JP4231531B2 - Newspaper - Google Patents

Description

  The present invention relates to newsprint. More specifically, for example, even when the proportion of waste paper pulp or the proportion of paper ash is high, blanket piling due to white spots, paper dust, etc. is effectively prevented, and a coating containing paper breakage and a surface treatment agent is used. The present invention relates to a newsprint that is free from liquid elution and color misalignment, has excellent workability, and is particularly suitable for offset printing.

  In recent years, as the environmental awareness of paper makers has increased, the proportion of waste paper pulp in newsprint has gradually increased. For example, it is not uncommon for newsprint to exceed 60%, and more than 80%. In addition, the use of neutral paper for newsprint is also progressing, so it is possible to capture flyers in old paper that could not be printed with acid paper, and the percentage of paper ash exceeds 4%. There are many, more than 6%.

  When the proportion of used paper pulp and the ash content increase, various problems generally occur in the quality of the printed surface during offset printing. However, the white spot in the image area is one of the most important problems.

  White spots generally occur on the surface with weak surface strength, and paper fibers and fillers are peeled off from the paper surface by the ink during printing, and tend to occur especially on a solid surface with high tack. It has become a big problem with the increase of the surface. So far, as a method for suppressing the occurrence of white spots, for example, the amount of starch applied by a size press is individually increased on the front and back surfaces of paper (see Patent Document 1), polyacrylamide, etc. It has been proposed to apply a surface strength improver (see Patent Document 2).

  However, none of these methods can completely suppress the occurrence of white spots, and if the amount of starch applied is increased, the drying load increases, and the paper machine due to mist scattering of the coating solution. There was a problem of causing a paper break. Furthermore, when the coating amount of the coating liquid containing the surface treatment agent is increased in this way, Nepari (when the newspaper paper is printed in large quantities, the coating liquid containing the surface treatment agent is transferred to and accumulated in the blanket. There was also a problem that trouble occurred.

  In such a conventional technique, as pointed out earlier, a coating containing a surface treatment agent is applied to a surface having a weak surface strength, despite the difference in surface strength between the front surface and the back surface of the paper. It is only possible to increase the coating amount of the working liquid or to adjust the operating conditions of the press part, and it is not possible to achieve a uniform surface strength between the front surface and the back surface of the paper.

  In addition to the coating treatment techniques as described above, as a technique for suppressing the occurrence of white spots, as a roll in which wet paper is in direct contact with the final press of the press part of the paper machine, ceramic spraying is performed in a diameter range of 1000 to 2000 mm. Using a ceramic sprayed roll having a surface roughness Ra of 1.0 to 2.0 μm, and a technology for producing newsprint (see Patent Document 3), a top roll of a first press in a press part of a papermaking process, A technology for producing newspaper (see Patent Document 4), wherein the ratio of the amount of squeezed water with the bottom roll (TOP / BOT) is 0.8 or less and the groove width of the bottom roll surface is 0.6 to 1.0 mm. If the final press roll does not dewater through the felt from the wire surface side, there will be many vessels on the wire surface where the surface strength is weak and it will be transferred to the blanket. Focusing on the increase in the number of vessels and the occurrence of white spots on the final press roll, dewatering from the wire surface side through the felt on the final press roll, and the paper adhering to the paper surface in a weakly bonded state together with the paper A technique for eliminating the surface (see Patent Document 5) has been proposed.

However, in the case of newsprint with a relatively low proportion of waste paper pulp and a relatively low proportion of paper ash, the above-mentioned various problems may be caused by applying a coating liquid containing a surface treatment agent or by using a size press. Although it could be substantially solved by adjusting the roll specifications, water extraction conditions, and operating conditions, for example, the proportion of waste paper pulp is 60% or more, the proportion of paper ash is 4% or more, and more than 6% In such a case, in particular, the problem of the occurrence of white spots has not been solved.
JP 2004-218100 A Japanese Patent Laid-Open No. 10-2559591 JP 2006-328564 A JP 2002-115192 A JP 2003-293279 A

  In this way, especially when the proportion of waste paper pulp and the proportion of paper ash is high, there is less fuzz during the formation of the paper layer, fiber entanglement is reduced, the surface strength of the paper is reduced, and there is essentially a difference between the front and the back. Even when a small number of papermaking facilities are used, the difference between the front and back sides of the paper surface is manifested, and a considerable difference or unevenness in the surface strength between the front and back surfaces is the cause of the conventional problems.

  The present invention has been made in view of the prior art, and blanket piling due to white spots, paper dust, etc. is effectively prevented even when, for example, the proportion of waste paper pulp or the proportion of paper ash is high. In addition, there is no paper breakage, elution of the coating liquid containing the surface treatment agent, color misalignment, etc., and excellent workability. For example, newsprint paper suitable for offset printing, particularly under papermaking conditions exceeding the recent papermaking speed of 1500 m / min. The purpose is to provide.

The present invention
Newspaper paper in which a coating liquid containing a surface treatment agent is coated on the front and back surfaces of a base paper containing pulp and filler containing waste paper pulp as main raw materials,
A coating liquid comprising at least different surface treatment agents composed of a water-soluble polymer compound is applied to each surface on the front and back surfaces of the base paper,
The coating liquid coated on the surface of the base paper contains a surface treatment agent made of oxidized starch, and the coating liquid coated on the back surface of the base paper is hydroxyethylated starch and esterified starch. A surface treatment agent comprising at least one of
The difference (absolute value) of the drop water absorption between the front and back surfaces is 0 to 20 seconds, and relates to newsprint.

  According to the present invention, blanket piling due to white spots, paper dust, and the like is effectively prevented, and paper breakage and a surface treatment agent are included, even when, for example, the proportion of waste paper pulp or the proportion of paper ash is high. There is no elution of the coating liquid, no color misalignment, etc., and excellent workability, for example, newsprint paper suitable for offset printing is provided under papermaking conditions exceeding the recent papermaking speed of 1500 m / min.

(Embodiment)
The newsprint of the present invention comprises a coating liquid containing at least different surface treatment agents composed of a water-soluble polymer compound on the front and back surfaces of a base paper containing pulp and filler containing waste paper pulp as main raw materials. It is coated on each surface, and the difference (absolute value) in water absorption between the front and back surfaces is 0 to 20 seconds.

  First, the pulp used in the present invention will be described. The pulp constituting the base paper of the newsprint of the present invention includes waste paper pulp.

  It is preferable from the viewpoint of environmental protection to mix recycled paper pulp in this way, and in recent years, especially from the viewpoint of effective use of resources, utilization of recycled paper pulp and higher blending have been demanded. On the other hand, when the ratio of waste paper pulp is high, as described above, generally, there is less fuzz at the time of forming the paper layer, fiber entanglement is reduced, the surface strength of the paper is reduced, and the paper making equipment is essentially less in the front and back. Even if is used, a difference between the front and the back of the paper surface is developed, and a considerable difference or unevenness is likely to occur between the front and back surfaces in surface strength. That is, when waste paper pulp is used as the pulp constituting the base paper, the problem of blanket piling due to white spots, paper dust, etc. tends to occur particularly as the blending ratio increases.

  Among waste paper pulp, the use of newspaper deinked waste paper pulp that has been deinked from newspaper waste paper is the most efficient in terms of resource recycling, although its constituent materials are similar to those of newspaper paper. In waste paper, there are deinked pulp that has been recycled repeatedly. Repeating the regeneration process leads to a decrease in fiber entanglement, and the surface strength of the paper is more likely to be reduced. Easy to progress.

  However, in the present invention, as will be described later, each of the coating liquid containing the surface treatment agent applied to the surface of the base paper and the coating liquid containing the surface treatment agent applied to the back surface are both water-soluble polymers. Although it is composed of a compound, the coating liquid to be applied to the front and back surfaces contains at least different surface treatment agents, and the difference in drop water absorption between the front and back surfaces of the base paper is within a predetermined range. Despite the fact that pulp is contained, even when waste paper pulp is contained in a large amount of 60 to 100% by mass of the total amount of pulp, the newsprint of the present invention is caused by white spots, paper dust, etc. Blanket piling is effectively prevented, and there is no paper breakage, elution of the coating liquid containing the surface treatment agent, color misalignment, etc., and excellent workability.

  The waste paper pulp used in the present invention is manufactured from, for example, tea waste paper, craft envelope waste paper, magazine waste paper, newspaper waste paper, flyer waste paper, office waste paper, corrugated waste paper, upper white waste paper, Kent waste paper, imitation waste paper, old paper waste paper, etc. Examples of such a paper include a disaggregated waste paper pulp, a disaggregated / deinked waste paper pulp, and a disaggregated / deinked / bleached waste paper pulp. One or more of these can be appropriately selected and used.

  In the present invention, waste paper pulp is preferably blended in an amount of 60 to 100% by mass, more preferably 80 to 100% by mass, based on the weight reduction of newsprint and effective use of resources.

  As pulp which is a constituent component of newsprint paper, other than the waste paper pulp, for example, stone grand pulp (SGP), pressurized stone grand pulp (PGW), refiner ground, as long as the object of the present invention is not impaired. Mechanical pulp such as pulp (RGP), chemi-ground pulp (CGP), thermo-ground pulp (TGP), ground pulp (GP), thermo-mechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), refiner mechanical pulp (RMP) Hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached kraft pulp (NUKP), hardwood semi-bleached kraft pulp (LSBKP), coniferous semibleached kraft pulp ( NSBKP), Hardwood Acid pulp, such as chemical pulp such as soft wood sulfite pulp, be mentioned various known pulps, select one or more from among these can be appropriately used by adjusting the ratio.

  The base paper of the newsprint of the present invention contains a filler together with the pulp.

  The filler used in the present invention is not particularly limited, and is usually blended in a base paper constituting newsprint, for example, white carbon, kaolin, engineered kaolin, clay, delaminated clay, heavy calcium carbonate, light carbonate Inorganic or organic fillers such as calcium, talc, titanium dioxide, zeolite, barium sulfate, zinc oxide, aluminum oxide, magnesium oxide, silicic acid, hydrated silicic acid, colloidal silica, colloidal alumina, satin white, alone or 2 More than one type can be used at the same time.

  The blending amount of the filler is not particularly limited, but if it is too small, the effect of improving the printing operability and printability by the filler may not be sufficiently exhibited. It is preferable to adjust it to be at least%, and if it is too much, the surface strength of newsprint may be reduced or paper dust may be generated, so the paper ash content is 20% or less, and further 18% or less. It is preferable to adjust so that.

  In order to obtain the base paper constituting the newsprint of the present invention, the pulp slurry made of the pulp, if necessary, sizing agent such as alkyl ketene dimer, alkenyl succinic anhydride, sulfate band, etc. For example, a flocculant or the like may be added as appropriate, and for example, conditions such as pH may be adjusted, and paper making may be performed with a normal paper machine such as a twin wire type paper machine or a long net type paper machine. In the present invention, it is possible to make paper at a paper making speed of, for example, 1500 m / min or more, and further 1600 m / min or more.

  In recent years, when producing newsprint at a high speed, a twin wire type paper machine called a gap former is generally used. In the wire part of the gap former, the paper stock is run by being sandwiched between two wires and dehydrated approximately evenly from both the front and back surfaces to form wet paper. Further, a hybrid former, an on-top former or the like having a double-side dewatering mechanism is preferably used, and a normal suction roll method or a grooved press method is employed as the dewatering method. Furthermore, as press machines, straight through type, invar type, and reverse type are used in various combinations, and the difference in quality between the front and back of the resulting newspaper (base paper) has been reduced. In order to make the quality of the front and back surfaces uniform in the intended newsprint, at least different surface treatment agents are used on the front and back surfaces, as will be described later. It is necessary to apply the coating liquid containing to each surface, and to adjust the difference in drop water absorption on the front and back surfaces within a specific range.

  The paper ash content of the base paper obtained in this way is 4% or more, or even 6 in accordance with “Method for testing ash content of paper and paperboard” described in JIS P 8251, considering the neutralization of the newspapers obtained. 20% or less because, on the contrary, if the paper ash content is too much, the quality of the printed surface may be deteriorated in offset printing or the paper may be easily cut in the paper making process or the printing process. Further, it is preferably 18% or less.

The basis weight of the base paper is not particularly limited. However, in consideration of the paper quality strength and weight reduction of the obtained newspaper, it is 36 to 48 g / m in accordance with the “basis weight measurement method” described in JIS P 8124. It is preferably about ² .

  Next, the newsprint of the present invention can be obtained by applying a coating liquid containing a surface treatment agent comprising a water-soluble polymer compound to the front and back surfaces of the base paper.

In the present invention, both the coating liquid containing a surface treatment agent applied to the surface of the base paper and the coating liquid containing a surface treatment agent applied to the back surface are made of a water-soluble polymer compound. although, unlike the type of at least, moreover, the water-soluble polymer compound is applied to the water-soluble polymer compound and back is applied to the surface is, each one of certain ones der Rukoto major feature It is. As described above, since the coating liquid containing at least different types and each containing a specific surface treatment agent is applied to each surface on the front and back surfaces of the base paper, the base paper contains waste paper pulp. Even though waste paper pulp is contained in a large amount of 60 to 100% by mass of the total amount of pulp, blanket piling due to white spots, paper dust, etc. is effectively prevented, and the paper is cut off. In addition, there is no elution of the coating liquid containing the surface treatment agent, no color misalignment, etc., and newsprint paper with excellent workability can be obtained.

Water-soluble polymer compound is suitably used as a surface treatment agent is Starch, and a surface treating agent to be applied to the surface treatment agent and back to be applied to the surface is Ru different at least. Particularly, in the present invention, as described below, not a surface treatment agent for coating and the surface treating agent coated on the back surface by at least different surface, at least on the back surface of the human Dorokishiechiru starch and esterified starch 1 One kind of water-soluble polymer compound, on the other hand, because oxidized starch is used on the surface, blanket piling due to white spots, paper powder, etc. is further effectively prevented, and paper breakage and a surface treatment agent are included. coating solution elution, no color shift or the like, it is possible to obtain an excellent newsprint more workability.

As the starch, in the present invention, particularly hydroxyethyl starch, it can be preferably used esterified starch and oxidized starch.

  For example, although modified starch has the effect of improving tensile strength and surface strength while penetrating into paper, it exhibits neutrality or anionic property, so it has low fixability on the surface of an anionic pulp fiber and has a coating property. Is low. Therefore, in the present invention, it is preferable to use a cationic starch having high fixability to the surface of an anionic pulp fiber. Further, when hydroxyethylated starch, esterified starch and oxidized starch are used, the fixability to pulp fibers is high, the coating property is excellent, and the surface strength is also improved.

  Since the hydroxyethylated starch is firmly fixed to the pulp fiber by the interaction of the hydrogen bond of the hydroxylethyl group, it is considered that the amount of starch to be eluted is small and the surface tackiness can be reduced.

  Hydroxyethylated starch that can be suitably used in the present invention includes dry hydroxyethylated starch and wet hydroxyethylated starch. The dry hydroxyethylated starch is, for example, a hydroxyethylated starch as described in USP 5,766,366, USP 5,817,180 and the like in a solid state having a water content of 5 to 17%. Thus, the molecular weight is reduced by acid treatment with hydrogen chloride gas, hydrochloric acid, sulfuric acid or the like, or oxidation treatment with ammonium persulfate, hydrogen peroxide, chlorine gas or the like. Wet hydroxyethylated starch is obtained by lowering the molecular weight in a slurry (wet) state. Hydroxyethylated starch is excellent in viscosity stability, aging resistance, and film properties.

  When the esterified starch is used, the ink density and ink setting properties are dramatically improved. Examples of the raw material starch for obtaining such esterified starch include various starch-containing materials in addition to untreated starch and treated starch. Representative examples of such raw material starch include, for example, untreated starch such as wheat starch, potato starch, corn starch, sweet potato starch, tapioca starch, sago starch, rice starch, waxy corn flour, high amylose content corn starch; And starch-containing materials such as tapioca starch, corn flour, rice flour, etc., and processed starch obtained by subjecting it to oxidation, acid treatment and the like. Among these, tapioca starch is preferable in that the ester-modified product is superior to other cereal starches in terms of viscosity, coating properties, elasticity, and extensibility.

  In the esterified starch, the degree of esterification is not particularly limited, but the average number of ester bonds introduced is preferably 1 to 3, more preferably 1 to 2, per glucose unit. Of the esterified starches, hydroxyesterified starch is preferred. The hydroxyesterified starch can be easily and inexpensively obtained by subjecting the raw material starch to an oxidation treatment and reducing the carboxymethyl group to a hydroxyethyl group. Among them, it is optimal to use a hydrophobic group-containing ester-modified tapioca starch in which a hydrophobic group is introduced into the end group of the ester-modified starch.

Furthermore, the esterified starch that can be preferably used in the present invention has a carboxylic acid “—COOH” structure in the terminal group and is ionized like “—COO—” in the neutral region to form hydrogen bonds. The ester-modified starch, which exhibits thixotropic behavior based on rebound without being able to secure the connection due to the penetration, penetrates into the paper after application while showing fluidity when applied to the surface of newsprint paper. This is preferable from the viewpoint of exhibiting a high film property on the paper surface . The esterified starch such as this, the tapioca starch main raw material is ester-modified 1-octenyl succinate esterified starch is particularly preferred.

  The oxidized starch suitably used in the present invention is a modified starch conventionally used. For example, by oxidation reaction with sodium hypochlorite or the like, the molecular weight is reduced, and carboxyl groups, aldehyde groups, carbonyls in the molecule are reduced. And the like introduced.

  The starch used in the present invention has, for example, an average molecular weight of about 200,000 to 1,500,000, more preferably about 300,000 to 1,000,000, and a viscosity (50 ° C., solid content concentration of 10%) of 10 to 300 mPa · s. And preferably about 20 to 250 mPa · s.

Coating liquid containing a surface treatment agent to each coated on the front surface and the back surface of base paper, at least one water-soluble polymer compound is Starch, if necessary, for example, a surface paper strength such as polyacrylamide It can be obtained by appropriately mixing an agent and a surface sizing agent such as a styrene polymer, adding water, and adjusting the solid content concentration to, for example, about 2 to 20%.

As described above, in particular, in the present invention, the surface strength is weak Iura surface, and applying a coating fluid containing a surface treatment agent consisting of at least one arsenide Dorokishiechiru starch and esterified starch, whereas the surface the front surface strength strong, you applying a coating fluid containing a surface treatment agent comprising oxidised starch. Further, the surface strength is relatively strong surface, the water-soluble polymer compound of high permeability low viscosity, i.e. by coating a coating solution containing a surface treatment agent consisting of oxidized starch, together with the surface strength is relatively poor, It is preferable to apply a water-soluble polymer compound having a high film property, particularly hydroxyethylated starch, on the surface having high surface properties (roughness).

  In order to apply the coating liquid containing the surface treatment agent on the front and back surfaces of the base paper, conventionally used for coating a general coating liquid and other additives, such as transfer coaters and air doctors. Equipment such as a coater, blade coater, and rod coater can be used. In particular, a transfer roll coater type coating apparatus, for example, a gate roll coater, a rod metering size press, and a blade metering size press are preferably used.

The equipment comprising a gate roll coater, a rod metering size press, and a blade metering size press can simultaneously apply a coating solution containing a surface treatment agent on the front and back surfaces of the base paper on-machine. Furthermore, for example, even when the paper making speed exceeds 1500 m / min or when the basis weight is about 36 to 48 g / m ² and the weight is reduced, an excessive load is not applied to the base paper. It is possible to apply a coating solution containing a surface treatment agent on the front and back surfaces, and at the stage of preparing a coating solution containing a surface treatment agent, at least different types are provided by providing two preparation processes. It is also possible to apply the coating solution containing the surface treatment agent to each of the front and back surfaces and to apply the coating solution containing the surface treatment agent to each of the front and back surfaces with different coating amounts.

  In addition, when applying at least different materials on the front and back surfaces, for example, if a coating agent containing a pigment is applied only on the front surface, there will be a difference in the elongation of the paper between the front and back surfaces, causing problems such as curling. In order to solve the problem of curling or the like, the coating liquid containing at least different types of surface treatment agents as described above is used to apply water to the back surface to make the paper on the front and back surfaces uniform and to solve problems such as curling. In addition to means for coating each side of the back surface, such means can solve problems such as curling, but essentially the same quality of the front and back surfaces as in the present invention. It is difficult to obtain newspapers that have been improved.

The coating amount of the coating liquid containing the surface treatment agent is adjusted to 0.3 g / m ² or more, further 0.4 g / m ² or more in terms of dry solid content, respectively, on the front and back surfaces of the base paper. In addition, it is preferably adjusted to 3.0 g / m ² or less, more preferably 2.0 g / m ² or less in terms of dry solid content. When the coating amount of the coating liquid containing the surface treatment agent is less than 0.3 g / m ² , the whiteness of the coating liquid containing the surface treatment agent is particularly high when the ratio of the used paper pulp blending ratio and the paper ash content is high. There is a possibility that the effect of preventing blanket piling due to omission or paper dust may not be sufficiently exhibited. On the other hand, when the coating amount of the coating solution containing the surface treatment agent exceeds 3.0 g / m ² , the coating solution containing the surface treatment agent elutes during printing and adheres to the blanket of the offset printing press, and again in the newspaper. Printing failure due to transfer to the paper, and the adhesiveness of the paper surface increases due to water absorption, causing the paper to be taken into the blanket, causing paper breakage, or by using a coating solution containing a surface treatment agent. Since the uniformity may be lowered, it is desirable that the coating liquid containing the surface treatment agent is not applied more than necessary.

  In the present invention, the surface strength of the front and back surfaces of the base paper before coating is measured with a surface strength measuring device (RI tester (RI-2 type printability tester), manufactured by Ishikawajima Sangyo Co., Ltd.). Evaluation is performed based on the presence or absence of white spots after printing, and the type and concentration of the surface treatment agent can be determined based on this evaluation. The surface strength imparted by each surface treatment agent is known from the type of the water-soluble polymer compound that constitutes it. For example, if the coating amount of the coating liquid containing the surface treatment agent is the same, the type of surface treatment agent Depending on the surface strength applied, for example, if the type of surface treatment agent is the same, the surface strength of the paper and the coating amount of the coating liquid containing the surface treatment agent are approximately proportional. As shown, the surface treatment agent can be selected and the coating amount can be adjusted by evaluating the surface strength of the base paper before coating.

In addition, in this specification, surface strength is evaluated according to the following [Surface Strength Evaluation Method].
[Surface strength evaluation method]
After printing on the test piece with a surface strength measuring device (RI tester (RI-2 type printability tester), manufactured by Ishikawajima Industrial Machinery Co., Ltd.), visually check for white spots after printing. And evaluated based on the following evaluation criteria.
(Evaluation criteria)
1: The piece of paper is torn.
2: A piece of paper is delaminated.
3: White spots occur in 75% or more of the area of the paper piece.
4: White spots occur at 50% or more of the area of the paper piece.
5: White spots occur at 25% or more of the area of the paper piece.
6: A piece of paper is fluffed and white spots are slightly observed.
7: Slight fuzz is observed on the piece of paper.
8: A piece of paper fluffs and no white spots are observed.

  Thus, in the present invention, the coating amount of the coating liquid containing the surface treatment agent may be the same or different between the front surface and the back surface of the base paper. Depending on the type of surface treatment used for the surface and the surface strength of the front and back of the base paper, the difference in drop water absorption on the front and back of the resulting newspaper is within a specific range, and the quality of the front and back is made uniform. You may adjust so that.

  Newspaper paper obtained by applying a coating liquid containing a surface treatment agent to the front and back surfaces of the base paper is preferably subjected to a flattening treatment with a calendar facility such as a soft calendar, a super calendar, or a gloss calendar. . Among these calendar facilities, a soft calendar combining an elastic roll and a metal roll is used from the viewpoint that a moderate drop water absorption difference, Beck smoothness difference, etc. can be easily imparted to the front and back surfaces of newsprint. It is preferable.

  The paper passing process using the soft calendar is preferably performed by adjusting the nip pressure within a range of 5 to 50 kN / m, more preferably 12 to 25 kN / m. If the nip pressure is less than 5 kN / m, the smoothness of the paper surface that did not contact the metal roll in the dryer part may not be sufficiently improved. On the other hand, if it exceeds 50 kN / m, the smoothness of the paper surface may be reduced. There is a risk of becoming too high.

  As for the hardness of the elastic roll of the soft calender, it is preferable that the Shore hardness conforming to “Shore hardness test-test method” described in JIS Z 2246 is about 87 to 95 °. If the Shore hardness is less than 87 °, the durability of the elastic roll may be low, and sufficient smoothness may not be obtained. On the other hand, if it exceeds 95 °, a uniform profile may not be obtained. . In addition, the roughness of the elastic roll is the maximum value of the surface roughness in accordance with “Product Geometric Specification (GPS) —Surface Properties: Contour Curve Method—Terminology, Definition and Surface Property Parameters” described in JIS B 0601. It is particularly preferable that the thickness is less than about 0.5 μm because uneven ink deposition on the paper surface of newsprint can be sufficiently reduced.

  Further, in order to smooth the surface of the soft calender in contact with the metal roll, the surface temperature of the metal roll facing the elastic roll is about 40 to 150 ° C., further about 50 to 120 ° C., particularly about 60 to 100 ° C. It is preferable to do. By setting the surface temperature of the metal roll within such a range, a printed surface with a more uniform density can be obtained without any difference between the front and back surfaces even in multicolor printing, for example, where slight density unevenness affects. it can.

  The newsprint of the present invention thus obtained has a drop water absorption difference (absolute value) on the front and back surfaces of 0 to 20 seconds, preferably 0 to 17 seconds, and more preferably 0 to 10 seconds. If the drop water absorption difference (absolute value) exceeds 20 seconds, uneven drying occurs on the front and back sides of the newsprint drying process, operability decreases, and the paper curls due to, for example, dampening water during offset printing. Or a problem that the color shift at the time of the plaster becomes large.

  Also, the drop water absorbency of the front and back sides of the newsprint paper may be in the range of 30 to 150 seconds, or even 40 to 120 seconds, in terms of color misalignment at the time of plaster and edge breakage at the folder part. preferable.

  In the present specification, the drop water absorption refers to the time (seconds) required for 5 μL of 20 ° C. water dripped on the newspaper surface to be completely absorbed in the paper layer.

  Further, the newsprint of the present invention is flattened so that the Beck smoothness on the front and back surfaces is in the range of 25 to 65 seconds, further in the range of 30 to 60 seconds, particularly in the range of 35 to 55 seconds. However, it is preferable in terms of ensuring the running performance in a high-speed rotary press and the transportability between rolls at the time of inkjet printer or electrophotographic printing. Further, the difference (absolute value) in Beck smoothness between the front and back surfaces is preferably 0 to 20 seconds, and more preferably 0 to 15 seconds, in order to prevent the meandering of the paper and the printing misregistration. If the difference (absolute value) of the Beck smoothness exceeds 20 seconds, there is a possibility that the difference in ink deposition between the front surface and the back surface of the paper becomes large.

  In order to improve the smoothness of newsprint, conventionally, for example, a technique of performing a soft calendering process in one nip or two nips has been proposed. However, if the quality difference between the front and back surfaces is large, physical flattening is performed. Although the effect of the treatment is recognized, for example, as described above, a twin wire paper machine called a gap former, a hybrid former having a double-sided dewatering mechanism, an on-top former, a suction roll method or a grooved press method In modern paper machines that can greatly correct the quality difference between the front and back surfaces by using various combinations of dewatering, straight-through, invar, and reverse presses, For example, the proportion of waste paper pulp is 60% or more, the proportion of paper ash is 4% or more, In the case of newsprint exceeding 6%, yet the effect is small.

  The difference in quality between the front and back sides of newsprints is that the dehydration conditions in the wire part and press part are slightly different between the front and back sides during the paper making process, so there is a difference in the smoothness between the front and back sides and the thickness. Since the distribution of fillers and fine fibers in the direction differs between the front and back surfaces, it is thought to be caused by differences in the ink transfer properties between the front and back surfaces, especially on paper surfaces with low smoothness. The inking property is poor, and the image density is remarkably different between the front surface and the back surface.

  However, in the newsprint of the present invention, the front and back surfaces of the base paper are both made of a water-soluble polymer compound, but at least different surface treatment agents are applied to the respective surfaces according to the properties of the front and back surfaces. In addition, since it is preferably flattened with a soft calender or the like, a permanent effect is exhibited, and the difference (absolute value) in Beck smoothness between the front and back surfaces is preferably 0 to 20 seconds. Can be adjusted within the range.

  In addition, in this specification, Beck smoothness means the value measured based on "the smoothness test method by a paper and paperboard-Beck smoothness tester" of JISP8119.

  Next, the newspaper of the present invention will be described in more detail based on the following examples, but the present invention is not limited to these examples.

Production Examples 1 to 4 and Comparative Production Examples 1 to 6 (Manufacture of base paper)
The pulp slurry containing newspaper deinked waste paper pulp (DIP) and mechanical pulp (TMP) at the ratio shown in Table 1 was beaten with a refiner to prepare a pulp slurry having a Canadian Standard Freeness (CSF) of 150 mL. With respect to 100 parts by mass of the obtained pulp slurry, 0.1 parts by mass of alkyl ketene dimer sizing agent (product name: AD-1624, manufactured by Nippon PMC Co., Ltd.) and sulfuric acid band (flocculating agent) 0. After adding 3 parts by mass and further adding hydrated silicic acid and talc as fillers to 6% in terms of paper ash content, using a twin wire type paper machine, papermaking was performed at the speed shown in Table 1. And a base paper having a basis weight of about 45 g / m ² was obtained.

  The paper ash content of the obtained base paper was measured according to JIS P 8128. The results are shown in Table 1. Further, the surface strength of each of the front and back surfaces of the base paper was evaluated according to the above [Surface Strength Evaluation Method]. The results are also shown in Table 1.

Preparation Examples 1 to 4 and Comparative Preparation Examples 1 to 8 (Preparation of coating liquid containing surface treatment agent)
To the water-soluble polymer compound shown in Table 2, an acrylic polymer (trade name: FD8812, manufactured by BASF) was added as a surface sizing agent at a ratio shown in Table 2 with respect to 100 parts by mass of the water-soluble polymer compound solid content. Then, water was added thereto, and the mixture was stirred and mixed to prepare a coating liquid (for front surface or back surface) containing a surface treatment agent having a solid content concentration shown in Table 2.

The water-soluble polymer compounds shown in Table 2 are as shown below.
・ Starch 1: oxidized corn starch (trade name: MS-3800, manufactured by Nippon Shokuhin Kako Co., Ltd.)
-Starch 2: wet low molecular weight hydroxyethylated starch (trade name: PG-270, manufactured by PENFORD)
・ Starch 3: Esterified starch (trade name: Filmkote-370, manufactured by National star Chemicals)
-Starch 4: dry low molecular weight hydroxyethylated starch (trade name: ETHYLE-2025, manufactured by STALEY)
-PVA: polyvinyl alcohol (solid content concentration: 10%, trade name: Kuraray Poval KRE164, manufactured by Kuraray Co., Ltd.)

Examples 1-4 and comparative examples 1-8 (manufacture of newsprint)
Table with a combination of a coating liquid containing a base paper shown in 3 and surface treatment agent, a gate roll coater and a transfer roll coater method (Example 1-4) consisting of a rod metering size press or size press method (Comparative Example 1 The surface treatment agent for the surface is included on each of the front and back surfaces of the base paper so that the coating amount on the front surface and the back surface is the amount shown in Table 3 in terms of dry solid content. The coating liquid containing the coating liquid or the surface treating agent for the back surface was applied and dried. Thereafter, the front and back surfaces were flattened with a soft calendar (Examples 1 to 4 , Comparative Example 5) or a machine calendar (Comparative Examples 1 to 4 and 6 to 8) to obtain newspaper.

In addition, the planarization process with the soft calendar in Examples 1 to 4 and Comparative Example 5 was performed under the following conditions.
Nip pressure: 5 to 40 kN / m
Hardness of elastic roll: Shore hardness (conforms to JIS Z 2246) 90 °
Elastic roll roughness: Maximum surface roughness (according to JIS B 0601) 0.4 μm
Surface temperature of the metal roll facing the elastic roll: 90 ° C

  Each physical property was measured for each of the front and back surfaces of the obtained newspaper by the following method. These results are shown in Table 4.

(A) Surface strength It evaluated according to [Surface strength evaluation method].

(B) Drop water absorption The time (seconds) until 5 μL of 20 ° C. water dropped on the paper surface was completely absorbed in the paper layer was measured.

(C) Beck smoothness Measured according to JIS P 8119.

Next, the characteristics of the newspapers of Examples 1 to 4 and Comparative Examples 1 to 8 were examined based on the following Test Examples 1 to 3. The results are shown in Table 5.

Test Example 1 (Blanket Piling)
Using an offset printing machine (model number: LITHOPIA BTO-N4, manufactured by Mitsubishi Heavy Industries, Ltd.), after continuous 50,000 copies of color four-color printing with ink for offset printing, generation of paper dust in the blanket non-image area And the presence or absence of deposition was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
(Double-circle): Generation | occurrence | production of paper dust is not recognized at all.
○: Slight generation of paper dust is observed.
(Triangle | delta): Generation | occurrence | production of paper dust and accumulation on a blanket are recognized.
X: A lot of paper dust is deposited on the blanket.
Of the above evaluation criteria, the cases of ○ and ○ are judged to be actually usable.

Test example 2 (white seal)
Using an offset printing machine (model number: LITHOPIA BTO-N4, manufactured by Mitsubishi Heavy Industries, Ltd.), single-color printing of ink (black) for web offset printing is performed, and the solid surface has a halftone dot area ratio of 100%. The presence or absence of was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: No white spots are observed at all.
○: Slight white spots are observed.
Δ: White spots are observed over the entire surface.
X: White spots are remarkable over the entire surface.
Of the above evaluation criteria, the cases of ○ and ○ are judged to be actually usable.

Test Example 3 (Paper Adhesion and Starch Adhesion to Blanket)
Using an offset printing machine (model number: LITHOPIA BTO-N4, manufactured by Mitsubishi Heavy Industries, Ltd.), whether or not there is a paper break during printing (due to an increase in paper stickiness due to water absorption), and starch on the blanket after printing The presence or absence of adhesion (because of the starch elution caused the blanket surface to become whitish) was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
(Double-circle): There is no generation | occurrence | production of the paper break during printing and adhesion of starch to the blanket surface.
○: No paper break occurred during printing, and the blanket surface becomes slightly whitish.
Δ: No paper break occurs during printing, but the blanket surface is generally whitish.
(However, it is not blanket piling with paper dust and filler)
X: Paper is removed from the blanket during printing, and breakage occurs.
Of the above evaluation criteria, the cases of ○ and ○ are judged to be actually usable.

From the results shown in Table 5, each of the newspapers of Examples 1 to 4 is of a different type on the front surface and back surface , and each is coated with a coating liquid containing a specific surface treatment agent, In addition, since the difference in the drop water absorption between the front and back surfaces is 20 seconds or less, the proportion of waste paper pulp is as high as 60% by mass or more of the total amount of pulp, and the proportion of paper ash is as high as about 4% or more. In spite of the papermaking conditions exceeding the above, blanket piling due to white spots and paper dust is sufficiently prevented, and there is almost no elution of the coating liquid including paper breakage and surface treatment agent, which makes it suitable for offset printing. It turns out that it was equipped.

  On the other hand, the newspapers of Comparative Examples 1 to 8 are all coated with a coating liquid containing the same surface treatment agent on the front and back surfaces, or contain the surface treatment agent only on one of the surfaces. The coating liquid is not applied, and the difference in water absorption between the front and back surfaces exceeds 20 seconds. Therefore, white spots, blanket piling due to paper dust, paper breakage, and coating with a surface treatment agent. It can be seen that the liquid does not have characteristics suitable for offset printing, such as elution.

  The newsprint of the present invention can be suitably used, for example, for offset printing under papermaking conditions exceeding the recent papermaking speed of 1500 m / min.

Claims (3)

Newspaper paper in which a coating liquid containing a surface treatment agent is coated on the front and back surfaces of a base paper containing pulp and filler containing waste paper pulp as main raw materials,
A coating liquid comprising at least different surface treatment agents composed of a water-soluble polymer compound is applied to each surface on the front and back surfaces of the base paper,
The coating liquid coated on the surface of the base paper contains a surface treatment agent made of oxidized starch, and the coating liquid coated on the back surface of the base paper is hydroxyethylated starch and esterified starch. A surface treatment agent comprising at least one of
A newsprint having a drop water absorption difference (absolute value) on its front and back surfaces of 0 to 20 seconds. Base paper, the used paper pulp intended by blending 60 to 100 mass% of pulp based on the total amount and is a paper ash content conforming to JIS P 8251 is not less than 4%, newsprint of claim 1. The coating amount of the coating liquid containing the surface treatment agent is adjusted to 0.3 to 3.0 g / m ² in terms of dry solid content on the front surface and the back surface of the base paper, respectively. The newsprint listed.