Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2002-06-10
2004-08-31
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S328000, C428S330000, C428S337000, C428S340000, C428S341000, C428S342000, C428S452000, C428S512000, C428S513000, C428S514000, C428S537500
Reexamination Certificate
active
06783847
ABSTRACT:
TECHNICAL FIELD
The present invention relates to base paper for offset printing, particularly to newsprint paper for offset printing, which has a high whiteness degree, excellent water absorption resistance and ink acceptability by providing a coated layer of an inorganic surface preparation agent mainly comprising colloidal silica or silica sol, which has fewer adhesion problems such as surface tack, curling caused by adhesion and has low paper powder accumulation at offset printing and strike through after offset printing, and which contains low chemical oxygen demand (COD) load in wastewater when recycled is low.
BACKGROUND ART
In recent years, printing technologies have made great progress in conversion to offset printing, color printing, high-speed mass printing and automation of printing. With the advance of technologies, regarding printing paper as well, improvement of its various physical properties is demanded from workability and printability aspects.
Particularly, offset paper (newsprint paper, rolls of newsprint) is generally a type of paper mainly comprising mechanical pulp and deinked pulp (“DIP”). Even though the offset paper is classified into medium- or low-grade paper, it has more rigorous quality requirements for it than for general printing paper, because the specified number of copies needs to be printed without fail within the specified time in the specified time slot. Consequently, newsprint paper is special paper which can be uniquely classified in paper classification. Since lightness in weight, high DIP composition, etc. are currently demanded for newsprint paper, various improvements on newsprint paper need to be made while overcoming the minus factors. Thus, it is more difficult to improve newprint paper in comparison to general high-quality printing paper. For that reason, diverting technologies used for high-quality printing paper directly to newsprint paper is difficult. Conversely, it is relatively easy to divert technologies used for newsprint paper to general printing paper.
In newspaper printing, conversion from letterpress to offset printing is rapidly progressing along by the introduction of more computer systems in light of the demands for speeding up and automating printing, adding more color supplements and various kinds of printing, etc.
This recent diffusion of offset printing demands newsprint paper to possess qualities different from those of newsprint paper for letterpress. Quality requirements for offset newsprint paper include, for example, 1) low surface tack, i.e., good peeling property, 2) low paper powder accumulation on a blanket, 3) no web paper breaks caused by dampening solution during offset printing while maintaining adequate water-absorption resistance, 4) adequate print ink setting property, 5) high opacity and no strike-through, and 6) adequate friction coefficients. Among these quality requirements, particularly 1) lowering of surface tack, 2) improving of water absorption resistance, 3) improving of print ink acceptability, 4) high opacity and no strike-through, etc. are important issues that need to be addressed.
General printing paper possesses a low content of mechanical pulp and a high content of hardwood bleached kraft pulp (LBKP), while newsprint paper possesses a high content of mechanical pulp and DIP. Therefore, newsprint paper has more miniaturized fibers, and a problem with paper powder is more likely to occur. Additionally, when a mechanical pulp content is high, cohesion between miniaturized fibers is weak and a paper surface state is coarse. Consequently, paper powder falls off from the paper surface and tends to increase the paper powder accumulation on the blanket during the printing.
In 1989, 96% of newsprint paper had a basis weight of 46 g/m
2
and in 1993, 80% of newsprint paper had a basis weight of 43 g/m
2
. Since newsprint paper is becoming lighter and lighter, problems such as lowered opacity and lowered paper strength, etc. occur. To compensate for these problems, a compounding ratio of an inorganic and an organic filler or pigment needs to be increased. However, by increasing a compounding ratio of a filler and a pigment, it facilitates the filler or the pigment to desorb, coupled with thinner and lighter paper. In the case of offset printing using a dampening solution, a tendency in desorption further increases because the dampening solution weakens cohesion between pulp fibers. These desorption tendencies become more serious problems as newsprint paper is getting lighter and lighter. For example, it becomes increasingly difficult to improve the newsprint paper of basis weight below 40 g/m
2
than to improve the newsprint paper of basis weight above 43 g/m
2
.
Furthermore, a higher compounding ratio of DIP brings about an increase in DIP-derived miniaturized fibers and increased filler and pigment quantities and causes problems such as increased paper powder and lowered paper strength, coupled with a lighter weight of the paper. Additionally, DIP manufactured from magazine recycled waste paper contains tacky substances comprising a hot-melt adhesive, an acrylic adhesive and a vinyl acetate adhesive, which are used as a glue for the back of a magazine. If these tacky substances exist in a large quantity on a paper surface, the tacky substances adhere to a canvas, a belt, a roll surface, etc. and contact the paper when the paper passes through a paper manufacturing machine and/or a printing press causing such problems as web paper breaks and holes (adhesion troubles). Particularly, in the case of an offset web press type that controls paper running by bringing a steel belt into contact with a roll surface, this tendency is prominent. As a paper surface adheres to the steel belt, web paper breaks or holes (curling caused by adhesion) occur.
Improving paper surface strength was considered as a measure for addressing these newsprint paper problems. Known measures of improving the surface strength of newsprint paper are divided roughly into those by non-coating and those by coating.
Measures by non-coating include methods by changing a compounding ratio of raw materials, changing papermaking conditions, increasing a quantity of paper strength fortifier, etc. However, with these methods, it is difficult to respond to the rigorous quality requirements of newsprint paper.
Measures by coating are methods for coating (externally applying) a starch, a modified starch (oxidized starch, starch derivatives, etc.) or surface preparation agents such as polyvinyl alcohol on the surface of base paper for newsprint. These measures have become effective means for improving the surface strength.
From an economic standpoint, on-machine coating of a surface preparation agent on the newsprint paper is a commonly employed method. A gate roll coater, a method for forming and transferring a film with which high-speed coating is possible, is used. Characteristics of this gate roll coater method are summarized, for example, in Proceedings of the Japan Technical Association of the Pulp and Paper Industry Vol. 43, No. 4 (1989), p.36, the Paper Pulp Technical Times Vol. 36, No.12 (1993), p.20 among others. The method using the gate roll coater makes it possible to efficiently lay a coating solution on the paper surface and is useful for improving the paper surface as compared with the two-roll size press method used for general printing paper. More specifically, in the two-roll size press method the coating solution deeply penetrates into the base paper as the base paper passes through a pond of the coating solution whereas, in the gate roll coater method, penetration of the coating solution into the base paper is considerably controlled, because the coating solution forms a film beforehand and the film formed is transferred onto the paper surface. For this reason, a coating layer is formed evenly on the surface of the base paper with the gate roll coater method.
To control curling caused by adhesion, which is mentioned above, there are such means as removal or micro scattering of a tacky substance from raw materials, c
Fujiwara Hideki
Komai Jyunichi
Minami Toshiaki
Nakamura Mitsutoshi
Oohira Yukiko
Knobbe Martens Olson & Bear LLP
Nakarani D. S.
Nippon Paper Industries Co. Ltd.
LandOfFree
Offset printing paper does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Offset printing paper, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Offset printing paper will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3285045