JP2003278087A - Pulp treating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treating technique of pulp capable of reducing lowering degree of pulp whiteness in beating treatment step and to provide a treating technique of pulp capable of reducing bleaching cost. <P>SOLUTION: After a washing and dust-removing step of cooked pulp and before a final bleaching step, pulp suspension is mechanically mixed and pulp fiber is fibrillated by imparting high shearing force to a pulp fiber to lower unbeaten freeness of pulp after breaching treatment. Then, bleached pulp is beaten to a target freeness by a beating machine. Lowering degree of whiteness in the beating step can be minimized by reducing the difference between the unbeaten freeness and the target freeness and beating load is lowered to minimize the lowering degree of whiteness in the beating step. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD OF THE INVENTION

2. Description of the Related Art In the pulp bleaching process, chlorine-based bleaching chemicals such as chlorine and hypochlorite have conventionally been combined with alkali extraction for the purpose of decomposing and removing lignin which is an impurity from chemical pulp to enhance the whiteness of pulp. Has been used.
However, in recent years, as environmental awareness has increased, reduction of organic chlorine compounds emitted from the bleaching process of pulp and paper mills has been rapidly promoted, and ECF bleaching that does not use chlorine and further progress of chlorine bleaching chemicals TCF bleaching, which is not used at all, is becoming the mainstream worldwide.

Under such circumstances, researches on bleaching agents to replace chlorine bleaching chemicals have been actively conducted, and oxygen, hydrogen peroxide,
Bleaching agents such as peracetic acid, chlorine dioxide and ozone have been put to practical use. Regarding ozone, the development of high-performance equipment that can generate high-concentration ozone at low cost has progressed, and the development of a high-share mixer that can efficiently mix medium- or high-concentration pulp and ozone has resulted in the recent progress of ECF. Practical application of ozone bleaching stage in bleaching and TCF bleaching has been started.

When paper is produced from bleached pulp as a raw material, if high strength is required for the paper, a beating treatment is carried out before the bleached pulp is made into paper by a paper machine. There are various types of beating machines, but all of them are to fibrillate pulp fibers with metal beating teeth of the beating machine to enhance the entanglement of pulp fibers and at the same time increase hydrogen bonds between the fibers. The index indicating the degree of beating of pulp is usually the freeness, and the target freeness of pulp is determined for each paper brand. The pulp is beaten until the predetermined freeness is reached.

Since this beating process is a process of mechanically rubbing the pulp, heat is generated by the friction between the pulp and the beating tooth made of metal, and the whiteness of the pulp is lowered by the influence of this heat. There is a phenomenon. The lower the target freeness, in other words, the larger the difference in freeness between the unbeaten pulp and the beaten pulp, the greater the degree of decrease in whiteness due to the beating treatment. Paper made from low freeness pulp,
Due to this decrease in whiteness, the whiteness may fall below the target whiteness range requested by the user.
In order to avoid this, it is necessary to set and control the whiteness of the pulp after the pulp bleaching is high. The amount of bleach used in the pulp bleaching process must be increased to increase the degree of bleaching, which increases the bleaching cost.

When a non-chlorine bleaching agent such as oxygen, hydrogen peroxide, peracetic acid or ozone is used, there is a problem that the bleaching cost becomes high, and chlorine, hypochlorite and chlorine dioxide are used. If you are using a chlorine bleach such as
In addition to the above problems, there is a problem that the emission amount of organic chlorine compounds increases. As described above, from the economical aspect of bleaching cost and also from the environmental aspect, it is desired to develop a pulp treatment technique capable of reducing the reduction width of the pulp whiteness in the beating treatment step.

[0006]

SUMMARY OF THE INVENTION A first object of the present invention is to provide a pulp processing technique capable of reducing the width of decrease in pulp whiteness in the beating process. The second problem is to reduce the bleaching cost by this technique.

[0007]

[Means for Solving the Problems] After the washing and dusting step of cooked pulp and before the final bleaching step of the bleaching step, the pulp suspension is mechanically mixed to give a high shearing force to the pulp fibers. To reduce the unbeaten freeness of the pulp after bleaching. Then, the bleached pulp is beaten to a target freeness with a beater. By reducing the difference between the unbeaten freeness and the target freeness and lowering the beating load, the degree of decrease in whiteness in the beating step can be reduced.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Pulp applied to the present invention includes soda method, sulfite method, and pulp produced by the Kraft method. Further, as the Kraft method, modified methods such as MCC, EMCC, ITC, Although the Lo-solid method and the like are known, the method is not limited to those methods, and it is applicable regardless of whether oxygen delignification treatment has been performed or not. Also, as a material, conifer,
Applicable to hardwood.

The pulp obtained by digesting hardwood and / or coniferous chips is washed, coarse undigested material such as knot meal is removed by a screen, and sent to a bleaching step. When the oxygen delignification treatment is performed, the dust is removed by a screen, then the oxygen delignification is performed, and the resultant is sent to the bleaching step. After this dust removal step, the mechanical mixing treatment of the present invention can be performed between the final stages of the bleaching step. The mechanical mixing process can be performed at any place in the pulp transfer pipe except for each reaction tower and the washing device. The mechanical mixing process is performed in at least one place.

The mechanical mixing treatment of the present invention is carried out by a mixer, but any mixer capable of imparting a high shearing force to pulp to fibrillate it and lowering the freeness can be used. Specific examples include a medium-concentration fluidizing mixer. Medium-concentration fluidizing mixers include a type that applies a high shearing force to the gap between the impeller and the stator, a type that generates turbulent flow within the radius of rotation of the rotor, and a type that repeats volume changes in the flow path as the rotor rotates. However, it can be used without particular limitation.

The mixer used for the mechanical mixing treatment may be installed only for the purpose of imparting a high shearing force to the pulp to fibrillate it and reduce the freeness, and for the purpose of mixing bleaching chemicals such as ozone. It may be installed as. In the case of a mixer for ozone bleaching, it is usually installed in 1 to 2 stages in series because of the mixing of pulp and ozone gas, but in order to cause a sufficient freeness reduction of the present invention, it is installed in 2 to 4 stages in series. Is desirable.

The pulp concentration during the mechanical mixing treatment of the present invention is preferably in the range of 3 to 20% by weight of solid content. Preferably 5 to 20
Solid content weight%, and more preferably 6 to 20 solid content weight%. When the pulp concentration is less than 3% by weight of solid content, the energy of the mixer is mainly consumed for stirring the water, the energy transfer to the pulp fiber becomes poor, and the freeness decrease range is not sufficient. On the other hand, if the solid content exceeds 20% by weight, the flow of pulp becomes insufficient, and the degree of decrease in freeness becomes small.

In the case of hardwood pulp, the degree of decrease in the freeness of pulp by the mechanical mixing treatment of the present invention is preferably in the range of 20 to 200 ml, preferably 30 to 150 ml, more preferably 40 to 150 ml.
ml. In the case of softwood pulp, the range of 50-350 ml is good, preferably 75-300 ml, more preferably 100-300 ml.
Is. Hardwood pulp less than 20 ml, softwood pulp 50 ml
When the amount is less than the above, the effect of suppressing the whiteness reduction of the pulp after beating, which is a feature of the present invention, is small. On the other hand, 200 ml of hardwood pulp
If the amount of ultrafine pulp or softwood pulp is more than 350 ml, the effect of suppressing the decrease in whiteness of the pulp after beating is sufficient, but there is a problem that dehydration becomes poor in the pulp washing process in the bleaching process.

After the bleaching treatment, the unbeaten pulp having a lowered freeness is beaten to a predetermined freeness with a beater. Various types of beaters can be used without particular limitation. The beating treatment by the beating machine is reduced by the amount corresponding to the decrease in the unbeaten freeness, the width of decrease in the pulp whiteness at the time of beating is reduced, and the whiteness of the pulp after beating is increased. As a result, the whiteness of the paper product increases. Therefore, when the whiteness of the paper product is constant, the amount of bleaching chemicals used can be reduced and the bleaching cost can be reduced.

[0015]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples. Hardwood kraft pulp subjected to oxygen delignification treatment (Kappa number: 10.3, whiteness 53.5%) was used in Examples 1 to 3 and Comparative Example 1. The method of measuring the whiteness of pulp, the method of measuring freeness, and the method of beating are as follows. 1. Whiteness: Measured according to JIS P8123 using a Hunter whiteness meter. 2. Freeness: The freeness of pulp was measured using a Canadian Freeness Tester. 3. Beating treatment: Using a PFI mill, the beating degree was changed by changing the treatment rotation number to prepare pulps having different freeness. The pulp concentration is shown by solid weight%, and the bleaching chemical addition rate is shown by weight% with respect to the pulp solid content. The pulp whiteness after bleaching was adjusted to be the same in Examples 1 to 3 and Comparative Example 1.

[0016]

Example 1 Sulfuric acid was added to a 10% by weight suspension of hardwood kraft pulp subjected to oxygen delignification treatment to adjust the pH to 3.0. Using a medium-concentration fluidizing mixer, ozone gas was added to this pulp in 0.25% by weight divided into two stages, and subjected to ozone treatment (hereinafter referred to as Z treatment). Without cleaning it
It was diluted to 3% by weight and treated with chlorine dioxide. Chlorine dioxide addition rate is 0.3%, temperature 60 ℃, treatment time 60 minutes. Further pulp concentration 15%
After substitution cleaning with, the sample was treated with alkali / hydrogen peroxide. Sodium hydroxide addition rate 0.7%, pH = 11.5, hydrogen peroxide addition rate 0.3%, temperature 60 ° C., treatment time 90 minutes. Then, after displacement washing with 15% by weight, final bleaching was performed with chlorine dioxide bleaching. Temperature 70 ℃,
Chlorine dioxide addition rate 0.35%, reaction completed pH = 4.4. The bleached pulp has an unbeaten freeness of 548 ml and a whiteness of 8
It was 9.6%. This was beaten with a PFI mill. The results of freeness and whiteness of the obtained pulp are shown in Table 1, and comparison with Comparative Example 1 is shown in FIG.

[Table 1]

[0017]

Example 2 The medium-concentration fluidizing mixer used in Example 1 was used to treat the pulp with a pulp concentration of 10% by weight without adding a bleaching agent. Thereafter, the same pH adjustment as in Example 1 and bleaching treatment of ozone / chlorine dioxide-alkali / hydrogen peroxide-chlorine dioxide sequence were performed. The unbeaten freeness of pulp after bleaching treatment is
It was 500 ml, and the whiteness was 89.6%. This was beaten with a PFI mill. The results of freeness and whiteness of the obtained pulp are shown in Table 2 and comparison with Comparative Example 1 is shown in FIG.

[Table 2]

[0018]

Example 3 The medium fluidizing mixer used in Example 1 was treated with a pulp concentration of 10% by weight and without the addition of a bleaching agent. This was diluted to 3% by weight and treated with chlorine / chlorine dioxide. Chlorine addition rate 0.9%, chlorine dioxide addition rate 0.3%, temperature 60 ℃, reaction time
60 minutes. This was replaced and washed with a pulp concentration of 15% and alkali /
Treated with hydrogen peroxide. Sodium hydroxide addition rate 0.7%, pH
= 11.5, hydrogen peroxide addition rate 0.3%, temperature 60 ℃, treatment time 90
Minutes. Next, after substitution cleaning with a pulp concentration of 15%, a final chlorine dioxide treatment was performed. Temperature 70 ℃, chlorine dioxide addition rate 0.35%, reaction completed pH = 4.4. The unbeaten freeness of pulp after bleaching treatment is
It was 578 ml and the whiteness was 89.6%. This was beaten with a PFI mill. The results of freeness and whiteness of the obtained pulp are shown in Table 3 and comparison with Comparative Example 1 is shown in FIG.

[Table 3]

[0019]

Comparative Example 1 The same bleaching sequence as in Example 3 was performed except that the treatment with the medium-concentration fluidizing mixer in Example 3 was omitted. The bleached pulp had an unbeaten freeness of 625 ml and a whiteness of 89.6%. PFI this
Beaten on the mill. The results of freeness and whiteness of the obtained pulp are shown in Table 4. A comparison with Examples 1, 2 and 3 is shown in FIG.

[Table 4]

[0020]

[Figure 1] Compared to Comparative Example 1, the bleached pulps of Examples 1, 2, and 3 have the same whiteness, but the unbeaten freeness is lower by 77 ml, 125 ml, and 47 ml, respectively. As shown in FIG. 1, this difference in freeness is maintained even after beating, and it is clear that the pulp after beating has a higher whiteness at the same freeness.

[0021]

EFFECT OF THE INVENTION Between the washing and dusting step of cooked pulp and before the final bleaching step of the bleaching step, the pulp suspension is mechanically mixed to give a high shearing force to the pulp fiber, fibrillate it, and bleach it. It reduces the unbeaten freeness of the subsequent pulp. Then, the bleached pulp is beaten to a target freeness with a beater. By reducing the difference between the unbeaten freeness and the target freeness and lowering the beating load, the degree of decrease in whiteness in the beating step can be reduced. If the whiteness of the paper product is constant, the amount of the bleaching chemical used can be reduced and the bleaching cost can be reduced by the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tatsuaki Iwaki             143 Yufutsu, Tomakomai City, Hokkaido Nippon Paper Co., Ltd.             Inside the company Yufutsu factory F-term (reference) 4L055 AA03 AC06 AD02 AD03 AD05                       AD07 AD08 AD10 BA11 BB01                       BB03 BB11 BB12 BB13 BB15                       BB17 BB18 BB20 BB22 BB30                       EA05 FA05 FA22

Claims (5)

[Claims] 1. A pulp suspension is mechanically mixed after the washing and dust removal step of cooked pulp and before the final bleaching step of the bleaching step to reduce the unbeaten freeness of the pulp after bleaching. By so doing, the beating load is reduced, and the width of decrease in the whiteness of the pulp after beating is reduced. 2. The method for treating pulp according to claim 1, wherein the mechanical mixing treatment is performed with a medium-concentration fluidizing mixer. 3. The method according to claim 1, wherein the mechanical mixing treatment is carried out in a medium-concentration fluidizing mixer, and the unbeaten freeness of the pulp after bleaching and the mixing of a bleaching chemical are carried out at the same time. 2. The method for treating pulp according to 2. 4. The medium concentration fluidizing mixer used in the mechanical mixing treatment is a mixer for mixing the pulp suspension and ozone gas in the ozone bleaching stage, according to any one of claims 1 to 3. One of the pulp treatment methods. 5. The degree of decrease in the freeness of pulp by mechanical mixing treatment is 20 to 200 ml for hardwood pulp and 5 for softwood pulp.
It is 0-350 ml, Claim 1 to Claim 4 characterized by the above-mentioned.
The method for treating pulp according to any one of 1.