WO2004007837A1

WO2004007837A1 - Novel calcium carbonate loading material, paper containing the loading material, and process for producing the same

Info

Publication number: WO2004007837A1
Application number: PCT/JP2002/007127
Authority: WO
Inventors: Chandra Heriyanto; Lunawati; Ming Tsung Tsai
Original assignee: Pt. Pabrik Kertas Tjiwi Kimia Tbk.; Suzuki, Rikio
Priority date: 2002-07-12
Filing date: 2002-07-12
Publication date: 2004-01-22
Also published as: JP4091940B2; JPWO2004007837A1; CN1639419A

Abstract

A process for papermaking, characterized in that a calcium carbonate obtained by treating a calcium carbonate slurry with a low-concentration sulfuric acid is used as a loading material to form a paper by an ordinary method. The concentration of the sulfuric acid is such that the concentration of calcium sulfate yielded is lower than the solubility of calcium sulfate at the temperature used for the sulfuric acid treatment. When this calcium carbonate loading material treated with low-concentration sulfuric acid is used, texture is prevented from deteriorating although first-pass retention and loading material retention increase. Thus, a paper having a loading material content as high as at least 30 wt.% can be easily produced without any trouble.

Description

TECHNICAL FIELD The present invention relates to a novel calcium carbonate filler, paper using the filler, and a method for producing the same.

The invention of this application relates to a novel calcium carbonate filler and a paper using the filler and a method for producing the same, and particularly to a calcium carbonate filler having a surface treated with sulfuric acid, a paper using the filler, and a method for producing the same. Background art

In order to improve the whiteness and opacity of paper, and to improve properties such as surface smoothness, it is widely used to add fillers made of mineral powder to paper, especially from the viewpoint of cost reduction. In the range of 10 to 20% by weight, from the aspect of high smoothness and high gloss, in the range of 20 to 30% by weight, and for special paper such as porcelain paper (baked into porcelain) Has a filler content of more than 50% by weight. Normally, talc, olefin, clay, titanium dioxide, white carbon (amorphous silica), calcium carbonate, and the like are used as fillers, but calcium carbonate is particularly often used in neutral papermaking. You. On the other hand, as the speed and size of paper machines have increased in recent years, the demand for filler yield, that is, the improvement of filler retention, has increased, and a method of adding various retention aids for the purpose of obtaining higher retention has been proposed. Have been. The retention aids used in the recent neutral papermaking process can be broadly classified into the following four types. That is,

(a) Organic substance alone: An organic polymer electrolyte is used. It can be classified into nonionic, anionic, cationic and amphoteric, but a typical example is a cationic polyacrylamide polymer.

(b) Composite system: composed of colloidal silica and cationized starch. ' (c) Hydrocor system: a system consisting of a high-molecular cationic polymer and a special inorganic pigment. Typical examples include a cationic polyacrylamide and bentonite.

(d) Dual polymer system: a system composed of anionic high molecular weight polymer and highly cationic low molecular electrolyte. Typical are anionic polyacrylamides and cationic low molecular weight acrylamides. By using the retention aid as described above, the filler retention can be increased, so that the amount of filler added to the paper can be effectively increased. However, the amount of filler usually added is about 5 to 20% by weight. However, it is necessary to increase the amount of filler further to produce paper containing high-concentration filler, and to make the paper machine in that case. It was difficult to make the vehicle run smoothly. The reasons are as follows.

(1) Increasing the amount of filler added in the paper machine decreases the first-pass retention (FPR) and filler retention (FR) in the wire part, causing an increase in white water concentration. As the concentration of white water in the system increases, the amount of components in the wire part increases and the strength of the wet paper decreases, resulting in more frequent paper breaks in the press part.

(2) Increasing the amount of the retention aid to increase FPR and FR results in poor paper formation and paper with many pinholes, resulting in poor paper quality. Become. Another problem is that the stock pulp on the wire drains faster, resulting in a noticeable wire mark on the paper.

(3) In the usual process, the problem that the felt becomes sticky frequently occurs, which causes trouble in running property. The retention of various raw materials in the wire part of the paper machine depends on the pulp raw material's freeness, raw material concentration, raw material flow rate, raw material temperature, raw material blending, raw material thickness on the wire, retention enhancement aid addition rate, water quality, etc. It is known that these factors vary in a complex manner, and they have not been completely captured in actual operations. On the other hand, high filling In order to manufacture paper containing paper, it is necessary to consider not only filler retention but also formation of wet paper, smoothness, adhesiveness to felt, size effect, strength of wet paper, sedimentation of filler, etc. is there. Disclosure of the invention

In view of all of the above reasons, the present inventors increased the binding of the filler to the pulp fiber by treating the surface of the calcium carbonate as the filler to create more active calcium carbonate. Various experiments were repeated and examined on the possibility of producing filler-containing paper.As a result of treating the surface of calcium carbonate with sulfuric acid at a low concentration, the fillers between the pulp fibers and the treated fillers were treated with each other. It has also been found that good binding properties are obtained between the treated filler and the retention aid, and that the calcium carbonate filler has a greater retention effect. That is, the present inventors have found that when calcium carbonate filler treated with a low concentration of sulfuric acid is used, the filler retention is improved in the case of a normal filler content, and the wet paper having a high filler content is made. In this case, the amount of calcium carbonate filler to be added can be reduced as compared with the conventional one, so that paper containing as much as 30% by weight or more of high filler can be easily manufactured. It is thought that when calcium carbonate slurry is treated with sulfuric acid at a low concentration, a part of the surface of the calcium carbonate fine particles is changed to calcium sulfate. However, it was not possible to obtain good quality paper simply by adding calcium sulfate to calcium carbonate. The exact reason why the use of calcium carbonate treated with such a low concentration of sulfuric acid as a filler increases the affinity as a filler over calcium carbonate itself is not clear at present, and will be awaited for further study There is a need. In the case of acidic papermaking, it is known that when reusing coated broke, calcium carbonate in the coating paint is treated with sulfuric acid or a sulfuric acid band to lower the pH, and then reprocessed. However, the filler obtained in this way is acidic and cannot be used for neutral papermaking. Accordingly, an object of the present invention is to provide a calcium carbonate filler surface-treated with a low concentration of sulfuric acid, a paper using the filler, and a method for producing the same. It is a further object of the present invention to provide a high filler content paper of as much as 30% by weight or more by using a calcium carbonate filler surface-treated with a low concentration of sulfuric acid, and to provide a method for producing the same. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram illustrating a simplified paper making process of a paper machine for actual operation used in the present invention.

FIG. 2 is a diagram showing the relationship between the number of papermaking operations and the filler content in the product in Example 1 and Comparative Example 1.

FIG. 3 is a graph showing the relationship between the number of paper making operations and the filler content in white water in Example 1 and Comparative Example 1. BEST MODE FOR CARRYING OUT THE INVENTION

In a first aspect of the present invention, there is provided a calcium carbonate filler treated with a low concentration of sulfuric acid in a calcium carbonate slurry. In such an embodiment, the concentration of the sulfuric acid is preferably such that the concentration of the generated calcium sulfate is lower than the solubility of the calcium sulfate at the temperature during the treatment.

In a second aspect of the present invention, there is provided a paper containing a calcium carbonate filler treated with a low concentration of sulfuric acid in a calcium carbonate slurry. In such an embodiment, the content of the calcium carbonate filler treated with a low concentration of sulfuric acid in the calcium carbonate slurry can be 5 to 50% by weight.

Further, in a third aspect of the present invention, there is provided a method for producing paper by using a calcium carbonate treated with a low-concentration sulfuric acid in a calcium carbonate slurry as a filler and making a paper by an ordinary method. When paper making is performed using such a filler, the binding between the filler and the fiber, the binding between the fillers, and the binding between the filler and the cationic polyacrylamide as a retention aid are increased, so that the filler retention is improved. As a result, the filler content in the raw material for insertion can be reduced by that much, and the strength of the wet paper is reduced. In addition, even in a paper machine, even if filler is added at a high concentration, the machine can run smoothly on the press part of the paper machine.

In such an embodiment, the concentration of the sulfuric acid is preferably such that the concentration of the generated calcium sulfate is smaller than the solubility of the calcium sulfate at the temperature at the time of the sulfuric acid treatment. By doing so, the precipitation of calcium sulfate does not occur. The problem of calcium sulfate deposition or scale formation in the paper machine can be avoided. In another embodiment of the present invention, it is desirable to use cationic polyacrylamide in an addition amount of from 200 ppm to 150 ppm (in terms of dry raw material) as a retention aid. According to such a method, the binding between the carbonic acid filler treated with the low concentration of sulfuric acid and the fibers of the pulp, the binding between the fillers and the binding between the filler and the cationic polyacrylamide are increased. The strength of the wet paper is increased, the adhesiveness on the felt during the papermaking process is reduced, the running property in the press part is also improved, and the drawbacks due to the addition of the retention aid as in the prior art are reduced. . According to still another aspect of the present invention, the carbonic acid treated with the low-concentration sulfuric acid is added before a fan pump in a papermaking process or to a mixed chest of each raw material, and the cationic polyacrylic is further added. A method for producing paper is provided wherein the amide is added before or after the screen during the papermaking process. According to such a method, the retention of filler is better, and the paper machine can run more smoothly and without stickiness. Furthermore, most of the sulfuric acid-treated calcium carbonate is added before the fan pump during the papermaking process or to the mixing chest, and the cationic polyacrylamide is added before the screen or before the fan pump during the papermaking process. And separately adding said sulfuric acid-treated calcium carbonate filler in the dry state after the screen in an amount of 0.5 to 30 kg per t of paper. According to such a method, the filler retention in the wire part is improved compared to the one without the sulfuric acid treatment. However, even with a high filler content, the papermaking runs smoothly and without stickiness, making it possible to produce paper at high speed. Hereinafter, specific examples of the present invention will be specifically described using Examples and Comparative Examples. The simplified manufacturing process of the paper machine 1 for the actual operation used in the present invention is as shown in FIG. In the paper machine 10, the raw material containing water, pulp, filler, etc., introduced from the raw material inlet 12 is mixed with the white water from the white water silo 14 through the mixing chest 13 at a predetermined ratio. Then, the paper is transferred by a fan pump 16, cleaned by a cleaner 18 and a screen 20 to remove impurities, and then passed through a head pox 22 to be made with a wire part 24. The white water 26 filtered by the wire part 24 is returned to the white water silo 14 for circulating use, and the wet paper web 28 that has been formed passes through the press part 30 and the dryer part 32 to form a predetermined product paper. It is intended to be manufactured. It is known that the following relational expression holds in the above paper machine. That is,

Raw material weight in paper = Raw material weight in headbox-Raw material weight in white water

… (1) First pass retention = (weight of raw material in paper / weight of raw material in head box) X 100% · · · (2) Filler retention = (weight of filler in paper / in weight of head box) (3) In the actual operation, if it is recognized that the equilibrium state has been reached,

Raw material weight in paper = inserted raw material weight · · · · (4)

Therefore, first, from the above relational expressions (1) to (3), the approximate expression (4) and FIG. 1 above, the first pass retention (FPR), the filler retention (FR), the filler content in the paper and the white water A simple simulation calculation was performed on the relationship between filler contents, and the conditions for increasing the filler content in the paper were compared with those of ordinary papermaking. Examined. The results calculated per 100 tons of raw material to be inserted are shown in Table 1 below.

【table 1】

Note) Filler “ton” in white water indicates tonnage per 100 tons of raw material in terms of dry raw material.

The results are as follows: FPR = 80% FR = 60%, filler content in paper = 18% by weight (converted to dry raw material, same hereafter), filler weight in white water, = 9.6 tons (per 100 tons of raw material in terms of dry raw material, the same applies hereinafter), and when the FPR is a constant value of 80%, the filler content in the paper is maintained at 22% by weight (Condition 1 3) If we try, FR will decrease from 60% to 50%, and the filler in the white water will be much more than the normal condition, and the filler in the white water will be the same as the normal condition. It is shown that, when it is maintained at 6 tons (condition 47), the filler content in the paper increases from 22% by weight (condition 4) to 25% by weight (condition 7) with the improvement of FR. Therefore, the present inventors have found from the above simple simulation calculation that in order to increase the filler content in paper, it is necessary to increase the filler retention and to keep the filler content in the white water constant. The conclusion has been reached. Under normal conditions, if the filler concentration in the white water is constant, the system process will proceed smoothly. Next, an experiment was conducted to confirm the difference in action between the calcium carbonate filler treated with the low-concentration sulfuric acid used in the present invention and the ordinary calcium carbonate filler. The calcium carbonate may be heavy calcium carbonate obtained by pulverizing limestone or light oxide prepared by baking limestone to form calcium oxide and reacting with carbon dioxide gas to recrystallize. Any of the calcium can be used. In the present invention, these calcium carbonates are made into a slurry and treated with a low-concentration sulfuric acid to further activate the surface of the carbonic acid calcium particles. The amount of sulfuric acid to treat the surface of the calcium carbonate is no more than 150 Oppm at room temperature (25 ° C) in the calcium carbonate slurry. This limit is due to problems with the formation of calcium sulfate formed and to prevent similar scaling in paper machines.

That is, when calcium carbonate is treated with sulfuric acid at a low concentration, soluble calcium sulfate is generated. However, when the amount of the generated calcium sulfate exceeds its solubility, sulfated calcium precipitates, which causes a scale problem in a paper machine. This is because it occurs. In time and, solubility product Ks of calcium sulfate (2 5 ° C) is 2. a 3 X 10- ⁴ mo l ² l one ^2, also the solubility product K s of calcium carbonate (2 5 ° C) 4. Since it is 8 × 10 ¹⁹ mo 1 ² ¹⁻² , the maximum addition amount of sulfuric acid to the calcium carbonate slurry can be calculated from these values. When the calculation is made taking the common ion effect into consideration, the addition amount of sulfuric acid is up to about 1480 ppm at 25 ° C. However, in the present invention, sulfuric acid less than about 1480 ppm at 25 ° C is used. The use is sufficient to more activate the surface of the calcium carbonate particles and provides good fluidity. The value of the solubility product of calcium sulfate and calcium carbonate is based on G. Svehla revision,

Ogel's Text Book of Macro and Semi-Micro Qualitative Inorganic Analysys, 5th Edition ". Hereinafter, specific examples of the present invention will be specifically described with reference to Examples and Comparative Examples.

(Example 1 and Comparative Example 1)

As Example 1 and Comparative Example 1, an experiment was conducted to confirm the difference in filler retention between the presence and absence of sulfuric acid treatment of calcium carbonate filler. First, as Example 1, a calcium carbonate slurry having a concentration of 25% by weight was treated with sulfuric acid at 348 ppm. The composition of the raw materials to be inserted into the paper machine is as follows.

a. Pulp: bleached hardwood kraft pulp (LB KP) = 90%,

Softwood bleached kraft pulp (NBKP) = 10, Beating degree = 350 cc (CS F: Canadian standard freeness) 8 b. Filler addition amount = 40% by weight (in terms of dry raw material)

c Cationic starch = 8 kg (per ton of paper, converted to dry material)

d. Internal sizing agent = 9 kg (per ton of paper, converted to dry material)

e. Cationic polyacrylamide

= 700 p pm (equivalent to dry material)

Comparative Example 1 was the same as Example 1 except that the calcium carbonate filler was not subjected to the sulfuric acid treatment.

A semi-automatic paper machine manufactured by TMI (Testing Machine Inc.) was used as the production equipment, and the raw materials a to e above were sequentially filled into a tank corresponding to a former, and all white water was batch-processed for the next run. It was returned and paper-made. Papermaking was performed up to 10 times for each of the ordinary filler without sulfuric acid treatment (Comparative Example 1) and the filler treated with sulfuric acid (Example 1). The relationship between the content and was examined. The results are shown in FIGS. 2 and 3, respectively.

From the results shown in Figures 2 and 3, the following can be concluded. That is, the filler retention was worse in the process of Comparative Example 1 using the calcium carbonate filler without the sulfuric acid treatment than in the process of the Example 1 with the sulfuric acid treatment, and as a result, the filler concentration in the white water was lower. It increases significantly with the number of papermaking cycles.

(Example 2 and Comparative Example 2)

In Example 2 and Comparative Example 2, a measurement test of the size effect by the sizing agent was performed. Example 2 uses the same raw material as the insert raw material of Example 1, and Comparative Example 2 uses the same raw material as the insert raw material of Comparative Example 1, and performs 12 batches in the same manner as in Example 1. The sizing degree of each of the twelve types of papers obtained for each was measured according to the Stekigt sizing degree test method (JIS-P 8122 " ¹⁹⁷⁶ ), and the average value was determined. As shown in Table 2.

[Table 2] Sample number Comparative example 2 (second) Example 2 (second)

1 4.74 9.Ί 1

2 4.2 8 7.34

3 4.4 9 1 0.3 1

4 3.9 0 8.97 7

5 4.3 8 1 0.6.0

6 5.2 2 9 1 6

7 5.1 6 9. 8 2

8 4.04 8.5 0

9 3.4 3 7.08

1 0 4.5 6 6.5 2

1 1 4. 9 9 1 0.84

1 2 6.3 7 8.89

Average 4.6 3 8. 9 3

In Comparative Example 2 in which a normal calcium carbonate filler was used, the filler content of the raw material inserted into the paper machine was as large as 40% by weight (in terms of dry raw material). In Example 2 using calcium filler, the sizing property was about twice as large as that of Comparative Example 2 even with the same sizing agent content. This means that as the filler content is increased, the sizing effect is degraded due to the adsorption of the sizing agent, but with the use of the sulfated calcium carbonate filler, the surface of the filler becomes less adsorbed by the sizing agent. It is presumed that the decrease in size effect means that it is small, probably because it is small. Therefore, the use of sulfuric acid-treated calcium carbonate filler can reduce the amount of internal sizing agent compared to the case of a normal process, and the amount of sizing agent added can be increased even when producing paper with high filler content. You don't have to.

(Examples 3, 4 and Comparative Examples 3, 4) In Examples 3 and 4 and Comparative Examples 3 and 4, a felt adhesive test using a sizing agent was performed. In Example 3, papermaking was performed in the same manner as in Example 1, except that the same raw materials were used as in Example 1. In Example 4, papermaking was performed in the same manner as in Example 3, but 5 kg of calcium carbonate (dry state, per ton of paper) treated with sulfuric acid as in Example 1 was added after the screen. Different from 3.

Further, as Comparative Example 3, papermaking was performed in the same manner as in Comparative Example 1 using the same raw materials as in Comparative Example 1. In Comparative Example 4, paper was made in the same manner as in Comparative Example 3, except that a hide mouth col system was employed as a retention aid, and 2.5 kg of bentonite (dry state, per ton of paper) was equivalent to a former. It differs from Comparative Example 3 in that paper is made after filling the tank.

For the measurement of felt adhesiveness, a dry felt was used, and pressure was applied on wet paper to check the state of the felt surface. The results are as shown in Table 3.

[Table 3]

When ordinary calcium carbonate filler is added in a lump, it has a little tackiness (Comparative Example 3), and becomes more tacky when the hydrocoll method, which is known as a method for improving filler retention, is used. In Example 4), when the calcium carbonate filler treated with sulfuric acid according to the present invention is used, even if the filler is added all at once, there is almost no tackiness (Example 3), and the same filler is separately added separately after the screen. When added, the tackiness is completely eliminated (Example 4).

(Example 5 and Comparative Example 5)

In Example 5 and Comparative Example 5, an experiment was performed to confirm the degree of formation of the paper. This formation degree was determined in Example 5 by using the same raw material as the inserted raw material in Example 1 and in Comparative Example 5. In the same manner as in Example 1, the same raw material as that used in Comparative Example 1 was used to make 10 batches of paper, and the degree of formation of each of the 10 types of paper obtained was determined.

Measurements were made using a “Kajaani Formation Analyzer” (manufactured by Kajaani, Finland), and the average value of each was determined. The results are shown in Table 4.

[Table 4]

From the results in Table 4, it can be seen that the use of the sulfuric acid-treated filler according to the present invention improves the formation degree by about 15 points. (Examples 6, 7 and Comparative Example 6)

As Examples 6, 7 and Comparative Example 6, tests were performed using actual machines. The raw materials to be inserted are as follows. A filler obtained by treating a calcium carbonate slurry (20% by weight solid content) with a sulfuric acid concentration of 660 ppm was used as a filler.

a. Pulp: Hardwood bleached kraft pulp (LBKP) = 90%, Softwood bleached kraft pulp (NBKP) = 10%, beating degree = 350 cc CSF

b. Cationic starch = 8kg (per ton of paper, converted to dry raw material)

c. Internal sizing agent = 9 kg (equivalent to dry raw material per ton of paper)

d. Purple dye content = 30 p pm

e. Fluorescent dye content = 700 ppm

g. Cationic polyacrylamide content = 75 Oppm (in terms of dry raw material) The purple dye and fluorescent dye are used to give whiteness to paper.

Using the inserted raw materials described above, in Examples 6 and 7, the operation was performed by changing the flow rate of the filler so that the filler content in the product was 30% by weight and 38% by weight, respectively, in a dry state. Also, in Comparative Example 6, the filler content in the product was changed to a dry state using an insertion raw material having the same composition as the input raw material in Example 6, except that a calcium carbonate slurry (20% by weight solid content) not treated with sulfuric acid was used. The operation was carried out so as to be 21% by weight and the basis weight of all the manufactured products was kept at a constant value of 50 cm ² . Table 5 summarizes these results. The size of is based on the Stockigt size degree test method ^{(JIS- P 81 2 2 1976)} .

[Table 5]

In Comparative Example 6 in which a normal calcium carbonate filler was used, the filler content in the product was not so large as 21% by weight, so that it was excellent in runnability and no tackiness. If calcium filler is used, the filler content in the product Even if it is 30% by weight (Example 6) and 38% by weight (Example 7), which are greatly increased as compared with Comparative Example 6, the running property is excellent as in Comparative Example 6, and there is no stickiness. , In addition, Firstno λ. The retention, the filler retention and the sizing degree were almost the same as those of Comparative Example 6.

(Example 8 and Comparative Example 7)

As Example 8 and Comparative Example 7, tests were performed using actual machines. The raw materials inserted in Example 8 are as follows. The calcium carbonate used was a calcium carbonate slurry that had been treated with 11 O O pm sulfuric acid.

Raw material of Example 8:

a. Pulp: Hardwood bleached kraft pulp (LBKP) = 90%,

Softwood bleached kraft pulp (NBKP) = 10%, beating degree = 3 50 c c CS F

b. Sulfuric acid-treated calcium carbonate slurry (solid content 45% by weight)

c Cationic starch = 1 OKg (per ton of paper, converted to dry raw material)

d. Internal sizing agent = 1 lKg (per ton of paper, converted to dry raw material)

e. Purple dye content = 50 p pm

ί. Fluorescent dye content = 2500 p pm

g. Cationic polyacrylamide content = 250 ppm (in terms of dry raw material) Of the above raw materials, add a sulfuric acid-treated calcium carbonate slurry as a filler before fan pump 16 (see Fig. 1), and use the same calcium carbonate slurry. Was added after screen 20 at a rate of 25 kg (equivalent to dry raw material per ton of paper). The resulting product had a filler content of 25% by weight (dry state) and a basis weight of 56 g / cm. Table 6 shows the results of the operation to achieve ² . The raw materials for insertion in Comparative Example 7 are as follows.

Raw material for Comparative Example 7:

a. Pulp: Hardwood bleached kraft pulp (LBKP) = 90%,

Softwood bleached kraft pulp (NBKP) = 10%, Beating degree = 350 c c CSF

b. Calcium carbonate slurry (solid content 45% by weight)

c. Cationic starch = 10 Kg (per ton of paper, converted to dry raw material) d. Internal sizing agent = 10 kg (per ton of paper, converted to dry raw material) e. Purple dye content = 50 ppm

f. Fluorescent dye content = 2500 ppm

g. Cationic polyacrylamide content = 250 ppm (equivalent to dry raw material) h. Bentonite = 3 kg (equivalent to dry raw material per ton of paper)

Of the above raw materials, a calcium carbonate slurry as a filler was added in front of a fan pump 16 (see FIG. 1), and bentonite as a filler retention aid by a hide col method was added after a screen 20. . Table 6 shows the results of operation performed together with the results of Example 8 so that the obtained product had a filler content of 25% by weight (dry state) and a basis weight of 56 gZcm ² .

[Table 6]

According to the results shown in Table 6, the use of the sulfuric acid-treated calcium carbonate filler according to the present invention improved the first pass retention by 3% as compared with the case using conventional calcium carbonate, and However, it was confirmed that filler retention was improved by 10%. As described above, the following effects are obtained when paper is made using calcium carbonate treated with a low concentration of sulfuric acid according to the present invention.

First, filler retention increases, but formation does not degrade. Calcium carbonate filler treated with a low concentration of sulfuric acid improves first pass retention, probably because of its binding to fibers, but the addition of a cationic retention aid enhances fast bath retention. To improve. Generally, in a normal system using an anionic retention aid, the filler agglomerated by the retention aid forms a small floc and can be attached to the fiber by the retention aid. As a result, formation deteriorates. The filler does not disperse on the fiber surface. Also, some paper machines with well-designed conventional wire parts can achieve filler retention greater than 50%, and this type of paper machine can be used with ordinary calcium carbonate fillers. Although it is easy to produce a paper with a high filler content to a certain extent, in the case of a paper machine with a low filler retention, the filler treated according to the present invention can improve the filler retention by 5% or more. Will be able to do so. Second, the use of the calcium carbonate filler whose surface has been treated with sulfuric acid according to the present invention increases the adhesion of the filler to the fiber and allows a high filler content to be achieved. The effect is great, and paper with high smoothness and high density can be easily obtained. In addition, in general high-filler-containing paper, the thickness becomes thinner when the smoothness is increased, but the use of the calcium carbonate filler whose surface is treated with sulfuric acid according to the present invention increases the smoothness of the obtained high-filler paper. As a result, as a result, the paper machine can obtain the same smoothness at a smaller pressure in the calender part, and can increase the thickness of the high-filled paper. Third, by using the calcium carbonate filler whose surface has been treated with sulfuric acid according to the present invention, since the filler and fine fibers on the surface of the wet paper web are more bonded to the fibers, the tackiness of the wet paper web on the felt is reduced. Less. In addition, by treating the surface of calcium carbonate with sulfuric acid, the surface of the filler becomes more difficult to adsorb the internal sizing agent (AKD, ASA, etc.), and the amount of the internal sizing agent added is high-filled paper. There is no significant difference compared to the normal process, and the size effect is not reduced because the internal sizing agent reacts and changes with the fiber rather than with the filler. Fourth, the use of calcium carbonate filler whose surface has been treated with sulfuric acid according to the present invention increases the affinity between the filler and the fiber and between the filler and the filler. Gives web strength and when applied to a paper machine, gives good runnability in the press part of the paper machine.

Claims

The scope of the claims

1. Calcium carbonate filler treated with low concentration of sulfuric acid in calcium carbonate slurry.

2. The calcium carbonate filler according to claim 1, wherein the concentration of the sulfuric acid is such that the concentration of the generated calcium sulfate is lower than the solubility of the calcium sulfate at the temperature during the sulfuric acid treatment.

3. Paper containing calcium carbonate filler treated with low concentration of sulfuric acid in calcium carbonate slurry.

4. The paper c according to claim 3, wherein the content of the calcium carbonate filler treated with a low concentration of sulfuric acid in the calcium carbonate slurry is 5 to 50% by weight or more.

5. A method for producing paper, comprising using a calcium carbonate filler that has been treated with a low concentration of sulfuric acid in a calcium carbonate slurry and making the paper by an ordinary method.

6. The paper manufacturing method according to claim 5, wherein the concentration of the sulfuric acid is such that the concentration of the generated calcium sulfate is lower than the solubility of the calcium sulfate at the temperature during the sulfuric acid treatment.

7. The paper production according to claim 5, wherein a cationic polyacrylamide is further used as a retention improving auxiliary in an addition amount of 200 ppm to 150 ppm (in terms of dry raw material). Method.

8. Add the sulfuric acid-treated calcium carbonate before the fan pump or in the mixing chest during the papermaking process, and further add the cationic polyacrylamide during the papermaking process. 8. The method for producing paper according to claim 7, wherein the addition is performed before or after the screen.

9. Add most of the sulfuric acid-treated calcium carbonate before the screen during the papermaking process or to the mixing chest, and add the cationic polyacrylamide before the screen or before the fan pump during the papermaking process; 9. The paper according to claim 7, wherein the sulfuric acid-treated calcium carbonate filler is separately added in a dry state after the screen in an amount of 0.5 to 30 kg per ton of paper. Production method