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Caracterização Físico-Química de Sistemas de Molha para Impressão offset - A Influência de aditivos
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Abstract(s)
O sistema de molha na impressão offset convencional é usado para diferenciar as áreas de grafismo e contragrafismo. Nas áreas da matriz que recebem água não é depositada tinta, possibilitando a deposição de tinta somente nas áreas de grafismo. Um bom e bem regulado sistema de molha é, assim, fundamental na impressão offset.
As características de acidez (pH) e condutividade (), bem como a influência dos agentes tensioactivos adicionados, são de extrema relevância no comportamento do sistema de molha em conjunto com o sistema de tintagem.
O isopropanol (i-PrOH) tem sido o agente tensioactivo mais usado, mas regista-se uma tendência mundial para a sua substituição, tendo em conta os inerentes problemas tóxicos para os impressores e o ambiente.
O presente estudo teve por finalidade a caracterização físico-química de sistemas de molha convencionais (água/i-PrOH) – de amostras preparadas em laboratório e amostras reais - e não convencionais (água/substituto de álcool) em termos da sua acidez, condutividade, densidade e tensão superficial.
Esta caracterização foi efectuada em dois momentos distintos: (i) em soluções de molha preparadas e (ii) em soluções de molha após duas semanas de utilização. Os ensaios foram todos conduzidos a temperatura controlada (25,0 °C).
O presente trabalho permitiu aferir da relevância de um apertado controlo na vigilância das propriedades físico-químicas que caracterizam os sistemas de molha convencionais e não convencionais, cujos intervalos de variação condicionam necessariamente o resultado da impressão offset.
The function of the dampening system is to separate two different areas: the printing area and the non printing area. Applying an accurate and thin layer of dampening solution is critical for a good printing process. Some characteristics of this solution such as pH or conductivity, and the influence of some additives are extraordinarily important for a good performance of the dampening system and therefore for the quality of the final result, i.e., a good printing. One of the most important additives used in dampening solutions has been isopropyl alcohol (i-PrOH) which reduces its surface tension. However nowadays, there is an increasing tendency for its substitution due to environmental and safety aspects. Alcohol This study aimed at characterizing conventional dampening systems, i.e., H2O/i-PrOH systems, either prepared in laboratory or real samples, and non conventional dampening systems, i.e., H2O/alcohol substitute, in terms of their acidity, conductivity, density and surface tension This physicochemical characterization was done in two different situations: (i) in dampening solutions recently prepared and (ii) in dampening systems after two weeks of use. All the experiments were carried out at a controlled temperature of 25,0 °C. The present study allowed an evaluation of the importance of knowing the physicochemical properties of dampening solutions and of controlling their range of variation which clearly influences the quality of the printing process.
The function of the dampening system is to separate two different areas: the printing area and the non printing area. Applying an accurate and thin layer of dampening solution is critical for a good printing process. Some characteristics of this solution such as pH or conductivity, and the influence of some additives are extraordinarily important for a good performance of the dampening system and therefore for the quality of the final result, i.e., a good printing. One of the most important additives used in dampening solutions has been isopropyl alcohol (i-PrOH) which reduces its surface tension. However nowadays, there is an increasing tendency for its substitution due to environmental and safety aspects. Alcohol This study aimed at characterizing conventional dampening systems, i.e., H2O/i-PrOH systems, either prepared in laboratory or real samples, and non conventional dampening systems, i.e., H2O/alcohol substitute, in terms of their acidity, conductivity, density and surface tension This physicochemical characterization was done in two different situations: (i) in dampening solutions recently prepared and (ii) in dampening systems after two weeks of use. All the experiments were carried out at a controlled temperature of 25,0 °C. The present study allowed an evaluation of the importance of knowing the physicochemical properties of dampening solutions and of controlling their range of variation which clearly influences the quality of the printing process.