JP2647306C - - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to paper whose deterioration is prevented. 2. Description of the Related Art A sizing agent is usually used to impart water resistance to paper and prevent recording bleeding. In a conventional acidic papermaking, the paper is treated with a rosin-based sizing agent or the like, and treated with aluminum sulfate as a fixing agent to give a desired sizing degree. Further, this aluminum sulfate was also effective in generating pitch and slime. However, when aluminum sulfate is used, the presence of a sulfate group causes a dehydration reaction with the passage of time, which causes a problem of so-called deterioration such as yellowing and reduction in strength of the paper. In acidic papermaking, usually, aluminum sulfate is added to the pulp at 1 to 2%, and the pH of the pulp slurry at this time becomes 4 to 5. When the pulp slurry is neutralized for the purpose of preventing paper deterioration, the effect of the rosin-based sizing agent rapidly decreases at pH 6 or more as shown in FIG. Can not. On the other hand, there is a so-called neutral paper having excellent deterioration prevention. In a neutral paper, a neutral sizing agent such as an alkyl ketene dimer or an alkenyl succinic anhydride is used as a sizing agent, a cationic polymer is used as a retention aid, and calcium carbonate is used as a filler. In the neutral papermaking technique, the extraction pH of the paper is about 7.9 to 9.0. In this case, the pH of the pulp slurry for papermaking is as alkaline as the extraction pH, so that the entire paper layer structure is the same. pH. Neutral papermaking has many operational problems, such as generation of pitch and slime and contamination with a neutral sizing agent, as compared with conventional acidic papermaking, and has the disadvantage of increasing costs. DISCLOSURE OF THE INVENTION The present inventors have studied a paper excellent in operability and deterioration prevention and a method for producing the same. As a result, in a system using aluminum sulfate and a hydrophobized modified rosin emulsion sizing agent in combination. It has been found that good results can be obtained by using a water-soluble alkaline salt in a pulp slurry for papermaking and further coating an alkali metal salt of an acid having a pKa of 5 to 14, thereby achieving the present invention. Therefore, an object of the present invention is to provide a paper which prevents deterioration of the paper and is excellent in operability and a method for producing the paper, despite the sizing method using aluminum sulfate. The object of the present invention is to provide at least one filler, and aluminum sulfate,
Coated paper made with a papermaking pulp slurry containing a hydrophobized modified rosin emulsion-based sizing agent and a water-soluble alkaline salt, wherein the at least one filler is dispersed in water at 10% by weight. The pH of the dispersion at this time (hereinafter referred to as the pH of the dispersion at the time of dispersion of 10% by weight of the filler) is 4 to 8,
The pH of the paper pulp slurry is adjusted to 6.5 to 7.5, and
It is characterized in that it is made by applying an alkali metal salt of an acid having a pKa of 5 to 14 in an aqueous solution at 5 ° C, and the coated paper has a cold water extraction pH of 7.5 to 9.0. Achieved by paper. In the present invention, pitch and slime are prevented from being generated by adding aluminum sulfate to the pulp slurry for papermaking. Furthermore, the use of a hydrophobic modified rosin emulsion-based sizing agent reduced the stain on the paper machine, realized the sizing degree and effectively prevented the paper from deteriorating. In the present invention, only the surface layer of the sheet is made slightly alkaline by size press coating or the like during the paper making process after the sheet is formed, so that the paper is prevented from deteriorating. Although the deterioration of the paper is greatly affected by light, a sufficient effect was obtained by taking measures against the surface layer of the paper. As for the deterioration of paper, as shown in FIG. 2, when the extraction pH of the paper is 6 or less, the deterioration becomes a practical problem. In addition, as mentioned earlier in FIG.
Above H6, the size drops sharply. The present inventors have studied the sizing agent and found that a hydrophobically modified rosin emulsion-based sizing agent can be used from the viewpoint that the sizing agent exhibits a sizing degree at pH 6 or more and can be used in combination with aluminum sulfate. The hydrophobized rosin emulsion-based sizing agent is known under the trademark "Size Pine NTS" or the like supplied from Arakawa Chemical Industries, Ltd., and is described in detail in the paper pulp technology Times, January 1992. Have been. Even with a hydrophobically modified rosin emulsion-based sizing agent, if the pH is 8 or more, the sizing degree decreases, and the sizing agent cannot be put to practical use. Therefore, in the present invention, the pH of the pulp slurry for papermaking is adjusted.
Is adjusted to 6.5 to 7.5, and further, an alkaline salt is applied so that the final cold water extraction pH of the paper is 7.5 to 9.0, preferably 7.6 to 8.6. . Paper extraction p
When H is 9.0 or more, the pen writing size (J, TAPPI Standard Test Method for Paper and Pulp No. 12) decreases as shown in FIG. 3 and cannot be put to practical use. Therefore, by this papermaking method,
It has been found that a sufficient degree of sizing can be achieved and effective prevention of paper deterioration can be realized. In order to adjust the pH of the pulp slurry for papermaking to 6.5 to 7.5 with a water-soluble alkaline salt, an alkaline salt such as calcium carbonate conventionally used for neutral papermaking is not used as a filler. A filler having a pH of 4 to 8 at the time of dispersion of 10% by weight is used. However, even if a small amount of an alkaline salt such as calcium carbonate is mixed, it can be used as long as the pH of the liquid at the time of dispersion is in the range of 4 to 8. When the pH of the liquid at the time of dispersion exceeds 8, it is not easy to add a water-soluble alkaline salt to the pH range of the present invention, and the sizing degree is reduced even when a hydrophobic modified rosin emulsion sizing agent is used. I do. Further, when the pH of the liquid at the time of dispersion is 4 or less, the pH of the pulp slurry for papermaking lowers, and a large amount of a water-soluble alkaline salt for adjustment is required, which tends to cause deterioration. Examples of the filler include kaolinite, illite, titanium dioxide, plastic pigment and the like, or a mixture of two or more thereof. If so, other fillers can be used in combination. In addition, even if the filler has a pH of 4 or less, or 8 or more, it can be used as long as the pH of the liquid at the time of dispersion can be adjusted to 4 to 8 by surface treatment or coating on the filler. it can. In the present invention, it is particularly preferable to use kaolinite, illite or titanium dioxide from the viewpoint of operability. The filler is usually added to the paper in an amount of 3 to 30% by weight. The hydrophobized rosin emulsion-based sizing agent used as a sizing agent in the present invention is used as a general papermaking chemical, and the amount of addition is 0.05 to 0.5.
7% is appropriate. In the present invention, aluminum sulfate is used from the viewpoint of operability. The amount of aluminum sulfate used is 0.1 to 5.0%, and preferably 0.5 to 3.0%. Since the pulp slurry for acidic paper making using aluminum sulfate has a pH of 4 to 5, the pH of the pulp slurry is adjusted to 6.5 to 7.5 by a water-soluble alkaline salt.
Adjust to Examples of the water-soluble alkaline salt include hydroxides such as sodium hydroxide and potassium hydroxide, silicates such as sodium silicate, carbonates such as sodium carbonate, potassium carbonate and sodium hydrogen carbonate, hydrogen carbonate, and phosphorus. There are phosphates such as sodium acid and disodium hydrogen phosphate and hydrogen phosphate. The amount of the water-soluble alkaline salt added is such that the pH of the pulp slurry for papermaking is 6.5 to 7.5.
Can be appropriately adjusted within the range, but 0.01 to 5.0% is appropriate. The pulp used in the present invention is mainly made of chemical pulp from the viewpoint of preventing deterioration. However, even if recycled pulp or mechanical pulp is used, paper with relatively little deterioration can be obtained. In addition, cationized starch, a retention aid, a dye, a paper strength agent, an antifoaming agent, and the like can be appropriately added as internal additives. Further, in the present invention, pKa5-14
Preferably, an alkali metal salt of an acid of 6 to 13 is applied. Usually, pKa 5-1
The aqueous solution of the alkali metal salt of acid 4 exhibits weak alkalinity to alkalinity, and by applying this aqueous solution, deterioration can be prevented without impairing the sizing degree. If the pKa is less than 5, the aqueous solution of the alkali metal salt of the acid becomes neutral to acidic,
The pH adjustment effect is lost. On the other hand, if it exceeds pKa14, the alkalinity becomes too strong, which adversely affects the degree of size. The acid that can be used is not particularly limited, regardless of whether it is an inorganic compound or an organic compound, as long as it has a pKa of 5 to 14 in an aqueous solution at 25 ° C. Examples of the alkali metal include sodium and potassium. Salts that can be used include, for example, sodium hydrogen carbonate (pKa 6.35),
Sodium carbonate (pKa 10.33), disodium hydrogen phosphate (pKa 7.2)
0) and sodium phosphate (pKa 12.35). The coating amount is adjusted so that the cold water extraction pH of the paper is 7.5 to 9.0.
It is from 0.01 to 5.0 g / m ² , preferably from 0.02 to 2.0 g / m ² . The coating method can be selected from existing coating methods such as a size press coat, an air knife coat, a blade coat, a roll coat, and a bar coat, but a size press coat is preferable from the viewpoint of operability. An aqueous polymer, a surface sizing agent, a pigment, a dispersant, an antifoaming agent, a dye, a flow modifier, and the like can be added to the aqueous solution of an alkali metal salt of an acid having a pKa of 5 to 14. The paper of the present invention is used for general office paper, printing paper, base paper for various coatings, transfer paper for indirect electrostatic copying, and the like. As described in detail above, the paper of the present invention has a pH of 4 to 8 when the filler is dispersed at 10% by weight, despite the size method using aluminum sulfate, When making a paper by adjusting the pH of the pulp slurry for papermaking to 6.5 to 7.5 using this, an alkali metal salt of an acid having a pKa of 5 to 14 in a 25 ° C. aqueous solution is applied, and the pH of the paper is extracted with cold water. Is adjusted to 7.5 to 9.0, so that the paper is excellent in expressing the size and preventing deterioration of the paper and excellent in operability. In the present invention, the papermaking slurry is kept near neutrality, and after the sheet is formed, only the surface layer of the sheet is made slightly alkaline by a size press or the like during the papermaking process to prevent deterioration of the paper. Although the deterioration of the paper is greatly affected by light, a sufficient effect can be obtained by taking measures against the surface layer of the paper. EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto. In the examples,% indicates pulp weight%. In addition, cold water extraction pH is measured according to JISP8133. As the pKa value, a value described in Chemical Handbook Basic Edition, 3rd Edition (edited by The Chemical Society of Japan, published by Maruzen, 1984) was used. Example 1 80 parts by weight of LBKP (csf 390 ml), 20 parts by weight of kaolinite (pH at the time of dispersion of 10% by weight is 4.9), 1.5% of aluminum sulfate, hydrophobic modified rosin emulsion system size Agent (Size Pine NTS, Arakawa Chemical Industries, Ltd.)
A pulp slurry for papermaking was prepared with 3% and 0.3% sodium hydroxide. This pH
Was 6.6. When the pulp slurry for papermaking is made into high-quality paper of 64.0 g / m ² , sodium carbonate (pKa 10.33) is produced by a size press.
Was applied in a 0.3% aqueous solution. At this time, the coating amount of sodium carbonate was 0.2 g / m.
² , and the cold water extraction pH was 7.9. Table 1 shows the Stechigt sizing degree, yellowing degree and bending strength of the high-quality paper after the treatment with a fade meter. There was no problem in operability such as contamination of the dryer during papermaking. Example 2 80 parts by weight of LBKP (csf 390 ml), 20 parts by weight of illite (pH at the time of dispersion of 10% by weight of 6.7), 2.0% of aluminum sulfate, hydrophobized modified rosin emulsion-based sizing agent (Size Pine NTS, Arakawa Chemical Industry Co., Ltd.) 0.3%,
A pulp slurry for papermaking was prepared with 0.4% sodium hydroxide and 0.3% cationized starch. This pH was 7.3. This papermaking pulp slurry is made into paper,
When producing 55.2 g / m ² of high quality paper, a 0.5% aqueous solution of sodium hydrogen carbonate (pKa 6.35) was applied by a size press. At this time, the coating amount of sodium bicarbonate was 0.3 g / m ² , and the cold water extraction pH was 7.6. Table 1 shows the results of evaluating this high quality paper in the same manner as in Example 1. There was no problem in operability such as contamination of the dryer during papermaking. Comparative Example 1 A high quality paper was obtained in the same manner as in Example 1 except that sodium hydroxide was not added and sodium carbonate was not applied. At this time, the pH of the pulp slurry for papermaking was 5
6.6 and the cold water extraction pH of the paper was 5.5. Table 1 shows the results of evaluating this high quality paper in the same manner as in Example 1. Comparative Example 2 80 parts by weight of LBKP (csf 390 ml), 20 parts by weight of calcium carbonate (pH at the time of dispersion of 10% by weight of 9.4), hydrophobized modified rosin emulsion sizing agent (
A pulp slurry for papermaking was prepared at 0.20% of Size Pine NTS (Arakawa Chemical Industries, Ltd.). This pH was 7.9. The pulp slurry for papermaking was made to obtain high quality paper. The cold water extraction pH of this high quality paper was 7.8. Table 1 shows the results of evaluating this high quality paper in the same manner as in Example 1. There was a problem in operability such as contamination of the dryer during papermaking. [Table 1]

[Brief description of the drawings]   FIG. 1 is a graph showing a relationship between pH and sizing degree of a pulp slurry for papermaking.   FIG. 2 is a graph showing the relationship between paper extraction pH and paper deterioration.   FIG. 3 is a graph showing the relationship between paper extraction pH and pen writing size.

Claims (1)

Claims: 1. Coated papermaking with at least one filler, and a papermaking pulp slurry containing aluminum sulfate, a hydrophobized modified rosin emulsion sizing agent and a water-soluble alkaline salt. Paper, wherein the at least one filler has a pH of 4 to 8 when dispersed in water at 10% by weight, and the pulp slurry for papermaking has a pH of 6.5 to 7.5. The coating is performed by applying an alkali metal salt of an acid having a pKa of 5 to 14 in an aqueous solution at 25 ° C., and the coated paper has a cold water extraction pH of 7.5 to 9 .0, characterized by being .0. 2. The paper according to claim 1, which is used as a transfer paper for indirect electrostatic copying.