材的感光层主要由成膜树脂、油溶性红外染料构成，在生产和显影等环节要使用化学试剂，存在诸多非环保因素。本研究拟利用细乳液聚合法制备含830nm红外吸收染料的聚合物纳米微球，该微球和相应成膜树脂组成的感光涂层经过830nm红外激光选择性曝光，曝光区的微球因发生热致亲和性变化，粒子间的边界消失，失去水溶解性，而非曝光区的微球保持不变，仍具水溶解性，经水显影可得到阴图型图像，实现信息记录。主要研究其中的热致相变化机理，为后续材料的选择和版材性能的改进提供理论依据。

本研究，设计并制备了以氢键物理交联和双键化学交联两种成像原理构筑免化学处理CTP版材的热敏成像体系。（1）利用氢键物理交联原理，设计并制备了苯乙烯-丙烯腈的含酸乳液和氧化胺树脂，并和水溶性红外染料一并构筑了热敏成像层。在此过程中，研究了聚合物乳胶粒子和氧化胺树脂之间的氢键相互作用关系。利用该成像体系制备的热敏成像层经过曝光后，利用中性水显影能在铝板基上获得清晰的曝光图像，图像的版基附着力（百格测试）有了大幅度改进，相对于原来的苯乙烯-丙烯腈乳液制备的成像层，附着力等级能从原来的1B提升到了3B；（2）利用化学交联原理，设计并制备了含双键官能团的聚合物乳液，通过两步法将含双键的反应型季铵盐通过离子交换引入苯乙烯-丙烯腈乳液，得到改性乳胶颗粒，该乳胶颗粒可稳定的形成非水分散体。同时，也制备了与之相匹配的丙烯酸酯聚合物成膜树脂。这两种成像原料与碘鎓盐和近红外染料一并构筑热敏成像层。该成像层经过红外激光曝光，中性水显影后也可形成稳定的可见图像。此成像过程中，由于热诱导使聚合物颗粒和成膜树脂发生高温自由基交联聚合，图像的清晰度和版基附着力有了进一步提升，附着力等级最终可以提升到5B。以上分子设计和制备方法以及曝光成像的实验结果表明：热敏免化学处理CTP版材的成像材料，主要的原料为纳米聚合物乳胶粒子、成膜树脂以及830nm红外染料，在成像原理中引入交联体系可以有效的提高图像质量和版基附着力，甚至可能对未来的印刷耐印力也有较大的影响。该研究，为热敏免化学处理CTP版材进一步实现应用提供了分子设计方向和改进方法。