JPH0246720B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field The present invention is aimed at preventing the occurrence of vascular muck (referred to as Vessel pick) during printing caused by pulp containing vascular elements such as chemical pulp or semi-chemical pulp manufactured from hardwood. The present invention relates to printing paper and coated paper having a multilayer structure. Prior art and its problems Chemical pulp or semi-chemical pulp produced from hardwoods has wood fibers, parenchyma cells, and vessel elements (hereinafter referred to as vessels) as the main components.
Due to the morphological characteristics of these constituent elements, it is known that they exhibit properties different from those of pulp derived from coniferous trees when forming a paper layer structure from them. Incidentally, chemical pulp derived from coniferous trees is mostly composed of fibrous components called tracheids. By the way, in general, the cell diameter of the vessel is larger than that of wood fibers, etc., and the cell wall is thinner, so that it is easily crushed into a flat state in the paper layer structure. Therefore, if vessels in this condition exist on the surface of the paper layer, this can cause vessel pickling when offset printing is performed on this paper, which can be a major hindrance in the printing process. Become. The phenomenon of vessel swelling occurring in offset printing is caused by insufficient bonding between the vessels and other paper layer constituent elements such as wood fibers. As mentioned above, the occurrence of vessel swelling in the paper layer during printing is due to the presence of vessels in the paper layer as a constituent element, so to prevent this, it is necessary to contain vessels. It would be better to use pulp made from tree species that are not polluted or have a low vascular content, but in recent years, from the perspective of securing raw wood resources for papermaking, it has become necessary to use hardwoods as raw materials for papermaking, and the amount used has decreased. is also increasing. Therefore, with the increase in the amount of paper produced from pulp derived from hardwoods, which originally have a high vascular content, countermeasures against vascular swelling have become an important issue. Incidentally, vessel smear caused by hardwood-derived pulp can be said to be a phenomenon in which vessels existing on the surface of the paper layer are stripped off by the tack of ink on the printing plate surface during the printing process. Conventionally, methods that have been generally used to prevent the occurrence of vascular swollen include wood species with a low vascular content or small vascular shape that cause vascular swelling to a relatively small extent. Tree species are selected and used. However, such measures limit the types of log trees that can be used and do not make good use of hardwood resources. In particular, this is not a good measure when using tropical hardwoods (with large vessels and high content), which are said to be abundant in raw wood resources, as raw materials for papermaking. In addition, the methods generally used as proactive measures to prevent the occurrence of the above-mentioned duct swelling include adding an adhesive internally to promote the bonding of the ducts within the paper layer;
Application of an adhesive using a size press or the like, that is, a surface size treatment method, has been put into practical use as an effective method. However, by adding such adhesives inside the paper layer or coating them on the surface of the paper layer, the resistance to ink tack can be strengthened, but if it is used too much, the original properties of the paper can be impaired, such as making the paper stiffer. There's a problem. In addition to the above methods, several methods have been proposed for strengthening the beating of the raw material pulp to prevent the occurrence of ductal bloat. For example, a method of beating the raw pulp to a sufficiently low freeness to enhance the bond between paper layer components such as vessels and wood fibers [J. Colley, J.
Ward: “Appita”, 29 (5), 344 (1976)],
A method of deforming, destroying, and downsizing vessels by high-concentration beating of raw pulp [JNMcGovern: "Pulp Paper",
[December 1977, p. 58; and others] has been proposed, and in particular, regarding the latter method, Byrd further reported that using an eccentric refiner is very effective in preventing the occurrence of canal swelling. [V.
L. Byrd, et al.: Paper Trade J., 151 (46), 55.
(1967): 153 (47), 54 (1969)]. however,
As is well known in these methods of beating, as the pulp advances, the shrinkage rate of the sheet during drying generally increases, and the rate of dimensional change of the sheet due to changes in humidity increases. . In particular, when high-concentration beating is used, the sheet shrinkage rate during drying increases compared to low-concentration beating even if the beating is at a normal beating level, resulting in a deterioration in the dimensional stability of the paper and an increase in bulk. There are disadvantages such as deterioration and decrease in opacity. In other words, it can be said that the method of beating as a preventive measure against the occurrence of ductal bloat involves inherent problems that cannot be avoided. Problems to be Solved by the Invention The present invention has been made in view of the above-mentioned situation, and is intended to solve the problem of canal swelling caused by pulp containing hardwood-derived chemical pulp or semi-chemical pulp. It is an object of the present invention to provide printing paper and coated base paper having a multi-layer structure to effectively prevent the occurrence of the occurrence of pulp generation without restrictions on the species of logs used to manufacture pulp or problems such as deterioration of paper quality due to beating of pulp. Take it as a challenge. The present inventors used a scanning electron microscope to closely observe the surface structure of the paper in contact with the printing plate in order to investigate the mechanism of the occurrence of vessel blemishes during printing. We found that the greater the number of coated fibers, the less likely it is that vascular swollenness will occur, and we found that coating a pulp layer that does not cause vascular swelling on top of a pulp layer that easily causes vascular swelling will reduce the occurrence of vascular swelling. We have discovered that this can be completely prevented and have come up with the present invention. That is, in the present invention, on a pulp layer that contains ducts to the extent that duct swelling is likely to occur, a layer containing ducts that does not contain ducts, or even if ducts are present, to an extent that does not cause duct swelling. We have succeeded in solving the above problem by forming the paper into a multilayer structure consisting of at least two layers coated with a pulp layer that is only present. The present invention will be explained in detail below. Structure of the Invention The structural feature of the present invention is that on a layer of pulp that contains vessels and causes vessel swell during printing, the layer does not have vessels or substantially causes vascular swell during printing. The present invention relates to printing paper and coated base paper having a multilayer structure, in which the surface as a printing surface made of non-reactive pulp is coated in a high moisture state by a papermaking means to form a multilayer structure. Here, "pulp that does not substantially cause vascular swelling during printing" means that even if it contains vascular vessels, the amount of vascular vessels is small or their shape is small, so that they do not cause problems during actual printing. Refers to pulp that does not cause ductal swelling that would cause. Further, the printing paper to which the present invention is directed should be distinguished from conventional paperboard having a multilayer structure. That is, in the above-mentioned printing paper, the thickness of the pulp coating layer that becomes the printing surface is 1 g/m ² to about 20 g/m ² , and in particular, the thickness of the coating layer is extremely thin with a thickness of 1 to 2 g/m ² . Even if it is, during printing, the occurrence of vascular swelling due to the ductal blubber-producing pulp layer located below is not observed, and it is possible to exhibit printable properties. In contrast, with conventional paperboard, the surface pulp (bleached pulp) layer needs to be extremely thick to cover the lower layer, which is made up of a pulp layer of inferior quality, and generally has a thickness of about 55 to 70 g/ ^m2 . It needs to be thick (see "White Paperboard/Paper Carton" published by Paper Industry Times, 1979, p. 53). Means for Solving the Problems In the printing paper and coated base paper having a multilayer structure according to the present invention, the pulp that forms the surface layer (coating layer) that is the printing surface does not cause vascular swelling as described above. A high-quality pulp, that is, a pulp that does not contain vessels, or even if it does contain vessels, does not pose a problem in actual printing and does not cause substantial vessel swelling, As such pulp, it is usually preferable to use softwood pulp that does not have vessels, but it is also possible to use beech pulp (Buna BKP), etc., which does not easily cause vessel swelling due to its relatively small vessel shape. On the other hand, a wide variety of hardwood-derived pulps, such as lauan wood-derived pulps, are used as the pulp that forms the lower layer and causes vessel swelling. In addition, the vessels in chemical pulp produced from hardwoods with many vessels are concentrated and separated using a liquid cyclone, and the pulp fraction with a reduced vessel content is used as the surface layer, and the vessel content is reduced. It is also possible to use an increased pulp fraction in the lower layer in the case of printing papers in which it is not necessary to completely prevent the occurrence of vascular blemishes. If the thickness of the above-mentioned high-quality pulp to be coated on the pulp layer that is likely to cause vascular swelling is ¹ g/m2 or more, it is possible to significantly reduce the occurrence of vascular swelling caused by the underlying pulp layer ( When the thickness is 2 to 5 g/m ² (the thickness can be reduced to about 1/4), the above-mentioned canal swelling can be virtually prevented. Regarding this point, the present inventors used bleached kraft pulp (hereinafter abbreviated as BKP), which was prepared from undyed lauan wood as a pulp that easily causes vascular swelling, as the lower layer.
Vascular vessels in the lower layer of lauan BKP are coated with a dyed beech BKP that hardly causes vascular smearing, with a thickness in the range of 1 to 20 g/ ^m2 , as a surface layer. However, the surface beech
Table 1 shows the results of observing the coating with BKP fibers using an optical microscope.

[Table] As shown in the table above, when the thickness of the surface pulp is 1 g/ ^m2 , 1 to 5 fibers must be on the vessels in the lower pulp, but vessel swelling occurs. is reduced to about 1/4, and
Even if the thickness of the surface pulp is 2g/ ^m2 , the fibers
It can be said that it is extremely surprising that almost no duct swelling was observed even though the lower layer was sufficiently transparent with only 7 fibers resting on the lower pulp. Next, in order to form a printing paper having a multilayer structure according to the present invention, that is, a paper having a structure in which a surface layer of pulp, which becomes a printing surface, is coated on a lower pulp layer, a paper machine as shown below is assembled. This can be done by using a multi-layer papermaking technique. Traditionally, in the field of paperboard production with very thick paper layers, wet paper paper is layered on felt using a circular mesh paper machine, multiple fourdrinier paper machine, etc., or paper sheets already formed on wire are used. It has been developed as a papermaking technology that involves spraying and forming new paper layers one after another on top of existing wet paper layers. However, recently, even in the field of manufacturing thin paper such as printing paper and paper sheets, paper making techniques have been developed by combining head boxes developed for multilayer paper making with twin wire paper machines or Fourdrinier paper machines. It has become possible to make paper with a multilayer structure in a single process. In other words, as a head box for multilayer papermaking,
Beloit's Converflo Strata-Flo, KMW's
HTB-3L, Escher Wyss Stepflow M.
Using Tampella's Contra-Flow or the like, the paper stocks of each layer are flowed out in parallel from stock inlets to form layered paper layers. In multi-layer paper making using these single head boxes, the raw material pulp is mixed appropriately at the interface between each paper layer, so it is possible to make paper that has greater strength in the Z direction than conventional paper making and is less prone to delamination. There are advantages to being able to do so. The advantage of applying multilayer papermaking technology to paper manufacturing is that, like in the case of paperboard, high-quality pulp is used for the surface layer and inexpensive pulp is used for the inner layer.
%, it is possible to obtain paper that is visually similar to that obtained using high-quality pulp, and it is possible to design paper quality that depends on the paper layer structure.
Incidentally, when using the above multilayer papermaking technology for printing paper, the surface layer is made of short fibers and the inner layer is made of long fibers, and the surface layer is made of mechanical pulp and the inner layer is made of chemical pulp, which improves the paper's smoothness and ink absorption. Improved sex,
It has been reported that it is possible to produce printing paper that is bulky and has good compressibility [JI Bergström, "Norsk Skogind.", 31 ,
133 (1977) and JABriston et al.
Papperstidn.), 86 , R164 (1983)]. EXAMPLES The present invention and its effects will be specifically explained below with reference to Examples. Example 1 A TAPPI type standard hand-sheet machine was modified to use a multi-layer sheet hand-sheet machine that can simulate multi-layer paper making with a single headbox, that is, can continuously supply different types of pulp slurry while being filtered and dewatered. Handmade paper 2 with different pulp types for the surface layer and lower layer and different thicknesses of the surface pulp layer
A layered sheet was prepared. This handmade two-layer sheet
A printing test was conducted using an IGT universal printing tester to investigate the relationship with canal swelling. Beech BKP is a hardwood that is used as surface pulp, but its vessels are relatively small, so it does not easily cause tube swelling.
(PFI mill beaten with a pulp concentration of 10%. Freeness 375 ml) was used. In addition, as the lower pulp, lauan BKP (freeness 400 ml), a South Sea wood with large vessels and prone to causing tube swelling, was used. Handmade sheets made using these two types of pulp with different surface layer thicknesses and a total basis weight of 60 g/ ^m2 were injected with IPI ink No. .3, printing was performed at a printing speed of 1.75 m/sec and a printing linear pressure of 18.75 Kgf/cm, and the number of vascular swells was measured. These results are shown in Table 2.

[Table] As is clear from Table 2, as the thickness of the surface pulp increases, the number of canal blemishes decreases rapidly. When the surface layer thickness is only 1 g/ ^m2 , it is reduced to less than one-fourth of that when there is no surface pulp, that is, when the lower lauan pulp is completely exposed, and it is clearly prevented from causing vascular swelling. The effect is expressed. Further, when the surface pulp thickness is 2 g/m ² or more, the number of vascular swells is reduced to 1/20 or less compared to lauan BKP, and the occurrence of sagging can be substantially prevented. Example 2 A handmade sheet made in the same way as in Example 1, with a surface layer made of coniferous pulp without vessels (abbreviated as NBKP, freeness 520 ml) and a lower layer made of lauan BKP (freeness 405 ml), which tends to cause vascular swelling. was prepared and subjected to a printing test under the same conditions as in Example 1.
The results obtained are shown in Table 3.

[Table] As is clear from Table 3, if the surface layer thickness is only 1 g/m ² and there is no surface layer pulp, if a pulp that does not cause vascular swelling is used, even if the surface layer pulp is different in type, Compared to the state where the lower layer lauan pulp is completely exposed, it is reduced to only one-fourth or less, and the effect of preventing the occurrence of ductal swelling is clearly expressed. Furthermore, the surface pulp thickness is 2g/
m ² or more, the number of canal tubes is 10 compared to Rawan BKP.
It is possible to substantially prevent the occurrence of canal swelling. Example 3 Unbeaten lauan was fractionated into a portion with reduced vessel content (accept side pulp) and an increased portion (reject side pulp) using a liquid cyclone (Sentry Cleaner Model 600). The conditions for fractionation treatment are: pulp concentration 0.25%, inlet gauge pressure 3.0
Kgf/cm ² and redirect rate 30.7%. The number and average area of vessels in the pulp are 88 vessels/mg and 0.0716 mm ² / vessel in the untreated unbeaten pulp, 68 vessels/mg and 0.0531 mm 2 / vessel in the accept side pulp, and 0.0531 mm ² / vessel in the reject side pulp, respectively. It was 211 pieces/mg, ^{0.0879 mm 2} /piece. In the same manner as in Example 1, the acceptance side pulp (freeness 375 ml) with reduced vessel content among these fractionated pulps was used as the surface layer,
A handmade sheet with a lower layer of rejected pulp with increased vessel content (400 ml of freeness) was prepared, and a printing test was conducted under the same conditions as in Example 1.
The results obtained are shown in Table 4.

[Table] As is clear from Table 4, the paper with exposed pulp on the lauan redirect side (Test No. 1), which has a high vessel content and a large average area of vessels, has a very large number of vessel flakes. However, compared to this case, when the thickness of the pulp on the surface lauan acceptance side is 1 g/m ² , the number of canal tubes decreases to about one-third, and is 1.5 g/m2.
At m ² or more, the number reaches about one-fifth or less, that is, the level of the number of canals in the surface pulp itself. If it is not necessary to completely prevent canal swelling and only need to keep it below a certain level, use pulp that satisfies the conditions when used alone as in this example on the surface layer at 1 g/m ² or more to achieve the purpose. You can get printing paper that matches the specifications. Example 4 Buna BKP (pulp concentration 5%) was used as the surface pulp.
PFI mill refined. freeness 395ml), lauan BKP (5% concentration beaten, freeness) as the lower pulp
375 ml) using a paper-making method that uses a hand-paper machine that has traditionally been carried out in laboratories.
A layered sheet was prepared. That is, first, a wet paper of Lauan BKP was formed as a lower layer on the wire by a standard hand-sheeting operation, and a filter paper was layered and couched, followed by sheeting. Then,
A wet paper made of beech BKP to serve as the surface layer was formed on the wire, and a filter paper with the wet paper made of lauan BKP was layered on top of it and couched, and the two-layered wet paper was made. After pressing and drying according to a conventional method, it was subjected to a printing test. Printing conditions are printing speed 1.25m/
The second embodiment is the same as the first embodiment except that the second embodiment is sec.
The results obtained are shown in Table 5.

[Table] As is clear from Table 5, even with the conventional paper-combining method different from Examples 1 to 3, when the surface pulp thickness is 1 g/m ² , the number of vessel stubbles is reduced by about 5 times. It decreased to 1, and at 2 g/m ² it decreased to 1/25. Examples 1 to 3 of the paper layer structure even if the paper making method is different
By doing the same as above, it is possible to substantially prevent duct swelling. However, in this papermaking method, there is no entanglement of fibers on the papermaking surfaces, so if the printing conditions are made harsher by increasing the printing speed, delamination is likely to occur. Example 5 A wet paper of lauan BKP (10% concentration beaten, freeness 400 ml) was formed as a lower layer on the wire using a hand-sheeting device, and after layering filter paper and couching, it was sheeted. . Next, Rawang BKP
Place the filter paper with the wet paper attached on the Buchner funnel, reduce the pressure with an aspirator, and while suctioning the Buna BKP (10
% concentration beating. The surface layer was formed by spraying a dilute suspension of 375 ml of Freeness. After pressing and drying this wet paper having a two-layer structure in accordance with a conventional method, it was subjected to a printing test under the same conditions as in Example 4. The results obtained are shown in Table 6.

[Table] As is clear from Table 6, different from Examples 1 to 3 (multilayer papermaking) and Example 4 (combination papermaking),
Even when the method of preparing a handmade sheet with a multilayer structure was used, the number of ductal swelling was reduced to less than one-tenth when the surface pulp thickness was 2 g/m ² . Examples 1 to 4 of the paper structure even if the paper making method is different
By doing the same as above, it is possible to substantially prevent duct swelling. However, similar to Example 4, this papermaking method had a drawback in that delamination was likely to occur.

Claims (1)

[Scope of Claims] 1. On a layer made of pulp that contains vessel elements and causes vessel blemishes during printing, the layer does not contain vessel elements or substantially does not cause vascular blemishes during printing. Printing paper and coated base paper with a multilayer structure, which are formed by coating a surface layer of pulp as a printing surface in a high moisture state by a papermaking means to form a multilayer structure. 2. The printing paper and coated base paper according to claim 1, wherein the surface layer serving as the printing surface is formed to have a thickness of at least about 1 g/cm ² .