JPS6311478B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a new paper that is excellent in preventing print-through after printing and has good strength. More specifically, the present invention relates to a new paper that is excellent in preventing print-through and has good strength. , relating to paper in which the volume of pores with a pore radius of 0.75 microns or less is larger than the volume of pores with a pore radius of 7.5 microns or more, and the volume of pores with a pore radius of 0.75 microns or less is 0.1 cc/g or more. be. Note that the pore radius and pore volume of paper in the present invention refer to values obtained by measuring with a mercury porosimeter, and specifically, the pore radius is determined by measuring the pressure (P atm) with a mercury porosimeter. This is the radius γ calculated from γ=75000/P.
In addition, silicon dioxide that is not incorporated into calcium silicate, that is, is blended with it, is contained in distilled water.
Put 1g of calcium silicate in cc and use ultrasonic wave (output
50W) for 30 minutes to separate silicon dioxide. Conventionally, various types of paper have been used.
In general, paper made only from pulp has the best strength (hereinafter expressed as tear length), but it not only has the disadvantage of ink bleed through after printing, but also has poor whiteness and poor paper strength. Due to insufficient transparency and smoothness, it is not used except for some papers.
Generally, the above-mentioned drawbacks have been improved by adding fillers such as kaolin, talc, and titanium oxide to the pulp. However, since the above-mentioned filler has almost no oil absorption, it is not possible to prevent printing ink from penetrating, and paper for practical use has been manufactured by increasing the thickness of the paper, increasing the amount of filler, etc. In particular, paper that uses titanium oxide as a filler has extremely high opacity, so
Due to this influence, the strike-through can be prevented to some extent, but when the amount of titanium oxide added exceeds 6% (by weight), there is a defect that the tearing length decreases significantly. on the other hand,
Increasing the paper thickness, increasing the amount of filler, etc. is not only uneconomical, but also makes handling of the paper inconvenient, so attempts have been made to add oil-absorbing fillers to the pulp. For example, hydrated silicic acid called white carbon is a typical filler mentioned above. However, although a filler having the above-mentioned oil absorption amount is used in a small amount and exhibits an effect of preventing bleed through, the strength of the paper is extremely reduced, so it cannot necessarily be said to be a satisfactory filler.
The properties of paper change depending on the type of filler added to the long-lasting pulp, but the anti-bleeding effect and the strength of the paper are two sides of the same coin, and the development of paper that satisfies both properties is a major challenge. It was hot. The inventors of the present invention have been diligently conducting research to produce paper that is excellent in preventing print-through and has good paper strength. As a result, the prevention of paper bleed-through is affected by the pore volume of the paper's small pore radius, and the factors that reduce paper strength depend on the pore volume of the paper's large pore radius. The present inventors have discovered that two objects can be achieved by making paper using a specific filler and producing paper with a specific pore volume, leading to the completion of the present invention. That is, in the present invention, the volume of pores with a pore radius of 0.75 microns or less is obtained by paper-making a pulp and a filler made of specific silicic acid particles.
Larger than micron pore volume and pore radius
The paper has a pore volume of 0.75 microns or less and 0.10 cc/g or more. Although the paper of the present invention is not particularly limited in its composition, it is generally difficult to control the pore radius in synthetic paper, and paper mainly composed of pulp and a specific filler is usually targeted. be done. In addition, commercially available paper, such as paper made from pulp and known fillers, usually has pores with a pore radius of 0.75 microns or less and a pore volume of 7.5 microns or more, as shown in the comparative examples described later. It is smaller than the volume. From this point as well, it can be seen that the paper of the present invention is novel. Conventionally, it has been thought that the properties of the filler are a factor that determines the bleed-through prevention and strength of paper. However, according to the research of the present inventors, not only the properties of the filler but also the pore radius distribution of the paper itself are factors that determine the prevention of bleed-through and strength.
It has been discovered that paper having such a pore radius distribution can be obtained by using the above-mentioned specific siliceous particles as a filler. In other words, although the pore radius distribution of paper changes depending on the papermaking technology, it is most influenced by the type of filler.
Filler selection is an important factor. A technique for keeping the pore radius distribution of the paper within the range specified by the present invention will be described later, but the paper of the present invention will have the following properties when described in detail. In other words, a pore volume of the paper itself with a pore radius of 0.75 microns or less has an effect on preventing strike-through, and a pore volume with a pore radius of 7.5 microns or more has a large effect on a decrease in the strength of the paper. The strength of paper is provided by the adhesion and entanglement of pulp fibers, and if there are any factors that interfere with this, the strength of paper will decrease. Generally, when filler is added to paper, it acts to prevent adhesion and entanglement between fibers, so the strength of the paper tends to decrease in relation to the amount added. In addition, the particle size and form of the filler, and the ease with which the powder or agglomerated grains break down, etc., also correlate with the strength. For example, if the particle size is too fine, the filler will adhere to the surface of the fibers, preventing adhesion of the fibers and causing a decrease in strength.On the other hand, if the particle size is too coarse, the added filler will not be fully effective. In addition, the filler must be in a shape that allows for good intertwining with pulp fibers and a good yield. Furthermore, the ease with which powder or aggregate particles crumble means that during wet pressing during papermaking, the filler crumbles and flows into the pores formed by the pulp fibers, without interfering with adhesion or entanglement between the fibers. It is necessary to do so. At this time, if the filler does not crumble easily or contains impurities, it will not flow into the pores formed by the pulp fibers, and new pores caused by the filler will be formed at that location. This prevents adhesion and entanglement between fibers of the pulp, resulting in a decrease in strength. These phenomena can be made clearer by observing the pore volume values with a pore radius of 7.5 microns or more. For example, when calcium silicate made from hydrated silicic acid or insoluble silica, which is called white carbon, is used, the volume of pores with a pore radius of 7.5 microns or more cannot be reduced even if wet pressing is performed during paper making.
The decrease in tear length is significant. Further, by using a specific calcium silicate, etc., which will be described later, this value can be easily reduced and paper with less decrease in tearing length can be obtained. Therefore, the larger the volume of pores with a pore radius of 0.75 microns or less, the greater the effect of preventing paper from bleeding through, and the smaller the volume of pores with a pore radius of 7.5 microns or more, the smaller the decrease in paper strength tends to be. In addition, the present invention has a large strike-through prevention effect,
To obtain paper with less strength loss, the paper pore radius is 0.75.
It is necessary that the pore volume of microns or less be larger than the pore volume of pores with a pore radius of 7.5 microns or more. Moreover, in order to effectively prevent paper from bleeding through, the pore volume with a pore radius of 0.75 microns or less should be at least 0.10 cc/g or more, preferably 0.15 cc/g or more.
It is necessary that it is cc/g or more. Furthermore, if the volume of pores with a pore radius of 7.5 microns or more is larger than 0.3 cc/g, the strength of the paper will decrease significantly even if the volume of pores with a pore radius of 0.75 microns or less is larger than 0.3 cc/g. Therefore, it is generally preferable to limit the volume of pores with a pore radius of 7.5 microns or more to 0.3 cc/g. The paper of the present invention can be produced, for example, by adding the siliceous filler in the form of powder or slurry to the pulp produced in the pulping process, which has been bleached, dried, and beaten as necessary, and then made into paper using a conventional method and dried. Bye. The filler may be mixed with the pulp prior to paper making or may be added during paper making. As mentioned above, it is preferable for the paper of the present invention to have a pore volume with a pore radius of 7.5 microns or more as small as possible, so it is generally preferable to reduce the pore volume by wet pressing during paper making. Ru. The pulp is not particularly limited and any known pulp may be used, but pulps obtained from softwoods and hardwoods, which are generally used as papermaking pulp for newspapers, low-grade printing paper, intermediate-grade paper, high-grade paper, book paper, etc., are preferred. used for. As mentioned above, the pore radius and pore volume of the paper itself change depending on the paper-making technique, such as wet pressing, but what is most affected are the properties and amount of filler added. The amount of the filler to be added may be determined in advance depending on the type of filler, but it is most commonly added in the range of 1 to 40 parts, preferably 2 to 25 parts per 100 parts of pulp. In general, if the particle size of the filler is too small, it tends to separate from the paper during paper making, and conversely, if the particle size is too large, it tends to become unevenly entangled with the fibers. Therefore, in general, a filler containing 90% (by weight) or more of particles having a particle size of 2 to 30 microns is preferably used. The filler for producing the paper of the present invention is composed of silicic acid particles having an aggregate form of flakes with an average longitudinal diameter of 0.1 to 30 microns and a thickness of 0.005 to 0.1 micron, and these silicic acid particles are more preferably used. (a) Calcium silicate having a skeleton of gyrolite and containing silicon dioxide in an incorporated form in a range of 4 to 70% by weight based on gyrolite. (b) 4 to 70% by weight of silicon dioxide and 13% by weight based on gyrolite, with a skeleton of gyrolite;
Calcium silicate/calcium sulfate complex containing calcium sulfate. (c) The calcium silicate or calcium silicate.
Silica obtained by acid treatment of calcium sulfate complex. or (d) the calcium silicate or calcium silicate.
Complex of calcium sulfate complex and aluminum oxide. It consists of at least one species. These inorganic particles can be synthesized by the following method. For example, water-soluble silicates such as sodium silicate and potassium silicate and water-soluble calcium compounds such as calcium chloride, calcium nitrate, and gypsum are combined into SiO ₂ /CaO
By reacting at a reaction temperature of 150 to 250° C. with a molar ratio in the range of 1.6 to 3.2, calcium silicate having a gairolite crystal structure and a SiO ₂ /CaO molar ratio of 1.6 to 3.2 can be obtained. This calcium silicate has the general formula 2CaO・3SiO ₂・nSiO ₂・mH ₂ O (however, m
is a positive number and n is generally a number from 0.1 to 3.4), and it is assumed that amorphous silicon dioxide exists in the form incorporated into the crystal, and its grain boundaries or constituent bonding form are transparent type. It cannot be identified even from photographs taken with an electron microscope at a magnification of 200,000 to 200,000 times. The form in which the above-mentioned amorphous silicon dioxide is incorporated into the crystal is gyirolite calcium silicate, that is,
2CaO・3SiO ₂・2H ₂ O and amorphous silicon dioxide i.e.
Although it is composed of nSiO ₂ ·mH ₂ O, amorphous silicon dioxide is not simply in a blended form, but is formed by containing amorphous silicon dioxide during the production of gyarolite type calcium silicate. Judging from transmission electron micrographs and the like, the amorphous silicon dioxide is very microscopically dispersed, for example, uniformly dispersed at 100 Å or less, and participates in crystal formation together with gyrolite calcium silicate. By taking an electron micrograph (3,000 to 10,000 times magnification) of the calcium silicate obtained by the above method, it can be confirmed that the calcium silicate has an aggregated form similar to the petals of a rose flower. The size, shape, etc. of the flakes vary depending on the type of raw materials, raw material ratio, manufacturing conditions, etc., and cannot be unconditionally limited, but generally the average diameter in the longitudinal direction is 0.1.
Most of them are circular, elliptical, etc. with a thickness of ~30μ and a thickness of about 0.005~0.1μ. Hereinafter, in this specification, the calcium silicate may be abbreviated as petal-like silica. When using calcium sulfate, that is, gypsum (in this specification, gypsum is used to include not only dihydrate salts but also hemihydrate salts and anhydrides) as the water-soluble calcium compound, gypsum aqueous A mixed system in which alkali silicate is gradually added to the suspension and reacted, or a reacted precipitate is filtered and washed if necessary, and then a slurry solution is hydrothermally treated to form petal-shaped silica. You can get Cal. However, if the molar ratio of CaSO ₄ /Na ₂ O or K ₂ O in the raw material is 1.1 or more, a composite of petal-shaped silica and gypsum is obtained. The gypsum exists in a form incorporated in the petal-shaped silica, similar to the amorphous silicon dioxide in the petal-shaped silica, and the gypsum content is generally 13% (by weight).
To a certain extent, even if an electron micrograph is taken, the grain boundaries or the constituent bond form cannot be confirmed. However, when the content of the gypsum generally exceeds 13% (by weight), a blend of gypsum in addition to the above-mentioned composite of the petal-shaped silica and gypsum is obtained. When the amount of gypsum mixed in the composite of gypsum and gypsum increases, the volume of pores with a pore radius of 7.5 μm or more tends to increase, and the tearing length of the paper decreases. Therefore, the gypsum content in the composite of the petal-shaped silica and gypsum is preferably 10% or less. In addition, the petal-shaped silica or a composite of the petal-shaped silica and gypsum is treated with sulfate band [Al ₂ (SO ₄ ) ₃ .
18H ₂ O] to form an aluminum oxide complex of calcium silicate. The complex has the general formula _aAl2O3.2-3a / _{2CaO.bSiO2.mH2O} (where a is 0.06 to _0.2 , b is 1.6 to _3.2 , and m is a positive number). This is what is shown. The composite can also be suitably used as a filler for the paper of the present invention. When the petal-shaped silica or the composite of petal-shaped silica and gypsum obtained by the above method is heated with a mineral acid such as hydrochloric acid to forcefully extract calcium, 2 oxide is formed while retaining the original petal form. Silicon can be obtained. Silicon dioxide obtained from this petal-shaped silica or a composite of petal-shaped silica and gypsum (hereinafter abbreviated as petal-shaped silica) is also suitably used as a filler for the paper of the present invention. This petal-shaped silica can be confirmed by taking electron micrographs (3,000 to 10,000 times magnification), and it can be seen that the average diameter in the longitudinal direction is 0.1 to 30μ, and the thickness is
It consists of a collection of thin flakes of about 0.005 to 0.1μ.
In addition, most of them have a circular or elliptical shape, with an appearance similar to the petals of a rose flower. Moreover, it was confirmed from the results of X-ray diffraction that it was amorphous silicon dioxide. However, when the petal-shaped silica or a composite of the petal-shaped silica and other compounds increases the SiO ₂ /CaO molar ratio of the raw materials during production, the amorphous silicon dioxide is mixed with the petal-shaped silica and gypsum. It comes in a blended form similar to that described in the complex. 2 that exists outside the crystal structure of the amorphous silicon dioxide in the blended state, that is, the petal-shaped silica.
Silicon oxide tends to increase the volume of pores with a radius of 7.5 μm or more in paper, so it is preferable to avoid contamination as much as possible. Similarly, when insoluble silicon dioxide, such as hydrated silicic acid called white carbon, siliceous earth, etc., is used as a silica source material, calcium silicate, which has a structure similar to petal-shaped silica, may be used depending on the reaction conditions. can get. However, in this case, unreacted silicon dioxide is blended and mixed with the petal-shaped silica, and therefore cannot serve as a filler for obtaining the paper of the present invention. As will be described in detail in Examples and Comparative Examples below, the calcium silicate obtained by using the above-mentioned insoluble silicon dioxide as a silica source material does not appear to be the petal-shaped silica or a composite of the petal-shaped silica and other compounds. There are similarities between the above, but the fact that the former contains unreacted blended silicon dioxide is that 1 g of the sample is placed in 100 c.c. of distilled water and dispersed for 30 minutes using ultrasound (50 W). Since it can be separated by allowing the silica to separate, it can be easily distinguished from the petal-shaped silica. The unreacted silicon dioxide can also be identified from a photograph taken with a transmission electron microscope at a magnification of about 200,000 to 200,000 times. The paper of the present invention may be used in combination with conventional fillers such as titanium oxide, kaolin, talc, etc. and the siliceous filler as long as it has the specific pore volume, and is not particularly limited. do not have. For example, if a paper with high opacity is required, titanium oxide may be added to the filler, and if within the specified pore volume, it will provide good opacity, anti-bleed through and reduced tear length. You can get less paper. Generally, in order to improve the glossiness of the paper surface, coating pigments are applied as a water-based paint along with adhesives and other additives to one or both sides of the paper, and the paper is finished using a supercalender or other gloss machine and then printed. The paper obtained is suitable for purposes such as personal and decorative purposes, and the paper of the present invention can be subjected to similar treatments without any problems and the characteristics of the present invention are not lost. In order to explain the present invention in detail, the following Examples, Comparative Examples, and Reference Examples will be given and explained, but the present invention is not limited to these Examples. still,
In the following Examples and Comparative Examples, coniferous sulfite pulp was used as the pulp unless otherwise specified.
The cotton used was one that had been pre-defined using a beating machine (shopper freeness 27.8°SR). In addition, the basis weight and thickness of the paper in the following examples and comparative examples,
The tear length, pore volume, etc. are the values under the standard conditions of handmade sheets (20°C, 65%RH). Furthermore, the bulk specific volume, oil absorption, refractive index, and particle size distribution of the filler were measured by the following methods. (b) Bulk specific volume The powder was ground in a mortar to a particle size that could pass 80% through a 200 mesh sieve. Using this crushed material, JIS K6220
It was measured using the bulk specific gravity measurement method described in Section 6.8. (b) Oil absorption The powder was crushed in a mortar to a particle size of 80% through a 200 mesh sieve. Using this crushed material, JIS K6220
It was measured according to the oil absorption measurement method described in Section 19. (c) Refractive index Solvents were prepared by mixing α-chlornaphthalene and cyclohexane in various proportions, and measurements were made using the immersion method using this solvent. The immersion method was based on Toshio Sudo's Clay Mineralogy P100-103 (1974). (d) Particle size distribution For this measurement, Coulter Counter Model TA manufactured by Coulter Electronics, Inc. of the United States was used. The particle size of commercially available fillers is the catalog value. Reference example 1 0.3144 mol/calcium chloride aqueous solution (100
cc) and 0.3144 mol/sodium silicate (SiO ₂ /
Na ₂ O molar ratio 2.6) aqueous solution (100 c.c.) under atmospheric pressure 25
The mixture was mixed at ℃ (SiO ₂ /CaO molar ratio 2.6). A white precipitate was produced at the same time as the mixture was mixed, but the mixture was placed in an autoclave, sealed, and reacted at 200°C for 5 hours. The pressure at this time is 15Kg/cm ² G and the water ratio is 30
It was hot. The reaction product was washed twice with 100 c.c. of filtered ion-exchanged water and then dried at 100°C for 8 hours. The yield of this dried product was 7.35 g. This dried product did not shrink or solidify during drying, and was soft and easily powdered. The bulk specific volume is 14.2cc/g, the oil absorption is 4.21cc/g, and the refractive index is
It was 1.50. The general formula of calcium silicate obtained in the above procedure is 2CaO・3SiO ₂・2.05SiO ₂・
I was able to display 2.4H ₂ O. A scanning electron micrograph of this calcium silicate, magnified 10,000 times, was as shown in FIG. As is clear from FIG. 1, the calcium silicate obtained in this reference example was found to be composed of an aggregate of flakes with an average diameter in the longitudinal direction of 2 μm and a thickness of 0.1 μm or less. In addition, a transmission electron micrograph taken at a magnification of 100,000 times was as shown in Figure 2. As is clear from FIG. 2, although the calcium silicate obtained in this experiment contained silicon dioxide, it was not possible to discern its grain boundaries or bond form. Further, from the results of X-ray diffraction of the above-mentioned calcium silicate, it was found that it was a gyrolite crystal. Furthermore, distilled water was added to 1 g of the petal-shaped silica obtained above.
Add 100c.c. and use a tabletop ultrasonic cleaner (50W)
When the mixture was dispersed for 30 minutes, it was confirmed that silicon dioxide was not separated at all, and that no silicon dioxide was contained as a blend. Reference Example 2 Petal-shaped silica 10 obtained in the same manner as Reference Example 1
After adding 100ml of 6N-hydrochloric acid to
Allow to react for 1 hour. The reaction product was washed twice with 100 ml of filtered ion-exchanged water and heated to 100°C.
It was dried for 8 hours. The yield of this dried product was 7.75 g. This dried material did not shrink or solidify during drying and was soft. Also, the bulk specific volume of the dried product is
12.9cc/g, oil absorption 3.5cc/g and refractive index 1.45
It was hot. The dry product obtained in the above operation has a silicon dioxide content of 8.5
It contained % water by weight. This silicon dioxide was photographed using an electron microscope and magnified 10,000 times.
It was as shown in the figure. As is clear from this,
It had a shape similar to the petal-shaped silica obtained in Reference Example 1. Reference Example 3 Pour 6.5 g of dihydrate gypsum (100 mesh) into 98 c.c. of water and stir for 20 minutes. While stirring this slurry, 100 c.c. of 0.3144 mol/sodium silicate (SiO ₂ /Na ₂ O molar ratio 2.6) was added to 6 c.c./at 25°C under atmospheric pressure.
It was added over a period of 16 minutes and 40 seconds at a speed of 1 minute. The subsequent operations were carried out in the same manner as in Reference Example 1 to obtain 8.2 g of powder. The results of X-ray diffraction of this powder showed a mixture of peaks of anhydrite type and gyrolite type calcium silicate. The general formula of the powder is 2CaO・3SiO ₂・2.05SiO ₂・0.20CaSO ₄・
It was confirmed that it can be displayed at 2.37H ₂ O. The above powder was photographed with a scanning electron microscope at a magnification of 10,000 times, and the results were as shown in FIG. As is clear from Fig. 4, it was confirmed that the flower was composed of petals with a longitudinal diameter of 2 μm and a thickness of 0.1 μm or less. However, in the photograph, crystals that appeared to be type anhydrite could not be visually identified. The bulk specific volume of the powder is 15.2cc/
g, and the oil absorption amount was 4.30 cc/g. Reference Example 4 10g of petal-shaped silica obtained in the same manner as Reference Example 1 was
After making 10% slurry, 10% sulfuric acid band [Al ₂
(SO ₄ ) _{3.18H 2} O] 4 ml was slowly added and the reaction was allowed to proceed for 1 hour while stirring. The reaction product was washed twice with 100 c.c. of filtered ion-exchanged water and then dried at 100°C for 8 hours. This dried product was chemically stable even when it was dried and powdered or as a slurry. The bulk specific volume of the dried product is 13.8cc/g.
The oil absorption amount was 4.09cc/g. In addition, the dried product obtained in the above procedure is an aluminum oxide complex of calcium silicate, whose general formula was determined from the results of chemical analysis.
It could be expressed as 0.11Al ₂ O ₃・0.835CaO ・2.52SiO ₂・2.4H ₂ O. Reference Example 5 Calcium silicate was synthesized using water-insoluble silicon dioxide as a starting material. 5% white carbon slurry (5g as _SiO2 ) and 5% calcium hydroxide slurry (2.03g as CaO) under atmospheric pressure.
Mix for 1 hour at 25℃ (Prepared SiO ₂ /CaO molar ratio
2.30). Place it in an autoclave and seal it for 200 minutes.
The reaction was carried out for 15 hours at a temperature of ℃. The reaction product was washed twice with 100 c.c. of filtered ion-exchanged water and then washed with 100 c.c.
It was dried at ℃ for 8 hours. The yield of this dry matter is 8.56g
It was hot. This dried material did not shrink or solidify during drying and was soft. Also, the bulk specific volume of this dried product is 5.8
cc/g, and the oil absorption amount was 1.52 cc/g. The general formula of calcium silicate obtained in the above procedure could be expressed as CaO.2.28SiO _{2.2.5H 2} O from the results of chemical analysis. This scanning electron micrograph of calcium silicate
The result of enlarging the image 5000 times was as shown in Figure 5. As is clear from FIG. 5, the shape was similar to the petal-like silica of Reference Example 1. This calcium silicate was photographed using a transmission electron microscope at a magnification of 50,000 times, and the results were as shown in FIG. As is clear from FIG. 6, it was clearly confirmed that unreacted silicon dioxide particles were blended. The unreacted silicon dioxide particles were separated by the following procedure. 100 c.c. of distilled water was added to 1 g of this calcium silicate and dispersed for 30 minutes using ultrasonic waves as in Reference Example 1, resulting in two phases of unreacted silicon dioxide and calcium silicate. Unreacted 2
After removing the silicon oxide phase (upper phase in this case), we chemically analyzed the SiO ₂ /CaO molar ratio of calcium silicate.
It becomes 1.8 and is mixed by blending from calculation2
Silicon oxide was confirmed to be 12.1% by weight. Example 1 As a filler, the petal-shaped silica obtained in Reference Example 1 with a molar ratio of SiO ₂ /CaO of 2.52 was ground with a cyclone mill manufactured by Hosokawa Iron Works, and the particle size was 97% by weight from 2 to 30μ, and the average particle size was 16μ. (The amount of pulp was fixed and the basis weight of additive-free paper was 48 g/ ^m2 )
After adding 2.0% by weight of sulfuric acid band [Al ₂ (SO ₄ ) ₃ 18H ₂ O] to the pulp (absolutely dry), a filler was added as a slurry, and paper was made according to the JIS P8209 method for preparing handmade paper for pulp testing. The amount of filler added is % by weight based on the pulp (bone dry). For comparison, Table 1 includes the papermaking results when no filler was added. As is clear from Table 1, it was confirmed that the petal-shaped silica not only exhibits a small decrease in tearing length and is effective in preventing strike-through, but also improves whiteness and opacity. Since the petal-shaped silica contains relatively few impurities and is a relatively loose agglomerated grain, there was almost no wire abrasion during paper making. Note that No. 1 in Table 1 is a comparative example in which no filler was used.

[Table] (*2) Amount of ink accepted (*3) Indicates the whiteness of the side of the paper opposite to the printed side after printing.
Example 2 Four types of petal-shaped silica shown in Table 2 were synthesized in the same manner as in Reference Example 1, and ground in a cyclone mill in the same manner as in Example 1.

【table】

[Table] Paper was made in the same manner as in Example 1 except that the above-mentioned silica was used as a filler. The results are shown in Table-3. As is clear from Table 3, these petal-shaped silicas not only exhibited a small decrease in tearing length and were effective in preventing strike-through, but also improved whiteness and opacity.

【table】

[Table] Example 3 As a filler, the petal-shaped silica obtained in Reference Example 2 was pulverized in the same manner as in Example 1, and 97% by weight of particle size 2-30μ was obtained.
Paper was made in the same manner as in Example 1, except that particles having an average particle size of 12.7 μm were used. The results are shown in Table 4. As is clear from the results in Table 4, the tearing length of paper to which petal-like silica has been added is slightly inferior to that of petal-like silica, but the tearing length does not decrease drastically like that of white carbon in Comparative Example 1, which will be described later. confirmed. Note that No. 1 in Table 4 is a comparative example in which no filler was used.

[Table] Example 4 Petal-shaped silica obtained in Reference Example 3 as a filler
The gypsum composite was crushed in the same manner as in Example 1, and the particle size was 2~
Paper was made in the same manner as in Example 1, except that 30μ, 94% by weight, and an average particle size of 16μ were used. The results are shown in Table-5. As is clear from the results in Table 5, the paper-making results of the petal-shaped silica-gypsum composite were confirmed to be as good as in Example 1. Note that No. 1 in Table 5 is a comparative example in which no filler was used.

[Table] Example 5 As a filler, the petal-shaped silica aluminum oxide composite obtained in Reference Example 4 was ground in the same manner as in Example 1, and the particle size was 92% by weight from 2 to 30μ, and the average particle size was 16μ. Table 6 shows the results of paper making performed in the same manner as in Example 1 except that . As is clear from Table 6, similar to Example 1, good results were obtained with the petal-shaped silica aluminum oxide composite. Note that No. 1 in Table 6 is a comparative example in which no filler was used.

[Table] Example 6 Petal-shaped silica obtained in Reference Example 1 (same particle size distribution as Example 1) and titanium oxide [Ishihara Sangyo Co., Ltd. trade name Typeta W-10 particle size 0.15 to
Paper was made in the same manner as in Example 1, except that 4% by weight of sulfuric acid was added to the pulp (absolutely dried) using a mixture of equal amounts of 0.25μ]. The results are shown in Table-7. As is clear from Table 7, it was confirmed that paper making within the scope of the present invention using petal-shaped silica and titanium oxide would be more effective due to the synergistic effect. This paper was found to have characteristics in whiteness, opacity, and whiteness after printing, although the tearing length was slightly reduced compared to the petal-shaped silica of Example 1 alone. Note that No. 1 in Table 7 is a comparative example in which no filler was used.

[Table] Example 7 Petal-shaped silica obtained in Reference Example 3 as a filler
Paper was made in the same manner as in Example 6, except that a mixture of equal amounts of gypsum composite (same particle size distribution as in Example 4) and titanium oxide was used. The results are shown in Table 8. As is clear from Table 8, good results were confirmed with the mixture of the petal-shaped silica-gypsum composite and titanium oxide as in Example 6. Note that No. 1 in Table 8 is a comparative example in which no filler was used.

[Table] Comparative Example 1 As a filler, commercially available kaolin [trade name Toku-S, manufactured by Omori Sangyo Co., Ltd., particle size 10μ or less, 87% by weight], talc (manufactured by Nippon Talc Co., Ltd., average particle size 9 ~
10μ), titanium oxide [manufactured by Ishihara Sangyo Co., Ltd., product name: Taipeke W-10, particle size 0.15-0.25μ], and white carbon [manufactured by Tokuyama Soda Co., Ltd., product name: Tokusil
Paper was made in the same manner as in Example 1, except that GU-N (single particle size: 15 to 25 mμ) was used. The results are shown in Table 9. As is clear from Table 9, it is difficult to control the volume of pores with a pore diameter of 7.5μ or more in paper using white carbon, and although it is somewhat effective in preventing bleed-through, its use is limited due to a decrease in tear length. It was hot. A similar phenomenon was found when titanium oxide was used. Kaolin and talc were also confirmed to have poor whiteness, opacity, and whiteness after printing, although the decrease in tearing length was small.

[Table] Comparative Example 2 Same as Example 1, except that the calcium silicate of Reference Example 5 was crushed in the same manner as in Example 1, and the filler had a particle size of 2 to 30μ at 92% by weight and an average particle size of 16μ. The paper was made by performing the following operations. The results are shown in Table 10. As is clear from Table 10, it was confirmed that calcium silicate made from water-insoluble silicon dioxide as a starting material significantly reduced the fracture length for the reasons mentioned above. It was also found that the volume of pores with a pore diameter of 0.75 μm or less was smaller than that of the petal-shaped silica of Example 1, and a sufficient effect of preventing strike-through was not expected. Pore diameter 7.5μ
It was confirmed that the above pore volume value could not be reduced to a pore volume value of 0.75 μm or less in pore diameter, and that paper satisfying the present invention could not be obtained. Note that No. 1 in Table 10 is a comparative example in which no filler was used.

[Table] Example 8 Hardwood ground pulp as pulp (previously defibrated to a constant level with a beater (shotzper freeness)
Paper was made in the same manner as in Example 1, except that the petal-shaped silica obtained in Reference Example 1 (same particle size distribution as Example 1) was used as the filler. The results are shown in Table-11. As is clear from Table 11, it was possible to obtain paper with little decrease in tearing length and in which bleed-through was prevented. The rate of decrease in fracture length was similar to that of talc in Comparative Example-3. Note that No. 1 in Table 11 is a comparative example in which no filler was used.

[Table] Comparative Example 3 The same method as in Example 1 was used, except that the same hardwood ground pulp as that used in Example 8 was used as the pulp, and the talc and white carbon shown in Comparative Example 1 were used as fillers. The operation was performed and paper was made. The results are shown in Table-12. As is clear from Table 12, it was confirmed that the decrease in fracture length was in the same trend as Comparative Example 1, less in talc, and more significant in white carbon. In addition, both talc and white carbon had little effect on preventing bleed-through.

【table】 [Brief explanation of the drawing]

Figures 1 and 2 are micrographs of petal-shaped calcium silicate, Figure 3 is a micrograph of petal-shaped silica,
FIG. 4 is a micrograph of a petal-shaped calcium silicate-gypsum composite, and FIGS. 5 and 6 are micrographs of calcium silicate as a comparative example.

Claims (1)

[Claims] 1. Paper obtained by paper-making pulp and inorganic filler, wherein the inorganic filler has an aggregate form of flakes with an average diameter of 0.1 to 30 microns and a thickness of 0.005 to 0.1 micron. The resulting paper has a pore volume with a pore radius of 0.75 microns or less that is larger than a pore volume with a pore radius of 7.5 microns or more, and a pore volume with a pore radius of 0.75 microns or less. 0.1cc/g or more.