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Paper substrate, as the most common used substrate for printing labels or packaging, is traditionally produced from cellulose fibres derived from wood. The growth of a large number of industries has led to a significant increase in the use of such resource, which consequently led to a global awareness of the possibility of forest exploitation and the importance of reusing waste paper as a source of fibres. Hence, paper fibres can be recycled up to seven times and it is important to enrich paper pulp with virgin fibres during paper production. In such a way, the characteristics of the paper and the quality of the printed elements are improved. In this paper, cereal straw as an alternative resource of virgin fibres was turned into pulp and mixed with recycled wood pulp to conduct printing substrates using laboratory equipment. Since aging is an inevitable process of any printing substrates and prints, and the degradation of print quality due to aging largely depends on the properties of the printing substrate, ink and type of printing. This research was focused on analyzing optical stability of prints made on printing substrates with straw pulp by UV inkjet technique after natural and artificial aging. From a comparison of the aging processes based on the Euclidean difference results, it was observed that natural aging of UV inkjet prints yields less colour changes compared to artificial aging. Greater or equal optical stability after aging was perceived for prints on printing substrates with wheat, barley and triticale pulp compared to prints on substrates made with recycled wood pulp. [ABSTRACT FROM AUTHOR]

Paper recycling is becoming increasingly important as the production of packaging and various printed products grows. As alternative to wood fiber that is the most common raw material in paper production this research examines the quality of paper which is made with addition of non-wood fibers derived from wheat straw. For this purpose, laboratory paper substrates were made by blending recycled newspaper pulp and wheat straw pulp in different proportions. In this study we analyse rub resistance of laboratory paper substrates with variable content of wheat pulp printed in full tone with black and yellow inks by digital ink jet printing technique. The main objective of this research is to determine whether this kind of print has necessary durability for carrying stable illustrations. One of the main characteristics of print quality is resistance to rubbing which is very important for packaging during transport, storage and the end use. Rub resistance test was executed according to BS 3110 standard. The print durability was assessed through the Euclidean color difference and the individual CIE L*a*b* differences before and after the rub tests. The analysis showed that the increase of wheat pulp content in paper substrates has affected the increase of color difference. Greater rub resistance was observed on substrates with lower share of wheat pulp. Samples printed with yellow ink showed overall greater durability than samples printed with black ink. In further analysis we observed that for the black prints the difference in lightness (ΔL') of the CIE L*a*b* color space was most affected as the prints became lighter with the number of rubbing cycles. In samples printed with yellow ink most affected was the color difference on yellow-blue axis (Δb') meaning that the yellowness of the prints was degrading with the number of rubbing cycles. [ABSTRACT FROM AUTHOR]

Flexographic and digital printing are currently the fastest growing branches in the printing industry. The selection of printing substrates for these printing techniques is large, but paper substrates are the most widely used. Paper manufacturing is based mainly on the use of renewable fibers, and the dominant fiber resource for the pulp and paper industry is wood which is accounting for 90% of the world's fiber utilization. As woods consumption for paper production is still high, there are various possibilities to reduce it. One way is by reducing the proportion of wood pulp in paper by adding straw pulp of various cereals such as wheat. Wheat straw has numerous advantages and can be used in pulp form as a source of primary fibers for paper production. As paper as a multi-component material, besides fibers composed of cellulose, hemicellulose and lignin also includes additives, minerals and synthetic polymers. Due to its complex nature it is prone to deterioration when exposed to elevated temperature, humidity and light. Paper ageing is irreversible change and is the best indicator of paper optical permanence. Objective of this study was to determine the optical stability of prints after undergoing aging treatment with elevated temperature and UV light for 48 and 96 hours. Laboratory papers containing wheat pulp were printed by two printing techniques with cyan and yellow inks to compare better optical stability: UV inkjet and flexographic technique. The optical stability of all prints was observed based on the difference in the reflection spectra (ΔR). The results indicated that all laboratory papers printed with cyan ink with flexographic technique show better optical stability than the ones printed with digital technique. Laboratory papers printed with yellow ink by both techniques show good optical stability. [ABSTRACT FROM AUTHOR]