JPH09176985A - Production of filler added paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method producing a filter added paper having a high opacity a white paper and a high after-printing opacity while maintaining strength threrof. SOLUTION: This method producing a filler added paper is to make a paper by adding a hydrated silicic acid slurry to a raw material of paper containing a pulp, a sedimentary calcium carbonate, a heavy-type calcium carbonate or their mixture. In this case, the hydrated silicic acid satisfied the following particle characteristics of (A) to (C):(A) 250-350ml/100g oil absorbing amount; (B) 4.6-6.0cc/g total pore volume and a mean pore radius is in the range of 200-400Å; and (C) a mean particle diameter is in any of the ranges of 3.0-15μm measured by a laser method, 2.0-4.0μm measured by a Coulter method and 0.5-3.5μm measured by a centrifugal sedimentation method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a paper with a filler internally added, and in particular, it has a high whiteness and is excellent not only in the opacity of white paper but also in the opacity after printing and with a small decrease in paper strength. The present invention relates to a manufacturing method of.

[0002]

2. Description of the Related Art From the standpoint of protecting forest resources and reducing environmental load including the problem of garbage, it is necessary to reduce the weight of paper. This is because the weight reduction reduces the weight of wood fibers required to transmit the same amount of information, and the amount of waste also decreases. Especially for newsprint, the basis weight is 50g / m ² to 43,
Some have moved to 40 or less. In such weight reduction, the optical properties of the paper, particularly the opacity and the opacity after printing, deteriorate, and so-called "strikethrough" becomes a problem. This problem applies not only to newsprint paper, but to general lightweight printing paper as well, but these papers are bulky (thickness) due to their light weight.
Is also a big problem. Conventionally, hydrated silicic acid called white carbon and calcined clay have been used to solve these problems. The hydrated silicic acid for internal addition is a porous filler having a primary particle size of about 0.01 to 0.05 μm, and usually agglomerates to a higher degree and has a particle size of 5 to 10 μm when measured by a Coulter counter. Since it has excellent properties, it is effective in preventing strike-through caused by the penetration of oil-based printing ink. However, since the particle size is relatively large, the ability to scatter incident light is low. That is, although the ability to maintain the opacity after printing is maintained, the ability to improve the opacity of white paper is small. On the other hand, other internal fillers for papermaking typified by titanium dioxide have a small particle size and a high ability to scatter light, but a low ability to suppress penetration of printing ink. Usually, for printing paper such as newsprint, these fillers are used alone or in combination so as to satisfy the required quality. In addition, since the specific gravity of the inorganic filler is generally higher than the apparent specific gravity of the cellulose fiber, the higher the filler content in the paper, the higher the density of the paper and the lower the bulk. Since the above-mentioned white carbon, hydrated silicate of the same kind, and special precipitated calcium carbonate are porous, the bulk increases as the filler content in the paper increases. Precipitating calcium carbonate or fine ground heavy calcium carbonate is a requirement for papermaking in a neutral or alkaline range, but it has the advantage of excellent recyclability and storage stability. And improve opacity.

[0003]

However, in the case of extremely reducing the weight as described above, it is not possible to achieve both the opacity of blank paper and the opacity after printing by any combination of conventional fillers. In addition, since the filler such as white carbon has a large particle diameter, it significantly inhibits the interfiber bond, resulting in a decrease in strength. Further, since calcium carbonate is a crystal and has little oil absorption, it has little effect of preventing strike-through.Therefore, for the purpose of preventing strike-through, if the above white carbon is added in papermaking in a neutral or alkaline range, Part of the silicic acid dissolves in the alkali and the oil absorption is significantly reduced. The present invention has a large pore volume,
Also, paying attention to the fact that hydrated silicic acid in the form of extremely fine particles is superior to the existing hydrated silicic acid and hydrated silicate in the effect of preventing strike-through of paper, and calcium carbonate has high whiteness and high opacity. The present invention provides a method for producing a paper having high opacity of white paper and high opacity after printing while maintaining strength by adding.

[0004]

The hydrated silicic acid used to achieve the above object is a hydrated silicic acid obtained by neutralizing an aqueous solution of sodium silicate with a mineral acid, and has an oil absorption of 250-250.
350ml / 100g, total pore volume 4.0-6.0c
c / g, the average pore radius is in the range of 200 to 400 angstrom, and the average particle size is 3.0 to 15 μm as measured by the laser method, 2.0 to 4.0 μm as measured by the Coulter method, or centrifugal. A characteristic feature of the composition is that it has particle characteristics in the range of 0.5 to 3.5 μm as measured by the sedimentation method.

As the respective characteristic values of the hydrated silicic acid according to the present invention, the values obtained by the following measuring methods are used.

(1) Oil absorption; according to JIS K5101 method (2) BET specific surface area; powdered hydrated silicic acid sample 0.0
5 to 0.1 g of "Flow soap 23 manufactured by Shimadzu Corporation
00S / N type "and degassing condition at 300 ° C for 30 minutes.

(3) Total pore volume: 0.05 g of powdered hydrated silicic acid sample was degassed under vacuum for 30 minutes, then mercury was injected, and the pore volume was pressurized to 1 to 1900 bar to pressurize the pore volume with mercury. Method (apparatus used: Carlo Erba Co., Ltd., mercury porosimeter 200 type). The measuring pressure corresponds to a pore radius of 75000 angstroms to 39 angstroms.

(4) Average pore radius; determined from the specific surface area S and the total pore volume V obtained during the measurement of the total pore volume as a value calculated by radius (r) = V / S.

(5) Particle size distribution measurement; (a) Laser method; A sample slurry of hydrated silicic acid was added drop-wise in pure water containing 0.2% by weight of sodium hexametaphosphate dispersant to form a uniform dispersion. Particle size measurement is performed using a method particle size measuring device [apparatus used; manufactured by Nikkiso Co., Ltd., "Microtrack 9220FRA type is used].

(B) Coal tar method: Sample hydrated silica silicate slurry was added dropwise to 3 drops of 50 ml of pure water containing 0.2% by weight of sodium hexametaphosphate and ultrasonically dispersed for 3 minutes to prepare a uniform dispersion as Coulter Counter TA type. (Coulter Electronics Co., Ltd.) is used to measure the particle size.

(E) Centrifugal sedimentation method: A sample hydrated silicic acid slurry is dropped into a pure water solution containing 0.2% by weight of sodium hexametaphosphate and measured as a measurable concentration (apparatus used: "Micron. Photosizer SK
N-1000 type "is used.) A portion having a particle diameter of 1 ml or less is measured by centrifugation, and a portion having a particle diameter of 1 ml or more is measured by gravity sedimentation.

The particle properties of the finely hydrated silicic acid according to the present invention are as follows:
First, it is characterized by a total pore volume of 4.0-6.0 cc / g and an average pore radius in the range of 200-400 Angstroms. This total pore volume is at a higher level than that of hydrated silicic acid obtained by a conventional method of wet-milling a reaction-completed slurry, which is 4 cc / g or less, and has a porous structure. . Therefore, when it is used as a filler for paper, it effectively absorbs the ink liquid and thus functions effectively. If the total pore volume is less than 4.0 cc / g, the absorption capacity is insufficient and the strike-through preventing effect is not effectively imparted, and if it exceeds 6.0 cc / g, other properties are impaired. Invite.

This total pore volume is related to the pore radius of the pores distributed in the tissue, but in practice the pore radius is 100.
Since the adsorption equilibrium water is always filled in the micropores smaller than angstrom, it does not function for adsorption, and the adsorption power becomes weaker than 104 angstroms and does not contribute to the adsorption ability. The hydrated silicic acid of the present invention having a total pore volume in the range of 4.0 to 6.0 cc / g has an average pore radius of approximately 100 to 40.
In the range of 0 Å (center pore radius of 50% pore volume is 1500 to 3500 Å),
It is located in the range of superior adsorptivity compared to conventional hydrated silicic acid. Therefore, it is suitable not only for paper fillers but also for various applications as described later.

The second requirement for the particle characteristics of the finely hydrated silicic acid according to the present invention is that the average particle size of the finely hydrated silicic acid is 3.0 to 15 μm as measured by the laser method, and the value measured by the Coulter method. It is a point in any range of 2.0 to 4.0 μm or 0.5 to 3.5 μm as measured by the centrifugal sedimentation method. The particle size of hydrated silicic acid shows different measured values depending on the laser method, the Coulter method and the centrifugal sedimentation method, which is considered to be because the silicic acid particles are porous and strongly hydrated.

As described above, the hydrated silicic acid according to the present invention is characterized in that it is finer particles than conventional ones, and tends to take a particularly small value when measured by the centrifugal sedimentation method. Further, the reason why the value is relatively large in the measurement by the laser method is that particles having a size of 1 μm or less tend to be transparent and cannot be detected, which is significant for evaluating the particle size of relatively large secondary particles. . Further, the hydrated silicic acid according to the present invention is also characterized in that the oil absorption amount is in the range of 250 to 350 ml / 100 g in combination with the above-mentioned particle characteristics, which is a relatively larger value than the conventional one. To take. This characteristic is also one of the preferable characteristics as a paper filler.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A hydrated silicic acid having the above-mentioned particle properties is produced by adding mineral acid to an aqueous solution of sodium silicate to produce hydrated silicic acid by a neutralization reaction.
After addition the reaction system temperature below the boiling point of ₂ as a 6-10% by weight of sodium silicate in the neutralization equivalent of the amount of mineral acid equivalent to 30 to 50% 70 ° C. or higher, a strong shearing force within the aging time First to perform a thorough wet crushing process based on
The second step in which a substantial amount of the mineral acid is added at a temperature higher than the temperature of the step and the previous step and the mixture is aged to precipitate almost all the amount of silica, and the pH of the slurry is adjusted to 5 by adding the mineral acid. It is manufactured by a process consisting of a third step of adjusting to the range of 3.

The first step is a step of adjusting the concentration of an aqueous solution of sodium silicate and heating it, adding the first stage mineral acid, and performing wet pulverization and aging. Sodium silicate solution is SiO ₂ / Ma ₂ O
It is preferable that the molar ratio is 2.9 to 3.4, and the silica concentration must be set in the range of 6 to 10 weight percent. If the silica concentration exceeds 10 weight percent, uniform stirring cannot be performed when the viscosity increases during the first step, and silica having good particle characteristics cannot be obtained. At a low concentration below 6 weight percent, the production efficiency deteriorates.
The concentration-adjusted sodium silicate solution is heated from 70 ° C. to a temperature range below the boiling point of the solution. If the temperature is lower than 70 ° C., the deposition rate of silica becomes slow and it takes a long time to complete the reaction in the first stage.

Sulfuric acid is preferably used as the mineral acid for the neutralization reaction. The concentration of sulfuric acid is not particularly limited, but if it is too thin, the reaction system becomes thin and the capacity becomes too large, which is not industrial. High-concentration 98% sulfuric acid has a large calorific value and can be advantageously used in terms of energy, if sufficient mixing can be performed at the addition position. The addition amount of the mineral acid in the first step is set in the range of 35 to 50% of the neutralization equivalent of sodium silicate. This addition amount range is related to the structural properties of hydrated silicic acid. Even if it is less than 35%, it is 50%.
Even if it exceeds the above range, the high structural property of the precipitated silica is impaired and the strike-through preventing effect and the yield are reduced when it is used as a filler for paper. The time required for the addition is relatively short for 5 to 20 minutes, and it is preferable to complete the addition before the precipitation of silica. Further, the higher the temperature and the concentration of silica, and the larger the amount of mineral acid added, the more the silica is deposited in a shorter time, so it is desirable to adjust the addition rate according to these conditions. If added within 5 minutes, the constitution of a uniform reaction system becomes insufficient.

In the first step, a particularly important operating requirement is that, in addition to the above reaction conditions, the addition of mineral acid is followed immediately by thorough wet milling based on strong shear forces. The wet crushing has a crushing effect even after the silica is precipitated after the addition of the mineral acid, but it is preferable to start the precipitation of silica or immediately before that. According to the research conducted by the inventors, it was found that crushing from the beginning of precipitation is effective. Therefore, the crushing will proceed at the same time as the aging treatment performed after the addition of the mineral acid. This process step in the prior art is called a maturation operation, and was usually applied only to promote the precipitation of silica by continuing the normal stirring operation under heating for a predetermined time. By carrying out thoroughly, the reaction system becomes extremely uniform, and the pulverization efficiency is remarkably improved to produce preferable particles. The aging time varies depending on the temperature, but it is 80 ℃
2 to 3 hours, and 90 ° C for 1 to 2 hours. The wet crushing is completed within the aging time and is not performed after the second step. Therefore, the aging in this step will occur between the complete milling process after partial neutralization.

Here, thorough wet pulverization means an operation of using a pulverizer or a disperser capable of applying a strong shearing force to prevent the agglomeration of silica particles produced as much as possible. Therefore, depending on the crusher used, it is desirable to continuously and repeatedly perform crushing treatment throughout the aging time. It is particularly preferable that the silica particles (dispersion degree) produced in this step have an average particle diameter of 2.0 to 1.0 μm by the Coulter method.

The pulverizer used for wet pulverization includes a ball mill in a broad sense such as a ball mill and a rod mill, a medium milling type pulverizer such as a tower mill, attritor, satry mill, sand grinder, and annula mill, a colloid mill, a homomixer, and an in-line mill. And a high speed rotary crusher. Since the silica particles precipitated in the present invention are extremely fine, and particularly the silica precipitated in the first step is easily crushed, it can be crushed with a disperser or an emulsifier in addition to the crusher described above. Can be used in combination with a crusher.

In the second step, while maintaining the slurry temperature from 80 ° C. to the boiling point of the solution or lower, at a temperature of the temperature of the previous step or higher, a substantial residual amount of mineral acid is dividedly added as a second stage and almost the entire amount is added. In this step, the silica is deposited to strengthen the connection of the silica particles deposited in the first step. That is, it is preferable to control the neutralization rate by the mineral acid in this step so that the neutralization rate is 80 to 95% as the first-stage addition, and the addition is performed over about 15 to 30 minutes. After the addition, in order to complete the reaction, it is preferable to perform aging for a while under a normal boundary balance.

The particle size of the final hydrated silicic acid after the second step is surprisingly substantially the same as that after the first step. As described above, the fact that the particle diameter does not change in the second step means that nucleation, particle growth, particle aggregation in the first step,
This shows that the hydrated silicic acid having a high structure having the above-mentioned characteristics is synthesized by the smooth progress of the control of the aggregate diameter by thorough wet pulverization and the strengthening of the bond in the aggregated particles in the second step. Therefore, the crushing process after the second step is not performed. The reason for this is that it breaks the highly structured silica structure that has been formed. Further, the slurry viscosity is high in the stage of the first step, but after the second step, the slurry viscosity is reduced to about 1/5, which is advantageous for handling.

The third step is a step of adjusting the pH of the slurry to a range of 5 to 3 by further adding a mineral acid subsequent to the second step. The addition of the mineral acid at this stage causes the pH component to return due to the elution of the alkaline component contained in the hydrated silicic acid, and since the change in this pH range is large, it takes about 60 to 60 minutes to slowly add the acid. It is preferable to carry out. Therefore,
The operation difference between the second step and the third step is only the addition rate of the mineral acid, and the other conditions are substantially the same. It is also a good idea to use low concentrations of sulfuric acid to precisely adjust the pH. Note that the addition of the mineral acid here is exclusively for adjusting the pH of the reaction system and the reaction is substantially completed in the previous step. Therefore, the addition amount is usually at most 20 of the neutralization equivalent.
%, Preferably about 5%. Operationally, this is a gentle addition process with some interruption in view of the relationship with the previous process.

The hydrated silicic acid obtained in the third step is
Since sodium sulfate produced as a by-product may be mixed, it is preferable to perform filtration, washing with water and repulp treatment.

The hydrated silicic acid according to the present invention is as described above.
Even if it is contained in a small amount in paper, it has a high effect of preventing strike-through due to its high absorption of printing ink. That is, when blended in paper, it improves opacity after printing. However, with respect to the opacity of white paper, unless the hydrated silicic acid is added in an amount of at least 3% by weight per pulp, it does not contribute to increase the opacity of paper. Hydrated silicic acid as a filler for papermaking is more expensive than other raw materials for papermaking, and when it is highly mixed, it causes paper powder. It is less than or equal to percent. Therefore, hydrated silicic acid hardly contributes to increase the opacity of paper. Therefore, in order to maintain the opacity of white paper and improve the opacity after printing, the following methods are generally considered.

(1) A pulp material having high opacity, such as GP, is blended or the beating degree is adjusted.

(2) In order to increase the light-scattering power of the paper, the basis weight is increased, or the fiber-fiber bond is decreased by adjusting the wet pressure, chemicals or the like.

(3) In order to increase the light absorption coefficient of the paper, a colored raw material having a low whiteness is used, or the paper is colored.

(4) In order to increase the light scattering coefficient of paper,
Add a filler with a high light scattering coefficient.

The methods (1) to (3) are effective for improving the opacity of the paper, but the properties of the paper may change significantly. The method (4) is the simplest method, but since the filler having a high light scattering coefficient is expensive, not limited to inorganic and organic substances, it is not recommended to use it for printing paper such as general newsprint. It causes the price to rise, which is unfavorable for social ethics. Therefore, as a result of diligent studies, a method of improving both the opacity after printing of paper and the opacity of blank paper was devised by combining an inexpensive filler such as calcium carbonate with the hydrated silicic acid of the present invention. First, the hydrated silicic acid according to the present invention is dispersed in water and preliminarily flocculated with a sulfuric acid band or a cationic polymer electrolyte flocculant. Examples of cationic polymer flocculants include cationic polyacrylic amide derivatives and cationic starch. At this time, strong agglomeration deteriorates the formation, which is counterproductive for improving opacity. That is, the cationic polyelectrolyte coagulant in this case has an auxiliary role, and when a cationized substance is present in white water or the like and hydrated silicic acid coagulates in the papermaking process, a small amount of these coagulants is used. Good to use. If a large amount of cations are already present, the use of nonionic or anionic dispersants is also conceivable. In the normal papermaking process, hydraulic shearing force is applied at this stage by a stirrer or pump, so apparently no agglomeration occurs at this stage, but in the static particle size distribution measurement described above, measurement by the laser method is performed. Aggregation is preferably performed so that the value is in the range of 3.5 to 18 μm. After this dispersion, it is added to the paper stock and papermaking is performed. A general-purpose filler other than the hydrated silicic acid is mixed in advance with pulp, chemicals, etc. in this stock material. For example, as the filler, either precipitated light calcium carbonate or heavy calcium carbonate, or a mixture thereof is used.
As a filler, any one of talc, clay, kaolin, etc., or a mixture thereof may be added. As the pulp, either mechanical pulp or chemical pulp, or a mixture thereof may be used. As an additive chemical, any one of a sulfuric acid band, a yield improver, a paper strength enhancer, a sizing agent, or a mixture thereof may be used. Normally, when pulp and filler are mixed together in papermaking in such a system, non-uniform millimeter-scale flocs are generated due to physical filtration and surface chemical interactions, which is a cause of decreased opacity. Becomes In the present invention, the hydrated silicic acid according to the present invention is used not only as an opacity improver after printing but also as a microscopic dispersant for flocs. Originally, anionic polymeric dispersants have been used for this type of treatment, but these agents do not have the ability to improve opacity. Fine hydrated silicic acid is used for dispersion that does not deteriorate the formation, and voids effective for light scattering are formed between coarse fillers such as talc and kaolin. Further, the same effect is exhibited by interposing between pulp and fine fibers. Of course, if hydrated silicic acid intervenes too much between the fibers, interfiber bonding will be hindered and the strength of the paper will decrease, but there is no problem if the normal addition rate is 5% by weight or less of calcium carbonate. This reduction in strength can be prevented by changing the blended pulp or using a paper strength enhancer. Therefore, if the hydrated silica addition rate is 25% by weight or less, papermaking is practically possible. In order to obtain the effect of improving the print opacity and the opacity of white paper, it is necessary to add hydrated silicic acid and calcium carbonate in an amount of 0.05 wt% or more, respectively. Highly opaque and expensive fillers such as calcined clay, calcined kaolin, and titanium dioxide may be used as fillers to be used in combination, but in the present invention, calcium carbonate, and even low-cost fillers such as talc and kaolin have the effect of improving opacity by the above mechanism. Can be expected.

The hydrated silicic acid according to the present invention has a total pore volume of 4.0 to 6.0 cc / g and an average pore radius of 200 to 40.
2. While having a high level of porous structure in the range of 0 angstrom, the average particle size is measured by a laser method.
0 to 15 μm, measured value by Coulter method is 2.0 to
4.0 μm or 0.5 to 0.5 as measured by centrifugal sedimentation method
It is in any fine range of 3.5 μm, and particularly when applied as a filler for paper, it exhibits a weight reduction and an excellent effect of preventing strike-through, and exhibits a high filler yield. Therefore, in many cases, the specific surface area is in the range of 100 to 200 m ² / g, and the oil absorption amount is 250 to 350 ml / 100 g, which is a unique particle characteristic showing a relatively high value. Further, the hydrated silicic acid according to the present invention is agglomerated with a cationic polyelectrolyte aggregating agent in advance, and other fillers, mainly calcium carbonate and pulp, are added after the addition, so that not only the opacity after printing but also the opacity of white paper can be improved. High paper can be manufactured.

[0033]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples. In addition, in measuring the properties of hydrated silicic acid, the total pore volume was measured by a mercury porosimeter 200 manufactured by Carlo Erba Co.
Type 0, laser method average particle size is Microtrack 9220FRA manufactured by Nikkiso Co., Coulter method average particle size is Coulter Electronics Coulter Counter TAII type, centrifugal sedimentation method average particle size is Micro Photosizer SKN manufactured by Seishin Enterprise Each of -1000 was used, and the effect of preventing strike-through of the paper and the filler yield were measured by the following methods.

Measurement of paper strike-through prevention effect; NBK was used as a papermaking raw material by an oriented paper machine manufactured by Kumagai Riki Kogyo Co., Ltd.
A pulp slurry having a mixing ratio (weight) of P: TMP: GP: DIP = 20: 30: 20: 30 was used, and the filler slurry obtained in each example was used as a filler, and the basis weight was 40 g.
/ M ² , ash content in the paper is 1 to 4 weight percent, dehydrated by a press, and dried by a cylinder dryer to prepare a sheet sample. Single-sided printing was performed on this sheet sample using a news ink for keyless offset [Toyo Ink Co., Ltd. New King VANTEAN black]. 24 in an atmosphere of 20 ° C and 65% RH
After leaving for a period of time, the reflectance of the printed back side is measured with a Macbeth reflection densitometer, and the strike-through value (opacity after printing) is calculated by the following formula.
Was calculated.

Strikethrough value = (Reflectance of printed back surface / Reflectance of unprinted back surface) × 100 (%) Based on the strikethrough value of the sheet sample prepared by adding the filler slurry of Comparative Example 1, The rising value from the value was used as the strike-through prevention effect.

Measurement of filler yield: The ash content in the paper measured according to JIS P8128 was divided by the addition rate of the filler slurry added at the time of sheet making to calculate.

The opacity was measured by a Hunter reflectometer manufactured by Kumagai Riki Co., Ltd. according to JIS-P8138.

The tensile strength was measured by a tensile tester manufactured by Toyo Seiki Co., Ltd. according to JIS-P8113.

The ash content was measured at 525 ° C. according to JIS-P8128.

Production Example of Hydrated Silicic Acid Slurry Commercially available No. 3 sodium silicate (SiO ₂ : 20.
2%, Na ₂ O: 9.5%) was diluted with water to prepare a 6.7 weight percent diluted sodium silicate solution as SiO ₂ . First, as a first step, this sodium silicate solution is heated to 90 ° C.
After heating to 70 ° C., sulfuric acid (concentration: 95% by weight) in an amount corresponding to 40% of the neutralization equivalent was added over 7 minutes under sufficient vigorous stirring so that a coarse gel was not generated. The liquid after the addition of sulfuric acid was transparent and no solid matter was observed. After the addition was completed, the resulting partially neutralized solution was transferred to a high speed rotary pulverizer type mixer. During this liquid transfer, a large amount of silica was deposited to form a slurry. The grinding process was carried out for 2 minutes. After the pulverization, the slurry was returned to the original reaction vessel, the temperature was reheated to 90 ° C., and the mixture was maintained for 2 hours under stirring for aging. A minute amount of the slurry after completion of aging was sampled and the particle size was measured by the Coulter method.

Next, in the second step, the slurry temperature is set to 9
The temperature was raised to 5 ° C., sulfuric acid having the same concentration as in the first step was added to 85% of the neutralization equivalent over 15 minutes, and aged for 15 minutes.

Subsequently, in the third step, 1N sulfuric acid was added to the aged slurry over 30 minutes to adjust the slurry pH to 4.5.

After the completion of the third step, the slurry was filtered and washed with water to recover a 10 weight percent slurry of hydrated silicic acid repulped in pure water. The resulting slurry was filtered and dried to measure the total pore volume, average pore radius, BET specific surface area and oil absorption. The results are shown in Table 1 in comparison with the applied variable conditions.

Example 1 0.5% by weight of a cationic polyelectrolyte was added to the obtained hydrated silicic acid slurry, and the mixture was added to 300 with a laboratory stirrer.
An appropriate aggregation state was maintained at rpm. Separately, 0.3 weight percent of cationized starch per absolute dry pulp was added and mixed to the pulp slurry, and then 2 weight percent of precipitated calcium carbonate (average particle diameter 1.0 μm) per pulp was added and mixed. Subsequently, a cationic polyelectrolyte flocculant (Percol, Allied Colloid Co., Ltd.) is added in an amount of 0.05% by weight with respect to the pulp, and bentonite is added and dispersed in an amount of 0.1% by weight with respect to the pulp. Immediately before the papermaking, a hydrated silicic acid slurry containing a cationic polyelectrolyte was added to this paper stock so that the total ash content was 3% by weight, to prepare a sheet. The strikethrough value and opacity of this sheet were measured and are shown in Table 1.

Example 2 A sheet was produced under the same conditions as in Example 1 except that bentonite was not added. The physical properties of the obtained sheet were measured and evaluated in the same manner as in Example 1, and the results are also shown in Table 1.

Example 3 A sheet was prepared under the same conditions except that heavy calcium carbonate (average particle diameter 5.0 μm) was used instead of the precipitated calcium carbonate in Example 1. The physical properties of the obtained sheet were measured and evaluated in the same manner as in Example 1, and the results are also shown in Table 1.

Example 4 A sheet was prepared under the same conditions as in Example 1 except that the precipitated calcium carbonate was mixed with 1% by weight of the pulp and the talc produced in China was mixed with 1% by weight of the pulp. The physical properties of the obtained sheet were measured and evaluated in the same manner as in Example 1, and the results are also shown in Table 1.

Example 5 A sheet was prepared under the same conditions as in Example 1 except that the precipitated calcium carbonate was blended with 1% by weight of the pulp, and kaolin manufactured by Huber Co., USA was blended with 1% by weight of the pulp. The physical properties of the obtained sheet were measured and evaluated in the same manner as in Example 1, and the results are also shown in Table 1.

Example 6 In Example 1, the amount of the precipitated calcium carbonate added was changed to 38% by weight of pulp. A sheet was produced under the same conditions as in Example 1 except for the above. Physical properties of the obtained sheet were measured and evaluated in the same manner as in Example 1, and the results are shown in Table 1.
It was also attached to.

Comparative Example 1 In Example 1, the filler other than the hydrated silicic acid obtained in the above-mentioned production example of the hydrated silicic acid slurry was not added, and the filler in the paper was adjusted to 2% by weight. A sheet was prepared under the same conditions. About the obtained sheet, Example 1
The physical properties were measured and evaluated in the same manner as in, and the results are also shown in Table 1.

Comparative Example 2 1% by weight of each of the precipitated calcium carbonate and the hydrated silicic acid obtained in the production example of the hydrated silicic acid slurry in Example 1 was simultaneously mixed with pulp, and otherwise the same conditions were used. A sheet was prepared. Physical properties of the obtained sheet were measured and evaluated in the same manner as in Example 1, and the results are shown in Table 2.
It was also attached to.

Comparative Example 3 A sheet was prepared under the same conditions except that the cationic polyelectrolyte flocculant was not added to the hydrated silicic acid obtained in the production example of the hydrated silicic acid slurry in Example 1. Physical properties of the obtained sheet were measured and evaluated in the same manner as in Example 1, and the results are also shown in Table 2.

Comparative Example 4 A hydrated silicic acid slurry was manufactured under the same conditions as in the same manufacturing example except that the pulverization treatment in the first step in the manufacturing example of the hydrated silicic acid slurry was not performed. A sheet was produced from the obtained slurry under the same conditions as in Comparative Example 1. The physical properties of the obtained sheet were measured and evaluated in the same manner as in Example 1, and the results are also shown in Table 2.

From the results shown in Tables 1 and 2, the hydrated silicic acid of the examples satisfying the requirements of the total pore volume and the average particle size according to the present invention has the effect of preventing strike-through as compared with Comparative Example 4 which is the standard. It is recognized that it is excellent in, and by combining with calcium carbonate, not only the opacity after printing,
It can be seen that white paper opacity and whiteness are also increased. However, as shown in Example 6, when the compounding amount of calcium carbonate exceeds 37% by weight, the strength is remarkably reduced, so that the compounding ratio needs to be 35% by weight or less for practical use. Further, as shown in Examples 4 and 5, the combination of calcium carbonate and other fillers is also inferior in whiteness improvement effect to calcium carbonate alone, but is superior in opacity after printing and white paper opacity to the standard. Is recognized. On the other hand, as shown in the comparison between Comparative Example 2 and Example 1, simply mixing the hydrated silicic acid according to the present invention with other fillers has a low effect of improving opacity, and thus other fillers were mixed. Later, it is recognized that it is preferable to add hydrated silicic acid immediately before papermaking. In this case, addition of the cationic polymer electrolyte is effective as shown in Comparative Examples 1 and 3. Further, as shown in Example 2, by using the hydrated silicic acid according to the present invention in combination with the cationic polymer electrolyte, Example 1 with high yield can be obtained without using bentonite conventionally used for neutral papermaking. Similar performance to can be achieved.

[0055]

As described above, according to the present invention, it is possible to manufacture not only the opacity after printing but also the opacity of white paper. Therefore, it is not only a large contribution to the paper manufacturing industry, but using this method it is possible to reduce the pulp, which is a wood resource, while maintaining not only the opacity after printing with the filler component but also the opacity of white paper. As a result, the contribution to forest resources and environmental protection is extremely large. The method for producing a paper using the hydrated silicic acid of the present invention is not limited to newsprint, and is, for example, general high-quality or medium-quality printing paper, lower grade paper,
It is also useful in a method for producing coated paper base paper, PPC paper, foam paper, ink jet paper, thermal paper base paper, carbonless paper base paper, and the like.

[0056]

[Table 1]

[0057]

[Table 2]

Claims (3)

[Claims] 1. A method for producing a paper with internal filler by adding a hydrated silicic acid slurry to a paper stock containing pulp and sedimentary calcium carbonate, ground calcium carbonate, or a mixture thereof to prepare paper. Japanese silicic acid is the following A ~
C: A. The oil absorption amount is 250 to 350 ml / 100 g, and B. The total pore volume is 4.0 to 6.0 cc / g, the average pore radius is in the range of 200 to 400 angstroms, and C.I. The average particle size is 3.0 to 1 as measured by the laser method.
5 μm, measured by Coulter method: 2.0 to 4.0 μm
m, which is in the range of 0.5 to 3.5 μm as measured by the centrifugal sedimentation method, satisfying the following particle characteristics: 2. The method for producing a paper with internal filler as claimed in claim 1, wherein the hydrated silicic acid slurry is a slurry of a mixture with a cationic polymer electrolyte. 3. The precipitated calcium carbonate or ground calcium carbonate, or a mixture thereof is added to the pulp in an amount of 0.05 to 35% by weight, and the hydrated silicic acid is added in an amount of 0.05 to 25% by weight to the pulp. The method for producing a filler-added paper according to claim 1 or 2, characterized in that: