Study On Lightweighting Of Offset Paper

As the condition of environment and resource continues to get worse, and digital lifestyle gets its population, lightweighting of paper is drawing more and more attention. This study, which takes offset printing paper as object, develops lightweighting technique through research on pulp treatment process, filling technology, wet end chemical, especially research on mixed fillers and filler pre-flocculation.First, the influence of reducing grammage is studied. The result shows that thickness, opacity, tensile strength, folding strength and stiffness decrease when grammage reduces from 70 g·m-2 to 67 g·m-2.During the research of BKP treatment process and pulp mixture ratio, BKP beaten in different consistence is used to make handsheet. It turns out that 40°SR is the best beating degree when beating in low consistence. While beating in middle consistence, tensile strength and folding strength is higher than that when beating in low consistence, and the gap gets larger as beating degree increases. But increasing beating consistence cannot make up the loss caused by lightweighting. Handsheet in different BKP proportion are compared. The result shows that the bigger the BKP proportion is, the higher the paper strength is, and when BKP proportion is 30%, tensile strength and folding strength is the same as the handsheet before lightweighting.Then experiments about filling with different kinds of fillers were made. PCC and calcium silicate were more suitable for paper lightweightiong because they can improve thickness and opacity. Then handsheet filled with mixed filler which is made by blending PCC or calcium silicate and GCC in different proportion are made and tested next. It turns out with the increase of PCC or calcium silicate proportion, opacity and thickness raise constantly, but tensile strength, folding strength and sizing value keep reducing. The best filling process is using mixed filler which is made by blending PCC and GCC, and the proportion of PCC is 25%.Next, Experiments are done to study the flocs properties of PCC, GCC and their compound at different CS dosage, as well as to study the effect of pre-flocculation methods of mixed fillers on paper properties. There are four different methods, which are PCC pre-flocculated only, GCC pre-flocculated only, mixed filler pre-flocculated and PCC/GCC pre-flocculated separately. The result shows that particle size of flocs increased at first and then decreased with the raise of CS dosage. PCC is easier to be flocculated than GCC. Paper gets the best tensile strength and folding strength when. The tensile strength is increased by 6.94%, and folding strength increased by 28.13% when PCC and GCC were flocculated separately.The study of cationic starch dosage shows that raising dosage of CS can promotes the paper strength, especially folding strength. When increasing CS dosage and pre-flocculating PCC and GCC separately, the loss of thickness, opacity, stiffness and strength caused by lightweighting can be made up.The result of pilot test on 200 mm paper machine shows that the key properties of 64.4 g/m2 offset paper is almost the same as that of 68.7 g/m2 offset paper without process promotion after process promotion.