JP4752805B2 - Low density book paper - Google Patents

Description

An object of the present invention is to provide a flexible low-density book paper that has excellent opacity, surface smoothness, and surface strength while having a low density.

In recent years, publications have been required to reduce the cost of printed matter and reduce the weight of paper, and in books, the density of paper has been reduced. However, in order to reduce the density, there are methods such as the use of low-density pulp and bulking agent, and on the hard side, such as paper machine press roll and calender roll low pressure, but the paper surface smoothness and ink acceptability are Since the ink is lost, the ink inking property of the printed matter is impaired. The conventional technology has improved the paper surface smoothness and surface sizing agent as an improvement, but there are problems such as shifting in the high-density direction, increasing the stiffness of the paper, and losing flexibility. Not enough low density book paper is available.

As a pulp raw material, which is the main raw material of paper, to reduce the density, the chemical pulp is extracted from the lignin, which is a reinforcing material in the fiber with chemicals. The mechanical pulp produced is more advantageous because the fibers are stiffer. Among these, ground pulp (GP) is advantageous for reducing the density. Ordinary paper pulp softens and fibrillates fibers by beating, but beating is a process contrary to the reduction in density, and it is a good means to reduce the density that is not performed as much as possible. .

However, GP and thermomechanical pulp (TMP) are mechanical pulps, and blending with fine paper has problems with standards, fading over time, and deterioration of ink acceptance on the printing surface, resulting in poor printing surface quality. It becomes.

Therefore, lowering the density of fine paper that contains only chemical pulp is greatly affected by the pulped tree species. That is, if the wood fiber itself is coarse, the density can be reduced. Hardwood pulp is mainly blended with hardwood, but it is also required to select and use tree species that can be made relatively hard with hardwood.

In addition, the increase in the amount of used paper pulp has been screamed because of the recent increase in environmental protection and the need for resource protection. Waste paper pulp is a mixture of chemical pulp and mechanical pulp, and the nature of the pulp tends to be higher than that of mechanical pulp. On the other hand, calcium carbonate, talc, kaolin, and clay, which are generally used as a filler contained in paper or a pigment in coated paper, tend to increase in density due to their blending. As described above, the increase in the density of the paper pulp and the increase in the filler content are directed to increase the paper density.

As described above, it is very difficult to achieve sufficient paper density reduction only from the pulp surface when considering the situation of wood resources and paper quality design.

As a study on reducing the density during paper making, the refiner treatment of the pulp raw material should be operated at as low a load as possible during paper making, then the press pressure should be as low as possible in the press process, or some of the presses may be released, The calendar process performed for imparting smoothness to the surface of the paper is preferably carried out at as low a pressure as possible or released. Furthermore, it is desirable not to increase the adhesion amount of the surface coating of a water-soluble polymer such as starch, which is performed for the purpose of imparting the surface strength of paper during printing.

In addition to such devices for pulping and papermaking, in recent years, the development of low-density chemicals for internal use has progressed, and low-density chemicals for paper have been marketed and used by paper manufacturers (for example, (See Patent Documents 1 and 2).

Several methods using porous fillers with low bulk specific gravity have also been disclosed (Patent Documents 3 and 4), and the paper bulking effect and the ability to absorb ink components during printing are superior to other fillers. However, the ability to increase the opacity of the paper was lower than calcium carbonate and talc. In addition, since the particle size distribution is broad, the surface strength is poor, causing problems such as piling and dusting during printing due to coarse particles, and a decrease in fiber-to-fiber bond strength (internal bond strength) due to fine particles. There was a problem.

Using the low density pulp mentioned above, low load of refiner processing at the time of papermaking, operation under low pressure conditions of press and calendar, addition of low density chemicals, etc. The surface quality shifts in the direction of deterioration.

Moreover, the strength of the sheet is lowered as the density is lowered, the surface strength during printing is lowered, and there is a concern about smearing and internal peeling during offset printing.

Therefore, in order to obtain a low-density printing paper having a higher level of quality than the current state, which has both excellent opacity and surface smoothness, but also has low tenacity (bulkyness) characteristics, However, there was a limit to this method, and it was difficult to obtain a target high level of quality.
Japanese Patent Laid-Open No. 10-226974 JP 2005-256205 A Japanese Patent Laid-Open No. 10-226982 JP 2000-282392 A

  An object of the present invention is to provide a low-density book paper that is flexible and bulky while having excellent opacity, surface smoothness, and surface strength.

As a result of studying low-density book paper that is excellent in strength, smoothness, and opacity while being low in density, the present inventors have incorporated a specific filler, and reduced the density of the base paper to starch and styrene-butadiene. By applying a surface treatment agent containing latex in a specific range, a low-density book paper that is flexible and bulky while having excellent opacity, surface smoothness, and surface strength was found, and the present invention was achieved. This application includes the following inventions.

Chemical pulp as the main pulp material, oil absorption is 360ml / 100g-500ml / 100g, average particle diameter by laser method is 15-30μm, particle diameter (μm) is the logarithm of particle volume relative to particle diameter 50% of starch and styrene-butadiene latex are contained on a base paper containing 1.0 to 5.0% by mass of hydrated silicic acid having a standard deviation of distribution of 0.3 to 0.4 and an ash content of 18 to 27%. Low density with a surface treatment agent containing 0.5 / 1.5 to 1.5 g / m ² per side, density of 0.60 g / cm ³ or less, and opacity of 92% or more Book paper.

  The low-density book paper according to the present invention has excellent opacity, surface smoothness, surface strength, and flexibility while having a low density.

In the present invention, a surface treatment agent containing 18 to 26% of ash and containing starch and styrene-butadiene latex in a ratio of 50/50 to 90/10 on a base paper mainly composed of chemical pulp is 0.1% per side. By applying 5 to 1.5 g / m ^2, it is possible to provide a low-density book paper having excellent pickability, piling, and powder falling during printing, and having excellent offset printability.

When the raw material is mainly chemical pulp, the smoothness and strength of the base paper will be high, but when adding a chemical that lowers the density, the internal bond strength will decrease greatly and the porous filling will have a low bulk specific gravity. In the case where the density is reduced by blending, the opacity can be maintained, but it is considered that the internal bond strength, the surface strength, and the surface smoothness are problematic.

In this invention, the surface treating agent which mix | blended starch and the styrene-butadiene type latex in the range of 50 / 50-90 / 10 is apply | coated in the range of 0.5-1.5 g / m < ² > per side.
If the ratio of styrene-butadiene latex in the surface treatment agent exceeds 50%, sufficient surface strength can be imparted. However, latex-derived wrinkles can cause paper breaks and defects in the drying process and calendar process after coating. Reduce productivity. When the ratio of the styrene-butadiene latex is less than 10%, the surface strength is insufficient, so that piling and powder falling cannot be suppressed, and the printing workability is remarkably lowered. In addition, water resistance is insufficient, and surface sizing agent, internal sizing agent, etc. need to be added to give offset printing suitability, which is disadvantageous in terms of cost.
If the coating amount of the surface treatment agent is more than 1.5 g / m ² , the low density and flexibility are impaired, which is not preferable. ^{On the other hand} , when the amount is less than 0.5 g / m ² , the surface strength and powder fall off are not preferable.

There is no restriction | limiting in particular in starch, For example, well-known starch, such as an oxidized starch, esterified starch, cationized starch, enzyme modified starch, aldehyde-ized starch, hydroxyethylated starch, is used.

In the present invention, the styrene-butadiene latex is a concentration gradient type latex in which the composition from the inside to the outside of the particle continuously changes or a core-shell type latex. The Tg of the latex is preferably -20 to 20 ° C. in consideration of the balance between the surface strength and Nepari. In particular, the concentration gradient type latex preferably has a surface layer Tg of 0 ° C. or higher.

There are no particular restrictions on the coating machine. For example, a known coating machine such as a two-roll size press coater, a gate roll coater, a blade coater, or a rod metering coater can be used. This is preferable because the amount of the ink impregnated into the paper layer is small, the coating amount can be reduced, and the influence on the flexibility is small.

In the present invention, the oil absorption amount of the base paper is 360 ml / 100 g to 500 ml / 100 g, the average particle diameter by laser method is 15 to 30 μm, and the standard of the distribution of the particle volume with respect to the particle diameter when the particle diameter (μm) is expressed logarithmically. It is preferable to contain 1.0-5.0 mass% of hydrated silicic acid whose deviation is 0.3-0.4.

In order to obtain high opacity, a high oil absorption of 360 to 500 ml / 100 g is preferable. For book paper printed on both sides, opacity after printing is also important. The oil absorption is measured by the method of JIS K 5101.

Moreover, the average particle diameter of the hydrated silicic acid of the present invention is 15 to 30 μm in average particle diameter measured by a laser method in consideration of the yield in suction during dehydration at the wire part. Those are preferred. There is a method of adding a yield improver in order to increase the yield, but there is a limit because increasing the addition rate impairs the texture. What is bigger than 30μm? Since the number of particles present in the paper decreases, the light scattering effect of hydrated silicic acid decreases and the opacity decreases, which is not preferable.

The hydrated silicic acid of the present invention preferably has a bulk specific gravity of 0.15 g / ml or less, more preferably 0.06 to 0.12 g / ml. The low bulk specific gravity occupies more volume in the paper, contributing to lower density and ink absorption.

Furthermore, the particle size distribution is important, and large particles exceeding 50 μm are not preferable because they not only deteriorate the surface properties of book paper but also lead to a powder-off phenomenon during printing. Also, small particles of less than 10 μm are not preferable because the yield is poor. The particle size distribution of the hydrated silicic acid used in the present invention is preferably sharp, and the smaller the standard deviation of the particle volume distribution relative to the particle size when the particle size (μm) is expressed in logarithm, the more preferable. However, hydrated silicic acid, which is an aggregate of primary particles, has a sharp distribution of primary particles of hydrated silica with a sharp distribution of secondary particles. It is estimated that the stability is inferior, and those having a standard deviation in the range of 0.3 to 0.4 considering the mechanical stability are preferred. Those in this range can maintain the particle state even when subjected to a share due to stirring, and thus are excellent in yield on paper and ink absorption in paper.

Furthermore, when the specific surface area at the primary particle level of the hydrated silicic acid is small, the bonding force between the particles decreases, and when the specific surface area is too large, the primary particles are small, and the secondary particle pressure is considered to break down. It is considered and not preferable.
The specific surface area of the hydrated silicic acid of the present invention is preferably 50 to 140 m ² / g. Further, the pore volume for absorbing the ink vehicle for improving opacity after printing is preferably 4.0 cc / g or more. In the present invention, the pore diameter and the corresponding pore volume are measured using a mercury porosimeter (type: Pore Sizer-9320, manufactured by Micromeritics). The pore volume is an integrated capacity having a pore diameter of 0.01 μm to 10 μm.
Here, the specific surface area is the surface area of all pores assuming that the pore shape is a geometric cylinder using a pore sizer 9230 (manufactured by Micromeritics), and the pressure was indented with the pressure within the measurement range. It is a value obtained from the relationship of mercury content. The pore diameter is also a median pore diameter obtained from an integral specific surface area curve using a pore sizer 9230 (manufactured by Micromeritec).

  The porous filler of the present invention has an average particle size of 15 to 30 μm, more preferably 10 to 2030 μm. When the average particle size of the porous filler exceeds 30 μm, the particle size distribution is deteriorated and the number of fine particles and coarse particles increases, and the internal strength and the surface strength may be lowered. In addition, the average particle diameter in the present invention is a value that is measured by a laser diffraction method using SALD2000J (manufactured by Shimadzu Corporation) and is 50% in volume integration. As the particle size distribution of the porous filler, the standard deviation (σ) is preferably 0.350 or less, and more preferably 0.300 or less. With such a particle size distribution, both coarse particles and fine particles are reduced, and better internal bond strength and surface strength can be obtained.

<Method for producing hydrated silicic acid>
Next, a method for producing hydrated silicic acid will be described. The alkali silicate aqueous solution used in the present invention is not particularly limited, but a sodium silicate aqueous solution or a potassium silicate aqueous solution is preferable. In the case of sodium silicate, the molar concentration of the aqueous alkali silicate solution is preferably selected from the range where the molar ratio (SiO ₂ / Na ₂ O) is 2.0 to 3.4. This alkaline silicate aqueous solution may contain particles that are hardly soluble in alkali. Specifically, calcium carbonate, magnesium hydroxide, magnesium oxide, magnesium carbonate, nickel carbonate, barium carbonate, calcium hydroxide, manganese hydroxide, magnesium, manganese, potassium manganate, iron, nickel, zinc oxide, calcium oxide, Manganese oxide etc. are mentioned.

  These hydrated silicic acids are prepared by adding 20-50% of the amount of mineral acid required for neutralizing the alkali silicate in the operation of neutralizing the alkali silicate aqueous solution by adding a mineral acid. It is necessary to first add at ˜60 ° C., then raise the temperature to 70 ° C. or higher and then provide aging time if necessary, and add the remaining mineral acid (second mineral acid) necessary for neutralization Become. It is desirable to add the neutralizing mineral acid over a sufficient time. It is intended not to cause a large pH change locally. However, since the concept of production efficiency is important in actual situations, it is desirable to devise so that the neutralization reaction can be completed within 300 minutes. As the mineral acid used when the hydrated silicic acid is precipitated in the present invention, known ones can be used without any limitation, and these may be used alone or in combination of two or more. Specific examples of the mineral acid include hydrochloric acid, sulfuric acid, nitric acid and the like, and sulfuric acid is easily used and is preferably used because it is relatively inexpensive. The concentration of the mineral acid is not particularly limited, but generally may be selected from the range of 10 to 30% by weight. Moreover, the pH of the slurry containing the product after all the mineral acid has been added is adjusted to a range of 2 to 6.5, preferably 4 to 6.

  By applying a stirring load of 150 to 300 kJ per kg of hydrated silicic acid from the start of the addition of the first mineral acid to the start of the addition of the second mineral acid, the hydrated silicic acid characterized by the above physical properties is collected. It can be obtained efficiently. As the equipment used for stirring, it is possible to use a mixer used in the usual manner, such as a propeller, a turbine, a paddle, an anchor, and a ribbon as a stirring blade alone or in appropriate combination, depending on the conditions of synthesis. What is necessary is just to select so that the said stirring load may be achieved. A homomixer or various mills can also be combined. Of course, a baffle plate may be provided in the agitation tank to cause turbulent flow, or a part of the reaction solution may be taken out and applied with a load such as an in-line mixer to return to the tank. Although the rotational speed also depends on the blade diameter and reaction conditions, the blade peripheral speed is preferably in the range of 100 to 600 m / min.

  In this process, the reaction in which the silicic acid content in the aqueous alkali silicate solution precipitates as the secondary particles is the most active, so improving the uniformity of the reaction system makes the properties of the primary and secondary particles uniform. Result. Giving a stirring load of 150 kJ per kg of silicic acid is an operation necessary to achieve the uniformity. Furthermore, if an agitation load exceeding 300 kJ is applied, the formed secondary particles are destroyed, resulting in a hydrated silicic acid having a poor yield such that the particle size of the final product falls below, for example, 15 μm. . Furthermore, it may deviate from the effect of the present invention in which the standard deviation of the particle volume distribution with respect to the particle size when the particle size (μm) is expressed in logarithm is limited to a range of 0.3 to 0.4. This is not preferable.

  In the mineral acid solution and / or the metal salt solution of the mineral acid used in the present invention, examples of the mineral acid include hydrochloric acid, sulfuric acid, nitric acid and the like, and the metal salt of the mineral acid includes a sodium salt of the mineral acid, A potassium salt, a calcium salt, an aluminum salt, etc. are mentioned. Among these, sulfuric acid and aluminum sulfate are preferable from the viewpoint of cost and handling, and an aqueous solution is preferable.

  The addition amount of the mineral acid solution and / or the metal salt solution of the mineral acid is in the range of 95 to 150% of the theoretically required neutralization amount, and the amount for adjusting the pH of the resulting slurry to be in the range of more than 2.5 and not more than 10 It is preferable that When the addition amount of the mineral acid solution and / or the metal salt solution of the mineral acid is less than 95% of the theoretically required neutralization amount or the pH of the resulting slurry exceeds 10, the alkaline silicate aqueous solution as the raw material There is a lot of waste. On the other hand, if it exceeds 150% of the theoretically necessary neutralization amount or the pH of the resulting slurry is 2.5 or less, the filtrate pH generated when concentrating the porous filler becomes too low and difficult to handle. Become.

At the time of precipitation of the silicon-containing particles, it is preferable to stir at a speed of 5 to 15 m / sec with a stirring device. Here, the peripheral speed is an index of the shearing force, and the shearing force increases as the peripheral speed increases. When the peripheral speed is less than 5 m / sec, the shearing force is too small, and even when alkali-resistant fine particles are included, it may be difficult to obtain an appropriate average particle size and narrow particle size distribution.
On the other hand, when the peripheral speed at the time of precipitation exceeds 15 m / sec, the shearing force becomes too large, the particle size of the porous filler becomes small, and the internal bond strength may be lowered when blended in paper. In addition, the load power increases and the equipment costs increase.
As the stirring device, an agitator, a homomixer, a pipeline mixer or the like is preferable. Although it is possible to use a pulverizer such as a ball mill or a sand grinder, it is not preferable because problems such as an increase in fine particles and a thickening of the slurry tend to occur.

The mineral acid solution and / or the metal salt solution of the mineral acid may be added to the alkali silicate aqueous solution all at once, but since it has a better particle size distribution, it is divided into two or more stages. It is preferable to add.
When adding the mineral acid solution and / or the metal salt solution of the mineral acid in two or more stages, since the particle size distribution is particularly good, the temperature of the first stage alkali silicate aqueous solution is set to 20 to 70 ° C., In the second and subsequent stages, it is preferable to set the temperature to 70 ° C. or higher. In the first stage, it is preferable that the addition amount of the mineral acid solution and / or the metal salt solution of the mineral acid is in the range of 10 to 50% of the theoretically required neutralization amount.

In both the first and second stages, the mineral acid solution and / or the metal salt solution of the mineral acid can be added all at once or continuously to the alkali silicate aqueous solution.
After completion of the addition of the mineral acid solution and / or the metal salt solution of the mineral acid, an aging step of stirring while maintaining the temperature at the time of addition may be included as necessary.

  When adding the mineral acid solution and / or the metal salt solution of the mineral acid in one stage, the temperature of the alkali silicate aqueous solution is preferably 60 ° C. to the boiling point of the solution, and 75 ° C. to the boiling point of the solution. More preferably. The mineral acid solution and / or the metal salt solution of the mineral acid can be added to the alkali silicate aqueous solution all at once or continuously.

<Addition of hydrated silicic acid to pulp>
Next, when the hydrated silicic acid according to the present invention is added as a filler to a pulp raw material, it imparts high opacity, particularly opacity after printing, to paper obtained by papermaking. The reason is considered to be that the ability to suppress the penetration of ink printed on paper is increased by increasing the amount of voids inside the particles and increasing the amount of oil absorption.

  By adding the hydrated silicic acid-based filler according to the present invention to the pulp raw material during papermaking, high opacity, in particular, opacity after printing, is imparted to the obtained paper by 10 μm or less inside the particles. It is thought that the oil absorption increased as the pore volume of the pores increased, and the ability to suppress the penetration of ink printed on paper increased.

  The raw paper raw pulp in the present invention is mainly chemical pulp, and hardwood bleached kraft pulp (LBKP) is used. The freeness of the pulp is not particularly limited, but the low density bulky book paper of the present invention preferably has a Canadian standard freeness (CSF) in the range of 400 to 500 ml. Freeness outside this range is not preferable because it is impossible to achieve both density and printability.

When making paper, add the above-mentioned hydrated silicic acid in an amount of 1.0 to 5.0% by mass, and add other fillers so that the filler content in the paper is 18.0 to 26.0% by mass. There are no other restrictions, and it is possible to make any of acid, neutral and alkaline paper using a known paper machine such as a long web paper machine, on-top wire paper machine, gap former, etc. It is also possible to add paper-making chemicals such as a density-reducing chemical, a sizing agent, a paper strength enhancer, a yield improver, a wet paper strength enhancer, and a dye.

  The base paper thus obtained is finished by passing the paper through various known and official finishing devices such as a super calender, gloss calender, soft calender and the like. In the case of the present invention, for the purpose of increasing the bulk, it is necessary to carry out a finishing work that is easy to smooth and glossy if necessary, and a method of finishing by passing through a calendar equipped with a hard resin roll or the like. Preferably, the linear pressure is preferably 50 kg / cm or less.

The low-density book paper of the present invention has a density of 0.6 g / cm ³ or less and an opacity of 92% or more and a whiteness of 77.0% or more.
Furthermore, it has the rigidity that does not impair the workability of the printing press and the flexibility to easily turn it as a book.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to only these examples. Moreover, unless otherwise indicated, the part and% in an example show a mass part and mass%, respectively. The addition rate of a filler and a chemical | medical agent shows solid content weight% with respect to dry pulp weight.
The following physical properties were measured for the low density book papers as Examples and Comparative Examples obtained as described below, and the results are shown in Table 1.

Physical properties of hydrated silica (oil absorption)
Measured according to JIS K 5101.
(Standard deviation of average particle size and particle size distribution)
It is a value measured by a laser diffraction scattering method using SALD2000J (manufactured by Shimadzu Corporation) and is 50% in volume integration.
The standard deviation is the standard deviation of the particle volume distribution relative to the particle size when the particle size is expressed in logarithm.
(Pore diameter and pore volume)
The pore diameter is a median pore diameter obtained from an integral specific surface area curve using a pore sizer 9230 (manufactured by Micromeritics), and the pore volume is also measured by a mercury intrusion method using a pore sizer 9230. The value integrated at 0.01 μm to 10 μm.
(Specific surface area)
Using a pore sizer 9230 (manufactured by Micromeritics), the surface area of all pores assumed to be a geometric cylinder is obtained from the relationship between the pressure in the measurement range and the amount of mercury injected.

Physical properties of book paper (ash content)
It was measured by the method described in JIS P8251.
(Whiteness)
The whiteness in the present invention was measured by a method described in ISO 3688 using a spectral whiteness colorimeter (manufactured by Suga Test Instruments Co., Ltd.).
(Opacity)
Conforms to JIS P8149.
(Smoothness)
JAPAN TAPPI No. 5-B (Oken type smoothness) was measured.
(Clark stiffness)
As a measure of flexibility, Clark stiffness (JIS P8143) is measured. Since the paper with the same paper thickness and higher basis weight has lower Clark stiffness, the following correction formula was adopted.
(Stiffness correction value) = (Clark stiffness measurement value) × (actual basis weight) × 9.81 / 100 ²
The lower this number, the more flexible the paper.

(Surface strength, powder removal)
With a sheet-fed offset printing press (model: Heidelberg SM102-6-P-LX, ink used: Dainippon Ink, Fusion GS type ink, indigo, red, yellow, printing speed: 10,000 sheets / h) After continuous printing of 2000 sheets, the surface strength was evaluated (visually evaluated for vessel picking and piling of printed matter), and the state of powder falling on the blanket was visually evaluated. Using [Example 1] as a standard (score 3), the surface strength and powder loss were rated 5 for superior, 4 for slightly superior, 2 for inferior, and 1 for inferior.

[Example 1]
100 parts of hardwood bleached kraft pulp was beaten with a refiner and adjusted to 460 ml CSF, 2% cationized starch (P3Y, made by Piraab Starch Co. Ltd), 1.5% sulfuric acid band, paper strength enhancer (PS1263, manufactured by Arakawa Chemical Co., Ltd.) 0.15%, paper thickness improver (PT8104, manufactured by Seiko PMC Co., Ltd.) 0.7%, oil absorption as a filler is 380 ml / 100 g, average particle size 20 μm, particle size distribution Add 2.0% hydrated silicic acid (original product 1) with a standard deviation of 0.33 and 30% light calcium carbonate (original product), adjust the papermaking pH with sulfuric acid, and turn on the resulting paper stock Paper was made with a top wire paper machine. Surface treatment agent prepared by adjusting starch (P4N, manufactured by PIRAAB STARCH Co. Ltd) concentration gradient type styrene-butadiene latex (PA-5021C, manufactured by Nippon A & L Co., Ltd.) at a ratio of 75/25 with a gate roll coater per side .5 g / m ² was applied on both sides and soft calendered to obtain a high quality book paper with a basis weight of 74.8 g / m ² and a density of 0.58 g / cm ³ .

Example of hydrated silicic acid production (own product 1)
240 g of commercially available JIS No. 3 sodium silicate aqueous solution (manufactured by Tokuyama, solid concentration 30%) was diluted to 1000 g with pure water, and the hydrated silicic acid (silicon dioxide) concentration was 72 g / kg, and placed in a 2 L stainless steel beaker. At 50 ° C., 17.9 g of anhydrous sodium sulfate was added. While stirring with a three-one motor, 72 g of sulfuric acid (concentration 20%) corresponding to 40% of the total amount of acid required for neutralizing sodium silicate was continuously added over 16 minutes. After the addition of sulfuric acid was completed, the temperature was raised to 90 ° C. over 25 minutes with stirring. Stirring was continued as it was at this temperature, and aging was performed for 9 minutes, and it was confirmed that the amount of electric power so far was 200 kJ / kg per unit weight of the final product. Subsequently, 108 g of sulfuric acid corresponding to 60% of the total acid requirement was continuously added over 20 minutes, followed by aging for another 20 minutes. (Own products 2 to 4 are manufactured by adjusting the stirring time and the split addition ratio of sulfuric acid)

[Example 2]
100 parts of hardwood bleached kraft pulp was beaten with a refiner, adjusted to 470 ml CSF, 2% cationized starch (P3Y, made by PIRAAB STARCH Co. Ltd), 1.5% sulfuric acid band, paper strength enhancer (PS1263, Arakawa Chemical Co., Ltd.) 0.15%, paper thickness improver (PT8104, Seiko PMC Co., Ltd.) 0.8%, oil absorption as a filler is 380 ml / 100 g, average particle size 20 μm, particle size distribution Add 2.0% hydrated silicic acid (original product 1) with a standard deviation of 0.33 and 32% light calcium carbonate (original product), adjust the papermaking pH with sulfuric acid, and turn on the resulting paper stock Paper was made with a top wire paper machine. A surface treatment agent prepared by adjusting starch (P4N, manufactured by PIRAAB STARCH Co. Ltd) and core-shell type styrene-butadiene latex (T-2635 (manufactured by JSR)) at a ratio of 50/50 was 0.6 g / m ² per side. A high-quality book paper having a basis weight of 74.1 g / m ² and a density of 0.57 g / cm ³ was obtained by applying to both sides and performing a soft calendar process.

[Example 3]
The surface treatment agent was adjusted to a ratio of 90/10 starch (P4N, manufactured by PIRAAB STARC Co. Ltd) and concentration gradient styrene-butadiene latex (PA-5021C, manufactured by Nippon A & L Co., Ltd.) to 1.0 g per side. A high-quality book paper having a basis weight of 74.9 g / m ² and a density of 0.58 g / cm ³ was obtained in the same manner as in [Example 2] except that / m ^{2 was} applied.

[Comparative Example 1]
100 parts of hardwood bleached kraft pulp was beaten with a refiner and adjusted to 460 ml CSF, 2% cationized starch (P3Y, made by Piraab Starch Co. Ltd), 1.5% sulfuric acid band, paper strength enhancer (PS1263, manufactured by Arakawa Chemical Co., Ltd.) 0.15%, paper thickness improver (PT8104, manufactured by Seiko PMC Co., Ltd.) 0.7%, oil absorption as a filler is 380 ml / 100 g, average particle size 20 μm, particle size distribution Add 2.0% hydrated silicic acid (original product) with a standard deviation of 0.51 and 30% light calcium carbonate (original product 2), adjust the papermaking pH with sulfuric acid, and turn on the resulting paper stock Paper was made with a top wire paper machine. Surface treatment agent prepared by adjusting starch (P4N, manufactured by PIRAAB STARCH Co. Ltd) concentration gradient type styrene-butadiene latex (PA-5021C, manufactured by Nippon A & L Co., Ltd.) at a ratio of 75/25 with a gate roll coater per side 0.0 g / m ² was applied on both sides, and a soft calendar process was performed to obtain a high-quality book paper with a basis weight of 74.8 g / m ² and a density of 0.60 g / cm ³ .

[Example 4]
100 parts of hardwood bleached kraft pulp was beaten with a refiner, adjusted to 470 ml CSF, 2% cationized starch (P3Y, made by PIRAAB STARCH Co. Ltd), 1.5% sulfuric acid band, paper strength enhancer (PS1263, Arakawa Chemical Co., Ltd.) 0.15%, paper thickness improver (PT8104, Seiko PMC Co., Ltd.) 0.8%, oil absorption as a filler is 350ml / 100g, average particle size 20μm, particle size distribution Add 2.0% hydrated silicic acid (original product 3) with a standard deviation of 0.40 and 32% light calcium carbonate (original product), adjust the papermaking pH with sulfuric acid, and turn the resulting paper on top Paper was made with a wire paper machine. A surface treatment agent prepared by adjusting starch (P4N, manufactured by PIRAAB STARCH Co. Ltd) and core-shell type styrene-butadiene latex (T-2635 (manufactured by JSR)) at a ratio of 75/25 was 0.4 g / m ² per side. A high-quality book paper having a basis weight of 74.1 g / m ² and a density of 0.59 g / cm ³ was obtained by applying to both sides and carrying out a soft calendar process.

[Comparative Example 2]
A basis weight of 74.3 g / m ² and a density of 0.58 g / cm ³ were obtained in the same manner as in [Example 1] except that the surface treatment agent of [Example 1] was applied to 0.4 g / m ² per side. I got a good quality book paper.

[Comparative Example 3]
A basis weight of 79.6 g / m ² and a density of 0.61 g / cm ³ were obtained in the same manner as in [Example 1] except that the surface treatment agent of [Example 1] was applied at 1.6 g / m ² per side. I got a good quality book paper.

[Comparative Example 4]
High-quality book paper of 75.5 g / m ² and density of 0.59 g / cm ^{3 in} the same manner as in [Example 2] except that the surface treatment agent of [Example 2] is applied at 0.4 g / m ² per side. Got.

[Comparative Example 5]
As a filler, the amount of oil absorption 380 ml / 100 g, the average particle size 20 μm, the standard deviation of the particle size distribution is 0.51 hydrated silicic acid (own product 2) 2.0%, and the surface treatment agent of [Example 2] per side A high-quality book paper of 80.0 g / m ² and density of 0.62 g / cm ³ was obtained in the same manner as in [Example 2] except that 1.7 g / m ^{2 was} applied.

[Comparative Example 6]
To a pulp slurry obtained by beating 100 parts of hardwood bleached kraft pulp with a refiner, 1.6% cationized starch (P3Y, manufactured by PIRAAB STARCH Co. Ltd), 1.5% sulfuric acid band, paper strength enhancer (PS1263, Arakawa Chemical Co., Ltd.) 0.15%, paper thickness improver (PT8104, Seiko PMC Co., Ltd.) 0.7%, oil absorption 380ml / 100g as filler, average particle size 20μm, standard deviation of particle size distribution After adding 2.0% hydrated silicic acid (self product 4) and 32% light calcium carbonate (original product) and adjusting the papermaking pH with sulfuric acid, the resulting stock is turned on-top wire papermaking. Paper is made with a machine, and starch (P4N, manufactured by PIRAAB STARCH Co. Ltd) is applied as a surface treatment agent with a gate roll coater at 0.6 g / m ² per side. A high-quality book paper having a basis weight of 74.8 g / m ² and a density of 0.58 g / cm ³ was obtained by calendering.

[Comparative Example 7]
A basis weight of 75.2 g / m ² and a density of 0.58 g / cm ³ were obtained in the same manner as in [Comparative Example 6] except that the surface treatment agent of [Comparative Example 6] was applied to each surface at 1.2 g / m ² . I got a good quality book paper.

[Comparative Example 8]
100 parts of hardwood bleached kraft pulp was beaten with a refiner, adjusted to 470 ml CSF, 2% cationized starch (P3Y, made by PIRAAB STARCH Co. Ltd), 1.5% sulfuric acid band, paper strength enhancer (PS1263, Arakawa Chemical Co., Ltd.) 0.15%, paper thickness improver (PT8104, Seiko PMC Co., Ltd.) 0.8%, oil absorption 380ml / 100g as filler, average particle size 20μm, particle size distribution Add 2.0% hydrated silicic acid (original product 1) with a standard deviation of 0.33 and 32% light calcium carbonate (original product) and adjust the papermaking pH with sulfuric acid. Paper was made with a wire paper machine. A surface treatment agent prepared by adjusting starch (P4N, manufactured by PIRAAB STARCH Co. Ltd) and core-shell type styrene-butadiene latex (T-2635 (manufactured by JSR)) at a ratio of 40/60 is 1.0 g / m ² per side. A high-quality book paper having a basis weight of 74.1 g / m ² and a density of 0.59 g / cm ³ was obtained by applying to both sides and carrying out a soft calendar process.

[Comparative Example 9]
100 parts of bleached kraft kraft pulp was beaten with a refiner and adjusted to 470 ml CSF with a slurry of 2% cationized starch (P3Y, made by PIRAAB STARCH Co. Ltd), 1.5% sulfate band, increased paper strength Agent (PS1263, manufactured by Arakawa Chemical Co., Ltd.) 0.15%, paper thickness improver (PT8104, manufactured by Seiko PMC Co., Ltd.) 0.8%, oil absorption as a filler is 380 ml / 100 g, average particle size 20 μm, particle size Add 2.0% hydrated silicic acid (original product 1) with a standard deviation of 0.33 and 24% light calcium carbonate (original product) and adjust the papermaking pH with sulfuric acid. Paper was made with an on-top wire machine. A surface treatment agent prepared by adjusting starch (P4N, manufactured by PIRAAB STARCH Co. Ltd) and core-shell type styrene-butadiene latex (T-2635 (manufactured by JSR)) at a ratio of 40/60 is 1.0 g / m ² per side. A high-quality book paper having a basis weight of 74.1 g / m ² and a density of 0.56 g / cm ³ was obtained by applying to both sides and carrying out a soft calendar process.

Claims (1)

Chemical pulp as the main pulp material, oil absorption is 360ml / 100g-500ml / 100g, average particle diameter by laser method is 15-30μm, particle diameter (μm) is the logarithm of particle volume relative to particle diameter 50% of starch and styrene-butadiene latex are contained on a base paper containing 1.0 to 5.0% by mass of hydrated silicic acid having a standard deviation of distribution of 0.3 to 0.4 and an ash content of 18 to 27%. The surface treatment agent containing at a ratio of / 50 to 90/10 is applied to 0.5 to 1.5 g / m ² per side, the density is 0.60 g / cm ³ or less, and the opacity is 92% or more. Characteristic low-density book paper.