JP3531153B2 - Modified causticized light calcium carbonate - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic wire which is a problem when making paper by using a filler containing light calcium carbonate produced in the causticizing step of kraft pulp as a main component as an internal filler for neutral papermaking. The present invention relates to a technique for improving deterioration of wear resistance of the.

[0002]

2. Description of the Related Art A filler is usually added to paper used for printing or writing for the purpose of improving whiteness, opacity, smoothness, writability, touch and printability.
Paper is conventionally made at around pH 4.5. In so-called acidic papermaking, talc, clay, titanium oxide, etc. are used as fillers. At this time, a plastic wire is used for the wire of the paper machine because of its long life and easy handling.

In recent years, the use of domestically produced calcium carbonate as a filler in place of expensive talc and clay, which are imported products, reduces costs, improves paper strength, and further promotes the closure of white water. , Paper making in neutral or weakly alkaline areas, which has many advantages in terms of cost, environmental measures, etc., is shifting to so-called neutral paper making,
It is a situation in which it will continue to spread.

Calcium carbonate used as a filler in this neutral papermaking is produced by heavy calcium carbonate obtained by dry or wet mechanical crushing of natural limestone, and chemically synthesized, that is, by blowing CO ₂ into quicklime or slaked lime. There is precipitated calcium carbonate (synthetic calcium carbonate). Further, recently, light calcium carbonate produced by utilizing the causticizing step of the kraft pulp step (hereinafter referred to as causticizing light calcium) has also begun to be used.

Of these, causticized light calcium is excellent in that when it is used as an internal filler, sufficient opacity is obtained, in addition, size and paper strength are not significantly reduced, and the manufacturing cost is low. ing. However, when paper is made using causticized light calcium as the internal filler, the abrasion resistance of the plastic wire is inferior to that when talc is used as the internal filler.

When the wire is heavily worn, the wire must be replaced frequently, but during that time, the operation of the paper machine needs to be stopped, and accordingly, the productivity is reduced and the papermaking efficiency is deteriorated. In particular, in twin-wire paper machines, which have made remarkable progress in recent years, the effect of stopping the wire exchange on productivity is further increased by increasing the size and speed of the paper machine. In addition, plastic wires are generally expensive, so if the wear of the filler is high,
Either bronze wire was used, or neutral papermaking was abandoned and acid papermaking was continued.

[0007]

Neutral papermaking has been widely used in Europe, but in Europe, marine microorganisms such as foraminifera, which has a low degree of wire wear and a high degree of whiteness, are used. Chalk, which is one of the origin calcium carbonates, is widely distributed, so in the 1970s, conversion to neutral papermaking, which used this as a filler, started rapidly.

[0008] Neutral papermaking spread to North America and Japan after that, but unlike in Europe, chalk with low wire abrasion was not distributed in these areas, so heavy calcium carbonate obtained by grinding limestone has been used. It was In addition, the causticized light calcium produced in the causticizing process of kraft pulp, which has great advantages in terms of cost and environmental measures, tends to have a large particle size with an indefinite morphology, similar to heavy calcium carbonate. Aggravates wire wear. These factors are also a major factor behind the slow shift to neutral papermaking in Europe.

An object of the present invention is to improve the wear resistance of a plastic wire when using causticized light calcium as a filler for internal addition, and to further promote neutral papermaking.

[0010]

[Means for Solving the Problems] As a result of intensive studies conducted by the present inventors on the wear resistance of a plastic wire, which is a problem during papermaking when causticized light calcium is used as an internal filler for neutral papermaking. , A causticized light calcium filler as a main component is dispersed in water, and an acidic sulfate is added to the dispersion to neutralize the pH of the dispersion to 6.0 to 10.0. It has been found that a filler having a low wire wear property can be obtained by reacting calcium with a sulfate to modify the filler, and the present invention has been completed. Here, the sulfate having acidity shows acidity when the sulfate is dissolved in water, and examples thereof include a sulfate band (aluminum sulfate), copper sulfate, zinc sulfate and the like. Among these, it is preferable to use a sulfuric acid band that is commonly used in the papermaking industry for size, fixation of chemicals such as dyes and fillers, and improvement of pulp fiber yield in the process of acidic papermaking. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS From the above studies, it was found that the effect of improving the wear resistance of the plastic wire is not so great when the causticized light calcium is made into a small particle size simply by crushing. This is because the pulverization results in a small particle size and a slight abrasion property is improved, while sharp edges are increased, so that the soft plastic wire is sharply and deeply damaged. Especially when the particle size is excessively reduced, this effect is extremely large. In addition, causticized light calcium contains some impurities such as calcium hydroxide in the particles. The causticized light calcium wears the plastic wire because the calcium hydroxide elutes during papermaking and cracks occur in the causticized light calcium particles, which is caused by the shearing force of the stirrer, fan pump, etc. in the papermaking process. It is considered that the cracks increase sharp edges as in the case of crushing.

As a countermeasure for the abrasion resistance of the causticized light calcium plastic wire, it is possible to use a mixture of talc, but the unneutralized causticized light calcium does not have a sufficient wire protection effect even when mixed with talc. It was

As a result of diligent studies, the present inventors have found that the causticized light calcium dispersion is treated with an acid sulfate in order to reduce sharp edges that are considered to promote wear existing in the causticized light calcium itself. It was found that an excellent effect can be obtained by the Japanese treatment. Further, it has been found that the wire wear property is further improved by mixing and using the neutralized causticized light calcium and talc as a filler.

That is, a causticized light calcium dispersion (usually pH)
11.0 to 13.0) is pulverized by a pulverizer such as a sand mill, and then neutralized with an acidic sulfate to pH 6.0 to 10.0. Here, p is obtained by the treatment with acid sulfate.
If it is not less than H10, neutralization will be insufficient, sharp edges will not be reduced, and wire abrasion will not be improved. Also, pH 6
If it is less than the above, elution of the light calcium carbonate itself occurs, which is not realistic. Furthermore, as a neutralizing method, water is repeatedly washed instead of addition of acidic sulfate, and even if the pH is 6 to 10, edges and cracks remain in the causticized light calcium particles, The wear resistance of plastic wires is not improved.

In the crushing process, the average particle size is 0.8
It is preferable to grind to a range of up to 2.0 μm. When the average particle size is smaller than 0.8 μm, the wire wear is not sufficiently improved due to an increase in sharp edges due to an excessively small particle size, even if neutralized with an acidic sulfate.
On the other hand, when it is larger than 2.0 μm, the effect of reducing the particle size is not obtained, and therefore the abrasion resistance is not sufficiently improved.

In the neutralization treatment, when the causticized light calcium is a powder, it is pulverized to a desired particle size and then dispersed in water, or dispersed in water and then pulverized to a desired particle size for dispersion. Neutralization is carried out by adding acidic sulfate as it is or as an aqueous solution. Further, when a dispersion containing calcium carbonate as a main component obtained from the causticizing step is used, the concentration may be adjusted appropriately, and pulverization may be performed for neutralization. The present invention is the same in both steps. The effect can be obtained.

Furthermore, when the modified causticized light calcium of the present invention is used as a filler for papermaking, when the modified causticized light calcium is a powder, it is dispersed in water to form a dispersion, which is used as a dispersion from the manufacturing process. When it is obtained, the concentration is adjusted appropriately before use.

Although the mechanism for improving the wear resistance of the plastic wire is unknown, the causticized light calcium dispersion liquid in which a sharp edge is generated by the pulverization treatment is neutralized with a sulfate having an acidity to form an edge. It is considered that the sulfate salt is deposited on the part and the sharpness or number of edges is reduced. Also, by reacting the calcium hydroxide in the causticized light calcium particles with the acidic sulfate,
It is considered that the plastic wire is less likely to be eluted during the papermaking process, the number of cracks in the particles is reduced, the number of particles is less likely to be broken, and the sharp edges are lessened, so that the abrasion of the plastic wire is improved.

[0019]

EXAMPLES The effects of the present invention will be specifically described below with reference to examples, but the present invention is not limited to these. The% and parts described in the examples are% by weight and parts by weight.

<Evaluation test of wire abrasion resistance> Device: Japan Filcon type wire abrasion tester Measurement conditions: Slurry concentration 0.5%, flow rate 0.65 l / min,
Roll material ceramic, roll diameter 60φ, roll speed
The test was conducted under the conditions of 1500 rpm, contact angle 111 degree, load 1.25 kg, wire type COS60, wire size 40 × 140 mm, test time 90 minutes, and the wear resistance was evaluated by the following formula 1.

[0021]

[Formula 1] <Measurement of average particle diameter> The average particle diameter was measured using Micron Photosizer (manufactured by Seishin Enterprise Co., Ltd.).

The wire abrasion resistance evaluation tests and average particle diameters of the following Examples and Comparative Examples were all performed in the same manner, and the evaluation results are shown in Table 1.

[Example 1] (Preparation of sample) Causticized light calcium was dispersed in water using a turbine blade type stirrer so that the solid content was 35% to prepare a dispersion liquid. Using a sand grinder (SGI-2 type, manufactured by Inoue Seisakusho Co., Ltd.), this dispersion was filled with glass beads.
It was treated with 1.7 parts, a disk rotation speed of 1440 rpm, and a dispersion liquid amount of 1.2 parts, and pulverized to an average particle size of 1.0 μm. The pH at this time was 13.0. While this was dispersed in water using a turbine blade type stirrer, a sulfuric acid band was added and neutralized until the pH of the dispersion reached 7.0 to obtain a modified causticized light calcium dispersion. This was diluted to a solid content concentration of 0.5% and subjected to a wire abrasion test.

[Example 2] The same procedure as in Example 1 was carried out except that the mixture was pulverized with a sand grinder until the average particle size became 2.0 µm, and a sulfuric acid band was added until the pH of the dispersion became 10.0.

[Example 3] The same procedure as in Example 1 was repeated except that the particles were pulverized with a sand grinder to an average particle size of 0.5 µm.

[Example 4] The same procedure as in Example 1 was carried out except that the particles were pulverized with a sand grinder to an average particle size of 3.0 µm.

Example 5 As in Example 1, the modified causticized light calcium dispersion obtained by neutralizing the dispersion with a sulfuric acid band until the pH of the dispersion reached 7.0 was added to the modified causticized light calcium dispersion. 70 solids
Talc having an average particle diameter of 10 μm was mixed with 30 parts by weight so as to have a solid content of 30 parts, diluted to a slurry concentration of 0.5%, and subjected to a wire abrasion test.

[Comparative Example 1] The same procedure as in Example 1 was carried out except that after pulverizing with a sand grinder, a sulfuric acid band was added until the pH of the dispersion became 11.5.

[Comparative Example 2] The same procedure as in Example 1 was carried out except that after grinding with a sand grinder, washing treatment with water was performed until the pH reached 9.5.

[Comparative Example 3] The same procedure as in Example 1 was carried out except that after pulverizing with a sand grinder to an average particle size of 3.0 µm, the sample was washed with water until pH 9.5 was reached.

[Comparative Example 4] A causticized light calcium dispersion obtained by crushing with a sand grinder and washing with water until pH 9.5 was added to the causticized light calcium solid content in the same manner as in Comparative Example 2.
The talc used in Example 3 was mixed with 70 parts so as to have a solid content of 30 parts, diluted to a slurry concentration of 0.5%, and subjected to a wire abrasion test.

[0032]

[Table 1]

[0033]

EFFECT OF THE INVENTION Causticized light calcium is treated with a sulfate having an acidity.
By neutralizing and modifying to H6.0 to 10.0, the wire wear is remarkably improved as compared with the non-modified causticized light calcium having the same particle size. This allows the use of the light calcium carbonate produced in the causticizing process of the craft plant.

Further, this reforming can be carried out by using the existing equipment as it is, the transition to neutral papermaking is promoted, and its industrial value is extremely large.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-112599 (JP, A) JP-A 1-226719 (JP, A) JP-A 62-238898 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C01F 11/18 D21C 11/04 D21H 17/67

Claims (3)

(57) [Claims] 1. Light calcium carbonate produced in the causticizing step of kraft pulp is used as a raw material, and this is crushed by a wet crusher, and the average particle diameter by light transmissive centrifugal sedimentation is 0.8.
Modified caustic light calcium carbonate obtained by neutralizing the dispersion to a pH of 6.0 to 10.0 by adding an acidic sulfate to the filler dispersion after adjusting the dispersion to be not less than μm and not more than 2.0 μm. 2. The modified causticized light calcium carbonate according to claim 1, wherein a sulfuric acid band is used as the acidic sulfuric acid salt. 3. A papermaking method comprising using the modified causticized light calcium carbonate according to claim 1 or 2 as a filler during papermaking.