JP2003336195A - Flexible printing paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printing paper having good texture, touch and turn-over facility and scarcely generating the web breakage on a paper machine or printing press. <P>SOLUTION: The paper contains a softening agent and has a breaking length of ≤4 km. The product of three factors consisting of the density of the paper manufactured by a paper machine, the breaking length in the paper-making direction and the Young's modulus in the paper-making direction is set within the range of 2×10<SP>18</SP>to 10×10<SP>18</SP>g.N/m<SP>4</SP>, preferably 2×10<SP>18</SP>to 5×10<SP>18</SP>g.N/m<SP>4</SP>. The softening agent is added to the paper stock before paper-making in an amount of 0.1-5 wt.% based on the bone-dry weight of the pulp. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing paper having excellent flexibility and bulkiness, and more particularly to a printing paper suitable for use in books.

[0002]

2. Description of the Related Art Book papers have important properties such as texture, touch, and ease of turning. In particular, recently, there is a demand for lightness, that is, bulkiness (low density) while having a sense of volume (thickness of paper) and easy turning when a book is formed. Conventionally, if the paper thickness is increased, the stiffness of the paper is increased and it is difficult to turn the paper. Therefore, it is difficult to achieve both the volume feeling and the ease of turning the paper.

The properties of paper such as texture, touch, and ease of turning are factors that influence the flexibility of the paper, but the flexibility of the paper is complicatedly related to the stiffness, elasticity, strength, and other properties. , It is difficult to make a numerical value. For the purpose of improving the texture as a book paper, JP-A-8-246390
The publication discloses thin-leaf book paper containing a specific spindle-shaped calcium carbonate as a filler and blended with mechanical pulp having a water retention value of 100 to 150%. In addition, JP-A-10-204790
In the gazette, the freeness contains 90% by weight or more of hardwood kraft pulp of CSF 500 ml or more, the hardwood kraft pulp contains 50 to 100% by weight of dipterocarp pulp, contains calcium carbonate as a filler, and has a density of 0.6.
Low Density Books paper ~0.65g / cm ³ are disclosed.
However, these book papers are disadvantageous in terms of cost because they need to be blended with a special pulp, have insufficient flexibility, and are not excellent in texture, touch and turning.

On the other hand, with the increasing environmental protection, it is an unavoidable problem to reduce the weight of paper in order to effectively use the pulp for papermaking manufactured from forest resources. Even so, weight reduction is becoming a major trend. Here, reducing the weight of paper means reducing the weight while maintaining the thickness of the paper, that is, low density (bulky) paper.

First, as a method for reducing the density (bulking) of paper, paper pulp, which is the main raw material for paper, is being studied. Wood pulp is generally used as the pulp for papermaking. As pulp for lowering the density, chemical pulp is used to extract lignin, which is a reinforcing material in the fiber, and chemical pulp is used. Mechanical pulp such as thermomechanical pulp obtained has more rigid fibers and is more effective for lowering the density, and groundwood pulp in particular contributes to lowering the density. However, groundwood pulp is a mechanical pulp, and there is a problem in terms of specification in blending with high-quality paper. Further, blending causes a problem in paper quality, such as fading over time, and thus cannot be blended. Similarly, blending of thermomechanical pulp into high-quality paper is impossible.

In the case of high-quality paper, only the chemical pulp is mixed on the pulp side, but the density of the paper is greatly affected by the pulping tree species. That is, when the wood fibers themselves are coarse, the density can be reduced. Hardwood pulp is mainly mixed with hardwood pulp, but gumwood, maple, and birch are among the hardwood species that can be relatively low in density. However, it is difficult to identify, collect, and pulp only these tree species in the midst of the current trend of environmental protection.

On the other hand, in medium-quality paper or lower-grade paper, mechanical pulp is blended, which is usually a lower density than fine-quality paper. However, blending rigid fibers makes it difficult to print paper when printing (from mechanical pulp). The amount of the binding fiber is limited, and the mechanical strength of the bleached chemical pulp is lowered. Further, increasing the mechanical pulp, which usually has a lower degree of whiteness than the bleached chemical pulp, lowers the whiteness. Further, in recent years, there has been a demand for an increase in the content of waste paper pulp due to an increase in environmental protection and a need for resource protection. Recycled paper pulp is rarely pulped by being clearly classified according to the type such as high-quality paper, newspaper, magazines, leaflets, coated paper, etc., because it is pulped as it is mixed,
The nature of pulp tends to be higher than that of virgin mechanical pulp. The reason for this is that the fiber content of waste paper pulp is a mixture of chemical pulp and mechanical pulp. In addition, talc, kaolin, clay, and calcium carbonate, which are commonly used as a filler component contained in paper or a pigment component of the coating layer of coated paper, have a higher density than pulp, so the density of Tends to be high.
Therefore, increasing the blending ratio of waste paper pulp tends to increase the paper density. As described above, it is extremely difficult to achieve a sufficiently low paper density only from the pulp side, considering the situation of wood resources and paper quality design.

[0008] Usually, the pulp for papermaking softens the fibers to be fibrillated by a beating treatment, but the beating treatment tends to reduce the bulk, and therefore it is desirable not to do as much as possible in order to increase the bulk. However,
If the beating process is insufficient, the strength will decrease.

As a method for lowering the density during papermaking, the press pressure should be as low as possible in the pressing step during papermaking, and no calendering should be carried out to impart smoothness to the paper surface. Is mentioned. Further, it is desirable that the surface coating of the water-soluble polymer such as starch, which is carried out for the purpose of imparting the surface strength of the paper at the time of printing, to be as low as possible.

In addition to such contrivances at the time of pulping and papermaking, studies have also been conducted on fillers to be added to paper next to pulp. For example, Japanese Patent Application Laid-Open No. 5-339898 discloses a method of achieving a low density by blending hollow synthetic organic material capsules as a filler. In addition, a synthetic organic foaming filler (for example, trade name: EXPANSEL, manufactured by Nippon Philite Co., Ltd.) that achieves bulkiness by expanding with the heat of the dryer section of the papermaking machine is also proposed. However, the methods using these synthetic organic foaming fillers have problems that it is difficult to set the drying conditions during papermaking, the surface strength is weak, and the printing glossiness is lowered.

Japanese Patent Publication No. 52-39924 has proposed a method using a shirasu balloon, but it has a poor mixing property with paper-making pulp, and the paper containing the same causes uneven printing. There is.

[0012] Further, JP-A-8-13380 discloses a method of adding fine fibrillated cellulose, but it is necessary to specially prepare fine fibrillated cellulose, and further, the pulp freeness at the time of papermaking is improved. CSF40
It is necessary to adjust the amount to 0 ml or more, preferably CSF 500 ml or more, and it is difficult to adjust the freeness with a stock material containing a large amount of mechanical pulp, and it is difficult to implement with medium-quality paper or lower grade paper.

Further, although the paper thickness is increased by these methods, the stiffness of the paper increases exponentially as the paper thickness increases, so that the flexibility of the paper is not improved, so that the texture, the feel, and the ease of turning are improved. It was insufficient.

[0014]

SUMMARY OF THE INVENTION The object of the present invention is that the texture, touch and turning property are good, the paper density is low (bulky), there is little breakage during printing, and the flexibility is excellent in printability. To provide printing paper.

[0015]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that the paper contains a softening agent, and the density of the paper, the breaking length in the papermaking direction and the papermaking process. The product of the three Young's moduli in the direction is 2 × 10 ¹⁸ or more 10 × 10 ¹⁸ g
It has been found that by specifying N / m ⁴ or less, it is possible to obtain a bulky flexible printing paper which has good texture, touch, and easy turning.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have made paper sheets compatible with the flexibility, lightness, and volume feeling (high paper thickness) required for book paper, such as texture, touch, and ease of turning. We considered quantifying the properties that flexibility affects. First, the Clark stiffness was examined, but the value of the Clark stiffness did not necessarily correlate with the actual texture, and even if the Clark stiffness was low, a good texture was not always obtained. In addition, it was found that the lower the strength and Young's modulus of the paper, the better the texture of the paper. On the other hand, when the paper thickness is increased by a conventionally known method in order to obtain a light and volume feeling, the flexibility deteriorates. Therefore, when the flexibility of the paper was further investigated, it was found that a flexible paper can be produced by simultaneously lowering the strength and Young's modulus.

That is, in order to obtain the lightweight, bulky and flexible paper which is the object of the present invention, it is effective to reduce the strength, Young's modulus and density of the paper at the same time in a well-balanced manner. As a result, it was found that there is a good correlation with the product of the paper density, the breaking length in the papermaking direction and the Young's modulus in the papermaking direction. That is, the lower the product of these three values, the more flexible and bulky (low density) the paper is.
If the product of those values is in the range of 2 × 10 ¹⁸ or more and 10 × 10 ¹⁸ g · N / m ⁴ or less, the texture and feel are good, the weight is light and bulky, and further on paper machines and printing machines. It was found that the paper has few paper breakage problems. In particular, if the product of the three values is in the range of 2 × 10 ¹⁸ or more and 5 × 10 ¹⁸ g · N / m ⁴ or less, it is suitable as a book paper. As mentioned above, there is a concern that paper breaks on paper machines and printing machines may occur due to the reduction in strength, but when Young's modulus is simultaneously reduced, when the load is applied and the paper is within the elastic range of the paper, Since it is easy to stretch, it is presumed that partial stress concentration is unlikely to occur, and even if the strength is reduced, paper breakage is less likely to occur.

The printing paper of the present invention needs to be made by a paper machine in order to specify the breaking length of the paper in the paper-making direction and the Young's modulus in the paper-making direction to the above-mentioned values. That is,
In the case of paper with a non-oriented fiber orientation produced by a hand machine or the like, the breaking length in the papermaking direction and the Young's modulus in the papermaking direction of the present invention cannot be adjusted. Further, even if a hand machine capable of imparting orientation is used, it is impossible to make the press, drying and calendering conditions the same as those of a paper machine, so that the density of the present invention should be adjusted. I can't. Therefore, as the paper machine, a publicly known machine such as a Fourdrinier paper machine or a twin wire type paper machine such as an on-top former type, a hybrid former type and a gap former type is used.

The density is a normal value and the product of the three values is 2 × 10 ¹⁸
Papers with g · N / m ^{4 or} less have an excessively low breaking length or a low Young's modulus, are excessively flexible and have no stiffness, and are also excessively low in strength during papermaking. Paper breakage easily occurs during printing. Further, the paper having a normal breaking length and Young's modulus and the product of the three values being less than 2 × 10 ¹⁸ g · N / m ⁴ has an excessively low density. It is necessary to extremely reduce the pressure at the time of pressing or calendering, and therefore the smoothness is extremely low and it is difficult to print.

On the other hand, when the density is a normal value and the product of the three values is 10
Papers with a weight exceeding × 10 ¹⁸ g · N / m ⁴ have an excessively high breaking length or a high Young's modulus, which makes the paper stiff and deteriorates the texture. Further, breaking length, paper having a Young's modulus product of 3's value in the normal value exceeds ^{10 × 10 1 8 g · N} / m 4 is a density that extremely high, an object of the present invention It does not result in bulky and bulky paper.

Further, the present inventors have found that the breaking length in the papermaking direction is important for the flexibility of paper. Since the breaking length depends on the strength of the interfiber bond, it is considered to be an index of paper flexibility. The value of the product of the above three is 2 × 10 ¹⁸ or more 5
In ^{× 10 18 g · N / m} 4 or less, and breaking length has good flexibility as a book paper equal to or less than 4km.

The product of the density of paper, the breaking length in the papermaking direction and the Young's modulus in the papermaking direction is 2 × 10 ¹⁸ or more and 10 × 10 ¹⁸ g · N
In order to achieve the range of / m ⁴ or less, means for reducing the density of paper, the breaking length in the papermaking direction, and the Young's modulus in the papermaking direction are used alone or in combination. Examples of methods for reducing the density of paper include a method of improving the compounding ratio of low-density pulp and low-density filler, the use of bulky chemicals, and reduction of the press pressure in the papermaking process. Examples of the method for reducing the breaking length of paper include a method for improving the compounding ratio of the filler. Further, as a method of lowering the Young's modulus of paper, use of a softening agent and the like can be mentioned.

The softening agent used in the present invention has an action of inhibiting interfiber bonding of pulp or softens the fibers themselves. For example, there are surfactants having a hydrophobic group and a hydrophilic group that have this action. For example, oil-based nonionic surfactants, sugar alcohol nonionic surfactants, sugar nonionic surfactants, Polyhydric alcohol type nonionic surfactant, higher alcohol, ester compound of polyhydric alcohol and fatty acid, polyoxyalkylene adduct of higher alcohol or higher fatty acid, polyoxyalkylene adduct of higher fatty acid ester, ester of polyhydric alcohol and fatty acid A polyoxyalkylene adduct of a compound,
Although fatty acid polyamidoamine etc. can be illustrated, if it is possible to improve flexibility, it is not limited to such compounds and combinations. The use of a softening agent capable of lowering the breaking length and the density in addition to lowering the Young's modulus is an essential form in the present invention.

The product of the density, the breaking length in the paper making direction and the Young's modulus in the paper making direction of the paper of the present invention is 2 × 10 ¹⁸ or more and 10 × 10 or more.
^In order to achieve the range of ¹⁸ g · N / m ⁴ or less, the addition amount of the softening agent is determined in consideration of pulp composition, filler content, internal additive chemicals and the like. Normally, per pulp dry weight
Papermaking may be carried out by adding 0.1 to 5% by weight to the stock.

The flexible printing paper of the present invention uses, as a raw material pulp, chemical pulp (softwood bleached kraft pulp (NBK).
P) or unbleached kraft pulp (NUKP), hardwood bleached kraft pulp (LBKP) or unbleached kraft pulp (LUKP), etc., mechanical pulp (ground pulp (G
P), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), etc., deinked pulp (DI
P) is used alone or mixed in any ratio.

The pH of the flexible printing paper of the present invention is acidic,
It may be neutral or alkaline. Further, when a filler is contained in the paper, the breaking length and Young's modulus tend to be reduced, so it is preferable to include a filler. As the filler, known fillers such as hydrated silicic acid, white carbon, talc, kaolin, clay, calcium carbonate, titanium oxide and synthetic resin filler can be used.

Further, the flexible printing paper of the present invention may contain a sulfuric acid band, a sizing agent, a paper strengthening agent, a yield improving agent, a coloring agent, a dye, an antifoaming agent, etc., if necessary.

In addition, a surface treatment agent containing a water-soluble polymer as a main component may be applied for the purpose of improving surface strength and sizing property within a range that does not affect density, breaking length and Young's modulus. . As the water-soluble polymer, oxide starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol and the like usually used as a surface treatment agent can be used alone or in a mixture thereof. In addition to the water-soluble polymer, a paper strength enhancer for water resistance and surface strength improvement and an externally added sizing agent for sizing can be added to the surface treatment agent. The surface treatment agent can be applied by a coating machine such as a two-roll size press coater, a gate roll coater, a blade metalling coater, or a rod metalling coater.

As described above, the product of the three factors of the density, the breaking length in the papermaking direction and the Young's modulus in the papermaking direction is 2 × 10 ¹⁸ or more and 10 × 10 ¹⁸ g · N / m ⁴ by containing the softening agent. By specifying the following, it is possible to obtain a printing paper which is bulky, lightweight and excellent in flexibility. The bulky flexible printing paper of the present invention is, in addition to book paper, offset printing paper, letterpress printing paper, gravure printing paper, electrophotographic paper, or coated paper, inkjet recording paper, thermal recording paper, pressure-sensitive recording paper, etc. It can also be used as a base paper.

[0030]

[Examples] For the papers produced in the examples and comparative examples, the density, the breaking length in the papermaking direction and the Young's modulus in the papermaking direction were measured to calculate the product of the three, and the texture was evaluated. The measuring methods for these items are as follows. Density: According to JIS P 8118-1998. Breaking length: According to JIS P 8113-1998, the breaking length of the paper in the papermaking direction was measured, and this value was taken as the breaking length. Young's modulus: According to JIS P 8113-1998, the tensile elastic modulus of the paper in the paper making direction was measured, and this value was defined as the Young's modulus. Evaluation of flexibility: The touch and texture were evaluated by 10 people's monitors in four grades: ◎ very excellent, excellent, △ somewhat problematic, × problematic.

[Example 1] LBKP (freeness of 410 ml) was used as the pulp component, and Kao Co., Ltd. was used as the softening agent.
On-machine size press coater was used to make paper by using on-top former type paper machine with paper stock prepared by making KB-115 manufactured by K.K. in the amount of 0.4% by weight with respect to pulp and calcium carbonate as a filler to 28% by weight with respect to paper weight. Was applied so that the coating amount was 5.1 g / m ² to produce high quality book paper, and the results are shown in Table 1.

[Comparative Example 1] LBKP (freeness of 410 ml) was used as a pulp component, and a stock material prepared by using calcium carbonate as a filler in an amount of 25% by weight based on the weight of the paper was prepared.
Paper is made with an on-top former type paper machine, and starch is applied with an on-machine size press coater at 3.7 g /
A high quality book paper was produced by coating so as to give m ² and the results are shown in Table 1.

[Comparative Example 2] A paper stock prepared by using LBKP (freeness of 345 ml) as a pulp component and calcium carbonate as a filler in an amount of 25% by weight based on the weight of paper,
Paper is made with an on-top former type paper machine, and starch is applied with an on-machine size press coater at 3.7 g /
A high quality book paper was produced by coating so as to give m ² and the results are shown in Table 1.

[Comparative Example 3] A paper stock prepared by using LBKP (freeness of water 317 ml) as a pulp component and calcium carbonate as a filler in an amount of 26% by weight based on the weight of paper,
Paper is made with a paper machine, and starch and polyvinyl alcohol (weight ratio 85:
15) was applied so that the application amount was 4.4 g / m ² , high quality book paper was manufactured, and the results are shown in Table 1.

[Comparative Example 4] As a pulp component, a mixed pulp (freeness of 350 ml) containing 95 parts by weight of LBKP and 5 parts by weight of softwood kraft pulp (hereinafter referred to as NBKP) was used.
A paper stock prepared by adjusting calcium carbonate to 20% by weight per paper weight as a filler is made into paper by an on-top former paper machine, and starch and polyvinyl alcohol (weight ratio 85:15) are made by an on-machine size press coater. The coating amount was 4.5 g / m ^2, and high quality book paper was manufactured. The results are shown in Table 1.

[Comparative Example 5] A paper stock prepared by using LBKP (freeness of 350 ml) as a pulp component and calcium carbonate as a filler in an amount of 29% by weight based on the weight of paper,
Paper was made with a Fourdrinier paper machine, and starch was applied with an on-machine size press coater so that the coating amount was 3.7 g / m ² , high quality book paper was manufactured, and the results are shown in Table 1.

[Comparative Example 6] A stock prepared by using LBKP (freeness of 360 ml) as a pulp component and calcium carbonate as a filler to 28% by weight based on the weight of the paper was prepared.
Paper is made by an on-top former type paper machine, and starch is applied by an on-machine size press coater at an amount of 3.8 g /
A high quality book paper was produced by coating so as to give m ² and the results are shown in Table 1.

[Comparative Example 7] A paper stock prepared by using LBKP (freeness of 360 ml) as a pulp component and calcium carbonate as a filler so as to be 28% by weight based on the weight of paper,
Paper is made by an on-top former type paper machine, and starch is applied by an on-machine size press coater at an amount of 3.8 g /
A high quality book paper was produced by coating so as to give m ² and the results are shown in Table 1.

[0039]

[Table 1]

Example 2 A mixed pulp containing 10 parts by weight of NBKP, 35 parts by weight of LBKP, 40 parts by weight of GP and 15 parts by weight of TMP was used as a pulp component, and KB-115 manufactured by Kao Corporation was used as a softening agent. A paper stock prepared by using a twin-wire type paper machine to prepare a paper stock prepared so that 1% by weight per pulp and 10% by weight kaolin as a filler per paper weight, and a starch coating amount of 3.0 g / m by an on-machine size press coater. ² was applied to produce a medium-quality book paper, and the results are shown in Table 2.

[Example 3] A mixed pulp containing 3 parts by weight of NBKP, 70 parts by weight of GP and 27 parts by weight of DIP was used as a pulp component, and KB-08 manufactured by Kao Corporation was used as a softening agent.
A paper stock prepared by adjusting W to 1% by weight with respect to pulp was paper-made by a twin-wire paper machine to produce a medium-quality book paper, and the results are shown in Table 2.

[Example 4] A mixed pulp containing 10 parts by weight of NBKP, 35 parts by weight of LBKP, 40 parts by weight of GP and 15 parts by weight of TMP was used as a pulp component, and KB-115 manufactured by Kao Corporation was used as a softening agent. A paper stock prepared by using a twin-wire type paper machine to prepare a paper stock prepared so that 1% by weight per pulp and 10% by weight kaolin as a filler per paper weight, and a starch coating amount of 3.0 g / m by an on-machine size press coater. ² was applied to produce a medium-quality book paper, and the results are shown in Table 2.

[Example 5] A mixed pulp containing 10 parts by weight of NBKP, 35 parts by weight of LBKP, 40 parts by weight of GP, and 15 parts by weight of TMP was used as a pulp component, and KB-115 manufactured by Kao Corporation was used as a softening agent. A paper stock prepared by using a twin-wire type paper machine to prepare a paper stock prepared so that 1% by weight per pulp and 10% by weight kaolin as a filler per paper weight, and a starch coating amount of 3.0 g / m by an on-machine size press coater. ² was applied to produce a medium-quality book paper, and the results are shown in Table 2.

Example 6 A mixed pulp containing 9 parts by weight of NBKP, 7 parts by weight of LBKP, 42 parts by weight of GP and 42 parts by weight of TMP was used as a pulp component, and KB-115 manufactured by Kao Corporation was used as a softening agent. 0.6% by weight per pulp,
A paper stock prepared by using calcium carbonate as a filler so as to be 5% by weight based on the paper weight is made into paper by a twin wire type paper machine, and a starch coating amount of 1.8 g / m ² is obtained by an on-machine size press coater. It was applied to produce a medium-quality book paper, and the results are shown in Table 2.

Example 7 A mixed pulp containing 9 parts by weight of NBKP, 7 parts by weight of LBKP, 42 parts by weight of GP, and 42 parts by weight of TMP was used as a pulp component, and KB-115 manufactured by Kao Corporation was used as a softening agent. 0.8% by weight per pulp,
A paper stock prepared by using calcium carbonate as a filler so as to be 5% by weight based on the paper weight is made into paper by a twin wire type paper machine, and a starch coating amount of 1.8 g / m ² is obtained by an on-machine size press coater. It was applied to produce a medium-quality book paper, and the results are shown in Table 2.

[Embodiment 8] A mixed pulp containing 75 parts by weight of LBKP and 25 parts by weight of TMP was used as pulp.
Using a fourdrinier paper machine, a stock prepared by using Kao Corporation's KB-115 as a softening agent in an amount of 0.8% by weight per pulp and calcium carbonate as a filler in an amount of 20% by weight per paper weight is used. , Apply starch with an on-machine size press coater so that the coating amount becomes 6.0 g / m ² ,
A medium quality book paper was manufactured and the results are shown in Table 2.

[Comparative Example 8] A mixed pulp containing 19 parts by weight of NBKP, 28 parts by weight of LBKP, 20 parts by weight of GP, 20 parts by weight of TMP and 13 parts by weight of DIP was used as a pulp component, and calcium carbonate was used as a filler in an amount of 8% by weight based on the weight of paper. The paper stock prepared as described above is made into paper with a twin wire type paper machine, and starch is applied with an on-machine size press coater so that the applied amount is 1.8 g / m ² to produce a medium-quality book paper, The results are shown in Table 2.

[Comparative Example 9] The results are shown in Table 2 for commercially available medium quality paper (trade name: New Cream Bulky, manufactured by Oji Paper Co., Ltd.).

[Comparative Example 10] NBKP52 as pulp
Using a mixed pulp in which 1 part by weight, 8 parts by weight of LBKP, and 41 parts by weight of GP are mixed, and an amorphous silicate as a filler is adjusted to 6% by weight based on the weight of paper, a paper stock is made by a twin wire type paper machine, Starch was applied by an on-machine size press coater to a coating amount of 1.8 g / m ² to produce a medium-quality book paper, and the results are shown in Table 2.

[Comparative Example 11] LBKP75 as pulp
20 parts by weight of calcium carbonate as a filler is used by using a mixed pulp containing 1 part by weight and 25 parts by weight of TMP.
The paper stock prepared as described above is made into paper by a Fourdrinier paper machine, and starch is applied by an on-machine size press coater to an applied amount of 6.0 g / m ² , to produce a medium-quality book paper, The results are shown in Table 2.

[Comparative Example 12] A mixed pulp containing 6 parts by weight of NBKP, 10 parts by weight of GP, 16 parts by weight of TMP and 68 parts by weight of DIP was used as a pulp component, and the prepared paper material was paper-made by a twin wire type paper machine. Starch was coated with an on-machine size press coater to a coating amount of 0.7 g / m ² to produce newsprint, and the results are shown in Table 2.

[0052]

[Table 2] As shown in Tables 1 and 2, the product of density, the breaking length in the papermaking direction and the Young's modulus in the papermaking direction is 2 × 10 ¹⁸ or more and 10 × 10 ¹⁸ g · N containing a softening agent. It was found that when it is within the range of / m ⁴ or less, it is excellent in flexibility and excellent as a book paper regardless of the difference in pulp composition and filler.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takehide Kasahara             5-21-1 Oji, Kita-ku, Tokyo Nippon Paper Industries             Central Research Institute Co., Ltd. (72) Inventor Hideki Fujiwara             5-21-1 Oji, Kita-ku, Tokyo Nippon Paper Industries             Central Research Institute Co., Ltd. F-term (reference) 4L055 AA02 AA03 AC02 AC03 AC06                       AG12 AG27 AG34 AG35 AG47                       AH01 AH13 AH37 AH50 BE08                       EA07 EA08 EA32 FA16 GA15

Claims (5)

[Claims] 1. A printing paper produced by a paper machine, comprising:
Containing a softening agent, the product of density, breaking length in the papermaking direction and Young's modulus in the papermaking direction is 2 × 10 ¹⁸ or more 10 × 10 ¹⁸ g
A flexible printing paper having N / m ⁴ or less. 2. A printing paper produced by a paper machine, comprising:
Containing a softening agent, the product of the density, the breaking length in the papermaking direction and the Young's modulus in the papermaking direction is 2 × 10 ¹⁸ or more 5 × 10 ¹⁸ g
A flexible printing paper having N / m ⁴ or less. 3. The flexible printing paper according to claim 1, wherein the breaking length in the papermaking direction is 4 km or less. 4. A softening agent is used in an amount of 0.1 to 5 per dry weight of pulp.
The flexible printing paper according to any one of claims 1 to 3, wherein the flexible printing paper is added to the paper material in a weight% range to be made into paper. 5. The flexible printing paper according to any one of claims 1 to 4, wherein a surface treatment agent containing a water-soluble polymer as a main component is applied.