Study On The Newsprint Printability And The Improvement Color Newspaper Of Printing Quality

The newsprint is an important culture paper and an important carrier that spreads information and culture.The newsprint printability has an important influence to the newspaper printing quality.In this thesis,the printability of newsprint using secondary fibers as a furnish of improving colorful newspaper printing quality have been researched combined with the characteristics of currently colorful newspaper printing.The basic properties of newsprint used commonly in our country have been tested,the influence of storage condition on the newsprint properties has been analyzed,The fluctuating temperature and humidity affect newsprint printability greatly,and low temperature and low humidity are good for newsprint storage,the temperature of 18℃to 25℃and humidity form 60%to 70%of warehouse are beneficial for the newsprint storage.There is close relation between newsprint printability and the water-ink balance during offset printing.The newsprint absorbs less water along with the increment of IPA content in fountain solution at the same time,and the absorption rate decreases with the increase of IPA.The average tensile strength of cross direction increases from 15.36KN/m to 18.47KN/m as IPA concentration increases,the tensile strength will increases 0.62KN/m along with per 2%increase of IPA concentration in fountain solution.The lowest stretch of newspaper at break is 0.2%as the IPA volume content in fountain solution is 16%. Increasing concentration of IPA in fountain solution will be beneficial to register but harmful to ink emulsification.A suitable IPA content in fountain solution can prevent the deforming of newsprint effectively and guarantee the printing quality of color newspaper.The color density,dot gain,printing difference and color difference of yellow,magenta, cyan and black ink printed on the newsprint have been compared,the effects of newsprint on the tone replication and color replication have been analyzed,and the optimal range of solid density of newsprint has been obtained,which will guarantee the reasonability of tone replication and color replication and set up the parameters of ink supply,printing pressure and ink thickness.By the experiment and analysis of dot gain regularity in CTP technology, the curves of system grey balance of replicating technology which is suited for color newspaper printing have been drawn,the dot gain regularities by AMS and FMS in the printing process of newsprint have been compared,the methods of optimal solid density with screening have been established,and digital working procedure and technology for color newspaper printing have been formed.The value of ink Tack descends slowly with the increase of emulsion rate,the higher the viscosity of the ink,the stronger of resisting emulsion ability,and the lower the emulsion rate.The order of the ink viscosity is Y＜C＜M＜K,and the order of emulsion rate is K＜M＜C＜Y,so the best color newspaper printing sequence is C-M-Y-K.During the printing process of 5000 scopes of newspaper,the concentration of fountain solution declines from 3.5%to 3.2%,the pH value rises from 4.98 to 5.54,the conductivity decreases from 1237Ns to 675Ns.Using the advanced digital proof system for standard establishment and color correction in ink-jet proof on newsprint,the best technique parameters have set up.Taking the Kubelka-Munk laws as foundation,the light interaction of ink and paper by existing models has been analyzed,including surface reflection of ink and multiple intemal reflection of paper,and light absorption and scattering and so on,the Clapper-Yule color prediction model has been modified aiming at the two possibilities of long and short distance of light scattering in newspaper.A new color prediction model has been established by bring in proportional coefficient 'h' which represents the proportion of long and short distance of light scattering in newsprint.The 'h' calculated is equal to 0.43.By using advanced flexographic printability testing instrument,it has confirmed that dot screen lines has great influence on dot gain through the experiment results,and the degree of flexographic plate hardness has great influence on dot gain,The relationship between printing pressure and dot gain has been set up,the imitate equations at various conditions have been deduced,the values of R~2 are all above 0.95,which will offer technical and theoretical support for application of flexographic printing method in color newspaper printing.