JPH0364640B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to printing paper that has high strength and opacity and is excellent in preventing ink from bleeding through. In recent years, wood prices have soared due to a lack of wood resources.
In order to cope with the soaring transportation prices due to the rise in oil prices, attempts have been made to reduce the weight of printing paper, such as newsprint, by thinning it and reducing its basis weight. However, reducing the weight of paper causes a problem in that strength, opacity, and the effect of preventing ink bleed through, which are properties required for printing paper such as newsprint, deteriorate. Therefore, conventionally, by mixing chemical pulp, which produces paper with high strength, and mechanical pulp, which produces paper with high opacity, it is possible to improve each of the above properties, suppress the deterioration of the above properties, and use printing paper. We were working on reducing the weight of the However, chemical pulp tends to improve the strength of the paper but decrease the opacity of the paper, and mechanical pulp tends to improve the opacity of the paper but decrease the strength of the paper. Therefore, with the above-mentioned means, it has been difficult to reduce the weight of printing paper while satisfying both strength and opacity. Furthermore, the paper obtained by the above method is currently unable to achieve almost any improvement in the effect of preventing ink bleed through. The present inventors have conducted repeated research in order to solve the above-mentioned problem in reducing the weight of printing paper. the result,
By adding inorganic powder with specific properties to mixed pulp consisting of mechanical pulp and chemical pulp, printing paper with excellent strength, opacity, and ink bleed-through prevention effect can be obtained, making it suitable for lightweight printing. We have completed the present invention by discovering that That is, in the present invention, for 100 parts by weight of mixed pulp consisting of 95 to 50% by weight of mechanical pulp and 5 to 50% by weight of chemical pulp, the average diameter in the longitudinal direction is 0.1 to 30 microns and the thickness is 0.005 to 0.1 micron. (a) Calcium silicate, which has the form of aggregates of flakes, has a skeleton of gyrolite and contains silicon dioxide in the range of 4 to 70% by weight based on gyrolite. (b) Calcium silicate has a skeleton of gyrolite and contains silicon dioxide in the range of 4 to 70% by weight based on gyrolite. 70% silicon dioxide and 13% by weight
Calcium silicate/calcium sulfate complex (c) containing the calcium silicate or calcium sulfate in an incorporated form (c)
Complex of calcium sulfate complex and aluminum oxide. 0.1 of at least one inorganic powder selected from
It is a printing paper containing ~6 parts by weight. In the present invention, a mixed pulp consisting of mechanical pulp and chemical pulp is used as the pulp constituting the printing paper. The mechanical pulp is used to maintain the opacity of the printing paper, and any pulp obtained by mechanically treating wood or wood chips can be used without particular limitation. For example, ground wood pulp (GP),
Commonly used pulps include refined groundwood pulp (RGP), thermomechanical pulp (TMP), and chemimechanical pulp. Moreover, waste paper pulp of the above-mentioned pulp can also be used as the mechanical pulp. Among the above-mentioned mechanical pulps, groundwood pulp and refined groundwood pulp are particularly preferably used because of their high opacity. Further, the chemical pulp is used to maintain the strength of the printing paper, and pulp obtained by chemically treating wood or chips can be used without particular limitation. For example, sulfite pulp (SP), kraft pulp (KP), soda pulp, etc. are common. In particular, sulfite pulp and kraft pulp are strong and are preferably used in the present invention. In the present invention, the mixing ratio of mechanical pulp and chemical pulp in the mixed pulp is 95 to 50% by weight, preferably 93 to 70% by weight of mechanical pulp, and 5 to 5% by weight of chemical pulp.
50% by weight, preferably 7-30% by weight is suitable. In the mixed pulp, if the ratio of mechanical pulp is greater than the above range, the opacity of the paper obtained will improve to some extent, but the strength will tend to decrease. Furthermore, if the ratio of chemical pulp is greater than the above range, the strength of the paper obtained will improve, but the opacity will tend to decrease, making it difficult to obtain paper suitable for weight reduction. The inorganic powder used in the present invention has an aggregate form of flakes with an average diameter in the longitudinal direction of 0.1 to 30 microns and a thickness of 0.005 to 0.1 micron. Calcium silicate (b) containing in incorporated form silicon dioxide in the range of 4 to 70% by weight of silicon dioxide and 13% by weight based on gyarolite, based on gyarolite.
or (c) a calcium silicate/calcium sulfate complex containing the calcium silicate or calcium sulfate in an incorporated form;
It consists of at least one of a calcium sulfate complex and an aluminum oxide complex. These inorganic powders 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 mixed at a reaction temperature of 150 to 250°C at a molar ratio of SiO ₂ /CaO of 1.6 to 3.2. By reacting with , calcium silicate having a diairolite crystal structure and a SiO ₂ /CaO molar ratio of 1.6 to 3.2 is obtained. This calcium silicate is estimated to be represented by the general formula 2CaO・SiO ₂・nSiO ₂・mH ₂ O (where m is a positive number and n is generally a number from 0.1 to 3.4), and amorphous silicon dioxide is contained in the crystal. It exists in an incorporated form, and its grain boundaries and constituent bonding forms cannot be identified even from photographs taken with a transmission electron microscope at a magnification of 20,000 to 200,000 times. In addition, insoluble silicon dioxide such as activated clay, hydrated silicic acid, diatomaceous earth, etc. and calcium compounds such as slaked lime, quicklime, etc. are mixed at a SiO ₂ /CaO molar ratio of 1.8 to 2.5.
By reacting at a reaction temperature of ~250°C, the calcium silicate mixed with silicon dioxide can be obtained. Among the above-mentioned methods for producing calcium silicate, calcium silicate obtained by a method using water-soluble silicate as a raw material has the following properties such as paper strength,
It is highly effective in improving the opacity and the effect of preventing ink bleed through, and is therefore preferably used in the present invention. 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 a collection of flakes resembling rose petals. The size, shape, etc. of the flakes vary depending on the type of raw materials, raw material ratio, manufacturing conditions, etc., and cannot be absolutely limited, but generally the average diameter in the longitudinal direction is 0.1.
~30 microns, with a thickness of about 0.005 to 0.1 microns, often circular or elliptical. Hereinafter, in this specification, the calcium silicate may be referred to as petal-shaped calcium silicate. When using calcium sulfate, that is, gypsum (in this specification, gypsum is used to include not only dihydrate salts but also hemihydrate salts and anhydrous salts) as the water-soluble calcium compound, gypsum aqueous A mixed system in which silica alkali is gradually added to the suspension and reacted, or a reacted precipitate is filtered out and a slurry solution after washing if necessary is hydrothermally treated to form a petal-shaped product. Calcium silicate can be obtained. However, CaSO ₄ /Na ₂ O or
When the molar ratio of K ₂ O is 1.1 or more, a composite of petal-shaped calcium silicate and gypsum is obtained. The gypsum exists in a form incorporated into the petal-like calcium silicate, similar to the amorphous silicon dioxide in the petal-like calcium silicate, and generally, when the gypsum content is up to about 13% by weight, there is no difference in electron micrographs. No grain boundaries or constitutive bonding forms can 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-like calcium silicate and gypsum is obtained. When the amount of gypsum mixed in the composite with gypsum increases, the effect of improving the strength of the resulting printing paper tends to decrease. Therefore, the gypsum content in the composite of petal-like calcium silicate and gypsum is 10
It is preferable to make it less than % by weight. Further, by reacting the petal-shaped calcium silicate or a complex of petal-shaped calcium silicate and gypsum with sulfuric acid band [Al ₂ (SO ₄ ) _{3.18H 2} O], a calcium silicate/aluminum oxide composite is obtained. The complex has the general formula _aAl2O3・_2-3a /2CaO・_bSiO2・_mH2O (where a is 0.06 to 0.2 and b is 1.6 to
3.2, and m is a positive number. ) is shown. The greatest feature of the printing paper of the present invention is that the specific mixed pulp contains the inorganic powder. As mentioned above, even if a mixed pulp of chemical pulp and mechanical pulp is used, it is almost impossible to obtain paper with excellent strength and opacity. Further, the effect of preventing ink bleed-through is hardly improved. In the present invention, by incorporating the inorganic powder into the above-mentioned specific mixed pulp, it is possible to achieve both excellent strength and opacity that could not be achieved with the above-mentioned mixed pulp alone, and also to have an excellent ink strike-through prevention effect. You can get printing paper. In the printing paper of the present invention, the ratio of mixed pulp and inorganic powder is 0.1 to 6 parts by weight, preferably 0.3 to 4 parts by weight of inorganic powder to 100 parts by weight of mixed pulp.
Parts by weight. When the amount of the inorganic powder is less than the above range, the strength and opacity of the printing paper and the effect of preventing ink bleed through tend to decrease. Further, even if the inorganic powder is used in an amount exceeding the above range, the effect reaches a ceiling and is not economical. As the method for producing the printing paper of the present invention, any known wet papermaking method may be employed without any limitation. In addition, the printing paper of the present invention generally contains mixed pulp in an amount within a range that does not adversely affect the above-mentioned properties.
Known fillers in an amount of not more than 100 parts by weight,
Additives such as pigments and paper strength enhancers, and other pulps such as semi-chemical pulps may be included as appropriate. As understood from the above description, the printing paper of the present invention is excellent in all of paper strength, opacity, and ink strike-through prevention effect, and is therefore useful for reducing the weight of printing paper. In particular, it is suitably used as a printing paper with a basis weight of 40 to 50 g/m ² where the above-mentioned properties are significantly deteriorated due to weight reduction. EXAMPLES Examples are shown below to specifically explain the present invention, but the present invention is not limited to these Examples. Reference Example 1 880 g of gypsum dihydrate and 20 g of water were added to a mixing reactor and stirred well. (Reaction step) Next, while stirring this slurry, 0.243 mol/sodium acid acid (SiO ₂ /Na ₂ O molar ratio 2.5) was added at 25°C under atmospheric pressure.
20 was added over 40 minutes at a rate of 0.5/min.
In this case, the charged CaSO ₄ /Na ₂ O・nSiO ₂ molar ratio is
It was 1.05. The slurry obtained in the above reaction step was taken out into a filter cloth covered with a filter cloth and placed under reduced pressure (400 mm
Hg) After filtration, 30 g of water was added to wash the product. (Washing step) The cake obtained in the above washing step was transferred to a stirring tank, and 35% of water was added thereto and stirred uniformly to form a slurry. (Slurrying process) The slurry obtained in the slurrying process was transferred to an autoclave (inner volume 50), sealed, and heated at 200°C for 5 hours.
Hydrothermal treatment was performed. After the reaction was completed, a product slurry was obtained. A portion of the slurry was filtered under reduced pressure using a Nutssie filter, and the resulting product was dried at 110° C. for 8 hours or more and its physical properties were measured. The bulk specific volume was 12.8 cc/g, and the oil absorption amount was 4.2 cc/g. Furthermore, as a result of X-ray diffraction,
The pattern of gyrolite type calcium silicate was shown. Chemical analysis results are CaO 24.9%, SiO ₂ 65.8%,
Burning weight loss was 9.3%. From this result, the calcium silicate obtained in the above procedure is 2CaO・3SiO ₂・
It was confirmed that it was 1.93SiO ₂ .2.32H ₂ O. Photos taken with an electron microscope at 10,000x magnification confirmed that the flower is composed of a collection of petals with an average longitudinal diameter of approximately 2 μm and a thickness of less than 0.1 μm. Reference example 2 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 formed at the same time as the mixture was mixed, but the mixture was placed in an autoclave, sealed, and allowed to react at a temperature of 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 filtered, washed twice with 100 c.c. of ion exchange, 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.
Also, bulk specific volume is 14.2cc/g, oil absorption is 4.21
cc/g, and the refractive index was 1.50. The general formula of calcium silicate obtained in the above procedure is 2CaO・3SiO ₂・
It was possible to display 2.05SiO ₂・2.42H ₂ O. A scanning electron micrograph of this calcium silicate, magnified 10,000 times, shows that it is composed of an aggregate of flakes with an average longitudinal diameter of 2 microns and a thickness of 0.1 micron or less.
The shape resembled the petals of a flower. Furthermore, as a result of a transmission electron micrograph taken at a magnification of 100,000 times, it was not possible to discern the grain boundaries or bonding form of the calcium silicate obtained in this experiment, even though it contained silicon dioxide. Further, from the results of X-ray diffraction of the above-mentioned calcium silicate, it was found that it was a gyrolite crystal. Furthermore, 100 c.c. of distilled water was added to 1 g of petal-shaped calcium silicate obtained above, and the mixture was heated in a tabletop ultrasonic cleaner (50 W).
When the mixture was dispersed for 30 minutes, no silicon dioxide was dispersed, confirming that no silicon dioxide was mixed. Reference Example 3 Pour 6.5 g of gypsum dihydrate (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. When the above-mentioned powder was photographed with a scanning electron microscope at a magnification of 10,000 times, it was confirmed that it was composed of petal-like flakes with a longitudinal diameter of 2 microns and a thickness of 0.1 micron or less. However, in the photograph, crystals that appeared to be type anhydrite could not be visually identified. The powder had a bulk specific volume of 15.2 cc/g and an oil absorption of 4.30 cc/g. Reference Example 4 1.0 g of petal-shaped calcium silicate obtained in the same manner as Reference Example 1 was made into a 10% slurry, and then 4 ml of 10% sulfuric acid band [Al ₂ (SO ₄ ) _{3.18H 2} O] was slowly added and stirred. The reaction was allowed to proceed for 1 hour. The reactants are filtered,
After washing twice with 100 c.c. of ion-exchanged water, it was dried at 100°C for 8 hours. This dried product was chemically stable whether it was dried and powdered or left 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, and its general formula is based on the results of chemical analysis.
It could be expressed as 0.11Al ₂ O ₃・0.835CaO ・2.52SiO ₂・2.4H ₂ O. Example 1 The slurry obtained after hydrothermal synthesis of calcium silicate obtained in Reference Example 1 was used as an inorganic powder. Pulp is mechanical pulp, GP20% by weight, RGP56% by weight
and chemical pulp, mixed pulp consisting of 24% by weight of NBKP, and other semi-chemical pulps.
33 parts by weight of CGP was added to 100 parts by weight of the above mixed pulp. The above-mentioned inorganic powder was added in a slurry state after hydrothermal synthesis to the above-mentioned pulp which had been thoroughly decomposed by adding water, and the proportions to the mixed pulp were varied, and then sulfate band [Al ₂ (SO ₄ ) _{3.18H 2} O] 1 part by weight was added as an aqueous solution to 100 parts by weight of the above pulp (absolutely dry), stirred uniformly, and paper was made according to JISP 8209 "Hand-sheeted paper preparation method for pulp testing".
The paper was made so that the basis weight of the resulting printing paper was 49 g/m ² . Table 1 shows various properties of the obtained printing paper. For comparison, Table 1 also shows the papermaking results without the addition of the inorganic powder.

[Table] Example 2 In Reference Example 1, three types of petal-shaped calcium silicates shown in Table 2 were synthesized by changing the molar ratio of the raw silicate and calcium compound, and the results were obtained after hydrothermal synthesis in the same manner as in Example 1. It was used as an inorganic powder in a slurry state. In addition, the SiO ₂ /CaO molar ratio, oil absorption amount,
The bulk specific volume is a value measured after drying the slurry after hydrothermal synthesis in an oven (at 110° C. for 8 hours or more).

[Table] Paper was made in the same manner as in Example 1, except that the above-mentioned petal-shaped calcium silicate was used as the inorganic powder. The results are shown in Table-3.

[Table] Note that No. 1 is a comparative example.
Example 3 Paper was made in the same manner as in Example 1, except that the mixed pulp shown in Table 4 was used.
The results are shown in Table-5.

【table】

[Table] Note that 1, 2, 3, 7 and 8 are comparative examples.
Example 4 The pulp composition was fixed as a mechanical pulp of 20% by weight of GP, 10% of RGP, and 45% of TMP, and a semichemical pulp of 25% by weight of CGP as other pulps, and NBKP as a chemical pulp.
was used. The tensile strength of the resulting printing paper is 2.0Kg
Paper was made in the same manner as in Example 1, except that the amounts of inorganic powder, NBKP, and pulp with the above-mentioned fixed composition were changed so that f. The results are shown in Table-6. As is clear from Table 6, it was confirmed that the petal-shaped calcium silicate has a paper strength-enhancing effect, which makes it possible to reduce the amount of NBKP added, and is effective in improving whiteness, opacity, and preventing strike-through. Note that No. 1 in Table 6 is a comparative example in which petal-shaped calcium silicate was not added.

[Table] Example 5 In Example 4, the basis weight of printing paper was 49g/ ^m2 .
The tensile strength of the printing paper was adjusted to 2.0 Kgf in the same manner as in Example 4, except that the weight was reduced to 45 g/m ² .
The results are shown in Table-7. As is clear from Table 7, it is difficult to maintain the physical properties (tensile strength, opacity) of 49 g/m ² by adding pulp alone. However, when petal-shaped calcium silicate was coexisting, both tensile strength and opacity improved, and whiteness and
It was confirmed that it was effective in preventing strike-through.

[Table] Example 6 The same operation as in Example 1 was carried out except that the petal-shaped calcium silicate obtained in Reference Example 2 was used in a slurry state as the inorganic powder. For comparison, Table 8 includes the paper making results when no filler was added.

[Table] Comparative Example 1 The same operation as in Example 1 was performed except that talc (average particle size 9 to 10 μm) was used in place of the inorganic powder in Example 1. For comparison, Table 9 includes the papermaking results when no filler was added.

[Table] Example 7 In Example 1, the calcium silicate gypsum complex obtained in Reference Example 3 and the calcium silicate amminium oxide complex obtained in Reference Example 4 were used as the inorganic powder, and the pulp components Printing paper was produced in the same manner except that no semichemical pulp was added to the paper. Table 10 shows the properties of the obtained printing paper.
Shown below.

【table】

Claims (1)

[Claims] 1. Mechanical pulp 95 to 50% by weight and chemical pulp 5 to 50% by weight
For 100 parts by weight of mixed pulp consisting of % by weight,
The average longitudinal diameter is 0.1-30 microns and the thickness is
(a) Calcium silicate having an aggregate form of flakes of 0.005 to 0.1 micron, having a skeleton of gyrolite and containing silicon dioxide in an incorporated form in the 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. or (c) the calcium silicate or calcium silicate.
Complex of calcium sulfate complex and aluminum oxide. At least one kind of inorganic powder selected from 0.1~
Printing paper containing 6 parts by weight. 2. The printing paper according to claim 1, having a basis weight of 40 to 50 g/m ² .