JPH06166987A - Silicic acid hydrate filler for paper-making, its production and paper filled therewith - Google Patents

Abstract

PURPOSE:To obtain a hydrated silicic acid filler which can give excellent opacity not accompanied with increased friction coefficient of paper, to provide the production process therefor and to produce the paper containing the filler. CONSTITUTION:This silicic acid filler for paper-making is composed of fine particles of amorphous silicic acid hydrate as a product in neutralization of aqueous sodium silicate solution containing fine particles of amorphous metal compounds. The filler can be produced by the process characterized by substituting an aqueous solution of an acidic metal sulfate, a precursor of the hardly soluble metal oxide hydrate for a part of the sulfuric acid added by dividing in portions in the wet process for the filler from sodium silicate to carry out the reaction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrated silicic acid filler for papermaking, which is excellent in opacity, a method for producing the same, and a paper in which the filler is internally added.

[0002]

2. Description of the Related Art In recent years, the weight of paper has been reduced due to the demand for resource saving and energy saving. When the paper is lightweight and thin, the strength of the paper tends to decrease, and the opacity of the paper and the opacity of printing also decrease, so-called strike-through easily occurs. Strikethrough is a phenomenon in which printed patterns and letters can be seen through from the back side, and it is difficult to read when the strikethrough is noticeable. See-through is show-through due to the decrease in opacity of white paper,
This is a phenomenon caused by mutual involvement of strike-through in which the vehicle of printing ink penetrates in the thickness direction of the paper to reduce the opacity.

In order to prevent this strike-through, various inorganic and organic fillers are generally added to the paper, and at present, as a typical strike-through preventive filler which is relatively inexpensive, it has a specific particle state. Hydrated silicic acid of
2-74620, JP-A-58-502004). Further, as a method for producing such silicic acid for papermaking, for example, Japanese Patent Laid-Open No.
-16705, JP 47-16706, JP 60-65
713 and JP 61-141767 are known.

Further, in using a silicic acid filler for papermaking, for example, one used in combination with a nonionic polymer (JP-A-58).
-60098, JP 62-15391), those using special silicic acid (JP 58-98494), those used as a mixture of colloidal silicic acid and cationized amphoteric guar gum (special (Kaisho 58-502064), CaF ₂ , Mg
Those used in combination with F ₂ (Japanese Patent Laid-Open No. 60-209099), those used in combination with urea resin and the like (Japanese Laid-Open Patent Nos. 61-4756 and 61)
-245399), a combination of zeolite or aluminosilicate (Japanese Patent Laid-Open No. 61-70098, Japanese Patent Laid-Open No. 61-
No. 97499), and a combination of lime mats (Japanese Patent Laid-Open No. 61-1)
79398), those used in combination with calcium sulfate and calcium silicate (JP-A-63-99397), and the like.

Inorganic fillers for papermaking other than silicic acid include, for example, magnesium silicate (JP-A-52-77204), zeolite (JP-A-55-90417), calcium silicate.
(JP-A-58-91898, JP-A-59-43197), a reaction product of a clay mineral and an alkaline earth metal hydroxide (JP-A-60-200821), aluminum silicate or Aluminum modified silicic acid (JP-A-61-502338), a core of clay mineral with an amorphous silica film formed (JP-A-1
(−77699 gazette) has been proposed.

[0006]

As described above, hydrated silicic acid is most practically used as the inorganic strike-through prevention filler used in lightweight paper, but it is a fine particle. Therefore, in the papermaking process, the yield in the paper is poor, and when the internal addition amount of hydrated silicic acid is increased to further improve the strike-through prevention effect, the friction coefficient of the paper increases and It also reveals drawbacks such as poor paper running properties.

Therefore, in its use, although it has been used in combination with other chemicals and fillers and surface modification as described above, none of them is an essential improvement. For example, use in combination with urea resin powder is not effective. Although it is excellent in reducing the friction coefficient, there is a problem such as a significant cost increase compared to the addition of silicic acid alone.

[0008] In view of the above problems, the present inventors have made earnest studies on the improvement of silicic acid filler within a range that can be economically carried out. The present invention has been completed by discovering that the presence of the above compound makes an excellent papermaking filler.

That is, an object of the present invention is to provide a hydrated silicic acid filler for papermaking which is excellent in opacity without increasing the friction coefficient of the paper, a method for producing the same, and a paper in which the filler is internally added. is there.

[0010]

The hydrated silicic acid filler for papermaking of the present invention is preferably a fine amorphous metal compound in the fine amorphous hydrated silicic acid obtained by the neutralization reaction of an aqueous sodium silicate solution. Is characterized in that it is contained in an amount of 1 to 20% by weight.

Further, the present invention provides a method for producing a hydrated silicic acid filler for papermaking, which is a method for producing a silicic acid filler for papermaking based on a wet method in which sulfuric acid is divided into an aqueous solution of sodium silicate. The constitutional feature is that the aqueous solution of acidic metal sulfate, which is a precursor of the sparingly soluble hydrated oxide, is replaced with and reacted.

Further, the paper according to the present invention is characterized by internally adding the hydrated silicic acid filler for papermaking.

As described above, the hydrated silicic acid-based filler for papermaking according to the present invention is composed mainly of fine amorphous hydrated silicic acid containing a fine amorphous metal compound.

Here, the fine amorphous metal compound is a reaction product of an aqueous solution of sodium silicate and an acidic soluble metal salt, and in many cases, it is a metal silicate, as will be understood from the production method described later. Although it is a fine particle of an acid salt, it may partially contain a hydrated metal oxide which is a hydrolysis product. Examples of such a metal compound include one or two kinds of metal compounds selected from magnesium, zirconium, and titanium. Magnesium is most practical and preferable.

The content of the metal compound is preferably in the range of 1 to 20% by weight, more preferably 1 to 15% by weight in terms of metal oxide, and the silicic acid is 85 to 99% by weight as SiO _2. Is in the range. The reason for this is that, as will be described later, the improvement properties as a paper filler are insufficient when the content of the metal compound is less than 1% by weight, and the higher the content, the better, but it is not economical to exceed 20% by weight.

The hydrated silicic acid-based filler for papermaking according to the present invention is indefinite because no clear diffraction line characteristic is observed in X-ray diffraction analysis. It is a fine, amorphous, uniform aggregate in which it is not possible to distinguish between silicate and metal compounds.

In many cases, the hydrated silicic acid filler for papermaking according to the present invention can be used in the papermaking process without washing and drying the slurry obtained by the production method described below. The dried powder can be slurried for use. However, in this case, it is desirable to perform re-agglomeration by a strong shearing dispersion treatment such as a colloid mill and a homogenizer, and further to perform wet classification if necessary before use.

In the above dry powder, the oil absorption and the whiteness decrease as the content of the metal compound increases, but in the filler-added paper using the slurry,
In particular, the opacity gradually increases to have a preferable function for preventing strike-through, and the whiteness is improved on the contrary.

The raw material sodium silicate aqueous solution used is SiO 2.
₂ / Na ₂ O in a molar ratio of 2 to 4, particularly JI
No. S3 sodium silicate is suitable, and it is diluted with water and has a concentration in the range of 5 to 15% by weight, particularly 5 to 10% by weight as SiO ₂ . On the other hand, the raw sulfuric acid is not particularly limited in concentration, but in the present invention, concentrated sulfuric acid may be used from the viewpoint of productivity. Furthermore, as a raw material metal sulfate used as a partial substitute for sulfuric acid, which is a feature of the present invention,
It means an aqueous solution of magnesium sulfate, zirconium sulfate, titanium sulfate, zirconium oxysulfate, titanium oxysulfate, etc. The concentration is preferably the same as the above reason. The amount of the metal sulfate used is such that the metal oxide is mixed with the raw material sulfuric acid in an amount within the above range.

In the present invention, a mixed solution containing a metal sulfate in an aqueous solution of sodium silicate is used at a reaction system temperature of 70 ° C. or higher, preferably 8
It is necessary to carry out the reaction at 0 to 95 ° C., and in this case, the stoichiometric amount necessary for the reaction of the reaction formulas (1) and (2) described below is intermittently added to the mixture at least twice. .

In the case of producing hydrated silicic acid by neutralizing an aqueous solution of sodium silicate, such a method of divided addition of acid is known.
(See, for example, JP-B-51-25235 and JP-A-62-252312), which is also necessary in the present invention in terms of operation and product quality, and is particularly important when concentrated sulfuric acid is used.
For example, the addition amount of the mixed solution in the first time is preferably 20 to 50%, particularly 30 to 45% of the stoichiometric amount, and the reaction is substantially performed in the second time, and the remaining amount is left in the third time. The amount is added to adjust the pH of the reaction system until the pH is around 5, and the reaction is terminated. It is desirable that the reaction system be circulated by a pump so that a strong shearing action works, and after the addition of the mixed solution each time, a desired aging time of, for example, about 1 to 2 hours is provided and an addition interval is set. It is necessary.

After completion of the reaction, the mother liquor is separated by a conventional method,
If necessary, this mother liquor can be recovered as sodium sulfate, while the filter cake can be made into a product as a hydrated silicate filler for papermaking by adjusting the slurry after washing to a desired concentration, and if necessary, You may commercialize as a powder. If necessary, the slurry obtained above may be wet pulverized or classified to adjust the viscosity, and then be used as a product slurry.

[0023]

The method for producing a hydrated silicic acid-based filler for papermaking according to the present invention is, in principle, the same as the method for producing a wet hydrated silicic acid by neutralizing an aqueous solution of silica silicate and sulfuric acid. The present invention is characterized in that metal sulfate-containing sulfuric acid is used instead of sulfuric acid. In this case, the main reaction represented by the formula (1) occurs, and Na ₂ O · nSiO ₂ + H ₂ SO ₄ → nSiO ₂ ↓ + Na ₂ SO ₄ + H ₂ O (1) Further, the metal sulfate is changed to magnesium sulfate. And if
The main reaction represented by the formula (2) occurs, and Na ₂ O · nSiO ₂ + MgSO ₄ → MgO · nSiO ₂ ↓ + Na ₂ SO ₄ ··· (2) Further, since the reaction system is alkaline, the formula (3) It is conceivable that hydrolysis will occur. MgSO ₄ +2 NaOH → Mg (OH) ₂ ↓ + Na ₂ SO ₄ (3)

Therefore, the hydrated silicic acid-based filler for papermaking according to the present invention has a fine amorphous form in which hydrated silicic acid is the main agent and insoluble metal compounds such as magnesium silicate and magnesium hydroxide are simultaneously co-precipitated. It is considered to be a mixture of particles. Such a mixture is improved and particularly effective in improving the opacity of paper and preventing strike-through, as compared with a conventional filler for papermaking which is hydrated silicic acid.

[0025]

EXAMPLES In order to specifically describe the present invention, examples and comparative examples will be described below. Example 1 A reaction vessel equipped with a stirrer and a circulation pump was charged with 100 parts by weight of JIS No. 3 sodium silicate and 300 parts by weight of water,
The reaction system is maintained at a temperature of 85 to 90 ° C. all the time with vigorous stirring. Then, a mixed solution (18.7 parts by weight) of 14.3 parts by weight of concentrated sulfuric acid (98% by weight), 1.8 parts by weight of magnesium sulfate crystal (MgSO ₄ .7H ₂ O) and 2.6 parts by weight of water was prepared. The reaction was carried out while adding and aging in the manner shown in 1.

[0026]

[Table 1] First time Second time Third time Addition amount (% relative to the total amount) 40 40 40 Addition time (min) 8 15 30 Aging time (min) 120 30 30

After the completion of the reaction, the pH of the reaction system was adjusted to 5.5, followed by aging, filtration and dispersion, washing with water, and redispersion in water to obtain a 9 wt% slurry product.

Example 2 In Example 1, concentrated sulfuric acid and magnesium sulfate crystals (M
gSO ₄ .7H ₂ O) under the same operation and conditions as in Example 1 except that 33.4 parts by weight of a mixed solution (11.4 parts by weight of concentrated sulfuric acid, 9 parts by weight of magnesium sulfate, 13 parts by weight of water) were used. The reaction was carried out by divided addition and aging to obtain a 9 wt% slurry.

Example 3 In Example 1, concentrated sulfuric acid and magnesium sulfate crystals (M
gSO ₄ · 7H ₂ O) mixed with a solution 51.7 parts by weight (concentrated sulfuric acid 7.7 parts by weight, 17.9 parts by weight of magnesium sulfate, water 2
5.9 parts by weight) was used to carry out the reaction by divided addition and aging under the same operations and conditions as in Example 1 to obtain a 9% by weight slurry.

Example 4 In Example 1, concentrated sulfuric acid and magnesium sulfate crystals (M
gSO ₄ · 7H ₂ O) mixed with a solution 88 parts by weight (concentrated sulfuric acid 0.
5 parts by weight, magnesium sulfate 35.8 parts by weight, water 51.7
(Parts by weight) was used to carry out the reaction by divided addition and aging under the same operations and conditions as in Example 1 to obtain a 9% by weight slurry.

Example 5 In Example 1, instead of JIS No. 3 sodium silicate, JIS No. ₂ sodium silicate (SiO ₂ = 28.3%, Na ₂ O) was used.
= 11.7%) with 100 parts by weight, the mixed solution 113 parts by weight of concentrated sulfuric acid and magnesium sulfate crystals _{(MgSO 4 · 7H 2 O)} ( concentrated sulfuric acid 0.1 parts by weight, 46.2 parts by weight of magnesium sulfate, 9 wt% by reacting by divided addition and aging under the same operations and conditions as in Example 1 except that water (66.7 parts by weight) was used.
A slurry of was obtained.

Comparative Example 1 In Example 1, instead of the mixed solution of concentrated sulfuric acid and magnesium sulfate, 15 parts by weight of total concentrated sulfuric acid was reacted by divided addition and aging under the same operations and conditions as in Example 1 to obtain 9% by weight.
A slurry of was obtained. After washing and filtering each of the above-obtained slurries, they were dried and pulverized at a temperature of 110 ° C. for 12 hours, and then conditioned at 65 ° RH at 20 ° C., and the properties of white fine powder obtained were examined. However, the results shown in Table 2 were obtained.

[0033]

[Table 2]

Papermaking Example An oriented paper machine manufactured by Kumagai Riki Kogyo Co., Ltd. was used as a papermaking raw material, NBKP: LBKP: TMP: GP = 10: 10:
Using a pulp slurry having a mixing ratio of 50:30 and using the filler slurries prepared in Examples 1 to 5 and Comparative Example 1 as a filler, papermaking was performed so that the basis weight was 40 g / m ² and the ash content in the paper was 2%. After being dehydrated by a press, it was dried by a cylinder dryer. In addition, a blank was prepared without adding the filler slurry. After adjusting the humidity in an atmosphere of 20 ° C. and 65% RH, opacity, whiteness, print opacity, and dynamic friction coefficient were measured. The results of these measurements are shown in Table 3.

[0035]

[Table 3]

[0036]

The hydrated silicic acid filler for papermaking according to the present invention not only improves the opacity and whiteness of the paper as compared with the conventional silicic acid filler, but also lowers the friction coefficient of the paper. The degree becomes good in proportion to the content of the metal compound. Further, according to the present invention, it is possible to industrially advantageously produce an improved hydrated silicic acid filler for papermaking without substantially changing the production method similar to that of conventional hydrated silicic acid. You can

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiro Kobayashi 5-21-1, Oji, Kita-ku, Tokyo Inside the Central Research Laboratory, Tojo Paper Manufacturing Co., Ltd. (72) Isao Shikano 5--21, Prince, Kita-ku, Tokyo Central Research Institute, Tojo Paper Co., Ltd.

Claims (6)

[Claims] 1. A hydrated silicic acid-based filler for papermaking, characterized in that the fine amorphous hydrated silicic acid obtained by the neutralization reaction of an aqueous solution of sodium silicate contains a fine amorphous amorphous metal compound. 2. The hydrated silicic acid filler for papermaking according to claim 1, wherein the fine amorphous metal compound is a magnesium compound. 3. The hydrated silicic acid filler for papermaking according to claim 1, wherein the content of the fine amorphous metal compound is 1 to 20% by weight in terms of oxide. 4. A method for producing a silicic acid filler for papermaking, which is based on a wet method in which sulfuric acid is divided into an aqueous solution of sodium silicate, and an acidic metal sulfate aqueous solution in which a part of sulfuric acid is a precursor of a sparingly soluble hydrated metal oxide. The method for producing a hydrated silicic acid-based filler for papermaking, which comprises reacting the same with the above. 5. The method for producing a hydrated silicic acid filler for papermaking according to claim 4, wherein the acidic metal sulfate aqueous solution is a magnesium sulfate aqueous solution. 6. A paper comprising the hydrated silicic acid filler for papermaking according to any one of claims 1 to 3 as an internal additive.